CN111974357B - Method for preparing chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by using lignin - Google Patents
Method for preparing chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by using lignin Download PDFInfo
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Abstract
The invention relates to a method for preparing a chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by utilizing lignin. The lignin-based composite adsorbents of different types are used for adsorbing and removing chlorinated aromatic hydrocarbons, and a new possibility is provided for efficient and low-cost removal of chlorinated aromatic hydrocarbons in incineration flue gas and comprehensive utilization of lignin resources.
Description
Technical Field
The invention belongs to the field of atmospheric pollution treatment, and particularly relates to a method for preparing a chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by using lignin.
Background
Chlorinated aromatic hydrocarbon pollutants such as dioxin and the like in incineration flue gas have the characteristics of carcinogenicity, teratogenicity and mutagenicity and high toxicity, 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 pollutant molecules by utilizing the interaction between an adsorbent and the pollutant molecules. Commonly used adsorbents include activated carbon, molecular sieves, Metal Organic Framework Structures (MOFs), and the like. The preparation process of the molecular sieve and the MOF is complex, the adsorption capacity is limited, and the hydrothermal stability is poor. Commercial activated carbon has better hydrothermal stability, however coal-based activated carbon is a main source of commercial activated carbon, and coal is a non-renewable fossil resource. Meanwhile, a small amount of metal ions exist in the coal-based activated carbon, impurities such as iron ions and the like are usually removed by using high-strength acid washing, the cost is increased to a certain extent, and waste acid is recycled. Therefore, aiming at pollution control of chlorinated aromatic hydrocarbon pollutants in incineration flue gas, development of efficient and low-cost novel adsorption materials by utilizing renewable resources has become one of the research hotspots in the current environmental field.
Lignin is the only renewable resource of aromatic compounds in nature. In the paper making industry, most lignin is discharged into rivers or burnt in a black liquor form, and waste of biomass resources is caused while water pollution and air pollution are caused. Therefore, the method for preparing the adsorbing material by utilizing the waste resource-lignin in the paper making industry to eliminate the chlorinated aromatic hydrocarbon in the incineration flue gas not only relieves the environmental pollution pressure, but also has economic feasibility. Meanwhile, the lignin-based composite adsorbent is used as an adsorbing material for purifying the high-toxicity chlorinated aromatic hydrocarbon, and has the following advantages: (1) the lignin contains a large amount of hydroxyl groups, can perform chemical reactions such as esterification, etherification, graft copolymerization and the like, and can optimize the specific surface area and the microporosity of the lignin-based composite adsorption material through modification and modification, thereby improving the adsorption selectivity and the adsorption efficiency of the lignin-based composite adsorption material on chlorinated aromatic polar pollutants; (2) the lignin basic structure units comprise aromatic structures such as syringyl, guaiacyl and p-hydroxy structures, the basic structure units are linked by C-O/C-C to form a complex three-dimensional network structure, and the adsorption performance of the lignin-based composite adsorption material can be improved by optimizing the lignin structure; (3) the lignin-based composite adsorbent prepared from lignin with an aromatic structure is beneficial to adsorption of aromatic pollutants such as chlorinated aromatic hydrocarbon.
At present, the preparation method and the application of lignin-based carbon materials are reported in patents. The patent (CN 106044744B) reports a preparation method and application of a graphene/lignin-based composite hierarchical pore carbon sheet material. The patent (CN 110518243A) reports the application of lignin in the preparation of a lithium battery graphite negative electrode material, and the patent firstly stabilizes the lignin, then pyrolyzes the lignin at 1200-1500 ℃, and finally graphitizes the lignin at 2500-2800 ℃ to obtain the graphite negative electrode material. Patent (CN 106167263a) reports a method for preparing activated carbon from papermaking black liquor lignin, in which lignin and an alkaline activator are first mixed by ball milling, and then heated to 400-600 ℃ for carbonization, and then heated to 750-1000 ℃ for activation. And finally, adjusting the pH value of the soak solution to be neutral by using acid, and drying to obtain the finished product of the activated carbon, which is used for environmental protection aspects such as urban sewage treatment, drinking water treatment, furniture purification and the like, and removing odor, toxic pollutants, heavy metals and the like.
