Integrated processes and systems for co-production of titanium dioxide and caustic soda

Abstract

Integrated processes and systems for the co-production of titanium dioxide and caustic soda. A chlor-alkali process is integrated with a chloride process of titanium dioxide production to produce both caustic soda and titanium dioxide. A chlor-alkali unit produces caustic soda, chlorine, and hydrogen. The chlorine produced in the chlor-alkali unit then serves as an input for a titanium dioxide production unit. Some or all of the hydrogen is combusted to generate the heat required for the titanium dioxide production unit, and / or used in other processes, such as a reducing agent in the production of direct reduced iron (DRI).

Description

INTEGRATED PROCESSES AND SYSTEMS FOR CO-PRODUCTION OF TITANIUM DIOXIDE AND CAUSTIC SODACROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of provisional U.S. Patent Application No. 63 / 734,566 filed December 16, 2024, the contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION

[0002] The invention generally relates to production processes for titanium dioxide (TiO2), and more particularly to methods and systems for co-production of TiO2 and caustic soda (sodium hydroxide, NaOH).

[0003] Traditional titanium dioxide production processes and systems (including manufacturing plants, facilities, etc.) have primarily utilized either a sulfate process or a chloride process. The sulfate process involves dissolving titanium ore in concentrated sulfuric acid, resulting in titanium sulfate, which is then hydrolyzed and calcined to produce titanium dioxide. The chloride process involves high-temperature chlorination of titanium ore (typically ilmenite or rutile) in the presence of coke and chlorine gas at atmospheric pressure and elevated temperatures (e.g., 800°C to 1000°C) to produce titanium tetrachloride (TiCh), which is subsequently purified through various separation steps including distillation to remove impurities and then oxidized at temperatures between 900°C and 1400°C, forming titanium dioxide pigment. See, e.g., Gazquez et al., "A Review of the Production Cycle of Titanium Dioxide Pigment," Materials Sciences and Applications, Vol. 5, Pgs. 441-458 (2014) (DOI: 10.4236 / msa.2014.57048), the contents of which are incorporated herein by reference in the entirety. However, the chloride process is energy intensive and typically uses large amounts of fossil fuel to provide the process heat needed for the driving the various reactions. This may also lead to having a larger carbon footprint, which is less desirable for its environmental impact.

[0004] Therefore, it would be desirable to have processes and systems for producing titanium dioxide that provide for more efficient energy usage and / or have a smaller carbon impact on the environment.BRIEF SUMMARY OF THE INVENTION

[0005] The intent of this section of the specification is to briefly indicate the nature and substance of the invention, as opposed to an exhaustive statement of all subject matter and aspects of the invention. Therefore, while this section identifies subject matter recited in the claims, additional subject matter and aspects relating to the invention are set forth in other sections of the specification, particularly the detailed description, as well as any drawings.

[0006] The present invention provides, but is not limited to, integrated processes and integrated systems adapted for the co-production of titanium dioxide and caustic soda.

[0007] According to a nonlimiting aspect, an integrated process for the co-production of titanium dioxide and caustic soda includes using a chlor-alkali unit to produce caustic soda, chlorine, and hydrogen by a chlor-alkali process. The chlorine is used as input in a chlorinator of a chloride process to produce titanium dioxide, and at least a portion of the hydrogen is combusted to generate heat for the chloride process.

[0008] According to another nonlimiting aspect, an integrated system for co-production of titanium dioxide and caustic soda includes a chlor-alkali unit for producing caustic soda, chlorine, and hydrogen by electrolysis of a saltwater brine, a titanium dioxide production unit for producing titanium dioxide with a chloride process using a titanium-bearing feedstock, chlorine from the chlor-alkali unit, and heat energy produced using at least a portion of the hydrogen from the chloralkali unit to produce the titanium dioxide. A first piping system couples the chlor-alkali unit to the titanium dioxide production unit for conducting the chlorine from the chlor-alkali unit to the chloride process production unit. A second piping system couples the chlor-alkali unit to the titanium dioxide production unit for conducting the portion of the hydrogen from the chlor-alkaliunit to the chloride process production unit.

[0009] Technical aspects of processes and / or integrated systems as described above preferably include the ability to provide a more energy efficient and / or lower carbon usage ("decarbonized") system for co-production of titanium dioxide and caustic soda.

[0010] These and other aspects, arrangements, features, and / or technical effects will become apparent upon detailed inspection of the figures and the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic diagram of an integrated process for the co-production of titanium dioxide and caustic soda, wherein the process generates caustic soda, chlorine, and hydrogen by a chlor-alkali process according to a nonlimiting embodiment of the invention.

[0012] FIG. 2 is a schematic diagram of an integrated process that co-produces titanium dioxide and caustic soda and generates caustic soda, chlorine, and hydrogen by a chlor-alkali process according to another nonlimiting embodiment of the invention.

[0013] FIG. 3 is a schematic diagram of an integrated process that co-produces titanium dioxide and caustic soda and generates caustic soda, chlorine, and hydrogen by a chlor-alkali process according to a further nonlimiting embodiment of the invention.

