Vapour phase catalytic process for the selective conversion of HCC-140 to HCFC-142

Abstract

The invention provides a process for manufacturing 1-chloro-2,2-difluoroethane (HCFC- 142) from 1,1,2-trichloroethane (HCC-140) and optionally, one or more of E / Z-1,2- dichloroethene (HCO-1130(E / Z)), E / Z-1-fluoro-2-chloroethene (HCFO-1131(E / Z)), and 1- fluoro-1,2-dichloroethane (HCFC-141). The invention also provides to a process for manufacturing a difluoroethyl derivative from HCFC-142 obtained using the process of the invention.

Description

[0001] VAPOUR PHASE CATALYTIC PROCESS FOR THE SELECTIVE CONVERSION OF HCC-140 TO HCFC-142 FIELD OF THE INVENTION The present invention relates to a process for manufacturing 1-chloro-2,2-difluoroethane (HCFC-142) from 1,1,2-trichloroethane (HCC-140) and optionally, one or more of E / Z-1,2- dichloroethene (HCO-1130(E / Z)), E / Z-1-fluoro-2-chloroethene (HCFO-1131(E / Z)), and 1- fluoro-1,2-dichloroethane (HCFC-141), in the vapour phase in the presence of a zinc chromia catalyst. The invention also relates to a process for manufacturing a difluoroethyl derivative from HCFC-142 obtained using the process of the invention. BACKGROUND PFAS (per- and polyfluoroalkyl substances) compliant materials are important in many commercial and industrial sectors, such as the energy sector, low global warming potential (GWP) refrigerant blends, agrochemicals, and pharmaceuticals. 1-chloro-2,2- difluoroethane (HCFC-142), which will be exempt from any PFAS legislation, is becoming an increasingly important feedstock material in the production of a wide range of PFAS compliant fluorinated materials. HCFC-142 is a useful -CF2 precursor that can be used in the production of many different difluoroethyl compounds of commercial interest, such as difluoroethyl alcohol, esters, ethers, and alkenes. For example, 2,2-difluoroethanol is of commercial interest for at least: as a feedstock for fluorinated electrolytes in lithium-ion batteries; as an intermediate in the synthesis of pesticides, such as penoxsulam; and in the synthesis of medicaments, such as mPGE. This is discussed further by Jiang Q., Li H., Xu W., et al, in a 2012 paper titled ‘Application of 2,2-difluoro-ethanol’ in Zhejiang Chemical Industry, 43(10):5-8. 2,2-Difluororethanol can be prepared from HCFC-142, for example by hydrolysis. The conversion of HCFC-142 to 2,2-difluoroethanol is discussed in CN 104030886. In another example, difluoroethylene compounds, such as 1,1-difluoroethylene (HFO- 1132a) and E / Z-1,2-difluorooethylene (HFO-1132(E / Z)), can be prepared from HCFC-142. Both HFO-1132a and HFO-1131(E / Z) have applications as heat transfer fluids. In addition, HFO-1132a is a monomer in the production of polyvinylidene (PVDF). PVDF is of growing interest due to its applications in lithium-ion batteries. The lithium-ion battery market is expected to rise dramatically in the near future meaning a cheap, sustainable method of PVDF production is of high importance, in which difluoroethyl compounds, such as HCFC- 142, could prove to be an important precursor. The production of 1,1-difluoroethylene (HFO-1132a), and E / Z-1,2-difluorooethylene (HFO- 1132(E / Z)) from HCFC-142 is discussed by Dolbier W R., Romelaer R., Baker J M., in a 2002 paper titled ‘Anomalous elimination of HCl from 2-chloro-1,1-difluoroethane. Likely involvement of a 1,2-FCl interchange mechanism’ in Tetrahedron Letters 43:8075-8077 and its mechanism discussed further by Beaver M R., Heard G L., Holmes B E., in a 2003 paper titled ‘Theoretical calculations of product percentage yields for the thermal decomposition of 2-chloro-1,1-difluoroethane’ in Tetrahedron Letters 44:7265-7268. Currently, HCFC-142 is a minor by-product in PVDF production, however increasing demand for HCFC-142 requires new dedicated production processes to be developed. Most conveniently, HCFC-142 is prepared by the hydrofluorination of 1,1,2-trichloroethane (HCC-140) or E / Z-1,2-dichloroethene (HCO-1130(E / Z)) using liquid or vapour phase catalytic process technology. Both routes have been investigated but in their present state of development neither are suitable for large scale commercial operation without significant improvements. The conversion of HCC-140 to HCFC-142 can be unselective with respect to by-products and poisons that foul the catalyst (tars in the case of liquid phase processes and coke in the case of vapour phase processes). Although some of the by-products can be recycled, many are refractory and have a very high fouling propensity and so the reactor feed composition would soon become dominated by them leading to uncontrollable fouling. In addition, the desired product, HCFC-142, can be over fluorinated to the undesired by- products 1,1,2-trifluoroethane (HFC-143) and 1,1,1-trifluoroethane (HFC-143a) and so conditions need to be carefully chosen to limit this. HCO-1130(E / Z) is frequently found as a by-product in the conversion of HCC-140 to HCFC- 142, indicating that it is an intermediate in the route to HCFC-142. HCO-1130(E / Z) is most likely formed from the dehydrochlorination of HCC-140. However, this is not the only pathway HCC-140 can take as, alternatively, direct substitution of chlorine (Cl) for fluorine (F) is possible, thereby avoiding the formation of unsaturated hydrocarbon intermediates, such as HCO-1130(E / Z). Two possible routes for the conversion of HCC-140 and HCO-1130(E / Z) to HCFC-142 are represented in Scheme 1 below. The righthand route shows conversion to HCFC-142 via the HCl / HF addition and elimination pathway. The lefthand route shows the conversion to HCFC-142 via the direct Cl / F substation pathway.