However, the following problems are reported in the lignin-based carbon materials: 1) the preparation steps are complicated, and more chemical raw materials are consumed. For example, some lignin-based carbon materials require pre-carbonization, activation with chemical reagents such as KOH, and subsequent carbonization; 2) the cost is high. For example, graphene is compounded with lignin carbon, so that large-area popularization is not easy to carry out; 3) the energy consumption is higher. At present, the preparation temperature of the lignin-based carbonaceous material is mostly required to be carbonized at the temperature higher than 400 ℃, and the carbonization temperature is even up to 2500 ℃ by some methods. In addition to the above problems, currently, lignin-based carbon materials are mostly used as electrode materials or for purifying pollutants in water, and researches for selectively purifying highly toxic aryl chloride pollutants in incineration flue gas by using lignin to prepare carbonaceous adsorption materials are not available. Therefore, the lignin-based composite adsorbent with simple development steps, low cost, low energy consumption and strong operability has important research value for adsorption of chlorinated aromatic hydrocarbon in incineration flue gas.
Disclosure of Invention
The invention aims to provide a method for preparing a chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by utilizing lignin.
The purpose of the invention is realized by the following technical scheme:
the method is characterized in that waste lignin of different types in the paper making industry is combined with sludge, the lignin-based composite adsorbent with high specific surface area and high graphitization degree is obtained through low-temperature heat treatment, and finally the composite adsorbent is used for adsorbing and removing chlorinated aromatic hydrocarbon. Further, the lignin-based composite adsorbent is used for selectively adsorbing chlorinated aromatic hydrocarbons in incineration flue gas.
A method for preparing a chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by using lignin comprises the following steps:
(1) preparing a lignin/sludge mixed material: sieving lignin with a 40-150 mesh sieve, drying in a vacuum oven at 60 ℃ for 12-24h, drying sludge, mixing the dried lignin and sludge with a proper amount of water according to a certain mass ratio, weighing 5g of the mixture, putting the mixture into a 100ml ball milling tank, adjusting the rotating speed to 180-220rpm, ball milling for 18-24h, and then putting the ball milling tank into the vacuum oven to dry to constant weight to obtain the lignin/sludge mixed material. Wherein the water is added in an amount that the water can be completely absorbed by the dried sludge, no water can be seen on the surface, and the sludge is in a wet state.
(2) Preparing a lignin-based composite adsorbent: and (2) placing the mixed material obtained in the step (1) in a pyrolysis furnace, and carrying out heat treatment at the temperature of 100-250 ℃ in the nitrogen atmosphere to obtain the lignin-based composite adsorbent.
The method comprises the following steps of using a lignin-based composite adsorbent for adsorbing and removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas, using o-dichlorobenzene-DCB as a chlorinated aromatic hydrocarbon representative compound, using toluene as other types of pollutants, and continuously testing the adsorption performance of the composite adsorbent by using a fixed bed adsorption-online detection device until adsorption is saturated; and (4) detecting the adsorbed pollutants by GC-FID, and calculating to obtain the adsorption capacity of the lignin-based composite adsorbent. When continuously testing, the total gas flow is 50-200ml/min, the o-DCB or toluene concentration is 20-200ppm, the adsorbent mass is 50-500mg, and the adsorption temperature is 15-100 ℃.
And (3) using the lignin-based composite adsorbent obtained in the step (2) for adsorbing and removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas, using o-dichlorobenzene (1, 2-dichlorobenzzene, o-DCB) as a chlorinated aromatic hydrocarbon representative compound, using toluene as other types of pollutants, and continuously testing the adsorption performance of the composite adsorbent by using a fixed bed adsorption-online detection device until adsorption is saturated. And (4) detecting the adsorbed pollutants by GC-FID, and calculating to obtain the adsorption capacity of the lignin-based composite adsorbent.
Preferably, the industrial lignin in step (1) includes at least one of birch lignin, poplar lignin, pine lignin, corn stalk lignin, etc.
