US3652446A

US3652446A - Combination process for liquefaction of coal and catalytic cracking of selected fractions thereof

Info

Publication number: US3652446A
Application number: US877314A
Authority: US
Inventors: Herbert P Dengler; Bernard L Schulman
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1969-11-17
Filing date: 1969-11-17
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28

Abstract

The present process is a combination of a liquid fluidized bed catalytic coal liquefaction zone and a fluidized catalytic cracking zone. In the liquefaction zone, finely divided coal is contacted with the fluidized catalyst bed while in a solvent oil and in contact with molecular hydrogen. A liquefaction zone product stream, containing a substantial amount of liquid materials boiling in an intermediate temperature range (e.g., 430* F. to 950* F.), is obtained, and boiling intermediate boilding range material separated from the remainder of the product stream. A first portion of the intermediate boiling range material is charged into a fluid catalyst cracking zone wherein the first portion is contacted with a cracking catalyst such as silica alumina under cracking conditions to obtain a cracking zone product stream which contains a substantial amount of heavy liquid materials hereinafter referred to as ''''cat cycle oil.'''' The heavy liquid materials in the cat cycle oil will boil not lower than the intermediate boiling range material. The cat cycle oil is separated from the remainder of the cracking zone product stream and admixed with a second portion of the intermediate boiling range material to obtain the slurry oil used as a solvent oil in the liquefaction zone. By the present process, the cat cycle oil, which is very refractory due to a low hydrogen content, is reacted with hydrogen in the liquefaction zone to increase the hydrogen content and to crack some of the heavier components of that stream. The hydrogenated oil is also more susceptible to cracking in the catalytic cracking step. Thus, the cat cycle oil is used as a slurry oil while at the same time being upgraded so that it can be recycled to the catalytic cracking zone for further reduction in molecular weight.

Description

United States Patent Dengler et al.

[451 Mar. 28, 1972 [54] COMBINATION PROCESS FOR LIQUEFACTION OF COAL AND CATALYTIC CRACKING OF SELECTED FRACTIONS THEREOF [72] Inventors: Herbert P. Dengler, Fairhaven; Bernard L.

Schulman, Livingston, both of NJ.

[73] Assignee: Esso Research and Engineering Company [22] Filed: Nov. 17, 1969 [21] Appl. No.: 877,314

[51] Int. Cl ..Cl0g 1/08 [58] Field of Search ..208/ 10 [56] References Cited UNITED STATES PATENTS 2,885,337 5/1959 Keith et al. ..208/8 3,188,179 6/1965 Gorin ..208/10 3,488,280 1/1970 Schulman ..208/10 Re2 5 .77 0 4/1965 Johanson... ....208/10 3,519,555 7/1970 Keith et al. ....208/l0 3,488,279 1/1970 Schulman ..208/10 RECYCLE GAS [57] ABSTRACT The present process is a combination of a liquid fluidized bed catalytic coal liquefaction zone and a fluidized catalytic cracking zone. In the liquefaction zone, finely divided coal is contacted with the fluidized catalyst bed while in a solvent oil and in contact with molecular hydrogen. A liquefaction zone product stream, containing a substantial amount of liquid materials boiling in an intermediate temperature range (e.g., 430 F. to 950 F.), is obtained, and boiling intermediate boilding range material separated from the remainder of the product stream. A first portion of the intermediate boiling range material is charged into a fluid catalyst cracking zone wherein the first portion is contacted with a cracking catalyst such as silica alumina under cracking conditions to obtain a cracking zone product stream which contains a substantial amount of heavy liquid materials hereinafter referred to as cat cycle oil." The heavy liquid materials in the cat cycle oil will boil not lower than the intermediate boiling range material. The cat cycle oil is separated from the remainder of the cracking zone product stream and admixed with a second portion of the intermediate boiling range material to obtain the slurry oil used as a solvent oil in the liquefaction zone.

