JPH0736887B2 - Wastewater treatment equipment mixed with organic solvents - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an organic solvent mixed wastewater treatment apparatus used when separating and recovering a hydrophobic organic solvent from wastewater containing a hydrophobic organic solvent. is there.

(Prior Art) A pervaporation membrane method is known as a method for separating and recovering an organic solvent from wastewater containing the organic solvent. In this method, the permeate side of the membrane is depressurized, the permeate is continuously concentrated in the membrane, the permeate is evaporated under a low vapor pressure, and the permeate is separated in the gas phase state. ing.

According to this method, the evaporation amount of the non-permeable substance can be reduced,
The heat loss due to the latent heat of vaporization can be reduced to that extent.

(Problems to be solved) In this pervaporation membrane method, in order to increase the separation rate and enable the treatment of a large amount of waste water, a combination with other separation methods may be considered. The combination is irrational because it loses the energy-saving property, the easiness of operation and the like which are the advantages of the pervaporation membrane method.

The object of the present invention is toluene, xylene, hexane, MEK.
, Etc. are hydrophobic organic solvents, and paying attention to the fact that they can be separated with a small amount of energy by utilizing the difference in specific gravity, and by the combination of the pervaporation membrane method and liquid-liquid tank separation, low energy and simple operation can be performed. It is to provide an organic solvent mixed wastewater treatment device capable of separating and recovering toluene, xylene, hexane, MEK and the like from wastewater.

(Means for Solving the Problem) A treatment apparatus for organic solvent mixed wastewater according to the present invention is a liquid-liquid separation tank for separating wastewater containing a hydrophobic organic solvent into a solvent phase and an aqueous phase, and collecting the solvent phase. And a preheater for heating the aqueous phase liquid from the liquid-liquid separation tank, and a pervaporation membrane for separating the heated aqueous phase liquid from the preheater into a solvent concentrated component and a solvent diluted component, and releasing the solvent diluted component A module, a return pipe for returning the concentrated solvent from the module to a liquid-liquid separation tank through a cooler, and a drainage supply pipe connected to the inlet side of the return pipe of the cooler. The configuration is characterized by.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, which is used when the boiling point of the organic solvent is higher than that of water.

In FIG. 1, reference numeral 1 denotes a liquid-liquid separation tank, in which waste water containing a hydrophobic organic solvent is separated into a solvent phase of an upper layer and an aqueous phase of a lower layer by a difference in specific gravity. 2 is a solvent recovery pipe. Reference numeral 3 is a pervaporation membrane module, and the membrane used is one that blocks organic solvents well and allows water vapor to permeate well. Reference numeral 4 is a supply pump for supplying water in the water phase of the liquid-liquid separation tank 1 to the pervaporation membrane module 3, 5 is a preheater, and 6 is a heating medium circulation pipe. Reference numeral 7 is a return pipe for returning the non-permeated liquid of the pervaporation membrane module 3 to the liquid-liquid separation tank 1, and 8 is a cooler. 9 is a vacuum pump for reducing the pressure on the permeation side of the pervaporation membrane module 3, 10 is a condenser provided between the permeation membrane module 3 and the vacuum pump 9, 11 is a condensed water discharge pipe, and 12 is a non-condensable gas. It is a discharge pipe. 13 is the cooler 8 and the condenser
It is a cooling medium circulation pipe for 10. A drainage supply pipe 14 is connected to the return pipe 7 before the cooler 8.

In order to separate and recover the organic solvent from the wastewater containing a hydrophobic organic solvent having a boiling point higher than that of water, for example, toluene or xylene, using the embodiment shown in FIG. Is introduced into the liquid-liquid separation tank 1 while being cooled by the cooler 8 through the drainage supply pipe 14. In this liquid-liquid separation tank 1, wastewater is separated into an upper solvent phase and a lower aqueous phase due to the difference in specific gravity. This lower aqueous phase contains an equilibrium dissolved amount of organic solvent at the operating temperature. However, since the temperature of the liquid in the tank 1 is low due to the introduction of the waste water through the cooler 8, the equilibrium dissolution amount of the organic solvent in the lower aqueous phase becomes small, and the liquid between the solvent phase and the aqueous phase becomes small. Liquid separation is efficiently performed. This lower aqueous phase is supplied to the pervaporation membrane module by the supply pump 4 while being heated by the preheater 5 (since the pervaporation membrane method is an endothermic phenomenon, the separation efficiency can be increased by increasing the fluid temperature on the supply side. For). As the membrane of this pervaporation membrane module, a selective permeable membrane having excellent permeability to water vapor and impermeable to the above-mentioned hydrophobic organic solvent is used. Thus, the permeate side of this module is depressurized by the vacuum pump 9 to a pressure lower than the vapor-liquid equilibrium pressure under the heating temperature by the preheater 5, and the moisture in the supply liquid is permeated while being evaporated, The permeated water vapor is condensed in the condenser 10, and the condensed water is discharged from the discharge pipe 11,
The uncondensed gas is discharged from the discharge port of the vacuum pump 9.
On the other hand, the solvent concentrate on the non-permeation side of the pervaporation membrane module is cooled by the cooler 8 via the return pipe 7, and then returned to the lower aqueous phase of the liquid-liquid separation tank 1, and thereafter the above is recycled as one cycle. Go.

