AU2005260789A1 - Method of treatment of Fischer-Tropsch derived hydrocarbons - Google Patents

Description

WO 2006/005085 PCT/ZA2005/000101 TREATMENT OF HYDROCARBONS Field of the Invention 5 The invention relates to hydrothermal treatment of hydrocarbons prior to further processing. In particular, the invention provides for a pre-treatment regime for Fischer-Tropsch (F-T) hydrocarbons prior to downstream processing. The invention also relates to a chemical treatment of hydrocarbons prior to further processing. 10 Background to the Invention The inventors have identified an area for process optimization in the processing of hydrocarbons. In particular, the inventors have identified an 15 area for process optimization in the processing of F-T synthesis products by hydroconversion in general. F-T derived product streams contain oxygenates and to a certain extent metals and/or metal species. Ketones, aldehydes, alcohols, esters and 20 carboxylic acids are the main constituents of the oxygenate fraction. Carboxylic acids and alcohols are able to form under appropriate conditions carboxylate and/or alkoxide complexes and/or metalloxanes with the metals and/or metal species present. These metal carboxylates and/or alkoxides and/or metalloxanes may form deposits in processing equipment and catalyst 25 beds. Eventually the deposits in the catalyst beds may grow to such an extent that shutdowns of reactors are inevitable. The identified problem may be summarized as the plugging of downstream processing catalyst beds or bed by a constituent of said product streams or a 30 reaction product of a constituent of said product. streams. Summary of invention Although not being bound by theory, the inventors believe that the plugging is 35 being caused by organometallic material and/or fine particulates. The 1 WO 2006/005085 PCT/ZA2005/000101 organometallic material and/or fine particulates are likely to be rich in aluminium, and/or silicon, and/or titanium, and/or zirconium, and/or cobalt, and/or iron, and/or alkaline earth elements such as calcium and barium etc. 5 The synthesis products from the F-T process were analyzed and it was found that the condensate fraction is devoid of metal impurities (1 ppm or less), but that the wax contains metal impurities in the order of 10 - 100 ppm. This indicates that the F-T process and/or filtration system and/or refractory materials and/or chemically leached metals or metal species may be the 10 source of the metal impurities. There are possibly two forms of metal oxygenate species that contribute to bed plugging and either one or both may be important: 15 a) Fine particulates: for example, fine particulates of less than 1 micron in diameter which can be stabilized by surface-active compounds (such as the oxygenates) allowing them to remain in suspension. However, when this surface layer is disrupted, the particulates precipitate and form deposits on collector media. 20 b) Organometallic type compounds: for example, in the case of aluminium as the metal source, the formation of organoaluminium compounds of the Al-O-R type, like alkoxy-aluminium, aluminium carboxylates and alumoxanes, or of the AI-R type, like alkyl-aluminium, or combinations thereof are possible. 25 Bed-plugging has been seen with various catalysts and it occurs as a localized plug or as distributed particulate matter. It is hypothesized that the F-T synthesis product stream carries 30 organometallic material and/or solubilized fine catalyst particulates and/or filter aid and/or refractory material and/or chemically leached metals or metal species from the reactor system in low concentrations. The wax contains oxygenates like acids and alcohols that help to keep the fine particulates in solubilized form in the wax. 2 WO 2006/005085 PCT/ZA2005/000101 During hydroconversion, it is believed that these oxygenates that keep the particulates in suspension, and/or the ligands of the organometallic components, are hydrogenated and/or protonated and the modified metal 5 species are then deposited on the hydroconversion reactor catalyst bed, leading to what is termed "bed-plugging". Thus the inventors, after deliberation and experimentation, propose the following solution which may at least partially alleviate the above described 10 problem. According to a first aspect of the invention, there is provided a method of treatment of hydrocarbons , said method including hydrothermal treatment at a temperature of above 100 0 C of metal oxygenate components in F-T derived 15 hydrocarbons. The method may include chemical treatment of the metal oxygenate components in the F-T derived hydrocarbons, to modify the metal oxygenates,. 