Coiled Tube Reverse Preparation Of Diethoxymethane And Its Purification

Diethoxymethane(DEM)is widely used as a reaction solvent and chemical reaction reagent as an important chemical industrial raw material.To change the conventional homogeneous protonic acid for the preparation of DEM by alcohol-formaldehyde condensation in an intermittent reaction.This paper proposes the use of a non-homogeneous solid acid catalyst instead of the traditional protonic acid to replace the intermittent reaction method with a continuous reaction method,which effectively avoids the alkali neutralization and catalyst removal steps and the catalyst can be used continuously.For the characteristics of the aqueous reaction system,the polystyrene-based sulfonic acid resin and niobium-tungsten composite bimetallic oxide were prepared from the perspective of hydrophobicity and water resistance,respectively,and applied to the alcohol-formaldehyde condensation reaction.Concentrated sulfuric acid was used as the sulfonating agent to directly sulfonate the polystyrene substrate and introduce sulfonic acid groups,and the sulfonation degree was measured to be 60.8%with a sulfonic acid group content of 3.9856mmol/g.Characterization of functional groups,thermal stability,surface morphology,pore structure,acid strength of polystyrene matrix before and after sulfonation by IR,TG-DTG,SEM,BET,NH₃-TPD,etc.The results showed that the polystyrene matrix is hydrophobic and the sulfonate group is hydrophilic,which can allow the reactant molecules to adsorb on the surface for condensation without the interference of water in the reaction system and has good catalytic activity.The reaction conditions were optimized by single-factor investigation and orthogonal experimental design method,and the optimum reaction conditions were obtained as follows:reaction temperature of75?,mass air velocity of 2.14 h^-1,alcohol to aldehyde molar ratio of 5:1,and reaction pressure of atmospheric pressure,and the formaldehyde conversion reached 90.9%and diethoxymethane selectivity reached 71.2%under these operating parameters.The tungsten-niobium composite bimetallic oxides with different tungsten-niobium molar ratios were prepared by co-mixing method and applied to the alcohol-formaldehyde condensation reaction.The best catalytic preparation parameters were:W/Nb molar ratio of 4:1 and calcination temperature of 400?,when the electronic interaction between tungsten and niobium was the strongest;The crystalline shape,thermal stability,surface morphology,surface electronic valence,acid site type and acid strength of the compounded bimetallic oxides were characterized by XRD,TG-DTG,SEM,XPS,Py-IR,NH₃-TPD,etc.The results showed that the compounded bimetallic oxide contained a large number of medium to strong acid sites,and the acid type was mainly L-acid-based and B-acid-based,with synergistic catalysis;and the atomic valence of the surface elements changed,indicating that the two were not simply mixed but had strong interactions between tungsten and niobium electrons.The reaction conditions were optimized by single-factor experiments combined with orthogonal experimental design,and the optimum reaction conditions were obtained as follows:reaction temperature 75?,mass air velocity 0.89 h^-1,alcohol to aldehyde molar ratio5:1,and reaction pressure at atmospheric pressure,with formaldehyde conversion of91.9%and diethoxymethane selectivity of 89.9%under these operating parameters.After the above catalyst exploration,the separation study of the product mixture after alcohol-formaldehyde condensation was carried out using tungsten-niobium composite bimetallic oxide as catalyst to obtain high purity of diethoxymethane and to recover excess ethanol.The process flow of one-step distillation to concentrate the mixture and two-step extraction and distillation to dehydrate and deethanolize was determined,and the separation process was simulated by Aspen Plus simulation software,and each process was simulated and optimized by combining with orthogonal experimental design to obtain the optimal operating parameters.Under the optimal operating conditions,the content of diethoxymethane reached 99.9%,which provided a theoretical basis for further experimental validation of the operation.