Final Report Summary - COMMOF (COMPOSITE MEMBRANES WITH METAL ORGANIC FRAMEWORKS FOR HIGH EFFICIENCY GAS SEPARATIONS)
The ultimate objective of this project is identification of composite membranes composed of polymers and highly selective metal organic framework (MOF) particles for ultra-high efficiency carbon dioxide/methane (CO2/CH4) separations using atomically detailed computational techniques. Recent studies showed that polymer/MOF composite membranes represent an important avenue for enhancing the performance of polymer membranes significantly for CO2 separations. The fundamental challenge is the choice of appropriate polymer/MOF pairs for specific separation of interest. Even if only one polymer is considered there are hundreds of MOFs that could be potentially used as filler particles in polymers. This project employs state-of-the art atomically detailed simulations for identification of highly selective MOFs and uses the results of simulations to model polymer/MOF composite membranes for CO2/CH4 separations. The aim of computational screening strategy performed in this project is to predict the material properties needed to characterize the performance of composite membranes in advance and greatly accelerate the development of practical polymer/MOF composite membranes.
The work carried out to achieve the project's objectives is as follows: training graduate students for the project, developing computational codes to analyze the MOF database, establishing and screening the MOF database, performing gas adsorption and gas diffusion simulations in selected MOFs, modeling gas permeability of MOFs using the information obtained from the molecular simulations, performing a literature survey to get the permeability of gases in polymers, modeling gas permeability and selectivity of polymer/MOF composite membranes using Maxwell and Bruggeman permeation models, using different permeation models to improve the accuracy of predictions, constructing the selectivity versus permeability curves for many polymer/MOF composite membranes for CO2/CH4 separation and examining the effects of electrostatic interactions on the performance of polymer/MOF composite membranes. We completed all these steps successfully during the project.
A description of the main results achieved at the end of the project is listed below:
-Several MOFs with high CO2 selectivity and permeability were identified in the initial screening of the MOF database. These MOFs are not only good candidates for composite membranes but also highly promising materials as pure MOF membranes. In addition to modeling them as MOF/polymer composite membranes, we also computed the performance of pure MOF membranes in CO2/CH4 separations and showed that these MOF membranes can significantly outperform traditional zeolite and polymer membranes by exhibiting high CO2 selectivity.
-Several theoretical permeation models, including the Maxwell, Bruggeman, Lewis-Nielson, Pal, Felske, and modified Felske models, were tested by comparing their predictions with the available experimental data for gas permeability in MOF/polymer composite membranes and identified the best predicting models. These models can be used to accurately model other nanoporous material-based composite membranes such as zeolite/polymer composites. On the basis of these results, it was shown that Maxwell model gives the best predictions among the models based on the ideal morphology concept and the modified Felske model gives the best predictions among the models considering interfacial morphologies.
-After identifying the model that makes the best predictions, we examined the performance of 80 new MOF/polymer composite membranes composed of 10 different MOFs and 8 different polymers for CO2/CH4 separations. Our results show that selecting the appropriate MOF as filler particles in polymers can enhance the gas permeability of pure polymers significantly and result in composite membranes with extraordinarily high CO2 selectivities relative to those of pure polymer membranes.
- We related the microscopic characteristics such as gas diffusion in the MOF's pores with the macroscopic quantities such as gas permeability through the MOF in order to identify promising materials prior to carrying out extensive calculations. We examined the relationship between the energy barrier to CO2 permeation and the CO2 permeability in various MOFs and concluded that MOFs that exhibit lower energy barriers to CO2 molecules are the ones with higher CO2 permeabilities. These MOFs have larger pore sizes compared to the others, which is an important result to fasten the screening process.
- Separation performance of Zn-Atz-based mixed matrix membranes (MMMs) composed of various polymers and Zn-Atz fillers was investigated. Addition of Zn-Atz into polymers carries many polymers well above the Robeson’s upper bound due to high H2 permeability and high H2 selectivity. Zn-Atz enhances both selectivity and permeability when it is incorporated into polymers suffering from low selectivity.
- Including electrostatic interactions between adsorbate and MOF atoms (EIAM) is crucial in modeling of pure MOF membranes but has less significance for modeling MOF-filled MMMs. The results of this study showed that for rapid screening of MOF/polymer MMMs, the EIAM can be neglected as a reasonable approximation if the MOF volume fraction is less than 0.3. For higher MOF volume fractions, the EIAM should be included in the computational model.
The results obtained from this project were published as 7 papers in peer-reviewed high prestige international journals, 2 more publications were submitted and they are currently under review.
