Background to the Invention During gasification of coal various hydrocarbon streams are produced which are processed further to obtain a range of chemical products. One such hydrocarbon stream is a so-called crude tar feed stream that is further refined to produce tar.

Said crude tar feed stream contains solid particles that are typically fine coal particles and/or ash and which must be separated from the tar feed prior to refining.

The inventor is aware of decanting and filtration methods used in the industry to separate the unwanted solid particulate matter from the crude tar feed prior to refining.

These methods are very costly and filtration especially is difficult to carry out since the fluid flow properties of the crude tar feed may vary greatly often resulting in the formation of a water-tar emulsion as well as the viscosity and density of the crude tar feed varying around that of water, making process control difficult.

The inventor therefore believes, that a need exists for a cost-effective method of separating a substantial amount of solid particulate matter from a crude tar feed as described above.

In the specification that follows the term"crude tar feed"is to be interpreted as meaning a hydrocarbon feed stream produced during coal gasification and which is to be refined further to produce tar.

Summary of the Invention According to the invention there is provided a method of reducing solid particulate matter content of a crude tar feed, which crude tar feed includes a hydrocarbon fluid fraction, a water fraction, and a solid particulate matter fraction which is at least partially coated with the hydrocarbon fluid fraction, the method including at least the steps of :- introducing a solvent into the crude tar feed; and removing from the solid particulate matter at least a portion of the hydrocarbon fluid fraction that coats the solid particulate matter while decreasing the density of the crude tar feed to well below the density of water and of the solid particulate matter in the crude tar feed.

A typical crude tar feed when analysed according to ASTM D1160 has the following boiling point analysis as shown in table 1.

Table 1: Dl 160 Tar Analysis Volume % oc IBP 183. 5 5 214. 1 10 242. 7 15 275. 3 20 303. 9 25 325. 8 30 341. 7 35 354. 8 40 368. 7 45 383. 4 50 399. 9 55 414. 4 60 428. 1 65 430. 0 70 372. 3 75 485. 1 80- 85 90 - 95 (FBP) - Recovered (volume %) 79. 4 No measurements were taken above 500°C.

The method may further include the step of allowing the resulting mixture to settle into a water phase and a hydrocarbon phase or tar phase for a predetermined period of time and to allow at least a fraction of the solid particulate matter to migrate from the hydrocarbon phase into the water phase.

The migration mechanism for the solid particulate matter from the hydrocarbon phase into the water phase may be gravity settling.

The method may include the use of a wetting agent as a settling aid for settling fine particles from out of the hydrocarbon phase into the water phase.

The method may include the use of a de-emulsifying agent as a settling aid for settling fine particles from out of the hydrocarbon phase into the water phase.

The method may further include the step of separating the water phase and the solvent from the hydrocarbon phase by any suitable separation process.

The water and solvent phase may be separated from the hydrocarbon phase by centrifugation or distillation.

The hydrocarbon fluid fraction that coats the solid particulate matter in the crude tar feed may be a tar fraction including asphaltenes.

The solvent may be any solvent capable of washing off matter that coats the solid particulate matter so as to free the solid particulate matter for migration from the hydrocarbon phase into the water phase.

The solvent may be a solvent rich in benzene but may alternatively be a solvent rich in toluene, xylene, paraffins, pyridine, quinoline or the like.

A benzene rich solvent may typically include about 40 mass percent benzene and alkyl benzenes, about 27 mass percent xylenes and toluene, about 17 mass percent alkenes and dienes, about 10 mass percent alkanes and about 3 mass percent alcohols and carbonyls, the remainder of the solvent being made up by miscellaneous compounds.

The solvent may have about 39 mass% benzene, about 21.5 mass% toluene, and about 4 mass% xylene.

The solvent may have an analysis approaching that appearing in table 2 below.

