CN109999768B - Straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas - Google Patents
Straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas Download PDFInfo
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Abstract
The invention relates to a straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, which is applied to adsorption and removal of chlorinated aromatic hydrocarbon pollutants. The adsorbent takes crop straws as raw materials, and the surface of the natural straws is modified by adopting a graft polymerization process through alkali-urea pretreatment. And uniformly mixing the modified straws with the carbon material with high specific surface area according to a certain proportion, and finally carrying out extrusion granulation to prepare the straw-based composite adsorbent. Compared with commercial activated carbon, the prepared straw-based composite adsorbent has better performance of adsorbing chlorinated aromatic hydrocarbon.
Description
Technical Field
The invention belongs to the field of atmospheric pollution treatment, and particularly relates to a straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas.
Background
The chlorinated aromatic hydrocarbon pollutants such as dioxin and the like in incineration flue gas have high toxicity and carcinogenic, teratogenic and mutagenic 'tri-induced effects', and the pollution control on chlorinated aromatic hydrocarbon is widely concerned at home and abroad. The adsorption method is a main means for removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas, and is to enrich chlorinated aromatic hydrocarbon on the surface of an adsorbent so as to achieve the purpose of removing the chlorinated aromatic hydrocarbon pollutants from the flue gas. The key point of the adsorption method is the selection of an adsorbent, and the activated carbon has been widely applied to removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas due to the fact that the activated carbon has a high specific surface area and a developed pore structure. Although activated carbon has the obvious advantages of large adsorption capacity, high adsorption efficiency and the like, the commercial activated carbon for adsorbing gas pollutants is usually prepared by two processes of oxygen-free roasting and chemical activation, so that the preparation process is complex and the cost is high; in addition, activated carbon saturated with adsorbed pollutants has been listed in national hazardous waste records, and higher cost is also required for treatment. Aiming at pollution control of chlorinated aromatic hydrocarbon pollutants in incineration flue gas, development of a novel adsorbing material with high efficiency and low cost becomes one of research hotspots in the field of current environment functional materials.
The crop straw is a byproduct of agricultural production and is a renewable biomass resource. With the adjustment of agricultural energy structure and the promotion of intensive production mode in China, only a small part of straws are still used as fuel, fertilizer and feed in the traditional sense, a large amount of straws are discarded or incinerated in the open air at will every year, and the waste of biomass resources is caused while the atmospheric pollution and the land resource utilization are tense. In recent years, crop straws are researched and used for preparing novel biomass adsorbing materials, and the advantages of preparing the adsorbing materials by using the straws mainly include: (1) the material itself often has a rough appearance and a porous capillary structure, both of which are conducive to physical adsorption. (2) Because a large number of hydroxyl groups exist in the cell wall polymer, the cell wall polymer can be subjected to chemical reactions such as esterification, etherification, graft copolymerization and the like, and can be modified, so that the adsorption selectivity and the adsorption efficiency of the cell wall polymer on pollutants can be improved. At present, a plurality of straw-based modified adsorption materials are well applied to the aspect of environmental pollution treatment, and a patent (CN 106219657A) reports a modified biomass adsorbent and a preparation method and application thereof, wherein the preparation method takes straws as raw materials, the straws are subjected to crosslinking reaction with epoxy chloropropane under an alkaline condition, and the crosslinked product is reacted with trimethylamine aqueous solution to obtain a strong-alkaline anion adsorbent for adsorbing and removing NO in eutrophic water3 -And PO4 3-Has better adsorption effect at pH 3-9. A patent (CN 107252678A) reports a sulfydryl modified cassava straw adsorbent and a preparation method and application thereof, the preparation method prepares the cassava straw adsorbent with chelating functional groups on the surface by crushing, alkalizing and sulfydryl modifying cassava straws, and the adsorption of heavy metal Cd in wastewater by the cassava straw adsorbent is improved2+The ability of the cell to perform. A patent (CN 106824125A) reports a preparation method of a cellulose-based composite material with high adsorption performance, cellulose is made into microspheres, and pyrrole monomers are polymerized on the surfaces of the microspheres in situ, and the adsorption of the composite material prepared by the patent to a negative dye Congo red in wastewater is as high as 237 mg/g. But are reported so farThe straw modification-based adsorption material is mainly used for purifying water pollutants, and no related report for adsorbing and removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas is found.
