Patent Application
20180134575
THIS INVENTION relates to production of VCl4. In particular, the invention relates to a process for the production of VCl4.
About 50% of the world market for titanium is for alloyed titanium. About 80% of the alloy market is for Ti6Al4V (Grade 5 alloy, i.e. an alloy containing 6% Al and 4% V). This can be produced using the blended elemental approach by mixing commercially pure grade Ti powder with AlV master alloy powder. However, the aluminium vanadium master alloy powder is expensive, products produced via the blended elemental approach have lower fatigue properties than products produced from pre-alloyed powder, the diffusion of V into Ti is retarded by Al and long sintering times are required. It is therefore desirable to produce pre-alloyed Ti powder containing vanadium. However, in 2015, the market for titanium vanadium powders such as pre-alloyed Ti6Al4V powder was very small due to the high cost of such powders. A large growth in the market is expected if such powders can be produced at a lower cost.
Pre-alloyed Ti powder containing V can in principle be produced by premixing TiCl4 and VCl4 (and AlCl3 if desired) and then reducing the mixture together. However, the problem with this approach is that VCl4 is a specialty product used as a catalyst for ethylene and propylene polymerization and the world market for it is extremely limited (in 2015 the world market for it was believed to be in the order of 150 tons per annum). Obtaining sufficient quantities of VCl4 for a commercial scale Ti6Al4V plant (say 10000 tons per annum) would thus be difficult. In addition, VCl4 is unstable and slowly decomposes to VCl3 and Cl2.
There is thus a need for a process for the production of VCl4 in increased quantities that is commercially viable. It would be an advantage if such a process could produce oxygen-free VCl4. It would also be an advantage if such a process has the potential to produce an admixture of VCl4 and TiCl4.
U.S. Pat. No. 6,423,291 describes a process for the production of TiCl4 by chlorinating titanium values suspended in an inert liquid. VCl4 is not mentioned as a product that can be produced in a similar way by the chlorination of suitable reagents.
U.S. Pat. No. 3,407,031 describes a process for the manufacture of chlorides of vanadium by chlorinating a mixture of a ferro-alloy, a carbide and a hard metal of vanadium with sodium chloride or chlorine or ferric chloride using NaFeCl4 as a high temperature liquid medium under atmospheric pressure.
US 20110182787 describes a method for producing TiCl4 by using a low grade titanium material capable of continuous industrialized production. The method is characterized in that the low grade titanium material containing a certain proportion of titanium carbide is caused directly to react with chlorine at 600-700° C. to produce the titanium tetrachloride. VCl4 is not mentioned and the chlorination process occurs in the gas phase.
According to the invention, there is provided a process for the production of VCl4, the process including
By “oxygen-free vanadium compound starting material” is meant a starting material consisting essentially of a vanadium compound which does not include oxygen in its molecular or crystal structure, in contrast to a vanadium compound which does include oxygen in its molecular or crystal structure, such as VOCl3 or V2O5. It is however not intended that the oxygen-free vanadium compound starting material must necessarily be entirely free of oxygen-containing materials or impurities. Although it is desirable to prevent oxygen ingress into the reaction environment, it will in practice in a commercial production facility be difficult, if not impossible, to ensure that the oxygen-free vanadium compound starting material does not include any compounds with oxygen.
As will be appreciated, with the reaction pressure being higher than the vapour pressure of the liquid reaction medium at the reaction temperature of the process, the liquid reaction medium is prevented from boiling, even at the commencement of the reaction of the oxygen-free vanadium compound starting material suspended in the liquid reaction medium with the chlorinating agent, i.e. even before the composition of the reaction mixture has changed significantly as a result of the production of liquid VCl4. In fact, the reaction pressure is selected to be sufficiently high so that the reaction mixture, made up typically predominantly of the liquid reaction medium but including suspended solids material and eventually also produced liquid VCl4, is prevented from boiling.
The oxygen-free vanadium compound starting material may be in a finely divided solid form, with a particle size that may be less than 3000 μm, preferably less than 100 μm, the starting material having an average particle size that may thus be in the range of 1-3000 μm, preferably 50-100 μm. The process may accordingly include, as a preliminary step, size reduction of a solid oxygen-free vanadium compound starting material, for example by milling, to achieve the above maximum and average particle sizes.
The reaction mixture may thus be in the form of a slurry comprising at least the liquid reaction medium and suspended particulate oxygen-free vanadium compound starting material, for example a slurry in which the suspended particles form 2-50% by volume, preferably 10-30% by volume.
