Permeation Of Ethylene Research Articles

Concentration gradient driven molecular dynamics: a new method for simulations of membrane permeation and separation.

In this study, we introduce a new non-equilibrium molecular dynamics simulation method to perform simulations of concentration driven membrane permeation processes. The methodology is based on the application of a non-conservative bias force controlling the concentration of species at the inlet and outlet of a membrane. We demonstrate our method for pure methane, ethane and ethylene permeation and for ethane/ethylene separation through a flexible ZIF-8 membrane. Results show that a stationary concentration gradient is maintained across the membrane, realistically simulating an out-of-equilibrium diffusive process, and the computed permeabilities and selectivity are in good agreement with experimental results.

Polymeric ionic liquid membranes containing IL–Ag+ for ethylene/ethane separation via olefin-facilitated transport

This work focuses on the separation of light olefins from their corresponding paraffins using membranes due to their lower energy consumption and operating costs in comparison to the traditionally used methods which are highly energy intensive. Although polymeric ionic liquids (PILs) have attracted much attention as interesting materials to prepare improved gas separation membranes, their exploitation for light olefin/paraffin separation has never been attempted before. In this work, we propose the use of PILs as alternative polymer matrices for olefin/paraffin separation. A new series of facilitated transport membranes of poly([pyr11][NTf2]) incorporating different amounts of the ionic liquid ([pyr14][NTf2]) and the silver salt (AgNTf2) were prepared by a film casting process and their ethane and ethylene permeation properties were measured at 293 K using a time-lag apparatus. The results show that the preparation of PIL/IL composite membranes increases the permeability of both C2H4 and C2H6, overcoming the hindered gas diffusion in the pure PIL. Nevertheless, the presence of the IL in the composite membrane promotes reduced C2H4/C2H6 permselectivity. The addition of the silver salt greatly boosts the solubility of the olefin in the membranes. Furthermore, increasing the silver ion concentration in the PIL/40% IL system leads to enhanced overall C2H4/C2H6 permselectivity surpassing the upper bound for polymeric membranes, indicating that PILs have interesting potential as polymer matrices for olefin-facilitated transport membranes.

Preparation and characterization of polyimide and polyethersulfone blend membrane for gas separation

ABSTRACTPolyimides (PI) have been studied as the basic materials for preparing gas separation membranes attributable to their high gas selectivity. This paper deals with the preparation and characterization of blended polyimide membranes with polyethersulfone (PES) to study separation of ethylene from nitrogen gas at different feed pressures. For improving performance of PI membranes, two procedures were used. First, using polymeric additives such as polyvinylidene fluoride (PVDF) and PES in low content and second, blending of PI casting solution with high amount of PES. Infrared spectroscopy and scanning electron microscopy (SEM) images were employed to characterize the membranes. Pyromellitic dianhydride‐co‐4, 4′‐oxy dianiline (PMDA/ODA) polyimide membranes was synthesized using polyamic acid (PAA) as precursor materials. The ideal selectivity of 100% (ethylene permeation only) was achieved at 1 bar using PMDA/ODA polyimide membranes containing 1 wt% PVDF. Addition of PES did not have any significant influence on ideal selectivity of the prepared membranes. PES‐(PMDA/ODA) polyamic acid blend membranes were prepared using different blending ratios of PES (25 wt%) and PAA (15 wt%). The blending ratio of casting solutions of PES/PAA solutions exhibited a main influence on the ideal selectivity. The ideal selectivity of 2.9 for ethylene was achieved at 3 bar using blend membranes with 0.5 wt% PAA solution. PES‐PMDA/ODA polyimide membranes were also prepared from blend casting solutions by thermal imidization. Immiscible blend membranes were obtained at different blending ratios of the casting solutions with high gas permeance and poor selectivity. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Selective ethylene‐permeable zeolite composite double‐layered film for novel modified atmosphere packaging

AbstractThe composite double‐layered films, for the packaging application of postharvest fruits and vegetables, were prepared by laminating low‐density polyethylene (LDPE) and poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) modified with zeolite ZSM‐5. The film was characterized by scanning electron microscope and differential scanning calorimeter and tested for permeation of ethylene (C2H4), oxygen (O2), carbon dioxide (CO2), and water vapor. It was found that the C2H4 permeability of the films was improved because of an enhanced adsorption of C2H4 by the incorporated zeolite (0–10 wt%). The preconcentrated layer (zeolite/SEBS) leads to a higher C2H4 concentration gradient across the film. Moreover, the high dispersion of zeolite increased the C2H4 permeation. When compared with O2 and CO2, the composite films were more selective to C2H4. However, the C2H4 permeation decreased in the presence of O2 because of a competitive adsorption. In addition, the films possessed appreciate tensile properties for packaging application. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Numerical Investigation of Hydrocarbon Enrichment of Process Gas Mixtures by Permeation through Polymeric Membranes

AbstractIn membrane‐based gaseous separations, a consensus on the distribution of the components of the permeate stream in the immediate membrane vicinity has yet to be reached and the possibility of an underestimation of selective gas permeance due to lack of gas mixing on the permeate side exists. In this work, a numerical study of the permeation of ethylene and propylene in their binary mixtures with nitrogen through a composite poly(dimethylsiloxane) coated polysulfone membrane was performed. Continuity and momentum equations, along with gas compressibility and permeance properties for individual species of the gas mixture, were introduced into a comprehensive computational fluid dynamics (CFD) model. Simulation results showed that irrespective of the stage‐cut, gases with higher selectivity were well mixed in the vicinity of the membrane on the permeate side.

