Title of Invention	CATALYST FOR PURIFICATION OF PET DRAWING OVEN GAS, METHOD OF PURIFYING PET DRAWING OVEN GAS USING SAME CATALYST, AND METHOD OF PREVENTING CONTAMINATION OF PET DRAWING OVEN
Abstract	Provided are a catalyst for degrading, with a high degree of conversion, a PET oligomer in a drawing oven gas of a PET drawing apparatus; a catalyst for oxidatively degrading aldehydes, such as acetaldehyde, simultaneously; a catalyst having high durability; and a method of purifying the gas in a drawing oven (tenter) by the catalyst. The catalyst for purification of the PET oligomer-containing PET drawing oven gas contains at least one of the inorganic oxides alumina and zirconium oxide, and platinum. The method of purifying the PET drawing oven gas, and a method of preventing contamination of the PET drawing oven comprise the steps of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in the drawing oven into contact with the above catalyst provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and circulating the resulting degraded gas to the drawing oven.

Title of Invention

CATALYST FOR PURIFICATION OF PET DRAWING OVEN GAS, METHOD OF PURIFYING PET DRAWING OVEN GAS USING SAME CATALYST, AND METHOD OF PREVENTING CONTAMINATION OF PET DRAWING OVEN

Abstract

Provided are a catalyst for degrading, with a high degree of conversion, a PET oligomer in a drawing oven gas of a PET drawing apparatus; a catalyst for oxidatively degrading aldehydes, such as acetaldehyde, simultaneously; a catalyst having high durability; and a method of purifying the gas in a drawing oven (tenter) by the catalyst. The catalyst for purification of the PET oligomer-containing PET drawing oven gas contains at least one of the inorganic oxides alumina and zirconium oxide, and platinum. The method of purifying the PET drawing oven gas, and a method of preventing contamination of the PET drawing oven comprise the steps of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in the drawing oven into contact with the above catalyst provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and circulating the resulting degraded gas to the drawing oven.

