Abstract:

Polymethoxy dimethylether (DMM_3—7) as a diesel additive can improve diesel cetane number and fuel utilization rate, and has broad application prospects. For the synthesis of DMM_3—7 from dimethoxymethane (DMM) and trioxymethylene(TOX), this work systematically studied the effects of different conditional parameters on the conversions and products selectivity with the sulfolane-treated sulfonic acid as the catalyst and the reaction routes were proposed according to the results of products analysis by GC-MS. It was observed that trace amounts (mg/kg level) of H₂O left in the reaction system significantly influenced the reactants conversions and products selectivity. With raising H₂O content, more white precipitation paraformaldehyde (PF) was gradually produced, while methanol was substantially generated to lower the selectivity of DMM_3—7. The sulfolane-treated method was first proposed and sulfolane solvent was acted as dehydration and pore-forming reagent, that resulted in the absorbed H₂O in the surface/pores of NKC-9_sulfolane obvious decrease from 2154 mg/kg to 198 mg/kg. Meanwhile, 13X molecular sieve was applied to significantly reduce H₂O content of DMM from 710 mg/kg to 54 mg/kg. When the reaction temperature is 313 K (40℃), the reaction is 2 h, the pressure is 1.0 MPa, and the mass ratio of DMM to TOX is 2/1, the DMM and TOX conversion rates and the DMM_3-7 mass selectivity increase from 48.27%, 88.41% and 45.27% to 52.91%, 93.34% and 61.58%, respectively. Comparing to literatures reports, the mass selectivity to DMM_3-7 was higher than 60% that makes it promising for industrial applications.

Key words: polymethoxy dimethyl ether (DMM_n), dimethoxymethane (DMM), trioxane (TOX), sulfonic acid resin, treated by sulfolane

摘要：

聚甲氧基二甲醚（DMM_3～7）作为柴油添加剂可提高柴油十六烷值和燃料利用率，具有广阔应用前景。以环丁砜处理后的磺酸树脂为催化剂，用于甲缩醛（DMM）和三聚甲醛（TOX）合成DMM_3~7反应，系统地研究了不同条件因素对反应过程中原料转化率和产物选择性的影响，并推断了反应机理。发现：反应体系中含有不同微量（mg/kg级）H₂O对原料转化率和产物选择性影响较大；当H₂O含量超过一定值时，有白色沉淀多聚甲醛（PF）生成，PF选择性随H₂O含量增加而增大，同时生成大量甲醇，导致目标产物DMM_3~7选择性降低。创新地采用环丁砜对酸性磺酸树脂NKC-9进行脱水处理，使固体催化剂表面及孔道吸附H₂O含量从2154 mg/kg显著降至198 mg/kg；同时使用13X分子筛对原料DMM进行吸附脱水处理，使DMM中H₂O含量从710 mg/kg明显降至54 mg/kg。当反应温度313 K（40℃）、反应2 h、压力1.0 MPa、DMM与TOX质量比2/1时，DMM和TOX转化率以及DMM_3～7质量选择性分别从48.27%、88.41%以及45.27%显著提升至52.91%、93.34%和61.58%。与文献报道的数据相比，改性后的磺酸树脂在低温下即表现出极佳的催化效果，DMM_3～7质量选择性突破60%。

关键词: 聚甲氧基二甲醚, 甲缩醛, 三聚甲醛, 磺酸树脂, 环丁砜处理