RU2728331C1 - Porous block filter material for purifying drinking water from iron and a method for production thereof - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to porous block filtration material for purification of drinking water from iron, containing fine particles of activated carbon with particle size of 0.15–0.3 mm, specific filtration surface from 800 m/g, iodine number from 800 mg/g and static exchange capacity by copper from 0.7 mg-eq/g, and polymer binder in following ratio of components, wt%: activated carbon 80–90, polymer binder 10–20, with pore size 50–100 mcm. Filter material is obtained by extrusion or hot pressing of mixture of powdered material with particle size of 0.15–0.3 mm from activated carbon with specific filtration surface area of 900 m/g, iodine number from 900 mg/g, static copper exchange capacity from 0.8 mg-eq/g, with water content of 8–12 % and polymer binder, and the process is carried out at a compression ratio of mixture of 15–20 % and temperature of 10–40 °C is higher than softening point of polymer binder at ratio of activated carbon: polymer binder of 80–90:10–20 wt%. Porous block material is made in the form of plates or hollow bodies of various shapes. Polymer binder contains polymers from classes of polyolefins and/or polyesters and/or copolymers thereof with a melt index of 2–20 g/10 min according to ASTM D 1238 at 190 °C and load 25 kg. Porous block material is intended for use as part of pressure and gravity filter cartridges for purification of drinking water from iron and other contaminants.EFFECT: providing high-efficiency purification of drinking water – at level of 90–99 % of iron during a considerable consumer resource, efficient additional purification of water from chlorine present in water, organochlorine compounds, heavy metals, for example, lead, copper, and other contaminants due to developed adsorption surface.5 cl, 1 dwg, 4 ex, 1 tbl

Description

The invention relates to filter materials, in particular, to a porous block filter material for purifying drinking water from iron and to a method for its production. The proposed porous block filter material is intended for use as part of pressure and gravity type filter cartridges used to purify drinking water from iron and other pollutants and can be used to improve the quality of drinking water purification.

At present, household filters are widely used among the population for purifying drinking water from toxic pollutants: chlorine, organochlorine compounds, heavy metals and iron. The release of iron from the group of heavy metals into an isolated pollutant is due to the fact that, due to its inherent specific physicochemical properties, water purification from it is carried out by others, different from the purification of traditional heavy metals (for example, copper, lead, etc.) materials and methods.

Iron is usually present in purified water in the form of a water-soluble ferrous iron cation Fe ⁺⁺ , which can be removed from water by cation exchange using traditional heavy metal sorbents such as cation exchangers or zeolites. However, in the presence of oxygen or other oxidizing agent dissolved in water, Fe ⁺⁺ transforms into the form of the ferric cation Fe ⁺⁺⁺ , which, when interacting with water, forms colloidal particles of iron hydroxide and iron oxide, which are difficult to remove due to their small size.

The classical method for removing iron from water is the oxidation of Fe ⁺⁺ by bubbling water with ozone, oxygen or air or by passing water through a granular oxidizer of manganese compounds (BIRM, etc.) and subsequent coagulation of the obtained colloidal iron and filtration of the precipitate of hydrate oxide and iron oxide through finely porous filters (DIRECTORY OF THE BEST EFFECTIVE TECHNOLOGIES, D. A. Danilovich, Moscow, 2015, pp. 55-70).

This method has proven itself well in stationary filters for water purification, requiring significant space for placement, electricity supply, connection to the water supply network and to the sewerage system. In cartridges of small pressure and gravity filters, this technology is not applicable due to the small size of the filters and their autonomy. In such filters, the removal of iron is carried out either with the help of granular or fiber cation exchangers that carry out the sorption of ferrous iron, which is subsequently oxidized by oxygen dissolved in water to ferric, present in water in the form of colloidal particles of iron hydroxide, which, in turn, are filtered out by mesh or linen cartridge materials (patents RU 2010007, 1994; RU 2533715, 2014; RU 2236279, 2004). A positive feature of such filters is effective water purification, in addition to iron, from chlorine, organochlorine compounds and heavy metals. The disadvantage of such filters is the periodic breakthrough of unfiltered colloidal iron into the filtered water. The same drawback is characteristic of a filter, in which the filtering medium, including activated carbon, additionally contains a granular mixture of calcium and magnesium carbonates, covered with a porous film consisting of oxides of magnesium, calcium and iron (Patent RU 2218984, 2003).

