Adsorption of vanillin and syringaldehyde onto a macroporous polymeric resin

Abstract

Pulp and paper mill and biorefinery side-streams are rich in lignin which can be partially converted to vanillin and syringaldehyde through an oxidation process. These value-added compounds can be recovered with an integrated separation process encompassing an adsorption step. In this work the potential of a macroporous polymeric resin, Sepabeads SP700, was assessed. The resin was characterized regarding particle size, solid density, apparent density and particle porosity by means of laser dispersion, helium pycnometry and mercury intrusion porosimetry, respectively. Values within the ranges given by supplier were achieved: solid density, apparent density, particle size and particle porosity were 1294 g L-1, 1012 g L-1, 483 mu m and 0.73 mL(pores) mL(particle)(-1), respectively. Batch equilibrium isotherms for three different temperatures 283/288, 298 and 333 K were found for vanillin and syringaldehyde in aqueous solutions. Experimental results were fitted to Langmuir and Freundlich isotherm models. Equilibrium isotherms were validated by fixed bed studies at different temperatures and feed concentrations. A mathematical model comprising the equilibrium isotherms, linear driving force approximation, and intraparticle mass transfer resistances was used to describe the adsorption/desorption histories of concentration at the outlet of the fixed bed experiments. Although Langmuir model reasonably fit to the experimental results, the empirical Freundlich model was best to describe the experimental results for equilibrium concentrations bellow 1 g L-1.