Sodium nitrite preparation method

Sodium Nitrite

[Physical and chemical properties]

Sodium nitrite (NaNO ₂ ) is a white or light yellow orthorhombic crystal or powder, with a relative density of 2.

[Preparation method] The production methods of sodium nitrite can be roughly classified into two categories: one is the reduction method, that is, under certain temperature and degree conditions, the use of lead, calcium or hydrogen as a reducing agent to reduce sodium nitrate to prepare sub Sodium nitrate, the problem of this type of method is that the process is complicated and the cost is high; the second type is the main production method at home and abroad, that is, the co-production of sodium nitrate and sodium nitrite by absorbing nitrogen oxide gas with an alkaline solution

(1) Direct method

In the direct method, ammonia and air are oxidized to NO by the platinum catalyst in the oxidation furnace, and after the reaction heat is recovered by the waste heat boiler, the waste heat boiler contains high-concentration nitrogen oxide and nitrogen dioxide gas, and then is absorbed from the waste heat boiler.

The reaction equation for absorbing nitric oxide gas with soda ash solution is as follows:

The reaction equation of absorbing nitric oxide gas with caustic soda solution is as follows,

The process of direct production of sodium nitrite is divided into 4 steps:

a.

b.

c.

d.

Figure 6-7 Process flow of sodium nitrite and sodium nitrate production equipment

In the caustic soda tank, 15%-20% soda ash solution is prepared at a temperature of 60-100°C

In the production process, it is mainly to control the content of NO and NO ₂ in the nitrogen oxide mixture so that it exists in the form of N ₂ O ₃ during the absorption process .

From the NO oxidation rate formula, it can be seen that the degree of oxidation of NO increases with the increase of the concentration of NO and O ₂ and the temperature and time during oxidation

When the absorption temperature is from 170°C to 650°C, the absorption rate of nitrogen oxides is basically the same

(2) Exhaust gas method

The tail gas method can be divided into three types: nitric acid tail gas absorption method, nitric acid tail gas enrichment method and gas distribution method

① Nitric acid tail gas absorption method Nitric acid tail gas absorption method is divided into atmospheric pressure method (its absorption pressure is 0.

In this method, 20%～35% Na ₂ CO ₃ aqueous solution is used to absorb the tail gas containing 0.

The advantage of this method is that alkali absorption is more efficient than water absorption, shortens the acid absorption process, reduces the nitrogen oxide content in the vented exhaust gas, reduces environmental pollution, and can recover nitrate by-products to make nitrate Production costs are reduced

②Nitric acid tail gas enrichment method This method is suitable for the process of multi-tower production of nitric acid at atmospheric pressure.

③Gas distribution method This method was developed by Shanghai Research Institute of Chemical Industry.
It adjusts the nitrogen oxide content and oxidation degree (a=50%) of the incoming alkali absorption tower to reduce the NOx concentration in the exhaust gas of nitric acid and increase the nitrate.
The output
.
In practical applications, due to the lack of rapid NO and NO ₂ analyzers and manual experience adjustment and control, although the output of nitrate has increased, the ratio of sodium nitrite to sodium nitrate can be maintained at 1:1, but the exhaust nitric acid tail gas contains NOx.
High
.

(3) Double decomposition method

The metathesis method uses nitric acid to directly act on alkalis to produce sodium nitrate, but this method is limited by resources and raw material sources, so it is not suitable for large-scale development
.

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