Study On The Catalytic Conversion Of Biomass Derived Carbohydrates To Alkyl Lactate

With the consumption of fossil resources, and growing concern about theenvironmental problems brought out by the utilization of fossil resources, more andmore attention has been paid to production of fuels and chemicals from renewableresources. Biomass is the most abundant renewable resource in the world, andcarbohydrates are the main components of biomass resources. Production of fuels andchemicals from carbohydrates is an important way to utilize biomass resources.Lactic acid and its ester are important platform chemicals prepared from biomassderived carbohydrates, which are widely used in food, cosmetic, chemical andpharmaceutical industries. In addition, lactic acid and its ester are also used as greensolvents and materials for synthesis of biodegradable polymer--poly-lactic acid.Currently, lactic acid and its esters are mainly produced by microbial fermentation.The method has the drawbacks of low product concentration and space-time yield. Inrecent years, much attention has been paid to production of lactic acid and its estersthrough catalytic conversion of carbohydrates. Various acid catalysts are used tocatalyze carbohydrates into lactic acid or its esters, among which Sn containing Lewis(L) acid catalysts exhibit unique selectivity to lactic acid or its esters.In this thesis, production of alkyl lactate through catalytic conversion of biomassderived carbohydrates was selected as the target reaction. Transformation of a simplesugar of1,3-dihydroxyacetone (DHA) and a complex sugar of glucose to methyllactate (MLA) was studied detailedly. First, Sn-USY zeolite was prepared bydealumination-adulteration method. The obtained Sn-USY zeolites were characterizedby XRD, FTIR, N2physisorption, DRUVS, TEM, and Py-adsorbed IR. The catalyticperformance of Sn-USY zeolites was tested in the conversion of DHA to MLA. Theresults showed that treatment of H-USY with nitric acid can effectively remove theframework aluminum and generate T vacant sites. After incorporation of Sn4+by thesolid-state ion exchange method, the Sn4+in T-sites generate a large amount of L acidsites, which catalyze the conversion of DHA to MLA efficiently. The conversion of DHA was nearly complete and the yield of MLA was97%at40oC for5h. Moreover,Sn-USY zeolite can be recycled. After reusing five times, the conversion of DHAremained unchanged, and the yield of MLA was still as high as85%.Subsequently, the conversion of glucose to MLA catalyzed by homogeneous metalsalt catalyst of SnClnwas investigated. It is found that neutralizing the Br nsted acidsites generated by the hydrolysis/alcoholysis of SnClnwith base can effectivelyinhibit side reactions and improve the selectivity of MLA. The highest MLA yieldwas obtained at the molar ratio of NaOH/SnCl4of1:1. With SnCl4-NaOH (1:1) ascatalyst, the reaction conditions including the amount of catalyst and glucose and thereaction temperature and time were optimized. The yield of MLA from glucose,fructose and sucrose was47%,57%and51%, respectively, at160oC for2.5h. Thecatalyst can transform the reaction solution of glucose in high concentration. MLAyield still reached44%at glucose content of20wt%. The catalyst can be recycledand the performance is comparable to that of the fresh one after four catalytic runs.