WO2024175668A1 - Dehalogenation of inorganic non-metal halogenides - Google Patents

Abstract

The present invention relates to a process for dehalogenating inorganic non-metal halogenides, characterized by contacting the halocarbon compound with elementary oxygen in the presence of a catalyst, the catalyst being a metal catalyst.

Description

Our reference: 240378WO EBO/BOE/rsc 21.02.2024

Dehalogenation of inorganic non-metal halogen compounds

The present invention relates to a process for the dehalogenation of inorganic non-metal halogen compounds.

Inorganic non-metal halogen compounds are used in various technical fields. Some examples are given below.

Sulfur hexafluoride SFe is used, for example, as a gas with electrical insulation properties in electrical systems, as a protective gas in the production of reactive metals (magnesium) and as an etchant in the electronics industry, as well as numerous other smaller applications, such as a contrast agent in medicine. Sulfur hexafluoride has a GWP (Global Warming Potential) of 23,900. This corresponds to an impact on global warming of the same number of CO2 equivalents. This makes it the most powerful known greenhouse gas with industrial application.

There is no known suitable material recycling of "used", i.e. contaminated, sulphur hexafluoride. The state of the art is the energy-intensive and technically demanding thermal cracking in cracking furnaces to produce low-value aqueous hydrofluoric acid (HF) and toxic sulphur dioxide, which must be absorbed.

Sulfur tetrafluoride SF4 is used, for example, as a fluorinating agent for inorganic oxides, sulfides or carbonyls. Phosphorus(III) fluoride PF3 is a toxic, odorless, colorless gas in low concentrations. PFs is Standard conditions a colorless, very toxic and non-flammable gas with a pungent odor.

In the chemical industry, boron trifluoride BF3 can be used as a catalyst or as a starting material for the production of various boron compounds for a variety of chemical reactions. Gaseous boron trifluoride and boron trifluoride adducts are mainly used as catalysts or co-catalysts, for example in the production of polymers, high-quality lubricating oils, pharmaceuticals, flavors and fragrances and other fine chemicals, as well as for the synthesis of boron compounds such as alkylboranes, aminoboranes and reagents for the Suzuki coupling. It is also used in the semiconductor industry as a boron supplier for ion implantation (p-doping), for the surface treatment of steel and glass and in neutron detectors.

Sulfuryl fluoride SO2F2 is a colorless and odorless gas that is used as an insecticide on foods such as grains, nuts, shellfish and dried fruits. It is also used to combat wood pests in objects, rooms or buildings. However, the gas has a high greenhouse potential. Emissions of this gas are increasing in port cities in particular, as the gas is used there as a disinfectant for wood during export. This is due, among other things, to the fact that the containers containing the gas have to be pumped out, which means that residues still end up in the environment. The pumped-out gas is usually condensed out, but can usually only be reused in a few cycles due to contamination.

Current disposal methods generally consist of hydrolysis and/or thermal recycling of hazardous substances to be disposed of with low value and limited return to the industrial recycling cycle ("closing the loop"). There is therefore a need for a process for the disposal of inorganic non-metal halogen compounds in which they are converted into compounds that are less harmful to the climate and less toxic. At the same time, the process should be sustainable in terms of the energy and resources required and, if possible, also in terms of the products obtained.

Surprisingly, it has been shown that disposal by dehalogenation is possible, whereby halogen atoms in the inorganic non-metal halogen compounds are replaced by hydrogen by means of heterogeneous catalysis on a metal catalyst. In a first embodiment, the object underlying the present invention is therefore achieved by a process for dehalogenating inorganic non-metal halogen compounds, which is characterized in that the inorganic non-metal halogen compound is brought into contact with elemental hydrogen in the presence of a catalyst, whereby the catalyst is a metal catalyst.

The present process thus enables the removal of halogens from inorganic compounds. In this process, a halogen-nonmetal element compound present in the molecule (i.e. in the inorganic nonmetal-halogen compound) is separated. The nonmetal is either reduced or the free valence is saturated by a hydrogen atom. Both variants are referred to in the invention as dehalogenation.

