Process for dehydrochlorination of HCFC-244bb to produce HFO-1234yf

Abstract

The present application relates to a process for the dehydrochlorination of HCFC-244bb for the preparation of HFO-1234yf. The present invention discloses a process for the preparation of 2, 3, 3, 3-tetrafluoropropene (HFO-1234yf), the process comprising: providing a composition comprising 2-chloro-1, 1, 1, 2-tetrafluoropropane (HCFC-244bb) to a reactor comprising a heater surface at a surface temperature of greater than about 850 DEG F (454 DEG C); and then contacting the composition with a heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to produce HFO-1234yf.

Description

[0001] This application is a divisional application of an invention patent application with an application date of June 5, 2019, application number 201980040695.7, and name “Method for dehydrochlorinating HCFC-244bb to prepare HFO-1234yf”. Technical Field

[0002] The present disclosure relates to a process for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf). Specifically, the present disclosure relates to a process for dehydrochlorinating 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in the preparation of HFO-1234yf. Background Art

[0003] Hydrofluoroolefins (HFOs) such as tetrafluoropropylene are known effective refrigerants, fire extinguishing agents, heat transfer media, propellants, foaming agents, frothers, gaseous dielectrics, disinfectant carriers, polymeric media, particulate removal fluids, carrier fluids, polishing abrasives, displacement desiccants, and power cycle working fluids. Due to the questionable environmental issues associated with the use of some of these fluids, including the relatively high global warming potential associated therewith, in addition to zero ozone depletion potential (ODP), it is also desirable to use fluids with the lowest possible global warming potential (GWP). Therefore, there is considerable interest in developing environmentally friendly materials for the above-mentioned applications.

[0004] It has been determined that HFOs with zero ozone depletion and low global warming potential may fill this need. However, the toxicity, boiling points, and other physical properties of these chemicals vary greatly from isomer to isomer. One HFO with valuable properties is 2,3,3,3-tetrafluoropropene (HFO-1234yf or 1234yf).

[0005] HFO-1234yf has been shown to be a low-toxic, low-global warming compound and can therefore meet the increasingly stringent requirements for refrigerants in mobile air conditioners. Therefore, compositions containing 1234yf are among the substances being developed for many applications. Summary of the invention

[0006] The present disclosure provides a method for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf), the method comprising: providing a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor comprising a heater surface having a surface temperature greater than about 850°F (454°C); and then contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb, thereby preparing HFO-1234yf.

[0007] In one form thereof, the present disclosure provides a process for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: providing a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor comprising a heater surface having a surface temperature greater than about 850°F (454°C); and contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb, thereby producing HFO-1234yf.

[0008] The surface temperature of the heater surface may be about 870°F (466°C) to about 1,200°F (649°C). The contact time may be 0.1 seconds to 9 seconds. In some embodiments, the heater surface may include a catalytic surface. The catalytic surface may include electroless nickel, nickel, stainless steel, nickel-copper alloy, nickel-chromium-iron alloy, nickel-chromium alloy, nickel-chromium-molybdenum, or a combination thereof. In other embodiments, the heater surface may not be a catalytic surface.

[0009] The method may also include: evaporating the composition; and then heating the evaporated composition to a temperature of about 575°F (302°C) to 1,200°F (649°C) before providing the composition to the reactor. The method may also include: providing HFO-1234yf, HCl, and unreacted HCFC-244bb to a distillation column; separating the HFO-1234yf and HCl from at least a portion of the HCFC-244bb in the distillation column; recycling the separated HCFC-244bb to the composition before evaporating the composition; providing the HFO-1234yf and HCl to an HCl separation unit; and separating the HCl from the HFO-1234yf to form a product stream comprising the HFO-1234yf. The product stream may include HFO-1234yf at a concentration greater than 99.1% by weight, based on HCFC-244bb-free. The product stream may also contain 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 weight percent, based on HCFC-244bb free, as an indication of a low rate of carbon accumulation in the reactor. Heating the evaporated composition may include exchanging heat between the evaporated composition and HFO-1234yf and HCFC-244bb from the reactor prior to providing the HFO-1234yf and HCFC-244bb to the distillation column.

