Cascade adsorption method for waste gas containing volatile organic compounds

Abstract

The invention discloses a cascade adsorption method for waste gas containing volatile organic compounds, which adopts cascade combination of an adsorption material A and an adsorption material B, the air speed of gas on the adsorption material A is 3000-5000h <-1 >, and the air speed of gas on the adsorption material B is 500-5000h <-1 >. Wherein the adsorption material A is selected from one or a combination of more than two of zeolite, attapulgite, bentonite, activated carbon, metal oxide and metal hydroxide, and the adsorption material B is a carbon-based material containing nitrogen groups. By regulating and controlling the pore size and the functional group of the adsorption material, selective adsorption of the VOCs waste gas containing low-carbon light hydrocarbon is realized, and the adsorption efficiency is high.

Description

Technical Field

[0001] This invention belongs to the field of VOCs waste gas treatment technology, specifically involving a cascade adsorption method for waste gas containing volatile organic compounds. Background Technology

[0002] Adsorption, catalytic oxidation, high-temperature incineration, absorption, condensation, and membrane separation are widely used in the recovery and treatment of various waste gases containing volatile organic compounds (VOCs). Adsorption technology is a non-destructive treatment technology for VOCs, typically designing the pores and functional groups of adsorption materials based on the polarity and molecular size of the adsorbed molecules. Because VOCs are diverse, a single adsorption material can only effectively adsorb specific types of VOCs, resulting in poor broad-spectrum adsorption. It is particularly noteworthy that laboratory and laboratory waste gases are more complex, and activated carbon is almost always used as the adsorption material at the end of treatment. Activated carbon has a good adsorption effect on large molecular pollutants, but its susceptibility to smoldering and strong hydrophilicity make it difficult to maintain long-term stable adsorption performance, especially for light hydrocarbons (including but not limited to liquefied petroleum gas components).

[0003] Chinese invention patent 202110562057.0 reports on the adsorption treatment of VOCs containing light hydrocarbons. This method involves four-stage condensation of the gas, with adsorption materials (activated carbon, diatomaceous earth, and puffed soybean powder) used at the end to remove the light hydrocarbons. However, this method removes the light hydrocarbons almost entirely through cryogenic treatment (minimum condensation temperature ~120℃) and pressurization, resulting in high energy consumption. Tianjin University disclosed an adsorption process in CN110180321A that uses a series of preferential and non-preferential adsorbents, where the non-preferential adsorbents include silica gel and zeolite, and the preferential adsorbents include activated carbon. This improves the overall desorption capacity of the adsorbents; however, the total adsorption capacity of the adsorbents is not improved. CN109513311B discloses a method for treating waste gas using dynamic fluidized bed staged adsorption to achieve high efficiency and energy saving. A mixed gas containing acidic gases, volatile organic gases, and specific types of volatile organic gases is sequentially introduced into a multi-stage adsorption reaction system consisting of a first adsorption bed system, a second adsorption bed system, and a third adsorption bed system for purification. However, this patent does not describe the adsorption and removal effect on light hydrocarbon components. CN108452635B discloses a method for optimizing the formulation of VOCs adsorption materials. Although this process involves cascade adsorption, it does not disclose the adsorption effect of the cascade adsorption materials on light hydrocarbons.

[0004] Therefore, there is an urgent need for a method that consumes little energy and can effectively adsorb volatile organic compounds in waste gas containing low-carbon light hydrocarbons. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a cascade adsorption method for waste gas containing volatile organic compounds.

[0006] The technical solution adopted in this invention is: A cascade adsorption method for waste gas containing volatile organic compounds employs a cascade combination of adsorbent A and adsorbent B, with the gas space velocity on adsorbent A being 3000~5000 h⁻¹. ~1 The gas space velocity on adsorbent B is 500~5000 h⁻¹. ~1 The adsorbent A is selected from one or more combinations of zeolite, attapulgite, bentonite, activated carbon, metal oxides, and metal hydroxides, and the adsorbent B is a carbon-based material containing nitrogen groups.

[0007] In the preferred carbon-based material containing nitrogen groups, the carbon content is 89-98 wt%, the oxygen content is 1-10 wt%, and the nitrogen content is 0.5-6 wt%. More preferably, the carbon content is 91-97 wt%, the oxygen content is 1-7 wt%, and the nitrogen content is 0.9-5 wt%. Even more preferably, the carbon content is 95-97 wt%, the oxygen content is 1-5 wt%, and the nitrogen content is 1.1-4.2 wt%.

[0008] The preferred adsorption temperature is 10~60℃, the more preferred adsorption temperature is 10~48℃, and the even more preferred adsorption temperature is 10~30℃.

