JPS5850926B2 - Production method of calcium nitrite aqueous solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing an aqueous calcium nitrite solution by contacting and absorbing a gas containing nitrogen monoxide and nitrogen dioxide obtained by air oxidizing ammonia into a slaked lime slurry.

Calcium nitrite has traditionally been used as a rust preventive agent, cement admixture, etc., but when actually used,
It is desired to provide a product in the form of an aqueous solution at a temperature of about 30 to 40° C. rather than in a solid state.

An aqueous solution of calcium nitrite can be easily obtained by dissolving solid calcium nitrite in water, but commercially available solid calcium nitrite is made by concentrating and drying a calcium nitrite solution. , this method is extremely inefficient.

A relatively preferable method for obtaining a calcium nitrite aqueous solution with high purity and high concentration includes, for example, Japanese Patent Application Laid-Open No. 54-431
The method described in Japanese Patent No. 96 is already known.

This method includes NO obtained by air oxidation of ammonia and NO2, and the No/N02 molar ratio is 1.2.
A high temperature gas of ~1.5% is continuously supplied and absorbed into a 20-40% aqueous slurry of slaked lime, while the reaction temperature is maintained at 40-70°C and unabsorbed gas is continuously discharged. The molar ratio N obtained by recovering and oxidizing the unabsorbed gas in the first stage reaction, which is carried out until the residual slaked lime concentration reaches 3 to 10, and then in the second stage reaction.
NO and NO at low concentrations with an O/NO2 molar ratio of 1.2 to 1.5.
The gas containing 2 is converted into 3 obtained by the above first stage reaction.
Continuously supply slurry containing ~10φ slaked lime,
This is a method whose main step is an absorption reaction at 0 to 700C.

Although this prior art is a preferable method with less raw material loss and simple steps, it has the disadvantage that it is not suitable for large-scale industrial production.

In other words, according to the above-mentioned prior art, in order to carry out industrial production at an annual rate of several thousand tons, large reactors, especially large condensers and large sky oxidizers are required. If the reaction is carried out under pressure at a high temperature of 70° C. or higher, the by-product rate of calcium nitrate will increase, making it impossible to obtain calcium nitrite having a purity of 95 or higher.

The current challenge is to establish efficient large-scale production technology for highly purified and highly concentrated calcium nitrite aqueous solutions.

As a result of detailed experimental research, the present inventors found that the gas containing NO and NO2 obtained by ammonia oxidation was
0 to b It has been found that when the reaction is carried out, there is almost no decrease in the reaction rate due to a decrease in the solubility of slaked lime.

Furthermore, it was completely unexpected that if a gas with an NO/NO2 molar ratio increased to 1.6 or more was absorbed and reacted with a slurry of 20 to 40 slaked lime at high temperature under pressure, an increase in the by-product rate of calcium nitrate could be avoided. They discovered new facts that had not previously been obtained and completed the present invention.

The first object of the present invention is to obtain a highly purified calcium nitrite aqueous solution with a calcium nitrite production ratio of 95 or higher and a high concentration of 30% or higher. Another object of the present invention is to provide a method for producing the above-mentioned highly pure and highly concentrated calcium nitrite aqueous solution that can be produced on a large scale without the need for nitrogen monoxide, which is obtained by air oxidation of slaked lime slurry and ammonia. Another object of the present invention is to provide a method for efficiently producing a highly pure and highly concentrated calcium nitrite aqueous solution from raw materials slaked lime and -nitrogen oxide and nitrogen dioxide gas through a simple process. It is an object of the present invention to provide a method for efficiently producing a highly purified and highly concentrated calcium nitrite aqueous solution with little loss.

