ST was used as the second step pretreatment. During the second
step pretreatment, 35 g of acid treated RS and 200 mL standard sulfomethylation
reagent [1% (w/v) sodium hydroxide, 3% (w/v)
formaldehyde and 2% (w/v) sodium bisulfite] were added to a
500 mL high pressure reactor and kept it react at a given temperature
for a certain time. After the reaction, it was cooled to room
temperature. The ST residues (the two-step treated RS) were collected
and washed extensively with tap water until neutral pH,
dried at 65 C and weighted. Then they were used for their composition
analysis and subsequent ethanol fermentation. The ST
hydrolyzate containing the lignosulfonate was directly recovered
as a cement water reducer.