Ultrafiltration operation mode and its application
Different from ordinary filtration, ultrafiltration adopts porous asymmetric ultrafiltration membrane to realize liquid-liquid separation on the surface of the membrane. The filtration mode is cross flow, that is, the feed liquid flows parallel to the membrane surface. Ultrafiltration can be divided into intermittent operation and continuous operation according to operation mode.
Intermittent operation
According to the circulation mode of intercepting liquid, intermittent operation is divided into two operation modes: full circulation of intercepting liquid and partial circulation of intercepting liquid. In the ultrafiltration process, in order to reduce the influence of concentration polarization and membrane pollution, a high feed liquid flow rate must be maintained in the membrane tank. Therefore, a large number of circulation of intercepted liquid must be adopted to maintain the high flow rate. In addition, due to the small permeation flux of the membrane, the feed liquid also needs to circulate on the membrane for many times to meet the concentration requirements.
Intermittent ultrafiltration has the advantages of high transmittance, high separation efficiency, simple operation, small equipment and membrane area, and can realize the rapid concentration of a small amount of stock solution. Therefore, it is suitable for laboratory and small-scale product treatment. The disadvantage of intermittent ultrafiltration is that the processing capacity is small, while the processing capacity of continuous ultrafiltration is large, and the residence time of feed liquid on the membrane is short, so the concentration ratio is low, so a large membrane area is required.
Continuous operation
The effects of continuous plate ultrafiltration and intermittent plate ultrafiltration in the filtration and purification of cephalosporin C fermentation broth were compared. It was found that continuous plate ultrafiltration had the advantages of low membrane pollution, easy recovery of membrane flux after cleaning, good filtrate quality and uniform filtrate unit.
Continuous ultrafiltration can be divided into single-stage and multi-stage according to equipment technology. According to the circulation mode of intercepted liquid, it can be divided into non circulation and partial circulation. Among them, single-stage partial circulation and multi-stage partial circulation are widely used in the process. The characteristic of single-stage continuous ultrafiltration is that the ultrafiltration process is always carried out under high concentration, so the permeability and rejection rate are low. In order to overcome this disadvantage, multi-stage continuous operation is generally adopted. The concentration of circulating liquid in each section of multistage ultrafiltration increases in turn, and the concentrated liquid is led out in the last section. Therefore, the feed liquid in the previous sections can be operated at a lower concentration.