The production method of the present invention includes: 0) Ammonia is obtained by air oxidation, and nitrogen monoxide (NO) and nitrogen dioxide (N
The total amount of O2) is 5 to 12 volumes, the NO/NO2 molar ratio is 1.6 to 2.5, and the temperature is 190 to 30
By continuously supplying gas at 0°C into a 20 to 40 weight water-related slurry of slaked lime while maintaining the reaction temperature at 75 to 1100C, the concentration of residual slaked lime can be reduced to 2 to 10%.
The process of absorbing and reacting until it reaches a certain weight, and continuously discharging the unabsorbed gas outside the reaction zone. (B) Collecting the unabsorbed gas discharged in (B), and adding nitrogen gas to it as necessary. NO by supplying and oxidizing at 85-151°C
/NO2 molar ratio from 1.6 to 2.5, and
The step of adjusting the total amount of nitrogen monoxide and nitrogen dioxide to 1 to 5 volumes φ, the produced calcium nitrite obtained in the steps (c) and (b) is dissolved, and the residual slaked lime concentration is 2 to 5.
By continuously supplying the gas obtained in step (b) into a 10 weight cup of aqueous slurry under a pressure of 2,0 to 10 kg/- while maintaining the reaction temperature at 75 to 1100 G. The absorption reaction is carried out until the concentration of residual slaked lime becomes 3 weight φ or less, and the unabsorbed gas is continuously discharged out of the reaction zone, and the liquid obtained in step (c) is passed through. It is characterized by

In the present invention, the production rate of calcium nitrite, that is, the purity, is expressed as the ratio of the production amount of calcium nitrite to the production amount of calcium nitrate and calcium nitrite.

The highly concentrated slaked lime slurry used in the present invention can be easily obtained by dispersing commercially available industrial product slaked lime in water, but if the concentration is 20% or less, the above (a) to)
Depending on the method in which the above steps are combined, the highly concentrated calcium nitrite aqueous solution that is the object of the present invention cannot be obtained, and if the concentration is 40% or more, basic calcium nitrite Ca (NO2 )・Ca(OH)22H
20 (hereinafter referred to as double salt).

), the viscosity of the reaction slurry increases, making it difficult to absorb nitrogen oxide and nitrogen dioxide gas smoothly;
Furthermore, it also causes precipitation of calcium sulfite, which is both undesirable.

The gas obtained by air oxidation of ammonia used in the present invention is prepared by a normal method to a pressure of 10 to 9/-
Easily obtained as the following gases: - Nitrogen oxide and nitrogen dioxide 5 to 12 parts by volume, oxygen 5 to 10 parts by volume, water 13 to 1 part
Consists of 8 capacity factors and nitrogen residuals.

This gas first consists of nitrogen monoxide NO and nitrogen dioxide NO2.
The NO/NO2 molar ratio of 1.6 to 2.5 is required.

If this molar ratio is less than 1.6, when the gas is absorbed into the slaked lime slurry in step (a), the proportion of calcium nitrate produced increases, making it impossible to obtain a high-purity calcium nitrite aqueous solution.

Further, as this molar ratio increases beyond 2.5, the absorption reaction rate of nitrogen monoxide and nitrogen dioxide in the step (a) decreases, and the reaction becomes inefficient, which is not preferable.

However, the gas used in step (a) is NO.
It is not enough to limit the /N02 molar ratio as described above; it is also necessary to limit the total concentration of nitrogen monoxide and nitrogen dioxide in the gas to a specific range.

If the concentration is less than 5 volumes φ, the reaction rate will be low and the efficiency of the device will be reduced.

In addition, if the trapezoidal concentration of -nitrogen oxide and nitrogen dioxide is high, it will not cause any trouble in the reaction, but in order to produce such gas by the ammonia oxidation method, it is usually necessary to have a concentration of 12 volumes or less. preferable.

Furthermore, the gas obtained by the above ammonia oxidation is
If the temperature is below 150°C, water vapor in the gas will condense and produce nitric acid, so it is necessary to avoid using the temperature below 150°C in step (a) of the present invention.

When the temperature of this gas is about 150 to 190°C, the proportion of calcium nitrate as a by-product tends to decrease in the step (a) of the present invention, but the reaction rate does not become sufficiently high.

When the temperature of this gas is 190°C or higher, the present invention
In the process, the by-product ratio of calcium nitrate is significantly reduced and the reaction rate is increased, so that the object of the present invention is achieved.

