Effect of substrate mass concentration
Fig. 7 shows the effect of initial total substrate mass concentration (CS0) on the reducing sugar production. Higher substrate concentration appears to have two positive effects of (i) faster initial reaction rate and (ii) higher reducing sugar production. These two effects are shown by both the experimental data and the model simulation. The model underestimated the reducing sugar production at lower substrate concentration with overestimation at higher substrate concentration.
When the effect of substrate concentration is examined on the basis of substrate conversion ratio, the positive effects of high substrate concentration are diminished as the conversion ratio decreased with increased substrate mass concentration (Fig. 8). This trend again was reflected in both experimental and simulated data. Therefore, the benefit of increasing substrate concentration would depend on a balanced assessment of the economics of increased reactor productivity and the cost of a lower substrate conversion ratio. The low substrate conversion ratio could be partially rectified in an integrated reaction and separation process where the substrate and enzyme are retained and the reducing sugars and their inhibitory effect reduced. The authors are currently undertaking studies of the integrated process in a membrane reactor system.