[0009] The preferred adsorbent A has a specific surface area of ​​100~3000 m². 2 / g, pore volume 0.1~3.1cm 3 / g, with a mesoporosity of 50~90%.

[0010] The preferred adsorbent B has a specific surface area of ​​600~3200 m². 2 / g, pore volume 0.8~3.1cm 3 / g, with a microporosity of 80~93%.

[0011] The preferred regeneration conditions for adsorbent A and adsorbent B are: desorption temperature of 70~120℃, and vacuum or inert gas purging.

[0012] The nitrogen-containing carbon-based material described in this invention is prepared by modifying activated carbon with a modifier.

[0013] The modification method is as follows: Activated carbon, modifier and solvent are fully mixed in a mass ratio of 10:(1~7):(0.5~8), refluxed for a period of time, filtered and calcined to obtain the product.

[0014] The modifier is selected from a combination of nitrogen-containing compounds and oxygen-containing compounds.

[0015] The nitrogen-containing compound is preferably at least one of the following: nitrogen heterocyclic structure (pyridine, pyrimidine, or triazine), fluorenyl structure, nitrogen anthracene, aromatic amine (aniline with substituents), melamine, urea, amide, alkaloid, and biological protein.

[0016] The oxygen-containing compound is preferably at least one of an acid and a base. The acid is further preferably one or a combination of two or more of phosphoric acid, sulfuric acid, nitric acid, perchloric acid, acetic acid, peracetic acid, oxalic acid, adipic acid, malic acid, tartaric acid, citric acid, and stearic acid. The base is further preferably one or a combination of two or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide.

[0017] The solvent is preferably at least one of water and alcohol, and the alcohol is more preferably at least one of monohydric alcohol and polyhydric alcohol.

[0018] The monohydric alcohol can be any type of monohydric alcohol known in the art, such as C16 alcohols with one hydroxyl group. 1~20 Alkanes, for example, include methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol.

[0019] The polyol can be any type of polyol known in the art, such as C-type polyols with 2 to 10 (preferably 3 to 6) hydroxyl groups. 2~20 Alkanes, such as ethylene glycol, diethylene glycol, propylene glycol, glycerol, pentaerythritol, or polymers of such polyols, such as polyethylene glycol, polyvinyl alcohol, etc., or may be those contained in the C... 2~20 Polyhydroxyalkyl (poly)amines are obtained by inserting one or more nitrogen atoms into an alkane chain, such as monoethanolamine and triethanolamine.

[0020] The beneficial effects of this invention are as follows: By employing a combination of two adsorbent materials and controlling the pore size and functional groups of the adsorbent materials, this invention achieves selective adsorption of VOCs containing low-carbon light hydrocarbons. Larger VOC molecules are preferentially adsorbed and retained in region A of the adsorbent material, while smaller low-carbon light hydrocarbon molecules are adsorbed in region B. Overall, the tandem adsorption process is cost-effective, improves VOCs treatment efficiency, and extends the service life of the adsorbent materials. It is particularly suitable for applications in laboratories and testing facilities where multiple VOC components are present and low-carbon light hydrocarbons constitute a certain proportion. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0022] In this invention, the surface area is determined by the BET specific surface area measurement method.

[0023] Pore ​​volume was determined using the BJH (Barrett-Joyner-Halenda) method, and micropores were calculated using the t-plot method.

[0024] The carbon and nitrogen contents were determined by an elemental analyzer, and the oxygen content was determined by X-ray fluorescence spectroscopy.

[0025] Unless otherwise specified, all raw materials used in the following examples are commercially available.

[0026] The following example uses the exhaust gas generated by a laboratory building. The typical pollutants in this exhaust gas are benzene compounds, alcohols, esters, and liquefied petroleum gas (non-methane total hydrocarbons are 120~350 mg / m³). 3 The concentration of C3-C5 hydrocarbons is 40-70 mg / m³. 3 Intermittent emissions, with a single exhaust outlet air volume of 15000 Nm³. 3 / h, the extracted air volume is 1000Nm 3 / h, to examine the adsorption effect of the adsorption material. Example 1

[0027] After the outlet, 0.3 m³ of molded honeycomb A1 and 0.4 m³ of nitrogen-containing carbon-based material B1 are installed sequentially; the molded honeycomb A1 is composed of attapulgite and 13X molecular sieve mixed in a mass ratio of 2:5, and its specific surface area is 271 m². 2 / g, pore volume 0.37cm 3 / g, with a mesoporosity of 90%; the nitrogen-containing carbon-based material B1 is in particulate form with a specific surface area of ​​2133m². 2 / g, pore volume 2.3cm 3 / g, microporosity 88%, carbon content 94.6wt%, oxygen content 2.1wt%, nitrogen content 3.1wt%; the tail gas composition after adsorption for 5 hours at 20-25℃ is shown in Table 1.

