Title of Invention

"A PROCESS FOR THE PREPARATION OF CRACKING CATALYST FOR THE MAXIMIZATION OF OLEFINIC LPG"

Abstract

The present invention discloses a process of preparing Cracking catalyst capable of producing high yield of C3-C4 olefins with heavy feedstock having Conradson carbon residue of >3wt% and high metals content. The process comprises the preparation of Cracking catalyst having modified zeolite Y with high silica to alumina ratio and low UCS and pentasil type of zeolite embedded in silica-alumina matrix. The main feature of the Cracking catalyst include low hydrogen transfer activity, high thermal stability and low coke formation tendency.

Full Text

The present invention relates to a process for the preparation of cracking catalyst for the maximization of olefinic LPG. Particularly this invention relates to a process for the preparation of Cracking catalyst having high selectivity for olefinic LPG, more specifically having high content of propylene and butylenes. The invention more specifically relates to a process for the preparation of active silica-alumina matrix and highly dealuminated Y-zeolite separately and their mixing together to prepare the catalyst. The catalyst prepared by the process of the present invention has high activity, high hydrothermal stability, improved coke selectivity, reduced hydrogen transfer and capability of cracking C5-C12 olefins to C3-C4 olefins. The catalyst prepared by the present invention is thermally stable as it can withstand the process conditions used in the regeneration which involves the burning of the deposited coke/residual hydrocarbon. Fluid Catalytic Cracking (FCC) and Steam Cracking are the major processes for the production of light olefins. Currently around 70% of the world's propylene demand is met by steam cracking and remaining 30% by FCC. However in near future propylene demand is expected to grow by 5 to 6% per year, which has generated increasing interest to produce more propylene from FCC units. Increasing propylene beyond normal FCC yield is not practical with conventional FCC catalyst systems. To get incremental propylene over cracking of the C5-C12 gasoline component is required. This gasoline component is difficult to crack as H-transfer and free radical reactions begin to dominate over p-scission reaction. Incremental propylene therefore cannot be justified at the cost of loss of gasoline & the increase in coke & dry gas yield. Propylene yields from FCC units can be doubled or tripled by using a combination of catalyst technology and higher severity process conditions. Conventional FCC produces up to 5 wt% propylene. Deep Catalytic Cracking (DCC) is the high severity version of Fluid Catalytic Cracking (FCC) process and uses the same principle for the upgradation of heavier feeds. Its overall scheme is similar to FCC, but higher yields of olefins can be obtained by selection of suitable catalyst and process variables. DCC catalyst should have high hydrothermal stability and low hydrogen transfer activity as compared to conventional FCC/RFCC catalyst to maximize olefins. DCC catalyst is mainly composed of two component i.e. matrix and zeolite. It may contain some additive to enhance the activity and / or selectivity of the desired products. Matrix plays an important role which contains larger percentage of mesopores as compared to zeolite component. The composition and type of matrix material is also an important factor for making right type of catalytic active matrix. The requisite characteristics of active silica alumina matrix like surface area, pore volume, pore size distribution, acidity etc are controlled by varying the different parameters such as silica sol concentration, pH of the mix, ageing time, degree of agitation etc. DCC feed has larger molecules of hydrocarbon and cannot diffuse in to the micropores of zeolite. To make full use of zeolite, the larger hydrocarbon molecules of the feed are first cracked on the surface of catalytically active matrix. The cracked molecules smaller in size can diffuse easily in micropores of the zeolite to give the desired product. The modified highly dealuminated zeolite - Y is hydrothermally stable and can withstand the process conditions used in the regeneration of coked catalyst