The method of PMI foam chemical defoaming fermentation:
A defoaming method that uses chemical defoaming agent to eliminate foam is also the most widely used defoaming method. According to the factors of foam formation, defoamers with different action mechanisms can be selected. The defoamers are all surface active agents and have low surface tension. When there is an electric double layer formed by a polar surface active material on the surface of the foam, adding another surface active material with the opposite polarity can neutralize the electrical properties, destroy the stability and qualitative characteristics of the foam, and make the foam broken; or add a stronger polarity The substance competes with the foaming agent for space on the surface of the foam, reduces the mechanical strength of the foam liquid film, and then promotes the collapse of the foam. When the liquid film of the foam has a large viscosity, some substances with low molecular cohesion can be added to reduce the surface viscosity of the liquid film, causing the liquid of the liquid film to be lost, causing the foam to break, thereby achieving the purpose of eliminating the foam.
According to the principle of defoaming and the nature and requirements of the fermentation broth, an ideal defoamer must have the characteristics: the defoamer must have low surface tension, the defoaming effect is rapid, and the efficiency is high; PMI foam has enough at the gas-liquid interface A large spreading coefficient requires that the defoaming agent has a certain degree of hydrophilicity; the solubility of the defoaming agent in water is small to maintain its long-lasting defoaming or anti-foaming performance; the transfer of oxygen during the fermentation process and the extraction process The separation and extraction of the product in the medium do not have any effect.
High temperature resistance, does not interfere with the use of dissolved oxygen, pH and other measuring instruments; convenient sources of defoamers, low prices; non-toxic to microorganisms, humans and animals. The defoamers commonly used in the PMI foam fermentation industry are divided into four categories: natural oils, polyethers, higher alcohols and silicone resins, of which the first two are the most used. Commonly used natural oil-based defoamers include corn oil, soybean oil, rice bran oil, cottonseed oil and lard, etc. In addition to being used as defoamers, these substances can also be used as carbon sources, but their defoaming ability is not strong, so the required dosage Big.
The method of mechanical defoaming during PMI foam fermentation:
According to the law of foam growth and decline in the fermentation process, there are two ways to control foam: one is to reduce the chance of foam formation, by adjusting the composition of the medium (such as adding less or slowly adding the medium composition that is easy to foam), and changing Certain culture conditions (such as ph, temperature, aeration, stirring rate) or changing the fermentation process (such as batch feeding) to control.
Mechanical defoaming is a physical defoaming method that breaks and eliminates bubbles with the help of strong mechanical vibration or pressure changes. The defoaming device can be installed inside or outside the tank. A defoaming paddle can be installed above the stirring shaft in the tank, and the foam is crushed by the effect of the cyclone centrifugal field. A small amount of defoaming agent can also be added to the defoaming rotor to enhance the defoaming effect. The method outside the tank is to draw the foam out of the tank, after the foam is broken by the acceleration of the nozzle or centrifugal force, the liquid returns to the fermentation tank.
The advantage of mechanical defoaming is that it does not need to introduce foreign substances (such as defoamers) into the fermentation broth, saves raw materials, reduces the chance of contamination, and does not increase the burden of the downstream extraction process. However, the effect of PMI foam is often not as fast and reliable as defoaming agents. It requires certain equipment and consumes a certain amount of power. Its biggest disadvantage is that it cannot fundamentally eliminate the formation of foam, so it is often used as an auxiliary method of defoaming.