[0010] In another form thereof, the present disclosure provides a method for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf), the method comprising: evaporating a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb); dividing the composition into a first portion and a second portion; heating the evaporated first portion of the composition to a temperature of about 575°F (302°C) to 1,200°F (649°C); providing the composition to a reactor comprising a heater surface having a surface temperature greater than about 850°F (454°C); and contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb, thereby preparing HFO-1234yf. The reactor may include a first stage and a second stage downstream of the first stage. The first portion may be provided to the first stage, and the second portion may be provided to the second stage.

[0011] The method may also include: providing HFO-1234yf, HCl, and unreacted HCFC-244bb to a distillation column; separating the HFO-1234yf and HCl from at least a portion of the HCFC-244bb in the distillation column; recycling the separated HCFC-244bb to the composition before evaporating the composition; providing the HFO-1234yf and HCl to an HCl separation unit; and separating the HCl from the HFO-1234yf to form a product stream comprising the HFO-1234yf. The product stream may include a concentration of greater than 99.1% by weight of HFO-1234yf, based on a HCFC-244bb-free ratio. The product stream may also include a concentration of less than 0.1% by weight of 1,1,1,2-tetrafluoroethane, based on a HCFC-244bb-free ratio, as an indication of a low rate of carbon accumulation in the reactor.

[0012] Heating the first portion of the evaporated composition may include exchanging heat between the first portion of the evaporated composition and the HFO-1234yf and HCFC-244bb from the reactor prior to providing the HFO-1234yf and HCFC-244bb to the distillation column. The surface temperature of the heater surface may be from about 870°F (466°C) to about 1,200°F (649°C). The contact time may be from 0.1 seconds to 9 seconds. The heater surface may include a catalytic surface. The heater surface may not be a catalytic surface.

[0013] The above and other features of the present disclosure and the manner of achieving the same will become more apparent and will be better understood by referring to the following description of the embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1is a process flow diagram illustrating a portion of a method for preparing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure.

[0015] Figure 2 is a process flow diagram illustrating a portion of another method for preparing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0016] A variety of processes for making HFO-1234yf are known, such as those described in the following patents: U.S. Pat. No. 8,058,486, published on November 15, 2011, entitled “INTEGRATED PROCESS TO PRODUCE 2,3,3,3-TETRAFLUOROPROPENE”, U.S. Pat. No. 8,975,454, published on March 10, 2015, entitled “PROCESS FOR PRODUCING 2,3,3,3-TETRAFLUOROPROPENE”, and U.S. Pat. No. 8,975,454, published on July 1, 2014, entitled “PROCESS FOR PRODUCING 2,3,3,3-TETRAFLUOROPROPENE”. No. 8,766,020, all of which are incorporated herein by reference in their entirety.

[0017] The preparation of HFO-1234yf from 1,1,2,3-tetrachloropropene (HCO-1230xa or 1230xa) and hydrogen fluoride can be generalized as a three-step process. Step 1 can be understood as the preparation of 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf or 1233xf) from 1230xa in a gas phase reactor according to the following reaction scheme:

[0018]

[0019] Step 2 can be understood as preparing 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb or 244bb) from 1233xf in a reactor such as a liquid phase reactor according to the following reaction scheme:

[0020]

[0021] Step 3 can be understood as a dehydrochlorination reaction to prepare 2,3,3,3-tetrafluoropropene (HFO-1234yf) from 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in a reactor such as a gas phase reactor according to the following reaction scheme:

[0022]

[0023] More specifically, the balance formula of step 3 can be:

[0024] Formula 1244bb1234yf+HCI

[0025] Figure 1 is a process flow diagram illustrating step 3 of a method for preparing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure. Figure 1 The process flow 10 showing step 3 can include a stream of composition 12 containing liquid 244bb flowing into heater 14. The stream of composition 12 containing liquid 244bb can come from any process according to step 2 above, or from any other source of liquid 244bb. The stream of composition 12 can also include residues such as unreacted 1233xf, recycled 1234yf, HF, HCl, and trace impurities.

