Latest Production Processes of Sodium Cyanide

1. Introduction

Sodium cyanide (NaCN) is a crucial chemical compound widely used in various industries, such as gold mining, electroplating, and chemical synthesis. The Production processes of Sodium cyanide have been continuously evolving to improve efficiency, reduce costs, and enhance environmental friendliness. This article will introduce several of the latest production processes of Sodium Cyanide.

2. Ammonia - Sodium Method

2.1 Process Principle

In the ammonia - sodium method, metallic sodium and petroleum coke are first added to a reactor in a certain proportion. The temperature is then raised to 650 °C, and ammonia gas is introduced. As the temperature is further increased to 800 °C, a reaction occurs over a period of 7 hours, during which metallic sodium is completely converted into sodium cyanide. After that, the reactants are filtered at a temperature of 650 °C to remove excess petroleum coke. The molten product is then discharged and cast into the desired shape to obtain sodium cyanide products.

2.2 Advantages and Disadvantages

• Advantages: This process has a relatively simple reaction principle, and the raw materials sodium and ammonia are relatively common in the chemical industry.

• Disadvantages: The high - temperature reaction conditions require a large amount of energy consumption. Also, the use of metallic sodium poses certain safety risks due to its high reactivity.

3. Cyanide Melt Method

3.1 Process Principle

Cyanide melt and lead oxide are added to an extraction tank. The typical ratio of cyanide melt to lead oxide is (500 - 700):1. The addition of lead oxide helps in desulfurization by forming a lead sulfide precipitate. The extraction liquid is then allowed to settle, and the resulting clear liquid contains 80 - 90 g/L of NaCN. In a generator, this liquid reacts with concentrated sulfuric acid to generate hydrogen cyanide gas. After condensation to remove water, the hydrogen cyanide gas enters an absorption reactor and reacts with liquid alkali (sodium hydroxide solution) to form sodium cyanide.

3.2 Advantages and Disadvantages

• Advantages: This process can effectively remove sulfur impurities through the addition of lead oxide, which is beneficial for improving the quality of the final product.

• Disadvantages: The use of lead oxide may lead to environmental pollution problems associated with lead. Additionally, the process involves multiple steps such as extraction, reaction, and absorption, which increases the complexity of operation.

4. Andrussow Process (Anshig Method)

4.1 Process Principle

The Andrussow process uses natural gas, ammonia, and air as raw materials. First, natural gas is washed in a water - washing tower to remove inorganic sulfur and part of the organic sulfur. After filtration, the refined natural gas should have a sulfur content of ≤1 mg/m³ and the content of hydrocarbons above C₂ should be less than 2%. Liquid ammonia is vaporized in a vaporizer, and air is filtered through a filter. The three raw materials are then mixed in a mixer at a ratio of ammonia:methane:air = 1:(1.15 - 1.17):(6.70 - 6.80). The mixed gas enters an oxidation reactor with a platinum - rhodium alloy as the catalyst. At a temperature of 1070 - 1120 °C, a reaction occurs to generate a mixed gas containing 8.5% hydrogen cyanide.

The gas is cooled and then enters an ammonia - absorption tower, where residual ammonia is absorbed by sulfuric acid. After that, it is cooled by water and hydrogen cyanide is absorbed by low - temperature water. The tail gas is discharged after being washed by an alkali - wash tower. The hydrogen cyanide solution absorbed by water is heat - exchanged and then enters a desorption tower. At the top of the desorption tower, hydrogen cyanide with a purity of 98% is obtained. This hydrogen cyanide then reacts with an alkali solution to form a sodium cyanide solution, which is further processed through evaporation, crystallization, drying, and shaping to obtain the final sodium cyanide product.

4.2 Advantages and Disadvantages

• Advantages: In regions with rich natural gas resources, the cost of raw materials is relatively low. The process has been relatively mature in industrial applications, and the production scale can be relatively large.

• Disadvantages: In areas lacking natural gas resources, affected by factors such as natural gas shortages, policies, and prices, the production cost may fluctuate significantly. The high - temperature reaction conditions require high - temperature - resistant equipment and consume a large amount of energy.

5. Flame Process

5.1 Process Principle

Natural gas, oxygen, and ammonia are used as raw materials. These three gases are filtered separately to remove impurities and then enter a mixer after being stabilized and metered. Part of the oxygen is used as the main oxygen to enter the mixer, and the other part is directly fed into the nozzle for ignition. The three raw materials are combined in a certain proportion and undergo a combustion reaction to synthesize hydrogen cyanide at a temperature of 1500 °C.

