Processes for producing high-purity trifluoroiodomethane

This applicationis a broadening reissue application of and claiming priority to U.S. Pat. No. 10,941,091, entitled Processes for Producing High-Purity Trifluoroiodomethane, issued Mar. 9, 2021, whichclaims priority to U.S. Provisional Application No. 62/774,520, filed Dec. 3, 2018,the entire disclosures ofwhichisareherein incorporated by referencein its entirety.

The present disclosure relates to processes for producing high-purity trifluoroiodomethane (CFI). Specifically, the present disclosure relates to processes for purifying trifluoroiodomethane resulting in high yields of high-purity trifluoroiodomethane.

Trifluoroiodomethane (CFI), also known as perfluoromethyliodide, trifluoromethyl iodide, or iodotrifluoromethane, is a useful compound in commercial applications as a refrigerant or a fire suppression agent, for example. CFI is a low global warming potential molecule with almost no ozone depletion potential. CFI can replace more environmentally damaging materials.

There are several known processes for producing CFI and compositions including CFI. Many of these processes involve the direct catalytic iodination of a suitable precursor compound containing a CFgroup moiety. In many of these processes, a crude process stream including the CFI may also include organic impurities, acid impurities, and water. The organic impurities may include fluorinated and iodinated hydrocarbons such as pentafluoroethane (HFC-125), hexafluoropropene (HFO-1216), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,3,3,3-pentafluoropropene (HFO-1225zc), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), and/or methyl iodide (CHI), for example. The organic impurities may also include carbon dioxide (CO). The organic impurities may be formed as byproducts during the production of the CFI and/or may be present in the reactants or other starting materials used to produce the CFI.

CHI exhibits moderate-to-high acute toxicity for inhalation and ingestion, according to the U.S. Department of Agriculture. The specification for CHI in high-purity CFI needed for toxicity assessment is less than 5 ppm. The concentration of CHI in the crude process stream may typically be about 1,000 ppm, and may be as high as 5,000 ppm.

The acid impurities may include hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen iodide (HI), and/or trifluoroacetic acid (TFA), for example. The acid impurities may be formed as byproducts during the production of the CFI and/or may be present in the reactants or other starting materials used to produce the CFI. The concentration of acid impurities in the crude process stream may range from about 20 ppm to about 100 ppm. The water may also be present in the reactants or other starting materials used to produce the CFI. The concentration of water in the crude process stream may range from about 5 ppm to about 100 ppm. The presence of the acid impurities and water in the crude process stream creates a corrosive medium which may have detrimental effects on downstream processing equipment, such as distillation columns, pumps, piping, sensors, storage tanks, etc. The corrosion resulting in replacement and/or repair of the equipment may reduce the overall efficiency of the purification processes. High-purity CFI must have no more than 1 ppm of acid impurities and no more than 10 ppm water.

Thus, there is a need for purification processes that remove enough of the organic impurities (especially CHI), acid impurities and water to produce high-purity CFI.

The present disclosure provides processes for purifying trifluoroiodomethane (CFI) resulting in high yields of high-purity trifluoroiodomethane.

In one form thereof, the present disclosure provides a method for purifying trifluoroiodomethane. The method includes providing a process stream comprising trifluoroiodomethane, organic impurities, and acid impurities; reacting the process stream with a basic aqueous solution, the basic aqueous solution comprising water and at least one base selected from the group of an alkali metal carbonate and an alkali metal hydroxide; and separating at least some of the organic impurities from the process stream.

In the reacting step, the at least one base may include an alkali metal carbonate. A concentration of the alkali metal carbonate in the basic aqueous solution may be from about 0.01 wt. % to about 20 wt. %. A concentration of the alkali metal carbonate in the basic aqueous solution may be from about 0.5 wt. % to about 5 wt. %. The alkali metal carbonate may include sodium carbonate.

The at least one base may include an alkali metal hydroxide. A concentration of the alkali metal hydroxide in the basic aqueous solution may be from about 0.01 wt. % to about 20 wt. %. A concentration of the alkali metal hydroxide in the basic aqueous solution may be from about 0.5 wt. % to about 1 wt. %. The alkali metal hydroxide may include potassium hydroxide.

In the reacting step, a temperature of the process stream may be from about 5° C. to about 80° C. and a pressure of the process stream may be from about 1 psig to about 100 psig.

In the providing step, the organic impurities may include methyl iodide. The concentration of the methyl iodide in the process stream, in GC area % of total organic compounds, may be reduced by from about 1% to about 70% by the reacting step. The reacting step may precede the separation step. The reacting step may follow the separation step.

