The mechanism of macromolecular ultrafiltration with microporous membranes is discussed, focusing on factors that control membrane flux and solute retention. Flux is limited by mass transfer conditions on the feed solution side of the membrane (concentration polarization). Solute retention is determined by geometric properties of the membrane pores and the macromolecules in solution, as well as concentration polarization.Ultrafiltration data for solutions of Dextran fractions and a Carbowax fraction are presented and compared with theory. Agreement for turbulent flow, laminar flow, and stirred cell ultrafiltration systems i s good.uring the past decade ult'rafiltratiori has been advanced D from a laboratory curiosity to a n important industrial unit operation. Practical applications include a broad spectrum of solution concentrations and/or fractionations. I n an ultrafiltration process ( Figure 1) a feed solution is introduced into a membrane unit, where solvent and certain solutes pass through the membrane under a n applied hydrost'atic pressure. Solutes unable to pass the membrane are retained, concentrated, and removed in solution. The porosity of the membrane determines, primarily on the basis of size, which solutes pass through and which are retained by the membrane. The pore structure of this molecular sieve is such that i t is inherently "nonplugging," and stable fluxes for long-term operation are achievable. RIany ultrafiltration applications involve the retent,ion of relatively high molecular weight solutes, accompanied by the removal t'hrough the membrane of lower molecular weight impurities. Of current interest are the coiiceiitratioii and purification of enzyme solutions, and the fracbioiiation of cheese whey for protein recovery (deFilippi and Goldsmith, 1970).For this t'ype of operation, the use of a high-flux membrane leads to low-pressure operation, frequently below 50 psi. As 110 phase change occurs during ultrafiltration, it offers several attractions. Energy requirements for concentration by ult,rafiltration, compared with those for evaporation, are relatively loiv. In addition, sensitive macrosolutes such as funct,ional proteills may be treated without denaturatiori. This paper examines ultrafilt,ration parameters which determine ultrafiltration rate and select'ivity. Data for turbulent flow, laminar flow, and stirred-cell membrane systems are presented and compared with theoretical predictions. ExperimentalUltrafiltration experiments were 1)erformed with membranes in three different ultrafiltration systems. A flow schematic, identical for each system, is shown in Figure 2.Solutions from a feed reservoir were pumped through the ultrafiltration system. Inlet and/or outlet pressures were measured with pressure gages to within 0.5 psi, and the retentate flow was measured with a rotameter. Ultrafiltration rates were measured volumetrically. The operating pressure was controlled with a back-pressure regulator. 130th retentate and permeate solutions were recycled to the feed reservoir. The feed sol...

A new passive sampling device (GASBADGE dosimeter) has been developed for personal/ambient monitoring of industrial air pollutants. Compact and convenient to use (no pump, wet chemicals, or length of stain estimation required, etc.), it may be either worn or used for area monitoring. The operating principle is based upon Fick's first law of diffusion. Analysis of the collection element after exposure yields the time-weighted (TWA) exposure concentration. Promising results have been obtained to date in controlled exposures with sulfur dioxide and nitrogen dioxide. Preliminary data also indicate the applicability of the GASBADGE dosimeter to the monitoring of a wide variety of organic vapors.

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~ due to the change in concentration from gas to melt, AS,, this reduction of entropy must be attributed to changes in the translational or rotational motions of the molecule, the vibrational motions making negligible contribution to the entropy. The rotational entropy, S,, of the free water molecule, calculated by statistical mechanical methods,'g is given in Table 11. This term alone is of sufficient magnitude to account for the observed entropy of solution. The tight bonding of water molecule to cations suggested by the enthalpy of solution could lead to a loss of most of the rotational entropy of the gas molecule. At more elevated temperatures the increasing thermal energy would then cause increased libration about the lowest energy orientation so that less of the rotational entropy would be lost. The decrease in the ratio (asz,)/S, with rise in temperature supports this theory.The change in the partial molal heat capacity of water from vapor to solution is 6.9 cal deg-l mol-'.Although E, probably varies with temperature, the solubility data are not of sufficient accuracy to reveal this. Since the heat capacity of water vaporlg is 8.0 cal deg-I mol-l, almost independent of temperature within the range considered, the partial molar heat capacity of water a t infinite dilution in the melt is 14.9 cal deg-' mol-'. This is significantly less than the heat capacity of liquid water20 in the same temperature range, 18.6-22.0 cal deg-' mol-l. The difference may be attributed to the contribution of the hydrogen bond network to heat capacity in water as well as to a restriction of the rotational heat capacity of water bonded to cations in the melt. 09189The break-in period for CO oxidation over pressed-disk catalysts of silica-supported palladium was investigated, Kinetic parameters and infrared spectra of adsorbed CO were monitored during this period. At various stages of break-in, the reaction was interrupted and spectra of chemisorbed CO at 35' were determined in the absence of oxygen. Break-in did not commence until the catalyst was exposed to 02. For a stabilized catalyst, the apparent activation energy was 15 kcal/mol lower and the apparent preexponential a factor of lo7 lower than the values observed prior to break-in. Apparent discrepancies in literature values of peak frequencies were correlated with the state of the catalyst with respect to break-in. The break-in phenomenon was interpreted as arising from a redistribution of surface structures resulting from surface diffusion of palladium.

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