Extracting high β-O-4 content lignin and by-producing substrate susceptible to enzymatic hydrolysis by a green flow through process

• MA was used to extract lignin by FT process at atmospheric pressure for the first time. • FT process was carried out without VOCs release and explosion risk. • The dilution factor of extraction liquid for precipitating lignin was only 3. • Exceeded 80% β-O-4 bonds were preserved and 30% monophenol yield was obtained. • Cellulose-rich residue was efficiently converted into glucose at a low cellulase loading. Maleic acid (MA), a solid dicarboxylic acid can be obtained from renewable lignocellulose, was used to extract lignin through flow through (FT) process for the first time. Due to the high boiling point and flash point of MA, the FT process was carried out at atmospheric pressure without VOCs release and explosion risk. 50 wt% MA aqueous solution could extract 60% lignin from birch wood, and the dilution factor for precipitating lignin was only 3. MA-extracted lignin preserved more than 80% of β–O–4 bonds and a monophenol yield (＞30%) comparable to that of milled wood lignin was obtained by catalytic hydrogenolysis. The recyclability of MA was demonstrated through three rounds of lignin extraction by recovered MA. And the cellulose-rich residue could be efficiently converted into glucose (glucose yield＞90%) at a low cellulase loading of 10 FPU/g glucan due to the rich carboxyl groups of lignin. In addition, the low corrosiveness of MA and the mild operating conditions make the process have strong industrial application prospects.