Preferably, the mass ratio of the lignin to the sludge in the step (1) is 1:1-5:1, and the preferred mass ratio is 3: 1-5: 1; the content of alumina in the sludge is 10-20 wt%, the content of calcium oxide is 8-15 wt%, and the content of alumina in the sludge is 10-15 wt%, and the content of calcium oxide in the sludge is 8-10 wt% is preferred. .
Preferably, the low-temperature heat treatment temperature in the step (2) is 100-.
Preferably, in the step (2), the heat treatment time is 0.5-4 h.
The saturated adsorption capacity of the lignin-based composite adsorbent to o-DCB is 70-250mg/g, and the adsorption capacity to toluene is 40-55 mg/g.
Compared with commercial activated carbon, the invention has the following advantages and beneficial effects:
1. in the lignin-based composite adsorbent prepared by the invention, a ball milling process is introduced, so that a lignin polymolecular layer is adsorbed on sludge particles, and a plurality of sites can be formed between carbon, nitrogen and carbon and oxygen in the preparation process of the lignin-based composite adsorbent, thereby facilitating the reaction of lignin and active substances calcium oxide and aluminum oxide in sludge; by controlling the heat treatment temperature (100 ℃ and 250 ℃), the chemical reaction inside the lignin and sludge mixed material is regulated and controlled, and then the structure of the lignin-based composite adsorbent is regulated, so that the adsorbent is partially carbonized, and functional groups such as aromatic structures, hydroxyl groups, methoxyl groups and the like inside the lignin are retained, so that the lignin-based composite adsorbent has good adsorption selectivity on organic pollutants with similar molecular weights, the specific surface area and the microporosity of the lignin-based composite adsorbent can be improved, and the adsorption selectivity and the adsorption efficiency on chlorinated aromatic hydrocarbon polar pollutants are improved. The lignin-based composite adsorbent can be obtained by one-step low-temperature heat treatment, has the advantages of simple preparation process, easy operation control and the like, is convenient to popularize and use, and has the advantages of low energy consumption, low cost, economy and environmental protection compared with the high-temperature carbon/activation of the traditional carbonaceous adsorbent.
2. The lignin-based composite adsorbent prepared by the invention selects the precursor material as waste lignin in the paper making industry, and is a renewable resource with rich source and low price; sludge of a domestic sewage treatment plant is selected as a raw material, active substances, namely calcium oxide and aluminum oxide, contained in the sludge can cause lignin to undergo epoxidation modification, and the modified lignin has a structure similar to that of aromatic compounds, so that the aromatic compound absorption is greatly improved; the generated lignin-based composite adsorbent has stable chemical properties and has good tolerance capability to strong alkali, strong acid and high temperature.
3. The lignin-based composite adsorbent prepared by the invention is used for selectively adsorbing and purifying high-toxicity chlorinated aromatic hydrocarbon pollutants in incineration flue gas; chlorinated aromatic hydrocarbon has a benzene ring, and the benzene ring has a large pi bond, so that the chlorinated aromatic hydrocarbon has a complex structure, the study on the adsorption of the chlorinated aromatic hydrocarbon is difficult, and the study on an adsorbent with high adsorption capacity is few at present. The lignin-based composite adsorbent developed by the patent greatly improves the adsorption capacity of chlorinated aromatic hydrocarbon compared with commercial activated carbon due to the retention of an aromatic structure and corresponding functional groups, and provides possibility for replacing the commercial activated carbon as an adsorbent for chlorinated aromatic hydrocarbon pollutants in incineration flue gas. In example 1, o-dichlorobenzene and toluene were used as the laboratory chlorinated aromatic hydrocarbon simulated gas, the saturated adsorption capacities of the poplar/pine/corn stalk lignin-based composite adsorbent to o-DCB were 220mg/g, 198 mg/g and 209mg/g, respectively, and the saturated adsorption capacity of the commercial activated carbon to o-DCB was 47 mg/g; meanwhile, the lignin-based composite adsorbent selectively adsorbs chlorinated aromatic hydrocarbons, the toluene adsorption capacity of the poplar/pine/corn straw lignin-based composite adsorbent is 53/45/48mg/g respectively, and the toluene adsorption capacity of the commercial activated carbon is close to that of chlorinated aromatic hydrocarbons and is 37 mg/g.
