Method for removing trace toxic polycyclic aromatic hydrocarbons in coal-based residues

Abstract

The invention relates to a method for removing trace toxic polycyclic aromatic hydrocarbon in coal-based residues, which comprises the following steps of: crushing the residues to obtain residues before modification, and grinding and uniformly mixing the residues before modification and a modifier to obtain mixed powder; adding the mixed powder, a catalyst and a system solvent into a reactor, and carrying out a chemical reaction for removing toxic polycyclic aromatic hydrocarbon; a reaction product is collected and recycled through rotary evaporation, modified residues are obtained after solids are dried and ground, and the solvent is recycled; according to the method, the content of the toxic polycyclic aromatic hydrocarbon in the coal-based residues is reduced to the greatest extent by preferably selecting the multifunctional composite modifier and establishing an efficient removal method of the polycyclic aromatic hydrocarbon, and indexes such as the softening point, the needle penetration and the solubility in the residues are improved; the content of trace toxic polycyclic aromatic hydrocarbon in the coal-based residues can be reduced, the rheological property and stability of the residues are improved, and the pavement standard of road asphalt is met.

Description

Technical Field

[0001] The invention relates to the field of coal chemical industry, and in particular to a method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues. Background Art

[0002] In the process of coal conversion, processing and utilization such as direct liquefaction and indirect liquefaction, unreacted coal, tar, semi-coke and other carbon-containing coal-based residue by-products are produced, accounting for about 10-30% of the raw materials. It has the characteristics of wide sources, low prices, high carbon content, and good flow properties and easy graphitization after heating. Therefore, the rational processing and efficient utilization of coal-based residues play an important role in the recycling of coal-based solid waste resources and the high-quality development of the coal chemical industry.

[0003] Polycyclic aromatic hydrocarbons (PAHs) are a class of hydrocarbons with toxicity (carcinogenic and teratogenic). They are aromatic organic compounds with relatively stable chemical properties and strong inertness formed by two or more benzene rings bonded together by chemical bonds. PAHs react with DNA in the human body, affecting the normal biochemical process of cells, thus causing cancer, especially leading to a sharp increase in the incidence of lung cancer and skin cancer. Among the more than 400 PAHs that have been discovered, 16 have been included in the list of "priority controlled pollutants" by the US Environmental Protection Agency (EPA). Among the first batch of 68 limited pollutants announced by my country's National Environmental Protection Agency, PAHs account for 7.

[0004] Since the total content of 16 PAHs in coal-based residues is about 5000-30000ppm, if these residues rich in toxic polycyclic aromatic hydrocarbons are not treated, it will cause environmental pollution and seriously restrict the subsequent processing and utilization of coal-based residues. Therefore, developing environmentally friendly, large-scale, and industrially applied coal-based residue resource utilization technology and improving the economic and environmental protection of coal chemical technology have become one of the bottleneck problems that need to be solved in the promotion and application of technology.

[0005] Chinese patent application No.: 202011305346.4 discloses a method for preparing modified environmentally friendly asphalt, which comprises mixing a block copolymer with modified silica to obtain a modified block copolymer, mixing a base material with waste rubber powder, adding the modified block copolymer and coumarone resin, stirring to obtain a blank, mixing the blank with an aldehyde compound, and adding an accelerator to react to obtain an environmentally friendly asphalt product. This preparation method only introduces the benzopyrene content in the environmentally friendly asphalt, and does not provide a detailed description of the content and reduction degree of other polycyclic aromatic hydrocarbons that are of concern.

[0006] Chinese patent application No.: 201410539042.2 discloses a modified petroleum asphalt with low carcinogenic polycyclic aromatic hydrocarbons content and its preparation method. After heating the petroleum asphalt under certain conditions, p-toluenesulfonic acid and p-terephthalic acid (or trioxymethylene) are added, and the polycyclic aromatic hydrocarbons content in the prepared modified asphalt is significantly reduced. This method is mainly aimed at petroleum asphalt. During the implementation process, the petroleum asphalt is heated to 250-300°C. After the material reaches the predetermined softening point, air is blown in to cool it to 150-180°C, and the modifier is added. Whether this method is suitable for the removal of toxic polycyclic aromatic hydrocarbons in coal-based asphalt or coal-based residues has not been elaborated in detail.

