Polymer Membranes for Gas Separation

Producción CientíficaOver the past decade, polymeric membranes have been widely investigated for a variety of industrial gas separation applications. In today’s competitive and ever-changing environment, membrane gas separation is now widely accepted as an economic process to produce moderate purity stream gases. [Texto extraído del artículo de Bibiana Comesaña Gándara]

Recent trends and advances in biogas upgrading and methanotrophs-based valorization

Producción CientíficaThe global quest for sustainability in industrial activities and waste management has recently boosted biogas production worldwide. However, the rapid decrease in the levelized cost of electricity of renewable energies will soon entail electricity prices from biogas much higher than those from solar or wind power. In this context, the upgrading of biogas into biomethane represents an alternative to on-site biogas combustion. Membrane separation technology is rapidly dominating the biogas upgrading market and displacing scrubbing and adsorption technologies driven by the recent breakthroughs in material science. Similarly, biogas biorefineries have recently emerged as an innovative platform for biogas valorization capable of biotransforming methane into added value products. The limited number of bioproducts naturally synthesized by methanotrophs can be boosted via metabolic engineering of methanotrophs, while novel bioreactor configurations capable of supporting a cost-effective methane mass transfer from the gas phase to the methanotrophic broth are currently under investigation to facilitate the full scale implementation of biogas biorefineries.Junta de Castilla y Leon - FEDER (program CLU 2017–09, CL-EI-2021–07 and UIC 315)European Commission-H2020-MSCA-IF-2019 project UP-GRAD (894515)Ministerio de Ciencia, Innovación y Universidades (project IJC2019–040495-I

Upgrading of raw biogas using membranes based on the ultrapermeable polymer of intrinsic microporosity PIM-TMN-Trip

The potential of an ultrapermeable benzotriptycene-based polymer of intrinsic microporosity (PIM-TMN-Trip) for the upgrading of biogas is investigated. Permeation experiments were performed using an in-house bespoke permeation unit for pure gases and gas mixtures, and included tests with model mixtures as well as real biogas from a sewage treatment plant, under dry and humid conditions. Permeability and CO2/CH4 selectivity for either pure gases or for real biogas were high and lie close to or on the recently defined 2019 Robeson upper bound based on ideal permselectivities. In addition, a remarkable increase in CO2/CH4 selectivity was observed after two weeks of continuous exposure to CO2 due to a significant decrease of CH4 permeability. The constant CO2 permeability and increased selectivity upon ageing suggest that ageing in the presence of CO2 causes a rearrangement, rather than a reduction of the fractional free volume. The mixed gas permeability experiments were performed with high stage-cut in order to mimic a real separation process, and the results confirmed the potential of PIM-TMN-Trip membranes for biogas upgrading.Web of Science618art. no. 11869

Gas separation membranes made through thermal rearrangement of ortho methoxypolyimides

Producción CientíficaOrtho-methoxypolyimides were prepared by the classical chemical imidization method and also by azeotropic imidization, using 3,3’-dimethoxybenzidine (DMAB) and hexafluoroisopropylidene diphthalic anhydride (6FDA) as monomers. High molecular weights were achieved by both methods, and the physical properties of the materials were investigated by spectroscopic and thermal analytical techniques. Polymers exhibited excellent thermal properties and film-forming ability, which allowed them to be tested as dense membranes for gas separation after a convenient treatment at high temperature (450 °C) to promote thermal rearrangement (TR). Spectroscopic evidences indicated that the final composition of the TR materials seemed not to correspond to TR-polibenzoxazoles, as it is the case when ortho-hydroxypolyimides are exposed to similar thermal treatments. A detailed study was carried out with the purpose of elucidating the actual mechanism of rearrangement, comparing ortho-hydroxypolyimides and ortho-acetylpolyimides with the ortho-methoxypolyimides obtained in this work. Results led to the conclusion that the chemical nature of the final TR materials attained from ortho-methoxypolyimides is rather complex because imide, cyclolactam and benzoxazole groups seems to be formed under thermal treatment, and the proportion of the different moieties greatly depends on the ortho-substituent, on the synthesis route used to prepare the polyimide and on the time-temperature schedule applied in the thermal rearrangement. The gas permeation properties exhibited by thermally treated ortho-methoxypolyimides compared very well with those of other TR-PBOs reported so far, showing O2 permeability of 94 barrers and CO2 permeability of 540 Barrers.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Synthesis and gas permeation properties of tetraoxidethianthrene-based polymers of intrinsic microporosity

