Membrane process, Asahi Chemical

Asahi Chemical Membrane Chlor—Alkali Process, Asahi Chemical Industry Co., Ltd., Tokyo, Japan, 1987. 

Nafion Perfluorinated Membranes, Introduction, E.I. duPont de Nemours Co., Inc., Wilmington (1987). Asahi Chemical Membrane Chlor-Alkali Process, Asahi Chemical Industry Co., Ltd., Tokyo (1987). 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

The PEM (proton exchange membrane) material is a perfluorosulfonic acid polymer film. Several manufacturers make PEMs in one form or another. We used one made by du Pont called Nation 117. Nation 117 is a transparent polymer film about 175 microns (0.007 inches) thick. Dow Chemical Co., Asahi Chemical Co., and Chloride Engineers Ltd. make something similar. A patent describing how one PEM manufacturer s film is processed is listed in the references section at the end of this article. 

In the United States, electrodialysis was developed primarily for desalination of water, with Ionics being the industry leader. In Japan, Asahi Glass, Asahi Chemical (a different company), and Tokuyama Soda developed the process to concentrate seawater [8], This application of electrodialysis is confined to Japan, which has no domestic salt sources. Electrodialysis membranes concentrate the salt in seawater to about 18-20% solids, after which the brine is further concentrated by evaporation and the salt recovered by crystallization. 

Ogawa, Shinsaku, "Asahi Chemical Membrane Chlor Alkali Process,"... 

Perfluorocarboxylic Acid Membrane and Membrane Chlor-Alkali Process Developed by Asahi Chemical Industry... 

After intensive research and development work, Asahi Chemical filed the basic patents of fluorinated carboxylic acid membrane and carboxylic and sulfonic acid membrane and the related electrolysis processes in 1974 (1 - 8). 

With a multilayer membrane containing both carboxylic and sulfonic acid groups, however, it is possible to neutralize proton from the anolyte with hydroxyl anion at the surface of or in the membrane before the proton reaches the carboxylic acid layer facing the catholyte, and thus achieve high chlorine purity and longer anode life, as indicated in Table I. This is one of the essential features of the Asahi Chemical process patented in various countries (39). Another advantage of the... 

Asahi Chemical has developed an unique anode coating which satisfies the requirements of the membrane process, and has used it industrially since 1975. This coating is a completely solid solution of ruthenium, titanium and oxygen, in which the molar percentage of ruthenium is at least 50% of the total metal content and various other metal components are incorporated to provide high oxygen overvoltage (26, 78). 

Energy Consumption. Electric power consumption of electrolysis is the major part of the energy consumption in a chlor-alkali process. The power consumption of the membrane process has recently been greatly reduced by various improvements. The latest performance of Asahi Chemical s membrane process realized at a commercial plant and also in an industrial scale cell is shown in relation to current density in Figure 13 (82). 

Seko, M., New development of the Asahi Chemical membrane chlor-alkali process, presented at the Chlorine Institute Inc., 22nd Chlorine Plant Managers Seminar, Atlanta Geogia... 

Ogawa, S., Asahi Chemical Membrane Chlor-alkali Process, presented at Seminar on Developments in Chlor-alkali Industry, New Delhi India Mar. 7-8, 1980. 

M. Seko, S. Ogawa and K. Kimoto, Perfluorocarboxilic acid membrane and membrane chlor-alkali process developed by Asahi Chemical Industry, Perfluorinated Ionomer Membranes, ACS Symposium Series, ed. A. Eisenberg and H.L. Yeager, American Chemical Society, Washington DC 1982, Vol. 180, p. 365. 

Since the first membrane cell installation at the Nobeoka plant by Asahi Chemical Industry in 1975, several membrane cell plants have been constructed, especially in Japan, as a pollution-free chlor-alkali process. By the end of 1982, the total capacity of the membrane cell process in the world was estimated to be about 600,000 tons of NaOH per year.112... 

Bilayer carboxylate membranes can be produced by surface modification of Nafion-type membranes. In a process used by Asahi Chemical the sulfonate on a Nafion-type surface is reduced to sulfinic and sulfenic acids, then oxidized to a carboxylate layer of 2-10 pm thickness ... 

The reduction takes place at the cathode with a catholyte composed of aqueous quaternary ammonium salt. The anolyte is sulfuric acid. ions generated at the anode pass through the membrane and neutralize the OH" ions generated in the catholyte. Commercial installations are operated by Solutia (spun off from Monsanto), BASF, Asahi Chemical, and Rhodia. Some of these manufacturers have developed undivided cells for this process. 

M. Seko, New Development of the Asahi Chemical Membrane Chlor-AlkaK Process. In Proceedings of the Oronzio DeNora Symposium Chlorine Technology, Venice (1979), p. 141. 

First electrochemical production of adiponitrilehad developed by Monsanto in 1963 and commercialized in 1965. Monsanto process adopted a homogeneous electrolysis system. On the other hand, Asahi Chemical Industry (presently Asahi Kasei Chemicals) started the commercial adiponitrUeplant withan emulsion electrolysis system in 1971. Both of the processes were operated in the divided cell equipped with separator such as ion exchange membrane in the first stage of development and have improved into operation in undivided cell in order to reduce higher cell voltage caused by resistance of separator. 

Asahi Chemicals Industries in Japan in the early 1970s introduced a commercial process which also uses a lead cathode in a membrane cell The catholyte stream is, however an emulsion of acrylonitrile and 12% eihyltributylammonium bisulphate in water. As a result, the aqueous solution is saturated with acrylonitrile (about 7%) and the product - adiponitrile - extracts back into the excess acrylonitrile within the cell In this process the number of unit processes in the product isolation is much reduced the letraalkylammonium salt remains in the aqueous phase and the organic products can be separated by distillation. Moreover, the cell voltage is much reduced The catholyte is quite acidic, and the major by-product is propiontlrtle. 

Perfluorinated membranes based on weak acid functions have been developed by Asahi Chemicals (Japan). Their EW is similar to that of the above membranes. The exact synthesis process of the membrane is not indicated. They have been developed for the chlor-alkali industry where they are used in bilayer membranes. In these membranes a strongly acidic membrane (-SO3H) (pK < 1) is coated on one side, and the second side is coated with a thin layer of a weak-acid membrane (-COOH) = 3). 

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