INTERACTION OF HYDROGEN WITH FLUOROELASTOMER: SORPTION AND DEGRADATION
ABSTRACT
Hydrogen (H2) applications have received extensive attention for the preparation of energy transition. Thus, it is essential to understand H2 gas transport properties in elastomers and degradation of elastomers under high pressure and high temperature. However, the effect of pressure on the gas sorption of H2 in fluoroelastomers (FKMs) as well as its relation to molecular properties of the gas remain unclear. Hydrogen gas solubility in FKM as a function of pressure was carried out, and a linear relationship was observed that was consistent with Henry’s law. A correlation between the solubility coefficient of H2 gas and critical temperature was quantitatively established. The temperature dependence of the solubility coefficient of H2 in FKM at 3000 kPa and the correlation between heat of sorption and molecular properties of the gas were investigated. Furthermore, the diffusion coefficient and permeability coefficient of H2 gas in FKM were systematically studied and compared with those of N2 and CO2 systems. Similarly, degradation of the FKM revealed that increasing aging temperature, aging pressure, and aging time have deleterious effects on degradation of FKM materials in hydrogen, more so than those in nitrogen. Spectroscopic analysis indicates abstraction of fluorine and crosslinking. Thus, this study enhances our current understanding of H2 gas transport properties in FKM and degradation of FKM under high pressure and temperature and provides insight into elastomer performance under an H2 environment to design superior formulations.
Parr reactor test setup.
(a) H2 gas sorption in FKM as a function of time at various pressures and 50 °C. (b) Solubility of H2 gas as a function of pressure in FKM at 50 °C. The solubility was measured when the gas sorption reached an equilibrium state.
Solubility of H2, N2, and CO2 as a function of pressure in FKM at 50 °C. The solubility was measured when the gas sorption reached an equilibrium state.
Relationship between Tc and S of gases in FKM at 50 °C.
(a) Temperature dependence of S of H2 in FKM at 3000 kPa. Inset: van’t Hoff plot used to determine of sorption of H2. (b) Correlation of with Tc of gases in FKM. The error bars represent the SE associated with three independent measurements on three separate samples.
(a) D of H2 gas as a function of temperature in FKM at 3000 kPa. (b) D of H2 gas as a function of pressure in FKM. Inset: simplified Fickian diffusion model used to determine D of H2 gas in FKM at selected temperatures and pressures.
(a) Comparison of diffusion coefficient of H2, N2, and CO2 at various pressures and 50 °C in FKM. (b) Correlation the D of gases with kinetic diameter of gases in FKM.
Permeability coefficient of H2, N2, and CO2 as a function of pressure in the FKM at 50 °C.
Stress–strain plots showing the effect of increase in (a) aging time, (b) pressure, and (c) temperature for experiments in hydrogen.
Tensile strength, Young’s modulus, and elongation at break showing the effect of increase in aging time (a–c); increase in aging temperature (d–f); and increase in aging pressure (g–i) for aging of FKM in hydrogen.
Effects of aging on IR absorbance of FKM elastomer aged at 6.20 MPa, 175 °C, and 72 h in hydrogen gas.
(a) Effects of aging pressure on IR absorbance peaks for FKM aged in hydrogen gas. (b) Plot of peak area absorbance ratio of CF3, CF2, and CF with respect to C–O–C vs aging time.
Mechanism of degradation of FKM: (a) free radical reaction and (b) hydrodefluorination at high temperature.
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