Table 2: Solvent Analysis Components Mass % 1, 2 Propadiene 0. 0303 C3-Hydrocarbons 0. 0041 Methanol 0. 1415 1-Butene + Iso-Butene + 1,3-Butadiene 0.6427 Butane 0. 3558 t-2-Butane 0. 2484 c-2-Butene 0. 2416 Ethanol 0. 0011 1,2-Butadiene 0.0025 Acetonitrile + 3-Methyl-1-Butene 0. 1527 Acetone 0. 6080 Iso-Pentane 0. 2875 1,2-Butadiene 0.0045 1-Pentene 0. 5563 Ethanethiol 0. 0000 2-Methyl-1-Butene 0. 2591 Pentane 1. 0591 Isoprene 0. 1987 t-2-Pentene 0. 4954 c-2-Pentene 0. 2807 2-Methyl-2-Butene 0. 5917 t-1, 3-Pentadiene 0. 2767 1,3-Cyclopenladiene + c-1.3-Pentadiene 0.5694 Propanenitrile 0. 0766 2-Propanethiol 0. 0000 Cyclopentene 0. 6667 4-Methyl-1-Pentene 0. 0708 3-Methyl-1-Pentene 0. 0354 Cyclopentane 0. 4747 1.1,2-Trimethyl-Cyclopropane 0.0000 2,3-Dimethyl-1-Butene 0.0000 2-Methyl-Pentane 0. 4447 MEK 0. 7107 3-Methyl +Pentane 0. 1489 1-Hexene + 2-Methyl-l-Pentene 1, 3731 2-Methyl-Furan 0. 0232 1,4-Hexadiene + Propanethiol 0. 0310 Unidentified hydrocarbons eluting before hexane 0. 0016 Hexane +2-Ethyl-1-Butene 1. 8169 t-3-Hexene 0. 1309 c-3-Hexene 0. 0404 t-2-Hexene 0. 3540 2-Methyl-2-Pentene 0. 2083 3-Methyl-Cyclopentene + c-3-Methyl-2-Pentene 0. 3083 4-Methyl-Cyclopentene 0. 1100 c-2-Hexene 0. 1881 2,3-Dimethyl-1,3-Butadiene 0.0297 t-3-Methyl-2-Pentene +2, 4-Hexadiene 0. 1886 1,3-Hexadiene 0.0132 2,2-Dimethyl-Pentane 0.0015 Methyl-Cyclopentane 0. 7909 2.3-Dimethyl-2-Butene 0. 0621 2-Methyl-1, 3-Pentadiene 0. 0626 5-methyl-1,3-Pentadiene 0.1640 4-Methyl-1,3-Pentadiene 0. 0532 1-Methyl-1,3-Pentadiene 0.1277 3-Methyl-1,3-Pentadiene 0.0826 1-Methyl-Cyclopentene + Benzene 39. 1160 Thiophene 0. 2175 3,4-Dimethyl-2-Pentene 0.0060 5-Methyl-1-Hexene 0. 0323 Cyclohexane 0. 2221 C6-Diene 0. 0000 1,3-Cyclohexadiene 0.2261 4-Methyl-l-Hexene 0. 0774 2-Pentanone 0. 2739 2-Methyl-Hexane 0. 1586 2,3-Dimethyl-Pentane 0.1100 1,1-Dimethyl-Cyclopentane 0.0162 C6-Diene 0. 0209 Cyclohexene 0. 2119 3-Methyl-Hexane 0. 2019 3-Heptene 0. 0160 1-t-3-Dimethyl-Cyclopentane 0. 1028 1-c-3-Dimethyl-Cyclopentane 0. 0872 1,2-Dimethyl-Cyclopentane 0.0876 2-Methyl-1-Hexene 0. 0282 1-Heptene 0. 9523 3-Methyl-t-3-Hexene 0. 0269 2,4-Dimethyl-1,3-Pentadiene 0.0063 1-3-Heptene + Dimethyl-Cyclopentene 0. 3019 Unidentified hydrocarbons eluting between hexane and heptane 0. 0358 Heptane 1. 9769 2-Methyl-2-Hexene 0. 0084 3-Methyl-c-3-Hexene 0. 0146 t-2-Heptene 0. 2454 C7-Diene 0. 0097 Dimethyl-Cyclopentene 0. 1814 c-2-Heptene0. 1913 3-Ethyl-Cyclopentene 0. 0674 Methyl-Cyclohexane + 1-ethyl-cyclopentene 0. 4411 Pyridine 0. 0184 C7-Nephthene 0. 0000 2-Hexanone 0. 0107 C8-Cyclic-Olefin (131°C) 0.0149 Ethyl-Cyclopentene 0. 2501 C7-Dienes 0. 3983 Trimethyl-Cyclopentane 0. 0363 C7-Diene 0. 0527 Methyl-Cyclohexene 0. 3507 Toluene 21. 5059 2-Methyl-Thiophene 0. 0333 3-Methyl-Thiophene 0. 1847 1-Methyl-Cyclohexene 0. 1461 C7-Diene 0. 0758 2-Methyl-Heptane 0. 2158 4-Methyl-Heptane 0. 0925 3-Methyl-Heptane 0. 1488 2-Methyl-1-Heptene 0. 0545 1-Ethyl-3-Methyl-Cyclopentane 0. 0398 1-Octene 0. 6739 Unidentified hydrocarbons eluting between heptane and octane 0. 4223 3-Octene 0. 1002 Octane 1. 1548 t-2-Octene 0. 1329 c-2-Octene 0. 0659 Prophyl-Cyclopentane 0. 1801 Ethyl-Benzene 1. 0267 M+P-Xylene 4. 0595 Styrene 0. 2210 O-Xylene 0. 9339 1-Nonene 0. 2220 Unidentified hydrocarbons eluting between octane and nonane 1. 2996 Nonan 0. 4562 Prophyl-Benzene 0. 0738 Ethyl-Methyl-Benzene 0. 3548 1,3,5-Trimethyl-Benzene 0.1148 1-ethyl-2-Methyl-Benzene 0. 0509 Benzofuran 0. 0421 1,2,4-Trimethyl-Benzene 0.1711 1-Decene 0.0701 Unidentified hydrocarbons eluting between nonane and decane 0.6376 Decane 0. 1280 1,2,3-Trimethyl-Benzene 0.0405 Indane 0. 4655 Indene 0. 1124 O-Cresol 0. 0161 1-Undecene 0. 2329 Unidentified hydrocarbons eluting between decane and undecane 0. 4182 Undecane 0. 2666 Naphthalene 0. 0878 Unidentified hydrocarbons eluting after undecane 0. 6708 Total 100. 000