Full Text	DESCRIPTION TECHNICAL FIELD [0001] This invention relates to a catalyst for oxidatively degrading volatile PET oligomer components contained in a hot draft within a drawing oven when drawing a polyester resin (PET) by a drawing apparatus to produce a PET film; a method of purifying a PET drawing oven gas with the use of the catalyst; and a method of preventing contamination of a PET drawing oven with the use of the catalyst. BACKGROUND ART [0002] When a PET film is produced using a drawing apparatus (usually called a tenter), a PET resin is heated with hot air or draft. During drawing, PET oligomers, for example, low polymers such as cyclic trimers apt to form during polymerization, and volatile organic compounds formed by oxidative degradation, such as 4-carboxybenzaldehyde, monohydroxyterephthalate, and terephthalic acid, sublime or volatilize from the film, and mix into the hot draft. The PET oligomers are sublimable. Thus, if the hot draft containing them contacts a low-temperature site within the oven or a circulation system, the PET oligomers solidify, and deposit on the wall of the oven or within piping, presenting a cause of contamination or clogging. The adhesion of the PET oligomers onto the surface of the film causes the problem of quality deterioration. [0003] (Prior art) Under these circumstances, a gas purification catalyst and its related technologies have been developed as a field of technologies for purifying the oven gas. [0004] Patent Document 1 discloses a technology which passes a hot draft within a tenter through an oxidation catalyst layer comprising a platinum group metal (ruthenium, rhodium, palladium, osmium, iridium or platinum). [0005] Patent Document 2 discloses a technology which comprises burning and removing oligomers formed within a tenter by an oxidation catalyst when producing a PET film while circulating a hot draft within the tenter, and blowing the hot draft after removal against the surface of the film. [0006] Patent Document 3 discloses a technology in which a platinum catalyst is disposed in a hot draft circulation path in a method for preparation of a biaxially oriented polyester film, and low molecular weight substances volatilizing from the film and entering a circulating hot draft are combusted efficiently in the presence of the platinum catalyst. [0007] Patent Document 4 discloses a technology which uses a filter incorporating a platinum catalyst block for removal of oligomers. [0008] Patent Document 5 discloses a technology in which a tenter is provided with a catalyst for degrading and removing sublimates generated from a thermoplastic resin. [0009] (Problems with the conventional technologies) As described above, the documents cited above introduce the facts that an oxidation catalyst is used for treatment of a drawing oven gas of a PET drawing apparatus; that a platinum group metal (ruthenium, rhodium, palladium, osmium, iridium or platinum) is used as an active component of the oxidation catalyst; and that the treated gas is circulated and used again. [0010] None of the documents, however, report the details of the catalyst. PET oligomers have relatively large molecular weights, and thus are difficult to oxidize completely. As a result, a coky substance is prone to deposit on the catalyst, causing a decrease in activity. Moreover, the gas within the PET drawing oven may involve silicon-containing compounds and organic sulfur compounds which are regarded as resulting from additives to the PET resin. Since such compounds become causes of decreased catalytic activity, durability to them is also of importance. Furthermore, aldehydes such as acetaldehyde are formed during PET drawing. Thus, there is a demand for a catalyst which degrades and removes them at the same time. CITATION LIST PATENT LITERATURE [0011] PLT1: JP-A-59-98821 PLT 2: JP-B-60-45577 PLT3: JP-A-11-342535 PLT 4: JP-A-11-77823 PLT 5: JP-A-2002-144420 SUMMARY OF INVENTION TECHNICAL PROBLEM [0012] Objects of the present invention are, therefore, to provide a catalyst which degrades, with a high degree of conversion, PET oligomers in a drawing oven gas of a PET drawing apparatus; provide a catalyst which oxidatively degrades aldehydes, such as acetaldehyde, simultaneously; provide a catalyst of high durability; a method of purifying a PET drawing oven gas with the use of the catalyst; and a method of preventing contamination of a PET drawing oven with the use of the catalyst. SOLUTION TO PROBLEM [0013] The inventors of the present invention have found a catalyst, which can solve the above-mentioned problems, by a specific combination of an active component and a carrier in an attempt to oxidize and combust a PET oligomer component. Through this finding, the inventors have accomplished the present invention. The gist of the present invention is as follows: [1] A catalyst for purification of a PET drawing oven gas, the catalyst comprising at least one of inorganic oxides which are alumina and zirconium oxide (component 1); and platinum (component 2). [2] The catalyst for purification of a PET drawing oven gas according to [1], further comprising zeolite (component 3), and wherein a weight ratio between the component 1 and the component 3 is 90:10 to 10:90. [3] The catalyst for purification of a PET drawing oven gas according to [2], wherein a SiO2/Al2O3 molar ratio of the zeolite used is 5 or higher, but 100 or lower. [4] The catalyst for purification of a PET drawing oven gas according to [2] or [3], further comprising at least either of platinum-supporting alumina particles and platinum-supporting zirconium oxide particles; and zeolite particles. [5] The catalyst for purification of a PET drawing oven gas according to [1], further comprising cerium oxide (component 4), and wherein a content of the cerium oxide is 1 to 100 parts by weight per 100 parts by weight of the component 1. [6] The catalyst for purification of a PET drawing oven gas according to [5], wherein the cerium oxide is CeO2, a complex oxide composed of CeO2 and ZrO2 (CeO2- ZrO2), or a complex oxide comprising the CeO2 • ZrO2 and an oxide of at least one of La, Y, Pr and Nd. [7] The catalyst for purification of a PET drawing oven gas according to any one of [1] to [6], wherein a content of the platinum is 0.01 to 10% by weight based on the component 1. [8] A catalyst for purification of a PET drawing oven gas, comprising at least one of inorganic oxides which are alumina and zirconium oxide (component 1), platinum (component 2), zeolite (component 3), and cerium oxide (component 4), and wherein a content of the component 3 is such that a weight ratio between the component 1 and the component 3 is 90:10 to 10:90, and a content of the component 4 is 1 to 100 parts by weight per 100 parts by weight of the component 1. [9] A catalyst for purification of a PET drawing oven gas, comprising the catalyst according to any one of [ 1 ] to [8] supported on a catalyst substrate. [10] The catalyst for purification of a PET drawing oven gas according to any one of [1] to [9], wherein a drawing oven gas is a gas containing acetaldehyde as well as a PET oligomer, and the catalyst oxidatively degrades these two components. [11] A method of purifying a PET drawing oven gas, comprising: a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of [1] to [10] provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven. [12] A method of preventing contamination of a PET drawing oven, comprising: a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of [1] to [10] provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven. ADVANTAGEOUS EFFECTS OF INVENTION [0014] According to the catalyst of the present invention, the following prominent effects are achieved: [ 1 ] The catalyst for purification of a PET drawing oven gas according to the present invention oxidatively degrades, with a high degree of conversion, a sublimable polymer contained in the PET drawing oven gas, such as a PET oligomer, thereby converting it into CO2 and H2O. This catalyst minimally declines in activity, and excels in durability. [2] Aldehydes formed during the drawing of the PET film simultaneously undergo oxidative degradation. [3] Purification of a PET drawing oven gas, which has been difficult to achieve using known catalysts, can be achieved for a long term. By so doing, contamination of the drawing oven can be prevented, and labor for maintenance and management of the drawing oven can be lessened. BRIEF DESCRIPTION OF DRAWINGS [0015] [Fig. 1] is an outline view of a reactor 1 for evaluation of a catalyst. [Fig. 2A] shows the infrared absorption spectrum of a PET oligomer. [Fig. 2B] shows the infrared absorption spectrum of a PET resin. [Fig. 3] is an outline view of a reactor 2 used for the simultaneous degradation test of the PET oligomer and acetaldehyde. DESCRIPTION OF EMBODIMENTS [0016] Embodiments of the present invention will now be described below. [0017] (Field of application) An object to which the catalyst of the present invention is applied is an oven gas containing a PET oligomer generated during production of a PET film in a PET drawing oven. The PET oligomer refers to a volatile (sublimable) organic component generated from a PET resin or a PET film in the aforementioned heating step which is carried out during drawing of the PET resin. Herein, an average particle diameter refers to the average particle diameter of secondary particles measured by the laser method, unless otherwise specified. A specific surface area is a value measured by the BET process. [0018] The catalyst of the present invention will be described below. [0019] Component 1: Alumina (A12O3) Alumina (Al2O3), one of the components of the catalyst according to the present invention, is active alumina in general use as a catalytic carrier, such as γ -alumina or δ -alumina, particularly, γ -alumina. As the alumina, it is preferred to use active alumina having a specific surface area of 10 m2/g or more, preferably 50 to 300 m2/g. The preferred alumina has an average particle diameter of 0.1 µ m to 100 µ m, more preferably in the range of 0.1 to 50 µ m. The shape of the alumina is arbitrary. As the alumina mentioned here, use can be made of a commercially available product, such as alumina marketed by Nikki-Universal Co., Ltd. (product name: NST-5 and NSA20-3×6), or alumina produced by SUMITOMO CHEMICAL CO, LTD. (product name: e.g., NK-124). [0020] Component 1: Zirconium oxide (ZrO2) Zirconium oxide (may be called zirconia) as the component 1 is a single substance, zirconia (chemical formula: ZrO2), which is generally used as a catalytic carrier, or a complex oxide composed of magnesia and zirconia. Its specific surface area is an important factor for supporting platinum to be described below (component 2) in a highly dispersed state, and for enhancing the property of contacting a gas to be treated. The specific surface area is preferably 5 m /g or more, more preferably 10 to 150 m /g. The average particle diameter is preferably 0.1 µ m to 100 µ m, more preferably in the range of 0.1 to 50 µ m, in order to enhance the property of contacting the gas. As the zirconium oxide mentioned here, it is possible to use, for example, a commercially available product, such as the RC series of DAIICHIKIGENSO KAGAKU KOGYO CO., LTD. or the XZO series of Nippon Light Metal Company, Ltd. Component 2: Platinum In the catalyst of the present invention, platinum (Pt) of the above-mentioned embodiment (corresponding to [1] in the Means for solving the problems) is contained, as a metal content, in a range of 100 ppm by weight (0.01% by weight) to 10% by weight, preferably 200 ppm by weight or more, more preferably 500 ppm by weight or more, based on at least one of the inorganic oxides Al2O3 and ZrO2 (component 1). This Pt content may be set in consideration of the oligomer content in the oven gas to be treated, the reaction temperature, the space velocity, and the duration of use of the catalyst. If the Pt content is less than 100 ppm by weight, the oxidation reaction may be insufficient. If it exceeds 10% by weight, on the other hand, a further increase in the reaction is not observed, and this is uneconomical. In the catalyst of the present invention, platinum exhibits higher activity against the PET oligomer than do other platinum group elements, such as ruthenium, rhodium, palladium, osmium, and iridium. [0021] In the catalyst of the present invention, platinum is used as being supported on either or both of Al2O3 particles and ZrO2 particles as the component 1. Also, platinum may be supported on zeolite as component 3 or cerium oxide particles as component 4 which will be described later. Basic methods of producing the catalyst of the present invention will be illustrated as follows: [A] A method which comprises coating a slurry containing the component 1 and the component 2 on a catalyst substrate (e.g., honeycomb), followed by drying, to form a catalyst layer serving as a catalyst precursor, impregnating the catalyst layer with an aqueous solution of a Pt compound, and performing drying, firing, and reduction. [B] A method which comprises preparing particles of the component 1 having a prescribed amount of Pt supported thereon (for example, Pt/Al2O3 particles, Pt/ZrO2 particles); mixing these particles with particles of the component 3 or component 4; coating a slurry containing the mixture on a catalyst substrate by means such as a wash coat; and performing drying and firing to form a catalyst layer. [0022] Component 3: Zeolite The catalyst of the present invention (corresponding to [2] in the Means for solving the problems) has a preferred embodiment in which zeolite as the component 3 is contained in addition to at least one of the inorganic oxides Al2O3 and ZrO2 (component 1) and Pt (component 2). The content of the component 3 is such that the weight ratio between the component 1 and the component 3 is 90:10 to 10:90, preferably 80:20 to 20:80, more preferably 70:30 to 30:70. When the proportion of the component 3 contained is 10% or more, the activity in degrading the PET oligomer is enhanced further, with the result that the durability of the catalyst is increased, and its effect of preventing contamination of the oven is improved. If the proportion of the component 3 exceeds 90%, the proportion of the component 1 becomes relatively low, so that the degradation rate of the PET oligomer tends to lower. The presence of zeolite is presumed to catalytically degrade the PET oligomer into low molecular weight components and accelerate the oxidizing action of the component 1. The zeolite may be a natural product or a synthetic product. Examples of the naturally occurring