Disclosure of Invention
The invention aims to provide a straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas and a preparation method thereof. Meanwhile, the modified straws are used as main adsorbing materials and mixed with a small amount of (A) with higher specific surface area>500m2The straw-based composite adsorbent is prepared from the carbonaceous material of/g), and provides a new possibility for solving the problems of high efficiency, low cost removal of chlorinated aromatic hydrocarbon in incineration flue gas and comprehensive utilization of crop straws.
The purpose of the invention is realized by the following technical scheme:
a straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas is characterized in that crop straws are used as raw materials of the adsorbent, alkali-urea pretreatment is carried out, styrene and acrylic acid monomers are selected as grafting monomers, and a suspension polymerization method is adopted to modify the straws. Uniformly mixing the modified straws with the carbon material with high specific surface area according to a certain proportion, wherein the mass of the modified straws is larger than that of the carbon material, and finally, carrying out extrusion granulation to prepare the straw-based composite adsorbent.
The preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas comprises the following steps:
(1) straw pretreatment: crushing straws by a high-speed crusher, sieving the crushed straws by a sieve with 80-200 meshes, putting the sieved part in a vacuum oven, drying the crushed straws for 12-24h at the temperature of 60-120 ℃, and storing the dried straws in a dryer for later use; preparing an aqueous solution of a NaOH-urea system, wherein the mass fraction of NaOH in the aqueous solution of the NaOH-urea system is 4-12%, the mass fraction of urea in the aqueous solution of the NaOH-urea system is 2-14%, and placing the aqueous solution of the NaOH-urea system into a refrigerator for precooling to-15-5 ℃; dispersing the dried straw powder in the pre-cooled NaOH-urea system aqueous solution according to the mass ratio of 1:10-1:20 and continuing until the reaction is complete; after low-temperature alkali treatment, centrifugally separating and washing the straws to be neutral by using deionized water, and drying the obtained straw samples in a vacuum oven to constant weight;
(2) straw modification treatment: dispersing the pretreated straws obtained in the step (1) in deionized water, adding styrene, acrylic acid monomer and initiator, stirring and heating to 55-80 ℃ under the protection of nitrogen, and reacting for 4-8 h; after the reaction is finished, introducing air, cooling for 0.5-2h by using ice water, centrifuging, washing a reaction product by using ethanol (95%) and deionized water, and drying in an oven to constant weight to obtain a modified straw material;
(3) synthesis of the composite adsorbent: and (3) mixing the modified straw material obtained in the step (2) with a carbonaceous material and deionized water, and preparing the granular straw-based composite adsorbent through a screw extruder.
In the above preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, preferably, the straws in the step (1) include crop straws such as corn straws, rice straw straws, wheat straws, reed straws and the like.
In the above preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, preferably, the acrylic acid monomer in the step (2) is one of methyl methacrylate, acrylic acid, butyl acrylate and butyl methacrylate.
In the above preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, preferably, the mass ratio of styrene to acrylic acid monomer in the step (2) is 1:1-10:1, and the mass ratio of the addition amount of styrene to the addition amount of pretreated straw is 0.1-2: 1.
In the above method for preparing a straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, preferably, the initiator in step (2) is one of benzoyl peroxide, lauroyl peroxide and hydrogen peroxide, and the addition amount ratio of the initiator to the straw is 0.4-1 mL/g.
In the above preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, preferably, the carbonaceous material in the step (3) includes graphite carbon, carbon nanotubes, activated carbon and biochar.
In the above preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, preferably, in the step (3), the mass ratio of the carbonaceous material to the modified straw material is 1:2-1:20, and the mass ratio of the deionized water to the modified straw material is 1:1-1: 5.
