RU2272669C2 - Process for isolating volatile chemical compounds from gas-air mixtures - Google Patents

Abstract

FIELD: gas treatment processes.

SUBSTANCE: process comprises passing gas-air mixture through powdered polymer adsorbent bed followed by desorption, said powdered polymer adsorbent being, more specifically, polyvinylchloride powder with particle size 0.16 to 10.00 mm and total particle porosity 29 to 52%. Adsorption is conducted in periodic mode in fixed bed adsorbers. Desorption is effected under vacuum at residual pressure from 0.001·104 to 2.5·104 Pa.

EFFECT: enabled quantitative isolation of a wide spectrum of organics at simplified purification technology.

1 tbl, 23 ex

Description

The invention relates to the field of chemical technology, and in particular to a method for the extraction of volatile chemical compounds from air-gas mixtures using a polyvinyl chloride-based polymer adsorbent, and can be used to purify gas-air emissions in chemical plants and to extract target volatile chemical compounds in exhaust gases during recovery.

One of the important problems of chemical production is the formation of gas-air mixtures, as a result of which there is an irretrievable loss of expensive chemical components, the emissions of which lead to environmental pollution. Sources of air pollution are all gas and petrochemical, coal chemical, many biochemical, plasma chemical and paint and varnish production, power plants and motor vehicles operating on the basis of hydrocarbon energy carriers.

Air purification from organic compounds, depending on the source of pollution and material and technical capabilities, is carried out using various catalytic systems, adsorbents, absorbents, adsorption and membrane technologies, microbiological purification and combustion technologies, cryogenation, photooxidation and oxidation when an electric discharge is applied to a gas-air mixture and accelerated electrons. Catalytic methods for purifying air from hydrocarbons, carbon oxides, and nitrogen include contacting the gas flows with the catalysts. As catalysts for the process, platinum and rhodium (US Pat. 5490977 USA, 02/13/1996), iron shavings (US Pat. 2048174 of the Russian Federation, 11/20/1995), copper, manganese, chromium oxides or a mixture of oxides of these metals deposited on a metal carrier are used as catalysts. (Pat. 21114686 RF, 07/10/1998), palladium in a composition with oxides of nickel, aluminum, chromium and a mixture of oxides of palladium, nickel, chromium and aluminum (Pat. 2054959 RF, 02/27/1996). Contacting of gas flows with catalytic systems is carried out at a temperature of 160-1100 ° C.

A known method of cleaning gas emissions containing 0.0005-0.05 wt.% Vinyl chloride (US Pat. 4045538 USA, 1977) by the catalytic oxidation of vinyl chloride by the action of oxygen at a temperature of 250-300 ° C. The activity of the catalyst depends on the oxidation temperature of vinyl chloride, the relative humidity of the gas containing vinyl chloride, and on the initial and final concentration of vinyl chloride in the gas. It decreases during the oxidation of vinyl chloride as a result of reversible poisoning with water, so the catalyst is regenerated. The disadvantages of this method are its complexity and restriction on the content of vinyl chloride in gas emissions (not more than 0.05% wt.).

A known method for the extraction of vinyl chloride from gas emissions with its content from 1 * 10 ^-4 to 0.1 wt.%, Which consists in processing gas emissions at a temperature of 80 ° C with a suspension containing 2-60 wt.% Polyvinyl chloride (PVC) with a size grains of 40-300 mesh. (50-350 microns), dispersion stabilizer and surfactant. Vinyl chloride is desorbed by direct steam. The method allows to reduce the content of vinyl chloride in gas emissions by 10-100 times. The disadvantages of the method include a restriction on the initial content of vinyl chloride, which does not allow it to be used to clean concentrated emissions. A significant drawback is the low degree of purification of gas emissions. In addition, special measures must be taken to prevent the pricing and subsidence of the suspension (JP 52-130479, 1977).

