ES2802124T3 - Integrated HFC trans-1234ze manufacturing process - Google Patents

Abstract

A process for the production of trans-1,3,3,3-tetrafluoropropene comprising: (a) dehydrofluorinating 1,1,1,3,3-pentafluoropropane in the presence of a catalyst selected from the group consisting of fluorinated metal oxides a bulk and bulk metal fluorides in the absence of an oxygen-containing gas to thereby produce a result comprising cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and hydrogen fluoride; (b) optionally recovering hydrogen fluoride from the result of step (a); (c) isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropene to trans-1,3,3,3-tetrafluoropropene; (d) recovering trans-1,3,3,3-tetrafluoropropene; and (e) recycling cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane back to step (a) or to step (a) and (c).

Description

DESCRIPTION

Integrated HFC trans-1234ze manufacturing process

Background of the invention

The invention relates to an integrated process for the manufacture of trans-1,3,3,3-tetrafluoropropene (HFO trans-1234ze). More particularly, the invention relates to a process for the manufacture of 1HFO trans-1234ze by the first catalytic dehydrofluorination of 1,1,1,3,3-pentafluoropropane to thus produce a mixture of cis-1,3,3,3- tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride. Then optionally recover hydrogen fluoride, catalytically isomerize cis-1234ze to trans-1234ze and recover trans-1,3,3,3-tetrafluoropropene. Integration of an isomerization reactor loaded with a suitable isomerization catalyst helps convert cis-1234ze to its trans isomer, allowing for increased single-pass throughput of trans-1234ze.

Chlorofluorocarbons (CFCs) such as trichlorofluoromethane and dichlorodifluoromethane have been used as refrigerants, blowing agents, and diluents for gas sterilization. In recent years, there has been widespread concern that certain chlorofluorocarbons may be detrimental to the Earth's ozone layer. As a result, there is a worldwide effort to use halocarbons that contain fewer or no chlorine substituents. Consequently, the production of hydrofluorocarbons, or compounds containing only carbon, hydrogen and fluorine, has been the subject of increasing interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions, and power cycle working fluids. In this regard, trans-1,3,3,3-tetrafluoropropene (trans-1234ze) is a compound that has the potential to be used as a zero ozone depletion potential (ODP) refrigerant. and a low global warming potential (GWP) refrigerant, blowing agent, aerosol propellant, solvent, etc., and also as a fluorinated monomer.

It is known in the art to produce HFO-1234ze (ie, hydrofluorolefin-1234ze). For example, the US patent.

5,710,352 teaches the fluorination of 1,1,1,3,3-pentachloropropane (HCC-240fa) to form HCFC-1233zd and a small amount of HFO-1234ze. US Patent 5,895,825 teaches the fluorination of HCFC-1233zd to form HFC-1234ze. US Patent 6,472,573 also teaches the fluorination of HCFC-1233zd to form HFO-1234ze. US Patent 6,124,510 teaches the formation of cis and trans isomers of HFO-1234ze by dehydrofluorination of HFC-245fa in the presence of an oxygen-containing gas using a strong base or a chromium-based catalyst. European patent EP 0939071 describes the formation of HFC-245fa by fluorination of HCC-240fa through the intermediate reaction product which is an azeotropic mixture of HCFC-1233zd and HFO-1234ze.

These known processes have been determined to be uneconomical in relation to the performance of your product. It has also been observed that a significant amount of cis-1234ze is generated along with its trans isomer in these known processes. Therefore, there is a need for means by which trans-1234ze can be isolated from product mixtures and cis-1234ze can be recycled by fluorination to HFC-245fa or, more preferably, converted to trans-1234ze. Accordingly, the present invention provides an integrated process for producing trans-1234ze from which highly pure trans-1234ze can be obtained in higher yield than prior art processes and cis-1234ze can be isomerized to trans-1234ze in contrast with known processes. In particular, it has now been discovered that trans-1234ze can be formed by dehydrofluorinating 1,1,1,3,3-pentafluoropropane in the absence of an oxygen-containing gas to produce a mixture of cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride. Then optionally, but preferably by recovering hydrogen fluoride, catalytically isomerizing cis-1234ze to trans-1234ze, and then recovering trans-1,3,3,3-tetrafluoropropene. The unconverted cis-1234ze and HFC-245fa can be recycled directly.