zeolite are mordenite, erionite and ferrierite. Example of the synthetic product are Y type zeolite or zeolite-Y; MFI type zeolite such as ZSM-5; and ß type zeolite. The molar ratio between silica and alumina (SiO2/Al2O3 molar ratio) which are constituents of the zeolite is preferably 5 or higher, but 100 or lower, because such zeolite has high durability to silicone, and has high activity in degrading the PET oligomer. Moreover, the zeolite may be of a proton type (H type) or of a metal-substituted type (including, for example, one substituted with a metal such as Na or Fe, or ammonium-substituted one). There are no special limitations on the particle size of the zeolite. However, in forming a catalyst layer on a substrate, such as a honeycomb, with the use of a slurry containing the zeolite as a mixture with particles of Al2O3 or ZrO2 as the component 1, it is preferred to enhance the dispersion of both types of particles and the property of contacting each other. Thus, the preferred average particle diameter is 0.1 µ m to 100 µ m, more preferably 0.1 to 50 M m. [0023] The zeolite used in the present invention includes an FCC (fluid catalytic cracking) catalyst which is usually used in the petroleum refining industry. The FCC catalyst is a catalyst containing 10 to 40% by weight of alumina and 90 to 60% by weight of silica, and having the action of decomposing hydrocarbons of large molecules contained in heavy oil. It is effective as the component 3 of the present invention. Component 4: CeO2 The catalyst of the present invention contains the component 1 and the component 2, and may further contain cerium oxide as component 4. The cerium oxide is one or more cerium oxides selected from the group consisting of ceria (CeO2), a ceria-zirconia complex oxide (CeO2 • ZrO2), and a complex oxide comprising the CeO2 and ZrO2 and an oxide of at least one of La, Y, Pr and Nd. The catalyst of the present invention containing the cerium oxide has high activity in degrading the PET oligomer, involves little formation of carbon, excels in durability, and is thus particularly excellent in the effect of preventing contamination of the oven. Furthermore, the catalyst of the present invention includes a catalyst containing the component 1, the component 2, the component 3 and the component 4. The content of the cerium oxide is 1 to 100 parts by weight, preferably 5 to 100 parts by weight, more preferably 10 to 100 parts by weight, with respect to 100 parts by weight of the component 1. If it is less than 1 part by weight, the effect is insufficient. The presence of the cerium oxide exceeding 100 parts by weight does not result in the effect of enhancing the activity or durability further. [0024] In the composition of the catalyst of the present invention, the cerium oxide exists as particles. The average particle diameter of this oxide is 0.1 µ m to 100 µ m, more preferably 0.1 to 50 µ m. Particles in this range are preferred in enhancing an increase in the activity of the catalyst obtained by mixing with particles of the component 1. [0025] As an alternative means, it is possible to incorporate the cerium oxide in the catalyst by impregnating particles of Al2O3 or ZrO2, as the component 1, with a solution of a cerium compound such as cerium nitrate, ammonium cerium nitrate, cerium chloride, cerium acetate, alkoxycerium, or an ammonium or ammine complex compound, followed by heating to 400 to 800°C. [0026] Incorporation of other components The catalyst of the present invention contains the component 1, the component 2 and the component 3 as essential components, but does not exclude the incorporation of other components, unless they impair the desired actions and effects. [0027] A catalyst, which exhibits high degrading activity and durability at a temperature close to the temperature of PET drawing, namely, at 200 to 350°C, is preferred for attaining the objects of the present invention. Along this line, a catalyst of a composition containing zirconium oxide (component 1), platinum (component 2) and cerium oxide (component 4) and in which the content of the component 4 is 10 to 100 parts by weight per 100 parts by weight of the component 1 is one of particularly preferred embodiments. Another preferred embodiment of the present invention is a catalyst of a composition containing at least one of the inorganic oxides alumina and zirconium oxide (component 1), platinum (component 2), zeolite (component 3), and cerium oxide (component 4), and in which the content of the component 3 is such that the weight ratio between the component 1 and the component 3 is 80:20 to 20:80, the component 3 is zeolite having a SiO2/Al2O3 molar ratio of 5 or more, but 100 or less, and the content of the component 4 is 1 to 100 parts by weight, more preferably 10 to 100 parts by weight, per 100 parts by weight of the component 1. [0028] Method of preparing the catalyst To be applied to purification of a drawing oven gas, the catalyst of the present invention is used in a form supported on a substrate (a carrier for supporting a catalyst). Needless to say, it is preferred for the substrate to be in a form having heat resistance, having a high efficiency of contact, and involving a small pressure loss. Concretely, a honeycomb, a sheet, a mesh, a pipe, a filter, a punching metal, and a foam metal are named. There are no limitations on the material for the substrate, but the preferred material is one having heat resistance or corrosion resistance. Its examples are cordierite, alumina, silica, silica-alumina, carbon fiber, metal fiber, glass fiber, ceramic fiber, stainless steel, and titanium. For example, the substrate is wash-coated with a slurry containing the catalyst of the present invention to prepare a honeycomb catalyst. [0029] Methods of producing a honeycomb catalyst supporting the catalyst will be described below. [0030] Production method 1: The honeycomb catalyst is produced by a step 1 of preparing a slurry containing particles of at least one of the inorganic oxides of alumina and zirconium oxide (component 1), zeolite particles (component 2), and a binder component; a step 2 of coating a predetermined amount of the slurry on a honeycomb, followed by drying, to form a catalyst precursor containing the component 1 and the component 2; and a step 3 of impregnating the catalyst precursor with an aqueous solution of a Pt compound before firing or after firing, drying it at 100 to 200°C, then firing it in air at a temperature in a range of 450 to 650°C, and if desired, reducing and firing the fired product in a hydrogen atmosphere. As the Pt compound, dinitrodiammineplatinum, chloroplatinic acid, platinum nitrate, and tetraammineplatinum dichloride are enumerated. [0031] Production method 2: Another method is a method comprising a step 1 of preparing particles having Pt carried on the alumina (Pt/Al2O3) or particles having Pt carried on the zirconium oxide (Pt/ZrO); a step 2 of preparing a slurry containing the supporting particles, zeolite particles, and a binder component; and a step 3 of coating a honeycomb with the slurry, followed by performing drying and firing under the above-mentioned conditions. [0032] With any of the above methods, the thickness of the catalyst layer supported on the honeycomb substrate may be set in such a manner as to be capable of effectively exhibiting the effects of the catalyst and in consideration of economy, and the suitable thickness is usually 10 µ m or more, but 500 µ m or less. The appropriate amount of the catalyst supported per liter of the honeycomb is 10 to 50 g as the total weight of the component 1 and the component 2. [0033] Method of purifying PET drawing oven gas A method of purifying the drawing oven gas will be described below. The catalyst of the present invention is disposed within the PET drawing oven or in a hot draft circulation system, and a hot draft is brought into contact with this catalyst. As a result, a PET oligomer contained in the hot draft is degraded by the catalyst to be converted into CO2 and H2O, whereby the oven gas can be purified. To exhibit the degrading activity of the catalyst of the present invention, the preferred temperature range is 200 to 350°C, preferably 210 to 350°C, more preferably 220 to 350°C. At a temperature lower than 200°C, the degradation reaction of the PET oligomer does not proceed sufficiently, and the undegraded PET oligomer tends to remain, or carbon monoxide (CO) tends to form. At a temperature in excess of 350°C, the reaction proceeds sufficiently. However, during the circulation of the treated gas for use, the gas needs to be cooled to a temperature suitable for the heat treatment of the PET film (normally, 200 to 230°C), resulting in a waste of energy. The space velocity (SV) of the gas is not limited, but normally, the SV of 1,000 to 200,000 hr-1 is preferred, although depending on the concentration of the PET oligomer, in order to burn the PET oligomer component in the hot draft completely. The catalytically treated gas (treated gas) is refluxed to the heat treatment oven. On this occasion, the total amount of the treated gas may be refluxed, or a part of the treated gas may be discarded, and the remainder after introduction of fresh air may be refluxed. Method of preventing contamination of PET drawing oven The method of preventing contamination of a PET drawing oven according to the present invention is a method comprising a step 1 of bringing a hot draft, which contains an oligomer within a PET drawing oven, into contact with the catalyst of the present invention installed inside the drawing oven or in a hot draft circulation system at a temperature of 200 to 350°C, preferably 210 to 350°C, more preferably 220 to 350°C, to degrade the oligomer oxidatively; and a step 2 of refluxing all or a part of a treated gas to the drawing oven. The method with these steps decreases the content of the oligomer in the hot draft. Thus, the amount of deposition of the oligomer on the interior of the oven or the hot draft circulation system can be decreased to prevent the contamination of the oven. [0034] The present invention will be described in more detail based on Examples and Comparative Examples presented below, but is in no way limited thereby. (Example 1) Preparation of catalyst> Preparation of catalyst 1: Pt(0.1)/Al2O3(100) Particles (Pt(0.1)/Al2O3, 100 g) having 0.1% by weight of Pt supported on a γ -alumina powder (produced by Nikki-Universal Co., Ltd., average particle diameter 5 µ m), and 25 g of boehmite as a binder were mixed into 350 g of an acidic aqueous solution of nitric acid to prepare a slurry. This slurry was coated on a cordierite honeycomb (produced by NGK Insulators, Ltd., 200 cells/square inch) by the wash coat process such that the weight of a catalyst layer per liter of the honeycomb would be 50 g (excluding the binder). The excess slurry was blown away with compressed air, and then dried for 3 hours at 150°C in a dryer. Then, the dried product was fired in air for 2 hours at 500°C to obtain a catalyst 1 of a honeycomb type supporting a catalyst layer of Pt/Al2O3. Preparation of catalyst 2: Pt(0.1)ZrO2(100) Using particles (Pt(0.1 )/ZrO2) having 0.1% by weight of Pt supported on a ZrO2 powder (produced by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD., average particle diameter 5 µ m, BET specific surface area 100 m2/g), a honeycomb type catalyst 2 was obtained in the same manner as for the catalyst 1. The Pt content of the catalyst 2 was 0.1% by weight (a proportion to ZrO2). Preparation of comparative catalyst Rl: Pt(0.1)/TiO2(100) Using particles (Pt(0.1)/TiO2) having 0.1% by weight of Pt supported on a TiO2 powder (produced by Millennium Pharmaceuticals, Inc., average particle diameter 1 µ m, BET specific surface area 330 m /g), a honeycomb type comparative catalyst A was obtained in the same manner as for the catalyst 1. The Pt content of the comparative catalyst Rl was 0.1% by weight (a proportion to TiO2). Preparation of catalyst 3: Pt(0.1)/Al2O3(50)+HY(50) A Y type zeolite powder (50 g; produced by UOP, commercial name LZY85, average particle diameter 2 µ m, SiO2/Al2O3 molar ratio 5.9, H type substituted product), 50 g of a γ -Al2O3 powder (produced by Nikki-Universal Co., Ltd., BET specific surface area 169 m2/g), and 10 g (as SiO2 solid content) of silica sol (Nissan Chemical Industries, Ltd., SNOWTEX C) as a binder were added to 350 g of demineralized water to prepare a slurry. This slurry was coated on the honeycomb used in the catalyst 1 by the wash coat process such that a particle layer composed of a mixture of Al2O3 particles and HY particles (weight ratio 50:50) would amount to 50 g per liter of the honeycomb. Then, the coated honeycomb was dried for 3 hours at 150°C in a dryer, and then fired in air for 2 hours at 500°C. Then, the particle layer was impregnated with an aqueous solution of dinitroammineplatinum containing a prescribed amount of Pt. Then, the impregnated particle layer was dried and fired in a hydrogen atmosphere to obtain a honeycomb type catalyst 3 containing 0.1% by weight of Pt (a proportion to the total amount of Al2O3 and HY). Preparation of catalyst 4: Pt(0.1)/Al2O3(80)+HY(20) A particle layer comprising a mixture of Al2O3 and HY (weight ratio 80:20) was formed on a honeycomb carrier in the same manner as for the catalyst 3, except that 80 g of the Y type zeolite (HY) and 20 g of the γ -Al2O3 particles were used. Then, a honeycomb type catalyst 4 containing 0.1% by weight of Pt (a proportion to the total amount of Al2O3 and HY) was obtained in the same manner as for the catalyst 3. Preparation of catalyst 5: Pt(0.1)/ZrO2(50)+HY(50) A honeycomb type catalyst 5 containing 0.1% by weight of Pt (a proportion to the total amount of ZrO2 and HY) in a particle layer of a mixture of ZrO2 and HY (weight ratio 50:50) formed on a honeycomb carrier was obtained in the same manner as for the catalyst 3, except that ZrO2 particles (produced by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD., average particle diameter 5 µ m, BET specific surface area 100m2/g) were used instead of the Al2O3 particles. Preparation of catalyst 6: Pt(0.1)/Al2O3(50)+ß zeolite(50) A honeycomb type catalyst 6 containing 0.1% by weight of Pt (a proportion to the total amount of Al2O3 and ß zeolite) in a particle layer of a mixture of Al2O3 and ß zeolite (weight ratio 50:50) formed on a honeycomb carrier was obtained in the same manner as for the catalyst 3, except that a ß zeolite powder (produced by UOP, average particle diameter 2 µ m, SiO2/Al2O3 molar ratio 25) was used instead of the HY. (Example 2) The honeycomb catalysts prepared in Example 1 were mounted on a reactor 