The current invention relates to improvements in the chloride process for manufacturing titanium dioxide. In particular, the current invention relates to methods and compositions for improving the operating efficiencies of the chloride process. The chloride process normally uses natural rutile ore. However, synthetic rutiles, usually made from ilmenite, and titanium-containing slags are also used in the chloride process. In this process, the titanium dioxide contained within these materials is chlorinated to form titanium tetrachloride. Following purification steps, the resulting tetrachloride is oxidized in the gaseous phase back to titanium dioxide. In the chlorination step, the ore and* coke are mixed in a fluidized bed reactor at temperatures of about 900° C and reacted with chlorine gas. The reaction produces gaseous titanium tetrachloride which is transferred to a condensing system after being scrubbed of unreacted solids and certain other impurities. The condensed tetrachloride is further purified by chemical treatment and distillation prior to being oxidized to titanium dioxide. Current systems commonly use ore and coke particles larger than about 225 μm in order to minimize the loss of raw material during the fluidization process. However, as the reaction progresses, attrition and the reaction process reduce the size of the raw materials. As a result, a substantial portion of the reactants are lost from the reactor as blow-over. Depending on the flow rate of gases through the reactor, blow-over losses typically begin as particle sizes drop below -140 U.S. Mesh, that is, below 100 μm. This physical characteristic of the chlorination step limits the available raw materials to those materials having particle sizes suitable for retention within the reactor for the time periods necessary to react at least a portion of the raw material. While at least a portion of the blow-over ore and coke may be recovered, the industry has yet to discover a satisfactory, cost efficient means of recycling the blow-over fines. For example, the recovered coke and titanium ore fines are typically smaller than lOOμm, with a significant portion of the recovered particles smaller than 44 μm (-325 U.S. Mesh). Particles of this size typically blow out of the reactor prior to reacting. Additionally, blow-over coke particles have been found to be generally non-reactive when returned to the fluidized bed reactor. Thus, blow-over particles require further processing in order to be usable in the chlorination process. Efforts have been made as a consequence to agglomerate and sinter blow-over ore. Unfortunately, these efforts have focused on the use of binders which adversely affect the chlorinator or do not retain their structure under reactor conditions. Inorganic binders such as bentonite, sodium silicate and other inorganic substances inherently contain elements or species that contribute to fouling of the fluidization bed. Organic binders such as coal tar are sufficient to agglomerate blow- over particles at room temperature; however, they tend to disintegrate upon introduction into the chlorinator releasing the blow-over fines prior to their reaction. Clearly the titanium dioxide industry requires improvements to the methods and compositions used in the chlorination process. The current invention seeks to overcome the problems currently experienced by the titanium dioxide industry by providing methods and compositions for recovering and using blow-over fines as reactants in the chlorination process. Additionally, the current invention provides methods and compositions which increase the available virgin raw materials for use in the chloride process for manufacturing titanium dioxide. In one aspect, the current invention provides novel feedstock compositions and methods for preparing the same for use in a titanium ore chlorinator. In a first embodiment, the method of the current invention comprises blending particles of titanium ore, particularly those of a size previously unsuitable for use in a fluidized bed chlorinator, with a binder. Thereafter the mixture is fed to a briquetter or other suitable device and formed into briquettes. Following drying, the resulting titanium ore composition has sufficient crush strength to permit use within a fluidized bed chlorinator. Typically, the crush strength is at least 13.6 kg. In another aspect, the method comprises blending petroleum coke particles, particularly those of a size or character previously unsuitable for use in a fluidized bed chlorinator, with a binder. Thereafter the mixture is fed to a briquetter or other suitable device and formed into briquettes. Following drying, the resulting coke briquettes display a sufficient crush strength to permit use within a fluidized bed chlorinator, typically at least 13.6 kg. In still another embodiment, the method comprises blending particles of the titanium ore and petroleum coke with a binder. Thereafter the mixture is fed to a briquetter and formed into briquettes. Following drying, the resulting ore/coke composition has sufficient crush strength to permit use within a fluidized bed chlorinator. Typically, the briquettes of the current invention have a crush strength of at least 13.6 kg. Still further, the current invention provides a method for preparing a feedstock composition for a fluidized bed chlorination reactor which comprises forming an initial mixture comprising