The solvent may be Rectisol Naphtha solvent available from Sasol in South Africa.

The mass ratio of crude tar feed to solvent on addition of the solvent may be between 1: 5 and 3: 2 and is typically about 2: 5, or even 1: 1.

The method may include adding water to the crude tar feed before, during or after the addition of the solvent, but typically after addition of the solvent.

The amount of water added is a function of the amount of solid particulate matter particles contained in the crude tar feed and is typically 0,4 volume percent or more of the crude tar feed.

The crude tar feed, solvent and water may be fed to a settling tank to allow separation of the hydrocarbon phase and water phase from the mixture.

The solvent and crude tar feed may be mixed prior to the addition of water to allow the solvent to access the matter coating the solid particulate matter particles in the crude tar feed.

The feed line to the settling tank may include a valve, mixing orifice or any other suitable mixing device to achieve high shear mixing in a fluid flowing into the settling tank. The fluid flowing into the settling tank may be a crude tar feed or a crude tar feed-water mixture and is typically a crude tar feed-water-solvent mixture.

The temperature and pressure in the settling tank may be such that the solvent remains a liquid, i. e. below the boiling point of the solvent.

The pressure in the settling tank may be between atmospheric and 14 bar and is typically about 1-3 bar.

The temperature in the settling tank may be between ambient and 150°C and is typically about 30-40°C.

The settling tank may be a conventional desalination tank known in the art or may be any other suitable settling tank. Typically, however, the settling tank is a conical bottom type tank.

The crude tar feed, water and solvent mixture may be allowed to separate in the settling tank for between 15 and 120 minutes, preferably between 30 and 90 minutes and typically for about 45 minutes.

Migration of the solid particulate matter from the hydrocarbon phase to the water phase may be improved by ionisation of the solid particulate matter.

Methods such as electrostatic precipitation may be used to improve settling of the solid particulate matter into the water phase.

After a sufficient degree of separation has been achieved, the water phase that now contains the solid particulate matter that has migrated out of the hydrocarbon phase may be pumped out of the settling tank.

The remaining hydrocarbon phase may then be subjected to trim filtration to obtain the desired solid particulate matter content which is typically about 0,02 percent by mass when measured by the ashing method or loss on ignition method.

Thereafter the hydrocarbon phase may be fed to an evaporator for distillation where the solvent is distilled from the tar fraction after which the solvent may be recycled.

A method analogous to the method as described above may be used in other applications where solid particulate matter needs to be separated from a viscous liquid coating said matter, for example, the method may be used to separating catalyst particles from a fluid catalytic cracking slurry or for separating solid particulate matter from an oily mixture.