However, if the temperature of this gas rises to 300°C or higher, the reaction temperature in step (a) of the present invention is reduced to 75-11°C.
This is not efficient because the amount of heat removal required to maintain the temperature at 0° C. increases significantly.

In order to mass-produce the target product by increasing the amount of the slaked lime slurry and gas supplied to the reaction zone, it is necessary to increase the heat removal rate, and to solve this problem without using a large cooler. 1. The reactant temperature, ie the temperature of the slurry, must be increased.

However, in the slaked lime slurry of Sections 620 to 40, the partial pressure of water vapor becomes equal to the partial pressure of water vapor in the girth at about 70°C under normal pressure. To avoid evaporation, it is necessary to carry out the reaction under pressure.

As mentioned above, since the gas obtained by ammonia oxidation has a pressure of approximately 10 kg/f or less as a preferable pressure for industrial production, the maximum temperature of the slurry that can be raised is approximately 110°C corresponding to the maximum gas pressure of 10 kg/cnL. It is.

Therefore, in step (a) of the present invention, the reaction is carried out at a temperature of 75 to 110° C. under a pressure sufficient to prevent the slurry from concentrating due to water evaporation, that is, at a pressure of 2 to 10 kg/i by the feed gas.

The reason why the reaction rate for producing calcium nitrite does not decrease even though the solubility of suspended calcium hydroxide decreases when the temperature of the slurry is high is thought to be due to the high temperature of the supplied gas.

According to the method of the present invention, the gas is continuously supplied into the slurry while maintaining the reaction temperature at the specific temperature,
Unabsorbed gas is continuously vented out of the reaction zone.

The reaction zone is a zone where gas and slurry come into contact and a reaction occurs.

Due to the absorption reaction, nitrogen monoxide and nitrogen dioxide in the gas are consumed, but since the consumption ratio of NO/NO2 is different from the NO/NO2 ratio in the supplied gas, the gas The NO/NO2 ratio in the slurry gradually increases, and even if the gas is brought into contact with the slurry for a long period of time, the reaction rate decreases significantly and is not efficient.

According to the invention, the NO/NO2 molar ratio is between 1.6 and 2.5.
Calcium nitrite is efficiently produced by continuously supplying a gas to the slurry and continuously discharging unabsorbed gas containing unreacted nitrogen monoxide and nitrogen dioxide from the reaction zone.

Furthermore, in the method of the present invention, it is necessary to stop the gas absorption reaction in step (a) when the concentration of residual slaked lime reaches 2 to 10% by weight.

When leaving slaked lime on the windward side, (c)
In the process, a large amount of low concentration gas must be absorbed and reacted, which is undesirable as it takes a long time for one reaction.

In addition, if the reaction progresses to less than 2 weight ratios, the above (a)
In the process, the production rate of calcium nitrate increases, making it impossible to obtain a high-purity calcium nitrite aqueous solution.

Thus, although calcium nitrite can be produced efficiently and efficiently while suppressing the production of calcium nitrate and the precipitation of the double salt by the step (a) of the present invention, the remaining Separating and removing the 2 to 10 layers of slaked lime not only results in the loss of slaked lime but also requires a further concentration step, making it possible to easily and efficiently produce the high purity and highly concentrated calcium nitrite solution that is the objective of the present invention. cannot be manufactured.

In step (c) of the method of the present invention, the low concentration slaked lime slurry that dissolves the produced calcium nitrite obtained in step (a) further contains nitrogen monoxide and nitrogen dioxide at a specific molar ratio and at a low concentration. The purpose is to eliminate the above-mentioned drawbacks by bringing the product into contact with a gas, and to provide an efficient manufacturing method by using the exhaust gas from the step (a) as the gas.

If the total concentration of nitrogen monoxide and nitrogen dioxide in the gas used in step (c) is high, this is not preferable because the proportion of calcium nitrate produced in step (c) will increase.

