Effects of MgCl2 and Mg(NO3)2 loading on catalytic pyrolysis of sawdust for bio-oil and MgO-impregnated biochar production

Abstract

For high-quality utilization of biomass resources, co-production of bio-oil and MgO-impregnated biochar from catalytic pyrolysis of Mg-loaded biomass samples is a prospective approach. In this study, the effects of MgCl2 and Mg(NO3)2 loading on catalytic pyrolysis of sawdust for production of high value-added bio-oil and biochar, as well as the catalytic pyrolysis process mechanism were explored. The thermal degradation process behavior and the pyrolysis products of non-condensable gas, bio-oil and biochar were obtained by thermogravimetric analyzer (TGA) and lab-scale fixed-bed reactor system. The product properties were analyzed and characterized by gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), N2 adsorption-desorption, X-rays diffraction (XRD) and transmission electron microscopy (TEM). The obtained results indicated that the loading of Mg salts favored the thermal degradation process of catalytic pyrolysis due to the weakened hydrogen-bonding networks and disrupted the crystalline structures. The enhanced cross-linking and repolymerization reactions of pyrolysis intermediates by the catalytic effect of Mg resulted in the increased non-condensable gas and biochar yields and the decrease of bio-oil yield. The loading of Mg salts also resulted in the decreased CO yield and increased CO2 yield. The relative contents of ketones and furans increased, and the relative contents of phenols and sugars decreased for Mg-loaded SD samples in bio-oil. In addition, the Mg salts loading also favored the formation of developed pore structure and uniformly dispersed MgO nanoparticles in obtained biochar. In general, catalytic pyrolysis of MgCl2-loaded or Mg(NO3)2-loaded sawdust is a feasible method to obtain high value-added bio-oil and MgO-impregnated biochar products.