Coaromatization of Propane and Methanol on H-ZSM-5/(Zn/ZSM-5) Composite

The propane aromatization is generally carried out at temperatures >500 degrees C due to its low reactivity. The addition of methanol into propane can mitigate the reaction endothermicity and the degree of increase with the added methanol amount. However, it is unexpected that the traditional Zn/ZSM-5 catalyst leads to a serious methanol decomposition, and it enhances with the aromatization temperature. To alleviate this phenomenon, high-silica H-ZSM-5 and low-silica Zn/ZSM-5 were loaded in the upper and the down layers, respectively. By optimizing the Si/Al ratio of H-ZSM-5, Zn content of Zn/ZSM-5, and reaction conditions, the aromatics selectivity in the coaromatization of propane and methanol reaches 55.0% with BTX (benzene, toluene, and xylene) accounting for 91.6% of the aromatics. More interestingly, methanol was not severely decomposed even at 480 degrees C. Mechanistic studies show that methanol is first converted into C-2(=)-C-4(=) on the up-layer-loaded H-ZSM-5 and then transformed into aromatics on the down-layer-loaded Zn/ZSM-5. This suggests that two-step aromatization of methanol and propane mixture and, in particular, of neat methanol should be of choice, as this process not only effectively inhibits methanol decomposition but also is beneficial to the production of aromatics, particularly, of BTX.