By the present process, the cat cycle oil, which is very refractory due to a low hydrogen content, is reacted with hydrogen in the liquefaction zone to increase the hydrogen content and to crack some of the heavier components of that stream. The hydrogenated oil is also more susceptible to cracking in the catalytic cracking step. Thus, the cat cycle oil is used as a slurry oil while at the same time being upgraded so that it can be recycled to the catalytic cracking zone for further reduction in molecular weight.

9 Claims, 3 Drawing Figures 0 GAS C '43OF. FLUID CATALYTIC CRACKING RESIDUE cgsas C5-43OF.

RESIDUE FRACTIONATOR 1 -7.9 WT. H2

FIG. 3.

C GAS FLUID CATALYTIC CRACKING FRACTIONATOR-- CATALY TIC LIQUEFACTION SLURRY OIL F I G 2 RECYCLE GAS PATENTEDMAR28 m2 F I G 2 MAKE-UP no COAL INVEN'IORS H ERBERT P. DENGLER, BY BERNARD L SCHULMAN I ?//Qm} A TTORNEY.

R E SI DENCE TIME H0 URS I w H w COMBINATION PROCESS FOR LIQUEFACTION OF COAL AND CATALYTIC CRACKING OF SELECTED FRACTIONS THEREOF BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the production of low boiling hydrocarbon streams, such as naphtha, by the catalytic liquefaction of solid materials such as coal, followed by the catalytic cracking of the heavier components obtained from such liquefaction. The liquefaction reaction is carried out in the presence of a liquid fluidized bed of catalyst and molecular hydrogen.

2. Description of the Prior Art The prior art in the field of coal liquefaction suggests that the coal liquids be upgraded by hydrocracking, an expensive process. It has been found, however, that some liquids obtained in the catalytic liquefaction of coal can be sent directly to catalytic cracking. The prior art suggests that hydrotreating of the effluent from the catalytic cracking liquefaction zone is required prior to introduction of the liquid into the catalytic cracking zone. Further, the cat cycle oil is separately hydrotreated and reintroduced into the catalytic cracking zone. This involves the use of two hydrogenation reactors in addition to the liquefaction zone and also involves the use of a separate slurry oil, which may be obtained by fractionation from the liquefaction zone effluent.

The present invention, contrarily, provides a much simplified system which avoids the use of the hydrogenation zones both for the cat cracker feed and the cat cycle oil.

SUMMARY OF THE INVENTION The present invention is directed to the use of a combination process to produce light hydrocarbon streams from coal. In the first reaction zone of the process, the catalyst is maintained as a liquid-fluidized bed and the coal, slurry oil and molecular hydrogen are commingled and contacted with the catalyst under coal liquefaction conditions. It is the presence of catalyst and hydrogen which produces the upgrading of the slurry oil during the liquefaction step. The effluent from the liquefaction zone is fractionated to obtain an intermediate boiling range stream' which is the feedstock to a catalytic cracking zone wherein it is cracked to produce light materials. A portion of the intermediate boiling range stream is recycled into the liquefaction zone for use as a slurry oil. The cat cycle oil obtained from the catalytic cracking zone is also employed as a part of the slurry oil. It has been found that the cat cycle oil from the catalytic cracking zone is suitable for use as s slurry oil and, further, is itself hydrogenated in the liquefaction zone so as to improve its suitability for reintroduction into the catalytic cracking zone. It is well known that hydrocarbon streams of low average hydrogen content are quite refractory and are not desirable as feedstocks into a catalytic cracking zone, since the materials tend to produce an undue amount of gases and carbon laydown. Thus, the additional hydrogen in the oil molecule improves the quality of the cat cycle oil as a component for catalytic cracking.

BRIEF DESCRIPTION OF THE DRAWING The drawings contain the following three figures:

FIG. 1 is a schematic representation of the process of the present invention in its preferred embodiment, showing the combination of the liquid fluidized catalyst coal liquefaction zone with the catalytic cracking zone, and including the intermediate and final fractionation towers with the appropriate recycle streams;

FIG. 2 is a representation of the relationship between the hydrogen uptake at one hour residence time in the liquefaction zone as a function of hydrogen partial pressure and liquefaction zone temperature. The hydrogen uptake in weight percent represents the increase in hydrogen content of the 430 F.+ cat cycle oil; and I FIG. 3 is a graphical representation of the effect of residence time on hydrogen uptake in the 430 F.+ cat cycle oil.