Inorganic non-metal halogen compounds in the sense of the present invention are compounds in which the free valences of a non-metal element are saturated with at least one halogen atom. According to the invention, it is particularly intended to use those compounds in the process in which the free valences of the inorganic non-metal are saturated with at least one halogen atom and optionally also with at least one oxygen atom. According to the invention, halogen atoms are selected from F, Cl, Br, I and At, in particular F, Cl and Br, preferably F. In this case, a non-metal element-halogen compound can have one, two or three different halogen atoms according to the invention, in particular it has one or two different halogen atoms, particularly preferably it is a compound between a non-metal element and a halogen atom, particularly preferably between a non-metal element and fluorine. In a further preferred embodiment, it is a compound between a non-metal element and a halogen atom, wherein the compound has at least one oxygen, preferably one or two oxygen atoms. According to the invention, the non-metal element is in particular phosphorus, sulfur, boron, carbon, selenium, silicon or phosphorus. The non-metal element is preferably selected from sulfur, phosphorus, boron, silicon or carbon, particularly preferably selected from sulfur, carbon or phosphorus, especially preferably selected from sulfur or phosphorus. In a particularly preferred embodiment, the inorganic non-metal halogen compound according to the invention is thus a compound between chlorine and/or fluorine and/or bromine with sulfur, phosphorus, boron, silicon or carbon, wherein the compound in a particularly preferred embodiment has at least one oxygen atom, in particular a compound between chlorine and/or fluorine and/or bromine with sulfur, carbon or phosphorus, wherein the compound in a particularly preferred embodiment has at least one oxygen atom, particularly preferably a compound between chlorine and/or fluorine and/or bromine with sulfur or phosphorus, wherein the compound in a particularly preferred embodiment has at least one oxygen atom, preferably one or two oxygen atoms. Particularly preferably, these are the respective fluorine compounds. Examples of inorganic non-metal halogen compounds are SFe, SF4, SO2F2, SOF4, SOF2, SO2CI2, SOCI2, _CF4 , COF2, COCI2, SF2, PF3, _PF5 , _POF3 , HPO2F2, BF3 or SiF4. Surprisingly, it has been shown that heterogeneous catalysis enables the dehalogenation of inorganic non-metal halogen compounds under relatively mild conditions. Since the catalyst is not consumed, it is sufficient if small amounts of it are present, so that an economical process can be provided.

Metals that are particularly suitable as catalysts are metals in their native state. However, they can also be in the form of alloys or in the form of pure and mixed metal compounds or oxides of pure or mixed metal compounds.

Particularly suitable metals are the late transition metals, as well as those whose passivation layers or surfaces have Lewis acid properties. Passivation layers are, for example, surface layers that have arisen through the oxidation of the metal. Late transition metals include, in particular, platinum, palladium, nickel, cobalt, rhodium, iridium, silver and gold. These can be used alone as native metals or as alloys, mixtures of the metals, oxides of individual metals, halides of individual metals or mixtures of metal oxides or metal halides. Platinum and/or palladium are particularly suitable. According to the invention, the catalyst preferably consists of these metals.

The present invention now describes for the first time a process in which inorganic non-metal halogen compounds or gas streams containing inorganic non-metal halogen compounds are reacted with a reducing agent in the presence of a catalyst and thereby dehalogenated. At least one halogen atom per molecule of the non-metal halogen compound is split off. Hydrogen is used as the reducing agent. The free valence on the inorganic non-metal halogen compound, preferably carbon, sulfur or phosphorus, is saturated by a hydrogen atom. The split-off halogen atom also reacts with hydrogen, producing hydrohalic acid as a byproduct.

The contacting of the inorganic non-metal halogen compound with hydrogen in the presence of the catalyst takes place under relatively mild conditions. According to the invention, the process is preferably carried out at a temperature of 200 °C to 800 °C, in particular 400 °C to 600 °C. Temperatures of 300 °C or more are also possible. Temperatures of 700 °C or less are particularly preferred. The exact temperature depends on the choice of catalyst and the inorganic non-metal halogen compound.

