PRODUCTION OF VCl4

Abstract

A process (10) for the production of VCI.sub.4 includes suspending a solid particulate oxygen-free vanadium compound starting material in a liquid reaction medium to form a reaction mixture, and reacting the oxygen-free vanadium compound starting material suspended in the liquid reaction medium with a chlorinating agent (18) to produce liquid VCI.sub.4. The liquid reaction medium in the reaction mixture is maintained at a reaction temperature above its normal boiling point and the oxygen-free compound starting material and the chlorinating agent are reacted at a reaction pressure higher than the vapour pressure of the liquid reaction medium at the reaction temperature of the process so that the reaction mixture does not boil.

Claims

1. A process for the production of VCl.sub.4, the process including suspending a solid particulate oxygen-free vanadium compound starting material in a liquid reaction medium to form a reaction mixture; and reacting the oxygen-free vanadium compound starting material suspended in the liquid reaction medium with a chlorinating agent to produce liquid VCl.sub.4, the liquid reaction medium in the reaction mixture being at a reaction temperature above its normal boiling point and the oxygen-free compound starting material and the chlorinating agent being reacted at a reaction pressure higher than the vapour pressure of the liquid reaction medium at the reaction temperature of the process so that the reaction mixture does not boil.

2. The process as claimed in claim 1, in which the oxygen-free vanadium compound starting material is selected from the group consisting of vanadium nitride, vanadium carbide, vanadium carbonitride, vanadium silicide, ferro vanadium, and mixtures of two or more thereof.

3. The process as claimed in claim 1, in which the liquid reaction medium is a fully chlorinated liquid, which is not prone to being further chlorinated.

4. The process as claimed in claim 1, in which the liquid reaction medium is selected from the group consisting of liquid VCl.sub.4, liquid TiCl.sub.4, and mixtures thereof.

5. The process as claimed in claim 1, in which the reaction temperature is no more than 300 C. but at least 140 C. and in which the reaction pressure is at least 2 bar (absolute).

6. The process as claimed in claim 1, in which the chlorinating agent is selected from the group consisting of HCl, CCl.sub.4, SCl.sub.2, Cl.sub.2 and mixtures of two or more thereof.

7. The process as claimed in claim 1, in which at least a portion of the liquid VCl.sub.4 formed in the reaction mixture evaporates, the process including condensing at least some of the gaseous VCl.sub.4 to provide condensed VCl.sub.4, the condensed VCl.sub.4 being withdrawn as a liquid VCl.sub.4 product or the condensed VCl.sub.4 being returned to the reaction mixture.

8. The process as claimed in claim 7, which includes withdrawing gaseous chlorinating agent from above the reaction mixture together with evaporated VCl.sub.4, cooling the gaseous chlorinating agent during the condensing of the gaseous VCl.sub.4 and recycling cooled chlorinating agent to the reaction mixture for reacting with the suspended solid particulate oxygen-free vanadium compound starting material, the cooled recycled chlorinating agent serving to at least assist in cooling the reaction mixture thereby to maintain the liquid reaction medium at a desired reaction temperature above the normal boiling point of the liquid reaction medium but with the reaction mixture not boiling.

9. The process as claimed in claim 1, which includes maintaining a positive Cl.sub.2 pressure above the reaction mixture to limit co-production of VCl.sub.3 and VCl.sub.2 as undesirable by-products.

10. The process as claimed in claim 5, in which the reaction temperature is no more than 220 C. and in which the oxygen-free vanadium compound starting material is vanadium nitride or ferro vanadium.

11. The process as claimed in claim 1, in which the liquid reaction medium is liquid TiCl.sub.4 and in which the liquid VCl.sub.4 that is produced is withdrawn as a liquid admixture of liquid VCl.sub.4 and liquid TiCl.sub.4.

12. The process as claimed in claim 5, in which the reaction pressure is at least 6 bar (absolute).

13. The process as claimed in claim 1, in which the liquid reaction medium is a liquid other than VCl.sub.4 and in which VCl.sub.3 and/or VCl.sub.2 has a lower solubility than VCl.sub.4.

14. The process as claimed in claim 1, in which the chlorinating agent is fed into the reaction mixture, the rate of feeding of the chlorinating agent being manipulated to control the reaction pressure.