A series of nine polymers of intrinsic microporosity (PIMs) derived from different bis-catechol monomers and 2,3,7,8-tetrafluoro-5,5′,10,10′-tetraoxidethianthrene (TOT) were synthesised and tested for their potential use as gas separation membranes. As powders, they demonstrate significant nitrogen adsorption at 77 K allowing apparent BET surface areas ranging from 432-785 m2g−1to be calculated. Six of the polymers were found to be soluble in quinoline facilitating the casting of self-standing films to allow the assessment of their gas separation properties. Spirobifluorene-based polymers exhibited the highest gas permeability, approaching the performance of the archetypalPIM-1, and the data for some are placed close to the 2008 Robeson upper bounds for O2/N2and CO2/CH4. Ageing studies showed a gradual decrease in permeability, accompanied by an increase in selectivity that moved the data more-or-less parallel to the Robeson upper bounds. The two polymers with the lowest and highest gas permeability were both tested over the temperature range 25-55 °C and an enhancement in permeability for all gases, with the exception of CO2, was observed along with decreased selectivity for almost all gas pairs. The latter seems to be due to the simultaneous drop in both diffusivity selectivity and solubility selectivity for all gas pairs, but especially those involving CO2, due to a strong decrease in solubility with increasing temperature. The analysis of the energetic and entropic selectivity provides further insight into the remarkable transport properties of PIMs. Overall, the tetraoxidethianthrene unit proves to be a suitable building block for use in PIM synthesis for applications in gas separation membranes and these PIMs have a one to two orders of magnitude higher permeability than more common polysulfones.</p

Gas permeability, fractional free volume and molecular kinetic diameters: The effect of thermal rearrangement on ortho-hydroxy polyamide membranes loaded with a porous polymer network

Producción CientíficaMixed-matrix membranes (MMMs) consisting of an ortho-hydroxy polyamide (HPA) matrix, and variable loads of a porous polymer network (PPN) were thermally treated to induce the transformation of HPA to polybenzoxazole (β-TR-PBO). Two different HPAs were synthesized to be used as a matrix, 6FCl-APAF and tBTpCl-APAF, while the PPN used as a filler was prepared by reacting triptycene and trifluoroacetophenone. The permeability of He, H2, N2, O2, CH4 and CO2 gases through these MMMs are analyzed as a function of the fraction of free volume (FFV) of the membrane and the kinetic diameter of the gas, allowing for the evaluation of the free volume. Thermal rearrangement entails an increase in the FFV. Both before and after thermal rearrangement, the free volume increases with the PPN content very similarly for both polymeric matrices. It is shown that there is a portion of free volume that is inaccessible to permeation (occluded volume), probably due to it being trapped within the filler. In fact, permeability and selectivity change below what could be expected according to densities, when the fraction of occluded volume increases. A higher filler load increases the percentage of inaccessible or trapped free volume, probably due to the increasing agglomeration of the filler. On the other hand, the phenomenon is slightly affected by thermal rearrangement. The fraction of trapped free volume seems to be lower for membranes in which the tBTpCl-APAF is used as a matrix than for those with a 6FCl-APAF matrix, possibly because tBTpCl-APAF could approach the PPN better. The application of an effective medium theory for permeability allowed us to extrapolate for a 100% filler, giving the same value for both thermally rearranged and non-rearranged MMMs. The pure filler could also be extrapolated by assuming the same tendency as in the Robeson’s plots for MMMs with low filler content.Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación/10.13039/501100011033 y Fondo Europeo de Desarrollo Regional (FEDER) - (projects PID2019- 109403RBC21, PID2019-109403RBC22 y EQC2019-006481-P)Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grant CLU2017-09, UIC082, VA088G19)Universidad de Valladolid - (PROYEMER-2021-05

Correlating Gas Permeability and Young’s Modulus during the Physical Aging of Polymers of Intrinsic Microporosity Using Atomic Force Microscopy

The relationship, during physical aging, between the transport properties and Young’s modulus for films of polymers of intrinsic microporosity (PIM) was investigated using pure gas permeability and atomic force microscopy (AFM) in force spectroscopy mode. Excellent agreement of Young’s modulus measured for the archetypal PIM-1 with values obtained by other techniques in the literature, confirms the suitability of AFM force spectroscopy for the rapid and convenient assessment of mechanical properties. Results from different polymers including PIM-1 and five ultrapermeable benzotriptycene-based PIMs provide direct evidence that size selectivity is strongly correlated to Young’s modulus. In addition, film samples of one representative PIM (PIM-DTFM-BTrip) were subjected to both normal physical aging and to accelerated aging by thermal conditioning under vacuum for comparison. Accelerated aging resulted in a similar decrease in permeability and increase in Young’s modulus as normal aging, however, significant differences suggest that thermally induced accelerated aging occurs throughout the bulk of the polymer film whereas normal aging occurs predominantly at the surface of the film. For all PIMs, the increased in film rigidity upon aging led to an increase in gas size selectivity