JPH0761860B2 - Ammonia gas purification method - Google Patents

Abstract

PURPOSE:To stably obtain high-purity liquid ammonia from an ammonia gas as an off-gas after chemical reaction containing carbon dioxide and moisture as impurities by removing such carbon dioxide prior to compression and liquefaction of the off-gas. CONSTITUTION:An impurity-contg. ammonia gas is passed through a solid alkali layer kept at a temperature higher than such a temperature as to prevent the solid alkali from dissolving owing to its deliquescence but lower than the dissolving temperature of the solid alkali; thereby, removing the carbon dioxide in the ammonia gas through its adsorption onto the solid alkali layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying ammonia gas containing carbon dioxide gas or water as impurities as off gas after a chemical reaction.

[0002]

2. Description of the Related Art Ammonia gas discharged as off-gas after a chemical reaction contains carbon dioxide gas and water as impurities. Conventionally, when recovering such ammonia gas as liquid ammonia, the off-gas is directly compressed / cooled and recovered as liquid ammonia.

[0003]

When liquefied directly ammonia gas containing carbon dioxide as an impurity [0008], by the reaction with carbon dioxide and some ammonia gas in the process carbamate ammonium or water entrained In some cases, there is a problem that ammonium carbonate is generated, the cylinder of the compressor is damaged, and the heat exchanger is scaled. Also,
Since the insoluble matter of the carbon dioxide gas compound is mixed in the obtained liquid ammonia, there is a problem that high-purity liquid ammonia cannot be obtained. The present invention focuses on such points, and aims to provide a method for purifying ammonia gas, which can remove carbon dioxide gas which is an impurity component of ammonia gas and stably obtain high-purity ammonia gas. To do.

[0004]

In order to achieve the above-mentioned object, the present invention contains carbon dioxide gas as an impurity.
The ammonia gas is cooled and ammonia gas and carbon dioxide gas
To produce ammonium carbamate.
Ammon lumbamate is filtered out and the
Ammonia gas containing carbon dioxide after passing through the engine
To the solid alkali under operating conditions such as gas pressure.
In the remaining non temperatures above and below solid alkaline melting point
It is characterized in that it is passed through a solid alkaline tank maintained at the temperature of .

[0005]

[Function] Ammonia gas containing carbon dioxide is cooled
As a result, ammonia gas and carbon dioxide gas
It reacts according to the reaction formula, and ammonium carbamate (NH ₂ C
OONH ₄ ) is generated. CO ₂ + 2NH ₃ → NH ₂ COONH ₄ + ΔH (where ΔH is the amount of heat generated and is −38.06 Kcal / mo at 25 ° C.
l . ) This ammonium carbamate is in the form of solid particles in the gas.
Are present in the
It The gas from which the ammonium carbamate has been removed is solid
Remains in the gas by passing through the alkaline tank
The carbon dioxide gas is solid alkali in the solid alkali tank.
Reacts with and is captured and removed. This will reduce carbon dioxide
Ammonia gas that does not contain much is obtained.

On the other hand, ammonia gas is added to the solid alkaline tank.
Before passing through, some ammonia gas and impurities are cooled by cooling.
By reacting with the carbon dioxide gas of
The concentration of carbon dioxide is decreasing, which causes solid
Moisture due to the reaction between carbon dioxide gas and solid alkali in the tank
Is reduced and the deliquescent of solid alkali is reduced. Well
In addition, the solid alkaline tank is solid under conditions such as gas pressure during operation.
Molds above the temperature at which water does not remain in the alkali and solid
Since the temperature is kept below the melting point of alkali,
Carbon dioxide and solid form under the conditions of ammonia gas refining operation
The water generated by the reaction with the alkali in the solid alkaline tank
Separated by heat without solid residue remaining in solid alkali
It is more certain that the type alkali can be melted by deliquescent.
Be stopped. Also, the temperature of the solid alkaline tank is
Since it is below the melting point of, the solid alkali will not melt.
Yes.

[0007]

The drawing shows a flow chart illustrating the method of the present invention. This ammonia gas refining method removes carbon dioxide gas contained as an impurity from ammonia gas discharged as off-gas after a chemical reaction, and reacts the contained carbon dioxide gas with ammonia gas to produce a reaction product. And a decarburizing step (B) for removing gaseous impurities.