Detailed Description of the Invention The invention will now be described by way of the following non-limiting examples with reference to the accompanying drawing.

In the drawings:- Figures 1, and 4 show schematic flow diagrams of a method of separating particulate matter from a crude tar feed that includes water and particulate matter in accordance with the present invention; and

Figures 2 and 3 show graphical representations of Tables 3 and 4 below.

In the Figures 1 and 4, reference numeral 10 generally indicates a process wherein a method of separating particulate matter from a crude tar feed which includes water and particulate matter in accordance with the present invention is utilised.

The method of separating particulate matter (not shown) from a crude tar feed 12 which includes water and particulate matter includes adding a solvent stream 14 to the crude tar feed 12 for removing matter that coats the solid particulate matter particles with a fluid constituent of the crude tar feed 12 by dissolving at least a portion of it and for decreasing the density of the crude tar feed 12 to well below the density of water and of the solid particulate matter in the crude tar feed 12.

The crude tar feed 12 typically contains about 10 percent by mass water. The size distribution of particulate matter in the crude tar feed 12 is typically such that 50 percent thereof is larger than 50 micron and 10 percent thereof is less than 10 micron.

The matter that coats the particles or particulate matter in the crude tar feed 12 is typically a tar fraction including asphaltenes.

The solvent may be any solvent capable of washing off matter which coats the solid particulate matter so as to free the solid particulate matter for migration from the hydrocarbon phase into the water phase.

The solvent 14 is a solvent rich in benzene and typically includes about 40 mass percent benzene and alkyl benzenes, about 27 mass percent xylenes and toluene, about 17 mass percent alkenes and dienes, about 10 mass percent alkanes and about 3 mass percent alcohols and carbonyls, the remainder of the solvent being made up by miscellaneous compounds.

The mass ratio of crude tar feed 12 to solvent 14 on addition of the solvent 14 is typically about 1: 1. The solvent 14 and crude tar feed 12 are allowed to mix thoroughly to allow the solvent 14 to access the matter coating the solid particulate matter particles in the crude tar feed 12.

A water stream 16 is also added to the crude tar feed 12. The amount of water 16 added is typically a function of the amount of solid particulate particles in the crude tar feed.

A wetting agent or demulsifier (chemical) is added to the water stream 16 to assist the solid particulate settling in the settling tank.

An additional water stream 22 is provided to provide additional water if necessary.

In Figure 1, the crude tar feed, solvent and water mixture 18 is fed to a settling tank 20 to allow separation of a hydrocarbon phase 24 and a water phase 26 from the mixture 18.

The feed line to the settling tank 20 includes a mixing device 28 to create high shear mixing in the mixture 18.

The mixture 18 is allowed to settle for about 45 minutes to allow the solid particulate matter to migrate from the hydrocarbon phase 24 into the water phase 26.

The settling tank 20 is a conventional desalination tank known in the art or conical bottom type for ease of solids removal..

The temperature and pressure in the settling tank 20 is such that the solvent 14 remains a liquid, i. e. below the boiling point of the solvent 14.

The pressure in the settling tank 20 is typically about 1-3 bar and the temperature in the settling tank 20 is typically about 30-40°C.

After a sufficient degree of separation has been achieved, the water phase 26 that now contains the solid particulate matter that has migrated out of the hydrocarbon phase 24 is pumped out of the settling tank 20. Stream 26 is then subjected to filtration to remove the solids from the water. Residue water is returned to the process.

As an alternative to Figure 1, (see Figure 4) instead of the crude tar feed, solvent and water mixture 18 is fed to a settling tank 20 to allow separation of a hydrocarbon phase 24 and a water phase 26 from the mixture 18, the mixture is fed to a centrifuge 50 which serves both as a contactor for the components of mixture 18 as well as to separate the solids from the water phase (26 in Figure 1) into which the particles have migrated and the hydrocarbon phase 24 is treated similarly to that in Figure 1 as is described below.

In Figures 1 and 4, the hydrocarbon phase 24 is fed to an evaporator 30 for distillation where the solvent 14 is distilled from the tar fraction 34 after which the solvent 14 is recycled.

The hydrocarbon phase 24 is subjected to trim filtration in filtration unit 32 prior to distillation.

The tar fraction 34 thus obtained typically contains about 0,02 mass percent solid particulate matter.

After distillation the tar fraction 34 is fed to a filtration unit (not shown).

