Modeling fixed and fluidized reactors for cassava starch saccharification with immobilized enzyme

Area of Science:

• Biochemical Engineering
• Enzyme Kinetics
• Biomass Conversion

Background:

• Previous modeling of cassava starch saccharification with immobilized enzymes yielded physically inconsistent results (negative kinetic constants).
• A simplified model grouped all dextrins into a single substrate, failing to capture complex reaction dynamics.

Purpose of the Study:

• To adapt and validate a multisubstrate model for cassava starch saccharification using immobilized enzymes in both fixed- and fluidized-bed reactors.
• To address physical inconsistencies observed in prior modeling approaches.

Main Methods:

• Adapted a previously developed multisubstrate model, incorporating intermediate substrates, reaction reversibility, substrate/product inhibition, and isomaltose formation.
• Determined kinetic parameters via initial velocity saccharification tests with immobilized enzymes and varying liquefied starch concentrations.
• Applied the refined model to simulate both fixed- and fluidized-bed reactor systems.

Main Results:

• The multisubstrate model successfully modeled saccharification in both reactor types without physical inconsistencies.
• Apparent glucose inhibition was found to be approximately seven times higher in the fixed-bed reactor compared to the fluidized-bed reactor.
• The model accurately accounts for complex reaction pathways, including dextrin competition and product inhibition.

Conclusions:

• The adapted multisubstrate model provides a physically consistent and accurate representation of cassava starch saccharification with immobilized enzymes.
• Reactor hydrodynamics significantly influence apparent glucose inhibition, with fixed-bed reactors exhibiting substantially higher inhibition.
• This improved modeling approach offers better insights into enzyme reactor performance and optimization for biofuel or biochemical production.