In the impurity removing step (A), a cooling step (1) of cooling the supplied impurity-containing ammonia (crude gas) to a temperature at which it does not liquefy, and passing the cooled crude gas through a filter. And a filtration step (2) for removing the reaction product. In the cooling step (1), if the temperature is such that the crude gas is not liquefied, for example, if the operating pressure is almost atmospheric pressure, cooling to 0 ° C produces solid particles of ammonium carbamate in the gas according to the following reaction formula. CO ₂ + 2NH ₃ → NH ₂ COONH ₄ + ΔH (where ΔH is the amount of heat generated and is −38.06 Kcal / mo at 25 ° C.
l. )

Since this reaction formula is an exothermic reaction, it shifts to the right equilibrium at lower temperatures, but if cooled more than necessary,
Ammonia liquefaction occurs, the required power of the refrigerator increases, the generation rate of ammonium carbamate slows, and a large gas storage section from the cooler to the filter is required. Therefore, in this embodiment, the crude gas is cooled by the cooler (4) using the refrigerator (3) so that the gas temperature becomes a low temperature of about 0 ° C.

In the filtration step (2), the cooled crude gas is passed through the filter tank (5) in which the filter material is packed in the casing to capture and remove ammonium carbamate in the crude gas. In addition, as a filter material to be filled in the filtration tank (5), it is preferable to use a net formed of a polymer material such as glass wool or fluororesin or a non-woven fabric having an appropriate space for ensuring the growth of ammonium carbamate. .

Since ammonium carbamate decomposes at 59 ° C., a regenerator (6) for regenerating the filter material by supplying air heated to 80 to 100 ° C. by a heater to the filtration tank (5) is attached. I am doing it. The regenerator (6) comprises a fan (7) for blowing the outside air and a heater (8) for heating the outside air. Further, after the regeneration, if a crude gas flows while the filter material is hot, ammonium carbamate will be decomposed, so a pre-cooling device (9) for cooling the filter material is attached to the filter tank ( 5 ). .
This pre-cooling device (9) vaporizes liquid nitrogen from a liquid nitrogen cylinder (10) in a vaporizer (11), and the vaporized nitrogen is filtered in a filtration tank.
( 5 ) is supplied to precool the filter material, and the inside of the filtration tank is purged. The regenerated gas and precooled gas discharged from the filtration tank ( 5 ) are guided to the detoxification device (12), and the ammonia gas components contained in the regenerated gas are collected and concentrated by the detoxification device.

The crude gas from which carbon dioxide has been removed in the form of ammonium carbamate in the filtration tank ( 5 ) is sent to the decarburization step (B), where the carbon dioxide remaining in the crude gas is removed. It The decarburization step (B) is composed of a preheater (13) and a carbon dioxide adsorption tank (14) as a decarburization device, and the preheater (13)
Then, the crude gas is kept at a temperature of at least 60 ° C. or more to make the carbon dioxide gas and the ammonia gas free and the adsorption tank
It is sent to (14).

[0013] Ya sodium water oxidation in the interior of the adsorption vessel (14)
Solid alkali such as water potassium oxide are filled with particulate. Since sodium hydroxide and potassium hydroxide have strong deliquescent properties, they can collect and dissolve surrounding water in a short time .
For this reason, adherence and agglomeration occur between granular sodium hydroxide and potassium hydroxide, and the gas passage is blocked.
This is considered to occur because the water generated by the following reaction is collected. 2NaOH + CO ₂ → Na ₂ CO ₃ + H ₂ O

Therefore, the outside of the adsorption tank (14) or the adsorption tank
(14) an electric heater was attached to the gas during operation of this pressure, etc.
Under the above conditions, water remains in the solid alkali in the adsorption tank (14).
Above a certain temperature, and the melting point of solid alkali (for example,
328 ° C for sodium hydroxide, potassium hydroxide
Is 360.4 ° C. ) The following temperature (eg 10
It is heated so that it is maintained at about 0 ° C. In this case, since the reaction between the solid alkali and carbon dioxide gas is an exothermic reaction, it is necessary to control the temperature of the adsorption tank (14) in consideration of this point. Steam may be used as the heating source.