The method may further include the additional step of drying to remove at least some of the water from the process stream immediately after the reacting step. After the reacting step, the drying step, and the separation step, the process stream may include at least about 99 wt. % trifluoroiodomethane, less than about 50 ppm methyl iodide, less than about 100 ppm water, and less than about 20 ppm acid impurities. The method may be a continuous process.

In another form thereof, the present disclosure provides a method for purifying trifluoroiodomethane. The method includes providing a process stream comprising trifluoroiodomethane, organic impurities, and acid impurities; contacting the process stream with an acid reactive agent; and separating at least some of the organic impurities from the process stream.

The acid reactive agent may include an alumina adsorbent. In the contacting step, the process stream may be in a liquid phase and temperature of the process stream may be from about −50° C. to about 50° C. and a pressure of the process stream may from about 1 psig to about 100 psig. In the contacting step, the process stream may be in a gas phase and a temperature of the process stream may be from about −20° C. to about 60° C. and a pressure of the process stream may be from about 1 psig to about 100 psig.

The contacting step may precede the separation step. The contacting step may follow the separation step.

The method may further include the additional step of drying to remove at least some of the water from the process stream immediately after the contacting step. After the contacting step, the drying step, and the separation step, the process stream may include at least about 99 wt. % trifluoroiodomethane, less than about 50 ppm methyl iodide, less than about 100 ppm water, and less than about 20 ppm acid impurities.

The above mentioned and other features of the disclosure, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of embodiments taken in conjunction with the accompanying drawings.

The present disclosure provides processes for purifying crude trifluoroiodomethane (CFI) resulting in high yields of high-purity CFI. It has been found that the neutralization of acids from process streams including CFI is especially challenging because CFI may chemically break down when contacted by basic solutions typically used for neutralizing acids, resulting in a loss of CFI product.

Acid impurities may be removed from the process stream by passing the process stream through a scrubber containing a basic aqueous solution. It has been found that by passing a crude process stream including CFI and acid impurities through the scrubber containing a basic aqueous solution including water and at least one base in defined concentration range, the acid impurities in the process stream may be effectively removed without significant breakdown of CFI. The base may be an alkali metal carbonate and/or an alkali metal hydroxide.

The basic aqueous solution may consist essentially of water and the at least one base. The basic aqueous solution may consist of water and the at least one base.

The base may comprise an alkali metal hydroxide. The base may consist essentially of an alkali metal hydroxide. The base may consist of an alkali metal hydroxide. The alkali metal hydroxide may be selected from a group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH), and combinations thereof. Preferably, the alkali metal hydroxide may comprise potassium hydroxide. More preferably, the alkali metal hydroxide may consist essentially of potassium hydroxide. Most preferably, the alkali metal hydroxide may consist of potassium hydroxide. The alkali metal hydroxide may consist essentially of sodium hydroxide. The alkali metal hydroxide may consist of sodium hydroxide. The alkali metal hydroxide may consist essentially of lithium hydroxide. The alkali metal hydroxide may consist of lithium hydroxide.

The crude process stream may also include organic impurities. It has been found that the basic aqueous solutions in which the base comprises alkali metal hydroxide may also remove a significant percentage of the organic impurity CHI. The CHI in the process stream may react with the alkali metal hydroxide in the basic aqueous solution within a scrubber to form methanol and an alkali iodide salt according to Equation 1 below:CHI+XOH→CHOH+XI,  Eq. 1:wherein XI is potassium iodide, sodium iodide, or lithium iodide. The methanol and the alkali iodide salts are easily soluble in the basic aqueous solution, and thus, removed from the process stream.

It has been found that CHI undergoes this reaction of Equation 1 more readily than CFI. Without wishing to be bound by any theory, it is believed that the difference in reactivity is due, at least in part, to a significantly better solubility of CHI in water than of CFI in water.

The composition of the organic compounds in the process stream may be measured as by gas chromatography (GC) and gas chromatography-mass spectroscopy (GC-MS) analyses. Graph areas provided by the GC analysis for each of the organic compounds may be combined to provide a GC area percentage (GC area %) of the total organic compounds for each of the organic compounds as a measurement of the relative concentrations of the organic compounds in the process stream.

