Method for producing HFO-1234yf by dehydrochlorinating HCFC-244bb

Abstract

To provide a process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf) from a composition including 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb).SOLUTION: A method includes providing a composition including 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor including a heater surface at a surface temperature greater than about 850°F (454°C), and then bringing the composition into contact with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to make HFO-1234yf.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to processes for producing 2,3,3,3-tetrafluoropropene (HFO-1234yf). In particular, the present disclosure relates to a process for the dehydrochlorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in the production of HFO-1234yf. [Background technology]

[0002] Hydrofluoroolefins (HFOs), such as tetrafluoropropene, are known to be effective refrigerants, fire extinguishing agents, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, liquid carriers, buffing agents, displacement desiccants, and power cycle working fluids. Due to the suspected environmental issues associated with the use of some of these fluids, including their associated relatively high global warming potential, it is desirable to use fluids that have the lowest possible global warming potential (GWP) in addition to also having zero ozone depletion potential (ODP). Thus, there is considerable interest in developing environmentally friendly materials for the aforementioned applications.

[0003] HFOs, which have zero ozone depletion and low global warming potential, have been identified as potentially meeting this need. However, the toxicity, boiling points, and other physical properties of such chemicals vary widely between isomers. One HFO with useful properties is 2,3,3,3-tetrafluoropropene (HFO-1234yf or 1234yf).

[0004] HFO-1234yf has been shown to be a low global warming compound with low toxicity and therefore can meet increasingly stringent refrigerant requirements in mobile air conditioning, and compositions containing 1234yf are among the materials being developed for use in many applications. Summary of the Invention

[0005] The present disclosure provides a process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf), comprising supplying 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 to make HFO-1234yf.

[0006] In one aspect of the disclosure, the disclosure provides a process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: supplying 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 to produce HFO-1234yf.

[0007] The heater surface may have a surface temperature of about 870° F. (466° C.) to about 1,200° F. (649° C.). The contact time may be from 0.1 seconds to 9 seconds. In some embodiments, the heater surface may include a catalytic surface. The catalytic surface may be electroless nickel, nickel, stainless steel, nickel-copper alloy, nickel-chromium-iron alloy, nickel-chromium ... In other embodiments, the heater surface may not be a catalytic surface.

[0008] The process may further include vaporizing the composition and then heating the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C) before feeding the composition to the reactor. The process may further include feeding the HFO-1234yf, HCl, and unreacted HCFC-244bb from the reactor 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 vaporizing the composition, feeding the HFO-1234yf and HCl to an HCl separation unit, and separating the HCl from the HFO-1234yf to form a product stream comprising HFO-1234yf. The product stream may include HFO-1234yf at a concentration of greater than 99.1 wt.% without HCFC-244bb. The product stream may further include 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 wt.% without HCFC-244bb as an indication of low carbon deposition in the reactor. Heating the vaporized composition may include exchanging heat between the vaporized composition and the HFO-1234yf and HCFC-244bb from the reactor prior to feeding the HFO-1234yf and HCFC-244bb to the distillation column.

[0009] In another aspect of the disclosure, the disclosure provides a process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: vaporizing 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 first portion of the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C), feeding the composition to a reactor comprising a heater surface at a surface temperature of 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 to make HFO-1234yf. The reactor can include a first stage and a second stage downstream of the first stage. The first portion can be fed to a first stage and the second portion can be fed to a second stage.

[0010] The process may further include feeding HFO-1234yf, HCl, and unreacted HCFC-244bb from the reactor to a distillation column, separating 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 vaporizing the composition, feeding HFO-1234yf and HCl to an HCl separation unit, and separating HCl from HFO-1234yf to form a product stream comprising HFO-1234yf. The product stream may comprise HFO-1234yf at a concentration of greater than 99.1 wt.% without HCFC-244bb. The product stream may further comprise 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 wt.% without HCFC-244bb as an indication of low carbon deposition in the reactor.

[0011] Heating the first portion of the vaporized composition may include exchanging heat between the first portion of the vaporized composition and the HFO-1234yf and HCFC-244bb from the reactor prior to feeding the HFO-1234yf and HCFC-244bb to the distillation column. The heater surface may have a surface temperature of 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 need not be a catalytic surface.

[0012] By reference to the following description of the embodiments, in light of the accompanying drawings, the present invention The above and other features of the disclosure, and the manner in which they are accomplished, will become more apparent and better understood. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a process flow diagram illustrating a portion of a process for producing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure.

