Unit permeation rate

A commercially available cellulose acetate film which we would now describe as homogeneous or isotropic, gave the results shown in Row 2 of Table I. The volumetric permeation rate of water per unit membrane area, called the water permeation flux Jl mVm day, and the water permeation constant. A, m m day atm were both very low, but a salt rejection of 94 percent was obtained. We define ... 

Time-dependent flux decline is plotted in Figure 8. The C02 permeation rate, in units of SCFH/ft2.100 psi, was calculated from performance data for the fifteen elements in series. This rate corresponds to that which would be obtained for pure CO2 under similar partial pressure differences. After an initial (40 hrs) nonlinear flux decline, the C02 rate experienced a 10% loss over the next 1,000 hours (40 days). As this flux decline is a log/log relationship, only 6% more would be lost over the next three years, the minimum expected element lifetime. Membrane systems can be easily designed to adapt to a changing permeation rate by adjusting the feed flow rates and/or pressure, by allowing for addition of more elements in series after a period of time, and by using a progressive element replacement schedule. 

Hydrogen permeation is dehned as the transport of hydrogen as dissociated hydrogen atoms and has units of moles of hydrogen gas per square meter per second (mol m.- sec ), which is the permeation rate. Known as Richardson s law this relation can be expressed as... 

Units of permeation rate cm (STP)/cm -s-cm Hg. Substrate 1-mil-thick silicone sheet (MEM 100, General Electric). 

Permeate flux is defined as the permeation rate per unit of membrane area. Thus, maximizing the flux will reduce system size and cost. Permeate flux can be calculated as follows (15) ... 

Alternately, Pi can of course be placed on a unit area basis (e.g., per square centimeter). In turn, the feed rate F, permeate rate F, and reject rate L would then be on the same common unit area basis. 

Whitestone did evaluate many alternatives prior to choosing RO. They decided to use RO because the initial cost was low, maintenance requirements were low and operator attention was minimal compared to the alternatives. Whitestone also calculated that the operating costs, both in manpower needs and in actual chemicals and membrane replacement, was less than other alternatives. Since the RO system would be operating on biologically active materials it was decided that cleaning every 8 hours would be appropriate. Therefore, an automatic Clean-In-Place (CIP) system was developed and installed with the RO unit. There is typically a 1 01 reduction in permeate rate due to fouling prior to the time that Whitestone cleans the RO unit. 

Normalized flux Permeation rate per unit filtering surface, normalized to a given set of operating conditions such as constant temperature, pressure and/ or concentration. 

In this report, transfilter flow refers to the linear velocity of retentate over the membrane surface (retentate velocity through a filter tube or lumen). Filter pressure was the gage pressure of the retentate at the filter inlet. The permeate side of the filter was maintained at atmospheric pressure for all experiments. Pressure drop was the difference between retentate pressures at the filter inlet and outlet. Flux was permeation rate per unit area of membrane. ... 

The permeability is defined in terms of the steady state permeation rate of component i per unit area divided by the normalized partial pressure difference of component i, Ap, acting across the membrane of thickness, C (see Fig. 1) (23,24). 

A perm expresses permeation rate in the units of grains per square foot of membrane, per inch of Hg pressure differential, per hour of time elapsed. (The perm measure does not include the thickness which is part of the permeability constant formula. Thus, a membrane of a given material will have a different "perm" value for each thickness of membrane measured.) The units are grains/ft.2 - in. Hg - h. 

When concentration polarization occurs, permeate fluxes become invariant with the transmembrane pressure, and increases in the permeation rate can be achieved only by enlarging the membrane surface area or by improved fluid management. The design of the UF membrane unit in the polarized regime must relate the flux to the optimal level of reactor VSS or total suspended solids (TSS) according to Michaels gel theory, to give... 

The inlet flow on the permeate side would be that of an inert gas, for instance, which continuously sweeps the lower side of the membrane and clears the permeate. If the flow is large compared to the volume, then we will have near zero concentrations of the permeate gas and maximal permeation rates. (In fact, this is what the steady-state analysis we just did imposed automatically.) We still need to consider only the component balances at this point. We will use all the same numbers and equations except that qll will be fixed at the inlet and outlet of the permeate side of the unit ... 

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. 

Clearly, from Fig. 1, the solubility of a solute in an organic solvent correlates very well with the permeability of the Nitella membrane for that solute. But it is also clear that the correlation is only partial. Thus, of two solutes with the same partition coefficient the one with smaller molecular weight would seem to permeate faster. Solute size as well as hpid solubility are both important determinants of permeation rate. The particular solvent chosen, olive oil, seems however to be a very good model for the ability of the membrane barrier to discriminate between the various permeants, since the overall increase in permeability as the structure of the permeant is varied correlates closely with the increase in partition coefficient. Were the two parameters to be strictly linked all the data would fall on the line of unit slope in the figure, the line of identity. Later we shall see cases where the data do not support such a close similarity between certain membranes and model solvents. 

Fig. 4 depicts the data of Sha afi et al. [11], of Savitz and Solomon (12) and of Klocke et al. [13] on the penetration of 23 different compounds into human red cells plotted as a log/log plot (cf. Fig. 1) against the relevant ether/water partition coefficient. The strong dependence of permeability on partition coefficient that was noted by Collander for plant cells is somewhat less obvious for the human erythrocyte. Values of the partition coefficient vary over a range of 10 for molecules which have the same permeation rate. Molecules with the same partition coefficient have permeation rates which vary over a range of 10. But a line of unit slope can be drawn through many of the points on the log/log plot showing the strong dependence of permeation coefficients on partition coefficients. 

The data In Table II Indicate that the permeation rate per unit partial pressure difference, R./AP, for both CO2 and N2 remained. ..---------------.—. ----- ------V. -n —j. T, varied... 

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