Comparação de diferentes modelos de reatores para a hidrólise enzimática da sacarose

Abstract

The objective of this work consisted in evaluating the performance of a given set of continuous ideal reactors models, aiming at the identification of which model gives the smallest space time for the production of inverted sugar by enzymatic hydrolysis of sucrose. Reactor conditions were: 850 g/L of sucrose, pH 5, 55º C, 0.1698 g/L of Novo Nordisk invertase and final conversion of 98%. The adopted kinetic model includes inhibition by the substrate (sucrose) and product (glucose + fructose), variation of water concentration, and enzyme thermal deactivation. The space time was calculated by coupling the kinetic rate expression with the design equation for ideal reactors. The resulting mathematical models were solved with the software called Derive. Disregarding enzyme thermal deactivation, the system CSTR+PFR requires the smallest space time (11.7000 h), while the second best choice is a single PFR (t = 11.7056 h). A single CSTR requires the largest space time, namely 114.43 h. The inclusion of thermal deactivation of the enzyme in the analysis has allowed to conclude that with a single CSTR it is impossible to reach the conversion of 98%, for the specified reactor conditions, unless the enzyme charge is increased. With the system CSTR+PFR it was possible to reach the final conversion of 98%, if the conversion of the CSTR was lower than 89.72%. With the recycle tubular reactor the conversion reaches 98% only for recycle ratios in the range of zero to .003, and as R →2,003, t → ∞. The reactor model with the minimum space time in the presence of enzyme deactivation is a single PFR with t= 16.9554 h. Therefore, product inhibition, in the case of high sucrose concentration and conversion, is a critical factor for the performance of the hydrolysis reactor. Neglecting invertase thermal deactivation leads to significant errors of undersizing the reactors, in addition to pointing to the wrong optimal reactor system.