1 shown below, and each catalyst was measured for degrading activity against a PET oligomer and durability. [0035] Reactor 1 Fig. 1 shows the outline of a flow-through reactor 1 used in the evaluation of the catalyst. A sample container 12 installed within a reaction tube 11 is charged with a solid PET oligomer (R) serving as a material for gas generation. The numeral 13 denotes a cylindrical honeycomb catalyst (diameter 21 mm, length 10 mm). A PET oligomer gas generated by heating is degraded by the catalyst 13, and the gas after treatment (called an exhaust gas) is cooled to about 130°C. The undegraded PET oligomer contained is trapped as a solid by a collection filter 14. The exhaust gas is discharged through a gas discharge pipe 16, and subjected to gas analysis. PET oligomer gas used in activity evaluation A sample gas for evaluation of degrading activity was generated using a solid PET oligomer building up within a PET drawing oven (actual machine). The infrared absorption spectrum of the solid PET oligomer used is shown in Fig. 2A. For reference, the infrared absorption spectrum of a PET resin is shown in Fig. 2B. [0036] Procedure For a single (called one cycle) degradation test, 15 g of a powder of the PET oligomer was placed in the container 12, and the reaction tube 11 was heated from outside to raise the temperature from room temperature up to 250°C at a rate of 5°C per minute. Then, air of 250°C was introduced from a gas introduction pipe 15 at a rate of 2.0 liters/min to a total amount of 100 liters. Air containing the sublimed PET oligomer was brought into contact with the catalyst at a temperature of 250°C to conduct a degradation test. CO in the exhaust gas was analyzed by an electrolytic CO analyzer. Each time the degradation test was completed through one cycle, the undegraded PET oligomer trapped by the collection filter 14 was measured as a carbon content by an LECO analyzer. The above procedure was repeated 15 times (15 cycles) for each catalyst to investigate the degrading activity and durability of the catalyst. [0037] Degradation rate of PET oligomer The degradation rate of the PET oligomer was determined by the following Equation 1: [0038] [Equation 1] Degradation rate of PET oligomer (%) = (C1 - C2)/C 1 × 100 (Equation 1) In Equation 1, Cl represents the weight of the undegraded PET oligomer expressed as the carbon content (weight), the undegraded PET oligomer being trapped by the collection filter when the cordierite honeycomb (free of the catalytic component) used in the preparation of the catalyst was mounted at the position of the catalyst 13 in Fig. 1, and the PET oligomer-containing gas was flowed under the aforementioned conditions; and C2 represents the weight of the undegraded PET oligomer expressed as the carbon content (weight), the undegraded PET oligomer being trapped on the collection filter when the catalyst was mounted, and the degradation test was conducted. The catalyst showing a high value of the PET oligomer degradation rate has a small C2, meaning that it has a high effect of preventing the contamination of the drawing oven. The results of the degradation test of the PET oligomer-containing gas performed through 15 cycles using each catalyst are shown in Table 1-1. Specifically, Table 1-1 shows the PET oligomer degradation rates and the CO concentrations (average values) in the degraded gas after 1 to 3 cycles, 8 to 10 cycles, and 13 to 15 cycles. [0039] [Table 1-1] (Table Removed) Ex.: Example C.Ex.: Comparative Example Cat.: Catalyst C.Cat.: Comparative Catalyst As clear from the above Table 1-1, the PET oligomer degradation rate of the comparative catalyst Rl (Pt/TiO2) was 78% after 1 to 3 cycles, but decreased to 15% after 8 to 10 cycles, and further to 5% or less after 13 to 15 cycles. On the other hand, those of the catalyst 1 (Pt/Al2O3) and the catalyst 2 (Pt/ZrO2) of the present invention were 50% or more after 1 to 15 cycles, and the catalyst 2, in particular, showed that of 70% or more for these cycles. The catalysts 3 to 6 containing zeolite showed much higher degrading activity and durability. The CO concentrations in the exhaust gas treated with the catalysts 1 to 6 of the present invention were low, making it clear that these catalysts oxidized the PET oligomer almost completely. Especially, the catalysts 2 and 5 containing ZrO2 showed high degradation rates after 15 cycles, and thus prove excellently effective in preventing the contamination of the PET drawing oven. (Example 3) Catalysts containing CeO2 were prepared as follows: Preparation of catalyst 8: Pt(0.1)/Al2O3(90)+CeO2(10) The Al2O3 powder (90 g) used in the preparation of the aforesaid catalyst 1, 10 g of a CeO2 powder (cerium oxide produced by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD., average particle diameter: 5 µ m), and 10 g (as a solid content) of the binder used in the preparation of the catalyst 3 were mixed into 350 g of demineralized water to prepare a slurry. This slurry was applied onto a cordierite honeycomb in the same manner as for the catalyst 3 so that a particle layer comprising a mixture of particles of both of Al2O3 and CeO2 (weight ratio 90:10) whose catalyst layer weighed 50 g (excluding the binder) per liter of the honeycomb would be formed on the honeycomb carrier. Then, in the same manner as for the catalyst 3, the particle layer was impregnated with an aqueous solution of dinitrodiammineplatinum to obtain a honeycomb type catalyst 8 supporting Pt. The Pt content in the catalyst layer of the catalyst 8 was 0.1% by weight. Preparation of catalyst 9: Pt(0.1)/ZrO2(90)+CeO2(10) The ZrO2 particles (90 g) used in the preparation of the aforesaid catalyst 2, 10 g of the CeO2 powder used in the catalyst 8, 10 g (as a solid content) of the binder used in the catalyst 3, and 270 g of demineralized water were mixed to prepare a slurry. Then, the same method as in the preparation of the catalyst 3 was performed to obtain a honeycomb type catalyst 9 provided with a catalyst layer at a ZrO2:CeO2 weight ratio of 90:10. The Pt content in the catalyst layer of the catalyst 9 was 0.1% by weight. Preparation of catalyst 10: Pt(0.n/ZrO2(50)+CeO2(50) A honeycomb type catalyst 10 provided with a catalyst layer at a ZrO2:CeO2 weight ratio of 50:50 was prepared in the same manner as for the catalyst 9, except that the weight ratio of ZrO2:CeO2 was changed to 50:50. The Pt content in the catalyst layer of the catalyst 10 was 0.1% by weight. (Example 4) The catalysts 8 to 10 and the comparative catalyst B were evaluated for degrading activity by the method of the aforementioned Evaluation 1. The results are shown in Table 1-2, along with the results for the aforesaid catalysts 1 and 2. The catalysts 9 and 10 containing ZrO2 and CeO2 kept showing high degrading activity through all cycles. [0040] [Table 1-2] (Table Removed) Ex.: Example C.Ex.: Comparative Example Cat.: Catalyst C.Cat.: Comparative Catalyst NA means the absence of a measured value. (Example 5) Preparation of catalyst A: Pt(1.8)/Al2O3 A honeycomb type catalyst 11 was prepared in the same manner as for the aforementioned catalyst 1, except that the amount of Pt supported was changed. The Pt content in the catalyst 11 was set at 1.8 g per liter of the honeycomb. Preparation of catalyst B: Pt(1.8)/ZrO2(100) A honeycomb type catalyst 12 was prepared in the same manner as for the aforementioned catalyst 2, except that the amount of Pt supported was changed. The Pt content in the catalyst 12 was set at 1.8 g per liter of the honeycomb. Preparation of catalyst C: Pt(1.8)/Al2O3(50)+HY(50) An inorganic particle layer of Al2O3 and HY (weight ratio 50:50) was formed on the surface of a honeycomb carrier in the same manner as for the aforementioned catalyst 3. Then, the inorganic particle layer was impregnated with an aqueous solution of dinitrodiammineplatinum containing a prescribed amount of Pt, followed by drying and firing in a hydrogen atmosphere, to obtain a catalyst 13 containing 1.8 g of Pt per liter of the honeycomb. (Example 6) The catalysts as the catalysts A, B and C were mounted on a PET drawing apparatus (actual machine) used in PET film production, and the drawing oven gas was treated for 9 months. The activity (degrading activity against the PET oligomer and acetaldehyde) of the catalyst after 9 months of use was tested by the following methods. [0041] Reactor 2 A simultaneous degradation test of a PET oligomer and acetaldehyde was conducted using a flow-through reactor 2 shown in Fig. 3. A sample container 22 placed within a sample evaporation container 20 of the reactor is charged with 2.5 g of a powder of a PET resin compound (indicated as S in Fig. 3). A catalyst 23 (cylindrical honeycomb catalyst; diameter 21 mm, length 50 mm) is installed in a reaction tube 21. A gas treated with the catalyst (i.e., an exhaust gas) is accommodated in a gas collection container 27 connected via connection piping 26, and is cooled there to 90 to 100°C from outside. The undegraded PET oligomer is recovered in a solid form into a sampling glass container 28 installed within the container, and is weighed. Simultaneously, the concentrations of CO and acetaldehyde in the exhaust gas are measured. The acetaldehyde concentration was measured with a GASTEC Detecting Tube No. 91. [0042] Procedure With air being flowed through a gas introduction pipe 25 of the reactor 2, the temperature was raised from room temperature up to 250°C over the course of 15 minutes. The temperature was maintained at 250°C for 45 minutes, and air of 250°C was flowed continuously to generate a PET oligomer and acetaldehyde from the PET resin. Air containing these substances was subjected to a degradation reaction by the catalyst under the conditions, temperate 300°C and space velocity SV 35000 h-1. Aldehyde removal rate The aldehyde removal rate was calculated from the following Equation 2, and the PET oligomer degradation rate was calculated from the aforementioned Equation 1. [0043] [Equation 2] Aldehyde removal rate (%) = 100 × (C1- C2)/C 1 (Equation 2) In Equation 2, C1 represents the concentration (ppm) of aldehyde in the exhaust gas upon treatment only with the honeycomb carrier mounted, and C2 represents the concentration (ppm) of aldehyde in the exhaust gas when the catalyst was mounted. [0044] Results The results of the activity test of the new catalysts and the catalysts after 9 months of usage are shown in Table 2. Table 2 also shows the results of weight analysis of silicon (Si) and sulfur (S) deposited on the catalysts after 9 months of use. [0045] [Table 2] (Table Removed) Ex.: Example Cat.: Catalyst * 1: Indicated as weight percentage based on the entire honeycomb catalyst (value after subtraction of Si content in the binder). As clear from the above Table 2, the catalysts A, B and C all exhibited high degradation rates against aldehyde as well as the PET oligomer. The catalysts B and C, in particular, underwent very small decreases in the degrading activity against the aldehyde and PET oligomer even after 9 months of use, proving to have excellent durability. Each of the catalysts used for 9 months has, deposited thereon, organic silicon compounds (Si) and sulfur compounds (S) which are assumed to have been contained in the PET resin. It is evident for the catalysts of the present invention to have high resistance to these catalytic poisons. REFERENCE SIGNS LIST [0046] 11,21 Reaction tube 12.22 Sample container 13.23 Catalyst 14 Collection filter 15, 25 Gas introduction pipe 16, 29 Gas discharge pipe 20 Sample evaporation container 26 Connection piping 27 Gas collection container 28 Sampling container WE CLAIM: 1. A catalyst for purification of a PET drawing oven gas, the catalyst comprising zirconium oxide (component 1) and platinum (component 2). 2. The catalyst for purification of a PET drawing oven gas according to claim 1, further comprising zeolite (component 3), and wherein a weight ratio between the component 1 and the component 3 is 90:10 to 10:90. 3. The catalyst for purification of a PET drawing oven gas according to claim 2, wherein a SiO2/Al2O3 molar ratio of the zeolite used is 5 or higher, but 100 or lower. 4. The catalyst for purification of a PET drawing oven gas according to claim 2 or 3, further comprising at least one of platinum-supporting zirconium oxide particles; and zeolite particles. 5. The catalyst for purification of a PET drawing oven gas according to claim 1, further comprising cerium oxide (component 4), and wherein a content of the cerium oxide is 1 to 100 parts by weight per 100 parts by weight of the component 1. 6. The catalyst for purification of a PET drawing oven gas according to claim 5, wherein the cerium oxide is CeO2, or a complex oxide composed of CeO2 and ZrO2 (CeO2• ZrO2), or a complex oxide comprising the CeO2• ZrO2 and an oxide of at least one of La, Y, Pr and Nd. 7. The catalyst for purification of a PET drawing oven gas according to any one of claims 1 to 6, wherein a content of the platinum is 0.01 to 10% by weight based on the component 1. 8. A catalyst for purification of a PET drawing oven gas, comprising zirconium oxide (component 1), platinum (component 2), zeolite (component 3), and cerium oxide (component 4), and wherein a content of the component 3 is such that a weight ratio between the component 1 and the component 3 is 90:10 to 10:90, and a content of the component 4 is 1 to 100 parts by weight per 100 parts by weight of the component 1. 9. A catalyst for purification of a PET drawing oven gas, comprising the catalyst according to any one of claims 1 to 8 supported on a catalyst substrate. 10. The catalyst for purification of a PET drawing oven gas according to any one of claims 1 to 9, wherein a drawing oven gas is a gas containing acetaldehyde as well as a PET oligomer, and the catalyst oxidatively degrades these two components. 11. A method of purifying a PET drawing oven gas, comprising: a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of claims 1 to 10 provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven. 12. A method of preventing contamination of a PET drawing oven, comprising: a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of claims 1 to 10 provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven. 13. The catalyst for purification of a PET drawing oven gas according to any one of claims 1 to 9, wherein the drawing oven gas is a gas containing an organosilicon compound and a sulfur compound as well as the PET oligomer, and the catalyst has an action of oxidatively degrading the PE oligomer, and simultaneously has an action of depositing the organosilicon compound and the sulfur compound in the catalyst.