The concentration of CHI in the process stream, in GC area % of total organic compounds, may be reduced by the reacting step in which the basic aqueous solution comprises alkali metal hydroxide by as little as about 1%, about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, or about 35%, or may be as much as about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, or about 80%, or within any range defined between any two of the foregoing values, such as about 1% to about 80%, about 5% to about 70%, about 10% to about 65%, about 15% to about 60%, about 20% to about 55%, about 25% to about 50%, about 30% to about 45%, or about 35% to about 40%, for example. Preferably, the concentration of CHI in the process stream may be reduced by the reacting step from about 1% to about 70%. More preferably, the concentration of CHI in the process stream may be reduced by the reacting step from about 5% to about 50%. Most preferably, the concentration of CHI in the process stream may be reduced by the reacting step from about 5% to about 30%.

While the CHI may be effectively removed from the process stream by distillation, as described below, removing significant amounts CHI by the basic aqueous solution prior to distillation may permit the distillation column to run more efficiently. CHI may represent the largest component of the organic impurities in the process stream. Removing a significant portion of the organic impurities ahead of the distillation column may increase the flow rate of the process stream through the distillation column and increase the rate at which high-purity CFI may be produced. Alternatively, or additionally, the reduction in organic impurities ahead of the distillation column may permit the use of a smaller distillation column to achieve a desired production rate of high-purity CFI.

Removing significant amounts CHI by the basic aqueous solution after distillation may also permit the distillation column to run more efficiently because distillation column will not have to be operated to produce CFI as pure as ultimately required. Removing a significant portion of the organic impurities after distillation may increase the flow rate of the process stream through the distillation column as fewer organic impurities need to be removed. Alternatively, or additionally, the reduction in organic impurities after the distillation column may permit the use of a smaller distillation column to achieve a desired production rate of high-purity CFI.

It has also been found that at higher concentrations of the alkali metal hydroxide, the CFI may react with the alkali metal hydroxide in the basic aqueous solution within the scrubber and break down to form carbonyl fluoride, an alkali fluoride salt, an alkali iodide salt, and water according to Equation 2 below:CFI+2XOH→CFO+XI+XF+HO  Eq. 2:wherein XI is potassium iodide, sodium iodide, or lithium iodide, and XF is potassium fluoride, sodium fluoride, or lithium fluoride. Thus, the concentration of the alkali metal hydroxide in the basic aqueous solution must be tightly controlled to limit this breakdown of CFI and preserve the yield of CFI in the purification process.

A concentration of the alkali metal hydroxide, as a percentage of the total weight of the basic aqueous solution, may be as little as about 0.01 weight percent (wt. %), about 0.02 wt. %, about 0.05 wt. %, about 0.1 wt. %, about 0.2 wt. %, about 0.5 wt. %, or about 1 wt. % or as great as about 2 wt. %, about 5 wt. %, about 10 wt. %, about 15 wt. %, or about 20 wt. %, or within any range defined between any two of the foregoing values, such as about 0.01 wt. % to about 20 wt. %, about 0.02 wt. % to about 15 wt. %, about 0.05 wt. % to about 12 wt. %, about 0.1 wt. % to about 10 wt. %, about 0.2 wt. % to about 5 wt. %, about 0.5 wt. % to about 2 wt. %, about 0.5 wt. % to about 5 wt. %, about 0.05 wt. % to about 1 wt. %, about 0.5 wt. % to about 1 wt. %, or about 0.1 wt. % to about 5 wt. % for example. Preferably, the concentration of the alkali metal hydroxide may be from about 0.1 wt. % to about 5 wt. %. More preferably, the concentration of the alkali metal hydroxide may be from about 0.5 wt. % to about 1 wt. %. Most preferably, the concentration of the alkali metal hydroxide may be about 0.5 wt. %.

It has also been found that the basic aqueous solutions in which the base comprises alkali metal carbonate do not remove a significant percentage of the organic impurity CHI, but do cause less significant breakdown of CFI. Thus, it may be preferred to employ basic aqueous solutions in which the base comprises alkali metal carbonate rather than alkali metal hydroxide to preserve more of the CFI, and rely exclusively on a separation process to remove the CHI from the process stream, as described below.

The base may comprise an alkali metal carbonate. The base may consist essentially of an alkali metal carbonate. The base may consist of an alkali metal carbonate. The alkali metal carbonate may be selected from a group consisting of sodium carbonate (NaCO), potassium carbonate (K2CO), and lithium carbonate (Li2CO), and combinations thereof. Preferably, the alkali metal carbonate may comprise sodium carbonate. More preferably, the alkali metal carbonate may consist essentially of sodium carbonate. Most preferably, the alkali metal carbonate may consist of sodium carbonate. The alkali metal carbonate may consist essentially of potassium carbonate. The alkali metal carbonate may consist of potassium carbonate. The alkali metal carbonate may consist essentially of lithium carbonate. The alkali metal carbonate may consist of lithium carbonate.

