A method for blocking polycyclic aromatic hydrocarbon precursors from generating chlorinated and brominated polycyclic aromatic hydrocarbons

Abstract

The present invention discloses a method for inhibiting the generation of chlorinated and brominated polycyclic aromatic hydrocarbons from polycyclic aromatic hydrocarbon precursors, belonging to the field of pollutant emission reduction. The present invention inhibits the generation of chlorinated and brominated polycyclic aromatic hydrocarbons (PAHs) by adding a calcium compound during the flue gas cooling stage after combustion in various thermal processes or during simulated thermal reactions involving PAHs in the laboratory. The present invention has an inhibition rate of over 90% on the concentration of chlorinated and brominated PAHs, and the calcium compound is low-cost and readily available. Adding an appropriate amount of the calcium compound during the thermal process can effectively inhibit the generation of chlorinated and brominated PAHs.

Description

Technical Field

[0001] The present invention belongs to the field of pollutant emission reduction, and in particular relates to a method for blocking polycyclic aromatic hydrocarbon precursors from generating chlorinated and brominated polycyclic aromatic hydrocarbons. Background Art

[0002] Typical thermal processes (including industrial production thermal processes, such as large coal-fired power plants, coal-fired boilers, coking plants, etc., as well as thermal processes involved in daily units and households, such as small heating boilers, household coal-fired stoves, etc.) will produce chlorinated and brominated polycyclic aromatic hydrocarbons (referring to polycyclic aromatic hydrocarbons with more than three rings). Chlorinated and brominated polycyclic aromatic hydrocarbons are difficult to degrade in the environment, have high lipophilicity, are easily accumulated in organisms, and have potential carcinogenicity, immunotoxicity and embryotoxicity. Chlorinated polycyclic aromatic hydrocarbons and brominated polycyclic aromatic hydrocarbons have chemical structures similar to dioxins, such as Figure 5 As shown in the figure, their toxicity is higher than that of the corresponding parent polycyclic aromatic hydrocarbons. Therefore, as potential persistent organic pollutants, their emission control has also received great attention (Reference: Jin R., Zheng M., Lammel G., et al. Chlorinated and brominated polycyclic aromatic hydrocarbons: Sources, formation mechanisms, and occurrence in the environment. Prog. Energy Combust. Sci., 2020, 76: 100803.). Currently, dioxin removal from industrial flue gas is primarily achieved through activated carbon powder adsorption combined with bag filters. While this combined process can achieve over 90% dioxin removal efficiency, it is less effective for other chlorinated and brominated polycyclic aromatic hydrocarbons (PAHs). (Reference: Lin B, Yang Y, Yang L, et al. Congener profiles and process distributions of polychlorinated biphenyls, polychlorinated naphthalenes and chlorinated polycyclic aromatic hydrocarbons from secondary copper smelting. Journal of Hazardous Materials, 2022, 423: 127-125.) Therefore, controlling the generation of chlorinated and brominated PAHs at their source is crucial for reducing their emissions.

[0003] During thermal processes, the formation of chlorinated and brominated PAHs occurs primarily through low-temperature heterogeneous catalytic synthesis in the post-combustion zone. Low-temperature heterogeneous catalytic synthesis encompasses both de novo and precursor synthesis. De novo synthesis involves the generation of halogenated aromatic hydrocarbons from a carbon source in the presence of halogens and metal catalysts, while precursor synthesis involves the adsorption of chlorobenzene, chlorophenol, and other pollutants onto the surface of particulate matter, followed by the generation of halogenated aromatic hydrocarbons in the presence of a catalyst. Anthracene and phenanthrene are two three-ring PAHs, and pyrene is a four-ring PAH. They are three of the 16 PAHs with higher concentrations. They are the main products of incomplete combustion of organic matter in thermal processes, and their concentrations are about three orders of magnitude higher than other chlorinated organic pollutants (Reference: Wu X., Wu G., Xie J., et al. Thermochemical formation of multiple unintentional persistent organic pollutants on metallurgical fly ash and their correlations. Chemosphere, 2019, 226: 492-501.). Therefore, blocking the reaction pathways that generate chlorinated and brominated PAHs with anthracene, phenanthrene, and pyrene as precursors is a key means to reduce their emissions in thermal processes.