The present invention may be more clearly understood by advertence to FIG. I wherein it is seen that coal, preferably comminuted to finer than mesh (Tyler), is introduced by way of line 100, combined with a slurry oil introduced by way of line 102 and introduced into the catalytic liquefaction zone 104. The coal and slurry oil may suitably be admixed in a slurry tank (not shown) or by means of an orifice mixer (not shown) or other suitable means. Hydrogen is introduced by way of line 106, and is made up of recycle gas 108 and fresh hydrogen makeup introduced by way of line 110. The upward velocity of the coal slurry is sufficient to maintain the catalyst bed in a fluidized condition, and the bed will have a distinct upper level 112 which represents a volume expansion of the bed of at least 10 percent and preferably 50 percent over the volume of the bed at rest.

The effluent from the catalytic liquefaction zone 104 is removed by way of line 114 and preferably passed through a separator 116 from whence the gaseous materials are removed and recycled by way of line 108. The remaining portion of the effluent, comprising unextracted coal residue and liquid is passed by way of line 118 into the fractionator 120. From the fractionator 120 are removed a C., gas stream, which contains butane and lighter gases which are removed by way of line 122, a C through 430 F. naphtha stream which is removed by way of line 124, a 950 F.+ bottoms stream which is removed by way of line 126 for coking or other disposition, and a 430 F. to 950 F. intermediate boiling range stream by way of line 128; i.e., the intermediate boiling range stream may suitably boil within the range from about 430 F to about 950 F. If the 950 F.+ bottoms stream is coked, the coker distillates can be used in the slurry oil. The 950 F.+ components in the coker distillate would, in that event, be partially converted to lower boiling materials by the reaction in the liquefaction zone. Coker oil in the intermediate boiling range would be cracked in the catalytic cracking zone.

The intermediate range boiling material is separated into two portions and a first portion is introduced by way of line 130 into the catalytic cracking zone 132. The second portion of the intermediate boiling range material is recycled by way of line 134 and line 102 for introduction into the catalytic liquefaction zone 104.

Within the fluid catalytic cracking zone 132, the intermediate boiling range material is contacted under cracking conditions with a cracking catalyst maintained in a fluidized bed, all as is well known in the art. Although shown as comprising a single zone 132, it is well known that a fluid catalytic cracking unit employs a catalyst regenerator and other associated equipment which is omitted from the schematic flow sheet for simplicity and clarity. As is seen from FIG. 1, and as is well known in the art, fluid catalytic cracking is carried out without added molecular hydrogen, thus being distinguished from hydrocracking.

The products from the fluid catalytic cracking zone are removed by way of line 136 and passed into the fractionator 138 for fractional distillation. The products from the fractionator 138 include a butane and lighter gas stream which is removed overhead by way of line 140, a naphtha side stream containing pentanes through 430 F. boiling material which is removed by way of line 142 and a 430 F.+ cat cycle oil which is removed by way of line 144. The cat cycle oil is combined with the second portion of the intermediate boiling range material which is removed from the fractionator 120 and the admixture is used as the slurry oil in the catalytic liquefaction zone 104.,

Note that the cat cycle oil which is withdrawn from the fractionator 138 contains only 7.9 weight percent hydrogen whereas, in order to constitute a suitable feedstock to the fluid catalytic cracking zone it should contain from about 9 to l 1 weight percent (suitably 10 weight percent) of hydrogen. In the present invention, such cat cycle oil streams will contain not more than 8.5 weight percent hydrogen, thus requiring the addition of hydrogen to enhance its susceptibility to cracking upon reintroduction into the catalytic cracking zone. By