20 The method may include one or more of the following treating stages: (i) extracting the modified metal oxygenates with the aid of one or more polar solvents; 25 (ii) filtering the modified metal oxygenates after sufficient time has been allowed for particle growth and/or adsorption onto a filterable particle; 30 (iii) adsorbing the modified metal oxygenate onto an adsorbent; (iv) settling of the modified metal oxygenates after sufficient time has been allowed for particle growth; 3 WO 2006/005085 PCT/ZA2005/000101 (v) by centrifuging out the modified metal oxygenates after sufficient time has been allowed for particle growth; (vi) by distilling the hydrocarbons from the treated streams; 5 (vii) flocculation of the modified metal oxygenates; (viii) magnetic precipitation; 10 (ix) electrostatic precipitation/settling; and (x) flotation of the modified metal oxygenates and fine particulates; or (xi) any combination of one or more of the above treatments. 15 F-T derived hydrocarbons contain oxygenates and to a certain extent metals and/or metal species. 20 Ketones, aldehydes, alcohols, esters and carboxylic acids are the main constituents of the oxygenate fraction. Carboxylic acids are able to form under appropriate conditions metal carboxylate complexes with the metal species present. 25 Alcohols are able to form under appropriate conditions metal alkoxide complexes with the metal species present. The metal oxygenate may be a metal carboxylate, a metal alkoxide or a 30 combination thereof or a metalloxane. The metal oxygenate may be a carboxy substituted metalloxane. The hydrothermal treatment may be carried out with water at above 100C, 4 WO 2006/005085 PCT/ZA2005/000101 preferably between 1200C to 3700C, and even as high a 4000C, typically 1600C to 2500C and a pressure of 1 to 100 bar, preferably 5 to 50 bar.. The water for the hydrothermal treatment may be water added for the purpose 5 of the hydrotreatment or reaction water already present in the F-T derived hydrocarbons, or a combination of both. The hydrothermal treatment may be carried out in a substantially single liquid phase system in which both the hydrocarbons and water are present, said 10 water being present at such levels as to ensure that substantially one liquid phase is present under the process conditions. The hydrothermal treatment may be carried out in the presence of an adsorbent such as silica. Adsorption of the modified metal oxygenates takes 15 place on the silica particles and these may subsequently be removed by filtration or other treating methods. The hydrothermal treatment may also be achieved by maintaining the product stream under the temperature and pressure used in the F-T reactor after a 20 primary filtration zone for sufficient time to enable particle growth and/or adsorption onto a filterable particle, i.e. the hydrothermal treatment may be carried out by maintaining the reactor conditions between primary and secondary filtration zones for sufficient time to allow for particle growth or adsorption onto a filterable particle. More specifically, the pressure may be 25 selected to be higher than the water vapour pressure at the prevailing temperature. Sufficient time will be between 1 to 60 minutes, preferably between 1 to 30 minutes and more preferably between 5 to 10 minutes. 30 The optional chemical treatment may include trans-esterification to exchange longer hydrocarbon chain carboxylic acids or alcohols with shorter chain carboxylic acids. The chemicals which may be used in the trans-esterification or ligand 5 WO 2006/005085 PCT/ZA2005/000101 replacement step include, methanol, ethanol, oxalic acid, acetic acid, propanoic acetic, salicylic acid, succinic acid, tartaric acid, lactic acid, malonic acid, glycine acid, citric acid, carbonic acid, maleic acid, fumaric acid, phthalic acid, the anhydrides of these acids (e.g. maleic anhydride) and thermal 5 decomposition products of these acids. Also included are solid acids such as silica-alumina and/or other mixed oxide systems that possess Bronsted acidity. The interaction between these listed chemicals and the metal oxygenates may be speeded up by the thermal treatments. 10 Hydrothermal treatment may result in hydroxylation and formation of metal hydroxides and/or metal oxyhydroxides and/or metalloxanes. The hydrothermal treatment may be done before, with or after the optional chemical treatment. 15 According to a second aspect of the invention, there is provided a method of treatment of hydrocarbons , said method including chemical treatment with one or more chemical treatment agents in a single liquid phase of metal oxygenate components in F-T derived hydrocarbons to modify the metal 20 oxygenates. The chemical treatment may be followed by one or more of the following treating stages: 25 (i) extracting the modified metal oxygenates with the aid of one or more polar solvents; (ii) filtering the modified metal oxygenates after sufficient time has been allowed for particle growth and/or adsorption onto a filterable particle; 30 (iii) adsorbing the modified metal oxygenate onto an adsorbent; (iv) settling of the modified metal oxygenates after sufficient time has been allowed for particle growth; 6 WO 2006/005085 PCT/ZA2005/000101 (v) by centrifuging out the modified metal oxygenates after sufficient time has been allowed for particle growth; 5 (vi) by distilling the hydrocarbons from the treated streams; (vii) flocculation of the modified metal oxygenates; (viii) magnetic precipitation; 10 (ix) electrostatic precipitation/settling; and (x) flotation of the modified metal oxygenates and fine particulates; or (xi) any combination of one or more of the above treatments. 