US2464271A - Coal liquefaction by hydrogenation - Google Patents

Description

Patented Mar. 15, 1949 COAL LIQUEFACTION BY HYDROGENATION Henry H. Storch and Lester L. Hirst, Pittsburgh, Pa., assignors to the United States of America as represented by the Secretary of the Interior No Drawing. Application December 24, 1943, Serial No. 515,474

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to us of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467) This. invention relates to hydrogenation, and more particularly to the destructive hydrogenation of solid carbonaceous materials susceptible thereto. Still more particularly, this invention relates to a low pressure process for the production of liquid hydrocarbons from coals, such as bituminous coal, lignite and the like, as well as to novel catalysts for carrying out the process.

Heretofore solid carbonaceous materials susceptible to destructive hydrogenation have been reacted with hydrogen at extremely high pressures ranging from 500 to 1,000 atmospheres to produce liquid hydrocarbons which have been employed for fuel oils and the like. However, the employment of extremely high pressure requires specialized and expensive equipment. Certain low pressure processes are also known for the production of liquid hydrocarbons from solid carbonaceous materials, such processes in general comprising the treatment of the solid carbonaceous materials with highly-hydrogenated solvents such as tetra-hydro-naphthalene, deca-hydronaphthalene, hydrogenated cresol, and the like. The principal difliculty with such solvent extraction processes resides in the fact that large quantities of gummy or tarry residues result, which rapidly render the equipment useless.

It is therefore an object of the present invention to provide a low pressure process for the destructive hydrogenation of solid carbonaceous materials susceptible thereto. Another object is to provide a process for the preparation of liquid hydrocarbons from normally solid carbonaceous materials. A further object is to provide a process for the destructive hydrogenation of solid carbonaceous materials susceptible thereto in which the re-precipitation and repolymeriaztion of said solid carbonaceous materials is prevented. Yet a further object is to provide a continuous process for the preparation of fuel oil from coal which can be carried out for extended operating periods. Another object is to provide novel and eflective catalysts for carrying out the foregoing processes.

The foregoing and other objects hereinafter apparent are accomplished in accordance with the present invention wherein a solid carbonaceous material susceptible to destructive hydrogenation is admixed with a liquid vehicle and a' dispersed catalyst, the mixture is heated to a temperature of at least 300 0., introduced together with excess hydrogen into a closed reaction zone maintained under an elevated pressure of not more than 90 atmospheres, then said mixture is advanced through the reaction zone while the.temperature of the reaction mixture is progressively elevated as the mixture is advanced, and the reaction mixture is discharged from the reaction zone at a final temperature of not more than 475 C. It has been discovered that repolymerization and re-precipitation of the normally solid carbonaceous material being destructively hydrogenated can be prevented by maintaining a controlled progressively increasing reaction temperature as the destructive hydrogenation is carried out. By beginning the destructive hydrogenation at a relatively low temperature, and progressively increasing the temperature in the reaction mixture as the reaction progresses, the deposition of coke and other residues in the equipment is substantially completely inhibited. The initial temperature of reaction is at least 300 C., and preferably within the more restricted range of from 350 C. to 400 C. Thereafter the temperature within the reaction zone is progressively elevated, as the reaction proceeds, to a maximum temperature of not more than 475 C. Preferably, the final reaction temperature is maintained within the more restricted range of from 425 C. to 450 0.

Suitable solid carbonaceous materials susceptible to destructive hydrogenation in accordance with the present invention include lignite, brown coal, subbituminous or bituminous coals, and preferably subbituminous coals such as the Monarch Bed coal of Wyoming and the like.

In preparing the coal or other carbonaceous material susceptible to destructive hydrogenation for reaction in accordance with the present invention, it is desirable to pulverize to a relatively fine state of sub-division, preferably such that it will pass through a standard Tyler screen of about mesh. After being pulverized, the coal is admixed with a sufficient amount of one of the usual liquid vehicles for destructive hydrogenation, preferably a recycle oil produced by a previous hydrogenation. In general, from one to three parts by weight of recycle oil or other liquid vehicle per part of coal provides a suitably fluent consistency for reaction. In starting a new plant, a topped high temperature coal tar which has been hydrogenated as hereinafter to be explained, provides a desirable liquid vehicle. It is preferable to avoid liquid vehicles derived from petroleum or other aliphatic sources.