[0014] FIG. 4 is a schematic diagram of an integrated process that co-produces titanium dioxide and caustic soda and generates caustic soda, chlorine, and hydrogen by a chlor-alkali process according to a yet another nonlimiting embodiment of the invention.

[0015] FIGS. 5 and 6 are schematic diagrams of integrated processes that co-produce titanium dioxide and caustic soda and generate caustic soda, chlorine, and hydrogen by a chlor-alkali process, wherein at least a portion of the generated hydrogen is utilized as a feedstock or material input in the production of direct reduced iron (DRI) according to additional nonlimiting embodiments of the invention.DETAILED DESCRIPTION OF THE INVENTION

[0016] The intended purpose of the following detailed description of the invention and the phraseology and terminology employed therein is to describe one or more nonlimiting embodiments of the invention, and to describe certain but not all aspects of what is depicted in the drawings, including the embodiment(s) to which the drawings relate. The following detailed description also identifies certain but not all alternatives of the embodiment(s). As nonlimiting examples, the invention encompasses additional or alternative embodiments in which one or more features or aspects shown and / or described as part of a particular embodiment could be eliminated and also encompasses additional or alternative embodiments that combine two or more features or aspects shown and / or described as part of different embodiments. Therefore, the appended claims, and not the detailed description, are intended to particularly point out subject matter regarded to be aspects of the invention, including certain but not necessarily all of the aspects and alternatives described in the detailed description.

[0017] As used herein the terms "a" and "an" to introduce a feature are used as open-ended, inclusive terms to refer to at least one, or one or more of the features, and are not limited to only one such feature unless otherwise expressly indicated. Similarly, use of the term "the" in reference to a feature previously introduced using the term "a" or "an" does not thereafter limit the feature to only a single instance of such feature unless otherwise expressly indicated.

[0018] FIGS. 1 through 6 represent nonlimiting but preferred embodiments of integrated processes and systems (which as used herein includes manufacturing plants, facilities, etc.) for the co-production of titanium dioxide (TiCh) and caustic soda (NaOH). In these embodiments, a chloralkali unit is used to produce caustic soda, chlorine, and hydrogen. The chlorine produced in the chlor-alkali unit then serves as an input for a titanium dioxide production unit / process, and at least some of the hydrogen is combusted in the presence of an oxidant, such as oxygen, to generate heat required for the titanium dioxide production unit / process. Such an arrangement is preferably (but not necessarily) capable of replacing the need for fossil fuel in a titanium dioxide productionprocess. By way of a nonlimiting example, a chlor-alkali process is integrated with the chloride titanium dioxide production process to produce both caustic soda and titanium dioxide, and the integrated production utilizes hydrogen produced by the chlor-alkali process to meet the thermal needs of the titanium dioxide production process, and in so doing is preferably capable of providing a production process that is more environmentally sustainable and is characterized by relatively lower carbon usage ("decarbonized") than conventional chloride processes for titanium dioxide production.

[0019] The chlor-alkali process is an electrolytic process that produces chlorine, hydrogen, and sodium hydroxide (caustic soda) through electrolysis of a saltwater brine. Typically, one of three main types of cell processes is used for the chlor-alkali process: a diaphragm cell process, a mercury cell process, or a membrane cell process. The membrane cell process has become an industry standard due to its environmental friendliness and energy efficiency. The chlor-alkali process operates under moderate temperature and pressure conditions and uses electrical energy to drive the electrolysis reaction. In the membrane cell process, which typically operates at about 80-90°C and atmospheric pressure, saturated brine flows into an anode chamber, where chlorine gas is produced. Sodium ions pass through an ion-selective membrane into a cathode chamber, combining with hydroxide ions to form sodium hydroxide. Hydrogen gas is also produced at the cathode. See, e.g., Otashu et al., "Demand Response-Oriented Dynamic Modeling and Operational Optimization of Membrane-Based Chlor-Alkali Plant," Computers & Chemical Engineering, (2018) (DOI: 10.1016 / j.compchemeng.2018.08.030), the contents of which are incorporated herein by reference in the entirety.

[0020] The chlor-alkali process has been integrated with other types of chemical production processes. For example, in the production of polyvinyl chloride (PVC), the chlorine produced by the chlor-alkali process has been immediately used to manufacture vinyl chloride monomer, a precursor to PVC. In another example, the chlor-alkali process has been integrated into the production process of propylene oxide and styrene monomer through the chlorohydrin process. In yet another example, the caustic soda produced in the chlor-alkali process has been integrated intoalumina refineries for bauxite processing.

[0021] FIGS. 1 through 6 represent nonlimiting but preferred embodiments in which, after undergoing any desired or necessary conditioning steps, a hydrogen-rich stream exits the chloralkali process and is directed to a hydrogen burner where it is combusted in the presence of an oxidant, such as oxygen, to generate heat. This heat is subsequently utilized in the adjoining titanium dioxide production unit to meet its thermal energy requirements. Additionally, the chloralkali unit produces streams of sodium hydroxide and chlorine, with the chlorine being used as a critical input in the titanium dioxide production process. As used herein, a stream is regarded as being rich in a certain compound (e.g., "chlorine-rich," "oxygen-rich," "hydrogen-rich," etc.) if such compound makes up at least 1% and preferably at least 5% of the molar composition of the stream.