Adsorption methods for purifying gas-air emissions from organic compounds are based on the use of traditional polymeric resins, polymeric materials, activated carbon, carbon fibers (US Pat. )

In particular, an unconventional adsorbent is known designed to absorb hydrocarbons from the vapor phase, containing coordination polymers based on lithium tert-butyl trialkyl borates [tert-C ₄ H ₉ OB (OR) ₃ Li: (R = C ₄ H ₉ -C ₁₁ H ₂₃ ) deposited on the surface of fibers and solid porous materials (US Pat. 2032459 RF, 04/10/1995). It is obvious that absorbents should absorb organic compounds from gas-air mixtures more efficiently than adsorbents. However, very few absorbents are known to date. So to remove chlorinated hydrocarbons from the exhaust air using a mixture of organic compounds with a high boiling point (application 4319102 Germany, 12/18/1994). The exhaust air is cleaned of hydrocarbons, alcohols, aldehydes, ethers by contacting the gas-air mixture with an aqueous emulsion containing peroxides and surfactants, followed by contacting the air and aqueous phase at 105 ° C with metal oxides IB, IIB, IV, V, VI, VIIB and VIII groups (German application 19530896, 01 D 53/75). Open cell pores (perforations) of various sizes, treated with a viscous solution of polybutene in 1,1,1-trichloroethane, are used as adsorbent in an air filter for automobile engines (US Pat. 5573811 USA, 12.11.1996).

From RU 2112582, 06/10/1998, filter material for cleaning liquid and gaseous substances is known made of activated carbon continuous porous monofilament with a diameter of 4-10 μm, a specific surface area of 590-2550 m ² / g and a sorption pore volume of 0.63-1.82 cm ³ / g, the surface of which is covered with a porous shell of silicon dioxide in an amount of 0.8-9.8% by weight of the fiber, moreover, this material is made in the form of a thread, cord or fabric. However, the specified filter material is obtained by a rather complicated technology, including the impregnation of cellulose hydrated fiber with a solution of organosilicon polymer in an organic solvent with a concentration of 0.8-4.2 wt.% For 2.5-15 minutes, its drying in air at 105-140 ° C, carbonization at 550-985 ° C in a protective gas environment and activation in an oxidizing environment at 855-960 ° C for 3-55 minutes. From RU 94025664, 06/27/1996, a sorbent based on porous granular ionite and iron (III) hydroxide is known to be more effective in extracting toxic anionic substances from aqueous and gaseous media by realizing the ion-exchange ability of the ion exchanger and increasing the content of iron hydroxide deposited in it pores. This sorbent is obtained by treating an ion exchanger with a solution of an iron (III) salt followed by precipitation of iron hydroxide with an alkali or ammonia solution, while porous granular anion exchangers are used as an ion exchanger and they are treated with an iron salt solution in media giving iron (III) anions (saturated solution) sodium chloride, 8 N., 11 N., hydrochloric acid, 0.01 N. sulfuric acid, etc.). Strong and weakly basic anion exchangers with different polystyrene, epoxy polyamide, vinyl pyridine, and other matrix structures are used as anion exchangers. The synthesized sorbents have a high absorption capacity for sulfide anions both due to anion exchange sorption and due to a higher content of active iron hydroxide. However, they can be used mainly for the purification of water and gases from other toxic substances of the anion type, for the extraction of which anion exchangers and adsorbents based on iron hydroxide borates, silicic acid, arsenic compounds and others are used. In addition, the used KU-2 cation exchanger is only a porous granular carrier of active iron hydroxide; its ion-exchange ability is realized only upon receipt of the sorbent, and not when it is used in purification processes.

If the methods described here are evaluated (analyzed) in terms of cost-effectiveness, environmental friendliness, manufacturability and selectivity, then the predominant importance of absorption and adsorption methods in all nominations is obvious.

For example, for technological conditions for the implementation of the adsorption method for the absorption of hydrocarbons from a gas-air medium, the use of expensive precious metals is not required, as in the catalytic method for the destruction (decomposition) of hydrocarbons. Technological equipment for implementing the adsorption method and equipment for fulfilling safety standards can be used in the simplest version. While for the neutralization of gaseous hydrocarbons at high and low temperatures, high-voltage electric discharge and accelerated electrons, equipment that meets the highest technical and technological requirements is required. Hydrocarbons by the adsorption method do not decompose (are not destroyed) to water and carbon dioxide, as in the technologies of catalysis, combustion and oxidation using an electric discharge and accelerated electrons, but accumulate in the pores of the adsorbent. This increases the competitive ability of the method in terms of environmental friendliness and profitability.