JP 11 140002 A describes a method for producing 1,3,3,3-tetrafluoropropene from 1,1,1,3,3-pentafluoropropane by passing 1,1,1,3,3-pentafluoropropane through a reaction zone that has an elevated temperature in the gas phase.

Description of the invention

The invention provides a process for the production of trans-1,3,3,3-tetrafluoropropene comprising:

(a) dehydrofluorinate 1,1,1,3,3-pentafluoropropane in the presence of a catalyst selected from the group consisting of bulk fluorinated metal oxides and bulk metal fluorides in the absence of an oxygen-containing gas to thereby produce a result that comprises cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride;

(b) optionally recovering hydrogen fluoride from the result of step (a);

(c) isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropene to trans-1,3,3,3-tetrafluoropropene; (d) recovering trans-1,3,3,3-tetrafluoropropene; Y

(e) recycling cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane back to step (a) or to step (a) and (c).

Also described herein is a continuous and integrated manufacturing process for the production of trans-1,3,3,3-tetrafluoropropene comprising:

(a) dehydrofluorinate 1,1,1,3,3-pentafluoropropane performed as a vapor phase reaction to thereby produce a result comprising cis-1,3,3,3 tetrafluoropropene, trans-1,3,3 , 3-tetrafluoropropene and hydrogen fluoride;

(b) recovering hydrogen fluoride from the result of step (a);

(c) isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropene to trans-1,3,3,3-tetrafluoropropene; Y

(d) recovering trans-1,3,3,3-tetrafluoropropene.

The first stage of the process involves the catalytic conversion of HFC-245fa by dehydrofluorination of HFC-245fa to produce a result comprising a combination of cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3 -tetrafluoropropene and hydrogen fluoride. Dehydrofluorination reactions are well known in the art. Preferably, the dehydrofluorination of HFC-245fa is carried out in a vapor phase, and more preferably in a fixed bed reactor in the vapor phase. The dehydrofluorination reaction can be carried out in any suitable reaction vessel or reactor, but should preferably be constructed from materials that are resistant to the corrosive effects of hydrogen fluoride such as nickel and its alloys, including Hastelloy, Inconel, Incoloy and Monel or fluoropolymer lined containers. These can be single pipes or multiple pipes packed with a dehydrofluorinating catalyst which can be one or more of fluorinated metal oxides in bulk form and metal halides in bulk form. Other catalysts include carbon-supported transition metals, metal oxides, and halides. Suitable catalysts do not exclusively include fluorinated chromium (fluorinated Cr2O3), fluorinated alumina (fluorinated Al2O3) and metal fluorides (eg, CrF3, A F 3). Other catalysts include carbon-supported transition metals (zero oxidation state) such as Fe / C, Co / C, Ni / C, Pd / C. The HFC-245fa is introduced into the reactor either in pure, impure form or together with an optional inert gas diluent such as nitrogen, argon or the like. In one embodiment of the invention, HFC-245fa is pre-vaporized or preheated prior to entering the reactor. Alternatively, the HFC-245fa vaporizes within the reactor. Useful reaction temperatures can range from about 100 ° C to about 600 ° C. Preferred temperatures can range from about 150 ° C to about 450 ° C, and more preferred temperatures can range from about 200 ° C to about 350 ° C. The reaction can be carried out at atmospheric pressure, superatmospheric pressure, or under vacuum. The vacuum pressure can be from about 0.7 kPa to about 0.10 MPa (about 5 torr to about 760 torr). The contact time of the HFC-245fa with the catalyst can range from about 0.5 seconds to about 120 seconds, however, longer or shorter times can be used.

In one embodiment, the process flow is in the downward or upward direction through a catalyst bed. It may also be advantageous to periodically regenerate the catalyst after prolonged use while in the reactor. Regeneration of the catalyst can be accomplished by any means known in the art, for example, by passing air or air diluted with nitrogen over the catalyst at temperatures from about 100 ° C to about 400 ° C, preferably from about 200 ° C to about 375 ° C. ° C, for about 0.5 hours to about 3 days. This is followed by a HF treatment at temperatures of from about 25 ° C to about 400 ° C, preferably from about 200 ° C to about 350 ° C for fluorinated metal oxide and metal fluoride catalysts or H2 treatment at temperatures of about 100 ° C to about 400 ° C, preferably about 200 ° C to about 350 ° C for carbon supported transition metal catalysts.