with retention of catalyst activity and zeolite crystallinity. The highly dealuminated zeolite-Y have high silica to alumina ratio which is essential requirement for high thermal and hydrothermal stability. Unit cell size of the highly dealuminated zeolite decreases due to decrease in framework aluminium sites of zeolite-Y as Si-0 bond is shorter than Al-0 bond. Hydrogen transfer reaction is suppressed by low aluminium sites density which is one of the most essential requirement of DCC catalyst. It is known in the art silica alumina matrix can be prepared by mixing the sodium silicate solution and aluminium salt solution such as aluminium nitrate, aluminium chloride, aluminium sulphate etc. at controlled pH. The gel so obtained is washed to remove impurities and mixed with clay. The catalyst prepared by these methods, however, suffer the following disadvantages: - Washing of gel is uneconomical - Low solid content of the slurry for spray drying - Low Apparent Bulk Density (ABD) - Low attrition resistance The matrix prepared by the process of present invention is silica-alumina based with some Kaolin clay. The ingredients were so chosen that no washing is required making the process economical. Disperal alumina was used as alumina source and commercially available soda free silica sol as silica source. Kaolin was also added to the silica-alumina sol which plays the role of densifier and is less expensive. In the matrix slurry highly dealuminated zeolite-Y is mixed in required quantity and vigorously stirred for approx. fifteen minutes. The Pentasil type zeolite is added as additive to enhance the selectivity of the olefins. The optimized catalyst system with Pentasil Zeolite which selectively functions as a component converting the gasoline range C5-C12 olefins into LPG C3-C4 olefins. The Pentasil catalyst plays a synergistic role along with other catalyst components. The shape selectivity of crystals limits the access of other molecules except C5-C12 olefins which further cracks via P-scission to lower olefins. It can be mixed along with dealuminated zeolite-Y or separately in the silica-alumina matrix slurry. The slurry may become thick due to gelation during spray drying. Some solution of acidified silica sol may be added to make slurry pumpable for spray drying. The addition of silica sol may form the film of silica around the spherical particles of catalyst which saves the catalyst from harmful effect of nickel and vanadium present in the heavier feed. The advantages of the present invention for the preparation of Deep Catalytic Cracking catalyst over the known processes in the prior art are as follows: (1) Use of highly dealuminated zeolite-Y having very low aluminium sites density to suppress hydrogen transfer reaction. (2) Use of shape selective Pentasil Zeolite in the formulation to have its maximum benefit to enhance olefins selectivity. (3) Use of soda free commercial silica sol in place of sodium silicate to avoid washing step to remove sodium. (4) Use of disperal alumina hydrate in place of aluminium salts to avoid washings step and to increase solid content of the slurry for spray drying. (5) No binder was used separately. The silica alumina sol having high percentage of alumina itself serves the purpose of binder and active matrix. (6) Use of acidified silica sol to make slurry pumpable (free flowing) in case thickening of the slurry occurs. The silica layer is formed around the spherical particles of the catalyst which prevents the harmful effect of contaminant metals such as nickel and vanadium. (7) Avoided the use of rare earths in catalyst formulation. The main object of the present invention is to provide a process for the preparation of cracking catalyst for the maximization of olefinic LPG which obviates the drawbacks as detailed above. Another objective of the present invention is to provide a process for the preparation of cracking catalyst to maximize C3-C4 olefins specially propylene and butylenes by using highly dealuminated Y-zeolite in active and thermally stable silica-alumina matrix along with Pentasil Zeolite. In carrying out the present invention, as a result of extensive investigations carried out by us, we found it advantageous the use of Pentasil Zeolite embeded in the