[0022] In some additional nonlimiting embodiments, the hydrogen-rich stream from the chloralkali process may be augmented with an additional hydrogen stream obtained from a supplemental hydrogen production unit, for example, in situations in which the hydrogen produced by the chlor-alkali unit is insufficient to fully meet the heat demand of the titanium dioxide production process. The supplemental hydrogen production unit may be, for example, a water electrolysis system, and is integrated into the process to generate the additional hydrogen stream. This electrolysis unit provides produces oxygen in addition to hydrogen, and the former can be used in the oxidation step of the chloride process of titanium dioxide production process, where titanium tetrachloride from the chlorinator is converted into titanium dioxide pigment. The process can also incorporate chlorine from the chlor-alkali unit to chlorinate a titanium-bearing feedstock, such as titanium bearing mineral and / or ores.

[0023] The ratio of the mass production capacities of titanium dioxide and caustic soda is believed to be a significant parameter of integrated process and system according to the present disclosure. Though not wishing to be held to any particular theories, an ideal ratio of titanium dioxide production capacity to caustic soda production capacity on a unit of mass basis ("mass-to- mass ratio") is in a range of about 0.05 to about 1.0, preferably about 0.1 to about 0.5. and morepreferably about 0.2 to about 0.4.

[0024] As noted above, the chlor-alkali unit may implement an electrolysis process that produces chlorine, hydrogen, and caustic soda by electrolysis of a saltwater brine. For example, the chlor-alkali unit may include a water electrolyzer to implement the electrolysis process. Additional processes and / or components may also be present in the chlor-alkali unit as understood in the art.

[0025] The titanium dioxide production unit may include a chlorinator that uses a titanium- bearing feedstock (e.g., titanium bearing ore) and chlorine as inputs. The chlorinator may be a fluidized bed reactor that mixes the titanium-bearing feedstock with chlorine at an elevated temperature to produce titanium tetrachloride (TiCh) in a chlorination reaction. A reducing agent for the chlorination reaction, such as coke, may also be present in the chlorinator. The chlorine may be delivered directly to the chlorinator with a first piping system connecting the chlor-alkali unit with the chlorinator. The first piping system may include additional vessels, valves, pumps and / or other components to aid in conducting the chlorine from the chlor-alkali unit to the titanium dioxide production unit. Additional processes and / or components may also be incorporated in the titanium dioxide production unit to subsequently process the TiCh to ultimately generate the titanium dioxide from the TiCh as understood in the art.

[0026] The hydrogen can be used to generate heat for the chloride process can be conducted from the chlor-alkali unit directly to the chlorinator with a second piping system that connects the chlor-alkali unit to the chlorinator. The combustion may be performed with a hydrogen burner that receives the hydrogen via the first piping system and combusts the hydrogen with oxygen to provide process heat to the chlorinator to help drive the chlorination reaction and / or other processes of the chloride process requiring process heat input.

[0027] In some nonlimiting configurations, a portion of the chlorine from the chlor-alkali unit may be separated out and used in one or more other integrated processes apart from the chloride process to produce titanium dioxide. For example, the separated-out chlorine may be used in the production of hydrochloric acid. Alternatively or in addition, a portion of the hydrogen from thechlor-alkali unit may be separated out and used as a material input in one or more other integrated processes apart from the titanium dioxide production. As examples, the separated hydrogen may be used in the oxidation step of the chloride process for converting titanium tetrachloride from the chlorinator into titanium dioxide pigment, or to produce other chemicals and materials including but not limited to metals and alloys, or to produce hydrochloric acid by reacting hydrogen with chlorine. Another application for the hydrogen produced by systems and processes disclosed herein is as a reducing agent in the production of direct reduced iron (DRI) from iron-bearing ores.

[0028] In embodiments in which supplemental hydrogen is produced with a supplemental hydrogen production unit for the chloride process, the supplemental hydrogen may be routed via the second piping system to one or more burners configured for combusting the hydrogen and providing process heat to the titanium dioxide production unit. In embodiments in which the supplemental hydrogen production unit also produces oxygen, the oxygen may be used as an input to the chloride process, either as an oxygenation supply for the hydrogen burner or to another component in the chloride process. The supplemental hydrogen production unit may include a water electrolyzer that splits water into component hydrogen and oxygen gases. A splitter may then be utilized to direct the supplemental hydrogen to the burner and to direct the supplemental oxygen to another component of the titanium dioxide production unit. In embodiments in which supplemental hydrogen is used, the mass-to-mass ratio of titanium dioxide to caustic soda production capacities can be about 0.1 to 10, preferably about 0.2 to 5. and more preferably about 0.35 to 1.0.