Optionally but preferably, the hydrogen fluoride is recovered from the result of the dehydrofluorination reaction. The recovery of hydrogen fluoride is carried out by passing the composition resulting from the dehydrofluorination reaction through a sulfuric acid extractor to remove the hydrogen fluoride, subsequently desorbing the hydrogen fluoride extracted from the sulfuric acid and then distilling the fluoride from desorbed hydrogen. The separation can be accomplished by adding sulfuric acid to the mixture while the mixture is in a liquid or gaseous state. The typical weight ratio of sulfuric acid to hydrogen fluoride ranges from about 0.1: 1 to about 100: 1. You can start with a liquid mixture of fluorocarbons and hydrogen fluoride and then add sulfuric acid to the mixture.

The amount of sulfuric acid required for separation depends on the amount of HF present in the system. From the solubility of HF in 100% sulfuric acid as a function of a temperature curve, the practical minimum amount of sulfuric acid can be determined. For example, at 30 ° C, approximately 34 g of HF will dissolve in 100 g of 100% sulfuric acid. However, at 100 ° C, only about 10 g of HF will dissolve in 100% sulfuric acid. Preferably, the sulfuric acid used in this invention has a purity of about 50% to 100%.

In one embodiment, the weight ratio of sulfuric acid to hydrogen fluoride ranges from about 0.1: 1 to about 1000: 1. More preferably, the weight ratio ranges from about 1: 1 to about 100: 1 and most preferably from about 2: 1 to about 50: 1. Preferably, the reaction is carried out at a temperature of from about 0 ° C to about 100 ° C, more preferably from about 0 ° C to about 40 ° C, and most preferably from about 20 ° C to about 40 ° C. The extraction is generally carried out at normal atmospheric pressure, however, those skilled in the art may use higher or lower pressure conditions. By adding sulfuric acid to the mixture of fluorocarbons and HF, two phases quickly form.

An upper phase that is rich in fluorocarbons and a lower phase that is rich in HF / sulfuric to acid is formed. By the term "rich" is meant, the phase contains more than 50% of the indicated component in that phase, and preferably more than 80% of the indicated component in that phase. The fluorocarbon extraction efficiency can range from about 90% to about 99%.

After separation of the phases, the upper phase rich in fluorocarbons is removed from the lower phase rich in hydrogen fluoride and sulfuric acid. This can be done by decantation, siphoning, distillation, or other techniques well known in the art. Optionally, the fluorocarbon extraction can be repeated by adding more sulfuric acid to the lower removed phase. With about a 2.25: 1 weight ratio of sulfuric acid to hydrogen fluoride, an extraction efficiency of about 92% can be obtained in a single step. Preferably, the hydrogen fluoride and sulfuric acid are removed thereafter. The low solubility of HF in sulfuric at high temperatures can be exploited to recover the 1HF from sulfuric. For example, at 140 ° C, only 4 g of HF will dissolve in 100% sulfuric acid. The HF / sulfuric acid solution can be heated up to 250 ° C to recover the HF. HF and sulfuric acid can be recycled. That is, the e1HF can be recycled to a previous reaction for the formation of the HFC-245fa and the sulfuric acid can be recycled for use in additional extraction steps.

In another embodiment of the invention, the recovery of hydrogen fluoride from the mixture of fluorocarbon and hydrogen fluoride can be carried out in a gas phase by a continuous process of introducing a stream of sulfuric acid into a stream of fluorocarbon and hydrogen fluoride. This can be done in a standard scrubber by flowing a stream of sulfuric acid countercurrent to a stream of fluorocarbon and hydrogen fluoride. Sulfuric acid extraction is described, for example, in US Patent No. 5,895,639.

Alternatively, the HF can be recovered or removed using water or caustic scrubbers, or contacted with a metal salt. When using a water extractor, the technique is similar to that of sulfuric acid. When caustic is used, HF is removed from the system as a fluoride salt in aqueous solution. When metal salt is used (for example, potassium fluoride or sodium fluoride), it can be used alone or in conjunction with water. E1HF can be recovered when metal salt is used.

