Enhancing Sugar Yield Through Enzymatic Hydrolysis Of Wheat Straw By Plasma Pretreatment

In the severe situation of global energy shortage and lack of resources,it is urgent to use biomass,a huge resource.However,current technical methods are difficult to act on the densely structured biomass and separate the important carbon-containing compounds cellulose,hemi-cellulose and lignin resources.In recent years,low energy consumption and high activity atmospheric pressure low-temperature plasma shows obvious strengthening effect in the application of waste biomass pretreatment,promoting reuse of biomass resources,which has been widely concerned.As a new type of pretreatment,its mechanism is still unclear.The strengthening effect and energy efficiency are related to many factors,including plasma reactor and working condition,biomass type and characteristics,etc.,which are the key and basic issues for its large-scale industrial applications.Based on these basic problems,this paper carried out the following research,pretreatment of wheat straw by atmospheric pressure low-temperature plasma:A flat tape dielectric barrier discharge-based atmospheric low-temperature plasma generator driven by a pulsed power supply is designed.Tungsten pin and conductive cotton are used as high voltage electrode and grounding electrode respectively,a48-hole plate is used as sample platform.This pulsed power supply is made by our own laboratory,with ambient air or pure gas through catheter as work gas.We explore the influence of pretreatment parameters on sugar yield through enzymatic hydrolysis of wheat straw,and search the best experimental parameters during plasma pretreatment of straw.The optimal pretreatment parameters obtained in this paper are: wheat straw passing 60-mesh sieve,with 50% humidity,applied to 22 k V voltage and 200 Hz frequency of negative pulse generator,under the condition of 5 mm discharge interval,static air as working gas,pretreated for 30 minutes.Compared with the control group,the yield of reducing sugar increased to 40% after pretreatment.Trends of physical and chemical properties of lignin influenced by plasma pretreatment are explored and whether they are consistent with wheat straw or not is compared.It is found that plasma can improve the solubility of both,simultaneously introduce oxygen-containing functional groups and destroy the recalcitrant structures that hinder their enzymatic hydrolysis.However,the mixed enzymatic hydrolysis of lignin before and after pretreatment and microcrystalline cellulose showed that the inhibition of lignin on the enzymatic hydrolysis process is not significantly improved.The physical and chemical properties of wheat straw before and after pretreatment showed that plasma pretreatment significantly damaged the surface smoothness and density of wheat straw.However,the change of chemical properties of straw is very weak,which is mainly reflected in the micro change of element and component content.To explore the mechanism of plasma strengthening wheat straw pretreatment effect,combined with radiation spectrum diagnosis and straw sample analysis,it is found that the acidification effect caused by plasma pretreatment is weak,simultaneously,thermal,electric field and ultraviolet radiation are not the main incentives of pretreatment for enhancing the sugar production rate.High chemical activity of discharge is the key factor to improve sugar production during enzymatic hydrolysis of straw sample after pretreatment.During the pretreatment process,strong oxidizing components,especially OH radicals,formed on the surface of wet straw,and active nitrogen components produced by air discharge are easy to be adsorbed on the surface of straw particles,which destroy the anti-degradation structure of straw and improve the efficiency of enzymatic hydrolysis of straw.