The principle of the invention is as follows: the straw raw material is crushed and sieved to enlarge the specific surface area. Then through low-temperature alkali treatment, substances in a solvent can form hydrogen bonds or covalent bonds with hydroxyl groups on cellulose macromolecules with higher bond energy at low temperature to gradually replace original hydrogen bonds between the cellulose macromolecules and hydrogen bonds in molecules, and the hydrogen bonds between partial cellulose molecules are destroyed, so that the cellulose is swelled, the accessibility of a reaction reagent is increased, and the further treatment of the cellulose is facilitated. And then, styrene and acrylic acid monomers are selected as grafting modified monomers, the hydrophobicity of cellulose is increased, and the spatial structure of the material is strengthened, so that the modified straw material with the surface provided with hydrophobic functional groups is prepared. The modified straw material is used as the main body of the composite adsorbent, and a small amount of carbon material with a high specific surface area is mixed to prepare the carbon material/modified straw composite adsorbing material, so that the dispersibility of the carbon material is improved, and the adsorption performance of the material is further improved. Finally, the composite material is extruded and granulated to prepare the granular composite adsorbent with certain mechanical strength. Compared with commercial activated carbon, the prepared straw-based composite adsorbent has better performance of adsorbing chlorinated aromatic hydrocarbon.
The invention also discloses an application of the straw-based composite adsorbent, and the adsorbent is applied to adsorption and removal of chlorinated aromatic hydrocarbon pollutants in incineration flue gas. O-dichlorobenzene (1, 2-dichlorobenzzene, o-DCB) is used as a representative chlorinated aromatic hydrocarbon compound, a fixed bed adsorption-on-line detection device is used for continuously testing the adsorption performance of the adsorbent, and the o-DCB after adsorption is detected by GC-FID to calculate the removal rate of the o-DCB; the test conditions were: total gas flow rate of 20-200mL/min, O2The content is 5-20%, the o-DCB concentration is 20-200ppm, the mass of the adsorbent is 50-500mg, the adsorption temperature is 15-100 ℃, and the adsorption is carried out at the time of adsorptionThe time interval is 20-100 min.
Compared with commercial activated carbon, the invention has the following advantages and beneficial effects:
1. in the straw-based composite adsorbent prepared by the invention, the modified straw material does not need oxygen-free roasting, and the adsorption capacity of the modified straw material on the chlorinated aromatic hydrocarbon pollutants is improved only by one-step chemical modification. After the modified straws are mixed with a small amount of carbonaceous material with higher specific surface area, the removal rate of the material to chlorinated aromatic hydrocarbon pollutants can be obviously improved, and the method has the outstanding advantages of simple preparation process, low cost and the like.
2. In the straw-based composite adsorbent prepared by the invention, the modified straw simultaneously selects styrene and acrylic acid monomers as graft modified monomers, so that the aromaticity and hydrophobicity of cellulose are increased, a spatial network structure can be formed after the two are polymerized, and high-efficiency adsorption capacity can be obtained by means of Van der Waals force and molecular gaps. The modified straw has unique physical and chemical properties, so that the modified straw has physical and chemical adsorption capacities.
3. The straw-based composite adsorbent prepared by the invention greatly improves the adsorption capacity of natural straw materials to chlorinated aromatic hydrocarbons, and provides possibility for replacing commercial activated carbon as an adsorbent for chlorinated aromatic hydrocarbon pollutants in incineration flue gas. As in example 1, when o-dichlorobenzene is used as a simulated gas of chlorinated aromatic hydrocarbons in a laboratory, when the adsorption time is 60min, the o-DCB removal rate of natural corn stalks is only 17.2%, and the o-DCB removal rate of commercial activated carbon is 86.1%, while the o-DCB removal rate of the prepared stalk-based composite adsorbent can reach 95.7%, and the adsorption performance evaluation result is shown in FIG. 1.
4. The straw-based composite adsorbent prepared by the invention provides a new method for removing chlorinated aromatic hydrocarbons in flue gas, expands the application range of biomass modified materials, and provides a new idea for effective resource utilization of agricultural waste straws.
Drawings
FIG. 1 shows the comparative evaluation results of the adsorption performance of the straw-based composite adsorbent prepared in example 1, natural corn straw and commercial activated carbon.
Detailed Description
The invention is described in detail below with reference to specific examples, which are not intended to limit the scope of the invention.
