AU2005260788B2

AU2005260788B2 - Treatment of hydrocarbons

Info

Publication number: AU2005260788B2
Application number: AU2005260788A
Authority: AU
Inventors: Jan Mattheus Botha; Jacobus Lucas Visagie
Original assignee: Sasol Technology Pty Ltd
Current assignee: Sasol Technology Pty Ltd
Priority date: 2004-07-06
Filing date: 2005-07-04
Publication date: 2010-07-01
Anticipated expiration: 2025-07-04
Also published as: GB2430442B; GB2430442A; BRPI0512755A; NO20070043L; BRPI0512755B1; RU2007101687A; NO343004B1; AU2005260788A1; GB0625234D0; ZA200610735B; WO2006005084A1; RU2364615C2

Description

WO 2006/005084 PCT/ZA2005/000100 METHOD OF TREATMENT OF FISCHER-TROPSCH HYDROCARBONS Field of the Invention 5 The invention relates to treatment of hydrocarbons to reduce deposit formation in process equipment. Background to the Invention 10 The inventors have identified an area for process optimization in processing of hydrocarbons. In particular, the inventors have identified an area for process optimization in the processing of F-T synthesis products by hydroconversion in general. 15 F-T derived product streams contain oxygenates and to a certain extent metals and/or metal species. Ketones, aldehydes, alcohols, esters and 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 20 present. These metal carboxylates and/or alkoxides and/or metalloxanes may form deposits in processing equipment and catalyst beds. Eventually the deposits in the catalyst beds may grow to such an extent that reactor shutdowns are inevitable. 25 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 reaction product of a constituent of said product streams. Summary of invention 30 Although not being bound by theory, the inventors believe that the plugging is being caused by organometallic material and/or fine particulates. The organometallic material is likely to be rich in aluminium, and/or silicon, and/or WO 2006/005084 PCT/ZA2005/000100 titanium, and/or zirconium, and/or cobalt, and/or iron, and/or alkaline earth elements such as calcium and barium etc. The synthesis products from the F-T process were analyzed and it was found 5 that the condensate fraction is devoid of metal impurities (of the order of 1 ppm or less), but that the wax contains metal impurities (of 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 source of the metal impurities. 10 There are possibly two forms of metal oxygenate species that contribute to bed plugging and either one or both may be important: a) Fine particulates, for example, fine particulates of less than 1 micron in 15 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 AI-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 organometallic material and/or solubilized fine catalyst particulates and/or filter aid and/or 30 refractory material and/or chemically leached metals from the reactor system in 3 low concentrations. The wax contains oxygenates like acids and alcohols that help to keep the fine particulates in solubilized form in the wax. During hydroconversion, it is believed that these oxygenates that keep the particulates in suspension, and/or the ligands of the organometallic components, 5 are hydrogenated and/or protonated and the modified metal species are then deposited on the hydroconversion reactor catalyst bed, leading to what is called "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 a Fischer-Tropsch (F-T) reaction mixture including synthesis gas, Fischer-Tropsch hydrocarbons, oxygenates and catalyst particles, said method including: 15 (a) modification of metal oxygenate components in the F-T reaction mixture in a hydrothermal reaction zone at hydrothermal reaction conditions; (b) exposing the F-T reaction mixture in the hydrothermal reaction zone to a filterable adsorbent to facilitate adsorption of the modified metal oxygenate components onto the filterable adsorbent, wherein the filterable adsorbent is 20 added into the hydrothermal reaction zone. The hydrothermal reaction conditions may at least partially coincide with F-T reaction conditions. The hydrothermal reaction conditions may include a temperature of above 100 C, preferably between 1200C to 3700C, and even as high as 400*C, typically 25 1600C to 2500C and a pressure of 1 to 100 bar, preferably 5 to 50 bar. The filterable adsorbent may be added into the hydrothermal reaction zone. The addition rate of the adsorbent may be determined by the amount of metal 30 WO 2006/005084 PCT/ZA2005/000100 oxygenates in the F-T wax. The addition rate may vary from 0.01 to 10 wt % of the F-T catalyst present in the reactor. The hydrothermal reaction zone may be in a Fischer-Tropsch reactor in which 5 synthesis gas is reacted in the presence of Fischer-Tropsch catalysts to produce Fischer-Tropsch hydrocarbons, oxygenates, and water. However, the hydrothermal reaction zone may be at least partially downstream of the F-T reactor, and typically close to or at Fischer-Tropsch reaction conditions. 10 The F-T reaction mixture may include synthesis gas, Fischer-Tropsch hydrocarbons, oxygenates, water, and catalyst particles. Modification may involve hydrothermal treatment, which may result in hydroxylation and formation of metal hydroxides and/or metal oxyhydroxides 15 and/or metalloxanes. The treatment stage may be followed by one or of the following treating stages: (i) extracting the modified metal oxygenates with the aid of polar 20 solvents; (ii) filtering the modified metal oxygenates after sufficient time has been allowed for particle growth and/or adsorption onto a filterable particle; 25 (iii) adsorbing the modified metal oxygenate onto an adsorbent; (iv) settling of the adsorbed metal oxygenates after sufficient time has been allowed for particle growth; 30 WO 2006/005084 PCT/ZA2005/000100 (v) by centrifuging out the modified metal oxygenates after sufficient time has been allowed for particle growth; (vi) flocculation of the modified metal oxygenates; 5 (vii) magnetic precipitation; (viii) electrostatic precipitation/settling; and 10 (ix) flotation of the modified metal oxygenates and fine particulates; or (x) any combination of one or more of the above treatments F-T derived hydrocarbons contain oxygenates and to a certain extent metals and/or metal species. 15 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 20 complexes with the metal species present. Alcohols are able to form under appropriate conditions metal alkoxide complexes with the metal species present. 25 The metal oxygenate may be a metal carboxylate, a metal alkoxide or a combination thereof or a metalloxane. The metal oxygenate may be a carboxy substituted metalloxane. 30 The Fischer-Tropsch reaction conditions may include a temperature of above 1600C, preferably between 2000C to 2800C, and even as high as 4000C, typically WO 2006/005084 PCT/ZA2005/000100 2300C to 2400C and a pressure of 18 to 50 bar, preferably between 20 to 30 bar. The Fischer-Tropsch reaction conditions may include the presence of water. 5 The filterable adsorbent may be silica, which leads to the adsorption of the modified metal oxygenates on the silica particles, which can subsequently be removed by filtration or other treating methods. 10 The treatment may also be achieved by maintaining the F-T product stream under the temperature and pressure of the FT reaction conditions after a primary filtration zone for sufficient time to enable particle growth 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 15 zones for sufficient time to allow for particle growth or adsorption onto a filterable particle. Sufficient time will be between 1 to 60 minutes, preferably between 1 to 30 minutes and more preferably between 5 to 10 minutes. Filter materials used in the filtration include clays, silica, silica-alumina, cellulose, 20 activated carbons, sintered metals and material filters such as nylons and polycarbonates. The adsorbents and/or filterable particles include clays, silica, silica-alumina, cellulose, activated carbons, sintered metals, titania and material filters such as 25 nylons and polycarbonates. Growing of filterable particulates may be influenced by thermal and/or hydrothermal treatment conditions, and optionally, on any chemical treatment conditions which, depending on the acid used as the chemical treatment agent as 30 well as the process conditions, reversible or irreversible particle growth may be obtained that in turn influences the removal of the modified metal species by WO 2006/005084 PCT/ZA2005/000100 filtration. Examples of Employing the Method of the Invention 5 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(02CR)z]n), alkoxides and combinations thereof that were leached from the catalyst, and/or support, and/or reactor, and/or filter clays and/or refractory materials . 10 The longer the hydrocarbon chain (-CR) of the carboxylate or alkoxide ligands attached to the metal, the more soluble is the component in the wax. Example 1. Hydrothermal treatment and addition of an adsorbent to the F-T 15 reactor for the removal of metal oxygenates present in the wax As was shown in examples elsewhere, hydrothermal treatment ex-situ the reactor of F-T wax, which contains metal oxygenates, results in the formation of modified metal oxygenates, which given sufficient time for particle growth, can be filtered 20 or adsorbed on filterable adsorbents such as silica. A novel approach is that all the steps involving the hydrothermal treatment of the wax for the modification of the metal oxygenates present and their adsorption on filterable particles can all take place in-situ the F-T reactor under the 25 hydrothermal environment prevailing in the F-T reactor at the FT reaction conditions of 22 bar and 2300C. The particle size of the silica used was 5 microns and 3 wt % relative to the F-T catalyst was added to the reactor. The results obtained in terms of aluminium 30 and cobalt content, after filtration and at different times after the addition of the silica are given in Table 1.

