JPS5940763B2 - Concentration method of ammonia aqueous solution using reverse osmosis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for concentrating an aqueous solution containing ammonia by reverse osmosis.

Chemical processes that handle ammonia or ammonia production processes discharge aqueous solutions containing small amounts of ammonia as a main component.

Conventionally, a distillation method or a stripping method has been used as a method for recovering ammonia from wastewater containing ammonia, but this treatment has the disadvantage that a large amount of heat is consumed.

On the other hand, reverse osmosis has been developed as a concentration method that consumes less energy, and is being put into practical use for desalinating seawater and treating wastewater containing impurities.

Attempts have been made to remove ammonia using this reverse osmosis method, but this method has the disadvantage of a low ammonia removal rate and poor efficiency.

For example, the lower the concentration of a general solution, the higher the solute removal rate by reverse osmosis, but when comparing the separation performance of salt water and ammonia water by reverse osmosis using a cellulose acetate membrane, it was found that Even with a stock solution solubility of 1%, it shows a rejection rate of 98% or more, but aqueous ammonia only shows a rejection rate of 20 to 30% at a stock solution concentration of 1001)I)m.

Furthermore, even when aromatic polyamide is used as a reverse osmosis membrane, the rejection rate is 98% in 1% saline solution, whereas the rejection rate is 1% in saline solution.
With 100 pp of ammonia water, the rejection rate is only 29%.

As an improved method of this reverse osmosis method, in JP-A-50-7731, ammonia is neutralized with sulfuric acid, hydrochloric acid, etc., and the pH is adjusted to 9.5.
A method for improving the ammonia rejection rate using an aqueous ammonium salt solution is disclosed below.

However, according to this method, complicated operations are required to further recover free ammonia from a concentrated aqueous ammonium salt solution, and in practice, it is difficult to recover free ammonia.

That is, these ammonium sulfates, chlorides, nitrates, phosphates, etc. are not decomposed by ordinary means such as heating.

An object of the present invention is to provide a method for efficiently separating and recovering ammonia from an aqueous solution containing a small amount of ammonia.

Another object of the present invention is to provide a method for separating ammonia from waste water mainly containing small amounts of ammonia to obtain waste water that does not contain ammonia.

Still another object of the present invention is to provide a method for recovering free ammonia from an aqueous solution containing a small amount of ammonia in a simple process.

Another object of the present invention is to provide a method for recovering ammonia from aqueous solutions containing small amounts of ammonia, which consumes less thermal energy.

Another object of the present invention is to provide an ammonia recovery method that is convenient for recovering ammonia from ammonia-containing wastewater from the urea synthesis process and recycling it to the urea synthesis process.

Another object of the present invention is to provide a method for separately recovering ammonia and urea from an aqueous solution containing them.

In order to achieve the above object, the present inventors conducted detailed research and found that when carbonic acid and ammonium hydroxide in an aqueous solution are separated by reverse osmosis, the removal rate is very poor, so ammonium carbonate is Although no attempt had been made to separate ammonium carbonate by reverse osmosis, as it was predicted that the rejection rate would be poor, it was surprising that ammonium carbonate could be separated from ammonium carbonate in an aqueous solution. Alternatively, they found that ammonia can be removed with a very high rejection rate by replacing it with ammonium bicarbonate and separating it by reverse osmosis, and have completed the present invention.

That is, the method of the present invention is a method of concentrating ammonia in an aqueous solution containing ammonia as a main component by reverse osmosis, in which carbon dioxide is dissolved in the aqueous solution and the molar ratio of ammonia and carbon dioxide in the aqueous solution is 0. .8:1-2.
This is a method of concentrating an ammonia-containing aqueous solution using reverse osmosis, in which the ratio is 0:1.

In the present invention, the amount of carbon dioxide dissolved in the aqueous solution containing ammonia is sufficient to convert the ammonia in the aqueous solution into ammonium carbonate or ammonium bicarbonate.

That is, the molar ratio of ammonia and carbon dioxide in the aqueous solution is 0.
．． Carbon dioxide is dissolved so that the molar ratio is in the range of 8:1 to 2:1, more preferably in the range of 0.8:1 to 1.2:1.

If the aqueous solution to be treated already contains carbon dioxide, the amount of carbon dioxide to be dissolved may be reduced accordingly.

Furthermore, if the aqueous solution contains an alkali other than ammonia, it is necessary to increase the amount of carbon dioxide dissolved to neutralize the alkali.

As the reverse osmosis membrane used in the reverse osmosis method of the present invention, reverse osmosis membranes used in normal reverse osmosis methods, such as an acetyl cellulose membrane and an aromatic polyamide membrane, are used.

There are no particular restrictions on the temperature and pressure at which reverse osmosis is performed in the method of the present invention, and the temperatures and pressures used in normal reverse osmosis methods are used.

According to the method of the present invention, ammonia is converted into ammonium carbonate,
Alternatively, the removal rate of ammonia can be improved by performing reverse osmosis instead of using ammonium bicarbonate.

