Continuous production method for preparing sodium cyanide from hydrocyanic acid

Abstract

The invention relates to the technical field of sodium cyanide production, in particular to a continuous production method for preparing sodium cyanide from hydrocyanic acid, which adopts a two-stage series continuous reaction-separation system, realizes segmented deep absorption and conversion of hydrocyanic acid gas, and greatly improves the production efficiency and the device utilization rate. And secondly, by accurately controlling the temperature of the circulating liquid and supplementing the alkali liquid, the stable and uniform reaction conditions are ensured, so that the continuous consistency of the product quality is ensured. Meanwhile, due to the design of closed-loop circulation and two-stage absorption, unreacted gas is thoroughly recycled, the safety risk of leakage of highly toxic gas is greatly reduced, the utilization rate of raw materials is increased through last-stage liquid phase backmixing, and loss caused by excessive alkali liquor is avoided. The whole process is compact and controllable, and safe, efficient and high-quality continuous industrial production is essentially realized.

Description

Technical Field

[0001] This invention relates to the field of sodium cyanide production technology, and more particularly to a continuous production method for sodium cyanide from hydrogen cyanide. Background Technology

[0002] Sodium cyanide (NaCN), as an important basic chemical raw material, plays an irreplaceable role in gold smelting, electroplating, pharmaceutical synthesis, and organic chemical industries. Its industrial production methods are mainly divided into the Angle process (using natural gas, ammonia, and air as raw materials), the light oil cracking process, and the hydrogen cyanide neutralization process, based on the raw material route. Among these, the hydrogen cyanide neutralization process, which involves a neutralization reaction between hydrogen cyanide (HCN) and sodium hydroxide (NaOH), has become an important process route under specific raw material supply conditions due to its relatively simple process flow and high product purity.

[0003] Traditional methods for producing sodium cyanide via hydrogen cyanide neutralization often employ batch reactor processes. The specific operation typically involves adding a sodium hydroxide solution to a reactor, and then, under cooling and stirring conditions, introducing hydrogen cyanide gas or liquid to initiate the reaction. While this process involves simple equipment and low investment, it suffers from a series of inherent drawbacks: 1. Low production efficiency: The reaction, cooling, discharging, and cleaning operations need to be carried out in separate steps, resulting in a long production cycle, low equipment utilization, and difficulty in meeting the needs of large-scale continuous production.

[0004] 2. Large fluctuations in product quality: Due to the intermittent operation, it is difficult to maintain absolute consistency in the reaction time, mixing state, cooling rate and other conditions of each batch of materials, which may lead to differences in the concentration, impurity content and other properties of different batches of products, making it difficult to control the quality stability.

[0005] 3. High safety risks: Hydrogen cyanide is a highly toxic and volatile substance. Frequent feeding, opening, and discharging during intermittent operation increases the risk of material leakage and personnel contact. If local mixing is uneven or cooling is insufficient during the reaction, it may lead to concentrated exothermic reactions, posing a potential safety hazard of temperature runaway.

[0006] 4. Limited raw material utilization: To prevent unreacted hydrogen cyanide from escaping during discharge, the reaction endpoint usually requires a slight excess of sodium hydroxide, which may affect further improvement of product purity and impose an additional load on the subsequent tail gas treatment system.

[0007] In summary, the traditional method of producing sodium cyanide using a batch reactor has several drawbacks in practical application, including low production efficiency, large fluctuations in product quality, high safety risks, and limited raw material utilization. Summary of the Invention

[0008] The purpose of this invention is to provide a continuous production method for sodium cyanide from hydrogen cyanide, which solves the problems of low production efficiency, large fluctuations in product quality, high safety risks, and limited raw material utilization in the traditional batch reactor method for producing sodium cyanide.

[0009] To achieve the above objectives, the present invention provides a continuous production method for sodium cyanide from hydrogen cyanide, the continuous production method for sodium cyanide from hydrogen cyanide comprising the following steps: First-stage neutralization reaction: Hydrogen cyanide gas is fed into the first-stage reactor and, together with a sodium cyanide solution containing sodium hydroxide, is fed into the first-stage reactor for neutralization reaction to obtain a first-stage gas-liquid mixture; First-stage separation: The obtained first-stage gas-liquid mixture is sent to a first-stage separator for gas-liquid separation to obtain first-stage liquid and first-stage gas; Primary cycle: A portion of the obtained primary liquid is collected as the product sodium cyanide solution, and the remaining primary liquid is returned to the primary reactor after cooling and replenishment with sodium hydroxide; Secondary neutralization reaction: The obtained primary gas is fed into a secondary reactor and, together with a sodium cyanide solution containing sodium hydroxide, is fed into the secondary reactor for a neutralization reaction to obtain a second-stage gas-liquid mixture; Secondary separation: The resulting second-stage gas-liquid mixture is fed to a secondary separator for gas-liquid separation to obtain a secondary liquid and a secondary gas; Secondary circulation: A portion of the secondary liquid is collected and transported to the primary separator, where it is separated from the primary gas-liquid mixture. The remaining secondary liquid is cooled, replenished with sodium hydroxide, and then returned to the secondary reactor. Exhaust gas treatment: The obtained secondary gas is transported as process exhaust gas to the exhaust gas purification system for treatment.

