Dissolution Rule Of Bamboo Components During Oxalic Acid Improved Pretreatment

With the growing demand for dissolving pulp and the deficiency of domestic wood resources, it is necessary to find alternative resources for production of dissolving pulp. Production of bamboo dissolving pulp could not only solve the problem of shortage of raw materials, but also realize high value utilization of bamboo resources. Prehydrolysis kraft process is one of the primary methods for dissolving pulp production and dilute acid is most common used in pretreatment stage. In this research, oxalic acid pretreatment was used as the efficient method to dissolve hemicelluloses but without seriously degrading cellulose; the degradation and dissolution of the bamboo components were thoroughly investigated; and therefore the selectively oxalic acid pretreatment conditions was explored.pH of the hydrolysate liquor and yield of hydrolysis were monitored in the process of oxalic acid pretreatment of bamboo chips with various oxalic acid concentration and the relationships between pH and yield were explored. pH and yield could reach to a level-off value in the course of hot water treatment, while the higher temperature favored to a level-off value with short time. pH was almost stable with the addition of1%oxalic acid, whereas the yield decreased. When the oxalic acid amount exceeded3%, pH increased and yield decreased gradually; furthermore the two values tended to be level-off. The final value was depended on the initial oxalic acid addition. There was a function of pH and yield with various temperature (not less than160℃) in the process of hot water treatment, but another function with lower temperature (150℃); whereas the slope of the both curves were almost the same. As with different oxalic acid addition, the similar curves were found, but the slopes of the line were depended on the initial oxalic acid addition.The effects of oxalic acid usage on the sugar components (xylose and glucose) and its degradation products (furfural and hydroxymethylfurfural) in hydrolysate were studyed. The results show that the monosaccharides and total sugar concentration were decreased after an initial increase with the extension of prehydrolysis time. Higher concentration oxalic acid pretreatment promoted the carbohydrate dissolution and monosaccharides degradation. In brief, higher concentration oxalic acid pretreatment could produce concentrate sugar in short time, otherwise concentrate sugar degradation products furfural and hydromethyl furfural resulted. Long time pretreatment also promote the degradation of furfural. The degradation of cellulose and cellulose structure change during oxalic acid pretreatment was studied. The results show that cellulose degraded gradually with increase of oxalic acid dosage and pretreatment time. The relationships between cellulose degradation and hemicellulose removal were investigated. The selectively oxalic acid pretreatment conditions was found at the temperature of160℃and oxalic acid dosage of3%; while the hemicellulose removal rate reached to65%and the cellulose DP still retain at a high level1250. Pretreatment gave rise to a higher crystalline index of cellulose because of the degradation and dissolution of amorphous cellulose. Cellulose degradation under oxalic acid pretreatment generally followed the zero reaction kinetics.The degradation rate could be greatly improved by increase of temperature and dosage of oxalic acid; meanwhile increase of oxalic acid dosage lowered the activation energy. When oxalic acid dosage was3%and5%, the degradation activation energy of73.69kJ/mol and32.14kJ/mol respectively.The migration and dissolution of lignin was studied during oxalic acid pretreatment. FE-SEM results showed that lignin droplets could migrate from inner layer to out layer; the transportation and migration accumulated lignin on the bamboo surface. Higher severity pretreatment aggravated more lignin covering on the bamboo surface. Lignin content of bamboo substrate decreased first and then increased and even exceeded the lignin content of the raw material. Oxalic acid pretreatment promoted the degradation, consendation reactions and even pseudo-lignin formation. CP/MAS13C-NMR result indicated the cleavage of β-O-4linkage in lignin units. Pseudo-lignin formation was further confirmed by holocellulose pretreatment.