[0026] The heater 14 can heat the liquid 244bb to at least its dew point at the process pressure, thereby producing an evaporation stream 16 of 244bb, which can be a saturated vapor or a superheated vapor. The process pressure can be below atmospheric pressure or above atmospheric pressure. The process pressure can be as low as -4 pounds per square inch (psig) (-28 kilopascals (kPa)), 0 psig (0 kPa), 20 psig (138 kPa), 30 psig (207 kPa), or 40 psig (276 kPa), or as high as 80 psig (552 kPa), 110 psig (758 kPa), 150 psig (1,034 kPa), 200 psig (1,379 kPa), or 300 psig (2,068 kPa) gauge pressure, or can be within any range defined between any two of the foregoing values, such as, for example, -4 psig (-28 kPa) to 300 psig (2,068 kPa), 0 psig (0 kPa) to 200 psig (1,379 kPa), 20 psig (138 kPa) to 150 psig (1,034 kPa), 30 psig (207 kPa) to 110 psig (758 kPa), 40 psig (276 kPa) to 80 psig (552 kPa), 80 psig (552 kPa) to 150 psig (1,034 kPa), or 40 psig (276 kPa) to 110 psig (758 kPa).

[0027] Heater 14 can heat, vaporize, and optionally superheat liquid 244bb to a temperature as low as 40°F (4°C), 100°F (38°C), 150°F (66°C), 200°F (93°C), or 250°F (121°C), or as high as 300°F (149°C), 350°F (177°C), 400°F (204°C), 450°F (232°C), or 500°F (260°C), or any two temperatures. (260°C), such as 40°F (40°C) to 500°F (260°C), 100°F (38°C) to 450°F (232°C), 150°F (66°C) to 400°F (204°C), 200°F (93°C) to 350°F (177°C), 250°F (121°C) to 300°F (149°C), or 400°F (204°C) to 500°F (260°C).

[0028] The evaporated stream 16 of 244bb can be passed through a heat exchanger 18 to increase the temperature of the evaporated 244bb, thereby producing a superheated evaporated stream 20 of 244bb. The heat exchanger 18 can be an economizer or exchanger to recover heat from the reactor effluent, as described below. The heat exchanger 18 can be, for example, a shell and tube heat exchanger. The superheated evaporated stream 20 of 244bb can be passed through a superheater 22 to further increase the temperature of the evaporated 244bb and produce a further superheated stream 24 of 244bb. The superheater 22 can be an electric heater known in the art, but other types of heaters are also contemplated. The temperature of the additional superheated stream 24 of 244bb may be as low as 575°F (302°C), 610°F (321°C), 650°F (343°C), 690°F (366°C), 735°F (392°C), 780°F (416°C), 830°F (443°C), 850°F (454°C), 870°F (466°C), 900°F (482°C), 930°F (499°C), or 960°F (516°C), or as high as 1,040°F (560°C), 1,080°F (582°C), 1,120°F (604°C), 1,160°F (627°C). , or 1,200℉(649℃), or in any range that can be defined between any two of the foregoing values, such as, for example, 575℉(302℃) to 1,200℉(649℃), 850℉(454℃) to 1,200℉(649℃), 870℉(466℃) to 1,160℉(627℃), 900℉(482℃) to 1,120℉(604℃), 930℉(499℃) to 1,080℉(582℃), 960℉(516℃) to 1,040℉(560℃), or 870℉(466℃) to 930℉(499℃).

