Process Research Of Methyl Acrylate Synthesis With Methyl Acetate And Formaldehyde Over Modified ZSM-5 Catalysts

Acrylic acid and its esters are important organic chemical intermediates and polymers.At present,the main synthetic process is propylene oxide esterification.This work developed a new process of methyl acrylate production through one-step synthesis by aldol condensation with acetic acid,methanol and formaldehyde.The method of efficient catalyst development was investigated and the effects of the pore structure and acid-base characteristics on the catalyst activity were found.The phase equilibrium of product mixture was determined and suitable separation method was obtained.The main findings of this paper are as follows:?1?A series of acid-base modified catalysts were designed and synthesized respectively using ?-Al₂O₃,SiO₂,TiO₂,ZrO₂ and ZSM-5 as support.The influences of various physical parameters such as specific surface area,pore structure and acid-base properties on acid-base catalysis process including the diffusion,adsorption,interface reaction and carbon deposition were systemically demonstrated.The results were shown that modified ZSM-5 exhibits better catalytic activity and selectivity.In particular,the important influences of acid-base properties and Si/Al ratio on the catalytic activity were studied.?2?The preparation methods of acid-base catalysts and the mechanism of selective catalysis and the regularities of acid-base adjustment catalyst were further clarified.B acid and L acid center in the P-modified ZSM-5 series catalyst were found playing different roles in the catalyzed process.The L acid center can promote the enolization of carbonyl compounds containing a-H and the B acid center mainly protonates with formaldehyde,but B acid was the reason of rapid carbon deposition.The effects of loading of active components,different phosphorus sources,calcination temperature and reaction temperature on the properties of the catalysts are clearly elucidated and the adjustment regularity of L acid and B acid with a variety of acid-base modifier was obtained after qualitatively and quantitatively being determined by pyridine and infrared spectroscopy and CO₂-TPD.The formation of aluminum metaphosphate will change the coordination number of aluminum in the framework,accompanied by the reducing in the B acid and increase in the L acid in the skeleton.According to the investigation on the catalytic activity for the reaction of methyl acetate and formaldehyde,it was found that the L acid promoted the aldol reaction,and the B acid was the main reason of rapid carbon deposition.?3?The effects of different formaldehyde sources containing formaldehyde solution,trioxymethylene,and paraformaldehyde on the catalytic performance of P/ZSM-5 catalyst were studied.The yield of acrylic acid and its ester in descending order was trioxymethylene?45.5%?>formaldehyde solution?43.2%?>paraformaldehyde?40.3%?.The catalyst life in descending order was formaldehyde aqueous solution>paraformaldehyde ? paraformaldehyde.When the formaldehyde aqueous solution was used as the material,the catalyst life will be shortened after recycling due to changes in the aqueous environment.The Pyridine infrared was performed to detect acid distribution on the catalyst surface.The results were found that the content of total B acid on the catalyst deactivated increased,and the L acid reduced in the presence of water.The influence regularity of L acid and B acid mentioned in?2?was further confirmed.?4?Thermodynamics and separation process of acrylic product system were systematically studied.The research object was aimed to the complex azeotropic system?MA-MeOAc-Me-H₂O?.The missing binary phase equilibrium data was obtained by the experiment and the VLE and LLE phase diagram of the ternary system and the phase diagram of the quaternary system were constructed.The thermodynamic properties were corrected step by step to obtain the more accurate thermodynamic model parameters.On this basis,the separation process was designed and the whole process was optimized and integrated based on the simulation software.In the end,the separation of the acrylic system was verified by the amplification experiment and the whole separation process was successfully realized.