JP2001232104A - Solid/liquid separation method of suspension - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid/liquid separation method capable of forming aggregate having the equal holding water in a remarkably smaller quantity compared to the conventional technique and obtaining a clear separated liquid in the aggregation by using a flocculant for suspension. SOLUTION: This solid/liquid separation method of the suspension is performed by adding a cationic temperature sensitive polymer and an anionic temperature sensitive polymer, which are converted from hydrophilicity to hydrophobicity with a transition temperature as the border line, as a temperature sensitive high molecular flocculant into the suspension and mixing the mixture in the hydrophilic temperature region equal to or below the transition temperature, and after that, heating the suspension to form the hydrophobic temperature region equal to or above the transition temperature to cause hydrophobic interaction and carrying out the solid/liquid separation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-liquid separation method for a suspension, and more particularly to a suspension using a temperature-sensitive polymer flocculant.
For example, it relates to a solid-liquid separation method for wastewater or sludge.

[0002]

2. Description of the Related Art Separation of fine particles suspended in a liquid (solid-liquid separation) is a major issue in water treatment, sewage treatment or sludge treatment discharged therefrom. Usually, aluminum sulfate (hereinafter referred to as "sulfate band"), polyaluminum chloride (hereinafter referred to as "PAC"), ferric chloride,
Inorganic flocculants such as polyiron and organic polymer flocculants such as polyacrylamide and its anion or cation derivative are used alone or in combination to measure aggregation and coarsening of fine particles, and then separation by sedimentation, Alternatively, separation of water from the aggregate by pressure such as filtration and squeezing has been performed.

[0003]

However, when an inorganic coagulant is used, aluminum or iron ions form hydroxides to form aggregates, so that only aggregates that are fragile and have a very high water content can be obtained. In addition, when a polymer flocculant is used, the hydrophilic polymer is crosslinked and adsorbed between the fine particles to form an aggregate, but at that time a large amount of water is embraced, which makes subsequent solid-liquid separation difficult. There was a problem that.
Therefore, prior to the solid-liquid separation step, there has been a demand for a method in which the formed aggregates are strong and do not contain water.

As a method of solving this problem, the present inventors have previously used a method of using a temperature-sensitive polymer, which changes from hydrophilic to hydrophobic by a change in temperature, as a coagulant (Japanese Patent Application No. 11-313,197).
-46541). This is a method to improve the solid-liquid separation method by generating agglomerates that are strong, have low moisture content, and are easy to squeeze and dewater, but focus on the property that the polymer used is simply temperature-sensitive. However, there is a problem that the required amount of addition is large.

[0005] The present invention has been made in view of such conventional problems, and uses a specific flocculant to produce an agglomerate having a much smaller amount of water equivalent to that of the prior art. Another object of the present invention is to provide a method for obtaining a clear separated solution.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies, and as a flocculant, a cationic temperature-sensitive polymer which changes from hydrophilic to hydrophobic by a temperature change, and an anionic polymer. The inventors have found that the above problem can be solved by using a thermophilic polymer, and have completed the present invention.

That is, the present invention has the following configuration. (1) As a temperature-sensitive polymer flocculant, a cationic temperature-sensitive polymer and an anionic temperature-sensitive polymer that convert from hydrophilic to hydrophobic at the transition temperature are suspended in a hydrophilic temperature range below the transition temperature. After adding and mixing to the liquid, the temperature of the suspension is raised to generate a hydrophobic interaction as a hydrophobic temperature region above the transition temperature, and solid-liquid separation is performed at the temperature after the temperature rise. A method for solid-liquid separation of a suspension. (2) The solid-liquid separation method according to the above (1), wherein a copolymer of an acrylamide derivative and / or a methacrylamide derivative monomer and a monomer having a cationic dissociating group is used as the cationic thermosensitive polymer. (3) The above (1) wherein a copolymer of N-isopropylacrylamide and cationic N, N-dimethylaminopropylacrylamide is used as the cationic thermosensitive polymer.
Or the solid-liquid separation method according to (2). (4) The solid-liquid separation method according to (1), wherein a copolymer of an acrylamide derivative and / or a methacrylamide derivative monomer and a monomer having an anionic dissociating group is used as the anionic thermosensitive polymer. (5) The solid-liquid separation method according to the above (1) or (4), wherein a copolymer of N-isopropylacrylamide and acrylic acid is used as the anionic thermosensitive polymer. (6) After adding the cationic temperature-sensitive polymer and stirring and mixing,
The above (1) in which an anionic thermosensitive polymer is added and mixed by stirring.
The solid-liquid separation method according to any one of (1) to (5).

