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• Zn species exchange protons of HZSM-5 zeolite decreasing Brønsted acid sites. • P species interact with Al framework causing its dealumination and loss of silanols. • Zn slows down methanol transformation but above all, the deactivation. • Zn has a greater effect on slowing the formation of intermediates and coke species. • Zn increases the propylene-to-ethylene ratio. The benefits of H-ZSM-5 zeolite modification with H 3 PO 4 or ZnCl 2 have been analyzed during the methanol to olefins (MTO) reaction. The catalysts were prepared, characterized and tested using three different reactors: fixed-bed, operando FTIR and UV–vis. The spent catalysts were further characterized for analyzing the nature and location of the species trapped. The results show that the zeolite modified with H 3 PO 4 has suffered a simultaneous dealumination, leading to a decrease of number of acid sites and activity. However, the zeolite modified with ZnCl 2 shows the inclusion of Zn transforming Brønsted into Lewis acid sites, leading to reaction intermediates (hydrocarbon pool species) that decreases the rate of reaction but improves propylene selectivity (+10%), slows downs coke formation (-42%) and expands catalytic lifetime (+80%). The distinct effect of Zn modification, typically associated with the promotion of aromatics, is explained on the grounds of the severe transformation of the strong and Brønsted acid sites. [ABSTRACT FROM AUTHOR]

A kinetic model of eight lumps (methane,ethylene, propylene, C2–3paraffins, butanes, C5+hydrocarbons(aliphatic hydrocarbons of five or more carbon atoms), and aromatics(benzene, toluene, and xylenes, BTX)) has been established for thetransformation of 1-butene over a 1 wt % K modified HZSM-5 zeolite(SiO2/Al2O3= 280) catalyst (of moderateacidity). The kinetic model allows quantifying product distributionat zero time on stream, and particularly propylene production, whichhas an increasing demand in petrochemical industry. The experimentaldata have been obtained in an isothermal fixed-bed reactor in the400–600 °C range and under a wide range of experimentalconditions: space time up to 1.6 (gcatalysth) (molCH2)−1and 1-butene partial pressure between0.375 and 1.35 bar. It has been proven that a simplified kinetic modelof five lumps (ethylene, propylene, butenes, C1–4paraffins and C5+hydrocarbons (aliphatics and aromatics))is also suitable. Both models predict a product distribution thatfits the experimental results in the range of operating conditionsstudied. [ABSTRACT FROM AUTHOR]

The effect operatingconditions have in the selective transformationof 1-butene into propylene has been studied on a catalyst of HZSM-5zeolite (SiO2/Al2O3= 280) modifiedwith 1 wt % K (of moderate acid strength) and agglomerated with bentoniteand alumina. The kinetic runs have been performed in a fixed bed reactorunder the following operating conditions: 400–600 °C;space time, up to 1.6 (gcatalyst·h) (molC)−1; and butene partial pressure, 0.375–1.35bar. The kinetic performance has been evaluated at zero time and throughouttime on stream in order to find the suitable conditions to maximizepropylene yield and selectivity and minimize deactivation by coke.A region of optimum propylene yield (>30%) and propylene selectivity(>50%) has been established for temperatures above 500 °Candspace time values depending on the reaction temperature. Furthermore,cofeeding 50% of inert gas is highly recommended in order to attenuatecoke deactivation. [ABSTRACT FROM AUTHOR]