SINGLE-STEP COAL LIQUEFACTION PROCESS

Abstract: A process for the single-step coal liquefaction is disclosed, which comprises reacting the same coal in an aqueous suspension with carbon monoxide in the presence of a CO-conversion catalyst selected from an alkaline hydroxide or carbonate, and in the presence of a hydrogenation catalyst selected from the transition metals or their compounds, by operating at temperatures comprised within the range of from 300 to 450°C for a reaction time comprised within the range of from 30 to 80 minutes.

Description: The present invention relates to a single-step coal liquefaction process. Coal liquefaction processes are known, using CO, water, and a catalyst, so as to produce "in situ" the hydrogen which is necessary for coal liquefaction. US-A-3 796 650 teaches the combined use of two catalysts, ammonia or an alkali metal hydroxide or carbonate in the first place, and an element of the VIII Group of the Periodic Table, or a compound thereof, in the second place, preferred being the sulphides in an amount of from 0,0017 to 10% by weight. The defect of such prior art processes is that the mixture of hydrocarbons thus obtained contains asphaltene precursors (PA), asphaltenes (A) and oils (OILS) in various proportions. It has been surprisingly ascertained that, by adding to the reaction mixture a molybdenum compound as a hydrogenation catalyst, the hydrogen so produced is better exploited, in that the quelity of the end products and the distribution of PA, A and OILS is such as to warrant for a better quality: moreover, the H/C ratio of the reaction products is improved. The products thus obtained are useful intermediates for producing liquid derivatives from coal. The invention, therefore, proposes a single-step coal liquefaction process, comprising reacting coal in an aqueous suspension with carbon monoxide, in the presence of a CO-conversion catalyst selected from alkali metal hydroxides and carbonates, characterized in that the liquefaction reaction is carried out in the additional presence, as the hydrogenation catalyst, of molybdenum, or a compound thereof, in an amount of not more than 1% by weight relative to coal, at a temperature of from 300°C to 450°C for a time of from 30 min to 80 min. The pressure under which the liquefaction of coal takes place depends both on the amount of water which is charged together with the coal to the reaction system, i.e., in the aqueous coal suspension, which should preferably be in a weight ratio comprised within the range of from 2/1 to 5/1 relatively to the coal used as the starting material; and on the partial pressure of charged carbon monoxide, which should be preferably comprised within the range of from 39,23 bar to 78,45 bar (40 to 80 atm); said pressure is preferably selected within a range comprised within the range of from 147,1 bar to 294,2 bar;(150 to 300 atm). Sodium and potassium hydroxides and carbonates are the preferred catalysts for the reaction of conversion of CO to CO₂ and H₂. The hyrogenation catalyst, per se known, can be, in the form of oxides or sulphides, and can be directly added or produced in situ by decomposition of soluble salts of molybdenum. The amount of said hydrogenation catalyst is smaller than, or equal to, 1% by weight relatively to the same coal fed to the reaction. The temperature can be kept essentially constant during the whole reaction time, and preferably equal to a value selected within the range of from 380 to 440°C, or it can be kept for a time of up to 20 minutes, and preferably comprised within the range of from 5 to 20 minutes, at a value selected within the range of from 300 to 370°C, to be then increased over a time comprised within the range of from 20 to 40 minutes, up to reach a value selected within the range of from 420 to 450°C, at which value it can be kept for a time of up to 20 minutes, and preferably comprised within the range of 5 to 20 minutes. During the liquefaction process, water is at a temperature close to, or higher than, the critical temperature, determining a density of the reaction medium comprised within the range of from 0.07 to 0.2 g/ml. In order to better illustrate the meaning of the present invention, an example is reported hereinunder, which anyway is not to be considered as being limitative of the same invention. Example 1 The test was carried out on an Illinois Nr. 6 coal, the elemental analysis of which is shown in Table 1. One gram of coal was treated with an aqueous solution of ammonium heptamolybdate, and then dried, so as to obtain a coal impregnated with the catalyst at a concentration of 0.2% of Mo per coal gram. The catalyst-impregnated coal was then charged to a reactor of 30 ml of capacity, together with 4 ml of a 0.1 M aqueous solution of Na₂CO₃. The reactor was then pressurized with 40 atm of carbon monoxide; it was then heated to 400°C and maintained at this temperature for 60 minutes. When the reaction was ended, the reactor was discharged and, after eliminating the aqueous phase, the reaction product was recovered with tetrahydrofuran (THF). The product fraction soluble in THF was then filtered off from unreacted coal and mineral materials. The THF-soluble material was then furthermore treated with hexane in soxhlet, in order to separate the fraction constituted by the oils. In total, by starting from 1 g of dmmf coal (dmmf = dry mineral matter free), when the process was ended, more than 0.9 g was recovered of a mixture of mostly non-distillable, THF-soluble hydrocarbons, 35% of which were soluble in paraffinic solvents (oils). The degree of hydrogenation of the mixture of THF-soluble products was increased by increasing the H/C ratio from 0.82 (the starting coal) to 1.05. The hydrogen used by the liquefaction system and computed on the basis of the gas-chromatographic analysis of the gas mixture recovered at the reaction end was of 20 mg/g of dmmf coal. Example 2 (Comparative Example) Still on 1 g of Illinois Nr. 6 coal, a test analogous to the preceding one was carried out, but without using the hydrogenation catalyst (ammonium heptamolybdate). Under the same reaction conditions, at the end of the process more than 0.9 g was recovered of a mixture of no longer distillable, THF-soluble hydrocarbons (H/C = 1.00), 26% of which were soluble in paraffinic solvents (oils). In this case, the hydrogen used by the system was of 16 mg/g of dmmf coal. Therefore, the use of a hydrogenation catalyst made it possible a mixture of hydrocarbons to be obtained, wherein the hydrocarbons soluble in paraffinic oils (oils) had increased from 26% to 35%. Furthermore, with the gaseous hydrocarbons produced being the same, an increase in use of hydrogen of about 20% was observed. Immediate and End Analysis of Illinois Nr. 6 Coal Air Dried Dry dmmf Moisture % 4.57 Ashes % 11.43 11.98 Volatile matters % 35.74 37.45 44.01 Fixed Carbon % 48.26 50.57 55.99 Carbon % 66.42 69.60 81.79 Hydrogen % 5.06 4.77 5.60 Nitrogen % 1.50 1.57 1.85 Sulphur % 3.43 3.59 Oxygen (diff.) % 12.16 8.49 10.76