[0029] An additional superheated stream 24 of 244bb may be provided to the reactor 26. Figure 1As shown, the reactor 26 may include a plurality of reactor sections 28a, 28b, 28c, and 28d that are fluidly connected to each other by reactor streams 30a, 30b, and 30c. Each of the reactor sections 28a, 28b, 28c, and 28d may include at least one immersion heater that includes a heater surface configured to contact the superheated 244bb. In the reactor 26, the superheated 244bb is contacted with the heater surface for a certain contact time, during which at least some of the 244bb in the composition is dehydrochlorinated to prepare 1234yf, and HCl is produced as a byproduct (Formula 1). The contact time may be less than 10 seconds. The contact time can be as short as 0.1, 0.5, 1, 2, 3, or 4 seconds, or as long as 5, 6, 7, 8, 9, or 10 seconds, or can be within any range defined between any two of the foregoing values, such as, for example, 0.1 to 10 seconds, 0.5 to 9 seconds, 1 to 8 seconds, 2 to 7 seconds, 3 to 6 seconds, 4 to 5 seconds, 0.1 to 9 seconds, or 5 to 9 seconds.

[0030] The heater surface may have a surface temperature as low as 850°F (454°C), 870°F (466°C), 900°F (482°C), 940°F (504°C), 965°F (518°C), 990°F (532°C), 1,010°F (543°C), or 1030°F (554°C), or as high as 1,080°F (585°C), 1,110°F (593°C), 1,140°F (616°C), 1,170°F (632°C), or 1,200°F (649°C), or within any range defined between any two of the foregoing values, for example. Such as 850℉(454℃) to 1,200℉(649℃), 870℉(466℃) to 1,200℉(649℃), 940℉(504℃) to 1,200℉(649℃), 965℉(512℃) to 1,170℉(632℃), 990℉(532℃) to 1,140℉(616℃), 1,010℉(543℃) to 1,110℉(593℃), 1,030℉(554℃) to 1,080℉(585℃), or 965℉(518℃) to 1,010℉(543℃).

[0031] In some embodiments, the heater surface can be a catalytic surface with respect to the reaction scheme shown above with reference to step 3. In some embodiments, the catalytic surface can include electroless nickel, nickel, stainless steel, a nickel-copper alloy, a nickel-chromium-iron alloy, a nickel-chromium alloy, a nickel-chromium-molybdenum alloy, or a combination thereof.

[0032] In some other embodiments, the heater surface is not a catalytic surface with respect to the reaction scheme shown above with reference to step 3. In some embodiments, the heater surface comprises gold, platinum, or a combination thereof.

[0033] The accumulation of carbon deposits (also known as coking) on ​​the heater surfaces of reactor 26 can reduce heat transfer between the heater surfaces and 244bb. Reactor 26 must be taken offline periodically so that the carbon deposits can be removed. Reduction in carbon deposits can reduce the frequency with which reactor 26 must be shut down for cleaning and increase the operating time and productivity of reactor 26. It is believed that the carbon deposits can be formed according to the following reaction scheme:

[0034]

[0035] Thus, the extent of carbon formation can be indicated by measuring the concentration of 1,1,1,2-tetrafluoroethane (HFC-134a or 134a) downstream of reactor 26. A reduction in carbon formation can be indicated by a decrease in the concentration of 134a. It was surprisingly found that a combination of a higher surface temperature (such as about 975°F to about 1005°F) and a short contact time (such as less than 10 seconds) can dehydrochlorinate 244bb to produce 1234yf while producing less carbon deposits. This was unexpected because one skilled in the art would not expect less carbon to be deposited at higher temperatures.

[0036] A stream 32 comprising 1234yf, HCl, and unreacted 244bb may flow from the reactor 26 and through the heat exchanger 18 to provide additional heat to the vaporized stream 16 of 244bb as described above and to cool the stream 32 of 1234yf, HCl, and unreacted 244bb. A cooled stream 34 of 1234yf, HCl, and unreacted 244bb may flow into a distillation column 36, wherein at least a portion of the unreacted 244bb may be separated from the 1234yf and HCl into a recycle stream 38 of unreacted 244bb. In some embodiments, substantially all of the unreacted 244bb may be separated from the 1234yf and HCl into the recycle stream 38. The recycle stream 38 of unreacted 244bb may be added to the stream of the composition 12 comprising 244bb flowing into the heater 14, as described above. Figure 1 shown.