Further, in the present invention, preferred embodiments are as follows. (7) The solid-liquid separation method according to (1), wherein the solid-liquid separation means is gravity sedimentation, centrifugal sedimentation, or pressure dehydration means. (8) The solid-liquid separation method according to (7) above, wherein a belt press, a filter press, a centrifugal dehydrator, a screw press, or a multiple disc dehydrator is used as the pressure dehydrating means. (9) The solid-liquid separation method according to (2) or (3), wherein the copolymerization ratio of the cationic monomer in the cationic thermosensitive polymer is 5 to 10 mol%.

(10) The solid-liquid separation method according to the above (4) or (5), wherein the copolymerization ratio of the anionic monomer in the anionic thermosensitive polymer is 5 to 10 mol%. (11) The above (2), (3), (4), (5), (9) or (1) wherein the molecular weights of the cationic temperature-sensitive polymer and the anionic temperature-sensitive polymer are both 4 to 15,000,000.
The solid-liquid separation method according to any one of the above (0). (12) The solid-liquid separation method according to the above (1), wherein the addition rate of the cationic temperature-sensitive polymer and the anionic temperature-sensitive polymer is 0.1 to 5% by weight in total with respect to the suspended solid. (13) The solid-liquid separation method according to (1), wherein the temperature of the suspension is adjusted to 35 to 70 ° C. by heating.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, “%” means “% by mass” unless otherwise specified. FIG. 1 is a flow sheet showing one embodiment of the suspension solid-liquid separation method of the present invention.

The stirring in the present invention employs a usual stirring device. It is not necessary to adjust the stirring speed in consideration of the formation and destruction of aggregates as in the prior art, but rather good stirring results in good results. As for the order of addition of the polymer, it is usually preferable to add and mix the cationic thermosensitive polymer and then add and mix the anionic thermosensitive polymer. However, in some cases, conversely, it is effective to add and mix the cationic thermosensitive polymer after adding and mixing the anionic thermosensitive polymer, and furthermore, it is effective to add and mix both at the same time. There is also.

The heating for raising the temperature may be performed by a usual heating method, and the temperature of the added suspension may be raised to the transition temperature of the used polymer or higher. Further, as the solid-liquid separation means, gravity sedimentation, centrifugal sedimentation, or press dewatering means such as belt press, filter press, centrifugal dehydrator, screw press, multiple rotating disk dehydrator, depending on the solids concentration of the suspension Can be selected as appropriate.

The polymer used in the present invention is not particularly limited, as long as it is cationic or anionic, and is a temperature-sensitive polymer that changes from hydrophilic to hydrophobic at a transition temperature. Usually, an acrylamide derivative and / or a methacrylamide derivative is used as a main monomer, and a monomer having a cationic dissociative group, for example, a monomer having a tertiary amine or a quaternary ammonium salt, or a monomer having an anionic dissociative group, for example, carboxylic acid is used. What is necessary is just to copolymerize in various ratios the monomer which has as a co-monomer.
Since the transition temperature varies depending on the chemical composition of the main monomer and the proportion of the cationic or anionic monomer, the polymer is selected according to the operating temperature to be used. As an example, Table 1 shows the relationship between the chemical composition of the main monomer and the transition temperature.

