Title of Invention

MULTI-STEP METHOD FOR PRODUCING TITANIUM DIOXIDE

Abstract

The invention relates to the production of titanium dioxide by oxidating titanium tetrachloride in a multi-step method, wherein oxygen and titanium tetrachloride are dosed in several steps. In the first step, gaseous TiCl4 is introduced stochiometrically or hyperstochiometrically into a preheated oxygen-containing gas flow in order to produce a TiO2 containing gas suspension. In the second or other steps liquid TiCl4 and oxygen-containing gas are introduced into the TiO2 containing gas suspension in order to produce additional TiO2. In one embodiment of the invention TiCl4 and oxygen-containing gas are added at a temperature of under about 50 °C in the second or other steps. Said invention is energy saving compared to other known methods known from the prior art.

Full Text

FORM 2 THE PATENT ACT 197 0 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13) 1. TITLE OF INVENTION MULTI-STEP METHOD FOR PRODUCING TITANIUM DIOXIDE 2. APPLICANT(S) a) Name : KRONOS INTERNATIONAL, INC. b) Nationality : GERMAN "Company c) Address : POSTFACH 10 07 20, 51307 LEVERKUSEN, GERMANY 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the invention and the manner in which it is to be performed : - The invention relates to the manufacture of titanium dioxide by oxidation of titanium tetrachloride in a multi-stage method, where both oxygen and titanium tetrachloride are added in several stages. Technological background of the invention In one of the commercially used methods for manufacturing titanium dioxide pigment particles, known as the chloride process, titanium tetrachloride (TiCl4) is reacted with an oxidising gas, such as oxygen, air, etc., and with certain additives in a tubular reactor to form titanium dioxide and chlorine gas: TiCl4 + 02->Ti02+2Cl2 The Ti02 particles are subsequently separated from the chlorine gas. Known additives are AlCl3 as a rutilising agent and steam or alkali salts as a nucleating agent. The oxidation process is customarily performed in one stage, i.e. the reaction components (educts), oxygen and gaseous titanium tetrachloride, are each added at only one point of the reactor. Owing to the high activation energy of TiCLi oxidation, the educts must, before addition, be heated to such a degree that an adiabatic mixed temperature of at least approx. 740 °C is reached. The oxidation reaction is highly exothermal, meaning that an adiabatic reaction temperature of approx. 1,850 °C is reached following complete conversion. Before the pigment produced is separated from the gas mixture in a filter, this mixture has to be cooled to a maximum of 450°C in order to avoid damage to the filter. This process is energetically unsatisfactory because large amounts of heat are dissipated into the cooling-water system. Single-stage oxidation is also disadvantageous in terms of product quality, since the extensive hot zone for oxidation promotes the formation of hard TiO2 aggregates. Consequently, there are various developments in the prior art for operating the process on a multi-stage basis. According to GB 1 064 569, both TiCU and O2 are added in two stages, in which context the respective quantity of O2 is sufficient for completely oxidising the respective quantity of TiCU. The teaching according to US 4,053,577 provides for a maximum of one of the educts to be introduced into the reactor in two stages. In the methods according to GB 2 037 266, US 4,803,056 and EP 0 583 063 Bl, gaseous TiCU is introduced into a hot oxygen stream, in two or more stages. The method according to EP 0 852 568 Bl provides for not only the TiCU to be added in two stages, but also the oxygen. However, the object of this method is effective control of the mean TiO2 particle size, and thus of the tone of the TiO2 pigment base material. In this case, TiCl4 vapour having a temperature of roughly 400 °C is first fed into an oxygen stream with a temperature of roughly 950 °C. The TiO2 particles are formed, and particle growth takes place, in the downstream reaction zone. TiCU vapour heated to a lesser extent (approx. 180 °C) is added at a second inlet point. Oxygen having a temperature between 25 "C and 1,040 °C is introduced at the second inlet point, the temperature of the mixture being sufficient to initiate the reaction. The multi-stage method according to US 6,387,347 is additionally said to reduce agglomeration. To this end, the previously heated, gaseous TiCU stream is split into two part streams before addition to the reactor. One part stream is oxidised in the first stage of the reactor. The second part stream is cooled by injection of liquid TiCU (de-superheating) and then added to the reactor. De-superheating takes place outside the reactor, the temperature not falling below the condensation temperature of the overall stream. US 2007/0172414 Al discloses a multi-stage method for the reaction of TiCl4 and O2 in which gaseous TiCU is fed into the reactor in the first stage, and liquid TiCU in the second stage and wherein the oxygen is present in a hyper-stoichiometric amount in the first stage. This method permits energy savings and improvement of the particle size range. Object and summary of the invention The object of the present invention is to create a method for manufacturing titanium dioxide by oxidation of titanium tetrachloride that permits further energy savings compared to the methods known from the prior art. The object is solved by a multi-stage method for manufacturing titanium dioxide by reaction of titanium tetrachloride with oxygen in a reactor, characterised by the following steps: a) Introduction of gaseous TiCl4 into a preheated, oxygen-containing gaseous stream in a first reaction zone of the reactor, where the molar ratio of TiCU : O2 in the reaction zone is at least 1, and formation of a gas suspension containing TiO2, b) Passing of the gas suspension containing