The oxygen-free vanadium compound starting material may be selected from the group consisting of vanadium nitride, vanadium carbide, vanadium carbonitride, vanadium silicide, ferro vanadium, and mixtures of two or more thereof.
Preferably, the oxygen-free vanadium compound starting material is vanadium nitride or ferro vanadium.
By “liquid reaction medium” is meant a liquid which reacts unacceptably neither with the solid particulate oxygen-free vanadium compound starting material nor with any chlorinating agent (Le. a reductant) in the reaction mixture at the reaction temperature and the reaction pressure. The liquid reaction medium may thus be a fully chlorinated liquid, which is not prone to being further chlorinated. In some embodiments of the invention, the liquid reaction medium is an inert liquid.
The liquid reaction medium may be selected from the group consisting of liquid VCl4, liquid TiCl4 and mixtures thereof. VCl4 is a bright red liquid with a normal boiling point of 154° C., whereas TiCl4 is a light yellow coloured liquid with a normal boiling point of 136.4° C.
In principle, also CCl4 may be used as liquid reaction medium. CCl4 is also a colourless liquid but has a normal boiling point of 76.7° C. For a variety of reasons, including that it is also a chlorinating agent and that it has a relatively low normal boiling point, thus requiring a rather high reaction pressure to prevent it from boiling, the inventors however do not believe that CCl4 will be practical in a commercial operation to produce VCl4.
The chlorination reaction to produce VCl4 is normally done at a temperature higher than the boiling points of the mentioned liquids, e.g. more than 140° C., or more than 160° C. preferably more than 170° C. and the process must therefore be operated at a pressure above atmospheric pressure to prevent boiling of the reaction mixture and hence complete evaporation of the liquid used as reaction medium. More specifically, if the operating temperature is 180° C., the pressure has to be higher than about 2.7 bar (absolute) and 1.9 bar (absolute) respectively when using TiCl4 or VCl4 as the liquid reaction medium.
Furthermore, the partial pressure of Cl2 in the reactor has to be high enough to ensure that little or no solid VCl3 is formed. This depends on the reactor operating temperature, the liquid reaction medium used and the concentration of VCl4 dissolved in the liquid reaction medium, but in the case when VCl4 is used as liquid reaction medium, the operating pressure has to be higher than about 6 bar (absolute) at minimum operating pressure conditions and higher than about 6.8 bar (absolute) at extremities of the more preferred reaction temperature range given below. As the temperature is increased the decomposition of liquid VCl4 to solid VCl3 and gaseous chlorine becomes less favourable, but the vapour pressure of VCl4 increases. As a result, there is a minimum in the required operating pressure as the temperature is increased.
Preferably, the reaction temperature is no more than about 300° C., more preferably no more than about 220° C., e.g. between about 170° C. and about 220° C.
The reaction pressure may be at least about 2 bar (absolute), or at least about 3 bar (absolute), preferably at least about 4 bar (absolute), more preferably at least about 6 bar (absolute), e.g. about 7 bar (absolute). As indicated hereinbefore however, the reaction pressure selected will be dependent, inter alia, on the liquid reaction medium chosen and the concentration of produced VCl4 in the liquid reaction medium. For example, when using TiCl4 as liquid reaction medium and the concentration of VCl4 dissolved in the TiCl4 is kept low, i.e. in the order of 5 mol %, a reaction pressure of 2 bar (absolute) would from a thermodynamic point of view be sufficient.
In one embodiment of the invention, the reaction temperature is no more than 300° C. but at least 170° C. and the reaction pressure is at least 3 bar (absolute).
In a further embodiment of the invention, the reaction temperature is no more than 220° C. and the oxygen-free vanadium compound starting material is vanadium nitride or ferro vanadium.
Typically, the reaction mixture comprising the liquid reaction medium will include at least some of the VCl4 produced. In other words, the VCl4 produced is in liquid form and is typically admixed with the liquid reaction medium to form part of the reaction mixture, although, as will be appreciated, at least some of the VCl4 produced may evaporate from the reaction mixture, with the extent of the evaporation depending on factors such as the reaction temperature, reaction pressure and concentration of VCl4 in the reaction mixture. In any event, regardless of composition, the reaction mixture is prevented from boiling by selecting a suitable reaction temperature and a suitable reaction pressure elevated above atmospheric pressure.
