Aluminophosphate molecular sieve catalysts VPI-5 and AIPO-11 were synthesized and the diffusion characteristics of hydrocarbons in AlPO-11 was investigated.
Diffusion of monoalkylbenzenes and xylene isomers were very rapid while the diffusion of trimethylbenzene isomers and cyclohexane was very slow.
The pore opening of the channels in AlPO-11 is reported to be 6.3×3.9Å, flatter but wider than that of ZSM-5 as well ZSM-23.
Rapid uptake of xylenes including m- and o-xylene and the slow uptake of cyclohexane can be attributed to the flatter but wider channel opening of AlPO-11.
For the diffusion of trimethylbenzene isomers in AlPO-11 channel, diffusion coefficients decreased in the order $1,2,4- > 1,2,3- > 1,3,5$-trimethylbenzene.
