Reversible Water-Free Process for the Separation of Acid-Containing Gas Mixtures

Abstract

Gas mixtures which comprise acids like HF, HCl and/or HBr and other constituents, especially gas mixtures which comprise or consist of carboxylic acid fluorides, C(O)F 2 or phosphorous pentafluoride and HCl and optionally HF, can be separated by ionic liquids. The process is performed reversibly. Ionic liquids are applied, the anion of which corresponds to a stronger acid than the acid to be removed. Highly purified products, for example, highly purified carbonyl fluoride can be obtained.

1 . A process for the reversible removal of acid or acids from a gas mixtures which comprises at least one acids and one or more other gaseous constituents, said process comprising contacting said gas mixtures in an absorption step with one or more ionic liquids which absorb the acid preferentially to other constituents of the gas mixtures, and whereby after contacting the gas mixture with the ionic liquids the absorbed acid is removed from the ionic liquid in a desorption step, and then at least one further absorption step is performed, whereby an ionic liquid is applied, the protonated anion of which corresponds to an acid which is stronger than the acid or acids to be removed from the gas mixture. 
     
     
         2 . The process according to  claim 1  wherein in total, at least two absorption steps and at least two desorption steps are performed. 
     
     
         3 . The process according to  claim 1  wherein the process is performed continuously. 
     
     
         4 . The process according to  claim 1  wherein the acid to be removed is HCl, and the anion of the ionic liquid is the trifluoromethansulfonic acid (triflate) or the fluorosulfonic acid anion. 
     
     
         5 . The process according to  claim 1  wherein the acid to be removed is HF, and the anion of the ionic liquid is the trifluoromethansulfonic acid (triflate) or the fluorosulfonic acid anion. 
     
     
         6 . The process according to  claim 1  wherein the acid to be removed is HBr, and the anion of the ionic liquid is the trifluoromethansulfonic acid (triflate) or the fluorosulfonic acid anion. 
     
     
         7 . The process according to  claim 1  wherein the constituents of the gas mixture have a boiling point below 50° C., at normal pressure (1 bar). 
     
     
         8 . The process according to  claim 1  wherein the acid to be removed is HCl or HF, and the gas mixture comprises PF 5 , C(O)F 2  or a carboxylic acid fluoride. 
     
     
         9 . he process according to  claim 1  wherein the acid to be removed from the gas mixture is HCl, HF, HBr, or combinations thereof, and the acid is removed under water-free conditions. 
     
     
         10 . The process according to  claim 8 , wherein the carboxylic acid fluoride is CH 3 C(O)F, CHF 2 C(O)F, CF 3 C(O)F, or C 2 F 5 C(O)F. 
     
     
         11 . The process according to  claim 1  wherein an ionic liquid is applied which comprises nitrogen in its cation. 
     
     
         12 . The process according to  claim 11  wherein the cation is selected from the group consisting of imidazolium, imidazolinium, pyrazolium, oxatriazolium, thiatriazolium, pyridinium, pyradizinium, pyrimidinium, and pyrazinium compounds. 
     
     
         13 . The process according to  claim 11  wherein the cation is an imidazolium cation which is substituted by one, two or three substituents, each with 1 to 24 carbon atoms, and wherein the substituents themselves are optionally substituted. 
     
     
         14 . The process according to  claim 13  wherein the cation is 1,3-dimethyl-imidazolium, 1-ethyl-3-methyl-imidazolium, 1-propyl-3-methyl-imidazolium, or 1-n-butyl-3-methyl-imidazolium. 
     
     
         15 . The process according to  claim 1  wherein 1-ethyl-3-methyl-imidazolium trifluoromethansulfonate (EMIM-triflat) is applied as ionic liquid to remove HCl. 
     
     
         16 . The process according to  claim 1  wherein 1-ethyl-3-methyl-imidazolium trifluoromethansulfonate (EMIM-triflat) is applied as ionic liquid to remove HF. 
     
     
         17 . The process according to  claim 1  wherein 1-ethyl-3-methyl-imidazolium trifluoromethansulfonate (EMIM-triflat) is applied as ionic liquid to remove HBr. 
     
     
         18 . The process according to  claim 1  wherein the contact between one ionic liquid and the gas mixture to be separated is performed at a temperature in the range of from 20 to 200° C. and a pressure of from 0.5 to 10 bars (abs). 
     
     
         19 . The process according to  claim 1  wherein the constituents absorbed in the ionic liquid are desorbed at a temperature in the range of from 0° C. to 300° C. and at a pressure which is lower than the pressure in the absorption step, and whereby optionally an inert gas is passed through the ionic liquid. 
     
     
         20 . The process according to  claim 1  wherein the gas mixture in said process is obtained by photochemical oxidation of CHClF 2  for the preparation of C(O)F 2 , or from fluorination reactions of phosphorous-chlorine compounds with HF. 
     
     
         21 . A purified gas selected from the group consisting of carbonyl fluoride, phosphorous pentafluoride, CH 3 C(O)F, CHF 2 C(O)F, CF 3 C(O)F and C 2 F 5 C(O)F, said purified gas comprising from 1 to 50 ppm, HCl. 
     
     
         22 . The process according to  claim 3  wherein three or more absorption steps and three or more desorption steps are performed. 
     
     
         23 . The process according to  claim 3  wherein five or more absorption steps and five or more desorption steps are performed. 
     
     
         24 . The process according to  claim 7  wherein the constituents of the gas mixture have a boiling point below 15° C. at normal pressure (1 bar). 
     
     
         25 . The process according to  claim 13  wherein the substituents themselves are substituted by alkyl groups, aryl groups, or combinations thereof. 
     
     
         26 . The process according to  claim 19  wherein the inert gas is selected from the group consisting of nitrogen, helium, argon, and neon. 
     
     
         27 . The process according to  claim 20  wherein the gas mixture in said process is obtained from the preparation of PF 5  from phosphorous(III) chlorides or phosphorous(V) chlorides and HF and optionally Cl 2  or F 2 . 
     
     
         28 . The process according to  claim 20  wherein the gas mixture in said process is obtained from processes which provide for the photochemical oxidation of chlorofluoralkanes or the fluorination of carboxylic acid chlorides with HF. 
     
     
         29 . The process according to  claim 26  wherein the carboxylic acid fluoride is selected from the group consisting of CH 3 C(O)F, CHF 2 C(O)F, CF 3 C(O)F, and C 2 F 5 C(O)F. 
     
     
         30 . The purified gas according to  claim 21  comprising from 1 to 15 ppm HCl.