Example 1
1) Preparing a composite adsorbent: weighing 40g of corn straw, crushing by a high-speed crusher, sieving by a 80-mesh sieve, placing the sieved part in a vacuum oven, drying for 24 hours at the temperature of 60 ℃, and storing in a dryer for later use. Preparing NaOH-urea system aqueous solution, wherein the mass fraction of NaOH is 7%, the mass fraction of urea is 12%, and putting the aqueous solution into a refrigerator to cool to 0 ℃. Dispersing the straw powder in a precooled NaOH-urea system and continuously stirring for 5min, wherein the mass ratio of the added straw powder to the NaOH-urea system solution is 1: 12. After the straws are subjected to low-temperature alkali treatment, centrifugal separation is carried out by a centrifugal machine at the rotating speed of 4000r/min, the straws are washed to be neutral by deionized water, and the obtained straw samples are placed in a vacuum oven to be dried to constant weight at the temperature of 60 ℃.5g of the alkali-treated straw sample is weighed and dispersed in 80mL of deionized water reaction system, and then 5g of styrene, 2g of butyl acrylate and 2mL of benzoyl peroxide are added. Stirring and heating to 60 ℃ under the protection of nitrogen, and reacting for 6 h. After the reaction was complete, air was introduced and the reaction mixture was cooled with ice water for 0.5 h. Centrifuging, washing the reactant with ethanol (95%) and deionized water, and drying in an oven at 60 ℃ to constant weight to obtain the modified straw material. Weighing 4g of modified straw material, and fully mixing with activated carbon and deionized water, wherein the mixing ratio is activated carbon: modified straw material: and (3) deionized water is 1:6:1, and finally, the granular straw-based composite adsorbent is prepared by extrusion granulation.
2) Experimental procedure for the adsorption of ortho-dichlorobenzene (o-DCB)
And evaluating the performance of the o-DCB in the chlorinated aromatic hydrocarbon model compound adsorbed and removed from the gas phase by using a fixed bed adsorption-online detection system, and calculating the o-DCB removal rate by detecting the adsorbed o-DCB through GC-FID.
Adsorption conditions: total gas flow rate of 60mL/min, O2The content is 10 percent, the o-DCB concentration is 50ppm, the mass of the adsorbent is 80mg, the adsorption temperature is 50 ℃, and the adsorption time is 60 min;
pretreatment of an adsorbent: pretreating the adsorbent at 120 ℃ for 2 h;
loading an adsorbent: 80mg of the adsorbent was packed in a stainless steel adsorbent bed (inner diameter: 5mm), and quartz wool pads were packed at both ends of the adsorbent.
3) The performance of the adsorbent for adsorbing and removing o-DCB is evaluated by the removal rate of o-DCB.
TABLE 1 efficiency of o-DCB adsorption removal by straw-based composite adsorbent described in example 1
Example 2
1) Preparing a composite adsorbent: weighing 40g of corn straw, crushing by a high-speed crusher, sieving by a 200-mesh sieve, placing the sieved part in a vacuum oven, drying for 24 hours at the temperature of 60 ℃, and storing in a dryer for later use. Preparing NaOH-urea system aqueous solution, wherein the mass fraction of NaOH is 7%, the mass fraction of urea is 12%, and putting the aqueous solution into a refrigerator to cool to 0 ℃. Dispersing the straw powder in a precooled NaOH-urea system and continuously stirring for 5min, wherein the mass ratio of the added straw powder to the NaOH-urea system solution is 1: 20. After the straws are subjected to alkali treatment, centrifugal separation is carried out by a centrifugal machine at the rotating speed of 4000r/min, the straws are washed to be neutral by deionized water, and the obtained straw samples are placed in a vacuum oven to be dried to constant weight at 60 ℃. Weighing 5g of the alkali-treated straw sample, dispersing the alkali-treated straw sample in 80mL of deionized water reaction system, and then adding 5g of styrene, 0.5g of acrylic acid and 2mL of 30% H2O2. Stirring and heating to 60 ℃ under the protection of nitrogen, and reacting for 6 h. After the reaction was complete, air was introduced and the reaction mixture was cooled with ice water for 0.5 h. Centrifuging, washing the reactant with ethanol (95%) and deionized water, and drying in an oven at 60 ℃ to constant weight to obtain the modified straw. Weighing 4g of modified straw, and fully mixing the modified straw with the carbon nano tube and deionized water according to the mixing ratio of the carbon nano tube: modifying straws: and (3) deionized water is added in a ratio of 1:9:4, and finally, the granular straw-based composite adsorbent is prepared by extrusion granulation.
