Preparation Of Cobalt-modified Hydrotalcite-derived Oxide And Supported DMC Catalyst And Study On Synthesis Of Polypropylene Glycol

Polypropylene glycol(PPG)is an important chemical raw material,which is widely used in many industrial fields,such as polyurethane plastics,daily chemical and automobile manufacturing.In order to develop green chemistry and promote sustainable development,it is a new development direction to replace the traditional homogeneous catalyst with heterogeneous catalyst.This paper opens up a new way of green synthesis of polypropylene glycol series products,avoids the acid neutralization and waste salt treatment in the traditional homogeneous alkali catalytic process,reduces the corrosion of equipment,and realizes the green synthesis of polypropylene glycol series products.Co Mg A1-LDH was prepared by nucleation/crystallization isolation method and cocurrent coprecipitation method,respectively.The heterogeneous solid base catalyst Co Mg A1-LDO was prepared by calcination using Co Mg A1-LDH as precursor.The crystal structure,morphology,thermal stability,physical properties and surface basicity of Co Mg A1-LDo were characterized by SEM,XRD,CO₂-TPD,FTIR,TG-DSC and N₂-BET.The optimum preparation conditions of the catalyst were discussed and applied to the synthesis of low molecular weight polypropylene glycol with glycerol as initiator and propylene oxide as monomer.The effects of reaction temperature,pressure,amount of catalyst,stirring rate and reaction time on the polymerization process and product performance were investigated by single factor experiments.The optimal polymerization process parameters were obtained by BBD response surface methodology.Under the conditions of reaction temperature of145°C,catalyst dosage of 4.8%,pressure of 2.3 MPa,stirring speed of 500 rpm and reaction time of 6 h,the conversion of propylene oxide can reach 90.37%,the molecular weight of polypropylene glycol can reach 670,and the physical and chemical properties can reach the national standard.The supported DMC catalyst was prepared by synchronous dropping method.The composition,crystal structure,complexing state,morphology and thermal stability of the catalyst were characterized by SEM,XRD,ICP,EA,FTIR and TG.The optimum preparation conditions of the catalyst were discussed,and the catalyst was applied to the synthesis of high molecular weight polypropylene glycol with small molecular weight poly propylene glycol(Mn=550)as initiator and propylene oxide as monomer.The effects of reaction temperature,pressure,amount of catalyst,stirring rate and reaction time on the polymerization process and product performance were investigated by single factor experiments.The optimal polymerization process parameters were obtained by BBD response surface methodology.Under the conditions of reaction temperature of 123°C,catalyst dosage of 0.05%,pressure of0.7 MPa,stirring rate of 480 rpm and reaction time of 6 h,the conversion of propylene oxide reached 90.32%and the content of aldehyde was low.The samples were characterized by IR and ¹H NMR,and their physicochemical properties were determined.The results show that the self-made samples in the laboratory have reached the national standard.In order to reduce the VOC content of the product,the self-made polypropylene glycol refining unit was used to refine the product by washing adsorption method.The effects of dealdehyde temperature,adsorbent dosage,deionized water dosage,dealdehyde time and extraction temperature on VOC and water content in the product were investigated.Under the conditions of dealdehyde temperature of 110?,adsorbent dosage of 1.2%,water dosage of 7%,dealdehyde time of 120 min and extraction temperature of 120?,the aldehyde value of the product can be reduced to 7 ppm and water content can be reduced to 0.07%.