Title of Invention

A PROCESS FOR HYDRO-STABILIZING A COAL LIQUEFIED OIL

Abstract

The present invention relates to a process for hydro-stabilizing a coal liquefied oil, characterized in filtering the coal liquefied oil, feeding it to an expanded bed reactor, contacting with hydrogen and a hydrorefining catalyst therein to hydrorefine the coal liquefied oil, then gas-liquid separating, fractionating the reactor effluent to obtain a hydrostabilized product of the coal liquefied oil. An expanded bed reactor is used in the process of the present invention. The process effectively alleviates the problem associated with the rapid increase of pressure drop in the reactor, inhibits the undesired rapid deactivation of the catalyst at the inlet of the reaction, and prolongs the on-stream period. In addition, it can remove nitrogen and oxygen from the coal liquefied oil, and improve the quality thereof.

Full Text

A Process For Hydro-stabilizing A Coal Liquefied Oil Technical Field The present invention concerns a process for hydrogenating the liquid hydrocarbons obtained by a destructive hydro-conversion of a coal. More specifically, the present invention relates to a process for hydro-stabilizing a coal liquefied oil. Background of the invention As early as 1913, Germany started on the studies of the preparation of liquid hydrocarbon products by directly liquefying coal, and industrialized the technology of preparing gasoline by directly liquefying lignite in 1927. Since the first world oil crisis in 1973, the developed counties attached much importance to the direct coal liquefaction technology, and gradually developed many direct coal liquefaction processes. The direct coal liquefied oil (coal liquefied oil) retains some features of the raw material coal, such as high olefin and aromatics content, high nitrogen and oxygen content, and worse storage stability. Generally, nitrogen in the coal liquefied oil is in a content of higher than 0.5% by weight; oxygen therein ranges from 1.5% to 7% by weight; and the content of aromatics therein is higher than 60%-70% by weight. Resins and asphaltenes therein are generally 10%-20% by weight. Due to said features, the substances disadvantageous to the subsequent transportation and processing will be easily produced if the coal liquefied oil is not pre-treated in time. The hydrorefining method, thereby, is needed to pre-treat the coal liquefied oil, to saturate olefins therein, to remove mostly oxygen and other heteroatoms such as nitrogen, sulfur and so on, so as to increase the stability of coal liquefied oil. Said hydrorefining method is used to saturate olefins and remove heteroatoms such as oxygen, nitrogen and the like, so as to increase the stability of the coal liquefied oil as the main object. Accordingly, the method is usually called as the process for hydro-stabilizing coal liquefied oil. In addition to a high content of aromatics and impurities such as nitrogen and oxygen, resins and asphaltenes, etc., the coal liquefied oil usually contains fine solid particles (diameter less than 5 urn) and metals (mainly Fe, Ca, Na, etc.), wherein the quantity of solid particles is determined by a solid-liquid separation method in the liquefaction unit, and the metal content is relevant to the coal type and the liquefaction catalyst. These fine particles and metals are derived from the unconverted coal powder and liquefaction catalyst, and will reach the hydro-stabilizing catalyst bed after passing through filters, and do severe harm to the hydrogenation catalyst and shorten the catalyst life. If a fixed bed reactor is used for hydro-stabilizing, the solid particles will deposit at the top of the catalyst bed, which will result in a rapid increase in the reactor pressure drop, and do harm to the on-stream period of the unit. In addition, asphaltenes (C7 insolubles) in the coal liquefied oil is generally in a higher content of 0.2% by weight or above, and C7 insolubles is a poison to the hydrogenating catalyst since it may result in rapid deactivation of the catalyst. The object of hydro-stabilizing the coal liquefied oil is to remove the impurities such as nitrogen, oxygen and the like, to saturate olefins and aromatics, and to increase the stability of the coal liquefied oil. However, the solid particles, metals and C7 insolubles in the coal liquefied oil make the object difficult to be achieved. During the process of hydro-stabilizing the coal liquefied oil by the fixed-bed hydrogenation reactor, the amount of the guard catalyst is usually increased to alleviate the adverse effects brought