A concentration of the alkali metal carbonate, as a percentage of the total weight of the basic aqueous solution, may be as little as about 0.01 weight percent (wt. %), about 0.02 wt. %, about 0.05 wt. %, about 0.1 wt. %, about 0.2 wt. %, about 0.5 wt. %, or about 1 wt. % or as great as about 2 wt. %, about 5 wt. %, about 10 wt. %, about 15 wt. %, or about 20 wt. %, or within any range defined between any two of the foregoing values, such as about 0.01 wt. % to about 20 wt. %, about 0.02 wt. % to about 15 wt. %, about 0.05 wt. % to about 12 wt. %, about 0.1 wt. % to about 10 wt. %, about 0.2 wt. % to about 5 wt. %, about 0.5 wt. % to about 2 wt. %, or about 0.5 wt. % to about 5 wt. %, for example. Preferably, the concentration of the alkali metal carbonate may be from about 0.1 wt. % to about 10 wt. %. More preferably, the concentration of the alkali metal carbonate may be from about 0.5 wt. % to about 5 wt. %. Most preferably, the concentration of the alkali metal carbonate may be about 5 wt. %.

Contact time between the process stream and the basic aqueous solution is not particularly critical and may be as short as 0.5 seconds. Contact time may be much longer and still not cause significant breakdown of CFI.

The process stream may be in a gas phase or in a liquid phase when passing through the scrubber. Pressure and temperature of the process stream passing through scrubber should be tightly controlled to limit unwanted secondary reactions involving CFI.

When passing through the scrubber, the process stream may be at a temperature as low as about 5° C., about 10° C., about 15° C., about 20° C., about 25° C., or about 30° C., or as high as about 40° C., about 50° C., about 60° C., about 70° C., or about 80° C., or any temperature within any range defined between any two of the foregoing values, such as about 5° C. to about 80° C., about 10° C. to about 70° C., about 15° C. to about 60° C., about 20° C. to about 50° C., about 25° C. to about 40° C., or about 20° C. to about 40° C., for example. Preferably, the process stream temperature in the scrubber may be from about 10° C. to about 50° C. More preferably, the process stream temperature in the scrubber may be from about 20° C. to about 40° C.

When passing through the scrubber, the process stream may be at a pressure as low as about 1 psig, about 2 psig, about 3 psig, about 5 psig, about 10 psig, about 20 psig, about 25 psig, or about 30 psig, or as high as about 40 psig, about 50 psig, about 60 psig, about 70 psig, about 80 psig, about 90 psig, or about 100 psig, or any pressure within any range defined between any two of the foregoing values, such as about 1 psig to about 100 psig, about 2 psig to about 90 psig, about 3 psig to about 80 psig, about 5 psig to about 70 psig, about 5 psig to about 60 psig, about 5 psig to about 50 psig, about 5 psig to about 40 psig, or about 5 psig to about 50 psig, for example. Preferably, the process stream pressure in the scrubber may be from about 3 psig to about 80 psig. More preferably, the process stream pressure in the scrubber may be from about 5 psig to about 50 psig.

Alternatively, or additionally, acid impurities may be removed from the process stream by passing the process stream through an adsorption column containing an acid active agent. An acid active agent is a material that adsorbs acids.

The acid active agent may comprise at least one adsorbent selected from the group of alumina, alkali metal oxides, alkaline earth metal oxides, metal hydroxides, aluminosilicate minerals, zirconias, and silica. The acid active agent may be an adsorbent selected from the group consisting of alumina, alkali metal oxides, alkaline earth metal oxides, metal hydroxides, aluminosilicate minerals, zirconias, silica, and combinations thereof.

It has been found that by passing the process stream including CFI through the adsorption column containing an acid active agent that does not initiate or favor the breakdown of CFI, the acid impurities in the process stream may be effectively removed without significant yield reduction of CFI.

The acid active agent may comprise alumina. The acid active agent may consist essentially of alumina. The acid active agent may consist of alumina. The alumina may comprise one or more types of alumina. The alumina may be an activated alumina, such as P-188 or CLR-204 available from UOP LLC, Des Plaines, Ill., HF-200XP from BASF, Iselin, N.J., or aluminum oxide catalyst support from Alfa Aesar, Haverhill, Mass., for example.