Known adsorbent (GOST 26996-86), used for adsorption of hydrocarbons from a gas-air mixture - polypropylene isotactic structure (GOST 26996-86).

The disadvantage of polypropylene adsorbent is its low adsorption capacity due to its high crystallinity. From Fr 2498470, 07/30/1982 a sorbent based on a macroporous polymer is known - a homo- or copolymer of ethyl vinyl benzene or divinyl benzene with styrene. However, this sorbent has a limited purpose and is used only for the separation of gas or liquid. An adsorbent is known from RU 2182849, 05.27.1992, which is a mixture of propylene stereopolymers with an atactic polypropylene content of 5 to 50 wt.% And is synthesized by suspension polymerization of propylene in heptane at a temperature of 50-70 ° C in the presence of a catalytic system: MSC-TiCl ₃ -Al (C ₂ H ₅ ) _x Cl _y , where MSC is a microspherical catalyst, TiCl ₃ is titanium trichloride, Al (C ₂ H ₅ ) _x Cl _y is ethyl aluminum chlorine-containing compounds.

The adsorption of hydrocarbons is carried out by passing (filtering) a gas-air mixture through an adsorbent bed, then the captured substances are desorbed from the adsorbent.

In the invention, a very complex mixture of aliphatic and aromatic hydrocarbons under the general name “Nefras” was used as an adsorbate, which is a waste product of the production of a microspherical catalyst at the Tomsk Petrochemical Plant. After five cycles of adsorption-desorption, the capacity of adsorbents decreases by only 5-8%.

An adsorbent with a content of atactic polypropylene fraction higher than 50 wt.% Passes from a powdery porous state to a paste, therefore it is not technologically advanced in use.

The closest in technical essence to the claimed invention is a known method for the extraction (adsorption) of aliphatic, aromatic, unsaturated hydrocarbons and halogen derivatives from the gas phase by passing (filtering) the gas-air flow through the adsorbent layer in the filter, followed by regeneration of the adsorbent by blowing air through the adsorbent layer (RU 2225756, March 20, 2004). To accelerate the process of regeneration of the adsorbent, the blowing of its layer with air is carried out at 50-60 ° C. The desorption of nephras from the adsorbent is controlled by the gravimetric method. After regeneration of the adsorbent, the process of absorption of hydrocarbons from the nefraso-air stream is repeated until the adsorbent capacity is fully utilized. As the adsorbent in the known method, an adsorbent is used, which is obtained by melt mixing from 5 to 15 wt.% Of atactic polypropylene with isotactic polypropylene in a Bembury-type mixer at a temperature of 170 ° C, 200 rpm of worms for 7-8 minutes. The resulting product, after cooling in liquid nitrogen, is crushed (crushed) by high-voltage pulses with a frequency of 7 s ^-1 , an amplitude of 200 kV and an energy of 500 J. To absorb hydrocarbons from the air-gas stream, an adsorbent fraction with a particle size of 200-500 μm is selected (seeded). Hydrocarbon adsorption is carried out by passing (filtering) the gas stream through the adsorbent layer in the filter. As an adsorbate, a complex mixture of aliphatic and aromatic hydrocarbons under the general name "Nefras" was used, which is a waste in the production of catalyst at the Tomsk Petrochemical Plant.

The known method is as follows. The gas-air flow is formed using a compressor at an initial pressure of 2.026 * 10 ⁴ Pa and with a rate of removal of the sorbate (nefras) from the bubbling tank 7-8 ml / h. The nefraso-air flow formed in this way is let through a layer of powdered adsorbent (PP, PAP-5, PAP-10, PAP-15 polypropylene) in the filter until the adsorption thermodynamic equilibrium is established. The amount of nephras absorbed by the adsorbent is determined by the gravimetric method. After equilibrium is established, the adsorbent is regenerated by blowing air through the adsorbent bed. The described known method for cleaning gas emissions from volatile chemical compounds has limited use due to the imperfection of the desorption stage, as well as its insufficient efficiency with respect to chlorinated hydrocarbons. The technical task of the present invention is to increase the efficiency of extraction of a wide range of organic substances from gas-air mixtures and simplify the extraction process.

