Phenomenological Modeling of Formic Acid Fractionation of Sugarcane Bagasse by Integration of Operation Parameters as an Extended Combined Severity Factor

In order to more conveniently simulate and optimize the solubilization of sugarcane bagasse components during formic acid (FA) fractionation, an extended combined severity factor (CSF(ext)) was defined to integrate various operation parameters as a single factor. Two phenomenological models based on Arrhenius and Logistic equations were further used to describe the phenomenological kinetics. Different data-processing methods were compared to fit the severity parameters and model constants. Both Arrhenius-based and Logistic-based models show satisfying fitting results, though the values of Arrhenius-based CSF(ext) (A-CSF(ext)) and Logistic-based CSF(ext) (L-CSF(ext)) were somewhat different under the same fractionation condition. The solubilization of biomass components increased with CSF(ext), but two distinct stages could be observed with inflection points at A-CSF(ext) of 42 or L-CSF(ext) of 43, corresponding to bulk and residual solubilization stages, respectively. For the enzymatic hydrolysis of cellulosic solids, the highest initial enzymatic glucan conversion (EGC@6h) was obtained at A-CSF(ext) of 39–40 or A-CSF(ext) of 40–41; however, for a long hydrolysis period (72 h), relatively high glucan conversion (EGC@72h) was observed at A-CSF(ext) of 42–43 or A-CSF(ext) of 43–44. Post-treatment for deformylation with a small amount of lime could help to recover the cellulose digestibility.