Study On Synthesis Of Polyoxymethylene Dimethyl Ethers From Methylal And Paraformaldehyde

The pollution of automobile exhaust has been paid more and more attention,and the solution to this problem has been put into action,but there are still many problems.Polyoxymethylene dimethyl ethers?PODE_n?are economical and environment-friendly diesel additive,which can improve diesel combustion performance,reduce pollutant emissions and improve engine thermal efficiency.However,there are some problems in industrial production,such as low activity of catalyst and easy deactivation.For these problems,a new acidic catalyst has been screened out with methylal and paraformaldehyde as raw materials,and the influencing factors of PODE synthesis and the performance of catalysts are also studied.First of all,the effects of mass ratio of methylal and paraformaldehyde,catalyst dosage,reaction temperature,reaction time,reaction pressure and stirring speed on the yield of PODE products and methylal conversion were studied when catalyst D was used to catalyze the synthesis reaction of PODE from methylal and paraformaldehyde.The results indicated that the reaction conditions?mass ratio of methylal and paraformaldehyde 2:1,amount of catalyst 3w%,reaction temperature 100?,reaction time 4h,reaction pressure 0.5MPa and stirring speed 250r/min?were optimal.The yield of PODE_2-7 and methylal conversion were 63.6%and 62.5%,respectively.Then,the effect of the composition of raw materials on methylal conversion and the yield of product was studied under the preferred reaction conditions.The results showed that methylal conversion and product yield were reduced by adding methanol to the raw materials;adding proper water could increase the methylal conversion rate,but decrease the yield of products;adding PODE₂,there were low conversion rate of methylal and high yield of products.Finally,the ion exchange and acid-base titration method were used to determine the exchange capacity of catalyst D for1.83mmol/g.And the pore structure and acid properties of catalyst D were characterized by N₂ isothermal adsorption desorption,NH₃-TPD and pyridine-IR technology.The results showed that catalyst D had large specific surface area,pore volume and pore size.The acid sites were mainly strong acid sites,and were proton acid sites and Lewis acid sites.