Abstract:
The present disclosure relates to reacting tin metal or SnCl 2  with crude TiCl 4  containing vanadium to produce pure TiCl 4 , SnCl 4 , and a vanadium solid co-product. The reaction is preferably done in a continuous fashion in two stages for maximum through-put and utility at an elevated temperature. Distillation can be used to purify the TiCl 4  produced and simultaneously yield a purified SnCl 4  product. The synthesis of SnCl 4  in this method utilizes waste chloride to save virgin chlorine which would otherwise be used.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No.  61 / 445 , 792 , filed Feb.  23 ,  2011 , which is incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a process for purifying TiCl 4  produced via a chloride process. 
       BACKGROUND OF THE INVENTION 
       [0003]    Pigmentary TiO 2  is commercially produced through the sulfate or the chloride process. The chloride process is also used to produce TiCl 4  for titanium metal production. In the chloride process, titanoferrous ore is carbochlorinated to produce TiCl 4  and a range of other metal chlorides from the ore impurities. The crude TiCl 4  produced in the carbochlorination is processed with a series of physical separation steps to produce a usable TiCl 4  product. One contaminating element found in titanoferrous ore is vanadium. The vanadium chlorination products, VOCl 3  or VCl 4 , have boiling points close to that of TiCl 4 , making removal more problematic. 
         [0004]    Removal of vanadium from crude TiCl 4  is thus one of the critical manufacturing steps in producing pure TiCl 4  for use in TiO 2  manufacture or any other use such as titanium metal manufacture. This process must be done keeping in mind the purity requirements of the pure TiCl 4  as well as the characteristics of the other materials made in the vanadium removal step. The disposition of the resulting vanadium stream has long had multiple technical issues including the processing difficulties of the stream, titanium yield loss, and limitations of use for this stream for other commercial products. 
         [0005]    One typical vanadium removal process uses an organic based treating agent, such as a fatty acid or a mineral oil, to remove the vanadium present in the crude TiCl 4 . In this purification method, the crude TiCl 4  is reacted in the liquid state with the organic liquid or melted solid, typically at elevated temperature. The liquid vanadium chlorides mixed in the TiCl 4  are converted to a solid form of vanadium, mixed with a solid organic matrix. The “vanadium-sludge” solid is then removed from the liquid TiCl 4 . 
         [0006]    The disadvantages to organic treatment are numerous. For example, the vanadium-organic sludge produced is very sticky and can be difficult to dry. In the vanadium reaction area, these sticky solids continually build-up on the walls of the process equipment, requiring washing. This washing is potentially hazardous, an uptime detractor, an on-going maintenance cost, and a capital cost. 
         [0007]    Another disadvantage of the organic treatment is that, due to the sticky nature of the solids, they can detract from TiCl 4  yield through incomplete drying in the evaporation step. Further, the organic treating agents themselves can react directly with the TiCl 4  producing a direct yield loss in this reaction. Additionally, the vanadium solids have some inherent hazards. The organic contamination in the vanadium sludge also makes it very difficult and hazardous to process the vanadium into a form that could be used in a commercial process, such as steel manufacture. Further, the practice of mixing the vanadium sludge with an iron chloride stream for drying has some side products that are undesirable. Finally, the reaction of the organic liquid and vanadium produces light organic fragments that contaminate the pure TiCl 4 . These light organic fragments can make the resulting pure TiCl 4  unsuitable for use in titanium metal manufacture as well as some other, non-TiO 2  products. In TiO 2  manufacture, the organic fragments can cause process control issues. 
         [0008]    Another typical vanadium removal process uses copper metal to remove the vanadium from the crude TiCl 4 . In this process, the copper can be introduced as a powder. The vanadium in the crude TiCl 4  reacts on the surface of the copper metal to form a vanadium solid. The resulting pure TiCl 4  can then be separated from the solids by evaporation. Alternatively, the crude TiCl 4  is boiled through a column that is packed with copper rings. The vanadium in the vapor reacts with the surface of the copper metal ring and the TiCl 4  proceeds through the column. 
