1. Principle of calcium salt method: The method uses two principles to achieve the extraction of citric acid from the citric acid fermentation liquid with more complex composition.
①The characteristic is utilized that calcium citrate has small solubility in hot water , and through reaction of citric acid and calcium carbonate (or calcium oxide, calcium hydroxide) , so as to achieve the result of separating citric acid from other composition of the fermentation solution;
②The principle which strong acid is used to produce weak acid is utilized. The sulfuric acid is used to decompose calcium citrate salt, then citric acid is obtained again;
2. Advantages and disadvantages of calcium salt method
①Advantages: The process is mature, the product quality is good and stable,and the comprehensive production cost is low;
②Disadvantages: Calcium sulfate is the by-product. If there is no complete industrial support, it is more troublesome to deal with this by-product;
3. Classification of calcium salt method
①One-step calcium salt method (referred to as citro-calcium method) : Calcium citrate is obtained by neutralization reaction between citric acid and calcium carbonate (or calcium oxide, calcium hydroxide) , and thencalcium citrate is obtained by reaction between calcium citrate and concentrated sulfuric acid. Because there is only one-step of neutralization reaction, calcium citrate is obtained, it is called one- step calcium salt method (citro-calcium method).
②Two-step calcium salt method (referred to as hydrogen calcium method) : Calcium hydrogen citrate is obtained by the two-step neutralization reaction of citric acid and calcium carbonate (or calcium oxide, calcium hydroxide), and then citric acid is obtained by reaction between calcium hydrogen citrate and sulfuric acid. Because there is two-step neutralization reaction, the reaction leads to the result of obtaining calcium hydrogen citrate, it is called two-step calcium salt method (hydrogen calcium method).
③Comparison of two kinds of calcium salt method：
| Serial number | Comparison item | One-step calcium salt method (citro-calcium method) | Two-step calcium salt method (hydrogen calcium method) |
|---|---|---|---|
| 1 | Investment | Less | More |
| 2 | Process | Simple | Additional neutralization |
| 3 | Consumption of calcium carbonate | 100% | 67～70% |
| 4 | Consumption of sulfuric acid | 100% | 67～70% |
| 5 | By-product calcium sulfate | 100% | 67～70% |
4. Continuous calcium salt method and intermittent calcium salt method
Calcium salt extraction process can be divided into continuous calcium salt method and intermittent calcium salt method. With the development of society, the labor cost is becoming more and more expensive, and the completely continuous calcium salt method has many advantages compared with the intermittent calcium salt method:
| Serial number | Comparison item | Completely continuous neutralization and acid hydrolysis (continuous calcium salt method) | Intermittent batch neutralization and acid hydrolysis (intermittent calcium salt method) |
|---|---|---|---|
| 1 | Equipment investment | Less | More |
| 2 | Process control | Simple and stable | It is manual batch control, which is greatly affected by personnel. |
| 3 | Meter configuration | High | Low |
| 4 | Personnel allocation | The manpower allocation can be reduced more than 20% | 100% |
| 5 | Employee labor intensity | Low | High |
1. Basic principle of chromatography:
By taking advantage of the different distribution coefficients between citric acid and non-citric acid substances from the fermentation liquid in the system composed of fixed phase (specific resin) and mobile phase (hot water). When the two phases make relative motion to each other, the citric acid and non-citric acid substances move together with the mobile phase, and they are distributed repeatedly in the two phases, so as to separate the citric acid.
2. Comparison between chromatography and calcium salt method
| Serial number | Comparison item | Calcium salt method | Chromatography | Remarks |
|---|---|---|---|---|
| 1 | Equipment investment | Less | More | |
| 2 | Process control | Simple and stable | To be optimized | |
| 3 | Product quality | High | Slightly lower | |
| 4 | Consumption of steam | 100% | 140% | |
| 5 | By-product calcium sulfate | 100% | 0 | |
| 6 | By-product calcium sulfate | 100% | 25% | Chromatographic residual liquid is cycled by calcium salt method. |
3. Applicable occasion of chromatography
①There is no suitable industrial support to effectively deal with calcium sulfate;
②The application requires that the local energy price is relatively cheap, and the increased cost of steam consumption does not lead the cost to rise significantly;
③There should be sufficient capital to afford high investment;