[0007] Chinese patent application No.: 201610895574.9 discloses a method for preparing an environmentally friendly modified coal tar pitch, in which the softening point of low-temperature coal tar pitch is 70-90°C, but coal-based residues with a softening point higher than 100°C are not described. Summary of the invention

[0008] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a method for removing trace toxic polycyclic aromatic hydrocarbons in coal-based residues, optimize modifiers and catalysts, and conduct modification research on coal-based residues in a system solvent to minimize the content of 16 toxic polycyclic aromatic hydrocarbons in the residues. The softening point, needle penetration and other performance indicators of the modified residues are improved, the pollution to the environment by subsequent processing is reduced, the rheology and stability of the residues are improved, and the standards for paving road asphalt are met.

[0009] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0010] A method for removing trace amounts of toxic polycyclic aromatic hydrocarbons from coal-based residues comprises the following steps:

[0011] Step 1, crushing the coal-based residue to obtain the residue powder before modification;

[0012] Step 2: Grind and mix the residual powder before modification and the modifier evenly to obtain a mixed powder, wherein the amount of the modifier added is 0.1 to 0.5 times the mass of the residual powder before modification;

[0013] Step 3, adding the mixed powder, catalyst and system solvent into the reactor at the same time, performing a chemical reaction to remove toxic polycyclic aromatic hydrocarbons, and obtaining a mixture; the amount of the catalyst added is 0.1 to 0.4 times the mass of the residual powder before modification; the amount of the system solvent added is 1 to 5 times the mass of the residual powder before modification;

[0014] Step 4: Collect and recover the mixture by rotary evaporation, and place the obtained solid in a drying oven for further drying, grind to obtain a modified residue powder, and recycle the solvent recovered after rotary evaporation.

[0015] The particle size of the residue before modification in step 1 satisfies D 50 ≤50~300μm.

[0016] The coal-based residue in step 1 includes one or more combinations of direct liquefaction residue, indirect liquefaction ash, oil-coal co-refining residue, coal pyrolysis residue, oil sludge, fly ash, and coal gangue carbonaceous materials. The content of toxic polycyclic aromatic hydrocarbons in the coal-based residue is 2000-50000 ppm.

[0017] In the step 2, the residual powder before modification is dried in a forced air drying oven at 100-120° C. for 2-6 hours.

[0018] The step three is added into the reactor to carry out the chemical reaction of removing toxic polycyclic aromatic hydrocarbons, the feed amount is 1-1000g, the reaction temperature is 50-200°C, the reaction time is 2-12h, the reaction pressure is 0-5.0MPa, the heating rate is 1-100°C / min, the stirring rate is 200-2000r / min, the reaction atmosphere is nitrogen, carbon dioxide or air, and the temperature control accuracy is ±1°C.

[0019] The modifier in step 2 is one or more combinations of terephthalaldehyde, terephthalic alcohol, formaldehyde, benzoic acid, polyethylene glycol, divinylbenzene, and trioxymethylene, and can be recycled.

[0020] The catalyst in step three is one or more combinations of concentrated sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, anhydrous aluminum chloride, and cobalt chloride, and can be recycled.

[0021] The system solvent in step three includes one or more combinations of methanol, toluene, cyclohexane, acetone, ethyl acetate, butyl acetate, and n-butanol, and can be recycled.

[0022] In the step 4, the rotary evaporation temperature is 40-100° C., and the rotary evaporation time is 1-12 hours; the drying temperature is 80-140° C., and the drying time is 1-12 hours.

[0023] The modifier in step 2 is terephthalaldehyde, and the catalyst in step 3 is concentrated sulfuric acid; the system solvent in step 3 is toluene, and the amount of terephthalaldehyde added is 0.3 times the mass of the residue powder before modification; the amount of concentrated sulfuric acid added is 0.4 times the mass of the residue powder before modification, and the amount of toluene solvent is 3 times the mass of the residue powder before modification. The chemical reaction in step 3 is carried out at a temperature of 90±3°C, a reaction time of 6h, and a stirring rate of 1000r / min to obtain a modified mixture.

