The synthetic reaction of trioxane from formalin on the zeolite catalysts

The synthetic reaction of trioxane from formalin on the zeolite catalysts was studied. High catalytic activities were observed over high silica zeolite with SiO2/Al2O3 ratios greater than 15, especially more than 25. This result became clear that an indispensable condition of developing the activity was the hydrophobic nature of high silica zeolite in the aqueous solution reaction. On the ZSM-5 zeolite with 20 mu m of large particle diameter, the selectivity of trioxane showed low value and formic acid and methyl formate were produced as by-products. However, the selectivity drastically increased with decreasing the particle diameter. The poison experiment of ZSM-5 by organic base proved the active site of this reaction was the acid site of only inside of pore and not outside of one. When the selectivities of various kinds of zeolites were compared, high selectivities were observed over mordenite and p-zeolite with pore of 12-membered oxygen ring and low one and the formation of a lot of formic acid and methyl formate over ZSM-5 and ZSM-35 zeolites with pore of 10-membered oxygen ring. The fine particle of ZSM-5 with 10-membered oxygen ring and zeolite with 12-membered one were profitable to the diffusion of trioxane with the large molecular size because of the shape selectivity of the zeolite which made the difference of selectivity in the particle size of ZSM-5 and a type of zeolite. It was confirmed by the results of the life test of catalyst, beta-zeolite and ion exchange resins, for 500 h that p-zeolite showed more stability to heat and longer life than ion exchange resins.