Extraction And Characterization Of Chemical Components From Wheat Straw By Formic Acid

Wheat straw is a rich renewable resource,which mainly consists of cellulose,hemicellulose and lignin.Effective separation and transformation of chemical components are prerequisites for its high value utilization.With the improvement of environmental protection awareness and the requirement of comprehensive utilization of renewable resources,the separation technology of biomass components in agriculture and forestry will take the road of high efficiency and environmental protection.Early studies mostly used batch method.The reaction time was long.The conditions were severe.The degradation of carbohydrates was serious,and the yield of hemicellulose was low.Recently,the flow-through treatment has been successfully applied in the fields of lignin refining and hemicellulose extraction.In this paper,the flow extraction method using formic acid has been developed,which can quickly separate chemical components of plant cell wall with reduced degradation of lignin and carbohydrate.This will be conducive to the subsequent realization of high-value utilization of hemicellulose and lignin.The experimental results and theoretical findings of this study have theoretical value for the non-destructive dissociation of plant cell wall,and practical guidance for the utilization of agricultural straw resources.Firstly,the traditional batch method and the flow-through method are compared.The experimental results show that the flow extraction has obvious advantages,such as higher extraction efficiency,the same lignin removal rate but shorter time,and better selectivity towards lignin.Under different conditions,the slope of the correlation curve between hemicellulose dissolution and lignin removal was 1.24,while the slope of the correlation curve between hemicellulose dissolution and cellulose loss was 0.27.The former is about4.6 times higher than the latter.The solid residue rich in cellulose shows remarkable recovery of hexosan and retains good crystal structure.At the same time,the effects of formic acid concentration and extraction temperature on carbohydrate dissolution and delignification in the process of formic acid flow extraction were also studied.The results showed that the dissolution of hemicellulose and the removal of lignin increased with the increased severity of experimental conditions.However,compared with formic acid concentration,temperature has a greater impact on hemicellulose dissolution and lignin removal.The higher the temperature,the faster the delignification rate,but it will not change the delignification selectivity.At the same formic acid concentration?72%?,the lignin removal concentration was less than 1 g/L at90?and only 13.4%and 11.5%of the lignin removal concentration at 110?and 130?.The highest proportion of glucose concentration in total dissolved sugar concentration was only 10.72%even at 130 C and 18 min.In addition,the higher formic acid concentration,the faster delignification rate,but higher formic acid concentration will cause a large number of carbohydrates degradation,destroying cellulose structure.When F90T130 is extracted for 11 minutes,the ratio of glucose to total dissolved sugar concentration has reached 10.96%.Finally,in order to study the changes of lignin structure in the process of flow extraction with formic acid,FT-IR,GPC,2D-HSQC,³¹P NMR and synchronous thermal analysis were carried out for the water-insoluble lignin?WIL?obtained after treatment.The results showed that the stretching vibration absorption peak intensity of non-conjugated carbonyl C=O increased significantly in the process of flow extraction by formic acid method,which indicated that lignin was esterified.GPC data show that WIL is chemically composed of lignin-derived oligo-phenols.In addition,the structures of?-O-4 in WIL extracted by formic acid flow method were well retained.In the WIL of F62T130t20 and F72T130t20,the retention rate of?-O-4 was as high as 81.4%.In F90T130t20 with higher formic acid concentration,the retention rate of?-O-4 is still about 46%,which is much higher than that of lignin obtained by other methods.However,the thermal stability of WIL decreased compared to milled wood lignin.The results show that the flow treatment method can effectively reduce the degradation of lignin and carbohydrate,and can be used as one of the optimum methods for biomass refining.