Equilibrium, kinetic and thermodynamic studies of acid soluble lignin adsorption from rice straw hydrolysate by a self-synthesized macro/mesoporous resin

Abstract

A self-synthesized HQ-8 resin was prepared using a O/W suspension polymerization technique and employed as a potential adsorbent for the removal of acid soluble lignin (ASL) from rice straw hydrolysate (RSH). The structure and morphology of the HQ-8 resin before and after the adsorption of ASL were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherms. A series of adsorption conditions such as pH value, adsorbent dose, initial concentration, and temperature were systematically investigated to obtain the optimum process parameters. Within the studied range of ASL concentrations, the adsorption equilibrium was found to follow the Freundlich isotherm model well, with R² > 0.988. The rate of ASL adsorption onto the HQ-8 resin was very quick, and equilibrium was reached within 50 min of contact. Furthermore, the maximum adsorption capacity of ASL on the HQ-8 resin was 64.61 mg g⁻¹ at 298 K at an initial solution pH of 1. The regression results revealed that the ASL adsorption kinetics was represented accurately by a pseudo-second-order model. The efficiency of the HQ-8 resin for the spontaneous and exothermic adsorption of ASL is attributed to the hydrophobic interaction between the cross-linked benzene ring of the HQ-8 resin and the aromatic ring of ASL. In addition, the activation energy of ASL adsorption onto the HQ-8 resin was 35.99 kJ mol⁻¹. In summary, the present adsorption studies of ASL from RSH revealed the potential of a self-synthesized HQ-8 resin to be applied as an alternative adsorbent for lignocellulose hydrolysate detoxification.