[0037] The separated 1234yf and HCl stream 40 may be processed to separate the HCl from the 1234yf by passing it through an HCl separation unit 42 to remove the HCl and produce a product stream 44 comprising 1234yf. Figure 1In the embodiment shown, the HCl separation unit 42 is a distillation column that produces an anhydrous HCl stream 45 in addition to the product stream 44. In other embodiments, the HCl separation unit 42 can be a falling film type HCl absorber using recycled dilute HCl solution and fresh make-up water. In other embodiments, the HCl separation unit 42 can be an adiabatic type HCl absorber known in the art. In other embodiments, the HCl separation unit 42 can be a scrubber using an alkaline aqueous solution.

[0038] The product stream 1234yf may also be a crude product stream containing byproducts such as 3,3,3-trifluoro-1-propyne (TFPY) in addition to 134a described above, as well as any 244bb not separated into the recycle stream 38. The byproducts may be separated from 1234yf in the product stream 44 by further processing (not shown) known in the art.

[0039] In some embodiments, the product stream 44 may contain 1234yf at a concentration greater than 99.10 weight percent (wt%), 99.20 wt%, 99.30 wt%, 99.40 wt%, 99.50 wt%, 99.60 wt%, 99.70 wt%, 99.80 wt%, 99.90 wt%, 99.91 wt%, 99.92 wt%, or 99.93 wt%, or greater than any value between any two of the foregoing values.

[0040] In some embodiments, the product stream 44 may include 134a at a concentration of less than 0.1 wt%, 0.05 wt%, 0.02 wt%, 0.010 wt%, 0.009 wt%, 0.008 wt%, 0.007 wt%, 0.006 wt%, 0.005 wt%, 0.004 wt%, 0.003 wt%, 0.002 wt%, or 0.001 wt%, or less than any value between any two of the foregoing values. Low values ​​of 134a in the product stream 44 indicate low carbon accumulation in the reactor 26. It has been found that carbon accumulation in the reactor 26 can be reduced by as much as 80% to 90% in the process stream 10 compared to prior art methods. Reducing carbon accumulation can reduce reactor downtime and costs associated with the required periodic cleaning of carbon from the reactor 26.

[0041] For consistency, the concentrations of product stream 44 described herein are based on a 244b-free basis. That is, for determinations of the weight percent of 1234yf, 134a, or other component concentrations in product stream 44, any 244bb in product stream 44 is not included.

[0042] Figure 2 is a process flow diagram illustrating step 3 of another method for preparing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure. Figure 1A process flow 46 for step 3 is shown, which can be used with Figure 1 The process flow 10 shown is the same except that the reactor 26 is replaced by a two-stage reactor 48 and the vaporized stream 16 of 244bb is divided into a first portion 50 and a second portion 52. The first portion 50 may flow through the heat exchanger 18 as described above with reference to Figure 1 As described for evaporated stream 16 of 244bb, superheated evaporated stream 20 of 244bb is produced. Superheated evaporated stream 20 of 244bb may be passed through superheater 22 to further increase the temperature of evaporated 244bb and form further superheated stream 24 of 244bb provided to reactor 48. Second portion 52 does not pass through heat exchanger 18 before being provided to reactor 48.

[0043] like Figure 2 As shown, the reactor 48 may include a first stage 54 and a second stage 56. The first stage 54 may include a plurality of reactor sections 58a, 58b, 58c, and 58d that are fluidly connected to each other through reactor streams 60a, 60b, and 60c. The second stage 56 may include a plurality of reactor sections 62a, 62b, 62c, and 62d that are fluidly connected to each other through reactor streams 64a, 64b, and 64c. Each of the reactor sections 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d may include at least one immersion heater that includes a heater surface configured to contact the superheated 244bb. As with the above-described reactor 26, in the reactor 48, the superheated 244bb is contacted with the heater surface for a certain contact time, during which at least some of the 244bb in the composition is dehydrochlorinated to produce 1234yf, and HCl is produced as a byproduct (Formula 1). The contact time and temperature of process stream 46 may be as described above for process stream 10 .