[0014] [Diagram 2] FIG. 2 is a process flow diagram illustrating a portion of another process for producing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Various processes are known for producing HFO-1234yf, such as those described in U.S. Pat. No. 8,058,486, entitled "INTEGRATED PROCESS TO PRODUCE 2,3,3,3-TETRAFLUOROPROPENE," issued Nov. 15, 2011; U.S. Pat. No. 8,975,454, entitled "PROCESS FOR PRODUCING 2,3,3,3-TETRAFLUOROPROPENE," issued March 10, 2015; and U.S. Pat. No. 8,766,020, entitled "PROCESS FOR PRODUCING 2,3,3,3-TETRAFLUOROPROPENE," issued July 1, 2014, each of which is incorporated by reference in its entirety.

[0016] The production 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 producing 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf, or 1233xf) from 1230xa in a vapor phase reactor according to the following reaction scheme: [ka]

[0017] Step 2 can be understood as producing 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: [ka]

[0018] Step 3 can be understood as a dehydrochlorination reaction of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to produce 2,3,3,3-tetrafluoropropene (HFO-1234yf) in a reactor, such as a vapor phase reactor, according to the following reaction scheme: [ka]

[0019] More specifically, the equilibrium equation for step 3 can be expressed as follows: [ka]

[0020] Figure 1 is a process flow diagram showing step 3 of a process for producing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure. Figure 1 shows that process flow 10 of step 3 can include a flow of composition 12 including liquid 244bb flowing into heater 14. Composition flow 12 including liquid 244bb can be from any process according to step 2 above or from any other source of liquid 244bb. Composition flow 12 can also include residuals such as unreacted 1233xf, recycled 1234yf, HF, HCl, and trace impurities.

[0021] The heater 14 can heat the liquid 244bb to at least its dew point at the process pressure, thereby creating a vaporized flow 16 of 244bb, which can be saturated or 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) gage, 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) gage, or can be anywhere from -4 psig (-28 kPa) to 300 psig (2,068 kPa), for example. The pressure may be within any range defined between any two of the preceding values, such as 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).

[0022] Heater 14 can heat, vaporize, and optionally superheat liquid 244bb to a low temperature of 40°F (4°C), 100°F (38°C), 150°F (66°C), 200°F (93°C), or 250°F (121°C), or to a high temperature of 300°F (149°C), 350°F (177°C), 400°F (204°C), 450°F (232°C), or 500°F (260°C), for example, between 40°F (40°C) and 500°F (260°C). 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).

[0023] The vaporized flow 16 of 244bb may pass through a heat exchanger 18 to increase the temperature of the vaporized 244bb to produce a superheated vaporized flow 20 of 244bb. The heat exchanger 18 may be an economizer or exchanger for recovering heat from the reactor effluent, as described below. The heat exchanger 18 may be, for example, a shell-and-tube heat exchanger. The superheated vaporized flow 20 of 244bb may pass through a superheater 22 to further increase the temperature of the vaporized 244bb to produce a further superheated flow 24 of 244bb. The superheater 22 may be an electric heater as known in the art, although other types of heaters are contemplated. The temperature of the further superheated flow 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 may be 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°F ( F (466° C.) to 930° F (499° C.), or within any range defined between any two of the foregoing values, such as, for example, 575° F. (302° C.) to 1,200° F. (649° C.), 850° F. (454° C.) to 1,200° F. (649° C.), 870° F. (466° C.) to 1,160° F. (627° C.), 900° F. (482° C.) to 1,120° F. (604° C.), 930° F. (499° C.) to 1,080° F. (582° C.), 960° F. (516° C.) to 1,040° F. (560° C.), or 870° F. (466° C.) to 930° F. (499° C.).

[0024] The further superheated flow 24 of 244bb can be fed to a reactor 26. As shown in FIG. 1, the reactor 26 can include multiple reactor sections 28a, 28b, 28c, and 28d fluidly connected to each other by reactor flows 30a, 30b, and 30c. Each of the reactor sections 28a, 28b, 28c, and 28d can include at least one immersion heater including a heater surface configured to contact the superheated 244bb. In the reactor 26, the superheated 244bb is contacted with the heater surface for a contact time during which at least a portion of the 244bb in the composition is dehydrochlorinated to make 1234yf and produce HCl as a by-product (Equation 1). The contact time can be less than 10 seconds. The contact time can be as short as 0.1 seconds, 0.5 seconds, 1 second, 2 seconds, 3 seconds, or 4 seconds, or as long as 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, or 10 seconds, or can be within any range defined between any two of the foregoing values, e.g., 0.1 seconds to 10 seconds, 0.5 seconds to 9 seconds, 1 second to 8 seconds, 2 seconds, to 7 seconds, 3 seconds to 6 seconds, 4 seconds to 5 seconds, 0.1 seconds to 9 seconds, or 5 seconds to 9 seconds.