formulation rather than using as a physical mixture in the catalyst. Preparation of catalyst using non-wash route also have many advantages such as, high yield of catalyst during spray drying, high ABD and attrition resistance. The composition of the catalyst is given in Table - 1. Accordingly, the present invention provides a process for the preparation of cracking catalyst for the maximization of olefininc LPG which comprises i) exchanging of NaY to NH4Y zeolite with 0.5N to 3.0N aqueous solution of NH4NO3 or (NH4)2SO4 at reflux temperature for a period of 1 to 4 hours; ii) hydrothermal treatment of NH4Y at a temperature of 650 to 850°C for a time period of 0.5 to 2.0 hour in presence of 100% steam; iii) preparing acidified silica solution of pH preferably 1 to 4 by the addition of nitric acid to commercial silica sol; iv) mixing of dispersal alumina hydrate powder in silica solution of step (iii) with vigorous stirring in a ratio preferably 2:1 to make silica-alumina sol by keeping the pH in the range of 2 to 3.5, v) mixing of Kaolin clay in silica-alumina of step (iv) in the ratio preferably 1:2 by keeping the pH below 3.0; vi) mixing of zeolite-Y prepared in step (ii) and Pentasil in the ratio of 4:1 wt/wt% to 3.0:0.5 wt/wt% by keeping pH below 3.0; vii) drying of slurry of step (vi) in oven at a temperature ranging from 25 to 150°C; viii) calcination of dried catalyst prepared in step (vii) at a temperature in the range of 400-600°C for a time period of 1 to 4 hours; ix) sizing of calcined catalyst of step (viii) to obtain 100 to 230 mesh size particles of the desired catalyst. In an embodiment of the present invention the ammonium salt used can be selected from NH4NO3 (NH4)2SO4 and NH4Cl. in another embodiment of the present invention the NH4Y be treated at a tempreture preferably 800°C for the duration of preferably 0.5 to 2.0 hours. In yet another embodiment of the present invention the silica-alumina sol is prepared, by mixing acidified silica sol and disperal alumina hydrate with vigorous stirring in the pH range of2.0to3.5. In still another embodiment of the present invention the Pentasil has the silica to alumina ratio in the range to 20 to 50. In still another embodiment of the present invention the pH of final slurry after mixing all the ingredients is kept between 2.0 to 3.5. In still another embodiment of the present invention the catalyst is calcined at a temperature preferably 500°C for a time period preferably 2 hours. In still another embodiment of the present invention the catalyst is steam treated in temperature range of 750 to 850°C for a period of 2 to 5 hours. In still another embodiment of the present invention the catalyst was tested with heavy feed having CCR between 3 to 5 wt% and (Ni+V) in the range of 30 to 50 ppm. In still another embodiment of the present invention the reaction was carried in the temperature range of 550 to 600°C preferably at 580°Cand cat to oil ratio in the range of 6 to 8.0 preferably at 7.5. In the present invention exchange of NaY to NH4Y zeolite is done to bring down the sodium level to below 1%. The salt may be chosen from NH4NO3, NH4(S04)2 and NH4C1. The concentration of salt solution is so adjusted to have 2-4 equivalents of cation per equivalent of total base exchange capacity. The NH4Y so prepared is subjected to hydrothermal treatment in the temperature range of 650°C - 850°C for 0.5 to 2.0 hours. The conditions are so chosen to have higher degree of dealumination of zeolite-Y having unit cell size in the range of 24.26 -24.28 A with substantial crystallinity retention. The zeolite-Y having low value of unit cell size is one of the most desired requirement for improved catalyst for olefins maximization to suppress hydrogen transfer reaction. H-transfer reaction is bimolecular reaction where e.g. an olefin (hydrogen receiver) and naphthene (hydrogen donor) each at adjacent acid sites on the catalyst, transfer hydrogen ions resulting in a saturated paraffin and an aromatic. Since this reaction is bimolecular and require adjacent acid sites, therefore the probability of H-transfer is not there in case of highly dealuminated zeolite-Y having isolated acid sites. A combination of a catalyst formulated with USY that contains no rare earths, a