[0002] Scheme 1 - Conversion of HCC-140 and HCFO-1130 to HCFC-142 In practice, the pathway favoured in the conversion of HCC-140 to HCFC-142 will likely depend on the reaction conditions. In contrast to HCC-140, the conversion of HCO- 1130(E / Z) is strongly exothermic. In addition, the HCl / HF addition and elimination pathway is vulnerable to oligomerisation / polymerisation, and consequently catalyst coking, as the greater energy of the reaction may allow this barrier to be reached. The intermediate species in the HCl / HF addition and elimination pathway are susceptible to attack by both halide (fluoride and chloride) and the -electrons from an alkene double bond. Attack by the latter results in oligomer formation which is thought to eventually lead to coke formation. The larger exotherm can also promote catalyst crystallisation which not only deactivates the catalyst but can cause a runaway exothermic reaction, which is especially dangerous at commercial plant scale. However, the conversion of HCC-140 is not without its own drawbacks. HCC-140 releases two moles of HCl per mole of HCFC-142 formed, in comparison only one mole of HCl is released when converting HCFO-1130(E / Z). Suitable catalysts, such a chromia and zinc chromia catalysts, are susceptible to HCl inhibition which reduces the instantaneous activity of the catalyst. The skilled person will know that over the lifetime of an industrial catalyst the activity is steadily reduced, and the catalyst must eventually be replaced in an expensive procedure. Therefore, there is a need in the art for an improved process for the preparation of HCFC- 142 that is well-suited for large scale commercial operation by providing low / acceptable levels of catalyst fouling together with excellent feedstock conversion and selectivity for the desired HCFC-142 product. SUMMARY OF THE INVENTION The present invention provides a vapour phase process for the preparation of 1-chloro- 2,2-difluoroethane (HCFC-142) starting from 1,1,2-trichloroethane (HCC-140), and optionally, one or more of E / Z-1,2-dichloroethene (HCO-1130(E / Z)), E / Z-1-fluoro-2- chloroethene (HCFO-1131(E / Z)), and 1-fluoro-1,2-dichloroethane (HCFC-141), in the presence of a zinc chromia catalyst. In a first aspect, the present invention provides a process for manufacturing HCFC-142 comprising: a) contacting a reaction feed with a zinc chromia catalyst in a reactor, the feed comprising: hydrogen fluoride (HF), HCC-140, and optionally, one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141, in the vapour phase, wherein the ratio of HF:organic is greater than about 20:1; and b) maintaining the reactor at a pressure above atmosphere. In a second aspect of the present invention, there is provided a process for manufacturing a difluoroethyl derivative comprising: a) a process for manufacturing HCFC-142 according to the first aspect; and b) forming the difluoroethyl derivative from HCFC-142. It may be that in the second aspect of the invention, the process comprises an additional step, between steps a) and b), wherein HCFC-142 is isolated from the reactor effluent after step a). Alternatively, step b) may be carried out directly on the reactor effluent obtained from step a), i.e. without any purification and / or isolation steps. Preferably, the difluoroethyl derivative is a difluoroethyl alcohol, ester, ether, or alkene compound. In one embodiment the difluoroethyl derivative is 2,2-difluoroethanol or a difluoroethylene compound. In one preferred embodiment, the difluoroethyl derivative is 2,2-dilfuoroethanol and it may be that the 2,2-difluoroethanol is produced from the hydrolysis of HCFC-142. Such a reaction is disclosed in CN104030886 wherein HCFC-142 (110.5g), sodium hydroxide (60g), sodium iodide (0.5g) and sulfolane (140g with water content of 1000ppm) are heated to 200 °C and stirred for 10 hours. After distillation at 120 °C, 2,2-difluororethanol was obtained in 87% yield. In another preferred embodiment, the difluoroethyl derivative is 1,1-difluoroethlyene or E / Z-1,2-dilfuoroethylene. In one embodiment the conversion of HCFC-142 to 1,1- difluoroethlyene and / or E / Z-1,2-dilfuoroethylene is a catalytic conversion. In another embodiment, it is a non-catalytic conversion. Such a non-catalytic reaction is disclosed in Dolbier W R., Romelaer R., Baker J M., ‘Anomalous elimination of HCl from 2-chloro-1,1- difluoroethane. Likely involvement of a 1,2-FCl interchange mechanism’ Tetrahedron Letters 2002, 43:8075-8077, wherein HCFC-142 diluted in an inert gas i.e. He or N2, is heated to 650 °C to produce a mixture of 1,1-difluoroethlyene and E / Z-1,2- dilfuoroethylene. The process for manufacturing HCFC-142 according to the first aspect of the invention will now be described in detail. The ratio labelled “HF:organic” refers to the molar ratio of hydrogen fluoride (HF) to organic compounds in the reactor feed. The organic compounds in the reactor feed comprise HCC- 140 and, optionally, one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141. The ratio of HF:organic in the feed is greater than about 20:1. Preferably, the ratio of HF:organic in the feed is greater than about 22:1, such as greater than about 23:1. Even more preferably, the ratio of HF:organic in the feed is greater than about 24:1, such as equal to or greater than about 25:1. The reactor is maintained at a pressure above atmosphere. Preferably, the reactor pressure may be above about 3 barg, such as above about 5 barg. Even more preferably, the reactor pressure may above about 10 barg, such as equal to or greater than about 15 barg. The inventors have surprisingly and unexpectedly found that in the process of the invention, the combination of conditions described herein leads to favourable outcomes with regards to: i) selectivity for the desired product, HCFC-142; ii) minimising selectivity for HCO-1130(E / Z); and iii) reducing catalyst fouling. In addition, the conditions are advantageously well suited for the sustainable recycling of by-products, such as one or more of HCO-1130(E / Z), HCFO-1131(E / Z) and HCFC-141, into the reactor feedstock. Without wishing to be bound by theory it is thought that the reaction conditions used in the process of the invention promote conversion of the reactor feed to HCFC-142 through the Cl / F direct substitution pathway whilst unexpectedly not causing an increase in selectivity of the un-desired HFC-143 or HFC-143a by-products. By favouring the Cl / F direct substitution pathway the level of unsaturated compounds