[0025] The heater surface shall be capable of withstanding a low surface temperature of 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 1,030°F (554°C), or a high surface temperature of 1,080°F (585°C), 1,110°F (585°C), 1,200°F (590°C), or 1,300°F (590°C). F (593°C), 1,140°F (616°C), 1,170°F (632°C), or 1,200°F (649°C), for example, 850°F (454°C) to 1,200°F (649°C), 870°F (466°C) to 1,200°F (649°C), 940°F (504°C), or 1,300°F (504°C), for example, 1,400°F (504°C), 1,500°F (504°C), 1,600°F (504°C), 1,700°F (504°C), 1,800°F (504°C), 1,900°F (504°C), 2,100°F (504°C), 2,200°F (504°C), 2,300°F (504°C), 2,400°F (504°C), 2,500°F (504°C), 2,600°F (504°C), 2,700°F (504°C), 2,800°F (504°C), 2,100°F (504°C), 2,200°F (504°C), 2,300°F (504°C), 2,400°F (504°C), 2,500°F (504°C), 2,500°F (504°C), 2,500°F (504°C), 2,600°F (504°C), 2,700°F (504°C), 2,800°F (504°C), 2,2 F (543°C) to 1,110°F (593°C), 1,030°F (554°C) to 1,080°F (585°C), or within any range defined between any two of the aforementioned values, such as 965°F (518°C) to 1,010°F (543°C).

[0026] In some embodiments, the heater surface can be a catalytic surface for the reaction scheme shown above with reference to step 3. In some embodiments, the catalytic surface can include electroless nickel, nickel, stainless steel, nickel-copper alloy, nickel-chromium-iron alloy, nickel-chromium alloy, nickel-chromium-molybdenum alloy, or combinations thereof.

[0027] In some other embodiments, the heater surface is not a catalytic surface for the reaction scheme shown above with reference to step 3. In some embodiments, the heater surface comprises gold, platinum, or a combination thereof.

[0028] The deposition of carbon deposits (also called coking) on ​​the heater surfaces of reactor 26 can reduce heat transfer between the heater surfaces and 244bb. Reactor 26 must be taken off-line periodically so that the carbon deposits can be removed. Reduction in carbon deposits can reduce the frequency at which reactor 26 must be taken out of service for cleaning, increasing the uptime and productivity of reactor 26. It is believed that carbon deposits can form according to the following reaction scheme: [ka]

[0029] Thus, the extent of carbon production 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 production can be indicated by a decrease in the concentration of 134a. Surprisingly, it has been found that higher surface temperatures, such as from about 975°F to about 1005°F, when combined with short contact times, such as less than 10 seconds, can dehydrochlorinate 244bb to make 1234yf while simultaneously producing less carbon deposits. This is unexpected, as one of ordinary skill in the art would not expect less carbon deposits at higher temperatures.

[0030] A flow 32 containing 1234yf, HCl and unreacted 244bb may flow from the reactor 26 and pass through a heat exchanger 18 to provide additional heat to the vaporized flow 16 of 244bb as described above, as well as to cool the flow 32 of 1234yf, HCl and unreacted 244bb. A cooled flow 34 of 1234yf, HCl and unreacted 244bb may flow to a distillation column 36 where at least a portion of the unreacted 244bb may be separated from the 1234yf and HCl into a recycle flow 38 of unreacted 244bb. In some embodiments, substantially all of the unreacted 244bb may be separated from the 1234yf and HCl into the recycle flow 38. The recycle flow 38 of b may be joined with the flow 12 of composition containing 244bb entering the heater 14 as shown in FIG.

