CN115999344A - Treatment method of molecular sieve crystallization tail gas - Google Patents
Treatment method of molecular sieve crystallization tail gas Download PDFInfo
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- CN115999344A CN115999344A CN202111231574.6A CN202111231574A CN115999344A CN 115999344 A CN115999344 A CN 115999344A CN 202111231574 A CN202111231574 A CN 202111231574A CN 115999344 A CN115999344 A CN 115999344A
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- molecular sieve
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Abstract
The invention provides a method for treating molecular sieve crystallization tail gas, which comprises the following steps: (1) The molecular sieve crystallization tail gas containing organic alkali and olefin is sent into a first absorption tower to be in first contact with phosphoric acid solution; (2) And sending the pre-purified tail gas discharged from the first absorption tower into a second absorption tower to be in second contact with the potassium permanganate solution. In the method, the quaternary ammonium base or other organic amine aqueous solution is alkaline and can be subjected to neutralization reaction with phosphoric acid, and most of organic bases such as quaternary ammonium base or organic amine can be removed by the neutralization reaction of the organic base and the phosphoric acid aqueous solution in the first step, so that the concentration of waste gas is reduced. However, olefins produced by the decomposition of quaternary ammonium bases cannot be absorbed by the dilute phosphoric acid reaction, and the exhaust gas may not reach the standard. The second step therefore employs an acidic potassium permanganate oxidation to remove olefins, such as ethylene, directly to carbon dioxide and water. The tail gas containing organic alkali and olefin can be treated up to the standard through two treatments.
Description
Technical Field
The invention relates to the field of molecular sieve preparation, in particular to a method for treating molecular sieve crystallization tail gas.
Background
In the pressure release process of the molecular sieve crystallization kettle, the organic template agent is used or decomposed, the raw materials react, and the like. For example, when a quaternary ammonium base templating agent is used, the usual Hoffman elimination reaction, i.e., the quaternary ammonium base will decompose when heated to 100-150 ℃. If the quaternary ammonium base hydrocarbon radical does not contain beta-H, tertiary amine and alcohol are generated when heating, the reaction formula is as follows (CH) 3 ) 4 N + OH - →(CH 3 ) 3 N+CH 3 OH; if the quaternary ammonium base has beta-H on its hydrocarbyl group, tertiary amine and olefin are formed upon heating, the reaction formula (CH 3 CH 2 ) 3 N + CH 2 CH 3 OH - →(CH 3 CH 2 ) 3 N+H 2 C＝CH 2 +H 2 O. Therefore, the crystallization tail gas contains Volatile Organic Compounds (VOCs) such as methanol, ethanol, ethylene, propylene, and organic amines. The VOCs are easy to react under the photo-thermal condition, and the peculiar smell can be discharged out of standard when the VOCs are directly discharged. The concentration fluctuation range of the molecular sieve crystallization tail gas is large, and the components are complex.
The VOCs are generally treated by adsorption or catalytic combustion. The adsorption method can effectively absorb a part of VOCs, the adsorption-condensation method is mostly adopted in actual use, the matched device is complex, and the adsorbent after adsorption also belongs to solid dangerous waste, so that secondary pollution can be caused. The catalytic combustion method is to convert VOCs into small molecular carbon dioxide or water under the action of a catalyst. However, in the actual use process, the treatment effect on the low-concentration VOCs is poor, and the energy consumption is high.
CN108744903 discloses a method for treating VOCs gas by combining plasma with potassium permanganate, which uses an electric field to excite gas and uses atomized potassium permanganate to oxidize VOCs gas. However, the method requires an additional electric field and has high energy consumption.
CN105344224a discloses a method for treating styrene waste gas, which comprises the steps of reacting ethylbenzene waste gas with alkaline potassium permanganate to eliminate styrene. However, the method only aims at styrene gas, adopts alkaline potassium permanganate solution, has low treatment efficiency, needs four-stage absorption towers, and needs air dilution for high-concentration VOCs.
