Waste lignocellulosic material, which is easily available, inexpensive, and renewable, represents a kind of significant cellulosic biomass as raw material to produce fuel ethanol with many advantages in bioethanol conversion
. Corn cob residue (CCR) is a kind of waste lignocellulosic material. During the production of furfural from the lignocellulosic materials with abundant pentose sugars, such as corncob, the hemicelluloses have been hydrolyzed to furfural in a dilute acid environment at high temperature, leaving the lignin and cellulose in the CCR
. It has been estimated that about 12–15 tons of CCR can be obtained after 1 ton of furfural is produced, and an average of 23 million tons of CCR were available annually for alternative use in China
. However, the residue, considered as waste, are widely utilized for burning at present, far away form resource utilization. It would be a better choice to produce bioethanol with such abundant lignocellulosic waste.
Among the available technologies for lignocelluloses-to-ethanol production, a conversion process based on enzymatic hydrolysis is considered the most promising for large-scale operation
[4, 5]. However, one of the key factors to construct the recalcitrance of lignocellulosic biomass is the presence of lignin, which plays the “glue” to bind cellulose and hemicellulose. Besides playing a physical barrier, lignin has also been found to irreversibly adsorb enzymes, which causes enzyme loss and decrease in the saccharification rate
. Therefore, delignification is always adopted to overcome the recalcitrance of lignocellulosic biomass and increase the enzymatic digestibility of cellulose.
The effect of lignin content on enzymatic hydrolysis of CCR has been evaluated, and it is found that the glucose yield was improved by increasing the lignin removal. However, the maximum glucose yield of CCR was obtained when the residue with a lignin content of about 21.0%
. The results further prove that the chemical and physical structure of lignin plays a significant role in determining the magnitude of inhibition of lignin to hydrolysis. There has been strong evidence
 supporting the role of hydrophilic interactions in the non-productive binding of cellulases to lignin. Multiple studies
[7, 8] have shown that the addition of the surfactant to cellulolytic hydrolysis improved hydrolysis yields. It reported that increasing the carboxylic acid content of the lignin seemed to significantly decrease the non-productive binding of cellulase and consequently increased the enzymatic hydrolysis of the cellulose
. So the hydrolysis yields of CCR may be benefited from the enhanced hydrophily of lignin after a temperate pretreatment.
The sulfite process has been used for pretreating wood chips for ethanol production. Sulfonation of lignin increases its hydrophilicity, which will promote the enzymatic hydrolysis process
[10, 11]. And the lignosulfonate has been used as pesticide emulsifier, oil field chemicals, dyeing and finishing auxiliaries for textile, which can been obtained from the concentrated sulfite pretreated solution. Traditional sulfite pulping has been in industry practice for more than a century and can be operated over a wide range of pH and temperature. And the active reagents in sulfite pretreatment liquor are also depended on the pH of the pretreatment temperature
. Sulfonation is always enhanced because of the acid or alkaline catalysis. The acid sulfite and neutral sulfite pretreatment has been well documented as the SPORL pretreatment
 with numerous publications to variety of feed stocks. And sulfite pretreated in alkaline environments also can increase the sulfonation and dissolubility of lignin. It has reported that during fraction of spruce by SO2-ethanol-water treatment, lignin is effectively dissolved, whereas cellulose is preserved in the solid (fiber) phase
. And the organophilic sulfite pretreatment is also a good choice for lignin separation and sulfonation because of the addition of ethanol, which caused a reduction of the surface tension and a benefit of solution penetration. Moreover, the hydrolysed lignin can be dissolved and recovered in the organophilic phase to obtained high purity lignin.
Our previous study has found that the glucan in CCR was easily degraded in severe pretreated processes. So in this study, the CCR were pretreated with sodium sulfite under moderate condition in acidic, alkaline, neutral, and ethanol environments to enhance the hydrophily of lignin by sulfonation reaction. And the objective is to compare the composition and characteristic variation of CCR during these sulfite pretreatments, and to compare the differences of saccharification rate and yield caused by these variations of the samples.