[0010] In the first-stage neutralization reaction step, hydrogen cyanide gas and sodium cyanide solution containing sodium hydroxide undergo a gas-liquid co-current neutralization reaction in a first-stage reactor. In the secondary neutralization reaction step, the primary gas and the sodium cyanide solution containing sodium hydroxide undergo a gas-liquid co-current neutralization reaction in the secondary reactor.

[0011] Both the primary reactor and the secondary reactor are packed tower reactors. Both the primary reactor and the secondary reactor are filled with structured packing material, the specific surface area of ​​which is not less than 200 m². 2 / m 3 .

[0012] The primary separator and the secondary separator are both either cyclone separators or vertical gravity settling separators.

[0013] The cooling processes in the primary circulation step and the secondary circulation step are completed by a primary cooler and a secondary cooler, respectively. Both the primary cooler and the secondary cooler are either plate heat exchangers or shell-and-tube heat exchangers.

[0014] In the first-stage circulation step, the sodium hydroxide solution is injected into the pipeline between the outlet of the first-stage cooler and the inlet of the first-stage reactor. In the secondary circulation step, the sodium hydroxide solution is injected into the pipeline between the outlet of the secondary cooler and the inlet of the secondary reactor.

[0015] In the primary circulation step, the ratio of the flow rate of the sodium cyanide solution extracted as the product to the total flow rate of the circulating liquid returned to the primary reactor after cooling and replenishment with sodium hydroxide is controlled between 0.1% and 5%. In the secondary circulation step, the ratio of the secondary liquid flow rate collected and transported to the primary separator to the total flow rate of the circulating liquid returned to the secondary reactor after cooling and replenishment with sodium hydroxide is controlled between 1% and 20%.

[0016] This invention discloses a continuous production method for producing sodium cyanide from hydrogen cyanide, employing a two-stage continuous reaction-separation system (the first-stage reaction-separation system comprises the first-stage neutralization reaction step and the first-stage separation step, and the second-stage reaction-separation system comprises the second-stage neutralization reaction step and the second-stage separation step). This achieves segmented deep absorption and conversion of hydrogen cyanide gas, significantly improving production efficiency and equipment utilization. Secondly, by precisely controlling the circulating liquid temperature and alkali replenishment (the cooling process and sodium hydroxide replenishment process in the first-stage and second-stage circulation steps), stable and uniform reaction conditions are ensured, thereby guaranteeing continuous consistency in product quality. Simultaneously, the closed-loop circulation and two-stage absorption design (the first-stage gas separated in the first-stage separator is further absorbed in the second-stage reactor) not only achieves complete recovery of unreacted gas, greatly reducing the safety risk of highly toxic gas leakage, but also enhances raw material utilization and avoids losses caused by excessive alkali through final-stage liquid-phase backmixing (in the second-stage circulation step, a portion of the second-stage liquid is returned to the first-stage separator and remixed with the first-stage gas-liquid mixture stream). The entire process is compact and controllable, essentially achieving safe, efficient, and high-quality continuous industrial production. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the continuous production method for sodium cyanide from hydrogen cyanide provided by the present invention. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] Please see Figure 1 This invention provides a continuous production method for sodium cyanide from hydrogen cyanide, the continuous production method for sodium cyanide from hydrogen cyanide includes the following steps: S1, First-stage neutralization reaction: Hydrogen cyanide gas is fed into the first-stage reactor and, together with a sodium cyanide solution containing sodium hydroxide, is fed into the first-stage reactor for a neutralization reaction to obtain a first-stage gas-liquid mixture; S2, Primary Separation: The obtained first-stage gas-liquid mixture is sent to the primary separator for gas-liquid separation to obtain primary liquid and primary gas; S3, Primary Circulation: A portion of the obtained primary liquid is collected as the product sodium cyanide solution, and the remaining primary liquid is returned to the primary reactor after cooling and replenishment with sodium hydroxide. S4, Secondary Neutralization Reaction: The obtained primary gas is fed into the secondary reactor and, together with a sodium cyanide solution containing sodium hydroxide, is fed into the secondary reactor for a neutralization reaction to obtain a second-stage gas-liquid mixture; S5, Secondary Separation: The obtained second-stage gas-liquid mixture is sent to a secondary separator for gas-liquid separation to obtain secondary liquid and secondary gas; S6, Secondary Circulation: A portion of the secondary liquid is collected and transported to the primary separator, where it is separated from the primary gas-liquid mixture. The remaining secondary liquid is cooled, replenished with sodium hydroxide, and then returned to the secondary reactor. S7. Exhaust Gas Treatment: The obtained secondary gas is transported as process exhaust gas to the exhaust gas purification system for treatment.

