Study On The Alcoholysis Of Wheat Straw To Methyl Levulinate Catalyzed By Copper Sulfate

Wheat straw is a by-product of agricultural crops,which represents an abundant of cellulose,hemicelluloses and lignin and is an important raw material for the conversion of levulinic esters.Methyl levulinate is widely used in the fields of additives,spices and energy as an important chemical product.However,at present,the study on the preparation of methyl levulinate from wheat straw has not yet been reported.In addition,the preparation of methyl levulinate from wheat straw has the advantages of low cost and environmental protection,and diverse high-value products were obtained when the wheat straw was investigated in the context of a biorefinery concept.It is an extremely promising way to achieve biomass conversion.In this paper,the conversion of wheat straw to methyl levulinate by copper sulfate was investigated.Firstly,the synthesis of methyl levulinate from wheat straw catalyzed by different metal sulfates was studied.Then the wheat straw was pretreated with alkaline solution and the alcoholysis of pretreated wheat straw was explored.Finally,wheat straw was subjected to two-stage pretreatment by acidic decanol and sodium hydroxide,then the effect of preparation of methyl levulinate from two stages pretreated wheat straw was conducted.Further,the comparison and economically analyze on the three reaction processes was carried out.The main conclusions are as follows:1.The catalytic activity of a serious of metal sulfates in methanol medium for the alcoholysis of wheat straw to methyl levulinate was investigated,among which copper sulfate showed the best catalytic activity.The response surface method was designed after the single factor study on the preparation of methyl levulinate catalyzed by copper sulphate,which gave a high methyl levulinate yield of 16.0 wt%under the conditions of182?,3.3 h and catalyst dosage of 0.64 g.In addition,the recycling of CuSO₄ was explored with the yield of methyl levulinate still reached14.8 wt%after five times were repeated,showing major changes in the crystal structure caused by agglomeration and water loss after characterized and analyzed by scanning electron microscopy?SEM?,Foueier transform infrared spectroscopy?FT-IR?,and X-ray diffraction?XRD?.2.First,the wheat straw was pretreated with NaOH,and the filtrate was used to extract lignin after treatment.The composition of the wheat straw before and after treatment was measured with a cellulose analyzer,and the morphological changes were observed with SEM.The results showed that the cellulose content in the wheat straw after treatment was increased with the morphology destroyed to a certain extent.Optimization of the pretreated wheat straw was conducted by using response surface method,and the average methyl levulinate yield of 22.9 wt%was obtained under the conditions of catalyst dosage 0.53 g,183?and 3.3 h.3.Two stages of wheat straw processing were investigated.In the first-stage process,a kind of bio-surfactant was generated by the reaction of decanol with hemicellulose in wheat straw,and the lignin component can be extracted as another value added by-product in the second stage.On the basis,the pretreated wheat straw was used as raw material for methyl levulinate production,and a yield of 20.2%can be obtained under the optimum reaction conditions.Meanwhile,the catalyst recycling experiments and characterized were further conducted,concluding that changes in the surface carbon and water content of the catalyst led to the activity decrease.In addition,compared with the XRD and SEM images of the untreated straw recovery catalyst,the removal of hemicellulose and lignin components in the straw can protect the crystal structure of the catalyst to some extent.4.The kinetics of alcoholysis of wheat straw to methyl levulinate was analyzed,and the main reaction pathway for the methyl levulinate production from wheat straw was proposed.The results of mass balances and preliminary economic analysis further indicated that a variety of products can be obtained by means of biorefinery,which will benefit the economy of the process and provide a new model for the sustainable utilization of wheat straw.