Experiments to ascertain the optimum crude tar feed solvent mass ratio, the optimum settling time in the settling tank and the optimum crude tar to additional water mass ratio were conducted-see Examples 1 to 3.

An explanation of the experiments conducted as well as their results are set out below.

The solvent used during all examples typically had the following composition in mass percent: 40 Benzene & Alkyl Benzenes 27 Xylenes & Toluene 17 Alkenes & Dienes 10 Alkanes 3 Alcohols & Carbonyls 3 Miscellaneous EXAMPLE 1 Determination of the optimum crude tar feed to solvent ratio A sample of crude tar feed was obtained from a tar feed tank and was homogenized by stirring continuously before use. The ash content of crude tar sampled was 2,115 mass percent.

The following mixtures of crude tar feed tar and solvent were prepared at room temperature (27 °C) using a 100-cm3 volumetric flask: a. 20 g of tar plus 80 g of solvent; b. 40 g of tar plus 60 g of solvent;

c. 50 g of tar plus 50 g of solvent; d. 60 g of tar plus 40 g of solvent; e. 80 g of tar plus 20 g of solvent; and f. crude tar only Mixtures a to f were shaken for 2 minutes and allowed afterwards to stand for 1 hour, thus allowing the solids to settle to the bottom of the flask.

An amount of sample was carefully decanted from each flask into respective crucibles, making sure that the solids at the bottom of the flask remained intact. Thereafter the sample in each respective crucible was ignited and allowed to burn in order to remove the carbonaceous material.

The residual material obtained in each crucible from was ashed at 600 °C.

The final ash obtained in was expressed as a percentage of the net tar fraction present in each of the tar-solvent mixtures. Results of ash content vs. tar-solvent ratio are tabulated in table 3, and Figure 2 graphically shows this relationship.

Table 3: Tar-Solvent mass ratio v solids content of tar fraction Tar-Solvent Ratio Solids Content of Tar Fraction (measured as ash content 80: 20 0, 184 60: 40 0, 097 50: 50 0, 059 40: 60 0, 057 20: 80 0, 052 EXAMPLE 2 Determination of the optimum settling time in the settling tank using a tar-solvent mixture containing 60 mass percent solvent and 40 mass percent crude tar feed

A sample of crude tar feed was obtained form a tar feed tank and was homogenized by stirring continuously before use.

The following mixtures of tar and solvent were prepared at room temperature (27 °C), using a 100-cm3 volumetric flask: a. 4 separate flasks, labelled as 1M, 2M, 3M and 4M, each containing 40 g of tar plus 60 g of solvent; and b. 4 separate flasks, labelled only as 1,2,3 and 4, each containing crude tar only.

The respective mixtures were shaken for 2 minutes and allowed afterwards to stand, thus allowing the solids to settle to the bottom of the respective flasks.

After 15 minutes, an amount of sample was carefully decanted from the respective flasks, labelled as MI and 1, into respective crucibles correspondingly labelled as MI and 1, making sure that the gross amount of solids at the bottom of each flask remained intact.

This procedure was repeated after 30,45 and 60 minutes for the respective mixtures labelled as M2 and 2, M3 and 3, M4 and 4.

The sample in each respective crucible was ignited and allowed to burn in order to remove the carbonaceous material.

The residual material obtained in each crucible was ashed at 600 °C.

The final ash obtained was expressed as a percentage of the net tar fraction present in each of the tar-solvent mixtures. Results of ash content vs. settling time are tabulated in Table 4 and Figure 3 graphically shows this relationship.

Table 4: Settling time v solids content of a 40/60 (m/m ! tar-solvent mixture with neat crude tar feed as reference Settling Time (min) 15 30 45 60 Solids content of tar fraction not treated with solvent in mass percent (measured as ash 1,974 1,621 1,476 1,377 content) Solids content of tar fraction treated with solvent in mass percent (measured as ash 0,224 0,111 0,063 0,054 content)

EXAMPLE 3 Characterisation of the solid material present in the crude tar feed and the effect of the addition of water to the tar-solvent mixture A mixture of 60 g solvent and 40 g of crude tar was prepared in a glass bottle. The bottle was stoppered and the content was shaken-up for 2 minutes. An amount of tap water (50 cm3) was added to the contents in the bottle and allowed to separate for 30 minutes.

The solid material settled into the water phase, and the organic liquid phase was then carefully decanted.