Then at least a portion of the cis-1,3,3,3-tetrafluoropropene is isomerized to trans-1,3,3,3-tetrafluoropropene. A stream of cis-1,3,3,3-tetrafluoropropene or its mixture with trans-1,3,3,3-tetrafluoropropene and / or 1,1,1,3,3-pentafluoropropane is fed to an isomerization reactor containing a suitable isomerization catalyst (e.g., bulk or supported fluorinated metal oxides, bulk or supported metal fluorides, carbon-supported transition metals, etc.) to convert the majority of cis-1234ze to trans-1234ze . The isomerization reaction can be carried out in any suitable reaction vessel or reactor, but should preferably be constructed from materials that are resistant to corrosion, such as nickel and its alloys, including Hastelloy, Inconel, Incoloy and Monel or lined vessels. with fluoropolymers. These can be single pipes or multiple pipes packed with an isomerization catalyst which can be a fluorinated metal oxide, metal fluoride, or a carbon-supported transition metal. Suitable catalysts do not exclusively include fluorinated chromium, chromium fluoride, fluorinated alumina, aluminum fluoride, and carbon supported cobalt. Useful reaction temperatures can range from about 25 ° C to about 450 ° C. Preferred temperatures can range from about 50 ° C to about 350 ° C, and more preferred temperatures can range from about 75 ° C to about 250 ° C. The reaction can be carried out at atmospheric pressure, superatmospheric pressure, or under vacuum. The vacuum pressure can be from about 0.7 kPa to about 0.10 MPa (about 5 torr to about 760 torr). The contact time of the cis-1,3,3,3-tetrafluoropropene with the catalyst can range from about 0.5 seconds to about 120 seconds, however, longer or shorter times can be used.

The trans-1,3,3,3-tetrafluoropropene can be recovered from the reaction product mixture comprising unreacted starting materials and by-products, including cis-1,3,3,3-tetrafluoropropene and any by-products and / or materials. starting by any means known in the art, such as by extraction and preferably distillation. The mixture of trans-1,3,3,3-tetrafluoropropene, unconverted cis-1,3,3,3-tetrafluoropropene, unreacted HFC-245fa and any by-products are passed through a distillation column. For example, the distillation can preferably be carried out in a standard distillation column at atmospheric pressure, superatmospheric pressure, or under vacuum. Preferably, the pressure is less than about 2 MPa (about 300 psig), more preferably less than about 1 MPa (about 150 psig), and most preferably less than 0.7 MPa (100 psig). The pressure in the distillation column inherently determines the distillation operating temperature. Trans-1,3,3,3-tetrafluoropropene has a boiling point of approximately -19 ° C; cis-1,3,3,3-tetrafluoropropene has a boiling point of about 9 ° C; HFC-245fa has a boiling point of approximately 15 ° C. The trans-1,3,3,3-tetrafluoropropene can be recovered as a distillate by operating the distillation column at a temperature of from about -10 ° C to about 90 ° C, preferably from about 0 ° C to about 80 ° C. Single or multiple distillation columns can be used. The distilled portion includes substantially all of the trans-1,3,3,3-tetrafluoropropene. The bottom stream from the distillation includes cis-1,3,3,3-tetrafluoropropene, HFC-245fa, a small amount of unrecovered HF, and any other impurities. Optionally, residual amounts of HF / HCl present in the bottom distillate are removed by passing through a water / caustic scrubber, and followed by a sulfuric acid drying column. The bottom stream is then further distilled using another distillation column. The cis-1234ze and HFC-245fa mixture is recovered as a distillate, which is then recycled back to the HFC-245fa dehydrofluorination reactor.

In the following alternative embodiments of the invention, the HFC-245fa dehydrofluorination reactor and the cis-1234ze isomerization reactor can be combined or independent. Isolation of trans-1234ze can be subsequent or prior to the cis-1234ze isomerization reaction.

Alternative 1:

(1) Combined reaction of dehydrofluorination of HFC-245fa and isomerization of cis-1234ze in a reaction vessel.

(2) Optional HF recovery.

(3) Isolation of trans-1234ze. The remaining mixture is recycled back to stage 1.

Alternative 2

(1) Catalytic dehydrofluorination of HFC-245fa in a composition comprising trans / cis-1234ze.

(2) Optional HF recovery.

(3) Isolation of trans-1234ze where the outlet stream from (2) is fed to a distillation column. The product, trans-1234ze, is isolated as a distillate from the rest of the mixture, ie, cis-1234ze, unreacted e1HFC-245fa, and other minor by-products. The residual amounts of HF / HCl present in the distillate are removed and then a drying step is carried out. The bottom stream from the distillation of (3) is divided into two streams and fed to stages (4) and (1), respectively. Optionally, a further distillation is carried out using another distillation column after step (3). In this distillation column, the mixture of cis-1234ze and HFC-245fa is recovered as a distillate, which is subsequently fed to step (4). The bottom stream from this second distillation column is recycled back to stage (1).