[0014]

[Table 1]

[0015]

[Table 2]

Specifically, as the cationic thermosensitive polymer, for example, a copolymer of N-isopropylacrylamide and cationic N, N-dimethylaminopropylacrylamide can be mentioned, and as the anionic thermosensitive polymer, N-isopropylacrylamide can be used. A copolymer of acrylamide and acrylic acid may be mentioned. When the operating temperature is around 30 ° C., N-isopropylacrylamide (NIPAM) or a derivative thereof may be used as a monomer. Also,
In addition to the ionic comonomer, a hydrophilic functional group such as an acrylamide group having no ionic property and a hydrophobic functional group such as a t-butyl group can be introduced to adjust the transition temperature. Usually, those in which about 10 to 20 mol% of these functional groups are introduced are used.

Further, the higher the molecular weight of the polymer used, the more preferable. Usually, a polymer having a molecular weight of about 100,000 to 20,000,000 is used, and a polymer having a molecular weight of about 4,000,000 to 15,000,000 is preferably used. These polymers can be produced by a radical polymerization method using N, N, N ', N'-tetramethylethylenediamine as a polymerization accelerator and ammonium peroxodisulfate as a polymerization initiator, but depending on the amount of these chemicals added. The degree of polymerization changes and the molecular weight can be adjusted.

The amount of the polymer to be added varies depending on the composition of the suspension to be treated, but the total amount of the cationic thermosensitive polymer and the anionic thermosensitive polymer is 0.1% per suspended solid.
A range of about 5% is good. If it is less than 0.1%, the effect is small. On the other hand, if it exceeds 5%, the cost is high and it is not preferable. The ratio of the cationic temperature-sensitive polymer to the anionic temperature-sensitive polymer varies depending on the case, but when the ratio (cationic temperature-sensitive polymer / anionic temperature-sensitive polymer) is generally selected in the range of 10 to 0.1. Good. The heating temperature varies depending on the polymer used, but is generally about 35 to 70 ° C. If the temperature is lower than 35 ° C., the effect of the transition is small,
On the other hand, if the temperature is higher than 70 ° C., the energy cost increases, which is not preferable.

Although the mechanism of action of the principle of the effect of the present invention is not clear, the present inventors presume as follows. Since the temperature-sensitive polymer is hydrophilic below the transition temperature, it is adsorbed cross-linking between suspended particles to form flocs when added in an appropriate amount in the same manner as a general polymer flocculant. Also,
When sufficiently added and the surface of the suspended particles is coated with the polymer, the dispersion is stabilized. When heated above the transition temperature in this state,
The surface of the suspended particles is made hydrophobic by making the adsorbed polymer hydrophobic. The hydrophobized suspended particles form flocs by hydrophobic interaction. Also, at this time, if an appropriate external force is applied, the rearrangement of particles easily occurs,
The water in the floc gap is spontaneously discharged due to the hydrophobized particles, and a compact is easily obtained.

However, when the ionic thermosensitive polymer is used as in the present invention, the adsorption to the suspended particles becomes stronger than that of the nonionic thermosensitive polymer. Even if the polymer transitions to hydrophobic, a strong hydration layer around the ionic groups prevents the polymers from sticking together due to hydrophobic interactions, resulting in floc formation and compaction due to hydrophobic interactions. Less likely to happen. Therefore,
The effect of the hydration layer is reduced by adding an ionic temperature-sensitive polymer having a charge opposite to that of the adsorbed ionic group to neutralize the charge. The adhesion between the polymers occurs, and a compact can be easily obtained as in the case of the nonionic temperature-sensitive polymer. Further, since a polymer complex is formed by adding a polymer having an opposite charge, a consolidation effect is more remarkably exhibited as compared with a conventional nonionic thermosensitive polymer.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings by way of embodiments. However, the present invention is not limited to only this embodiment.

Example 1 (Sample) As a suspension, a kaolin suspension was used. As a dispersant, 1 × 10 ⁻³ mol / l of sodium hydroxide was contained, and the solid concentration was 250 g / l. As a cationic thermosensitive polymer, a copolymer of N-isopropylacrylamide (NIPAM) and cationic N, N-dimethylaminopropylacrylamide (DMAPAA) (DMAPAA 5 mol%) [poly (NIPAM)
-Co-DMAPAA) 5 mol%], and N-isopropylacrylamide (NI
PAM) and acrylic acid (AAC) copolymer (AAC)
5 mol%) [poly (NIPAM-co-AAC) 5
mol%].