[0004] In recent years, adding calcium oxide as a retarder in industrial thermal processes is considered to be an economical and effective way to control the formation of dioxins. However, existing studies are all focused on the reaction of precursors containing organic chlorine sources such as chlorobenzene and chlorophenols to form dioxins (Reference: Yang Fan, Li Liewu, Tong Dongge, et al. Inhibitory effect of calcium-based composite oxides on the formation of dioxins from pentachlorophenol. Environmental Chemistry, 2015, 34(08): 1439-1445.), and there is a lack of research on the formation of chlorinated and brominated polycyclic aromatic hydrocarbons from non-halogen-substituted polycyclic aromatic hydrocarbon precursors such as anthracene, phenanthrene and pyrene, and there is currently a lack of retarding technology for chlorinated and brominated polycyclic aromatic hydrocarbons. Summary of the Invention

[0005] The present invention aims to address the shortcomings of the existing technology and provide a method for inhibiting the generation of chlorinated and brominated PAHs from PAH precursors. The method can be applied during the flue gas cooling phase after combustion in various thermal processes or during simulated thermal reactions involving PAHs in the laboratory. Adding a calcium compound during this phase effectively inhibits the thermochemical reaction of anthracene, phenanthrene, and pyrene to generate chlorinated and brominated PAHs, thereby reducing emissions of chlorinated and brominated PAHs.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] The present invention provides a method for blocking the generation of chlorinated and brominated polycyclic aromatic hydrocarbons from polycyclic aromatic hydrocarbon precursors, specifically, blocking the generation of chlorinated and brominated polycyclic aromatic hydrocarbons by adding a calcium compound into the thermal reaction process of the polycyclic aromatic hydrocarbon precursors.

[0008] Preferably, the polycyclic aromatic hydrocarbon precursor is one or a mixture of two or more of anthracene, phenanthrene and pyrene.

[0009] Preferably, the thermal reaction process is a flue gas cooling stage after combustion in a thermal process or a simulated thermal reaction involving polycyclic aromatic hydrocarbon precursors.

[0010] Furthermore, the temperature of the flue gas cooling stage and the simulated thermal reaction is 200-550°C.

[0011] Preferably, the chlorinated and brominated polycyclic aromatic hydrocarbons are one or a mixture of two or more of chlorinated / brominated acenaphthylene, chlorinated / brominated acenaphthylene, chlorinated / brominated fluorene, chlorinated / brominated phenanthrene, chlorinated / brominated anthracene, chlorinated / brominated fluoranthene, chlorinated / brominated pyrene, chlorinated / brominated triphenylene, chlorinated / brominated benz[a]anthracene, and chlorinated / brominated benzo[a]pyrene. The chemical structural formulas of the compounds are as follows: Figure 5 As shown, from left to right in the figure are: halogenated acenaphthylene (Cl / Br-Any), halogenated acenaphthene (Cl / Br-Ana), halogenated fluorene (Cl / Br-Fle), halogenated phenanthrene (Cl / Br-Phe), halogenated anthracene (Cl / Br-Ant), halogenated fluoranthene (Cl / Br-Flu), halogenated pyrene (Cl / Br-Pyr), halogenated triphenylene (Cl / Br-Triph), halogenated benz[a]anthracene (Cl / Br-BaA), and halogenated benzo[a]pyrene (Cl / Br-BaP).

[0012] Preferably, the calcium compound is one or a mixture of two or more of calcium oxide, calcium hydroxide and calcium carbonate.

[0013] Preferably, the added amount of the calcium compound is 0.5% to 15% of the mass of the polycyclic aromatic hydrocarbon precursor.

[0014] Preferably, the particle size of the calcium compound is not greater than 0.5 mm.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The method of the present invention can suppress the concentration of chlorinated and brominated polycyclic aromatic hydrocarbons by more than 90%. The calcium compound used in the present invention is low-cost and easily available. Adding an appropriate amount of the calcium compound during the thermal process can effectively suppress the formation of chlorinated and brominated polycyclic aromatic hydrocarbons. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1The concentrations of chloroanthracene generated by reacting anthracene as the polycyclic aromatic hydrocarbon precursor at 500° C. in Example 1 with no calcium compound added and 5 wt % calcium oxide added.

[0018] Figure 2 The concentrations of chlorophenanthrene generated by reacting at 300° C. in Example 2 with phenanthrene as the polycyclic aromatic hydrocarbon precursor without adding a calcium compound and with 0.5 wt % calcium oxide.