' This invention also provides novel catalysts for carryingout the low pressure destructive hydrogenation of carbonaceous materials susceptible thereto, the cataiystsbeing a, dispersed catalyst comprising a stanniferous substance in intimate admixture with a halogenous substance, and as a fixed or contact catalyst, a stainless steel. Both the dispersed catalyst and the stainless steel catalyst are extremely effective whenemployed separately, but when employed together, they are remarkably effective at low pressures and low temperatures in inhibiting the precipitation of coke-like materials.

Suitable stanniferous substances include metallic tin, and tin compounds such as tin sulfide, oxide, oxalate, or other tin compound soluble in strong mineral acids. In general, about 0.05 per- 'cent to 0.5 percent by weight and preferably between 0.1 percent and 0.3 percent by weight of the stanniferous substance "based on moistureand ash-free solid carbonaceous material is a sufflcient amount. The halogenous substance employed in the dispersed catalyst can be molecular chlorine, bromine, or iodine, and the like, but it is preferably in the form of an alkyl halide, or other volatile halogen compound. Iodoform con stitutes a preferred halogenous substance and in general, iodine or iodine compounds are superior to other halogenous substances. Usually from 0.02 percent to 0.2 percent by weight, based on moistureand ash-free coal or other solid carbonaceous material susceptible to destructive hydrogenation, is a sufficiently large amount of iodoform or other halogeneous catalytic substance. Greater or lesser amounts of the foregoing components of the dispersed catalyst can be employed, The dispersed catalyst is admixed with the dispersion of solid carbonaceous material in the liquid vehicle; and in the hydrogenation of coal, between 0.004 part and 0.006 part by weight of a mixture of equal parts by weight of tin sulfide and iodoform per part by weight of coal has been found to give a desired rate of hydrogenation.

While the foregoing dispersed catalyst alone will catalyze hydrogenation, it has been found that a still more beneficial effect upon the reaction can be secured when the reaction mixture, during at least the latter stages of the reaction, is passed over a fixed catalyst comprising a stain less steel. Suitable stainless steels include austenitic steel alloys with chromium and nickel which may also contain cobalt, molybdenum and the like, such as KAzSMO, Rezistall, and preferably the stainless steel which contains about 18 percent by weight of chromium and 8 percent nickel, the balance being largely iron. The stainless steel fixed catalyst is preferably in the form of wire, ribbons, machine turnings, or other form presenting a large surface to the reactants. The entire re-actlon vessel can be packed with the stainless steel catalyst, but it has been found, in. general, that packing the latter half of the reaction zone with stainless steel catalyst provides a suitable catalytic effect. By-the latter half of the reaction zone is meant that portion which is maintainedat the higher stages of reaction temperature, for example, above 400 C.

By the employment of the foregoing progressively increasing temperature schedule and catsired reaction, a suitable hydrogen pressure within the reaction zone being not more than 90 atmospheres, generally from 30 to 80 atmospheres,

and preferably the pressure is maintained withinthe more restricted range of 50 to '75 atmospheres.

In carrying out the destructive hydrogenation of coal or other carbonaceous materials susceptible thereto, the dispersed catalyst is added to the previously prepared coal-oil paste and then preheated to the initial reaction temperature.

alyst, it has been found that a relatively low Thereafter the mixture is introduced into a suitable reaction vessel together with a large excess of hydrogen and the reactioncommences smoothly. The reaction is exothermic in character and ingeneral, a progressively increasing temperature gradient is secured by suitable heating and cooling means forming a part of the converter system. As the material is passed through the convertersystem, the desired temperature gradient is maintained by heating and cooling, and the material is subjected to reaction for a contact time of between one-half and eight hours. and preferably for only about one to three hours, a reaction time of two hours being an average value. The reaction vessel in theportionnext adjacent the exit thereof is preferably packed with stainless steel turnings, and the reaction mixture containing dispersed catalyst thus ultimately contacts this fixed catalyst. After the reaction is completed, the reaction mixture is cooled, the pressure letdown to atmospheric, gaseous by-products and excess hydrogen discharged and the final mixture subjected to a topping distillation. Material boiling below 235 C. is separated from the remaining oily product, catalyst sludge and ash. The lower boiling material, which contains the tar acids and bases, is then successively washed with an aqueous acid material such as sulfuric acid andthereafter with aqueous alkali such as caustic soda solution, to remove said tar acids and bases. Approximately 2 percent of the reaction material comprises these industrially valuable tar acids and bases. The material boiling above 235 C. is subjected to centrifugal'separation, the ash being thereby reduced to 0.01 to 0.03 percent by weight of the final oil. The centrifuge product and the washed product are then mixed together and meet the specifications of the American Society for Testing Materials for number 5 and number 6 fuel oil. The heating value of the product is higher than the heating value of similar oils produced from petroleum.