(Test Method) A predetermined amount of the cationic thermosensitive polymer solution was added to 100 ml of the above kaolin suspension, and the mixture was sufficiently stirred with a magnetic stirrer. Then, a predetermined amount of the anionic thermosensitive polymer solution was added, and the magnetic stirrer was further added. Then, the mixture was transferred to a graduated cylinder (inner diameter: 37 mm) and immersed in a thermostat at a predetermined temperature. After the suspension reaches the predetermined temperature, a rod with a diameter of 27 mm is
After infiltration 5 times at a predetermined speed of m / min, the wire was pulled out and allowed to stand for 1 hour, and the sedimentation volume of the aggregate and the transmittance (600 nm) of the supernatant were measured. Since the agglomerates undergo a squeezing action due to the penetration of the rod, the aggregates that are more easily squeezed have a smaller sedimentation volume.

(Test Results) FIG. 2 shows the effect of the polymer addition rate on the sedimentation volume when the temperature of the thermostat is set at 60 ° C. FIG. 2 shows that the cationic thermosensitive polymer addition rate was 0.1%.
005 g / g-kaolin followed by the addition of an anionic thermosensitive polymer (（), the cationic thermosensitive polymer addition rate was 0.01 g / g-kaolin, followed by the anionic thermosensitive polymer Is added (□)
showed that. 0.005 cationic cationic polymer addition rate
The change in the case of adding an anionic thermosensitive polymer to that of g / g-kaolin is indicated by an arrow, and the addition rate of the polymer in that case is the total addition rate of both polymers. The change in the case where the cationic thermosensitive polymer addition rate is 0.01 g / g-kaolin is indicated by arrows.

In each case, the sedimentation volume was 50% with the cationic thermosensitive polymer alone, but it can be seen that the sedimentation volume decreased with the addition of the anionic thermosensitive polymer, and was approximately 27%. This state is an extremely strong dehydrated cake that is ticking, and it is impossible for a normal human power to penetrate the stick. When the sedimentation volume was about 27%, the supernatant liquid transmittance was 0.99 or more, indicating a very clear state. The total amount of the polymer added necessary to make this state varies somewhat depending on the addition ratio of the cationic thermosensitive polymer, but generally ranges from 0.01 to 0.1.
It was 0125 g / g-kaolin.

Comparative Example 1 As a comparison, a poly (N-isopropylacrylamide poly (NIPA) having no ionicity as a temperature-sensitive polymer was used.
The relationship between the polymer addition rate and the sedimentation volume when the same operation was performed using M) is shown by a double circle in FIG. As the polymer addition rate increased, the sedimentation volume gradually decreased to reach 28%, which was almost the same as in the present invention, and a very strong dehydrated cake with ticks was obtained, but it took 0.03 g / g to reach this state. -Requires kaolin polymer addition rate.

Comparative Example 2 For comparison, the cationic thermosensitive polymer [poly (NIPAM-co-DMAPAA) 5mo used in Example 1 was used.
1%] alone and the same operation was performed, the relationship between the polymer addition rate and the sedimentation volume is shown by a circle in FIG. The sedimentation volume gradually decreased as the polymer addition rate increased, and then increased. The minimum value of the sedimentation volume was 50%, and a strong dehydrated cake was not obtained.

Comparative Example 3 As a comparison, 5 m of the cationic thermosensitive polymer [poly (NIPAM) -co-DMAPAA] used in Example 1 was used.
ol%] was added at 0.01 g / g-kaolin, and then non-ionic poly N-isopropylacrylamide p was added.
The relationship between the polymer addition rate and the sedimentation volume when the same operation was performed with the addition of poly (NIPAM) is shown by the black circles in FIG. The sedimentation volume gradually decreased as the polymer addition rate increased, but the minimum value was 35%, and a strong dehydrated cake was not obtained. From the above results, it can be seen that the solid-liquid separation method of the present invention (Example 1) obtains a good dehydrated cake and supernatant with a lower polymer addition rate than the other methods (Comparative Examples 1, 2 and 3). .