15 The chemical treatment agents which may be used in the trans-esterification or ligand replacement step include, methanol, ethanol, oxalic acid, acetic acid, propanoic acetic, salicylic acid, succinic acid, tartaric acid, lactic acid, malonic acid, glycine acid, citric acid, carbonic acid, maleic acid, fumaric acid, phthalic 20 acid, the anhydrides of these acids (e.g. maleic anhydride) and thermal decomposition products of these acids. Also included are solid acids such as silica-alumina and/or other mixed oxide systems that possess Bronsted acidity. The interaction between these listed chemicals and the metal oxygenates may be speeded up by the thermal treatments. 25 The chemical treatment may be carried out in a single liquid phase in which both the hydrocarbons and one or more chemical treatment agents are present, said chemical treatment agent or agents being present at levels below their saturation level in the hydrocarbons, for example wax. 30 In the chemical treatment, the amounts of chemical treatment agents added may be such as to give a single liquid phase i.e. total dissolution of the chemical treatment agents in the hydrocarbons under the process conditions. 7 WO 2006/005085 PCT/ZA2005/000101 The chemical treatment may include trans-esterification to exchange longer hydrocarbon chain carboxylic acids or alcohols with shorter chain carboxylic acids. 5 The polar solvents include, amongst others, water, melted organic acids, ethylene glycol, ionic liquids and combinations thereof. Filter materials used in the filtration include clays, silica, silica-aluminas, silicated aluminas, cellulose, activated carbons, sintered metals and material 10 filters such as nylons and polycarbonates. The adsorbents and/or filterable particles include clays, silica, silica-aluminas, silicated aluminas, cellulose, activated carbons, sintered metals, titania and material filters such as nylons and polycarbonates. 15 The adsorbents may also be used as filter material. The adsorbents may be added during the chemical and/or hydrothermal treatment, or during any of the downstream processes. 20 Growing of filterable particulates is influenced by the thermal and/or hydrothermal treatment conditions, and optionally, depending on the acid used as the chemical treatment agent as well as the process conditions, reversible or irreversible particle growth may be obtained that in turn 25 influences the removal of the modified metal species by filtration. Examples of Employing the Method of the Invention 30 Reactor wax from a Low-Temperature F-T (LTFT) plant was analyzed and found to contain metal carboxylates (Mx[O2CR]y), carboxy substituted metalloxanes ([M(O)x(OH)y(O2CR)zln), alkoxides and combinations thereof 8 WO 2006/005085 PCT/ZA2005/000101 that were leached from the catalyst, and/or support, and/or reactor, and/or filter clays, and/or refractory materials. The longer the hydrocarbon chain (-CR) of the carboxylate or alkoxide ligands 5 attached to the metal, the more soluble is the component in the wax. It is believed that on addition of the shorter chain carboxylic acids or anhydrides and/or water to the wax, the long chain oxygenates bonded to the metal species and/or particulates are exchanged by the shorter chain 10 carboxylic acids and/or hydroxides if water is present by trans-esterification and/or ligand exchange and/or hydroxylation: -The modified metal oxygenates, obtained from the exchange of the longer hydrocarbon chain carboxylic acids with shorter chain carboxylic acids or hydroxylation with water, result in the modified metal oxygenates being more 15 soluble in polar solvents like water or ethylene glycol and can be extracted from the wax by these polar solvents. - The modified metal oxygenates, obtained from the exchange of the longer hydrocarbon chain carboxylic acids with shorter chain carboxylic acids or hydroxylation with water result in the growth of the particles that can then be 20 filtered out. - The modified metal oxygenates, obtained from the exchange of the longer hydrocarbon chain carboxylic acid with shorter chain carboxylic acids or alcohols or hydroxylation with water, result in the formation of extractable/adsorbable particles onto an adsorbent. 25 Experimental A) Demonstrating the removal of the metal species from the wax using 30 hydrothermal treatment The experimental set-up used for this investigation is displayed in Figure 1. It is a continuous process in down-flow mode. Application of pressure is optional. 