The process according to the invention preferably represents a heterogeneous catalysis. It can be carried out in the gas phase, but also in an inert solvent with dispersed catalyst under pressure in a high-pressure autoclave. For both the gas phase reaction and the reaction in suspension, the catalyst can be provided on a support, for example. Aluminum oxide is considered to be a particularly suitable support. The corresponding metal and not the support serves as the catalyst for the dehalogenation. In a preferred embodiment, the catalyst and in particular also the support are free of silicon, magnesium, tin and zinc. The support is particularly preferably made of aluminum oxide.

The contacting can be carried out, for example, in a furnace in which the inorganic non-metal halogen compound and hydrogen are passed together in gaseous form over the catalyst.

However, it is also possible according to the invention for the hydrogen to be provided as wet hydrogen. This wet hydrogen can also be passed in gaseous form together with the halogen-nonmetal compound over the catalyst. It is also possible for the halogen-nonmetal compound and the hydrogen to be brought into contact in a solvent. In this embodiment in particular, it is preferred if the hydrogen is provided as nitric hydrogen, i.e. forms directly in the solvent. However, it is also possible in this embodiment for hydrogen to be introduced into the solvent in gaseous form.

In this embodiment, acidic compounds such as sulfuric acid and other mineral and carboxylic acids, alkanes, halogenalkanes, aromatic solvents, alcohols, ethers and/or carbonates are used as solvents. Supercritical or liquefied gases are also conceivable.

However, the process according to the invention is particularly preferably a process in which inorganic non-metal halogen compounds are brought into contact with the catalyst with hydrogen in the gas phase.

In a preferred embodiment, the process according to the invention is characterized in that the inorganic non-metal halogen compound and hydrogen are provided at least in equimolar amounts. Equimolar refers to the number of halogen atoms in the inorganic non-metal halogen compound, with one hydrogen atom being provided for each halogen atom. Excess hydrogen may react with the non-metal, so that it is also possible to use hydrogen in excess.

If the inorganic non-metal-halogen compound also contains oxygen, equimolar can also refer only to the halogen atoms. In this case, the halogen-hydrogen compound is formed. The inorganic non-metal is then present as a non-metal-oxygen compound, which either left as is or reacted with hydrogen again in a subsequent step to obtain the non-metal and water. Accordingly, in these cases there must be two hydrogen atoms per oxygen atom.

According to the invention, it is included that oxygen-containing inorganic non-metal halogen compounds are reacted with hydrogen in two steps, as described above. It is also possible that the amount of hydrogen at the beginning of the reaction is provided in such amounts that one hydrogen atom per halogen atom in the inorganic non-metal halogen compound and two hydrogen atoms per oxygen atom in the inorganic non-metal halogen compound are introduced into the reaction chamber and react with one another in the presence of the catalyst.

The choice of a one-stage or two-stage process depends on the type of reactants and the desired process control.

According to the invention, unreacted reaction streams can be reused as reactants.

In the inorganic non-metal-halogen compound used as a starting material, all halogen atoms are removed from the molecule according to the invention. The non-metal is reduced according to the invention so that the corresponding element in pure form, the corresponding halogen-free non-metal oxide, is obtained. Alternatively and also according to the invention, the free valence on the non-metal element, which is created by the elimination of halogens, is fully or partially saturated with hydrogen.

The second product is anhydrous hydrohalic acids, such as HF, HCl, HI or HBr. In particular, anhydrous hydrofluoric acid (HF, also called a-HF) is a high-priced chemical that is subject to can be reused. Such products are not to be expected from the existing thermal recycling process, so that the process according to the invention is also economically relevant from this aspect.

However, depending on the non-metal halogen compound used, it is also possible that water is formed as a by-product. This by-product is observed when non-metal halogen compounds are reacted with at least one oxygen atom. In this case, halogen acids are obtained in aqueous solution.

In a preferred embodiment of the process according to the invention, the process is characterized in that the inorganic non-metal fluorine compound used has at least one oxygen atom, preferably one or two oxygen atoms.

The attached Figure 1 shows a schematic structure of a dehalogenation using the example of a defluorination in which inorganic non-metal halogen compounds are processed from a gas stream. The process can also be used analogously for other halogenated carbon compounds.