15. VCl.sub.4 produced in accordance with the process of claim 1.

Description

[0052] The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which

[0053] FIG. 1 shows one embodiment of a process in accordance with the invention for the production of VCl.sub.4;

[0054] FIG. 2 shows another embodiment of a process in accordance with the invention for the production of VCl.sub.4; and

[0055] FIG. 3 shows yet another embodiment of a process in accordance with the invention for the production of VCl.sub.4.

[0056] Referring to FIG. 1 of the drawings, reference numeral 10 generally indicates a process in accordance with the invention for the production of VCl.sub.4. The process 10 includes broadly a reactor 12 with an electrically driven agitator or stirrer 14. The reactor 12 is thus a stirred reactor and is temperature controlled, or at least heated, by means of a heating jacket 13 which may for example employ steam as a heating medium. The reactor 12 is provided with a feed line 16 and a chlorinating agent line 18. A reflux condenser 20 is in flow communication with the reactor 12 by means of a vapour withdrawal line 22 and a condensate return line 24. The reflux condenser 20 is also provided with a bleed line 26.

[0057] A reaction mixture withdrawal line 28 leads from the reactor 12 to a cooler 30 and from the cooler 30 to a filter 32. A product line 34 and a residue line 36 leave the filter 32.

[0058] The process 10 is typically conducted on a batch basis. The reactor 10 is thus loaded with a quantity of liquid VCl.sub.4 as a liquid reaction medium and suspended powdered vanadium and/or vanadium carbide as a starting material. This can be done consecutively by first feeding the liquid VCl.sub.4 through the feed line 16 into the reactor 12, then feeding the powdered starting material into the reactor 12 by means of the feed line 16, and then suspending the starting material in the liquid VCl.sub.4 by using the stirrer 14. Alternatively, the powdered vanadium or vanadium carbide starting material can be suspended in the liquid VCl.sub.4 to form a slurry, with the slurry then being fed into the reactor 12 by means of the feed line 16.

[0059] Typically, the powdered vanadium or vanadium carbide starting material has a particle size of about 50-100 m and the slurry contains about 10-30% by volume of the starting material. The powdered vanadium or vanadium carbide starting material is substantially oxygen free, in the sense that the starting material does not include a vanadium compound, or does not include a significant amount of a vanadium compound, such as V.sub.2O.sub.5, which includes oxygen in its molecular or crystal structure.

[0060] The slurry of liquid VCl.sub.4 and suspended oxygen-free vanadium compound starting material forms a reaction mixture and is heated under stirring in the reactor 12 by means of the heating jacket 13 to a temperature of about 200 C. Chlorine gas as a chlorinating agent is then fed into the reactor 12 through the chlorinating agent line 18 and the reactor 12 is pressure controlled to maintain a reaction pressure of about 7 bar (absolute). Preferably, the chlorinating agent, when in gaseous form, is bubbled through the reaction mixture whilst the stirrer 14 is employed to maintain the oxygen-free vanadium compound starting material in suspension and to disperse the chlorinating agent in the reaction mixture.

[0061] The vanadium in the oxygen-free vanadium compound starting material suspended in the liquid reaction medium (liquid VCl.sub.4) is thus chlorinated to produce more liquid VCl.sub.4 which is taken up by the reaction mixture. The chlorinating reaction is strongly exothermic. The reaction mixture in the reactor 12 is prevented from boiling by employing a reaction pressure above atmospheric pressure and by withdrawing gas comprising chlorine and evaporated gaseous VCl.sub.4 from a head space above the reaction mixture, cooling and hence condensing the gas in the reflux condenser 20 and returning VCl.sub.4 condensate, which may include dissolved chlorine, to the reaction mixture in the reactor 12. A small bleed is taken from the reflux condenser 20 by means of the bleed line 26 to prevent accumulation of inert gas at the top of the condenser, in particular N.sub.2 which may be present in the process 10 when starting up the process.

[0062] By means of the returned condensate, the temperature of the reaction mixture in the reactor 12 is controlled or at least reduced, whereas the chlorine feed is used to control the reaction pressure. If necessary or desirable, the reactor 12 can employ additional cooling means, such as cooling coils or the jacket 13 and a cooling utility such as cooling water to control the reaction temperature.