The stated technical problem is achieved by the fact that in the method for the extraction of volatile chemical compounds, including organochlorine compounds, esters, hydrocarbons from gas-air mixtures, including passing the gas-air mixture through a layer of powdered polymer adsorbent and its subsequent desorption, polyvinyl chloride powder with a particle size is used as a powdered polymer adsorbent 0.16-10.00 mm and a total porosity of 29 to 52%, desorption is carried out under vacuum, with a residual pressure of 0.001 * 10 ⁴ Pa to 2.5 * 10 ⁴ Pa, and the process is carried out using alternating adsorption cycles with a stationary adsorbent layer.

As the adsorbent in the claimed method, a polyvinyl chloride powder is used, obtained by suspension polymerization of vinyl chloride in the presence of a monomer-soluble initiator (benzoyl peroxide, lauryl peroxide, etc.), a protective colloid and, possibly, modifying additives, which together determine the preparation of a polyvinyl chloride powder with the indicated characteristics (Encyclopedia of Polymers, M., 1972, Soviet Encyclopedia, vol. 1, p. 488-450).

The essence of the invention is illustrated by the following examples.

Example No. 1.

The adsorber with a diameter of D = 0.012 m and a height of H = 0.25 m is filled with PVC powder, the particles of which have the following characteristics: particle size, d ₀ from 0.16 mm to 0.25 mm, specific surface S _beats = 2.3 m ² / g, porosity E = 29%.

Before conducting the experiments, the PVC powder is completely degassed by blowing with hot nitrogen for 24 hours. The specific surface area is measured by thermal desorption of argon using a sorbtometer. The porosity of the particles is determined from the values of the irreversibly absorbed plasticizer, which is measured according to GOST 25265-82. PVC particles are fractionated by sieving the polymer powder by sieves.

A nitrogen-vinyl chloride gas mixture is passed through an adsorber with a flow rate of Q = 60 cm ³ / min, with a content of vinyl chloride C _in = 20 vol.%. The temperature T _a = 25 ° C is maintained in the adsorber by thermostating the adsorber jacket and the initial gas mixture.

The gas mixture after leaving the adsorber is analyzed for residual vinyl chloride by gas chromatography.

The analysis shows the absence of vinyl chloride in the gas mixture after leaving the adsorber before the breakthrough C ⁰ = 0. A slip of vinyl chloride occurred after t = 7 min, which is the time of the protective action of this adsorbent layer. The vinyl chloride PVC capacity before breakthrough is C = 0.5% by weight.

Vinyl chloride desorption is carried out by maintaining a vacuum in the adsorber for 1 h, with a residual pressure W = 2.5 * 10 ⁴ Pa (~ 190 mm Hg). The desorption temperature is equal to the adsorption temperature. Vacuum is created by a water-jet pump. The desorbed vinyl chloride enters the condenser, where it condenses. The amount of collected vinyl chloride is determined by the gravimetric method. The qualitative composition of the captured compounds is determined by gas-liquid chromatography.

After desorption, the adsorption cycle is repeated and the gas mixture is analyzed after leaving the adsorber for the residual vinyl chloride content. The analysis shows the content of vinyl chloride in the gas mixture after the 1st adsorption-desorption cycle at a concentration of C = 7 * 10 ^-4 vol.% (Background concentration). Before the breakthrough, the background concentration does not increase.

Spend 10 cycles of adsorption-desorption under the same conditions, the analysis shows the content of vinyl chloride in the gas mixture at a concentration of C ¹⁰ = 7 * 10 ^-4 vol.%. Before the breakthrough, the background concentration does not increase.

Spend 30 adsorption-desorption cycles under the same conditions, the analysis shows the content of vinyl chloride in the gas mixture at a concentration of C ³⁰ = 7 * 10 ^-4 vol.%. Before the breakthrough, the background concentration does not increase. The time of the protective action of the layer of PVC particles before the breakthrough after 30 adsorption-desorption cycles does not decrease and amounts to t ³⁰ = 7 min.

The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Examples No. 2, 3, 4.

The method is carried out as in example No. 1. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Example No. 5.

Use an adsorber - a column with a height of 1.5 m and a diameter of 0.024 m, then in the conditions of example No. 1. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Examples No. 6 ÷ 10.

