李臻 宋河遠

摘 要：聚甲氧基二甲醚是一類分子式為CH3O（CH2O）nCH3 （簡寫 DMMn， n≥1）的醚類化合物，含氧量高（42 51%）且具有高的十六烷值（>30），能改善柴油的燃燒性能減少排放，因而被認為是理想的柴油含氧添加物。特別是當n=3-8時，DMM3 8具有與柴油相近的性質(zhì)，平均十六烷值> 76，按20%與柴油調(diào)和，碳煙和NOx的排放能分別降低80-90%和50%。DMMn分子中間為低分子量甲醛縮聚物，兩端由甲基封端，通常由提供甲基的化合物，如甲醇，二甲醚和甲縮醛，和提供低聚甲醛的化合物，如甲醛，三聚甲醛和多聚甲醛，反應(yīng)得到。因此，實現(xiàn)從甲醇到DMMn的轉(zhuǎn)化不僅能延長甲醇產(chǎn)業(yè)鏈，消耗過剩的甲醇產(chǎn)能，而且有利于節(jié)能減排目標的實現(xiàn)。在早期，以硫酸或者鹽酸為催化劑，催化甲醇和甲醛、多聚甲醛或者二氧戊烷反應(yīng)合成DMMn。BASF公司采用H2SO4或者 CF3SO3H 為催化劑，甲醇、DMM、三聚甲醛和多聚甲醛為原料得到DMM1 10，但是催化劑腐蝕嚴重，而且原料轉(zhuǎn)化率和DMM3-8的選擇性都很低。BP公司采用分子篩或者酸性樹脂為催化劑，通過復雜的工藝實現(xiàn)二甲醚和甲醛轉(zhuǎn)化為DMMn，但是，產(chǎn)物中DMM3-8低于10%。近年來，中科院蘭州化物所開展了離子液體催化甲醇和三聚甲醛反應(yīng)合成DMM3-8的研究，產(chǎn)品單程收率達到50%，DMM3-8選擇性大于70%。

關(guān)鍵詞：聚甲氧基二甲醚 甲醇 甲醛 催化劑 離子液體

Abstract：Polyoxymethylene dimethyl ethers are a kind of ether compounds with the formula CH3O（CH2O）nCH3 （abbreviated to DMMn， n≥1）. DMMn has high oxygen content （42 51%） with a high cetane number （>30） and is regarded as a promising diesel additive， which can improve the combustibility of the diesel oil， enhance the efficiency of combustion， and reduce the release of pollutants. Especially， DMM3 8 exhibits high oxygen content， moderate boiling points， excellent miscibility with diesel oil， and average cetane number of above 76； it was reported that by adding 20% DMM3 8 in the diesel oil， the amounts of powderous pollutants and NOx released upon combustion can be reduced by 80 90% and 50%， respectively. DMMn molecule is composed of formaldehyde oligomer in the midst and methyl in two ends； therefore， DMMn can be synthesized from the compounds providing methyl ends （such as methanol， dimethyl ether， and dimethoxymethane） and those compounds supplying formaldehyde oligomer （such as formaldehyde， trioxymethylene and polyformaldehyde）. As a result， the conversion of methanol to DMMn as an additive of diesel oil may not only extend the methanol industry chain and digest the large surplus production capacity of methanol， but also bring enormous benefits with respect to economics and environmental protection. At early stage， DMMn was obtained from methanol and formaldehyde， polyformaldehyde， or dioxacyclopentane， with sulfuric acid and hydrochloric acid as catalyst. In this respect， BASF Group used H2SO4 or CF3SO3H as catalyst to get DMM1 10， with methanol， DMM， trioxymethylene， and polyformaldehyde as raw materials， but the catalyst is corrosive and the conversion and selectivity to DMM3 8 is low. With zeolites or acidic ion exchange resins as catalyst， BP produced DMMn by conversion of dimethyl ether with formaldehyde through a complicated process； however， the DMM3 8 yield was still lower than 10%. In recent years， Lanzhou Institute of Chemical Physics， Chinese Academy of Sciences has made progress to synthesize DMM3 8 by using ionic liquid as catalyst in a homogeneous reaction system with methanol and trioxymethylene as feed； single-pass yield of DMMn reached 50% with the selectivity to DMM3 8 being 70% 80%.

Key word：Polyoxymethylene dimethyl ethers； Methanol； Formaldehyde； Catalyst； Ionic liquids

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