such titanium ore, petroleum coke, binder and pigmentary titanium dioxide. Sufficient water is added to the initial mixture to yield a final mixture. The resulting final mixture is formed into briquettes by a briquetter or other suitable device. Following drying, the resulting briquettes have sufficient crush strength to permit use within a fluidized bed chlorination reactor. Normally, crush strengths of at least 13.6 kg will be sufficient for use in a fluidized bed chlorinator. In yet another aspect, the current invention provides a method for chlorinating titanium ore, including recovering titanium ore and/or petroleum coke lost as blow-over from a fluidized bed chlorinator. Essentially, the method comprises the steps of combining the recovered titanium ore, the recovered petroleum coke or both the recovered ore and coke with a binder, optionally with pigmentary titanium dioxide, fresh, unrecovered ore and/or coke, and forming the mixture into briquettes by application of pressure. The briquettes are dried and returned to the fluidized bed chlorinator. 1. Methods for Preparing Chlorinator Feedstocks As noted above, previous attempts to recover and recycle blow-over particles have met with limited success. Recovered titanium ore particles are of value in the chlorination process only if the recovered particles have sufficient size to permit conversion to titanium tetrachloride prior to blowing out of the reactor. Recovered coke particles have likewise had no value in the chlorination process, as they have previously been essentially non-reactive when returned to the chlorination reactor. In order to overcome the deficiencies of the prior art practices, the current invention provides methods for preparing chlorinator feedstocks from reactant particles typically considered too small for direct introduction to a fluidized bed reactor or which have otherwise been found unsuitable, for example, due to non-reactivity in the case of recycled coke blow-over. As used herein, the term "titanium ore" includes ihnenites, leucoxenes, natural and synthetic rutiles and TiO2- containing slags. As used herein, "pigmentary titanium dioxide" refers to titanium dioxide having particle sizes from 0.1 to 4 μm with a rutile or anatase crystalline structure. Prior attempts to agglomerate small reactant particles failed due to unsatisfactory binder materials. To overcome the problems encountered by prior art methods, the methods of the current invention utilize an organic binder material containing carbohydrates, fatty acids or a mixture of carbohydrates and fatty acids. The preferred carbohydrates are sugars, with the most preferred carbohydrate being dried molasses. Any available dried molasses is suitable for use in the current invention, including but not limited to cane molasses, beet molasses, citrus molasses, hemicellulose extract and starch molasses. The most preferred molasses is dried cane molasses. The preferred fatty acids are oils, such as but not limited to linseed oil. As used herein, the term "organic binder" refers to any organic binder capable of combining with the blow-over fines and forming a final mixture, with or without water, suitable for briquetting. In the methods of the current invention, chlorinator feedstocks are prepared by combining an organic binder as described in the preceding paragraph i) with titanium ore, ii) with petroleum coke, iii) with titanium ore and petroleum coke, iv) with titanium ore and pigmentary titanium dioxide, v) with petroleum coke and pigmentary titanium dioxide or vi) with titanium ore, petroleum coke and pigmentary titanium dioxide. While the methods of the current invention are particularly useful for recycling blow-over fines recovered from the fluidized bed reactor, the methods of the current invention will also permit use of raw materials previously unsuitable for use as reactants in the fluidized bed reactor. Thus, coke particles and titanium ore particles smaller than about 100 μm may now be used as reactants in fluidized bed reactors. The method of the current invention utilizes a briquetting device preferably capable of applying at least 3447 kPa (500 psi) to a mixture to be formed into a solid. More preferably, the briquetting device is capable of compressing the mixture at pressures of 5515 kPa (800 psi) to 6895 kPa (1000 psi). In Tests 1-13 below, briquettes measuring approximately 1.3 cm x 1.9 cm x 3.8 cm (0.5" x 0.75" x 1.5") were formed by a Komerek 4 briquetter operating at 6894.8 kPa (1000 psi) and 4 rpms. Samples in Tests 14-23 were prepared using a 1.25 cm (0.5 inch) diameter die and a hydraulic press to form test pellets approximately 2.5 cm (1") long. In one preferred embodiment, the current invention prepares a chlorinator feedstock by blending titanium ore particles (whether fresh or recovered, blow-over particles or both), coke particles (whether fresh or recovered, blow-over particles or both) or a combination of such ore and coke particles with a binder. The blend may optionally further contain pigmentary titanium dioxide as an additional binding agent. The titanium ore and coke particles especially will include blow-over particles from a fluidized bed reactor or other convenient source. Particle sizes may range from 500 μm to less than 44 μm (mesh sizes from -35 U.S. Mesh to -325 U.S. Mesh). Typically, the particles will range in size from 225 μm to less than 44 μm. One preferred binder