4. The lignin-based composite adsorbent prepared by the invention provides a new method for removing chlorinated aromatic hydrocarbons in flue gas, and simultaneously provides a new idea for effectively recycling waste lignin and domestic sludge in the paper industry.
Drawings
FIG. 1 is a pore size diagram of commercial activated carbon under an electron microscope.
FIG. 2 is a scanning electron micrograph of the lignin-based composite adsorbent prepared in example 1.
Comparing fig. 1 and fig. 2, it can be seen from the images under scanning electron microscope that the prepared lignin-based composite adsorbent has a significantly increased number of pores compared with commercial activated carbon.
Fig. 3 is a graph of adsorption curves for commercial activated carbon.
FIG. 4 is a graph showing the adsorption profile of the lignin-based composite adsorbent prepared in example 1.
Comparing fig. 3 and fig. 4, it is apparent from the adsorption graphs of the two that the adsorption amount of the lignin-based composite adsorbent is much larger than that of the 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.
The sludge below is the sludge treated by a sewage treatment plant (the content of an important active substance in the sludge is 10-20 wt%, the content of calcium oxide is 8-15 wt%, and the other components are mainly organic matters), and the sludge is dried and directly used.
Example 1
1) Preparing the lignin-based composite adsorbent: weighing 5g of poplar lignin, pine lignin or corn straw lignin, sieving with a 60-mesh sieve, placing the sieved part in a vacuum oven, drying at 60 ℃ for 24h, and storing in a dryer for later use. And (2) drying the sludge, wherein the content of alumina in the sludge is 15 wt%, the content of calcium oxide in the sludge is 10 wt%, mixing the dried lignin and the sludge with a proper amount of water according to the mass ratio of 3:1, weighing 5g of the mixture, putting the mixture into a 100mL ball milling tank, adjusting the rotation speed to 200rpm, carrying out ball milling for 24 hours to obtain a lignin/sludge mixed material, and then putting the lignin/sludge mixed material into a vacuum oven to be dried to constant weight. Wherein the water is added in an amount that the water can be completely absorbed by the dried sludge, no water can be seen on the surface, and the sludge is in a wet state.
Placing the pretreated mixed material in a pyrolysis furnace for heat treatment, wherein the nitrogen flow is 100mL/min, the heat treatment temperature is 200 ℃, the heating rate is 10 ℃/min, and the heat treatment time is 1 h; after the reaction is finished, putting the mixture into an oven to be dried to constant weight, and obtaining three types of lignin-based composite adsorbents: poplar lignin-based composite adsorbent, pine lignin-based composite adsorbent and corn straw lignin-based composite adsorbent.
2) O-dichlorobenzene (o-DCB) and toluene adsorption experimental process
And evaluating the performance of the compound adsorbent for adsorbing and removing the chlorinated aromatic hydrocarbon model compound o-DCB in the gas phase by using a fixed bed adsorption-online detection system until the adsorption is saturated to obtain the time t for the adsorption saturation. And detecting the adsorbed o-DCB by GC-FID, and calculating the adsorption capacity of the adsorbent.
Adsorption conditions: the total gas flow is 60mL/min, the o-DCB and toluene concentration is 100ppm, the adsorbent mass is 100mg, and the adsorption temperature is 30 ℃;
loading an adsorbent: 100mg of the adsorbent was packed in a quartz tube adsorbent bed (inner diameter: 6mm), 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 calculating the adsorption capacity of the o-DCB and toluene, and the adsorption saturation capacity qsThe calculation is as follows:
wherein q issTo saturate the adsorption capacity of the adsorbent, tsTime taken for saturation adsorption, Q is total gas flow, m is adsorbent mass, C0The initial o-DCB or toluene mass concentration (mg/L) and C, the chromatographic detection of the o-DCB or toluene concentration.
