Structural changes of synthetic paulingite (Na,H-ECR-18) upon dehydration and CO2 adsorption

Funding: EPSRCThe structure of dehydrated calcined ECR-18, synthetic paulingite, topology type PAU, unit cell composition Na132H28Si512Al160O1344, has been determined by Rietveld refinement against synchrotron X-ray powder diffraction data. Upon dehydration the symmetry of Na,H-ECR-18 changes from Im3m to I 43m, with a corresponding decrease of cubic unit cell a parameter from 34.89412(1) A to 33.3488(3) A. This occurs as the framework distorts to afford closer coordination of Na+ cations by framework O atoms in 8-ring window sites of the seven cage types present. Na+ cations in 8R sites block the access of N2 molecules to the internal pore space at 77 K but CO2 adsorption at 308 K is observed, and is postulated to occur via a 'trapdoor' mechanism. In situ PXRD during CO2 adsorption at pressures up to 10 bar show reversible broadening of diffraction peaks that is attributed to local crystallographic strain.Publisher PDFPeer reviewe

Techniques for direct experimental evaluation of structure-transport relationships in disordered porous solids

Determining structure-transport relationships is critical to optimising the activity and selectivity performance of porous pellets acting as heterogeneous catalysts for diffusion-limited reactions. For amorphous porous systems determining the impact of particular aspects of the void space on mass transport often requires complex characterization and modelling steps to deconvolve the specific influence of the feature in question. These characterization and modelling steps often have limited accuracy and precision. It is the purpose of this work to present a case-study demonstrating the use of a more direct experimental evaluation of the impact of pore network features on mass transport. The case study evaluated the efficacy of the macropores of a bidisperse porous foam structure on improving mass transport over a purely mesoporous system. The method presented involved extending the novel integrated gas sorption and mercury porosimetry method to include uptake kinetics. Results for the new method were compared with those obtained by the alternative NMR cryodiffusometry technique, and found to lead to similar conclusions. It was found that the experimentally-determined degree of influence of the foam macropores was in line with expectations from a simple resistance model for a disconnected macropore network

NMR techniques and prediction models for the analysis of the species formed in CO2 capture processes with aminebased sorbents: a critical review

This is the author accepted manuscript. The final version is available from the American Chemical Society via the DOI in this recordCarbon dioxide (CO2) capture by aqueous alkanolamines is among the most mature and efficient technologies to curb the continuous emission of the greenhouse gas CO2 into the atmosphere. However, the widespread use of this technology is limited, mostly due to the energy penalty during CO2 desorption and amine regeneration. A key point to develop more efficient sorbents is the knowledge of the species formed in solution after the reaction of CO2 with the amine. Qualitative and quantitative analysis of ions in solutions can help to understand chemical reaction processes and probe chemical reaction mechanisms to discern important information including the CO2 absorption and desorption rates, the CO2 capture efficiency, the cyclic capacity, and the energy demand for regeneration, which are essential for the commercialization of this technology. Although many researchers have reported the speciation of primary, secondary, and tertiary amines when reacting with CO2 as determined by nuclear magnetic resonance (NMR) and other methods, a few discussed the state-of-the-art research in this area. This paper aims to review and compare NMR spectroscopy, pH + NMR analysis, and model prediction techniques for determining the speciation of CO2 loaded amine solution, to get information for better understanding the fundamental principles and up-to-date progress applied in various amine–CO2 systems. This review illustrates the applications of these three techniques to observe the morphology of CO2 loaded amine solutions including single amines, blended aqueous amines, and nonaqueous amine solutions. Furthermore, the operating principles are described in detail, and the strengths and weaknesses are discussed carefully. Of the three approaches, NMR spectrometry is proven to be more efficient in determining the proportion of ions in simple amine–CO2–H2O systems; however, for more complex systems, the process efficiency varies depending on the situation encountered. In sum, these three analytical techniques can help to design efficient amine materials with high CO2 separation performance and low energy cost.ICCOM institute of National Research Council of Italy (CNR)National Natural Science Foundation of ChinaHunan Province Science and Technology PlanJoint Fund of Basic and Applied Basic Research Fund of Guangdong ProvinceExcellent Youth Foundation of Hunan Province in ChinaResearch Foundation of Education Bureau of Hunan ProvinceResearch Start-up Foundation of Xiangtan UniversityHunan Key Laboratory of Environment Friendly Chemical Process Integration TechnologyNational Department of Education Engineering Research Centre for Chemical Process Simulation and OptimizationNational & Local United Engineering Research Centre for Chemical Process Simulation and Intensificatio

Structural changes of synthetic paulingite (Na,H-ECR-18) upon dehydration and CO₂ adsorption

The structure of dehydrated calcined ECR-18, synthetic paulingite, topology type PAU, unit cell composition Na132H28Si512Al160O1344, has been determined by Rietveld refinement against synchrotron X-ray powder diffraction data. Upon dehydration the symmetry of Na,H-ECR-18 changes from Im3m to I 43m, with a corresponding decrease of cubic unit cell a parameter from 34.89412(1) A to 33.3488(3) A. This occurs as the framework distorts to afford closer coordination of Na+ cations by framework O atoms in 8-ring window sites of the seven cage types present. Na+ cations in 8R sites block the access of N2 molecules to the internal pore space at 77 K but CO2 adsorption at 308 K is observed, and is postulated to occur via a 'trapdoor' mechanism. In situ PXRD during CO2 adsorption at pressures up to 10 bar show reversible broadening of diffraction peaks that is attributed to local crystallographic strain.</p