CN104117222a discloses a method and apparatus for purifying air containing polyester thermal decomposition product, the method designs 6 treatment units for purifying air containing amine, olefin and CO 2 The polyurethane thermal decomposition tail gas of diimide, diisocyanate, polyol, isocyanic acid and the like is treated, and because of the complex components of polyester, the method adopts sulfuric acid and potassium permanganate with higher concentration for treatment, and then two steps of dilute alkali and water purification are carried out. The method has complicated steps and high concentration of the absorption liquid, and more three wastes can be brought after the treatment.
Few articles or patents relate to the treatment of olefin-containing molecular sieve crystallization tail gas after quaternary ammonium hydroxide decomposition. Therefore, a new process needs to be developed to treat the tail gas after crystallization of the molecular sieve, so that the application range is wide, and the process is simple and efficient.
Disclosure of Invention
Aiming at the defects of the traditional VOCs treatment method, the invention provides a simple and secondary pollution-free treatment method for the molecular sieve crystallization tail gas.
After crystallization of the molecular sieve, the tail gas can contain volatile organic compounds such as ethylene, ethanol, organic amine and the like in the pressure relief process due to the template agent and decomposition products thereof. The invention provides that: and (3) treating tail gas after crystallization of the molecular sieve by adopting a combination mode of dilute phosphoric acid absorption and potassium permanganate acid solution absorption. The specific method comprises the following steps: the two towers are connected in series, and the first tower is used for introducing the molecular sieve crystallization tail gas containing high-concentration volatile organic compounds into a dilute phosphoric acid tower to remove most of organic compounds; and introducing olefin-containing organic matters with the concentration lower than 500ppm into a potassium permanganate solution leaching tower for oxidation absorption, and oxidizing ethylene, ethanol, organic amine and the like in the tail gas into small molecular substances such as carbon dioxide, water and the like. The purified tail gas can be directly discharged from the top of the tower.
According to the invention, the invention provides a method for treating molecular sieve crystallization tail gas, which comprises the following steps:
(1) The molecular sieve crystallization tail gas containing organic alkali and olefin is sent into a first absorption tower to be in first contact with phosphoric acid solution;
(2) And sending the pre-purified tail gas discharged from the first absorption tower into a second absorption tower to be in second contact with the potassium permanganate solution.
In the method, the quaternary ammonium base or other organic amine aqueous solution is alkaline and can be subjected to neutralization reaction with phosphoric acid, and most of organic bases such as quaternary ammonium base or organic amine can be removed by the neutralization reaction of the organic base and the phosphoric acid aqueous solution in the first step, so that the concentration of waste gas is reduced. However, olefins produced by the decomposition of quaternary ammonium bases cannot be absorbed by the dilute phosphoric acid reaction, and the exhaust gas may not reach the standard. The second step therefore employs an acidic potassium permanganate oxidation to remove olefins, such as ethylene, directly to carbon dioxide and water. The tail gas containing organic alkali and olefin can be treated up to the standard through two treatments.
Detailed Description
The following describes specific embodiments of the present invention in detail. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.
The invention provides a method for treating molecular sieve crystallization tail gas, which comprises the following steps:
(1) The molecular sieve crystallization tail gas containing organic alkali and olefin is sent into a first absorption tower to be in first contact with phosphoric acid solution;
(2) And sending the pre-purified tail gas discharged from the first absorption tower into a second absorption tower to be in second contact with the potassium permanganate solution.
In the invention, two towers are connected in series, and the first tower removes most of organic matters from the molecular sieve crystallization tail gas containing high-concentration volatile organic matters in the dilute phosphoric acid tower; and then introducing olefin-containing organic matters with lower concentration into a potassium permanganate solution tower for oxidation absorption, so that purified tail gas can be directly emptied from the tower top.
In the present invention, the organic base refers to an organic basic substance, and includes, but is not limited to, quaternary ammonium bases, organic amines, and the like.