suitable active matrix and use of Pentasil will assist in achieving the desired goal. During dealumination, increase in silica to alumina ratio, decrease in total acidity, increase in acid sites strength and development of mesopores up to 150 A also takes place. The dealuminated zeoiite-Y along with Pentasil is dispersed in matrix slurry prepared by the process of the present invention. The silica-alumina matrix have sufficient acidity / activity to crack the larger molecules of heavy feed which may diffuse into zeolite pores to crack further to give desired products i.e. olefins. The use of shape selective Pentasil zeolite as additive also enhances the olefins yield by cracking the straight chain paraffins inside the pores. The invention may be practiced as illustrated in the following examples. It may, however, be construed that the following examples are only representative and do not limit the scope of present invention. Example 1 This example illustrate the process for the preparation of improved Catalytic Cracking catalyst for the maximization of olefinic LPG. (a) Exchanging NaY zeolite to NH4Y zeolite by treating with ~2N solution of NH4NO3 or (NH4)2SO4 at reflux temperature for a period 1 to 4 hours by keeping solid to liquid ratio appox. 1:10. The treated zeolite is washed with DM water to remove impurities like sulphate or nitrate and dried at 110°C for 16 hours. (b) The NH4Y prepared in step (a) is hydrothermally treated at 800°C for one hour in presence of 100% steam (c) In 250 ml solution of commercial silica sol containing 8 percent silica and 9.5 pH was acidified by HNO3 to bring down the pH to 2.4 to 2.6. (d) 40 g disperal alumina hydrate powder (anhydrous basis) was added slowly with vigorous stirring by keeping the pH below 2.8 by the addition of nitric acid for -15 minutes. (e) 20g Kaolin clay powder (anhydrous basis) was added in the silica-alumina sol prepared in step (d) with vigorous stirring by keeping the pH below 2.8 by the addition of nitric acid for approx.15 minutes. (f) 15 g highly dealuminated Y-zeolite of step (b) and 5 g of Pentasil silica to alumina ratio approx. 40) was added in the slurry prepared in step (e) with vigorous stirring by keeping the pH below 2.8 by the addition of nitric acid for approx. 15 minutes. (g) The slurry prepared in step (f) was dried in oven at 110°C for 16 hours. (h) The dried material of step (g) was calcined in muffle furnace at 500°C for 2 hours, (i) The calcined catalyst was sized to get the 100 to 230 mesh size particles. The catalyst obtained in step (i) is fresh catalyst. This catalyst is designated as DCC-A. Example - 2 This example illustrate the process of catalyst preparation with Pentasil additive. The catalyst was prepared exactly as given in Example - 1 except step (f). In place of 5g Pentasil crystals, dealuminated zeolite-Y was used. This catalyst is designated as DCC-B and composition of DCC-A and DCC-B is given in Table - 1. Example - 3 It is essential to steam deactivate the freshly prepared catalyst in order to control activity, therefore, prior to activity and selectivity determination catalyst is steam deactivated. This example illustrate the process of steam deactivation / treatment of fresh catalyst for evaluation. (a) Loading of ~30g catalyst in four baskets fitted in fluid bed reactor. (b) Controlled heating of the catalyst under flow of nitrogen up to 250°C (c) Passing of 100% steam from 250°C to 788°C in place of nitrogen (d) Holding the temperature at 788°C for 3 hours in steam flow (e) Cooling of the catalyst in nitrogen flow. The physico-chemical properties of steamed catalyst is given in Table - 2. Example - 4 The catalyst prepared in example 1 & 2 was tested with a heavy feedstock having CCR of 3.56 wt% and metals (Ni+V) 36 ppm in advanced cracking evaluation (ACE-R) unit of Xytel at 580°C by keeping the Cat to oil ratio of 7.5. The feed injection time was 40 seconds. The product yield pattern is given in Table - 3. The gaseous yield with catalyst DCC-A under different temperature condition is given in Table - 4. Example -5 PERFORMANCE EVALUATION OF THE CATALYST PREPARED BY PRESENT INVENTION In order to evaluate the performance of the prepared DCC catalyst, Advanced Cracking Evaluation (ACE-R) unit of Xytel, USA