The present disclosure relates to a process for preparing titanium tetrachloride, and in particular to a process for preparing titanium tetrachloride that utilizes off gases from the carbo-chlorination process to prepare silicon and zircon tetrachloride.
The direct chlorination of zircon ore particles or silica particles in a carbo-chlorination process in which a fluidized bed reactor in the presence of high concentrations of carbon particles, and at a temperature within the range at which zircon will react with chlorine to form zirconium and silicon chlorides is known. The bed temperatures run well in excess of 1000° C., and this presents a number of issues. First, high levels of CO are generated in place of CO2. CO uses more coke in the carbo-chlorination process leading to higher operating costs. Next, the high temperature leads to accelerated brick wear in the chlorinator. Additionally, operating at lower temperatures to minimize brick loss, results in un-reacted chlorine in the chlorinator off gas. This un-reacted chlorine would be a chlorine yield loss and require additional treatment steps downstream.
A need exists for a process that recovers the CO generated in the direct chlorination of zircon ore particles, and a process for economically preparing titanium tetrachloride. A need also exists for a process that increases the life of the bricks in the chlorinator, and utilizes the un-reacted chlorine that results from running the carbon chlorination process at a lower temperature.
The present disclosure provides an improved process for preparing titanium tetrachloride comprising:
The disclosure solves the problem caused by CO generation in the chlorination of oxide particles, such as zircon and silica and mixtures thereof, especially the high levels formed at high temperatures as well as the problem of unreacted chlorine that results when low temperatures are used to avoid brick wear by feeding the CO-containing off gas to a carbo-chlorination process for forming titanium tetrachloride.
The ore which can be used as a feed source for the oxide is a oxide-bearing ore. The metal oxide-bearing ore is selected from the group consisting of zircon and silica. Sources for the ore include zircon sand and silica. The term “metal oxide” may be used herein to include silica as well as zircon.
Titanium tetrachloride can be produced by a two stage process shown in
In general, the process comprises a first carbo-chlorination process and a second carbon chlorination process. In the first carbon chlorination process a metal oxide-bearing ore can be reacted with chlorine and a carbon source to provide the corresponding metal chloride and gas comprising CO and CO2. In the second carbon chlorination process a titanium-bearing ore is reacted with chlorine and a carbon source in the presence of the gas from the first carbon chlorination process to form titanium tetrachloride. The titanium tetrachloride can be used in a process for making titanium dioxide in an oxidation process.
Referring to
The carbon used as the reducing agent can be in the form of relatively coarse granular material, the 8 to +100 mesh range being typical. The solids feed to the reactor can be adjusted to maintain a high ratio of unreacted carbon to total solids in the bed, and this is expected to improve yield. A ratio of about 1:2 by weight is typical, and acceptable results can be achieved if the ratio is maintained within the range of 1:3 to 3:4. Chlorine gas can be introduced into the reactor at a sufficient velocity and pressure to fluidize the bed and expand it to about twice its static volume. The velocity can be dependant on the size and materials in the bed. The reaction temperature can, preferably, be maintained within the range of about 1025 to about 1150° C. Since the reaction is exothermic, it can not be necessary to supply heat, except in small scale reactors having very high heat losses. To increase the reaction temperature for rate control, oxygen can be supplied along with the chlorine gas. The oxygen can be supplied in any desired volume ratio compared to chlorine up to as high as about 3:2, as long as a high CO/CO2 ratio in the exit gases is maintained. As a person skilled in the art of carbon chlorination would realize, this high CO/CO2 ratio in the exit gases can be maintained by controlling the proportion of carbon and oxygen in the reactor, by way of an example, the ratio can be maintained by the use of high ratios of carbon to zircon ore in the feed. However, the difference can vary depending upon the carbon and oxygen content of the starting materials.
Once the gases exiting the chlorinator are cooled in recovery device 15, the zirconium tetrachloride 16a can be collected as a powder and silicon tetrachloride 16b can be condensed and collected as a liquid by known methods to those skilled in the art. As an example, a suitable recovery device can be a condenser.