is dried cane molasses such as the product sold under the trade name "Kaptain Kid" by Harvest Brands Inc. of Pittsburg, Kansas. Other preferred binders include raw linseed oil and boiled linseed oil commercially available from several different manufacturers. Linseed oil is a naturally occurring triglyceride vegetable oil obtained from flax seeds by pressing or extraction. The boiled version contains chemical accelerators, called driers, to enhance the drying rate of the oil. Other suitable binders include common table sugar and corn syrup. Depending upon the availability of raw material in the requisite size ranges, the components of the mixture prior to briquetting will comprise from 65 to 95.5 percent by weight of titanium ore, of petroleum coke or of a combination of titanium ore and petroleum coke, from 0 to 10 percent by weight of pigmentary titanium dioxide and from 4.5 to 25 percent by weight of organic binder. For carbohydrate based binders such as molasses, from 4.5 to 10 percent by weight of binder is preferred. When using a dry organic binder, water is added to the dry components in an amount sufficient to produce a briquettable final mixture, generally containing from 3.7 percent to 20 percent water by weight of the non-aqueous components of the mixture. Typically the final mixture contains about 15 percent water by weight of the dry components (as shown by the examples below). When the binder is a liquid such as boiled linseed oil, water is optionally added as necessary to produce the desired briquettable final mixture. A briquettable final mixture will generally be characterized as forming a cohesive mass when the mixture is molded by hand. The final mixture is fed to a briquetter capable of applying sufficient pressure to the mixture to convert the mixture into a substantially solid briquette or other suitable form. Preferably, the briquetter will apply at least 3447 kPa (500 psi) while fornning the mixture into a solid mass. More preferably, the briquetter will apply between 5515 kPa (800 psi) and 6895 kPa (1000 psi) while forming the feedstock composition. The briquetting process takes place at a temperature ranging from O0C (32°F) to 60°C (1400F). Preferably, the briquetting process takes place at room temperature, namely, in the range of from 15.6°C (60°F) to 32.2°C (900F). Briquettes within the scope of the current invention are those which remain within the fluidized bed chlorinator for a sufficient period of time such that the ore and/or coke fines incorporated therein react to a much greater extent than would have previously been possible; thus, preferably the briquettes will be such that at least 70 percent of the titanium dioxide present will have been converted to titanium tetrachloride under the prevailing chlorination conditions and at least 60 percent of the petroleum coke will have reacted. In general, preferred briquettes for use in a fluidized bed chlorinator will measure 1.3 cm x 1.9 cm x 3.8 cm (0.5" x 0.75" x 1.5") and have a density of 0.20 g/cm3 to 0.39 g/cm3. However, briquettes as small as 1 cm in diameter and 0.5 cm in thickness should perform satisfactorily in a fluidized bed chlorinator. Briquettes of this size would have a volume of about 0.4 cm3. Following the briquetting process, the resulting feedstock composition is dried at a temperature ranging from 37.8°C (100°F) to about 260°C (500°F). Preferably, the feedstock composition is dried at about 1040C (22O0F). The final dried feedstock composition preferably will have a moisture content of less than 0.1 percent by weight of water. The crush strength of the resulting briquettes is preferably at least 13.6 kg. More preferably, the briquettes will have a crush strength of at least 22.7 kg when measured according to ASTM D4179. 2. Feedstock Compositions for Use in a Fluidized Bed Reactor In a related aspect, the current invention provides feedstocks for use in a fluidized bed chlorinator in a chloride process for making titanium dioxide. In general, those skilled in the art would consider particles smaller than about 100 μm as too small for use as reactants in the fluidized bed chlorinator. However, the present inventive feedstocks preferably comprise particles of reactant materials (such as titanium ore and petroleum coke) which range in size from 500 μm to smaller than 44 μm. As noted above, particles smaller than about 100 μm are generally carried out of a fluidized bed chlorinator prior to reacting. Thus, the feedstock compositions of the current invention broaden the range of reactant materials available for use in the fluidized bed chlorinator. In particular, the feedstock compositions of the current invention preferably contain blow-over particles from a fluidized bed chlorinator, and so improve the operating efficiency of the titanium dioxide manufacturing process. In one preferred embodiment, a feedstock composition of the current invention comprises from 4.5 to 25 percent by weight of organic binder and the balance, from 75 to 95.5 percent by weight, of titanium ore. The titanium ore may be either blow-over ore recovered from a fluidized bed chlorinator or an unrecovered, fresh ore having particle sizes smaller than about 225 μm. The organic binder is preferably a material containing primarily carbohydrates, preferably in the form of sugars or fatty acids or mixtures thereof. Preferred organic binders include sugar, corn syrup, dried