Problems encountered in the enrichment experiment and solutions?

In the nearly 1000h enrichment operation experiment, some problems were also encountered. The first is the issue of sterilization. Mannitol is a hexahydric alcohol with a sweet taste, and cellulose acetate film is a favorite substance for bacteria. During operation, the liquid temperature rises, which provides favorable conditions for the growth and reproduction of bacteria. Although a 1% formaldehyde solution is added to the raw material liquid for sterilization, the actual effect is not ideal. Especially in summer, the breeding problem of bacteria is more prominent. The material liquid in the circulating water tank sometimes fermented, and white mold was found at the inlet and outlet (even at the outlet of the ultrafilter). There are also green microorganisms in the pipes, elbows, etc., forming a felt-like shape.

According to the experimental situation, take the following measures:

  1. Shorten the pretreatment operation cycle as much as possible to keep the reverse osmosis feed liquid fresh;
  2. Add o in the raw material liquid. 5mg/L sodium hypochlorite sterilization}
  3. Add an ultraviolet lamp to the inlet of the reverse osmosis device for sterilization;
  4. In industrial applications, reverse osmosis should be operated continuously and concentrated once to prevent the mannitol solution from heating up;
  5. Ensure regular cleaning of pipes and membrane elements.

Membrane cleaning is also an important issue. In the concentration experiment, no chemical cleaning experiment has been carried out. In industrial applications, regular cleaning should be used. The increase in pressure drop is closely related to membrane cleaning. The unit pressure drop of the roll-type reverse osmosis module is generally 10kPa. If the pressure drop of the component increases, it proves that the membrane channel has been blocked. One of the solutions is to turn the components around and change the direction of the water inlet. After turning around, the high-pressure water flow can flush the obstruction out of the membrane surface, thereby reducing △P. In addition, chemical cleaning can also reduce △P. The anti-scaling agent sodium hexametaphosphate should be added to prevent the precipitation of cas04 and SiC)2 when the conventional reverse osmosis device is running. Because the previous electrodialysis can remove cas04, and the content of SiC]2 in the feed solution is also very small, there is no sodium hexametaphosphate during the concentration test. However, in industrial applications, an anti-scaling agent can be added regularly according to the situation.

Electrodialysis, ultrafiltration and reverse osmosis combined process to produce mannitol experiment opened up a new way for mannitol production. In the process of improvement, the reverse osmosis part should improve the antibacterial properties of the membrane elements, extend the life of the membrane elements, reduce costs, and make the joint production process more vital.

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