[0024] Compared with the prior art, the technical innovations of the present invention are:

[0025] 1. In the present invention, under the dual effects of the acid catalysis of the catalyst and the physical dilution of the solvent, the modifier of the coal-based residue is easily broken to form a carbon cation, which undergoes an electrophilic substitution reaction with the polycyclic aromatic hydrocarbon molecules in the residue, converting the polycyclic aromatic hydrocarbons into a non-toxic or low-toxic macromolecular polymer structure, greatly reducing the content of toxic polycyclic aromatic hydrocarbons in the coal-based residue. The method has the characteristics of a wide source of raw materials, a high removal rate of trace toxic polycyclic aromatic hydrocarbons, simple operation, solvent recycling, easy industrial scale-up, low cost, and environmental friendliness.

[0026] 2. The present invention adjusts the dosage of the modifier, catalyst and system solvent to preferably compound a multifunctional composite modifier. Under low addition ratios of the modifier, catalyst, system solvent and the like and mild reaction conditions, the removal rate of 16 polycyclic aromatic hydrocarbons (PAHs) in the modified residue reaches more than 90%, and the removal rate of the typical toxic substance benzopyrene (BaP) is greater than 95%, which is higher than the removal efficiency of similar technologies.

[0027] 3. The present invention establishes an environmental impact assessment system for coal-based residues, including a gas release and water pollution assessment system after residue heating. By reacting the coal-based residue with a multifunctional composite modifier, the polycyclic aromatic hydrocarbons content in the gas released after the residue is heated is less than 50 ppm, and the polycyclic aromatic hydrocarbons content in the water extract is less than 20 ppm, which has low environmental hazard and provides technical support for the environmentally friendly application of coal-based residues.

[0028] 4. The modified residue in the present invention is mixed with petroleum-based asphalt for evaluation and research, and the penetration is 5-20 (50°C, 0.1mm), and the softening point is 80-150°C. On the basis of efficient removal of polycyclic aromatic hydrocarbons, the rheological properties and stability of the residue are improved, which meets the paving standards of road asphalt.

[0029] In summary, the present invention adopts simple and easy technology, optimizes the modifier and catalyst, modifies the oil-containing solid slag in the system solvent, and greatly reduces the content of toxic polycyclic aromatic hydrocarbons in the coal-based residue. It has the characteristics of wide source of raw materials, high removal rate of trace toxic polycyclic aromatic hydrocarbons, simple operation, solvent recycling, easy industrial scale-up, low cost, and environmental friendliness, so that the performance of the modified solid slag is improved, and the pollution to the environment is reduced during the subsequent processing and utilization. DETAILED DESCRIPTION

[0030] Method for removing trace toxic polycyclic aromatic hydrocarbons from residues

[0031] The raw materials in the following examples are by-product residues of kerosene co-refining process, with a softening point of 110°C and a particle size of 2-3 cm blocks. The total content of 16 polycyclic aromatic hydrocarbons (PAHs) in the residue before modification is 18150 ppm, of which the content of benzopyrene (BaP) is 2130 ppm, and the four components of naphthalene, acenaphthylene, acenaphthene and fluorene are not detected.

[0032] Solvent extraction of the residue before and after modification to obtain PAHs enriched products

[0033] Specific process: weigh the residual powder before / after modification, put it into a pre-weighed filter paper tube, place it at the bottom of the extractor, connect the top outlet of the extractor to the condenser, connect the bottom outlet of the extractor to the distillation flask, add 100mL of extraction solvent to the distillation flask, the solvent boils and evaporates, condenses and refluxes into the extractor, fully contacts and reacts with the material in the filter paper tube, the extract refluxes with the solvent and is enriched in the flask, and the extraction is repeated until the reflux liquid is colorless and the experiment is stopped. After the extraction is completed, remove the extract in the distillation flask after it has cooled, and evaporate the solvent on a rotary evaporator. Rinse the remaining material in the flask repeatedly with a small amount of dichloromethane, dilute to a 50ml volumetric flask, and obtain the enriched polycyclic aromatic hydrocarbons.

