RU68353U1 - PHOTOCATALYTIC DEVICE FOR AIR CLEANING - Google Patents

Abstract

The utility model relates to the field of photocatalytic gas purification, including air, and can be used for air purification in residential and working premises from various organic and inorganic air pollutants. The photocatalytic device comprises a housing and a dust filter placed in the housing, a photocatalytic unit and a fan. The device is equipped with a catalytic filter installed at the output of the photocatalytic unit along the air stream. The catalytic filter is made in the form of a homogeneous capillary structure, the channels of which are located along the air flow, or from a material having a porous structure with open pores, on the inner walls of which a superoxide decomposition catalyst based on Fe / activated carbon nanoparticles is deposited.

The proposed device allows to minimize the content of products of incomplete oxidation of hydrocarbons, including organic superoxides, at the output of the photocatalytic device for air purification and, accordingly, to eliminate the negative consequences of their presence in the cleaned air, including unpleasant odors in residential and other rooms.

1 n.p., 4 w.p.

Description

The utility model relates to the field of photocatalytic gas purification, including air, and can be used for air purification in residential and working premises from various organic and inorganic air pollutants.

Currently, devices for the photocatalytic purification of gases, in particular air, using the phenomenon of oxidation of organic and inorganic substances adsorbed on the surface of a photocatalyst under the influence of ultraviolet radiation with a wavelength of less than 400 nm of air, are widely used due to their versatility in the destruction of almost all organic and many inorganic air pollutants. Typically, such devices contain a dust filter with a filtration class of at least G4, an adsorption filter containing activated carbon or other adsorbents, and a photocatalytic molecular purification unit. The photocatalytic unit is designed to oxidize volatile organic and certain inorganic impurities in air to harmless components (mainly carbon dioxide and water vapor) on the surface of a catalyst activated by soft UV light (A. Fujishima at al. "TiO2 Photocatalysis. Fundamental and Applications. "English translations, BKC Inc., Tokyo, Japan, 1999). However, these devices, in comparison with devices using other methods of air purification (adsorption, combustion, etc.), have a relatively low cleaning speed. Another disadvantage of these devices is the rapid decrease in the activity of the photocatalyst during the decomposition of aromatic and heteroatomic organic compounds. In addition, at concentrations of many hydrocarbon pollutants in the room exceeding 1-l0 ppm (ppm - part per million - the number of pollutant molecules per 1 million air molecules), products of incomplete oxidation of hydrocarbons appear at the output of photocatalytic air purification devices, and, in particular, organic superoxides. Superoxides are substances with the general chemical formula R ₁ - (O) _n -R ₂ , where n is 2, 3, 4, and R ₁ and R _{2 are} organic radicals or a hydrogen atom. The simplest superoxide is hydrogen peroxide. These compounds are strong oxidizing agents and are harmful to health (V.L. Antonovsky, S.L. Khursan, Physical chemistry

organic peroxides, M., ICC "Akademkniga", 2003, p. 30). Moreover, they already at very low concentrations of 1-10 ppb in the air have a sharp unpleasant odor, an example of which is an unpleasant odor in rooms after placing new furniture made of particleboard in them, performing repairs, etc.

At the same time, by the totality of their characteristics, photocatalytic devices are by far the most optimal and used devices for air purification in residential and working rooms of a relatively small volume, which ensured their greatest distribution in comparison with other types of purifiers, as well as conducting work on their further improvement .

A photocatalytic device for purifying air and gases from organic impurities is known, including a photocatalytic element containing a porous carrier made in the form of a tube, plate, hemisphere or cone of several layers of sintered glass beads, the surface of which is coated with anatase titanium dioxide powder (patent RU 2151632 , B01D 53/86, B01J 21/06, 1998). The specified device allows you to increase the speed of air purification by increasing the surface of the active layer of titanium dioxide, however, this increase is very small and, in addition, does not provide the elimination of other disadvantages inherent in devices of this type.

A photocatalytic device for purifying air and gases is known, including a fan, a photocatalytic unit containing porous ceramic supports with a titanium dioxide-based photocatalyst and an ultraviolet radiation source, as well as blocks for saturating the initial gas mixture with hydrogen peroxide vapor (patent specification RU 2259866, B01D 53 / 86, B01J 21/06, 1998). The specified device allows you to increase the rate of oxidation of organic substances and reduce the rate of deactivation of the catalyst, but does not allow to reduce the concentration of superoxides at the exit of the photocatalytic unit and, accordingly, to eliminate the unpleasant odor.