[0029] A supplemental heat source may be utilized to provide additional / supplemental process heat for the chloride process in the titanium dioxide production unit. For example, steam from the system may be used as an additional heat source alongside the heat generated from combusting the hydrogen.

[0030] Electrical power to operate the chlor-alkali process and the chloride process may be generated and / or supplied using both renewable energy sources, such as solar energy, wind energy, and biomass energy, and non-renewable energy sources, such as refined or unrefined petroleumproducts, natural gas, and / or other fossil fuels. The electrical power to operate the chlor-alkali process and the chloride process may be generated and / or supplied using exclusively renewable energy sources.

[0031] Turning now to the nonlimiting embodiments represented in the drawings, FIG. 1 is a flowsheet illustrating a first nonlimiting embodiment of an integrated system 10 and attendant processes for co-production of caustic soda and titanium dioxide. The integrated system 10 includes a chlor-alkali unit 12 for the production of caustic soda using the chlor-alkali process and a titanium dioxide production unit 14 for the production of titanium dioxide using the chloride process. A particular example of the chlor-alkali unit 12 includes a water electrolyzer that produces chlorine gas, hydrogen gas, and caustic soda by electrolysis of a saltwater brine. Additional processes and / or components may also be present in the chlor-alkali unit as understood in the art. A particular example of the titanium dioxide production unit 14 includes a fluidized bed reactor that mixes a titanium -bearing ore with the chlorine gas obtained from the chlor-alkali unit 12 at an elevated temperature in the presence of coke, which drives a chlorination reaction to produce titanium tetrachloride (TiCh). The chlor-alkali unit 12 (and its attendant processes) and the titanium dioxide production unit 14 (and its attendant processes) are integrated together to function together, for example by various piping systems, including a first piping system 16 for delivering chlorine gas produced by the chlor-alkali process to the titanium dioxide production unit 14 for use in the chloride process and a second piping system 18 for delivering hydrogen gas from the chlor-alkali process to a hydrogen burner 20 that provides process heat to the titanium dioxide production unit 14. An incoming stream 22, containing the primary raw material for the chloralkali process, such as saltwater brine, is processed in the chlor-alkali unit 12 to produce hydrogen, chlorine, and caustic soda. A hydrogen-rich stream is then transported, for example via the piping system 18, to the burner 20. The hydrogen-rich stream may undergo additional processing to ensure it meets the appropriate conditions for combustion. In the burner 20, the hydrogen from the hydrogen-rich stream is combusted in the presence of an oxidant, such as oxygen, to generate heat. This heat is conveyed as a process heat (thermal) stream 24 of process heat to the titanium dioxide production unit 14. It is noted that in the drawings solid lines with arrowheads for 16, 18, 22, 28,32, etc., represent material streams, indicating the flow of materials from one process unit to another, while broken lines with arrowheads (e.g., the process heat stream 24 in FIG. 1) depict the flow of heat energy, illustrating the transfer of heat between units. The process heat stream 24 can be one of any number of process heat streams that convey heat to various processes and units within the titanium dioxide production unit 14. Typically, the process heat stream 24 provides process heat to a chlorinator to help drive the chlorination reaction. The titanium dioxide production unit 14 encompasses all processes and equipment required for a chloride-route titanium dioxide production process. Thus, the process heat stream 24 signifies the transfer of heat from the burner 20 (or multiple burners) to one or more process components (units) within the overall titanium dioxide production unit represented by 14.

[0032] For the avoidance of doubt, examples of process units to which heat from the burner 20 is transferred in the titanium dioxide production unit 14 include, but are not limited to chlorine vaporization units, recycle-chlorine preheaters, titanium tetrachloride heating and vaporization units, distillation column reboilers, oxygen preheaters, air preheaters, spray dryers, water boilers, and steam generators. As is well known in the art, heat in the process heat stream 24 may be transferred by conduction, convection, or radiation. In the case of conductive heat transfer, the process heat stream 24 is directed through a heat-exchanger device that transfers thermal energy from the process heat stream 24 to another process stream. A common example of such a device is a shell-and-tube heat exchanger. In the case of convective heat transfer, the primary heat-transfer medium comprises combustion products exiting the burner 20 that are rich in water vapor, and the process heat stream 24 directly contacts a colder process medium to effect the transfer of thermal energy.

[0033] The chlor-alkali unit 12 also produces a chlorine-rich stream, which is directed via the piping system 16 to the titanium dioxide production unit 14 as a material input for the chlorination reaction that occurs within the unit 14. Like the hydrogen-rich stream, the chlorine-rich stream may undergo further processing to meet the specific requirements of the titanium dioxide production unit 14. By combining the chlor-alkali unit 12 and the titanium dioxide production unit14, the integrated system 10 produces both caustic soda and titanium dioxide as primary products. For example, the chlor-alkali unit 12 also generates a product stream 26 that is rich in caustic soda, and the titanium dioxide production unit 14 generates a product stream 28 that is rich in titanium dioxide. Thus, the integrated system 10 involves supplying heat energy to a chloride-route titanium dioxide production process of the titanium dioxide production unit 14 by burning hydrogen generated from an adjoining chlor-alkali unit 12, which also supplies chlorine as a raw material input to the titanium dioxide production unit 14. In this nonlimiting embodiment, the chlor-alkali unit 12 may generate sufficient hydrogen for combustion in the burner 20 to provide all the heat required for the operation of the adjoining titanium dioxide production unit 14.