In the above, the return liquid sent to the lower aqueous phase of the liquid-liquid separation tank 1 via the cooler 8 has a higher solvent concentration than the solvent concentration of the lower aqueous phase (because it is concentrated in the module), and moreover, the cooler Since it is cooled to almost the same low temperature as the lower aqueous phase by cooling when passing through 8, the solvent in the lower aqueous phase is in an excess solvent relative to the equilibrium dissolved state,
The excess solvent is separated, and the thickness of the upper solvent phase increases. That is, as the recycling proceeds, the solvent concentration by the pervaporation membrane module is increased and the thickness of the upper solvent phase in the liquid-liquid separation tank is increased. Therefore, in the liquid-liquid separation tank 1, the hydrophobic organic solvent-containing wastewater which is the liquid to be treated is timely or continuously depending on the amount of the condensed water discharged from the condenser 10 on the permeation side of the module. Supplied,
The solvent phase in the upper layer, that is, the separated hydrophobic organic solvent is overflowed, and the hydrophobic organic solvent can be recovered with high purity.

FIG. 2 shows another embodiment of the present invention, which is used when the boiling point of the hydrophobic organic solvent is lower than that of water.

In FIG. 2, 1 is a liquid-liquid separation tank, 2 is a solvent recovery pipe, 4 is a supply pump, 5 is a preheater, and 6 is a heating medium circulation pipe. Reference numeral 3 denotes a pervaporation membrane module, and a membrane having a permselectivity to an organic solvent is used. 11 is a non-permeate water discharge pipe. 9
Is a vacuum pump, 10 is a condenser, and 120 is a non-condensable gas discharge pipe. Reference numeral 7 is a return pipe for returning the condensed liquid of the permeated organic solvent vapor of the pervaporation membrane module 3 to the liquid-liquid separation tank 1. 8 is a cooler, 13 is the above cooler 8
And a cooling medium circulation pipe for the condenser 10. A drainage supply pipe 14 is connected to the return pipe 7 before the cooler 8.

In order to separate and recover the organic solvent from wastewater containing a hydrophobic organic solvent having a lower boiling point than water, for example, hexane, MEK, etc., by using the apparatus shown in FIG. Is introduced into the liquid-liquid separation tank 1 while being cooled by the cooler 8 by the drainage supply pipe 14, and the upper-layer solvent phase in the liquid-liquid separation tank 1 is recovered from the solvent recovery pipe 2 by overflow according to the amount of introduced wastewater. At the same time, the lower aqueous phase in the liquid-liquid separation tank 1 is preheated and supplied into the permeation membrane module 3 by the supply pump 4, and the permeation side of the permeation membrane module 3 is depressurized by the vacuum pump 9. In the organic solvent in the feed water, the permeation membrane module 3 permeates the membrane due to its selective permeation to the organic solvent vapor in the membrane, and in the meanwhile, vaporizes due to the pressure reduction on the permeate side to vaporize the organic solvent vapor. The water on the non-permeate side diluted with the organic solvent is discharged from the discharge pipe 11 by the permeation / separation of the organic solvent. On the other hand, the organic solvent vapor on the permeate side is condensed by the condenser 10, the condensed organic solvent is cooled by the cooler 8 via the return pipe 7, and then returned to the liquid-liquid separation tank 1, and the non-condensed gas is released by the discharge pipe 12.
It is discharged from 0, and thereafter, it is recycled as one cycle.

In the above, the membrane of the pervaporation membrane module 3 is selected according to the selective permeability to water vapor or organic solvent vapor. For example, a silicone rubber-based polyimide film is selected as a film having selective permeability to toluene vapor.
Further, as the type of the pervaporation membrane module, a spiral type, a hollow fiber type, a tubular type, a plate type or the like is used.