reason of the hydrogenation of the cat cycle oil in the catalytic liquefaction zone 104, the hydrogen content of the cat cycle oil is increased by about 2 weight percent. Note also that since the feedstock into the fluid catalytic cracking zone boils within the range of 430 to 950 F., only a small amount of high boiling polymers will be present in the bottoms stream from the fractionator 138. In essence, then, the 430 F.+ cat cycle oil is recycled and rehydrogenated for introduction into the catalytic cracking zone and, by such recycle, is ultimately consumed. The small amount of 950 F.+ materials (including undissolved coal and ashes) which are removed by way ofline 126 constitute the only drawoff from the system aside from the desirable naphtha streams and the product gas streams. Thus, rather than being faced with the production of a refractory stream of intermediate boiling range which is much less desirable than the naphtha stream, the present process allows recycling that stream to extinction without providing a separate hydrogenation zone to make it suitable for recycle into the catalytic cracking zone.

Referring now to FIG. 2, it is seen that the 430 F.+ cat cycle oil will be reacted with hydrogen to increase the hydrogen content. For example, if the coal liquefaction zone is being operated at 850 F. and the hydrogen partial pressure is maintained at about 2,250 p.s.i.a., the cat cycle oil will increase in hydrogen content by 2 weight percent. It is also seen by advertence to FIG. 2 that the amount of hydrogen uptake increases with an increase in the liquefaction zone temperature and also increases with the increase in hydrogen partial pressure. FIG. 2 is based on one-hour residence time, and the hydrogen uptake increases with residence time. Thus, it is seen that residence time, temperature, and hydrogen partial pressure may be adjusted to obtain the desired hydrogen uptake in the cat cycle oil.

Referring to FIG. 3, it is seen that rate of hydrogen uptake decreases with residence time, so that the fastest rate of hydrogen uptake is at the shorter residence time but that the total hydrogen uptake continues to increase even up to two hours. From FIG. 3 it is seen that a nominal l-hour residence time appears to be suitable from the practical operating standpoint.

SPECIFIC DISCUSSION OF THE INVENTION As has been hereinabove stated, the major components of the combination process of the present invention are found in the catalytic liquefaction zone and in the catalytic cracking zone. The conditions and significance of each of these zones will be separately hereinafter discussed.

Catalytic Liquefaction Zone The liquefaction of coal involves the depolymerization of coal molecules. When carried out in the presence of hydrogen and a catalyst, depolymerization and hydrogenation reactions occur simultaneously so as to obtain a liquid product and undissolved coal residue. The undissolved coal residue contains ash as well as carbonaceous materials not taken into solution in the slurry oil.

The use of a liquid fluidized catalyst bed in the liquefaction of coal has been well described in US. Pat. Re. No. 25,770 (Example 5), US. Pat. No. 3,321,393 and Canadian Pat. No. 788,435. In general, the catalytic liquefaction of coal can be carried out while using a catalyst chosen from the group consisting of cobalt, molybdenum, nickel, iron, tin, or combinations thereof, supported on a carrier such as alumina, magnesia, and silica. A particularly desirable catalyst is cobalt molybdate supported on alumina, as supplied in the trade under the trademark Nalco 47l." The catalyst particles can be provided over a wide range of sizes, for example, from to 325 mesh (Tyler). Under some circumstances catalysts as large as 3 mesh can be employed. Preferably, however, the catalyst will be about I60 mesh in average particle size.

Coal (meaning bituminous, semibituminous, subbituminous, and similar low-rank coals and lignite, and similar materials) in a finely divided form is introduced in a slurry oil, for example, about 0.2 pound of coal per pound of slurry. The coal is preferably comminuted to less that mesh (Tyler) in size, although larger particle sizes (e.g., up to 8 mesh) can be employed. A hydrogen-containing stream is introduced at a rate of about 43 thousand standard cubic feet of hydrogen per ton of coal, and, if necessary, a recycle fluid stream is used in order to maintain the catalyst bed in a fluidized state, with the bed expansion at least 10 percent and preferably about 50 percent as opposed to the volume of the bed at rest. The temperature is maintained at 800 to 900 F. with the hydrogen partial pressure from 1,000 to 4,000 p.s.i.g. The nominal liquid residence time expressed as LHSV is from 0.3 to 3, while the hydrogen rate can be from 40 M s.c.f. per ton of MAF coal to M s.c.f. per ton of m.a.f. coal, corresponding to 25 times the amount of hydrogen consumed. The solvent/coal weight ratio can range from I to 5, preferably 1 to 2. The solvent as hereinabove explained, is an admixture of the cat cycle oil and intermediate boiling range materials with the solvent containing from 10 to 100 volume percent of the cat cycle oil (preferably 20-40 volume percent). Operating conditions are chosen so that, upon fractionation of the liquid effluent, the intermediate boiling range stream contains from 9 to l 1 weight percent hydrogen (preferably about l0 weight percent).

