Liquid permeabilities

Gas permeation tests have been carried out for many carbon membranes. However, there is very limited data for the liquid permeation tests, especially for the application of carbon membranes for ultrafiltration (UF) or microfiltration (MF). Some studies [1,2] demonstrated that carbon UF membranes could be made by adding non-carbonizing polymers such as poly(ethylene glycol) (PEG) to the precursor solution. Encouraged by the findings of [3] and [4], Shah and co-woikers successfully made nanoporous carbon UF membranes suitable for bioprocessing applications [5]. 

Carbon membranes were fabricated by pyrolysis of a mixture of polyffurfuiyl alcohol) (PFA) and poly(ethylene glycol) (PEG) that was spin-coated on a mac-roporous stainless steel support. The stainless steel support was first modified by physical deposition of sub-micron-sized silica particles within the micropoies and then PFA/PEG/acetone solution was spin-coated onto the silica-modified support. Coated support was heated in a stream of Ar to 600°C for 4 h for pyrolysis. The process was repeated. Hydrauhc permeability was obtained under 40-50 psig. UF experiments with blue dextran as the solute was also condueted. Table 6.1 shows the hydraulic permeability and blue dextran sieving data. 

Dextran sieving curves were also evaluated by filtration of dextrans of different average molecular weights in kDa, i.e. 2000,167,75,40, and 10 kDa. Sieving coefficient versus dextran average molecular weight is given in Fig. 6.1. 

Ismail et al., Carbon-based Membranes for Separation Processes, 

The steady state volume flux Jy of an incompressible fluid though a porous medium of cross-sectional area A, thickness / and porosity e under a pressure differential AP, can be expressed in terms of the mean velocity in the pores Up 

If e and Kc are known or can be estimated, th and hence A the specific surface area of the porous medium can be determined. According to the well known Kozeny-Carman treatment 

The first part of the relation (4.33) is the well known Poiseuille equation for cylindrical capillaries. The mcdn problem is the lack of theoretical basis for assigning a value to i a priori (an empirical value of 1.5 is suggested by Kozeny). This obviously precludes the use of these equations as an independent method for determining Th or A. An example of experimental determination of Kc for y alumina membranes is given in Ref. [130]. The corresponding tortuosity is very high in agreement with the observed microstructure of this type of membrane made of plate-shaped crystallites. 

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Laboratory experiments have indicated that carbonate precipitation can alter the permeability of the core samples under reservoir conditions. The precipitation reduces the gas permeability in favor of the liquid permeability. This indicates that precipitation occurs preferentially in the larger pores. 

The challenge for modeling the water balance in CCL is to link the composite, porous morphology properly with liquid water accumulation, transport phenomena, electrochemical kinetics, and performance. At the materials level, this task requires relations between composihon, porous structure, liquid water accumulation, and effective properhes. Relevant properties include proton conductivity, gas diffusivihes, liquid permeability, electrochemical source term, and vaporizahon source term. Discussions of functional relationships between effective properties and structure can be found in fhe liferafure. Because fhe liquid wafer saturation, 5,(2)/ is a spatially varying function at/o > 0, these effective properties also vary spatially in an operating cell, warranting a self-consistent solution for effective properties and performance. 

Typically, the liquid permeabilities are obtained with water being the permeate and expressed in terms of L/h-m -bar. The gas permeabilities are often expressed in terms of air or nitrogen permeabilities. The retention characteristics can be generally and generically obtained by using some model molecules. The most commonly used model molecules are polyethylene glycol (PEG) polymers which are linear and flexible in nature, and... 

Random vs nonrandom liber polymer composite modulus hardness liquid permeability Anisotropy of physical properties... 

Coating (web) Pore dimension liquid permeability Composite modulus permeability... 

Two of the more recently developed polysulfide polymers are the mercaptan-terminated polyoxypropylene urethane polymer and the polythioether polymer. The urethane-backbone-based polymer is used in many sealant formulations for insulating glass applications. The thioether backbone contains sulfur, but no S—S bonds, which are the weakest part of the conventional polysulfide polymer. This polymer improves the thermal stability and reduces the gas—liquid permeability. 

Polyvinyl butyral - A nonvapor or liquid permeable plasticized polymer formulation with additive materials that forms a continuous film from an ethanol solution ( 5 min). 

PRECOAT FILTRATION - DIATOMACEOUS EARTH FILTRATION. The mOSt economical method of filtering fruit juices with a high suspended solids content is with precoat filters. In these, the filter sheet is created by precoating a liquid-permeable filtering element with the filter aid. In addition to diatomaceous earth, perlite and cellulose are also used as filter aids in fruit juice production. 