[0031] The separated 1234yf and HCl flow 40 can be processed to separate HCl from 1234yf by passing it through an HCl separation unit 42 to remove HCl and produce a product stream 44 containing 1234yf. In the embodiment shown in FIG. 1, 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 HCl absorber using recycled dilute HCl solution and fresh make-up water. In yet other embodiments, the HCl separation unit 42 can be an adiabatic HCl absorber, as known in the art. In yet other embodiments, the HCl separation unit 42 can be a scrubber using an aqueous basic solution.

[0032] Product stream 1234yf can be a crude product stream that includes 134a as described above, plus by-products such as 3,3,3-trifluoro-1-propyne (TFPY), as well as any 244bb that has not been separated into recycle stream 38. The by-products can be separated from 1234yf in product stream 44 by further processing (not shown) as known in the art.

[0033] In some embodiments, product stream 44 can include 1234yf at a concentration of 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 any value between any two of the foregoing values.

[0034] In some embodiments, product stream 44 may contain 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 any value between any two of the foregoing values. A low value of 134a in product stream 44 indicates low carbon loading in reactor 26. It has been found that carbon loading in reactor 26 in process flow 10 may be reduced by as much as 80% to 90% compared to prior art processes. Reducing carbon loading may reduce reactor downtime and costs associated with the need to periodically clean carbon from reactor 26.

[0035] For consistency, the concentrations of product stream 44 described herein are exclusive of 244bb, i.e., 244bb in product stream 44 is not included with respect to determining the weight percent of 1234yf, 134a, or other component concentrations in product stream 44.

[0036] FIG. 2 is a process flow diagram showing step 3 of another process for producing 2,3,3,3-tetrafluoropropene according to some embodiments of the present disclosure. FIG. 1 shows that the process flow 46 of step 3 can be the same as the process flow 10 shown in FIG. 1, except that the reactor 26 is replaced by a two-stage reactor 48 and the vaporized flow 16 of 244bb is split into a first portion 50 and a second portion 52. The first portion 50 can flow through a heat exchanger 18 as described above with respect to the vaporized flow 16 of 244bb with reference to FIG. 1 to produce a superheated vaporized flow 20 of 244bb. The superheated vaporized flow 20 of 244bb can pass through a superheater 22 to further increase the temperature of the vaporized 244bb and produce a further superheated flow 24 of 244bb that is fed to the reactor 48. The second portion 52 is fed to the reactor 48 without passing through the heat exchanger 18. There are.

[0037] 2, the reactor 48 can include a first stage 54 and a second stage 56. The first stage 54 can include a plurality of reactor sections 58a, 58b, 58c, and 58d fluidly connected to one another by reactor flows 60a, 60b, and 60c. The second stage 56 can include a plurality of reactor sections 62a, 62b, 62c, and 62d fluidly connected to one another by reactor flows 64a, 64b, and 64c. Each of the reactor sections 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d can include at least one immersion heater including a heater surface configured to contact the superheated 244bb. As with reactor 26 described above, in reactor 48, the superheated 244bb is contacted with a heater surface for a contact time during which at least a portion of the 244bb in the composition is dehydrochlorinated to make 1234yf with HCl as a by-product (Equation 1). The contact times and temperatures for process flow 46 can be as described above for process flow 10.

[0038] An interstage flow 66 fluidly connects the first stage 54 to the second stage 56, which is downstream of the first stage 56. The further superheated flow 24 of 244 bb from the first portion 50 enters the first stage 54. The second portion 52 may enter the second stage 56 along with the interstage flow 66 from the first stage 54, and the interstage flow 66 may be cooled before entering the second stage 56. The cooler interstage flow 66 entering the second stage 56 may allow the immersion heaters in the reactor sections 62a, 62b, 62c, and 62d of the second stage to operate at a higher heater skin temperature. Without wishing to be bound by any theory, it is believed that by operating at a higher heater skin temperature, the conversion of 244bb to 1234yf can be optimized without inducing higher temperatures in the flow containing 1234yf, HCl, and unreacted 244bb32 flowing from reactor 48.

[0039] The first portion 50 flowing through the heat exchanger 18 is less than the vaporized flow 16 of 244bb flowing through the heat exchanger 18 as described in Figure 1, and therefore the temperature of the superheated vaporized flow 20 of 244bb can be significantly higher than a given flow 32 containing 1234yf, HCl, and unreacted 244bb from the reactor 48. The superheater 22 can be reduced in size because the higher temperature of the superheated vaporized flow 20 of 244bb may require less heating. A smaller superheater 22 can result in significant capital and operating cost savings.

