JPH01262901A - Method for treating aqueous acidic or alkaline solution - Google Patents

Abstract

PURPOSE:To efficiently separate a pure water from an aqueous solution containing acid or alkali, by bringing the steam produced by heating said solution into contact with one side of a hydrophobic membrane to be passed therethrough to the other side thereof for cooling and condensation. CONSTITUTION:An aqueous solution containing a nonvolatile or low-volatile acid or alkali as a solute is heated to produce steam with the accompanying liquid droplets. This steam is brought into contact with one side of a steam- permeable but water-impermeable hydrophobic membrane (e.g., porous polytetrafluoroethylene membrane) to be passed therethrough to the other side thereof for the subsequent cooling and condensation and the liquid droplets separated thereby are brought back in the aforesaid aqueous solution, whereby a pure water can be separated from the aqueous acidic or alkaline solution at a high rate (650-700kg/m<2>.hr) or concentrated at a high rate over the almost entire pH range of the solution.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for treating an acid or alkali aqueous solution, for concentrating a non-volatile or low-volatile acid or alkali aqueous solution, or for treating an aqueous solution/alkali solution. It is used to separate pure water.

<Conventional technology> Non-volatile or low-volatile substances? It is known that a distillation method is used to concentrate an aqueous solution or to separate pure water from the aqueous solution.

<Problems to be Solved> However, in the distillation method, it is necessary to suppress accompanying water droplets as much as possible, and the concentration or separation rate cannot be increased, making efficient processing difficult.

<Means for Solving the Problems> Therefore, the principal inventor of the present invention increased the evaporation rate of the aqueous solution by the evaporator, separated the droplets that inevitably accompany this evaporation from the vapor, and Return the droplets to the solution at step 7, concentrate the aqueous solution, and add pure water (cooling of the stem air).
We have already proposed a method to obtain condensation.

By the way, the present inventors conducted intensive and extensive research on the treatment of aqueous solutions containing various solutes using a hydrophobic membrane, typified by a porous polytetrafluoroethylene membrane, to separate the droplets. For aqueous solutions containing non-volatile or low-volatile acids or alkalis as solutes, it is possible to efficiently
It has been found that it is possible to concentrate at high speed and to separate pure water.

When separating pure water from a stock solution or concentrating a solute, according to the conventional method, the separation rate and concentration rate vary greatly depending on the stock solution 4 degrees.
If the droplets are treated with a hydrophobic membrane in the accompanying vapor state,
They discovered that it is possible to separate or concentrate at a nearly constant rate over almost the entire PH range.

Based on this fact, the present invention provides a method for treating an acid or alkali aqueous solution that can efficiently concentrate or pure water the acid or alkali aqueous solution over almost the entire P Hil range at a constant high rate. A hydrophobic membrane that heats an aqueous solution containing a non-volatile or low-volatility acid or alkali as a solute to generate water vapor under droplet entrainment conditions, and allows the water vapor to pass through, but not water. It is characterized by contacting one side of the hydrophobic membrane, allowing the vapor to permeate through the other side of the hydrophobic membrane, and then cooling and condensing the membrane, and returning the droplets blocked by the membrane to the aqueous solution. It's a method.

Non-volatile or low volatile aqueous solutions of raw acids or alkalis to be treated according to the present invention include inorganic acids such as sulfuric acid, organic acids such as acetic acid and citric acid, and alkalis such as sodium hydroxide and potassium hydroxide. be.

Hydrophobic membranes include polyethylene and polypropylene.

Use polyolefins such as poly4-methylpentene-1, polysulfones such as polysulfone and polyethersulfone, and fluororesins such as polytetrafluoroethylene, vinylidene fluoride, and ethylene-tetrafluoroethylene copolymer. can. Also, is the hydrophilic membrane fluorine-based or silicone-based? It is also possible to use a material whose surface is coated with an aqueous resin to give it a hydrophobic function.

FIG. 1 shows the separation system used in the present invention.

To treat an acid or alkaline aqueous solution according to the present invention, the liquid in the raw water tank d is supplied to the evaporator C by a supply pump b and evaporated at a high speed. In this case, the generated vapor is accompanied by droplets containing nonvolatile components. This vapor is forced into the primary chamber of the membrane demister d. Further, the demister d is heated by the heating means to keep the inside of the demister d warm above the steam temperature. However, although vapor passes through the pores of the membrane 2 due to its gas phase, droplets containing non-volatile components cannot pass through the pores of the membrane 2 due to the aqueous nature of the membrane 2. Its passage is blocked. Therefore, while the droplets pass through the membrane, they are mixed on the surface of the membrane on the firebox side 1 and drain pipe 1.
．． is returned to the aqueous solution side (evaporator C or raw water tank a). f is a pure water tank. Therefore, the membrane demister
The vapor that can pass through the membrane d does not contain droplets containing non-volatile components, and by condensing this in the condenser e, a highly purified permeate can be obtained. Further, the acid or alkaline aqueous solution on the negative side can also be concentrated.