First, for example, SFe, which is present as a contaminated gas, is used. This is mixed with hydrogen and reacted over a platinum catalyst that is applied to an aluminum oxide carrier at a temperature of 400 °C to 600 °C. The escaping gas stream can be treated to liquefy anhydrous halogen acid, in this example hydrofluoric acid, and remove it from the gas stream. In addition, elemental sulfur can be removed from the gas stream. This condenses on the cool surfaces of the device. The remaining Gas stream can be added again to the mixing section and thus subjected to a new reaction in the presence of the catalyst.

It is therefore possible with the process according to the invention to convert inorganic non-metal halogen compounds and in particular inorganic non-metal fluorine compounds into the elementary non-metal element and the corresponding anhydrous hydrohalic acid. This does not produce any toxic or otherwise environmentally harmful products other than the desired target molecules, which can be reused as valuable materials and thus find their way into a circular economy. The process also takes place at mild temperatures, so that the energy requirement is also significantly lower than with previous processes.

In the following embodiment, the present invention is further explained in a non-limiting manner.

Implementation example 1:

A 25 x 500 mm quartz glass tube was filled in the middle with lg catalyst consisting of 5% platinum on aluminum oxide and fixed with quartz wool. This quartz tube was then placed in a tube furnace (Carbolite, type: MTF 12-25-250) and a gas mixture consisting of hydrogen and sulfur hexafluoride was passed through it. The hydrogen was dosed in a slight stoichiometric excess. The reaction took place in a range between 200 °C and 600 °C. The reaction became faster as the temperature increased. The yield was up to 76%, depending on the contact time with the catalyst.

The escaping reaction gas separated elemental sulphur in the form of a yellow to orange precipitate at the cooler parts of the glass tube From the remaining reaction gas, anhydrous HF could be condensed out with ice cooling and detected as pure hydrogen fluoride (HF).

Furthermore, it was possible to collect HF in a lye (e.g. in sodium hydroxide, potassium hydroxide or calcium hydroxide).

It is assumed that, upon full implementation, the following reaction occurred:

SF ₆ + 3 H ₂ -> 6 HF + 1/8 S ₈

Unreacted hydrogen and sulfur hexafluoride were recycled and passed over the catalyst again.

The reaction could be monitored using GC and GC-MS. This enabled hydrogen sulfide to be detected as an intermediate product.

An overdose of hydrogen can also lead to the formation of hydrogen sulphide if the sulphur is not separated from the reaction mixture in time or the reaction mixture is not cooled quickly enough.

Implementation example 2:

A 25 x 500mm quartz glass tube was filled in the middle with lg catalyst consisting of 5% palladium on aluminum oxide and fixed with quartz wool. This quartz tube was then placed in a tube furnace (Carbolite, type: MTF 12-25-250) and a gas mixture consisting of hydrogen and carbon tetrafluoride was passed through it. The hydrogen was dosed in a slight stoichiometric excess. The reaction took place in a range between 200 °C and 600 °C. As the temperature increased, the Reaction faster. The yield was up to 83%, depending on the contact time with the catalyst.

Hydrogen fluoride was separated as a liquid from the escaping reaction gas using an ice cooler and detected.

Furthermore, it was possible to collect HF in a lye (e.g. in sodium, potassium or calcium lye) and to detect it by ion chromatography.

It is assumed that, upon full implementation, the following reaction occurred:

CF4 + 4 H ₂ -> 4 HF + CH4

Unreacted tetrafluoromethane and hydrogen can be recycled and passed over the catalyst again.

The reaction could be monitored using GC and GC-MS, which demonstrated a step-by-step reduction.

Implementation example 3:

A 25 x 500 mm quartz glass tube was filled in the middle with lg catalyst consisting of 5% platinum on aluminum oxide and fixed with quartz wool. This quartz tube was then placed in a tube furnace (Carbolite, type: MTF 12-25-250) and the furnace slowly heated to 600 °C. After the furnace had reached this temperature, a gas mixture consisting of hydrogen and sulfuryl fluoride in a ratio of 1:3 was passed through it. The deposition of elemental sulfur can be observed in cooler areas of the tube furnace. Hydrogen fluoride and water as a liquid were separated and detected from the escaping reaction gas using an ice cooler.