9 WO 2006/005085 PCT/ZA2005/000101 Water is pumped, using an HPLC pump, from a reservoir placed on a balance, through a 1400C hot pipe. The water (2 wt % relative to the wax) joins the molten wax which is heated up to 1400C. The combined streams 5 then trickle over a sand bed heated to a temperature of 3500C. The inert material is used for better distribution or mixing between the aqueous and wax phases and to increase the residence time, giving growth opportunity for the modified aluminium oxygenates and improving the efficiency of the separation process. The product after the sand bed is passed through a 1 micron filter (or 10 smaller) to collect the modified aluminium oxygenate agglomerates. The wax product after the filter has an aluminium content of 1 ppm Al as determined by ICP. Filters of a size bigger than 1 micron can be used optionally in combination with a filter aid. 15 B) Examples demonstrating the removal of the metal species from the wax by chemical treatment followed by filtration: B.1- Citric acid as chemical treatment agent. For Experiments CH1, CH3 and CH5, 250 gram of F-T reactor wax containing 20 the oxygenated aluminium species (carboxylates and/or alkoxides) were added to a 600 ml autoclave. The wax was heated to the treatment temperature before the citric acid was added to the autoclave (time zero) and the stirrer started. Wax samples were taken with time on line and passed through a 0.85 micron filter. The filtered wax samples were then analyzed for 25 aluminium using ICP (see Table B1 for summary of the results). Table BI ppm A in wax after x minutes of stirring Exp. Wt% No. citric Temp x=O X=5 x=10 x=15 acid *C CH1 0.1 165 50 1 CH3 0.05 165 50 39 13 1 CH5 0.02 165 50 1 43 8 10 WO 2006/005085 PCT/ZA2005/000101 B.2.1 - Maleic anhydride as chemical treatment agent with different water levels for the hydrothermal treatment. 5 For experiments B2 a to c: wax (200 g) containing 50 ppm aluminium as aluminium oxygenates was first melted in an oven at 140 *C, and then placed in the Parr autoclave, and heated to 230 OC with stirring (700 rpm). Maleic anhydride (0.1 wt % in relation to wax loaded) was dissolved in water (4g in 10 exp B2 a, 6g in exp B2b and 16g in exp B2 c) and placed in a metal tube that was then connected to the Parr reactor. After the desired temperature was reached, the pressure of the vessel was increased to 10 bar through the metal tube. This ensured that all the aqueous solution was forced in the Parr autoclave. The first sample was taken 5 minutes after this addition. Samples 15 were also taken at 10 minutes. After the wax was sampled, the sampling bottle was placed in the oven at 140 *C. This wax was then hot filtered (140 *C) through a 0.45 gm filter paper. The wax was then analyzed for aluminium using iCP. As can be observed in Table B2A, water addition (hydrothermal treatment) improves the particle growth and thereby the 20 filterability of the modified metal oxygenates from the wax. Table B2A Experiment wt % maleic wt % water Al (ppm) left Al (ppm) left number anhydride after 5 minutes after 10 minutes B2 a 0.1 2 5 1 B2 b 0.1 3 2 B2c 0.1 8 <1 <1 25 B.2.2 Maleic anhydride treatment at different concentrations levels and different hydrothermal treatment temperatures. 30 In experiments B2 d to g: wax (200 g) containing 45 ppm aluminium was first melted in an oven at 140 *C, and then placed in the Parr autoclave, and heated to 230 *C for experiments B2 d to f, or 1700C for experiment B2g, with stirring (700 rpm). Maleic anhydride (see Table B2B for wt % added) was 11 WO 2006/005085 PCT/ZA2005/000101 dissolved in 4 g of water and placed in a metal tube that was then connected to the Parr reactor. After the desired temperature was reached, the pressure of the vessel was increased to 300psi through the metal tube. This ensured that all the aqueous solution was forced in the Parr autoclave. The first 5 sample was taken 5 minutes after this addition. Samples were also taken at 10 minutes. After the wax was sampled, the sampling bottle was placed in the oven at 140 0C. This wax was then hot filtered (140 *C) through a 0.8 [tm filter paper. The wax was then analyzed for aluminium using ICP. As can be observed from the results listed in Table B2B, maleic acid levels down to 0.01 10 wt % were sufficient to promote particle growth and thereby the filterability on the modified metal oxygenates from the wax at 230 0 C, but needed more time at 170 0 C. As these temperatures are above the decomposition temperature of maleic acid, it is speculated that the decomposition product of maleic acid, i.e. fumaric acid, is the active chemical agent. 15 Table B2B Experiment wt % maleic temperature Al (ppm) left Al (ppm) left number anhydride after 5 minutes after 10 minutes B 2 d 0.1 230 0 C 1 1 B 2 e 0.05 230 0 C 1 1 B 2 f 0.01 230"C 1 1 B 2 g 0.1 170 0 C 16 1 20 B.3 - Polyacrylic acid (PAA) The wax (200 g) containing 50 ppm aluminium was first melted in an oven at 140 CC, and then placed in the Parr autoclave, and heated to 165 0C with stirring (700 rpm). 