A more specific procedure is to pass through a converter a mixture of one part of powdered coal with one to two parts of a heavy recycle oil, and between 0.004 and 0.006 part of a mixture of equal parts by weight of tin sulfide and iodide in a hydrogen atmosphere under a pressure of 60 to 70 atmospheres and a temperature maintained at from 370 to 385 C. at entry and 400 to 415 C. at the point of exit of the reacting mixture, passing the reacting mixture through a second converter packed with bright stainless steel turnings under an initial temperature of from 410 to 420 C. and under a temperature of from 430 to 440 C. at the point of exit, sub- ,iecting the product of the second converter to a fractional condensation and removing solid particles of the fluid product by centrifuging.

The following examples illustrate how the invention may be carried out, but it is not limited thereto. Parts are by weight unless otherwise designated:

Example 1 One part bituminous coal from the Black Creek Bed in Walker County, Alabama, is pulverized to minus 80-mesh, (standard Tyler screen), and admixed with two parts of liquid vehicle, 0.001 part tin sulfide and 0.0005 part iodoform. (The liquid vehicle is prepared by hydrogenation of topped coke-oven tar at from 415 to 435 C. under a pressure of 65 to 70 atmospheres for 3 hours, in the presence of 0.001 part tin sulfide and 0.0005 part iodoform.) The mixture of coal, liquid vehicle, and dispersed catalyst is passed through a tubular preheater' made of stainless steel. The preheater is provided with heating and cooling means, and the temperature of the coal-oil paste is elevated therein to 120 C. A second preheater, similarly provided with heating and cooling means, is arranged in series with the first one, wherein the coal-oil paste is further preheated to 370 C. Thereafter, gaseous hydrogen, separately preheated also to 370 C., is admixed with the coal-oil paste containing dispersed catalyst, and the gas-paste-catalyst mixture is introduced into an elongated stainless steel converter provided with suitable heating and cooling means, and having a length to internal diameter ratio of to 1. An excess of hydrogen is preterably employed, the rate of hydrogen input being maintained between 5 and cubic feet per pound of coal-oil paste although only 0.063 part hydrogen per part coal is consumed. The pressure within the converter is maintained at 65-70 atmospheres by suitable valves and pumps, and the reaction temperature within the converter is gradually elevated by heating to 390 C. Over 3 /2 hours reaction time, the temperature is gradually elevated to 415 C., after which the pressure is released, the product cooled, and an additional 0.001 part tin sulfide and 0.0005 part iodoform is added. A successive hydrogenation of the primary product is carried out in a similar converter under similar conditions, but the initial conversion temperature is adjusted to 415 C., the final temperature to 435 C., and the reaction time is 3 hours. The reaction mixture is cooled, the pressure let down to atmospheric and the reaction mixture centrifuged to remove ash and a small amount of residue. The yield of oil produced, based on the weight of coal consumed, is 53.4 percent. Eighty percent of the oil produced is recycled to serve as liquid vehicle for another batch, and 20 percent is a final product. After extended operating periods, no coke is found in the equipment. The oil produced has the following characteristics:

Specific gravity at 26 C. 1.118 B. t. u. per pound 16,892 B. t. u. per gallon 157,600

Ash content, per cent 0.02, Viscosity, furol, seconds at 122 F 44.6 Flash point, F. 225 Distillation (Topping, American Wood Preservers Association Method) volume percent to 350 C 35. Insoluble (Bureau of Mines Tetralin- Cresol Method) percent 5.7

About 1 to 2.5 volume percent of the oil boils below 235 C., and the oil contains about 1 to 2' percent oxygen, in the form of tar acids, removable by washing with aqueous alkali solution.