[0040] 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 can include a tubular body surrounding an electric resistance wire that generates heat when an electric current is passed through the wire. Such an electric immersion heater can include a ceramic insulating material, such as magnesium oxide, between the wires in the same tube to conduct heat from the wire to the surrounding tubular body while at the same time electrically insulating the wires from each other. The outer surface of the tubular body can 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 the feeds, products, or by-products described above. Even if a leak occurs in the tubular body, the ceramic insulating material can prevent the leak from spreading further beyond the electric immersion heater.

[0041] In some embodiments, reactor sections 28a, 28b, 28c, 28d, 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d can be shell-and-tube reactors with 244bb flowing through the shell and the tubes are heated by electrical heater elements. In some other embodiments, reactor sections 28a, 28b, 28c, 28d, 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d can be U-tube reactors with electric flange immersion heaters.

[0042] In the embodiments shown in Figures 1 and 2, a reactor or reactor stage having four sections is shown. However, it is understood that the present disclosure includes embodiments having less than four sections or more than four sections. It is also understood that embodiments may include two or more reactors in series and / or parallel configurations to dehydrochlorinate 244bb to produce 1234yf.

[0043] In the above embodiment, heat exchanger 18 is used to improve the energy efficiency of the process for producing 2,3,3,3-tetrafluoropropene. However, it is understood that some embodiments may not include heat exchanger 18.

[0044] In the above embodiment, the superheater 22 further superheats the flow of 244bb to the reactor, however, it is understood that some embodiments may not include the superheater 22 and provide further superheating of the flow of 244bb by the reactor.

[0045] As used herein, the phrase "within any range defined between any two of the preceding values" means that any range may be selected from any two of the values ​​listed preceding such phrase, regardless of whether those values ​​are in the lower portion of the list or in the higher portion of the list. For example, a pair of values ​​may be selected from two lower values, two higher values, or a lower value and a higher value.

[0046] While this invention has been described with respect to exemplary designs, the invention can be further modified within the spirit and scope of the disclosure, and this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains. EXAMPLES

[0047] Example 1 A composition containing 96.0 wt. % 244bb, 3.5 wt. % 1233xf, and 0.5 wt. % other materials (as measured by gas chromatography) was vaporized at 70 psig to at least its dew point. The vaporized composition was superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated vaporized composition was introduced into a reactor containing four electrically heated sections. The superheater was configured such that the gas velocity was at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor was maintained between 993°F and 997°F with an average heater surface temperature of 995°F. The superheated vaporized composition passed through the reactor with an average contact time of 5.46 seconds based on the inlet conditions to the reactor. The output of the reactor was directed to a distillation column to separate the unreacted 244bb from the 1234yf and HCl. The bottom stream of the distillation output containing unreacted 244bb was collected for recycle. The overhead stream containing 1234yf and HCl was directed to another distillation column to separate HCl as an overhead product and to produce a crude product stream containing 1234yf. The process was maintained for 80 hours for an overall conversion of 21.3% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the table below. Example 2

[0048] A composition containing 96.2 wt. % 244bb, 3.6 wt. % 1233xf, and 0.2 wt. % other materials (as determined by gas chromatography) was heated at 70 psig for 30 min. Both were vaporized to their dew points. The vaporized composition was superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated vaporized composition was introduced into a reactor containing four electrically heated sections. The superheater was configured such that the gas velocity was at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor was maintained between 980°F and 995°F with an average heater surface temperature of 988°F. The superheated vaporized composition passed through the reactor with an average contact time of 5.46 seconds based on the inlet conditions to the reactor. The output of the reactor was directed to a distillation column to separate the unreacted 244bb from the 1234yf and HCl. The bottom stream of the distillation output containing the unreacted 244bb was collected for recycle. The overhead stream containing 1234yf and HCl was directed to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process was maintained for 92 hours for an overall conversion of 20.5% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the table below. Example 3

[0049] A composition containing 97.6 wt. % 244bb, 2.0 wt. % 1233xf, and 0.4 wt. % other materials (as measured by gas chromatograph) was vaporized at 70 psig to at least its dew point. The vaporized composition was superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated vaporized composition was introduced into a reactor containing four electrically heated sections. The superheater was configured such that the gas velocity was at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor was maintained between 989°F and 998°F with an average heater surface temperature of 993.5°F. The superheated vaporized composition passed through the reactor with an average contact time of 8.4 seconds based on the inlet conditions to the reactor. The output of the reactor was directed to a distillation column to separate the unreacted 244bb from the 1234yf and HCl. The bottom stream of the distillation output containing unreacted 244bb was collected for recycle. The overhead stream containing 1234yf and HCl was directed to another distillation column to separate HCl as an overhead product and to produce a crude product stream containing 1234yf. The process was maintained for 604 hours for an overall conversion of 30.3% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the table below. Comparative Example

