Process Development Of Polyoxymethylene Dimethyl Ethers

There exist disadvantages of low conversion of raw material, the refined difficult of crude product and the high cost in the traditional process. For this, Reactive and Extractive Distillation(RED) was introduced to product the high purity of methylal used methanol and formaldehyde as raw material. Then, Reactive Distillation(RD) was introduced to product polyoxymethylene dimethyl ethers used the high purity of methylal as raw material. Therefore, the equipment investment and energy consumption were significantly reduced. The process was studied systematically through the method of combining experiment and Aspen Plus simulation together.RED pilot was constructed to carry out continuous production of methylal. The process operating parameters were researched to provide data for industrial design. The feed ratio was1:2. The ditillation rate was1.2L/h, and the reflux ratio was1.2. On the basis of those parameters, the purity of methylal at the top of column was up to99%.The effect of reaction factors was investigated for the reaction used methylal as raw material and the reaction used methylal and paraformaldehyde as raw material. Experiment results show that SAPO-34has higher catalytic activity. For the first reaction, the obtained optimum process parameters were temperature135℃, reaction time6h, the amount of catalysts4.5%(mass%), the amount of water3.5%. For the second reaction, the reaction parameter were temperature165℃, reaction time6h,the amount of catalysts5%(mass%),feeding ratio ω(methylal):co(paraformaldehyde)=0.3:1.RD pilot was constructed to carry out continuous production. The parameters were: the temperature of the top of column73.0℃, the temperature of the bottom of column172.5℃, the dimethyl ether of top of column99.17%, the polyoxymethylene dimethyl ethers of bottom of the column94.01%, the methylal of bottom of the column3.21%, the dimethyl ether of bottom of the column1.24%, the water of bottom of the column1.54%.The process was simulated by ASPEN PLUS and the good agreement between simulation result and the pilot experiment indicated that the software can be used for this process simulation. Preliminary design of the continuous process for polyoxymethylene dimethyl ethers production was carried out, the process equipment parameters and technological conditions were designed and optimized by the use of computer simulation. The appropriate operating parameters were:total plate number18, with8for reaction,10for distillation; reflux ratio1.5; the flow rate of methylal65.8kmol/h, the feed stage13. Simulated based on this condition, the composition of methylal at the top of column was0.5%, the purity of polyoxymethylene dimethyl ethers at the bottom of column was up to98.5%.