RU2564354C1 - Method of producing sorbent based on thermally expanded graphite and sorbent - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing a sorbent based on thermally expanded graphite, modified with iron-containing phases with ferrimagnetic properties, includes the following steps: (A) preparing a mixture of intercalated graphite with a solution of an iron (II) and/or iron (III) salt in an organic liquid which decomposes when heated to release methane, where concentration of the iron salt in the solution is 10-50 wt %; (B) separating the liquid phase from the obtained mixture to obtain a solid phase in the form of intercalated graphite with iron compounds deposited thereon; (C) drying the solid phase to a granular state; and (D) thermally expanding the intercalated graphite with the deposited iron compounds to obtain the end product.

EFFECT: invention enables to obtain a sorbent based on thermally expanded graphite, which contains a magnetic phase represented by ferrimagnetic magnetite and maghemite with improved operational properties.

14 cl, 1 tbl

Description

Technical field

The invention relates to the field of inorganic chemistry, in particular, to the production of sorbents based on thermally expanded graphite with ferrimagnetic properties, which, in particular, can be used to clean various media from industrial pollutants, in particular for collecting spilled oil and other hydrocarbons from the surface of water bodies and soil, and also for localization of oil spills.

State of the art

In recent years, sorbents based on thermally expanded graphite have been used to clean various media from oil products and other hydrocarbons.

The first patents related to such sorbents appeared in the 80s of the last century.

In particular, patent GB 2149769 discloses the use of thermally expanded graphite (TEG) as a sorbent for absorption and solidification of liquid refined petroleum wastes and spent petroleum products. The use of such a sorbent is difficult due to the complexity of collecting spent and oil-saturated sorbent from cleaned surfaces, such as open water bodies, which leads to noticeable losses of the sorbent and insufficient purification of polluted media.

In recent years, the so-called “Magnetic” sorbents, which are powder sorbents with inclusions of ferromagnetic particles, which make it easy to remove contaminants from various media (see, for example, RU 2462303). Giving sorbents magnetic properties can provide a significant increase in the efficiency of their use, since it is possible to introduce sorbents into the medium to be cleaned in the form of a dispersed phase with a controlled interface surface. The collection of saturated sorbent from the surface of the cleaned media can be carried out using equipment equipped with an electromagnet or a permanent magnet.

These magnetic sorbents may contain a carbon component as a base.

RU 2445156 discloses a method for producing a magnetic sorbent, in accordance with which wood chips are treated with a 10% aqueous solution of iron (III) chloride and a 10% aqueous solution of zinc chloride at a certain ratio, then the resulting mixture is stirred, dried and carbonized in an inert gas stream in the temperature range 400-800 ° C, then the product is washed with water, filtered, washed again with water to a neutral medium and dried to constant weight.

The closest technical solution to the proposed one is the method of obtaining the sorbent according to patent RU 134155, comprising mixing intercalated graphite powder with magnetite powder (Fe ₃ O ₄ ) and an organic liquid, subsequent mixing of the resulting mixture, separating the organic liquid and drying the solid phase to a granular state, after which conduct its thermal expansion. In this case, magnetite is used as the iron compound, and gasoline, acetone, diesel fuel or gas condensate are used as the organic liquid. This method allows to obtain graphite sorbent for removing oil and oil products from the surface of the water, which after saturation with oil can be quite easily and almost completely collected from the surface of the water for further regeneration and reuse.

The disadvantages of this method include the uneven distribution of the iron compounds on the surface of the sorbent and the uneven distribution of particle sizes. Due to the fact that magnetite is insoluble in organic liquids, it simply unevenly deposits on the surface of the sorbent, as a result of which not a new stable phase of iron forms on the surface of intercalated graphite, but a simple mixture of intercalated graphite and magnetite that is not bound to its surface. During thermal expansion of oxidized graphite, part of the magnetite deposited on it under severe thermal conditions is able to oxidize to hematite, leading to a loss of magnetic properties of the resulting sorbent.