produced is reduced which is thought to reduce the catalyst fouling propensity of the by-products and stabilise intra- cycle performance. In a preferred embodiment, there is provided a process for manufacturing HCFC-142 comprising: a) contacting a reaction feed with a zinc chromia catalyst in a reactor, the feed comprising: HF, HCC-140 and optionally, one or more of HCO-1130(E / Z), HCFO- 1131(E / Z), and HCFC-141, in the vapour phase, wherein the ratio of HF:organic is greater than about 22:1; and b) maintaining the reactor at a pressure above about 3 barg. Advantageously, there is provided a process for manufacturing HCFC-142 comprising: a) contacting a reaction feed with a zinc chromia catalyst in a reactor, the feed comprising: HF, HCC-140 and optionally, one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC- 141, in the vapour phase, wherein the ratio of HF:organic is greater than about 23:1; and b) maintaining the reactor at a pressure above about 5 barg. In a more preferred embodiment, there is provided a process for manufacturing HCFC-142 comprising: a) contacting a reaction feed with a zinc chromia catalyst in a reactor, the feed comprising: HF, HCC-140 and optionally, one or more of HCO-1130(E / Z), HCFO- 1131(E / Z), and HCFC-141, in the vapour phase, wherein the ratio of HF:organic is greater than about 24:1; and b) maintaining the reactor at a pressure above about 10 barg. In an even more preferred embodiment, there is provided a process for manufacturing HCFC-142 comprising: a) contacting a reaction feed with a zinc chromia catalyst in a reactor, the feed comprising: HF, HCC-140 and optionally, one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141, in the vapour phase, wherein the ratio of HF:organic is greater than about 25:1; and b) maintaining the reactor at a pressure equal to or greater than about 15 barg. As reactor temperature increases, conversion of feedstock also increases as the system energy increases. However, increases in the reactor temperature can also cause selectivity for HCFC-142 to decrease together with an increase in the rate of catalyst crystallisation and fouling. Therefore, it is important that the reaction conditions used balance good feedstock conversion and HCFC-142 selectivity with low / acceptable levels of catalyst fouling. The temperature of the reactor in the process of the invention may be below about 350°C, such as equal to or below about 300°C. Preferably, the temperature of the reactor is equal to or below about 250°C, such as equal to or below about 220°C. More preferably, the temperature of the reactor is below about 250°C, for example below about 240°C. The temperature of the reactor in the process of the invention may be above about 180°C, such as equal to or above about 190°C. Preferably, the temperature of the reactor is equal to or above about 200°C, such as equal to or above about 210°C. Advantageously, the temperature of the reactor in the process pf the invention is from about 180°C to about 350°C, such as from about 190°C to about 300°C. Preferably the temperature of the reactor is from about 200°C to about 250°C, such as from about 210°C to about 220°C. In the process of the invention, it is expected that a higher contact time may also lead to a higher conversion of reactor feed. However, this can be at the expense of selectivity for the desired product, HCFC-142. For example, the skilled person would expect selectivity for the un-desired by products HFC-143 and HFC-143a to increase as contact time increases due to overfluorination. The contact time in the process of the invention may be from about 1 to about 500 seconds, such as from about 1 to about 300 seconds. Preferably, the contact time is from about 1 to about 200 seconds, such as from about 1 to about 100 seconds. Even more preferably, the contact time is from about 1 to about 50 seconds, such as from about 1 to about 20, 25, 30, 35, 40 or 45 seconds. Advantageously, the contact time is from about 5 to about 30 seconds such as from about 10 to about 25 seconds. Typically, the reactor feed will comprise fresh HF, a recycle stream comprising HF and fresh chlorinated organic feed containing e.g. HCC-140. In such embodiments, the HF reaction feed comprises fresh HF feed and recycled HF which further comprises HF and chlorinated and fluorinated organic intermediates e.g E / Z-1130, E / Z-1131 and 141. These HF containing feed streams are preferably combined, vapourised and superheated prior to introduction into the reactor. The fresh chlorinated organic feed is preferably combined with the vapourised and superheated stream that comprises HF as liquid droplets. These liquid droplets of the fresh chlorinated organic feed should be of a size that allows for rapid vapourisation and mixing with the vapourised and superheated stream that comprises HF for example 0.1-1000 um. These droplets may be produced by means, such as an atomizer, as may be known in the art. Rapid vapourisation of the fresh chlorinated organic feed and mixing with the vapourised and superheated stream that comprises HF can be aided by using a feed injector to produce the required chlorinated organic liquid droplets with the Venturi effect. The fresh chlorinated organic feed can be heated before it is introduced into the vapourised and superheated stream which comprises HF or it can be introduced at ambient temperature. The fresh chlorinated organic feed line can optionally include a particulate removal device (such as a mesh or straining device) to remove particulate matter such as that which might block the feed injection system. This particulate removal device may ideally be designed to remove particulate matter that is similar in size to the desired chlorinated organic feed droplet size. Optionally multiple parallel feed lines can be installed to facilitate maintenance (such as on-line clearing of blockages) without needing to shut down production. In the process of the invention, the reactor effluent comprises HCFC-142 and a mixture of by-products such as HCO-1130(E / Z), HCFO-1131(E / Z), HCFC-141, HFC-143, HFC-143a and HCC-140. In an embodiment, the reactor effluent comprises HCFC-142 and a mixture of by-products comprising HCO-1130(E / Z) and at least one of HCC-140, HFC-143, HFC- 143a, HCFC-141, HCFO-1131(E / Z). Conveniently, the largest organic component of the reactor effluent may be HCFC-142. Advantageously, in the process of the invention it may be that at least a portion of the by- product mixture is recycled to form part