Full Text

DESCRIPTION TECHNICAL FIELD
[0001] This invention relates to a catalyst for oxidatively degrading volatile PET oligomer components contained in a hot draft within a drawing oven when drawing a polyester resin (PET) by a drawing apparatus to produce a PET film; a method of purifying a PET drawing oven gas with the use of the catalyst; and a method of preventing contamination of a PET drawing oven with the use of the catalyst. BACKGROUND ART
[0002] When a PET film is produced using a drawing apparatus (usually called a tenter), a PET resin is heated with hot air or draft. During drawing, PET oligomers, for example, low polymers such as cyclic trimers apt to form during polymerization, and volatile organic compounds formed by oxidative degradation, such as 4-carboxybenzaldehyde, monohydroxyterephthalate, and terephthalic acid, sublime or volatilize from the film, and mix into the hot draft. The PET oligomers are sublimable. Thus, if the hot draft containing them contacts a low-temperature site within the oven or a circulation system, the PET oligomers solidify, and deposit on the wall of the oven or within piping, presenting a cause of contamination or clogging. The adhesion of the PET oligomers onto the surface of the film causes the problem of quality deterioration. [0003] (Prior art)
Under these circumstances, a gas purification catalyst and its related technologies have been developed as a field of technologies for purifying the oven gas. [0004] Patent Document 1 discloses a technology which passes a hot draft within a tenter through an oxidation catalyst layer comprising a platinum group metal (ruthenium, rhodium, palladium, osmium, iridium or platinum).
[0005] Patent Document 2 discloses a technology which comprises burning and removing oligomers formed within a tenter by an oxidation catalyst when producing a PET film while circulating a hot draft within the tenter, and blowing the hot draft after removal against the surface of the film. [0006] Patent Document 3 discloses a technology in which a platinum catalyst is disposed
in a hot draft circulation path in a method for preparation of a biaxially oriented polyester film, and low molecular weight substances volatilizing from the film and entering a circulating hot draft are combusted efficiently in the presence of the platinum catalyst. [0007] Patent Document 4 discloses a technology which uses a filter incorporating a platinum catalyst block for removal of oligomers.
[0008] Patent Document 5 discloses a technology in which a tenter is provided with a catalyst for degrading and removing sublimates generated from a thermoplastic resin. [0009] (Problems with the conventional technologies)
As described above, the documents cited above introduce the facts that an oxidation catalyst is used for treatment of a drawing oven gas of a PET drawing apparatus; that a platinum group metal (ruthenium, rhodium, palladium, osmium, iridium or platinum) is used as an active component of the oxidation catalyst; and that the treated gas is circulated and used again.
[0010] None of the documents, however, report the details of the catalyst. PET oligomers have relatively large molecular weights, and thus are difficult to oxidize completely. As a result, a coky substance is prone to deposit on the catalyst, causing a decrease in activity. Moreover, the gas within the PET drawing oven may involve silicon-containing compounds and organic sulfur compounds which are regarded as resulting from additives to the PET resin. Since such compounds become causes of decreased catalytic activity, durability to them is also of importance. Furthermore, aldehydes such as acetaldehyde are formed during PET drawing. Thus, there is a demand for a catalyst which degrades and removes them at the same time. CITATION LIST PATENT LITERATURE [0011] PLT1: JP-A-59-98821
PLT 2: JP-B-60-45577
PLT3: JP-A-11-342535
PLT 4: JP-A-11-77823
PLT 5: JP-A-2002-144420

