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Florence, KY, United States

Ribeiro Jr. C.P.,University of Texas at Austin | Ribeiro Jr. C.P.,Celanese Corporation | Freeman B.D.,University of Texas at Austin | Paul D.R.,University of Texas at Austin
Polymer | Year: 2011

The advantages of the Maxwell-Stefan (MS) formulation over Fick's law to describe multicomponent mass transfer are well recognized. However, in its original form, the MS equations are written in terms of mole fractions, which are ill-defined if one of the components is a polymer. To overcome this problem, a revised formulation of the MS equations written in terms of volume fractions is proposed. The resulting equations satisfy the Gibbs-Duhem restriction and are fully consistent with the multicomponent Flory-Huggins theory in the sense that we avoid any assumption regarding the size of the penetrants or of the polymer segments. This formulation is combined with the Flory-Huggins model to derive general expressions for modeling steady-state mass transfer across polymer films for both pure components and binary mixtures. The proposed MS formulation is used to analyze the separation of carbon dioxide/ethane mixtures by a cross-linked poly(ethylene oxide) membrane. For this particular system, at T≥25oC, mixed-gas permeability coefficients can be predicted with an average deviation of less than 5% without any input from multicomponent permeation data. © 2011 Elsevier Ltd. All rights reserved. Source


Comer A.C.,University of Kentucky | Comer A.C.,Geneva College | Ribeiro C.P.,University of Texas at Austin | Ribeiro C.P.,Celanese Corporation | And 3 more authors.
Polymer (United Kingdom) | Year: 2013

The glass-rubber and sub-glass relaxation characteristics of ortho-functionalized aromatic polyimides and thermally rearranged polymers were investigated by dynamic mechanical and dielectric methods. Soluble polyimides (HAB-6FDA; APAF-ODPA) were synthesized by chemical and thermal imidization and subject to thermal rearrangement at elevated temperature. For the thermal exposure histories investigated, mass loss studies indicated partial conversion of the polyimide precursor, suggesting the formation of TR copolymers containing both benzoxazole units and residual imide segments. Measurement of storage modulus and loss tangent was used to follow the thermal rearrangement process in-situ as reflected in the suppression of the polyimide glass transition as a function of precursor structure, the nature of the ortho functional groups and prior thermal exposure. In addition, changes in the position and intensity of local relaxations detected across the sub-glass temperature range were correlated with the degree of thermal rearrangement in these polymers. © 2012 Elsevier Ltd. All rights reserved. Source


Ribeiro C.P.,Energy and Environmental Research Center | Ribeiro C.P.,Celanese Corporation | Freeman B.D.,Energy and Environmental Research Center | Kalika D.S.,University of Kentucky | Kalakkunnath S.,ConocoPhillips
Journal of Membrane Science | Year: 2012

A series of aromatic polyimides and polybenzoxazoles was synthesized and tested as membrane materials for separation of aromatic/aliphatic mixtures by pervaporation. Homo- and random copolyimides were synthesized by a two-step polycondensation of a total of 6 diamines and 4 dianhydrides. Polybenzoxazoles and poly(benzoxazole-co-imide)s were prepared by the thermal rearrangement of ortho-functionalized polyimide films. Pervaporation experiments were conducted at 80°C with either toluene/n-heptane or benzene/n-heptane mixtures as feed streams. All polymers were selective towards the aromatic hydrocarbon, whose permeability could be changed by approximately 4 orders of magnitude depending on the chemical structure of the diamine. Pure-liquid sorption experiments at 25°C revealed that these large changes in hydrocarbon permeability were mainly caused by changes in the diffusion coefficient. The performance of the polymers was compared with previous results reported for other polymers, as well as with the performance of a commercial polyimide (Matrimid ®). © 2011 Elsevier B.V. Source


Forest J.J.,Celanese Corporation
Process Safety Progress | Year: 2012

It may seem that organizational culture is subjective and therefore difficult to measure. This article will show that an objective approach can be taken to survey and define process safety culture. With this data, gap analysis can be performed that compares survey data to the Center for Chemical Process Safety (CCPS) essential elements of process safety. This gap analysis can be used to identify strengths and weaknesses so that process safety performance can be improved. The survey method used, employs the CCPS process safety pillars, and categorizes responses according to the pillar elements, principles, and essential features required for excellence. The appropriate data collecting technique is shown that will give statistically meaningful results. Examples are given of grouping results by safety pillar categories and demographics of the survey population. Finally, a gap analysis method is shown that compares the survey results to CCPS essential elements so that improvement plans can be made. © 2012 American Institute of Chemical Engineers (AIChE). Source


Ribeiro C.P.,University of Texas at Austin | Ribeiro C.P.,Celanese Corporation | Freeman B.D.,University of Texas at Austin | Kalika D.S.,University of Kentucky | Kalakkunnath S.,Phillips 66
Industrial and Engineering Chemistry Research | Year: 2013

Aromatic random copolyimides were synthesized and tested as membrane materials for the separation of a mixture of aromatic and aliphatic hydrocarbons by pervaporation. The polymers were synthesized by a two-step polycondensation route with a total of 4 aromatic dianhydrides, 4 aromatic diamines, and 3 diamino-terminated aliphatic oligomers containing either ether or siloxane units. Pervaporation experiments were conducted at two temperatures with toluene/n-heptane and benzene/n-heptane mixtures as feed streams. All polymers were selective toward the aromatic hydrocarbon. Introduction of siloxane units in the polymer generally led to very high hydrocarbon permeability coefficients, but caused a reduction in selectivity relative to that of the aromatic homopolyimide. Incorporation of ether units, on the other hand, did not generally cause such large increases in permeability, nor large decreases in selectivity. The performance of these materials was compared with previous results reported in the literature for other polymers. © 2012 American Chemical Society. Source

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