[0050] A composition containing 97.9 wt. % 244bb, 1.8 wt. % 1233xf, and 0.2 wt. % other materials (as measured by gas chromatograph) was vaporized at 70 psig to at least its dew point. The vaporized composition was heated in a heat exchanger and then superheated in a superheater to a temperature ranging from 740°F to 800°F. The superheated vaporized composition was introduced into a conventional shell-and-tube reactor, containing the composition in the reactor tube. The reactor tube was surrounded by a shell containing a heating medium. The mixture average temperature inside the reactor tube was maintained at 900°F, and the surface temperature inside the reactor tube (in contact with the composition) was maintained at about 909°F. The superheated vaporized composition passed through the reactor with an average contact time of 58 seconds based on the inlet conditions to the reactor. The output of the reactor was directed to a distillation column to separate the unreacted 244bb from the 1234yf and HCl. The bottom stream of the distillation output containing unreacted 244bb was collected for recycle. The overhead stream containing 1234yf and HCl was directed to another distillation column to separate HCl as an overhead product and to produce a crude product stream containing 1234yf. The process was maintained for 396 hours for an overall conversion of 29.2% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the table below. [Table 1]

[0051] As shown in the table, Examples 1-3, with processes having higher heater surface temperatures and shorter contact times, produced significantly less 134a, which correlates with significantly less carbon deposition (coking) in the reactor. The present specification includes the following aspects of the invention. [1] 1. A process for making 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 of greater than about 850° F. (454° C.); contacting said composition with said heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of said HCFC-244bb to produce HFO-1234yf. [2] wherein the dehydrochlorination of the portion of the HCFC-244bb produces hydrochloric acid (HCl), and the process comprises: feeding the HFO-1234yf, HCl, and unreacted HCFC-244bb from the reactor to a distillation column; separating said HFO-1234yf and said HCl from at least a portion of said HCFC-244bb in said distillation column; recycling the separated HCFC-244bb to the reactor; and providing said HFO-1234yf and said HCl to an HCl separation unit; and separating said HCl from said HFO-1234yf to form a product stream comprising said HFO-1234yf, 2. The process of claim 1, wherein the product stream comprises HFO-1234yf in a concentration of greater than 99.1 wt.% with no HCFC-244bb, and 1,1,1,2-tetrafluoroethane in a concentration of less than 0.1 wt.% with no HCFC-244bb, as indicative of a low rate of carbon build-up in the reactor. [3] 1. A process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: vaporizing 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 first portion of the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C); feeding the composition to a reactor comprising a heater surface having a surface temperature of 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 fed to the first stage and the second portion being fed to the second stage; contacting said composition with said heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of said HCFC-244bb to produce HFO-1234yf.

Claims

1. 1. A process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: vaporizing a composition comprising at least 96% by weight of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb); dividing the composition into a first portion and a second portion; heating the first portion of the vaporized composition to a temperature of between 575°F (302°C) and 1,200°F (649°C); feeding the composition to a reactor comprising a heater surface having a surface temperature of 870°F (466°C) to 1,005°F (541°C), the reactor comprising a first stage and a second stage downstream of the first stage, the first portion being fed to the first stage and the second portion being fed to the second stage; contacting the composition 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 heating the vaporized composition comprises exchanging heat between the vaporized composition and HFO-1234yf and HCFC-244bb from a reactor prior to feeding the HFO-1234yf and HCFC-244bb to a distillation column.

2. 2. The process of claim 1, wherein the contact time is from 0.1 seconds to 9 seconds.

3. The process of any of claims 1 to 2, wherein the heater surface comprises a catalytic surface.

4. 4. The process of claim 3, wherein the catalytic surface comprises electroless nickel, nickel, stainless steel, nickel-copper alloy, nickel-chromium-iron alloy, nickel-chromium alloy, nickel-chromium-molybdenum alloy, or combinations thereof.

5. The process of any of claims 1 to 3, wherein the heater surface temperature is between 975°F (524°C) and 1,005°F (541°C).

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