by the solid particles, metals and C7 insolubles. Nevertheless, increasing the amount of the guard catalyst cannot completely resolve the problems associated with the rapid increase of the reactor pressure drop, and the deactivation of the catalyst. Moreover, increasing the guard catalyst used will take up the space of the primary catalyst, and increase the volume as required by the reactor. US6190542 discloses an in-line process for hydro refining the coal liquefied oil. In the process, the feedstock into the in-line hydrogenation unit comprises a naphtha and a diesel fraction or a full-range fraction of a coal liquefied oil. Heteroatoms are removed from the coal liquefied oil by the in-line hydrogenation, so as to increase the stability thereof and further produce a hydrogen donor solvent for the coal liquefaction unit. The in-line process means successively connecting the hydrogenation unit with the upstream coal liquefaction unit, and sharing one hydrogen system. The hydrogenation unit may not startup or shutdown individually. The startup and shutdown of the hydrogenation unit affect the running of other units, and the running of the hydrogenation unit may be affected by the running state of other units. To process the coal liquefied oil, US5332489 discloses a process for hydrocracking a coal liquefied oil, wherein a part of the hydrocracking product is used as the hydrogen donor solvent of the coal liquefaction unit, and the remaining product as the final product is drawn out of the coal liquefaction unit. In the aforesaid prior art, a conventional fixed bed reactor is used. The unconverted coal powder and coal liquefaction catalyst will deposit at the top of the reactor, which will result in a rapid increase in the reactor pressure drop and shorten the on-stream period. In addition, metals and asphaltenes (C7 insolubles) etc. in the coal liquefied oil will deposit on the surface of the catalyst at the upper part of the reactor, which will rapidly deactivate the catalyst at the upper part of the reactor. Summary of the Invention The object of the present invention is to provide a process for hydro-stabilizing a coal liquefied oil on the basis of the prior art, so as to prolong the on-stream period. The present invention relates to a process for hydro-stabilizing a coal liquefied oil, characterized in filtering the coal liquefied oil, feeding it to an expanded bed reactor, contacting with hydrogen and a hydrorefining catalyst therein to hydrorefine the coal liquefied oil, then gas-liquid separating, fractionating the reactor effluent to obtain the hydro-stabilized product of the coal liquefied oil. the coal liquefied oil may be fed into the expanded bed reactor from the bottom of the reactor together with hydrogen, or fed into the reactor from a lower part of the reactor. In a further embodiment, a high pressure separator is used for said gas-liquid separation, and the hydrogen-enriched gas from the high pressure separator is recycled to the expanded bed reactor. An expanded bed reactor is used in the process of the present invention for the hydro-stabilizing of the coal liquefied oil. The process effectively alleviates the problem associated with the undesired rapid increase of the reactor pressure drop, inhibits the undesired rapid deactivation of the catalyst at the inlet of the reaction, and prolongs the on-stream period. In addition, it can remove nitrogen and oxygen from the coal liquefied oil, and improve the quality thereof. According to the invention, the expansion volume ratio of the catalyst bed of said expanded bed reactor is not above 5%, which may be in a micro-expanded state, and renders little back mixing. The application of an expanded bed not only resolves the problem associated with the rapid increase of the reactor pressure drop, but also prolongs the on-stream period of the unit. Meanwhile, an expanded bed reactor has little back mixing, which is advantageous in the hydro-stabilizing effect over an ebullated bed reactor having great back mixing, and the operation of the former is relatively simple. Specifically, the present application involves the following inventions: 1. A process for hydro-stabilizing a coal liquefied oil, characterized in filtering the coal liquefied oil, feeding it to an expanded bed reactor, contacting with hydrogen and a hydrorefining catalyst therein to hydrorefine the coal liquefied oil, then gas-liquid separating, fractionating the reactor effluent to obtain a hydro-stabilized product of the coal liquefied oil. 2. The process according to Aspect 1, characterized in that the coal liquefied oil after filtered is fed into the expanded bed reactor from the bottom of the reactor together with the hydrogen. 