Minjie Hou,Leiming Wang,Yanning Sun,Yanzhu Guo,Xueru Sheng,Fengshan Zhang,Haidong Sun,Pedram Fatehi,Haiqiang Shi
Generally, lignin separation from prehydrolysis liquor (PHL) is accompanied by sugar removal, making the purification of PHL challenging. However, how sugar loss from PHL can be minimized in PHL purification is still unclear. In this work, a method for removing lignin from PHL was attested, which included treatments of PHL with poly aluminum chloride (PAC), activated carbon, and XAD-4 resin. The results exhibited that the PAC could form complexation with lignin facilitating lignin removal from PHL. At the PAC concentration of 15 mg/L, 10% of lignin was removed, while no significant sugar loss was observed. Subsequently, by treating PHL with activated carbon, 87% of the remaining lignin was removed from the PHL, while sugar loss was identified to be 14%. XAD-4 resin treatment could slightly improve the lignin removal from 87% to 92%. However, the XAD-4 was unselective in sugar removal and led to an increased sugar loss (from 14% to 37%). Interestingly, removing colloidal lignin by PAC benefited the subsequent activated carbon process for improving lignin removal. In other words, PAC removed not only colloidal lignin but also facilities lignin isolation (i.e., an increase from 81% to 87%) and prohibited sugar loss (a drop from 27% to 6%) in the subsequent activated carbon treatment.
Efficient micro-meso-macroporous solid acids spheres with controllable acid strength were successfully synthesized by simultaneous grafting of −SO3H and −SO2CF3 onto the network of commercial XAD-4 resin. The synthesized solid acids are designated as XAD-4-SO3H and XAD-4-SO3H-SO2CF3. Various characterizations show that XAD-4-SO3H and XAD-4-SO3H-SO2CF3 possess high BET surface areas, hierarchical porous structures with combined micro-meso-macropores, high concentrations of acid sites, and strong acid strength. Catalytic tests show that XAD-4-SO3H and XAD-4-SO3H-SO2CF3 exhibit superior activities and good reusability in various acid-catalyzed reactions including esterification of acetic acid with cyclohexanol, acylation of anisole with acetyl chloride, and catalytic synthesis of bisphenol A. Their activities were better than the solid acids of Amberlyst-15, SBA-15-SO3H-0.1, H3PW12O40, and acidic zeolites. This work develops a new method for scalable transformation of commercially macroporous resin into efficient porous solid acids, which promotes their wide use in industrial catalysis.
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