JPS5927203B2 - Membrane separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separately separating and removing several volatile substances from a solution containing them.

The stripping method, which is a typical method for conventionally removing volatile substances, adjusts temperature, pH, etc. to increase the vapor pressure of one component, and then blows in a large amount of air to remove one component from the solution. A method has been devised to remove it.

A typical example is a stripping method using ammonia aeration.

According to this method, in principle, it is possible to remove one component from the solution by introducing a large amount of gas such as air into the solution, but at the same time, it is possible to remove one component from the solution as the solvent evaporates. In order to lower the temperature and deteriorate the separation efficiency, it is necessary to externally inject evaporation energy accompanying the evaporation of the solvent.

The present invention ameliorates the above-mentioned drawbacks of conventional stripping systems.

That is, the present invention selectively removes a specific volatile substance among two or more volatile substances in a liquid (hereinafter referred to as "liquid to be treated") by removing adjacent specific volatile substances through a porous membrane. When a volatile substance is absorbed into a liquid by gas diffusion through the air layer within the pores of a porous membrane, the pH of the solution is adjusted so that only the specific volatility of the specific volatile substance is selectively increased. This is a separation method.

The first advantage of the present invention is that by using the solvent of the liquid to be treated as the solvent for the volatile substance absorption liquid, the movement of the solvent can be almost prevented in principle, and the evaporation of the solvent in the conventional stripping method can be prevented. It is possible to prevent the temperature drop caused by the heat exchanger, resulting in a major reduction in running costs.

Furthermore, a second advantage of the present invention is that stripping and absorption can be performed in one closed system, which is particularly advantageous when the evaporated component is a toxic gas.

That is, since stripping and absorption are performed through a single porous membrane, no scattering of toxic gas occurs during the blowing.

A third advantage of the present invention is that the stripping device and the absorbing device are integrated in accordance with the principle of the present invention, and as a result, the overall device can be made extremely compact.

This is the same as the membrane area and device size of conventional electrodialysis, and is obvious to those skilled in the art.

The fourth advantage of the present invention is that by adjusting only the pH of the liquid to be treated, it is possible to strip each of the evaporated components separately. Another advantage is that it is easy to collect.

There are many solutions that can be treated in the present invention, and the present invention will be explained by taking a coke waste liquid containing cyanide, phenol, ammonia, etc. as an example.

First, if the coke waste liquid is made acidic, preferably at pH 5 or less, the vapor pressure of acidic substances such as cyanide and phenol becomes high, but the vapor pressure of ammonia can be reduced to almost zero.

By introducing a large amount of air into this acidic liquid, cyanide, phenol, etc. can be removed, but since these are harmful substances, they need to be absorbed again.

In the method of the present invention, by using caustic soda or caustic potash as the absorption liquid, cyanide and phenol can be easily removed from the solution, and at the same time, cyanide and the like can be recovered.

It is also possible to use slaked lime.

Furthermore, if the solution from which cyanide and phenol have been removed is made alkaline, preferably at pH 9 or higher, the vapor pressure of ammonia can be increased and ammonia can be removed.

In this case, it is preferable to use an acid having no vapor pressure, such as sulfuric acid or phosphoric acid, as the absorption liquid.

This is because if an acid with vapor pressure is used, it will react with ammonia in the porous material and cause clogging.

In addition, for the purpose of preventing evaporation of the liquid water to be treated, the lower the acid concentration, the better, but normally it is better to use about 1 to 5% sulfuric acid.

This is because if the sulfuric acid concentration is low, the absorption rate becomes rate-limiting for the entire process and the processing rate decreases.

The order of cyanide, phenol removal and ammonia removal can also be reversed by reversing the pH adjustment.

Example An aqueous solution of ammonium chloride and sodium cyanide was adjusted so that the ammonia concentration and the cyanide equivalent concentration of sodium cyanide were each 5000 ppm.

A solution made to pH 11.5 by adding slaked lime was used as the solution to be treated, and was passed through a Teflon porous membrane with a pore size of 0.5 μm for 30 minutes.
It was brought into contact with a sulfuric acid solution.

The liquid to be treated and the sulfuric acid solution were circulated through a cell equipped with a membrane using a pump so that they flowed at a rate of 5.0 cm/sec at the membrane surface, and the decrease in ammonia concentration was determined as a function of time.

The ammonia concentration reduction occurred according to the theoretically expected curve.

That is, the logarithm of the ammonia concentration and time had a linear relationship regardless of the ammonia concentration.

Surprisingly, no deviation from the linear relationship occurred even at low ammonia concentrations below 5 ppm.

The solution from which ammonia had been removed by the above method was adjusted to pH 1 and brought into contact with a 5% aqueous solution of caustic soda through a porous membrane.

The relationship between the decrease in cyan concentration and time was the same as in the case of ammonia, and the relationship between the logarithm of cyan concentration and time was a linear relationship regardless of the concentration.

The processing speed of the above experiment was 1 (l) of the above solution at a concentration of 5 at room temperature.
1r/? to process down to ppm or less? Using a membrane of 1 hour with ammonia and 1.5 hours with cyanide.

Claims (1)

[Claims] 1. Selective removal of a specific volatile substance among two or more volatile substances in a liquid (hereinafter referred to as "liquid to be treated") by adjoining them through a porous membrane. When the specific volatile substance is absorbed by the liquid by gas diffusion through the air layer in the pores of the porous membrane, the pH of the solution is adjusted so that only the specific volatility of the specific volatile substance is selectively increased. Separation method to adjust. 2 The liquid to be treated is an aqueous solution containing cyanide, phenol, and ammonia, the specific volatile substance is ammonia, and the pH is
The separation method according to claim 1, wherein is 9 or more. 3. The separation method according to claim 2, wherein the specific volatile substance absorbing liquid is an aqueous solution of sulfuric acid or phosphoric acid. 4. The separation method according to claim 1, wherein the liquid to be treated is an aqueous solution containing cyanide, phenol, and ammonia, the specific volatile substances are cyanide and phenol, and the pH is 5 or less. 5. The separation method according to claim 4, wherein the specific volatile substance absorbing liquid is caustic soda or an aqueous solution of caustic potash.