3. The process according to Aspect 1, characterized in that a high pressure separator is used for said gas-liquid separation, and the hydrogen-enriched gas from the high pressure separator is recycled to the expanded bed reactor. 4. The process according to Aspect 1, characterized in that the expansion volume ratio of the catalyst bed in the expanded bed reactor is not above 5%. 5. The process according to Aspect 1, characterized in that the expanded bed reactor comprises one or more reactor(s), and each of said reactors comprises one or more catalyst bed(s). 6. The process according to Aspect 5, characterized in that, when there are more of said reactors, the number thereof is 2-4. 7. The process according to Aspect 5, characterized in that, when there are more of said catalyst beds, the number thereof is 2-4. 8. The process according to Aspect 1, characterized in that the process for hydro-stabilizing a coal liquefied oil is an off-line one. 9. The process according to Aspect 1, characterized in that the coal liquefied oil is a liquid product obtained by directly liquefying coal, and has a distillation range of C5-520TD. 10. The process according to Aspect 1, characterized in that the hydrorefining reaction is conducted at a hydrogen partial pressure of 4.0-30.0 MPa, a reaction temperature of 280-450C a liquid hourly space velocity of 0.1-10 h-1 and a hydrogen /oil ratio of 300-2800 Nm/3Vm3. 11. The process according to Aspect 1, characterized in that the hydrorefining catalyst is a catalyst wherein a Group VIB metal or/and a Group VIII non-noble metal is/are supported on an amorphous alumina or/and a silica-alumina, wherein the Group VIB metal is selected from Mo or/and W, and the Group VIII non-noble metal is selected from Co or/and Ni. Description of Drawings Fig. 1 outlines the diagram of one embodiment of the process for hydro-stabilizing the coal liquefied oil provided in the present invention. Detailed Description of the Invention In the present invention, the coal liquefied oil is hydro-stabilized by using an in-line or off-line process, preferably using an off-line process. The off-line process may avoid the effects of the water-vapor enriched in the coal liquefied oil on the hydrorefining catalyst. COX in the gas phase of the upstream coal liquefaction unit is kept away from the hydro-stabilizing unit, so as to reduce undesirable hydrogen consumption resulted from the production of CH4 by hydrogeaation of COX. Moreover, the off-line hydrogenation may avoid the effects of the unscheduled shutdown of the coal liquefaction unit on the hydro-stabilizing unit. If an in-line hydrogenation process is used, the hydrogenation unit will have to be undesirably shut down when there is any problem in the coal liquefaction unit. When the reactor temperature is reduced to below 100C, water in the gas phase will be absorbed by the hydrorefining catalyst, rendering reduction of the mechanical property of the hydrorefining catalyst and having a severe effect on the catalyst life. The present invention is characterized in using an expanded bed reactor, having the following features. (1) The feedstock is supplied from the bottom of the reactor, and the reaction product is discharged from the top thereof, i.e., feeding the feedstock from the bottom and discharging the product from the top. The feedstock distributing plate thereof is located at the bottom of the reactor, and is greatly different in structure from that of a fixed-bed reactor. Generally, a porous structure is used to realize the uniform distribution of the feedstock. On the contrary, the feedstock is supplied from the top of in case of the fixed bed-reactor, and the product is discharged from the bottom thereof. The feedstock distributing plate thereof is located at the top of the reactor, and generally, a bubbling cap structure is used for the feedstock distribution, and a product collector is required at the bottom of the reactor. (2) The catalyst bed has a expansion volume ratio of not above 5%. Under such an expansion volume ratio, the bed has a uniform expansion and little fluctuation during the operation, and the distribution of the catalyst particles in the bed is relatively uniform. A moderate expansion will loose the catalyst bed, and provides a larger space for accommodating the impurities such as the solid particles and metals so as to make them uniformly distributed throughout the catalyst bed and to avoid the rapid increasing