A kinetic model has been proposed for the synthesis of dimethyl ether in a single reaction step from (H 2 + CO) and (H 2 + CO 2 ), and the kinetic parameters have been calculated for a CuO-ZnO-Al 2 O 3 /γ-Al 2 O 3 bifunctional catalyst. The kinetic model suitably fits the experimental results obtained in an isothermal fixed bed reactor within a wide range of operating conditions: 225-325 °C; 10-40 bar; space time, 1.6-57.0 (g of catalyst) h (mol H 2 ) -1 . The crucial steps for modeling are the synthesis of methanol from (H 2 + CO)s synthesis from (H 2 + CO 2 ) is not importantsmethanol dehydration (very fast), and the water-shift reaction (in equilibrium). The inhibiting effect of water is also taken into account in the synthesis of methanol and the formation of hydrocarbons. The advantage of carrying out methanol dehydration in situ is noteworthy, given that it allows for attaining yields higher than 60% of carbon converted into DME and 5% into methanol, when (H 2 + CO) is fed at 30 bar and 275 °C. At higher temperatures, hydrocarbons (mainly methane) are produced.

A kinetic model of seven lumps has been established which allows the quantification of the product distribution (oxygenates, n-butane, C 2 -C 4 olefins, C 2 -C 4 paraffins (without n-butane), C 5-C 10 fraction, methane) in the transformation of methanol into hydrocarbons at high temperature (400-550 °C) on a HZSM-5 zeolite catalyst (SiO 2 /Al 2 O 3 ) 30) with high acidic strength (>120 kJ (mol of NH 3 ) -1 ) and agglomerated with bentonite and alumina. The kinetic model fits well the experimental data obtained in a fixed bed reactor, from small values of space time in which the formation of hydrocarbons is incipient, to a space time of 2.4 (g of catalyst) h (mol CH 2 ) -1 for a complete conversion of methanol. The rise in temperature increases the yield of C 2 -C 4 olefins, so that the maximum value (∼50%) is obtained at the ceiling temperature for the hydrothermal stability of the HZSM-5 (550 °C) and space times between 0.6 and 1 (g of catalyst) h (mol CH 2 ) -1 .

A kinetic model of lumps has been established for n-butane cracking over HZSM-5 zeolite catalyst (SiO2/Al2O3 = 30) in the 400−550 °C range, based on the results obtained in a fixed bed reactor (space time, up to 2.4 (g of catalyst) h (mol CH2)−1; He/n-butane molar ratio in the feed, up to 6/1; time on stream, 5 h). The model allows quantifying the distribution of the lumps of products (C2−C4 olefins, C2−C4 paraffins, methane, and C5−C10 components) in a wide range of temperatures, partial pressures of hydrocarbons in the reaction medium, and space times. The kinetic model steps for the transformation of n-butane into olefins and of olefins into paraffins and C5−C10 are second order with respect to the reactant, whereas the remaining steps are first order with respect to each reactant. When the target is the production of C2−C4 olefins, the yield is limited to 12%, at 550 °C.

The deactivation by coke of a HZSM-5 zeolite catalyst has been studied in the transformation of methanol into hydrocarbons by cofeeding butane (n-butane). This reaction is of interest as an energy-neutral integrated process that enhances the activity in the cracking reaction and upgrades the paraffins formed as byproducts. The process was carried out in a fixed-bed reactor under the following conditions: temperature, 550 °C; pressure, 1 bar; space time, 2.4 and 4.8 (g of catalyst) h (mol of CH 2 ) À1 ; time on stream, 5 h; methanol/butane molar ratio, up to 16/1. The coke was characterized using several analytical techniques (TGÀTPO, FTIR, Raman, and NMR spectroscopies), and the effects of cofeeding butane on the coke composition and structure were determined. The results in terms of coke content and composition, are explained in terms of the different pathways of methanol and butane transformation.

No abstract