TiO2 into at least one further reaction zone, c) Introduction of an oxygen-containing gas and liquid TiCU into the at least one further reaction zone and further formation of TiO2 in the gas suspension. Further advantageous embodiments of the invention are described in the sub-claims. Description of the invention The method according to the invention differs from the aforementioned multi-stage chloride processes for manufacturing titanium dioxide from the prior art in that the TiCU is added in gaseous form and stoichiometrically or in excess in relation to the oxygen in the first stage (step a)), and in liquid form and sub-stoichiometrically in the second and further stages (step b)). In step a) TiCl4 and O2 react in a first reaction zone of the reactor and form a gas suspension containing TiO2 (first stage). In step b) the gas suspension containing TiO2 is passed into at least one further reaction zone. In step c) oxygen-containing gas and liquid T1CI4 is introduced into the at least one further reaction zone and further TiO2 is formed in the gas suspension {second stage). The present method can be performed in two stages or more than two stages. In the first stage (step a)) the temperature of the preheated oxygen-containing gas is at least roughly 950°C. In the second or further stages (step c)) in one embodiment of the method the oxygen-containing gas is introduced with a temperature of at least roughly 200 °C. In a special embodiment of the method, the oxygen-containing gas added in the at least one further stage is "cold", i.e. it has a temperature of less than roughly 50 °C, for example a temperature of roughly 30 °C. This method leads to a further improvement in energy efficiency, since only the portion of the oxygen-containing gas that is required for the first stage needs to be heated in order to provide the activation energy for the reaction. In all other stages, the activation energy is provided by the reaction enthalpy of TiCl4 oxidation released in the upstream stages. In another embodiment of the method in step a) the gaseous TiCl4 is introduced into the reactor mixed with an oxygen-containing gas. Preferably, the 02-content of the gaseous mixture is roughly 20 vol.% maximum. In order to avoid a premature reaction of the components in the gaseous mixture the temperature must not exceed roughly 900 °C. The introduction of the gaseous TiCl4 mixed with oxygen-containing gas helps to prevent the formation of defects in the TiO2 structure and leads to improved brightness of the manufactured TiO2 pigment. In a special embodiment of the invention the method is performed in a cylindrical plug flow reactor. Exemplary embodiment of the method The practical example described below is merely one possible embodiment of the invention and not to be taken as restricting the invention. The method is performed in two stages, where the TiCl4 is added in equal quantities in the first and second stages. In the first stage, the temperature of the oxygen-containing gas stream is 1,650 °C, that of the gaseous TiCl4 introduced being 450 °C. The molar ratio of TiCl4 : O2 in the first reaction zone is roughly 1. Downstream of the first stage, at a point where the reaction of the first stage has taken place completely, an oxygen-containing gas is added first, followed by liquid TiCl4. In the second stage, the temperature of the oxygen-containing gas introduced is 30 °C, that of the liquid TiCl4 introduced likewise being 30 °C. Compared to the customary, one-stage method, the same temperatures are selected in the first combustion stage in this embodiment of the method according to the invention, but major energy savings result when preheating the educts owing to the substantially smaller quantities of oxygen-containing gas and TiCl4 to be heated in the first stage. However, in the second stage the educts do not have to be preheated. The total savings achieved correspond roughly to the ratio at which the TiCl4 is split up over the two stages, i.e. roughly 50% in the present example. As the practical example described is merely a possible embodiment of the invention, the present invention optionally also comprises the addition, familiar to the person skilled in the art, of additives for rutilisation (e.g. AlCl3) and for nucleation (e.g. alkali salts) in the reaction zone. WE CLAIM: 1. Multi-stage method for manufacturing titanium dioxide by reaction of titanium tetrachloride with oxygen in a reactor, characterised by the following steps: a) Introduction of gaseous TiCl4 into a preheated, oxygen-containing gaseous stream in a first reaction zone of the reactor, where the molar ratio of TiCl4 : O2 in the reaction zone is at least 1, and formation of a gas suspension containing TiO2, AS) Passing of the gas suspension containing TiO2 into at least one further reaction zone, c) Introduction of an oxygen-containing gas and liquid T1Cl4 into the at least one further reaction zone and further formation of TiO2 in the gas suspension. 2. Method of Claim 1, characterised in that the oxygen-containing gas is introduced first in Step c), followed by T1Cl4. 3. Method of Claim 1 or 2, characterised in that the temperature of the oxygen-containing gas is at least roughly 950 °C before the reaction in Step a) and less than roughly 50 °C before the reaction in Step c). 4. The method of Claim 1, characterised in that the further reaction zone is located at a point in the reactor where the reaction according to Step a) has taken place completely. 5. Method of Claim 1 or 2 characterised in that in Step a) gaseous TiCl4 mixed with an oxygen-containing gas is introduced. 6. Method of Claim 5, characterised in that in Step a) the O2 content of the gaseous mixture is roughly 20 vol.% maximum. 7. Method of Claim 5 or 6, characterised in that the gaseous mixture displays a temperature of roughly 900 °C maximum. 8. Titanium dioxide particles manufactured to any one of Claims 1 to 7.