The chlorinating agent may be chlorine or a suitable chlorine-containing compound, such as a chlorine-containing liquid or a chlorine-containing gas.
The chlorinating agent may be selected from the group consisting of HCl, CCl4, SCl2, Cl2 and mixtures of two or more thereof.
The chlorinating agent may thus be a liquid, e.g. SCl2, or the chlorinating agent may be a gas, e.g. HCl or molecular chlorine gas, i.e. Cl2.
The chlorinating agent may be dispersed in the liquid reaction medium by dissolving it and/or dispersing or sparging globules or bubbles thereof in the liquid, conveniently under stirred and preferably turbulent conditions, to promote thorough mixing of the reaction mixture and contact between its reactive constituents, particularly between the solid particulate oxygen-free vanadium compound starting material and the chlorinating agent. In other words, the chlorinating agent may be dispersed as a disperse phase in the liquid reaction medium which forms a continuous phase, the liquid reaction medium being agitated to promote dispersion of the chlorinating agent therein; and the agitation may be such as to produce turbulent conditions in the liquid reaction medium to promote maintenance of a homogeneous reaction mixture and rapid reaction between the solid particulate oxygen-free vanadium compound starting material and the chlorinating agent.
Advantageously, the process of the invention 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 VCl4 can be produced directly as a liquid rather than as a gas. The eventual reaction mixture, i.e. typically the chlorinated liquid reaction medium in admixture with VCl4 produced and suspended unreacted solid particulate oxygen-free vanadium compound starting material, any solids residue, any chlorinating agent taken up by the liquid reaction medium and any by-products taken up by the liquid reaction medium, is easy to handle in a reactor, whether on a batch basis or on a 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. Importantly, when using a different liquid reaction medium than VCl4 (for example liquid TiCl4 or a mixture of liquid VCl4 and liquid TiCl4), VCl3 may have a lower solubility in the liquid reaction medium than VCl4 thus inhibiting decomposition of dissolved VCl4 to VCl3 during the process. Thus, in one embodiment of the invention, the liquid reaction medium is a liquid other than VCl4, with VCl3 and/or VCl2 having a lower solubility in said liquid reaction medium than VCl4.
The process may be conducted in a reactor on a batch basis, i.e. batch wise. Instead, the process may be conducted in a reactor on a continuous basis.
A feature of the process, whether conducted batch wise or on a continuous basis is that, at the relatively low reaction temperatures mentioned hereinbefore, impurities such as silicates and aluminates are not chlorinated to any significant extent. Furthermore, any metallic iron will tend to be chlorinated to either ferrous chloride or ferric chloride, i.e. FeCl2 or FeCl3, which have relatively low vapour pressures at the reaction temperatures mentioned hereinbefore, particularly if the reaction temperature is below 290° C. Relatively little FeCl2 and FeCl3 will thus issue from the reaction mixture as vapour with evaporated VCl4 product, and the bulk thereof will remain dissolved in the reaction mixture where it forms a saturated solution, or will form a solid constituent attached to solids in the reaction mixture or slurry, issuing from the reactor as part of the solids residue, on which it can form a passivating layer.
The process may thus include withdrawing reaction mixture, which may include solids residue, from the reactor.
The process may include subjecting the reaction mixture to a separation operation. Thus, the process may include separating liquid VCl4 from solids residue, e.g. by filtration. Advantageously, when the liquid reaction medium is VCl4, no separation of liquid reaction medium and VCl4 produced is required to produce a VCl4 product.
The process may include recycling or pumping around the liquid reaction medium.
As mentioned hereinbefore, depending on factors such as the reaction temperature and the reaction pressure, a significant portion of the liquid VCl4 formed in the reaction mixture may evaporate. The process may thus include condensing gaseous VCl4 to provide condensed VCl4.
The process may include returning condensed VCl4 to the reaction mixture or to the reactor, i.e. to the reaction mixture.
Instead, condensed VCl4 may be withdrawn from the reactor or process as a liquid VCl4 product. In one embodiment of the invention, the liquid reaction medium is liquid TiCl4 and the liquid VCl4 that is produced is withdrawn as a liquid admixture of liquid VCl4 and liquid TiCl4.
Chlorine has a boiling point much lower than that of VCl4 so that typically gaseous chlorine withdrawn from above the reaction mixture together with evaporated VCl4 is not condensed with the VCl4. The process may include recycling uncondensed chlorine to the liquid reaction medium, i.e. to the reaction mixture for reacting with the suspended solid particulate oxygen-free vanadium compound.