molasses, raw linseed oil, boiled linseed oil and combinations thereof. Any available dried molasses is appropriate in the current invention, including but not limited to cane molasses, beet molasses, citrus molasses, ,hemicellulose extract and starch molasses. The most preferred molasses is dried cane molasses. One such suitable molasses is sold under the trade name "Kaptain Kid" by Harvest Brands Inc. of Pittsburg, Kansas. When placed in a fluidized bed chlorinator, preferably the titanium ore in these briquetted feedstock compositions will be retained in the chlorinator for a sufficient time such that at least about 70 percent of the titanium ore will be converted to titanium tetrachloride. More preferably, at least 75 percent of the titanium ore will be converted to titanium tetrachloride. In another preferred embodiment according to this particular aspect, the feedstock composition comprises from 4.5 to 25 percent by weight of organic binder, from 65 to 94.5 percent by weight titanium ore and from 1 to 10 percent by weight pigmentary titanium dioxide. Further, the titanium ore may be either blow-over particles recovered from a fluidized bed chlorinator or fresh, unrecovered ore particles smaller than about 100 μm. In this embodiment, the pigmentary titanium dioxide is an additional binder which combines with the organic binder to enhance the crush strength of the feedstock composition, when briquetted as described herein. When placed in a fluidized bed chlorinator preferably again at least about 70 percent of the total titanium dioxide content (via the ore and the pigmentary titanium dioxide) will be converted to titanium tetrachloride. More preferably, at least 75 percent of the titanium dioxide content will be converted to titanium tetrachloride. In another preferred embodiment, the feedstock composition comprises from 4.5 to 25 percent by weight of organic binder and the balance, from 75 to 95.5 percent by weight, of petroleum coke particles, which particles will typically be smaller than about 100 μm. When used as a reducing agent within a fluidized bed chlorinator from 63 percent to 93 percent of the coke contained in this feedstock composition preferably reacts. Further, as will be demonstrated below, whereas recycled petroleum coke blow-over fines have in the past proven generally non-reactive, recovered petroleum coke fines have in the context of the present invention been found to show much improved reactivity, so that the petroleum coke used in this particular feedstock composition can be fresh, unrecovered petroleum coke, recovered blow-over coke fines or a combination of fresh and recycled coke particles. In another preferred embodiment, the feedstock composition comprises from about 4.5 to about 25 percent by weight of organic binder, from about 65 to about 94.5 percent by weight of petroleum coke and from about 1 to about 10 percent by weight of pigmentary titanium dioxide. In this embodiment, the pigmentary titanium dioxide is an additional binder which combines with the organic binder to enhance the crush strength of the feedstock composition, when briquetted as taught above. When used as a reducing agent within a fluidized bed chlorinator from 63 percent to 93 percent of the coke contained within the feedstock preferably reacts. In yet another embodiment, the feedstock composition comprises from 4.5 to 25 percent by weight of organic binder and the balance, from 75 to 95.5 percent by weight, of a combination of petroleum coke particles and unreacted titanium dioxide particles. More preferably, the petroleum coke is from 30 to 70 percent by weight in the combination with the titanium dioxide particles, and the unreacted titanium dioxide particles are correspondingly present at from 70 to 30 percent by weight. In still another embodiment, the feedstock composition comprises from 4.5 to 25 percent by weight of organic binder, from 1 to 10 percent by weight of pigmentary titanium dioxide as an additional binder, and the balance, from 65 to 94.5 percent by weight of a combination of petroleum coke and titanium ore particles. Again, the coke and ore particles include especially those which heretofore have been considered too small to be of practical use in a fluidized bed chlorinator, typically being 100 μm and smaller. Most especially, the use of recovered blow-over coke and ore fines is contemplated. The following tables report the test results of sample feedstocks prepared according to the methods of the current invention. Tests 5-23 demonstrate the formation of briquettes suitable for use in a fluidized bed chlorinator. These tests demonstrate the ability to preparing briquettes having the necessary crush strength for use in a fluidized bed reactor. Preferred briquettes for use in a fluidized bed chlorinator will have a crush strength of 13.6 kg (30 lbs.) or greater when measured according to ASTM D4179. More preferably, the briquettes will have crush strengths greater than 36.3 kg (80 lbs.). In contrast to Tests 5-23, Tests 1-4 report the results of samples considered too soft for use in a fluidized bed chlorinator. Tests 15 and 21 and Tests 16 and 18 are noted to report crush strengths for samples having identical compositions. Although the samples have identical compositions, the test results for each pair differ. In this instance the differences are believed to result from differences in homogeneity in the tested samples.

