Poly PTMSP membranes

R. Srinivasan, S.R. Auvil, and P.M. Burban, Elucidating the mechanism(s) of gas transport in poly[l-(trimethylsilyl)-1-propyne] (PTMSP) membranes. J. of Membrane Science, 86 (1994) 67-86. 

For the first time, siUca-filled poly(l-trimethylsilyl-l-propyne) (PTMSP) layers on top of UF membranes for the pervaporative separation of EtOH-water mixtures was reported by Claes et al. (2010). Reduction of the thickness of the separating PTMSP top layer and addition of hydrophobic silica particles resulted in a clear flux increase as compared with dense PTMSP membranes. The performances of the supported PTMSP-silica nanohybrid membranes were significantly better than the best conunercially available organophilic PV membranes. The developed composite PTMSP-silica nanohybrid membranes exhibited EtOH-water separation factors around 12 and fluxes up to 3.5 kg/m h, establishing a sevenfold to ninefold flux inCTcase as compared with dense PTMSP membranes. 

In contrast, organophilic PV membranes are used for removal of (volatile) organic compounds from aqueous solutions. They are typically made of rubbery polymers (elastomers). Cross-linked silicone rubber (PDMS) is the state-of-the-art for the selective barrier [1, 43, 44]. Nevertheless, glassy polymers (e.g., substituted polyacetylene or poly(l-(trimethylsilyl)-l-propyne, PTMSP) were also observed to be preferentially permeable for organics from water. Polyether-polyamide block-copolymers, combining permeable hydrophilic and stabilizing hydrophobic domains within one material, are also successfully used as a selective barrier. 

Because the so-called ultrahigh free volume polymers aroused much interest during the last 10 years, they will be briefly described in this introductory chapter. The publication of the physical properties of poly(l-trimethylsilyl-l-propyne) (PTMSP) in 1983 [281] aroused much interest in the field of membrane research. Up to this time it had been believed that the rubbery poly(dimethyl si-loxane) has by far the highest gas permeability of aU known polymers. Very surprisingly, the glassy PTMSP showed gas permeabilities more than 10 times higher than PDMS. This could be attributed to its very high excess-free volume and the interconnectivity of the free volume elements. Since then a number of... 

The preferential affinity to EtOH depends on the balance between the hydro-philicity and the hydrophobicity of the membrane s material (Huang 1991). Qiu and Peinemann (2006) developed novel organic nanocomposite membrane for PV. The basic polymers were PDMS and poly(l-trimethylsilyl-l-propyne) (PTMSP). By implanting the hydrophobic organic molecules in PTMSP and PDMS, permselectivity to EtOH was enhanced. For example, PDMS with 20 wt% a-cyclodextrins provides a separation factor of 12 for EtOH (5 wt%)-water (95 wt%). Similarly, PTMSP with only 8 wt% a-cyclodextrins improved the enrichment of the low concentration of EtOH from 5 to 48 wt% and maintained the flux at 9 kg pm/m h. They claimed that the increased performance in EtOH-water separation with this organic nanocomposite membrane may lead to the practical industrial application by means of the PV process to produce bioethanol. 

Two methods are used for the preparation of capillary gas adsorption columns the suspension method, in which the inner walls of the column are coated with a suspension of the adsorbent, and the chemical method, in which an adsorption layer is formed on the walls of the column through a process of synthesis of the adsorbent in the capillary column. Recently, a new type of porous polymer (poly(l-(trimethylsilyl)-l-propin) (PTMSP)) has been suggested as an organic adsorbent and has been actively studied as a promising material in membrane technology. This polymer dissolves well in some volatile solvents, and a layer of it can be formed in a capillary column using simple techniques for coating from a solution of a stationary phase in a volatile solvent. 

Another possible approach to indirectly characterize the membrane morphology is based on the investigation of the free volume within the matrix. Density measurements [119,120] and positron annihilation lifetime spectroscopy evaluation [47] are common methods. Typically, the comparison between the theoretical density or free volume (calculated by simple additivity rules) and the experimental one can reveal the presence of a good interfacial morphology or the presence of interface voids or clustering formation. Fig. 7.13 shows the influence of filler content on the morphology of poly(trimethylsilyl propyne) (PTMSP)/Ti02 NCMs in terms of the volumetric fraction of interface voids as calculated from a comparison of the expected and measured membrane density [119],... 

Nagase et al. have studied the grafting of polyacetylene and its derivative onto poly(dimethylsiloxane) (PDMS) for membrane applications [118-121]. Poly(l-trimethyl-silyl-l-propyne) (PTMSP) is a polymer known to have excellent gas permeability but suffers from relatively low selectivity and a decrease in gas permeability over time. Graft copolymers of poly(l-phenyl-1-propyne) (PPP) onto PDMS were found to have improved gas permeability and selectivity, and the performance was related non-linearly to the PDMS content. A minimum oxygen permeability coefficient was found for a copolymer with 55 mol% PDMS [118]. The same membrane series was also foimd to be permselective for a range or organic liquids, including an ethanol/water mixture, and was used in pervaporation applications... 

Their applications and improved long-term stability for gas separation and pervaporation were further investigated. A maximum in the separation factor and rate was obtained for the PTMSP copolymer with 12 mol% PDMS. The membrane was able to convert a 7 wt% ethanol mixture to over 70 wt% in ethanol [120]. Good oxygen permeability and stability of over a month was also achieved for the PTMSP copolymers with over 60% PDMS [121]. In a separate study, PPP was foimd to have good permselectivity to water while PTMSP is alcohol permselective. These copolymers as well as a series of poly(phenyl acetylene) graft PTMSP copolymers were further studied for pervaporation applications [122]. 

Microporous polyethylene (PE) membranes with various pore diameters and porosities and microporous polytetrafluoroethylene (PTFE) membrane were used as substrates for the plasma graft polymerization (Table II). Besides these porous substrates, homogeneous poly[ l-(trimethyl si lyl)-l-propyne] (PTMSP), which has the highest gas permeability among polymeric materials, was used as the substrate. The poly[l-(trimethylsilyl)-l-propyne] was synthesized from l-(trimethylsilyl)-l-propyne according to the literature procedure (19). Films were prepared by casting polymers from toluene solutions. Hereafter, the respective substrate membranes will be abbreviated as shown in Table II. 

Polymeric membranes must have good permeabilities, permselectivities, and long4erm stability. Moreover, they must be compatible with the process environment in which they will be used. However, polymers with high permeability tend to have low selectivity and vice versa (1), Poly(l-trimethylsilyl-l-propyne) (PTMSP) has the highest intrinsic gas permeability of all known synthetic polymers. It was first synthesized by Masuda and Higashimura in the 1980 s (2). However, PTMSP has the lowest selectivities of all known polymers and exhibits unstable gas permeability (i). 

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