Although the type of the membrane demister is not particularly limited, for example, a plate type, hollow fiber membrane type, spiral type, or cartridge type can be used.

FIGS. 2A to 2D illustrate an embodiment of a plate-type membrane demister. As shown in FIG. 2A, the membrane demister main body is constructed by laminating a large number of units 3 consisting of a corrugated support plate 1 and membranes 2 disposed on both sides thereof at intervals so as to have the same phase. The so-called laminated membrane demister
The structure is such that a meandering gap formed between each unit 3 between the membranes 2 is used as a supply steam passage 4, and a gap between each membrane and the support plate is used as a permeation steam passage 5.

The specific structure of such a laminated membrane demister main body is shown in Figure 2B.
This is shown in the second diagram.

FIG. 2B shows a plan view of an example of the membrane support plate 1, and FIG. 2C shows a cross-sectional view taken along the line mc-c in FIG. 2B. A flat band 11 is formed along the center line in the longitudinal direction, and this band is used as a collection path for permeated vapor. Further, a through hole 13 having a flat annular portion 12 is bored in the center of the band, and this through hole 13 forms a permeated vapor outflow hole.

Further, holes 15 having flat annular portions 14 are bored at both ends of the membrane support plate 1 on both sides of the center line, and these through holes 15 form supply steam inflow holes. Further, the membrane support plate 1 has a corrugated shape 17 formed by processing, etc., except for its peripheral edge 16 and the flat annular portion around the through hole. The flat annular portions around each of the through holes 13 and 15 are formed in order to bring the ring spacer into close contact between the units 3, as will be described later.

The second diagram shows a laminated membrane demister in which a large number of units 3 each having membranes 2 disposed on both sides of such a corrugated membrane support plate 1 are laminated at intervals and in the same phase. , each unit 3 is fixed and sealed at one end via a puff king 21, and further includes a ring spacer 22 at an inner position close to the banking 21. A supply steam inflow hole 23 for introducing supply steam into the supply steam passage 4 is sandwiched between
is formed. Similarly, the other end of each unit 3 is also fixed and sealed with a puffing 24 and is sandwiched between ring spacers 25 for supplying steam for discharging the supplied steam from the supply steam passage 4. An outflow hole 26 is formed.

The permeated vapor extraction hole 27 is formed at the center of the unit 3. That is, the ring spacer 28 is formed at the center of the support plate constituting the unit.

<Example> Next, examples of the present invention will be described.

A polytetrafluoroethylene membrane with an average pore diameter of 0.2 μm and a porosity of 80% was used as the hydrophobic membrane, and a laminated membrane demister with a membrane area of 230 cm was used as the membrane demister.

As the aqueous solution, an aqueous sulfuric acid solution and an aqueous sodium hydroxide solution having pH values shown in Table 1 were used. For each raw aqueous solution,
Acquisition speed: 650-700kg/m!・hr (per unit time, per unit membrane area) When condensed water was obtained at a nearly constant rate of 4! We were able to obtain neutral pure water.

FIG. 3 shows the processing results including those of the above-mentioned examples, and it can be seen that pure water can be efficiently separated regardless of the pH of the aqueous solution.

<Effects of the Invention> As described above, according to the method for treating an acid or alkaline aqueous solution according to the present invention, pure water is heated at a high rate (60%) over almost the entire pH range of the aqueous solution from the acid or alkaline water solution.
50 to 700 kg/m"・hr) or high-speed WIM. Therefore, highly efficient separation or concentration treatment of acid or alkaline aqueous solutions is possible, and the speed is almost constant. It is also easy to connect with other processes, such as a pure water washing process.

Table 1

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the separation system used in the present invention, FIG. 2 A, FIG. 2 B, FIG. 2 C, and the second diagram are explanatory diagrams showing the membrane demister in the above separation system,
FIG. 3 is a chart showing the relationship between the PH of the aqueous solution and the PH of the condensed water in the treatment method according to the present invention. In the figure, d is a membrane demister, 1h is a heating means, and 2 is a hydrophobic membrane. Do-16-1) r 2/XjA

Claims (1)

[Claims] (1) Aqueous solution containing a non-volatile or low-volatile acid or alkali as a solute is heated to generate water vapor accompanied by droplets, and the water vapor is hydrophobic, which allows water vapor to pass through but does not allow water to pass through. The method is characterized by contacting one side of the hydrophobic membrane to allow the vapor to permeate through the other side of the hydrophobic membrane, and then cooling and condensing the liquid while returning the droplets blocked by the membrane to the aqueous solution. Method for treating acid or alkaline aqueous solutions.