(544ef) Equilibrium Analysis of Methylbenzene Intermediates for a Methanol-to-Olefins Process

Methanol-to-olefin (MTO) and methanol-to-propylene (MTP) process, has attracted great attention due to its importance both industrially and academically. But up to date, the only perspective which can be widely accepted is that the methylbenzenes intermediates play a central role in the chain growth process and the formation of olefins on ZSM-5 at steady state.1-4 The essence of HP has not been clearly identified yet, which has become one of the most important topics in zeolite catalysis.5-8 Considering the fast conversion of methanol, thermodynamics is thought to play the key role in resolving reactions among olefins and HP at higher conversion, and analysis at almost 100% of methanol conversion is quite necessary.

We carried out the MTO reaction over ZSM-5 in a fixed bed quartz reactor, and methanol was carried out with nitrogen. The products were analyzed with a chromatograph from Agilent Technologies. FID detectors were used to get the concentration of the higher olefins for its higher sensitivity for hydrocarbons.

Some important reaction in this system, such as cracking, isomerization and methylation, were reviewed. We calculated ΔG of some typical reactions, showed in Figure 1. The energy change of cracking and isomerization is obviously higher than methylation and chain growth, indicating that the whole methanol-to-olefins process is controlled by cracking and isomerization. However, the isomerization is often limited by steric factors. Therefore in zeolite micropores, cracking becomes the only factor which controls the whole process.