Disclosure of invention

The objective of the invention is to obtain a sorbent based on thermally expanded graphite containing a magnetic phase represented by ferrimagnetic magnetite (Fe ₃ O ₄ ) and maghemite (γ-Fe ₂ O ₃ ) with improved performance due to the uniform distribution of ferrimagnets on the surface of thermally expanded graphite, uniformity of sizes, due to the possibility and uniformity of the size distribution, as well as the high content of the iron-containing phase and increased magnetic properties.

The problem is solved by a method for producing a sorbent based on thermally expanded graphite modified with iron-containing phases with ferrimagnetic properties, in accordance with which it includes the following stages:

(A) obtaining a mixture of intercalated graphite with a solution of salt of 2 and / or 3 of valence iron in an organic liquid that decomposes upon heating from 600 to 900 ° C with evolution of methane, where the concentration of iron salt in the solution is from 10 to 50 mass. %;

(B) separating the liquid phase from the resulting mixture to obtain a solid phase in the form of intercalated graphite with iron compounds deposited thereon;

(C) drying the solid phase to a free-flowing state; and

(D) thermal expansion of intercalated graphite with iron compounds deposited on it at a temperature of from 600 to 900 ° C to obtain thermally expanded graphite modified with iron-containing phases with ferrimagnetic properties.

In particular embodiments of the invention, the object is achieved by a method in which the thermal expansion of intercalated graphite in step D is carried out in an air atmosphere.

In other particular embodiments of the invention, the object is solved by a method in which the thermal expansion of intercalated graphite in step D is carried out in a reducing atmosphere.

In this case, it is possible to use methane as the reducing atmosphere in stage D.

It is also possible thermal expansion in stage D to carry out in a gas-fired furnace.

As salt 2 and / or 3 of valence iron in stage A in the most desirable embodiments of the invention, a salt selected from the group consisting of Fe (NO ₃ ) ₃ , FeCl ₃ , FeSO _{4 is used} .

The most favorable combination of properties can be realized if a solution with a concentration of 40-50 mass is used as a solution of salt 2 and / or 3 of valence iron in an organic liquid in stage A. %

It is advisable as an organic liquid in stage A to use a liquid selected from the group comprising acetone, a mixture of acetone and octane, butanol-2.

As intercalated graphite in stage A, in the best embodiments of the invention, it is advisable to use nitrate graphite, especially obtained by electrochemical technology

The problem is also solved by a sorbent based on thermally expanded graphite modified with iron-containing phases with ferrimagnetic properties, which was obtained in accordance with the claimed method.

In the best embodiment of this invention, the iron-containing phase of the sorbent with ferrimagnetic properties is a mixture of Fe ₃ O ₄ and γ-Fe ₂ O ₃ oxides.

The sorbent may also contain a mixture of oxides γ-Fe ₂ O ₃ , and α-Fe ₂ O ₃ as an iron-containing phase with ferrimagnetic properties.

The sorbent may also optionally contain superparamagnetic iron (III) oxide nanoparticles with a size of less than 10 nm.

The implementation of the invention

The invention consists in the following.

The advantage of applying organic solutions of iron salts on the surface of intercalated graphite is the uniform distribution of salt on the surface of intercalated graphite, the uniform distribution of size, the ability to control the amount of deposited iron salt by changing the concentration of the solution. The iron salt, as well as the solvent molecules are uniformly sorbed onto the surface of intercalated graphite, firmly binding to it by the mechanism of chemical and physical sorption.

With the thermal expansion of intercalated graphite, it is possible to obtain a sorbent with a different proportion of the magnetic phase evenly distributed over the surface, depending on the thermal expansion atmosphere.

The method is carried out in several stages, in the first of which a mixture of intercalated graphite with a solution of salt of 2 and / or 3 valence iron in an organic liquid is formed, the salt concentration in which is 10-50%.