The method according to the invention preferably comprises:
(1) The molecular sieve crystallization tail gas containing organic alkali and olefin is sent into a first absorption tower from bottom to top to be in first contact with phosphoric acid solution which is introduced from top to bottom;
(2) And the pre-purified tail gas discharged from the first absorption tower is sent into a second absorption tower from bottom to top to be in second contact with potassium permanganate solution which is introduced from top to bottom. By adopting the preferable technical scheme, the molecular sieve crystallization tail gas containing organic alkali and olefin can be simply and efficiently treated.
According to the method of the invention, the molecular sieve crystallization tail gas preferably contains: one or more of quaternary ammonium base, organic amine, olefin and lower alcohol preferably contains three or more of quaternary ammonium base, organic amine, olefin and lower alcohol. The tail gas can be efficiently treated by the method.
According to the process of the present invention, the quaternary ammonium base is preferably of formula R 4 The OH compound is preferably tetramethylammonium hydroxide and/or tetraethylammonium hydroxide.
According to the method of the present invention, preferably the organic amine is trimethylamine and/or triethylamine.
Preferably, according to the process of the present invention, the olefin is ethylene and/or propylene.
According to the method of the present invention, preferably the lower alcohol is methanol and/or ethanol.
According to the method of the invention, the total organic matter concentration in the molecular sieve crystallization tail gas containing organic alkali and olefin is preferably 1000-2000 ppm. The method can treat crystallization tail gas in a wider range.
According to the method of the invention, the concentration of the organic waste gas outlet in the pre-purified tail gas is preferably less than 500ppm, preferably 0-100ppm. According to the method, the concentration of the organic matter outlet is reduced through the absorption of phosphoric acid, so that the workload of the subsequent potassium permanganate solution is reduced, and the load of three-waste treatment is further reduced.
According to the method of the present invention, preferably the pre-purified tail gas contains one or more of methanol, ethanol, ethylene, propylene and an organic base. The treatment method of the molecular sieve crystallization tail gas is simpler, and the absorption liquid is easy to recycle.
According to the process of the present invention, it is preferred that the first absorption column and the second absorption column are connected in series and are each a packed column. By adopting the preferable technical scheme, the molecular sieve crystallization tail gas can be continuously and efficiently treated, and the mass transfer can be enhanced by the packing tower, so that the concentration of the absorption liquid is reduced.
According to the method of the present invention, the first absorption tower and the second absorption tower may be various absorption towers, and for the present invention, it is preferable that each of the first absorption tower and the second absorption tower is a packed tower, and structured packing and/or bulk packing may be used, and more preferable that each of the packing used is silica pellets and/or alumina packing. By adopting the preferable technical scheme, the contact area between the gas and the solution can be increased.
According to the method of the present invention, the phosphoric acid solution is preferably 1 to 7% by mass. By adopting the preferable technical scheme, the tail gas after treatment can be ensured to be qualified, and the use amount of phosphoric acid can be reduced as much as possible.
According to the method of the present invention, preferably the conditions of the first contact include: introducing the tail gas into a packed tower from bottom to top, absorbing organic alkali in the tail gas by phosphoric acid solution in a countercurrent mode, and treating the absorption liquid to obtain a byproduct phosphorus-containing compound. By adopting the preferable technical scheme, the tail gas can be efficiently treated, the product absorbed by the low-concentration phosphoric acid is purer, and the by-product phosphorus-containing compound can be obtained after treatment.
According to the method of the invention, the pH of the potassium permanganate solution is preferably less than 7, preferably less than 4, and the mass fraction is 0.3-3%. The method of the invention has high oxidation efficiency of potassium permanganate under the condition of strong acidity.