Block porous filters for water purification from iron are known from the prior art (patent RU 2326715, 2008), which incorporate technologies for catalytic oxidation of ferrous iron with filter pore material and subsequent filtration of hydroxide precipitate by glands with pores of block porous material. The material of a cartridge filter for water purification is made in the form of layers of fibrous polymer material formed on a porous frame, in which the first layer along the flow of the purified water has a packing density of fibers, which ensures the retention of particles with a size of 10-20 microns, the second layer contains manganese oxide, manganese dioxide , calcium hydroxide, magnesium hydroxide, chloride and sulfate of ferrous copper, hydroxides and water-soluble salts from the group of elements: titanium, zirconium, niobium, hafnium, tantalum, capable of providing the transfer of ferrous iron compounds to ferric compounds, their hydrolysis and coagulation of hydrolyzed forms, the third the layer has a packing density of fibers, providing a retention of particles with a size of 5-20 microns, the fourth layer has a packing density of fibers, providing a retention of particles with a size of 1-2 microns, and the fifth layer is made in the form of a fibrous non-woven substrate placed on a porous frame. The porous block material specified in this patent is capable of sufficiently effectively purifying water from iron, but is difficult to manufacture and is not capable of purifying water from other contaminants.

Known filters for water purification from iron based on a porous block material - foamed titanium (patents RU 2006471 C1, 01.30. 1994; RU 2288172 C1, 27.11.2006; RU 183672 U1, 01.10.2018), in which the oxidized titanium surface is TiO ₂ - is a catalyst for the oxidation of ferrous iron, and the pores serve as a filter material and retain the precipitate of iron hydroxide. In patent RU 2288172, the porous filter material is made of sintered titanium with a porosity of 5-7 μm and additionally contains a middle cylinder made of porous polypropylene; in patent RU 183672, the filter element is made of one piece of porous titanium with a labyrinth structure of pores with a size from 0.1 μm to 4, 9 microns and a porosity of 80-95%. The disadvantage of the porous filter material according to patents RU 2288172 and RU 183672 is the need for frequent regeneration of the filter cartridge from such porous filter materials, which is due to the small size of the pores, not exceeding 7 μm.

The closest to the claimed porous block material is a porous filter material made of titanium powder, made by sintering titanium powder in the form of a tube or plate with a wall thickness of 0.9-10.0 mm and a pore size of 5-40 microns (RU 2006471 C1, 30.01. 1994 ). The specified prototype material purifies water from iron, while the efficiency of water purification depends on the iron content in the source water, the pore size of the material and the wall thickness of the cartridge made of this material. However, the efficiency of water purification from iron by the prototype material is insufficient. As indicated in the prototype patent, when filtering tap water with an initial ferrous iron content of 0.3 mg / l, a porous block material of sintered titanium with a pore size of 8-11 and 5-8 microns provides a decrease in the iron content only to 0.19 mg / l, which corresponds to only 37% efficiency. Such a low efficiency of water purification from iron does not meet the standards of GOST 31952-2012 “WATER-CLEANING DEVICES. General requirements for efficiency and methods of its determination ”. In addition, due to the absence of specific sorbents in the material - the prototype, it does not purify water from such common pollutants as chlorine, organochlorine compounds and heavy metals. Other disadvantages of the prototype filter material are the high cost of both titanium itself and the sintered porous material based on titanium.

The technical objective of the present invention is to increase the degree of water purification from iron by a porous block filter material as part of pressure and gravity type filter cartridges using available and inexpensive raw materials for their manufacture.

The technical problem posed is achieved by the proposed porous block filter material for purifying drinking water from iron, containing fine particles of activated carbon with a particle size of 0.15-0.3 mm, specific filtration surface from 800 m ² / g, iodine number from 800 mg / g and a static exchange capacity for copper from 0.7 mEq / g, and a polymer binder with the following ratio of components, wt. %:

Activated carbon 80-90 polymer binder 10-20

The proposed porous block filter material for purifying drinking water from iron contains pores with a size of 50-100 microns.

