Kinetics for enzymatic hydrolysis of rice hulls by the ultrasonic pretreatment with a bio-based basic ionic liquid

• The effective physicochemical pretreatment uses choline hydroxide and ultrasound.
• The network structure of rice hull is destroyed by the physicochemical pretreatment.
• Ultrasound can promote effectively the mass-transfer of the enzyme into rice hulls.
• Good TRS yield can be obtained at a much shorter hydrolysis time with ultrasound.
• A simplified kinetic model for enzymatic hydrolysis of rice hulls was developed.

The enzymatic hydrolysis of rice hulls by the ultrasonic pretreatment using a bio-based basic ionic liquid was investigated. The morphological and characteristic structures of rice hulls before and after the pretreatment were analyzed by field emission scanning electron microscope (FE-SEM), X-ray energy dispersive spectrometer (EDS), focal plane array-Fourier transform infrared spectroscopy (FPA-FTIR), high resolution X-ray diffractometer (HR-XRD), and elemental analyzer (EA). The network structure of rice hulls after the physicochemical pretreatment was seriously corroded and punched to expose the accessible organic region by removing silica, lignin and ash to enhance the hydrolysis reaction. In ultrasound-assisted enzymatic hydrolysis by cellulase, the total reducing sugar yield from rice hulls after the pretreatment was 43.5% at only 3 h of hydrolysis time, and was greater than that from untreated rice hulls (24.0%). A simplified kinetic model was proposed to describe the enzymatic hydrolysis of rice hulls in a heterogeneous system using an impeded reaction of enzyme, with a time-dependent decay coefficient, the initial observed rate constants, and ineffective coefficients were obtained to successfully describe the enzymatic hydrolysis of rice hulls.