The method is carried out as in example No. 5. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Example No. 11.

The method is carried out as in example No. 5, but 132 cm ³ / min of an air-vinyl chloride gas mixture is passed through an adsorber with a vinyl chloride content of 10 vol.%. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Examples No. 12-14.

The method is carried out as in example No. 5. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Example No. 15. Ethyl Chloride.

The adsorber with a diameter of 0.04 m and a height of 2.00 m is filled with PVC powder, the particles of which have the following characteristics: particle size from 0.50 mm to 1.00 mm, specific surface 4.9 m ³ / g, porosity - 50% .

Before conducting the experiments, the PVC powder is completely degassed by blowing with hot nitrogen for 24 hours. The specific surface area is measured by thermal desorption of argon using a sorbtometer. The porosity of the particles is determined from the values of the irreversibly absorbed plasticizer, which is measured according to GOST 25265-82. PVC particles are fractionated by sieving the polymer powder by sieves.

300 cm / min of a nitrogen-ethyl chloride gas mixture is passed through an adsorber with an ethyl chloride content of 18.1 vol.%. The temperature in the adsorber is + 20 ° C by thermostating the canister jacket and the initial gas mixture.

The gas mixture after leaving the adsorber is analyzed for residual ethyl chloride by gas-liquid chromatography.

The analysis shows the absence of ethyl chloride in the gas mixture after leaving the adsorber before the breakthrough C ⁰ = 0. The breakthrough of ethyl chloride occurred after t = 55 min, which is the time of the protective action of this adsorbent layer. The ethyl chloride PVC capacity before breakthrough is 0.9% by weight.

The desorption of ethyl chloride is carried out by maintaining for 1 h in a vacuum adsorber with a residual pressure of 2.5 * 10 ⁴ Pa (~ 190 mm Hg). The desorption temperature is equal to the adsorption temperature. Vacuum is created by a water-jet pump. Desorbed ethyl chloride enters the condenser, where it condenses. The amount of ethyl chloride collected is determined by the gravimetric method. The qualitative composition of the captured compounds is determined by gas-liquid chromatography.

After desorption, the adsorption cycle is repeated and the gas mixture is analyzed after leaving the adsorber for the residual content of ethyl chloride. The analysis shows the content of ethyl chloride in the gas mixture after leaving the adsorber after the 1st adsorption-desorption cycle at a concentration of C ¹ = 6 * 10 ^-4 vol.%. (background concentration). Before the breakthrough, the background concentration does not increase.

10 adsorption-desorption cycles are carried out under identical conditions, the analysis shows the content of ethyl chloride in the gas mixture after leaving the adsorber at a concentration of C ¹⁰ = 8 * 10 ^-4 vol.%. Prior to the breakthrough, the background concentration remains at the same level.

Spend 30 adsorption-desorption cycles under the same conditions, the analysis shows the content of ethyl chloride in the gas mixture after leaving the adsorber at a concentration of C ³⁰ = 8 * 10 ^-4 vol.%. Before the breakthrough, the background concentration does not increase. The time of the protective action of the layer of PVC particles before the breakthrough after 30 cycles of adsorption-desorption does not decrease and is 55 minutes.

The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in table No. 1.

Example No. 16. Chloroform.

The adsorber with a diameter of 0.04 m and a height of 2.00 m is filled with PVC powder, the particles of which have the following characteristics: particle size from 0.50 mm to 1.00 mm, specific surface 4.9 m ² / g, porosity - 50% .

Before conducting the experiments, the PVC powder is completely degassed by blowing with hot nitrogen for 24 hours. The specific surface area is measured by thermal desorption of argon using a sorbtometer. The porosity of the particles is determined from the values of the irreversibly absorbed plasticizer, which is measured according to GOST 25265-82. PVC particles are fractionated by sieving the polymer powder by sieves.

1170 cm ³ / min of a nitrogen-chloroform gas mixture is passed through an adsorber with a chloroform content of 5.5 vol.%. The temperature in the adsorber is + 20 ° C by thermostating the canister jacket and the initial gas mixture.

The gas mixture after leaving the adsorber is analyzed for residual chloroform by gas-liquid chromatography.

