The influence of reaction conditions in the transformation of methanol into gasoline (temperature, time on stream, and contact time) on the deposition and nature of coke (composition, H/C ratio) and on its location in the porous structure of a H-ZSM5 zeolite-based catalyst has been studied in an isothermal fixed-bed integral reactor. The distribution of the coke within the porous structure of the catalyst is similar to that proposed for other reactions on H-ZSM5 zeolites, and the highly hydrogenated character of coke and its instability is noteworthy. Coke deposition has been related to catalyst acidic site deterioration and to a kinetic model for catalyst deactivation in an integral reactor.

The effect on combustion in air of the nature of the coke deposited in HZSM5 zeolites used in the MTG process has been studied. This coke is highly hydrogenated and unstable, and its H/C ratio decreases during combustion or when a previous thermal treatment is carried out. Coke H/C ratio greatly affects its reactivity during combustion; consequently, a severe thermal equilibration treatment is recommended for reproducibility of results. Combustion kinetics of equilibrated coke, when it is released from the catalyst, has been proven to be similar to that of the coke deposited on other catalysts for several processes. Lower coke reactivity for aging and combustion, on being deposited within the HZSM5 zeolite, must be attributed to air−coke contact restrictions due to the location of the coke, which partially impedes the flow of air into the crystals.

From experimental results obtained in a wide range of operating conditions (temperature and contact time) in an isothermal fixed-bed integral reactor, the usefulness of the model of Schipper and Krambeck (Chem. Eng. Sci. 1986, 41, 1013−1019) for simulating the operation has been proven in the 300−375 °C range. The validity of a deactivation kinetic model dependent on the composition of the three lumps for the MTG process (oxygenates, light olefins, and the rest of the products) has been proven, for a wide interval of compositions of the lumps. These compositions correspond to different states of catalyst deactivation. The use of this model in the simulation of the integral reactor avoids noticeable errors inherent to the nonconsideration of the effect of composition on the deactivation.

A study has been made of the activity recovery of H-ZSM5 zeolite based catalysts, which have been used in reaction−regeneration cycles in the transformation of methanol into gasoline. Catalyst stability is sensitive to catalyst calcination conditions (temperature and time) and to zeolite Si/Al ratio. From experiments carried out on automated reaction−regeneration equipment provided with an isothermal fixed-bed reactor, optimum catalyst equilibration conditions have been determined, in order to minimize the irreversible deactivation in the regeneration step. The effect of this step on the catalyst acid structure has been studied.

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