This article explores the use of mechanical mixtures of a methanol synthesis catalyst (CuO/ZnO/Al 2 O 3) and acid catalysts (-Al 2 O 3) for enabling the one-step formation of dimethyl-ether from syngas. The study involved the determination of the optimal catalytic system composition and operating conditions in terms of reactant conversion and dimethylether yield. The catalysts mixture that exhibited the best performance consisted of 92.5% wt. of CuO/ZnO/Al 2 O 3 (7.5% wt. of -Al 2 O 3), when operated with an excess of H 2 (H 2 /CO > 1.5) and a small amount of CO 2 (4-6%) in the feed. The influence of temperature (250-270°C) was less marked, due to the influence of the equilibrium. The final purpose of the study of these properties is to develop one of the first kinetic models for the use of mechanical mixtures of commercial catalysts for this reaction. The experimental data were used to fit and validate a kinetic model based on four reactions: synthesis of methanol from CO, CO 2 , water gas shift reaction and methanol dehydration. At the studied reaction conditions, synthesis of methanol is kinetically relevant whereas water gas shift reaction and methanol dehydration are close to equilibrium. The inhibition caused by water was also accounted for in the kinetic model.

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The scope of this work is to explore the viability of the direct synthesis of dimethyl ether (DME) over bifunctional catalysts, such as mixtures of CuO/ZnO/Al2O3 and -Al2O3 at industrial scale. To accomplish this purpose, the process is simulated using a phenomenological mathematical model considering momentum, mass and energy balances, applied to both the catalyst particles and reactor bed, which is solved in 2D axi-symmetric coordinates. This constitutes a step beyond most of the available studies for the modelling of the DME synthesis reaction, based on simple 1D isothermal models.The use of this detailed model revealed the importance of intraparticle mass and heat transfer, with effectiveness factors within the range 0.5-1.1. At the reactor scale, radial phenomena were found to be relevant. A design-sensitivity analysis of mass flux, catalyst fraction, pressure, feed temperature, cooling potential and tube diameter on the reactor performance was carried out. An optimized reactor design that provides 80% CO conversion operating at inlet temperature and pressure 245°C and 40 bar, corresponds to 0.02 m diameter, 8.50 m length and 3600 h -1 gas-hourly space velocity with a yield of dimethyl ether of 0.53.

Direct synthesis of dimethyl ether from syngas over mixed catalysts constitutes a novel route aimed to replace the traditional two-step process. Many previous studies about this onestep process showed that catalyst deactivation is unavoidable. The present study wants to characterize the deactivation of CuO/ZnO/Al2O3 and -Al2O3 mechanical mixtures, and develop a deactivation model for predicting catalyst performance in presence of deactivation.It was demonstrated that water adsorbs over the -Al2O3 surface, blocking its active sites and causing a sharp conversion drop (mainly observed during the first hours on stream). This effect was reversible and could be avoided by increasing temperature (270°C or above). The other deactivation mechanism was the deposition of carbonaceous species over the catalyst surface. A deactivation model was proposed and fitted to the experimental data.

A systematic comparison of the use of trioxane and depolymerized paraformaldehyde as formaldehyde precursors for the acetalization of methanol to dimethoxymethane was performed, using the acidic ion exchange resin, Amberlyst 15, as catalyst. Experiments were carried out under isothermal conditions in batch and continuous fixed‐bed reactors. The influence of the main operating parameters, temperature (80–120 °C), space time (2.7–6.2 kg h m−3), and feed concentration (12–22 wt% of trioxane/formaldehyde, 2.5 wt% of water on methanol) on reaction rate and product selectivity were evaluated. When using trioxane as reactant, dimethoxymethane is the main reaction product, with more than 90% selectivity. The catalyst was found to be stable during all the experiments (more than 30 h on stream). However, water caused a reversible inhibitory effect on reaction rate, which can be accounted for by using a competitive adsorption model. A mechanistic kinetic model was proposed and validated using the experimental results. When trioxane is used as reactant, its decomposition to formaldehyde was found to be the rate‐limiting step of the reaction mechanism (activation energy 73.1 kJ mol−1). This was confirmed with additional experiments, in which trioxane was replaced by depolymerized formaldehyde. In this case, reaction rate considerably increased. © 2021 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.