Asahi process

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 Asahi process (Fig. 16-63) is used principally for high-volume water treatment. The hquid to be treated is passed upward through a resin bed in the adsorption tank. The upward flow at 30-40 m/h [12-16 gal/(min ft")] keeps the bed packed against the top. After a preset time, 10 to 60 min, the flow is interrupted for about 30 s, allowing the entire bed to drop. A small portion (10 percent or less) of the ion-exchange resin is removed from the bottom of the adsorption tank and transferred hydraulically to the hopper feeding the regeneration tank. 

The Asahi process for wet-spinning the copolymer involves water dilution at below 0°C of a solution of the copolymer in aqueous 68 wt% nitric acid (the azeotropic composition). The potential for slow self heating and decomposition have been investigated experimentally with variations in several parameters in a Sikarex safety calorimeter. At 20% polymer content, the slow self heating starts even at ambient temperature, and later involves evolution of 30 mol of uncondensable gas per kg of copolymer with comcommittant boiling of the nitric acid. A 2 step mechanism has been proposed. 

The Asahi process (Fig. 16-65) is used principally for high-volume... 

The high capital investment cost of the Asahi process is due to the necessity for large absorbers, evaporators, crystallizers, dryers, rotary kiln crackers and screw decanter separators. The major operating and maintenance costs are electricity, fuel oil, steam and chemicals such as soda ash, EDTA and limestone. The requirement for consumption of large amounts of utilities is associated with the operation principle and design of the Asahi process. According to the economic evaluation, equipment required for N0X and SO2 absorption (such as packed-bed absorbers) accounts for 20% of total direct capital investment for treatment of dithionate ion (such as evaporator, crystallizer, dryer, and cracker) it accounts for about 40% and for treatment of nitrogen-sulfur compounds (such as screw decanter and cracker) it accounts for only 2%. 

Zeolites have been used as (acid) catalysts in hydration/dehydration reactions. A pertinent example is the Asahi process for the hydration of cyclohexene to cyclo-hexanol over a high silica (Si/Al>20), H-ZSM-5 type catalyst [57]. This process has been operated successfully on a 60000 tpa scale since 1990, although many problems still remain [57] mainly due to catalyst deactivation. The hydration of cyclohexanene is a key step in an alternative route to cyclohexanone (and phenol) from benzene (see Fig. 2.19). The conventional route involves hydrogenation to cyclohexane followed by autoxidation to a mixture of cyclohexanol and... 

Other technologies, already commercially applied or under development, are summarized in Figure 2.63b. Alternative routes of synthesis include (i) ethene hydroformylation to propionaldehyde, which then forms methacrolein by condensation with formaldehyde methacrolein is then oxidized to methacrylic acid (BASF process) (ii) isobuthyraldehyde conversion into isobutyric acid and then oxidative dehydrogenation to methacrylic add (Mitsubishi Kasei/Asahi process) and (iii) oxidation of terf-butyl alcohol to methacrolein followed by oxidation to methacrylic acid and esterification. 

The hydrogenation of benzene to cyclohexene, follovv ed by the hydration of cycloolefin, vas developed by Asahi, and is currently employed by this company and some Chinese producers as the first step in the manufacture of AA in 1990 Asahi built a plant vdth a capacity of 60 000 tons yr. The partial hydrogenation reaction product is a mixture of unreacted benzene, cyclohexene and by-product cyclohexane. Figure 7.2 sho vs a simplified fio v sheet of the Asahi process. 

Figure 7.2 Simplified flow sheet of the Asahi process for benzene hydrogenation to cydohexene.

Figure 7.7 Simplified block-diagram of the Asahi process for the oxidation of KA Oil with nitrogen-diluted air. Source elaborated from [130].

Cyclohexene can be synthesized by partial hydrogenation of benzene, by partial dehydrogenation of cyclohexane, or by dehydrohalogenation of cyclohexyl halides. The hydrogenation of benzene is the most viable route in the Asahi process, cyclohexene is obtained with a 60% yield and 80% selectivity, with the remainder being converted into cyclohexane. Asahi has developed a process for the addition of water to cyclohexene to produce cyclohexanol that can then be oxidized to AA using the conventional nitric acid oxidation. 

The final condensation with formaldehyde at 60-90 C and atmospheric pressure takes place in the presence of H2S04 in two phases and then, after removal of the water phase, an additional treatment with, for example, tri-fluoroacetic acid in a homogeneous phase this has over 95% selectivity to the diurethane at a urethane conversion of about 40%. The last step, the thermal elimination of ethanol, is done at 230—280°C and 10—30 bar in a solvent the selectivity to MDI is over 93%. The Asahi process has not been used commercially [91]. 

The Asahi process involves initial partial hydrogenation of benzene to cyclohexene using heterogeneous ruthenium catalyst. The cyclohexene hydration proceeds with >99% selectivity at 10-15% conversion (Figure 11.11) [44]. 

A Hoechst process hydrolyzes 2-perfluoroalkylethyl iodides in N-methylpyrrolidone and water by heating at 150°C for 13 h [82]. An Asahi process... 

---