Table 1 different types of lignin-based composite adsorbents described in example 1 compare adsorption capacity to commercial activated carbon
In conclusion, the lignin-based composite adsorbents of different types prepared by the method have higher adsorption saturation capacity for chlorinated aromatic hydrocarbons and methylbenzene than that of commercial activated carbon under the same use condition; meanwhile, the lignin-based composite adsorbent prepared by the invention can selectively adsorb o-DCB.
Example 2
1) Preparing the lignin-based composite adsorbent: weighing 5g of poplar lignin, sieving the poplar lignin by a 60-mesh sieve, putting the sieved part in a vacuum oven, drying the poplar lignin for 24 hours at the temperature of 60 ℃, and storing the poplar lignin in a dryer for later use. And (3) drying the sludge, mixing the dried lignin and the sludge with a proper amount of water according to the mass ratio of 1:1, 2:1, 3:1 and 4:1, weighing 5g of the mixture, putting the mixture into a 100mL ball milling tank, adjusting the rotation speed to 200rpm, ball milling for 24 hours to obtain a lignin/sludge mixed material, and then putting the lignin/sludge mixed material into a vacuum oven to dry the lignin/sludge mixed material to constant weight. Wherein the water is added in an amount that the water can be completely absorbed by the dried sludge, no water can be seen on the surface, and the sludge is in a wet state.
Placing the pretreated mixed material in a pyrolysis furnace for heat treatment, wherein the nitrogen flow is 100mL/min, the heat treatment temperature is 200 ℃, the heating rate is 10 ℃/min, and the heat treatment time is 1 h; and after the reaction is finished, putting the mixture into an oven to dry the mixture to constant weight, thus obtaining the lignin-based composite adsorbent.
2) O-dichlorobenzene (o-DCB) adsorption experiment process
And evaluating the performance of the compound adsorbent for adsorbing and removing the chlorinated aromatic hydrocarbon model compound o-DCB in the gas phase by using a fixed bed adsorption-online detection system until the adsorption is saturated to obtain the time t for the adsorption saturation. And detecting the adsorbed o-DCB by GC-FID, and calculating the adsorption capacity of the adsorbent.
Adsorption conditions: the total gas flow is 60mL/min, the o-DCB concentration is 100ppm, the mass of the adsorbent is 100mg, and the adsorption temperature is 30 ℃;
loading an adsorbent: 100mg of the adsorbent was packed in a quartz tube adsorbent bed (inner diameter: 6mm), 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 calculating the adsorption capacity of the o-DCB, and the adsorption saturation capacity qsThe calculation is as follows:
wherein q issTo saturate the adsorption capacity of the adsorbent, tsTime taken for saturation adsorption, Q is total gas flow, m is adsorbent mass, C0The initial o-DCB concentration and C the chromatographic assay o-DCB concentration.
Table 2 adsorption saturation time t and corresponding adsorption saturation capacity of poplar lignin-based composite adsorbent described in example 2
In summary, as the ratio of lignin to sludge increases, the adsorbent adsorption saturation capacity increases. When the ratio of the two is 3:1, the saturated adsorption capacity of the obtained adsorbent is 220mg/g, and when the ratio is increased continuously, the adsorption capacity is increased continuously, but the increase amplitude is not obvious.
Example 3
1) Preparing the lignin-based composite adsorbent: weighing 5g of poplar lignin, sieving the poplar lignin by a 60-mesh sieve, putting the sieved part in a vacuum oven, drying the poplar lignin for 24 hours at the temperature of 60 ℃, and storing the poplar lignin in a dryer for later use. And (3) drying the sludge, mixing the dried lignin and the sludge with a proper amount of water according to the mass ratio of 3:1, weighing 5g of the mixture, putting the mixture into a 100ml ball milling tank, regulating the rotation speed to 200rpm, carrying out ball milling for 24 hours to obtain a lignin/sludge mixed material, and then putting the lignin/sludge mixed material into a vacuum oven to be dried to constant weight. Wherein the water is added in an amount that the water can be completely absorbed by the dried sludge, no water can be seen on the surface, and the sludge is in a wet state.
