Effects of pretreatment on aromatic production from catalytic pyrolysis of soy sauce residue for organic liquid hydrogen carriers

Aromatic hydrocarbons (AHs) represent important organic liquid hydrogen carriers due to their abundant unsaturated bonds. As the only renewable carbon source, biomass can be directionally converted into AHs through catalytic pyrolysis, offering a low-carbon and environmentally friendly approach. Soy sauce residue (SSR), a fermentation by-product with high volatility and thermal decomposability, shows unique advantages for catalytic pyrolysis into AHs. However, SSR contains high mass fraction of salts and ash, which adversely affect the selective production of AHs. In this study, high-salt SSR was selected as the raw material and pretreated with deionized water and dilute HCl solution to remove salts and ash. The effects of washing pretreatment on the intrinsic physicochemical properties, pyrolysis kinetics, product distribution, and hydrogen storage performance of the resulting AHs were investigated. The pretreatment led to a significant increase in cellulose and lignin content and a reduction in hemicellulose. Moreover, washing pretreatment effectively removed ash from SSR, reduced the catalytic effects of inherent ash, and enhanced both the yield of AHs and their hydrogen storage capacity. Compared to water washing, acid washing pretreatment proved more effective, with higher temperatures favoring the removal of inorganic matter. At a pretreatment temperature of 80℃, acid washing removed 90.57 % of salts and 83.25 % of ash. Under optimal pyrolysis conditions (650℃, HZSM-5/SSR ratio of 12), the AH yields increased from 16.10 wt% (untreated SSR) to 24.82 wt% (HCl-treated SSR), and the hydrogen storage capacity of AHs also increased from 11.37 g/kg (untreated SSR) to 17.09 g/kg (HCl-treated SSR).