         [0009]    The disadvantages of the copper process are primarily cost and waste stream handling. Copper metal is very expensive compared to the organic treating agents. The waste stream from the copper reaction is difficult to handle. Copper chloride is formed in the process, which coats the surface of the copper rings and stops the reaction from being able to go to completion. The copper chloride must be removed by washing with water when large copper rings are used. Washing and drying the rings for re-use can be a hazardous process. Either way, the resulting vanadium stream is contaminated with copper chloride. The copper chloride must be separated before the vanadium solid would be suitable for commercial use. 
         [0010]    Thus, the problem to be solved is removal of vanadium from TiCl 4  produced via the chloride process in an economical, efficient, and safe manner. 
       SUMMARY OF THE INVENTION 
       [0011]    Applicants have solved the aforementioned problems by using tin metal or SnCl 2  to remove vanadium from crude TiCl 4  produced via the chloride process. 
         [0012]    One aspect is for a process for the purification of TiCl 4  comprising contacting vanadium-containing crude TiCl 4  with tin to produce purified TiCl 4 , SnCl 4 , and solid vanadium and separating the solid vanadium from the purified TiCl 4  and SnCl 4 . In some aspects, the contacting and separating steps are performed by a two stage process comprising reducing the vanadium content in the vanadium-containing crude TiCl 4  by contacting the vanadium-containing crude TiCl 4  with a less than excess amount of tin to produce partially purified TiCl 4 , SnCl 4 , and solid vanadium; separating the solid vanadium from the partially purified TiCl 4  and SnCl 4 ; further reducing the vanadium content in the partially purified TiCl 4  by contacting the partially purified TiCl 4  with an excess of tin to produce purified TiCl 4 , SnCl 4 , solid vanadium, and excess tin; and separating the solid vanadium and excess tin from the purified TiCl 4  and SnCl 4 . 
         [0013]    Another aspect is for a process for the purification of TiCl 4  comprising contacting vanadium-containing crude TiCl 4  with SnCl 2  to produce purified TiCl 4 , SnCl 4 , and solid vanadium and separating the solid vanadium from the purified TiCl 4  and SnCl 4 . In some aspects, the contacting and separating steps are performed by a two stage process comprising reducing the vanadium content in the vanadium-containing crude TiCl 4  by contacting the vanadium-containing crude TiCl 4  with a less than excess amount of SnCl 2  to produce partially purified TiCl 4 , SnCl 4 , and solid vanadium; separating the solid vanadium from the partially purified TiCl 4  and SnCl 4 ; further reducing the vanadium content in the partially purified TiCl 4  by contacting the partially purified TiCl 4  with an excess of SnCl 2  to produce purified TiCl 4 , SnCl 4 , solid vanadium, and excess SnCl 2 ; and separating the solid vanadium and excess SnCl 2  from the purified TiCl 4  and SnCl 4 . 
         [0014]    Other objects and advantages will become apparent to those skilled in the art upon reference to the detailed description that hereinafter follows. 
     
    
     DETAILED DESCRIPTION 
       [0015]    Applicants specifically incorporate the entire contents of all cited references in this disclosure. Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range. 
         [0016]    When tin metal or SnCl 2  is reacted with the vanadium in the crude TiCl 4  (i.e., titanium tetrachloride produced by a chloride process, which has been subjected to partial purification procedures to remove some metal chlorides), a solid vanadium product is produced along with SnCl 4 . This treatment process works with all ranges of vanadium seen in the variety of ores available with levels from 100 ppm V to 3000 ppm V but has not been seen to have any limitations either with lower or higher concentrations. SnCl 4  is a liquid, not a solid like copper chloride. As a result, the SnCl 4  does not contaminate the vanadium solid. Tin metal, being a milder reducing agent, also does not appear to react with TiCl 4 , unlike copper metal. As a result, a simple two stage reactor system can be used with tin powder or SnCl 2  with essentially no extra yield loss of TiCl 4  or tin through reaction with the purified TiCl 4 . By the term “purified TiCl 4 ” it is meant that the concentration of the vanadium in the TiCl 4  is at least significantly lowered if not reduced to a level below that which can be detected by known analytical techniques. The product TiCl 4  has vanadium removed to a level suitable for use in the production of TiO 2  or titanium metal. Additionally, vanadium can be lowered to an operator specified concentration. 