As a polymer binder, the material contains polymers from the classes of polyolefins and / or polyesters and / or their copolymers with a melt index of 2-20 g / 10 min. according to ASTM D 1238 at 190 ° C and a load of 25 Kg.

The proposed porous block filter material for purifying drinking water from iron is obtained by extrusion or hot pressing of a mixture of powdered materials with a particle size of 0.1-0.3 mm from activated carbon with a specific filtration surface of 900 m ² / g, an iodine number of 900 mg / g, a static exchange capacity for copper from 0.8 meq / g, with a water content of 8-12% and a polymer binder, and the process is carried out at a mixture compression ratio of 15-20% and a temperature 10-40 ° C higher than the temperature softening the polymer binder at a ratio of activated carbon: polymer binder 80-90: 10-20 wt. %.

The porous block material is made in the form of plates or hollow bodies of various shapes.

The use of activated carbon as a sorbent, providing water purification from iron, became possible in the case of using activated carbon with unique properties, combining the properties of a cation exchanger that traps ferrous iron due to ion exchange, an oxidant that oxidizes ferrous iron into ferric, and an adsorbent, sorbing ferric hydroxide formed by the interaction of ferric iron with water. The manifestation of cation-exchange properties in such coal is due to the combination of a developed adsorption surface in it, providing contact of the treated water with the sorption centers of coal, and the presence of cation-exchange groups (carboxyl, hydroxyl, and phenolic):

(Monograph "OXIDIZED COAL", Tarkovskaya I.A., Kiev, Nauk, Dumka, 1981, p. 26), the number of which is expressed by the COE _Cu indicator (static exchange capacity for copper is the amount of Cu ⁺⁺ meq absorbed at room temperature of a sample of activated carbon, equal to 5 g, from 250 cubic cm of a 0.5% aqueous solution of copper sulfate for 2 hours). The oxidizing properties of activated carbon, due to which the conversion of ferrous iron into ferric iron occurs, have no unambiguous explanation. Perhaps this is due to the occurrence of two processes ("Catalytic oxidation of Fe (II) by activated carbon in the presence of oxygen. Effect of the surface oxidation degree on the catalytic activity", E. Ahumada, H. Lizama, F. Orellana , C. Suarez, A. Huidobro, A. Sepulveda-Escribano, F. Rodnguez-Reinoso, "Carbon, 40 (2002), pp. 2827-2834):

1. Oxidation of Fe (II) in the absence of oxygen:

- кислородсодержащие группы, расположенные на поверхности угля, с редокс-потенциалом выше, чем редокс-потенциал пары Fe³⁺/Fe²⁺;where: -

- oxygen-containing groups located on the coal surface with a redox potential higher than the redox potential of the Fe ³⁺ / Fe ²⁺ pair;

2. Oxidation of Fe (II) in the presence of oxygen:

2Fe ²⁺ + H ₂ O ₂ + 2H ⁺ → 2Fe ³⁺ + H ₂ O

могут быть хиноновые группы, присутствующие в значительном количестве в окисленных углях.In the latter case, the source

there may be quinone groups present in significant amounts in oxidized coals.

The adsorptive properties of activated carbon, which make it possible to adsorb colloidal particles of ferric hydroxide formed by the interaction of ferric iron with water, are due to the presence of pores in the porous block material obtained from activated carbon.

