Comparative Study On Pretreatment Processes For Different Utilization Of Switchgrass

With the increasing use of energy,the problems of energy shortage and climate deterioration are becoming increasingly prominent,which makes the development and utilization of alternative renewable energy more concerned.Switchgrass?Panicum virgatum,L.,Poaceae?with the advantages of high cellulose yield,resulting from low input and grow well in poor soils,has been identified as a promising candidate for production of low-cost biofuels,papermaking and nanocellulose.Pretreatment is a critical step to lower the overall cost of switchgrass conversion and to improve the process towards making the concept of biorefinery a reality.Different lignocellulosic biomass requires different pretreatment method for overcoming the natural recalcitrance.Therefore,we still need to compare the existing pretreatment strategies for utilization of switchgrass biomass.In this study,switchgrass was selected as the research object by comparing six kinds of commonly used biomass.Twelve chemical pretreatments including five dilute acid pretreatments?hydrochloric acid,sulfuric acid,phosphoric acid,nitric acid,acetic acid?,four dilute alkali treatments?ammonia water,sodium hydroxide,calcium hydroxide,alkaline H₂O₂?and other three chemical pretreatment methods?ethanol,hot water,FeCl₃?in laboratory scale were compared,resulting in the effective ways to change the cellulose,hemicellulose and lignin content for taking advantage of switchgrass.At the same time,the optimal conditions of different pretreatment were determined,the advantages and disadvantages of different pretreatment were compared,and the optimal conditions of different pretreatment were obtained.Then,the SEM,XRD,and FT-IR analyses were further conducted to confirm the structural changes in three optimal pretreated samples.Finally,it can be used to production of farnese verified by engineering Escherichia coli and Saccharomyces cerevisiae constructed in our laboratory.Main contributions of this work are as follows:?1?Various acids,such as H₂SO₄,HCl,H₃PO₄,CH₃COOH,and HNO₃,had been elaborated for mild switchgrass pretreatment in this study by the same method to make a comparison.The most significant cellulose yields and delignification were observed on the HNO₃ pretreatment of switchgrass,which can be used for the nanocellulose or fermentation sugar production.The experiment with 2.00%w/v HNO₃ at 125?for 30 min resulted in the highest cellulose?55.84±0.04%,w/w?and lowest hemicellulose?4.38±0.01%,w/w?with a perfect delignification?5.34±0.27%,w/w?of the pretreated switchgrass.?2?The effect of pretreatment with NH₃·H₂O₂,NaOH,Ca?OH?₂ and alkaline H₂O₂ on switchgrass showed that NaOH pretreatment was the most effective pretreatments for switchgrass with 1.00%w/v NaOH at 75?for 60 min resulted in the highest cellulose?53.85±1.84%,w/w?with a perfect delignification?11.10±0.02%,w/w?of the pretreated switchgrass.NaOH is one of the best choices for the optimization of lignin removal while minimizing carbohydrate loss,which could be successfully used in papermaking and biofuel production.?3?In the present study,the three other chemical pretreatment methods were also compared for the switchgrass utilization.The results showed that 8.00%?v/v?ethanol pretreatment with a catalyst of H₂SO₄ could obtain 58.56±0.33?w/w?cellulose with the condition of 150?for 40 min.In addition,ethanol could further be recovered by precipitation of pretreatment effluents,which makes the process much more sustainable and promising.?4?HNO₃,HCl,AHP and FeCl₃ were first employed to investigate the effect on switchgrass biomass in this study.These results provided that HNO₃ and H₃PO₄ pretreatments of switchgrass have the great potential for production of low-cost biofuels and high-value biochemical resulting from that the residual acid can be used as a fertilizer for microbe growth.When the switchgrass was treated with 8%alkaline hydrogen peroxide,the maximum cellulose yield was achieved.Samples pretreated with 0.05 M FeCl₃ solution under 150?for30 min exhibited maximum cellulose relaxation and hemicellulose removal.Although,at the investigated conditions,the effect of FeCl₃ pretreatment for switchgrass was slight,it can effectively remove hemicellulose,interrupt the ether bond and ester bond between lignin and carbohydrate.In addition,ferric chloride can be recycled after pretreatment.?5?In this work,HNO₃,NaOH and ethanol pretreatments were found to be the most effective pretreatments for switchgrass.The effects on the surface morphology,crystalline structure of these three methods,at the investigated optimal conditions,were further studied.These results provided the most crucial evidence that the intact structures of pretreated switchgrass were disrupted and the cellulose,hemicellulose and lignin were changed after pretreatments.Finally,the final fermentation results also showed that switchgrass can be effectively used in the production process of farnese after pretreatment.In conclusion,this study presents various attributes to the changes undergone by switchgrass when it was subjected to twelve pretreatments including five dilute acids,four alkaline,organosolv,ferric chloride,and the hydrothermal pretreatments.NaOH pretreated switchgrass was the most destroyed biomass and presented the highest cellulose content and lowest lignin content at the wild condition.While the HNO₃ and ethanol pretreatments were also proved to be the potential and suitable pretreatment methods for obtaining switchgrass cellulose.This study also aimed to improve the digestibility of the switchgrass in the simple and mild chemical pretreatments for various production purposes,such as fermentation sugars,paper and nanocellulose.The practical details of the pretreatments presented in this study were not only used to choose the best strategies for enhancing conversion process of switchgrass,but also to provide the guideline for better utilization of switchgrass.