[0034] Detection of polycyclic aromatic hydrocarbons in modified residues

[0035] The polycyclic aromatic hydrocarbons enrichment in the residue before and after modification was detected by gas chromatography-mass spectrometry, among which the contents of naphthalene, acenaphthylene, acenaphthene and fluorene were below the detection limit of gas chromatography-mass spectrometry and were ignored. The gas chromatography determination conditions were as follows: chromatographic column: HP-5 quartz capillary column (30m×0.25mm×0.25μm); chromatographic column temperature program: initial temperature 100℃, increased to 300℃ at 5℃ / min, maintained for 10min; injection temperature: 300℃; carrier gas: helium, purity ≥99.99%, flow rate 4mL / min; injection mode: split injection, split ratio 10:1; injection volume 1μL. Mass spectrometry conditions: electron impact (EI) ion source; electron energy 70eV; transmission line temperature 260℃; ion source temperature 230℃; mass scanning range (m / z) 60~640amu.

[0036] Example 1

[0037] This embodiment is a method for removing trace toxic polycyclic aromatic hydrocarbons in coal-based residues, comprising the following steps:

[0038] Step 1: Place the oil-coal co-refining residue in a pulverizer to crush it into particles with a particle size of <2 cm, and place it in a ball mill for ball milling to obtain particles with a particle size of D 50 Residue powder ≤50~300μm;

[0039] Step 2: Grind and mix the residual powder described in step 1 with a modifier to obtain a mixed powder; the modifier is terephthalaldehyde, and the amount of terephthalaldehyde added is 0.3 times the mass of the residual powder before modification;

[0040] Step 3, adding the mixed powder and the catalyst in step 2 into a modification reactor, wherein the catalyst is concentrated sulfuric acid, the amount of concentrated sulfuric acid added is 0.4 times the mass of the residue powder, the amount of toluene solvent added into the high-efficiency modified residue reactor is 3 times the mass of the residue powder, the reaction temperature of the high-efficiency modified residue is 90±3°C, the reaction time is 6h, the stirring rate is 1000r / min, and a modified mixture is obtained;

[0041] Step 4: Mix the modified residue in step 3 with toluene solvent, evaporate the toluene on a rotary evaporator and collect it for reuse, and place the modified residue in a drying oven for drying at a temperature of 120° C. for 6 hours, and grind it to obtain the modified residue powder.

[0042] Comparative Example 1

[0043] The difference between this comparative example and Example 1 is that the modifier is terephthalic acid methanol, and the amount of terephthalic acid methanol added is 0.3 times the mass of the residual powder.

[0044] Comparative Example 2

[0045] The difference between this comparative example and Example 1 is that the catalyst is anhydrous aluminum chloride, and the amount of anhydrous aluminum chloride added is 0.4 times the mass of the residual powder.

[0046] Comparative Example 3

[0047] The difference between this comparative example and Example 1 is that the catalyst is p-toluenesulfonic acid, and the amount of p-toluenesulfonic acid added is 0.4 times the mass of the residual powder.

[0048] Table 1 Removal rate of polycyclic aromatic hydrocarbons in Example 1 and comparative example

[0049]

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that in step 2, the amount of the modifier terephthalaldehyde added is 0.1, 0.2 or 0.4 times the mass of the residual powder.

[0052] Table 2 Removal rate of polycyclic aromatic hydrocarbons in Example 2

[0053]

[0054]

[0055] Example 3

[0056] The difference between this embodiment and embodiment 1 is that the amount of sulfuric acid added as a catalyst in step 3 is 0, 0.1, 0.2 or 0.3 times the mass of the residue powder.

[0057] Table 3 Removal rate of polycyclic aromatic hydrocarbons in Example 3

[0058]

[0059]

[0060] Example 4

[0061] The difference between this embodiment and embodiment 1 is that the system solvent in step 3 is cyclohexane, acetone, n-butanol or circulating solvent toluene.