[0034] With reference to FIG. 2, another integrated system 100 for co-production of caustic soda and titanium dioxide is shown. In this nonlimiting embodiment, the hydrogen produced by the chlor-alkali unit 12 is or may be insufficient to meet the total heat requirements of the system 100, in particular, that of the titanium dioxide production unit 14. To address this, a supplemental hydrogen production unit 30 is incorporated to generate supplemental hydrogen. This additional hydrogen, combined with the output from the chlor-alkali unit 12, provides the necessary fuel to meet the total heat requirements of the system 100. The system 100 is generally similar to the system 10 except for including the optional supplemental hydrogen production unit 30. The integrated system 100 includes the chlor-alkali unit 12, titanium dioxide production unit 14, burner 20, piping systems 16 and 18, process heat stream 24, and product streams 26 and 28, substantially as described previously herein. In situations where the chlor-alkali unit 12 does not generate sufficient hydrogen to meet the heat requirements of the titanium dioxide production unit 14, this embodiment is enhanced by incorporating the supplemental hydrogen production unit 30. The supplemental hydrogen production unit 30 may be, for example, a water electrolyzer, although other hydrogen production devices or hydrogen supplies could be used. The supplemental hydrogen production unit 30 processes an input stream 32, which would primarily contain water in the case of an electrolyzer, to produce a supplemental hydrogen stream 34 of hydrogen-rich gas. After undergoing any necessary processing to meet the burner's specifications, the supplemental hydrogen stream 34 is then directed to the burner 20 for providing supplemental fuel for heatingthe titanium dioxide production unit 14. In such a case where a supplemental hydrogen production unit 30 is desired or required, the mass-to-mass ratio of titanium dioxide to caustic soda production capacities can be 0.1 to 10, preferably 0.2 to 5.0, and more preferably 0.35 to 1.0.

[0035] With reference to FIG. 3, another integrated system 200 for co-production of caustic soda and titanium dioxide is shown. In this nonlimiting embodiment, the supplemental hydrogen production unit 30 also produces oxygen, which is utilized as a material input and / or as an oxidant in the titanium dioxide production unit 14. The system 200 is generally similar to the systems 10 and 100 except as described hereinafter. The integrated system 200 includes the chlor-alkali unit 12, titanium dioxide production unit 14, burner 20, piping systems 16 and 18, process heat stream 24, product streams 26 and 28, supplemental hydrogen production unit 30, input water stream 32, and supplemental hydrogen stream 34, substantially as described previously herein. In this embodiment, the supplemental hydrogen production unit 30 also generates oxygen. For example, the supplemental hydrogen production unit 30 may be a water electrolyzer that separates water into hydrogen and oxygen gases. These two gases may be separated to form an oxygen stream 36 of oxygen-rich gas as well as the supplemental hydrogen stream 34. The oxygen stream 36, after any necessary processing, is directed to the titanium dioxide production unit 14, where it is used as a material input and / or as an oxidant in the chloride process of the titanium dioxide production within the unit 14.

[0036] FIG. 4 represents yet another integrated system 300 for co-production of caustic soda and titanium dioxide. In this nonlimiting embodiment, the oxygen generated from the supplemental hydrogen production unit 30 is depicted as split into two different streams 36a and 36b, one of which serves as an oxidant in the burner 20 and the second as a material input and / or oxidant in the titanium dioxide production unit 14. The system 300 is generally similar to the system 200 except as described hereinafter. The integrated system 300 includes the chlor-alkali unit 12, titanium dioxide production unit 14, burner 20, piping systems 16 and 18, process heat stream 24, product streams 26 and 28, supplemental hydrogen production unit 30, water input stream 32, supplemental hydrogen stream, and supplemental oxygen stream 36, substantially as describedpreviously herein. In FIG. 4, the oxygen stream 36 from the supplemental hydrogen production unit 30 is split by splitter unit 38 into the two streams, referred to as a first oxygen stream 36a and a second oxygen stream 36b. The splitter unit 38 is operatively disposed between the supplemental hydrogen production unit 30 and the titanium dioxide production unit 14 and the burner 20. The first oxygen stream 36a is directed to the burner 20 by an appropriate piping system to be used as an oxidant. The second oxygen stream 36b is directed to the titanium dioxide production unit 14 by an appropriate piping system to serve as a material input and / or as an oxidant for the chloride process of titanium dioxide production within the unit 14. The split ratio for dividing the oxygen stream 36 into the first and second oxygen streams 36a and 36b can be determined by persons skilled in the art based on process design and system optimization requirements. The first oxygen stream 36a sent to the burner 20 can be utilized as a supplemental oxidant, with the main oxidant possibly being air or oxygen from another source, such as system air or other oxygen source. However, the first oxygen stream 36a may be utilized as the primary or only oxidant used in the burner 20.

