Ultrafiltration batch cell

Gel polarized ultrafiltration was recently analyzed for cross flow and unstirred batch cell systems by Trettin and Doshi (1980 a,b). We have shown in these papers that the widely used film theory does not predict the limiting flux accurately. The objective of this paper is to derive an expression for the permeate flux when the pressure independent ultrafiltration of macro-molecular solutions is osmotic pressure limited. We will also attempt to distinguish between gel and osmotic pressure limited ultrafiltration of macromolecular solutions. 

Goldsmith (1971) pointed out that developed osmotic pressures for macromolecular solutions were not necessarily negligible. The ultrafiltration of Carbowax 20M (polyethylene oxide) and various Dextrans was studied in thin channel and tube flow as well as stirred batch cell. Both turbulent and laminar flow regimes were considered. Data were analyzed with the use of Eq. (2) and the phenomenological relationship of Eq. (1) with Rg = 0. From Eq. (1) it was possible to calculate an average... 

Bovine serum albumin (BSA) (Sigma Chemicals — Cohn fraction V) was selected as a solute material to be studied in batch cell ultrafiltration. The justification of this choice was based on the fact that BSA has been used by previous investigators their work would offer a source of comparison to our results [Blatt, et al. (1970), Kozinski and Llghtfoot (1972), Shen and Probstein (1977, 1979), Probstein (1978, 1979), Goldsmith (1971),... 

It is theoretically shown for the unstirred batch cell that, in limiting cases, the assumption of constant wall (membrane) concentration with respect to time may be made even in the absence of gel formation. Although the assumption of constant wall concentration is similar in both gel and osmotic pressure limited ultrafiltration, it is important to recognize that in gel polarized ultrafiltration, wall concentration is also pressure independent since it corresponds to the solute solubility limit. This is not the case in osmotic pressure limited ultrafiltration... 

When the assumption of constant wall concentration is justified, data for the unstirred batch cell and thin channel systems may be interpreted using models presented in Trettln and Doshi (1980a, 1980b). Such an analysis is performed where agreement is shown to be very good between theory and osmotic pressure limited ultrafiltration experiments. 

In macromolecular ultrafiltration, 2is pressure is increased, permeate flux first Increases and then In a large number of cases levels out and remains more or less pressure Independent. This could be due to the increase In solute concentration at the membrane surface such that either gel formation occurs or the corresponding osmotic pressure approaches the applied pressure. Limiting flux for the gel polarized case was recently analyzed for cross flow and unstirred batch cell systems by Trettln and Doshi (1980,a, b). In this paper we have analyzed the osmotic pressure limited ultrafiltration for the two systems. Our unstirred batch cell data and the literature cross flow data agree quite well with the theory. We have further shown that an unstirred batch cell system can be used to determine whether pressure Independent ultrafiltration of macromolecular solution is gel or osmotic pressure limited. Other causes for the observed pressure Independence may be present but are not considered in this paper. 

I Ultrafiltration, Pellicon system, 10,000 MWCO CONCENTRATED ENZYME, 300-500 mL DEAE batch absorption I Ultrafiltration, Amicon cell CONCENTRATED ENZYME 15 mL I HPLC (carboxysulfone column)... 

Figure 6.3.26. Ultrafiltration, (a) UF in a batch cell macrosolute concentration profile infeed side (b) Piston driven UF in a batch cell bulk flow parallel to the force, (c) Observed behavior ofsolvent flux vs. AP in macrosolute ultrafiltration. For an explanation of (l)-(4), see the text.

The above analysis/description of solvent flux and macrosolute rejection/retention/ttansmission far an ultra-flllration membreme was carried out in the context of a pseudo steady state analysis in a batch cell (Figure 6.3.26 (a)). Back diffusion of the macrosolute from the feed solution-membrane interface to the bulk solution takes place by simple difflision against the small bulk flow parallel to the force direction. The resulting mass-transfer coefficients for macrosolutes will be quite small the solvent flux levels achievable will be quite low. For practically useful ultrafiltration rates, the mass-transfer coefficient is increased via different flow configurations with respect to the force. 

Fig. 1. Schematic of a process for batch suspension culture of mammalian cells, where UF is ultrafiltration and DF is diafiltration.

The simplest ultrafiltration is the stirred cell, a batch operation. The most compex is a continuous stages-in-series operation incorporating diafiltration. Industrial practice incorporates the full gamut of complexity. 

Subtilisin BPN was prepared through a series of protein purification steps applied to the fermentation broth. These steps included ultrafiltration ethanol precipitation DEAE (diethyl-aminoethyl) Tris Acryl batch anionic exchange SP (sulfopropyl) Tris Acryl column cationic exchange and, concentration with an Amicon stirred cell. The enzyme purity was determined to be -951 via spectroscopic assays that measure the ratio of active enzyme to total protein. In addition, purity was verified via HPLC and SDS-page (sodium dodecyl sulfate polyacrylamide gel electrophoresis). 

The production of substances that preserve the food from contamination or from oxidation is another important field of membrane bioreactor. For example, the production of high amounts of propionic acid, commonly used as antifungal substance, was carried out by a continuous stirred-tank reactor associated with ultrafiltration cell recycle and a nanofiltration membrane [51] or the production of gluconic acid by the use of glucose oxidase in a bioreactor using P E S membranes [52]. Lactic acid is widely used as an acidulant, flavor additive, and preservative in the food, pharmaceutical, leather, and textile industries. As an intermediate product in mammalian metabolism, L( +) lactic acid is more important in the food industry than the D(—) isomer. The performance of an improved fermentation system, that is, a membrane cell-recycle bioreactors MCRB was studied [53, 54], the maximum productivity of 31.5 g/Lh was recorded, 10 times greater than the counterpart of the batch-fed fermentation [54]. 

C over 24 h. Initial pH was adjusted with HCl (5 N) and NaOH (5 N) solution. Batch ultrafiltration was performed in a stirred cell (Amicon model 52, feed volume 50 ml, effective membrane area 12.5 cm ), usually at 3 bars, with membrane YM5 (Amicon, mw cut off 5,000 Dalton). The first 10 ml of permeate were discarded. The next two consecutive 10 ml were analysed to determine the mercury concentration with an atomic absorption spectrophotometer. The rejection coefficient (R) defined as below, was calculated from the feed and permeate concentration of mercury. 

Separation. The process by which the bacterial cells are separated from the culture fluid and soluble products. Centrifugation using either a batch or continuous flow process, or ultrafiltration, is commonly used. Precipitation of the cells by reducing the pH has been used as an alternative. In the case of vaccines prepared from cells, the supernatant fluid is discarded and the cells are resuspended in a saline diluent where vaccines are made from a constituent ofthe fluid, the cells are discarded. 

This particular fermentation is performed in 1+00 liter batches. Tangential flow filtration was carried out with a Pe licon cassette (Millipore Corp.). The filtration area was 25 ft using a 100,000 molecular weight cut off ultrafiltration membrane. The inlet pressure was maintained at 1+0 psig while the outlet pressure was 25 psig and recirculation rates of the cell suspension were 3 5 GPM tangential to the upstream membrane surface. Pumping of the cell suspension was performed with a Moyno screw pump. 

Continuous membrane bioreactors can have advantages. One is the removal of inhibition of cells by the product. This was shown in the oxidation of naphthalene (7.34) by Pseudomonas fluorescens.2ii An ultrafiltration membrane kept the cells and insoluble naphthalene on one side, while the soluble product was removed continuously from the other. The yield was three times that in a batch process. 

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