         [0017]    In the step of contacting the crude TiCl 4  with the tin material, the tin can be added to the TiCl 4  by any suitable addition or mixing method. The tin can be added as a fine powder using known engineering methods such as a star valve or screw feeder with appropriate consideration made for controlling TiCl 4  vapors back flowing into the system. When SnCl 2  is used, additional care must be taken to minimize moisture since SnCl 2  is hydroscopic. Mixing of the tin powder with the crude TiCl 4  may be done with agitation such as paddle mixer, sparging, or other engineering methods appropriate for the difficulties associated with handling TiCl 4 . In some embodiments, the amount of tin added to the crude TiCl 4  is an excess amount. For a given equipment size and temperature, the rate of the reaction will be adjusted by the amount of excess tin added. When a single stage configuration is used, excess amounts could be very high, such as 20 times excess. A two stage configuration allows less excess to be used in the final stage, and lower amounts such as eight times excess can be used. The excess used in the final stage is also utilized later in the first stage. 
         [0018]    SnCl 4  can be separated from the resulting pure TiCl 4  through, for example, distillation. SnCl 4  is a valuable product used as a catalyst and the starting material for the production of organometallic tin compounds that are used in a wide variety of applications. So, in this process, two valuable co-products are produced and many other technical problems are eliminated. 
         [0019]    First, a solid vanadium product is produced that is more suitable to become a feedstock into other processes such as the production of steel. The residual solid is not contaminated with treating agent such as copper chloride or organic residue that must be separated. 
         [0020]    Second, the reaction between the vanadium and tin can be driven to complete utilization of the tin. With copper rings, the solid copper chloride blocks the reaction surface of the fresh copper and must be washed off with aqueous HCl. With tin, liquid SnCl 4  is produced that is removed from the surface allowing the reaction to continue with more vanadium. The production of a liquid also avoids the issues of purification of the vanadium product seen with both organic treating agents and copper. The solid vanadium from this process is a flowable, black powder. It is moisture sensitive and hydroscopic, but has no combustion hazard since no carbon is present. It is also not sticky like the organic treating agent-produced vanadium solids. Therefore, the fouling potential of this material is low, significantly reducing the engineering complications in production as well as improving the safety of the process through elimination of equipment fouling. 
         [0021]    Third, a valuable product is produced in the reaction instead of material with disposal issues. SnCl 4  is typically made through the reaction of tin metal and chlorine at elevated temperatures. In this reaction, instead of using virgin chlorine, the chloride ligand is obtained in the purification process. These chlorine ligands would be lost, for example through the copper chloride disposal in other systems. In this case, the chloride, an expensive and energy intensive reagent, is conserved instead of lost. 
         [0022]    Fourth, no opportunity for undesirable production of Persistent Bio-accumulative and Toxic (PBT) organic compounds exists because no carbon is introduced into the system. When organic treating agents are used, the combination of heat, chlorine and carbon can under some conditions produce PBTs such as chlorinated dioxins and furans. 
         [0023]    In some embodiments, the SnCl 4  is subsequently recovered from the TiCl 4 . This separation can be accomplished through, for example, distillation. All of the SnCl 4  does not need to be removed from the TiCl 4  for the TiCl 4  to be used for TiO 2  production. Most of the SnCl 4  could be recovered in this process and recycled to produce a more concentrated SnCl 4  stream. The concentration of SnCl 4  does not impact the rate of the vanadium removal step One example of the separation of TiCl 4  and SnCl 4  would involve two separate distillation columns. The first column would be fed the product from the vanadium removal stage to the upper portion of the column. TiCl 4  suitable for commercial use would be collected from the bottom of the first column. The purity requirements for TiCl 4  used for TiO 2  or titanium metal manufacture would determine the configuration of this column, typically set using Aspen modeling conditions or similar engineering principles. The stream collected from the top of the first column would provide the reflux flow to the first column and feed a second column. The second column would be used to produce a finished SnCl 4  product from the top of the column. The material from the bottom of the second column would be high in TiCl 4  and lower in SnCl 4 . The bottom material would be recycled to the tank used to provide the reflux to the first column. In this manner, no TiCl 4  would be lost while conserving energy. The size of the columns and number of trays would be related to the amount of vanadium present in the crude TiCl 4  since that will determine the amount of SnCl 4  present. SnCl 4  can also be present in crude TiCl 4  due to tin oxide in the ores. The SnCl 4  from the crude TiCl 4  will also be accounted for in the distillation. 