of the feed. Surprisingly, the inventors have found the process of the invention allows for by-product recycling without the feed becoming dominated with by-products. In an embodiment of the invention, at least a portion of the by-product mixture is recycled to form part of the feed. Preferably, certain compounds, such as HCl, HFC-143 and HFC- 143a, are removed from the by-product mixture before the by-product mixture is recycled. Therefore, when at least a portion of the by-product mixture is recycled, the reactor feed will comprise HF, HCC-140 and one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141. It is preferred that the amount of HCC-140 in the reactor feed is greater than or equal to about 25 weight %, relative to the total organic content in the feed. The reactor effluent from the process of the invention may contain less than 25 weight % HCO-1130(E / Z), such as less than 20 weight % HCO-1130(E / Z). Preferably the reactor effluent contains less than 15 weight % HCO-1130(E / Z), such as equal to or less than 10 weight % HCO-1130(E / Z). Conveniently, the process of the invention may further comprise a step of recovering HCFC- 142 from the reactor effluent, such as through distillation. Alternatively, or additionally, the process of the invention may further comprise a step for recovering HFC-143 and / or HFC-143a from the reactor effluent. Preferably the process of the invention is performed in the absence of an oxidising co-feed such as oxygen (O2). Therefore, in preferred embodiments of the invention the reactor feed is substantially free of oxygen (O2). Preferably the HF in the reactor feed is anhydrous. Therefore, in preferred embodiments of the invention the HF is substantially free of water (H2O). By "substantially no" and "substantially free of", we include the meaning that the process of the invention contains 500 ppm or less of the stated component, preferably 300 ppm or less. The process of the invention uses a zinc chromia catalyst. The inventors have found that the above-described combination of conditions, together with a zinc chromia catalyst, provides advantageous levels of feedstock conversion and selectivity for HCFC-142 balanced with low / acceptable levels of catalyst fouling resulting in a process which is well suited to be performed at scale and for commercial adaptation. By the term "zinc chromia catalyst" we mean that the metal oxide catalyst comprises chromia (chromium (III) oxide) and zinc or a compound of zinc. Preferably, the zinc chromia catalyst used in the process of the invention is present in fluorinated form, e.g., as a fluorinated zinc chromia catalyst. By the term "fluorinated zinc chromia catalyst" we mean that the metal oxide catalyst comprises chromia (chromium (III) oxide) and zinc, or a compound of zinc, and fluoride for example a mixed zinc and chromium oxyfluoride. Fluorinated zinc chromia catalysts can be conveniently prepared by treating a mixed chromium and zinc oxide precursor formulation with a mixture comprising hydrogen fluoride at elevated temperature and pressure. For the avoidance of doubt any description of the catalyst that follows includes both the zinc chromia catalyst and the fluorinated zinc chromia catalyst. The pore structure of solid porous materials can be determined by several methods, one of the most commonly used is the adsorption and desorption of N2, based on the BET theory (Brunauer, Emmett and Teller) of the adsorption of multilayers of condensed gases onto solid surfaces, and the evaporation (desorption) of the adsorbed gas during desorption. Nitrogen is a common adsorbate for probing the micro and mesoporous regions. From the adsorption and desorption isotherms, the following can be calculated: BET surface area from the adsorption of a monolayer of N2; total pore volume taken from the amount of nitrogen adsorbed at P / Po= 0.99; and average pore diameters can be determined using different calculations either based on the BET theory or that of BJH (Barrett, Joyner and Halenda), either from the adsorption or desorption data. Preferably, the total pore volume of the zinc chromia catalyst used in the process of the invention is equal to or greater than 0.2 cm3 / g or 0.25 cm3 / g. It is also envisaged that the total pore volume of the zinc chromia catalyst may be equal to or greater than 0.3 cm3 / g or 0.35 cm3 / g, such as equal to or greater than 0.4 cm3 / g, 0.45 cm3 / g, 0.5 cm3 / g, 0.55 cm3 / g or even 0.6 cm3 / g when measured by N2adsorption porosimetry. Preferably, the average pore width of the zinc chromia catalyst used in the process of the invention is greater than or equal to 60 Å, such as greater than or equal to 70 Å. It is also envisaged that the total pore width of the zinc chromia catalyst may be equal to or greater than 90 Å or 100 Å, such as greater than or equal to 110 Å or greater than or equal to 120 Å when measured by N2BET adsorption porosimetry. Preferably, the average pore width of the zinc chromia catalyst used in the process of the invention is greater than or equal to 60 Å, such as greater than or equal to 70 Å. It is also envisaged that the total pore volume of the zinc chromia catalyst may be equal to or greater than 90 Å or 100 Å, such as greater than or equal to 110 Å or greater than or equal to 120 Å when measured by N2BJH desorption porosimetry. Catalysts such as those described in the European patent application EP3509740, which is incorporated herein by reference, may be deployed in the methods of the present invention. In an embodiment, the zinc chromia catalyst used in the process of the invention has a total pore volume of greater than 0.3 cm3 / g and the mean pore diameter is greater than or equal to 90 Å, wherein the total pore volume is measured by N2 adsorption porosimetry and the mean pore diameter is measured by N2 BET porosimetry. The zinc chromia catalyst used in the process of the invention may have a total pore volume of greater than 0.35 cm3 / g and the mean pore diameter is greater than or equal to 100 Å, wherein the total pore volume is measured by N2 adsorption porosimetry and the mean pore diameter is measured by N2 BET porosimetry. Conveniently, the zinc chromia catalyst used in the process of the invention has a total pore volume of greater than 0.4 cm3 / g and the mean pore diameter is greater than or equal to 110 Å, wherein the total pore volume is measured by N2 adsorption porosimetry and the mean pore diameter is measured by N2 BET porosimetry. In a one embodiment, the zinc chromia