B. Smit

Cutting the cost of carbon capture: a case for carbon capture and utilization

L. Joos, J. Huck, V. Van Speybroeck, B. Smit

Faraday Discussions

192, 391-414

2016

A1

Abstract

A significant part of the cost for Carbon Capture and Storage (CCS) is related to the compression of the captured CO2 to its supercritical state, at 150 bar and typically 99% purity. These stringent conditions may however not always be necessary for specific cases of Carbon Capture and Utilization (CCU). In this manuscript, we investigate how much the parasitic energy of an adsorbent-based carbon capture process may be lowered by utilizing CO2 at 1 bar and adapting the final purity requirement for CO2 from 99% to 70% or 50%. We compare different CO2 sources: the flue gases of coal-fired or natural gas-fired power plants and ambient air. We evaluate the carbon capture performance of over 60 nanoporous materials and determine the influence of the initial and final purity on the parasitic energy of the carbon capture process. Moreover, we demonstrate the underlying principles of the parasitic energy minimization in more detail using the commercially available NaX zeolite. Finally, the calculated utilization cost of CO2 is compared with reported prices for CO2 and published costs for CCS.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/C6FD00031B

Carbon Capture Turned Upside Down: High-Temperature Adsorption & Low-Temperature Desorption (HALD)

L. Joos, K. Lejaeghere, J. Huck, V. Van Speybroeck, B. Smit

Energy & Environmental Science

8, 2480-2491

2015

A1

Abstract

Carbon Capture & Sequestration (CCS) could reduce CO2 emissions from large fossil-fuel power plants in the short term, but the high energy penalty of the process hinders its industrial deployment. Moreover, the utility of nanoporous materials, known to be selective for the CO2/N2 separation, is drastically reduced due to the competitive adsorption with H2O. Taking advantage of the power plant's waste heat to perform CCS while at the same time surmounting the negative effect of H2O is therefore an attractive idea. We propose an upside-down approach for CCS in nanoporous materials, High-temperature Adsorption & Low-temperature Desorption (HALD), that exploits the temperature-dependent competitive adsorption of CO2 and H2O. First, we provide a theoretical background for this entropy-driven behavior and demonstrate under what conditions competitive adsorption can be in favor of CO2 at high temperature and in favor of H2O at low temperature. Then, molecular simulations in all-silica MFI provide a proof of concept. The International Zeolite Association database is subsequently screened for potential candidates and finally, the most promising materials are selected using a post-Pareto search algorithm. The proposed post-Pareto approach is able to select the material that shows an optimal combination of multiple criteria, such as CO2/H2O selectivity, CO2/N2 selectivity, CO2 uptake and H2O uptake. As a conclusion, this work provides new perspectives to reduce the energy requirement for CCS and to overcome the competitive adsorption of H2O.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/C5EE01690H

Molecular Simulation Study of the Competitive Adsorption of H2O and CO2 in Zeolite 13X

L. Joos, J.A. Swisher, B. Smit, A. Bruder

Langmuir

29 (48), 14743-14747

2013

A1

Abstract

Surfactants exhibit maxima in their critical micelle concentrations upon application of hydrostatic pressure, which is attributable to changes in their volumes of micellization from positive to negative values with increasing pressure. We present a direct molecular simulation analysis of the volumes of micellization of an anionic, cationic, and nonionic surfactant in aqueous solution at pressures up to 2500 bar. Excellent agreement with experiment is observed. A Kirkwood-Buff theory analysis based on proximal solvent distributions permits the breakdown of the volumes of micellization into constituent surfactant headgroup and tailgroup contributions. Although the micellization volume crossover is analogous to the transfer of an alkane from water to its pure liquid, significant differences are observed, including lower compressibilities of micelle volumes compared to that of the alkane liquid, negative partial compressibilites for anionic sulfated surfactant monomers, and large nonionic ethoxy headgroup contributions to the micellization volume.

DOI

http://dx.doi.org/10.1021/la402798f

On the thermodynamics of framework breathing: A free energy model for gas adsorption in MIL-53

A. Ghysels, L. Vanduyfhuys, M. Vandichel, M. Waroquier, V. Van Speybroeck, B. Smit

Journal of Physical Chemistry C

117, 11540-11554

2013

A1

Abstract

When adsorbing guest molecules, the porous metal-organic framework MIL-53(Cr) may vary its cell parameters drastically while retaining its crystallinity. A first approach to the thermodynamic analysis of this 'framework breathing' consists of comparing the osmotic potential in two distinct shapes only (large-pore and narrow-pore). In this paper, we propose a generic parametrized free energy model including three contributions: host free energy, guest-guest interactions, and host-guest interaction. Free energy landscapes may now be constructed scanning all shapes and any adsorbed amount of guest molecules. This allows to determine which shapes are the most stable states for arbitrary combinations of experimental control parameters, such as the adsorbing gas chemical potential, the external pressure, and the temperature. The new model correctly reproduces the structural transitions along the CO₂ and CH₄ isotherms. Moreover, our model successfully explains the adsorption versus desorption hysteresis as a consequence of the creation, stabilization, destabilization, and disappearance of a second free energy minimum under the assumptions of a first order phase transition and collective behavior. Our general thermodynamic description allows to decouple the gas chemical potential μ and mechanical pressure P as two independent thermodynamic variables and predict the complete (μ,P) phase diagram for CO₂ adsorption in MIL-53(Cr). The free energy model proposed here is an important step towards a general thermodynamics description of flexible metal-organic frameworks.