The closest analogue to the claimed device, selected as a prototype, is an adsorption-photocatalytic device for purifying air from volatile pollutants, comprising a housing, a dust filter, a photocatalytic unit and a fan (utility model patent RU 33035, B01J 20/00, F24F 3 / 16, 2003), in which an attempt was made to eliminate intermediate reaction products of the photocatalytic oxidation of hydrocarbons using a special adsorption filter installed along the flow between the dust filter

and photocatalytic unit. This filter partially eliminates these disadvantages, since the heat of adsorption of hydrocarbons on such a filter is small (10-20 kJ / mol) and therefore at room temperature it is able not only to absorb contaminants from the gas phase, but also to desorb them back into the air stream. In the case of short-term emissions of pollutants into the air, such a filter really reduces the concentration of intermediate products at the output of the photocatalytic unit, including the concentration of superoxides. However, in many rooms the sources of organic air pollution are constant and physically cannot be eliminated. Such sources may include building and furniture plastics, solvent fumes, paints and sealants, books, etc. With a constant supply of contaminants, this filter does not reduce the concentration of volatile organics entering the photocatalytic purification unit, since it is in a state saturated with this organic substance. Accordingly, the proposed adsorption filter cannot reduce the concentration of superoxides at the output of the device and eliminate the unpleasant odor.

The technical problem solved by the proposed utility model is the creation of a photocatalytic device for air purification, which minimizes the content of products of incomplete oxidation of hydrocarbons, including organic superoxides, at the output of the device during operation of the latter in rooms contaminated with hydrocarbons and, accordingly, eliminating the negative consequences of their presence in cleaned air, including unpleasant odors in residential and other rooms.

This task is ensured by the fact that, in contrast to the known device comprising a housing, a dust filter, a photocatalytic unit and a fan, it is new that the device is equipped with a catalytic filter mounted at the output of the photocatalytic unit along the air stream.

In addition, the catalytic filter is made in the form of a homogeneous capillary structure, the channels of which are located along the air flow, or from a material having a porous structure with open pores, on the inner walls of which a decomposition catalyst for superoxides is deposited.

In addition, the superoxide decomposition catalyst is based on Fe / activated carbon nanoparticles.

In addition, when performing the filter in the form of a uniform capillary structure, the length of the channels and their diameter are selected from the condition of providing at least

one collision of a superoxide molecule with a channel wall and a catalytic surface according to the ratio:

where: d is the diameter of the channel, mm;

L is the length of the channel, mm;

D _SO - diffusion coefficient of superoxide molecules in air under normal conditions, m ² / s;

D _SO is selected in the range ;

V is the linear velocity of the air flow along the channel, m / s.

In addition, when the filter is made of a material having a porous structure with open pores, the minimum filter thickness and the number of pores per unit length are selected from the condition that at least one superoxide molecule collides with the filter wall and the catalytic surface according to the ratio:

where: L is the minimum thickness (length) of the filter, mm;

N is the number of pores per unit length (per 1 m) in any direction, 1 / m;

D _SO - diffusion coefficient of superoxide molecules in air under normal conditions, m ² / s;

D _SO is selected in the range ;

V is the linear velocity of the air flow along the channel, m / s.

The use of a catalytic filter in the design of a photocatalytic device for air purification makes it possible to clean the air stream at the output of the photocatalytic unit from intermediate products of the photocatalytic oxidation of hydrocarbons and, accordingly, eliminate the negative consequences of their presence in the cleaned air.

The implementation of the catalytic filter in the form of a homogeneous capillary structure, the channels of which are located along the air flow, or from a material having a porous structure with open pores, on the inner walls of which a catalyst for decomposition of superoxides is deposited allows efficient cleaning of the air flow with relatively simple means and thereby improve manufacturability devices.

The implementation of the decomposition catalyst for superoxides based on Fe / activated carbon nanoparticles allows the decomposition of superoxides to harmless compounds at concentrations of 1-10 ppb and odorless;

The choice of parameters of the catalytic filter according to the ratios:

when pumping air through channels (1) or pores (2) during the movement of superoxide molecules through the filter, at least one collision of superoxide molecules with a catalytic surface ensures that superoxides decompose with probability close to 1 to harmless compounds at concentrations of 1-10 ppb and odorless.