activado», Ingeniare. Revista chilena de

, vol. 19 №2, 2011, pp. 174-185), обработкой перекисями или растворами концентрированных серных или азотной кислот («Effect of different oxidizing agent treatments on the surface properties of activated carbons» // Carbon. 1999. V. 37, №8. P. 1323-1332), или проведением процесса обжига (активации) при наличии окислителя (например, воздуха) при определенном температурно-временном режиме («Adsorptionserscheinungen in Losungen. Uber die verchiedenen Modifikationen der aktivierten kohle». Z.phys.Chem. 1929, 140, N1/2, s.81-88). Другим известным способом получения активированных углей с катионообменными и окислительными свойствами является их измельчение в окислительной среде («Химические превращения углей при механическом диспергировании», Хренкова Т.М., Диссертация на соискание ученой степени доктора химических наук, Москва, 1983 г.).Activated carbons with the properties of cation exchangers and ferrous iron oxidizing agents can be obtained by additional oxidation of activated carbons obtained by classical methods of burning in an atmosphere that does not contain oxidizing agents, for example, by ozonation (Impacto del tratamiento con ozono sobre las propiedades superficiales del

activado ”, Ingeniare. Revista chilena de

, vol. 19 No.2, 2011, pp. 174-185), treatment with peroxides or solutions of concentrated sulfuric or nitric acids ("Effect of different oxidizing agent treatments on the surface properties of activated carbons" // Carbon. 1999. V. 37, No. 8. P. 1323-1332), or by carrying out the firing (activation) process in the presence of an oxidizing agent (for example, air) at a certain temperature-time regime ("Adsorptionserscheinungen in Losungen. Uber die verchiedenen Modifikationen der aktivierten kohle". Z.phys.Chem. 1929, 140, N1 / 2, s.81-88). Another well-known method of producing activated carbons with cation-exchange and oxidizing properties is their grinding in an oxidizing environment ("Chemical transformations of coals during mechanical dispersion", Khrenkova TM, Dissertation for the degree of Doctor of Chemical Sciences, Moscow, 1983).

The technical result of the proposed invention is the creation of a porous block filter material that provides highly effective - at the level of 90-99% - purification of drinking water from iron over a significant service life of the filter and is characterized by a simple technology for its production and low cost, since inexpensive activated carbons are used for its manufacture and polymeric materials. In addition, the developed adsorption surface of activated carbon in combination with its high porosity also provides effective additional water purification from chlorine, organochlorine compounds, heavy metals, such as lead, copper, and other pollutants present in water.

To achieve the maximum contact of the purified water with the adsorbent during water purification, which ensures high efficiency of water purification, activated carbon must have a large contact surface, which is achieved by using powdered forms of activated carbon with a particle size of 0.15-0.3 mm, having an optimal volume ratio / surface, developed specific pore surface of the activated carbon itself (from 800 m2 / g), the presence of optimal through pores in porous block filter material 50-100 microns, which should ensure, on the one hand, good contact of the treated water with the pores activated carbon (for this, the pores of the material must be of the minimum size), on the other hand, there is a large volume of absorption (adsorption) of the formed iron hydroxide (for this, the pores of the material must be of the maximum size). That is why in the claimed porous block material the pore size is in the range of 50-100 microns, since when the pore size is less than 50 microns, the absorption volume of iron hydroxide becomes unsatisfactory, and when the pore size is more than 100 microns, breakthrough of iron hydroxide into purified water occurs. In addition to the contact surface, the efficiency of water purification from iron depends on the number of micropores in which ferrous iron is retained due to cation exchange. The content of micropores in activated carbon is characterized by an iodine number. When the iodine number of activated carbon in the porous block material is less than 800 mg / g, activated carbon does not provide a high efficiency of water purification from ferrous iron.

Another factor affecting the efficiency of water purification from iron by porous block materials is the outer surface of activated carbon particles accessible for contact, which is not covered with a polymer binder melt. Usually, a polymeric binder softens and blocks from 20 to 40% of the surface of the activated carbon particles, which leads to a significant deterioration in the properties of the material. The degree of blocking of the activated carbon surface by a polymer binder depends on many factors, among which the most significant are: the ratio of activated carbon: polymer binder, the nature of the polymer binder and its thermomechanical properties, the molding temperature and compression ratio during the molding of the mixture, and the water content in the activated carbon. The selected ratio of activated carbon: polymer binder 80-90: 10-20 wt. % in combination with other factors: the water content in activated carbon is 8-12% and the compression ratio of the initial mixture during molding is 15-20% - due, on the one hand, to the minimum content of the polymer binder, which provides the mechanical strength of the porous block filter material - with its content less than 10 masses. % and the water content in activated carbon is more than 12% and with a compression ratio of less than 15%, the material is not able to keep its shape; on the other hand, when the content of the polymer binder is more than 20 wt. %, water in activated carbon less than 8% and compression ratio during molding more than 20% polymer binder blocks a significant surface of activated carbon particles, which leads to a deterioration in the efficiency of water purification. The choice of a polymer binder from the class of polyolefins (for example, low-density polyethylene, high-pressure polyethylene, polypropylene) and / or polyesters (for example, polyethylene terephthalate) and / or their copolymers (for example, a copolymer of polyethylene with vinyl acetate) is due, on the one hand, to their chemical inertness and insolubility in water, on the other hand, sufficiently low softening temperatures, allowing to intensify the process of manufacturing the filter element.