catalyst used in the process of the invention has a total pore volume of greater than 0.45 cm3 / g and the mean pore diameter is greater than or equal to 120 Å, wherein the total pore volume is measured by N2 adsorption porosimetry and the mean pore diameter is measured by N2 BET porosimetry. In the process of the invention, the zinc chromia catalyst may comprise at least 80 weight % chromia, such as at least 85 weight % chromia. Preferably, the zinc chromia catalyst comprises at least 90 weight % chromia, such as at least 92 weight % chromia. Even more preferably the catalyst comprises at least 93 weight % chromia, such as at least 94 weight % chromia. Advantageously, the catalyst comprises at least 95 weight % chromia, such as at least 96 weight % chromia. The total amount of the zinc, or a compound of zinc, present in the zinc chromia catalysts utilised in the process of the invention is typically from about 0.01 weight% to about 25 weight %, preferably 0.1 weight % to about 25 weight %, conveniently 0.01 weight % to 6 weight % of the catalyst; and in some embodiments preferably 0.5 weight % to about 25 weight % of the catalyst, preferably from about 1 to 10 weight % of the catalyst, more preferably from about 2 weight % to 8 weight % of the catalyst, for example about 4 weight % to 6 weight % of the catalyst. Advantageously, the zinc chromia catalysts utilised in the process of the invention are unused, i.e. new. By 'unused' we mean that the catalyst possesses the total pore volume and average pore diameter, as specified above, before it has been contacted with any reagents or put under any pre-reaction conditions and / or the catalyst has not previously been used for catalysing a reaction or regenerated. The zinc chromia catalysts used in the process of the invention may be amorphous. By this we mean that the catalyst does not demonstrate substantial crystalline characteristics when analysed, for example, by X-ray diffraction. Alternatively, the zinc chromia catalysts may have a degree of crystallinity from 0.1 to 8.0% by weight of the catalyst in the form of one or more crystalline compounds of chromium and / or one or more crystalline compounds of zinc, such as from 0.1 to less than 8.0% by weight. Preferably, from 0.1 to about 7.5% by weight of the catalyst is in the form of one or more crystalline compounds of chromium and / or one or more crystalline compounds of zinc, such as from 0.1 to about 7.8% by weight. The zinc chromia catalysts utilised in the process of the invention may have a degree of crystallinity as defined above before use in a process of the invention. Preferably, the catalysts have a degree of crystallinity of from 0.1 to 5% by weight, for example from 0.2 to 2.5% by weight and most preferably from 0.3 to 1.5% by weight of the catalyst. Suitable catalysts may contain for example about 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 or 1.4% by weight of crystalline compounds of chromium, and / or crystalline compounds of zinc before use in a process of the invention. During use in a process of the invention the degree of crystallinity may change. Thus, it is possible that a zinc chromium catalyst has a degree of crystallinity as defined above before use in a process of the invention but will have a degree of crystallinity outside these ranges during or after use in the process of the invention. The metals in the catalyst are typically present in the form of metal oxides, oxyfluorides or fluorides. Thus, the crystalline material present in the zinc chromium catalyst is typically an oxide, oxyfluoride or fluoride of chromium and / or zinc, such as crystalline chromium oxide. The percentage of crystalline material in the catalyst can be determined by any suitable method known in the art. Suitable methods include X-ray diffraction (XRD) techniques. When X-ray diffraction is used the amount of crystalline material such as the amount of crystalline chromium oxide can be determined with reference to a known amount of graphite present in the catalyst (e.g. the graphite used in producing catalyst pellets) or more preferably by comparison of the intensity of the XRD patterns of the sample materials with reference materials prepared from suitable internationally recognised standards, for example NIST (National Institute of Standards and Technology) reference materials. Zinc chromia catalysts with total pore volumes and mean pore diameters can be synthesised according to the methods described in WO 2018 / 046928, which is incorporated in its entirety herein by reference. The desired level of crystallinity can then be induced to the zinc chromia catalyst to a controlled degree according to the methods described in WO 2006 / 106353, which is incorporated in its entirety herein by reference. In yet another aspect of the invention there is provided a process for the separation of HCFC-142 from a process stream which comprises HF, HCl, HCFC-142, HCO-1130(E) and at least one of HCO-1130(Z), HCO-1131(E), HCFO-1131(Z) and HFC-143, the process comprising: a) subjecting the process stream to a first distillation carried out in the range of about 10 to about 15 barg, to obtain a low boiling portion of composition comprising HCl and a high boiling portion of the composition comprising HF, HCFC-142, HCO- 1130(E) and at least one of HCO-1130(Z), HCO-1131(E), HCFO-1131(Z) and HFC- 143; b) subjecting the high boiling portion of the composition obtained from step a) to a second distillation, wherein the second distillation is carried out in the range of about 10 to about 15 barg to provide a high boiling composition comprising HF, HCFC-142, HCO-1130(E) and HCO-1130(Z) if present; and c) subjecting the high boiling portion of the composition obtained from step b) to a third distillation, wherein the third distillation is carried out in the range of about about 0 to about 5 barg to provide a low boiling portion of the composition comprising HF and a high boiling composition comprising HCFC-142, HCO-1130(E) and HCO-1130(Z) if present; d) subjecting the high boiling portion of the composition obtained from step c) to a fourth distillation, wherein the fourth distillation is carried out in the range of about 0 to about 1 barg to provide a low boiling portion of the composition comprising HCFC-142; e) recovering HCFC-142 to from step d). It has been surprisingly found that an azeotrope between HCFC-142 and HCO-1130(E) may be effectively separated by performing stages of distillation at the pressures described above. Moreover, it has