(4) Catalytic isomerization of cis-1234ze.

The cis-1234ze / HFC-245fa mixture from step (3) is fed to an isomerization reactor containing a suitable isomerization catalyst to convert the majority of cis-1234ze to trans-1234ze. The effluent from the catalytic reactor from stage (4) is fed to stage (3) for isolation trans-1234ze.

Alternative 3

(1) Catalytic dehydrofluorination of 245fa in trans / cis-1234ze.

(2) Optional HF recovery.

(3) Isolation of trans-1234ze

(4) Catalytic isomerization of cis-1234ze wherein the mixture comprising cis-1234ze and 245fa from step (3) is fed to an isomerization reactor containing a suitable isomerization catalyst to convert the majority of cis-1234ze to trans -1234ze.

(5) Isolation of trans-1234ze where the effluent from step (4) is fed to a distillation column. The product, trans-1234ze, is isolated as a distillate from the rest of the mixture, ie, cis-1234ze, the unreacted 245fa and other minor by-products. The bottom stream from the distillation from (5) is recycled back to step (1).

The following non-limiting examples serve to illustrate the invention.

Example 1

Dehydrofluorination of HFC-245fa on selected catalysts

Three different types of catalysts, namely fluorinated metal oxide, metal fluoride (s) and supported metal, were used for the dehydrofluorination of 245fa in Example 1. In each case, 20 cc of catalyst was used. A 100% feed of 245fa was flowed over catalyst at a rate of 12 g / hr. As shown in Table 1, all of the catalysts listed in Table 1 exhibited high activity (> 80% conversion of 245fa) and high selectivity to cis / trans-1234ze (> 90%) during the dehydrofluorination of 245.

Table 1

Example 2

Isomerization of cis-1234ze on selected catalysts

Three different types of catalysts, namely fluorinated metal oxide, metal fluoride (s) and supported metal, were used for the isomerization of cis-1234ze in Example 2. In each case, 20 cc of catalyst was used. A mixture of 85.3% cis-1234ze / 14.7% 245fa was flowed over catalyst at a rate of 12 g / h. For a specific catalyst, a suitable reaction temperature was carefully chosen so that there is almost no dehydrofluorination reaction to the HFC-245fa included in the feed. As shown in Table 2, all catalysts, except the 0.5% by weight Co / AC listed in Table 2, provided high activity (> 80% conversion of cis-1234ze) and high selectivity for trans-1234ze (> 95%) during cis-1234ze isomerization. The 0.5 wt% Co / AC catalyst exhibited moderate activity (45% conversion of cis-1234ze) and high selectivity to trans-1234ze (approximately 98%).

Table 2

Example 3

Isomerization of cis-1234ze in the presence of HF on fluorinated Cr2O3

In this example, the product stream from reactor 1 in which a dehydrofluorination reaction of 245fa was performed on a fluorinated C 2O3 catalyst was introduced at 350 ° C into reactor 2 which was also charged with a fluorinated Cr2O3 catalyst to Carry out the cis-1234ze isomerization reaction at 100 or 200 ° C in presence of HF (which was formed during dehydrofluorination of 245fa in reactor 1). Table 3 shows the flue gas compositions of the two reactors. At 100 ° C, the molar percentage of trans-1234ze was slightly higher in the exit gas of reactor 2 than in the exit gas of reactor 1, while the molar percentage of cis-1234ze was slightly lower and the molar percentage of 245fa was about the same thing. As a result, the molar ratio of trans-1234ze to cis-1234ze increased slightly (for example, from 3.96 to 4.36 after 1 hr in the stream) after the isomerization reaction, indicating that a small amount of cis-1234ze was converted to trans-1234ze through isomerization in reactor 2. At 200 ° C, the molar percentages of trans-1234ze and cis-1234ze were significantly lower in the reactor 2 exit gas than in the reactor 2 exit gas. reactor 1, while the molar percentage of 245fa was significantly higher. This indicates the occurrence of a hydrofluorination reaction between c / t-1234ze and HF. These results suggest that HF is preferably removed from the mixture before feeding it to the isomerization reactor to avoid hydrofluorination of trans / cis-1234ze to 245fa and increase the conversion of cis-1234ze to trans-1234ze.

