Optimal control of enzymatic hydrolysis of lignocellulosic biomass

Cellulose hydrolysis is a key step in lignocellulosic ethanol production. At present, commercial production of lignocellulosic ethanol is limited
due to the long hydrolysis times and requirement of large quantity of expensive enzymes. Therefore, reduction of the enzyme consumption as well
as hydrolysis time is crucial and model based optimisation methods can be used for the same.A semi-mechanistic model with cellobiose, glucose,
and xylose inhibition with Arrhenius based relationship between temperature and kinetic parameters and thermal deactivation of enzymes was used
for the present study. Optimal control problem with temperature as control variable was formulated after considering two different objective
functions. For the objective of glucose concentration maximisation at final batch time, the benefit of implementing optimal control increased with
reducing batch times. For the batch time of 24 hours, the final glucose concentration increased by 3.2%. For the objective of batch time
minimisation, the reduction of batch time was 5.8% and it was observed for a target glucose concentration of 45 g/kg of cellulose. The use of
optimal control can reduce the enzyme requirement up to 77.8% of endoglucanase and exoglucanase for glucose maximisation and 22.2% for batch
time minimisation. The above results show the usefulness of optimal temperature control in increasing the glucose concentration, and reducing the
batch time without increasing the enzyme used.