Selective Production of Platform Chemicals from Low-Temperature Pyrolysis of Biomass Mediated by Exogenous Acid–Intrinsic Base Balance

Abstract

The catalytic activity of intrinsic alkali and alkaline earth metals (AAEM) in biomass has been usually considered as a negative factor affecting the fast pyrolysis of biomass. Herein, this negative factor was turned into a positive one using 0.4%H2SO4 impregnation of pinewood, which can achieve the directional pyrolysis of pinewood into levoglucosan at low temperatures. Pyrolysis of 0.4%H2SO4-impregnated pinewood at 300 °C drastically improved the yield of levoglucosan from 2.3 to 53.6% while suppressing the formation of small oxygenates, noncondensable gases, and char. The introduction of the desired amount of exogenous H2SO4 combined with intrinsic AAEM in raw biomass, namely, exogenous acid–intrinsic base balance, was essential to achieve the directional pyrolysis of biomass at low temperatures to form levoglucosan. Exogenous H2SO4 accounted for the low-temperature activation of cellulose to form levoglucosan, while intrinsic AAEM were responsible for inhibiting the dehydration reactions to form levoglucosenone and char. Compared with the pyrolysis of raw pinewood at 500 °C, pyrolysis of 0.4%H2SO4-impregnated pinewood at 300 °C reduced the heat requirement by 78.5%. The kinetic analysis demonstrated that 0.4%H2SO4 impregnation improved the activation energy for pyrolysis of pinewood. In situ DRIFT experiment combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) analysis showed that H2SO4 can achieve the low-temperature activation of cellulose within pinewood to form levoglucosan. AAEM can inhibit the intramolecular dehydration of the C3 hydroxyl groups and C2 hydrogen atoms in the levoglucosan end/levoglucosan to form levoglucosenone and char. This finding provides a simple and energy-saving approach to achieve directional conversion of biomass into platform chemicals via low-temperature pyrolysis.

Topics & Concepts