sample 4 excluded from average

In order to further enhance feedstock reactivity, the composition of the current invention

preferably remains crush resistant during the reaction process. The crush strength of a briquette

during the chlorination process was determined by preparing ten samples having the same

composition, using ore and coke particles in combination in a 60:40 ratio by weight, 2.5 percent by

weight of molasses and 5 percent by weight of pigmentary titanium dioxide as an additional binder.

These samples were then chlorinated for 15 minutes at 900°C. The samples were removed from the

reactor and tested for crush strength in accordance with the procedures of ASTM D4179. The results

of the crush tests are reported in Table 1 below. The drop in crush strength following chlorination

is consistent with the reaction rate of the briquette components. As reported below in Tables 2 and 3,

at least 70 percent of the titanium dioxide and at least 60 percent of the coke present in the briquette

reacted after 15 minutes in the fluidized bed chlorinator. As the components react, the briquette

necessarily loses structure. However, despite the significant reaction rate, the strength of the briquette

ensures maximum reaction of the coke and ore with minimum repeat blow-over due to briquette

attrition. Accordingly, preferably feedstock compositions of the current invention will have a crush

strength of at least 610 grams following exposure to reaction conditions of 9000C in the presence of

chlorine. More preferably, the feedstock compositions will have a crush strength of at least 1.9

kilograms following exposure to reaction conditions of 9000C in the presence of chlorine.

18

3. Methods for Recycling Blow-over Particles

In another aspect, the current invention also provides methods for recovering and

reacting blow-over fines lost from a fluidized bed chlorinator. In particular, the current

invention recovers blow-over fines lost from fluidized bed chlorinators used in the chloride

process. As known to those skilled in the art, reactants readily blow out of the fluidized bed

reactor prior to reacting when, due to attrition and the reaction process, reactant size reaches

100 μm and smaller. A typical fluidized bed chlorinator operates at about 85-95 percent

efficiency with about 5-15 percent of the reactants lost as blow-over particles. As noted above,

attempts to recover and recycle blow-over particles have been less than successful due to

problems with binders and non-reactivity of blowover coke particles. Further, titanium ore

particles smaller than about 44 μm will not normally chlorinate; therefore, blow-over particles

smaller than 44 μm are generally considered waste products.

The method of the current invention recovers titanium ore and coke blow-over particles

from the gases exiting the fluidized bed reactor by traditional methods such as a baghouse or

cyclone. If desired, the particles may be separated by size or type. For example, the titanium ore

has greater value to the operator. Therefore, the operator may wish to recycle only the recovered

titanium ore. Separation systems suitable for isolating particles on the basis of weight and size

are well known to those skilled in the art.