The Fluid Catalytic Cracking Zone A standard fluid catalytic cracking unit can be employed, which comprises a reactor and a regenerator fluidly connected for the circulation of catalyst and for the recovery of the products from the fluid catalytic cracking zone. The use of a transfer-line reactor is particularly preferred, in combination with a catalyst containing a molecular sieve component. Any of the well-known cracking catalysts can be employed, such as the silica alumina catalyst which has been widely used. Currently available silica alumina catalyst which contains molecular sieves may also be employed if desired. Preferably a silica alumina catalyst containing 25 percent alumina and having an average particle size of about 40 to 80 microns will be used.

In the catalytic cracking zone conditions will include a tem' perature from 900 to l,l00 F. (preferably l,000 F. a pressure from 0 to 40 p.s.i.g. (preferably 25 p.s.i.g.), and a residence time of 20 to 200 minutes (for normal catalytic cracking units) or from I to 10 minutes (preferably 2 to 5 minutes) for transfer-line cracking. Thus, residence time can range from I to 200 minutes. A bed density from l0 to 30 lbs/cu. ft. is suitable. The carbon which is laid down on the catalyst during the cracking reaction is burned off of the catalyst in the regenerator. This regeneration combustion, as well known, provides the heat for the cracking reactions. If desired, the feedstock into the catalytic cracking zone may be preheated (e.g., to a temperature of about 600 F.) before introduction into the cracking zone. As is apparent from FIG. 1, and as is well known in the art, molecular hydrogen is not added into the fluid catalytic cracking zone.

By the use of the present invention, it has been made possible to operate a simplified system for obtaining gasoline from coal. The investment has been minimized and operating costs reduced. The present invention also makes it possible to improve the refractory characteristics of the heavy catalytic cycle oil without the employment of a separate and special hydrotreating unit.

Having disclosed our invention and a preferred embodiment thereof, we claim:

1. A process for producing liquid hydrocarbon products from coal which comprises:

in a liquid-fluidized bed catalytic liquefaction zone, contacting a slurry of coal in a solvent oil with molecular hydrogen and a hydrogenation catalyst under coal liquefaction conditions, whereby a liquefaction zone product stream is obtained which contains a substantial amount of liquid materials boiling in an intermediate temperature range,

separating said intermediate boiling range material from the remainder of said liquefaction zone product stream,

charging a first portion of said intermediate boiling range material into a fluid catalytic cracking zone, wherein said first portion is contacted without added molecular hydrogen with a cracking catalyst under cracking conditions to obtain a cat cycle oil stream which contains a substantial amount of heavy liquid materials boiling not lower than the intermediate temperature range,

separating said cat cycle oil from the remainder of said cracking zone product stream,

admixing a second portion of said intermediate boiling range material with said cat cycle oil to obtain a slurry oil, and

using said slurry oil as the solvent oil in said liquefaction zone.

2. A process as set forth in claim 1 wherein the intermediate boiling range material boils substantially within the range from about 430 F. to about 950 F., and

the cat cycle oil boils above about 430 F. and contains not more than 8.5 weight percent hydrogen.

3. A process as set forth in claim 2 wherein the intermediate boiling range material has a hydrogen content of about weight percent and the cat cycle oil has a hydrogen content of about 8 weight percent.