The final result of this project is identification of several highly CO2 selective MOF/polymer composite membranes from thousands of candidates for purification of natural gas which is an industrially, socially and economically significant separation process. The MOF/polymer modeling work introduced in this project will accelerate practical fabrication and development of MOF-based composite membranes that can capture CO2 efficiently. Energy efficient separation of CO2 from natural gas with high performance MOF/polymer membranes will increase the energy content of the natural gas and substantially decrease the cost of the natural gas. Efficient removal of CO2 will also result in reduced CO2 emissions and diminish the climate change problem. Separation of CO2 from natural gas with MOF/polymer membranes with high selectivity will also prevent liquidification problem of CO2 in the pipelines during transport of the natural gas and this will strengthen the energy supply security. Our results identified a composite membrane MMIF/Matrimid that can separate CO2 from CH4 with an extremely high CO2 selectivity of 200000 and CO2 permeability of ~1000 Barrers. These results will be beneficial for researchers working on membranes, MOF, polymers. We also believe that results will attract interest of industry working on natural gas purification and CO2 separation.
The work carried out to achieve the project's objectives is as follows: training graduate students for the project, developing computational codes to analyze the MOF database, establishing and screening the MOF database, performing gas adsorption and gas diffusion simulations in selected MOFs, modeling gas permeability of MOFs using the information obtained from the molecular simulations, performing a literature survey to get the permeability of gases in polymers, modeling gas permeability and selectivity of polymer/MOF composite membranes using Maxwell and Bruggeman permeation models, using different permeation models to improve the accuracy of predictions, constructing the selectivity versus permeability curves for many polymer/MOF composite membranes for CO2/CH4 separation and examining the effects of electrostatic interactions on the performance of polymer/MOF composite membranes. We completed all these steps successfully during the project.
A description of the main results achieved at the end of the project is listed below:
-Several MOFs with high CO2 selectivity and permeability were identified in the initial screening of the MOF database. These MOFs are not only good candidates for composite membranes but also highly promising materials as pure MOF membranes. In addition to modeling them as MOF/polymer composite membranes, we also computed the performance of pure MOF membranes in CO2/CH4 separations and showed that these MOF membranes can significantly outperform traditional zeolite and polymer membranes by exhibiting high CO2 selectivity.
-Several theoretical permeation models, including the Maxwell, Bruggeman, Lewis-Nielson, Pal, Felske, and modified Felske models, were tested by comparing their predictions with the available experimental data for gas permeability in MOF/polymer composite membranes and identified the best predicting models. These models can be used to accurately model other nanoporous material-based composite membranes such as zeolite/polymer composites. On the basis of these results, it was shown that Maxwell model gives the best predictions among the models based on the ideal morphology concept and the modified Felske model gives the best predictions among the models considering interfacial morphologies.
-After identifying the model that makes the best predictions, we examined the performance of 80 new MOF/polymer composite membranes composed of 10 different MOFs and 8 different polymers for CO2/CH4 separations. Our results show that selecting the appropriate MOF as filler particles in polymers can enhance the gas permeability of pure polymers significantly and result in composite membranes with extraordinarily high CO2 selectivities relative to those of pure polymer membranes.
- We related the microscopic characteristics such as gas diffusion in the MOF's pores with the macroscopic quantities such as gas permeability through the MOF in order to identify promising materials prior to carrying out extensive calculations. We examined the relationship between the energy barrier to CO2 permeation and the CO2 permeability in various MOFs and concluded that MOFs that exhibit lower energy barriers to CO2 molecules are the ones with higher CO2 permeabilities. These MOFs have larger pore sizes compared to the others, which is an important result to fasten the screening process.
- Separation performance of Zn-Atz-based mixed matrix membranes (MMMs) composed of various polymers and Zn-Atz fillers was investigated. Addition of Zn-Atz into polymers carries many polymers well above the Robeson’s upper bound due to high H2 permeability and high H2 selectivity. Zn-Atz enhances both selectivity and permeability when it is incorporated into polymers suffering from low selectivity.
- Including electrostatic interactions between adsorbate and MOF atoms (EIAM) is crucial in modeling of pure MOF membranes but has less significance for modeling MOF-filled MMMs. The results of this study showed that for rapid screening of MOF/polymer MMMs, the EIAM can be neglected as a reasonable approximation if the MOF volume fraction is less than 0.3. For higher MOF volume fractions, the EIAM should be included in the computational model.
The results obtained from this project were published as 7 papers in peer-reviewed high prestige international journals, 2 more publications were submitted and they are currently under review.
The final result of this project is identification of several highly CO2 selective MOF/polymer composite membranes from thousands of candidates for purification of natural gas which is an industrially, socially and economically significant separation process. The MOF/polymer modeling work introduced in this project will accelerate practical fabrication and development of MOF-based composite membranes that can capture CO2 efficiently. Energy efficient separation of CO2 from natural gas with high performance MOF/polymer membranes will increase the energy content of the natural gas and substantially decrease the cost of the natural gas. Efficient removal of CO2 will also result in reduced CO2 emissions and diminish the climate change problem. Separation of CO2 from natural gas with MOF/polymer membranes with high selectivity will also prevent liquidification problem of CO2 in the pipelines during transport of the natural gas and this will strengthen the energy supply security. Our results identified a composite membrane MMIF/Matrimid that can separate CO2 from CH4 with an extremely high CO2 selectivity of 200000 and CO2 permeability of ~1000 Barrers. These results will be beneficial for researchers working on membranes, MOF, polymers. We also believe that results will attract interest of industry working on natural gas purification and CO2 separation.