[0063] Once the reaction has progressed to convert substantially all of the vanadium in the starting material to liquid VCl.sub.4, the reaction mixture is withdrawn by means of the reaction mixture withdrawal line 28, cooled in the cooler 30 and filtered in the filter 32 to produce liquid VCl.sub.4 as a product, which is then withdrawn by means of the product line 34, and a solids residue which is withdrawn by means of the residue line 36. The reactor 12 can be depressurised by means of the bleed line 26. The solids residue may include compounds such as FeCl.sub.2 or FeCl.sub.3 formed in the reaction mixture from ferrous substances present in the starting material, or impurities such as silicates and aluminates introduced into the reaction mixture as part of the oxygen-free vanadium compound starting material. The solids residue may also include VCl.sub.3, formed by decomposition of VCl.sub.4 in the reactor 12. The formation of VCl.sub.3 can be limited by maintaining a positive chlorine pressure in the reactor 12, by limiting the reaction temperature and by employing a liquid reaction medium in which VCl.sub.3 is less soluble than VCl.sub.4.

[0064] If desired or necessary, the process 10 includes distilling (not shown) the VCl.sub.4 product to purify or concentrate the VCl.sub.4.

[0065] Referring to FIG. 2 of the drawings, another embodiment of a process in accordance with the invention for the production of VCl.sub.4 is shown and generally indicated by reference numeral 100. The process 100 is similar to the process 10 and unless otherwise indicated, the same reference numerals used for the process 10 are used to indicate the same or similar process features in the process 100.

[0066] The process 100 differs from the process 10 in that the condenser 20 is not a reflux condenser but a partial condenser. The process 100 further includes a hot drum 102 and a product cooler 104, with a recycle blower 106 being provided in a chlorinating agent recycle line 108, from which the bleed line 26 splits off. The hot drum 102 is also provided with a product line 110, with the product cooler 104 being located in the product line 110.

[0067] A reaction mixture recycle line 112 returns from the filter 32 to the reactor 12 and is provided with a recycle pump 114.

[0068] In the process 100, vanadium, ferro vanadium and/or vanadium carbide is used as an oxygen-free vanadium compound starting material, whereas liquid TiCl.sub.4 and not liquid VCl.sub.4 is used as the liquid reaction medium. Chlorine gas is used as the chlorinating agent.

[0069] The reactor 12 is also operated on a batch basis but starts with a charge of recycled or re-used liquid TiCl.sub.4 as the liquid reaction medium. Suspended powdered vanadium, ferro vanadium and/or vanadium carbide as an oxygen-free vanadium compound starting material is charged into the reactor as hereinbefore described with reference to the process 10. Again, chlorine gas is used as the chlorinating agent.

[0070] The reactor 12 is operated at a reaction temperature of about 180 C. and a reaction pressure of about 8 bar (absolute). At these conditions, evaporation of produced VCl.sub.4 (and also TiCl.sub.4) from the reaction mixture is significant, even though the reaction mixture is prevented from boiling. Evaporated VCl.sub.4 and TiCl.sub.4 and also unreacted chlorine gas are withdrawn by means of the vapour withdrawal line 22 and partially condensed in the condenser 20. VCl.sub.4-containing condensate (which also includes TiCl.sub.4) and uncondensed gas (mostly chlorine) are separated in the hot drum 102 with the VCl.sub.4-containing condensate then being withdrawn by means of the product line 110, cooled in the product cooler 104 and delivered as a cooled liquid VCl.sub.4-containing product. Uncondensed chlorinating agent, i.e. chlorine gas is withdrawn from the hot drum 102 and recycled by means of the chlorinating agent recycle line 108 and the recycle blower 106 to the chlorinating agent line 18 for return to the reactor 12.

[0071] As in the case of the process 10, the bleed line 26 is used to release inert gas from the process, in particular N.sub.2 which may be present in process 100 when starting up the process.

[0072] If desired or necessary, the process 100 includes distilling (not shown) the VCl.sub.4-containing product to purify or concentrate the VCl.sub.4. Instead, the VCl.sub.4-containing product, which is an admixture of VCl.sub.4 and TiCl.sub.4, can be used directly to produce vanadium-containing Ti alloy.

