The impact of toluene and xylene on the performance of cellulose triacetate membranes for natural gas sweetening

Abstract

The presence of condensable aromatic hydrocarbons in raw natural gas streams creates a significant challenge for acid gas removal through membrane separation. In this work, the impact of toluene and xylene on the gas separation performance of cellulose triacetate (CTA) membranes was studied. When operating at low CO 2 partial pressures (0.75 Bar), both toluene and xylene reduced the permeation of CO 2 at low vapour activities, due to competitive sorption and the pore-filling or anti-plasticisation effect. Conversely, at vapour activities greater than 0.5, toluene caused membrane plasticisation, possibly coupled with a decrease in crystallinity. On the other hand, when operating at 7.5 Bar CO 2 pressure, plasticisation was observed at a lower vapour activity of 0.3 for both toluene and xylene. This study shows that two penetrants can influence the plasticisation behaviour in a cooperative manner that cannot be described by a simple additive model. The study also shows that the permeabilities of toluene and xylene are comparable with that of methane.

Recent Advances of Polymeric Membranes in Tackling Plasticization and Aging for Practical Industrial CO2/CH4 Applications—A Review

“…Since the mid-1980s, CA for reverse osmosis membranes has been modified and commercialized for CO 2 separation from CH 4 [14]. Cellulose tri-acetate (CTA) membranes occupy 80% of the global market for natural gas removal because of their peculiar properties of low cost, ease to process, higher durability, long term reliability, high pressure resistance, and competitive gas-separation performance [43]. CA polymers with different degrees of acetylation can be dissolved using organic solvents, since acetylation significantly decreases hydrogen bonding, enabling them to be fabricated using the phase-inversion process.…”

“…Plasticisation has been found to happen at the particular plasticizer amount for specific polymers. The reduction in gas permeability might initially be partially due to "pore blocking", "competitive sorption" or "anti-plasticisation" phenomenon, where the free space is occupied by hydrocarbon and aromatics such as toluene, which obstruct the flow path [43]. In the partial immobilization model, it was assumed that not all gas molecules sorbed are mobile and contribute to the gas transport.…”

“…Advanced dual-mode sorption models such as the Flory-Huggins and Guggenheim-Andersonde-Boer model have been established [43]. The simplistic membrane model that does not account for such complex effects can deviate more than 20% from a more rigorous approach.…”

“…Several efforts have been made to find modelling descriptions for the onset of the plasticization effects associated with permeability increase with gas pressure, aiming at a deeper understanding of the mechanism; however, the search for a correlation between the "plasticization pressure" and material properties are still nonconclusive [60]. Kentish et al [43] attempted to model the plasticization sorption isotherms using advanced dual-mode sorption models such as the Flory-Huggins (FH) model and Guggenheim-Andersonde-Boer (GAB) model, but none are suitable, hence suggesting that a more advanced model with multiparameters is required to simulate this type of behaviour.…”

One-pot neutron imaging of surface phenomena, swelling and diffusion during methane absorption in ethanol and n-decane under high pressure

“…Methane has been forecast to become the second most used energy resource within the next two decades [ 1 – 3 ]. The production of this gas, which can be seen as a bridge to low-carbon energy future [ 4 ], is inherently related to its basic properties, such as its ability to absorb and diffuse in liquids.…”