[0028] The preparation method of carbon-based material B1 containing nitrogen groups is as follows: commercially available coconut shell activated carbon, 50% mass concentration nitric acid aqueous solution and melamine are refluxed at 60°C for 2 hours in a mass ratio of 10:4:1.5. The refluxed sample is filtered and calcined at 650°C for 3 hours to obtain porous adsorbent material B1.

[0029] Comparative Example 1 A 0.3 m³ molded honeycomb A1 is installed after the discharge outlet; the molded honeycomb A1 is composed of attapulgite and 13X molecular sieve mixed in a mass ratio of 2:5, and its specific surface area is 271 m². 2 / g, pore volume 0.37cm 3 The composition of the tail gas after adsorption at 20-25℃ for 5 hours with a porosity of 90% is shown in Table 1.

[0030] Comparative Example 2 A 0.4 m³ carbon-based material B1 containing nitrogen groups was installed after the exhaust port. The carbon-based material B1 containing nitrogen groups was the same as in Example 1. After adsorption at 20-25°C for 5 hours, the exhaust gas composition results are shown in Table 1. Example 2

[0031] After the outlet, 0.25 m³ of molded honeycomb A2 and 0.5 m³ of nitrogen-containing carbon-based material B2 are installed sequentially; molded honeycomb A2 is composed of attapulgite and Y molecular sieve mixed in a mass ratio of 2:6, and its specific surface area is 303 m². 2 / g, pore volume 0.40cm 3 / g, with a mesoporosity of 92%; the nitrogen-containing carbon-based material B2 is granular with a specific surface area of ​​1947m². 2 / g, pore volume 2.0cm 3 / g, microporosity 87%, carbon content 95.1wt%, oxygen content 1.4wt%, nitrogen content 3.1wt%; the tail gas composition after adsorption for 5 hours at 20-25℃ is shown in Table 1.

[0032] The preparation method of carbon-based material B2 containing nitrogen groups is as follows: commercially available coconut shell activated carbon, 70% mass concentration of phosphoric acid aqueous solution and melamine are refluxed at 110℃ for 2 hours in a mass ratio of 10:3:1.9. The refluxed sample is filtered and calcined at 680℃ for 3 hours to obtain porous adsorbent material B2. Example 3

[0033] After the outlet, install 0.2 m³ of commercial honeycomb activated carbon A3 and 0.5 m³ of nitrogen-containing carbon-based material B3 sequentially; the specific surface area of ​​commercial honeycomb activated carbon A3 is 940 m². 2 / g, pore volume 0.98cm 3 / g, with a mesoporosity of 52%; the nitrogen-containing carbon-based material B3 is in particulate form with a specific surface area of ​​1711 m². 2 / g, pore volume 1.7cm 3 / g, microporosity 80%, carbon content 96.1wt%, oxygen content 1.8wt%, nitrogen content 1.4wt%; the tail gas composition after adsorption for 5 hours at 20-25℃ is shown in Table 1.

[0034] The preparation method of carbon-based material B3 containing nitrogen groups is as follows: commercially available coconut shell activated carbon, 20% potassium hydroxide aqueous solution and urea are refluxed at 90°C for 1.5 hours in a mass ratio of 10:2:6. The refluxed sample is filtered, washed with water until neutral, and calcined at 750°C for 3 hours to obtain porous adsorbent material B3. Example 4

[0035] After the outlet, install 0.2 m³ of commercial honeycomb activated carbon A4 and 0.3 m³ of nitrogen-containing carbon-based material B4 sequentially; the specific surface area of ​​commercial honeycomb activated carbon A4 is 940 m². 2 / g, pore volume 0.98cm 3 / g, with a mesoporosity of 52%; the nitrogen-containing carbon-based material B4 is granular with a specific surface area of ​​1899m². 2 / g, pore volume 2.0cm 3 / g, microporosity 82%, carbon content 96.7wt%, oxygen content 2.1wt%, nitrogen content 1.1wt%; the tail gas composition after adsorption for 5 hours at 20-25℃ is shown in Table 1.

