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(11) | EP 0 087 929 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Process for the hydrogenation of carbonaceous material |
| (57) In the hydrogenation of coal and substances derived therefrom, the catalyst is provided
by adding nickel carbonate to the reaction mixture. |
[0001] The present invention relates to the hydrogenation of coal and substances derived therefrom, and particularly to the hydrogenation of these materials in the presence of a catalyst.
[0002] Slurries of coal with oil can be hydrogenated at high temperatures and high hydrogen pressures to yield methane and light petroleum liquids and gases. It is known to hydrogenate coal slurries in the presence of a heterogeneous catalyst, e.g. Co-Mo supported on an alumina or silica base. The use of such supported catalysts increases the take-up of hydrogen and improves the yield and quality of the desirable "distillate" fraction, that is to say light oils and liquid fuel, but this is economically prohibitive. Also, the alumina or silica base tends to promote coke formation which blinds and deactivates the catalyst. Coke should also be avoided because it clogs the hydrogenation reaction and reduces the yield of the desirable distillate. Furthermore, the presence in the carbonaceous feedstock of impurities e.g. sulphur, titanium dioxide, vanadium, clays and silica, fouls the catalyst and renders it inactive.
[0003] A great deal of research has gone into developing supported catalysts that can reduce coking and resist being fouled by impurities, but the limited stability of these supported catalysts has made their use uneconomic.
[0004] Unsupported heterogeneous catalysts have been proposed for the hydrogenation of coal, but they suffer from one or more of the disadvantages that:
(1) they are not as effective as supported catalysts;
(2) they are unstable under hydrogenation conditions;
(3) they are difficult to separate from the solid residue obtained after hydrogenation in order to be recycled.
[0005] The present invention is based on the discovery that in the catalytic hydrogenation of coal the use of nickel carbonate to provide the catalyst reduces coke formation and improves the conversion of the coal to hydrogenated products, including the desired distillate fraction.
[0006] Accordingly the present invention consists in a process for the hydrogenation of coal and substances derived therefrom in the presence of a catalyst, in which the catalyst is provided by the addition of nickel carbonate to the reaction mixture.
[0007] The coal is preferably ground and hydrogenated in the form of slurry with a heavy oil (pasting oil) and the nickel carbonate is preferably added to the coal in the form of a slurry of nickel carbonate in oil, either before or during hydrogenation.
[0008] The temperature at which the hydrogenation is carried out depends on the products desired, more light-weight products being produced at higher temperatures. While the use of high temperatures tendsto cause increased coke formation, we have found that the amount of coke is reduced by the addition of nickel carbonate. Also the nickel carbonate addition increases the amount of the desired distillate that is obtained by hydrogenation.
[0009] The hydrogenation process of the present invention is preferably carried out at a temperature in the range of from 400 to 500°C since at temperatures above 500°C coke formation is excessive and at temperatures below 400°C insufficient hydrogenation is achieved. The hydrogen partial pressure used is preferably from 3,500 to 35,000 kN/m2. Higher pressures are impracticable and lower pressures result in insufficient hydrogenation.
[0010] After hydrogenation, a typical procedure is to cool the reaction mixture, vent the gases through a condenser and distil the hydrogenation products to recover the liquid products (the distillate). The distillation residue or bottoms, which contains the catalyst, can then be mixed with further coal and the hydrogenation stage repeated. Advantageously some of the distillation bottoms is bled off to avoid an excessive build-up of coke and viscous heavy oil. The material bled off will of course contain some catalyst, and it is preferably coked to recover further distillate and the coke residue then treated to recover the nickel content of the catalyst.
[0011] Advantageously the nickel is leached from the coke by contacting it, in the presence of oxygen, with an aqueous mineral acid solution, e.g. of sulphuric acid, having a pH not greater than 3. The leaching is preferably performed at a temperature of at least 70°C, and most preferably not less than 100°C, and under an oxygen partial pressure of not less than 20 kN/m2 and most preferably not less than 275 kN/m2. The pH is advantageously about O. The nickel may be recovered from the leach solution in any known way, e.g. by electrowinning. Alternatively the nickel may be recovered from the coke residue by smelting it to a matte, e.g. with pyrrhotite.
