Gas transport parameters

Early fundamental studies of gas transport in polymers were almost entirely confined to hydrocarbon materials above their glass transition temperatures. The essentially nonpolar structures of the elastomers led to a number of reasonably successful attempts to correlate gas transport parameters with various physical characteristics of the gases and the polymers. These have been summarized and discussed in a number of papers In addition to studies with hydrocarbon elastomers a few studies of other amorphous polymers above their glass transition temperatures have dealt with polyvinyl acetate silicones and fluorocarbon polymers Recent studies have also dealt with poly(methyl aciylate) poly-(vinyl methyl ether) and poly(vinyl methyl ketone) With these more... 

Polymers I-VI were deposited on polysulfone (PSF) and polyamide (PA) hollow fibers according to the technique [6]. Gas transport parameters of the prepared composite membranes for the pair C4H10/CH4 have been measured. The results are presented in Table 1. 

Molecular dynamics calculations have been carried out to simulate a conformational model and vibrational spectra of poly(dichlorophospha-zenes). Molecular dynamics similations for [NP(OCH2CF3)2] and the isomers [NP(OBu")2] , [NP(OBu )2] and [NP(OBu )2] show a reasonable agreement between the calculated and experimental values of density and glass transition temperature as well as for gas transport parameters in these polymers.Small molecule models have been used for a theoretical approach of poly(thionylphosphazenes). ... 

Abstract The presented paper is a summary of our results on synthesis and polymerization of silyl-containing norbomenes and norbomadienes via ring-opening metathesis polymerization (ROMP) and addition processes as well as ring-opening polymerization (ROP) of silacyclobutanes and disilacyclobutanes. The synthesis of heterochain and carbochain polymer families with regularly varied substituents at Si atom and various number and location Si(CH3)3-substituents has been realized. Systematic study of gas transport parameters of polycarbosilanes series of different classes allowed us to find out real eorrelations between features of chemical polymer structure and its gas separation eharacteristics. 

This work is devoted to systematic study of gas transport parameters of polycarbosilanes obtained from silicon-containing cyclic monomers. This approach allowed us to synthesize carbochain and heterochain polymer femilies with regularly varied substituents at Si atom. On the other hand, such research on polymer series of different classes leads to basic correlations and helps one to understand relationships between features of polymer chemical structure and its gas separation characteristics. 

The investigation of gas permeability of the obtained polymers gave an opportunity to find out some correlations between polymer structure and its properties (Table 2). Introduction of SiMes pendant groups in ROMP polynorbomenes substantially increases permeability coefficients for light gases. At the same time the permselectivity for some gas pairs also increases, while in the majority of cases an increase in permeability is accompanied by reduced permselectivity and vice versa. It should be noted that cis or trans content in the obtained polycyclopentylenevinylenes did not exert some influence on the gas transport parameters [17]. 

The copolymers had good film-forming properties and high gas transport parameters. This especially concerns to the 1 1 copolymer. In this case, the... 

To implement the polymerization and copolymerization of various silacyclobu-tanes, we used catalysis by the propene complex of Pt, which was prepared by heating Speier s catalyst directly in the reaction ampoule before the experiment [21, 32]. In addition, the propene complex of Pt allowed one to achieve high yields of high-molecular-weight polymers of MSCBs carrying two phenyldimethylsilyl-methyl substituents and carbazolyl and diphenyl oxide moieties in substituents [23]. At 7-15°C, the propene Pt-complex made it possible to prepare random soluble copolymers of diallylsilacyclobutane and tetramethyldisilacyclobutane of various compositions [21, 32], In those works, gas transport parameters of copolymers of dimethylsila- and tetramethyldisilacyclobutanes were studied. 

For extrathoracic deposition of particles, the model uses measured airway diameters and experimental data, where deposition is related to particle size and airflow parameters, and scales deposition for women and children from adult male data. Similar to the extrathoracic region, experimental data served as the basis for lung (bronchi, bronchioles, and alveoli) aerosol transport and deposition. A theoretical model of gas transport and particle deposition was used to interpret data and to predict deposition for compartments and subpopulations other than adult males. Table 3-4 provides reference respiratory values for the general Caucasian population during various intensities of physical exertion. 

This chapter will only deal with the possible gas transport mechanisms and their relevance for separation of gas mixtures. Beside the transport mechanisms, process parameters also have a marked influence on the separation efficiency. Effects like backdiffusion and concentration polarization are determined by the operating downstream and upstream pressure, the flow regime, etc. This can decrease the separation efficiency considerably. Since these effects are to some extent treated in literature (Hsieh, Bhave and Fleming 1988, Keizer et al. 1988), they will not be considered here, save for one example at the end of Section 6.2.1. It seemed more important to describe the possibilities of inorganic membranes for gas separation than to deal with optimization of the process. Therefore, this chapter will only describe the possibilities of the several transport mechanisms in inorganic membranes for selective gas separation with high permeability at variable temperature and pressure. 

In the literature, one can find other empirical or semi-empirical equations representing the kinetics of powder reactions. One can certainly take into account grain size distribution, contact probability, deviations from the spherical shape, etc. in a better way than Carter has done. Even more important are parameters such as evaporation rate, gas transport, surface diffusion, and interface transport in this context. As long as these parameters are neglected in quantitative work, the kinetic equations are inadequate. Nevertheless, considering its technological relevance, a particular type of powder reaction will be discussed in the next section. 

The discussion directly following Eq (6) provides a simple, physically reasonable explanation for the preceding observations of marked concentration dependence of Deff(C) at relatively low concentrations. Clearly, at some point, the assumption of concentration independence of Dp and in Eq (6) will fail however, for our work with "conditioned" polymers at CO2 pressures below 300 psi, such effects appear to be negligible. Due to the concave shape of the sorption isotherm, even at a CO2 pressure of 10 atm, there will still be less than one CO2 molecule per twenty PET repeat units at 35°C. Stern (26) has described a generalized form of the dual mode transport model that permits handling situations in which non-constancy of Dp and Dh manifest themselves. It is reasonable to assume that the next generation of gas separation membrane polymers will be even more resistant to plasticization than polysulfone, and cellulose acetate, so the assumption of constancy of these transport parameters will be even more firmly justified. 

Based on the reference case, parametric calculations were conducted specifying the actuation condition and time of isolation valves as a parameter. Table 2 shows the actuation times of isolation valves, calculation results of secondary cooling system isolation time and amount of helium gas transportation from primary to secondary. 

In previous sections, we examined the design parameters for gas-liquid, gas-solid, liquid-liquid, gas-liquid-solid, biological polymerization, and special types of mechanically agitated reactors. In this section we present a brief review on available techniques for the measurement of various mixing and transport parameters for a mechanically agitated vessel. Both physical and chemical techniques are examined. 

If a transport parameter rc — CS/CL is defined, where Cs is the concentration of C at the catalyst surface, then Peterson134 showed that for gas-solid reactions t)c < rc, where c is the catalyst effectiveness factor for C. For three-phase slurry reactors, Reuther and Puri145 showed that rc could be less than t)C if the reaction order with respect to C is less than unity, the reaction occurs in the liquid phase, and the catalyst is finely divided. The effective diffusivity in the pores of the catalyst particle is considerably less if the pores are filled with liquid than if they are filled with gas. For finely divided catalyst, the Sherwood number for the liquid-solid mass-transfer coefficient based on catalyst particle diameter is two. 

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