GB2138839A

GB2138839A - Refining of coal

Info

Publication number: GB2138839A
Application number: GB08403482A
Authority: GB
Inventors: Cornelis Kleynjan; Quintin John Beukes
Original assignee: Sasol Operations Pty Ltd
Current assignee: Sasol Operations Pty Ltd
Priority date: 1983-02-28
Filing date: 1984-02-09
Publication date: 1984-10-31
Also published as: AU2482584A; JPH0579717B2; AU558838B2; CA1231906A; GB2138839B; JPS59166587A; DE3406845A1; GB8403482D0; DE3406845C2

Abstract

A method of refining coal includes a two-step process. The process includes contacting coal with a solvent in a first step, thereby to refine the coal partially in a first reaction. Thereafter some of the solvent is removed, and, in a second step, the partially refined coal from the first step is allowed to remain in contact with the residual solvent for further refining of the coal in a second reaction. After the second reaction, at least some of the residual solvent is removed, thereby to produce solvent refined coal from which coke may be produced.

Description

SPECIFICATION Refining of coal THIS INVENTION relates to the refining of coal. It relates in particular to a method of refining coal, and to solvent refined coal (hereinafter also referred to as 'SRC').

According to the invention, there is provided a method of refining coal, which includes, in a two-step process, contacting coal with a solvent in a first step, thereby to refine the coal partially in a first reaction; removing some of the solvent; and allowing, in a second step, the partially refined coal from the first step to remain in contact with the residual solvent, for further refining of the coal in a second reaction.

The method may include, after said second reaction, removing at least some of the residual solvent, thereby to produce solvent refined coal.

The solvent may be an oil. The oil may be a coal derived oil-fraction, having a boiling range from about 80"C to about 450"C, for example about 200"C to about 450"C.

The oil-to-coal ratio in the first step may be from about 1:1 to about 5:1 (on a mass basis), preferably about 2:1, so that the oil and coal are in the form of an oil/coal slurry in the first step.

The method may include adding a catalyst to the slurry. The ratio of catalyst to coal in the slurry in the first step, may be about 1:50 (on a mass basis). The catalyst may be a metal-based catalyst.

The contacting in the first step may be effected at a temperature of about 350"C to about 480"C, for example about 400"C to 450"C, and at a pressure of about 5 x 103 kPa to about 30 x 103 kPa, for example about 20 x 103 kPa. The reaction may be effected in a hydrogen-rich atmosphere. The reaction time of the first reaction may be less than 20 minutes, for example about 10 minutes or less.

The removal of the oil may be effected by means of distillation. The volume of oil distilled off may be such that the oil and coal residue are still in the form of a slurry in the second step, and the concentration of the catalyst in the slurry in the second step is at least twice the concentration of the catalyst in the slurry in the first step.

The contacting in the second step may also be effected at a temperature of about 350"C to about 480"C, for example about 400"C to 450"C, and at a pressure of about 5 x 103 kPa to about 30 x 103 kPa, for example about 20 X 103 kPa. The reaction time of the second reaction may be between about 1 5 minutes and about 1 50 minutes.

The invention extends also to solvent refined coal when produced according to the method hereinbefore described.

The invention will now be described by way of the following non-limiting Examples: EXAMPLE 1 1.1 A bituminous coal, containing 36% (by mass) volatiles and 10% (by mass) ash, was powdered and slurried with 2 part (by mass) of a coal-derived oil fraction (solvent) having a boiling range of from about 200"C to about 420"C. 1 500 gms of this slurry was reacted ina 5 litre autoclave with 2% (by mass) Fe2O3 on coal as an added catalyst. In a first step, the coal was contacted with the solvent in a hydrogen-rich atmosphere for 10 minutes at a pressure of about 20 X 103 kPa and a temperature of 425"C, to refine the coal partially.

Thereafter, sufficient solvent was distilled off until a slurry having a catalyst concentration which was about three times higher than the catalyst concentration in slurry of the first step, remained in the autoclave. The now partially refined coal (i.e. the coal residue) was allowed to remain in contact with the residual solvent for a further 1 20 minutes in a second step at a temperature of 425"C and a pressure of about 20 x 103 kPa, for further refining. The autoclave was then cooled down and the contents worked up to recover the solvent refined coal (eg unreacted products removed and distillable oils recovered).

1.2 1500 gms of the slurry of 1.1 was again reacted in a 5 litre autoclave with 2% (by mass) Fe2O3 on coal as an added catalyst. The reaction conditions were the same as for the first step in 1.1. However, the reaction time in the first step was increased to 1 30 minutes, and no solvent was thereafter distilled off, ie the second step was not performed.

A comparison of the products obtained from 1.1 and 1.2 above (calculated as nett mass percentages on dry ash-free coal) is as follows: Experiment Experiment 1.1 1.2 CO + CO2 3,1 2,0 H20 8,0 7,2 C,-C3 8,2 11,7 C4-200 C 14,1 25,9 200-420"C 16,0 17,9 SRC (420"C plus) 42,2 67,9 Undussolved 2,3 3,2 The SRC obtained from both experiments was coked at 500"C (5 hours heating time and 4 hours coking time) and calcined for 30 minutes at 1 370"C.