been found that this process provides a high efficiency means for separating the various components of the process stream, such as for recovery or recycle. The process is thus of particular use in connection with the process for manufacturing HCFC-142 described herein. Preferably step (b) provides a low boiling composition comprising HFC-143 and HCFO- 1131(E / Z). This composition may be subject to a further distillation to recover HCFO- 1131(E / Z). Where the separation process is performed following a process for manufacturing HCFC- 142, HCFO-1131(E / Z) may be recycled to the reactor. In such a process, HFC-143 may be recovered. Similarly, where the separation process is performed following a process for manufacturing HCFC-142, in step (d) HCFO-1130(E / Z) may be recycled to the reactor having been isolated in a medium boiling composition. Water and other heavy components which may be present may be collected as a high boiling component in step (d). EXAMPLES The present invention will now be illustrated by the following non-limiting Examples, illustrated by the following drawings: Figure 1 shows a plot of selectivity for HCFC-142 in the effluent (weight %) against time (hours) during the reaction of Example 1, which was performed at 5 barg using a zinc chromia catalyst. Figure 2A shows a plot of selectivity for HCFC-142 in the effluent (weight %) against time (hours) during the reaction of Example 2A, which was performed at atmospheric pressure using a zinc chromia catalyst. Figure 2B shows a plot of selectivity for HCFC-142 in the effluent (weight %) against time (hours) during the reaction of Example 2B, which was performed at atmospheric pressure using a pure chromia catalyst. Example 1 – Preparation of HCFC-142 at 5 barg A commercially available zinc chromia catalyst (3mL, 2-3.35 mm of 6.5% ZnO / Cr2O3) was charged to a 0.5” OD Inconel 625 reactor supported by Inconel mesh. The catalyst was dried at 250 °C under 80 ml / min flowing nitrogen for at least 8 hours prior to pre- fluorination. HF vapour flowing at 5 ml / min was then passed over the catalyst along with 80 ml / min nitrogen at 250 °C and at 3 barg until HF breakthrough. The temperature was then ramped to 300 °C (25 °C / hr) and the nitrogen flow stepped down to 0 ml / min leaving neat HF passing over the catalyst. After HF breakthrough the reactor temperature was ramped to 380 °C (25 °C / hr) and held for 8 hours. The temperature was then reduced to the reaction temperature of 225 °C and the pressure increased to 5 barg. The reaction was then carried out by introducing a co-feed of HCC-140 (1,1,2-trichloroethane) vapour and HF vapour into the reactor. The flow rate of the feed was altered to target a HF:organic ratio of 25:1 and a contact time in the range of 18 to 24 seconds. Reactor off-gas was sampled periodically over 235 hrs of continuous running, into deionised water and analysed by GC to determine reaction progress. The results are shown in Table 1 below and a plot of selectivity of HCFC-142 against time is shown in Figure 1. After 235 hours of continuous running, the catalyst was regenerated, according to the procedure of example 3, from which the coke percentage can be calculated. After 235 hours, only 1.09% coke was produced. This indicates a surprisingly low fouling rate and implies that a much longer cycle time could be ran before reaching unsatisfactory levels of coke (typically >2%). As the results in table 1 below show, conversion of HCC-140 was consistently 100% throughout the cycle with no HCC-140 observed in the reactor off-gas. 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The catalyst was dried at 250 °C under 80 ml / min flowing nitrogen for at least 8 hours prior to pre- fluorination. The temperature was then ramped to 380 °C (25 °C / hr) and held for 8 hours with HF vapour flowing at 5 ml / min. The temperature was then reduced to the reaction temperature of 225 °C. The reaction was then carried out by introducing a co-feed of HCC- 140 (1,1,2-trichloroethane) vapour and HF vapour into the reactor. The flow rate of the feed was altered to target a HF:organic ratio of 25:1 and a contact time in the range of 18 to 24 seconds. Reactor off-gas was sampled periodically over 120 hrs of continuous running, into deionised water and analysed by GC to determine reaction progress. A plot of selectivity of HCFC-142 against time is shown in Figure 2A. Example 2B – Preparation of HCFC-142 at Atmospheric Pressure using a Pure Chromia catalyst The method as described in Example 2B was repeated, however this time using a commercially available pure chromia catalyst (2mL, 0.5-1.4mm of pure chromia). Reactor off-gas was sampled periodically from 0.5 to 38 hrs of continuous running, into deionised water and analysed by GC to determine reaction progress. A plot of selectivity of HCFC- 142 against time is shown in Figure 2B. The results show that the zinc chromia catalyst is a more effective catalyst for the production of HCFC-142 than a pure chromia catalyst. With the zinc chromia catalyst (example 2A), the product stream was dominated by HCO-1130Z and HCFC-142. When using pure chromia as the catalyst (example 2B), the preferred product was HCO-1130Z with a selectivity as high as 72% to just 19% HCFC-142. Example 3 – Catalyst Regeneration Prior to regeneration a temperature program was applied to the reactor with temperature ramping from 225 °C to 380 °C (25 °C / hour) and held at 380°C for 8 hours. This was done to purge the system of HF and organics and to protect the gas analyser. The catalyst was then treated with a 4:1 ratio of nitrogen:air and heated from 300 °C to 380 °C (25°C / hour) and held at 380 °C for 8 hours. For reactions performed at atmospheric pressure, 20ml / min nitrogen to 5 ml / min air was used, and for reactions performed at pressure, 80ml / min nitrogen to 20ml / min air was used. CO2, CO and O2 in the reactor off- gas was measured with a Rapidox 7100 Gas Analyzer. Coke percentage and rate could then be calculated. Examples 4 to 7 – Preparation of HCFC-142 The method as described in Example 1 was repeated, however this time using a different reaction temperature (200 or 250 °C), reaction pressure (8.8 or 10.0 barg) and a target HF:organic ratio of 40:1. The reactor off-gas was sampled by GC to determine reaction progress and the results are shown in Table 2 below, together with the reaction conditions. For each of Examples 4 to 7, the conversion of HCC-140 was consistently 100% with no HCC-140 observed in the reactor off-gas.