To ensure the most accessible surface of activated carbon for sorption, the process of manufacturing a porous block filter material is carried out at a temperature 10-40 ° C higher than the softening temperature of the polymer binder and at a compression ratio of the initial mixture of 15-20%. At a temperature lower than 10 ° C of the softening temperature of the polymer binder, the formation of a strong block material does not occur, and at a temperature higher than 40 ° C of the softening temperature of the polymer binder, a significant surface of the activated carbon is blocked as a result of the flow of the molten polymer binder.

Optimization of the combination of the above factors affecting the blocking of the activated carbon surface by the melt of the polymer binder (the ratio of the components of the mixture, the nature of the polymer binder, the processing temperature of the initial mixture and the degree of its compression, the water content in the initial activated carbon) makes it possible to obtain a porous block filter material with a large part of the activated carbon surface is not blocked by the polymer melt, and therefore the functional characteristics (filtration surface, iodine number, static exchange capacity for copper) are slightly less than those of the original activated carbon (no more than 10-15%).

COE _Cu must be at least 0.8 mEq / g. At lower COE _Cu values, the porous block filter material does not provide high efficiency of iron sorption for a given purification resource.

The manufacture of porous block filter material of various shapes: plates and hollow bodies is associated with the possibility of its use in flat cartridges of gravity filters and in cartridges in the form of a hollow cylinder of pressure and gravity filters. Below are examples of the claimed porous block filter material, and the table shows the test results on the effectiveness of water purification from iron. The above examples give an idea of the characteristics of the inventive porous block filter material for the complex purification of drinking water, but are not exhaustive. In the above examples, tests on the efficiency of water purification were carried out by placing a porous block filter material in the form of a hollow cylinder (1) in a pitcher filter cartridge (2) (Fig.). In this case, the cartridge itself, in addition to the porous block filter material, contained a fixation system with a funnel of a jug filter (3), and a plug of the bottom hole of the porous block filter material (4), hermetically connected to the porous block filter material by gluing. In the examples, the dimensions of the porous block filter material were: height 75 mm, outer diameter 62 mm, wall thickness 14 mm.

Evaluation of the efficiency of water purification was carried out in accordance with GOST 31952-2012 “WATER-CLEANING DEVICES. General requirements for efficiency and methods of its determination ”. The determination of the pore size was carried out by the porosimetry method (gas dynamic method). The specific surface area was determined by porosimetry (BET method).

The invention is illustrated by the following non-limiting examples.

Example 1. A porous block filter material is obtained from a mixture of activated carbon with a specific filtration surface of 1100 m2 / g, an iodine number of 1100 mg / g, COE _Cu 0.9 mg-eq / g, a water content of 10%, and a polymer binder ( low-pressure polyethylene with a softening point of 115 ° C) with a ratio of activated carbon: polymer binder - (85:15) wt. %. The particle size of the mixture components is 0.2-0.25 mm. The porous block material is obtained by extrusion of the above mixture at a temperature of 135 ° and a compression ratio of 15%. A porous block material was obtained with a pore size of 50 to 70 μm, a specific filtration surface of 1000 m2 / g, an iodine number of 1000 mg / g, and COE _Cu 0.8 mg-eq / g. The results of water treatment tests are presented in the table.