Example 4

Combined dehydrofluorination of HFC-245fa and isomerization of cis-1234ze

Two different types of catalysts, namely fluorinated metal oxide and metal fluoride, were used for the combined reaction in Example 4. In each case, 20 ml of catalyst was used. A mixture of 8.2% cis-1234ze / 91.8% HFC-245fa was flowed over catalyst at a rate of 12 g / h. For a specific catalyst, a suitable reaction temperature was carefully chosen so that both the dehydrofluorination of HFC-245fa and the isomerization of cis-1234ze can take place at the same time. The HFC-245fa conversion and the trans-1234ze selectivity during the combined reaction were calculated assuming that cis-1234ze remains unchanged before and after the reaction. As shown in Table 4, the nominal selectivity of trans-1234ze was approximately 94%, which was much higher than that of the dehydrofluorination reaction of HFC-245fa. This result indicates the occurrence of isomerization of cis-1234ze to trans-1234ze during the combined reaction with the cis-1234ze / HFC-245fa mixture as feed. This example demonstrated that under optimal operating temperature, dehydrofluorination of HFC-245fa and isomerization of cis-1234ze can be performed simultaneously on the same catalyst in the same reactor.

Table 4

These examples demonstrate that the selected catalysts are, in fact, active for the dehydrofluorination of HFC-245fa to cis / trans-1234ze and the isomerization of cis-1234ze to trans-1234ze.

Claims (15)

1. A process for the production of trans-1,3,3,3-tetrafluoropropene comprising: (a) dehydrofluorinate 1,1,1,3,3-pentafluoropropane in the presence of a catalyst selected from the group consisting of bulk fluorinated metal oxides and bulk metal fluorides in the absence of an oxygen-containing gas to thereby produce a result that comprises cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride; (b) optionally recovering hydrogen fluoride from the result of step (a); (c) isomerizing at least a portion of the cis-1,3,3,3-tetrafluoropropene to trans-1,3,3,3-tetrafluoropropene; (d) recovering trans-1,3,3,3-tetrafluoropropene; Y (e) recycling cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane back to step (a) or to step (a) and (c). The process of claim 1 further comprising the subsequent step of recovering cis-1,3,3,3-tetrafluoropropene, or a mixture of cis-1,3,3,3-tetrafluoropropene and 1,1,1, 3,3-pentafluoropropane after step (d). 3. The process of claim 1 wherein step (b) is performed. 4. The process of claim 1 wherein: (i) steps (a) and (c) are carried out independently; or (ii) steps (a) and (c) are combined and performed as a single process step. 5. The process of claim 1 wherein step (d) is performed after step (c). The process of claim 1 wherein step (d) is carried out after step (a) but before step (c). 7. The process of claim 1 wherein step (d) is performed after step (a) but before step (c); and then step (d) is repeated after step (c). The process of claim 1, wherein step (d) is carried out by distilling the result of step (c) and recovering trans-1,3,3,3-tetrafluoropropene as a distillate and a residue comprising one or more of hydrogen fluoride, cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane. 9. The process of claim 8 further comprising the subsequent step of removing hydrogen fluoride from the residue. The process of claim 8 further comprising the subsequent step of recovering at least one of cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane from the residue and recycling at least one of the cis-1,3,3,3-tetrafluoropropene and 1,1,1,3,3-pentafluoropropane recovered back to step (a). The process of any preceding claim, wherein said dehydrofluorination step (a) is carried out at a temperature of 100 ° C to 600 ° C, preferably 150 ° C to 450 ° C, more preferably 200 ° C. C to 350 ° C. The process of any preceding claim, wherein said dehydrofluorination step (a) is carried out in the presence of a catalyst selected from the group consisting of fluorinated chromium, chromium fluoride, fluorinated alumina, and aluminum fluoride. The process of any preceding claim, wherein said dehydrofluorination step (a) is carried out in the vapor phase. The process of claim 1, wherein said isomerization step (c) is carried out in the presence of a catalyst selected from the group consisting of bulk fluorinated metal oxides and bulk metal fluorides. The process of any preceding claim, wherein said isomerization step (c) is carried out at a temperature of 25 ° C to 450 ° C, preferably 50 ° C to 350 ° C, more preferably 75 ° C at 250 ° C.