Intensification of Catalytic Processes through the Pellet Structuring: Steady-State Properties of a Bifunctional Catalyst Pellet Applied to Generic Chemical Reactions and the Direct Synthesis of DME

Model Analysis of the Role of Kinetics, Adsorption Capacity, and Heat and Mass Transfer Effects in Sorption Enhanced Dimethyl Ether Synthesis

The role of kinetics, adsorption capacity, and heat and mass transfer effects in the sorption enhanced dimethyl ether synthesis (SEDMES) is investigated by means of a 2D+1D model of a single tube of an industrial-scale, externally cooled, multitubular reactor that simulates the reaction/adsorption step of the SEDMES cycle. The effect of the adsorbent/catalyst weight ratio is analyzed, showing that a trade-off between DME productivity and yield originates from the balance of kinetics and adsorption capacity in the reactor tube. The effects of internal diffusion in catalyst particles are shown to have a strong impact on effective reaction rates: significant yield/productivity improvements are obtained when using a mechanical mixture of catalysts with small particle diameters or by rearranging the distribution of the two active phases in hybrid or core@shell pellets. The thermal effects in the reactor, which are increasingly critical upon intensifying the SEDMES process conditions, are also addressed.

Numerical Investigation of Process Enhancement Using a Bifunctional Catalyst in a Dual Fluidized-Bed Reactor

The paper outlines the concept of process intensification and integration, with a particular focus on sorption-enhanced, solid-catalyzed chemical processes. An alternative and attractive solution to a system of parallel fixed-bed apparatuses is evaluated, which utilizes the solids’ circulation in a dual fluidized-bed reactor–regenerator system. This allows for continuous mode operation and greatly simplifies the control procedures. To illustrate some aspects related to the steady-state operation of such a dual system, a simplified mathematical model of two interconnected fluidized beds operating in the bubbling regime was developed. A generic reversible chemical reaction of the overall second-order, catalyzed by bifunctional pellets, integrating catalytic active sites and adsorption sites, was considered as a test case. The model was used to study the effects of the bed hydrodynamics, as well as of the chemical reaction and physical adsorption equilibrium constants. It was shown how the superposition of various chemical, physical and hydrodynamical phenomena affects the performance of the system.

Enhancement of the Direct Synthesis of Dimethyl Ether (DME) from Synthesis Gas by Macro- and Microstructuring of the Catalytic Bed

This work reports on a modelling study of the influence of the distribution of metallic and acidic active centers within a catalytic fixed-bed reactor for the direct synthesis of dimethyl ether (DME), conducted to demonstrate the potential of reactor-level and pellet-level structuring of catalytic active centers in process integration and intensification. To account for the pellet structure, the analysis was performed with the aid of a heterogeneous model considering both interphase and intrapellet mass transport resistances. The study evaluated, in terms of DME and methanol yield and selectivity, the performance of a tubular reactor loaded with a physical mixture of monofunctional catalyst pellets or structured bifunctional catalyst pellets with different arrangements of the catalytic centers. It was confirmed that bifunctional catalysts overperform significantly a physical mixture of monofunctional particles. Moreover, it was shown that the internal structure of a bifunctional catalyst pellet is an important feature that deserves to be exploited deeper, in view of further intensification of the DME synthesis process to be achieved with a better reactor design.