2) Experimental procedure for the adsorption of ortho-dichlorobenzene (o-DCB)
And evaluating the performance of the o-DCB in the chlorinated aromatic hydrocarbon model compound adsorbed and removed from the gas phase by using a fixed bed adsorption-online detection system, and calculating the o-DCB removal rate by detecting the adsorbed o-DCB through GC-FID.
Adsorption conditions: total gas flow rate of 60mL/min, O2The content is 10 percent, the o-DCB concentration is 50ppm, the mass of the adsorbent is 80mg, the adsorption temperature is 80 ℃, and the adsorption time is 60 min;
pretreatment of an adsorbent: pretreating the adsorbent at 120 ℃ for 2 h;
loading an adsorbent: 80mg of the adsorbent was packed in a stainless steel adsorbent bed (inner diameter: 5mm), and quartz wool pads were packed at both ends of the adsorbent.
3) The performance of the adsorbent for adsorbing and removing o-DCB is evaluated by the removal rate of o-DCB.
TABLE 2 efficiency of o-DCB adsorption removal by straw-based composite adsorbent described in example 2
Example 3
1) Preparing a composite adsorbent: weighing 40g of reed straw, crushing by a high-speed crusher, sieving by a 80-mesh sieve, placing the sieved part in a vacuum oven, drying for 12 hours at 120 ℃, and storing in a dryer for later use. Preparing NaOH-urea system solution, wherein the mass fraction of NaOH is 7%, the mass fraction of urea is 12%, and putting the solution into a refrigerator to cool the solution to 5 ℃. Dispersing the straw powder in a precooled NaOH-urea system and continuously stirring for 5min, wherein the mass ratio of the added straw powder to the NaOH-urea system solution is 1: 12. After the straws are subjected to alkali treatment, centrifugal separation is carried out by a centrifugal machine at the rotating speed of 4000r/min, the straws are washed to be neutral by deionized water, and the obtained straw samples are placed in a vacuum oven to be dried to constant weight at 60 ℃. Weighing 5g of the alkali-treated straw sample, dispersing the alkali-treated straw sample in 120mL of deionized water reaction system, and then adding 10g of styrene, 4g of methyl methacrylate and 4mL of 30% H2O2. Stirring and heating to 60 ℃ under the protection of nitrogen, and reacting for 8 h. After the reaction was completed, air was introduced and cooled with ice water for 2 hours. Centrifuging, washing the reactant with ethanol (95%) and deionized water, and drying in an oven at 60 ℃ to constant weight to obtain the modified straw. BalanceTaking 4g of modified straws, and fully mixing with activated carbon and deionized water, wherein the mixing ratio is activated carbon: modifying straws: and (3) deionized water is added in a ratio of 1:5:2, and finally, the granular straw-based composite adsorbent is prepared by extrusion granulation.
2) Experimental procedure for the adsorption of ortho-dichlorobenzene (o-DCB)
And evaluating the performance of the o-DCB in the chlorinated aromatic hydrocarbon model compound adsorbed and removed from the gas phase by using a fixed bed adsorption-online detection system, and calculating the o-DCB removal rate by detecting the adsorbed o-DCB through GC-FID.
Adsorption conditions: total gas flow rate of 60mL/min, O2The content is 20%, the o-DCB concentration is 50ppm, the mass of the adsorbent is 100mg, the adsorption temperature is 50 ℃, and the adsorption time is 60 min;
pretreatment of an adsorbent: pretreating the adsorbent at 120 ℃ for 2 h;
loading an adsorbent: 100mg of the adsorbent was packed in a stainless steel adsorbent bed (inner diameter: 5mm), and quartz wool pads were packed at both ends of the adsorbent.
3) The performance of the adsorbent for adsorbing and removing o-DCB is evaluated by the removal rate of o-DCB.