According to the organic solvent mixed wastewater treatment apparatus of the present invention, after cooling the solvent concentrate obtained by separation in the pervaporation membrane module, it is sent to the lower aqueous phase of the liquid-liquid separation tank and the solvent at low temperature -The solvent can be efficiently liquid-liquid separated based on the equilibrium property of water, and by recycling this, the thickness of the upper solvent phase in the liquid-liquid separation tank can be efficiently increased, and as a result, the solvent concentrated liquid in the pervaporation membrane module. Since the above-mentioned recycling is repeated to separate the liquid and liquid in the liquid-liquid separation tank to separate the solvent, the solvent can be efficiently separated. This is clear from the comparison between the following examples and comparative examples.

Example As the wastewater, toluene-containing wastewater having a mixing ratio of toluene / water of 1/99 was used, and the treatment apparatus shown in FIG. 2 was used. As the pervaporation membrane module 3, a spiral permeation vaporization membrane module using a silicone rubber-based polyimide membrane and having a membrane area of 14 m ² was used.

The amount of waste water supplied was 30 kg / hr, the temperature was cooled to 20 ° C. or lower by the cooler 8, and the liquid was introduced into the liquid-liquid separation tank 1. In this case, the equilibrium dissolved concentration of toluene in the lower aqueous phase was 0.045 wt%. The supply flow rate by the supply pump 4 was 300 kg / hr, and the preheating temperature by the preheater 5 was 60 ° C. The discharge rate by the discharge pipe 11 on the non-permeation side in the pervaporation membrane module 3 is set to about 30 kg / hr,
The circulation flow rate through the return pipe 7 was 270 kg / hr. The toluene concentration in the discharge water on the non-permeate side was 0.01 wt% and the toluene concentration on the circulation side was 0.049%. The required operating energy in this case was 18000 Kcal / hr.

Comparative Example In the apparatus of FIG. 2, the return pipe 7 is directly introduced into the liquid-liquid separation tank 1 via the cooler 8, and the drainage supply pipe 14 is introduced into the liquid-liquid separation tank 1 via the cooler 8. The other apparatus uses the same device as in FIG. 2, and the same discharge condition as that of the embodiment (discharge flow rate: 30 kg /
The operating energy required was 23000 kcal / hr when the operation was carried out so that the concentration of the released toluene was 0.01% by weight.

As described above, the reason why higher operating energy is required in the comparative example compared to the example is that in the comparative example, the return liquid is returned to the liquid-liquid separation tank without being cooled, and therefore, in the liquid-liquid separation tank of the return liquid. This is because the solvent phase / water phase separation cannot be effectively performed, and accordingly, the separation performance by the pervaporation membrane module must be increased by increasing the degree of vacuum and increasing the preheating temperature.

(Effect of the invention) The treatment apparatus for organic solvent mixed wastewater according to the present invention is a wastewater containing hydrophobic organic solvent by combining a pervaporation membrane module with low operating energy and a liquid-liquid separation tank driven by specific gravity difference gravity. It is possible to separate and collect the hydrophobic organic solvent from the wastewater at an excellent rate, and the organic solvent can be separated and collected from the wastewater with low energy. Further, since the liquid-liquid separation utilizing the difference in specific gravity is natural separation, there is no difference in the operation from the case of the pervaporation membrane method alone, and the operation is simple.

[Brief description of drawings]

1 and 2 are explanatory views showing different embodiments of the organic solvent mixed wastewater treatment apparatus according to the present invention. 1 ... Liquid-liquid separation tank, 2 ... Organic solvent recovery pipe, 3 ... Permeation vaporization membrane module, 4 ... Supply pump, 7 ... Return pipe, 8 ... Cooler, 9 ... Vacuum pump, 10 ... Condenser, 14 ... Waste water supply tube.

Claims (1)

[Claims] 1. A liquid-liquid separation tank for separating waste water containing a hydrophobic organic solvent into a solvent phase and an aqueous phase and recovering the solvent phase, and a preheater for heating the aqueous phase liquid from the liquid-liquid separation tank. And a permeation membrane module that separates the heated aqueous phase liquid from this preheater into a solvent concentrated component and a solvent diluted component, and releases the solvent diluted component, and the solvent concentrated component from the module is passed through a cooler to form a liquid liquid. An organic solvent mixed wastewater treatment apparatus comprising: a return pipe for returning to the separation tank; and a wastewater supply pipe communicating with the inlet side of the cooler of the return pipe.