Example 2 One part of Pittsburgh Bedbituminous coal is admixed with two parts recycle oil (product of a previous run), and with, based on moistureand ash-free coal, 0.3 percent tin sulfide and 0.15 percent iodoform. The coal-oil paste containing dispersed catalyst is hydrogenated in the apparatus of Example 1, with the exception that the latter half of the converter, (the portion at the more elevated temperature), is packed with stainless steel turnings, containing 18 percent by weight chromium and 8 per cent by weight nickel, the balance being principally iron. The coal-oildispersed catalyst mixture is passed continuously through the converter, the entrance temperature being maintained at 370 to 385 C., and the hydrogen pressure at 65-70 atmospheres. During a reaction time of 1.5 hours, hydrogen consumption is only 3 to 6 percent by weight based on moistureand ash-free coal consumed, although a substantial excess of hydrogen is passed through the converter. No coke forms in the equipment, and the reacted material is entirely soluble except for its ash content. The product of the hydrogenation is subjected to a topping distillation to remove materials boiling below 235 C., and the residual material is centrifuged to remove ash, catalyst residues, and a small amount of unreacted coal. The fraction boiling below 235 C. is washed with dilute caustic soda and dilute sulfuric acid to remove industrially valuable tar acids and bases. The resulting neutral oil, when mixed'with the centrifuged oil, fills the specification of the American Society for Testing Materials for number 5 and number 6 fuel oil, while its heating value is higher than similar oils produced from petroleum.

Although the fixed stainless steel catalyst is in general employed together with the dispersed catalyst, it nevertheless possesses decided catalytic properties apart from the dispersed catalyst and therefore can be employed alone in the present invention. Likewise, the entire converter can be packed with stainless steel turnings or other form thereof presenting extended surfaces.

The hydrogen employed for the hydrogenation process is preferably purified so as to reduce the content of inert gas to less than 5 percent. Small amounts of impurities such as sulfur compounds, carbon monoxide, water vapor, and the like exert no apparent detrimental effect upon the reaction. The novel catalysts of the present invention are active in the presence of sulfur compounds and therefore appreciable amounts of sulfur compounds can be tolerated.

It will be apparent that the foregoing invention provides a novel method for the preparation of liquid hydrocarbons from coal or other normally solid carbonaceous materials susceptible to destructive hydrogenation, and that a relatively low pressure is required in comparison with previous processes. By the employment of the temperature ranges and the temperature gradient of the present invention, the deposition of coke and other undesired materials in the reaction apparatus is substantially completely inhibited, thus permitting operation for extended periods of from 500 to 1,000 hours or more without any attention being required. The coal employed is converted to oil in good yield, while the re-precipitation or re-polymerization of coal is inhibited by the present invention. v

Since many apparently widely differing embodiments of the present invention will occur to one skilled in the art, it is apparent that various changes may be made in the invention without departing from the spirit and scope thereof.

What is claimed is:

A process of producing fuel oil directly from coal which comprises putting into a converter a mixture of one part of powdered coal with one to two parts of a heavy recycle oil, and between 0.004 and 0.006 part of a mixture of equal parts by weight of tin sulfide and iodide in a hydrogen atmosphere under a pressure of 60 to "70 atmospheres and a temperature maintained at from 370 C. to 385 C. at entry and from 400 C. to 415 C. at the point of exit of the reacting mixture passing the reacting mixture through a sectional condensation and removing solid particles REFERENCES CITED The following references are of record in the file of this patent:

Um'rm s'rA'rne PATENTS Number Name Date 1,863,670 Pier June 21, 1932 1,890,436 Krauch et al. I Dec. 6, 1932 1,915,394 Waterman June 27, 1933 1,923,576 Krauch et al. II Aug 22, 1933 2,073,578 Gwynn Mar. 9, 1937 2,088,214 Pflrrmann July 27, 193'! 2,098,400 Pier et al. Nov. 9, 1937 2,106,735 Gwynn II Feb. 1, 1938 2,132,613 Francon Oct. 11, 1938 2,291,300 Harvey July 28, 1942 2,319,991 Harvey II May 25, 1943 2,349,721 Harvey III May 23,1944 2,356,611

Peters Aug. 22, 1944