RU2705073C1 - Method and installation for cleaning tail gas - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: present invention relates to a method of cleaning tail gas containing nitrogen oxides and alkyl nitrite. Said method involves introduction of tail gas in the presence of oxygen in contact with an effective amount of alkyl alcohol for absorption of alkyl nitrite, introducing the resultant absorbed gas in the presence of the catalyst into contact with the reducing gas to reduce the level of nitrogen oxides, as well as washing of absorbed and reduced gas, thus obtaining cleaned tail gas. There is also proposed a plant for cleaning tail gas containing nitrogen oxides and alkyl nitrite. Cleaned tail gas has low content of nitrogen oxide and low content of alkyl nitrite.EFFECT: invention increases efficiency of cleaning tail gas.19 cl, 1 dwg, 1 tbl

Description

FIELD OF THE INVENTION

The present invention relates to methods and plants for purifying a tail gas containing nitrogen oxides and alkyl nitrites.

BACKGROUND OF THE INVENTION

Nitrogen oxides (NO _x ) are generally understood as NO ₂ and NO. NO _x can stimulate lung function and cause lung damage. NO _x can also reduce atmospheric visibility. In addition, NO _x reacts with water present in the air, forming acid rain, which leads to environmental degradation. Methyl nitrite (MN) is a highly flammable and explosive gas with strong toxicity. After inhalation, MN can form methemoglobin when in contact with red blood cells present in the blood, and as a result, such red blood cells lose their ability to carry oxygen. By the mechanism of its toxic effect, MN is similar to carbon monoxide (CO), but it is much more toxic than CO. Therefore, it is necessary to purify the tail gases containing NO _x and alkyl nitrites (RONO) by removing NO _x from them, reducing its concentration to a level that meets the relevant environmental standards, with the simultaneous conversion of MN present in such tail gases before releasing them into the atmosphere. The prior art method for purification of tail gas containing nitrogen oxides and alkyl nitrite, disclosed, for example, in document CN 101095997.

However, there remains a need for a simple, low-energy and efficient method for purifying gases containing nitrogen oxides and alkyl nitrites, and equipment for the purification of such gases.

SUMMARY OF THE INVENTION

In the framework of the present invention, a method for purification of tail gas containing oxides of nitrogen and alkyl nitrite.

A method for purifying a tail gas containing nitrogen oxides and alkyl nitrites is provided. This method includes (a) introducing tail gas in the presence of oxygen into contact with an effective amount of alkyl alcohol to effect absorption of alkyl nitrite to thereby produce an absorbed gas; (b) introducing the absorbed gas in the presence of an effective amount of the catalyst into contact with the reducing gas to reduce the level of nitrogen oxides to thereby obtain the absorbed and reduced gas; and (c) washing the absorbed and reduced gas to thereby obtain a purified tail gas.

The nitrogen oxide content of such a purified tail gas may be less than 50 ppm. The alkyl nitrite content of such a purified tail gas may be less than 10 ppm.

The molar ratio of nitrogen oxides in step (a) to oxygen in step (a) can be from 1:10 to 10: 1. The molar ratio of alkyl alcohol in step (a) to alkyl nitrites in step (a) may be from 1: 1 to 100: 1. Mentioned alkyl alcohol may be selected from the group consisting of methanol, ethanol, propanol and butanol.

Stage (a) can be carried out at a working pressure of from 0.1 to 1.0 MPa. Step (a) can be carried out at an operating temperature of from -30 ° C to 90 ° C.

Step (a) may be carried out in the first absorption column (1). The first absorption column (1) may be a packed column, a wash column, or an irrigation column.

The molar ratio of reducing gas to nitrogen oxides in step (b) may be from 1: 1 to 10: 1. The reducing gas itself may contain H ₂ , CO, NH ₃ or a combination thereof. Said catalyst may comprise Pd, Pt, Cu, Rh, or a combination thereof.

Step (b) can be carried out at a temperature of from 50 ° C to 500 ° C. Stage (b) can be carried out under pressure from 0 to 1 MPa gage. (from 0 to 10 bar g.). Stage (b can be carried out at a volumetric gas velocity of from 50 to 10,000 h ^-1 .