Example 2. A porous block filter material is obtained from a mixture of activated carbon with a specific filtration surface of 1500 m2 / g, an iodine number of 1250 mg / g, COE _Cu 1.15 mEq / g, a water content of 12%, and a polymer binder ( low-pressure polyethylene with a softening point of 115 ° C) with a ratio of activated carbon: polymer binder - (90:10) wt. %. The particle size of the mixture components is 0.15-0.20 mm. The porous block material is obtained by hot sintering the above mixture at a temperature of 130 ° and a compression ratio of 17%. The porous block material was obtained with a pore size of 60 to 90 μm, a specific filtration surface of 1250 m2 / g, an iodine number of 1150 mg / g, and COE _Cu 0.95 mg-eq / g. The results of water treatment tests are presented in the table.

Example 3. A porous block filter material is obtained from a mixture of activated carbon with a specific filtration surface of 1000 m2 / g, an iodine number of 1000 mg / g, COE _Cu 0.85 mEq / g, a water content of 9%, and a polymer binder ( low-pressure polyethylene with a softening point of 115 ° C) with a ratio of activated carbon: polymer binder - (80:20) wt. %. The particle size of the mixture components is 0.2-0.3 mm. The porous block material is obtained by hot sintering the above mixture at a temperature of 145 ° and a compression ratio of 20%. The porous block material was obtained with a pore size of 70 to 100 μm, a specific filtration surface of 900 m2 / g, an iodine number of 850 mg / g, COE _Cu 0.80 mg-eq / g. The results of water treatment tests are presented in the table.

Example 4. A porous block filter material is obtained from a mixture of activated carbon with a specific filtration surface of 900 m2 / g, an iodine number of 900 mg / g, COE _Cu 0.8 mg-eq / g, a water content of 8%, and a polymer binder ( low-pressure polyethylene with a softening point of 115 ° C) with a ratio of activated carbon: polymer binder - (80:20) wt. %. The particle size of the mixture components is 0.15-0.2 mm. The porous block material is obtained by hot sintering the above mixture at a temperature of 155 ° and a compression ratio of 20%. A porous block material was obtained with a pore size of 50 to 60 μm, a specific filtration surface of 800 m2 / g, an iodine number of 800 mg / g, and a COE _{Cu of} 0.7 mg-eq / g. The results of water treatment tests are presented in the table.

As follows from the results given in the table, the claimed porous block filter material provides high efficiency of water purification from iron 90-99% during a significant service life of the filter. In addition, the use of activated carbon as a sorbent also provides effective additional water purification from chlorine, organochlorine compounds, heavy metals and other pollutants present in water.

Claims (6)

1. Porous block filter material for purifying drinking water from iron, characterized in that the material contains fine particles of activated carbon with a specific filtration surface of 800 m ² / g, an iodine number of 800 mg / g, a static exchange capacity for copper from 0, 7 mEq / g and a particle size of 0.15-0.3 mm and a polymer binder with the following ratio of components, wt. %: Activated carbon 80-90 polymer binder 10-20 2. A porous block filter material for purifying drinking water from iron according to claim 1, characterized in that it contains pores with a size of 50-100 microns. 3. A porous block filter material for purifying drinking water from iron according to claim 1, characterized in that as a polymer binder it contains polymers from the classes of polyolefins and / or polyesters and / or their copolymers with a melt index of 2-20 g / 10 min ... according to ASTM D 1238 at 190 ° C and a load of 25 Kg. 4. A method of obtaining a porous block filter material for purifying drinking water from iron according to claim 1 by extrusion or hot pressing of a mixture of powdered materials with a particle size of 0.15-0.3 mm from activated carbon with a specific filtration surface of 900 m ² / g , iodine number from 900 mg / g, static exchange capacity for copper from 0.8 mg-eq / g, with a water content of 8-12% and a polymer binder, and the process is carried out at a mixture compression ratio of 15-20% and a temperature of 10 -40 ° C above the softening point of the polymer binder at the ratio of activated carbon: polymer binder (80-90) :( 10-20) wt. %. 5. A method of obtaining a porous block filter material for purifying drinking water from iron according to claim 4, characterized in that the porous block material is made in the form of plates or hollow bodies of various shapes.

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