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Claims

CLAIMS 1. A process for manufacturing 1-chloro-2,2-difluoroethane (HCFC-142) comprising: a) contacting a reaction feed with a zinc chromia catalyst in a reactor, the feed comprising: hydrogen fluoride (HF), HCC-140, and optionally, one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141, in the vapour phase, wherein the ratio of HF:organic is greater than about 20:1; and b) maintaining the reactor at a pressure above atmosphere.

2. The process of claim 1, wherein the ratio of HF:organic in the feedstock is greater than about 22:

1.

3. The process of claim 2, wherein the ratio of HF:organic in the feedstock is greater than about 23:

1.

4. The process of claim 3, wherein the ratio of HF:organic in the feedstock is greater than about 24:

1.

5. The process of claim 4, wherein the ratio of HF:organic in the feedstock is equal to or greater than about 25:

1.

6. The process according to any of the preceding claims, wherein the reactor is maintained at a pressure above about 3 barg.

7. The process according to claim 6, wherein the reactor is maintained at a pressure above about 5 barg.

8. The process according to claim 7, wherein the reactor is maintained at a pressure above about 10 barg.

9. The process according to claim 8, wherein the reactor is maintained at a pressure equal to or greater than about 15 barg.

10. The process according to any of the preceding claims, wherein the temperature of the reactor is maintained below about 350 ^C.

11. The process according to claim 10, wherein the temperature of the reactor is maintained equal to or below about 300°C.

12. The process according to claim 11, wherein the temperature of the reactor is equal to or below about 250°C, such as below about 200°C.

13. The process according to any preceding claim, wherein the temperature of the reactor is below 250°C, e.g. below 240°C.

14. The process according to any of claims 11-13, wherein the temperature of the reactor is or equal to or below about 220°C.

15. The process according to any of claims 1 to 9, wherein the temperature of the reactor is from about 180°C to about 350°C.

16. The process according to claim 15, wherein the temperature of the reactor is from about 190°C to about 300°C, or from 190°C to less than 250°C.

17. The process according to claim 16, wherein the temperature of the reactor is from about 200°C to about 250°C.

18. The process according to claim 17, wherein the temperature of the reactor is from about 210°C to about 220°C.

19. The process according to any of the preceding claims, wherein the reactant / catalyst contact time is from about 1 to about 300 seconds.

20. The process according to any of the preceding claims, wherein the amount of HCC-140 in the reactor feed is greater than or equal to about 25 weight %.

