Adsorption Characteristics of Refrigerants for Thermochemical Energy Storage in Metal-Organic Frameworks

The adsorption of fluorocarbons has gained significant importance as its use as refrigerants in energy storage applications. In this context, the adsorption behavior of two low global warming potential refrigerants, R125 fluorocarbon and its hydrocarbon analog, R170, within four nanoporous materials, namely MIL-101, Cu-BTC, ZIF-8, and UiO-66 has been investigated. By analyzing the validity of our models against experimental observations, we ensure the reliability of our molecular simulations. Our analysis encompasses a range of crucial parameters, including adsorption isotherms, enthalpy of adsorption, and energy storage densities, all under varying operating conditions.We find remarkable agreement between computed and observed adsorption isotherms for R125 within MIL-101. However, to obtain similar success for the rest of the adsorbents, we need to take into account a few considerations, such as the presence of inaccessible cages in Cu-BTC, the flexibility of ZIF-8, or the defects in UiO-66. Transitioning to energy storage properties, we investigated various scenarios, including processes with varying adsorption and desorption conditions. Our findings underscore the dominance of MIL-101 in terms of storage densities, with R125 exhibiting superior affinity over R170. Complex mechanisms governed by changes in pressure, temperature, and desorption behavior make for complicated patterns, demanding a case-specific approach. In summary, this study navigates the complex landscape of refrigerant adsorption in diverse nanoporous materials. It highlights the significance of operating conditions, model selection, and refrigerant and adsorbent choices for energy storage applications

Alcohol-Based Adsorption Heat Pumps using Hydrophobic Metal-Organic Frameworks

The building climate industry and its influence on energy consumption have consequences on the environment due to the emission of greenhouse gasses. Improving the efficiency of this sector is essential to reduce the effect on climate change. In recent years, the interest in porous materials in applications such as heat pumps has increased for their promising potential. To assess the performance of adsorption heat pumps and cooling systems, here we discuss a multistep approach based on the processing of adsorption data combined with a thermodynamic model. The process provides properties of interest, such as the coefficient of performance, the working capacity, the specific heat or cooling effect, or the released heat upon adsorption and desorption cycles, and it also has the advantage of identifying the optimal conditions for each adsorbent-fluid pair. To test this method, we select several metal-organic frameworks that differ in topology, chemical composition, and pore size, which we validate with available experiments. Adsorption equilibrium curves were calculated using molecular simulations to describe the adsorption mechanisms of methanol and ethanol as working fluids in the selected adsorbents. Then, using a thermodynamic model we calculate the energetic properties combined with iterative algorithms that simultaneously vary all the required working conditions. We discuss the strong influence of operating temperatures on the performance of heat pump devices. Our findings point to the highly hydrophobic metal azolate framework MAF-6 as a very good candidate for heating and cooling applications for its high working capacity and excellent energy efficiency

Enhancing the water capacity in Zr-based metal-organic framework for heat pump and atmospheric water generator applications

\u3cp\u3eAccording to the European Commission, in 2016 the residential sector represented 25.4% of the final energy consumption. Heating and cooling in EU households account for 69.1% of the total energy consumption. The fraction of 84% for heating and cooling is still generated from fossil fuels, and only 16% is generated from renewable energy. To decrease carbon dioxide emissions of fossil fuel consumption, it is crucial to find alternatives to supply the heating and cooling demand. Alternatives such as adsorption-based heat pumps and desiccant cooling systems are receiving much attention because of their moderate energy consumption. These systems are based on the energetic exchange during the adsorption/desorption of working fluids. In this work, we combined experiments and simulations to evaluate the viability of several zeolites and MOFs with water for cooling systems applications. We combined the study of adsorption mechanisms and the dynamics of water inside the pores of the structures, thereby obtaining an overall understanding of the working pair. We found that the Al content in FAU-topology zeolites is a key factor for an efficient process. We also identify ZJNU-30 metal-organic framework as a suitable candidate for cooling applications because of its outstanding water capacity, cooling capacity, and coefficient of performance.\u3c/p\u3

Understanding and Exploiting Window Effects for Adsorption and Separations of Hydrocarbons

The suitability of zeolites for a certain application strongly depends on their structural features. Among the types of shape selectivity, there is the still quite unexplored “cage or window effect” consisting of an unusual nonmonotonic increase of the Henry coefficient with chain length in cagelike zeolites when the guest hydrocarbon becomes too long to fit comfortably inside the wider part of the cages. This phenomenon has been addressed for alkanes in various zeolites, but a study dealing with alkenes is lacking. Because of both scientific interest and the impact on the petrochemical industry, we aimed at assessing window effects for a variety of alkenes regarding the position and number of the double bond. We used advanced molecular simulation techniques and considered the rigid all-silica channel-like OFF and cagelike ERI, CHA, and ITQ-29 zeolites. Our study reveals results similar to those of alkanes when the double bond is located at the chain extremes. Conversely, less molecular flexibility induced by intermediate positions of the double bond or the presence of more than one bond lead to a weakness of the window effect, except for the ITQ-29 because of its considerably larger cage. These findings result in significant values of this type of selectivity for separations of saturated and unsaturated hydrocarbons with chain lengths commensurate with the zeolite cages

π-Complexation for olefin/paraffin separation using aluminosilicates

International audienc

Enhancing the Water Capacity in Zr-Based Metal–Organic Framework for Heat Pump and Atmospheric Water Generator Applications

According to the European Commission, in 2016 the residential sector represented 25.4% of the final energy consumption. Heating and cooling in EU households account for 69.1% of the total energy consumption. The fraction of 84% for heating and cooling is still generated from fossil fuels, and only 16% is generated from renewable energy. To decrease carbon dioxide emissions of fossil fuel consumption, it is crucial to find alternatives to supply the heating and cooling demand. Alternatives such as adsorption-based heat pumps and desiccant cooling systems are receiving much attention because of their moderate energy consumption. These systems are based on the energetic exchange during the adsorption/desorption of working fluids. In this work, we combined experiments and simulations to evaluate the viability of several zeolites and MOFs with water for cooling systems applications. We combined the study of adsorption mechanisms and the dynamics of water inside the pores of the structures, thereby obtaining an overall understanding of the working pair. We found that the Al content in FAU-topology zeolites is a key factor for an efficient process. We also identify ZJNU-30 metal–organic framework as a suitable candidate for cooling applications because of its outstanding water capacity, cooling capacity, and coefficient of performance.Accepted Author ManuscriptEngineering Thermodynamic