PROCESS FOR SINGLE-STEP COAL LIQUEFACTION

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, characterized in that the reaction is caused to take place at a temperature firstly maintained for a time of up to 20 minutes equal to a value selected within the range of from 300 to 370°C, then is increased over a time comprised within the range of from 20 to 40 minutes, until a temperature value is reached, which is comprised within the range of from 420 to 450°C, at which value it is kept constant for a time of up to 20 minutes.

Description: This invention relates to a single-step coal liquefaction process. Coal-liquefaction processes are known, wherein carbon monoxide, water and a catalyst are used to produce, in situ , hydrogen to be used for liquefying coal: such procedures, however, produce hydrocarbon mixtures consisting of asphaltene precursors (PA), asphaltenes (A) and oils in different ratios to each other according to the individually adopted procedures. US-A-3796650 (URBAN) de-ashes and liquefies coal by contacting comminuted coal with water, at least a portion of which is in the liquid phase, a reducing gas and a compound selected from ammonia and carbonates and hydroxides of alkali metals, at liquefaction conditions including a temperature of 220°C to 370°C to provide a hydrocarbonaceous product. EP-A-311164, filed by the same Applicants hereof concurrently with the present application, liquefies coal by a single-step process using a conversion catalyst consisting of a hydroxide or a carbonate of an alkali metal, in the additional presence of a hydrogenation catalyst selected from the transition metals and their compounds at a temperature of from 330°C to 450°C for a time of from 30 min to 80 min. Applicants have now surprisingly ascertained that, by carrying out the liquefaction at determined temperature gradients, the process can be better controlled while concurrently improving the quality of the products in terms of distribution of PA, A, and oils and also the H/C ratio in the reaction products: the latter can be used as intermediates for producing liquid derivatives of coal. More particularly, the present invention provides a single-step coal liquefaction process comprising reacting an aqueous suspension of coal under an elevated pressure with carbon monoxide, in the presence of a conversion catalyst selected from the hydroxides and the carbonates of an alkali metal, characterized in that the temperature is initially maintained at from 300°C to 370°C for the first 20 minutes, whereafter the temperature is increased over a time of from 20 to 40 additional minutes until its value is comprised from 420°C to 450°C, the latter value being kept constant for up to 20 additional minutes. The coal liquefaction pressure depends on the amount of water in the aqueous suspension, which should preferably be in a weight ratio of from 2: 1 to 5: 1 relative to the coal, and on the partial pressure of CO, which should preferably be from 39,2264 bar (40 atm) to 78,4528 bar (80 atm). The overall pressure is preferably from 147,099 bar (150 atm) to 294,198 bar (300 atm). Water being at a temperature close to, or higher than, the critical point temperature (374,15°C), originates a density of the reaction medium of from 0,07 g/ml to 0,2 g/ml. Preferred catalysts for the conversion are the sodium and potassium hydroxides and carbonates. The invention is better shown by the following Example 1, which has a merely illustrative value and can be compared with the comparative Example 2, which is illustrative of the prior art. EXAMPLE 1 The test was carried out on an Illinois Nr. 6 coal, the elemental analysis of which is reported in Table 1. One gram of coal was 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 39,2264 bar (40 atm) of carbon monoxide, it was then heated to the temperature of 350°C, and was maintained at this temperature for 15 minutes; the reaction temperature was subsequently increased by 90°C over a 30-minute time, and was maintained equal to 440°C for a further 15 minutes. When the reaction was ended, the reactor was discharged and, after removing 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, 40% by weight 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 1.04. Example 2 (Comparative Example) Still on 1 g of Illinois Nr. 6 coal, a test analogous to the preceding one was carried out, with the difference that the reaction was carried out by heating the reaction mixture at 400°C for 60 minutes. Under the same reaction conditions, excluding temperature, at the end of the process more than 0.9 g was recovered of a mixture of mostly non-distillable, but THF-soluble hydrocarbons (H/C = 1.00), 26% of which were soluble in paraffinic solvents (oils). ― Therefore, carrying out the reaction at determined increasing temperature values made it possible a mixture of hydrocarbons to be obtained, wherein the hydrocarbons soluble in paraffinic oils (oils) had increased from 26% to 40%.

Claims: 1. A single-step coal liquefaction process comprising reacting an aqueous suspension of coal under an elevated pressure with carbon monoxide, in the presence of a conversion catalyst selected from the hydroxides and the carbonates of an alkali metal, characterized in that the temperature is initially maintained at from 300°C to 370°C for the first 20 minutes, whereafter the temperature is increased over a time of from 20 to 40 additional minutes until its value is comprised from 420°C to 450°C, the latter value being kept constant for up to 20 additional minutes. 2. Process according to Claim 1, wherein the reaction is carried out under an overall pressure of from 147,099 bar (150 atm) to 294,198 bar (300 atm). 3. Process according to Claim 2, wherein the temperature is initially maintained at from 300°C to 370°C for the 5 to 20 initial minutes, whereafter the temperature is raised to from 420°C to 450°C for the from 5 to 20 additional minutes. 4. Process according to Claims 1, 2 or 3, wherein the partial pressure of the carbon monoxide charge is from 39,2264 bar (40 atm) to 78,4528 bar (80 atm).

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