Predicting enhanced absorption of light gases in polyethylene using simplified PC-SAFT and SAFT-VR

International audienceAbsorption of light gases in polyethylene (PE) is studied using two versions of the Statistical Associating Fluid Theory (SAFT): SAFT for chain molecules with attractive potentials of variable range (VR) and simplified perturbed-chain (PC) SAFT. Emphasis is placed on the light gases typically present during ethylene polymerisation in the gas-phase reactor (GPR) process. The two approaches are validated using experimental binary-mixture data for gas absorbed in PE, and predictions are made for mixtures of more components. For most cases studied both SAFT versions perform equally well. For the case of ternary mixtures of two gases with PE, it is predicted that the less-volatile of the two gases acts to enhance the absorption of the more-volatile gas, while the more-volatile gas inhibits the absorption of the less-volatile gas. This general behaviour is also predicted in mixtures containing more gases, such as typical reactor mixtures. The magnitude of the effect may vary considerably, depending on the relative proximity of the gas-mixture saturation pressure to the reactor pressure; for example it is predicted that the absorption of ethylene may be approximately doubled if diluent gases, propane or nitrogen, are partially or completely replaced by less-volatile butane or pentane for a reactor pressure similar to 2 MPa. In the case of a co-polymerisation reaction, it is predicted that increases in absorption of both co-monomers may be obtained in roughly equal proportion. Our findings cast light on the so-called co-monomer effect, in which substantial increases in the rate of ethylene polymerisation are observed in the presence of hexene co-monomer, while suggesting that the effect is more general and not restricted to co-monomer. For example, similar rate increases may be expected in the presence of, e.g., pentane instead of hexene, but without the change in the branch structure of the produced polymer that is inevitable when the amount of co-monomer is increased

A novel time lag method for the analysis of mixed gas diffusion in polymeric membranes by on-line mass spectrometry: Method development and validation

European Union's Seventh Framework Program (FP7/2007-2013) under Grant agreement no. 608490. project M4CO2. CNR/FCT Italian/Portuguese Bilateral Project 2015-2016 "Advanced studies of the transport properties and gas separation by polymers of intrinsic microporosity (PIMs) and Ionic Liquid Gel Membranes via novel methods" and the CNR-CAS Bilateral Agreement 2016-2018 "Innovative polymeric membranes for pervaporation and advanced gas and vapour separations".A novel method to determine the individual diffusion coefficients of gases in a mixture during their permeation through polymeric membranes is described. The method was developed in two independent laboratories, using rubbery Pebax® and glassy Hyflon® AD60X membrane samples as standards, and validated using the Tröger's base containing Polymer of Intrinsic Microporosity, PIM-EA-TB. Monitoring of the permeate composition in real time by a quadrupole mass spectrometer allowed the analysis of the permeation transient for gas mixtures. Two operation modes, either with a vacuum in the permeate and a direct connection to the mass spectrometer via a heated restriction, or using a sweeping gas and a heated capillary sample inlet, give excellent agreement with the traditional time lag method for single gases. A complete overview of the method development, identification of the critical parameters, instruments calibration, data elaboration and estimation of the experimental accuracy are provided. Validation with PIM-EA-TB, shows that the method can also successfully detect anomalous phenomena, related to pressure and concentration dependency of the transport properties, physical aging or penetrant-induced dilation. Rapid online analysis of the permeate composition makes the method also very suitable for routine mixed gas permeability measurements.publishersversionpublishe

Permeability, Diffusion and Solubility of Gases in Polyethylene, Polyamide 11 and Poly (Vinylidene Fluoride)

The gases transport coefficients, permeability, diffusion and solubility, are determined by the time lag method on a specific permeation cell. Three semicrystalline polymers, polyethylene (PE), polyamide 11 (PA11) and poly(vinylidene fluoride) (PVF2), are studied in the presence of helium (He), argon (Ar), nitrogen (N2), methane (CH4) and carbon dioxide (CO2) for temperatures ranging from 40 to 80°C in the case of PE, and from 70 to 130°C for both other materials. The applied pressures are, in the majority of tests, of 10 MPa for He, Ar, N2 and CH4, and of 4 MPa for CO2, except in some particular cases where the influence of pressure was studied. In the case of PE, the influence of the volume fraction of the amorphous phase, ranging from 0. 21 to 0. 70, the influence of temperature and the influence of the nature of the gas on the transport processes are investigated. Also, the independence of these phenomena related to pressure and sample thickness, between 0. 5 and 6 mm, is shown. For PA11, after determining the influence of temperature and of the nature of the gas used, the effect of the plasticizer incorporation in this polymer was studied. Regarding PVF2, apart the classic parameters that are temperature and the kind of gas used, we compare the coefficients of transport of CH4 and CO2 in PVF2 made up by extrusion or by compression moulding. For each polymer, it is shown that permeability, diffusion and solubility depend on temperature following Arrhenius' laws. It also seems that diffusion is directly related to the gases molecule size and that the solubility coefficient can be linked to the epsilon/K gases parameter. The comparison of the results obtained with the available data in the literature seems satisfactory

