Study On Liquefaction And Degradation Of Wheat Straw Alkali Lignin Assisted By Microwave Irradiation

Lignin is an abundant natural bio resource, and the modified products of lignin hasachieved significant economic and social benefits in the industrial applications, but thepotential of its efficient utilization research is still considerable enormous in consideration ofits huge quantities. Alkali lignin is the chief component of the industrial lignin, but theapplication range and utility value of alkali lignin has been limited cause of its lack of stronghydrophilic group, poor surface activity and low reactivity. Small molecular compound can beobtained by liquefaction and degradation reaction of alkali lignin, which is an important wayto improve its application performance and make high efficient use of alkali lignin available.In this work, the liquefaction of lignin was conducted under microwave irradiationconditions, in which glycol was added into wheat straw alkali lignin and sulfuric acid wasused as the catalyst. The influence of the liquefication time, temperature, the additive amountof sulfuric acid and hydrogen donor solvent on the liquefied efficiency was investigated. Andthe optimal process variables for liquefaction of lignin was obtained. The change in thestructure of lignin before and after the liquefaction was characterization.It can be found out from HPLC that the main liquefied products are concluded to bephenol, guaiac based phenol,2methoxy4methyl phenol,2,6dimethoxy phenol, gallic acid,oxalic acid, vanillic acid and ferulic acid. Orthogonal experimental results show thatliquefaction temperature has the most impact on the liquefaction efficiency compared to thereaction time and the dosage of catalyst. With the increase of the reaction time, the yield ofthe total monophenolc products increases at first and then dropped. The maximum yield is13.47%wt.(based on the dry alkali lignin), which can be obtained when the reaction time is40min. G type phenolic compounds are the most abundant in the liquefied products, and theyield of2methoxy4methyl phenol accounts for more than half of the total monophenolicproducts. With the increase of the reaction temperature, the yield of the total monophenolicproducts also increases at first and then dropped. The maximum yield is12.41%wt., whichcan be obtained when the reaction temperature is120@. There are more H type phenolicchemicals (phenol) and S type phenolic chemicals obtained at the relatively low temperature (110@). The dosage of catalyst also has a great impact on the liquefication reaction of lignin,but it will be inappropriate if the dosage is too much and the optimal dosage is10%wt. Theaddition of the hydrogen donor solvent also has an effect, and sulfuric acid displays bettercatalytic effect comparing several kinds of solid catalyst. The optimal process variables are at120@for reaction for40min under10%of sulfuric acid dosage.Moreover,the structures of functional groups of the alkali lignin before and after theliquefaction were analyzed by means of GPC, FT IR and1H NMR. The results show that＄themolecular weight and its polydispersity of liquefied residue are greatly reduced compared tothe raw wheat straw alkali lignin, which means that ether linkages and carbon chain of ligninbreak in the process of liquefaction of lignin. The results of FT IR and1H NMR also showthat the linkages broken are mostly CαCβand CαO linkages, and some syringyl type lignintransfer to guaiacyl type lignin due to the methoxyl group of syringyl type lignin.