The analysis shows the absence of chloroform in the gas mixture after leaving the adsorber before the breakthrough C ⁰ = 0. A slip of chloroform occurred after t = 10 min, which is the time of the protective action of this adsorbent layer. The chloroform PVC capacity before breakthrough is 0.5 wt.%.

Chloroform desorption is carried out by maintaining for 1 h in a vacuum adsorber with a residual pressure of 1 * 10 ⁴ Pa (~ 76 mm Hg). The desorption temperature is equal to the adsorption temperature. Vacuum is created by a water-jet pump. Desorbed chloroform enters the condenser, where it condenses. The amount of chloroform collected is determined by the gravimetric method. The qualitative composition of the captured compounds is determined by gas-liquid chromatography.

After desorption, the adsorption cycle is repeated and the gas mixture is analyzed after leaving the adsorber for the residual chloroform content. The analysis shows the chloroform content in the gas mixture after the 1st adsorption-desorption cycle at a concentration of C ¹ = 7000 * 10 ^-4 vol.% (Background concentration). Before the breakthrough, the background concentration does not increase.

10 cycles of adsorption-desorption are carried out under the same conditions, the analysis shows the chloroform content in the gas mixture after leaving the adsorber at a concentration of C ¹⁰ = 7000 * 10 ^-4 vol.%. Prior to the breakthrough, the background concentration remains unchanged.

Spend 30 adsorption-desorption cycles under the same conditions, the analysis shows the chloroform content in the gas mixture after leaving the adsorber at a concentration of C ³⁰ = 7000 * 10 ^-4 vol.%. Before the breakthrough, the background concentration does not increase. The time of the protective action of the layer of PVC particles before the breakthrough after 30 cycles of adsorption-desorption does not decrease and is 10 minutes.

The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in table No. 1.

Example No. 17. Ethyl acetate.

The adsorber with a diameter of 0.018 m and a height of 1.50 m is filled with PVC powder, the particles of which have the following characteristics: particle size from 0.50 mm to 1.00 mm, specific surface area - 4.9 m ² / g, porosity - 50%.

Before conducting the experiments, the PVC powder is completely degassed by blowing with hot nitrogen for 24 hours. The specific surface area is measured by thermal desorption of argon using a sorbtometer. The porosity of the particles is determined from the values of the irreversibly absorbed plasticizer, which is measured according to GOST 25265-82. PVC particles are fractionated by sieving the polymer powder by sieves.

900 cm ³ / min of a nitrogen-ethyl acetate gas mixture is passed through an adsorber with an ethyl acetate content of 6.9 vol.%. The temperature in the adsorber is + 20 ° C by thermostating the canister jacket and the initial gas mixture.

The gas mixture after leaving the adsorber is analyzed for residual ethyl acetate by gas-liquid chromatography.

The analysis shows the absence of ethyl acetate in the gas mixture after leaving the adsorber before the start of the breakthrough With ⁰ = 0. A slip of ethyl acetate occurred after t = 10 min, which is the time of the protective action of this adsorbent layer. The ethyl acetate PVC capacity before breakthrough is 1.2% by weight.

The desorption of ethyl acetate is carried out by maintaining for 1 h in a vacuum adsorber with a residual pressure of 0.5 * 10 ⁴ Pa (~ 38 mm Hg). The desorption temperature is equal to the adsorption temperature. Vacuum is created by a water-jet pump. Desorbed ethyl acetate enters the condenser, where it condenses. The amount of ethyl acetate collected is determined by the gravimetric method. The qualitative composition of the captured compounds is determined by gas-liquid chromatography.

After desorption, the adsorption cycle is repeated and the gas mixture is analyzed after leaving the adsorber for the residual content of ethyl acetate. The analysis shows the content of ethyl acetate in the gas mixture after the 1st adsorption-desorption cycle at a concentration of C ¹ = 3000 * 10 ^-4 % vol. (background concentration). Before the breakthrough, the background concentration does not increase.

10 cycles of adsorption-desorption are carried out under the same conditions, the analysis shows the content of ethyl acetate in the gas mixture after leaving the adsorber at a concentration of C ¹⁰ = 3000 * 10 ^-4 vol.%. Prior to the breakthrough, the background concentration remains unchanged.