SUMMARY OF INVENTION TECHNICAL PROBLEM
[0012] Objects of the present invention are, therefore, to provide a catalyst which degrades, with a high degree of conversion, PET oligomers in a drawing oven gas of a PET drawing apparatus; provide a catalyst which oxidatively degrades aldehydes, such as acetaldehyde, simultaneously; provide a catalyst of high durability; a method of purifying a PET drawing oven gas with the use of the catalyst; and a method of preventing contamination of a PET drawing oven with the use of the catalyst. SOLUTION TO PROBLEM
[0013] The inventors of the present invention have found a catalyst, which can solve the above-mentioned problems, by a specific combination of an active component and a carrier in an attempt to oxidize and combust a PET oligomer component. Through this finding, the inventors have accomplished the present invention. The gist of the present invention is as follows:
[1] A catalyst for purification of a PET drawing oven gas, the catalyst comprising at least one of inorganic oxides which are alumina and zirconium oxide (component 1); and platinum (component 2).
[2] The catalyst for purification of a PET drawing oven gas according to [1], further comprising zeolite (component 3), and wherein a weight ratio between the component 1 and the component 3 is 90:10 to 10:90.
[3] The catalyst for purification of a PET drawing oven gas according to [2], wherein a SiO2/Al2O3 molar ratio of the zeolite used is 5 or higher, but 100 or lower. [4] The catalyst for purification of a PET drawing oven gas according to [2] or [3], further comprising at least either of platinum-supporting alumina particles and platinum-supporting zirconium oxide particles; and zeolite particles.
[5] The catalyst for purification of a PET drawing oven gas according to [1], further comprising cerium oxide (component 4), and wherein a content of the cerium oxide is 1 to 100 parts by weight per 100 parts by weight of the component 1. [6] The catalyst for purification of a PET drawing oven gas according to [5], wherein the
cerium oxide is CeO2, a complex oxide composed of CeO2 and ZrO2 (CeO2- ZrO2), or a complex oxide comprising the CeO2 • ZrO2 and an oxide of at least one of La, Y, Pr and Nd. [7] The catalyst for purification of a PET drawing oven gas according to any one of [1] to [6], wherein a content of the platinum is 0.01 to 10% by weight based on the component 1. [8] A catalyst for purification of a PET drawing oven gas, comprising at least one of inorganic oxides which are alumina and zirconium oxide (component 1), platinum (component 2), zeolite (component 3), and cerium oxide (component 4), and wherein a content of the component 3 is such that a weight ratio between the component 1 and the component 3 is 90:10 to 10:90, and a content of the component 4 is 1 to 100 parts by weight per 100 parts by weight of the component 1.
[9] A catalyst for purification of a PET drawing oven gas, comprising the catalyst according to any one of [ 1 ] to [8] supported on a catalyst substrate. [10] The catalyst for purification of a PET drawing oven gas according to any one of [1] to [9], wherein a drawing oven gas is a gas containing acetaldehyde as well as a PET oligomer, and the catalyst oxidatively degrades these two components. [11] A method of purifying a PET drawing oven gas, comprising:
a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of [1] to [10] provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and
a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven. [12] A method of preventing contamination of a PET drawing oven, comprising:
a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of [1] to [10] provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and
a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven. ADVANTAGEOUS EFFECTS OF INVENTION [0014] According to the catalyst of the present invention, the following prominent effects
are achieved:
[ 1 ] The catalyst for purification of a PET drawing oven gas according to the present
invention oxidatively degrades, with a high degree of conversion, a sublimable polymer
contained in the PET drawing oven gas, such as a PET oligomer, thereby converting it into
CO2 and H2O. This catalyst minimally declines in activity, and excels in durability.
[2] Aldehydes formed during the drawing of the PET film simultaneously undergo
oxidative degradation.
[3] Purification of a PET drawing oven gas, which has been difficult to achieve using
known catalysts, can be achieved for a long term. By so doing, contamination of the
drawing oven can be prevented, and labor for maintenance and management of the drawing
oven can be lessened.
BRIEF DESCRIPTION OF DRAWINGS
[0015] [Fig. 1] is an outline view of a reactor 1 for evaluation of a catalyst.
[Fig. 2A] shows the infrared absorption spectrum of a PET oligomer.
[Fig. 2B] shows the infrared absorption spectrum of a PET resin.
[Fig. 3] is an outline view of a reactor 2 used for the simultaneous degradation test of the PET oligomer and acetaldehyde. DESCRIPTION OF EMBODIMENTS
[0016] Embodiments of the present invention will now be described below. [0017] (Field of application)
An object to which the catalyst of the present invention is applied is an oven gas containing a PET oligomer generated during production of a PET film in a PET drawing oven. The PET oligomer refers to a volatile (sublimable) organic component generated from a PET resin or a PET film in the aforementioned heating step which is carried out during drawing of the PET resin. Herein, an average particle diameter refers to the average particle diameter of secondary particles measured by the laser method, unless otherwise specified. A specific surface area is a value measured by the BET process. [0018] The catalyst of the present invention will be described below. [0019] Component 1: Alumina (A12O3)
Alumina (Al2O3), one of the components of the catalyst according to the present invention, is active alumina in general use as a catalytic carrier, such as γ -alumina or δ -alumina, particularly, γ -alumina. As the alumina, it is preferred to use active alumina having a specific surface area of 10 m2/g or more, preferably 50 to 300 m2/g. The preferred alumina has an average particle diameter of 0.1 µ m to 100 µ m, more preferably in the range of 0.1 to 50 µ m. The shape of the alumina is arbitrary. As the alumina mentioned here, use can be made of a commercially available product, such as alumina marketed by Nikki-Universal Co., Ltd. (product name: NST-5 and NSA20-3×6), or alumina produced by SUMITOMO CHEMICAL CO, LTD. (product name: e.g., NK-124). [0020] Component 1: Zirconium oxide (ZrO2)
Zirconium oxide (may be called zirconia) as the component 1 is a single substance, zirconia (chemical formula: ZrO2), which is generally used as a catalytic carrier, or a complex oxide composed of magnesia and zirconia. Its specific surface area is an important factor for supporting platinum to be described below (component 2) in a highly dispersed state, and for enhancing the property of contacting a gas to be treated. The specific surface area is preferably 5 m /g or more, more preferably 10 to 150 m /g. The average particle diameter is preferably 0.1 µ m to 100 µ m, more preferably in the range of 0.1 to 50 µ m, in order to enhance the property of contacting the gas. As the zirconium oxide mentioned here, it is possible to use, for example, a commercially available product, such as the RC series of DAIICHIKIGENSO KAGAKU KOGYO CO., LTD. or the XZO series of Nippon Light Metal Company, Ltd.
Component 2: Platinum
In the catalyst of the present invention, platinum (Pt) of the above-mentioned embodiment (corresponding to [1] in the Means for solving the problems) is contained, as a metal content, in a range of 100 ppm by weight (0.01% by weight) to 10% by weight, preferably 200 ppm by weight or more, more preferably 500 ppm by weight or more, based on at least one of the inorganic oxides Al2O3 and ZrO2 (component 1). This Pt content may be set in consideration of the oligomer content in the oven gas to be treated, the reaction temperature, the space velocity, and the duration of use of the catalyst. If the Pt content is
less than 100 ppm by weight, the oxidation reaction may be insufficient. If it exceeds 10% by weight, on the other hand, a further increase in the reaction is not observed, and this is uneconomical. In the catalyst of the present invention, platinum exhibits higher activity against the PET oligomer than do other platinum group elements, such as ruthenium, rhodium, palladium, osmium, and iridium.
[0021] In the catalyst of the present invention, platinum is used as being supported on either or both of Al2O3 particles and ZrO2 particles as the component 1. Also, platinum may be supported on zeolite as component 3 or cerium oxide particles as component 4 which will be described later. Basic methods of producing the catalyst of the present invention will be illustrated as follows:
[A] A method which comprises coating a slurry containing the component 1 and the component 2 on a catalyst substrate (e.g., honeycomb), followed by drying, to form a catalyst layer serving as a catalyst precursor, impregnating the catalyst layer with an aqueous solution of a Pt compound, and performing drying, firing, and reduction.
[B] A method which comprises preparing particles of the component 1 having a prescribed amount of Pt supported thereon (for example, Pt/Al2O3 particles, Pt/ZrO2 particles); mixing these particles with particles of the component 3 or component 4; coating a slurry containing the mixture on a catalyst substrate by means such as a wash coat; and performing drying and firing to form a catalyst layer.
[0022] Component 3: Zeolite
The catalyst of the present invention (corresponding to [2] in the Means for solving the problems) has a preferred embodiment in which zeolite as the component 3 is contained in addition to at least one of the inorganic oxides Al2O3 and ZrO2 (component 1) and Pt (component 2). The content of the component 3 is such that the weight ratio between the component 1 and the component 3 is 90:10 to 10:90, preferably 80:20 to 20:80, more preferably 70:30 to 30:70. When the proportion of the component 3 contained is 10% or more, the activity in degrading the PET oligomer is enhanced further, with the result that the durability of the catalyst is increased, and its effect of preventing contamination of the oven is improved. If the proportion of the component 3 exceeds 90%, the proportion of the
component 1 becomes relatively low, so that the degradation rate of the PET oligomer tends to lower. The presence of zeolite is presumed to catalytically degrade the PET oligomer into low molecular weight components and accelerate the oxidizing action of the component 1.
The zeolite may be a natural product or a synthetic product. Examples of the naturally occurring zeolite are mordenite, erionite and ferrierite. Example of the synthetic product are Y type zeolite or zeolite-Y; MFI type zeolite such as ZSM-5; and ß type zeolite. The molar ratio between silica and alumina (SiO2/Al2O3 molar ratio) which are constituents of the zeolite is preferably 5 or higher, but 100 or lower, because such zeolite has high durability to silicone, and has high activity in degrading the PET oligomer. Moreover, the zeolite may be of a proton type (H type) or of a metal-substituted type (including, for example, one substituted with a metal such as Na or Fe, or ammonium-substituted one). There are no special limitations on the particle size of the zeolite. However, in forming a catalyst layer on a substrate, such as a honeycomb, with the use of a slurry containing the zeolite as a mixture with particles of Al2O3 or ZrO2 as the component 1, it is preferred to enhance the dispersion of both types of particles and the property of contacting each other. Thus, the preferred average particle diameter is 0.1 µ m to 100 µ m, more preferably 0.1 to 50 M m.
[0023] The zeolite used in the present invention includes an FCC (fluid catalytic cracking) catalyst which is usually used in the petroleum refining industry. The FCC catalyst is a catalyst containing 10 to 40% by weight of alumina and 90 to 60% by weight of silica, and having the action of decomposing hydrocarbons of large molecules contained in heavy oil. It is effective as the component 3 of the present invention.
Component 4: CeO2
The catalyst of the present invention contains the component 1 and the component 2, and may further contain cerium oxide as component 4. The cerium oxide is one or more cerium oxides selected from the group consisting of ceria (CeO2), a ceria-zirconia complex oxide (CeO2 • ZrO2), and a complex oxide comprising the CeO2 and ZrO2 and an oxide of at least one of La, Y, Pr and Nd. The catalyst of the present invention containing the cerium
oxide has high activity in degrading the PET oligomer, involves little formation of carbon, excels in durability, and is thus particularly excellent in the effect of preventing contamination of the oven. Furthermore, the catalyst of the present invention includes a catalyst containing the component 1, the component 2, the component 3 and the component 4. The content of the cerium oxide is 1 to 100 parts by weight, preferably 5 to 100 parts by weight, more preferably 10 to 100 parts by weight, with respect to 100 parts by weight of the component 1. If it is less than 1 part by weight, the effect is insufficient. The presence of the cerium oxide exceeding 100 parts by weight does not result in the effect of enhancing the activity or durability further.
[0024] In the composition of the catalyst of the present invention, the cerium oxide exists as particles. The average particle diameter of this oxide is 0.1 µ m to 100 µ m, more preferably 0.1 to 50 µ m. Particles in this range are preferred in enhancing an increase in the activity of the catalyst obtained by mixing with particles of the component 1. [0025] As an alternative means, it is possible to incorporate the cerium oxide in the catalyst by impregnating particles of Al2O3 or ZrO2, as the component 1, with a solution of a cerium compound such as cerium nitrate, ammonium cerium nitrate, cerium chloride, cerium acetate, alkoxycerium, or an ammonium or ammine complex compound, followed by heating to 400 to 800°C. [0026] Incorporation of other components
The catalyst of the present invention contains the component 1, the component 2 and the component 3 as essential components, but does not exclude the incorporation of other components, unless they impair the desired actions and effects.
[0027] A catalyst, which exhibits high degrading activity and durability at a temperature close to the temperature of PET drawing, namely, at 200 to 350°C, is preferred for attaining the objects of the present invention. Along this line, a catalyst of a composition containing zirconium oxide (component 1), platinum (component 2) and cerium oxide (component 4) and in which the content of the component 4 is 10 to 100 parts by weight per 100 parts by weight of the component 1 is one of particularly preferred embodiments. Another preferred embodiment of the present invention is a catalyst of a composition containing at least one of
the inorganic oxides alumina and zirconium oxide (component 1), platinum (component 2), zeolite (component 3), and cerium oxide (component 4), and in which the content of the component 3 is such that the weight ratio between the component 1 and the component 3 is 80:20 to 20:80, the component 3 is zeolite having a SiO2/Al2O3 molar ratio of 5 or more, but 100 or less, and the content of the component 4 is 1 to 100 parts by weight, more preferably 10 to 100 parts by weight, per 100 parts by weight of the component 1. [0028] Method of preparing the catalyst
To be applied to purification of a drawing oven gas, the catalyst of the present invention is used in a form supported on a substrate (a carrier for supporting a catalyst). Needless to say, it is preferred for the substrate to be in a form having heat resistance, having a high efficiency of contact, and involving a small pressure loss. Concretely, a honeycomb, a sheet, a mesh, a pipe, a filter, a punching metal, and a foam metal are named. There are no limitations on the material for the substrate, but the preferred material is one having heat resistance or corrosion resistance. Its examples are cordierite, alumina, silica, silica-alumina, carbon fiber, metal fiber, glass fiber, ceramic fiber, stainless steel, and titanium. For example, the substrate is wash-coated with a slurry containing the catalyst of the present invention to prepare a honeycomb catalyst.
[0029] Methods of producing a honeycomb catalyst supporting the catalyst will be described below.
[0030] Production method 1: The honeycomb catalyst is produced by a step 1 of preparing a slurry containing particles of at least one of the inorganic oxides of alumina and zirconium oxide (component 1), zeolite particles (component 2), and a binder component; a step 2 of coating a predetermined amount of the slurry on a honeycomb, followed by drying, to form a catalyst precursor containing the component 1 and the component 2; and a step 3 of impregnating the catalyst precursor with an aqueous solution of a Pt compound before firing or after firing, drying it at 100 to 200°C, then firing it in air at a temperature in a range of 450 to 650°C, and if desired, reducing and firing the fired product in a hydrogen atmosphere. As the Pt compound, dinitrodiammineplatinum, chloroplatinic acid, platinum nitrate, and tetraammineplatinum dichloride are enumerated.
[0031] Production method 2: Another method is a method comprising a step 1 of preparing particles having Pt carried on the alumina (Pt/Al2O3) or particles having Pt carried on the zirconium oxide (Pt/ZrO); a step 2 of preparing a slurry containing the supporting particles, zeolite particles, and a binder component; and a step 3 of coating a honeycomb with the slurry, followed by performing drying and firing under the above-mentioned conditions. [0032] With any of the above methods, the thickness of the catalyst layer supported on the honeycomb substrate may be set in such a manner as to be capable of effectively exhibiting the effects of the catalyst and in consideration of economy, and the suitable thickness is usually 10 µ m or more, but 500 µ m or less. The appropriate amount of the catalyst supported per liter of the honeycomb is 10 to 50 g as the total weight of the component 1 and the component 2. [0033] Method of purifying PET drawing oven gas
A method of purifying the drawing oven gas will be described below. The catalyst of the present invention is disposed within the PET drawing oven or in a hot draft circulation system, and a hot draft is brought into contact with this catalyst. As a result, a PET oligomer contained in the hot draft is degraded by the catalyst to be converted into CO2 and H2O, whereby the oven gas can be purified. To exhibit the degrading activity of the catalyst of the present invention, the preferred temperature range is 200 to 350°C, preferably 210 to 350°C, more preferably 220 to 350°C. At a temperature lower than 200°C, the degradation reaction of the PET oligomer does not proceed sufficiently, and the undegraded PET oligomer tends to remain, or carbon monoxide (CO) tends to form. At a temperature in excess of 350°C, the reaction proceeds sufficiently. However, during the circulation of the treated gas for use, the gas needs to be cooled to a temperature suitable for the heat treatment of the PET film (normally, 200 to 230°C), resulting in a waste of energy. The space velocity (SV) of the gas is not limited, but normally, the SV of 1,000 to 200,000 hr-1 is preferred, although depending on the concentration of the PET oligomer, in order to burn the PET oligomer component in the hot draft completely. The catalytically treated gas (treated gas) is refluxed to the heat treatment oven. On this occasion, the total amount of the treated gas may be refluxed, or a part of the treated gas may be discarded, and the remainder after
introduction of fresh air may be refluxed.
Method of preventing contamination of PET drawing oven
The method of preventing contamination of a PET drawing oven according to the present invention is a method comprising a step 1 of bringing a hot draft, which contains an oligomer within a PET drawing oven, into contact with the catalyst of the present invention installed inside the drawing oven or in a hot draft circulation system at a temperature of 200 to 350°C, preferably 210 to 350°C, more preferably 220 to 350°C, to degrade the oligomer oxidatively; and a step 2 of refluxing all or a part of a treated gas to the drawing oven. The method with these steps decreases the content of the oligomer in the hot draft. Thus, the amount of deposition of the oligomer on the interior of the oven or the hot draft circulation system can be decreased to prevent the contamination of the oven. [0034] The present invention will be described in more detail based on Examples and Comparative Examples presented below, but is in no way limited thereby.
(Example 1)
Preparation of catalyst>
Preparation of catalyst 1: Pt(0.1)/Al2O3(100)
Particles (Pt(0.1)/Al2O3, 100 g) having 0.1% by weight of Pt supported on a γ -alumina powder (produced by Nikki-Universal Co., Ltd., average particle diameter 5 µ m), and 25 g of boehmite as a binder were mixed into 350 g of an acidic aqueous solution of nitric acid to prepare a slurry. This slurry was coated on a cordierite honeycomb (produced by NGK Insulators, Ltd., 200 cells/square inch) by the wash coat process such that the weight of a catalyst layer per liter of the honeycomb would be 50 g (excluding the binder). The excess slurry was blown away with compressed air, and then dried for 3 hours at 150°C in a dryer. Then, the dried product was fired in air for 2 hours at 500°C to obtain a catalyst 1 of a honeycomb type supporting a catalyst layer of Pt/Al2O3.
Preparation of catalyst 2: Pt(0.1)ZrO2(100)
Using particles (Pt(0.1 )/ZrO2) having 0.1% by weight of Pt supported on a ZrO2 powder (produced by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD., average particle diameter 5 µ m, BET specific surface area 100 m2/g), a honeycomb type catalyst 2 was
obtained in the same manner as for the catalyst 1. The Pt content of the catalyst 2 was 0.1% by weight (a proportion to ZrO2).
Preparation of comparative catalyst Rl: Pt(0.1)/TiO2(100)
Using particles (Pt(0.1)/TiO2) having 0.1% by weight of Pt supported on a TiO2 powder (produced by Millennium Pharmaceuticals, Inc., average particle diameter 1 µ m, BET specific surface area 330 m /g), a honeycomb type comparative catalyst A was obtained in the same manner as for the catalyst 1. The Pt content of the comparative catalyst Rl was 0.1% by weight (a proportion to TiO2).
Preparation of catalyst 3: Pt(0.1)/Al2O3(50)+HY(50)
A Y type zeolite powder (50 g; produced by UOP, commercial name LZY85, average particle diameter 2 µ m, SiO2/Al2O3 molar ratio 5.9, H type substituted product), 50 g of a γ -Al2O3 powder (produced by Nikki-Universal Co., Ltd., BET specific surface area 169 m2/g), and 10 g (as SiO2 solid content) of silica sol (Nissan Chemical Industries, Ltd., SNOWTEX C) as a binder were added to 350 g of demineralized water to prepare a slurry. This slurry was coated on the honeycomb used in the catalyst 1 by the wash coat process such that a particle layer composed of a mixture of Al2O3 particles and HY particles (weight ratio 50:50) would amount to 50 g per liter of the honeycomb. Then, the coated honeycomb was dried for 3 hours at 150°C in a dryer, and then fired in air for 2 hours at 500°C. Then, the particle layer was impregnated with an aqueous solution of dinitroammineplatinum containing a prescribed amount of Pt. Then, the impregnated particle layer was dried and fired in a hydrogen atmosphere to obtain a honeycomb type catalyst 3 containing 0.1% by weight of Pt (a proportion to the total amount of Al2O3 and HY).
Preparation of catalyst 4: Pt(0.1)/Al2O3(80)+HY(20)
A particle layer comprising a mixture of Al2O3 and HY (weight ratio 80:20) was formed on a honeycomb carrier in the same manner as for the catalyst 3, except that 80 g of the Y type zeolite (HY) and 20 g of the γ -Al2O3 particles were used. Then, a honeycomb type catalyst 4 containing 0.1% by weight of Pt (a proportion to the total amount of Al2O3 and HY) was obtained in the same manner as for the catalyst 3.