4. A process as set forth in claim 2 wherein the liquefaction conditions include:

a temperature from about 800 F. to about 900 F., a pressure from about 1,000 p.s.i.g. to about 4,000

p.s.i.g., a LHSV from about 0.3 to about 3.0, a hydrogen rate from about 40 M s.c.f./ton to about 120 M s.c.f./ton,

a solvent/coal weight ratio from about 1 to about 5, and

the cat cycle oil constitutes from about 10 volume percent to about 100 volume percent of the solvent oil; and

the fluid catalytic cracking conditions include:

a temperature from about 900 F. to about l ,l00 F a pressure from about 0 p.s.i.g, to about 40 p.s.i.g., a residence time from about 1 minute to about 200 minutes, and a bed density from about 10 lbs/cu. ft. to about 30 lbs/cu.

5. A process as set forth in claim 4 wherein the catalyst in the liquefaction zone is cobalt molybdate and the catalyst in the fluid catalytic cracking zone is silicaalumina.

6. A process as set forth in claim 5 wherein the intermediate boiling range material has a hydrogen content of about 10 weight percent and the cat cycle oil has a hydrogen content of about 8 weight percent.

7. A process as set forth in claim 6 wherein the liquefaction zone conditions include:

a temperature of about 850 F., a pressure of about 2,000 p.s.i.g. to 3,000 p.s.i.g., a LHSV of about 1, a hydrogen rate of about M s.c.f./ton ofm.a.f. coal, a solvent/coal weight ratio of about 1, and

the heavy liquid materials constitute about 30 volume percent of the solvent oil.

8. A process as set forth in claim 7 wherein the catalytic cracking step is carried out in a transferline reactor and the residence time therein is from about 2 to about 5 minutes.

9. A process as set forth in claim 8 wherein the cracking catalyst contains a molecular sieve component.

Claims

2. A process as set forth in claim 1 wherein the intermediate boiling range material boils substantially within the range from about 430* F. to about 950* F., and the cat cycle oil boils above about 430* F. and contains not more than 8.5 weight percent hydrogen.
3. A process as set forth in claim 2 wherein the intermediate boiling range material has a hydrogen content of about 10 weight percent and the cat cycle oil has a hydrogen content of about 8 weight percent.
4. A process as set forth in claim 2 wherein the liquefaction conditions include: a temperature from about 800* F. to about 900* F., a pressure from about 1,000 p.s.i.g. to about 4,000 p.s.i.g., a LHSV from about 0.3 to about 3.0, a hydrogen rate from about 40 M s.c.f./ton to about 120 M s.c.f./ton, a solvent/coal weight ratio from about 1 to about 5, and the cat cycle oil constitutes from about 10 volume percent to about 100 volume percent of the solvent oil; and the fluid catalytic cracking conditions include: a temperature from about 900* F. to about 1,100* F., a pressure from about 0 p.s.i.g. to about 40 p.s.i.g., a residence time from about 1 minute to about 200 minutes, and a bed density from about 10 lbs/cu. ft. to about 30 lbs/cu. ft.
5. A process as set forth in claim 4 wherein the catalyst in the liquefaction zone is cobalt molybdate and the catalyst in the fluid catalytic cracking zone is silica-alumina.
6. A process as set forth in claim 5 wherein the intermediate boiling range material has a hydrogen content of about 10 weight percent and the cat cycle oil has a hydrogen content of about 8 weight percent.
7. A process as set forth in claim 6 wherein the liquefaction zone conditions include: a temperature of about 850* F., a pressure of about 2,000 p.s.i.g. to 3,000 p.s.i.g., a LHSV of about 1, a hydrogen rate of about 90 M s.c.f./ton of m.a.f. coal, a solvent/coal weight ratio of about 1, and the heavy liquid materials constitute about 30 volume percent of the solvent oil.
8. A process as set forth in claim 7 wherein the catalytic cracking step is carried out in a transferline reactor and the residence time therein is from about 2 to about 5 minutes.
9. A process as set forth in claim 8 wherein the cracking catalyst contains a molecular sieve component.