[0021] In this embodiment, a two-stage continuous reaction-separation system (the first-stage reaction-separation system comprises the first-stage neutralization reaction step and the first-stage separation step, and the second-stage reaction-separation system comprises the second-stage neutralization reaction step and the second-stage separation step) is employed to achieve segmented deep absorption and conversion of hydrogen cyanide gas, significantly improving production efficiency and equipment utilization. Secondly, by precisely controlling the circulating liquid temperature and alkali replenishment (the cooling process and sodium hydroxide replenishment process in the first-stage and second-stage circulation steps), stable and uniform reaction conditions are ensured, thereby guaranteeing continuous consistency in product quality. Simultaneously, the closed-loop circulation and two-stage absorption design (the first-stage gas separated in the first-stage separator is further absorbed in the second-stage reactor) not only achieves complete recovery of unreacted gas, greatly reducing the safety risk of highly toxic gas leakage, but also enhances raw material utilization and avoids losses caused by excessive alkali through final-stage liquid-phase backmixing (in the second-stage circulation step, a portion of the second-stage liquid is returned to the first-stage separator and remixed with the first-stage gas-liquid mixture stream). The entire process is compact and controllable, essentially achieving safe, efficient, and high-quality continuous industrial production.

[0022] Furthermore, in the first-stage neutralization reaction step, hydrogen cyanide gas and sodium cyanide solution containing sodium hydroxide undergo a gas-liquid co-current neutralization reaction in a first-stage reactor. In the secondary neutralization reaction step, the primary gas and the sodium cyanide solution containing sodium hydroxide undergo a gas-liquid co-current neutralization reaction in the secondary reactor.

[0023] In this embodiment, the co-current contact of gas and liquid reduces the flow resistance between the two phases, which is beneficial for the rapid dispersion and dissolution of hydrogen cyanide gas in the liquid phase, thereby enhancing the mass transfer process and increasing the reaction rate.

[0024] Furthermore, both the primary reactor and the secondary reactor are packed tower reactors; Both the primary reactor and the secondary reactor are filled with structured packing material, the specific surface area of ​​which is not less than 200 m². 2 / m 3 .

[0025] In this embodiment, the use of structured packing can provide a larger gas-liquid contact area, significantly enhancing the mass transfer efficiency between the two phases and ensuring that the hydrogen cyanide gas is fully absorbed and reacted. The high specific surface area of ​​the packing also helps to uniformly distribute the liquid, reduce the system pressure drop, make the internal flow of the reactor more stable, and further improve the reaction conversion rate and operational continuity.

[0026] Furthermore, both the primary separator and the secondary separator are either cyclone separators or vertical gravity settling separators.

[0027] In this embodiment, the use of a cyclone separator or a vertical gravity sedimentation separator can efficiently and quickly separate the gas-liquid mixture after the reaction, ensuring that the liquid droplets entrained in the gas are effectively removed and the bubbles carried in the liquid are fully released.

[0028] Furthermore, the cooling processes in the primary circulation step and the secondary circulation step are completed by a primary cooler and a secondary cooler, respectively, both of which are either plate heat exchangers or shell-and-tube heat exchangers.

[0029] In this embodiment, plate or shell-and-tube heat exchangers are characterized by high heat transfer efficiency, compact structure, and easy maintenance. They can remove the heat released by the reaction in a timely manner, accurately control the temperature of the circulating liquid, and avoid side reactions or material volatilization caused by excessive temperature rise, thereby ensuring product quality and operational safety.

[0030] Furthermore, in the first-stage circulation step, the injection point of the sodium hydroxide solution is located in the pipeline between the outlet of the first-stage cooler and the inlet of the first-stage reactor; In the secondary circulation step, the sodium hydroxide solution is injected into the pipeline between the outlet of the secondary cooler and the inlet of the secondary reactor.

[0031] In this embodiment, the sodium hydroxide solution injection point is set after the cooler and before the reactor. This ensures that the added alkali solution is fully mixed with the cooled circulating liquid and enters the reactor at the same temperature, avoiding local overheating or uneven alkali concentration. This makes the reaction conditions more stable and is beneficial to improving the conversion rate and product consistency.

