US3503872A - Hydrocracking of coal tar - Google Patents

Description

United States Patent M 3,503,872 HYDROCRACKING 0F COAL TAR Richard A. Flinn, Emmaus, and Mehmet Orhan Tarhan,

Bethlehem, Pa., assignors to Bethlehem Steel Corporation, a corporation of Delaware No Drawing. Filed Feb. 2, 1968, Ser. No. 702,540

Int. Cl. C10g 13/02 US. Cl. 208-112 10 Claims ABSTRACT OF THE DISCLOSURE In a process for upgrading coal tar, the tar is hydrocracked by reacting it in the presence of hydrogen and a co'balt-molybdate on alumina catalyst at elevated temperature and pressure. A major portion of the reaction product comprises components boiling below 300 C., and these components are separated from the remainder of the reaction product by distillation. Components boiling above 300 C. are recycled to the hydrocracking zone to convert, ultimately, the entire feed to components boiling below 300 C.

Background of the invention This invention relates to a method of upgrading coal tar, and more particularly to the hydrocracking of coal tar.

Coal tar, obtained from the destructive distillation of bituminous coal in the manufacture of coal, contains a large number of components ranging from light oil to heavy oil and pitch, the boiling points of individual components ranging from about 80 upward. In tar, most components are present in such small quantity, that it is uneconomical to isolate and recover each of them separately. Furthermore, most of the very large molecules in tar are undistillable and have little commercial value.

The most readily salable products of coal tar are the light oils comprising benzene, toluene, xylene and solvent naphtha. However, light oil represents little more than of the coal tar. Naphthalene, the methyl naphthalenes and phenols are also desirable recovery products, and these compounds are present in commercially recoverable quantities. Consequently, the lower boiling oneand tworing aromatics, which constitute 15% to 30% of coal tar, are distilled from the tar and further refined. This distillation is referred to as topping, the distillate and residue being referred to as chemical oil and topped tar respectively. The bulk of the components in the tar are those which boil above 300 C. and remain in the topped tar, and include anthracene oil and pitch. These high boiling, high molecular weight, aromatic compounds, made up, for the most part, of three or more rings, constitute from 70% to 80% of crude coal tar. There is no large market for any of the individual compounds in the high boiling range, and, due to the fact that great quantities of coal tar are produced in the steel industry, much of it, especially the high boiling fraction can be used only as fuel.

It is therefore an object of this invention to hydrocrack high molecular weight compounds of coal tar into primarily lower molecular weight, oneand two-ring aromatic compounds.

Another object is to produce a coal tar product in which essentially all of the components boil below 300 C.

A further object is to obtain the lower molecular weight, aromatic compounds substantially free of compounds of similar boiling point which contain oxygen, nitrogen and/ or sulfur.

Another object is to hydrocrack the high molecular weight compounds with a minimum of carbon formation on the hydrocracking catalyst surface.

3,503,872 Patented Mar. 31, 1970 Summary of the invention We have found that the foregoing objects can be attained by hydrocracking coal tar, or portions thereof, containing high molecular weight compounds, in a reaction vessel in the presence of a specific catalyst consisting of a moderately active hydrogenation component, such as oxides or sulfides of cobalt-molybdenum, and a weakly acidic cracking support, such as alumina. The temperature at which the hydrocracking reaction is performed is within the range of from 300 to 450 C., while the pressure is maintained at between 500 and 5-000 p.s.i.g. or higher. Under the foregoing conditions, the coal tar is in liquid phase in the reaction vessel. Hydrogen is supplied to the reaction zone in an amount equivalent to from 350 to 3500 volumes of hydrogen per volume of coal tar feed. The process can be performed continuously or batchwise.

. Theoretical considerations on catalyst selection would suggest a combination of an active hydrogenation component, such as nickel-tungsten or nickel-molybdenum, with a highly acidic cracking component, such as silicaalumina or fluorine-promoted silica-alumina. Although such catalyst combinations were also found to convert topped tar to lower boiling hydrocarbons to some degree, the conversion was quite inferior to that obtained with the unpredicted combination of a moderately active hydrogenation component (cobalt-molybdate) and a mildly acidic cracking compound (aluminum oxide).

The invention is applicable to any coal tar which contains considerable amounts of heavy molecules, typified by those components which boil above about 300C. Coal tars may be obtained from sub-bituminous or bituminous coals in low temperature or high temperature carbonization processes. Tars obtained from bituminous coals by hightemperature carbonization, as practiced in metallurgical coke manufacture, present a feed material most beneficially treated by the method of this invention. However, other tars can also be treated, although they would require a more severe treatment for removal of oxygen, nitrogen and sulfur compounds, and low temperature tars would yield less aromatic product.

Detailed description In the following example, a topped coal tar, formed by removing about 20% of the low-boiling components from a coal tar produced by carbonizing bituminous coal at a coking temperature of about 1000 C., was used as feed. The topped tar had a specific gravity of 1.347, a carbon residue (Conradson) of 28-30%, and a softening point (ring and ball method) between 32 and 33 C.

The liquid coal tar feed contained essentially those components boiling above about 300 C., and thus represented all of the pitch and anthracene oils.

