An understanding for improved biomass pyrolysis: Toward a systematic comparison of different acid pretreatments

Naturally occurring AAEMs in biomass exhibit detrimental effects to biomass pyrolysis as producing less oil with lower quality. Acid pretreatments are cheap and effective methods for mitigating AAEMs effect, thus improving the pyrolysis performance. In the current study, a combination of different experiment techniques and theoretical kinetic analysis was conducted to systematically compare the effects of both acid infusion and washing pretreatments. By utilizing Py-GC/MS system, the product distribution from pyrolysis of raw and acid pretreated corn stovers was obtained. Compared to that of raw corn stover, significant reduction of char and improvement of sugars, especially levoglucosan (55% yield based on cellulose), from pyrolysis of acid washed corn stover were achieved because of the thorough removal of AAEMs in corn stover. As for acid infused corn stover, maintaining reaction in acid buffer condition (3 similar to 5 wt% acid infusion) kept the sugar yield at relatively high level. Further increase of acid infusion over 5 wt% resulted in strong dehydration reaction of sugars and sharp decrease of phenolic compounds. The DTG pattern and the key kinetic parameters of corn stover dramatically changed with acid pretreatment. Strong condensation reaction between cellulose and lignin in acid infused corn stover were also suggested by kinetic analysis. Besides, the evolution of major phenolic monomers from lignin component versus temperature was revealed by TG/PI-TOF-MS system. As for acid pretreated corn stover, the agglomeration associated with the increase of char production were further ascribed to the enhanced polymerization of vinyl-phenols and other simple phenols. Overall, the study provides insights into the fast pyrolysis behavior of acid pretreated biomass for producing high-quality bio-oil and value-added chemicals.

Automated summary

The study compares the effects of acid infusion and washing pretreatments on biomass pyrolysis products through a combination of experimental techniques and theoretical kinetic analysis. Acid washed corn stover showed reduction in char and improvement in sugars, especially levoglucosan, compared to raw corn stover, while sugar yield of acid infused corn stover remained relatively high under acid buffer conditions but decreased significantly with higher acid infusion levels. The kinetic analysis suggested strong condensation reactions between cellulose and lignin in acid infused corn stover, with increased production of vinyl-phenols and other simple phenols associated with enhanced char production. Overall, the study provides insights into fast pyrolysis behavior of acid pretreated biomass for high-quality bio-oil production and value-added chemicals.