Study On The Process Of Acid-catalyzed Degradation Of Hemicellulose In Ionic Liquids

Lignocellulose is the most abundant and renewable natural resource in the world.The acid-catalyzed hydrolysis of lignocellulose to fermentable sugars in ionic liquids has provided an effective technical tool for its utilization with high efficiency.At present,most researches on the acid-catalyzed hydrolysis of lignocellulose to fermentable sugars in ionic liquids are focused on cellulose hydrolysis,and the researches on hemicellulose hydrolysis are quite scarce.Therefore,the acid-catalyzed hydrolysis process of xylan(hemicellulose)to xylose in ionic liquids was investigated in this paper,and compared with the acid-catalyzed hydrolysis process of cellulose to glucose to provide technical support for lignocellulose comprehensive utilization.Firstly,the process of acid-catalyzed xylose degradation in ionic liquids was investigated under different reaction conditions.The results indicated that the initial concentration of xylose had no effect on its conversion ratio during the process of acid-catalyzed xylose degradation in ionic liquids in the case of equal reaction time.The degradation rate of xylose and the generation rate of furfural were increased with the temperature increasing.Under the condition of initial xylose concentration of 10 mg/mL,water concentration of 0.01 mg/mL and the sulfuric acid concentration of 0.3%,the degradation rate of xylose in ionic liquids was low and there was almost no furfural formed below 100 ?.When the reaction temparature was 170 ?,xylose reached its lowest concentration at 20 min,and the furfural yield was 63.3%.The degradation rate of xylose and the generation rate of furfural were also increased with the sulfuric acid concentration increasing under its concentration less than 0.5%.The addition of water could inhibit the degradation of xylose,the degradation rate of xylose and the generation rate of furfural were decreased with the increase of the water amount.Based on its kinetic analysis,the activation energy of the acid-catalyzed xylose degradation in ionic liquids was 84.18 kJ/mol.Then,the process of acid-catalyzed hydrolysis of xylan in ionic liquids was studied under different reaction conditions.And the time course curves of xylose and furfural formation were obtained.The results shown that the yields of xylose and furfural were not changed at different xylan initial concentrations during the xylan degradation at the same reaction time,but the generation rate of xylose and furfural were increased with the increase of the temperature and the acid concentration.Under the condition of initial xylan concentration of 10 mg/mL,water concentration of 0.01 mg/mL and the sulfuric acid concentration of 0.3%,when the temperature is below 100 ?,there was almost no furfural formation during the process of acid-catalyzed hydrolysis of xylan in ionic liquids,so the lower temperature was beneficial to the production of xylose.However,the reaction needed longer time because the degradation rate of xylan and xylose was slow at the lower temperature.When the temperature was over 140 ?,the degradation rate of xylan was very fast and the xylose reached its highest concentration at 15 min,but the xylose yield was low because the degradation rate of xylose was also fast at the higher temperature.Therefore,the optimum temperature for the process of acid-catalyzed hydrolysis of xylan in ionic liquids was 120 ?.Under the condition of initial xylan concentration of 10 mg/mL,water concentration of 0.01 mg/mL and the temperature of 120 ?,when the sulfuric acid concentration increased from 0.3% to 0.7%,the time that the xylose reached the maximum concentration reduced from 60 min to 30 min.Although higher sulfuric acid concentration could shorten reaction time,in consideration of the cost and xylose yield,the optimum sulfuric acid concentration for the process of acid-catalyzed hydrolysis of xylan in ionic liquids was 0.3%.The increase of water concentration could promote the degradation of xylan and inhibit the production of furfural,so increasing the amount of water was beneficial to increase the xylose yield.Finally,the process of acid-catalyzed hydrolysis of cellulose in ionic liquids was investigated and compared with the process of acid-catalyzed hydrolysis of xylan under the same reaction conditions.And the time course curves of glucose and 5-hydroxymethyl furfural formation for the process of acid-catalyzed hydrolysis of cellulose in ionic liquids were obtained.The results demonstrated that these two processes had similar kinetic characteristic.Their initial concentration had no effect on their main products' yield at the same reaction time,and their degradation rate increased with the increase of the temperature and the acid concentration.Comparatively speaking,the temperature had greater impact on xylan degradation process at lower temperature.