TABLE 3 efficiency of o-DCB adsorption removal by straw-based composite adsorbent described in example 3
Example 4
1) Preparing a composite adsorbent: weighing 40g of wheat straw, crushing by a high-speed crusher, sieving by a 80-mesh sieve, placing the sieved part in a vacuum oven, drying for 24 hours at the temperature of 60 ℃, and storing in a dryer for later use. Preparing NaOH-urea system aqueous solution, wherein the mass fraction of NaOH is 9%, the mass fraction of urea is 9%, and putting the aqueous solution into a refrigerator to cool the aqueous solution to 0 ℃. Dispersing the straw powder in a precooled NaOH-urea system and continuously stirring for 5min, wherein the mass ratio of the added straw powder to the NaOH-urea system solution is 1: 12. After the straws are subjected to alkali treatment, centrifugal separation is carried out by a centrifugal machine at the rotating speed of 4000r/min, the straws are washed to be neutral by deionized water, and the obtained straw samples are placed in a vacuum oven to be dried to constant weight at 60 ℃.5g of the alkali-treated straw sample is weighed and dispersed in 80mL of deionized water reaction system, and then 10g of styrene, 1g of butyl methacrylate and 2mL of lauroyl peroxide are added. Stirring and heating to 80 ℃ under the protection of nitrogen, and reacting for 4 h. After the reaction was complete, air was introduced and the reaction mixture was cooled with ice water for 0.5 h. Centrifuging, washing the reactant with ethanol (95%) and deionized water, and drying in an oven at 60 ℃ to constant weight to obtain the modified straw. Weighing 4g of modified straw, and fully mixing the modified straw with graphite carbon and deionized water, wherein the mixing ratio is graphite carbon: modifying straws: and (3) deionized water is added in a ratio of 1:3:3, and finally, the granular straw-based composite adsorbent is prepared by extrusion granulation.
2) Experimental procedure for the adsorption of ortho-dichlorobenzene (o-DCB)
And evaluating the performance of the o-DCB in the chlorinated aromatic hydrocarbon model compound adsorbed and removed from the gas phase by using a fixed bed adsorption-online detection system, and calculating the o-DCB removal rate by detecting the adsorbed o-DCB through GC-FID.
Adsorption conditions: total gas flow rate of 60mL/min, O2The content is 10 percent, the o-DCB concentration is 50ppm, the mass of the adsorbent is 200mg, the adsorption temperature is 50 ℃, and the adsorption time is 60 min;
pretreatment of an adsorbent: pretreating the adsorbent at 120 ℃ for 2 h;
loading an adsorbent: 200mg of adsorbent was packed in a stainless steel adsorbent bed (inner diameter: 5mm), and quartz wool pads were packed at both ends of the adsorbent.
3) The performance of the adsorbent for adsorbing and removing o-DCB is evaluated by the removal rate of o-DCB.
TABLE 4 efficiency of o-DCB adsorptive removal by straw-based composite adsorbent as described in example 4
Example 5
1) Preparing a composite adsorbent: weighing 40g of rice straw, crushing by a high-speed crusher, sieving by a 80-mesh sieve, placing the sieved part in a vacuum oven, drying for 24 hours at the temperature of 60 ℃, and storing in a dryer for later use. Preparing NaOH-urea system solution, wherein the mass fraction of NaOH is 6%, the mass fraction of urea is 4%, and putting the solution into a refrigerator to cool the solution to 0 ℃. Dispersing the straw powder in a precooled NaOH-urea system and continuously stirring for 5min, wherein the mass ratio of the added straw powder to the NaOH-urea system solution is 1: 12. After the straws are subjected to alkali treatment, centrifugal separation is carried out by a centrifugal machine at the rotating speed of 4000r/min, the straws are washed to be neutral by deionized water, and the obtained straw samples are placed in a vacuum oven to be dried to constant weight at 60 ℃.5g of the alkali-treated straw sample is weighed and dispersed in 80mL of deionized water reaction system, and then 1g of styrene, 1g of butyl acrylate and 2mL of benzoyl peroxide are added. Stirring and heating to 60 ℃ under the protection of nitrogen, and reacting for 6 h. After the reaction was complete, air was introduced and the reaction mixture was cooled with ice water for 0.5 h. Centrifuging, washing the reactant with ethanol (95%) and deionized water, and drying in an oven at 60 ℃ to constant weight to obtain the modified straw. Weighing 4g of modified straw, and fully mixing with activated carbon and deionized water, wherein the mixing ratio is activated carbon: modifying straws: and (3) deionized water is added in a ratio of 1:20:4, and finally, the granular straw-based composite adsorbent is prepared by extrusion granulation.
