GB2080328A - Coal extract processing - Google Patents

Abstract

Coal extract or coal oil is hydrotreated by passage, together with hydrogen, through a tubular reactor immersed in a bed of fluidised particles, at a temperature of from 350 to 450 DEG C and under non- streamline flow conditions, the reactor containing a fixed bed of catalyst. The fluidised bed permits very accurate temperature control and improved hydrocracking and hydrofining is achieved.

Description

SPECIFICATION Coal Extract Processing This invention concerns the processing of coal extracts, and more especially concerns the hydrocracking of coal extracts.

Coal extracts are well known in the art of coal chemistry and are prepared by the digestion of coal particles in a solvent oil at high temperatures, approximately 300-4500C is suitable, under pressure and for times in the region of 30 mins to 2 hours. Thereafter, the residual undissolved carboniferous and mineral matter is removed, and this can be done in a variety of ways including centrifugation and filtration. An alternative method of preparing coal extracts involves the solution of coal substance in a supercritical fluid and separating the solution from the residual matter. Such "supercritical gas extraction" methods are described in the art.

It has previously been proposed to hydrogenate either catalytically or non-catalyticaily coal derived materials in order to increase the yield of liquid products for fuels or for chemical feedstocks.

One such prior proposal was the "Synthoil" process which operated for tome years as a pilot plant inl the USA. A mixture of a slurry of coal in recycled oil and hydrogen was passed through a tubular reactor packed with pellets of Co-Mo/SiO2-A1203 catalyst before the gas was separated and the liquid was passed through a solids separator to remove refractory coal substance and mineral matter. The tubular reactor was heated within a furnace and temperature control of the exothermic reaction was achieved to some extent by injection of quench oil. The reactor was operated under flow conditions to ensure turbulent flow as this was thought to prevent ash deposition on the catalyst surface.Experience has shown, however, a substantial rate of catalyst deactivation and contamination which, together with other problems, has led to the abandonment of the Synthoil process.

The present invention provides a method for the hydrotreatment of coal extract or coal oil having less than 0.1% of ash, comprising the passage of said extract or oil and hydrogen through a tubular reactor immersed in a bath of fluidised particles, at a temperature of from 350 to 4500C and under non-streamline flow conditions, said reactor containing a fixed bed of hydrotreatment catalyst.

The tubular reactor is suitably of minimum internal diameter to length ratio, as this increases the relative area of catalyst in contact with the walls of the reactor. If the reactor is operated wholly or partially in a trickle bed mode, it has been found the channeling of liquid close to the walls significantly distorts the flow pattern and therefore increasing the relative amount of catalyst to wall contact increases contact of catalyst with liquid. Preferably, however the reactor is operated in the flooded mode since this has been found to give better contact between catalyst and liquid. However, physical restraints on the arrangement of the reactor, for example the necessity to fold the reactor in order to retain it within a fluidised bed, may make it necessary to operate successive lengths of reactor in trickle bed and flooded modes. The reactor may be in any convenient form.

The use of a fluidised bed in which the reactor is immersed achieves significant advantages in that an extremely close control of temperature is achieved without the use of injection of quench oil or hydrogen into the reaction mix, which obviously distorts the reaction taking place; runaway reaction temperatures are a problem in such catalytic exothermic reactions. The particles forming the fluidised bed may be any particles stable at the reaction temperature and capable of acting as a heat carrier without excessive attrition losses. Corundum and alumina are convenient materials to form the bed.

The hydrotreatment catalyst is conveniently a commercially available hydrocracking catalyst, suitably of the Co/Mo or W/Ni on SiO2/AI203 type, although other catalysts may be used. It is sometimes preferred to use a guard catalyst such as alumina containing small amounts of cobalt and molybdenum, which is effective in removing metals, such as iron, which may deactivate the hydrotreatment catalyst.

Suitably, the reaction is carried out at a pressure of from 50 to 400 bar, preferably 1 50 to 250 bar. The Liquid Hourly Space Velocity (LHSV) has been found in experimental work to be conveniently of the order of 1, but this may, of course, vary in individual circumstances depending upon the feedstock and desired products, reactor dimensions, catalyst etc.

The invention will now be described by way of example only.