[0037] Any of the processes and integrated systems 10, 100, 200, and 300 of FIGS. 1 through 4 may use steam as a heat energy source that is operatively connected to the integrated system 10, 100, 200, or 300 as needed in any suitable way, for example, by suitable piping systems. The production of such steam may involve burning hydrogen to supply heat to one or more units within the system's steam production network. The steam may be generated using waste heat streams recovered from one or more units within the system, with heat from burning hydrogen optionally integrated into the heat recovery network for steam generation.

[0038] The processes and integrated systems 10, 100, 200, and 300 may be adapted to include a combination of heat energy sources from renewable fuels and / or nonrenewable fuels. For example, incorporating sources of hydrogen and / or fossil fuels and / or other suitable alternative energy sources can provide more flexible operation where heat energy is derived from a combination of hydrogen and / or oxygen generated by the chlor-alkali unit 12 and / or the supplemental hydrogen production unit 30 as well as other sources, such as natural gas, petroleum products, and otherfossil fuels, biomass, solar energy, geothermal energy, and other renewable energy sources.

[0039] In some configurations, the hydrogen -rich stream (carried by the piping system 18) from the chlor-alkali unit 12 may contain hydrogen in excess of what is needed for combustion at the bumer(s) 20. In such cases, the excess hydrogen may be separated from the hydrogen-rich stream before the required amount is directed to the burner 20 for combustion to generate process heat for the titanium dioxide production unit 14. The removed excess hydrogen can then be utilized for other process requirements, including as a material input for producing other chemicals and materials, including but not limited to metals and alloys, within the system. For example, the excess hydrogen could be used in the production of hydrochloric acid by reacting hydrogen with chlorine.

[0040] Another potential application of this hydrogen is its use as a reducing agent in the production of Direct Reduced Iron (DRI) from iron-bearing ores. FIG. 5 illustrates an exemplary embodiment of such configuration related to the use of hydrogen or excess hydrogen as a material input. In FIG. 5, a system 400 is depicted as comprising a splitter 50 that divides the hydrogen stream produced in the chlor-alkali unit 12 into streams 18a and 18b. The stream 18a is directed to the hydrogen burner 20, while the stream 18b is routed to the unit 14 as a feed stream serving as a reactant or process input for one or more reactions or operations within the unit 14. In this embodiment, the unit 14 may function as a titanium dioxide production unit, a direct-reduced-iron (DRI) production unit, or a combined TiCh-DRI processing unit. The integration of TiCh and DRI production within a single unit is feasible due to the nature of certain titanium-bearing feedstocks. For example, ilmenite, typically containing over 40% TiCh and over 40% iron oxides, can be processed to yield both DRI and titanium dioxide. Accordingly, the present invention is envisioned to encompass such integrated processing. In such cases, the process heat stream 24from the burner 20 may be used to supply or satisfy the thermal requirements for titanium dioxide production, DRI production, or both within the unit 14. It should be noted that a common application of hydrogen in DRI production is its use as a reductant during the reductive roasting of iron -bearing feedstocks such as ilmenite.

[0041] FIG. 6 represents a further embodiment in which excess hydrogen may also be produced from the combination of both the chlor-alkali unit 12 and the supplemental hydrogen production unit 30, resulting in a combined hydrogen output that exceeds the heat energy requirements of the integrated system 10, 100, 200, 300. In FIG. 6, a system 500 is depicted in which the stream supplemental hydrogen stream 34 from the supplemental hydrogen production unit 30 is combined with hydrogen stream from the chlor-alkali unit 12 within a mixer-splitter device 60. After appropriate conditioning, the mixer-splitter 60 aggregates the hydrogen streams and subsequently divides them into the streams 18a and 18b, the former stream 18a being directed to the burner 20 as previously described, while the second stream 18b is supplied to the unit 14 (DRI or combined DRI- TiCh) unit as a process feed. In particular, stream 18b may serve as a reductant for a DRI production process.

[0042] If the thermal requirements of any of the systems are met, any excess hydrogen generated in the process may be repurposed for other processes within the system, such as serving as a reducing agent in the production of DRI, or sold. These and other uses of this excess hydrogen may be determined by individuals skilled in the art.

[0043] The chloride process of titanium dioxide production is highly energy-intensive, requiring significant quantities of fuel for generation of process heat to drive the various reactions. Since the chlor-alkali process produces hydrogen, which can serve as a cleaner alternative to fossil fuels, the processes and integrated systems 10, 100, 200, 300, 400, and 500 provide an opportunity for integration that can improve the energy efficiency and / or reduce carbon usage from fossil fuels. By leveraging the chlorine and hydrogen outputs of the chlor-alkali process, a synergistic system is provided that may, in some configurations, meet both the material and energy demands of the titanium dioxide production system. This integration gains further significance in markets where there is demand for both titanium dioxide and caustic soda, or markets that rely heavily on imports for a combination of titanium dioxide and caustic soda. Furthermore, the integrated systems may be designed to convert excess chlorine into liquid chlorine or chlorine derivatives, such as hypochlorites used in water purification, creating a diversified revenue stream. Thus, the integratedapproaches disclosed herein address market demands while also fostering sustainable and environmentally friendly operations.

