Asahi Chemicals adiponitrile process

Asahi 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 tetraethylammonium 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 Rhcjme Poulenc subsidiary, Rhodia, in Brazil under license from Asahi. 

The original process used aqueous tetraethylammonium ethylsulfate as the electrolyte, a lead cathode, and a lead-silver alloy anode. The Mark II process, commercialized in the mid-1970s, uses an emulsion of acrylonitrile in aqueous sodium phosphate containing a salt of the hexamethylene-bis-(ethyldibutylammonium) cation. The process was invented in 1959 by M. M. Baizer at Monsanto Corporation, St. Louis, MO. It was commercialized in 1965 and has been continuously improved ever since. The process is also operated in Japan by Asahi Chemical Industry Company. In 1990, the world production of adiponitrile by this process was over 200,000 tonnes per year. 

Asahi Chemical Industries in Japan in the early 1970s introduced a commercial process which also uses a divided cell with a lead cathode. The catholyte stream, however, contains two phases, acrylonitrile and 12% tetrabutylammonium bisulphate in water. As a result the aqueous phase contains about 7% acrylonitrile and the product adiponitrile extracts into the organic phase in the cell. The catholyte has a lower pH and hence the major byproduct is propionitrile. This technology therefore uses less tetraalkylammonium salt and leads to a lower cell voltage as well as reducing the number of extraction stages. 

Careful selection of the supporting electrolyte is a key point in the hydrodimerization process. Monsanto has chosen tetraethylammonium p-toluenesulfonate for their solution process. In concentrations of from 20% to 40%, it increases the solubility of acrylonitrile in the anolyte and retards the formation of byproduct. Asahi Chemical uses less hydrophobic supporting electrolyte, in concentrations of about 10%, for their emulsion process. Thus, adiponitrile formed in the emulsion process is separated from the reaction mixture by physically breaking down the emulsion and then separating the oil layer. The loss of supporting electrolyte and the electric power consumption are lower in the emulsion process than in the solution process. 

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. 

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