Step (b) may be carried out in a reactor. Such a reactor may be a fixed bed reactor.

Said absorbed and reduced gas in step (c) may be washed with water or with alkyl alcohol. The alkyl alcohol used in step (c) may be methanol, ethanol, propanol or butanol. The alkyl alcohol used in step (c) may be identical to the alkyl alcohol used in step (a). The molar ratio of alkyl alcohol or water in step (c) to alkyl nitrites in step (a) can be from 1: 1 to 1000: 1.

Step (c) may be carried out in a second absorption column (2). The second absorption column (2) may be a packed column, a wash column, or an irrigation column.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 shows a method and apparatus for absorbing and removing nitrogen oxides (NO _x ) and alkyl nitrites present in a gas in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a method for purifying a tail gas containing nitrogen oxides (NOx) and alkyl nitrites (RONO). The present invention was developed on the basis of an unexpected discovery by the authors of a new purification method that allows RONO and NO _x to be removed from the tail gas, respectively, by absorption with alkyl alcohol and through a catalytic reduction reaction to such an extent that the NO _x content of the tail gas thus purified below 50 ppm, and the RONO content therein is below 10 ppm. Also, an installation is proposed here that implements the indicated cleaning method.

Moreover, a method for purifying tail gas is provided. Nitrogen oxides (NO _x ) and alkyl nitrites (RONO) are present in this tail gas. The method includes contacting tail gas with an effective amount of alkyl alcohol in the presence of oxygen to absorb alkyl nitrite, contacting the resulting absorbed gas with a reducing gas in the presence of an effective amount of catalyst to reduce the level of nitrogen oxides, and washing the resulting absorbed and reduced gas. The result is a purified tail gas.

Nitrogen oxides include, for example, nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ). The initial content of nitrogen oxides in such a tail gas may be more than 50,000 or 100,000 ppm. In the purified tail gas, the content of nitrogen oxides may be less than about 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 or 10 ppm, preferably less than about 50 ppm

Alkyl nitrites include, for example, methyl nitrite (MN) and ethyl nitrite. In the purified tail gas, the content of alkyl nitrites may be less than about 20, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1 ppm, preferably less than about 10 ppm

In the alkyl nitrite absorption step, the molar ratio of nitrogen oxides to oxygen may be from about 1:10 to about 10: 1, preferably from about 1: 5 to about 5: 1, and more preferably from about 1: 2 to about 2: 1.

The molar ratio of alkyl alcohol to alkyl nitrites may be from about 1: 1 to about 100: 1, preferably from about 2: 1 to about 50: 1, and more preferably from about 5: 1 to about 30: 1. Said alkyl alcohol may be selected from the group consisting of methanol, ethanol, propanol and butanol.

The alkyl nitrite absorption step may be carried out at a working pressure of from about 0.1 to 1.0 MPa, preferably from about 0.1 to 0.7 MPa, and more preferably from about 0.1 to 0.3 MPa.

The alkyl nitrite absorption step may be carried out at a working temperature of from about −30 ° C. to about 90 ° C., preferably from about −10 ° C. to about 60 ° C., and more preferably from about 0 ° C. to about 50 ° C.

The stage of absorption of alkyl nitrites can be carried out in an absorption column (1), the function of which can be performed by a packed column, a washing column or an irrigation column.

In the reduction step, the molar ratio of reducing gas to nitrogen oxides may be from about 1: 1 to about 10: 1, preferably from about 1: 1 to about 5: 1, and more preferably from about 1: 1 to about 3: 1. The reducing gas itself may contain H ₂ , CO, NH ₃ or a combination thereof. Said catalyst may comprise Pd, Pt, Cu, Rh, or a combination thereof.

The recovery step can be carried out at a temperature of from about 50 to 500 ° C, preferably from about 100 to 450 ° C, and more preferably from about 150 to 350 ° C. The recovery step can be carried out under pressure from about 0 to 1 MPa gage. (from 0 to 10 bar gage), preferably about 0 to 0.8 MPa gage. (from 0 to 8 bar gage), and more preferably about 0 to 0.5 MPa gage. (from 0 to 5 bar g.). The recovery step can be carried out at a gas volumetric velocity of from about 50 to 10,000 h ^-1 , preferably from about 70 to 5,000 h ^-1 , and more preferably from 100 to 2,000 h ^-1 .