[0073] Once the reaction has substantially progressed to completion, the reaction mixture is withdrawn from the reactor 12 by means of the reaction mixture withdrawal line 28, filtered to remove solids residue by means of the residue line 36, and returned to the reactor 12 by means of the reaction mixture recycle line 112 and the recycle pump 114 for use with the next batch of vanadium-containing starting material.

[0074] Thus, as will be appreciated, in the process of FIG. 2, although VCl.sub.4 is produced as liquid in the reaction mixture, the VCl.sub.4 is allowed to evaporate and is withdrawn from the reactor 12 as a gas, before being condensed and reproduced as a liquid product, which includes TiCl.sub.4.

[0075] FIG. 3 shows a further embodiment of a process in accordance with the invention for producing VCl.sub.4. The process is generally indicated by reference numeral 200 and again the same reference numerals as were used in FIGS. 1 and 2 are used in FIG. 3 to indicate the same or similar process features, unless otherwise indicated.

[0076] In the process of FIG. 3, vanadium nitride or vanadium carbonitride are used as the solid particulate oxygen-free vanadium compound starting material whereas recycled liquid TiCl.sub.4 is used as the liquid reaction medium and chlorine gas is used as the chlorinating agent.

[0077] The reactor 12 starts with a charge of recycled or re-used liquid TiCl.sub.4 as the liquid reaction medium. Suspended powdered vanadium nitride and/or vanadium carbonitride as a starting material is charged into the reactor as hereinbefore described with reference to the process 10. The reactor 12 is operated on a batch basis at a reaction temperature of about 180 C. and a reaction pressure of about 8 bar (absolute).

[0078] As is the case with the process 100, operating conditions are selected such that significant quantities of TiCl.sub.4 and of the liquid VCl.sub.4 produced in the reaction mixture as a result of the chlorination of the oxygen-free vanadium compound starting material by the chlorine gas are allowed to evaporate and are withdrawn by means of the vapour withdrawal line 22. The withdrawn vapour is then however subjected to a product recovery stage 202 in which liquid VCl.sub.4 and liquid TiCl.sub.4 are separated from other components withdrawn by means of the vapour withdrawal line 22 and then produced as a liquid VCl.sub.4-containing product (which also includes TiCl.sub.4) withdrawn by means of the product line 110. The recovery stage 202 consists essentially of a condenser cooler and cold liquid collection drum.

[0079] Gaseous components are withdrawn from the product recovery stage 202 by means of a transfer line 203 and are fed into a Cl.sub.2 separation stage 204 where Cl.sub.2 is separated from other gases, in particular nitrogen which is produced as a by-product when chlorinating vanadium nitride or vanadium carbo-nitride and returned by means of the chlorinating agent recycle line 108 to the chlorinating agent line 18 and hence to the reactor 12. Gaseous by-products such as N.sub.2 are withdrawn from the Cl.sub.2 separation stage 204 by means of an off-gas line 206. The Cl.sub.2 separation stage 204 may consist of a VCl.sub.4 and TiCl.sub.4 scrubbing column or columns followed by a refrigeration unit to condense and separate the bulk of unreacted chlorine from the nitrogen before recycling the chlorine to the reactor 12.

[0080] As is the case with the process 100, in the process 200 the reaction mixture, once the reaction has progressed to completion, is withdrawn by means of the reaction mixture withdrawal line 28, separated in the filter 32 to remove solids residue from the reaction mixture, and returned to the reactor 12 by means of the reaction mixture recycle line 112 and the recycle pump 114 for use with the next batch of oxygen-free vanadium-containing starting material.

[0081] The process of the invention, as illustrated, advantageously employs relatively low reaction temperatures, allows good control of the highly exothermic chlorinating reaction(s) as the reaction(s) take(s) place in a liquid reaction medium, and has the potential to provide high yields as VCl.sub.4 can be produced directly as a liquid rather than as a gas. The reaction mixture is easy to handle in a reactor, whether on a batch or continuous basis, and the process promises a reduction in chlorine losses and waste chlorine treatment compared to processes in which a liquid reaction medium is not employed. As it is possible to select a liquid reaction medium in which VCl.sub.3 has a lower solubility than VCl.sub.4, decomposition of VCl.sub.4 to VCl.sub.3 during the process of the invention, as illustrated, is advantageously inhibited.