分子筛催化剂上甲醇与三聚甲醛缩合制聚甲醛二甲醚

Synthesis of polyoxymethylene dimethyl ethers from methanol and trioxymethylene with molecular sieves as catalysts

对HY、HZSM-5、Hβ和HMCM-22分子筛催化剂上甲醇与三聚甲醛缩合制聚甲醛二甲醚(PODEn或DMMn)的反应性能进行了研究,考察了分子筛种类和酸性对产物分布的影响。结果显示,以酸性分子筛为催化剂,甲醇与三聚甲醛可缩合得到聚甲醛二甲醚。HY分子筛上反应产物主要为短链的甲缩醛(DMM);HZSM-5和Hβ分子筛上产物以DMM1～3为主,其柴油添加剂组分DMM3～8的收率分别为6.40%和13.78%;HMCM-22分子筛为催化剂时,长链的聚合物收率明显增加,其柴油添加剂组分DMM3～8的收率可以达到29.39%。NH3-TPD表征结果表明催化剂表面的酸性对产物分布有着明显的影响:表面弱酸位有利于短链产物DMM的生成,而中等强度的表面酸性位则能促进柴油添加组分DMM3～8的生成。

Polyoxymethylene dimethyl ethers （PODEn or DMM, ） were synthesized by the condensation of methanol and trioxymethylene over the catalysts of several molecular sieves like HY, HZSM-5, HI3 and HMCM- 22; the effect of their acidic properties on product distribution was investigated. The results indicated that the acidic molecular sieves, especially HMCM-22, are catalytically active for the condensation of methanol and trioxymethylene to form DMM~. Over HY, the main product is dimethoxymethane （DMM）, with a selectivity of 92.87%. Over HZSM-5 and HI3, the main products turn to be DMM1-3 and the yields of D/k/[b/I3 -8, which are ideal additives for diesel fuel, reach 6.40% and 13.78%, respectively. With HMCM-22 as the catalyst, the formation of long chain DMMn products is further enhanced and the yield of DMM3 -8 attains 29.39%. The results of NH3-TPD demonstrated that the product distribution is related to the surface acidic properties of the catalyst used; short chain DMM may be primarily formed on weak acidic sites, while the acidic sites of medium strength can enhance the formation of diesel fuel additive components DMM_3 - 8