WO 2006/005084 PCT/ZA2005/000100 Table 1: Aluminium and Cobalt Content of Wax Time after silica Al content (ppm) Co content (ppm) addition(hours) Before silica addition 13.5 1.6 6 2.7 <0.55 30 1 <0.55 59 1.5 0.87 66 0.38 <0.55 5 Example 2: Adding a filterable particle/adsorbent under hydrothermal conditions to modify and adsorb modified metal oxygenates. 10 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 (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 15 to the reaction mixture and samples were taken at 5 and 10 minutes (Table 2) and passed through a 2.5 micron filter. The water modified the metal complex so that it could adsorb onto the filterable particle. Table 2: Adsorbent Addition 20 ppm of wt % silica Time Al % Al Al in added (min) (ppm) removal starting wax 45 0.1 5 1 98 10 <1 >98 27 0.05 5 3 91 WO 2006/005084 PCT/ZA2005/000100 10 <1 >98 66 0.01 5 25 62 10 22 67 Example 3: Adsorbing the modified metal oxygenate onto an adsorbent. 5 In these experiments, contaminated wax was pumped at a set temperature through a 10 mm diameter tube containing adsorbent or filter material. The pressure listed is caused by the wax flow rate and adsorbent characteristics. In these experiments, contaminated wax containing 22 ppm aluminium and other 10 metals such as cobalt, was pumped through a spray dried Degussa silica (Aerosil 380) as filter/absorbent with water been added (see table 3). Almost complete removal of the aluminium was achieved.