The recovery step may be carried out in a reactor. Such a reactor may be a fixed bed reactor.

At the washing step, the absorbed and reduced gas can be washed with water or with alkyl alcohol. The alkyl alcohol used in the washing step may be methanol, ethanol, propanol or butanol. The alkyl alcohol used in the washing step may be identical to the alkyl alcohol used in the absorption step. The molar ratio of alkyl alcohol or water used in the washing step to the alkyl nitrites used in the absorption step may be from about 1: 1 to about 1000: 1, preferably from about 2: 1 to about 500: 1, and more preferably from about 5: 1 to about 300: 1.

The washing step may be carried out in a second absorption column (2). The second absorption column (2) may be a packed column, a wash column, or an irrigation column.

A tail gas purification plant containing nitrogen oxides and alkyl nitrites is also proposed. This installation consists of a first absorption column (1), a reactor and a second absorption column (2). In the first absorption column (1), the tail gas in the presence of oxygen is exposed to an effective amount of alkyl alcohol in order to absorb alkyl nitrite, resulting in the absorption of gas. In the reactor, the absorbed gas in the presence of an effective amount of catalyst is exposed to a reducing gas in order to reduce the level of nitrogen oxides, as a result of which the absorbed and reduced gas is formed. In the second absorption column (2), the absorbed and reduced gas is flushed. The result is a purified tail gas.

The first absorption column (1) may be a packed column, a wash column, or an irrigation column. Such a reactor may be a fixed bed reactor. The second absorption column (2) may be a packed column, a wash column, or an irrigation column.

The term “about” as used herein to refer to a measured value, for example, quantity, percent, and the like, is intended to encompass deviations within ± 20% or ± 10%, more preferably ± 5%, even more preferably ± 1 % and even more preferably ± 0.1% of the indicated value, since such deviations correspond to the norm.

Sample 1. Purified gas 1

The tail gas was purified, resulting in the formation of purified gas 1. A gas containing nitrogen oxides (NO _x ) and methyl nitrite (MN), together with the air mixture, was introduced into the first wash column. The molar ratio of NO _x to oxygen (O ₂ ) in the air mixture was 1:10. Methanol was introduced to absorb MN, the molar ratio of which to MN was 1: 1. The operating pressure was 0.1 MPa. The operating temperature was -30 ° C. The gas from the top of the absorption column, together with hydrogen (H ₂ ), was sent to a fixed-bed reactor equipped with a Pt-containing catalyst to carry out catalytic reduction in the presence of a reducing gas at a molar ratio of reducing gas to NO _{x of} 1: 1. The reaction temperature was 500 ° C. The reaction pressure was 0 bar g. The gas volumetric velocity was 50 h ⁻¹ . From the fixed-bed reactor, the recovered gas was sent to the second wash column to perform water washing before the cleaning procedure at a molar ratio of water to methyl nitrate of 1000: 1, and after washing, the used water was discharged in the form of wastewater. The gas from the top of the wash column was purified gas 1. Then, the purified gas 1 was purified by burning.

Table 1 shows the data on the main technological conditions used to obtain purified gas 1, as well as the content of methyl nitrite at the level of 8 ppm and the NOx content at 43 ppm.

Sample 2. Purified gas 2

The tail gas was purified, resulting in the formation of purified gas 2. A gas containing nitrogen oxides (NO _x ) and ethyl nitrite, together with the air mixture, was introduced into the first packed column. The molar ratio of NO _x to oxygen (O ₂ ) in the air mixture was 10: 1. Ethanol was introduced to absorb ethyl nitrite, the molar ratio of which to ethyl nitrite was 100: 1. Working pressure was 1.0 MPa. The operating temperature was 90 ° C. The gas coming from the top of the packed column, together with CO, was launched into a fixed-bed reactor equipped with a Pt-based catalyst to carry out catalytic reduction in the presence of a reducing gas at a molar ratio of reducing gas to NO _{x of} 10: 1. The reaction temperature was 50 ° C. The reaction pressure was 1 MPa gage. (10 bar g.). The gas volumetric velocity was 10,000 h ⁻¹ . The reduced gas was sent to the second packed column to carry out the washing procedure with ethanol at a molar ratio of ethanol to the ethyl nitrite present in the tail gas of 1: 1, and after washing, the used ethanol was introduced into the first packed column for reuse at the absorption stage. The gas coming from the top of the wash column was purified gas 2. The purified gas 2 was then cleaned by burning.

