France, Liam John
Characterisation of carbonaceous species formed over mordenite.
PhD thesis, University of Glasgow.
Full text available as:
The halide free carbonylation of methanol is a reaction of industrial relevance. A process based upon the use of a proton-form mordenite catalyst, which cokes during reaction, is currently under investigation. This study explores the carbonaceous deposits formed upon mordenite from various methanol and dimethylcarbonate containing feedstreams. Dimethylcarbonate was investigated because it generates dimethylether upon decomposition.
13C CP MAS NMR spectroscopic studies demonstrate that the carbonaceous deposits formed over mordenite from methanol containing feedstreams contained very similar compounds (poly-methylated aromatics and polycyclic species). A combination of elemental analysis and 13C CP MAS NMR spectroscopy demonstrated that under a methanol-only feedstream for 5 minutes at 300oC, samples contained approximately 5.8 wt% carbon (which was around 45% of the 12.3 wt% observed at 300 minutes) and a distribution of species (methylated aromatics and polycyclic compounds) similar to that observed at longer times on stream (60, 180, 300 and 420 minutes). This is in contrast to the observations made after 2 minutes on stream where 3.3 wt% carbon and a relatively small amount of aromatic species were deposited. The species formed from a methanol/CO/H2 feedstream were found to be similar.
Similar species were evident in coked samples generated from both dimethylcarbonate and dimethylcarbonate/CO/H2. However the carbon content for samples generated with dimethylcarbonate-only was found to be lower (9.5 wt%) for samples generated at 250oC for 300 minutes compared to those generated with methanol-only under equivalent conditions. The sample coked at 300oC displayed similar carbon contents, whereas the coked mordenite sample generated at 500oC displayed an increase in the carbon content (18.3 wt%) compared to (17.6 wt%) samples generated with methanol-only. Although similar carbon contents were observed for syn-gas containing feedstreams, the 13C CP MAS NMR studies evidenced acetic acid for samples generated at 300oC for 300 minutes with a dimethylcarbonate/CO/H2 feedstream, whereas this was not observed employing a methanol/CO/H2 feedstream at equivalent conditions. Samples generated at 250oC exhibited similar species (methylated aromatics) regardless of the presence of syn-gas. This was also true for samples generated at 500oC which exhibited polycyclic species. The sample generated at 150oC exhibited only adsorbed methanol under methanol/CO/H2, whereas under a dimethylcarbonate feedstream species indicative of methanol, dimethylether, dimethylcarbonate and zeolite bound methoxy groups were observed.
Actions (login required)