Olefins membranes

A variety of synthetic polymers, including polycarbonate resins, substituted olefins, and polyelectrolyte complexes, are employed as ultrafiltration membranes. Many of these membranes can be handled dry, have superior organic solvent resistance, and are less sensitive to temperature and pH than cellulose acetate, which is widely used in RO systems. 

One of the most studied applications of Catalytic Membrane Reactors (CMRs) is the dehydrogenation of alkanes. For this reaction, in conventional reactors and under classical conditions, the conversion is controlled by thermodynamics and high temperatures are required leading to a rapid catalyst deactivation and expensive operative costs In a CMR, the selective removal of hydrogen from the reaction zone through a permselective membrane will favour the conversion and then allow higher olefin yields when compared to conventional (nonmembrane) reactors [1-3]... 

Hydrogenations involving consecutive reactions are common in the organic process industry and even in the hydrogenation of fats. In the fine chemicals industry we have examples of acetylenic (triple) bonds to be selectively converted to olefinic (double) bonds. Lange et al. (1998) have shown, for the comversion of the model substance 2-hexyne into cis-2-hexene, how catalytically active microporous thin-film membranes can accomplish 100% selectivity. This unusual selectivity is attributed to avoidance of backmixing. 

Membrane banners are applied to the exterior of the foundation and also beneath the floor slab during construction. Materials used for the membrane barriers range from coextruded poly olefin to polyvinyl chloride to foil sheets with many other materials in between. All membrane barriers must have the edges sealed to prevent radon from migrating around the edges and back into the building. 

Okamoto, K.,S. Kawamura, M. Yoshino, H. Kita, Y. Hirayama, N. Tanihara, and Y. Kusuki, Olefin/ paraffin separation through carbonized membranes derived from an asymmetric polyimide hollow fiber membrane, Ind. Eng. Chem. Res., 38, 4424,1999. 

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

New approaches to catalyst recovery and reuse have considered the use of membrane systems permeable to reactants and products but not to catalysts (370). In an attempt to overcome the problem of inaccessibility of certain catalytic sites in supported polymers, some soluble rho-dium(I), platinum(II), and palladium(II) complexes with noncross-linked phosphinated polystyrene have been used for olefin hydrogenation. The catalysts were quantitatively recovered by membrane filtration or by precipitation with hexane, but they were no more active than supported... 

Stable membranes are generally produced with polyelectrolytes where the charged group is on a side chain attached to either a cyclic or olefinic backbone. 

Solid PVA-Co2+ composite asymetric membranes have been prepared starting from PVA and two different salts Co(N03)2 and Co(CH3COO)2, respectively, in order to separate cyclohexene/cyclohexan mixtures. A facilitated transport mechanism has been evidenced, due to the capacity of Co2+ ions to coordinate the olefin molecules [82], The authors reported stronger complexation of Co2+ ions with cyclohexene in the case of PVA/ Co(CH3COO)2 mixtures then in the case of PVA/ Co(N03)2 mixtures. It was found that for a concentration ratio of ([Co2+]/[OH]) by 0.75 mol/mol, the permeation flux of PVA membrane containing Co2+ increases 2-3 times and the separation factor increses 50 times compared with pure PVA membrane. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

M., Mukai, S.R., Kawase, M., and Hashimoto, K. (2003) Methanol to olefins using ZSM-5 zeolite catalyst membrane reactor. Chem. Eng. Sci.,... 

There are several lines of research which indicate that ozone can react with proteins, amino acids and olefinic groups of membrane lipids (16, 17). Regarding unsaturated fatty acids, Swanson ( ) concluded that these olefinic groups were... 

The most likely identity of these components are the membrane lipids. We suggest, therefore, that the primary reaction of ozone with the envelope membranes involves the disorganization of the membranes via constituents other than the lipids. A similar possibility has been developed by Mudd al. (17) who found that ozone does not react readily with lecithin when in a bilayer configuration. In addition, Swanson et al. ( ) reported that the electron microscopic image of most cellular membranes is not affected by prior treatment with ozone. The rationale in their discussions is that the architecture of the membrane restricts the ability of ozone to react with the olefinic groups. 

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