Study On Catalytic Conversion Of Lactic Acid To 2,3-Pentanedione

2,3-Pentanedione which is oil-like liquid with yellow green colour,is mainly used as food flavor materials,gelatin hardener,photo adhesive.Its natural form existing in Finland pine and other essential oils,is far from meeting the demand.The existing synthetic methods are as follows: 1)in the presence of hydroxylamine hydrochloride and nitrogen,2,3-pentanedione is synthesized by the oxidation of methyl acetone with sodium nitrite and dilute hydrochloric acid.2)It is also produced from hydroxy acetone and hexanal by catalyzed condensation reaction in the presence of acid.However,a large number of liquid acids is used in the above two synthetic methods.A large number of waste acid is discharged in the processes,resulting in a greater harm to the environment.Therefore,the cleaner processes for 2,3-pentanedione is urgent nowadays.In recent years,biomass and its derivatives have become one of the most important research subjects because of their sustainability,renewability and environmental friendliness.Based on this,in the dissertation,bio-lactic acid is choosen as raw materials through catalytic condensation synthesis of LA to 2,3-pentanedione.The synthesis of 2,3-pentanedione had some problems now.In the used catalyst,acid-base properties did not match with the condensation reactions,leading to low selectivity of 2,3-pentanedione.The active component was easy to loss in the reaction process,resulting in poor stability.From the perspective of molecular design of catalyst,we constructed the condensation reaction catalyst,combined with the modern characterization,to disclose the relation between acidbase properties of catalyst and activity,and to further explore the effect of catalyst preparation conditions and reaction conditions on the reaction.On this basis,we proposed a possible mechanism of condensation synthesis of LA to 2,3-pentanedione.The main contents of this dissertation are as follows: The catalyst was prepared by impregnation method and coprecipitation method.The structure of the catalyst is characterized by XRD and FT-IR.Energy spectrum(EDX/Mapping)can analyze the element composition.The texture and appearance of the catalyst are analyzed by BET and SEM.The distribution and density of acid and base sites on the catalyst surface are studied by chemical adsorption and desorption(CO2-TPD/NH3-TPD).The catalyst activity was evaluated by fixed bed micro reactor for gas-solid catalytic reaction.In this dissertation,we mainly studied the three systems containing silica supported alkali metal nitrate,cesium doped Mg-Al complex and Cs doped hydroxyapatite.Catalyst system 1: The catalysts were prepared by impregnation method using different alkali metal nitrate and the catalysts were used for the condensation reaction of lactic acid to 2,3-pentanedione.The effects of reaction temperature and loading of nitrate on the condensation reaction were investigated.In 4.4%(x,mole fraction)CsNO3/SiO2,the yield of 2,3-pentanedione was 54.1% at the reaction temperature of 300 ?.The correlation between the activity of the catalyst and the characterization of CO2-TPD revealed that the basic position was the key to the reaction.The more basic site was,the better the activity was.Catalyst system 2: Although the initial activity of the catalyst system was relatively high,the stability was poor.The reason was the loss of the active component Cs in the catalytic reaction.In order to solve the problem of the stability of the catalyst,a series of Cs doped Mg-Al composite catalysts were prepared by means of in situ molecular assembly,and the active component Cs was doped into the carrier structure.The effect of Mg/Al ratio on the catalytic activity was investigated.In the selection of the most preferred catalyst,the yield of 2,3-pentanedione was up to 30% with the reaction temperature of 300?.The yield of 2,3-pentanedione was not high,but its stability had been greatly improved.Catalyst system 3: Although the catalytic activity of catalyst system 2 was not high,the stability was good,which indicated that the molecular assembly method was feasible for doping the active component Cs.Under the guidance of this idea,we prepared Cs doped hydroxyapatite catalyst by molecular assembly.The effects of calcination temperature and doping amount of cesium nitrate on the performance of the catalyst were investigated.The effects of two factors on the performance of the catalyst were investigated.In addition,the reaction temperature,the feed rate and the concentration of lactic acid were optimized.In choosing the best proportion and the optimum calcination temperature,when reaction temperature was 290 degrees celsius conditions,the yield could reach about 65%.More importantly,the stability of the catalyst was very good,up to 40 h.Through the discovery of characterization of the catalysts,the acid-base position of the catalysts surface was the key to influence the catalytic activity.When alkali / acid ratio was 7-8,the reaction had a good catalytic performance.Based on this,we put forward the synergistic reaction mechanism of lactic acid to 2,3-pentanedione.