In one embodiment of the invention, the process thus includes withdrawing gaseous chlorinating agent from above the reaction mixture together with evaporated VCl4, cooling the gaseous chlorinating agent during the condensing of the gaseous VCl4 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.
The process may include purifying the VCl4 produced. Purifying the VCl4 produced may include subjecting the VCl4 produced to a fractional distillation operation.
The process typically includes maintaining a positive Cl2 pressure above the reaction mixture to limit co-production of undesirable by-products such as VCl3 and VCl2. Advantageously, VCl3 and VCl2 also have a lower solubility in the non-vanadium containing liquid reaction media mentioned hereinbefore (i.e. liquid TiCl4) than VCl4 thereby further limiting co-production of VCl3 and VCl2 in the reaction mixture.
When the process is carried out batch wise, in one embodiment of the process of the invention, it may be carried out in a reactor such as a temperature-controlled pressure vessel which is stirred or otherwise agitated, the pressure vessel containing a charge of liquid reaction medium and a charge of milled oxygen-free vanadium compound starting material, such as vanadium or vanadium carbide, together forming a reaction mixture or slurry. The slurry may be heated to a desired reaction temperature, with a chlorinating agent as hereinbefore described, e.g. molecular chlorine liquid or gas then being admitted to the pressure vessel until a desired reaction pressure is reached. The chlorine will act strongly exothermically with vanadium values in the oxygen-free vanadium compound starting material, to produce VCl4. The reaction mixture or slurry in the vessel is prevented from boiling by maintaining a sufficiently high reaction pressure, with any VCl4-containing vapour emanating from the reaction mixture being condensed in a reflux condenser and returned to the reaction mixture to prevent the temperature and pressure in the vessel from exceeding the desired reaction temperature and desired reaction pressure respectively. The reaction mixture is eventually withdrawn from the reactor, cooled and separated to produce a liquid VCl4 product and a solids residue.
When the process is carried out batch wise, in another embodiment of the process of the invention, it may be carried out in a reactor such as a temperature-controlled pressure vessel which is stirred or otherwise agitated, the pressure vessel containing a charge of liquid reaction medium and a charge of milled oxygen-free vanadium compound starting material, such as vanadium, ferro vanadium or vanadium carbide, together forming a reaction mixture or slurry. The slurry may be heated to a desired reaction temperature, with a chlorinating agent as hereinbefore described, e.g. molecular chlorine liquid or gas then being admitted to the pressure vessel until a desired reaction pressure is reached. The chlorine will act strongly exothermically with vanadium values in the oxygen-free vanadium compound starting material, to produce VCl4. The reaction mixture or slurry in the vessel is prevented from boiling by maintaining a sufficiently high reaction pressure, with any VCl4-containing vapour emanating from the reaction mixture being condensed in a condenser with uncondensed, cooled chlorinating agent being recycled to the reaction mixture and condensed VCl4 being withdrawn as a liquid VCl4 product, with the cooled, recycled chlorinating agent and withdrawal of the condensed VCl4 product serving to prevent the temperature and pressure in the vessel from exceeding the desired reaction temperature and desired reaction pressure respectively. The reaction mixture is eventually filtered to remove any solids residue and returned to the reactor for a subsequent batch operation.
When the process is carried out batch wise, in yet another embodiment of the process of the invention, it may be carried out in a reactor such as a temperature-controlled pressure vessel which is stirred or otherwise agitated, the pressure vessel containing a charge of liquid reaction medium and a charge of milled oxygen-free vanadium compound starting material, such as vanadium nitride or vanadium carbonitride, together forming a reaction mixture or slurry. The slurry may be heated to a desired reaction temperature, with a chlorinating agent as hereinbefore described, e.g. molecular chlorine liquid or gas then being admitted to the pressure vessel until a desired reaction pressure is reached. The chlorine will act strongly exothermically with vanadium values in the oxygen-free vanadium compound starting material, to produce VCl4. The reaction mixture or slurry in the vessel is prevented from boiling by maintaining a sufficiently high reaction pressure, with VCl4-containing vapour emanating from the reaction mixture being subjected to a product recovery stage to recover VCl4 product. Gaseous chlorinating agent withdrawn from a head space above the slurry with the gaseous VCl4 is subjected to a chlorine separation stage, after having passed through the product recovery stage, to separate chlorine from any off-gas, and the gaseous chlorine is recycled to the reaction mixture, with the cooled, recycled chlorinating agent and withdrawal of the separated liquid VCl4 product serving to prevent the temperature and pressure in the vessel from exceeding the desired reaction temperature and desired reaction pressure respectively. The reaction mixture is eventually filtered to remove any solids residue and returned to the reactor for a subsequent batch operation.