The conditions of the preferred second contact according to the process of the present invention include: introducing the tail gas treated in the step (1) into a tower from bottom to top, absorbing the tail gas by a potassium permanganate solution in a countercurrent mode, wherein the circulation time of the potassium permanganate solution is 25-35 min for one time, and preferably, the used potassium permanganate absorption liquid is regenerated by adopting other processes. In the invention, the countercurrent filling material is selected to enhance the mass transfer effect of oxidation, so that less potassium permanganate three wastes can be generated.
The method according to the invention further comprises: and circularly washing the second absorption tower for a plurality of times by adopting a potassium permanganate solution before or after absorption. By adopting the preferable technical scheme, the active ingredients in the potassium permanganate solution can be adsorbed on the solid filler in advance, so that the defect of disqualification of the short tail gas when the working condition is started can be avoided.
The present invention will be described in detail by way of examples, which should not be construed as limiting the scope of the invention thereto.
Example 1
The mixed gas is adopted for feeding, molecular sieve crystallization tail gas is simulated, the concentration of total VOCs in inlet waste gas is 2000ppm, wherein the volume fractions of triethylamine, ethylene and ethanol are respectively 50%, 25% and 25% based on 100% by volume of organic matters. The carrier gas is air, and the flow rate of the air is 170mL/min. The first tower adopts 100mL of inert ceramic ball filler as a dispersion medium, the concentration of the adopted dilute phosphoric acid is 5wt%, and the dilute phosphoric acid is introduced into the first tower from top to bottom, and the flow rate is 80mL/min. The mixed waste gas is introduced into the first tower from bottom to top to absorb the waste gas, and the concentration of VOCs at the outlet is 400ppm. Column two also used 100mL of inert porcelain ball filler as dispersion medium. The concentration of the potassium permanganate solution used was 2wt% and its pH was less than 3, which was introduced into column two from top to bottom. And then the waste gas at the outlet of the first absorption tower is introduced into the second absorption tower from bottom to top. The circulating solution was changed every 30 min. The total VOCs at the final outlet was less than 0.1ppm.
Example 2
The mixed gas is used for feeding, the crystallization tail gas of the molecular sieve is simulated, the concentration of the total VOCs in the inlet waste gas is 1000ppm, wherein the volume fractions of tetramethyl ammonium hydroxide, ethylene and methanol are respectively 50%, 25% and 25% based on 100% by volume of organic matters. The carrier gas is air, and the flow rate of the air is 170mL/min. Column one uses 100mL of inert porcelain ball filler as dispersion medium. The concentration of the dilute phosphoric acid adopted is 5wt%, and the dilute phosphoric acid is introduced into the first tower from top to bottom, and the flow rate is 80mL/min. The mixed waste gas is introduced into a first tower from bottom to top to absorb the waste gas, and the VOCs concentration at the outlet is 300ppm. Column two also used 100mL of inert porcelain ball filler as dispersion medium. The concentration of the potassium permanganate solution used was 2wt% and its pH was less than 3, which was introduced into column two from top to bottom. And then the waste gas at the outlet of the first absorption tower is introduced into the second absorption tower from bottom to top. The circulating solution was changed every 30 min. The total VOCs at the final outlet was less than 0.1ppm.
Example 3
Unlike example 1, the gases and liquids of the first and second columns were fed from the same direction. The final total VOCs concentration was 12ppm.
Example 4
The difference from example 1 is that the packing was removed in column one and column two. The final total VOCs concentration was 20ppm.
Example 5
Unlike example 1, the pH of potassium permanganate was 5. The final total VOCs concentration was 14ppm.
