The nature of carbonaceous deposits formed upon mordenite from various feeds

Using a mordenite catalyst, BP Chemicals’ SaaBre process is a route to acetic acid using dimethyl ether and CO. An improvement on the Cativa process, it does not require a methyl halide promoter and therefore a hastelloy reactor. It is also a heterogeneous reaction, removing the costly separation processes used with Cativa. As with the methanol to gasoline process, the carbonaceous deposits play a large part in the chemistry of the system and changes can give large effects on deactivation times and selectivity. This study investigates the carbonaceous deposits found upon mordenite under methanol, dimethyl carbonate and a range of mixed feeds to mimic the effects of products and byproducts in the methanol stream. Studies have shown that the transition temperature between methanol dehydration to DME, and MTG chemistry occurs between 255°C-260°C with a 50 % methanol feed and decreases by around 20°C with a 90 % methanol feed. This is associated with the growth of the hydrocarbon pool, an alkyl aromatic system within the pores of the zeolite which is the active catalyst for the MTG process. Investigation of the formation of these species has used 13C and 17O enriched methanol feeds to allow determination of the species present by MASNMR whilst looking at several variables. Studies of framework nuclei, 27Al and 29Si, have also been performed to give greater insight into how the chemical environment of the zeolite changes as the coke is deposited in the zeolite. Time-resolved in situ diffraction studies have probed the reaction of methanol and the effect it has on the unit cell of the framework. These studies have shown an anisotropic expansion of the unit cell associated with the growth of alkyl aromatic compounds, and also an unexplained contraction within the first few minutes of reaction. EPR studies have looked to elucidate the nature of radical species in the coked mordenite samples as a function of time and have produced spectra with sufficient hyperfine coupling to propose tentative identification with the aid of the B3LYP level of DFT simulations. The differences in the nature of coke between H-MOR and H-Ga-MOR were also investigated with the aid of MAS-NMR spectroscopy. Several feeds including dimethyl carbonate, and mixed feeds of methanol and acetone, acetic acid, acetaldehyde and TFA, have been investigated to see how they affect the carbonaceous deposits. Mechanistic routes have also been deduced with the use of complementary 13C enriched feeds