TECHNICAL FIELD

The present invention relates to a porous formed article, a method for producing a porous formed article, and a production apparatus for a porous formed article.

BACKGROUND ART

In recent years, environmental standards against harmful substances such as phosphorus, boron, arsenic and fluorine in drinking water, industrial water, industrial effluent, sewage treatment water and various environmental waters have been strengthened in terms of eutrophication problems caused by environmental pollution. Thus, there has been a growing demand for techniques for removing these harmful substances.

Phosphorus, one of the causative substances of eutrophication, is more strongly controlled, particularly, in closed water. Also, techniques for recovering and reusing phosphorus from effluent have been demanded because the depletion of this element is also of concern.

Boron is an essential element for plant cultivation, but is known to have adverse effects on plant growth when present excessively. As for human bodies, the possibility has been pointed out that boron contained in drinking water influences the health and particularly causes health problems such as reduction in reproductive functions.

Arsenic is contained in effluent from the non-ferrous metal refining industry, thermal discharges from geothermal power plants and ground water of specific areas, etc. The toxicity of arsenic has been long known. Reportedly, arsenic is bioaccumulative and causes chronic intoxication, weight loss, disturbance of perception, liver disorder, dermal deposition and skin cancer, etc.

Fluorine is contained in large amounts in effluent from the metal refining industry, the glass industry and the electronic material industry, etc. The influence of fluorine on human bodies is of concern. Excessive ingestion of fluorine is known to cause chronic fluorine poisoning such as fluorosis, bone sclerosis and thyroid gland disorder.

The outputs of these harmful substances are increasing yearly. Thus, there is a demand for techniques for efficiently removing these harmful substances. There is also a growing demand for the selective removal of specific ions such as phosphate or borate ions in the field of conventional effluent processing as well as from water for use in metal plating, pharmaceutical production, etc.

For example, techniques using an adsorbing agent comprising an inorganic ion adsorbent powder such as aqueous ferrite of zirconium or aqueous cerium oxide carried by a polymer material are known as techniques for removing various harmful substances as mentioned above.

Also, a porous formed article comprising an organic polymer resin and an inorganic ion adsorbent is known to adsorb phosphorus, boron, or the like.

For example, Patent Literature 1 discloses that a formed article having no skin layer on the surface and having excellent surface opening properties is obtained by the adoption of a method which involves dissolving an organic polymer resin in an appropriate good solvent, further dissolving and mixing therein a water-soluble polymer that is soluble in the good solvent and has affinity for the organic polymer resin, and suspending an inorganic ion adsorbent powder as an adsorption substrate in the resulting polymer solution, followed by shape forming in a coagulation bath containing a poor solvent.

Patent Literature 2 discloses that a porous formed article having only a small amount of secondary aggregates of an inorganic ion adsorbent in the porous formed article is excellent in adsorption performance and also has large strength.

Patent Literature 3 discloses that a porous formed article comprising an organic polymer resin having a hydroxy group and an inorganic ion adsorbent powder is a porous formed article that is highly durable against a washing agent such as an oxidizing agent, repetitively usable, and suitable for adsorbing agents.

Adsorbing agents consisting of the porous formed articles disclosed in Patent Literatures 1 to 3 are free from a thin membrane, called a skin layer, on the surface of the porous formed articles and are excellent in the internal porosity of the adsorbing agents. Therefore, a feature of these adsorbing agents is that the diffusion rate of an object to be adsorbed such as phosphorus or boron into the inside of the adsorbing agents is fast. Patent Literatures 1 to 3 further disclose that adsorption is performed at a fluid flow rate (SV) of 30.

CITATION LIST

Patent Literature

Patent Literature 1: International Publication No. WO 2005/056175

Patent Literature 2: Japanese Patent Laid-Open No. 2009-297707

Patent Literature 3: International Publication No. WO 2011/062277

SUMMARY OF INVENTION

Technical Problem

However, in recent years, ultrahigh-speed processing at SV120 much faster than the conventional fluid flow rate of SV30 has been required, particularly, for the purpose of using water in metal plating, pharmaceutical production, etc.

There is a demand for further improvement in the conventional porous formed articles as disclosed in Patent Literatures 1 to 3.

An object of the present invention is to provide a porous formed article that can remove ions, particularly, phosphate ions, in water to be processed at an ultrahigh speed and has a large adsorption capacity.

Solution to Problem

The present inventors have conducted diligent studies and consequently completed the present invention by finding that the problems described above can be solved by a porous formed article comprising an organic polymer resin and an inorganic ion adsorbent and having the most frequent pore size of 0.08 to 0.70 μm measured with a mercury porosimeter.

