Extraction And Degradation Of Lignin From Wheat Straw

With the increasing shortage of petrol and coal resources, researchers are more andmore interested in looking for new replacements for fossil resources. It will be a greatbreakthrough of the usage of renewable resources if biomass straw, bagasse, wood sawdust,and so on, can be degraded to valuable chemical products after some pretreatment. Thereare profuse cellulose and lignin in wheat straw, which is one of the most abundantagricultural wastes. In order to use wheat straw effectively in the future, this research wasfocused on the optimization of the extraction condition of lignin from wheat straw by highboiling solvent methods and the degradation condition of high boiling solvent-lignin tomonocyclic derivatives of benzene.The medium used in lignin extraction by high boiling solvent methods was1,4-butanediol, with the merits of high boiling point, low saturated pressure, and goodsolubility of lignin. As a matter of fact, extraction of lignin using1,4-butanediol as themedium was more carried out in china, mainly from bagasse, wood, peanut shell, pine-nuthull and rice husk. In prior researches, the reaction temperature was around200℃, whichmay be high enough to change the structure of lignin heavily. What’s more, it was the firsttime to extract lignin from wheat straw in an auto-clave under the catalysis of NaOH in1,4-butanediol medium. This article optimized the effect of temperature, reaction time,liquid-to-straw ratio, the dosage of NaOH, and so on, on the lignin yield. And finally, theoptimum conditions of lignin extraction was obtained as the following conditions:120℃,reaction time for3h,6-to-1liquid-to-straw ratio of60%1,4-butanediol,1-to-10NaOH-to-straw ratio. Lignin yield was up to73.7%under the above conditions.What’s more, the degradation of lignin adopted two-steps methods. The first step wasthe alcoholysis of lignin, and the second step was hydrogenolysis of lignin. Ligninalcoholysis can cleave the C-O bonds of lignin effectively,while lignin hydrogenolysis canfurther reduce substituents on the benzene ring. And the two-step method integrate themerits of alcoholysis and hydrogenolysis. Lignin alcoholysis was conducted in50%(v/v)of methanol medium under the catalysis of NaOH, and lignin hydrogenolysis wasconducted in50%(v/v) of methanol medium under the catalysis of Ni/C. Raw materials inthis method was cheap and easily available. In the lignin alcoholysis process, thedegradation rate of lignin was up to72.5%, the yield of degradation products was up to50%. And lignin hydrogenolysis effect the structure of the alcoholysis products, which wascharacterized by GC-MS.