Spend 30 adsorption-desorption cycles under the same conditions, the analysis shows the content of ethyl acetate in the gas mixture after leaving the adsorber at a concentration of C ³⁰ = 3000 * 10 ^-4 vol.%. Before the breakthrough, the background concentration does not increase. The time of the protective action of the layer of PVC particles before the breakthrough after 30 cycles of adsorption-desorption does not decrease and is 10 minutes.

The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in table No. 2.

Example No. 18. A-76 gasoline vapors (including propane, butane, etc.).

The adsorber with a diameter of 0.05 m and a height of 3.00 m is filled with PVC powder, the particles of which have the following characteristics: particle size from 0.5 mm to 10.0 mm, specific surface 4.9 m ² / g, porosity - 50% .

Before conducting the experiments, the PVC powder is completely degassed by blowing with hot nitrogen for 24 hours. The specific surface area is measured by thermal desorption of argon using a sorbtometer. The porosity of the particles is determined from the values of the irreversibly absorbed plasticizer, which is measured according to GOST 25265-82. PVC particles are fractionated by sieving the polymer powder by sieves.

250 cm ³ / min of a gas mixture of nitrogen-gasoline vapor is passed through an adsorber with a gasoline vapor content of -20.0 vol.%. The temperature in the adsorber is + 20 ° C by thermostating the canister jacket and the initial gas mixture.

The gas mixture after leaving the adsorber is analyzed for residual hydrocarbon content by gas-liquid chromatography.

The analysis shows the absence of gasoline vapors in the gas mixture after leaving the adsorber before the start of the breakthrough С ⁰ = 0. The breakthrough of gasoline vapor occurred after t = 15 min, which is the time of the protective action of this adsorbent layer. The capacity of PVC for gasoline before the breakthrough is 0.5 wt.%.

The desorption of gasoline vapors is carried out by maintaining for 1 h in a vacuum adsorber with a residual pressure of 2.5 * 10 ⁴ Pa (~ 190 mm Hg). The desorption temperature is equal to the adsorption temperature. Vacuum is created by a water-jet pump. Desorbed hydrocarbons enter the condenser, where it condenses. The amount of hydrocarbons collected is determined by the gravimetric method. The qualitative composition of the captured compounds is determined by gas-liquid chromatography.

After desorption, the adsorption duty cycle is repeated and the gas mixture is analyzed after exiting the adsorber to the residual gasoline vapor content. The analysis shows the gasoline vapor content in the gas mixture after the 1st adsorption-desorption cycle at a concentration of C ¹ = 7 * 10 ^-4 vol.%. (background concentration). Before the breakthrough, the background concentration does not increase.

10 adsorption-desorption cycles are carried out under the same conditions, the analysis shows the gasoline vapor content in the gas mixture after leaving the adsorber at a concentration of C ¹⁰ = 7 * 10 ^-4 vol.%. Prior to the breakthrough, the background concentration does not change.

Spend 30 adsorption-desorption cycles under the same conditions, the analysis shows the gasoline vapor content in the gas mixture after leaving the adsorber at a concentration of C ³⁰ = 7 * 10 ^-44 vol.%. Before the breakthrough, the background concentration does not increase. The time of the protective action of the layer of PVC particles before the breakthrough after 30 adsorption-desorption cycles does not decrease and is 15 minutes.

Example No. 19 (for comparison).

The adsorber according to example No. 1 is filled with coal of a gas series CET brand having a specific surface area of ~ 1230 m ² / g, iodine number ~ 1150 mg / g, total pore volume of ~ 1 cm ³ / g, granule size - from 2 mm to 5 mm.

60 cm ³ / min of a nitrogen-vinyl chloride gas mixture is passed through an adsorber with a vinyl chloride content of 20% by volume. The temperature in the adsorber is + 25 ° С by thermostating of the jacket and the initial gas mixture.

The gas mixture after leaving the adsorber is analyzed according to example No. 1. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

Example No. 20 (for comparison).

The adsorber according to example No. 5 is filled with coal of the SKT gas series according to example No. 19. 130 cm ³ / min of an air-vinyl chloride gas mixture is passed through an adsorber, with a content of vinyl chloride of 50 vol.%. The adsorber cooling jacket cannot cope with warming up. The adsorbent ignited. The process conditions are shown in the table.