Specifically, the present invention is as follows:

[1]

A porous formed article comprising an organic polymer resin and an inorganic ion adsorbent and having the most frequent pore size of 0.08 to 0.70 μm measured with a mercury porosimeter.

[2]

The porous formed article according to [1], wherein an outer surface opening ratio is 5% or more and less than 30%.

[3]

The porous formed article according to [1] or [2], wherein a specific surface area measured with a mercury porosimeter is 10 to 100 m2/cm3.

[4]

The porous formed article according to any of [1] to [3], wherein a ratio of the most frequent pore size of a median size (the most frequent pore size/median size) measured with a mercury porosimeter is 0.80 to 1.30.

[5]

The porous formed article according to any of [1] to [4], wherein the porous formed article is spherical particles having an average particle size of 100 to 2500 μm.

[6]

The porous formed article according to any of [1] to [5], wherein the inorganic ion adsorbent contains at least one metal oxide represented by the following formula (I):
MNxOn.mH2O  (I)
wherein x is 0 to 3, n is 1 to 4, m is 0 to 6, and M and N are different from each other and each represent a metal element selected from the group consisting of Ti, Zr, Sn, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Si, Cr, Co, Ga, Fe, Mn, Ni, V, Ge, Nb and Ta.
[7]

The porous formed article according to [6], wherein the metal oxide contains at least one material selected from any of the following groups (a) to (c):

(a) hydrous titanium oxide, hydrous zirconium oxide, hydrous tin oxide, hydrous cerium oxide, hydrous lanthanum oxide and hydrous yttrium oxide,

(b) a mixed metal oxide of at least one metal element selected from the group consisting of titanium, zirconium, tin, cerium, lanthanum and yttrium, and at least one metal element selected from the group consisting of aluminum, silicon and iron, and

(c) activated alumina.

[8]

The porous formed article according to any of [1] to [7], wherein the organic polymer resin contains at least one component selected from the group consisting of an ethylene vinyl alcohol copolymer (EVOH), polyacrylonitrile (PAN), polysulfone (PS), polyethersulfone (PES) and polyvinylidene fluoride (PVDF).

[9]

A column packed with a porous formed article according to any of [1] to [8].

[10]

A method for producing a porous formed article comprising an organic polymer resin and an inorganic ion adsorbent, comprising the steps of:

(1) crushing and mixing a good solvent for the organic polymer resin and the inorganic ion adsorbent to obtain slurry;

(2) dissolving the organic polymer resin and a water-soluble polymer in the slurry obtained in the step (1);

(3) shape-forming the slurry obtained in the step (2);

(4) promoting coagulation of the shape-formed product obtained in the step (3) by controlling the temperature and humidity of a spatial portion coming into contact with the shape-formed product, until the shape-formed product is coagulated in a poor solvent; and
(5) coagulating the coagulation-promoted shape-formed product obtained in the step (4), in a poor solvent.
[11]

The method for producing a porous formed article according to [10], wherein a relative humidity of the spatial portion coming into contact with the shape-formed product in the step (4) is 65 to 100%.

[12]

The method for producing a porous formed article according to [10] or [11], wherein the good solvent for the organic polymer resin is at least one solvent selected from the group consisting of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC) and dimethylformamide (DMF).

[13]

The method for producing a porous formed article according to any of [10] to [12], wherein the poor solvent is water or a mixture of the good solvent for the organic polymer resin and water.

[14]

The method for producing a porous formed article according to any of [10] to [13], wherein a temperature of the poor solvent in the step (5) is 40 to 100° C.

[15]

The method for producing a porous formed article according to any of [10] to [14], wherein the step (3) comprises the step of using a nozzle disposed on a side of a rotating container so that the slurry obtained in the step (2) is scattered from the nozzle to form liquid drops.

[16]

A production apparatus for a porous formed article comprising a rotary container which scatters liquid drops by centrifugal force, and a coagulation vessel which retains a coagulating liquid, and comprising a control unit which has a cover placed over a spatial portion between the rotary container and the coagulation vessel and controls the temperature and humidity of the spatial portion.

[17]

The production apparatus for a porous formed article according to [16], wherein the control unit is a unit which warms the coagulating liquid retained in the coagulation vessel to control the temperature and humidity of the spatial portion through the use of steam generated from the coagulating liquid.

Advantageous Effects of Invention

The present invention can provide a porous formed article that can remove ions, particularly, phosphate ions, in processed water at an ultrahigh speed and has a large adsorption capacity.