It is assumed that, upon full implementation, the following reaction occurred:

SO2F2 + 4 H ₂ -> 2 HF + 1/8 S ₈ + 2 H2O

The reaction was monitored using GC and GC-MS. This enabled a step-by-step reduction to be demonstrated, which can be described as follows:

SO2F2 + H ₂ -> 2HF + SO2

SO2 + 2 H ₂ -> 2 H2O + 1/8 S ₈

Unreacted sulfuryl fluoride and hydrogen can be recycled and passed over the catalyst again.

Implementation example 4:

A 25 x 500 mm quartz glass tube was filled in the middle with lg catalyst consisting of 5% platinum on aluminum oxide and fixed with quartz wool. This quartz tube was then placed in a tube furnace (Carbolite, type: MTF 12-25-250) and the furnace slowly heated to 800 °C. After the furnace had reached this temperature, it was flowed through with a gas mixture consisting of hydrogen and sulfuryl fluoride in a ratio of 3:1.

Hydrogen fluoride and water as a liquid were separated and detected from the escaping reaction gas using an ice cooler. It is assumed that, upon full implementation, the following reaction occurred:

SO2F2 + 4 H2 -> 2 HF + H2S + 2 H2O

The reaction could be monitored using GC and GC-MS. This made it possible to demonstrate a step-by-step reduction, assuming that analogous steps to Example 3 were carried out, with the addition of hydrogen sulfide formation (presumably from elemental sulfur).

Claims

Patent claims 1. A process for the dehalogenation of inorganic non-metal halogen compounds, characterized in that the inorganic non-metal halogen compound is brought into contact with elemental hydrogen in the presence of a catalyst, wherein the catalyst is a metal catalyst. 2. Process according to claim 1, characterized in that the inorganic non-metal halogen compound has at least one oxygen atom. 3. Process according to claim 1 or 2, characterized in that metals in the native state, in the form of alloys and in the form of pure and mixed metal compounds and oxides are used as metal catalyst, wherein the metal/metals are selected from Pt, Pd, Ni, Co, Rh, Ir, Ag and/or Au and those whose surfaces and/or passivation layers have Lewis acid properties. 4. The method according to claim 3, characterized in that the catalyst is selected from Pt, Pd, Ni, Ag, Co, Rh, Ir and/or Au, in particular from Pt and/or Pd and/or Ni. 5. Process according to at least one of claims 1 to 4, characterized in that the contacting takes place at a temperature in the range from 200 °C to 800 °C, in particular from 400 °C to 600 °C. 6. Process according to at least one of claims 1 to 5, characterized in that the catalyst is applied to a support, in particular aluminum oxide. 7. Process according to at least one of claims 1 to 6, characterized in that it is a process for the defluorination of inorganic non-metal fluorine compounds. 8. Process according to at least one of claims 1 to 7. Characterized in that it is a process for the defluorination of inorganic non-metal fluorine compound and the inorganic non-metal fluorine compound preferably has at least one oxygen atom. 9. The method according to at least one of claims 1 to 8, characterized in that the non-metal is selected from phosphorus, sulfur, boron, carbon, selenium, silicon or phosphorus, preferably selected from sulfur, phosphorus, boron, silicon or carbon, particularly preferably selected from sulfur, carbon or phosphorus and especially preferably selected from sulfur or phosphorus. 10. Process according to at least one of claims 1 to 9, characterized in that the inorganic non-metal halogen compound and hydrogen are passed in gaseous form over the catalyst. 11. The method according to at least one of claims 1 to 10, characterized in that the hydrogen is provided as nascent hydrogen. 12. The method according to at least one of claims 1 to 11, characterized in that the contacting takes place in a solvent. 13. The method according to claim 12, characterized in that the solvent is selected from sulfuric acid and other mineral and carboxylic acids, alkanes, halogenalkanes, aromatic solvents, alcohols, ethers and/or carbonates.