The technological process of producing citric acid from corn

1 Introduction to the process of producing citric acid from corn

Citric acid is an organic acid with a large output in the world, and it is an anhydrous substance. The main production processes of citric acid are: There are three types: biological fermentation method, fruit extraction method and chemical synthesis method.

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 the corn residue and excess protein, turn to the fermentation process, mix the bacteria and sugar liquid and introduce them into sterile air for deep fermentation. The fermentation tank maintains a suitable temperature of 35-37°C for growth. Compared with the traditional use of dried potatoes as raw materials Generally speaking, using corn as an emerging raw material to produce citric acid has the advantages of fast acid production, short fermentation cycle, low cost, and strong dissolved oxygen capacity. Generally speaking, the overall acid production income can be increased by about 10.

2 Improvement of corn flour fermentation production process

Traditional citric acid production uses dried potatoes as raw materials and is produced through biological fermentation and calcium salt extraction processes. This method produces The products are of poor quality, high cost, and serious environmental pollution. In order to further expand economic benefits, improve production efficiency, and achieve clean and pollution-free production, the citric acid production and extraction process needs to be improved. In terms of raw materials, corn flour, rice, straw, etc. have been developed. Industrial ion chromatography, mother liquor purification treatment and waste sugar liquid recycling technology are used in the process. This not only effectively reduces the cost, but also eliminates the remaining waste from citric acid production. By-products must be rationally utilized by optimizing the process, and small waste emissions are conducive to environmental protection. 2.1 Development of other nutrients in corn

When corn produces citric acid, only the starch in corn is used. Other nutrients in corn can be recovered, purified and developed during the production process to produce by-products such as corn gluten meal, fiber feed and high value-added corn oil. This kind of "eat dry and squeeze out" production idea effectively improves economic benefits.

2.2 Clear liquid fermentation and adjustment of culture medium

In order to improve the dissolved oxygen effect of the culture medium, impurities (solid matter) and excess in the culture medium should be removed in a timely manner during the production process. Nutrients, so that the culture medium will be in a clear liquid state, the dissolved oxygen capacity will be enhanced, and the fermentation cycle will also be shortened. In addition, after reasonable adjustment of the natural culture medium, there is no need to add trace elements, auxins, nitrogen sources, inorganic salts and other components. In this way, the medium with appropriate proportions of various components greatly improves the conversion rate and acid production rate.

. 2.3 Low-temperature liquefaction technology

Under normal pressure conditions, the use of low-temperature liquefaction technology can not only ensure the quality of the culture medium, but also meet the process requirements of complete liquefaction.

2.4 Utilize high-tech production technology

When cultivating corn, use mutation breeding to select mutant varieties suitable for producing citric acid (such as mutant varieties with higher starch content) A large number of corn varieties have been cultivated, and the high-tech technology of high-concentration corn flour citric acid plate domestication has been adopted to cultivate and select high-quality strains with high conversion rate, short fermentation cycle and high acid production rate. Apply high-tech means to large-scale fermentation production processes to achieve dual gains of economic and environmental benefits. 2.5 Purification of mother liquor

An improved process for the purification of citric acid mother liquor is to first purify the mother liquor with concentrated sulfuric acid (to remove carbon-prone substances in the mother liquor). After removing impurities, it is then passed into the acidolysis process for acidification. Hydrolysis (removal of calcium ions in the acidolysis solution), thus improving the utilization of sulfuric acid. Such process improvements can effectively reduce sulfuric acid consumption and emissions. 2.6 Improvement of citric acid extraction process

Currently, most domestic citric acid manufacturers use the calcium salt method. There are two main improvement methods. One is to react the filtered citric acid solution with calcium carbonate to generate calcium hydrogen citrate and then use sulfuric acid to perform a metathesis reaction to obtain a high-concentration citric acid solution; the other is to add a filter after the concentration is completed. The device removes calcium carbonate particles precipitated during the concentration process, 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 Recycling of waste sugar liquid

In citric acid production, citric acid is first converted into waste sugar liquid and then fermented. Here, a kind of waste sugar is introduced The method of liquid utilization is to reuse the waste sugar liquid for pulping of raw materials. This greatly reduces the discharge of waste sugar liquid, greatly reduces the cost of sewage treatment, saves water, and ensures the yield of citric acid. , quality and extraction progress.

2.8 Calcium salt ion exchange method

The calcium salt method is a traditional method for producing citric acid in my country. With the advancement of science and technology this year, the process and equipment have been optimized and improved. Production automation is basically realized.

2.9 Electrodialysis Technology

Electrodialysis is a highly efficient membrane separation technology. Its principle is to utilize the selective permeability of anion and cation exchange membranes under the action of electric field force. Citrate radicals and hydrogen ions combine to form citric acid. The loss of citric acid is small during the whole process, and the average yield reaches 92.7. Compared with the acidification and precipitation of calcium citrate method in the traditional citric acid extraction process, this improved process does not require the addition of calcium components, is simpler, facilitates automated production, has little impact on the environment, has a short production cycle and is easy to automate. . The disadvantage is that it will increase the production cost of citric acid (the membrane fee of electrodialysis is higher) and consume more electricity.

3 Use corn serum to ferment citric acid

When using coarse corn flour to produce citric acid in the traditional process, due to the rich protein content in coarse corn flour, there are many useless components during fermentation. And it is easy to cause the bacteria to grow wildly, which is not conducive to acid production. There are obvious advantages when using corn qingye for citric acid fermentation.

3.1 Advantages of corn claret fermented with citric acid

After liquefying corn flour, claret is made into claret. The protein content in claret is low, solids and other impurities can be effectively removed, and the fat in the clear liquid can be effectively removed. The content is low, which improves the conversion rate and dissolved oxygen content, and shortens the production cycle.

3.2 Research on the fermentation process using corn serum as raw material

Here we study corn serum as raw material, a fermentation tank with a capacity of 300M3, and Aspergillus niger as the strain. , to explore the optimized process conditions of citric acid fermentation. Use a slant culture medium, use corn steep liquor as the nitrogen source, add 15% corn serum and 25% corn flour, set the fermentation temperature to 37°C, ventilation ratio 1:0.3, inoculation amount 12, fermentation tank rotation speed 90r/min, pH value Adjust to 5-6 and run for 64 hours. The average sugar-acid conversion rate is as high as 98. Under these optimized conditions of citric acid fermentation, the mycelium of the Aspergillus niger strain is plump, evenly stretched, and moderately tight.