A theoretical comparison of multifunctional catalyst for sorption-enhanced reforming process

Abstract

This work presents the first side-by-side comparison of the two leading multifunctional catalyst designs reported in the literature today for sorption-enhance reforming processes. Twodimensional unsteady-state models were developed to compare the performance of a core-shell multifunctional catalyst, consisting of a calcium-based sorbent core enclosed in a porous shell of methane steam reforming or water-gas shift catalyst, against an equivalent case of a uniformdistributed multifunctional design in which catalyst and sorbent materials are uniformly distributed within the particle. Additionally, these two multifunctional catalyst designs were compared against the conventional two-pellet approach, where the capture and catalytic properties are distinguished into separate pellets. Both multifunctional catalyst designs (i.e. coreshell and uniform-distributed) had greater adsorbent utilization and higher H 2 outlet concentration up to breakthrough time than the conventional two pellet design. The uniformdistributed multifunctional catalyst design had greater adsorbent utilization up to breakthrough conditions as compared to the core-shell design. This behavior may be attributed to the fact that for the uniform-distributed multifunctional, the active catalyst is constantly producing CO 2 next to an adsorbent active site. For the core-shell multifunctional catalyst design, decreasing catalystshell thickness resulted in performance approaching the uniform-distributed case. For the case of exothermic water-gas shift reaction coupled with CO 2 chemisorption, the core-shell design mitigated local bed hot-spot magnitudes by ~40 K.

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

“…Under the assumption that production of component C is the objective, the yield of product C with respect to reactant A, Y CA , is employed to assess the pellet performance. Following [7], yield is defined as the ratio between the actual production rate of C and the consumption rate of A in the absence of internal and external transport resistances: Figure 5 reports the yield, Y CA , as a function of the pellet radius R p , calculated using Equation (6). Figure 5a shows the values of Y CA calculated from the solution presented in Figure 3.…”

“…However, the concept of structuring the functionalities at the pellet level has not been entirely examined yet. Integration of the catalytic and adsorptive functionalities has received recently significant attention [2,6]. Evaluation of the performance of bifunctional pellets integrating catalytic and adsorptive functions applied to the Claus process [2], water-gas shift reaction [2,6] and methane steam reforming [6] has revealed the great influence of the spatial arrangement of different functionalities within the pellet, with non-uniform distributions being very often superior over the uniform.…”

“…Integration of the catalytic and adsorptive functionalities has received recently significant attention [2,6]. Evaluation of the performance of bifunctional pellets integrating catalytic and adsorptive functions applied to the Claus process [2], water-gas shift reaction [2,6] and methane steam reforming [6] has revealed the great influence of the spatial arrangement of different functionalities within the pellet, with non-uniform distributions being very often superior over the uniform. The concept of optimal distribution of a single catalytic activity within the pellet was investigated comprehensively in the past [7], but the number of reports dealing with the influence of the spatial distribution of two or more types of catalytic active sites within the pellet on its performance is very limited, even when considering generic systems of chemical reactions [1].…”

Alkali Metal CO2 Sorbents and the Resulting Metal Carbonates: Potential for Process Intensification of Sorption-Enhanced Steam Reforming

“…Theoretical studies conclude that 98 having catalyst and chemisorption sites closer will improve mass transfer as well as, potentially maintain a relatively higher CO2 partial pressure for chemisorption. 18 In 100 principle, CO2 molecules would have shorter distance to travel to chemisorption sites at 101 or beneath the surface of the sorbent, resulting in faster reaction kinetics and lower residence times in the reactor. 19 Alkali metal ceramics, which in the context of this review refers to binary-metal oxides composed of at least a metal belonging to the alkali metal group of chemical elements, have been widely researched as alternative sorbents to CaO, due to their ability to trap CO2 as alkali metal carbonates under a wide range of temperatures.…”

Adsorption with chemical reaction in porous catalyst pellets under alternate concentration fields. Uniform temperature case

“…multifunctional, catalyst pellets the presence of the adsorbent is intentional and is resulting from the production technology and their application (Dietrich et al, 2005;Grünewald and cpe.czasopisma.pan.pl; degruyter.com/view/j/cpe Agar, 2004;Lugo and Wilhite, 2016). Therefore taking into account the sorption of reagents in the dynamics of such objects is fully justified.…”