[0044] These processes and integrated systems, in some nonlimiting configurations, can leverage the synergistic integration of the chlor-alkali process and the chloride-route titanium dioxide production process to provide a more efficient process and / or reduce or eliminate the carbon footprint generated by the integrated systems. The integrated systems and processes for coproduction of titanium dioxide and caustic soda integrate two distinct chemical processes, the chlor-alkali process for caustic soda production and the chloride process for titanium dioxide production, leveraging the material outputs of the primarily electrically powered chlor-alkali process. This integration enables the use of chlorine from the chlor-alkali process as a material input for the chloride-route titanium dioxide production process while utilizing hydrogen to meet its heat energy needs. The hydrogen output of the chlor-alkali process may allow the heat required in the titanium dioxide production process to be entirely hydrogen-based, paving the way for a potentially fully decarbonized system. Complete decarbonization of a system could also be achieved when the electricity used across the system is sourced entirely from renewable energy, such as solar, wind, biomass, geothermal, or other renewable sources commonly known in the art.

[0045] In view of the above, it can be seen that many different arrangements of the integrated systems and the associated processes are possible, some nonlimiting examples of which are listed hereinafter.

[0046] In some arrangements, an integrated process for the co-production of titanium dioxide and caustic soda is provided that involves utilizing a chlor-alkali unit to produce caustic soda, chlorine, and hydrogen. The chlorine may then be used as an input for titanium dioxide production. The hydrogen may be combusted with an oxidant, such as oxygen or others known in the art, to generate heat for the system. The mass-to-mass ratio of titanium dioxide to caustic soda production capacities is preferably between 0.05 to 1.0, more preferably 0.1 to 0.5, and most preferably 0.2 to 0.4.

[0047] In some arrangements, a portion of the chlorine from the chlor-alkali unit may beseparated and utilized in other integrated processes apart from titanium dioxide production.

[0048] In some arrangements, a portion of the hydrogen from the chlor-alkali unit may be separated and utilized as a material input in other integrated processes, including but not limited to titanium dioxide production.

[0049] In some arrangements, a supplemental hydrogen production unit, such as a water electrolyzer, may be added to produce additional hydrogen to meet the heat requirements of the system. In such an arrangement, the mass-to-mass ratio of titanium dioxide to caustic soda production capacities is preferably between 0.1 to 10, more preferably 0.2 to 5.0, and most preferably 0.35 to 1.0.

[0050] In some arrangements, the supplemental hydrogen production unit may also generate oxygen, which may then be utilized as an input in the titanium dioxide production process.

[0051] In some arrangements, a portion of the chlorine from the chlor-alkali unit may be separated and utilized in other integrated processes apart from titanium dioxide production.

[0052] In some arrangements, a portion of the hydrogen from the chlor-alkali unit may be separated and utilized as a material input in other integrated processes, including but not limited to titanium dioxide production or the production of DRI.

[0053] In some arrangements, the integrated process may include using steam as an additional heat source alongside the heat generated from burning hydrogen.

[0054] In some arrangements, the entire system may rely exclusively on renewable energy sources, such as, but not limited to, solar, wind, biomass, or any combination thereof, to generate and supply electrical power to operate all hydrogen-producing units, including the chlor-alkali unit, and other units requiring electrical energy.

[0055] In some arrangements, the entire system may use a combination of renewable energy sources, such as solar, wind, biomass, or any combination thereof, and non-renewable energy sources, such as fossil fuels or natural gas, to generate and supply electrical power to operate all hydrogen-producing units, including the chlor-alkali unit, and other units requiring electricalenergy.

[0056] As previously noted above, though the foregoing detailed description describes certain aspects of one or more particular embodiments of the invention, alternatives could be adopted by one skilled in the art. For example, the integrated systems 10, 100, 200, 300, 400, and 500 and their components could differ in appearance and construction from the embodiments described herein and shown in the drawings, functions of certain components of the integrated systems 10, 100, 200, 300, 400, and 500 could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function, and various materials could be used in the fabrication of the integrated systems 10, 100, 200, 300, 400, and 500 and / or their components. As such, and again as was previously noted, it should be understood that the invention is not necessarily limited to any particular embodiment described herein or illustrated in the drawings.

Claims

CLAIMS:

1. An integrated process for the co-production of titanium dioxide and caustic soda, the process comprising: producing caustic soda, chlorine, and hydrogen by a chlor-alkali process using a chloralkali unit; using the chlorine as input in a chlorinator of a chloride process to produce titanium dioxide; and combusting at least a portion of the hydrogen to generate heat for the chloride process.

2. The integrated process of claim 1, wherein the mass-to-mass ratio of titanium dioxide to caustic soda production capacities is about 0.05 to 1.0.