The total concentration of nitrogen monoxide and nitrogen dioxide in the gas used in this step (c) is preferably 5 volume ratio or less, especially 3 volume ratio or less, but if the concentration is too low, the production rate of calcium nitrite will decrease. Usually, the appropriate concentration is 1 volume or more.

The NO/NO2 molar ratio of the gas used in the step (c) is preferably 1.6 to 2.5 for the same reason as the reason for limiting the molar ratio of the gas used in the step (a).

Furthermore, for the same reason as the limiting reason in the step (a) above, in order to prevent water evaporation in the slurry, the slurry at a temperature of 75 to 11% under a pressure of 2 to 10 kg/i by the supply gas.
The reaction proceeds at 0°C.

In the step (c), in order to efficiently generate calcium nitrite, gas is continuously supplied into the slurry, and nitrogen monoxide and nitrogen dioxide in the gas are brought into contact with the slurry to form water in the slurry. The unabsorbed gas that reacts with calcium oxide, most of which is absorbed and consumed, and the concentration of nitrogen monoxide and nitrogen dioxide is reduced, is continuously discharged out of the reaction zone.

In the step (c), calcium nitrite is further produced by the contact between the gas and the slurry, but in order to completely consume the slaked lime in the slurry, the gas must be supplied for a long time, so the slaked lime is completely consumed. It is not efficient to supply gas until the temperature is reached.

In the step (c), it is efficient to stop the reaction while a small amount of calcium hydroxide remains in the solution, that is, 3 parts or less, usually about 0.5 to 1.5 parts.

As the gas containing nitrogen monoxide and nitrogen dioxide at low concentrations used in the step (c), the exhaust gas from the step (a) is used, thereby avoiding loss of nitrogen monoxide and nitrogen dioxide.

The step (b) is provided for this purpose.

Since the exhaust gas in the step (a) has a NO/NO2 molar ratio of approximately 4 or more, it is collected and the molar ratio is reduced to 1.
It is necessary to adjust it to between 6 and 2.5.

A sky tower oxidizer is used to adjust this molar ratio, and (a)
This can be easily carried out by conducting the exhaust gas in the process of 2 to oxidize nitrogen monoxide with 4 to 5 volumes of oxygen contained in the exhaust gas.

In this oxidation reaction, the exhaust gas is fed into an air column oxidizer with a temperature of 85 to 150
This process can be easily carried out by staying at ℃ for a sufficient period of time.

Advantageously, the exhaust gas in step (a) is usually at a temperature of 90 to 1300C.

It can be easily oxidized by passing it through an oxidizer without requiring special heating.

Furthermore, advantageously, since the exhaust gas in step (a) still has a high pressure, the above-mentioned oxidation reaction can be carried out without requiring a large-sized sky tower oxidizer.

In some cases, a pipe may be used instead of the sky tower oxidizer, and according to the present invention, the oxidizer can be downsized as well as the cooler, which brings great benefits in industrial production. It is.

- The total concentration of nitrogen oxide and nitrogen dioxide can be easily adjusted to 1 to 5 volumes by supplying nitrogen gas to the sky oxidizer together with the exhaust gas, if necessary.

However, when using a gas obtained by air oxidation of ammonia in which the total concentration of nitrogen monoxide and nitrogen dioxide is 5 to 12 volumes as the gas used in the step (a), The total concentration of nitrogen monoxide and nitrogen dioxide in the exhaust gas is 5 volumes or less, usually 1 to 3 volumes higher, and can be used in the step (c) without any particular concentration adjustment.

According to the method of the present invention, an aqueous solution containing calcium nitrite at a high concentration can be obtained by combining the above steps (a), (b), and (c); In addition to a small amount of slaked lime, insoluble impurities contained in the raw materials may also be present in the solution, and by separating and removing them, a highly pure and highly concentrated calcium nitrite aqueous solution can be obtained.

The solution obtained in step (c) above can be easily filtered, so it can be used as a step to separate and remove impurities)
It is preferable to additionally set up a filtration step.

Filtration can be carried out by conventional methods.