Contact time between the process stream and the adsorption column containing the acid active agent is not particularly critical and may be as short as 0.5 seconds. Contact time may be much longer and still not cause significant breakdown of CFI.

The process stream may be in a gas phase or in a liquid phase when passing through the adsorption column comprising the acid active agent.

When passing through the adsorption column in the liquid phase, the process stream may be at a temperature as low as about −50° C., about −45° C., about −40° C., about −35° C., about −30° C., about −25° C., about −20° C., or about −15° C., or as high as about −10° C., about −5° C., about 0° C., about 5° C., about 10° C., about 15° C., about 20° C., about 25° C., about 30° C., about 35° C., about 40° C., about 45° C., or about 50° C., or any temperature within any range defined between any two of the foregoing values, such as about −50° C. to about 50° C., about −40° C. to about 45° C., about −30° C. to about 40° C., about −25° C. to about 35° C., about −10° C. to about 30° C., or about 0° C. to about −25° C., for example. Preferably, the process stream temperature in the adsorption column may be from about 0° C. to about 35° C. More preferably, the process stream temperature in the adsorption column may be from about 10° C. to about 30° C.

When passing through the adsorption column in the liquid phase, the process stream may be at a pressure as low as about 1 psig, about 5 psig, about 10 psig, about 20 psig, about 25 psig, or about 30 psig, or as high as about 40 psig, about 50 psig, about 60 psig, about 70 psig, about 80 psig, about 90 psig, or about 100 psig, or any pressure within any range defined between any two of the foregoing values, such as about 1 psig to about 100 psig, about 5 psig to about 90 psig, about 10 psig to about 80 psig, about 15 psig to about 70 psig, about 20 psig to about 60 psig, about 25 psig to about 50 psig, about 30 psig to about 40 psig, or about 20 psig to about 50 psig, for example. Preferably, the process stream pressure in the adsorption column may be from about 10 psig to about 90 psig. More preferably, the process stream pressure in the adsorption column may be from about 20 psig to about 50 psig.

When passing through the adsorption column in the gas phase, the process stream may be at a temperature as low as about −20° C., about −15° C., about −10° C., about −5° C., about 0° C., about 5° C., about 10° C., or about 15° C., or as high as about 20° C., about 25° C., about 30° C., about 35° C., about 40° C., about 45° C., about 50° C., about 55° C., or about 60° C., or any temperature within any range defined between any two of the foregoing values, such as about −20° C. to about 60° C., about −10° C. to about 50° C., about 0° C. to about 40° C., about 10° C. to about 30° C., about −5° C. to about 50° C., or about 15° C. to about 40° C., for example. Preferably, the process stream temperature in the adsorption column may be from about −5° C. to about 50° C. More preferably, the process stream temperature in the adsorption column may be from about 15° C. to about 40° C.

When passing through the adsorption column in the gas phase, the process stream may be at a pressure as low as about 1 psig, about 5 psig, about 10 psig, about 20 psig, about 25 psig, or about 30 psig, or as high as about 40 psig, about 50 psig, about 60 psig, about 70 psig, about 80 psig, about 90 psig, or about 100 psig, or any pressure within any range defined between any two of the foregoing values, such as about 1 psig to about 100 psig, about 5 psig to about 90 psig, about 10 psig to about 80 psig, about 15 psig to about 70 psig, about 20 psig to about 60 psig, about 25 psig to about 50 psig, about 30 psig to about 40 psig, or about 20 psig to about 50 psig, for example. Preferably, the process stream pressure in the adsorption column may be from about 10 psig to about 90 psig. More preferably, the process stream pressure in the adsorption column may be from about 15 psig to about 80 psig.

The water may be removed from the process stream by a drying step. The drying step may comprise contacting the process stream with a desiccant. The desiccant may comprise at least one adsorbent selected from the group of anhydrous calcium chloride, anhydrous calcium sulfate, concentrated sulfuric acid, silica, activated charcoal and zeolites. The desiccant may be selected from the group consisting of anhydrous calcium chloride, anhydrous calcium sulfate, concentrated sulfuric acid, silica, activated charcoal, zeolites, and combinations thereof. The desiccant may preferably be a 3 A molecular sieve. It has been found that a 3 A molecular sieve does not initiate or favor the breakdown of CFI.

It is preferred that the drying step occur immediately after the acid impurities are removed from the process stream. This is so that when the acid impurities are removed from the process stream by passing the process stream through a scrubber containing the basic aqueous solution, water picked up in the scrubber can be removed as well as any moisture present in the crude CFI process stream.