The coefficient of thermal expansion was determined for the calcined coke by means of the X-ray diffraction method. The coefficient of thermal expansion (CTE) was 0,4 X 10-6 for the calcined coke obtained from Experiment 1.1, and 0,7 x 10-6 for the calcined coke obtained from Experiment 1.2.

From the above results, it can be seen that a superior quality coke is obtained from the two-step method of the present invention.

Furthermore, the two-step method is self-sufficient as regards solvent requirements. Experiment 1.2 gave coke of a poorer quality and there was a large deficiency in process solvent.

EXAMPLE 2 1 500 gms of the slurry of Example 1 was again reacted in a 5 litre autoclave with 2% (by mass) Fe203 on coal as an added catalyst.

In a first step, the coal was contacted with the solvent in a hydrogen-rich atmosphere for 10 minutes at a pressure of about 20 x 103 kPa and a temperature of 425"C. Thereafter, sufficient solvent was distilled off until a slurry having a catalyst concentration which was about 3 times higher than the catalyst concentration of the slurry of the first step, remained in the autoclave. The temperature of the autoclave was raised to 445"C, and the contacting continued for a further 60 minutes in a second step, at a pressure of about 20 X 103 kPa.

The following product spectrum was obtained (calculated as nett mass percentages on dry ash-free coal): CO+CO2 2,4 H20 8,5 C1-3 13,2 C4-200 C 20,9 200-420"C 14,4 SRC (420"C plus) 38,5 Undissolved 2,2 Calcined coke was produced from the SRC in the same way as in Example 1, and was again of high quality, having a CTE value of 0,4 X 10-6. This method yielded 35% liquid products in the diesel and petrol boiling range (C4-200 C and 200"C-420"C respectively.

self-sufficient as regards solvent requirements.

Experiment 1.2 gave coke of a poorer quality and there was a large deficiency in process solvent.

EXAMPLE 2 1 500 gms of the slurry of Example 1 was again reacted in a 5 litre autoclave with 2% (by mass) Fe2O3 on coal as an added catalyst.

The following product spectrum was obtained (calculated as nett mass percentages on dry ash-free coal): CO + CO2 2,4 H20 8,5 C,-3 13,2 C4-200 C 20,9 200-420"C 14,4 SRC (420"C plus) 38,5 Undissolved 2,2 Calcined coke was produced from the SRC in the same wasy as in Example 1, and was again of high quality, having a CTE value of 0,4X 10-6. This method yielded 35% liquid products in the diesel and petrol boiling range (C4-200 C and 200"C-420"C respectively.

EXAMPLE 3 1 500 gms of the slurry of Example 1 was again reacted in a 5 litre autoclave with 2% (by mass) Fe203 on coal as a catalyst, under the same reaction conditions as in Example 2, in first and second steps similar to those described hereinbefore with reference to Example 2. The only difference was that the reaction time of the second step was increased from 60 to 120 minutes, thereby to increase the production of liquid fuels.

The following product spectrum was obtained (calculated as nett mass percentages on dry ash-free coal): CO + CO2 2,7 H20 8,6 C,-3 13,5 C4-200 C 20,4 200-420 C 17,3 SRC (420"C plus) 35,8 Undissolved 2,4 The total yield of liquid products was 37,7% while the CTE value of calcined coke produced from the SRC, was 0,3 X 10-6.

EXAMPLE 4 Again, 1 500 gms of the slurry of Example 1 was used, and to this was added 2% (by mass) Foe205 on coal as an added catalyst.

Both the first and second steps were effected in a continuous flow reactor. For the first step, a 1 litre autoclave was used, while for the second step a vertical open tube reactor having a 25 mm diameter was used. The reaction time was 1 5 minutes in the autoclave and 1 20 minutes in the open tube reactor. The contact temperature and pressure for both steps was 425"C and 20 X 103 kPa respectively. The following product spectrum was obtained (calculated as nett mass percentages on dry ash-free coal): CO + CO2 2,8 H20 10,0 C,-3 8,4 C4-200 C 19,3 200-420"C 20,3 SRC (420"C plus) 37,8 Undissolved 1,4 Calcine coke with a CTE value of 0,4 x 10-6 was produced from the SRC as hereinbefore described.

The 200-420"C fraction recovered after the first and second steps can be recycled (ie used to form the slurry for the first step).

Excess oil can be used elsewhere, eg it can be up-graded to diesel oil.

The Applicant is aware of methods of depolymerizing coal which comprises solvation of coal with a solvent in a single step. During the solvation, the coal is depolymerised, but coal fragments have a strong tendency to combine with solvent molecules or fragments in side reactions, thus resulting in a shortage in recy cle solvent. To prevent or reduce the occurrence of these unwanted side reactions, a good catalyst system and high hydrogen pressure are normally used.