3. The integrated process of claim 2, wherein the mass-to-mass ratio of titanium dioxide to caustic soda production capacities is about 0.1 to 0.5, preferably about 0.2 to 0.4.

4. The integrated process of claim 1, wherein the combusting comprises combusting the portion of the hydrogen with oxygen.

5. The integrated process of claim 1, further comprising conducting the chlorine from the chlor-alkali unit directly to the chlorinator with a first piping system connecting the chlor-alkali unit with the chlorinator.

6. The integrated process of claim 1, further comprising conducting the portion of the hydrogen from the chlor-alkali unit directly to the chlorinator with a piping system connecting the chlor-alkali unit with the chlorinator.

7. The integrated process of claim 1, wherein the chlorinator comprises a fluidized bedreactor that mixes a titanium-bearing feedstock with the chlorine at an elevated temperature to produce titanium tetrachloride.

8. The integrated process of claim 1, wherein the chlor-alkali unit comprises is a water electrolyzer that produces the chlorine, the hydrogen, and the caustic soda by electrolysis of a saltwater brine.

9. The integrated process of claim 1, further comprising: separating a portion of the chlorine from the chlor-alkali unit; and using said separated portion of the chlorine to produce titanium dioxide and / or as a reductant in the production of direct reduced iron (DRI).

10. The integrated process of claim 9, wherein the at least one other integrated process includes an oxidation step of the chloride process for converting titanium tetrachloride from the chlorinator into titanium dioxide pigment.

11. The integrated process of claim 1, further comprising: separating a second portion of the hydrogen from the chlor-alkali unit; and using the second portion of the hydrogen as a reductant in the production of direct reduced iron (DRI).

12. The integrated process of claim 1, further comprising: separating a second portion of the hydrogen from the chlor-alkali unit; and using the second portion of the hydrogen as a material input to produce hydrochloric acid.

13. The integrated process of claim 1, further comprising: producing supplemental hydrogen with a supplemental hydrogen production unit; and producing additional heat for the chloride process with the supplemental hydrogen.

14. The integrated process of claim 13, wherein the supplemental hydrogen production unit comprises a water electrolyzer.

15. The integrated process of claim 13, wherein the mass-to-mass ratio of titanium dioxide to caustic soda production capacities is about 0.1 to 10.

16. The integrated process of claim 15, wherein the mass-to-mass ratio of titanium dioxide to caustic soda production capacities is about 0.2 to 5, preferably about 0.35 to 1.0.

17. The integrated process of claim 13, further comprising: producing oxygen with the supplemental hydrogen production unit; and using the oxygen as an input to the chloride process.

18. The integrated process of claim 1, further comprising using steam as an additional heat source alongside the heat generated from combusting the portion of the hydrogen.

19. The integrated process of claim 1, further comprising generating and supplying electrical power to operate the chlor-alkali process and the chloride process using exclusively renewable energy sources.

20. The integrated process of claim 19, wherein the renewable energy sources comprise at least one of solar energy, wind energy, and biomass energy.

21. The integrated process of claim 1, further comprising generating and supplying electrical power to operate the chlor-alkali process and the chloride process using both renewable energy sources and non-renewable energy sources.

22. The integrated process of claim 21, wherein the renewable energy sources comprise at least one of solar energy, wind energy, and biomass energy, and wherein the non-renewable energy sources comprise fossil fuels.

23. An integrated system for co-production of titanium dioxide and caustic soda, the integrated system comprising: a chlor-alkali unit for producing caustic soda, chlorine, and hydrogen by electrolysis of a saltwater brine; a titanium dioxide production unit for producing titanium dioxide with a chloride process using a titanium-bearing feedstock, chlorine from the chlor-alkali unit, and heat energy produced using the hydrogen from the chlor-alkali unit to produce the titanium dioxide; a first piping system coupling the chlor-alkali unit to the titanium dioxide production unit for conducting the chlorine from the chlor-alkali unit to the chloride process production unit; and a second piping system coupling the chlor-alkali unit to the titanium dioxide production unit for conducting at least a portion of the hydrogen from the chlor-alkali unit to the chloride process production unit.

24. The integrated system of claim 23, further comprising a burner operatively coupled to the second piping system and configured for combustion of the portion of the hydrogen and for providing heat from the combustion to the titanium dioxide production unit to drive the chloride process.

25. The integrated system of claim 24, further comprising a supplemental water electrolyzer configured to provide at least one of supplemental hydrogen and supplemental oxygen to the titanium dioxide production unit.

26. The integrated system of claim 25, further comprising a splitter configured to direct the supplemental hydrogen to the burner and to direct the supplemental oxygen to another componentof the titanium dioxide production unit.

27. The integrated system of claim 23, wherein the titanium dioxide production unit comprises a chlorinator comprising a fluidized bed reactor that mixes the titanium-bearing feedstock with the chlorine at an elevated temperature produced using the portion of the hydrogen to produce titanium tetrachloride (TiCh).

28. The integrated system of claim 23, wherein the chlor-alkali unit comprises a water electrolyzer that produces chlorine, hydrogen, and caustic soda through electrolysis of saltwater brine.

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