The term "salts of 2 and / or 3 valence iron" means any salt or mixture of salts in which iron has a valency of 2 and / or 3. The most accessible salts that meet these conditions are the following: Fe (NO ₃ ) ₃ , FeCl ₃ , Fe ₂ (SO ₄ ) ₃ , FeCl ₂ , FeSO ₄ , iron acetate (II), (III), as well as various crystalline hydrates of these salts. These salts, as well as organic solvent molecules, are adsorbed onto the surface of the intercalated compound, forming a stable phase of iron.

At the second stage, thermal expansion of intercalated graphite with iron salts and solvent molecules adsorbed on its surface in the atmosphere of air or methane is carried out when it is heated to form a thermally expanded graphite compound with an iron-containing phase deposited on its surface.

The resulting material is a composite material consisting of thermally expanded graphite particles coated with particles of ferrimagnetics such as magnetite (Fe ₃ O ₄ ) and maghemite (γ-Fe ₂ O ₃ ), as well as a small amount of superparamagnetic iron oxide nanoparticles ( III) with a size of less than 10 nm.

The term "ferrimagnet" means a material in which the magnetic moments of atoms of different sublattices are oriented antiparallel, but the number of spins oriented in opposite directions is different, and therefore the total magnetic moment is nonzero.

The term "superparamagnetic particles" means particles of a sufficiently small size, uniformly magnetized throughout the volume. In the absence of an external magnetic field, the average magnetization of superparamagnetic particles is zero, but in an external magnetic field such particles behave like paramagnets regardless of temperature, the magnetic susceptibility of superparamagnets is much greater than paramagnets.

Heating for thermally expanded graphite can take place, for example, in an air atmosphere or a reducing atmosphere.

The production of thermally expanded graphite with a ferrimagnetic iron-containing phase occurs in two stages. At the first stage, the IG is impregnated with an organic solution of an iron (II) or (III) salt. At the second stage, thermal expansion of the impregnated IG in the atmosphere of methane or air occurs, while the stages are carried out according to the following schemes:

The use of intercalated graphite impregnated in a solution of salts of 2 and / or 3 valence iron to obtain thermally expanded graphite makes it possible to achieve uniform distribution and high content of ferrimagnetic iron compounds, in particular magnetite (Fe ₃ O ₄ ) and maghemite (γ-Fe ₂ O ₃ ) , with particle sizes from a few nanometers to tens of micrometers.

In addition to these iron compounds, as mentioned above, superparamagnetic nanoparticles of iron oxide (III) with a size less than 10 nm are formed, exhibiting superparamagnetic properties.

Thus, during thermal expansion in air, the iron-containing phase is represented by ferrimagnetic particles of γ-Fe ₂ O ₃ , a small number of superparamagnetic particles of iron oxide (III) with a size of less than 10 nm and particles of α-Fe ₂ O ₃ that do not have magnetic properties.

During thermal expansion in a reducing atmosphere, the iron-containing phase contains ferrimagnetic particles Fe ₃ O ₄ and γ-Fe ₂ O ₃ and superparamagnetic nanoparticles of iron oxide (III) with a size of less than 10 nm

This thermally expanded graphite is a hydrophobic material due to the fact that the main component of the free energy of the surface of thermally expanded graphite is dispersion.

A similar effect cannot be achieved in the known method, where the iron-containing component is insoluble in an organic liquid, and the organic liquid itself is used only for wetting intercalated graphite.

As salts of 2 and / or 3 of valence iron, in particular, the following salts can be used: anhydrous FeCl ₃ , FeCl ₃ · 6H ₂ O, Fe (NO ₃ ) ₃ · 9H ₂ O, FeSO ₄ · 7H ₂ O, however this list is not exhaustive.

Thus obtained samples of thermally expanded graphite have a low bulk density (up to 1-2 g / l), a high iron content in terms of pure iron (up to 20 wt.%), A fraction of the magnetic component in the iron-containing phase up to 100%, and a high saturation magnetization ( up to 17 eme / g), the presence of superparamagnetic iron (III) oxide nanoparticles with a size of less than 10 nm (up to 10%), as well as a high sorption capacity with respect to liquid hydrocarbons (up to 100 g / g with respect to oil) and high surface hydrophobicity .

