How to choose
defoamer for fermentation accordingly?
Foam is a
phenomenon often encountered in daily life and industrial and agricultural
production. In industrial and agricultural production, sometimes foam is needed
in production, and then foam needs to be produced in production; sometimes foam
is not needed in production, and foam needs to be eliminated at this time.
Foam refers to a
gas-liquid dispersion system in which a gas is dispersed in a liquid, the gas
is a dispersed phase, and the liquid is a dispersion medium. Pure liquids are
difficult to form foam, because there is only a very thin layer of water film
between the foams. This layer of water film is very unstable and easily
damaged. The blister life of pure water is within 0.5 s. Therefore, it is
difficult to generate foam. Only with the addition of surfactants or high
molecular compounds can a stable foam be formed.
How to foam generation
The creation of a
bubble must meet two conditions:
Gas-liquid two-phase contact.
Because foam is the dispersion of gas in a
liquid, it is possible to produce foam only when the gas and liquid are
continuously and sufficiently in contact. This is a necessary condition for a
bubble to form.
The presence of surfactants, so that the
foaming speed is higher than the bursting speed, which is a sufficient
condition for foam generation. The foaming speed is higher than the bursting
speed, which refers to the life of the bubble. No matter how you inflate the
pure water, it is impossible to get foam and only single bubbles appear.
Because the bubbles produced by pure water have a short life span, they can only
exist for an instant, so stable foam cannot be obtained. To obtain a stable
foam, add a small amount of surfactant to the water and then inflate the water.
Because the presence of the surfactant not only facilitates foaming, but also
causes the foaming speed to exceed the foam breaking speed, thereby obtaining a
stable foam.
At present, in
fermentation industries such as pharmaceutical fermentation, monosodium
glutamate fermentation, and long-chain dibasic acid fermentation, fermentation
requires a large amount of nutrients during the fermentation production
process. Therefore, many high-molecular substances such as sucrose and starch
are added. Aerobic bacteria, so during the fermentation production process, it
is necessary to blast under agitation to increase the oxygen content in the
fermentation broth and provide the oxygen required for the fermentation of the
bacteria; therefore, a large amount of foam is bound to be produced during the
fermentation of aerobic bacteria. Due to the appearance of a large amount of
foam, if the defoaming is not performed, part of the fermentation broth will
overflow. In order to reduce material loss and increase the effective volume of
the equipment, the primary fermentation tank and the secondary fermentation
tank are eliminated in the industrial production process. Bubble processing.
There are two methods of defoaming, one is mechanical defoaming, and the other
is defoaming by adding defoaming agent. Due to the poor mechanical defoaming
effect and large investment, few manufacturers use it. At present, the
defoaming methods used in the domestic fermentation industry generally use
defoaming agents, because defoaming agents are added for fast defoaming, low
investment and easy use. Simple operation and obvious effects.
Application of
defoamer
The general process
of adding defoamer in the fermentation production process is: add the defoamer
to the stirring kettle, add water to the stirring kettle and stir to prepare a
certain concentration of defoaming solution, and then heat the disinfection
solution to disinfect the defoaming solution. Add foam to the foaming
fermentation tank for defoaming, Please check below Figure 1.
There are a
variety of defoamers used in microbial fermentation. Natural oils and fats such
as peanut oil, corn oil, soybean oil, rice bran oil, and animal oil were used
in the early fermentation. Due to the easy oxidation of natural oils and high
biotin content, it is not good for The elimination of foam also affects the
production of fermentation products, and is gradually replaced by other
defoamers. At present, the main defoamers added to the fermentation industry
production process are polyether defoamers and silicone defoamers. These two
types of defoamers are different. Polyether defoamers are formed by different reactions
with ethylene oxide and propylene oxide at a certain temperature and pressure.
The initiators are monohydric alcohols, dihydric alcohols, trihydric alcohols,
and N-type polyfunctional groups. , Etc., is a non-ionic surfactant, this type
of defoamer product contains only C, N, O, H several elements. Polyether
defoamer has the characteristics of long antifoam time, good effect and fast
defoaming speed. After high temperature sterilization during the use of
fermentation, the product performance remains unchanged. It still has long
antifoam time, good effect and defoaming speed. Fast features. As the polyether
defoamer contains only C, N, O, and H elements, it is added during the
fermentation process, which not only has no effect on the fermentation broth,
but also provides C and N nutrients, which is beneficial to the fermentation
broth fermentation. Silicone-based defoamer is made by mixing dimethyl silicone
oil, emulsifier, thickener, water, and white carbon black. It is an emulsified
product, which contains C, Si, O, H, etc. Various elements. Silicone-based
defoamers have the characteristics of fast defoaming speed, good foam
suppression at normal temperature, delamination at high temperature, slow
defoaming speed, and general foam suppression effect. During the use of
fermentation, after the high-temperature sterilization, the silicone defoamer
delaminated, the silicone oil floated above and the water was below, and the
defoaming effect was significantly reduced in the application, and the
defoaming process was unstable. Since the silicone defoamer contains silicon,
it is added to the fermentation broth during use, which affects the
fermentation and slightly reduces the conversion rate of the fermentation. At
the same time, it is difficult to separate the silicon from the fermentation
broth. The elements must remain in the produced product, reducing the purity of
the product, and at the same time whether there are side effects on the use of
the product, remains to be observed in the application.
In industrial
applications, test in a 150m3 fermenter in a monosodium glutamate
plant. During the fermentation foaming process, silicone defoamer and polyether
defoamer, polyether defoamer and silicone defoamer are added. The speed is
about the same, and the foam in the fermenter can be quickly burst, but the
time is not long. The fermenter with the silicone defoamer will foam after a
while, and the polyether defoamer will take a long time to foam.
Polyether-based defoamer has better foam suppression effect than silicone
defoamer. In the experiment, on average, about 100 kg of silicone defoamer was
consumed per fermentation tank of fermentation broth, while only 75 kg was
consumed with polyether defoamer. It shows that polyether defoamer is better
than silicone defoamer
Defoamer for Fermentation
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