The Effect Of CaO₂/Fe²⁺ Pretreatment On The Substrate Properties And Enzymatic Hydrolysis To Producing Sugar Of Different Biomasses

In order to solve the energy crisis effectively,developing renewable energy to instead non-renewable energy has become one of the hot spots in global research.In recent years,bioethanol has emerged as one of the representatives of renewable biomass energy.Due to its wide source and low cost,it has received extensive attention from scholars.Biomass is an important raw material of bioethanol,the structure of biomass is complex.So it needs to be pretreated before used,in order to facilitate subsequent utilization efficiency.The pretreatment methods are various.Using Fenton system to pretreat the biomass can obtain good effect and make the cellulose in biomass easier to be converted into ethanol.However,H₂O₂ is an strong unstable oxidant.When H₂O₂ acts on the biomass,it will be autogenous decomposition and droop its efficiency.Using CaO₂instead of H₂O₂ to form CaO₂ heterogeneous modified Fenton system can treat biomass effective.This system not only can destroy the inherent structure of biomass,but also can change the components and the crystallinity of biomass.Ultimately,it will improve the accessibility of the enzyme and enzymatic hydrolysis performance.In this paper,we choosed four kinds of biomasses materials,which include Eichhornia crassipes,Sugarcane bagasse,Alternanthera philoxeroides and cotton stalk to pretreat by CaO₂/Fe²⁺system.Raw materials were used as controls.This study explored the impacts of CaO₂/Fe²⁺molar ratio,pretreatment time and temperature single factor on reducing sugar yield,reducing sugar conversion rate and components.Then we selected the optimized pretreatment conditions.Based on the single factor experiments,3 factors and 4 levels of orthogonality experiments were set to pretreat four kinds of biomasses.Using statistical analysis programs to optimize experiment scheme and then determining the change of the functional groups and the crystallinity of biomasses under the optimal pretreatment conditions of the single factor experiments and orthogonality experiments.The main results were as follows:?1?Pretreatment of biomasses with CaO₂/Fe²⁺system could destroy the components and structure of biomass,then improve the effect of enzymatic hydrolysis.In the single factor experiments,the optimal pretreatment conditions of Eichhornia crassipes,Sugarcane bagasse,Alternanthera philoxeroides and Cotton stalk were CaO₂/Fe²⁺molar ratio8:1,temperature 35?,pretreatment time 72 h,CaO₂/Fe²⁺molar ratio4:1,temperature45?,pretreatment time 96 h,CaO₂/Fe²⁺molar ratio4:1,temperature 25?,pretreatment time 72 h and CaO₂/Fe²⁺molar ratio8:1,temperature 35?,pretreatment time 72 h.In this condition,the samples after pretreatment of Eichhornia crassipes,Sugarcane bagasse,Alternanthera philoxeroides and Cotton stalk should be enzymatic hydrolysis.It's reducing sugar yields could respectively reach 43 times,15 times,3 times and 45 times which were compared with raw materials.The reducing sugar conversion rate of Eichhornia crassipes,Sugarcane bagasse,Alternanthera philoxeroides and Cotton stalk were 17 times,9 times,2 times and 44 times when compared to raw materials,respectively.?2?Orthogonal experimental results showed that CaO₂/Fe²⁺molar ratio is the main influencing factor in the four kinds of biomasses,and the pretreatment time and temperature were secondary influencing factors.At the same time,we can see the optimal pretreatment conditions were inconsistent between the orthogonal experiments and the single factor experiments.This indicated that the single factor experiments is not comprehensive.?3?Pretreatment of biomasses with CaO₂/Fe²⁺system could not only change crystalline region structure but also amorphous region structure of biomass.In the meantime,the change of the crystallinity index was mainly related to the degree of removal of the crystalline regions and amorphous regions.?4?After pretreatment by CaO₂/Fe²⁺system and enzymatic hydrolysis 72 h,the correlation with the removal rate of hemicellulose and lignin and reducing sugar yields were positive.