Transport Properties of Gases in Polymers: Experimental Methods

The permeability of gases in polymers is a property inherent to their structure, which results, firstly, from the absorption of fluids by the material, then, from the diffusion of these products through the polymer matrix. The capacity of a gas to cross more or less fast a material can be used in numerous industrial domains. For example, polymers of low permeability are looked for in domains as different as the oil production, the food packaging or the automotive industry. For oil applications, the main function of polymers is to ensure the leakproof of pipes for example. In that case, materials are in contact of gas at high temperature and high pressure. As the information concerning the gases transport coefficients in these extreme conditions was not available in literature, devices able to give access to these properties were developed. In this paper, the methods for obtaining the transport coefficients and a brief bibliographical review of the various existing experimental techniques are presented. Then, the various experimental devices developed are described in detail

Transport Properties of Gases in Polymers: Bibliographic Review

After some general considerations and basic equations on transport phenomena in polymers, this review, exclusively bibliographical, presents different concepts and theoretical models that have been proposed and developed to describe the transport mechanism of molecular species in polymers by diffusion. Based on numerous previous studies, it will show how the permeability of gases (or organic vapours) depends strongly on the polymer structure (degree of crystallinity, thermal and mechanical histories), on the penetrant size and nature as well as on the conditions of temperature and pressure

New Insights in Polymer-Biofuels Interaction

This paper deals with polymer-fuel interaction focusing on specific effects of biofuels on polyethylene (PE) in automotive applications. The practical objective is to develop a predictable approach for durability of polyethylene tanks in contact of ethanol based or biofuel based fuels. In the case of ethanol, the main consequence on PE durability is a reduction of the rate of stabilizer extraction; this latter phenomenon can be modeled by first order kinetics with a rate constant that obeys the Arrhenius equation. Concerning biodiesels, the study was focused on soy and rapeseed methyl ester which were compared to methyl oleate and methyl linoleate used as model compounds. Here, PE-fuel interactions can be described as well as physical interaction, linked to the oil penetration into the polymer, as chemical interaction linked to an eventual co-oxidation of PE and oil. Both aspects were investigated. Concerning biofuel transport in PE, it appeared that the oil diffusivity depends only of temperature and oil molar mass. Some aspects of the temperature dependence of the oil solubility in PE are discussed. About chemical interaction between oil and PE, it was put in evidence that unsaturated fatty esters promote and accelerate PE oxidation. A co-oxidation kinetic model was proposed to describe this process

New Insights in Polymer-Biofuels Interaction

This paper deals with polymer-fuel interaction focusing on specific effects of biofuels on polyethylene (PE) in automotive applications. The practical objective is to develop a predictable approach for durability of polyethylene tanks in contact of ethanol based or biofuel based fuels. In the case of ethanol, the main consequence on PE durability is a reduction of the rate of stabilizer extraction; this latter phenomenon can be modeled by first order kinetics with a rate constant that obeys the Arrhenius equation. Concerning biodiesels, the study was focused on soy and rapeseed methyl ester which were compared to methyl oleate and methyl linoleate used as model compounds. Here, PE-fuel interactions can be described as well as physical interaction, linked to the oil penetration into the polymer, as chemical interaction linked to an eventual co-oxidation of PE and oil. Both aspects were investigated. Concerning biofuel transport in PE, it appeared that the oil diffusivity depends only of temperature and oil molar mass. Some aspects of the temperature dependence of the oil solubility in PE are discussed. About chemical interaction between oil and PE, it was put in evidence that unsaturated fatty esters promote and accelerate PE oxidation. A co-oxidation kinetic model was proposed to describe this process

Influence of type of mechanical loading, mentrual status and training season on bone density in young women athletes

This paper deals with polymer-fuel interaction focusing on specific effects of biofuels on polyethylene (PE) in automotive applications. The practical objective is to develop a predictable approach for durability of polyethylene tanks in contact of ethanol based or biofuel based fuels. In the case of ethanol, the main consequence on PE durability is a reduction of the rate of stabilizer extraction; this latter phenomenon can be modeled by first order kinetics with a rate constant that obeys the Arrhenius equation. Concerning biodiesels, the study was focused on soy and rapeseed methyl ester which were compared to methyl oleate and methyl linoleate used as model compounds. Here, PE-fuel interactions can be described as well as physical interaction, linked to the oil penetration into the polymer, as chemical interaction linked to an eventual co-oxidation of PE and oil. Both aspects were investigated. Concerning biofuel transport in PE, it appeared that the oil diffusivity depends only of temperature and oil molar mass. Some aspects of the temperature dependence of the oil solubility in PE are discussed. About chemical interaction between oil and PE, it was put in evidence that unsaturated fatty esters promote and accelerate PE oxidation. A co-oxidation kinetic model was proposed to describe this process

Analyse et simulation de l'influence de la température et de la pression sur les coefficients de transport du CO2 dans du PVDF

Ce travail est consacré à l'optimisation des coefficients de transport de gaz dans les polymères. Il consiste à modéliser l'influence de la température et de la pression sur le coefficient de diffusion. La modélisation est validée par optimisation sur le système CO2-PVDF. Un modèle quadratique en pression généralisant des travaux existants est proposé. Ce modèle décrit en particulier l'effet des hautes pressions sur les coefficients de transport