The water phase with the solid material was filtered through a Whatman 41 filter paper.

The solid material was washed with benzene until the residual oil/tar attached to it has been removed, indicated by a clear benzene wash-solution.

The benzene-washed solid material was dried in an oven at 105 °C.

The dried solid material was then ashed at 900 °C and the remaining ash fused with LiBOz at 900 °C.

The flux was dissolved in hydrochloric acid (1: 1), diluted to a known volume and the metal content determined using ICP-AES.

The carbon, hydrogen, nitrogen and sulphur content of the benzene-washed solid material were determined, using the Carlo Erba Elemental Analyser.

Results obtained appear in Table 5 below.

Table 5: Typical Composition of the solid material settled out from the crude tar feed Solid material recovered form crude tar COMPONENT RESULT. mass % Al 3, 49 Si 4, 76 Ca 2, 27 Mg 0, 52 Fe 0, 51 K 0, 16 Na 0, 19 Other metals 0, 58 Loss on ignition @ 72, 77 900 °C Ash content 27,23 C 64, 58 H 2, 01 N 1, 47 S 0, 70 Ash of solid material COMPONENT RESULT, mass % Al aSA1203 24, 20 Si as Si02 37, 39 Ca as Ca0 11, 65 Mg as Mg0 3, 14 Fe as Fe203 2, 68 K as K20 0, 73 Na as Na2O 0, 96 Other balance Discussion of Results of Examples 1 to 3 For the purpose of this investigation any reference to solids content of the tar fraction implicates the ash content of the tar fraction as determined per the procedure described in Example 1.

The solids content (measured as ash content) of the crude tar feed as sampled was 2,115 mass percent. The solids remaining in suspension reduced to 1,974 mass percent for a settling time of 15 minutes and to 1,377 mass percent after a settling time of 60 minutes.

Table 3 and Figure 2 show that for a settling time of 1 hour, little variation in the solids content of the tar fractions (measured as ash content) is obtained for the tar-solvent mixtures, containing 50 mass percent or less tar.

Adequate separation of the solid material from the tar should be obtained for any tar-solvent mixture containing less than or equal to 50 mass percent tar.

A tar-solvent mixture containing 50 percent tar relates to a solids content of 0,059 mass %, a tar-solvent mixture containing 40 percent tar relates to a solids content of 0,057 mass % and a tar-solvent mixture containing 20 percent tar relates to a solids content of 0,052 mass% Table 4 and Figure 3 show that for a chosen optimum ratio of 40% tar and 60% solvent settling of the solid material is obtained within 15 minutes, after shaking the mixture for 2 minutes.

An amount of 0,224 mass% of solids (measured as ash content) was measured after a settling period of 15 minutes, which reduced further to 0,054 mass percent after 1 hour.

With the addition of water to the tar-solvent mixtures containing respectively 60% and 80% solvent, it was observed that the water phase clearly separates from the organic phase and that the solid material settles into the water phase.

The solid material removed from the tar and washed with benzene to remove traces of oil and tar still attached to it, analysed to be coal.

The results obtained showing carbon (65 mass %), hydrogen (2 mass%), nitrogen (1,5 mass %), sulphur (0,7 mass %), Al (3,5 mass%), Ca (2 mass %), Mg (0, 5 mass %) and Si (5 mass %) confirmed this observation.

On analysing the ash obtained after a loss on ignition at 900 °C was performed on the solid material, a typical coal-ash analysis was obtained: Al as A1203 = 24 mass% Si as Si02 = 37 mass% Ca as CaO = 12 mass% Mg as MgO = 3 mass% Fe as Fe203 = 3 mass%

Thus, the solvent used does act as a suitable dissolvent for the tar and it was found that a homogeneous mixture of crude tar and solvent is obtained where the solvent component of the mixture equals or exceeds 50 mass percent.

The viscosity and density of these mixtures allow for the settling of the denser solid material into the water phase.

From the various ratios of crude tar to solvent investigated, an optimum ratio of 60 mass % solvent to 40 mass% of crude tar is suggested. This will allow for an optimum tar-solvent mixture for further processing. See Table 3 and Figure 2 for detailed results.

An additional filtration of the tar-solvent mixture will reduce the ash content to within the desired limit of less than or equal to 0,02 mass%.

Evaluating the suggested optimum 40: 60 ratio of crude tar to solvent, partial settling of the solid material occurred within 15 minutes of the mixture being prepared.