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Claims

1. A method of treatment of a Fischer-Tropsch (F-T) reaction mixture including synthesis gas, Fischer-Tropsch hydrocarbons, oxygenates and catalyst 5 particles, said method including: (a) modification of metal oxygenate components in the F-T reaction mixture in a hydrothermal reaction zone at hydrothermal reaction conditions; (b) exposing the F-T reaction mixture in the hydrothermal reaction zone to a filterable adsorbent to facilitate adsorption of the modified metal oxygenate 10 components onto the filterable adsorbent, wherein the filterable adsorbent is added into the hydrothermal reaction zone.

2. A method as claimed in claim 1, wherein the hydrothermal reaction conditions at least partially coincides with F-T reaction conditions.

3. A method as claimed in claim 1 or claim 2, wherein the hydrothermal 15 reaction is carried out at a temperature of above 100C.

4. A method as claimed in claim 3, wherein the hydrothermal reaction is carried out at a temperature of between 1200C to 370*C.

5. A method as claimed in claim 3, wherein the hydrothermal reaction is carried out at a temperature of as high as 400*C. 20

6. A method as claimed in claim 3, wherein the hydrothermal reaction is carried out at a temperature of between 1600C to 250*C.

7. A method as claimed in any one of the preceding claims, wherein the addition rate of the adsorbent is determined by the amount of metal oxygenates in the F-T reaction mixture. 25

8. A method as claimed in claim 7, wherein the addition rate varies from 0.01 to 10 wt % of the F-T catalyst present in the reactor. 12

9. A method as claimed in any one of the preceding claims 2 to 8, wherein the hydrothermal reaction zone is in a Fischer-Tropsch reactor in which synthesis gas is reacted in the presence of Fischer-Tropsch catalysts to produce Fischer Tropsch hydrocarbons, oxygenates, and water. 5

10. A method as claimed in any one of the preceding claims 2 to 9, wherein the hydrothermal reaction zone is at least partially downstream of a Fischer Tropsch reactor but close to or at Fischer-Tropsch reaction conditions.

11. A method as claimed in any one of the preceding claims, wherein modification involves hydrothermal treatment, which results in hydroxylation and 10 formation of one or more of metal hydroxides, metal oxyhydroxides, and metalloxanes.

12. A method as claimed in any one of the preceding claims, followed by one or any combination of the following treating stages: i) extracting the modified metal oxygenates with the aid of polar solvents; 15 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 adsorbed metal oxygenates after sufficient time has been allowed for particle growth; 20 v) by centrifuging out the modified metal oxygenates after suffieicnt time has been allowed for particle growth; vi) flocculation of the modified metal oxygenates; vii) magnetic precipitation; viii) electrostatic precipitation/settling; and 25 ix) flotation of the modified metal oxygenates and fine particulates.

13. A method as claimed in any one of the preceding claims, wherein the metal oxygenate is selected from the group including at least a metal carboxylate, a metal alkoxide, a carboxy substituted metalloxane, and a combination thereof. 13

14. A method as claimed in any one of the preceding claims 2 to 13, wherein the Fischer-Tropsch reaction conditions includes a temperature of between 1800C and 400*C.

15. A method as claimed in claim 14, wherein the Fischer-Tropsch reaction 5 conditions includes a temperature of 2300C to 2400C.

16. A method as claimed in any one of the preceding claims, wherein water is present in the Fischer-Tropsch reaction mixture.

17. A method as claimed in any one of the preceding claims, including maintaining the F-T product stream under hydrothermal reaction conditions after 10 a primary filtration zone for sufficient time to enable particle growth or adsorption onto a filterable particle.

18. A method as claimed in claim 17, including hydrothermal treatment carried out by maintaining the Fisher-Tropsch reaction conditions between primary and secondary filtration zones for sufficient time to allow for particle growth or 15 adsorption onto a filterable particle.

19. A method as claimed in any one of claims 13 to 18, wherein one or more of the filter materials, adsorbents, and filterable particles used in the filtration are selected from the group including clays, silica, silica-alumina, cellulose, activated carbons, sintered metals, material filters, and combinations thereof.

20 20. A method as claimed in claim 19, wherein a filterable adsorbent is silica which leads to the adsorption of the modified metal oxygenates on the silica particles.

21. A method as claimed in claim 20, wherein the modified metal oxygenates are cobalt or aluminium oxygenates. 25 14

22. A method substantially as hereinbefore described with reference to the accompanying examples. SASOL TECHNOLOGY (PTY) LTD WATERMARK PATENT & TRADE MARK ATTORNEYS P28183AU00