[0044] The interstage stream 66 fluidly connects the first stage 54 to the second stage 56 downstream of the first stage 56. The additional superheated stream 24 of 244bb from the first portion 50 flows into the first stage 54. The second portion 52 can flow into the second stage 56 along with the interstage stream 66 from the first stage 54, thereby cooling the interstage stream 66 before it enters the second stage 56. The immersion heaters in the second stage reactor sections 62a, 62b, 62c, and 62d are able to operate at higher heater surface temperatures because the cooler interstage stream 66 enters the second stage 56. Without wishing to be bound by any theory, it is believed that by operating at higher heater surface temperatures, the conversion of 244bb to 1234yf can be optimized without causing higher temperatures in the stream 32 comprising 1234yf, HCl, and unreacted 244bb flowing out of the reactor 48.

[0045] The first portion 50 flowing through the heat exchanger 18 is less than the evaporation flow 16 of 244 bb flowing through the heat exchanger 18, such as Figure 1 As shown, the temperature of the superheated vaporized stream 20 of 244bb can be significantly higher than the temperature of the given stream 32 including 1234yf, HCl and unreacted 244bb from the reactor 48. The size of the superheater 22 can be reduced because the higher temperature of the superheated vaporized stream 20 of 244bb can require less heating. A smaller superheater 22 can save a lot of capital and operating costs.

[0046] In some embodiments according to the present disclosure, the immersion heater is an electric immersion heater. In some embodiments, the electric immersion heaters can each be individually controlled to provide the desired heater surface temperature in different sections of the reactor. In some embodiments, the electric immersion heater may include a tubular body encapsulating a resistance wire that generates heat when an electric current passes through the resistance wire. Such an electric immersion heater may include a ceramic insulating material, such as magnesium oxide, between the wires within the same tube to electrically insulate the wires from each other while also conducting heat from the wires to the enclosed tubular body. The outer surface of the tubular body may form the heater surface, as described above. The ceramic insulating material is also a safety feature. The ceramic insulating material is largely non-reactive with respect to the above-mentioned feed, product, or by-product. If a leak occurs in the tubular body, the ceramic insulating material prevents the leak from spreading further outside the electric immersion heater,

[0047] In some embodiments, reactor sections 28a, 28b, 28c, 28d, 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d may be shell and tube reactors in which 244bb flows through the shell and the tubes are replaced by electric heater elements. In some other embodiments, reactor sections 28a, 28b, 28c, 28d, 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d may be U-tube reactors with electric flange immersion heaters.

[0048] exist Figure 1 and Figure 2 In the illustrated embodiment, the reactor or reactor stage is shown with four sections. However, it should be understood that the present disclosure includes embodiments with less than four sections or more than four sections. It should also be understood that embodiments may include two or more reactors configured in series and / or in parallel for dehydrochlorinating 244bb to produce 1234yf.

[0049] In the above-described embodiment, heat exchanger 18 is used to improve the energy efficiency of the process for preparing 2,3,3,3-tetrafluoropropene. However, it should be understood that some embodiments may not include heat exchanger 18.

[0050] In the above described embodiment, superheater 22 further superheats the stream 244bb reaching the reactor. However, it should be understood that some embodiments may not include superheater 22, relying on the reactor to provide further superheating of the stream 244bb.

[0051] As used herein, the phrase "in any range defined between any two preceding values" literally means that any range can be selected from any two values ​​listed before such phrase, regardless of whether these values ​​are in the lower part of the list or in the upper part of the list. For example, a pair of values ​​can be selected from two lower values, two higher values, or a lower value and an upper value.

[0052] Although the present invention has been described with respect to exemplary designs, the present invention may be further modified within the spirit and scope of the present disclosure. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains.