[0032] Furthermore, in the primary circulation step, the ratio of the flow rate of the sodium cyanide solution extracted as product to the total flow rate of the circulating liquid returned to the primary reactor after cooling and replenishment with sodium hydroxide is controlled between 0.1% and 5%. In the secondary circulation step, the ratio of the secondary liquid flow rate collected and transported to the primary separator to the total flow rate of the circulating liquid returned to the secondary reactor after cooling and replenishment with sodium hydroxide is controlled between 1% and 20%.

[0033] In this embodiment, by controlling the extraction ratio of the first-stage circulation step, the material balance and reactant concentration within the system can be maintained while ensuring continuous production. By controlling the partial liquid back-mixing of the second-stage circulation step to the previous stage, the system absorption efficiency can be further optimized, the heat and material distribution uniformity can be enhanced, thereby improving the overall raw material utilization rate, reducing alkali consumption, and ensuring the long-term process stability.

[0034] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A continuous production method for sodium cyanide from hydrogen cyanide, characterized in that, Includes the following steps: First-stage neutralization reaction: Hydrogen cyanide gas is fed into the first-stage reactor and, together with a sodium cyanide solution containing sodium hydroxide, is fed into the first-stage reactor for neutralization reaction to obtain a first-stage gas-liquid mixture; First-stage separation: The obtained first-stage gas-liquid mixture is sent to a first-stage separator for gas-liquid separation to obtain first-stage liquid and first-stage gas; Primary cycle: A portion of the obtained primary liquid is collected as the product sodium cyanide solution, and the remaining primary liquid is returned to the primary reactor after cooling and replenishment with sodium hydroxide; Secondary neutralization reaction: The obtained primary gas is fed into a secondary reactor and, together with a sodium cyanide solution containing sodium hydroxide, is fed into the secondary reactor for a neutralization reaction to obtain a second-stage gas-liquid mixture; Secondary separation: The resulting second-stage gas-liquid mixture is fed to a secondary separator for gas-liquid separation to obtain a secondary liquid and a secondary gas; Secondary circulation: A portion of the secondary liquid is collected and transported to the primary separator, where it is separated from the primary gas-liquid mixture. The remaining secondary liquid is cooled, replenished with sodium hydroxide, and then returned to the secondary reactor. Exhaust gas treatment: The obtained secondary gas is transported as process exhaust gas to the exhaust gas purification system for treatment.

2. The continuous production method for sodium cyanide from hydrogen cyanide as described in claim 1, characterized in that, In the first-stage neutralization reaction step, hydrogen cyanide gas and sodium cyanide solution containing sodium hydroxide undergo a gas-liquid co-current neutralization reaction in a first-stage reactor. In the secondary neutralization reaction step, the primary gas and the sodium cyanide solution containing sodium hydroxide undergo a gas-liquid co-current neutralization reaction in the secondary reactor.

3. The continuous production method for sodium cyanide from hydrogen cyanide as described in claim 2, characterized in that, Both the primary reactor and the secondary reactor are packed tower reactors; Both the primary reactor and the secondary reactor are filled with structured packing material, the specific surface area of ​​which is not less than 200 m². 2 / m 3 .

4. The continuous production method for sodium cyanide from hydrogen cyanide as described in claim 3, characterized in that, Both the primary separator and the secondary separator are either cyclone separators or vertical gravity settling separators.

5. The continuous production method for sodium cyanide from hydrogen cyanide as described in claim 4, characterized in that, The cooling processes in the primary circulation step and the secondary circulation step are completed by a primary cooler and a secondary cooler, respectively. Both the primary cooler and the secondary cooler are either plate heat exchangers or shell-and-tube heat exchangers.

6. The continuous production method for sodium cyanide from hydrogen cyanide as described in claim 5, characterized in that, In the first-stage circulation step, the sodium hydroxide solution is injected into the pipeline between the outlet of the first-stage cooler and the inlet of the first-stage reactor. In the secondary circulation step, the sodium hydroxide solution is injected into the pipeline between the outlet of the secondary cooler and the inlet of the secondary reactor.

7. The continuous production method for sodium cyanide from hydrogen cyanide as described in claim 6, characterized in that, In the first-stage circulation step, the ratio of the flow rate of the sodium cyanide solution extracted as the product to the total flow rate of the circulating liquid returned to the first-stage reactor after cooling and replenishment with sodium hydroxide is controlled between 0.1% and 5%. In the secondary circulation step, the ratio of the secondary liquid flow rate collected and transported to the primary separator to the total flow rate of the circulating liquid returned to the secondary reactor after cooling and replenishment with sodium hydroxide is controlled between 1% and 20%.

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