A sample gas containing 1% carbon dioxide in ammonia gas was passed through the adsorption tank (14) at room temperature (20 to 21 ° C.) into granular sodium hydroxide at a space velocity of 1000 to 5000 h ^-1. , The gas passage pressure loss in the adsorption tank (14) at the time when a gas containing a carbon dioxide gas amount equivalent to 4 to 5% of the theoretical fixed carbon dioxide gas amount of sodium hydroxide in the adsorption tank (14) is passed. Soared.

Then, the sodium hydroxide layer was kept at 100 ° C., and a sample gas at room temperature containing 1% carbon dioxide in ammonia gas was passed at a space velocity of 1000 to 5000 h ⁻¹ . As a result, there was no increase in pressure loss in the adsorption layer ( 14 ),
When the carbon dioxide concentration at the outlet was confirmed by gas chromatography, the concentration was 10 ppm or less. Also,
When the weight change of the column focusing on silica gel was measured for the gas taken out from the adsorption tank ( 14 ), the increase in weight corresponding to the water generated during the reaction between carbon dioxide gas and solid alkali was also measured. It was confirmed that the generated water formed in the solid alkaline tank was retained in the gas tank without being accumulated in the solid alkaline tank.

On the other hand, a sample gas containing 1% carbon dioxide gas in ammonia gas was cooled to 0 ° C., and the cooled sample gas was passed through a filtration tank (5) provided with a space corresponding to a residence time of 5 minutes. When the carbon dioxide concentration at the outlet of the filtration tank was confirmed by gas chromatography, the carbon dioxide amount was 130 ppm.

[0018]

EFFECT OF THE INVENTION Ammonia gas containing carbon dioxide gas is solidified.
Ammonia gas cooled before passing through the alkaline tank
Ammonium carbamate by reacting a part of
To produce this ammonium carbamate with a filter
Ammonia gas sent to the solid alkaline tank for removal
The concentration of carbon dioxide in the bath is decreasing,
Generated by the reaction of solid alkali with carbon dioxide at
Is reduced. As a result, carbon dioxide gas and solid alkali
The solid alkali deliquesces due to the water generated in the reaction,
Adhesive agglomeration occurs between solid alkali particles and gas passage
Is prevented from being blocked and pressure in the solid alkaline tank is reduced.
The solid alkali can be used effectively without loss.
Long maintenance cycle such as replacement of solid alkali
Maintenance labor can be reduced. Moreover, due to cooling
The reaction of ammonia gas and carbon dioxide produces carbamate
Carbon dioxide is almost completely removed by generating and removing mon
Compared to what is removed, this removal of carbon dioxide gas is rough
Ammonia gas is consumed in the production of ammonium carbamate.
Can be reduced.

Further , gas pressure during operation of the solid alkaline tank, etc.
Above the temperature at which water does not remain in the solid alkali under
And at a temperature below the melting point of the solid alkali.
Then, the solid alkali is deliquescent due to the water, and
With this, it is possible to more reliably prevent the formation of adhered lumps. Well
Also, the temperature of the solid alkali tank should be below the melting point of the solid alkali.
Therefore, the solid alkali does not melt by heat.
This melts the solid alkali and blocks the gas passage.
Can be prevented more reliably. Moreover, maintenance
The cycle can be made longer and the maintenance work can be reduced.
Wear.

It should be noted that the ammonia gas before the treatment contains moisture.
Even if it is rare, ammonia gas and carbon dioxide gas
It reacts with water to form solid particulate ammonium carbonate.
It is filtered out like ammonium lumbamate.
Therefore, the concentration of water reaching the solid alkaline tank is low and suppressed.
available.

[Brief description of drawings]

FIG. 1 shows a flow chart illustrating the method of the present invention.

Claims (2)

[Claims] 1. An atmosphere containing carbon dioxide as an impurity
The ammonia gas is cooled and ammonia gas and carbon dioxide gas
To produce ammonium carbamate.
Ammon lumbamate is filtered out and the
Ammonia gas containing carbon dioxide after passing through the engine
To the solid alkali under operating conditions such as gas pressure.
Above the temperature that does not remain and below the melting point of solid alkali
A method for purifying ammonia gas, which comprises passing through a solid alkaline tank maintained at the temperature of . 2. The solid alkali bath is set at 60 ° C. to 360 ° C.
The temperature range is maintained within a certain range.
A method for purifying ammonia gas as described .