[0053] Example

[0054] Example 1

[0055] A composition comprising 96.0 wt % of 244bb, 3.5 wt % of 1233xf and 0.5 wt % of other materials (measured by gas chromatography) is evaporated to at least its dew point at 70 psig. The evaporated composition is superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated evaporated composition is introduced into a reactor comprising four electric heating sections. The superheater is configured so that the gas velocity is at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor is maintained between 993°F and 997°F, with an average heater surface temperature of 995°F. Based on the inlet conditions of the reactor, the superheated evaporated composition passes through the reactor with an average contact time of 5.46 seconds. The reactor output is directed to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream (including unreacted 244bb) of the distillation output is recovered for recycling. The overhead stream containing 1234yf and HCl is directed to another distillation column to separate HCl as the overhead product and produce a crude product stream containing 1234yf. The process is maintained for 80 hours to give a total conversion of 204bb to 1234yf of 21.3%. The product stream is analyzed by a gas chromatograph using techniques well known in the art. The results are shown in the table below.

[0056] Example 2

[0057] A composition comprising 96.2 wt % of 244bb, 3.6 wt % of 1233xf and 0.2 wt % of other materials (measured by gas chromatography) is evaporated to at least its dew point at 70 psig. The evaporated composition is superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated evaporated composition is introduced into a reactor comprising four electric heating sections. The superheater is configured so that the gas velocity is at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor is maintained between 980°F and 995°F, with an average heater surface temperature of 988°F. Based on the inlet conditions of the reactor, the superheated evaporated composition passes through the reactor with an average contact time of 5.46 seconds. The reactor output is directed to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream (including unreacted 244bb) of the distillation output is recovered for recycling. The overhead stream containing 1234yf and HCl is directed to another distillation column to separate HCl as the overhead product and produce a crude product stream containing 1234yf. The process is maintained for 92 hours to give a total conversion of 204bb to 1234yf of 20.5%. The product stream is analyzed by a gas chromatograph using techniques well known in the art. The results are shown in the table below.

[0058] Example 3

[0059] A composition comprising 97.6 wt % of 244bb, 2.0 wt % of 1233xf and 0.4 wt % of other materials (measured by gas chromatography) is evaporated to at least its dew point at 70 psig. The evaporated composition is superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated evaporated composition is introduced into a reactor comprising four electric heating sections. The superheater is configured so that the gas velocity is at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor is maintained between 989°F and 998°F, with an average heater surface temperature of 993.5°F. Based on the inlet conditions of the reactor, the superheated evaporated composition passes through the reactor with an average contact time of 8.4 seconds. The reactor output is directed to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream (including unreacted 244bb) of the distillation output is recovered for recycling. The overhead stream containing 1234yf and HCl is directed to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process is maintained for 604 hours to achieve a total conversion of 204bb to 1234yf of 30.3%. The product stream is analyzed by a gas chromatograph using techniques well known in the art. The results are shown in the table below.

[0060] Comparative Example

[0061] A composition comprising 97.9 wt % 244bb, 1.8 wt % 1233xf and 0.2 wt % other materials (measured by gas chromatography) is evaporated to at least its dew point at 70 psig. The evaporated composition is heated in a heat exchanger and then superheated in a superheater to a temperature in the range of 740°F to 800°F. The superheated evaporated composition is introduced into a conventional shell-and-tube reactor, wherein the reaction tube contains the composition. The reaction tube is surrounded by a shell containing a heating medium. The bulk temperature in the reaction tube is maintained at 900°F, and the surface temperature in the reaction tube (in contact with the composition) is maintained at about 909°F. Based on the inlet conditions of the reactor, the superheated evaporated composition passes through the reactor with an average contact time of 58 seconds. The reactor output is directed to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream (including unreacted 244bb) of the distillation output is recovered for recycling. The overhead stream containing 1234yf and HCl is directed to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process is maintained for 396 hours to give a total conversion of 204bb to 1234yf of 29.2%. The product stream is analyzed by a gas chromatograph using techniques well known in the art. The results are shown in the table below.