21. The process according to any of the preceding claims, wherein the feed to the reactor does not contain O2.

22. The process according to any of the preceding claims, wherein the composition of HCO- 1130(E / Z) in the reactor outlet is less than 25 weight %.

23. The process according to claim 22, wherein the composition of HCO-1130(E / Z) in the reactor outlet is less than 20 weight %.

24. The process according to claim 23, wherein the composition of HCO-1130(E / Z) in the reactor outlet is less than 15 weight %.

25. The process according to claim 24, wherein the composition of HCO-1130(E / Z) in the reactor outlet is equal to or less than 10 weight %.

26. The process according to any of the preceding claims, wherein the reactor effluent comprises HCFC-142 and a by-product mixture comprising HCO-1130(E / Z) and at least one of HCC-140, HFC-143, HFC-143(a), HCFO-1131(E / Z), and HCFC-141.

27. The process according to any of the preceding claims further comprising the step of recovering HCFC-142 from reactor effluent.

28. The process according to any of the preceding claims, wherein at least a portion of the by-product mixture is recycled to form part of the feed.

29. The process according to claim 28, wherein the feed to the reactor comprises: HF, HCC- 140 and one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141, wherein at least a portion of the one or more of HCO-1130(E / Z), HCFO-1131(E / Z), and HCFC-141 originates from the reactor effluent.

30. The process according to any of the preceding claims, wherein the zinc chromia catalyst has a total pore volume of greater than 0.3 cm3 / g and the mean pore diameter is greater than or equal to 90 Å, wherein the total pore volume is measured by N2 adsorption porosimetry and the mean pore diameter is measured by N2 BET porosimetry.

31. The process according to claim 30, wherein the total pore volume of greater than 0.35 cm3 / g, for example greater than 0.4, 0.45, 0.5, 0.55, or 0.6 cm3 / g when measured by N2 adsorption porosimetry.

32. The process according to claim 30 or 31, wherein the mean pore diameter is greater than or equal to 100 Å, for example greater than or equal to 110 or 120 Å when measured by N2 BET porosimetry.

33. The process according to any of the preceding claims, wherein the zinc chromia catalyst comprises at least 80 weight %, such as at least 85, 90, 92, 93, 94, 95 or 96 weight % chromia.

34. The process according to any of the preceding claims, wherein the total amount of the zinc, or a compound of zinc, present in the zinc chromia catalyst is about 0.01% by weight to about 25% by weight of the catalyst.

35. The process according to claim 34, wherein the total amount of the zinc, or a compound of zinc, present in the zinc chromia catalyst is from 0.5% by weight to about 25% by weight of the catalyst, preferably from about 1 to 10% by weight of the catalyst, more preferably from about 2 to 8% by weight of the catalyst, for example from about 4 to 6% by weight of the catalyst.

36. The process according to any of the preceding claims, wherein the zinc chromia catalyst is a fluorinated zinc chromia catalyst.

37. The process according to any of the preceding claims, further comprising a process for the purification of HCFC-142 from the reactor effluent, the process comprising: a) subjecting the effluent to a first distillation carried out in the range of about 10 to about 15 barg, to obtain a low boiling portion of composition comprising HCl and a high boiling portion of the composition comprising HF, HCFC-142, HCO-1130(E) and at least one of HCO-1130(Z), HCO-1131(E), HCFO-1131(Z) and HFC-143; b) subjecting the high boiling portion of the composition obtained from step a) to a second distillation, wherein the second distillation is carried out in the range of about about 10 to about 15 barg to provide a high boiling composition comprising HF, HCFC-142, HCO-1130(E) and HCO-1130(Z) if present; and c) subjecting the high boiling portion of the composition obtained from step b) to a third distillation, wherein the third distillation is carried out in the range of about about 0 to about 5 barg to provide a low boiling portion of the composition comprising HF and a high boiling composition comprising HCFC-142, HCO-1130(E) and HCO-1130(Z) if present; d) subjecting the high boiling portion of the composition obtained from step c) to a fourth distillation, wherein the fourth distillation is carried out in the range of about 0 to about 1 barg to provide a low boiling portion of the composition comprising HCFC-142; e) recovering HCFC-142 to from step d).

38. A process according to claim 37, wherein step (b) provides a low boiling composition comprising HFC-143 and HCFO-1131(E / Z), preferably wherein this composition is subject to a further distillation to recover HCFO-1131(E / Z), for example for recycle to the reactor.

39. A process according to claim 37 or claim 38, wherein in step (d) HCFO-1130(E / Z) is recycled to the reactor having been recovered in a medium boiling composition.

40. A process for manufacturing a difluoroethyl derivative comprising: a) a process for manufacturing HCFC-142 according to any of claims 1 to 38; and b) forming the difluoroethyl derivative from HCFC-142.

41. The process according to claim 40, wherein the difluoroethyl derivative is 2,2- dilfuoroethanol; optionally wherein step b) comprises the hydrolysis of HCFC-142.

42. The process according to claim 40, wherein the difluoroethyl derivative is a dilfuoroethylene compound.

43. The process according to claim 42, wherein step b) comprises the catalytic conversion of HCFC-142 to 1,1-difluoroethlyene and / or E / Z-1,2-dilfuoroethylene.

44. The process according to claim 42, wherein step b) comprises the non-catalytic conversion of HCFC-142 to 1,1-difluoroethlyene and / or E / Z-1,2-dilfuoroethylene.

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