The composite catalyst composed of sulfuric acid and alkyl imidazole-based acidic ionic liquid was used to replace pure sulfuric acid as the catalyst for the synthesis of trioxane. 1-ethyl-3-methylimidazolium hydrosulfate ([EMIM][HSO₄]), 1-butyl-3-methylimidazolium hydrosulfate ([BMIM][HSO₄]), and 1-hexyl-3-methylimidazole hydrosulfate ([HMIM][HSO₄]) were chosen to form composite catalysts with sulfuric acid. The effects of ionic liquid types, formaldehyde concentration (35 ~ 55 wt%), and temperature (353 ~ 368 K) on the reaction were studied. When H₂SO₄ / [EMIM][HSO₄] was used as catalyst with a dosage of 0.6 mol/kg of formaldehyde solution, the optimal catalytic performance was obtained at 373 K with the 50 wt% formaldehyde solution as initial reactant. Compared to that with pure H₂SO₄ as the catalyst, the trioxane concentration in the reaction system was sharply increased with an increment of 17% by the synergy of ionic liquid [EMIM][HSO₄]. The equilibrium constant was increased from 3.08 × 10⁻⁵ to 4.19 × 10⁻⁵ by the addition of [EMIM][HSO₄]. The reaction was intensified by the inhibition of reverse reaction. It indicates that the addition of [EMIM][HSO₄] has complicated effects on the reaction. The research results provide a deep understand for the catalytic performance of mineral acid/ionic liquid composite catalysts.

以硫酸和烷基咪唑基酸性离子液体组成的复合催化剂代替纯硫酸作为合成三恶烷的催化剂。1-乙基-3-甲基咪唑硫酸氢盐 ([EMIM][HSO ₄ ])、1-丁基-3-甲基咪唑硫酸氢盐 ([BMIM][HSO ₄ ]) 和 1-己基-3-甲基咪唑硫酸氢盐 ([HMIM][选择 HSO ₄ ]) 与硫酸形成复合催化剂。研究了离子液体类型、甲醛浓度（35~55 wt%）和温度（353~368 K）对反应的影响。当 H ₂ SO ₄ / [EMIM][HSO ₄] 以0.6 mol/kg甲醛溶液为催化剂，以50 wt%甲醛溶液为起始反应物，在373 K下获得最佳催化性能。与纯H ₂ SO ₄为催化剂相比，在离子液体[EMIM][HSO ₄ ]的协同作用下，反应体系中的三恶烷浓度急剧增加17% 。通过添加[EMIM][HSO ₄ ] ，平衡常数从3.08 × 10 ^-5增加到4.19 × 10 ^-5。逆反应的抑制使反应加剧。表明加入 [EMIM][HSO ₄] 对反应有复杂的影响。研究结果为深入了解无机酸/离子液体复合催化剂的催化性能提供了依据。