[0062] Table – Gas Chromatography Results

[0063] Example 1 Example 2 Example 3 Comparative Example 1234yf 99.922% by weight 99.934% by weight 99.938% by weight 99.946% by weight 134a 0.0045 wt% 0.0045 wt% 0.0073 wt% 0.0109 wt% TFP 0.0563 wt% 0.0365 wt% 0.0354 wt% 0.0190 wt% other 0.0172 wt% 0.0250 wt% 0.0193 wt% 0.0241 wt%

[0064] As shown in the table, Examples 1-3 from processes with higher heater surface temperatures and shorter contact times produced significantly less 134a, which correlated with significantly less carbon accumulation or coking in the reactor.

Claims

1. A method for preparing 2,3,3,3-tetrafluoropropylene (HFO-1234yf), the method comprising: providing a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor comprising a heater surface having a surface temperature greater than about 850°F (454°C); and The composition is contacted with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to produce HFO-1234yf.

2. The method of claim 1, wherein the dehydrochlorination of the portion of the HCFC-244bb produces hydrochloric acid (HCl), the method further comprising: The reactor provides HFO-1234yf, HCl and unreacted HCFC-244bb to the distillation column; separating the HFO-1234yf and HCl from at least a portion of the HCFC-244bb in the distillation column; recycling the separated HCFC-244bb to the reactor; providing the HFO-1234yf and HCl to a HCl separation unit; and separating the HCl from the HFO-1234yf to form a product stream comprising the HFO-1234yf, Wherein the product stream comprises HFO-1234yf at a concentration greater than 99.1 weight percent on a HCFC-244bb-free basis and 1,1,1,2-tetrafluoroethane at a concentration less than 0.1 weight percent on a HCFC-244bb-free basis as an indication of a low rate of carbon accumulation in the reactor.

3. A method for preparing 2,3,3,3-tetrafluoropropylene (HFO-1234yf), the method comprising: evaporating a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb); dividing the composition into a first part and a second part; heating the first portion of the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C); providing the composition to a reactor comprising a heater surface having a surface temperature greater than about 850°F (454°C), the reactor comprising a first stage and a second stage downstream of the first stage, the first portion being provided to the first stage and the second portion being provided to the second stage; and The composition is contacted with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to produce HFO-1234yf.

4. A composition comprising HFO-1234yf, obtained by: providing a composition comprising at least 96 weight percent 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor comprising a heater surface having a surface temperature greater than about 850°F (454°C); and The composition is contacted with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to produce HFO-1234yf, wherein the composition comprises 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 weight percent, based on HCFC-244bb-free.

5. A composition comprising HFO-1234yf obtained by the process according to claim 4, wherein the composition comprises 1,1,1,2-tetrafluoroethane in a concentration of 0.0001 wt% to 0.1 wt% based on HCFC-244bb free.

6. A method for preparing HFO-1234yf from 1,1,2,3-tetrachloropropylene (HCO-1230xa) and hydrogen fluoride, comprising the following steps: Step 1: Prepare 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) and hydrogen chloride by reacting 1230xa with hydrogen fluoride in a gas phase reactor; Step 2: preparing 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) by reacting 1233xf with hydrogen fluoride in a liquid phase reactor; and Step 3: Preparation of 2,3,3,3-tetrafluoropropene (HFO-1234yf) by dehydrochlorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in a gas phase reactor.

7. A product stream comprising a concentration of greater than 99.1 weight percent HFO-1234yf and a concentration of less than 0.1 weight percent 1,1,1,2-tetrafluoroethane, based on HCFC-244bb free.

8. A method of indicating the extent of carbon formation by measuring the concentration of 1,1,1,2-tetrafluoroethane (HFC-134a) downstream of a reactor, wherein a reduction in carbon formation can be indicated by a decrease in the concentration of 134a.

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