Preparation of catalyst 5: Pt(0.1)/ZrO2(50)+HY(50)
A honeycomb type catalyst 5 containing 0.1% by weight of Pt (a proportion to the total amount of ZrO2 and HY) in a particle layer of a mixture of ZrO2 and HY (weight ratio 50:50) formed on a honeycomb carrier was obtained in the same manner as for the catalyst 3, except that ZrO2 particles (produced by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD., average particle diameter 5 µ m, BET specific surface area 100m2/g) were used instead of the Al2O3 particles.
Preparation of catalyst 6: Pt(0.1)/Al2O3(50)+ß zeolite(50)
A honeycomb type catalyst 6 containing 0.1% by weight of Pt (a proportion to the total amount of Al2O3 and ß zeolite) in a particle layer of a mixture of Al2O3 and ß zeolite (weight ratio 50:50) formed on a honeycomb carrier was obtained in the same manner as for the catalyst 3, except that a ß zeolite powder (produced by UOP, average particle diameter 2 µ m, SiO2/Al2O3 molar ratio 25) was used instead of the HY.
(Example 2)

The honeycomb catalysts prepared in Example 1 were mounted on a reactor 1 shown below, and each catalyst was measured for degrading activity against a PET oligomer and durability. [0035] Reactor 1
Fig. 1 shows the outline of a flow-through reactor 1 used in the evaluation of the catalyst. A sample container 12 installed within a reaction tube 11 is charged with a solid PET oligomer (R) serving as a material for gas generation. The numeral 13 denotes a cylindrical honeycomb catalyst (diameter 21 mm, length 10 mm). A PET oligomer gas generated by heating is degraded by the catalyst 13, and the gas after treatment (called an exhaust gas) is cooled to about 130°C. The undegraded PET oligomer contained is trapped as a solid by a collection filter 14. The exhaust gas is discharged through a gas discharge pipe 16, and subjected to gas analysis.
PET oligomer gas used in activity evaluation
A sample gas for evaluation of degrading activity was generated using a solid PET
oligomer building up within a PET drawing oven (actual machine). The infrared absorption spectrum of the solid PET oligomer used is shown in Fig. 2A. For reference, the infrared absorption spectrum of a PET resin is shown in Fig. 2B. [0036] Procedure
For a single (called one cycle) degradation test, 15 g of a powder of the PET oligomer was placed in the container 12, and the reaction tube 11 was heated from outside to raise the temperature from room temperature up to 250°C at a rate of 5°C per minute. Then, air of 250°C was introduced from a gas introduction pipe 15 at a rate of 2.0 liters/min to a total amount of 100 liters. Air containing the sublimed PET oligomer was brought into contact with the catalyst at a temperature of 250°C to conduct a degradation test. CO in the exhaust gas was analyzed by an electrolytic CO analyzer. Each time the degradation test was completed through one cycle, the undegraded PET oligomer trapped by the collection filter 14 was measured as a carbon content by an LECO analyzer. The above procedure was repeated 15 times (15 cycles) for each catalyst to investigate the degrading activity and durability of the catalyst. [0037] Degradation rate of PET oligomer
The degradation rate of the PET oligomer was determined by the following Equation 1: [0038] [Equation 1]
Degradation rate of PET oligomer (%) = (C1 - C2)/C 1 × 100 (Equation 1)
In Equation 1, Cl represents the weight of the undegraded PET oligomer expressed as the carbon content (weight), the undegraded PET oligomer being trapped by the collection filter when the cordierite honeycomb (free of the catalytic component) used in the preparation of the catalyst was mounted at the position of the catalyst 13 in Fig. 1, and the PET oligomer-containing gas was flowed under the aforementioned conditions; and C2 represents the weight of the undegraded PET oligomer expressed as the carbon content (weight), the undegraded PET oligomer being trapped on the collection filter when the catalyst was mounted, and the degradation test was conducted. The catalyst showing a high value of the PET oligomer degradation rate has a small C2, meaning that it has a high effect

of preventing the contamination of the drawing oven.

The results of the degradation test of the PET oligomer-containing gas performed through 15 cycles using each catalyst are shown in Table 1-1. Specifically, Table 1-1 shows the PET oligomer degradation rates and the CO concentrations (average values) in the degraded gas after 1 to 3 cycles, 8 to 10 cycles, and 13 to 15 cycles. [0039] [Table 1-1]
(Table Removed)
Ex.: Example
C.Ex.: Comparative Example
Cat.: Catalyst
C.Cat.: Comparative Catalyst
As clear from the above Table 1-1, the PET oligomer degradation rate of the comparative catalyst Rl (Pt/TiO2) was 78% after 1 to 3 cycles, but decreased to 15% after 8 to 10 cycles, and further to 5% or less after 13 to 15 cycles. On the other hand, those of the catalyst 1 (Pt/Al2O3) and the catalyst 2 (Pt/ZrO2) of the present invention were 50% or more after 1 to 15 cycles, and the catalyst 2, in particular, showed that of 70% or more for these cycles. The catalysts 3 to 6 containing zeolite showed much higher degrading activity and durability. The CO concentrations in the exhaust gas treated with the catalysts 1 to 6 of the present invention were low, making it clear that these catalysts oxidized the PET oligomer almost completely. Especially, the catalysts 2 and 5 containing ZrO2 showed high degradation rates after 15 cycles, and thus prove excellently effective in preventing the contamination of the PET drawing oven.
(Example 3)

