Batch ultrafiltration

Schoutens GH, Nieuwenhuizen MCH, Kossen NWF (1984) Butanol from whey ultrafiltrate batch experiments with Clostridium beijerinckii LMD 27.6. Appl Microbiol Biotechnol 19 203-206... 

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. 

Bioreactors a) batch stirred tank b) continuous stirred tank c) continuous packed-bed i) downward flow, ii) upward flow and iii) recycle d) continuous fluidised-bed e) continuous ultrafiltration. Redrawn from Katchalski - Katzir E. (1993) Trends in Biotechnology II, 471-477. 

Aim of this work was to optimise enzymatic depolymerization of pectins to valuable oligomers using commercial mixtures of pectolytic enzymes. Results of experiments in continuous and batch reactor configurations are presented which give some preliminary indications helpful to process optimisation. The use of continuous reactors equipped with ultrafiltration membranes, which assure removal of the reaction products, allows to identify possible operation policy for the improvement of the reaction yield. 

A first application using ferroceneboronic acid as mediator [45] was described for the transformation of p-hydroxy toluene to p-hydroxy benzaldehyde which is catalyzed by the enzyme p-cresolmethyl hydroxylase (PCMH) from Pseudomonas putida. This enzyme is a flavocytochrome containing two FAD and two cytochrome c prosthetic groups. To develop a continuous process using ultrafiltration membranes to retain the enzyme and the mediator, water soluble polymer-bound ferrocenes [50] such as compounds 3-7 have been applied as redox catalysts for the application in batch electrolyses (Fig. 12) or in combination with an electrochemical enzyme membrane reactor (Fig. 13) [46, 50] with excellent results. 

Cabral and coworkers [253] have investigated the batch mode synthesis of a dipeptide acetyl phenylalanine leucinamide (AcPhe-Leu-NH2) catalyzed by a-chymotrypsin in a ceramic ultrafiltration membrane reactor using a TTAB/oc-tanol/heptane reverse micellar system. Separation of the dipeptide was achieved by selective precipitation. Later on the same group successfully synthesized the same dipeptide in the same reactor system in a continuous mode [254] with high yields (70-80%) and recovery (75-90%). The volumetric production was as high as 4.3 mmol peptide/l/day with a purity of 92%. The reactor was operated for seven days continuously without any loss of enzyme activity. Hakoda et al. [255] proposed an electro-ultrafiltration bioreactor for separation of RMs containing enzyme from the product stream. A ceramic membrane module was used to separate AOT-RMs containing lipase from isooctane. Application of an electric field enhanced the ultrafiltration efficiency (flux) and it further improved when the anode and cathode were placed in the permeate and the reten-tate side respectively. 

Figure 10.13 shows a typical batch ultrafiltration setup. As the solution is pumped through the filter unit, the permeate is collected and the retentate is recycled. The volume of the solution reduces with time and the solute concentration increases. Develop a correlation for the time required to reduce the solution volume from V0 to V. Assume that the concentration polarization is negligible. Also assume that the membrane totally rejects the solute. 

Just like chemical processes, biocatalytic reactions are performed most simply in batch reactors (Figure 5.5a). On a lab scale and in the case of inexpensive or rapidly deactivating biocatalysts, this is the optimal solution. If the biocatalyst is to be recycled, but the mode of repeated batches is to be maintained, a batch reactor with subsequent ultrafiltration is recommended (batch-UF reactor Figure 5.5b). The residence times of catalyst and reactants are identical in all batch reactor configurations. 

The simplest type of ultrafiltration system is a batch unit, shown in Figure 6.17. In such a unit, a limited volume of feed solution is circulated through a module at a high flow rate. The process continues until the required separation is achieved, after which the concentrate solution is drained from the feed tank, and the unit is ready to treat a second batch of solution. Batch processes are particularly suited to the small-scale operations common in the biotechnology and pharmaceutical industries. Such systems can be adapted to continuous use but this requires automatic controls, which are expensive and can be unreliable. 

Figure 6.17 Flow schematic of a batch ultrafiltration process...

For treating water containing VOCs with separation factors of more than 500, for which concentration polarization is a serious problem, feed-and-bleed systems similar to those described in the chapter on ultrafiltration can be used. For small feed volumes a batch process as illustrated in Figure 9.16 is more suitable. In a batch system, feed solution is accumulated in a surge tank. A portion of this solution is then transferred to the feed tank and circulated at high velocity through the pervaporation modules until the VOC concentration reaches the desired level. At this time, the treated water is removed from the feed tank, the tank is loaded with a new batch of untreated solution, and the cycle is repeated. 

Gamble, D.S., M.I. Haniff, and R.H. Zienius (1986a). Solution phase complexing of atrazine by fulvic acid A batch ultrafiltration technique. Anal. Chem., 54 727-731. 

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]. 

Optimal Design of Batch Ultrafiltration-Diafiltration Process... 

Ultrafiltration, which uses selective membranes to separate materials on the basis of different molecular sizes, has become a valuable separation tool for a wide variety of industrial processes, particularly in the separation of dispersed colloids or suspended solids. In many cases where a high degree of separation is desired, a batch ultrafiltration process is used because it is the most economical in terms of membrane area. 

A comprehensive mathematical analysis of batch ultrafiltration coupled with diafiltration is presented. The time cycle of the ultrafiltration-diafiltration has been correlated with the volume initially charged, percent of solute recovered, membrane area and flux. The optimum diafiltration volumes which result in the minimum cycle time or the minimum membrane area were solved for in terms of the operating conditions. 

The schematic of a typical batch ultrafiltration process used for separating suspended solids is shown in Figure 1. 

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