Improvement of wheat (T. aestivum) straw catalytic fast pyrolysis for valuable chemicals production by coupling pretreatment of acid washing and torrefaction

Abstract

The present work investigated the coupling pretreatment of acid washing and torrefaction to address secondary cracking of target products and condensation of intermediates and improved bio-oil quality and hydrocarbon selectivity of the catalytic fast pyrolysis (CFP) process. The total hydrocarbon yields in CFP increased from 28.06 wt% to 55.31 wt% by torrefaction and 46.29 wt% by coupling pretreatment. The acid washing resulted in fewer acids and phenols and more sugars in bio-oil by decreasing the AAEMs. The removal rate of the potassium was up to 96.7 %, and other elements were above 83 %. Torrefaction elevated the C/O ratio and the higher calorific value of biomass. It could also decrease the acid content in obtained bio-oil in the CFP process. In addition, the TG/TGA results showed that higher torrefaction temperature decreased the total weight loss of biomass. Meanwhile, the acid washing pretreatment improved the resolution of the two pyrolysis peaks of the DTG curve. These results showed that the AAEMs removal and intermediates inhibition could elevate the selectivity of the valuable chemical. • Acid washing removed 83 wt% of AAEMs to facilitate valuable chemicals conversion; • Torrefaction elevated the C/O ratio and the higher calorific value of wheat straw; • The coupling pretreatment improved bio-oil quality and hydrocarbons selection; • The CFP with pretreated biomass reduced phenols, acids, and ketones production.