Table 4 and Figure 3 show the relationship between the settling time and solids content of this tar-solvent mixture.

The addition of water to the organic phase consisting of the tar-solvent mixture, enhances the settling of the solid material from the organic phase into the water phase.

The solid material removed from the crude tar consists mainly of fine coal particles. On ashing this material at 900 °C, a typical coal ash composition is analysed as shown in Table 5.

Example 4 A procedure to remove solids, mainly coal ash, from tar was carried out.

The procedure comprised using a solvent, as per table 2 above, to solvate tar from the solids and to allow the settling of the solids into a water phase.

The addition of a wetting agent or some de-emulsifying agents was also investigated as to aid the settling of the very fine particles from the hydrocarbon mixture into the water phase.

Results obtained show that use of the wetting-or de-emulsifying agents dosed at a level of 50 µl / dm3 of hydrocarbon phase will aid the removal of solids from the tar fraction to a level of < 0.02 mass%, see Table 6.

Rectisol Naphta of table 2 was mixed with crude tar feed in a 1: 1 mass ratio.

Different wetting-and demulsifying agents were dosed at respective levels of 10-, 30 and 50 al per liter of the hydrocarbon phase.

The following agents were investigated: Dispersall a wetting agent <BR> <BR> <BR> <BR> EC2134ATM-a demulsifier<BR> <BR> <BR> <BR> <BR> <BR> EC2043A ademulsifier SAX816 a combination of a wetting & demulsifying agent (s) All the above wetting and de-emulsifying products were obtained from Nalco-Chemserve.

An amount of water (20% of the volume of the total hydrocarbon phase) was added to the hydrocarbon phase and allowed to mix by vigorous shaking of the total mixture.

The solids were then allowed to migrate by settling into the water phase using a retention time of 60 minutes.

The hydrocarbon phase was analysed for solids content by igniting a known portion of the hydrocarbon phase, thus allowing it to burn in order to remove excess of carbonaceous material. The residue obtained in this manner was further ashed at 600 °C for 2 hours. The amount of final residue obtained was measured and expressed as mass% solids to be present in the hydrocarbon phase.

As a result of initially preparing a 1: 1 (m/m) mixture of tar and Rectisol Naphta the result obtained had to be multiplied by 2 to obtain the actual solids content of the tar fraction alone (without the presence of Rectisol Naphta).

A blank run was included without addition of any wetting or demulsifier agent.

The results are shown in tables 6 and 7 below. Table 6: Solids Content Of Hydrocarbon Phase Treated With Different Wetting-And Demulsifying Agents Note : Value in brackets represents an average from duplicate results ASH CONTENT OF HYDROCARBON PHASE AFTER TREATMENT, mass% DOSAGE Blank DISPERSALL EC2134A EC2043A SAX 816 LEVEL [no agent] [wetting agent] Demulsifier Demulsifier Demulsifier & 1/dm3 Wetting Agent 0.1323 0.1287 --- --- --- --- 0 [0.1305] 0.1263 0.0231 0.0175 0.0198 0. 1112 0.0305 0.0230 0.0178 10--- [0.1188] [0.0268] [0.0202] [0.0188] 0.0233 0. 0211 0. 0170 0. 0184 0.0177 0. 0258 0.0153 0.0202 30 --- [0.0205] [0.0234] [0.0162] [0.0193] 0.0024 0. 0018 0. 0024 0.0047 0.0031 0.0021 0.0043 0.0078 50 --- [0.0027] [0.0020] [0.0031] [0.0062]

Table 7: Solids Content of Tar Fraction Alone After Treatment Calculated From Table 1 Note : Value in Table below is obtained by multiplying average valyue in Table 6 by 2 ASH CONTENT OF TAR FRACTION ALONE, AFTER TREATMENT, mass% DOSAGE Blank DISPERSALL EC2134A EC2043A SAX 816 LEVEL [no agent] [wetting agent] Demulsifier Demulsifier Demulsifier & 1/dm3 Wetting Agent 0 0. 2610--------- 10--0. 2376 0. 0536 0. 0404 0. 0376 30 --- 0.0410 0.0468 0.0324 0.0386 50---0. 0054 0. 0040 0. 0062 0. 0124

It is to be appreciated, that the invention is not limited to any specific embodiment or configuration as hereinbefore generally described or illustrated.