The essence of the proposed technical solutions is illustrated by the following drawing:

Figure 1 is a longitudinal section of a photocatalytic device

The proposed device consists of a housing 1, in which a dust filter 2, a photocatalytic unit 3, including a porous carrier 4 with a photocatalyst based on titanium dioxide and an ultraviolet radiation source 5, at the output of which a catalytic filter 6 is installed, are sequentially installed along the air flow. made of a material having a homogeneous open-pore capillary or porous structure, on the inner walls of which a superoxide decomposition catalyst is applied, made on the basis of Fe / activated carbon nanoparticles. The device is equipped with a fan 7 to provide forced supply of cleaned air to the photocatalytic device installed at the outlet or inlet of the device. The parameters of the catalytic filter 6 are selected from the condition of providing, when air is pumped through the channels or pores of the collision of superoxide molecules with the catalytic surface, which ensures the decomposition of superoxides to compounds harmless at concentrations of 1-10 ppb and odorless with a probability of close to 1. For this, in the case of a filter in the form of a homogeneous capillary structure (made, for example, of ceramics, metals or plastic), the channels of which are located along the air flow and have a length L, the diameter of the channel d is chosen so as to ensure at least at least one collision of a superoxide molecule with a channel wall and a catalytic surface, namely, according to the ratio:

where: D _SO is the diffusion coefficient of superoxide molecules in air under normal conditions, m ² / s;

V is the linear velocity of the air flow along the channel, m / s.

The filter can also be made of open-cell isotropic materials, such as polyurethane foam, ceramic foam, foam metals. The pore surface of these materials should also be coated with a highly effective superoxide decomposition catalyst. In this case, the minimum thickness (length) of the filter L and the number of pores N per unit length (per 1 m) in any direction are also selected from the condition of providing a single collision of the superoxide molecule with the wall of the catalytic filter according to the ratio:

or taking into account the values of k and m

where: m is the porosity of the foam, i.e. the ratio of the pore volume in the sample to the geometric volume of the sample.

For materials based on foamed polyurethane with open pores m = 0.95.

k is a geometric parameter that describes the increase in the path length of the air flow compared to the geometric thickness (length) of this material in the direction of air flow. For foams, k = 2.

V is the linear velocity of the air flow in the cross section of the filter, m / s.

For reliable operation of the filter when selecting its parameters according to formulas (1) and (2), the value of the diffusion coefficient D _SO is selected in the range , which corresponds to diffusion coefficients of superoxides with a molecular weight of more than 120 AU in air under normal conditions, i.e. at a pressure of 101 KPa and a temperature of 20 ° C. In this case, the probability of collision with the catalytic surface of the walls of the channels or pores for superoxides with a lower molecular weight becomes close to 1.

The device operates as follows. The cleaned air is pumped through a fan 7 through a photocatalytic device, where in the course of the air flow it is sequentially passed through a dust filter 2, which purifies the air from dust particles, a photocatalytic block 3, where the volatile organic and some inorganic are oxidized on the catalyst surface under the influence of ultraviolet radiation impurities present in the air to harmless components, after which the cleaned air is passed through a catalytic filter Filter 6, where, when air passes through the channels or pores of the filter, a collision of the superoxide molecules remaining in the air, after the photocatalytic reaction, with the catalytic surface occurs, which ensures the decomposition of superoxides to harmless compounds at concentrations of 1-10 ppb and odorless.

In the above examples, to measure the concentration of superoxides at the outlet of a photocatalytic device equipped with a catalytic filter (Figure 1), the Optek 3.02 PA chemiluminescent gas analyzer, made in Russia, was used. Acetone vapor was added to the air entering the photocatalytic purifier. Acetone vapor concentration was maintained at 20 ppm.

Example 1. The catalytic filter was made of corrugated aluminum foil 0.15 mm thick and 30 mm wide. The filter had triangular channels with an inscribed circle diameter of 1.2 mm. An Fe / active carbon nanoparticle catalyst was applied to the surface of the foil after forming the filter. As a result, the catalytic filter had a thickness of 30 mm, the effective diameter of the channels was 1 mm, and the overall dimensions of the filter were 100-100 mm. The catalytic filter 6 was installed at the output of the photocatalytic unit 3 in front of the fan 7. The air flow rate was varied in the range from 1.5 m / s to 5 m / s by increasing the supply voltage of the DC motor of fan 7. The intake pipe of the superoxide concentration meter was placed in the air stream fan. The results of measuring the concentration of superoxides depending on the air flow rate are presented in table 1.

Table 1 No. Air speed, m / s Concentration of superoxide at the outlet, ppb Note one 1,5 fifteen filter not installed 2 5 fifteen filter not installed 3 1,5 less than 1 filter installed four 2,5 less than 1 filter installed 5 3 1,2-2 filter installed 6 four 5 filter installed 7 5 10 filter installed

Given the geometric parameters of the filter, i.e. the channel length L is 30 mm, the channel diameter is 1 mm, formula (1) allows you to calculate the maximum linear air flow rate at which the catalytic filter effectively cleans the air of superoxides:

V = 1.8-2.4 m / s

at a diffusion coefficient of superoxide molecules in air D _SO from before .

