Tue, 27 September, 2022
A paper co-authored by NIC student Hamad Raheem has been published by the Multidisciplinary Digital Publishing Institute (MDPI), a publisher of open access scientific journals.
The paper, which was co-written with TWI’s Bernadette Craster and Ashwin Seshia of the University of Cambridge’s Department of Engineering, is titled, ‘Analysis of Permeation and Diffusion Coefficients to Infer Aging Attributes in Polymers Subjected to Supercritical CO2 and H2 Gas at High Pressures.’
The paper investigated the examination and understanding of the permeation flux behaviour of polymers that are exposed to high-pressure and high-temperature fluids continuously and over long time spans.
The study looked into evidence of structural alterations in polymer specimens as indicators of material aging. This involved monitoring transport coefficients at pressure steps from 10-400 barg and at temperatures ranging from 30-90°C.
Continuous flow permeation methodology is a well-established technique for applications including membrane separation processes and polymeric pressure barriers used for fluid containment in the oil and gas industry.
This study used a novel methodology that allows the permeating flux of supercritical CO2 and H2 gas through raised-temperature polyethylene and polyvinylidene fluoride films at differing elevated temperatures and pressures to be determined across several months using gas chromatography.
Changes in temperature and stepwise increases in gas pressure were introduced during the measuring period to determine the activation energy for permeation as well as transport coefficients of permeation, diffusion, and sorption. The polymer film was not allowed to outgas during these changes in temperature or pressure.
The permeation experiments were completed with differential scanning calorimetry tests that tracked changes in polymer crystallinity before and after exposure of the specimen to plasticising gases, which revealed the extent of structural alterations inflicted on the specimen as a result of the high temperature and pressure loads.
The study shows how those specimens that were exposed to high starting pressures aged more than those who had a more gradual increase in feed pressure. The report also investigates the relationship between transport coefficients and fractional free volume in the polymer once exposed to high pressure and temperature conditions. Finally, the benefit of using fugacity in place of feed pressure for the calculation of the permeability coefficient is explored.
This study contributes to the understanding of how prolonged exposure of polymeric specimens to CO2 and H2 gas under stepwise pressure and temperature loading impacts flux behaviours and crystallinity, providing important information on the use of polyethylene-based specimens for oil field deployment.
You can see the report in full here.