Permeation characterization

Information about transport diffusion in catalyst particles can also be deduced during the initial, unsteady state period of a permeation experiment. In this stage, the number of molecules passing the plug of catalyst per unit time will increase from zero until the rate of permeation characterizing the steady state behavior is attained. In the limit t - oo, the total amount of molecules which have permeated in the time interval 0... t is given by the relation [1,2, 12]... 

HPLC and NMR study of the reduction of whey permeate Characterization of cheese by statistical analysis of time domain results... 

Transport properties of PVA/PEl/PEG composite membranes sorption and permeation characterizations. Cent. Eur. J. 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

If the solute size is approximately the (apparent) membrane-pore size, it interferes with the pore dimensions. The solute concentration in the permeate first increases, then decreases with time. The point of maximum interference is further characterized as a minimum flux. Figure 4 is a plot of retention and flux versus molecular weight. It shows the minimum flux at ca 60—90% retention. 

In early hterature, the molecular weights of PVDC and VDC copolymers were characterized by the absolute viscosity of a 2 wt % solution in (9-dichlorobenzene at 140°C. The exact correlation between this viscosity value and molecular weight is not known. Gel-permeation chromatography is the... 

Second, most membrane materials adsorb proteins. Worse, the adsorption is membrane-material specific and is dependent on concentration, pH, ionic strength, temperature, and so on. Adsorption has two consequences it changes the membrane pore size because solutes are adsorbed near and in membrane pores and it removes protein from the permeate by adsorption in addition to that removed by sieving. Porter (op. cit., p. 160) gives an illustrative table for adsorption of Cytochrome C on materials used for UF membranes, with values ranging from 1 to 25 percent. Because of the adsorption effects, membranes are characterized only when clean. Fouling has a dramatic effect on membrane retention, as is explained in its own section below. 

It is basically a fractionation process that depends not only on molecular size, but also on chemical composition, stereo-configuration, branching, and crosslinking. For multicomponent systems, fractionation with different ion polymolecularity, chemical heterogeneity and sequence length distribution, solubility or elution fractionation is of primary importance. Therefore, gel permeation chromatography or size exclusion chromatography is used as an important tool for the characterization of PBAs. 

ADMET polymers are easily characterized using common analysis techniques, including nuclear magnetic resonance ( H and 13C NMR), infrared (IR) spectra, elemental analysis, gel permeation chromatography (GPC), vapor pressure osmometry (VPO), membrane osmometry (MO), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The preparation of poly(l-octenylene) (10) via the metathesis of 1,9-decadiene (9) is an excellent model polymerization to study ADMET, since the monomer is readily available and the polymer is well known.21 The NMR characterization data (Fig. 8.9) for the hydrogenated versions of poly(l-octenylene) illustrate the clean and selective nature of ADMET. 

Idris, O.H.M. Williams, P. A. Phillips, G.O. (1998). Characterization of gum from Acacia Senegal trees of different age and location using multidetection gel permeation chromatography. Food Flydrocolloids, Vol. 12, No. 4, (October 1998), pp. 379-388, ISSN 0268-005X. 

High-Performance Gel Permeation Chromatography Characterization of Oligomers Used in Coatings Systems... 

The pH-partition theory or nonionic permeability hypothesis was first described by Jacobs in 1940 [66]. According to this concept, only neutral, preferably nonpolar compounds are able to cross biological membranes. The transcellular permeability pH-profile is then essentially characterized by the membrane partition coefficient and the pKa of the compound. The simplest quantitative description of membrane permeation is given by ... 

The efficiency of a membrane module is characterized by the recovery or conversion ratio CR = permeate flow rate/feed flow rate. Low conversion means that fluid has to be repeatedly cycled past the TFF module to generate permeate. High-efficienCT NFF has CR = 1. 

Complementary to the passage, one can also consider the retention of a component as R = 1 - S (also called rejection). Retention can also be either an observed or an intrinsic measurement. Retention is useful in considering retained products during concentration mode operation. Other component separation characterizations include the log reduction value LRV =- logS which is used to characterize high-efficiency separations with permeate products (sterilization). The beta ratio P = I/S is sometimes used in NFF for clarification applications. 

Multiple-Component Separation Separation Factor Consistent with the characterization of different separation methods, one can define a separation factor a,j (also called selectivity) for components i andj that compares their relative concentrations in the permeate stream to those in the feed stream ... 

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