(108d) High-Pressure CO2 Sorption, Diffusion and Permeation in Different Polymers for Carbon Capture and Transport Application

Carbon Capture and Storage (CCS) value chain is one of the most viable solutions to limit the CO₂ release in the atmosphere, with the aim to reach the net zero CO₂ emissions and, thus, to prevent global warming [1]. CCS has been widely studied all over the world since it might be the most straight full solution to capture, transport and store CO₂ in geological reservoir, with the potential to be applied at short-medium times. Pipelines and ships represent the unique solution to transfer the liquefied carbon dioxide from the captured emission point to the storage site [2]. In fact, industrial carbon transport chain requires to deal with dense CO₂ phases, either in its supercritical or in liquid state (pressure higher than 10 MPa and temperature around -30°C), which can affect the performance of the materials due to a physical change in their structure.

In this concern, polymeric materials play a relevant role in the protection of metals transport equipment (such as pipeline, pumps, vessels, liners...) [1] since metals are susceptible to corrosion when exposed to supercritical-phase CO₂ [3]. However, polymers may absorb CO₂ molecules that can interact with the matrix by changing the material performances, leading to plasticizing effect or Rapid gas decompression (RGD) damage.

Among the various classes of polymers, fluorinated materials look promising for their potential application for CO₂ capture as membrane materials and CO₂ transport, either in pipelines or in ship vessels, due to their excellent thermal and chemical resistance, combined with a pronounced favourable interaction with CO₂ [4,5]. Together with thermoplastics, also rubbery polymers are very-well known in gas transport chain due to their enhancement as gaskets and sealants in metal joint [6].

This work aims to characterize different materials by measuring and predicting CO₂ behaviour in polymers in order to better understand the relationship between the pressurized-gas and the materials properties (either mechanical or thermal) in view of their use in CCS chain.

In particular, it explores the sorption, diffusion and permeation properties of different fluorinated polymers (PVDF, PTFE, PVF, ETFE, FEP and PFA) and one elastomer (EPDM) when they are exposed to high-pressure Carbon Dioxide, since their industrial applicability is related to their barrier behaviour and their intrinsic mechanical response. Tests have been performed through pressure decay technique and permeation experiments in a wide range of temperature and pressure, in order to investigate the materials response at different operating conditions.

Afterwards, the results obtained through the experimental campaign have been modelled via thermodynamic equation of state (EoS) model (Lattice Fluid / Non-Equilibrium Lattice Fluid (NELF) [7,8]), obtained by the resolution of phase equilibrium problem (Eq. 1).

μ^pol_i (T,p,ω_i) = μ^g_i (T,p) Eq.1

Lattice Fluid Eos, based on Flory-Huggins theories, aim to be able to predict both gas sorption and transport under different operating conditions thanks to the description of the matter as a lattice whose sited can be void or occupied by molecules [9]. So that, from the statistical thermodynamics, the entropy and the internal energy of such systems might be calculated to obtain a high precision liquid-phase behavior. On the other hand, NELF approach is an extension of LF model which stands for the determination of gas solubility even in glassy polymeric matrix [7], where the polymer density is no longer reaching the equilibrium.

The description of CO₂ transport in supercritical phase must account the solubility isotherms of the penetrant and the changes in the diffusion coefficient with concentration, which is a function of the kinetic mobility coefficient and the thermodynamic factor. In this concern, the Standard Transport Model (STM) has proved to be very reliable in the description of gas permeability behavior as a function of pressure [10]. That allows to understand the penetrant-polymer interaction and the effect of dense phase CO₂ on polymer-based materials, as well as to predict the molecular behaviour of these commercial polymers in a wide range of temperature and pressure.

The experimental results obtained through out this characterization on thermoplastics and elastomer shows that CO₂ solubility increases with pressure due to the increases of the gas density, while it decreases with temperature, by following the Van’t Hoff equation. On the contrary, both diffusion coefficient and CO₂ permeability are positively affect by pressure and temperature increase, in accordance with Arrhenius law [11].

Figure 1 shows how temperature affects the transport behaviour in the different polymers for (1a) solubility and (1b) diffusion coefficient. It is interesting to notice how the solubility of EPDM at 35°C is in line with the others obtained for Fluoropolymers, while the diffusion coefficient, as well as permeability, differ more than one order of magnitude. This behaviour can definitely be imputed to the higher FFV (fractional free volume) of the EPDM respect to thermoplastic materials, which guarantees faster mass transport kinetics in rubbers. At the same time, the comparison of sorption (Fig. 2a) and transport data (Fig. 2b) by means of the dedicated model, allows the reliable prediction of the effects of CO₂ on the polymers investigated at all desired temperature and pressure ranges, relevant for CO₂ transport (e.g. dense phases, up to supercritical conditions) or capture applications.