Documents:

606-MUMNP-2010-ABSTRACT(GRANTED)-(6-3-2013).pdf

606-mumnp-2010-abstract.pdf

606-MUMNP-2010-CANCELLED PAGE(1-10-2012).pdf

606-mumnp-2010-certificate.pdf

606-MUMNP-2010-CLAIMS(AMENDED)-(1-10-2012).pdf

606-MUMNP-2010-CLAIMS(AMENDED)-(13-12-2012).pdf

606-MUMNP-2010-CLAIMS(GRANTED)-(6-3-2013).pdf

606-MUMNP-2010-CLAIMS(MARKED COPY)-(13-12-2012).pdf

606-mumnp-2010-claims.pdf

606-MUMNP-2010-CORRESPONDENCE(15-4-2010).pdf

606-MUMNP-2010-CORRESPONDENCE(30-4-2010).pdf

606-MUMNP-2010-CORRESPONDENCE(IPO)-(6-3-2013).pdf

606-mumnp-2010-correspondence.pdf

606-mumnp-2010-description(complete).pdf

606-MUMNP-2010-DESCRIPTION(GRANTED)-(6-3-2013).pdf

606-MUMNP-2010-EP DOCUMENT(1-10-2012).pdf

606-MUMNP-2010-FORM 1(30-4-2010).pdf

606-mumnp-2010-form 1.pdf

606-mumnp-2010-form 18.pdf

606-MUMNP-2010-FORM 2(GRANTED)-(6-3-2013).pdf

606-MUMNP-2010-FORM 2(TITLE PAGE)-(GRANTED)-(6-3-2013).pdf

606-mumnp-2010-form 2(title page).pdf

606-mumnp-2010-form 2.pdf

606-MUMNP-2010-FORM 3(1-10-2012).pdf

606-MUMNP-2010-FORM 3(13-12-2012).pdf

606-MUMNP-2010-FORM 3(15-4-2010).pdf

606-mumnp-2010-form 3.pdf

606-mumnp-2010-form 5.pdf

606-mumnp-2010-form pct-ib-304.pdf

606-mumnp-2010-form pct-isa-210.pdf

606-MUMNP-2010-FORM-PCT-ISA-237(30-4-2010).pdf

606-MUMNP-2010-FORM-PCT-RO-101(30-4-2010).pdf

606-MUMNP-2010-GENERAL POWER OF ATTORNEY(1-10-2012).pdf

606-mumnp-2010-general power of attorney.pdf

606-MUMNP-2010-PETITION UNDER RULE 137(13-12-2012).pdf

606-MUMNP-2010-REPLY TO EXAMINATION REPORT(1-10-2012).pdf

606-MUMNP-2010-REPLY TO EXAMINATION REPORT(13-12-2012).pdf

606-MUMNP-2010-SEARCH AND EXAMINATION REPORT(13-12-2012).pdf

606-mumnp-2010-wo international publication report a2.pdf

606-mumnp-2010-wo international publication report a3.pdf