The feed was introduced into a reaction vessel and treated therein for a residence time of about 4 hours, in the presence of a cobalt-molybdate on alumina catalyst. The catalyst to feed weight ratio was 0.25. Hydro-gen was introduced into the reaction vessel during the hydrocrackoperation in an amount suificient to maintain a pressure of 3000 p.s.i.g. within the vessel. Throughout the four hour reaction period, the temperature in the vessel was maintained at about 400 C.

The cobalt-molybdate catalyst comprised 3% cobalt oxide and 15% molybdenum oxide thoroughly dispersed on a support of gamma alumina (A1 0 The catalyst had a surface area of approximately 320 square meters per gram, and was used in the form of inch diameter pellets. The atomic ratio of cobalt to molybdenum was 0.5.

Upon completion of the hydrocracking treatment, the

3 feed was condensed to separate vapors therefrom, and discharged as liquid from the reaction vessel and distilled. Somewhat more than 70% (73.1%) of the reaction product boiled below 300 C.

While the batch method just described for the performance of this invention is adequate when relatively small quantities of coal tar are to be handled, it will be recognized that the greatest economic benefits can be realized When using the invention for processing large quantities of tar in a continuous process. As an example of the manner by which the method of the invention can be performed continuously, at topped, high temperature coal tar, having the same characteristics as that used in the previous example, is used as feed. The coal tar is fed continuously to the reaction zone of a pressure vessel containing a bed of cobalt-molybdate on alumina catalyst. The catalyst is of the type used in the previous example. Feed is supplied to the reaction vessel at a liquid hourly space velocity (LHSV) of 0.5. Hydrogen is fed to the reaction zone in the ratio of 350 to 3500 standard volumes of hydrogen per volume of liquid feed. Reaction zone temperature and pressure are maintained at 400 C. and 3000 p.s.i.g. respectively. Treated feed is withdrawn from the reactor continuously as liquid product and vapor, and the product is distilled to separate the portion boiling below 300 C. from the higher boiling components. These higher boiling components are recycled with incoming feed to the hydrocracking reaction vessel. In a continuous process of this type, where unreacted product is recycled, ultimately all of the feed is converted by hydrocracking to a product containing only those components which boil below 300 C.

Pressure within the reaction zone for either the batch or continuous method may range from about 500 p.s.i.g. to any practical upper limit, as, for example, 5000 p.s.i.g. preferably between 1000 and 3000 p.s.i.g., while a residence time ranging from 1-10 hours is satisfactory. Broadly, the operating temperature range may be from 300-450 C., While the preferred temperature range is from 350410 C.

In a continuous process, hydrogen may be introduced at a rate of between 350 and 3500 standard volumes of hydrogen per volume of liquid feed, and preferably between 750 and 1700 standard volumes of hydrogen per volume of feed. The liquid hourly space velocity (LHSV) is from 0.1-1.

The cobalt-molybdate catalyst may contain cobalt and molybdenum in either oxide or sulfide form with the atomic ratio of cobalt to molybdenum ranging from 0.1 to 1.0, the preferred range being from 0.2 to 0.6. The alumina support may be in either the gamma or eta form. Specific surface area in square meters per gram of catalyst may be from 100-400, preferably from 150-350. The total cobalt and molybdenum, calculated as metal, present in the catalyst represents between 6-14% of the total catalyst.

We claim:

1. A method for upgrading a liquid coal tar feed with a boiling point above 300 C. which comprises hydrocracking by reacting said feed with hydrogen in a reaction zone in contact with a cobalt molybdate on alumina catalyst at a temperature of from 300-450 C. and a pressure of from 500-5000 p.s.i.g. wherein hydrogen is supplied at a rate of from 350 to 3500 standard volumes of hydrogen per volume of liquid feed and thereby producing a reaction product in which a major portion comprises components having a boiling point below 300 C.

2. A method according to claim 1 in which the reaction product is fractionated by distillation into components boiling below 300 C. and higher boiling components.

3. A method according to claim 2 in which the higher boiling components of the reaction product are returned to said reaction zone.

4. A method according to claim 1 in which the reaction residence time is from 1-10' hours.

5. A method according to claim 1 in which the temperature is from 345 -400 C.

6. A method according to claim 3 in which the pressure is from 1000-3000 p.s.i.g.

7. A method according to claim 1 in which the catalyst support is substantially all gamma or eta alumina.

8. A method according to claim 1 in which the tar is fed to the reaction zone at a rate of between 0.1 and 1.0 LHSV.

9. A method according to claim 7 in which the specific surface area of the catalyst in square meters per gram of catalyst is from -350.

10. In a method according to claim 1, the steps of condensing the reaction product, separating resultant gases from liquid, distilling the liquid and thereby separating components of the liquid product boiling below 300 C. from residual components and recycling the residual components to the reaction zone.

References Cited UNITED STATES PATENTS 1,852,988 4/1932 Varga 20-8-10 1,845,439 2/1932 Pier et val. 208-112 1,620,075 3/ 1927 Clancy 208-112 1,938,328 12/1933 Grifiith 2081l2 3,162,594 12/1964 Gorin 20857 2,686,150 8/1954 Porter et al 196--56 2,913,397 11/1959 Murray et al. 208107 3,324,029 6/1967 King 20844 DELBERT E. GANTZ, Primary Examiner VERONICA OKEEFE, Assistant Examiner