has been used. The activity and product selectivities are the main parameters for considering the relative performance of the catalysts. The fresh DCC catalyst was steam deactivated at 788°C for about 3 hours in the 100% steam as given in example 3 and then evaluated using (ACE-R) unit. The yield structure of catalyst DCC-A with 5% Pentasil and DCC-B without Pentasil is given in Table - 3. The higher yield of LPG (40.67%) with propylene and butelenes content of 15.82 and 7.85% respectively was obtained with DCC-A catalyst having Pentasil. In case of DCC-B catalyst without Pentasil yield of LPG is 12.063 % only. This clearly shows the beneficial effect of addition of Pentasil in DCC catalyst formulation. The relative hydrogen transfer and isomerization activity of the catalyst prepared as example 1 & 2 are 2.85 and 1.15 respectively at 580°C. Thus, the present invention provides a process for the preparation of DCC catalyst which is capable of producing more olefins specially propylene and butylene. Table -1 (Table Removed) Table - 2 Physico-chemical Properties of Steamed Catalysts (Table Removed) Table - 4 Gaseous yield with DCC-A Catalyst (Table Removed) We Claim: 1) A process for the preparation of cracking catalyst for the maximization of olefininc LPG which comprises: i) exchanging of NaY to NH4Y zeolite with 0.5N to 3.ON aqueous solution of NH4NO3 or (NH4)2SO4 at reflux temperature for a period of 1 to 4 hours; ii) hydrothermal treatment of NH4Y at a temperature of 650 to 850°C for a time period of 0.5 to 2.0 hour in presence of 100% steam; iii) preparing acidified silica solution of pH preferably 1 to 4 by the addition of nitric acid to commercial silica sol; iv) mixing of dispersal alumina hydrate powder in silica solution of step (iii) with vigorous stirring in a ratio preferably 2:1 to make silica-alumina sol by keeping the pH in the range of 2 to 3.5, v) mixing of Kaolin clay in silica-alumina of step (iv) in the ratio preferably 1:2 by keeping the pH below 3.0; vi) mixing of zeolite-Y prepared in step (ii) and Pentasil in the ratio of 4:1 wt/wt% to 3.0:0.5 wt/wt% by keeping pH below 3.0; vii) drying of slurry of step (vi) in oven at a temperature ranging from 25 to 150°C; viii) calcination of dried catalyst prepared in step (vii) at a temperature in the range of 400-600°C for a time period of 1 to 4 hours; ix) sizing of calcined catalyst of step (viii) to obtain 100 to 230 mesh size particles of the desired catalyst. 2. A process as claimed in claim 1, wherein the ammonium salt used can be selected from NH4NO3, (NH4)2SO4, and NH4C1. 3. A process as claimed in step ii) of claim 1, wherein the NH4Y is hydrothermally treated at a temperature preferably 800°C. 4. A process as claimed in claim 1, wherein the Pentad has the silica to alumina ratio in the range to 20 to 50. 5. A process as claimed in claim 1, wherein the pH of final slurry after mixing all the ingredients is kept between 2.0 to 3.5. 6. A process as claimed in claim 1, wherein the catalyst is calcined at a temperature preferably 500°C for a time period preferably 2 hours. 7. A process as claimed in claim 1, wherein the catalyst is steam treated in temperature range of 750 to 850°C for a period of 2 to 5 hours. 8. A process as claimed in claim 1, wherein the catalyst was tested with heavy feed having Conradson carbon residue(CCR) between 3 to 5 wt% and (Ni+V) in the range of 30 to 50 ppm. 9. A process as claimed in claim 1, wherein the reaction was carried in the temperature range of 550 to 600°C preferably at 580°C having catalyst to oil ratio in the range of 6 to 8.0 preferably at 7.5. 10. A process for the preparation of cracking catalyst for the maximization of olefinic LPG substantially herein described with references to the examples

Documents:

784-DEL-2005-Abstract-(30-09-2011).pdf

784-del-2005-abstract.pdf

784-DEL-2005-Claims-(30-09-2011).pdf

784-del-2005-claims.pdf

784-DEL-2005-Correspondence Others-(30-09-2011).pdf

784-del-2005-correspondence-others.pdf

784-DEL-2005-Description (Complete)-(30-09-2011).pdf

784-del-2005-description (complete).pdf

784-DEL-2005-Form-1-(30-09-2011).pdf

784-del-2005-form-1.pdf

784-del-2005-form-18.pdf

784-del-2005-form-2.pdf

784-DEL-2005-Form-3-(30-09-2011).pdf

784-del-2005-form-3.pdf