WO2006005084A1

WO2006005084A1 - Treatment of hydrocarbons

Info

Publication number: WO2006005084A1
Application number: PCT/ZA2005/000100
Authority: WO
Inventors: Jan Mattheus Botha; Jacobus Lucas Visagie
Original assignee: Sasol Technology (Pty) Ltd
Priority date: 2004-07-06
Filing date: 2005-07-04
Publication date: 2006-01-12
Also published as: AU2005260788B2; RU2007101687A; GB2430442B; BRPI0512755B1; GB0625234D0; GB2430442A; AU2005260788A1; NO343004B1; RU2364615C2; ZA200610735B; NO20070043L; BRPI0512755A

Abstract

The invention provides a method of treatment of a Fischer-Tropsch (F-T) reaction mixture, 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 absorbent to facilitate adsorption of the modified metal oxygenate components onto the filterable absorbent.

Description

METHOD OF TREATMENT OF FISCHER-TROPSCH HYDROCARBONS

Field of the Invention

The invention relates to treatment of hydrocarbons to reduce deposit formation in process equipment.

Background to the Invention

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.

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 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.

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

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 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 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.

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 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.

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 Al-R type, like alkyl-aluminium, or combinations thereof are possible.

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 refractory material and/or chemically leached metals 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.

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 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 problem.

According to a first aspect of the invention, there is provided a method of treatment of a Fischer-Tropsch (F-T) reaction mixture, 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 components onto the filterable adsorbent.

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 120°C to 37O⁰C, and even as high a 400°C, typically 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 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 hydrothermai reaction zone may be 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. However, the hydrothermai reaction zone may be at least partially downstream of the F-T reactor, and typically close to or at Fischer-Tropsch reaction conditions.

The F-T reaction mixture may include synthesis gas, Fischer-Tropsch hydrocarbons, oxygenates, water, and catalyst particles.

Modification may involve hydrothermai treatment, which may result in hydroxylation and formation of metal hydroxides and/or metal oxyhydroxides 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 solvents;

(ii) filtering the modified metal oxygenates after sufficient time has been allowed for particle growth and/or adsorption onto a filterable particle;

adsorbing the modified metal oxygenate onto an adsorbent;

(iv) settling of the adsorbed 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) flocculation of the modified metal oxygenates;

(vii) magnetic precipitation;

(viii) electrostatic precipitation/settling; and

(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.

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.

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 combination thereof or a metalloxane.

The metal oxygenate may be a carboxy substituted metalloxane.

The Fischer-Tropsch reaction conditions may include a temperature of above 160°C, preferably between 200°C to 280°C, and even as high as 400°C, typically 230°C to 24O⁰C 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.

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.

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 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, 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 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 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 filtration.

Examples of Employing the Method of the Invention

Reactor wax from a Low-Temperature F-T (LTFT) plant was analyzed and found to contain metal carboxylates (M_x[θ2CR]y), carboxy substituted metalloxanes

([M(O)_x(OH)y(θ2CR)_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 .

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 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 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 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 and cobalt content, after filtration and at different times after the addition of the silica are given in Table 1. Table 1: Aluminium and Cobalt Content of Wax

Example 2: Adding a filterable particle/adsorbent under hydrothermal conditions to modify and adsorb modified metal oxygenates.

The wax (200 g) containing soluble metal oxygenates was first melted in an oven at 140 ⁰C. To the melted wax was added 0.1-0.01 wt % Aerosil 380 (Degussa). The wax was then heated to 170 °C 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 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

ppm of wt % silica Time Al % AI

Al in added (min) (ppm) removal starting 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

Example 3: 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 pressure listed is caused by the wax flow rate and adsorbent characteristics.

In these experiments, contaminated wax containing 22 ppm aluminium and other 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.

F536 GCC Rev 2 Sasol

Claims

1. A method of treatment of a Fischer-Tropsch (F-T) reaction mixture, 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 components onto the filterable adsorbent.

2. A method as claimed 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 reaction is carried out at a temperature of above 100⁰C.

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

6. A method as claimed in claim 3, wherein the hydrothermal reaction is carried out at a temperature of between 160°C to 250⁰C.

7. A method as claimed in any one of the preceding claims, wherein the filterable adsorbent is added into the hydrothermal reaction zone.

8. A method as claimed in claim 7, wherein the addition rate of the adsorbent is determined by the amount of metal oxygenates in the F-T wax.

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

10. A method as claimed in any one of the preceding claims 2 to 9, 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.

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

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

13. A method as claimed in any one of the preceding claims, wherein the treatment stage is followed by one or of the following treating stages:

i) extracting the modified metal oxygenates with the aid of 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 adsorbed 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) flocculation of the modified metal oxygenates;

vii) magnetic precipitation;

viii) electrostatic precipitation/settling; and

ix) flotation of the modified metal oxygenates and fine particulates; or any combination of one or more of the above treatments

14. 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.

15. A method as claimed in any one of the preceding claims 2 to 14, wherein the Fischer-Tropsch reaction conditions includes a temperature of between 180°C and 400°C.

16. A method as claimed in claim 15, wherein the Fischer-Tropsch reaction conditions includes a temperature of 230°C to 240°C .

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

18. A method as claimed in any one of the preceding claims, wherein the filterable adsorbent is selected from the group including at least 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.

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

20. A method as claimed in claim 19, 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 adsorption onto a filterable particle.

21. A method as claimed in any one of claims 13 to 20, 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.