The starting material for producing the sorbent can be intercalated graphite powder obtained by reacting the starting graphite powder with strong oxidizing agents, such as, for example, Bronsted acids and Lewis acids. Such interaction can be carried out both chemically and by electrochemical technology.

The use of nitrate graphite obtained by electrochemical technology as intercalated graphite leads to the formation of a more developed surface than with other technologies, which can further improve properties such as bulk density, iron content, and sorption capacity.

Intercalated graphite is mixed with a solution of salts of 2 and / or 3 of valence iron in an organic liquid with an iron salt concentration of 10 to 50% by weight. When the iron content is less than the lower declared value, the amount of sorbed iron is not enough to impart magnetic properties to the sorbent. When the iron content is at a higher value, a supersaturation of the solution and precipitation of iron are observed. In this case, an uneven distribution of particles of the iron compound on the surface of the IG and an uneven size distribution will be observed.

Suitable organic liquids for implementing the proposed method are widely available acetone, octane, butanol-1, butanol-2, isopropyl alcohol, ethanol, tetrahydrofuran, toluene, methylene, carbon tetrachloride, but other liquids can also be used, as well as mixtures thereof, allowing to dissolve salts 2 and / or 3 valence iron, as well as wetting intercalated graphite.

The operation of thermal expansion can be carried out in the traditional way - by heating in air. In this case, when heated, the organic liquid decomposes with the release of methane, which is able to partially restore the iron-containing phase, which leads to the formation of γ-Fe ₂ O ₃ particles on the surface of thermally expanded graphite, which gives the sorbent ferrimagnetic properties. But in this case, due to thermal expansion in the oxidizing atmosphere of atmospheric oxygen, a rather high amount of antiferromagnetic hematite (α-Fe ₂ O ₃ ) is formed.

However, it is possible to conduct heating directly in a reducing atmosphere.

Methane can be selected as a reducing atmosphere because of its low cost and availability. In this case, magnetite Fe ₂ O ₄ is predominantly formed, as well as a small amount of γ-Fe ₂ O ₃ , and the content of the magnetic component in the iron-containing phase can reach 100%, i.e. Under these conditions, the iron-containing phase is quantitatively reduced to magnetic, which increases the magnetic properties of the sorbents. Also, during thermal expansion in methane, oxygen-containing groups of thermally expanded graphite are reduced, while its hydrophobicity increases.

In both cases, in these temperature conditions, in addition to ferrimagnetic Fe ₂ O ₄ and γ-Fe ₂ O ₃ and antiferromagnetic α-Fe ₂ O ₃ , superparamagnetic iron (III) oxide nanoparticles with a size of less than 10 nm are formed.

The temperature of thermal expansion can vary in a fairly wide range - as follows from the literature, intercalated graphite can thermally expand in the temperature range from 200 to 1200 ° C.

Thermal expansion can also be carried out using a gas-fired oven, in which heating is carried out by a gas burner operating on natural gas, which also creates a reducing atmosphere.

An example embodiment of the invention

To a dry powder of intercalated graphite obtained by electrochemical oxidation in nitric acid, solutions of iron salts (Fe (NO ₃ ) ₃ , FeCl ₃ , FeSO ₄ ) in an organic liquid with an iron salt concentration of 10 to 47% in a ratio of 1 to 5 by weight were added. then the mixture was stirred. As an organic liquid in examples of the method used acetone, a mixture of acetone and octane, butanol-2.

After mixing was completed, the liquid was separated by filtration, and the solid phase was dried to a free-flowing state during the day and heated in an electric furnace in air, in a quartz reactor filled with methane or in a gas-flame furnace in a natural gas medium at a temperature of 350 to 1200 ° C for thermal expansion of intercalated graphite particles.

The resulting product ideally consists of thermally expanded graphite particles with ferrimagnetic particles of oxide Fe ₃ O ₄ (foaming in a gas-flame furnace or in an atmosphere of methane) and γ-Fe ₂ O ₃ (foaming in air) deposited on its surface.