[0012] In any event, when only part of the distillation residue or bottoms is recycled, the remainder being bled off and treated to recover its nickel content, a corresponding amount of nickel carbonate should be added to the reaction mixture to maintain its catalyst content.
[0013] As will be appreciated from the above discussion, the process of the present invention may be performed either on a batch basis or continuously, although the latter is preferred.
[0014] The reactions that occur in the hydrogenation of coal and coal-derived material are complex. It may be that the nickel carbonate does not itself act as a catalyst but that it is converted under the conditions prevailing during hydrogenation into a different chemical species and it is that different species that acts as a catalyst. Whether or not that is the case, we have found that the addition of nickel carbonate to the hydrogenation reaction is beneficial.
[0015] . The exact chemical composition of the nickel carbonate is not critical, and for the purpose of this specification and claims the term nickel carbonate includes basic nickel carbonate, which is the form in which it is most cheaply and readily available.
[0016] The catalytic hydrogenation of coal according to the invention will now be described in more detail, by way of example only, in the following Example, in which the results obtained with the use of nickel carbonate are compared with those of two other tests, in one of which no catalyst was used and in the other cobalt carbonate was added to the reaction mixture.
Example
[0017] In each of three tests, 100 g of Cape Breton high-volatile bituminous coal was charged to a low pressure autoclave with 300 g of Domtar aromatic oil, which is a coke oven tar having a boiling point of 260-330°C, which served as pasting oil. In Test No. I no catalyst addition was made, and in Tests 2 and 3 0.92 g of NiC03 and CoCO3 respectively was added. The compositions of the coal and oil were as follows, in percent by weight:
[0019] The slurry was pressurised and transferred to a high pressure autoclave. A mixture of 2 volumes hydrogen and one volume carbon monoxide was introduced to give a H2 partial pressure at room temperature of 13,800 kN/m2, and the mixture was heated to 450°C. When this temperature was attained, the hydrogen partial pressure was increased to 18,000 kN/m2 and held there for 1 hour. The-autoclave contents were then cooled to 250°C and most of the gas vented through a cold trap and assayed. The slurry was recycled to the low pressure autoclave where 100 g of coal was again added and the above steps repeated. After the 3rd cycle 150-200 g of slurry were bled from the system and after the 5th cycle all the slurry was discharged. This was accomplished by collecting the hot slurry (250°C) in a let-down vessel while venting vapours through a cold trap. The hot slurries were mixed with several volumes of benzene to form a low viscosity slurry which was then filtered through a steam jacketed Buchner filter. The solids collected were then washed, dried and assayed for ash and organic content. The benzene in the filtrate was then flashed off at reduced pressure and the oil produced assayed for C, H, N, 0, S and asphaltene. From the data collected a net product yield was calculated. The results are set out in the Table below.
[0020] The asphaltene content of the coal liquid increased progressively through the five cycles, the final value being substantially the steady state value for the catalysed tests In the absence of catalyst (Test No. 1) the asphaltene would continue to increase until the slurry could not be handled.
1. A process in which coal or a substance derived therefrom is hydrogenated in the
presence of a catalyst, characterised in that the catalyst is provided by the addition
of nickel carbonate to the reaction mixture.
2. A process according to claim 1, characterised in that the hydrogenation is carried
out at a temperature of from 400 to 450°C under a hydrogen partial pressure of from
3,500 to 35,000 kN/m2.
3. A process as claimed in claim 1 or claim 2, characterised in that the hydrogenation
products are distilled and the catalyst-containing distillation residue is mixed with
further carbonaceous material and subjected to a further hydrogenation step.
4. A continuous process according to claim 3, characterised in that only part of the
catalyst-containing distillation residue is recycled, the remainder being bled off
and treated to recover its nickel content, and a corresponding amount of nickel carbonate
is added to the hydrogenation reaction mixture to maintain its catalyst content.