of the reactor pressure drop due to depositions at the inlet of the reactor. The bed expansion volume ratio must be controlled below 5%, which will reduce the back mixing, and improve the hydro-stabilizing effect. Moreover, the product quality from the expanded bed reactor is better than that from the ebullated bed reactor having greater back mixing. (3) There is no mass recycled in said expanded bed reactor, unnecessary for the external recycle pump and for the in-line replacement of catalysts. Thus, the operation of said expanded bed reactor is simpler than that of the ebullated bed reactor. The filtered coal liquefied oil is supplied from the bottom of the expanded bed reactor, so as to stir up the catalyst in the expanded bed and make it floating upward, also assisted by the hydrogen fed from the bottom. At this time, the space between the individual catalyst particle increases, and the unconverted coal powder and the coal liquefaction catalyst in the coal liquefied oil, thereby, will be uniformly distributed throughout the reactor, rather than deposit at the inlet of the reactor. Accordingly, it may prevent the solid particles from easily depositing at the top of the reactor, resulting in an undesired rapid increase of the reactor pressure drop, when a fixed-bed reactor is used. Meanwhile, since the expansion volume ratio of the catalyst-bed layer in the expanded bed reactor catalyst used in this present invention is controlled below 5%, the bed expansion is uniform and shows a very little fluctuation in it. The catalyst is not at an extensively fluidized state, the product from the outlet of the expanded bed reactor will not carry a great amount of solid particles and impurities, thus advantageous to a further processing of the hydrostabilized coal liquefied oil in the downstream unit. Additionally, the catalyst particle will slowly flow across the bed of the reactor since the catalyst bed is in an expanded state, so that metals and asphaltenes in the coal liquefied oil will uniformly deposit on the surface of the catalyst in the reactor bed, which will be in favor of prolonging the on-stream period. In the process of the present invention, the expanded bed reactor used may comprises one or more reactor(s), wherein each of said reactors may comprise one or more catalyst bed(s). If there are more of said reactors, the number thereof may be 2-4; and if there are more of said catalyst beds, the number thereof may be 2-4. The coal liquefied oil and the hydrogen may be fed together to the expanded bed reactor from the bottom of the reactor after mixed, or alternatively, fed respectively from a low part and the bottom of the reactor. In a preferred embodiment, the coal liquefied oil and the hydrogen are fed together to the expanded bed reactor from the bottom of the reactor after mixed. In the hydro-stabilizing unit of the present invention, may be used a common hydrorefining catalyst, preferably one having a high hydrodenitrogenation activity. Nitrogen is in a very high content in the coal liquefied oil, and sulfur therein is in a relatively low content. The hydro-stabilizing unit in the direct coal liquefaction technology is used , mainly to produce a hydrogen donor solvent for the coal liquefaction unit, or the hydro-stabilized product from the coal liquefied oil. If denitrogenation can be achieved to the maximum extent in the hydro-stabilizing unit, the hydrogen donor solvent will have a low nitrogen content, so as to reduce the nitrogen content in the coal liquefied oil obtained as a whole, to increase the quality of the coal liquefied oil and to be advantageous to the further processing in the downstream units. As stated above, the coal liquefied oil usually carries an undesirable amount of catalysts used in the coal liquefaction and unconverted coal powder. A filtrating equipment is generally set up prior to the feedstock pump of the hydro-stabilizing unit in this invention to filtrate most of the solid particles in the coal liquefied oil, but fine solid particles having diameter less than 5 m may easily pass through the filtrating equipment. The expanded bed reactor used in the present invention may absorb a plurality of said solid particles, hence lower the limitation on the content of the solid particles in the feedstock. However, the filtrating equipment is preferably used for economic consideration, to reduce the amount of the solid particles in the reactor as much as possible and prolong the hydrorefining catalyst life. In one embodiment, the processing route of the present invention is briefly stated as