Studies On Catalytic Conversion Of Biomass-derived Carbohydrates To Methyl Lactate In Near-critical Methanol

With the depletion of fossil resources,developing alternative renewable and green energy has become an urgent problem.Considering a wide range of biomass resources and its renewable property,a large number of high value chemicals(levulinic acid,?-valerolactone and methyl lactate,etc.)can be prepared from biomass.Methyl lactate(MLA)can be used as a good organic solvent,thus it has a wide applications in medical industry.The production of MLA now is esterification of lactic acid,produced by biologic fermentation,with methanol under sulfuric acid or other catalysts.There are some disadvantages of this method:high requirements for microorganisms;side reactions(dehydration and coking)of lactic acid;corrosion of equipment by sulfuric acid.Biomass,derived from green plants,can be degraded into organic compounds with low weight molecular under relatively mild conditions.Therefore,the production of MLA by chemical catalysis is of great significance.The critical of chemical catalysis for the MLA production is to find appropriate catalysts which are stable,environmental friendly and hold good performance on the conversion of biomass-derived carbohydrates to MLA.Preparation of MLAfrom biomass-derived carbohydrates innear-critical methanol catalysts were conducted in this dissertation.Screening,synthesis and catalytic performance of catalysts were also studied.The reaction conditions about conversion of carbohydrates to MLA is optimized and the stability of the catalysts were also investigated.The purpose of this work is to discover the efficient and stable heterogeneous catalysts for the conversion of biomass to produce MLA and to explore the influence factors on performance of catalysts.At las the general rule of the heterogeneous catalytic conversion of glucose was discussed.It plays an important role in offering the theoretical basis and experimental basis for the efficient catalytic system of MLA production and with low cost of the industrialization process efficient production of MLA The main work are as follows:Firstly,the catalytic conversion of glucose over 13 different metallic oxides were evaluated to compare the yield of MLA,it was found that the NiO shows the best catalytic activity.The highest yield(36.2%)of MLA was achieved over NiO at 200?with 3 h.Then,the catalytic performance of four kinds of NiO bought from different manufacturers were investigated.The results indicated that NiO from Aladdin showed the best catalytic performance for the MLA yield(36.2%).XRD,TEM,NH3-TPD are measured to illustrate the reason.It was concluded that the main factors affecting the catalytic performance of NiO are the acid strength and the acidity of the catalyst.The higher the medium acidity,the better the catalytic performance in our reaction system.In this reaction system,46.2%yield of MLA was achieved over NiO from Aladdin under optimal conditions and was recycled three times without any significant change.Secondly,a series of Ni/2-Hmim-X(X,the mole rations of nickel nitrate/2-Hmim)was synthesized through homogeneous precipitation method and applied on the production of MLAfrom biomass sugar.Ni/2-Hmim-4/1 shows the best catalytic effect(36.0%MLA yield)among 11 different Ni/2-Hmim-X.A gradual increase in surface area of Ni/2-Hmim-X was discovered with the increase of X by the results of BET The XRD result indicated the increased of?-NiOOH/?-Ni(OH)2 ratio made the MLA yield went up steadily when X increased in Ni/2-Hmim-X.Therefore,it was deduced that the valence of Ni influenced the reactionresults and the catalytic performance of?-NiOOH with high valence state is much better than?-Ni(OH)2 with low valence state.Therefore,the catalytic conversion of different biomass sugar to prepare MLA over Ni/2-Hmim-4/1 catalyst was evaluated.The results showed Ni/2-Hmim-4/1 achieved the best catalytic performance on the conversion of fructose,the corresponding yield of MLA was 45.9%.A complete conversion of glucose and 40.0%yield of MLA was discovered over Ni/2-Hmim-4/1 under optimal 'conditions by optimization of reaction conditions.At last,Ni/2-Hmim-4/1 performed good catalytic effect after being used three times.Lastly,several MOF-74 samples with different metals were synthesized by a simple mixing method at room temperature for the conversion of biomass sugar.The Mg-MOF-74 showed the best catalytic performance at the same reaction condition on the basis of the yield of MLA.100%conversion of glucose and 27.5%yield of MLA was obtained over Mg-MOF-74 at 200?with 3 h.It was proved by the results of XRD and FT-IR that MOF-74 with good crystallinity was prepared.BET data showed Mg-MOF-74 has the maximum surface area.Then,the catalytic conversion of different biomass sugar to prepare MLA over Mg-MOF-74 catalyst was evaluated.The results showed Mg-MOF-74 performed the best catalytic effect on the conversion of sucrose,the yield of MLA was 47.4%.A complete conversion of glucose and 34.5%yield of MLA was discovered over Mg-MOF-74 under optimal conditions by optimization of reaction conditions.In addition,Mg-MOF-74 performed good catalytic performance after being used three times.