Reuse of H-ZSM-5 zeolite in catalytic pyrolysis of dried distiller's grains with solubles (DDGS): effect of regeneration on catalyst properties and bio-oil quality

Abstract

This work evaluates the stability and reusability of hydrothermally synthesized H-ZSM-5 zeolite as a catalyst in the pyrolysis of dried distiller's grains with solubles (DDGS), a by-product of the corn bioethanol industry. Five consecutive reaction cycles at 550 °C were tested, comparing two catalyst reuse strategies: (A) with intermediate oxidative regeneration in air at 500 °C and (B) without regeneration. Fresh zeolite, regenerated-reused and reused-without-regeneration zeolites were characterized by, X-ray diffraction, N2 adsorption, infrared Fourier transformed pyridine-adsorbed and thermogravimetric analysis. Phase yields and BTEX selectivity of the bio-oil were evaluated by gas chromatography. Results show that oxidative regeneration preserves the accessibility of acid sites and prolongs catalytic activity across cycles, at the cost of progressive dealumination. Without regeneration, coke blockage rapidly suppresses BTEX selectivity, with the performance converging toward that of purely thermal pyrolysis.