         [0024]    One embodiment is for crude TiCl 4  to be purified in two stages. In the first stage, the vanadium concentration is only partially reduced so that the tin metal or SnCl 2  reaction can be driven to completion. The solid vanadium product is separated from this stage and a liquid (or vapor) TiCl 4  stream containing vanadium is transferred to a second stage. This step preferably occurs at least at the boiling point of TiCl 4  (136° C.). More preferably, this step occurs under pressure at temperatures elevated above the boiling point of TiCl 4  (about 150° C. to about 200° C. range). The vanadium solids can be collected in a drying chamber, for example a drying chamber found after a purge separation (see, e.g., U.S. Pat. No. 7,368,096, incorporated herein by reference). Alternatively, they may be collected by other known engineering methods such as, for example, filtration. 
         [0025]    In the second stage, the vanadium is removed to the desired low levels and excess tin metal or SnCl 2  is present. The vanadium content can be controlled through a feedback loop measured by a UV/Vis or UV/Vis diode array instrument. The excess tin metal or SnCl 2  stream (containing some vanadium solid) is removed and can be sent to the first stage for further reaction. The TiCl 4 /SnCl 4  with no vanadium is then separated, in one embodiment in a distillation column. 
         [0026]    Distillation may be operated in different methods depending on the end use of the TiCl 4 . In one embodiment, the initial TiCl 4 /SnCl 4  mixture is sent to a rough distillation column where a stream containing low enough amounts of SnCl 4  in TiCl 4  is produced from the bottom of the column and a high SnCl 4  stream is produced from the top of the column. The bottom stream of TiCl 4  can be used to produce TiO 2 . The top stream can be sent to a polishing distillation column which is used to produce a pure SnCl 4  stream from the top and a rough TiCl 4 /SnCl 4  stream from the bottom. The bottom stream from this column can be recycled back to the start of the first distillation column. Through the use of multiple distillation columns, essentially no TiCl 4  yield loss occurs and both a TiCl 4  product and SnCl 4  product can be produced. A third distillation column (or batch operation of the second distillation column) can be used in some embodiments to produce a TiCl 4  product ideal for titanium metal production. The benefit of using elemental tin or SnCl 2  compared to organic treating agents is no organic residue is present in the TiCl 4 , which is highly detrimental to the titanium metal. 
         [0027]    The TiCl 4  product of the process described herein can be used in any application for which titanium tetrachloride is useful. The TiCl 4  can be used as a starting material for making titanium dioxide and derivatives thereof especially as a feedstream for the well-known chlorination and oxidation processes for making titanium dioxide. 
         [0028]    Titanium dioxide can be suitable for use as a pigment. The majority of TiO 2  produced is used for this property. Common applications are in paints, paper and plastics. The TiCl 4  produced in this process is suitable for use in production of TiO 2  for all of these applications. 
         [0029]    Titanium dioxide is useful in, for example, compounding; extrusion of sheets, films and shapes; pultrusion; coextrusion; ram extrusion; spinning; blown film; injection molding; insert molding; isostatic molding; compression molding; rotomolding; thermoforming; sputter coating; lamination; wire coating; calendaring; welding; powder coating; sintering; cosmetics; and catalysts. 
         [0030]    Alternatively, titanium dioxide can be in the nano-size range (average particle diameter less than 100 nm), which is usually translucent or transparent. TiO 2  of this particle size range is typically used for non-optical properties such as photo-protection. 
         [0031]    The TiCl 4  from this process is also suitable for use to produce titanium metal through any of the known commercial pathways such as the Kroll and Hunter processes. The TiCl 4  is also suitable for use in the production of titanium based catalysts such as organo-titanates or Ziegler-Natta type catalysts. 