2) Experimental procedure for the adsorption of ortho-dichlorobenzene (o-DCB)
And evaluating the performance of the o-DCB in the chlorinated aromatic hydrocarbon model compound adsorbed and removed from the gas phase by using a fixed bed adsorption-online detection system, and calculating the o-DCB removal rate by detecting the adsorbed o-DCB through GC-FID.
Adsorption conditions: the total gas flow is 150mL/min, O2The content is 10 percent, the o-DCB concentration is 50ppm, the mass of the adsorbent is 80mg, the adsorption temperature is 50 ℃, and the adsorption time is 60 min;
pretreatment of an adsorbent: pretreating the adsorbent at 120 ℃ for 2 h;
loading an adsorbent: 80mg of the adsorbent was packed in a stainless steel adsorbent bed (inner diameter: 5mm), and quartz wool pads were packed at both ends of the adsorbent.
3) The performance of the adsorbent for adsorbing and removing o-DCB is evaluated by the removal rate of o-DCB.
TABLE 5 efficiency of o-DCB removal by adsorption with straw-based composite adsorbent described in example 5
Example 6
1) Preparing a composite adsorbent: weighing 40g of corn straw, crushing by a high-speed crusher, sieving by a 80-mesh sieve, placing the sieved part in a vacuum oven, drying for 24 hours at the temperature of 60 ℃, and storing in a dryer for later use. Preparing NaOH-urea system aqueous solution, wherein the mass fraction of NaOH is 7%, the mass fraction of urea is 12%, and putting the aqueous solution into a refrigerator to cool to-10 ℃. Dispersing the straw powder in a precooled NaOH-urea system and continuously stirring for 15min, wherein the mass ratio of the added straw powder to the NaOH-urea system solution is 1: 12. After the straws are subjected to alkali treatment, centrifugal separation is carried out by a centrifugal machine at the rotating speed of 4000r/min, the straws are washed to be neutral by deionized water, and the obtained straw samples are placed in a vacuum oven to be dried to constant weight at 60 ℃.5g of the alkali-treated straw sample is weighed and dispersed in 80mL of deionized water reaction system, and then 1g of styrene, 0.1g of acrylic acid and 2mL of benzoyl peroxide are added. Stirring and heating to 60 ℃ under the protection of nitrogen, and reacting for 6 h. After the reaction was complete, air was introduced and the reaction mixture was cooled with ice water for 0.5 h. Centrifuging, washing the reactant with ethanol (95%) and deionized water, and drying in an oven at 60 ℃ to constant weight to obtain the modified straw. Weighing 4g of modified straw, and fully mixing with activated carbon and deionized water, wherein the mixing ratio is activated carbon: modifying straws: and (3) deionized water is added in a ratio of 1:9:3, and finally, the granular straw-based composite adsorbent is prepared by extrusion granulation.
2) Experimental procedure for the adsorption of ortho-dichlorobenzene (o-DCB)
And evaluating the performance of the o-DCB in the chlorinated aromatic hydrocarbon model compound adsorbed and removed from the gas phase by using a fixed bed adsorption-online detection system, and calculating the o-DCB removal rate by detecting the adsorbed o-DCB through GC-FID.
Adsorption conditions: total gas flow rate of 60mL/min, O2The content is 5%, the o-DCB concentration is 150ppm, the mass of the adsorbent is 80mg, the adsorption temperature is 50 ℃, and the adsorption time is 60 min;
pretreatment of an adsorbent: pretreating the adsorbent at 120 ℃ for 2 h;
loading an adsorbent: 80mg of the adsorbent was packed in a stainless steel adsorbent bed (inner diameter: 5mm), and quartz wool pads were packed at both ends of the adsorbent.
3) The performance of the adsorbent for adsorbing and removing o-DCB is evaluated by the removal rate of o-DCB.
TABLE 6 efficiency of o-DCB adsorptive removal by straw-based composite adsorbent as described in example 6
In conclusion, under the same use condition, the removal efficiency of the straw-based composite adsorbent prepared by the invention is higher than that of commercial activated carbon, and the removal efficiency reaches the best when the adsorption time is 60 min.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, but rather as the subject matter of any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention.