0.1 wt % PAA was added to 2 wt % water and placed in a 25 metal tube that was then connected to the Parr reactor. After the desired temperature was reached, the pressure of the vessel was increased to 10 bar through the metal tube. This ensured that all the aqueous solution was forced in the Parr autoclave. The first sample was taken 5 minutes after this addition. Samples were also taken at 10 minutes. After the wax was 30 sampled, the sampling bottle was placed in the oven at 140 0C. This wax was 12 WO 2006/005085 PCT/ZA2005/000101 then hot filtered (140 0C) through a 0.45 ptm filter paper. The wax was then analyzed for aluminium using ICR As can be observed from the results, PAA was effective in removing the modified metal oxygenates at 1650C. 5 Table B3 wt % PAA wt % water Al (ppm) left after Al (ppm) left after 5 minutes 10 minutes 0.1 2 <1 <1 10 B.4: Use of hydrothermal conditions and a filterable particle/adsorbent to modify and adsorb modified metal oxygenates. The wax (200 g) containing soluble metal oxygenates was first melted in an oven at 140 C. To the melted wax was added 0.1-0.01 wt % Aerosil 380 15 (Degussa). The wax was then heated to 170 0C with stirring (200 rpm). Water (4 ml) was placed in a metal tube that was connected to the Parr reactor. After the desired temperature was reached, a sample was taken. Thereafter, the water was added to the reaction mixture and samples were taken at 5 and 10 minutes (Table B4) and passed through a 2.5 micron filter. 20 The water modified the metal complex so that it could adsorb onto the filterable particle. Table B4 ppm of Al wt % silica Time (mn) Al (ppm) % Al removal in starting added wax 45 0.1 5 1 98 10 <1 >98 27 0.05 5 3 91 10 <1 >98 66 0.01 5 25 62 10 22 67 25 B.5 Influence of acid used on grown particle stability. For experiments B5 a to e: wax (250 g) containing the soluble metal 30 complexes was first melted in an oven at 165 *C. To the melted wax was 13 WO 2006/005085 PCT/ZA2005/000101 added 0.1 wt % citric acid. After the desired temperature was reached, a sample was taken after 5 minutes and treated as specified in Table B5. Table B5 Al ppm after Experiment Treatment before filtration filtration B5a Filtrate immediately 7 B5b Keep melted in oven (13oC) for 45 minunites 2 B5c Cool down (wax solidify), keep for 45 minutes before melting again and filter. 30 B5d cool down (wax solidify), keep for 2 days before melting again and filter at 140oC. 18 B5e Cool down (wax solidify), keep for 2 days before melting again and filter at 200 0 C. 4 5 In experiment B5f, wax (200 g) containing 45 ppm aluminium was first melted in an oven at 140 C, and then placed in the Parr autoclave, and heated to 1700C with stirring (700 rpm). Maleic anhydride (0.1 wt %) dissolved in water 10 (2 wt %) was placed in a metal tube that was then connected to the Parr reactor. After the desired temperature was reached, the pressure of the vessel was increased to 300psi through the metal tube. This ensured that all the aqueous solution was forced in the Parr autoclave. Two samples were taken after 15 minutes after this addition. After the wax was sampled, one 15 sample was placed in the oven at 140 OC. This wax was then hot filtered (140 0C) through a 0.8 tm filter paper. Sample 2 was cooled down before being reheated to 1400C and filtered. The aluminium content of the wax was determined using ICP analysis. Unlike the citric acid treated wax, the filterability of the maleic acid treated wax remained the same, whereas the 20 reaction conditions determine the filterability of the citric acid treated wax. TableB5B: experiment B5 f. Wt % Maleic Temperature Sample 1 (ppm Al) Sample 2 (ppm Al) anhydride 0.1 170-C <1 <1 25 C. 1 Adsorbing the modified metal oxygenate onto an adsorbent. In these experiments, contaminated wax was pumped at a set temperature through a 10 mm diameter tube containing adsorbent or filter material. The 14 WO 2006/005085 PCT/ZA2005/000101 pressure listed is caused by the wax flow rate and adsorbent characteristics. In experiment C1, contaminated wax containing 14 ppm aluminium and other metals such as cobalt, was pumped through a cellulose Arbocel BVB40 as filter/absorbent without water or acid been added (see table Cl). No removal 5 of aluminium was observed. In experiment C2, experiment C1 was repeated but 2 wt % water was added to the wax (see Table C2). The addition of water led to the complete removal for continuous filtering of up to 2.5 hours. 10 In experiment C3, experiment C2 was repeated but with Vitacel LOO as filter material/adsorbent. In experiment C4, experiment C2 was repeated but with Celpure S1000 as 15 filter material/adsorbent. In experiment C5, experiment C2 was repeated but with spray dried Degussa silica (Aerosil 380) as filter material/adsorbent. 20 in experiment C6 a to j, the wax and water mixture was pumped through a packed bed with 19 minutes residence time, before been pumped through a Fitracel 9001 filter material. For experiments C6 a to e only water was added. This was done at different temperatures. For experiments C6 f to j, a 0.1 M maleic acid in water solution was also added at different temperatures. 25 30 15 WO 2006/005085 PCT/ZA2005/000101 z v Vo V V V V v V 0 E v - 'v v QI) O)L tn a - 1 C) ) o O - ') 1- (D (- It 0D . .0 U-) C3 N-O co 0 CO C\] oO ~ 00 N0 01 co N- N-,. C: C3) EE E C i~ 10 ~ 0 LV 0 NV C0 LV) > <.2 E 0~ C L 0 0 0 CLw .4. 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Claims (27)