However, as a rule, the composition of the iron-containing phase of graphite foamed in air was a mixture of oxides γ-Fe ₂ O ₃ (up to 20 wt.%) And α-Fe ₂ O ₃ (up to 75 wt.%), In which superparamagnetic nanoparticles of iron oxide (III) (up to 7 wt.%) with a size of less than 10 nm were present.

The composition of the iron-containing phase of graphite foamed in a gas-flame furnace or in a methane atmosphere was a mixture of Fe ₃ O ₄ (up to 80%) and γ-Fe ₂ O ₃ (up to 15 wt.%) Oxides, in which superparamagnetic oxide nanoparticles were also present iron (III) size less than 10 nm, although in some cases the content of Fe ₃ O ₄ and γ-Fe ₂ O ₃ reached its maximum value, and the magnetic phase was completely represented by ferrimagnetic oxides Fe ₃ O ₄ and γ-Fe ₂ O ₃ .

The magnetic characteristics of the sorbent were measured by the following method.

The test for the ability of attraction to the magnet was carried out using permanent Nd-Fe-B magnets with a magnetic field of up to 4 kOe and a strength gradient of 1 kE / mm. For this, the magnet was closely approached to thermally expanded graphite and the presence of elongation was recorded.

The magnetic characteristics of the sorbent were measured by the following method. The magnetic characteristics of the samples (saturation magnetization M _s and coercive force H _s ) were measured on a Faraday weighing magnetometer. The principle of operation of the device is to measure the force F _z when an external magnetic field is applied to the sample. This force is related to the material properties by the following formula:

- градиент напряженности магнитного поля, g - ускорение свободного падения. При условии малого размера образца $$\frac{\partial H}{\partial z}=const$$

, поэтому возможно измерение силы вдоль оси z с помощью чувствительных весов с последующим построением петли магнитного гистерезиса и вычислением магнитных характеристик образцов. Максимальная напряженность приложенного магнитного поля составляла 18000 Э. Измерения выполнены при комнатной температуре с погрешностью 5%.where χ is the magnetic susceptibility and m is the mass of the sample, H is the intensity, and $$\frac{\partial H}{\partial z}$$

is the gradient of the magnetic field, g is the acceleration of gravity. Subject to small sample size $$\frac{\partial H}{\partial z}=const$$

Therefore, it is possible to measure the force along the z axis using sensitive weights, followed by constructing a magnetic hysteresis loop and calculating the magnetic characteristics of the samples. The maximum intensity of the applied magnetic field was 18000 E. The measurements were performed at room temperature with an error of 5%.

The test for the ability of magnetically attracting PG / α-Fe samples after sorption of hydrocarbons was studied using Nd-Fe-B permanent magnets with a magnetic field strength of up to 4 kOe and an intensity gradient of up to 1 kE / mm. For this, the magnet was closely approached to penografit and the presence of elongation was recorded.

According to measurements of the ability to attract to the magnet and saturation magnetization M _s : "+ -" - M _s = 0-1 eme / g; "+" - M _s = 1-2 eme / g; «+» - M _s = 2-3 emu / g; "++" - M _s = 3-5 eme / g; "+++" - M _s => 5 eme / g.

Sorption properties were measured in accordance with the following.

Samples of thermally expanded graphite of known mass in powder form were placed in a mesh basket with a cell diameter of 1 mm ² and then together with the basket were placed in a glass container containing sorbate (oil) with a liquid thickness of 5 cm. After 15 minutes, the mesh basket was removed from the container and settled within 30 s. Next, the sample was weighed and sorption capacity (S) was determined in units of g of absorbed substance per 1 g of sample according to the following formula:

S = (m _{GH after sorption} -m _{GH before sorption} ) / m _{GH before sorption}

The contact wetting angle was measured on an Attension The Sigma Tensiometer System instrument, and the wettability of thermally expanded graphite samples compressed into a shape of tablets with a diameter of 1.27 cm and a density of 0.03 g / cm ^{3 was} studied with respect to water and octane using the Wilhelmy method: the test sample was fixed on the scales and immersed in the test liquid to a depth of 5 mm at a speed of 5 mm / min and fixed the change in the F / L value from the immersion depth, where F is the force acting on the sample and L is the perimeter of the wetted sample. Contact wetting angles were determined by the formula:

cosθ = F / (σ · L), where σ is the surface tension of the fluid.