A stream of non-condensable gases comprising CO and CO2, typically comprising a major proportion of CO and CO2 with a minor proportion of other gaseous materials from the reaction, such as unreacted chlorine, is withdrawn from the recovery device 15 via line 17. This stream of non-condensable gases can be referred to as an off-gas, more particularly, a first off-gas.
In other embodiments of the first carbon chlorination process the metal oxide can be SiO2 which is free of ZrO2. Various technologies to chlorinate SiO2 can include but are not limited to 1) SiO2 carbon chlorination with external heating as described in U.S. Pat. No. 3,010,793, 2) Co-chlorination of SiO2 and silicon metal as described in U.S. Pat. No. 3,197,283, 3) Co-chlorination of Silicon Carbide and SiO2 as described in U.S. Pat. No. 2,843,458, or 4) Chlorination of silica and carbonized biomass as described in U.S. Pat. No. 4,847,059. Typically, reaction temperatures are maintained in the range of about 1000° C. to about 1300° C., more typically in the range of about 1100° C. to about 1200° C.
Referring to
The process additionally can be incorporated into a process for oxidizing titanium tetrachloride to make titanium dioxide. In this manner the process can use the first off-gas comprising carbon monoxide, shown as the non-condensable gas 17 in
An alternate embodiment for recovering the chlorine gas from the zirconia and/or silica chlorination stream can be to feed the off-gas containing CO and Cl2 as a gaseous feed to the oxidation reactor used in the process for oxidizing titanium tetrachloride to make titanium dioxide, as discussed above. Referring to
Thus, the disclosure additionally relates to a process for preparing titanium tetrachloride comprising:
In another alternative embodiment, the exit gas from the first fluidized bed chlorinator containing silicon tetrachloride can be incorporated into the titanium tetrachloride oxidation process to treat the titanium dioxide product with silicon tetrachloride to form a silica-treated titanium dioxide product. In this embodiment the silicon tetrachloride can be fed along with the TiCl4 feed to the oxidation reactor, to the titanium dioxide-containing discharge of the TiCl4 oxidation reactor, or to the flue downstream of the oxidation reactor as described in U.S. Pat. Nos. 5,562,764; 6,852,306; and 7,029,648. By adding the exit gas containing silicon tetrachloride at these locations, the silicon tetrachloride can react to form SiO2 on the titanium dioxide and the excess Cl2 can be recovered by feeding a Cl2-containing product stream from the oxidation reactor to the second fluidized bed chlorinator via line 18b.
Titanium tetrachloride (TiCl4), ferrous chloride (FeCl2), ferric chloride (FeCl3) and chlorides of other contaminating metals and impurities are simultaneously formed, volatilized and removed as a gaseous mixture along with CO and CO2 from the chlorinator 19 through line 21, which gaseous mixture is then delivered to a cyclone/condenser unit 22 to remove precipitating and condensing compounds which are discharged through line 23. The gaseous phase which is withdrawn and contains TiCl4, CO, CO2, HCl, Cl2, COS and entrained fine solids can be sent to a TiCl4 purification unit 24 in order to separate the TiCl4 vapor from the other gaseous components and thus obtain pure TiCl4 vapor which is removed through line 25. The ratio of CO:CO2 exiting the TiO2 chlorination stage is much lower than the CO:CO2 ratio exiting the ZrO2 or SiO2 chlorination process.
An economically useful operation would be to chlorinate high titania zircon ores. Typically, high TiO2-containing zircon ores contain about 0.15 wt. % to about 45 wt. % TiO2, more typically from about 2 wt. % to about 10 wt. % TiO2, based on the total amount of the ore. The high TiO2 zircon ores can be used in the first fluidized bed chlorinator. Such ores are available at a lower price than low TiO2 ores. The titanium tetrachloride and silicon tetrachloride that is condensed can be separated by means of distillation or condensed separately with the titanium tetrachloride fed to the second fluidized bed chlorinator for chlorinating titanium dioxide-containing feedstock.
This application claims the benefit of U.S. Provisional Application No. 60/692,792 filed Aug. 1, 2007, incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US08/71860 | 8/1/2008 | WO | 00 | 1/13/2010 |
Number | Date | Country | |
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60962792 | Aug 2007 | US |