Acrylamide biocatalytic process

Another example in which a biocatalytic transformation has replaced a chemo-catalytic one, in a very simple reaction, is the Mitsubishi Rayon process for the production of acrylamide by hydration of acrylonitrile (Fig. 1.42). Whole cells of Rhodococcus rhodocrous, containing a nitrile hydratase, produced acrylamide in >99.9% purity at >99.9% conversion, and in high volumetric and space time yields [121]. The process (Fig. 1.42) currently accounts for more than 100000 tons annual production of acrylamide and replaced an existing process which employed a copper catalyst. A major advantage of the biocatalytic process is the high product purity, which is important for the main application of acrylamide as a specialty monomer. 

The cells are immobilized in a polyacrylamide gel, and during fed-batch processing yields of 400 g acrylamide per litre are achieved. The biocatalytic process is far simpler than the classical chemical process, which requires a copper catalyst and a polymerization inhibitor. Furthermore, the bioroute has a selectivity of >99% at >99% conversion. 

Biocatalytic processes and technologies are penetrating increasingly in all branches of the chemical process industries. In basic chemicals, nitrile hydratase and nitri-lases have been most successful. For example, acrylamide from acrylonitrile is now a 30,000 t/a process. In fine chemicals, enantiomerically pure amino acids are produces by several different companies. 

FIGURE 9.20. Biocatalytic production of acrylamide Mitsubishi process. 

The biocatalytic acrylamide process is run by the Nitto Chemical Corp., now part of the Mitsubishi Rayon Corp., in Tokyo Bay on a scale of 30 000 tpy, in fed-batch mode up to 25-40% acrylamide at 0-10°C to complete conversion and with product yields > 99.9%, conditions under which a significant cost differential can be assumed with respect to the conventional chemical process. 

Figure 1.15 The biocatalytic synthesis of acrylamide from acrylonitrile is performed in Japan on a scale of 10000 tons per year. The bacterial cells are immobilized in a poly(acrylamide) gel, and the process is run at pH 8.0-8.5 in semi-batch mode, keeping the substrate concentration below 3%.

Japan, this process replaced an add-catalyzed process, and also avoided the acrylic acid by-produd [29]. Biocatalytic acrylamide processes are now running at 50 000 tpa worldwide. 

This has been impressively demonstrated by Nitto Chemical Industries with the biocatalytic manufacture of acrylamide, an important building block for polymers and copolymers, produced in quantities of over 200000 t/y [80]. The chemocata-lytic route to acrylamide (32) uses a reduced Raney copper catalyst for hydration. This metal-catalyzed process has been shown to be superior to the acid-catalyzed hydration, but catalyst poisoning and waste-water problems due to heavy-metal content cause some problems (eq. (10)) [81, 82]. 

A remarkable example of a lyase-catalyzed commercial process, developed by the Japanese company Nitto and operative since 1985, is the biocatalytic production of acrylamide using immobilized whole cells of Rhodococcus rhodochrous [17]. The enzyme responsible for water addition to the double bond of acrylonitrile is nitrile hydratase ... 

Another interesting example is Mitsubishi s new route for the biocatalytic production of acrylamide [155], an intermediate produced in over 100 000 tons per year. The biocatalytic route (Figure 2.20a) is somewhat simpler than the chemical process (Cu catalyst). It is based on immobilized whole cells of Rh. rhodocrous J1 and operates under mild conditions (5 °C), that is, no polymerization inhibitors... 

Figure 12.1-4. Comparison of the biocatalytic and the conventional chemical process for acrylamide production.

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