Comparative example 1
The mixed gas is adopted for feeding, molecular sieve crystallization tail gas is simulated, the concentration of total VOCs in inlet waste gas is 2000ppm, wherein the volume fractions of triethylamine, ethylene and ethanol are respectively 50%, 25% and 25% based on 100% by volume of organic matters. The carrier gas is air, and the flow rate of the air is 170mL/min. The tower adopts 100mL of inert porcelain ball filler as a dispersion medium, the concentration of the adopted dilute phosphoric acid is 5wt%, and the dilute phosphoric acid is introduced into the tower from top to bottom, and the flow rate is 80mL/min. The mixed waste gas is introduced into the first tower from bottom to top to absorb the waste gas, and the VOCs concentration at the outlet is 400ppm. The emission requirements are not met. At present, a single phosphoric acid absorption tower is often adopted for crystallization tail gas, so that ethylene in the mixed gas is difficult to absorb.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of individual specific technical features in any suitable way. The various possible combinations of the invention are not described in detail in order to avoid unnecessary repetition. Such simple variations and combinations are likewise to be regarded as being within the scope of the present disclosure.
Claims (10)
1. The method for treating the molecular sieve crystallization tail gas is characterized by comprising the following steps of:
(1) The molecular sieve crystallization tail gas containing organic alkali and olefin is sent into a first absorption tower to be in first contact with phosphoric acid solution;
(2) And sending the pre-purified tail gas discharged from the first absorption tower into a second absorption tower to be in second contact with the potassium permanganate solution.
2. A process according to claim 1, wherein the process comprises:
(1) The molecular sieve crystallization tail gas containing organic alkali and olefin is sent into a first absorption tower from bottom to top to be in first contact with phosphoric acid solution which is introduced from top to bottom;
(2) And the pre-purified tail gas discharged from the first absorption tower is sent into a second absorption tower from bottom to top to be in second contact with potassium permanganate solution which is introduced from top to bottom.
3. The process according to claim 1 or 2, wherein the molecular sieve crystallization tail gas comprises: one or more of quaternary ammonium base, organic amine, olefin and lower alcohol, preferably three or more of quaternary ammonium base, organic amine, olefin and lower alcohol; wherein the quaternary ammonium base has a general formula of R 4 The compound of OH is preferably tetramethyl ammonium hydroxide and/or tetraethyl ammonium hydroxide, the organic amine is trimethylamine and/or triethylamine, the olefin is ethylene and/or propylene, and the lower alcohol is methanol and/or ethanol.
4. A process according to any one of claims 1 to 3, wherein the total organic concentration in the crystallized tail gas of the molecular sieve containing organic base and olefin is from 1000 to 2000ppm and the organic concentration in the pre-purified tail gas is less than 500ppm, preferably from 0 to 100ppm.
5. The process of any one of claims 1-4, wherein the pre-clean-up tail gas comprises one or more of methanol, ethanol, ethylene, propylene, and organic amines.
6. The process according to any one of claims 1 to 5, wherein the first absorption tower and the second absorption tower are connected in series and are each a packed tower.
7. A process according to any one of claims 1 to 6, wherein the first and second absorption columns are packed columns, preferably the packing used each is a structured packing and/or a bulk packing, preferably silica pellets and/or alumina packing.
8. A process according to any one of claims 1 to 7, wherein,
the mass fraction of the phosphoric acid solution is 1-7%; and/or the conditions of the first contact include: introducing the tail gas into a packed tower from bottom to top, absorbing organic alkali in the tail gas by phosphoric acid solution in a countercurrent mode, and treating the absorption liquid to obtain a byproduct phosphorus-containing compound.
9. A process according to any one of claims 1 to 8, wherein,
the pH value of the potassium permanganate solution is less than 7, preferably less than 4, and the mass fraction is 0.3-3%; and/or
The conditions of the second contact include: introducing the tail gas treated in the step (1) into a tower from bottom to top, absorbing the tail gas by the potassium permanganate solution in a countercurrent mode, wherein the circulation time of the potassium permanganate solution is 25-35 min for one time, and preferably regenerating the used absorption liquid.
10. The process of any one of claims 1-9, wherein the process further comprises: and circularly washing the second absorption tower for a plurality of times by adopting a potassium permanganate solution before or after absorption.
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| CN202111231574.6A CN115999344A (en) | 2021-10-22 | 2021-10-22 | Treatment method of molecular sieve crystallization tail gas |
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