Claims (7)
1. A straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas is characterized in that crop straws are used as raw materials, alkali-urea pretreatment is carried out on the raw materials, the surfaces of natural straws are modified by adopting a graft polymerization process, modified straws are used as main adsorption materials, the modified straws and carbon materials with high specific surface area are uniformly mixed according to a ratio, the mass ratio of the carbon materials to the modified straws is 1:2-1:20, and finally, the straw-based composite adsorbent is prepared by extrusion granulation;
the straw modification treatment process comprises the following steps: dispersing the pretreated straws in deionized water, adding styrene, acrylic acid monomer and initiator, stirring and heating to 55-80 ℃ under the protection of nitrogen, and reacting for 4-8 h; after the reaction is finished, introducing air, cooling for 0.5-2h by using ice water, centrifuging, washing a reaction product by using ethanol and deionized water, and drying in an oven to constant weight to obtain a modified straw material; wherein the mass ratio of the styrene to the acrylic acid monomer is 1:1-10:1, and the mass ratio of the addition amount of the styrene to the addition amount of the straws is 0.1-2.
2. The preparation method of the straw-based composite adsorbent for purifying chlorinated aromatic hydrocarbons in incineration flue gas, which is disclosed by claim 1, comprises the following steps of:
(1) straw pretreatment: crushing straws by a high-speed crusher, sieving the crushed straws by a sieve with 80-200 meshes, putting the sieved part in a vacuum oven, drying the crushed straws for 12-24h at the temperature of 60-120 ℃, and storing the dried straws in a dryer for later use; preparing an aqueous solution of a NaOH-urea system, wherein the mass fraction of NaOH in the aqueous solution of the NaOH-urea system is 4-12%, the mass fraction of urea in the aqueous solution of the NaOH-urea system is 2-14%, and placing the aqueous solution of the NaOH-urea system into a refrigerator for precooling to-15-5 ℃; dispersing the dried straw powder in the pre-cooled NaOH-urea system aqueous solution according to the mass ratio of 1:10-1:20 and continuing until the reaction is complete; after low-temperature alkali treatment, centrifugally separating and washing the straws to be neutral by using deionized water, and drying the obtained straw samples in a vacuum oven to constant weight;
(2) straw modification treatment: dispersing the pretreated straws obtained in the step (1) in deionized water, adding styrene, acrylic acid monomer and initiator, stirring and heating to 55-80 ℃ under the protection of nitrogen, and reacting for 4-8 h; after the reaction is finished, introducing air, cooling for 0.5-2h by using ice water, centrifuging, washing a reaction product by using ethanol and deionized water, and drying in an oven to constant weight to obtain a modified straw material;
(3) synthesis of the composite adsorbent: and (3) mixing the modified straw material obtained in the step (2) with a carbonaceous material and deionized water, and preparing the granular straw-based composite adsorbent through a screw extruder.
3. The method of claim 1 or 2, wherein the stalks comprise corn stalks, rice straw stalks, wheat straw or reed stalks.
4. The preparation method of the straw-based composite adsorbent according to claim 2, wherein the acrylic acid monomer is one of methyl methacrylate, acrylic acid, butyl acrylate and butyl methacrylate.
5. The preparation method of the straw-based composite adsorbent according to claim 2, wherein the initiator is one of benzoyl peroxide, lauroyl peroxide and hydrogen peroxide, and the ratio of the initiator to the added amount of the straw is 0.4-1 mL/g.
6. The preparation method of the straw-based composite adsorbent according to claim 2, wherein the carbonaceous material is at least one of graphite carbon, carbon nanotubes, activated carbon or biochar, and the mass ratio of the deionized water to the modified straw material in the step (3) is 1:1-1: 5.
7. The application of the straw-based composite adsorbent as defined in any one of claims 1 to 6, wherein: the adsorbent is applied to adsorbing and removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas, o-dichlorobenzene (1, 2-dichlorobenzzene, o-DCB) is used as a chlorinated aromatic hydrocarbon representative compound, a fixed bed adsorption-on-line detection device is used for continuously testing the adsorption performance of the adsorbent, and the o-DCB removal rate is obtained by calculation after the o-DCB after adsorption is detected by GC-FID; the test conditions were: total gas flow rate of 20-200mL/min, O2The content is 5-20%, the o-DCB concentration is 20-200ppm, the mass of the adsorbent is 50-500mg, the adsorption temperature is 15-100 ℃, and the adsorption time is 20-100 min.
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