Table 1 shows the data on the main technological conditions used to obtain purified gas 2, as well as the content of methyl nitrite at the level of 9 ppm and the content of nitric oxide at the level of 43 ppm.

Sample 3. Purified gases from 3 to 6 and comparative gas samples from 1 to 3

Additional studies were conducted on the purification of tail gas containing nitric oxide and alkyl nitrite, according to the method described in the example, with the exception of the excellent conditions listed in table 1. Table 1 shows the data on the process conditions used to obtain purified gases from 3 to 6 and comparative gas samples from 1 to 3, as well as the values of the content of methyl nitrite and nitric oxide in them.

Although the claimed invention is illustrated and described herein with reference to specific embodiments, it is not limited to the demonstrated characteristics. Conversely, various changes may be made to these characteristics within the scope and range of equivalents of the claims without departing from the invention itself.

Claims (26)

1. The method of purification of tail gas containing nitrogen oxides and alkyl nitrite, including: (a) introducing tail gas in the presence of oxygen into contact with an effective amount of alkyl alcohol to effect absorption of alkyl nitrite to thereby produce an absorbed gas; (b) introducing the absorbed gas in the presence of an effective amount of the catalyst into contact with the reducing gas to reduce the level of nitrogen oxides to thereby obtain the absorbed and reduced gas; and (c) washing the absorbed and reduced gas to thereby obtain a purified tail gas; moreover said catalyst contains Pd, Pt, Cu, Rh, or a combination thereof; step (b) is carried out at a temperature of from 50 to 500 ° C; step (b) is carried out at a gas volumetric velocity of from 50 to 10,000 h ^-1 ; the absorbed and reduced gas in step (c) is washed with water or alkyl alcohol. 2. The method according to p. 1, in which the content of nitric oxide in the purified tail gas is less than 50 hours per million 3. The method according to p. 1, in which the content of alkyl nitrite in the purified tail gas is less than 10 hours per million 4. The method according to p. 1, in which the molar ratio of nitrogen oxides to oxygen in step (a) is from 1:10 to 10: 1. 5. The method according to p. 1, in which the molar ratio of alkyl alcohol in step (a) to alkyl nitrites in step (a) is from 1: 1 to 100: 1. 6. The method of claim 1, wherein the alkyl alcohol is selected from the group consisting of methanol, ethanol, propanol and butanol. 7. The method according to p. 1, in which step (a) is carried out at a working pressure of from 0.1 to 1.0 MPa. 8. The method according to p. 1, in which step (a) is carried out at an operating temperature of from -30 to 90 ° C. 9. The method according to p. 1, in which step (a) is carried out in the first absorption column. 10. The method of claim 9, wherein the first absorption column is a packed column, a wash column, or an irrigation column. 11. The method according to p. 1, in which the molar ratio of reducing gas to nitrogen oxides in step (b) is from 1: 1 to 10: 1. 12. The method of claim 1, wherein the reducing gas comprises H ₂ , CO, NH _3, or a combination thereof. 13. The method according to p. 1, in which step (b) is carried out under pressure from 0 to 1 MPa gage. (from 0 to 10 bar g.). 14. The method of claim 1, wherein step (b) is carried out in a reactor. 15. The method of claim 14, wherein said reactor is a fixed bed reactor. 16. The method according to p. 1, in which the molar ratio of alkyl alcohol in step (c) to alkyl nitrite in step (a) is from 1: 1 to 1000: 1. 17. The method according to claim 1, further comprising introducing an alkyl alcohol after step (c) to step (a). 18. The method of claim 1, wherein step (c) is carried out in a second absorption column. 19. The method of claim 18, wherein the second absorption column is a packed column, a wash column, or an irrigation column.

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