Prolonged reaction times, which are necessary to decrease the heteroatom content under these conditions, lead to high yields of liquid and gaseous products and subsequently low yields of solid SRC. If, on the other hand, the SRC production is maximised by using short reaction times, this product still contains too high a heteroatom content to make it suitable for the manufacture of high quality electrode coke.

During the depolymerization reaction, gases such as hydrogen sulphide, carbon dioxide, carbon monoxide, ammonia and water are evolved which indicates that the heteroatoms sulphur, nitrogen and oxygen are liberated from the coal molecules during depolymerization.

Without wishing to be bound by theory, the Applicant believes that heretoatoms in the molecular structure of a coking feed hinder the graphitisation thereof at higher temperatures, by increasing the viscosity and decreasing the plastic range of the mesophase (J Dubois, C Aqache and J L White-Metallography 3 (1970) 337-360). Hydrocracking is then needed to decrease the hetero atom content of the solvent refined coal as far as possible.

In US Patent 4 210 517 of the Mitsui Mining Compnay Limited and the Mitsui Coke Company Limited, the ratio of N+S+O C is correlated with the quality of the calcined coke and it was shown that the lowest values correspond with the better quality coke. This shows again that the hetero atom content of the basic 'pitch' must be low and the carbon content high.

In the methods known to the Applicant, either a low yield of good quality SRC or a high yield of poor quality SRC is obtained.

The Applicant believes that in the two-step method provided by this invention (in which said side reactions are minimized or reduced as a result of the removal of some of the solvent of the first step), the reaction conditions can be chosen so that (i) a high yield of high quality SRC (ie low hetero atom content), and self-sufficiency as regards solvent requirements, can be obtained, or (ii) a lower yield of high quality SRC with a high yield of liquid products, can be obtained. The SRC will be suitable for the manufacture of high quality electrode coke.

The Applicant further believes that large quantities of high quality SRC and self-sufficiency as regards solvent requirements can be obtained by means of the two-step method of the invention, without the use of the added metal-based catalyst (ie utilizing only the natural catalytic activity present in the coal). However, substantially equally large quantities of high quality SRC and a similar degree of selfsufficiency as regards solvent requirements can be obtained when a metal-based catalyst is used, in which case a higher reaction temperature and shorter reaction time can be utilized to obtain a similar product spectrum.

By using a metal-based catalyst and altering the reaction conditions in the first and second steps, the amount of liquid products obtained can be varied.

This process also has the advanage that a lower initial catalyst concentration can be used (as compared with known processes), resulting in lower overall catalyst usage than is possible with said known processes.

Claims

1. A method of refining coal, which includes, in a two- step process, contacting coal with a solvent in a first step, thereby to refine the coal partially in a first reaction; removing some of the solvent; and allowing, in a second step, the partially refined coal from the first step to remain in contact with the residual solvent, for further refining of the coal in a second reaction.

2. A method according to Claim 1 which includes, after said second reaction, removing at least some of the residual solvent, thereby to produce solvent refined coal.

3. A method according to Claim 2, wherein the solvent is an oil, and the coal is in pulverized form.

4. A method according to Claim 3, wherein the oil is a coal-derived oil fraction, having a boiling range from about 80"C to about 450"C.

5. A method according to Claim 3 or Claim 4, wherein the oil-to-coal ratio in the first step is from about 1:1 to about 5:1 (on a mass basis), so that the oil and coal are in the form of an oil/coal slurry in the first step.

6. A method according to Claim 5, which includes adding a catalyst to the slurry.

7. A method according to Claim 6, wherein the ratio of catalyst to coal in the slurry in the first step, is about 1:50 (on a mass basis).

8. A method according to Claim 6 or 7, wherein the catalyst is a metal-based catalyst.

9. A method according to any one of Claims 6 to 8 inclusive, wherein the contacting in the first step is effected at a temperature of about 350"C to about 480"C and at a pressure of about 5 X 103 kPa to about 30 X 103 kPa.

10. A method according to any one of Claims 6 to 9 inclusive, wherein the first reaction is effected in a hydrogen-rich atmosphere, and wherein the reaction time of the first reaction is less than 20 minutes.

11. A method according to any one of Claims 6 to 10 inclusive, wherein the removal of the oil is effected by means of distillation.

1 2. A method according to Claim 11, wherein the volume of oil distilled off is such that the oil and coal residue are still in the form of a slurry in the second step and the concentration of the catalyst in the slurry in the second step is at least twice the concentration of the catalyst in the slurry in the first step.

1 3. A method according to Claim 11 or Claim 12, wherein the contacting in the second step is effected at a temperature of about 350"C to about 480"C, and at a pressure of about 5 X 103 kPa to about 30 X 103 kPa.

14. A method according to Claim 13, wherein the reaction time of the second reaction is between about 15 minutes and about 150 minutes.

1 5. A new method of refining coal, substantially as described and exemplified herein.

1 6. Solvent refined coal when produced according to a method as claimed in any one of Claims 2 to 1 5 inclusive.