The reaction gas is quenched by spraying water and then cooled in a cooler. It then enters an ammonia - absorption tower, where the residual ammonia in the reaction gas is absorbed by 15% - 20% sulfuric acid, and ammonium sulfate can be recovered. The reaction gas containing hydrogen cyanide is cooled by water and then absorbed by low - temperature water to form a 1.5% hydrogen cyanide solution. This solution is distilled in a distillation tower to obtain hydrogen cyanide with a content of 98% - 99%. Finally, it is absorbed by an alkali solution, and after evaporation, crystallization, drying, and shaping, the sodium cyanide product is obtained.

5.2 Advantages and Disadvantages

• Advantages: This process can achieve relatively high - purity hydrogen cyanide production. The recovery of ammonium sulfate as a by - product can bring certain economic benefits.

• Disadvantages: The high - temperature combustion reaction requires a large amount of energy input. The process also involves complex operations such as gas mixing, combustion, quenching, and absorption, which require high - level process control.

6. Light Oil Pyrolysis Method

6.1 Process Principle

Light oil and ammonia are mixed in an atomizer in a certain proportion and pre - heated to 280 °C. The mixture then enters an electric arc furnace for a pyrolysis reaction. Petroleum coke is used as a carrier, and nitrogen is used as a protective gas to prevent oxidation in a closed environment. At a temperature of 1450 °C, a reaction occurs to generate hydrogen cyanide gas. The gas is then dust - removed, cooled, and further processed through steps such as ammonia removal, water washing, absorption, and distillation to obtain pure hydrogen cyanide. Finally, hydrogen cyanide reacts with an alkali solution (sodium hydroxide) to form sodium cyanide.

6.2 Advantages and Disadvantages

• Advantages: The process technology is relatively mature. It can use light oil, a relatively common raw material in the petrochemical industry.

• Disadvantages: There are difficulties in desulfurization and impurity removal of hydrogen cyanide. The product has high energy consumption, and the treatment of "three wastes" (waste gas, waste water, and waste residue) is difficult. The production cost is relatively high.

7. Acrylonitrile By - Product Method

7.1 Process Principle

In the process of producing acrylonitrile by the ammoxidation of propylene, hydrogen cyanide gas is produced as a by - product (the amount is equivalent to 4% - 10% of the acrylonitrile production). The gas containing hydrogen cyanide is absorbed by an alkali solution. After evaporation, concentration, separation, and drying, the sodium cyanide product is obtained.

7.2 Advantages and Disadvantages

• Advantages: This is a by - product utilization process, which can make full use of resources and reduce production costs to a certain extent.

• Disadvantages: The production of sodium cyanide is limited by the production scale of acrylonitrile. The quality of the by - product hydrogen cyanide may be affected by the main production process of acrylonitrile, which requires strict control and purification.

8. Methanol Ammoxidation Method

8.1 Process Principle

Air passes through a filter and a pre - heater and then enters a reaction furnace. Liquid ammonia is vaporized and methanol is evaporated. They enter a mixing pre - heater and then react with air in the reaction furnace. Under the action of a catalyst mainly composed of Fe - Mo oxide, the reaction generates hydrogen cyanide. The hydrogen cyanide gas enters a de - ammonia tower to remove ammonia and then obtains hydrogen cyanide. Finally, it is absorbed by an alkali solution to prepare sodium cyanide.

8.2 Advantages and Disadvantages

• Advantages: The use of methanol and ammonia as raw materials is relatively common, and the catalyst can be recycled and reused to a certain extent. The process can be adjusted according to the production needs.

• Disadvantages: The catalyst is sensitive to reaction conditions, and small changes in temperature, pressure, and raw material ratio may affect the activity and selectivity of the catalyst, thus affecting the yield and quality of the product.

9. Conclusion

The production processes of sodium cyanide each have their own characteristics. The choice of production process depends on various factors such as raw material availability, cost, environmental requirements, and production scale. With the continuous development of technology, new production processes may emerge in the future, aiming to further improve the efficiency and environmental performance of sodium cyanide production. As the demand for sodium cyanide in different industries continues to grow, the optimization and innovation of production processes will play a crucial role in meeting market needs while ensuring sustainable development.