Examples No. 21-23 (for comparison).

Following the example of No. 1. The process conditions and characteristics of the gas mixture after exiting the adsorber are shown in the table.

From the above examples of the proposed method No. 1-14, it is seen that when extracting vinyl chloride from gas emissions using PVC powder as an adsorbent with a particle porosity of 29% to 52%, the degree of extraction is preserved compared to the prototype (the content of vinyl chloride in gas mixture after exiting the adsorber is less than 10 * 10 ^-4 vol.%) and does not depend on the specific surface of the PVC particles, the diameter of the PVC particles, the temperature of the adsorbent, the concentration of vinyl chloride in gas emissions. In addition, the use of a non-combustible product as an adsorber increases the safety of the process and makes it possible to extract volatile chemical compounds from gas mixtures containing oxygen, for example air-vinyl chloride, which will expand the technological capabilities of the method.

From the above examples, according to the proposed method No. 1-14, it is also seen that the use of PVC powder as an adsorbent in the extraction of vinyl chloride from gas emissions with a particle size of 0.16-10.00 mm and a total porosity of particles from 29% to 52% allows the stage of desorption without heating the adsorbent by creating a moderate vacuum in the adsorber (at a residual pressure of 0.001 * 10 ⁴ Pa to 2.5 * 10 ⁴ Pa), easily achieved under industrial conditions, and the degree of extraction of volatile chemical compounds from gases is compared with prototype, with wounding (vinyl chloride content of the gas mixture after leaving the adsorber less than 10 x 10 ^-4 vol.%) and does not depend on the number of desorption cycles. Moreover, under the given desorption conditions, the protective action time of the adsorbent is constant and also independent of the number of operating cycles. Similar results are achieved using the proposed method for the extraction of hydrocarbons and ethers (see examples No. 15-18).

From the comparison examples No. 19-22, it follows that when coals are used as an adsorbent, the time of the protective action increases significantly, however, desorption of vinyl chloride from coal by moderate vacuum is impossible. For desorption of vinyl chloride from coal, it is necessary to treat the latter with hot steam, which will significantly complicate the process equipment design.

It also follows from comparison examples that activated carbon adsorbers cannot be used to clean oxygen-containing systems.

In addition, from the examples cited for comparison it follows that the use, when extracting volatile chemical compounds from gas emissions, as an adsorbent of PVC powder with a particle porosity of more than 52% or less than 29% does not allow achieving the required degree of gas purification from vinyl chloride.

From comparison example 23, it follows that desorption at a residual pressure of more than 2.5 * 10 ⁴ Pa leads to a decrease in the efficiency of extraction of volatile chemicals from gas emissions even when using PVC powder with a particle porosity of from 29% to 52%. Desorption at a residual pressure of less than 0.001 * 10 ⁴ Pa leads to the use of multi-stage vacuum pumps, the use of which, due to the complexity of their operation and low reliability, significantly complicates the hardware design of the process and means a qualitative leap in increasing the complexity of the technology.

Thus, from the above examples it follows that when used as an adsorbent for the extraction of volatile chemical compounds, for example vinyl chloride, from gas emissions of PVC powder with a particle size of 0.16-10.00 mm and a total porosity of particles from 29% to 52% and desorption under vacuum at a residual pressure of 0.001 * 10 ⁴ Pa to 2.5 * 10 ⁴ Pa, the process equipment is simplified, the safety is enhanced and the technological capabilities of the method are expanded when the extracted compound is contained, for example, vinyl chlorine ida in the gas mixture after leaving the adsorber less than 10 * 10 ^-4 vol.%.

Claims (1)

A method for extracting volatile chemical compounds, including organochlorine compounds, ethers, hydrocarbons, from gas-air mixtures, comprising passing a gas-air mixture through a layer of powdered polymer adsorbent and subsequent desorption, characterized in that polyvinyl chloride powder with a particle size of 0.16-10 is used as an adsorbent 00 mm and a total porosity of particles from 29 to 52%, desorption is carried out under vacuum at a residual pressure of 0.001 · 10 ⁴ to 2.5 · 10 ⁴ Pa, while the adsorption process is carried out in periodic mode having in adsorbers with a stationary adsorbent layer.