Green Process For Preparation Of Methyl Acrylate

The improvement of the green process of a variety of traditional chemicalindustry techniques has been becoming an inevitable trend in order to maintain thesustainable development of human society. The domestic and foreign demand formethyl acrylate, an important chemical raw material with wide range of uses, is onthe increase. Currently, the main preparation methods of methyl acrylate consists ofacetylene method、propylene oxidation method、acrylonitrile hydrolysis method、ketene method、propane oxidation method、ethylene oxidation carbonylation method,methyl formate method and etc. However, the traditional methods are far from beingideal due to their heavy pollution to the environment, high energy consumption,highly toxic intermediates and low yield. The research on the efficient greensynthesis of methyl acrylate is hence of important academic value and practicalsignificance.This assiduous research is based on the ideas of green chemistry. In theresearch, the industrial by-product methyl acetate was used as raw material,non-toxic and environmentally friendly catalyst was applied, efficient and cleansynthesis method was adopted to realize highly selective and atom economic aldolreaction in order to achieve the green synthesis of methyl acrylate. The researchprocess includes: the preparation of three-dimensionally ordered macroporouscatalyst carrier, the design and synthesis of the acid-base bifunctional catalyst, thedetermination of the catalytic synthesis route, the evaluation of catalytic effect, thekinetics study on the whole catalytic process and the analysis and the life cycleassessment of methyl acrylate. The details of the research and the research findingsare shown as follows.Three-dimensionally ordered macroporous/mesoporous SiO₂carrier for thegreen synthesis process of methyl acrylate was prepared in accordance with therequirements of the pore size and the microscopic arrangement of the requiredcatalyst carrier. The influencing factors of synthesizing monodisperse colloidalpolystyrene crystal template by means of emulsion polymerization method as well as the assembly method of colloidal polystyrene crystal were discussed; themonodisperse colloidal polystyrene crystal template was assembled with SiO₂precursory sol in different ways, the removal method of template was also studied;the microstructure and pore structure parameters of three-dimensionally orderedmacroporous/mesoporous SiO₂carrier, and polystyrene colloidal polystyrene crystaltemplate were characterized by way of DTA-DTG, SEM, TEM, physical andchemical adsorption/desorption methods.The informations about template, particlesize, pore size distribution, micromorphology of the catalyst carrier were obtained.The influencing factors of synthesizing colloidal polystyrene crystal template werediscussed; dropwise impregnation method was determined as the optimal method toassemble PS and SiO₂sol-gel; the combination of solvent extraction andtemperature-programmed calcinations was determined as the removal method oftemplate. The prepared SiO₂carrier was cage-like three-dimensionally orderedmacroporous/mesoporous material.Three-dimensionally ordered macroporous/mesoporous SiO₂was used ascarrier to synthesize V2O5-P2O5/SiO₂and Cs₂O-Sb₂O₅/SiO₂catalyst respectively,and two types of process were adopted to synthesize methyl acrylate.V2O5-P2O5/SiO₂catalyst which was used to catalyze methylal and methyl acetateto synthesize methyl acrylate was studied. The factors, such as P-V atomic ratio, thechoice of carrier, microwave load conditions and the amount of the activecomponent were discussed in detail. The microstructure of the catalyst wascharacterized. The preparation conditions of V2O5-P2O5/SiO₂catalyst wereoptimized: microwave load active component was conducted at90℃,withmacroporous SiO₂used as carrier,20-40mesh number catalyst particles, and P:V:Simolar ratio at2.6:1:8. Under these conditions, the prepared catalyst was proved topossess preferable catalytic performance, with the active site loaded uniformly onthe surface of the carrier; the optimal process conditions for synthesizing methylacrylate were determined, namely, methylal/methyl acetatemolar ratio at1:2, feedspace velocity at3.2h-1，reaction temperature at370℃，consequently the selectivityof methyl acrylate reached68.31%，and the yield up to40.29%.The Cs₂O-Sb₂O₅/SiO₂catalyst with the acid-base bifunctionality was designedand prepared which was used in the process of catalyzing formaldehyde and methyl acetate to synthesize methyl acrylate. The catalyst was characterized by means ofSEM、TEM、NH₃–TPD and CO₂–TPD. The results show that the synthesizedCs₂O-Sb₂O₅/SiO₂catalyst has uniform and orderly macroporous/mesoporous，withthe acid and base active sites which could promote aldol reaction. The processconditions of the catalytic reaction for formaldehyde and methyl acetatesynthesizing methyl acrylate were researched and the optimal process conditionswere determined as: methyl acetate/formaldehyde molar ratio at3:1, feed spacevelocity at4-5h–1, reaction temperature at390℃. Under these conditions, the yieldof methyl acrylate could reach50.12%，and selectivity at60.9%.In order to improve the reaction efficiency, the filling up technique ofV2O5-P2O5/SiO₂and Cs₂O-Sb₂O₅/SiO₂catalysts in the fixed bed reactor wasstudied systematically. Coupling was made in the process of synthesizing methylacrylate with methylal and methyl acetate, also formaldehyde and methyl acetate asreactants. The “performance relay” of the catalysts was utilized effectively, whichresulted in the increase and improvement of the use efficiency of methyl acetate, theselectivity and yield of methyl acrylate, without changing the performance of theoriginal catalyst. Besides, two kinetic equations of catalytic reaction wereestablished, and the life cycle of the process was assessed. The results show that thereaction efficiency of the synthesis of methyl acrylate is effectively promoted whenthe two catalysts are filled up in appropriate subsections of the reaction tube in thefixed bed reactor. The optimal filling up technique was determined when the twocatalysts were tandem split-packed from top to bottom in the reactor. WhenV2O5-P2O5/SiO₂catalyst was filled up at subsection4and Cs₂O-Sb₂O₅/SiO₂catalyst at subsection6, and the temperature of the oven was400oC, the conversionrate of methylal was70.78%, the selectivity of methyl acrylate was90.78%, and themethyl acrylate yield reached64.26%. Macro and micro kinetic equations wereestablished respectively for the two reaction processes and it was also proved thatthe degree of fitting between theoretical and experiment value was relatively high.A life cycle assessment of the whole synthesis process was made in whichcatalyst subsection loading pattern was applied to catalyze methylal and methylacetate to synthesize methyl acrylate. The research results reveal that the mainenvironmental burden stage of this process is the course of production of methanol, the main environmental burden types are the green house effect and acidificationeffect, environmental burden from the synthesis of methyl acrylate through methylaland methyl acetate is controlled at minimum, which only accounts for6.10%of thelife cycle environmental burden of the whole process for preparation of methylacrylate.