[0036] The preparation method of carbon-based material B4 containing nitrogen groups is as follows: coconut shell activated carbon, 40% mass concentration perchloric acid aqueous solution and pyridine are refluxed at 110℃ for 3 hours in a mass ratio of 10:3:4. The refluxed sample is filtered and calcined at 650℃ for 3 hours to obtain porous adsorbent material B4. Example 5

[0037] After the outlet, install 0.3 m³ of molded honeycomb A5 and 0.5 m³ of nitrogen-containing carbon-based material B5 sequentially; the molded honeycomb A5 is composed of attapulgite and activated carbon mixed in a mass ratio of 1:3, and its specific surface area is 480 m². 2 / g, pore volume 0.64cm 3 / g, with a mesoporosity of 78%; the nitrogen-containing carbon-based material B5 is granular with a specific surface area of ​​1899m². 2 / g, pore volume 2.0cm 3 The microporosity was 82%, the carbon content was 96.7 wt%, the oxygen content was 2.1 wt%, and the nitrogen content was 1.1 wt%. The tail gas composition after adsorption at 20-25℃ for 5 hours is shown in Table 1.

[0038] The preparation method of carbon-based material B5 containing nitrogen groups is the same as that in Example 4. Example 6

[0039] After the outlet, 0.3 m³ of molded honeycomb A6 and 0.4 m³ of nitrogen-containing carbon-based material B6 are installed sequentially. Molded honeycomb A6 is composed of attapulgite and 13X molecular sieve mixed in a mass ratio of 2:5, and its specific surface area is 271 m². 2 / g, pore volume 0.37cm 3 / g, with a mesoporosity of 90%; the specific surface area of ​​nitrogen-containing carbon-based material B6 is 2133m². 2 / g, pore volume 2.3cm3 / g, microporosity 88%, carbon content 94.6wt%, oxygen content 2.1wt%, nitrogen content 3.1wt%; the preparation method of nitrogen-containing carbon-based material B6 is the same as in Example 1.

[0040] After adsorption at 20-25℃ for 50 hours, A1 and B1 were regenerated by nitrogen desorption for 5 hours at a desorption temperature of 90℃. After regeneration, they were adsorbed again under the same conditions as in Example 1. The composition of the tail gas after 5 hours of adsorption is shown in Table 1.

[0041]

[0042] As can be seen from Table 1, the present invention can effectively selectively adsorb VOCs containing low-carbon light hydrocarbons from waste gas. After adsorption treatment, the content of non-methane total hydrocarbons in the waste gas ranges from 120 to 350 mg / m³. 3 Reduced to 3.9~7.4 mg / m³ 3 C3-C5 hydrocarbons range from 40-70 mg / m³ 3 Reduced to 1.2~2.2 mg / m³ 3 .

[0043] Although the invention has been described in detail herein with reference to exemplary embodiments, it should be understood that the invention is not limited to the described embodiments. Other variations, modifications, and embodiments within the scope of the invention will be recognized by those skilled in the art and who have access to the teachings herein. Therefore, the invention should be broadly interpreted in accordance with the claims set forth below.

Claims

1. A cascade adsorption method for waste gas containing volatile organic compounds, characterized in that, A cascade combination of adsorbent A and adsorbent B is used, with the gas space velocity on adsorbent A being 3000~5000 h⁻¹. ~1 The gas space velocity on adsorbent B is 500~5000 h⁻¹. ~1 The adsorbent A is selected from one or more combinations of zeolite, attapulgite, bentonite, activated carbon, metal oxides, and metal hydroxides, and the adsorbent B is a carbon-based material containing nitrogen groups.

2. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 1, characterized in that, In carbon-based materials containing nitrogen groups, the carbon content is 89-98 wt%, the oxygen content is 1-10 wt%, and the nitrogen content is 0.5-6 wt%.

3. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 2, characterized in that, The carbon content is 91-97 wt%, the oxygen content is 1-7 wt%, and the nitrogen content is 0.9-5 wt%.

4. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 3, characterized in that, The carbon content is 95-97 wt%, the oxygen content is 1-5 wt%, and the nitrogen content is 1.1-4.2 wt%.

5. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 1, characterized in that, The adsorption temperature is 10~60℃.

6. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 5, characterized in that, The adsorption temperature is 10~48℃.

7. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 6, characterized in that, The adsorption temperature is 10~30℃.

8. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 1, characterized in that, The specific surface area of ​​adsorbent A is 100~3000 m² 2 / g, pore volume 0.1~3.1cm 3 / g, with a mesoporosity of 50~90%.

9. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 1, characterized in that, The specific surface area of ​​adsorbent B is 600~3200 m². 2 / g, pore volume 0.8~3.1cm 3 / g, with a microporosity of 80~93%.

10. The cascade adsorption method for waste gas containing volatile organic compounds according to claim 1, characterized in that, The regeneration and cyclic adsorption of adsorbent A and adsorbent B are carried out under the following conditions: desorption temperature of 70~120℃, and vacuum or inert gas purging.

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