Claims: A single-step coal liquefaction process, comprising reacting coal in an aqueous suspension with carbon monoxide, in the presence of a CO-conversion catalyst selected from alkali metal hydroxides and carbonates, characterized in that the liquefaction reaction is carried out in the additional presence, as the hydrogenation catalyst, of molybdenum, or a compound thereof, in an amount of not more than 1% by weight relative to coal, at a temperature of from 300°C to 450°C for a time of from 30 min to 80 min. Process according to Claim 1, wherein a constant temperature of from 380°C to 440°C is maintained throughout the liquefaction reaction. Process according to Claim 1 , wherein the reaction temperature is maintained, during the first 20 min of reaction, at a value of from 300°C to 370°C, whereafter the temperature is raised, during a time of from 20 min to 40 min, to a value of from 420°C to 450°C, and is so maintained, for the last 20 min. Process according to Claim 3, wherein the reaction temperature is maintained at a value of from 300°C to 370°C for a time of from 5 min to 20 min, and is subsequently maintained at a value of from 420°C to 450°C for a time of from 5 min to 20 min.

Inventors: DELBIANCO, ALBERTO, GIRARDI, ERMANNO
Applicants: ENIRICERCHE S.P.A.
Application year: 1988
Main classification: C10G1
IPC codes: C10G1