Citric acid is an organic acid with large output in the world, and it is an anhydrous substance. The production technology of citric acid mainly includes biological fermentation, fruit extraction and chemical synthesis.
Using corn flour as raw material to produce citric acid is conducive to achieving the goals of low energy consumption, low pollution and high efficiency. After filtering out corn residue and excess protein, the corn residue is transferred to the fermentation process, the strain is mixed with sugar solution, and sterile air is introduced for deep fermentation, and the fermentation tank is kept at a suitable temperature of 35-37℃ for growth. Compared with the traditional dried potato raw materials, the production of citric acid with corn as a new raw material has the advantages of fast acid production, short fermentation period, low cost and strong oxygen dissolving ability. Generally speaking, the total yield of acid production can be increased by about 10%.
2. Improvement of corn flour fermentation process.
The traditional production of citric acid is made from dried potato by biological fermentation and calcium salt extraction. The products produced by this method are of poor quality, high cost and serious environmental pollution. In order to further expand economic benefits, improve production efficiency and realize clean and pollution-free production, it is necessary to improve the extraction process of citric acid production. In terms of raw materials, corn flour, rice and straw have been developed, and industrial ion chromatography, mother liquor purification treatment and waste sugar liquor recycling technology have been adopted in the process, which not only effectively reduces the cost, but also rationally utilizes the remaining citric acid production by-products through optimizing the process, and the waste discharge is rarely conducive to environmental protection. 2. 1 Development of other nutrients in maize
When corn produces citric acid, only the starch in corn is used. Other nutrients in corn can be recovered, purified and developed in the production process, and by-products such as corn gluten meal, fiber feed and corn oil with high added value can be produced. This production idea of "eating dry and squeezing out" has effectively improved the economic benefits.
2.2 clear liquid fermentation and medium adjustment
In order to improve the dissolved oxygen effect of the culture medium, impurities (solids) and redundant nutrients in the culture medium should be removed in time during the production process, so that the culture medium is in a clear state, the dissolved oxygen capacity is enhanced, and the fermentation period is shortened. In addition, after reasonable adjustment, natural culture medium does not need to add trace elements, auxin, nitrogen source, inorganic salt and other components, so that the culture medium with appropriate proportion of various components is greatly improved.
The conversion rate and acid yield are improved. 2.3 Low temperature liquefaction technology
Under normal pressure, low temperature liquefaction technology can not only ensure the quality of culture medium, but also meet the technical requirements of complete liquefaction.
2.4 the use of high-tech production technology
When cultivating corn, maize varieties suitable for citric acid production (such as mutant varieties with high starch content) are selected by mutation breeding, and high-tech is domesticated by citric acid plate with high concentration of corn flour to cultivate and screen high-quality strains with high conversion rate, short fermentation period and high acid production. High-tech means are applied to large-scale fermentation production process to achieve double harvest of economic benefits and environmental benefits. 2.5 Purification of mother liquor
An improved process for purifying citric acid mother liquor is to purify the mother liquor with concentrated sulfuric acid (to remove easy carbon substances in the mother liquor), and then introduce impurities into the acidolysis process for acidolysis (to remove calcium ions in the acidolysis solution) to improve the utilization rate of sulfuric acid. This process improvement can effectively reduce the consumption and emission of sulfuric acid. 2.6 Improvement of Citric Acid Extraction Process
At present, most domestic citric acid manufacturers use calcium salt method. There are two main improvement methods. Firstly, the filtered citric acid solution reacts with calcium carbonate to generate calcium hydrogen citrate, and then it is decomposed by sulfuric acid to obtain a high concentration citric acid solution; Secondly, after the concentration is completed, a filtering device is needed to remove calcium carbonate particles precipitated in the concentration process, which effectively improves the utilization rate of ion exchange resin, reduces the burden of ion exchange and improves the quality of citric acid products.
2.7 Recovery of waste sugar solution
In the production of citric acid, citric acid is first converted into waste sugar solution, and then the fermentation process is carried out. This paper introduces a utilization method of waste sugar solution, that is, the waste sugar solution is reused for raw material pulp mixing, which greatly reduces the discharge of waste sugar solution and the cost of sewage treatment, and ensures the yield, quality and extraction progress of citric acid while saving water.
2.8 calcium salt ion exchange method
Calcium salt method is a traditional method to produce citric acid in China. This year, with the progress of science and technology, the technology and equipment were optimized and improved, and the production automation was basically realized.
2.9 electrodialysis technology
Electrodialysis is an efficient membrane separation technology. Its principle is to combine citrate and hydrogen ions into citric acid under the action of selective osmotic electric field force of anion exchange membrane. In the whole process, the loss of citric acid was less, and the average yield reached 92.7%. Compared with the traditional citric acid extraction process, this improved process does not need to add calcium, which is simpler, easier to realize automatic production, less environmental impact, short production cycle and easy to carry out automatic production. Its disadvantage is that it will increase the production cost of citric acid (the membrane cost of electrodialysis is higher) and consume more electric energy.
3. Fermentation of citric acid by corn steep liquor
In the traditional process of producing citric acid from coarse corn flour, because coarse corn flour is rich in protein, there are many useless components in fermentation, which is easy to cause the crazy growth of bacteria and is not conducive to acid production. However, using corn to ferment citric acid in the clear night has obvious advantages.
Advantages of fermenting citric acid with 3. 1 corn in clear night
Corn flour is liquefied and made into clear night. The protein content in the clear night is low, impurities such as solids are effectively removed, and the fat content in the clear liquid is low, which improves the conversion rate and dissolved oxygen and shortens the production cycle.
3.2 Study on fermentation technology with corn clear liquid as raw material
Using corn clear liquor as raw material and Aspergillus Niger as strain, the fermentation was carried out in a 300M3 fermentor, and the optimum technological conditions of citric acid fermentation were discussed. Using slant culture medium, using corn steep liquor as nitrogen source, adding 15% corn serum and 25% corn flour, the fermentation temperature was set at 37℃, the aeration ratio was 1∶0.3, the inoculation amount was 12%, the fermentation speed was 90r/min, the pH value was adjusted to 5 ~ 6, and the average conversion rate of sugar and acid was achieved. Under the optimum conditions of citric acid fermentation, the mycelium of Aspergillus Niger strain is full, evenly stretched and moderately elastic.