If the foam phase is thought of as a pseudo continuous fluid with an apparent viscosity Vapp = it follows that Papp is greater than that of the aqueous liquid phase. (For the tests here, values of Uapp were on the order of 1 to 50 times that of water). Because of this, when foam and liquid move through a porous medium under an applied pressure drop, the foam, being the most viscous phase, must occupy a larger region of the pore space. Consequently, as observed, the gas saturation is increased over that of non-dispersed phase flow and the liquid permeability is correspondingly decreased. 

Dow Chemical developed a modification of the trickle-bed cell, in which a liquid permeable membrane separated two chambers [72]. As shown in Fig. 17, a packed-... 

Nagase Y, Naruse A, and Matsui K. Chemical modification of polysulphone. 2. Gas and liquid permeability of polysulpho-ne/polydimethylsiloxane graft copolymer membranes cf Polymer. 1990 31(1) 121-125. 

Intrinsic gas permeabilities from literature were found to produce unrealistically high interior pressures. Simulations show that the permeability of liquid has a large influence on the time of conversion of the moist wood samples. Liquid permeabilities 10 times lower than the gas permeability were found. There was a discrepancy between measured and simulated temperature gradient found for moist samples probably explained by radial variations in material properties and structural dependence of the heat transfer properties. 

INFLUENCE FROM LIQUID PERMEABILITY ON TIME OF CONVERSION... 

Fig. 6. Influence from liquid permeability. Measured temperatures (solid lines) from Figure la and 5b, and simulated centre temperatures (dotted lines) of the wood sample for Case 6 and 7, Table 1,44% moisnire.

In earlier work a sensitivity analysis of simulations of dry wood shows an 8% reduction in time of pyrolysis at 1 mm reduction of the final charcoal radius [I], This was shown to be in the same range as the influence from an exothermic heat of pyrolysis (150 kJ/kg). In this paper the inclusion of an axial convective flow is shown to influence the time of pyrolysis in the same range, a reduction of 6% (evaluated from Figure 2a where the times of conversion of Case 1 and Case 3 are estimated to 750 and 708 seconds respectively). For wood with a moisture content above the fibre saturation point the axial liquid permeability is shown to dominate the influence on the conversion time. 

Table A2. Data of gas and liquid permeability used in simulations. 

Liquid permeability Hagen- Poiseuille Kozeny- Carman Cylindrical Voids between spheres 0.1-10 p Pore hydraulic radius Experimental simplicity. Assumptions laminar flow in HP equation, zero wetting angle, no pre-existing agent on the surface. Great influence of pore geometry and tortuosity on the interpretation of results. Network effects. 

Gas and liquid permeability are influenced by the choice of filler. The platelet structure of mica or talc as a filler in paints and plastics decreases the transmission of gases and liquids. 

Liquid permeability increases 25% for every 10°C increase in temperature. 

Effective Permeability. Bernard and co-workers (31, 32) pursued pioneering studies to quantify gas and liquid permeabilities in the presence of foam. They either coinjected surfactant solution and nitrogen, or used alternating slugs of each. For consolidated porous media with absolute permeabilities that range from 0.1 to 0.25 /zm2, they found several... 

At low gas pressures and for small pore size, the mean free path of the gas molecules may be on the order of the pore size and therefore velocity slip occurs (Knudsen effect), resulting in higher permeabilities. However, an increase in the permeability due to an increase in gas pressure has been found in some experiments. Scheidegger [24] discusses the effect of the Knudsen slip, the internal surface roughness, surface absorption, capillary condensation, and molecular diffusion on the measured permeability. By examining these effects at the pore level, it becomes clear that the measured gas and liquid permeabilities can be noticeably different. 

Fig. 11.11 Photographs showing non-mercury instruments for the determination of porosity and related data, (a) Capillary flow po-rometer for gas as well as liquid permeability and the testing of filter integrity (b) gas pycnometer (c) bulk/absolute density analyzer (d) BET sorptometer (courtesy PMI, Ithaca, NY, USA).

Non-compatibilized PP/PA blends for films, sheets or bottles with good printability and low liquid permeability Mesrobian and Ammondson, 1962... 

A DEA group was appended onto a polyethylene porous hollow-fiber membrane with a density of 2.2 mmol per gram of the resultant DEA-EA fiber. The inner and outer diameters of the hollow fiber were 2.4 and 4.4 mm, respectively. The liquid permeability, i.e., the permeation rate per unit of inside surface area, of the DEAEA fiber for the buffer was maintained at 50% of that of the original hollow fiber. Volume swelling of the porous hollow fiber accompanied by graft polymerization prevented the graft chains from filling the pores. 

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