       EXAMPLES 
       [0032]    The present invention is further defined in the following Examples. It should be understood that these Examples, while indicating preferred embodiments of the invention, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the preferred features of this invention, and without departing from the spirit and scope thereof, can make various changes and modification of the invention to adapt it to various uses and conditions. 
       Example 1 
       [0033]    Stock Soluntion and One Stage Removal with Elemental Sn 
         [0034]    A stock solution containing 3540 ppm V as VOCl 3  in TiCl 4  was prepared. A simple reaction flask was assembled containing a 250 mL round bottom flask, a magnetic stirrer, a heating mantle, and a powder addition funnel. For collection of the distillate, a simple Dean Stark trap was used with a large dry ice trap attached. A 100 mL aliquot of the bright yellow stock solution was added to the round bottom flask. After heating the solution to 100° C., 3.1 g of powdered elemental Sn (&lt;45 micron size, Aldrich, 98.8%) was added all together to the flask using the powder addition funnel. The mixture was refluxed together for 4 hours removing all of the yellow color from the distillate. The colorless TiCl 4  was then distilled from the solids and collected using the Dean Stark trap. After removal of the TiCl 4 , the solids were dried in situ with flowing N 2 . The overheads were measured to contain &lt;10 ppm V as well as containing 2700 ppm Sn present as SnCl 4 . 
       Example 2 
       [0035]    Crude TiCl 4  and Two Stage Removal with Elemental Sn 
         [0036]    A 100 mL aliquot of commercial crude TiCl 4  was added into a 250 mL reaction flask equipped with a magnetic stirrer, heating mantle, powder addition funnel and Dean Stark trap for condensate collection. The crude TiCl 4  contained a range of impurities including vanadium, iron and other elements including SnCl 4 . The dark yellow TiCl 4  was heated to 100° C. and mixed with 1.2 g of powdered elemental Sn. The TiCl 4  and Sn were refluxed together for 12 hours to ensure that an endpoint had been achieved. The distillate was still a strong yellow color indicating that only a portion of the vanadium was removed. Another 1.1 g of Sn was then added. The slurry was refluxed for 1 more hour. All of the color was removed from the distillate. The TiCl 4  was then distilled from the solids. The overheads were measured to contain &lt;1 ppm V. They also contained 2000 ppm of Sn which includes the SnCl 4  which was present in the crude TiCl 4 . 
       Example 3 
       [0037]    Stock Solution and Two Stage Removal with SnCl 2    
         [0038]    A stock solution containing 3700 ppm V as VOCl 3  in TiCl 4  was prepared. A reaction flask was assembled containing a 250 mL round bottom flask, a magnetic stirrer, a heating mantle, and a powder addition funnel. For collection of the distillate, a Dean Stark trap was used with a large dry ice trap attached. A 100 mL aliquot of the bright yellow stock solution was added to the round bottom flask. After heating to 100° C., 4.4 g of powdered SnCl 2  was added using the solids addition funnel. The mixture was refluxed together for 5 hours removing part of the yellow color from the distillate. Another 4.1 g of powdered SnCl 2  was added. The solution was refluxed for 5 hours more, followed by distilling the TiCl 4  from the solids. The overheads were measured to contain &lt;10 ppm V as well as containing 6100 ppm Sn present as SnCl 4 . 
       Example 4 
       [0039]    Stock Solution and One Stage Removal with Sn 
         [0040]    A 100 mL aliquot of purified TiCl 4  was added into a 250 mL reaction flask equipped with a magnetic stirrer, heating mantle, powder addition funnel and Dean Stark trap for condensate collection. An aliquot of 2.07 g of VCl 4  was added by syringe, creating a dark solution. Using the powder addition funnel, 1.33 g of powdered elemental Sn (&lt;45 micron size, Aldrich, 98.8%) was added at room temperature. The mixture was heated at reflux for 4 hours with all of the color being removed from the overheads. The liquid was distilled from the solids and measured to contain &lt;5 ppm V plus 2500 ppm Sn, present as SnCl 4 .