An enhanced in situ fed-batch hydrolysis and kinetic study for producing biomass-based levulinic acid at high solid loadings

Levulinic acid (LA), regarded as one of the top twelve biomass-based platform chemicals, has been extensively studied by numerous researchers. In this study, a high LA concentration and yield were obtained through an enhanced in situ feeding strategy with a high loading of furfural residue (FR). The effects of batch process, onetime feeding and two-time feeding strategy on the hydrolysis performance (LA yield and concentrations, as well as intermediate glucose yield and concentrations) were investigated. The humin-based byproducts generated during different processes were also characterized by SEM, FT-IR and XRD analysis. The best results of one-time feeding strategy were obtained at 3 wt% H2SO4, 170. C for 60 min with an initial FR concentration of 15% supplemented to 20% at 0th min. Under these conditions, the LA concentration and yield reached 30.00 g/L and 15% (51.1 mol%), respectively. Furthermore, a hybrid model integrated with the shrinking core model and a quasi-first-order kinetic model was adopted to elucidate the kinetic behavior of LA production from highly concentrated substrates through batch and feeding processes. The results indicated that a one-time feeding strategy can lower the activation energy required for FR degradation to glucose to 96.6 kJ/mol (R-2 > 0.97). Similarly, the activation energy for the conversion of glucose to 5-hydroxymethylfurfural (5-HMF) and the subsequent formation of LA from 5-HMF were reduced to 80.9 kJ/mol (R-2 > 0.97) and 23.3 kJ/mol (R-2 > 0.97), respectively. Notably, the reaction rate of glucose to form humins was slightly reduced. This research helps to optimize the LA yield and concentration directly via an enhanced in situ feeding approach, providing valuable process operation and kinetic information for the industrial LA production from FR.