Study On The Preparation Technology And Reaction Process Of Polyoxymethylene Dimethyl Ethers

As a kind of new diesel additives with coal-based methanol as raw materials, polyoxymethylene dimethyl ethers(PODE) can effectively improve the efficiency of diesel combustion, reducing emissions of NOx and CO. The development of polyoxymethylene dimethyl ethers can not only makethe fule more efficient and cleaner, but also deepen the use of coal based methanol and develop a new way which coal convert to high-quality liquid fuel.In the paper, paraformaldehyde((HCHO)n) from different habitats and different cation exchange resins are choosed to react with methylal(DMM) for the synthesis reaction of polyoxymethylene dimethyl ethers. Then pick out the optimum reaction system. Under this reaction system, the effects of different reaction factors like the amount of catalyst, feed ratio, reaction temperature, etc, are investigated and the optimum reaction conditions are determined through the orthogonal experiment. In addition, the reaction process is basicly studied by changing the reaction temperature, the amount of methanol and feed ratio.The research results show that:(1) The effect of reaction which chooses paraformaldehyde made in Spainas raw material and WS-1 as catalyst is the best. The reaction conversion rate and the yield of PODEn=2~7 reach high level. The content of long chain product is high and the total amount of by-products is small. But the acid value of product is a little high.(2) The reaction conversion rate is positively correlated with the amount of catalyst, reaction temperature and time. With the increase of the amounts of catalyst and paraformaldehyde, reaction temperature and time, the target product yield shows a trend of decrease after the first increase.(3) According to the result of orthogonal experiment, the optimum reaction conditions are as follows: n(DMM):n((HCHO)n)=1:1.8, w(WS-1)=9%, T=105℃, P=1.0MPa, t=10h. After the reaction, the conversion rate of paraformaldehyde is 81.19%, and the yield of PODEn=2~7 is 45.12%.(4) According to the research of the reaction process by changing reaction temperature, we can find that the amount of formaldehyde decreases linearly with the reaction process. The higher the temperature is, the faster the rate is. Under lower temperature(T≤100℃), the decomposition of paraformaldehyde is faster than the reaction of formaldehyde and methylal when the reaction time is within 1 hour.(5) After adding methanol to raw materials, the amount of formaldehyde no longer presents linear decrease with the reaction, the product selectivity begins to appear small fluctuations in the reaction process. The more the addition of methanol is, the longer the duration of the fluctuation is.(6) When the molar ratio of methylal to paraformaldehyde is 1:1, 1.5:1 and 2:1, the consumption rate of formaldehyde appears an initial fast followed by a slow. When the molar ratio of methylal to paraformaldehyde is 1:2, the content of formaldehyde first appears a peak and then appears a linear decrease. A reciprocal transformation between products with different chain lengths can be obviously observed in the reaction process.