Dehydration of methanol to produce dimethyl ether (DME) was studied at relatively high temperatures (400−600 °C) on biomass-derived phosphorus-containing carbon impregnated with a zirconium salt. Highly thermally stable zirconium phosphate surface groups could be obtained on the final catalyst, which were responsible for the high stability and selectivity to DME of the catalyst at temperatures lower than 400 °C. However, harder operation conditions, closer to those of the industrial process, were evaluated to analyze the changes of the catalyst surface properties with the reaction temperature and the possible causes of deactivation. Thus, high methanol conversion and selectivity to DME were also observed in the temperature range of 400−600 °C, although deactivation was detected. Coke deposition was responsible for a decrease in microporosity and surface concentration of zirconium and phosphorus of the catalyst. Temperature-programmed desorption, 31 P magic angle spinning nuclear magnetic resonance, and X-ray photoelectron spectroscopy results suggest that the Zr−O−P groups from zirconium phosphate species were responsible for the long-term stability of the catalyst and that the C−O−P-type active sites were deactivated very fast. However, coke deposition on Zr− O−P-type active sites caused a slow and irreversible deactivation, while deposited coke on the C−O−P-type active sites was easily eliminated by the oxidative treatment in air. A reaction scheme that accounted for the gas product distribution and the production of coke was proposed. A kinetic model for coke formation as a function of time on stream that successfully represents the experimental results was also propounded, which yielded a value for the activation energy for the production of coke of 124 kJ/mol.

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A Zr-loaded P-containing biomass-derived activated carbon (ACPZr) has been tested for methanol dehydration between 450 and 550 °C. At earlier stages, methanol conversion was complete, and the reaction product was mainly dimethyl ether (DME), although coke, methane, hydrogen and CO were also observed to a lesser extent. The catalyst was slowly deactivated with time-on-stream (TOS), but maintained a high selectivity to DME (>80%), with a higher yield to this product than 20% for more than 24 h at 500 °C. A kinetic model was developed for methanol dehydration reaction, which included the effect of the inhibition of water and the deactivation of the catalyst by coke. The study of stoichiometric rates pointed out that coke could be produced through a formaldehyde intermediate, which might, alternatively, decompose into CO and H2. On the other hand, the presence of 10% water in the feed did not affect the rate of coke formation, but produced a reduction of 50% in the DME yield, suggesting a reversible competitive adsorption of water. A Langmuir–Hinshelwood reaction mechanism was used to develop a kinetic model that considered the deactivation of the catalyst. Activation energy values of 65 and 51 kJ/mol were obtained for DME and methane production in the temperature range from 450 °C to 550 °C. On the other hand, coke formation as a function of time on stream (TOS) was also modelled and used as the input for the deactivation function of the model, which allowed for the successful prediction of the DME, CH4 and CO yields in the whole evaluated TOS interval.

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