As will be appreciated, although VCl4 is produced directly as a liquid in the liquid reaction medium, typically as a result of a solids-gas reaction in the liquid reaction medium, any vented VCl4 withdrawn from a head space above the slurry can be regarded as product and can be condensed and separated from other constituents of the vented vapour, such as chlorine gas and other gases or vapours, the chlorine optionally being recovered for subsequent use in chlorinating another batch of starting material. Solid residues will remain in the pressure vessel or reactor, typically suspended in the liquid reaction medium. The aforesaid batch reaction cycle can then be repeated, by loading a fresh charge of oxygen-free vanadium compound starting material into the vessel and chlorinating it as set forth above. Accumulated solid residues can be cleared periodically from the vessel, and the charge of liquid reaction medium can be discarded and replaced, if and when it becomes unacceptably contaminated by dissolved or suspended impurities.
When the process is carried out continuously, in a further embodiment of the process of the invention, a solid particulate oxygen-free vanadium compound starting material, milled to a desired maximum particle size and with a desired average particle size, is mixed with a liquid reaction medium such as TiCl4 to form a slurry in which the solid material forms say 10-30% by volume. The slurry may then be heated to a temperature preferably of at least 170° C. as for batch operation and transferred, e.g. by pumping, as a slurry feed to a suitable reactor operating preferably at at least 170° C. such as a temperature-controlled pressure vessel which is agitated, for example an upflow slurry bubble-column reactor which may be fitted with baffles to resist back mixing and to the bottom of which liquid or gaseous molecular chlorine is introduced as chlorinating agent, e.g. via a sparger. As is the case with batchwise operation, the introduced chlorine reacts with vanadium values, in strongly exothermic fashion, to produce VCl4 in the slurry as a liquid. The reaction mixture or slurry in the vessel is prevented from boiling by maintaining a sufficiently high reaction pressure, with any VCl4-containing vapour emanating from the reaction mixture being condensed in a reflux condenser and returned to the reaction mixture (e.g. directly into the slurry feed, directly into the reactor or indirectly via a mixing step where the slurry feed is formed) to prevent the temperature and pressure in the vessel from exceeding the desired reaction temperature and desired reaction pressure respectively. Instead, the reaction mixture or slurry in the vessel is prevented from boiling by maintaining a sufficiently high reaction pressure, with any VCl4-containing vapour emanating from the reaction mixture being condensed in a condenser with uncondensed, cooled chlorinating agent being recycled to the reaction mixture and condensed VCl4 being withdrawn as a liquid VCl4 product, with the cooled, recycled chlorinating agent and withdrawal of the condensed VCl4 product serving to prevent the temperature and pressure in the vessel from exceeding the desired reaction temperature and desired reaction pressure respectively. In yet a further possible embodiment, the reaction mixture or slurry in the vessel is prevented from boiling by maintaining a sufficiently high reaction pressure, with VCl4-containing vapour emanating from the reaction mixture being subjected to a product recovery stage to recover VCl4 product. Gaseous chlorinating agent withdrawn from a head space above the slurry with the gaseous VCl4 is subjected to a chlorine separation stage, after having passed through the product recovery stage, to separate chlorine from off-gas, and the gaseous chlorine is recycled to the reaction mixture, with the cooled, recycled chlorinating agent and withdrawal of the separated VCl4 product serving to prevent the temperature and pressure in the vessel from exceeding the desired reaction temperature and desired reaction pressure respectively. The liquid reaction medium (if a substance other than VCl4 is used therefor) may be condensed and recycled to the reactor. Non-condensable gases from this partial condensation may, after extraction of any residual VCl4 or chlorine gas therefrom, be discarded as off-gas, the extracted VCl4 and chlorine optionally being recycled to the reactor.
Spent slurry withdrawn from the top of the reactor may have the VCl4 contained therein recovered, e.g. by filtration, the filtrate being VCl4 which may be recycled to the initial slurry-forming mixing step, or to the slurry formed in the initial mixing step. Filter cake from the filtration step may then be dried, dried filter cake being subjected to waste treatment, e.g. to recover or neutralize salts such as FeCl2 or FeCl3 therein, before being discarded, and VCl4 from the drying may be recovered and recycled together with the recycled filtrate.