1. A method of treatment of hydrocarbons, said method including hydrothermal treatment at a temperature of above 100'C of metal oxygenate components in F-T derived hydrocarbons.

2. A method as claimed in claim 1, said method including chemical treatment of the metal oxygenate components in the F-T derived hydrocarbons, to modify the metal oxygenates.

3. A method as claimed in claim 1 or claim 2, wherein the treatment is followed by one or more of the following treating stages: - i) extracting the modified metal oxygenates with the aid of one or more polar solvents; - ii) filtering the modified metal oxygenates after sufficient time has been allowed for particle growth and/or adsorption onto a filterable particle; - iii) adsorbing the modified metal oxygenate onto an adsorbent; - iv) settling of the modified metal oxygenates after sufficient time has been allowed for particle growth; - v) by centrifuging out the modified metal oxygenates after sufficient time has been allowed for particle growth; - vi) by distilling the hydrocarbons from the treated streams; - vii) flocculation of the modified metal oxygenates; - viii) magnetic precipitation; - ix) electrostatic precipitation/settling; and - x) flotation of the modified metal oxygenates and fine particulates; or any combination of one or more of the above treatments. 22 WO 2006/005085 PCT/ZA2005/000101

4. A method as claimed in any one of the preceding claims , wherein the metal oxygenate is a metal carboxylate, a metal alkoxide, a metalloxane, or a combination of two or more thereof.

5. A method as claimed in any one of claims 1 to 3, wherein the metal oxygenate is a carboxy substituted metalloxane.

6. A method as claimed in any one of the preceding claims, wherein the hydrothermal treatment is carried out with water at above 100 C.

7. A method as claimed in claim 6, wherein the hydrothermal treatment is carried out with water between 1200C to 3700C.

8. A method as claimed in claim 6, wherein the hydrothermal treatment is carried out with water at temperature of up to 4000C.

9. A method as claimed in any one of the preceding claims, wherein the water for the hydrothermal treatment is selected from water added for the purpose of the hydrotreatment, reaction water already present in the F-T derived hydrocarbons, or a combination of both.

10. A method as claimed in any one of the preceding claims, wherein the hydrothermal treatment is carried out in a substantially single liquid phase system in which both the hydrocarbons and water are present, said water being present at such levels as to ensure that substantially one liquid phase is present under the process conditions.