The method of the present invention can be carried out either batchwise or continuously.

A preferred embodiment is a continuous process.

That is, the concentration of slaked lime in the slurry was set to 2 in the first reaction tank.
A highly concentrated slaked lime slurry and a gas containing nitrogen monoxide and nitrogen dioxide at a high concentration are continuously supplied while maintaining the weight of the slaked lime slurry at ~10% by weight, and the slaked lime slurry and the gas are brought into contact with each other. The liquid is continuously taken out and transferred to the second reaction tank, while the unabsorbed gas in the first reaction tank is continuously discharged from the first reaction tank and recovered. After adjusting the molar ratio by supplying and oxidizing the obtained gas, the obtained gas is continuously supplied to the second reaction tank and brought into contact with the liquid sent from the first reaction tank, and the unabsorbed gas is continuously removed. At the same time, a highly pure and highly concentrated calcium nitrite aqueous solution is continuously obtained by continuously taking out the liquid, supplying it to a filter, and filtering it.

Moreover, as another embodiment, after passing through the 0 steps, (
The process of recovering the exhaust gas from step (c) again and adjusting the molar ratio and, if necessary, the concentration again in the same manner as step (b) (dX-addition setting, and the liquid obtained in step (c)) A step (b) is additionally set in which the gas obtained in the above step (') is continuously collected, the gas obtained in the above step (') is continuously supplied, the gas is catalyzed and absorbed, and the unabsorbed gas is continuously discharged. A method may also be adopted in which the liquid obtained in step (b) is continuously taken out and filtered.

In the same manner as above, further (mouth "), (four")... and (
It is also possible to carry out a method in which the multi-stage steps of c"), (c"'), etc. are added and the reaction is carried out until the concentration of residual calcium hydroxide becomes 3 parts by weight or less, preferably 1 part or less.

However, in terms of equipment, it is most preferable to combine the simple steps (a), (b), (c), and (c) for efficiency and implementation.

According to the method of the present invention, a high-purity calcium nitrite aqueous solution of 30 to 400 to 40% by weight and a calcium nitrite production ratio of 95% or higher can be efficiently produced as a product without requiring large-sized equipment. It can be industrially mass-produced as a rust preventive agent, cement admixture, etc.

The present invention will be described in more detail below with reference to Examples, but the technical scope of the present invention is not limited thereto.

Example 1 1,750 kg of industrial grade 1 slaked lime, 85 kg of calcium nitrite, and 4,500 kg of water were put into a first reaction tank with a diameter of 2.0 m and a height of 3.8 m, stirred to form a slurry, and then placed at the bottom of the tank while stirring. The concentration of nitrogen monoxide and nitrogen dioxide produced by air oxidation of ammonia through a porous nozzle was 9.4 by volume, and the molar ratio of nitrogen monoxide and nitrogen dioxide (
NO/NO2) 1.7, gas at a temperature of about 230°C 13
The gas was continuously blown at a rate of 0.00 Nm/hr for 80 hours, and the unabsorbed gas was continuously discharged.

During this time, the pressure of the reaction thread was 2.8kg1cr&,
The reaction solution was cooled and maintained at 78-83°C, and the pH value was maintained above 11.

Thus, the reaction solution containing 30.4% calcium nitrite, 1.1% calcium nitrate, and 3.4% calcium hydroxide.8.
Obtained 5 tons.

During this period, the concentration of the total amount of unabsorbed nitrogen oxide and nitrogen dioxide in the exhaust gas was about 2.0 volume.

Next, the above liquid is transferred to a second reaction tank, and the entire amount of gas discharged from the first reaction tank is passed through an air column oxidizer, so that the molar ratio of nitrogen monoxide to nitrogen dioxide (NO/No□) is approximately 1. After adjusting to 7, the pressure of one reaction system was 2.5 kg/CI? by continuously blowing from the porous nozzle provided at the bottom of the tank. 8 while keeping the liquid temperature at 75 to 80°C and the pH at 11 or higher.
．． The reaction was continued for 0 hours, and unabsorbed gas was continuously discharged.