follows. In the hydro-stabilizing of the coal liquefied oil of the present invention, the coal liquefied oil is filtered firstly to remove most of the catalyst residue and unconverted coal powder carried in the coal liquefied oil, and then mixed with a hydrogen-enriched gas or/and fresh hydrogen (make up hydrogen). The mixture is heat-exchanged with the hydrostabilized product, and fed into a heating furnace, and supplied from the bottom of the expanded bed reactor into the reactor to hydrorefine the coal liquefied oil. The effluents from the hydro-stabilizing reactor primarily comprise NH3, H2S, H2O generated from the hydro-stabilizing reaction, and the hydro-refined oil. Upon a gas-liquid separation via a conventional high pressure separator, a hydrogen-enriched gas and a liquid stream are obtained, wherein the hydrogen-enriched gas may be recycled to said reactor for reuse, and the liquid stream from the high pressure separator is supplied into a low pressure separator for further gas-liquid separation. Then, the gas stream separated from the low pressure separator is fed into a fuel gas system as fuel gas, and the liquid stream separated from the low pressure separator is supplied into a distillation tower to produce a naphtha fraction, a diesel fraction and a unconverted fraction, as required. In a further embodiment, the feedstock is fed into the expanded bed reactor from a lower part of the reactor, then mixed with hydrogen in the reactor. The hydrorefining catalyst used in the present invention may be a catalyst wherein a Group VIB metal or/and a Group VIII non-noble metal is/are supported on an amorphous alumina or/and a silica-alumina, wherein said Group VIB metal is not particularly limited, but is preferably selected from Mo or/and W, and said Group VIII non-metal is not particularly limited, but is preferably selected from Co or/and Ni. Both said Group VIB metal and Group VIII non-noble metal have very high hydrodenitrogenation activity. The coal liquefied oil feedstock used in the process of the present invention is any of the liquid product obtained by directly liquefying a coal. Generally, the liquid product having a distillation range of C3-520 V, preferably C5-450C may be used therein. The heavier the fraction of the coal liquefied oil is, the higher the content of the impurities such as metals and asphaltenes therein is and the worse the effect thereof on the life span of the hydrorefining catalyst is. In the feedstock, nitrogen is generally in a content of not greater than 2.0 wt%, preferably not greater than 1.2 wt%; and sulfur is usually in a content of not greater than 5.0 wt%. The processing operation of the present invention varies along with the properties of the oil feedstock, such as nitrogen content, aromatics content, distillation range and the like. The hydrorefining reaction of the present invention is conducted at a hydrogen partial pressure of 4.0-30.0 MPa, a temperature of 280-450C, a liquid hourly space velocity of 0.1-10 h-1 and a hydrogen /oil ratio of 300-2800 Nm3/Vm3. The process of the present invention is further exemplified by referring to the drawing, without any limitation thereon. The accompanying drawing, which is included to provide a further understanding of the invention and is incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention. Fig. 1 shows the diagram of one embodiment of the process for hydro-stabilizing the coal liquefied oil provided in the present invention, in which the feedstock and the hydrogen are fed together into the expanded bed reactor from the bottom of the reactor. Some auxiliary equipments, such as pump, air cooler and valve, are omitted from Fig. 1, which is known to those ordinarily skilled in the art. The invention is described more fully hereinafter with reference to the accompanying drawing, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In Fig. 1, the coal liquefied oil is fed into a filtering equipment 3 via a pipeline 2, and filtrated to remove part of the solid particles carried in the coal liquefied oil. After the filtrated coal liquefied oil is increased to a required reaction pressure by a feedstock pump, it is mixed with hydrogen from pipeline 4, heat-exchanged with a heat exchanger 5, then heated via a heating furnace 6, and supplied via pipeline 7 into the hydro-stabilizing expanded bed reactor 8 from the bottom thereof. The mixture contacts with the hydrorefining catalyst bed for hydrorefining the coal liquefied oil, removing the impurities from the oil feedstock, such as metal, sulfur, nitrogen and the like, and saturating