[0019] Figure 3 The concentrations of brominated anthracene and brominated phenanthrene generated by reacting at 400° C. with phenanthrene as the polycyclic aromatic hydrocarbon precursor without adding a calcium compound and with 10 wt % calcium hydroxide in Example 3 are shown.

[0020] Figure 4 The concentrations of chlorofluoranthene, chloropyrene, chlorobenz[a]anthracene and chlorobenzo[a]pyrene generated by reacting at 500° C. with pyrene as the polycyclic aromatic hydrocarbon precursor without adding a calcium compound and with 15 wt % calcium carbonate in Example 4 are shown.

[0021] Figure 5 It is the chemical structure formula of chlorinated and brominated polycyclic aromatic hydrocarbons (X: Cl or Br). DETAILED DESCRIPTION

[0022] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0023] Example 1

[0024] In this embodiment, anthracene is used as a polycyclic aromatic hydrocarbon precursor. Under the catalysis of copper chloride, anthracene can generate chloroanthracene at 500° C. However, after adding 5 wt % of calcium oxide, the amount of chloroanthracene generated is reduced by 98.1%.

[0025] Table 1: The inhibition of anthracene to chloroanthracene by 5wt% calcium oxide at 500℃

[0026] sample Amount of chloroanthracene generated from anthracene (μg / g) Anthracene + copper chloride 348.5 Anthracene + copper chloride + 5wt% calcium oxide 6.5 Inhibition rate of calcium oxide on chloroanthracene 98.1％

[0027] The blocking effect of Example 1 is as follows Figure 1 As shown. Figure 1 As can be seen in the figure, the concentrations of various chlorinated anthracenes decreased significantly after adding 5 wt% calcium oxide, with the total concentration of chlorinated anthracenes reduced by 98.1%. In the legend: 1-ClAnt is 1-chloroanthracene, 2-ClAnt is 2-chloroanthracene, 9-ClAnt is 9-chloroanthracene, 1,4-Cl2Ant is 1,4-dichloroanthracene, 1,5-Cl2Ant is 1,5-dichloroanthracene, 9,10-Cl2Ant is 9,10-dichloroanthracene, and 1,5,9,10-Cl4Ant is 1,5,9,10-tetrachloroanthracene.

[0028] Example 2

[0029] In this embodiment, phenanthrene is used as a polycyclic aromatic hydrocarbon precursor. Under the catalysis of copper chloride, phenanthrene can generate chlorophenanthrene at 300° C. After adding 0.5 wt % of calcium oxide, the amount of chlorophenanthrene generated is reduced by 90.1%.

[0030] Table 2: The inhibition of phenanthrene to chlorophenanthrene by 0.5wt% calcium oxide at 300℃

[0031] sample Amount of chlorophenanthrene generated from phenanthrene (μg / g) Phenanthrene + copper chloride 431.6 Phenanthrene + copper chloride + 0.5wt% calcium oxide 42.6 Inhibition rate of calcium oxide on chlorophenanthrene 90.1％

[0032] The blocking effect of Example 2 is as follows Figure 2 As shown. Figure 2 As can be seen in the figure, the concentrations of various chlorophenanthrene analogs were significantly reduced after adding 0.5wt% calcium oxide, and the total concentration of chlorophenanthrene was reduced by 90.1%. In the legend: 3-ClPhe is 3-chlorophenanthrene, 9-ClPhe is 9-chlorophenanthrene, 2-ClPhe is 2-chlorophenanthrene, and 9,10-Cl2Phe is 9,10-dichlorophenanthrene.

[0033] Example 3

[0034] In this embodiment, phenanthrene is used as a polycyclic aromatic hydrocarbon precursor to generate brominated anthracene and brominated phenanthrene at 400° C. under the catalysis of copper bromide. After adding 10 wt % calcium hydroxide, the amount of brominated anthracene and brominated phenanthrene generated is reduced by 95.2%.