11. A method as claimed in any one of the preceding claims, wherein the hydrothermal treatment is carried out in the presence of an adsorbent. 23 WO 2006/005085 PCT/ZA2005/000101

12. A method as claimed in claim 11, wherein the adsorbent includes silica.

13. A method as claimed in claim 12, wherein adsorption of the modified metal oxygenates takes place on the silica particles and these particles are subsequently removed by filtration or other treatment methods.

14. A method as claimed in any one of the preceding claims, wherein the hydrothermal treatment is achieved by maintaining the product stream under the temperature and pressure used in the F-T reactor after a primary filtration zone for sufficient time to enable particle growth and/or adsorption onto a filterable particle.

15. A method as claimed in claim 14, wherein the pressure is selected to be higher than the water vapour pressure at the prevailing temperature.

16. A method as claimed in any one of the preceding claims, wherein the chemical treatment includes trans-esterification to exchange longer hydrocarbon chain carboxylic acids or alcohols with shorter chain carboxylic acids.

17. A method as claimed in claim 16, wherein the chemicals which are used in the trans-esterification or ligand replacement step are selected from the group including methanol, ethanol, oxalic acid, acetic acid, propanoic acetic, salicylic acid, succinic acid, tartaric acid, lactic acid, malonic acid, glycine acid, citric acid, carbonic acid, maleic acid, fumaric acid, phthalic acid, the anhydrides of these acids, and thermal decomposition products of these acids.

18. A method as claimed in claim 16, wherein the chemicals which are used in the trans-esterification or ligand replacement step are selected from the group including silica-alumina and/or other mixed oxide systems that possess Bronsted acidity. 24 WO 2006/005085 PCT/ZA2005/000101

19. A method as claimed in any one of the preceding claims, wherein the hydrothermal treatment results in hydroxylation and formation of one or more of metal hydroxides, metal oxyhydroxides, and metalloxanes.

20. A method as claimed in any one of the preceding claims, wherein the hydrothermal treatment is performed before, with or after the chemical treatment.

21. A method of treatment of hydrocarbons , said method including chemical treatment with one or more chemical treatment agents in a single liquid phase of metal oxygenate components in F-T derived hydrocarbons to modify the metal oxygenates.

22. A method as claimed in claim 21, wherein the chemical treatment is followed by one or more of the following treating stages: i) extracting the modified metal oxygenates with the aid of one or more polar solvents; ii) filtering the modified metal oxygenates after sufficient time has been allowed for particle growth and/or adsorption onto a filterable particle; iii) adsorbing the modified metal oxygenate onto an adsorbent; iv) settling of the modified metal oxygenates after sufficient time has been allowed for particle growth; v) by centrifuging out the modified metal oxygenates after sufficient time has been allowed for particle growth; vi) by distilling the hydrocarbons from the treated streams; vii) flocculation of the modified metal oxygenates; viii) magnetic precipitation; ix) electrostatic precipitation/settling; and x) flotation of the modified metal oxygenates and fine particulates; or any combination of one or more of the above treatments. 25 WO 2006/005085 PCT/ZA2005/000101

23. A method as claimed in claim 21, wherein the chemical treatment agents which are used in the trans-esterification or ligand replacement step are selected from the group including methanol, ethanol, oxalic acid, acetic acid, propanoic acetic, salicylic acid, succinic acid, tartaric acid, lactic acid, malonic acid, glycine acid, citric acid, carbonic acid, maleic acid, fumaric acid, phthalic acid, the anhydrides of these acids, and thermal decomposition products of these acids, and solid acids including but not limited to silica-alumina and/or other mixed oxide systems that possess Bronsted acidity.

24. A method as claimed in claim 21, wherein the chemical treatment is carried out in a single liquid phase in which both the hydrocarbons and one or more chemical treatment agents are present, said chemical treatment agent or agents being present at levels below their saturation level in the hydrocarbons.

25. A method as claimed in any one of claims 21 to 24, wherein the polar solvents are selected from the group including at least water, melted organic acids, ethylene glycol, ionic liquids, and combinations thereof.

26. A method as claimed in any one of claims 21 to 25, wherein one or more of the adsorbents, filter material, and filterable particles are selected from the group including at least clays, silica, silica-aluminas, silicated aluminas, cellulose, activated carbons, sintered metals, titania and material filters such as nylons and polycarbonates.

27. A method as claimed in any one of the claims 21 to 26, wherein the adsorbents are added during the chemical treatment, the hydrothermal treatment, during any of the downstream processes, or during two or more of the aforementioned steps. 26