Study On Catalytic Conversion Of Bio-Based Platform Molecules Furans And Esters And Their Mechaism

In 21^st century,although fossil fuels have entered into shale gas era,global climate change and pressure of environmental protection make academics and industries pay much attention to develop and utilize clean energy.The investments from governments on solar energy,wind energy,hydroelectric energy,tidal energy,nuclear energy etc are increasing year by year.Biomass is the unique renewable organic carbon resource which can be used to alternative fossil fuels to produce high energy fuel and value added chemicals.Plant-based lignocellulose is the biggest part in inedible biomass.Biological and chemical process can be used to highly selective conversion of lignocellulose into small molecular bio-based platform chemicals.It is a very important pathway for synthesis of biofuels and chemicals from these platform chemicals.Furans and esters bio-based platform chemicals such as 5-hydroxymethylfurfural（HMF）,furfural,furfuryl alcohol and levulinic esters are the most common bio-derived compounds which are produced from lignocellulose.Catalytic hydrogenation and acid-catalyzed reaction are two main process to utilize these compounds.For example,HMF（furfural/furfuryl alcohol）can be hydrogenated to2,5-Dimethylfuran（Methylfuran）etc.However,there are still many challenges in these processes.Such as new products synthesis from furan derivatives,avoiding the utilization of homogeneous or high cost catalysts and toxic solvents in the furfuryl alcohol alcoholysis reaction,production of 1,4-pentanediol catalyzed by cheap metal heterogeneous catalysts,etc.In order to solve these problems,development of highly efficient catalysts and new technologies is desired.Firstly,a novel approach was developed for the production of 2,5-hexanedione（HDN）and 3-methyl-2-cyclopenten-1-one（3-MCO）from 5-hydroxymethylfurfural（HMF）by water splitting with Zn.Hydrogen species could be produced by the reaction between Zn and high temperature water.The in-situ H species was used to hydrogenate HMF to HDN and 3-MCO selectively.The optimum reaction conditions for HDN production are 0.2 mmol HMF,25 mmol Zn,7.5 mL H₂O,250 ^oC,140 min.The highest yield of HDN was 27.3%.When reaction time increased to 480 min,the highest 30.5%yield of 3-MCO was obtained.Other furans such as furfural and furfuryl alcohol could also be converted by using this method to obtain cyclopentenone products.The in-situ H species displayed much higher activity than the external gaseous H₂ in the conversion of HMF.After the analysis of intermediates,a proposed mechanism for HMF conversion by water splitting with Zn was proposed.Secondly,an efficient process for the production of levulinate esters from furfuryl alcohol over commercialα-Fe₂O₃ as acid catalyst was developed.This method avoided the use of homogeneous catalysts and toxic solvents.Also,the catalyst was cheap and abundance.After optimizing the reaction conditions,the optimum conditions are 0.23 mmol furfuryl alcohol,7.5 mmolα-Fe₂O₃,10 mL ethanol,250 ^oC,140 min.The highest yield of ethyl levulinate was 83%.Andα-Fe₂O₃could also used to catalytic production of methyl levulinate and butyl levulinate,the highest yield of esters was 73%and 86%respectively.NH₃-TPD test displayed that acid ofα-Fe₂O₃ is the reason forα-Fe₂O₃ promoting the furfuryl alcohol alcoholysis.Therefore,a plausible reaction mechanism for the formation of levulinate ester from furfuryl alcohol was proposed.Thirdly,an air stable skeletal Co catalyst was developed to catalytic transfer hydrogenation of ethyl levulinate（EL）into gamma-valerolactone（GVL）with isopropanol as hydrogen donor.After optimizing the reaction conditions,the optimum conditions are 0.2 mmol EL,10 mg skeletal Co,30 mg HZSM-5,140 ^oC,3 h.The highest yield of GVL was 96.2%.This air stable skeletal catalyst could keep its activity for more than one week in air,and could be reused at least four times without loss its activity.Finally,a non-noble ternary skeletal CuAlZn catalyst was designed for direct hydrogenation of ethyl levulinate（EL）to 1,4-pentanediol（1,4-PDO）.After optimizing the reaction conditions,the optimum conditions are 70 mg CuAlZn-3.5 h,10 mL1,4-dioxane,6 MPa H₂,160 ^oC,6 h.The highest yield of 1,4-PDO was 98%.Solvent is a very important factor for 1,4-PDO selectivity.In addition,specific surface area decrease is possible reason for the decrease activity of skeletal CuAlZn when it was reused.After the analysis of obtained intermediates,a proposed mechanism for EL conversion was given.