[0035] Table 3: The inhibition of phenanthrene to bromoanthracene and bromophenanthrene by 10wt% calcium hydroxide at 400℃

[0036] sample Amount of brominated anthracenes and brominated phenanthrene generated from phenanthrene (μg / g) Phenanthrene + copper bromide 621.6 Phenanthrene + copper bromide + 10wt% calcium hydroxide 29.9 Inhibition rate of calcium hydroxide on brominated anthracene and brominated phenanthrene 95.2％

[0037] The blocking effect of Example 3 is as follows Figure 3 As shown. Figure 3 As can be seen in the figure, the concentrations of individual brominated phenanthrene and brominated anthracene analogs were significantly reduced after the addition of 10 wt% calcium hydroxide, and the total concentration of brominated phenanthrene and brominated anthracene decreased by 95.2%. In the legend: 3-BrPhe is 3-bromophenanthrene, 9-BrPhe is 9-bromophenanthrene, 2-BrPhe is 2-bromophenanthrene, 1-BrAnt is 1-bromoanthracene, 9-BrAnt is 9-bromoanthracene, 1,8-Br2Ant is 1,8-dibromoanthracene, 1,5-Br2Ant is 1,5-dibromoanthracene, 9,10-Br2Ant is 9,10-dibromoanthracene, and 9,10-Br2Phe is 9,10-dibromophenanthrene.

[0038] Example 4

[0039] In this embodiment, pyrene is used as a polycyclic aromatic hydrocarbon precursor. Under the catalysis of cupric chloride, chlorofluoranthene, chloropyrene, chlorobenzo[a]anthracene, and chlorobenzo[a]pyrene can be generated at 500°C. After adding 15wt% calcium carbonate, the amount of chlorofluoranthene, chloropyrene, chlorobenzo[a]anthracene, and chlorobenzo[a]pyrene generated is reduced by 93.4%.

[0040] Table 4: The inhibition of pyrene to chlorofluoranthene, chloropyrene, chlorobenzo[a]anthracene and chlorobenzo[a]pyrene by 15wt% calcium carbonate at 500℃

[0041]

[0042] The blocking effect of Example 4 is as follows Figure 4 As shown. Figure 4 As can be seen in the figure, the concentrations of various chlorinated fluoranthenes, chlorinated pyrenes, chlorinated benz[a]anthracenes, and chlorinated benz[a]pyrene analogs all decreased significantly after adding 15 wt% calcium carbonate, with the total concentration reduced by 93.4%. In the legend: 3-ClFlu is 3-chlorofluoranthene, 3,8-Cl2Flu is 3,8-dichlorofluoranthene, 1-ClPyr is 1-chloropyrene, 7-ClBaA is 7-chlorobenz[a]anthracene, 7,12-Cl2BaA is 7,12-dichlorobenz[a]anthracene, and 6-ClBaP is 6-chlorobenzo[a]pyrene.

[0043] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for retarding the generation of chlorinated and brominated polycyclic aromatic hydrocarbons from polycyclic aromatic hydrocarbon precursors, characterized in that: By adding calcium compounds to the thermal reaction process of PAH precursors, the formation of chlorinated and brominated PAHs is inhibited; The polycyclic aromatic hydrocarbon precursor is one or a mixture of two or more of anthracene, phenanthrene and pyrene; The chlorinated and brominated polycyclic aromatic hydrocarbons are one or a mixture of two or more of chlorinated / brominated acenaphthylene, chlorinated / brominated acenaphthene, chlorinated / brominated fluorene, chlorinated / brominated phenanthrene, chlorinated / brominated anthracene, chlorinated / brominated fluoranthene, chlorinated / brominated pyrene, chlorinated / brominated triphenylene, chlorinated / brominated benz[a]anthracene, and chlorinated / brominated benzo[a]pyrene.

2. The method of claim 1, wherein the method comprises: The thermal reaction process is a flue gas cooling stage after thermal combustion or a simulated thermal reaction involving polycyclic aromatic hydrocarbon precursors.

3. The method for retarding the generation of chlorinated and brominated polycyclic aromatic hydrocarbons from polycyclic aromatic hydrocarbon precursors according to claim 2, characterized in that: The temperature of the flue gas cooling stage and the simulated thermal reaction is 200-550°C.

4. The method of claim 1, wherein the precursor of polycyclic aromatic hydrocarbons is blocked to generate chlorinated and brominated polycyclic aromatic hydrocarbons, The calcium compound is one or a mixture of two or more of calcium oxide, calcium hydroxide and calcium carbonate.

5. The method of claim 1, wherein the precursor of polycyclic aromatic hydrocarbons is blocked to generate chlorinated and brominated polycyclic aromatic hydrocarbons, The added amount of the calcium compound is 0.5% to 15% of the mass of the polycyclic aromatic hydrocarbon precursor.

6. The method of claim 1, wherein the method comprises: The particle size of the calcium compound is not greater than 0.5 mm.

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