Unusual behavior of poly(ethylene oxide)/AgBF 4 polymer electrolyte membranes for olefin–paraffin separation

Solid polymer electrolyte membranes comprising of poly(ethylene oxide) and silver tetrafluoroborate were prepared for olefin and paraffin permeation with a focus on the study of membrane stability issues. The membrane initially showed very high permselectivities for the permeation of ethylene–ethane and propylene–propane. The high permselectivity, however, could not be retained for a prolonged period of permeation. The membrane stability was investigated by varying the feed pressure and operating temperature in a cyclic fashion. It was observed that in addition to the gradual decline in membrane performance with permeation time that has been observed previously, conditioning of the membrane with the olefin permeant could result in an irreversible decrease in the membrane performance, presumably due to the silver–PEO and silver–olefin complexation interactions. Continued studies on improving the membrane stability are needed for practical olefin–paraffin separation applications.

Reactive polymer membranes for ethylene/ethane separation

Olefin/paraffin separations by distillation are highly energy intensive. Facilitated transport, or reactive membranes have long been investigated as an alternative and/or complementary separation technology to conventional distillation. However, stability problems associated with facilitated transport membranes have been the primary obstacle in the development of commercial FT processes. In this paper, we report the development of a polymer membrane containing silver(I) ion that facilitates the transport of ethylene in the absence of solvent. Blends of ionically conductive and electrically conductive polymers were found to have the appropriate electronic environment to allow reaction of silver(I) ion and ethylene. The results for the ethylene/ethane separation were obtained with composite membranes of silver(I)-form Nafion ® and 2 wt% poly(pyrrole). Permeation measurements were performed with ethylene/ethane mixtures at total feed pressures ranging from 760 to 1900 mmHg and at temperatures of 40°C to 70°C. Pure gas permeability measurements were obtained at a total feed pressure of 1900 mmHg and temperatures of 30°C and 40°C. Ethylene/ethane separation factors with the silver(I)-form Nafion-poly(pyrrole) composite membranes increased from 8 to 15 as temperature decreased. Ethylene permeabilities increased from 0.2 to 1 Barrer over the temperature range of 30°C to 70°C. An ethylene/ethane mixed gas permeability ratio of about 2 was observed with non-reactive proton-form Nafion-poly(pyrrole) composite membranes. Ethylene permeation measurements as a function of membrane thickness suggested that the facilitated transport of ethylene approached the reaction-limited regime at membrane thickness of 5 μm. The complexation between ethylene molecules and silver(I) ions in Nafion-poly(pyrrole) composite membrane was observed with FTIR spectroscopy.

Evaluation of the ethylene permeability of polyvinyl chloride (PVC)

AbstractThe aim of this study was to evaluate ethylene permeation through a food packaging‐grade polyvinyl chloride at 3,10,17 and 25°C. The transmission rates were calculated to estimate the permeability (P) at these temperatures. This permeability is influenced by the temperature, giving values from 120 000cm3 μm/m2. d atm at 3°C to 367000cm3 μm/m2. d atm at 25°C. Other parameters, such as the selectivity factor (p), the temperature coefficient (Q10) and the activation energy (Ea). were compared to values obtained for other gases (O2 and CO2) using the same film and supplier.

A simple and reliable ethylene gassing system for plant studies

An ethylene permeation system was tested in a study of flower abscission of Verticordia nitens (Lindley) Endl. Various concentrations of ethylene in air were generated by passing air, at a flow rate of 2 L/min, through chambers containing various lengths of polyvinyl chloride (PVC) tubing pressurised (50 kPa) with ethylene. Ethylene permeating through lengths of PVC tubing of 1.5, 15, 150, and 1500 cm (8 mm internal diameter, 1.5 mm wall thickness) gave ethylene concentrations in the outflow airstreams of 0.12, 0.99, 7.8, and 100 �L/L, respectively. Increasing the ethylene pressure in 150-cm-long tubing linearly increased the permeation of ethylene (0.07 �L/L. kPa). A log-linear abscission response of V. nitens flowers to increasing ethylene concentration was demonstrated using this system. Use of silicone tubing (8-mm internal diameter, 1.5-mm wall thickness) resulted in an ethylene flux 75 times that of the same length of PVC tubing. Higher flux through silicone tubing should allow development of ethylene permeation gassing systems suitable for use in fruit ripening and degreening rooms.

Selective permeation of ethylene and propylene through rh 3+—Polyethylene glycol liquid membranes

Solubilities and permeabilities of ethylene and propylene were examined for a liquid membrane consisting of polyethylene glycol containing a series of transition metal ions. In the Rh 3+—added system, olefin uptake by the metal ion occurred reversibly and the permselectivity of olefin gas against N 2 was improved. Addition of KNO 3 to the Rh 3+—PEG system resulted in further enhancement of the permselectivity. Results of sorption and permeation measurements demonstrated that the olefin transport mediated by Rh 3+ becomes more predominant as a result of the salting-out effect induced by the added salt.