Placing the pretreated mixed material in a pyrolysis furnace for heat treatment, wherein the nitrogen flow is 100ml/min, the heat treatment temperature is respectively set at 100 ℃, 150 ℃, 200 ℃ and 250 ℃, the heating rate is 10 ℃/min, and the heat treatment time is 1 h; and after the reaction is finished, putting the mixture into an oven to dry the mixture to constant weight, thus obtaining the lignin-based composite adsorbent.
2) O-dichlorobenzene (o-DCB) adsorption experiment process
And evaluating the performance of the compound adsorbent for adsorbing and removing the chlorinated aromatic hydrocarbon model compound o-DCB in the gas phase by using a fixed bed adsorption-online detection system until the adsorption is saturated to obtain the time t for the adsorption saturation. And detecting the adsorbed o-DCB by GC-FID, and calculating the adsorption capacity of the adsorbent.
Adsorption conditions: the total gas flow is 60mL/min, the o-DCB concentration is 100ppm, the mass of the adsorbent is 100mg, and the adsorption temperature is 30 ℃;
loading an adsorbent: 100mg of the adsorbent was packed in a quartz tube adsorbent bed (inner diameter: 6mm), 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 calculating the adsorption capacity of the o-DCB, and the adsorption saturation capacity qsThe calculation is as follows:
wherein q issTo saturate the adsorption capacity of the adsorbent, tsTime taken for saturation adsorption, Q is total gas flow, m is adsorbent mass, C0The initial o-DCB concentration and C the chromatographic assay o-DCB concentration.
Table 3 adsorption saturation time t and corresponding adsorption saturation capacity of poplar lignin-based composite adsorbent described in example 3
In summary, as the heat treatment temperature increases, the adsorbent adsorption saturation capacity increases. When the heat treatment temperature is 200 ℃, the saturated adsorption capacity of the obtained adsorbent is 220mg/g, and the adsorption capacity of the adsorbent is not increased any more when the heat treatment temperature is continuously increased.
Example 4
1) Preparing the lignin-based composite adsorbent: weighing 5g of poplar lignin, sieving the poplar lignin by a 60-mesh sieve, putting the sieved part in a vacuum oven, drying the poplar lignin for 24 hours at the temperature of 60 ℃, and storing the poplar lignin in a dryer for later use. And (3) drying the sludge, mixing the dried lignin and the sludge with a proper amount of water according to the mass ratio of 3:1, weighing 5g of the mixture, putting the mixture into a 100ml ball milling tank, regulating the rotation speed to 200rpm, carrying out ball milling for 24 hours to obtain a lignin/sludge mixed material, and then putting the lignin/sludge mixed material into a vacuum oven to be dried to constant weight. Wherein the water is added in an amount that the water can be completely absorbed by the dried sludge, no water can be seen on the surface, and the sludge is in a wet state.
Placing the pretreated mixed material in a pyrolysis furnace for heat treatment, wherein the nitrogen flow is 100ml/min, the heat treatment temperature is 200 ℃, the heating rate is 10 ℃/min, and the heat treatment time is respectively set to be 0.5, 1, 1.5 and 2 h; and after the reaction is finished, putting the mixture into an oven to dry the mixture to constant weight, thus obtaining the lignin-based composite adsorbent.
2) O-dichlorobenzene (o-DCB) adsorption experiment process
And evaluating the performance of the compound adsorbent for adsorbing and removing the chlorinated aromatic hydrocarbon model compound o-DCB in the gas phase by using a fixed bed adsorption-online detection system until the adsorption is saturated to obtain the time t for the adsorption saturation. And detecting the adsorbed o-DCB by GC-FID, and calculating the adsorption capacity of the adsorbent.
