Alaitz Atutxa

Regeneration of a catalyst based on a SAPO-34 used in the transformation of methanol into olefins

The regeneration by coke combustion of a catalyst based on a SAPO-34 used in the transformation of methanol into olefins (ethene and propene) has been studied. It has been observed that coke combustion kinetics are strongly dependent on the nature of the coke (H/C ratio), which in turn is a consequence of the reaction conditions (especially of the water content in the feed) and of the ageing level of the coke prior to its combustion. A severe ageing treatment is needed in order for combustion kinetics to be reproducible. Combustion is delayed due to the fact that coke is not an inert material but is bound to the acid sites. © 1999 Society of Chemical Industry

Development of Alternative Catalysts Based on HZSM-5 Zeolite for the BTO Process

The catalytic behaviour of a commercial HZSM-5 zeolite (Si/Al=30) for the selective transformation of bio-ethanol into olefins (BTO process) has been improved by two alternative methods: a) treatment with 0.2M alkali solution for a short time; and b) impregnation with Ni. By means of experimentation in an isothermal fixed bed reactor connected on-line to a GC for the analysis of the reaction products, it has been proven that moderate alkali treatment (10 min) slightly modifies the superficial structure and acidity of the HZSM-5 zeolite, which provokes a significant increase in the concentration of C2-C4 olefins, whereas deactivation rate and hydrothermal stability are similar. Moreover, 1 wt% nickel content in the catalyst is the optimum in order to obtain the better compromise concerning hydrothermal stability of the catalyst, coke deactivation, total yield of olefins and selectivity to C3-C4 olefins in the 400-500 °C range. In fact, the average production rate of C3-C4 olefins is twice as high as that of the parent zeolite in 8 h time on-stream experiments at 450 °C and 75wt% water content in the feed. Both methods are highly interesting because of the simplicity and reproducibility for obtaining economic and selective catalysts for the BTO process at moderate temperatures (catalysts modified by alkali treatment) and high temperatures (nickel based catalysts).

Study of Complex Reactions under Rapid Deactivation -- Improvements in the Reaction Equipment and in the Methodology for Kinetic Calculation

The technological development of catalytic processes under rapid deactivation requires the rigorous calculation of the deactivation kinetic equation in order to be useful in the simulation and optimization of industrial processes. Accordingly, suitable equipment for reaction and product analysis and a rigorous methodology for kinetic data analysis are required. These aspects are approached in this paper using the transformation of methanol into olefins on a SAPO-18 as the model reaction. In this reaction, deactivation is rapid and there is also an initiation period depending on process conditions. The correct use of gas chromatography allows for improving the collection of experimental data of composition with time-on-stream, given that, on the one hand, it minimizes the time required for analysis (4 min), and on the other, a better homogenization of the reaction product sample is achieved, which allows for a more accurate determination of the composition corresponding to a given time-on-stream. Furthermore, the rigorous kinetic modelling of deactivation requires a data analysis methodology that considers the past history of the catalyst and an activity to be defined based on a rigorous physical meaning. Accordingly, the concept of the integrated kinetic model has been used in this paper, whose basis is the calculation of kinetic parameters by simultaneously solving the zero time-on-stream kinetic model and the kinetic equation for deactivation.

Kinetic Study of the Simultaneous Cracking of Paraffins and Methanol on HZSM-5 Zeolite Catalysts

A study has been carried out on the effect of acid catalyst properties and operating conditions (methanol/n-butane ratio in the feed, temperature, space time, time on stream) on the yield of light olefins (C2-C4) in the simultaneous cracking of n-butane and methanol. The operation has been carried out in an isothermal fixed bed reactor in the 400-575 °C range, using catalysts prepared based on HZSM-5 zeolites (with different Si/Al ratio), HY, Ni/HZSM-5 and SAPO-18. The results are evidence of a synergism between the transformation reactions of both reactants, whose consequence is an increase in the yield of olefins that correspond to the transformation of methanol and the cracking of n-butane. Furthermore, catalyst deactivation by coke is significantly attenuated compared to the corresponding transformation of methanol. Based on the effect of operating conditions on product distribution, a kinetic model is proposed by combining the schemes corresponding to the transformation of individual components.