Example A reactor was constructed consisting of 8 stainless steel U-tubes, connected in series by pressure fittings which enable each tube to be removed for charging with and emptying of catalyst. The internal diameter of each tube was 8 mm and the total length of the U-tubes and connecting fittings which was immersed in a fluidized bed was 20 m. The first U-tube was packed with a guard catalyst of 0.5% Co, 2.0% Mo on a support of 6.3 mm (- in) spheres of y-alumina. Tubes 2 to 8 of the reactor were packed with a commercial alumina-supported cobalt molybdenum hydrocracking catalyst (Comox 451, availabe from Laporte) of 3.2 mm (8 in) pellets, after the pellets had been calcined for 2 hours at 5500C. The last 30 cm of Tube 8 was also packed with guard catalyst.The total volume of Comox 451 catalyst was 853 cc (531 g) and that of the guard catalyst 97 cc (129 g).

The tubular reactor was mounted in a vessel fitted with external electrical heaters and an air distribution base plate, which was charged with sufficient Alundum grains (120 mesh, Norton Abrasives Ltd) to cover the top of the reactor U-tubes.

The catalyst was pre-sulphided by passing a 3% solution of carbon disulphide in hydrogenated anthracene oil through the reactor for 24 hours.

A coal solution was prepared by extracting a medium volatile bituminous coal in a hydrogenated anthracene oil, subsequently filtered to give a nominally 20% coal in solvent solution, containing 0.04% ash. The coal solution was stored in a heated, stirred vessel and fed through a high pressure pump to the reactor. Simultaneously, hydrogen was compressed to the same pressure and the mixture of solution and hydrogen was passed through the reactor under varying conditions, and the products were collected and analysed.

Temperatures during the series of tests were from 376 to 443 OC; LHSV's were from 0.4 to 1.8.

Pressures ranged from 205 to 215 bar.

0.40 Kg/hr of coal solution was fed together with 0.38 Kg/hr of hydrogen at a pressure of 215 bar through the reactor which was maintained at an average temperature of 431 OC. Nominal LHSV was 0.5 hr-' and the Modified Reynolds Number for the hydrogen was 269, and for the mixture was 1 8, so that transitional flow was experianced through the reactor.

The results of analysis are set out below: Elemental analysis: Feedstock Light Products Heavy Products C% 90.4 88.7 89.9 H% 6.8 10.7 9.6 0% 1.7 0.3 < 0.2 N% 0.85 0.10 < 0.10 S ppm ND < 50 < 50 H/C atomic ratio 0.90 1.45 1.28 Ash 0.04 ND ND ND=Not Determined.

Boiling Ranges (%) Feeds to ck Total Liquid Product 1 BP-1700C - 7.3 170-2500C 2.4 10.4 250--3009C 7.8 23.6 300-3550C 36.4 33.5 355--420"C 25.6 18.0 +4200C 27.8 3.5 In general, it was found that high conversions of high boiling point material ( > 4200 C) to material boiling below this temperature was achieved, the conversion increasing from 62% to 89% as the temperature was increased from 4220 C to 4430C at an LHSV of 0.5. The yield of liquids boiling below 2500C was more than doubled by this increase in temperature.

It was also found that the method of the invention was capable of yielding a product slate in which one fraction was obtained in sufficient quantities to recycle as solvent for the extraction of coal at a LHSV of 1.0. Comparative tests with a conventional trickle bed hydrocracking reactor necessitated a LHSV of 0.25-0.5.

Very little deactivation of the catalyst was noted after 200 hours operation, although there was carbon and iron deposition noted upon the catalyst on inspection.

Based on the results obtained, design studies indicate that a 1 -tonne per hour feed of coal extract or oil can be hydrotreated in a reactor of 1 5.2 cm (6 in) internal diameter and 20 m length while maintaining non-streamline flow.

Claims (7)

Claims

1. A method for the hydrotreatment of coal extract or coal oil having iess than 0.1% of ash, comprising the passage of said extract or coal oil and hydrogen through a tubular reactor immersed in a bath of fluidized particles, at a temperature of from 350 to 4500C and under non-streamline flow conditions, said reactor containing a fixed bed of hydrotreatment catalyst.

2. A method according to claim 1, wherein the reactor is operated in the flooded mode or partflooded, part-trickle bed mode.

3. A method according to claim 1 or 2, wherein the catalyst is a Co/Mo or W/Ni hydrocracking catalyst.

4. A method according to any one of the preceding claims, wherein the pressure in the reactor is from 50 to 400 bar.

5. A method according to claim 4, wherein the pressure is from 1 50 to 250 bar.

6. A method according to any one of the preceding claims, wherein the Liquid Hourly Space Velocity is approximately 1.

7. A method according to claim 1, substantially as hereinbefore described.