olefins and polycyclic aroraatics. If there are more beds, cold hydrogen needs to be introduced between some of the beds of the reactor to control the reaction temperature since hydrorefining reaction is a strong exothermic one. The effluent from the hydro-stabilizing reactor 8 is discharged via pipeline 9 into the heat-exchanger 5 for heat-exchanging, and then supplied via pipeline 10 into a hot high pressure separator 11 in which it is divided into two streams, wherein one of them is a hot vapor stream, comprising hydrogen as a main component, and some gaseous hydrocarbons, and further some hydrogen sulfide and ammonia. Said hot vapor stream is supplied into a cool high pressure separator 13 to be divided into two streams, wherein one of them is a hydrogen-enriched gas comprising hydrogen primarily, and some hydrogen sulfide and ammonia gas. Said hydrogen-enriched gas is compressed via a recycle compressor, and mixed via pipeline 14 with fresh hydrogen from pipeline 1, and then recycled to reactor 8 via pipeline 4. The other stream from the hot high pressure separator 11 is fed into a hot low pressure separator 16 via pipeline 12 to further remove light hydrocarbons and dissolved hydrogen. The effluent from the top of the hot low pressure separator 16 is mixed via pipeline 17 with the effluent from the bottom of the cool high pressure separator 13 supplied via pipeline 15, and then supplied into a cool low pressure separator 19 and divided into fuel gas and liquid hydrocarbons, where the fuel gas as a product is discharged via pipeline 20 from the unit. The effluent from the bottom of the cool low pressure separator 19 is mixed via pipeline 21 with the effluent from the bottom of the hot low pressure separator 16 supplied via pipeline 18, and then supplied into a distillation tower 23 via pipeline 22. After fractionation, the gas obtained at the top of the tower, a naphtha fraction, a jet fuel fraction or a diesel fraction, and a unconverted fraction are drawn out of the reactor respectively via pipelines 24, 25, 26 and 27. An expanded bed reactor is used in the process of the present invention. The process effectively alleviates the problem associated with the undesired rapid increase of the pressure drop in the reactor, inhibits the rapid dcactivation of the catalyst at the inlet of the reaction, and prolongs the on-stream period. Meanwhile, it can remove nitrogen and oxygen from coal liquefied oil, and improve the quality of coal liquefied oil. Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The following example is used to further disclose the process, but is not used to limit the invention. The coal liquefied oil in the Example is filtered, and the hydrorefining catalyst therein is RJW-2 produced by the Sinopcc Changling Catalyst Factory. The density of the coal liquefied oil feedstock and products is determined by a hydrometer method, and under the Chinese national standard of GB/T 1884-92 (equivalent to ASTM D4052-95). The bromine number of the feedstock and the products is determined by a microcoulometric method, and under the Chinese standard of SH/T 0630-1996 (equivalent to ASTM D1492-00). The oxygen content in the feedstock and the products is determined by an element analyzer, and under the standard of ASTM D5622-00. The sulfur content in the feedstock is determined by an energy-dispersive X-ray fluorescence spectrometry, and under the standard Chinese national of GB/T 17040-1997 (equivalent to ASTM D4294-90). The nitrogen content in the feedstock is determined by a chemiluminescent method), and under the Chinese standard of SH/T 0704-2001 (equivalent to ASTM D5762-98). The distillation range of the feedstock is determined by a vacuum distillation method, and under the Chinese national standard of GB/T 9168-1997 (equivalent to ASTM Dl 160-95). The distillation range of the products is determined by a distillation method, and under the Chinese national standard of GB/T 6536-1997 (equivalent to ASTM D86-95). The sulfur content in the products is determined by a microcoulometric method, and under the Chinese standard of RIPP 62-90. Example 1 The experiment was conducted on a pilot plant-scale expanded bed hydrogenation unit, and the feedstock was the coal liquefied oil. The properties of the oil feedstock, the process parameters and the product properties were respectively listed in Tables 1, 2 and 3. It could be seen that, under a relatively mild operation condition, the bromine number of the hydrostabilized product was very low, which showed that most of

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