Example 1 shows that a filter consisting of uniform (identical in diameter) channels, the walls of which are coated with a superoxide decomposition catalyst, effectively destroys superoxides if the passage time through the channel is sufficient for at least one collision of these molecules with the channel wall. The geometric parameters of the filter for a given air performance of the photocatalytic air purification device can be calculated by the formula (1). Moreover, as follows from example 1, with an increase in the air flow rate over 2.4 m / s, to increase the efficiency of the filter, it is necessary to increase its length. The efficiency of the filter is also proportional to the number of channels and inversely proportional to their diameter, because on the one hand, it depends on the filter resistance to the passage of air flow, which is desirable to minimize, and on the other hand, on the conditions for ensuring guaranteed collision of superoxide molecules with the channel wall. These parameters are optimized taking into account technological limitations.

Example 2. The catalytic filter is made in the form of an open-pore polyurethane plate with a pore number per 1 m N equal to 1000. The pore surface was coated with a superoxide decomposition catalyst. Plate thickness with dimensions mm ranged from 10 mm to 60 mm. The filter was installed as in example 1. The linear velocity of the air flow through the filter was maintained using fan 3 equal to 2.5 m / s. In the incoming air stream, the acetone vapor concentration was 20 ppm. The results of measuring the concentration of superoxides at the outlet of the photocatalytic air purification device depending on the thickness (length) of the installed catalytic filters are presented in table 2.

table 2 No. The thickness of the catalytic filter, mm Concentration of superoxide at the outlet, ppb one 10 10 2 twenty 5 3 thirty less than 1 four 40 less than 1 5 fifty less than 1 6 60 less than 1

The concentration of superoxides at the output of the photocatalytic device not containing a catalytic filter, under the conditions described above, was 15 ppb.

A comparison of the experimentally found minimum thickness of the catalytic filter, at which superoxides are completely destroyed, with the value L calculated by formula (2) at a given flow rate and the number of pores per unit length of the porous material shows the possibility of using this formula to select a variable parameter of the catalytic filter, in in this case, L, when destroying superoxides and the associated unpleasant odor in the cleaned air stream.

The proposed photocatalytic device for air purification can be widely used in the creation and use of equipment for air purification in residential and working premises from various organic and inorganic air pollutants, because It allows to purify the air stream at the output of the photocatalytic unit from products of incomplete oxidation of hydrocarbons formed during the photocatalytic reaction under conditions of high concentrations of hydrocarbon pollutants in the air being cleaned, and, in particular, organic superoxides that are harmful to health and have a sharp unpleasant odor. At the same time, a reduction in the level of superoxides to a safe level and the complete elimination of unpleasant odors in residential and work premises is achieved, which ensures compliance with environmental requirements.

Claims (5)

1. A photocatalytic device for air purification, comprising a housing and a dust filter placed in the housing, a photocatalytic unit and a fan, characterized in that the device is equipped with a catalytic filter mounted at the output of the photocatalytic unit along the air stream. 2. The photocatalytic device according to claim 1, characterized in that the catalytic filter is made in the form of a homogeneous capillary structure, the channels of which are located along the air flow, or from a material having a porous structure with open pores, on the inner walls of which a superoxide decomposition catalyst is applied. 3. The photocatalytic device according to claim 2, characterized in that the superoxide decomposition catalyst is based on Fe / active carbon nanoparticles. 4. The photocatalytic device according to claim 2, characterized in that when the filter is made in the form of a uniform capillary structure, the length of the channels and their diameter are selected from the condition of providing at least one collision of the superoxide molecule with the channel wall and the catalytic surface according to the ratio:

where d is the diameter of the channel, mm; L is the length of the channel, mm; D _SO - diffusion coefficient of superoxide molecules in air under normal conditions, m ² / s; D _SO is selected in the range (6-8) · 10 ^-6 m ² / s; V is the linear velocity of the air flow along the channel, m / s. 5. The photocatalytic device according to claim 2, characterized in that when the filter is made of a material having a porous structure with open pores, the minimum filter thickness and the number of pores per unit length are selected from the condition that at least one superoxide molecule collides with the filter wall and catalytic surface according to the ratio:

where L is the minimum thickness (length) of the filter, mm; N is the number of pores per unit length (per 1 m) in any direction, 1 / m; D _SO - diffusion coefficient of superoxide molecules in air under normal conditions, m ² / s; D _SO is selected in the range

V is the linear velocity of the air flow along the channel, m / s.