Light olefins are mainly produced by naphtha steam cracking, which is among the more energy intensive processes in the petrochemical industry. To save energy, some alternatives have been proposed to partially replace or combine with cryogenic distillation the conventional technology to separate olefins and paraffins. Within this aim, facilitated transport membranes, mainly with Ag + cations as selective carriers, have received great attention owing to the high selectivity and permeance provided. However, to be used industrially, the undesirable instability associated with the Ag + cation should be considered. Poisonous agents and polymer membrane materials are sources of Ag + deactivation. In recent years, great achievements on the separation performance have been reported, but the current challenge is to maintain the selectivity in long-term separation processes. This work presents a critical analysis of the potential causes of Ag + deactivation and points out some alternatives that have been proposed to overcome the hurdle. This review highlights and critically analyses some perspectives of the ongoing development and application of facilitated transport membranes.
In this work, dense membranes from aqueous dispersions of poly(urethane‐urea) (PUU) based on poly(propylene glycol) (PPG) and a block copolymer composed of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG), EG‐b‐PG, with 7 wt % of the former were obtained. Nonpolluting formulations were synthesized with proportions of PPG and EG‐b‐PG as 1:0, 1:1, 1:3, and 3:1 in terms of equivalent number ratios. The effect of small and gradual increases in PEG segments was evaluated for the permeability of pure CO2, CH4, and N2, at room temperature. Slight increases in PEG‐based segments in PUU promoted some remarkable properties, which led to a simultaneous increase in CO2 permeability and ideal selectivity for CH4 (300%) and N2 (380%). Infrared spectroscopy showed that the PEG portions induced hydrogen bonds between NH of urethane and ether groups in the PEG portions, which promoted ordering of the flexible segments, confirmed by X‐ray diffractometry and small‐angle X‐ray scattering. Diffractometry techniques also confirmed the absence of crystalline domains, as did dynamic mechanical analysis. The produced membranes showed performance above Robeson's 2008 upper bound and seemed to be a superior polymeric material for CO2/CH4 and CO2/N2 separation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46003.
In this work, a comprehensive analysis of PVDF-HFP/BMImBF 4 /AgBF 4 facilitated transport membranes for olefin/paraffin separation is presented. Previous works of our research group have reported high flux and propylene selectivity under dry conditions and using synthetic gas mixtures, highlighting the promising potential of these experimental evidence for the previously theorized facilitated transport mechanisms and reveal a major influence of feed gas humidity on membrane performance. On the other hand, the industrial gas mixture produces no deviation from synthetic feed conditions due to trace contaminants. Finally, the carrier deactivation in long-term permeation has been quantified through a mathematical expression.
RESUMO -Na permeação de gases, a modificação de polímeros pela adição de nanopartículas para formar membranas de transporte facilitado destaca-se dentre as opções promissoras. Os objetivos deste trabalho foram avaliar alterações químicas, estruturais e térmicas de um poli(uretano-ureia) (PUU) pela adição de nanopartículas de prata (AgNps) e obter dados de pemeabilidade de CO 2 . Alterações nos espectros na região do infravermelho nas bandas de estiramento das ligações C-O-C e C=O e deslocamentos nos picos de difração obtidos por difração de raios X demonstram que houve interação entre as AgNps e o oxigênio éter do PUU. A interação polímero com AgNps diminuiu a estabilidade térmica dos domínios flexíveis, porém não alterou a decomposição inicial do polímero. As imagens de microscopia eletrônica de transmissão mostraram que houve baixa dispersão das AgNps. A presença das AgNps diminuiu a permeabilidade do CO 2 , mostrando a interferência dessas na sorção do gás. Foi proposto um mecanismo de interação entre as AgNps e o PUU e desse compósito com o CO 2 . INTRODUÇÃOO eteno é o principal insumo para a indústria petroquímica. De maneira geral, olefinas leves como eteno e propeno são obtidas através do craqueamento a vapor da nafta seguido por processos de destilação criogênica. Grande parte da energia utilizada nessa indústria é destinada ao processo de separação gasosa durante a destilação criogênica (Ren et al., 2008). Uma alternativa menos intensa em energia para promover tal separação está baseada nos processos de separação por membranas. Entretanto, para que esta tecnologia se torne viável, a membrana deve apresentar elevada seletividade para olefinas e deve se manter estável às condições de operação por um longo período de campanha (Bernado et al., 2009). Até o presente momento, as membranas desenvolvidas para a separação de olefinas e parafinas leves apresentaram baixa seletividade ou baixa estabilidade química, mantendo ainda desafiadora a busca por materiais mais promissores (Faiz e Li, 2012).Membranas baseadas no mecanismo de sorção/difusão não são capazes promover a separação desejada entre olefinas e parafinas leves. Entretanto, a dispersão ao longo da matriz Área temática: Engenharia de Materiais e Nanotecnologia 1
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