Adsorption conditions: the total gas flow is 60mL/min, the o-DCB concentration is 100ppm, the mass of the adsorbent is 100mg, and the adsorption temperature is 30 ℃;
loading an adsorbent: 100mg of the adsorbent was packed in a quartz tube adsorbent bed (inner diameter: 6mm), 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 calculating the adsorption capacity of the o-DCB, and the adsorption saturation capacity qsThe calculation is as follows:
wherein q issTo saturate the adsorption capacity of the adsorbent, tsTime taken for saturation adsorption, Q is total gas flow, m is adsorbent mass, C0The initial o-DCB concentration and C the chromatographic assay o-DCB concentration.
Table 4 adsorption saturation time t and corresponding adsorption saturation capacity of the poplar lignin-based composite adsorbent described in example 4
In summary, as the heat treatment time is prolonged, the adsorbent adsorption saturation capacity becomes large. When the heat treatment time is 1h, the saturated adsorption capacity of the obtained adsorbent is 220mg/g, the heat treatment time is continuously prolonged, and the adsorption capacity of the adsorbent is continuously increased, but the improvement range is not large.
Example 5
1) Preparing the lignin-based composite adsorbent: weighing 5g lignin mixture (including birch, poplar, pine and corn stalk lignin), sieving with 60 mesh sieve, placing sieved part in vacuum oven, drying at 60 deg.C for 24 hr, and storing in drier. And (3) drying the sludge, mixing the dried lignin and the sludge with a proper amount of water according to the mass ratio of 3:1, weighing 5g of the mixture, putting the mixture into a 100ml ball milling tank, regulating the rotation speed to 200rpm, carrying out ball milling for 24 hours to obtain a lignin/sludge mixed material, and then putting the lignin/sludge mixed material into a vacuum oven to be dried to constant weight. Wherein the water is added in an amount that the water can be completely absorbed by the dried sludge, no water can be seen on the surface, and the sludge is in a wet state.
Placing the pretreated mixed material in a pyrolysis furnace for heat treatment, wherein the nitrogen flow is 100ml/min, the heat treatment temperature is 200 ℃, the heating rate is 10 ℃/min, and the heat treatment time is respectively set to be 1 h; and after the reaction is finished, putting the mixture into an oven to dry the mixture to constant weight, thus obtaining the lignin-based composite adsorbent.
2) O-dichlorobenzene (o-DCB) adsorption experiment process
And evaluating the performance of the compound adsorbent for adsorbing and removing the chlorinated aromatic hydrocarbon model compound o-DCB in the gas phase by using a fixed bed adsorption-online detection system until the adsorption is saturated to obtain the time t for the adsorption saturation. And detecting the adsorbed o-DCB by GC-FID, and calculating the adsorption capacity of the adsorbent.
Adsorption conditions: the total gas flow is 60mL/min, the o-DCB concentration is 100ppm, the mass of the adsorbent is 100mg, and the adsorption temperature is 30 ℃;
loading an adsorbent: 100mg of the adsorbent was packed in a quartz tube adsorbent bed (inner diameter: 6mm), 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 calculating the adsorption capacity of the o-DCB, and the adsorption saturation capacity qsThe calculation is as follows:
wherein q issTo saturate the adsorption capacity of the adsorbent, tsTime taken for saturation adsorption, Q is total gas flow, m is adsorbent mass, C0The initial o-DCB concentration and C the chromatographic assay o-DCB concentration.
Table 5 adsorption saturation capacity of mixed lignin-based composite adsorbents described in example 5
In conclusion, the mixed lignin-based composite adsorbent prepared by the invention has similar adsorption saturation capacity to chlorinated aromatic hydrocarbon and toluene to that of a single lignin-based adsorbent under the same use condition. The above results show that the invention can still obtain better adsorption effect for mixed industrial lignin in paper mill.
