Studies On The Synthesis Of Polyoxymethylene Dimethyl Ethers

It is well known that polyoxymethylene dimethyl ethers(DMM3?8)is the novel and environmental protection diesel additive and it is beneficial for the energy saving and emission reduction.Its cetane number is higher than that of dimethyl ether,more than 76 on the average,and its properties are similar to those of diesel fuel,so it is not necessary to make any modification for vehicle engine when using DMM3?8 as diesel additive due to its remarkable properties.According to the domestic and foreign clean fuel situations and our country's energy structure and the task of saving energy and reducing emissions,developing a pathway to coal-based raw materials for the synthesis of clean substitute fuels with oil resources has an important strategic significance.This paper studies several preparation methods of DMM3?8.It is found that the synthetic route using methanol and formaldehyde as raw materials and the functional Br(?)nsted acidic ionic liquid as catalyst is very excellent.Firstly,twelve kinds of sulfonic acid functionalized ionic liquids with three kinds of cations and four kinds of anions were designed.The catalyst a which exhibited the best catalytic performance from three phenyl butylsulfonic phosphonic ionic liquids can be screened by comparisons of different anions for the sample with every anion in the batch autoclave under different reaction conditions.In addition,we investigated the effect of the reaction temperature,raw material mole ratio,catalyst dosage,N2 pressure and the reaction time on the yield and selectivity of DMM3?8,then we can draw the optimum reaction condition:reaction temperature 120 ?,nMeoH:nTOx = 2,catalyst dosage 2.2 wt%,N2 pressure 2.0 MPa,reaction time 4 h.At the same time,the similar optimum reaction conditions were determined by using response surface methodology to analyze the effects of all factors.The results shows that raw material molar ratio>reaction temperature>catalyst dosage>reaction pressure,and the optimal conditions:reaction temperature 100 ?,N2 pressure 2.061 MPa,nMeOH:nTOx =1.687,catalyst dosage 1.751 wt%.Finally,we compared catalytic activity of different anions using Imidazole and Pyridine ionic liquids,found that the effects of ions on the reaction activity were different under different process conditions.Under the same reaction conditions we drew the conclusion that the activity of ionic liquid was attributed to the interaction of ions by comparisons of the effect of cation with anion on the reaction.