of reagent grade and purchased from Wuhan Chemicals &
Reagent Corp., China.
2.2. Two-step pretreatment of rice straw
AT was used as the first step pretreatment. During the first step
pretreatment, 20 g of RS after cutting and washing and 180 mL
given concentration sulfuric acid were added to a three-necked
flask with reflux and kept it boiling for a given time. The AT residues (acid treated RS) were collected and washed extensively with
tap water until neutral pH, dried at 65C and weighted. Then they
were cut to 10–20 mesh for their composition analysis and subsequent ST. The AT hydrolyzate was reused for AT of RS after adjusting its volume to 180 mL with fresh given concentration sulfuric
acid. After the AT hydrolyzate was recycled to certain times, it
was used to recover xylose. The xylose recovery from the AT hydrolyzate and its purification were carried out as described by Curreli
et al.[23]. The xylose yield was calculated as follows:
Xylose yieldð%Þ¼The recovered xylose
0:88=The total dissolved hemicellulose100
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 65C 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