Study On The Conversion Of Cellulose-derived Levulinic Acid And Its Esters To ?-valerolactone And 5-methyl-2-Pyrrolidone

The transformation of lignocellulosic biomass to various platform molecules has received widespread attention over the years,because these biomass-derived platform molecules hold a great promise to replace petroleum-derived counterparts for the production of materials,fuel as well as chemicals.As one of the most prospective platform molecules,cellulose-derived levulinic acid(LA)and its esters(LE)can be readily obtained by acid-catalyzed degradation of biomass and further converted into various value-added downstream products.In this thesis,the hydrogenation and reductive amination of LA/LE for the preparation of y-valerolactone(GVL)and 5methyl-2-pyrrolidone(5-MP)were studied.To realize two-step preparation of yvalerolactone(GVL)from lignocellulosic biomass with methanol as hydrogen source,improve catalytic efficiency in solvent-free systems,as well as develop a feasible reaction system for 5-methyl-2-pyrrolidone(5-MP)production directly from LA/LE,two Cu-based catalysts were synthesized and two efficient solvent-free catalytic systems were developed.First of all,a MgO-doped dual functional Cu-Mg oxide catalyst was prepared by urea hydrolysis method for methyl levulinate(ML)hydrogenation as well as the H2 production through MeOH reforming.With MeOH as in-situ H-source,Cu0.87Mg0.13Ox offered a GVL yield up to 90.6%at 220? in 4 h.Results of catalyst characterization indicate that the incorporation of MgO greatly facilitates the stabilization of Cu2+and Cu+ species under H2 atmosphere.This robust and highly-stable Cu0.87Mg0.13Ox could be recycled for over seven consecutive runs without activity dip.Notably,Cu0.87Mg0.13Ox also provided nearly 70%GVL yield from methanolysis products of cellulose even in the presence of humins.Thus,a facile one-pot two-step strategy for GVL production from cellulose was developed,and the economy was improved by avoiding the energy-consuming ML separation and purification process.Secondly,(n)CuOx-CaCO3(n:the molar ratio of Cu to Ca)were prepared by oxalate gel precipitation method and served as an efficient catalyst for the catalytic transformation of ML to GVL using methanol as in-situ H-source.The Cu/Ca molar ratio had a great influence on the catalytic performance;among the catalysts with varied Cu/Ca molar ratios,(3/2)CuOx-CaCO3 provided the highest GVL yield of 95.6%from ML at 240? in 3 h.According to characterizations,the CaCO3 was conducive to the stabilization of Cu+species in CuOx-CaCO3 catalyst,which greatly facilitated the hydrogenation of ML to GVL.(3/2)CuOx-CaCO3 exhibited superior catalytic performance,stability and the reusability,compared with the CuO prepared by the same method.(3/2)CuOx-CaCO3 was stably recycled for over 8 consecutive runs.Unaffected by humins,CuOx-CaCO3 also displayed excellent catalytic performance in methanolysis products of cellulose.Therefore,the desirable production of GVL from cellulose biomass without external hydrogen and ML seperation and purification steps could be realized.Thirdly,aiming at the bottleneck problem of heterogeneous catalyzed solvent-free hydrogenation of LA to GVL,a salt-promoted solvent-free reaction system with a small amount of choline chloride(ChCl)was investigated.Efficient conversion of LA into GVL was realized over Ru/C with ChCl;the selectivity of GVL was 100%with the complete convserion of LA(5 MPa H2,150? in 2.5 h).Under the same reaction conditions,only 70.1%LA was converted with the GVL yield of 67.4%without ChCl.According to the results of NMR and FT-IR analysis,the carboxylic group in LA was confined by the interaction with ChCl,which weakened the competitive adsorption between the carbonyl and carboxylic groups of LA on the catalyst surface.The carbonyl group was more easily adsorbed to the surface of Ru/C,which improved the hydrogenation efficiency of carbonyl group in LA.An equimolar H2O was produced along with the GVL after the hydrogenation and esterification of LA.However,the H2O won't become an azeotrope with GVL,thus the distillation separation of H2O is relatively easy.The ChCl won't dissolved in GVL,so the recrystallization of ChCl occurred after the evaporation of H2O.The separation of Ru/C,ChCl and GVL was convenient,and the used catalyst and ChCl could be recovered for 6 cycles without downgrading of the GVL yield.Finally,we systematically studied the solvent-free conversion of biogenic LA/LE into the unprotected 5-methyl-2-pyrrolidone(5-Mp)over Ru/C,with urea and formic acid(FA)as the N-source and H-source.5-MP yield of 86.4%was achieved within 6 h at 130? with the molar ratio of LA:FA:Urea as 1:1.2:1.5.Unlike the conventional reaction pathway of LA amination,in which the imine is a key intermediate,LA was aminated to 5-MP through the formation of amide intermediates in this study.For various N-sources,based on the theoretical calculation,aniline tends to break its N-H bond rather than C-N bond;while the urea tends to break its C-N bond during the reaction,due to the lower C-N bond energy(399.7 KJ/mol)compared with the N-H bond(462.3 KJ/mol).Two N atoms in urea were equally available for the LA amination,improving the atomic economy of the reaction system.The spent Ru/C could be reused for at least 11 consecutive runs with highly stable activity.This catalytic reaction system shows a high tolerance to H2O and humins.A 5-MP yield of 50.9%was achieved with cellulose acid-catalyzed hydrolysate(containing LA and FA,calculated based on cellulose)as substrate at 130? in 6 h.Thus,the preparation of 5-MP from cellulosebased carbohydrates is feasible,and the energy-intensive separation and purification of LA and FA from aqueous solution can be avoided.