Catalysts containing CeO2 were prepared as follows:
Preparation of catalyst 8: Pt(0.1)/Al2O3(90)+CeO2(10)
The Al2O3 powder (90 g) used in the preparation of the aforesaid catalyst 1, 10 g of a CeO2 powder (cerium oxide produced by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD., average particle diameter: 5 µ m), and 10 g (as a solid content) of the binder used in the preparation of the catalyst 3 were mixed into 350 g of demineralized water to prepare a slurry. This slurry was applied onto a cordierite honeycomb in the same manner as for the catalyst 3 so that a particle layer comprising a mixture of particles of both of Al2O3 and CeO2 (weight ratio 90:10) whose catalyst layer weighed 50 g (excluding the binder) per liter of the honeycomb would be formed on the honeycomb carrier. Then, in the same manner as for the catalyst 3, the particle layer was impregnated with an aqueous solution of
dinitrodiammineplatinum to obtain a honeycomb type catalyst 8 supporting Pt. The Pt content in the catalyst layer of the catalyst 8 was 0.1% by weight.
Preparation of catalyst 9: Pt(0.1)/ZrO2(90)+CeO2(10)
The ZrO2 particles (90 g) used in the preparation of the aforesaid catalyst 2, 10 g of the CeO2 powder used in the catalyst 8, 10 g (as a solid content) of the binder used in the catalyst 3, and 270 g of demineralized water were mixed to prepare a slurry. Then, the same method as in the preparation of the catalyst 3 was performed to obtain a honeycomb type catalyst 9 provided with a catalyst layer at a ZrO2:CeO2 weight ratio of 90:10. The Pt content in the catalyst layer of the catalyst 9 was 0.1% by weight.
Preparation of catalyst 10: Pt(0.n/ZrO2(50)+CeO2(50)
A honeycomb type catalyst 10 provided with a catalyst layer at a ZrO2:CeO2 weight ratio of 50:50 was prepared in the same manner as for the catalyst 9, except that the weight ratio of ZrO2:CeO2 was changed to 50:50. The Pt content in the catalyst layer of the catalyst 10 was 0.1% by weight.
(Example 4)

The catalysts 8 to 10 and the comparative catalyst B were evaluated for degrading activity by the method of the aforementioned Evaluation 1. The results are shown in Table 1-2, along with the results for the aforesaid catalysts 1 and 2. The catalysts 9 and 10 containing ZrO2 and CeO2 kept showing high degrading activity through all cycles. [0040]
[Table 1-2]
(Table Removed)
Ex.: Example
C.Ex.: Comparative Example
Cat.: Catalyst
C.Cat.: Comparative Catalyst
NA means the absence of a measured value.
(Example 5)

Preparation of catalyst A: Pt(1.8)/Al2O3
A honeycomb type catalyst 11 was prepared in the same manner as for the aforementioned catalyst 1, except that the amount of Pt supported was changed. The Pt content in the catalyst 11 was set at 1.8 g per liter of the honeycomb.
Preparation of catalyst B: Pt(1.8)/ZrO2(100)
A honeycomb type catalyst 12 was prepared in the same manner as for the aforementioned catalyst 2, except that the amount of Pt supported was changed. The Pt content in the catalyst 12 was set at 1.8 g per liter of the honeycomb.
Preparation of catalyst C: Pt(1.8)/Al2O3(50)+HY(50)
An inorganic particle layer of Al2O3 and HY (weight ratio 50:50) was formed on the surface of a honeycomb carrier in the same manner as for the aforementioned catalyst 3. Then, the inorganic particle layer was impregnated with an aqueous solution of dinitrodiammineplatinum containing a prescribed amount of Pt, followed by drying and firing in a hydrogen atmosphere, to obtain a catalyst 13 containing 1.8 g of Pt per liter of the honeycomb.
(Example 6)

The catalysts as the catalysts A, B and C were mounted on a PET drawing apparatus (actual machine) used in PET film production, and the drawing oven gas was treated for 9 months. The activity (degrading activity against the PET oligomer and acetaldehyde) of the catalyst after 9 months of use was tested by the following methods. [0041] Reactor 2
A simultaneous degradation test of a PET oligomer and acetaldehyde was conducted using a flow-through reactor 2 shown in Fig. 3. A sample container 22 placed within a sample evaporation container 20 of the reactor is charged with 2.5 g of a powder of a PET resin compound (indicated as S in Fig. 3). A catalyst 23 (cylindrical honeycomb catalyst; diameter 21 mm, length 50 mm) is installed in a reaction tube 21. A gas treated with the catalyst (i.e., an exhaust gas) is accommodated in a gas collection container 27 connected via connection piping 26, and is cooled there to 90 to 100°C from outside. The undegraded
PET oligomer is recovered in a solid form into a sampling glass container 28 installed within the container, and is weighed. Simultaneously, the concentrations of CO and acetaldehyde in the exhaust gas are measured. The acetaldehyde concentration was measured with a GASTEC Detecting Tube No. 91. [0042] Procedure
With air being flowed through a gas introduction pipe 25 of the reactor 2, the temperature was raised from room temperature up to 250°C over the course of 15 minutes. The temperature was maintained at 250°C for 45 minutes, and air of 250°C was flowed continuously to generate a PET oligomer and acetaldehyde from the PET resin. Air containing these substances was subjected to a degradation reaction by the catalyst under the conditions, temperate 300°C and space velocity SV 35000 h-1.
Aldehyde removal rate
The aldehyde removal rate was calculated from the following Equation 2, and the PET oligomer degradation rate was calculated from the aforementioned Equation 1. [0043] [Equation 2]
Aldehyde removal rate (%) = 100 × (C1- C2)/C 1 (Equation 2)
In Equation 2, C1 represents the concentration (ppm) of aldehyde in the exhaust gas upon treatment only with the honeycomb carrier mounted, and C2 represents the concentration (ppm) of aldehyde in the exhaust gas when the catalyst was mounted. [0044] Results
The results of the activity test of the new catalysts and the catalysts after 9 months of usage are shown in Table 2. Table 2 also shows the results of weight analysis of silicon (Si) and sulfur (S) deposited on the catalysts after 9 months of use. [0045]
[Table 2]
(Table Removed)
Ex.: Example
Cat.: Catalyst
* 1: Indicated as weight percentage based on the entire honeycomb catalyst (value after
subtraction of Si content in the binder).
As clear from the above Table 2, the catalysts A, B and C all exhibited high degradation rates against aldehyde as well as the PET oligomer. The catalysts B and C, in particular, underwent very small decreases in the degrading activity against the aldehyde and PET oligomer even after 9 months of use, proving to have excellent durability. Each of the catalysts used for 9 months has, deposited thereon, organic silicon compounds (Si) and sulfur compounds (S) which are assumed to have been contained in the PET resin. It is evident for the catalysts of the present invention to have high resistance to these catalytic poisons. REFERENCE SIGNS LIST [0046] 11,21 Reaction tube
12.22 Sample container
13.23 Catalyst
14 Collection filter
15, 25 Gas introduction pipe
16, 29 Gas discharge pipe 20 Sample evaporation container
26 Connection piping
27 Gas collection container
28 Sampling container

WE CLAIM:
1. A catalyst for purification of a PET drawing oven gas, the catalyst comprising zirconium oxide (component 1) and platinum (component 2).
2. The catalyst for purification of a PET drawing oven gas according to claim 1, further comprising zeolite (component 3), and wherein a weight ratio between the component 1 and the component 3 is 90:10 to 10:90.
3. The catalyst for purification of a PET drawing oven gas according to claim 2, wherein a SiO2/Al2O3 molar ratio of the zeolite used is 5 or higher, but 100 or lower.
4. The catalyst for purification of a PET drawing oven gas according to claim 2 or 3, further comprising at least one of platinum-supporting zirconium oxide particles; and zeolite particles.
5. The catalyst for purification of a PET drawing oven gas according to claim 1, further comprising cerium oxide (component 4), and wherein a content of the cerium oxide is 1 to 100 parts by weight per 100 parts by weight of the component 1.
6. The catalyst for purification of a PET drawing oven gas according to claim 5, wherein the cerium oxide is CeO2, or a complex oxide composed of CeO2 and ZrO2 (CeO2• ZrO2), or a complex oxide comprising the CeO2• ZrO2 and an oxide of at least one of La, Y, Pr and Nd.
7. The catalyst for purification of a PET drawing oven gas according to any one of claims 1 to 6, wherein a content of the platinum is 0.01 to 10% by weight based on the component 1.
8. A catalyst for purification of a PET drawing oven gas, comprising zirconium oxide (component 1), platinum (component 2), zeolite (component 3), and cerium oxide (component 4), and wherein a content of the component 3 is such that a weight ratio between the component 1 and the component 3 is 90:10 to 10:90, and a content of the component 4 is 1 to 100 parts by weight per 100 parts by weight of the component 1.
9. A catalyst for purification of a PET drawing oven gas, comprising the catalyst according to any one of claims 1 to 8 supported on a catalyst substrate.
10. The catalyst for purification of a PET drawing oven gas according to any one of claims 1 to 9, wherein a drawing oven gas is a gas containing acetaldehyde as well as a PET oligomer, and the catalyst oxidatively degrades these two components.
11. A method of purifying a PET drawing oven gas, comprising:
a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of claims 1 to 10 provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and
a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven.
12. A method of preventing contamination of a PET drawing oven, comprising:
a step 1 of bringing a hot draft containing a volatile PET oligomer generated during production of a PET film in a drawing oven into contact with the catalyst according to any one of claims 1 to 10 provided inside or outside the oven at a temperature in a temperature range of 200 to 350°C to degrade the volatile PET oligomer oxidatively; and
a step 2 of refluxing all or a part of a resulting degraded gas to the drawing oven.
13. The catalyst for purification of a PET drawing oven gas according to any one of
claims 1 to 9, wherein the drawing oven gas is a gas containing an organosilicon compound
and a sulfur compound as well as the PET oligomer, and the catalyst has an action of
oxidatively degrading the PE oligomer, and simultaneously has an action of depositing the
organosilicon compound and the sulfur compound in the catalyst.

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Patent Number

278747

Indian Patent Application Number

7076/DELNP/2010

PG Journal Number

54/2016

Publication Date

30-Dec-2016

Grant Date

29-Dec-2016

Date of Filing

06-Oct-2010

Name of Patentee

NIKKI-UNIVERSAL CO., LTD.

Applicant Address

6-3, OHSAKI 1-CHOME, SHINAGAWA-KU, TOKYO 141 - 8563, JAPAN,

Inventors:

#	Inventor's Name	Inventor's Address
1	SAKURAI, TAKANOBU	C/O NIKKI-UNIVERSAL CO., LTD., HIRATSUKA RESEARCH CENTER, 7-14-1, SHINOMIYA, HIRATSUKA-SHI, KANAGAWA 254-0014, JAPAN,
2	UENO, SHINICHI	C/O NIKKI-UNIVERSAL CO., LTD., HIRATSUKA RESEARCH CENTER, 7-14-1, SHINOMIYA, HIRATSUKA-SHI, KANAGAWA 254-0014, JAPAN,

PCT International Classification Number

B01J 23/42

PCT International Application Number

PCT/JP2009/057319

PCT International Filing date

2009-04-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102258/2008	2008-04-10	Japan
2	102306/2008	2008-04-10	Japan