Thus calcium nitrite34. 8.6 tons of liquid containing 1.4% by weight of calcium nitrate, 12% by weight of calcium hydroxide, and 1.4% by weight of other solids was obtained.

During this period, the total concentration of nitrogen monoxide and nitrogen dioxide in the exhaust gas was approximately 0.4 volume.

The obtained liquid was cooled and filtered to obtain calcium nitrite 3.
A clear calcium nitrite aqueous solution containing 31% by weight and 1.5% by weight of calcium nitrate was obtained.

Example 2 8.5 tons of an aqueous slurry having a calcium nitrite concentration of 29.5% by weight, a calcium nitrate content of 1.1% by weight, and a calcium hydroxide content of 4% by weight was fed into a first reaction tank with a slaked lime content of 29.5% by weight. Approximately 750 kg/H of 8% by weight aqueous slurry
Also, the NO/NO2 molar ratio is 1.7, - the total amount of nitrogen oxide and nitrogen dioxide concentration is 9.4, and the volume temperature is about 230
The gas obtained by ammonia oxidation at 130 ONm
"/)] were continuously supplied from the bottom of the tank to the first reaction tank under stirring.

The reaction system pressure was set to 2.8 kg/ffl, and the reaction temperature was set to 78~
Maintained at 83℃ and continuously heated for approximately 1000 k from the 4th reaction tank.
The contents were discharged at a rate of g/h, and the concentration of unreacted slaked lime was maintained at 4% by weight.

Unabsorbed gas is continuously discharged from the first reaction tank, and -
The total concentration of nitrogen oxide and nitrogen dioxide was 1.9 volumes.

The entire amount of this gas is passed through the sky tower oxidizer as it is, and the NO
/NO2 molar ratio was adjusted to 1.7.

The liquid continuously discharged from the first reaction tank was continuously supplied as it was to the second reaction tank, and the regulating gas was continuously supplied to the second reaction tank.

In the second reaction tank, the stirrer liquid temperature was 75 to 80°C and the pressure was 2.
5 kg/-, and the concentration of calcium hydroxide in the liquid is about 1
．． One reaction solution was kept at a weight of 5.5 and was continuously discharged at a rate of 1000 kg/H.

After cooling, this liquid was continuously supplied to a filter and thoroughly filtered.

The furnace solution was a clear aqueous solution containing 32.4 weight of calcium nitrite and 1.6 weight of calcium nitrate.

Claims (1)

[Claims] 1 (a) Obtained by air oxidation of ammonia, containing nitric oxide (NO) and nitrogen dioxide (NO2) of 5 to 1
A gas containing a large volume of 20 to 40% by weight, a No/N02 molar ratio of 1.6 to 2.5, and a temperature of 190 to 300'C is added to a water-related slurry of 20 to 40% by weight of slaked lime.
By continuously supplying the pressure of 0 to 10 kg/- while keeping the temperature at 75 to 110°C, the residual slaked lime concentration is absorbed and reacted to a weight ratio of 2 to 10%, and the final absorbed gas is continuously removed from the reaction zone.・＼Discharging process (b) Collect the end absorption gas discharged in (a), supply nitrogen gas to it as necessary, and oxidize it at 85 to 1508C to bring the No/N02 molar ratio to 1. 6 to 2.5, and the total amount of nitrogen monoxide and nitrogen dioxide is 1 to 5.
Step (c) Processing the produced calcium nitrite obtained in step (a) to dissolve the residual slaked lime concentration in the slurry having a weight ratio of 2 to 10, step (b). By continuously supplying the gas obtained by the gas under a pressure of 2.0 to 10 kg/CrIL while maintaining the reaction temperature at 75 to 110°C, an absorption reaction is carried out until the concentration of residual slaked lime becomes 3 weight coefficient or less. A highly pure and highly concentrated calcium nitrite aqueous solution comprising the following steps: (2) filtering the liquid obtained in step (c), and continuously discharging unabsorbed gas outside the reaction zone. manufacturing method.