When the chlorinating agent is fed into the reaction mixture, the rate of feeding of the chlorinating agent may be manipulated to control the reaction pressure.
The invention extends to VCl4 produced in accordance with the process of the invention.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which
Referring to
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.
The process 10 is typically conducted on a batch basis. The reactor 10 is thus loaded with a quantity of liquid VCl4 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 VCl4 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 VCl4 by using the stirrer 14. Alternatively, the powdered vanadium or vanadium carbide starting material can be suspended in the liquid VCl4 to form a slurry, with the slurry then being fed into the reactor 12 by means of the feed line 16.
Typically, the powdered vanadium or vanadium carbide starting material has a particle size of about 50-100 μm 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 V2O5, which includes oxygen in its molecular or crystal structure.
The slurry of liquid VCl4 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.
The vanadium in the oxygen-free vanadium compound starting material suspended in the liquid reaction medium (liquid VCl4) is thus chlorinated to produce more liquid VCl4 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 VCl4 from a head space above the reaction mixture, cooling and hence condensing the gas in the reflux condenser 20 and returning VCl4 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 N2 which may be present in the process 10 when starting up the process.
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.
Once the reaction has progressed to convert substantially all of the vanadium in the starting material to liquid VCl4, 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 VCl4 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 FeCl2 or FeCl3 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 VCl3, formed by decomposition of VCl4 in the reactor 12. The formation of VCl3 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 VCl3 is less soluble than VCl4.
If desired or necessary, the process 10 includes distilling (not shown) the VCl4 product to purify or concentrate the VCl4.
Referring to
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.
A reaction mixture recycle line 112 returns from the filter 32 to the reactor 12 and is provided with a recycle pump 114.
In the process 100, vanadium, ferro vanadium and/or vanadium carbide is used as an oxygen-free vanadium compound starting material, whereas liquid TiCl4 and not liquid VCl4 is used as the liquid reaction medium. Chlorine gas is used as the chlorinating agent.
The reactor 12 is also operated on a batch basis but starts with a charge of recycled or re-used liquid TiCl4 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.
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 VCl4 (and also TiCl4) from the reaction mixture is significant, even though the reaction mixture is prevented from boiling. Evaporated VCl4 and TiCl4 and also unreacted chlorine gas are withdrawn by means of the vapour withdrawal line 22 and partially condensed in the condenser 20. VCl4-containing condensate (which also includes TiCl4) and uncondensed gas (mostly chlorine) are separated in the hot drum 102 with the VCl4-containing condensate then being withdrawn by means of the product line 110, cooled in the product cooler 104 and delivered as a cooled liquid VCl4-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.
As in the case of the process 10, the bleed line 26 is used to release inert gas from the process, in particular N2 which may be present in process 100 when starting up the process.
If desired or necessary, the process 100 includes distilling (not shown) the VCl4-containing product to purify or concentrate the VCl4. Instead, the VCl4-containing product, which is an admixture of VCl4 and TiCl4, can be used directly to produce vanadium-containing Ti alloy.
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.
Thus, as will be appreciated, in the process of
In the process of
The reactor 12 starts with a charge of recycled or re-used liquid TiCl4 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).
As is the case with the process 100, operating conditions are selected such that significant quantities of TiCl4 and of the liquid VCl4 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 VCl4 and liquid TiCl4 are separated from other components withdrawn by means of the vapour withdrawal line 22 and then produced as a liquid VCl4-containing product (which also includes TiCl4) withdrawn by means of the product line 110. The recovery stage 202 consists essentially of a condenser cooler and cold liquid collection drum.
Gaseous components are withdrawn from the product recovery stage 202 by means of a transfer line 203 and are fed into a Cl2 separation stage 204 where Cl2 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 N2 are withdrawn from the Cl2 separation stage 204 by means of an off-gas line 206. The Cl2 separation stage 204 may consist of a VCl4 and TiCl4 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.
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.
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 VCl4 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 VCl3 has a lower solubility than VCl4, decomposition of VCl4 to VCl3 during the process of the invention, as illustrated, is advantageously inhibited.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015/03774 | May 2015 | ZA | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2016/052741 | 5/12/2016 | WO | 00 |
