Hydrocarbon composite membranes

Table 3 Conductivity data for heteropoly acid/imbibed hydrocarbon composite membranes, [ ] - control membrane data... 

Bessarabov s devices use composite membranes consisting of a thin silicone rubber polymer layer coated onto a microporous poly(vinylidene fluoride) support layer. These membranes have high fluxes and minimal selectivities for the hydrocarbon gases, but the dense silicone layer provides a more positive barrier to bleed-through of liquid than do capillary effects with simple micro-porous membranes. 

The activity of obtained composite membrane catalysts is investigated in the model reactions of hydrocarbons dehydrogenation. 

Besides the compact membrane catalysts described in Section II, there are two types of composite membrane catalyst porous and nonporous. Composite catalyst consists of at least two layers. The first bilayered catalyst was prepared by N. Zelinsky [112], who covered zinc granules with a porous layer of palladium sponge. The sponge became saturated with the hydrogen evolved during hydrochloric acid reaction with zinc and at room temperature actively converted hydrocarbon iodates into corresponding hydrocarbons. 

Composite membrane catalysts can also be assembled with polymeric supports or intermediate layers [117-119]. These membranes were tested as membrane catalysts for selective hydrogenation of some dienic hydrocarbons and proved to be as selective as monolithic palladium alloy membranes [117]. The use of polyarilyde has been proposed in order to widen the temperature range of polymer-supported membrane application... 

According to literary data, the following mixtures of aromatic/aliphatic-aromatic hydrocarbons were separated toluene/ n-hexane, toluene/n-heptane, toluene/n-octane, toluene/f-octane, benzene/w-hexane, benzene/w-heptane, benzene/toluene, and styrene/ethylbenzene [10,82,83,109-129]. As membrane media, various polymers were used polyetherurethane, poly-esterurethane, polyetherimide, sulfonyl-containing polyimide, ionicaUy cross-linked copolymers of methyl, ethyl, n-butyl acrylate with acrilic acid. For example, when a composite polyetherimide-based membrane was used to separate a toluene (50 wt%)/n-octane mixture, the flux Q of 10 kg pm/m h and the separation factor of 70 were achieved [121]. When a composite mebrane based on sulfonyl-containing polyimide was used to separate a toluene (1 wt%)/ -octane mixture, the flux 2 of 1.1 kg pm/m h and the separation factor of 155 were achieved [10]. When a composite membrane based on ionically cross-linked copolymers of methyl, ethyl, w-butyl acrylate with acrilic acid was used to separate toluene (50 wt%)//-octane mixture, the flux Q of 20-1000 kg pm/m h and the separation factor of 2.5-13 were achieved [126,127]. 

Composite metal membranes are most often the structure of choice when a reactive group 3-5 metal or alloy is the principle constituent of the membrane. The relative chemical reactivity of these metals dictates that an inert coating must be applied to at least the feed surface of the membrane. Palladium, or better yet a palladium alloy, customarily serves as the coating layer. If it can be guaranteed that the permeate side of the membrane will never be exposed to reactive gases (e.g., water, carbon oxides, and hydrocarbons), then a two-layer composite membrane is a satisfactory choice. However, normal operating procedures and the potential for process upsets typically favors the selection of a three-layer composite structure. 

R. Dittmeyer, Preparation and characterization of palladium composite membranes for hydrogen removal in hydrocarbon dehydrogenation reactors, Catal. Today 2001, 67, 33-42. 

Besides the well-established applications there are a number of emerging membrane gas separations. These are, for example, natural gas hydrocarbon dewpointing, olefin/paraffm separation and separation of hydrocarbon isomeres. These will be addressed in the following material section. The purpose of this chapter is to provide an overview of state-of-the-art and emerging materials for gas-separation membranes, to give some key features of integral asymmetric and composite membranes and finally to explain the influence of basic process parameters. 

Basic process data are available from the development of organic vapor separation. The real challenge is the transformation of the available knowledge into high-pressure applications. Several drawbacks such as the compaction of the substructure of composite membranes and the influence of the boundary layer On the membrane selectivity have to be overcome. Pour structure and polymer compositions have to be suited to the high operating pressure in the presence of higher hydrocarbons [22, 23]. 

Chang, J.H., Park, J.H., Park, G.G., Kim, C.S. and Park, 0.0. 2003. E roton-conducting composite membrane derived from sulfonated hydrocarbon and inorganic materials. 

The unusual solubility of gases and vapors in perfluoropolymers has several applications relevant to membrane gas separations. Perfluoropolymers have solubility selectivities that are significantly different from those of hydrocarbon-based polymers. The amorphous perfluoropolymers can be fabricated into thin, high-flux composite membranes, which possess the excellent chemical and thermal stability. Typical reported pure gas permeabilities and selectivities of these fine amorphous perfluoropolymers are shown in Table 16.8 [33]. 

DMFC polarization curves for the cell equipped with the composite membrane in a wide temperature range are reported in Fig. 2.12. The performance increases significantly with the cell temperature. The maximum power density for the cell with the composite membrane at 120 °C is 180 mW cm which is a performance of relevant interest for DMFCs being achieved with a hydrocarbon membrane [16]. 

In recent years, many kinds of materials have been developed to synthesize proton-conducting membranes for H2/air PEM fuel cells, and some have exhibited promising performance as potential candidates to replace PFSA membranes. The major membranes are (1) fluorinated membrane, (2) partially fluorinated membrane, (3) nonfluorinated (including hydrocarbon) membrane, and (4) nonfluorinated composite membrane. Among these, the hydrocarbon membrane is considered a promising alternative due to its low cost compared with PFSA membranes [61]. 

The recovery of organic vapors from waste gas streams using polymeric membranes is a well established process (7). Typically, composite membranes are used for this process. These membranes consist of a diin, selective rubbery layer coated onto a microporous support material. The selectivities of these membranes for organic vapors over nitrogen are typically about 10-100. Currently, commercial vapor separation membrane applications include small systems (10-100 scfin) to recover fluorinated hydrocarbons (Freons) and other high-value solvent vapors from process vent streams to large systems (100-1,000 scfin) for recovery of hydrocarbon vapors in the petrochemical industry (7). 

J. H. Chang, J. H. Park, G. G. Park, C. S. Kim and O. O. Park, Proton conducting composite membranes derived from sulfonated hydrocarbon and inorganic materials, J. Power Sources 124, 18-25 (2003). 

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