Example 2 The change in transmittance due to heating of the cationic thermosensitive polymer solution was measured, and the transition temperature of the cationic thermosensitive polymer was measured from the change in transmittance. As a cationic thermosensitive polymer,
NIPA having a copolymerization ratio of a cationic monomer of 0 to 10 mol%
M-DMAPAA copolymer [poly (NIPAM-c
o-DMAPAA] was used. Upon measurement, the polymer concentration was 5 g / liter. FIG. 3 shows the relationship between the light transmittance and the temperature of each polymer solution. In the case of the NIPAM polymer solution [poly (NIPAM)], the light transmittance is high in a low temperature region and the polymer is hydrophilic and is dissolved in water around 32 ° C., but the light transmittance is low in a high temperature region and the polymer is low. Is presumed to be hydrophobic and precipitated. From this, the transition temperature of poly (NIPAM) is 32 ° C.
It was estimated.

Similarly, FIG. 3 shows that DMAPAA 1 mol%
The polymer has a transition temperature of 42 ° C., about 50 ° C. for 2.5 mol% of DMAPAA, and about 52 ° C. for 5 mol% of DMAPAA.
° C. Also, at 10 mol% of DMAPAA, 6
It was 0 ° C or higher. From the above results, by changing the cationic monomer copolymerization rate of the cationic temperature-sensitive polymer,
It can be seen that the transition temperature can be freely controlled.

[0031]

According to the present invention, a cationic thermosensitive polymer and an anionic thermosensitive polymer are used as a thermosensitive polymer coagulant, added and mixed, and then the suspension is heated to a transition temperature. By causing a hydrophobic interaction as the above-mentioned hydrophobic temperature region, a nonionic thermosensitive polymer, or a cationic thermosensitive polymer or an anionic thermosensitive polymer alone, and a nonionic thermosensitive polymer with them. The solid-liquid separation of the suspension can be performed more efficiently as compared with the case where.

[Brief description of the drawings]

FIG. 1 is a flow sheet of an embodiment of the suspension solid-liquid separation method of the present invention.

FIG. 2 is a graph showing the effect of polymer addition rate on the settling volume of a suspension.

FIG. 3 is a graph showing a change in transmittance (measurement of transition temperature) due to heating of a polymer solution.

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Claims (6)

[Claims] 1. As a thermosensitive polymer coagulant, a cationic thermosensitive polymer and an anionic thermosensitive polymer that convert from hydrophilic to hydrophobic at a transition temperature are used in a hydrophilic temperature range below the transition temperature. After adding and mixing to the suspension, the temperature of the suspension is raised to generate a hydrophobic interaction as a hydrophobic temperature region above the transition temperature, and solid-liquid separation is performed at the temperature after the temperature rise. Solid-liquid separation method for a suspension. 2. The solid-liquid separation method according to claim 1, wherein a copolymer of an acrylamide derivative and / or a methacrylamide derivative monomer and a monomer having a cationic dissociative group is used as the cationic thermosensitive polymer. 3. The method according to claim 1, wherein a copolymer of N-isopropylacrylamide and cationic N, N-dimethylaminopropylacrylamide is used as the cationic thermosensitive polymer. 4. The solid-liquid separation method according to claim 1, wherein a copolymer of an acrylamide derivative and / or a methacrylamide derivative monomer and a monomer having an anionic dissociating group is used as the anionic thermosensitive polymer. 5. The solid-liquid separation method according to claim 1, wherein a copolymer of N-isopropylacrylamide and acrylic acid is used as the anionic thermosensitive polymer. 6. The solid-liquid separation method according to claim 1, wherein the cationic temperature-sensitive polymer is added and mixed with stirring, and then the anionic temperature-sensitive polymer is added and mixed with stirring.