In the process of analysis, the contact wetting angles were measured during immersion (θ _adv ) and extraction (θ _rec ), then the equilibrium contact angle (θ _equ ) was _determined by the formula:

cosθ _equ = 0.5cosθ _adv + 0.5cosθ _rec

The polar and dispersion components of the surface energy of penografit were determined by the method of Ouns, Wendt, Rabel and Kjelble:

where σ _L is the surface tension of the liquid, σ _L ^D , σ _L ^P is the dispersion and polar component of the surface tension of the liquid, σ _S ^D , σ _S ^P is the dispersion and polar component of the free energy of the surface of the solid.

Table 1 shows the test results of the sorbents depending on the content of iron in the sorbent, the type of salt, solvent, etc.

As follows from the data in the table, the sorbent in accordance with the invention has improved consumer properties, which will allow it to be used for cleaning contaminated environments, including water, from industrial pollutants, in particular for collecting spilled oil and other hydrocarbons from the surface of water bodies and soil, and also for localization of oil spills.

Claims (14)

1. A method of producing a sorbent based on thermally expanded graphite modified with iron-containing phases with ferrimagnetic properties, characterized in that it includes the following stages:
(A) obtaining a mixture of intercalated graphite with a solution of salt of 2 and / or 3 of valence iron in an organic liquid that decomposes upon heating from 600 to 900 ° C with evolution of methane, where the concentration of iron salt in the solution is from 10 to 50 mass. %;
(B) separating the liquid phase from the resulting mixture to obtain a solid phase in the form of intercalated graphite with iron compounds deposited thereon;
(C) drying the solid phase to a free-flowing state; and
(D) thermal expansion of intercalated graphite with iron compounds deposited on it at a temperature of from 600 to 900 ° C to obtain thermally expanded graphite modified with iron-containing phases with ferrimagnetic properties. 2. The method according to p. 1, characterized in that the thermal expansion of intercalated graphite in stage D is carried out in an air atmosphere. 3. The method according to p. 1, characterized in that the thermal expansion of intercalated graphite in stage D is carried out in a reducing atmosphere. 4. The method according to p. 3, characterized in that methane is used as the reducing atmosphere in stage D. 5. The method according to p. 3, characterized in that the thermal expansion in stage D is carried out in a gas flame furnace. 6. The method according to p. 1, characterized in that as a salt of 2 and / or 3 of valence iron in stage A, a salt selected from the group consisting of Fe (NO ₃ ) ₃ , FeCl ₃ , FeSO _{4 is used} . 7. The method according to p. 1, characterized in that as a solution of salt 2 and / or 3 of valence iron in an organic liquid in stage A, a solution with a concentration of 40-50 mass. % 8. The method according to p. 7, characterized in that as an organic liquid in stage A, a liquid selected from the group consisting of acetone, a mixture of acetone and octane, butanol-2 is used. 9. The method according to p. 1, characterized in that as intercalated graphite in stage A, nitrate graphite is used. 10. The method according to p. 9, characterized in that they use nitrate graphite obtained by electrochemical technology. 11. Sorbent based on thermally expanded graphite modified with iron-containing phases with ferrimagnetic properties, characterized in that it is obtained in accordance with any of paragraphs. 1-10. 12. The sorbent according to claim 11, characterized in that the iron-containing phase of the sorbent with ferrimagnetic properties is a mixture of Fe ₃ O ₄ and γ-Fe ₂ O ₃ oxides. 13. The sorbent according to claim 11, characterized in that the iron-containing phase with ferrimagnetic properties is a mixture of oxides γ-Fe ₂ O ₃ and α-Fe ₂ O ₃ . 14. The sorbent according to claim 11, characterized in that it further comprises superparamagnetic nanoparticles of iron oxide (III) with a size of less than 10 nm.