In the preferred embodiment, the titanium ore and petroleum coke particles are

recovered separately. Separate recovery of the two reactants permits blending of the ore and coke blow-over particles in proportions determined to produce feedstock material best suited for the operating conditions of the fluidized bed chlorinator. While separate recovery of the reactants is considered the preferred method for practicing the current invention, recovering the reactants in a single step and subsequently producing feedstock from the jointly recovered material is also within the scope of the current invention. Thus, according to the current invention, blow-over fines from a fluidized bed chlorinator are recovered from the gases leaving the reactor. The blow-over fines are combined with an organic binder and optionally with pigmentary titanium dioxide. The pigmentary titanium dioxide is a supplemental binder and strengthening agent. The organic binder comprises carbohydrates, preferably in the form of sugar, or fatty acids or combinations thereof. Preferred organic binders include sugar, corn syrup, dried molasses, raw linseed oil, boiled linseed oil and combinations thereof. The preferred dried molasses is dried cane molasses. The final blending step to produce the final mixture prior to briquetting is again deteimined by the physical nature of the organic binder. For dry organic binders, a sufficient amount of water is added following dry blending to produce a briquettable final mixture. In this embodiment, the final mixture generally contains from about 3.7 percent to about 20 percent by weight water. However, when the binder is a liquid, water is optionally added when necessary to produce a final mixture having the desired consistency as described above. Thus, addition of a liquid binder to the dry components may complete the formulation process, yielding the final mixture for briquetting. The final mixture is fed to a briquetter capable of applying sufficient pressure tothe mixture to convert the final mixture into a substantially solid briquette. Preferably, the briquetter will apply at least 3447.4 kPa (500 pounds per square inch) while forming the final mixture into a solid mass. More preferably, the briquetter will apply at least 5515 kPa (800 psi) while forming the feedstock composition. The briquetting process takes place at a temperature ranging from O0C (320F) to 60°C (14O0F). Preferably, the briquetting process takes place at room temperature, that is, from generally 15.60C (6O0F) to 32.20C (9O0F). Following the briquetting process, the resulting feedstock composition is dried at a temperature ranging from about 37.8°C (1000F) to about 2600C (5000F). Preferably, the feedstock composition is dried at about 104.40C (2200F). Preferably, the dried feedstock composition has less than 0.1% by weight water. Following drying, the feedstock composition has a crush strength of at least 13.6 kg (30 pounds) when measured according to ASTM D 4179. The dried feedstock composition is then ready for use in the fluidized bed chlorinator. At the operator's option, the feedstock composition may be the primary feedstock or it may be combined with raw material normally used in the chlorinator. No special techniques are required to feed the feedstock of the current invention into the chlorinator. Once in the chlorinator, the feedstock composition reacts with the chlorine gas. Reaction efficiencies of feedstock compositions prepared and used according to the current invention are reported below in Tables 2 and 3. As reported in Table 2, greater than 70 percent of the total TiO2 within the briquettes reacts when placed in a fluidized bed reactor for 15 minutes. Total TiO2 refers to the sum of the titanium dioxide present in the titanium ore and the pigmentary titanium dioxide used as a crush strength enhancer. The test results yielded TiO2 chlorination rates from 3.52 g/minute to 4.70 g/minute. In contrast, the second half of Table 2 reports chlorination rates for prior art methods and feedstocks of only 0.41 g/minute to 0.69 g/minute. Clearly, the feedstock compositions and methods of the current invention enhance the reaction rate of TiO2 in the fluidized bed chlorinator. Table 3 likewise demonstrates the improved reactivity of petroleum coke within briquettes prepared and reacted according to the current invention. As previously noted, blow- over petroleum coke used in prior art practices would not react within the fluidized bed chlorinator. However, as reported in Table 3, the recovered, blow-over petroleum coke fines contained within the briquettes reacts at a significantly better rate than even traditional, unrecovered petroleum coke prepared and used in accordance with the prior art. Specifically, greater than 60 percent by weight of the petroleum coke included in the briquettes reacted within in the fluidized bed reactor. For the briquettes, the coke reaction rate ranged from 4.08 g/minute to 6.20 g/minute. In contrast, the second half of Table 3 indicates prior art reaction rates for petroleum coke of no greater than 35.64 percent by weight and only 0.25 g/minute. Note, the prior art petroleum coke was not blow-over coke fines. Clearly, the method of the current invention improves operating economics by recycling blow-over fines, improving the reaction rate of the raw materials and reducing subsequent blow-over of reactants. Table 2

Table 3

Clearly, the methods and compositions of the current invention for recycling blow-over fines recovered from a fiuidized bed chlorinator provide significant improvements in the manufacture of titanium dioxide. Other embodiments of the current invention "will be apparent to those skilled in the art on consideration of this specification, which is consequently to be considered as exemplary of the invention and not as limiting in any way of the scope of the invention as properly defined by the claims which follow.