Finally, in Figure 3 is displayed the CO₂ solubility (Fig. 3a) and permeability (Fig. 3b) behaviour for PVDF and EPDM, at temperature down to 0°C and pressure up to 100 bar, which correspond to the operative conditions for liquefied- CO₂ transport in polymers. The data reported demonstrates how the interaction between polymer and dense-phase gas can be feasible predicted through the implementation of Thermodynamics EoS and Transport models, within the pressure range of interest.

From the experimental CO₂ sorption data at room conditions, following a rigorous physically sound model, it is possible to evaluate thermodynamic and kinetic parameters, such as Solubility, Diffusivity and Permeability. That allows the penetrant-polymer interaction and the effect of dense phase CO₂ on polymer-based materials to be understood, as well as proving essential performance information for targeted applications.

Moreover, by fitting those sorption data through a thermodynamic model, based on EoS, it is possible to describe and predict the molecular behaviour of these commercial polymers in wide temperature and pressure ranges, including super-critical conditions, relevant for CO₂ transport application, and to evaluate their future use in industrial applications.

This work is a step forward in understanding and modelling of the complex interaction between supercritical CO₂ and polymers, relevant for carbon transport chain, in view of their future use in industrial applications.

References

[1] D.Y.C. Leung, G. Caramanna, M.M. Maroto-Valer, An overview of current status of carbon dioxide capture and storage technologies, Renew. Sustain. Energy Rev. (2014). https://doi.org/10.1016/j.rser.2014.07.093.

[2] L. Ansaloni, B. Alcock, T.A. Peters, Effects of CO2 on polymeric materials in the CO2 transport chain: A review, Int. J. Greenh. Gas Control. 94 (2020) 102930. https://doi.org/10.1016/j.ijggc.2019.102930.

[3] A.C.C. de Leon, Í.G.M. da Silva, K.D. Pangilinan, Q. Chen, E.B. Caldona, R.C. Advincula, High performance polymers for oil and gas applications, React. Funct. Polym. 162 (2021). https://doi.org/10.1016/j.reactfunctpolym.2021.104878.

[4] L. Ansaloni, B. Alcock, T.A. Peters, Effects of CO2 on polymeric materials in the CO2 transport chain: A review, Int. J. Greenh. Gas Control. 94 (2020) 102930. https://doi.org/10.1016/j.ijggc.2019.102930.

[5] R.W. Baker, B.T. Low, Gas separation membrane materials: A perspective, Macromolecules. 47 (2014) 6999–7013. https://doi.org/10.1021/ma501488s.

[6] A.Z. Abas, A.M. Nor, M.F. Suhor, S. Mat, Non-metallic materials in supercritical CO2 systems, Proc. Annu. Offshore Technol. Conf. 3 (2014) 2452–2455. https://doi.org/10.4043/24963-ms.

[7] F. Doghieri, G.C. Sarti, Nonequilibrium lattice fluids: A predictive model for the solubility in glassy polymers, Macromolecules. 29 (1996) 7885–7896. https://doi.org/10.1021/ma951366c.

[8] I.C. Sanchez, R.H. Lacombe, Statistical Thermodynamics of Polymer Solutions, Macromolecules. 11 (1978) 1145–1156. https://doi.org/10.1021/ma60066a017.

[9] R.H. Lacombe, I.C. Sanchez, Statistical thermodynamics of fluid mixtures, J. Phys. Chem. 80 (1976) 2568–2580. https://doi.org/10.1021/j100564a009.

[10] E. Ricci, M.G. De Angelis, M. Minelli, A comprehensive theoretical framework for the sub and supercritical sorption and transport of CO2 in polymers, Chem. Eng. J. 435 (2022) 135013. https://doi.org/10.1016/j.cej.2022.135013.

[11] S. Lee, K.S. Knaebel, Effects of mechanical and chemical properties on transport in fluoropolymers. I. Transient sorption, J. Appl. Polym. Sci. 64 (1997) 455–476. https://doi.org/10.1002/(sici)1097-4628(19970418)64:3<455::aid-app4>3.3.co;2-m.

Acknowledgements

The authors acknowledge the financial support of the Research Council of Norway, under grant 308765.