State vector model for Contherm scraped surface heat exchanger used as an enzyme reactor in wheat starch conversions

A state vector was used to represent starch gelatinization and enzymic hydrolysis in a Contherm scraped surface heat exchanger. Wheat starch was hydrolysed in both small-scale batch and pilot Contherm experiments with Termamyl 60L α-amylase (2–3 ml kg⁻¹ dry solids (d.s.)) at temperatures of 90, 100, 105, 108, 110 and 120°C with feed solids contents of 30, 40 and 50% (w/w). Irreversible reactions were assumed to follow first-order kinetics in a completely-mixed reactor. Steady state conditions for the various feed solids contents were obtained from the model developed and asymptotic stability of the steady state could be demonstrated. The return of the model to steady state after small temporary disturbances was shown by employing Laplacian transfer functions. DE values of 16 to 27 could be obtained under steady state conditions after a residence time of about 7 min.