Furthermore, since the strongly alkaline ammonia water is not brought into contact with the reverse osmosis membrane, the life of the reverse osmosis membrane is long, and stable operation can be achieved over a long period of time.

Furthermore, concentrated ammonium carbonate or ammonium bicarbonate has the significant advantage that it can be easily decomposed into ammonia and carbon dioxide by slight heating.

Furthermore, the method of the present invention is particularly advantageous when used for the recovery of ammonia in wastewater from a urea production process.

That is, the concentrated ammonium carbonate or ammonium bicarbonate solution can be directly circulated to the 5-urea synthesis system to recover ammonia and carbon dioxide.

Furthermore, if reverse osmosis is performed by blowing carbon dioxide into an aqueous solution containing urea and ammonia, most of the urea will pass through the osmotic membrane, but ammonia will be eliminated. Urea and ammonia can also be separated and recovered by separating into an aqueous ammonium carbonate solution.

In the method of the present invention, whether to blow carbon dioxide into an aqueous solution containing ammonia to convert ammonia to carbonate or bicarbonate depends on the rejection rate during reverse osmosis, the purpose of the treatment after concentration, It can be selected as appropriate in consideration of economic efficiency, etc.

The method of the present invention will be explained in more detail below using Examples.

Example 1 Carbon dioxide was blown into aqueous ammonia with a concentration of 0.143 mol/l to completely dissolve 0.072 mol/13 of carbon dioxide and the ammonia/carbon dioxide molar ratio was 1.99.
:1) Using cellulose acetate membrane, 26℃, pressure 40
As a result of performing reverse osmosis at kg/cyrt (gauge), the ammonia concentration in the permeate was 0.058 mol/71, the ammonia rejection rate was 59.4%, and the carbon dioxide concentration was 0.00.
5 mol/A, and the carbon dioxide removal rate was 93.1%.

Here, the rejection rate is calculated by ((concentration of stock solution - concentration of permeate solution)/concentration of stock solution) x 100.

Example 2 Carbon dioxide was blown into aqueous ammonia with a concentration of 0.33 mol/11 to dissolve 0.283 mol/7 carbon dioxide (ammonia/carbon dioxide molar ratio 1.1).
7:1), as a result of performing reverse osmosis under the same conditions as in Example 1.
The ammonia concentration of the permeate is 0.0514 mol/C. The ammonia rejection rate is 84%, and the carbon dioxide concentration is 0.0410.
The mol/C carbon dioxide removal rate was 86%.

Example 3 Carbon dioxide was blown into aqueous ammonia with a concentration of 0.277 mol/l to dissolve 0.233 mol/l of carbon dioxide (ammonia/carbon dioxide molar ratio 1.19).
:1), As a result of performing reverse osmosis under the same conditions as in Example 1, the ammonia concentration of the permeate was 0.0523 mol/111
Ammonia removal rate is 81%, carbon dioxide concentration is 0.049
1 mol/A', and the carbon dioxide removal rate was 79%.

Example 4 Ammonia O 1429 mol/7 Urea 0.064 mo
0.215 rrio t/l in an aqueous solution containing l/l
of carbon dioxide was dissolved and reverse osmosis was performed in the same manner as in Example 1 (ammonia/carbon dioxide molar ratio 2:1). As a result, the ammonia concentration of the permeate was 0.156 mol/A1 ammonia rejection rate was 63. 6%, carbon dioxide concentration 0.015
The mol/C carbon dioxide removal rate is 93.0%, and the urea concentration is 0.052 rno l/l! N urea exclusion rate is 2
0.9%, the elimination rate of urea is low, but ammonia,
The carbon dioxide removal rate is almost the same as in the absence of urea.

Reference example 1 Aqueous ammonia with a concentration of 0.150 mof/l was subjected to reverse osmosis using an X cellulose acetate membrane at 26°C and a pressure of 40 kg/ffl (gauge) using the conventional method. As a result, the ammonia concentration in the permeate was as follows. The 0.141 mol/C ammonia rejection rate was 6.0%, and ammonia could hardly be separated.

Reference example 2 Ammonia 0.278 mol/l, urea 0.067 m
Using an aqueous solution containing o I as a stock solution, reverse osmosis was performed using the conventional method under the same conditions as Reference Example 1 without adding carbon dioxide, and the ammonia concentration in the permeate was 0.263 mol/l.
, ammonia rejection rate is 5.4%, urea concentration is 0.053
mol/7. The urea exclusion rate was 18.8%, and ammonia and urea could hardly be separated.

Claims (1)

[Claims] 1 In a method of concentrating ammonia in an aqueous solution containing ammonia as a main component by reverse osmosis, carbon dioxide is dissolved in the aqueous solution, and the molar ratio of ammonia and carbon dioxide in the aqueous solution is 0.8:1 to 2. A method for concentrating an ammonia-containing aqueous solution by reverse osmosis, which is characterized by concentrating at a ratio of .0:1.