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 (11)
1. A method for preparing a chlorinated aromatic hydrocarbon composite adsorbent for incineration flue gas by using lignin is characterized by comprising the following steps:
(1) preparing a lignin/sludge mixed material: sieving lignin by a 40-150 mesh sieve, respectively placing the lignin and the sludge in a vacuum oven for drying, mixing the dried lignin and the sludge with water according to a proportion, wherein the addition amount of the water can ensure that the lignin and the sludge are soaked in equal volume, then carrying out ball milling in a ball milling tank, wherein the ball milling rotation speed is 180-220rpm, and then placing in the vacuum oven for drying to constant weight to obtain a lignin/sludge mixed material; wherein the addition amount of water is such that no water can be seen on the surface of the sludge which is completely absorbed by the dried sludge, and the sludge is in a wet state;
(2) preparing a lignin-based composite adsorbent: and (2) placing the mixed material obtained in the step (1) in a pyrolysis furnace, and carrying out low-temperature heat treatment in a nitrogen atmosphere, wherein the low-temperature heat treatment temperature is 100-250 ℃, so as to obtain the lignin-based composite adsorbent.
2. The method of claim 1, wherein the method comprises combining different types of waste lignin and sludge in paper industry, performing low-temperature heat treatment to obtain lignin-based composite adsorbent with high specific surface area and high graphitization degree, and using the composite adsorbent for adsorption removal of chlorinated aromatic hydrocarbon.
3. The method according to claim 1 or 2, wherein the specific process of step (1) is: sieving lignin by a 40-150 mesh sieve, drying the lignin and sludge for 12-24h in a vacuum oven at 50-80 ℃, mixing the dried lignin and sludge with water according to a proportion, then weighing 5g of the mixture, putting the mixture into a 100mL ball milling tank, adjusting the rotating speed to 180 plus materials and 220rpm for ball milling for 18-24h, and then putting the ball milling tank into the vacuum oven for drying to constant weight to obtain a lignin/sludge mixed material;
the mass ratio of the lignin to the sludge is 1:1-5: 1;
the content of alumina in the sludge is 10-20 wt%, and the content of calcium oxide is 8-15 wt%.
4. The method as claimed in claim 1 or 2, wherein the low temperature heat treatment temperature is 150-220 ℃, the temperature rise rate is 5-20 ℃/min, and the nitrogen flow rate is 50-250 mL/min.
5. The method according to claim 4, wherein the low temperature heat treatment time is 0.5 to 4 hours.
6. The method according to claim 3, wherein the mass ratio of lignin to sludge is 3: 1-5: 1; the content of alumina in the sludge is 10-15 wt%, and the content of calcium oxide is 8-10 wt%.
7. The method of claim 2, wherein the different types of waste lignin in the paper industry comprise at least one of birch lignin, poplar lignin, pine lignin, corn stover lignin.
8. The lignin-based composite adsorbent is characterized by being prepared by the method of any one of claims 1 to 7, taking lignin and sludge as raw materials, mixing the lignin and the sludge according to the mass ratio of 1:1-5:1, ball-milling and uniformly mixing the lignin and the sludge, and partially carbonizing at the low temperature of 100-250 ℃ to prepare the lignin-based composite adsorbent.
9. The adsorbent according to claim 8, wherein the sludge contains 10 to 20 wt% of alumina and 8 to 15 wt% of calcium oxide.
10. The method for adsorbing chlorinated aromatic hydrocarbon by using the lignin-based composite adsorbent as claimed in claim 8 or 9 or the lignin-based composite adsorbent prepared by any one of claims 1 to 7, which is characterized in that the lignin-based composite adsorbent is used for adsorbing and removing chlorinated aromatic hydrocarbon pollutants in incineration flue gas, o-dichlorobenzene-DCB is used as a chlorinated aromatic hydrocarbon representative compound, toluene is used as other types of pollutants, and the adsorption performance of the composite adsorbent is continuously tested by using a fixed bed adsorption-online detection device until the adsorption is saturated; detecting the adsorbed pollutants by GC-FID, and calculating to obtain the adsorption capacity of the lignin-based composite adsorbent;
in continuous test, the total gas flow is 50-200mL/min, the o-DCB or toluene concentration is 20-200ppm, the adsorbent mass is 50-500mg, and the adsorption temperature is 15-100 ℃.
11. The method for adsorbing chlorinated aromatic hydrocarbon according to claim 10, wherein the saturated adsorption capacity of the lignin-based composite adsorbent to o-DCB is 70-250mg/g, and the adsorption capacity to toluene is 40-55 mg/g.
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