Hui Xu

Chemistry and Biochemistry

Faculty Advisor: Casey O'Brien

Operando Surface Enhanced Raman Spectroscopy (SERS) Platform for Studying the Structure and Dynamics of Amine-based Membranes in Complex Environments

Separation and removal of CO2 from mixed gas streams are important in many industrial processes, including natural gas and hydrogen purification, as well as reducing greenhouse gas emissions. [1-2]  Various strategies and technologies have been developed and used for CO2 capture in the past several decades, such as solvent adsorption [3-9], solid adsorption [3-8], and membrane-based separation.[3-8, 10] Among the various technologies, membrane separation, especially polymer-based facilitated transport membranes (FTMs) separation have been considered as a very promising technology with their inherent advantages, such as high energy efficiency, cost-effectiveness, operational simplicity, and flexibility to scale up. [6, 9-12] In these FTMs, the gas transport behavior is dominated by the facilitated transport mechanism, which exploits the preferential and reversible interaction between CO2 and reactive carriers to enhance CO2 permeability and selectivity. However, the limited understanding of the fundamental mechanisms of molecular- and nano-scale processes, which is crucial to membrane performance and changes over time especially in complex environments, has hindered the further development of the high-performance CO2 capture membranes.

To address the knowledge gap between polymeric membrane structure and performance, my work is to establish a new operando surface enhanced Raman spectroscopy (SERS) platform to monitor and detect the chemical structure and dynamics of membranes in realistic operating environments while simultaneously measuring the rate of CO2 transport across the membrane. Aspects of the CO2 transport mechanism can be elucidated by correlating the formation of intermediate species in the membrane to rates of CO2 transport across the membrane. We have successfully established such a new operando SERS platform and tested it with Polyvinylamine (PVAm) membrane, a commonly used amine-based membrane in CO2 separation due to the highest concentration of primary amino groups, as well as literature supported high CO2 permeance and selectivity. We show direct spectroscopic evidence of carbamate (NHCOO-) formation inside the PVAm membrane, which is the key intermediate for CO2 transportation across the PVAm membrane. As CO2 permeance of PVAm facilitated transport membrane is pressure-dependent, the effect of CO2 partial pressure on CO2 facilitated transport across PVAm membrane was also studied with our apparatus to study the trend and correlate the phenomenon with molecular- and nano-scale structure. We also demonstrate the utility of this new technique by investigating the mechanism of CO2 facilitated transport across different amine-type polymeric membranes (PVAm, PMVAm, PDVAm, and P4VP) during exposure to humidified CO2/CH4 gas mixtures. The new operando spectroscopy platform can also be applied to other types of membranes, such as mixed-matrix membranes, and ceramic membranes to provide detailed information under the realistic working circumstance, which could help to understand the key factors that determine membrane performance and design new membranes with enhanced performance. 

Project Objectives

Objective 1: Design, develop, and test a new experimental operando Raman spectroscopic platform that could probe the chemical structure and dynamics of membranes in realistic operating environments. We aim to establish a new experimental operando Raman spectroscopic platform, and demonstrate the utility of the new operando SERS platform to characterize the molecular structure of Polyvinylamine (PVAm) membranes and simultaneously measure their gas separation performance under realistic operating conditions to detect and identify the intermediates that related to CO2 transport through the membrane.

Objective 2: Model study of Amine-Containing CO2-Selective Membrane Process for Carbon Capture. Based on our operando Raman spectroscopic platform, we want to correlate polymeric membrane structure and performance, and build a simple facilitated transport model for CO2 transport through PVAm (a type of amine-containing FTMs). The model could be used to roughly explain some experimental results and could also be used to modify membrane separation condition for different demands.

Objective 3: Use the new operando Raman spectroscopic platform to study and address the knowledge gap between different amine-based polymeric membrane structures (PVAm, PMVAm, PDVAm, and P4VP) and performance. We aim to  investigate different amine-based membranes (PVAm, PMVAm, PDVAm, and P4VP) to understand the structure effect on CO2 transport mechanism, and to understand which amine types and operating conditions exhibit the optimal CO2 transport performance.

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[2]    Yang, H.; Xu, Z.; Fan, M.; Gupta, R.; Slimane, R. B.; Bland, A. E.; Wright, I., Progress in carbon dioxide separation and capture: a review. Journal of environmental sciences (China) 2008, 20 (1), 14-27.
[3]    Darabkhani, H. G.; Jurado, N.; Prpich, G.; Oakey, J. E.; Wagland, S. T.; Anthony, E. J., Design, process simulation and construction of a 100 kW pilot-scale CO2 membrane rig: Improving in situ CO2 capture using selective exhaust gas recirculation (S-EGR). J. Nat. Gas Sci. Eng. 2018, 50, 128-138.
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[5]    Pellegrini, L. A.; De Guido, G.; Valentina, V., Energy and exergy analysis of acid gas removal processes in the LNG production chain. J. Nat. Gas Sci. Eng. 2019, 61, 303-319.
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[7]    Hemmati, A.; Rashidi, H.; Hemmati, A.; Kazemi, A., Using rate based simulation, sensitivity analysis and response surface methodology for optimization of an industrial CO2 capture plant. Journal of Natural Gas Science and Engineering 2019, 62, 101-112.
[8]    Wenten, I. G.; Khoiruddin, K.; Aryanti, P. T. P.; Victoria, A. V.; Tanukusuma, G., Membrane-based zero-sludge palm oil mill plant. Rev. Chem. Eng. 2020, 36 (2), 237-263.
[9]    Babu, D. J.; He, G.; Hao, J.; Vahdat, M. T.; Schouwink, P. A.; Mensi, M.; Agrawal, K. V., Restricting Lattice Flexibility in Polycrystalline Metal–Organic Framework Membranes for Carbon Capture. Adv. Mater. 2019, 31 (28), 1900855.
[10]    Míguez, J. L.; Porteiro, J.; Pérez-Orozco, R.; Patiño, D.; Rodríguez, S., Evolution of CO2 capture technology between 2007 and 2017 through the study of patent activity. Appl. Energy 2018, 211, 1282-1296.