No abstract

No abstract

Understanding the role of zeolite topology in defining its catalytic performance is of prime importance for the development of catalytic processes. Herein, a first-principles-based microkinetic study of 1-butanol dehydration is used to illustrate the effect of different zeolites (i.e., H-FAU, H-ZSM-5, H-ZSM-22, and H-FER) on the dehydration activity and product selectivity. Under identical reaction conditions, microkinetic simulations show significant variation in dehydration rates and butene/ether selectivity profiles within the different zeolites. H-ZSM-5 has the highest catalytic activity, whereas H-FAU and H-FER exhibit a higher butene selectivity. In the large pore H-FAU, the weaker dispersive stabilization of the dimer makes the butene formation by monomolecular direct dehydration via a concerted anti elimination compete with di-n-butyl ether formation. In H-FER, steric constraints due to partial confinement of the protonated di-n-butyl ether in the 8-MR channel decrease its stability, favoring its further decomposition to butene via a concerted syn elimination of butanol. On the other hand, the higher ether selectivity in H-ZSM-5 and H-ZSM-22 is rationalized on the basis of a higher stability for adsorbed ether and a higher activation barrier for ether decomposition. In addition to the effect of the zeolite framework, this study further highlights the pivotal role of the reaction conditions in determining the most abundant reaction intermediate, dominant reaction paths, and underlying reaction mechanisms. In general, for all four zeolites, an increase in reaction temperature and a decrease in butanol feed partial pressure favors direct dehydration of butanol to butene (via butanol monomer). However, a decrease in reaction temperature and increase in butanol feed partial pressure favors dimer-mediated dibutyl ether formation. An increase in conversion favors direct dehydration and dibutyl ether decomposition to butene.

The storage capacity of an activated carbon bed is studied using a 2D transport model with constant inlet flow conditions. The predicted filling times and variation in bed pressure and temperature are in good agreement with experimental observations obtained using a 1.82 L prototype ANG storage cylinder. Storage efficiencies based on the maximum achievable V/V (volume of gas/volume of container) and filling times are used to quantify the performance of the charging process. For the high permeability beds used in the experiments, storage efficiencies are controlled by the rate of heat removal. Filling times, defined as the time at which the bed pressure reaches 3.5 MPa, range from 120 to 3.4 min for inlet flow rates of 1.0 L min À1 and 30.0 L min À1 , respectively. The corresponding storage efficiencies, η s , vary from 90% to 76%, respectively. Simulations with L/D ratios ranging from 0.35 to 7.8 indicate that the storage efficiencies can be improved with an increase in the L/D ratios and/or with water cooled convection. Thus for an inlet flow rate of 30.0 L min À1 , an η s value of 90% can be obtained with water cooling for an L/D ratio of 7.8 and a filling time of a few minutes. In the absence of water cooling the η s value reduces to 83% at the same L/D ratio. Our study suggests that with an appropriate choice of cylinder dimensions, solutions based on convective cooling during adsorptive storage are possible with some compromise in the storage capacity.

First principles microkinetic modelling shows that, unlike in H-ZSM-5 and H-ZSM-22, trans-2-butene formation in H-FER occurs via direct dehydration of 1-butanol.