[0062] Table 4 Removal rate of polycyclic aromatic hydrocarbons in Example 4

[0063]

[0064] Example 5

[0065] The difference between this embodiment and embodiment 1 is that the reaction time in step 4 is 2h, 4h or 8h.

[0066] Table 5 Removal rate of polycyclic aromatic hydrocarbons in Example 5

[0067]

[0068] Example 6

[0069] The difference between this embodiment and embodiment 1 is that the reaction time in step 3 is 6 hours, and the reaction temperature is 50° C., 70° C. or 110° C.

[0070] Table 6 Removal rate of polycyclic aromatic hydrocarbons in Example 6

[0071]

[0072]

[0073] The properties of the residue before and after modification are analyzed:

[0074] (I) The raw materials used in Examples 1 to 6 of the present invention are coal-based residues, which are treated to obtain modified residues. The industrial analysis and elemental analysis of the residues before and after modification are detailed in Table 6, and the key performance indicators of the residues before and after modification are detailed in Table 7.

[0075] Table 6 Industrial analysis and elemental analysis of residues before and after modification

[0076]

[0077] Table 7 Key performance indicators of residues before and after modification

[0078]

[0079]

[0080] (II) The raw materials used in Examples 1 to 6 of the present invention are coal-based residues, which are treated to obtain modified residues. The GC-MS components of the oil in the residues before and after modification are shown in Table 8.

[0081] Table 8 GC-MS components of oil in the residue before and after modification (wt%)

[0082] raw material Aliphatic hydrocarbons Aromatic hydrocarbons Sulfur compounds Oxygenated compounds Nitrogen compounds Other compounds Residue before modification 1.6 84.2 2.1 4.6 5.9 1.6 Residue after modification 39.8 33.5 5.2 12.5 5.2 3.8

[0083] It can be seen from the embodiments and comparative examples that the present invention preferably selects terephthalaldehyde as a modifier and concentrated sulfuric acid as a catalyst, modifies the oil-containing solid residue in a system solvent, controls the optimal reaction amount and reaction conditions, and reduces the content of 16 toxic polycyclic aromatic hydrocarbons that are prioritized by the US EPA in the oil-containing solid residue to the greatest extent, so that the performance of the modified solid residue is improved, and reduces pollution to the environment during subsequent processing and utilization.

Claims

1. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues, characterized in that: The following steps are involved: Step 1, crushing the coal-based residue to obtain the residue powder before modification; Step 2: Grind and mix the residual powder before modification and the modifier evenly to obtain a mixed powder, wherein the amount of the modifier added is 0.1 to 0.5 times the mass of the residual powder before modification; Step 3, adding the mixed powder, catalyst and system solvent into the reactor at the same time, performing a chemical reaction to remove toxic polycyclic aromatic hydrocarbons, and obtaining a mixture; the amount of the catalyst added is 0.1 to 0.4 times the mass of the residual powder before modification; the amount of the system solvent added is 1 to 5 times the mass of the residual powder before modification; Step 4: Collect and recover the mixture by rotary evaporation, and place the obtained solid in a drying oven for further drying, grind to obtain a modified residue powder, and recycle the solvent recovered after rotary evaporation.

2. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The particle size of the residue before modification in step 1 satisfies D 50 ≤50~300μm.

3. The method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The coal-based residue in step 1 includes one or more combinations of direct liquefaction residue, indirect liquefaction ash, oil-coal co-refining residue, coal pyrolysis residue, oil sludge, fly ash, and coal gangue carbonaceous materials. The content of toxic polycyclic aromatic hydrocarbons in the coal-based residue is 2000-50000 ppm.

4. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: In the step 2, the residual powder before modification is dried in a forced air drying oven at 100-120° C. for 2-6 hours.

5. The method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The step three is added into the reactor to carry out the chemical reaction of removing toxic polycyclic aromatic hydrocarbons, the feed amount is 1-1000g, the reaction temperature is 50-200°C, the reaction time is 2-12h, the reaction pressure is 0-5.0MPa, the heating rate is 1-100°C / min, the stirring rate is 200-2000r / min, the reaction atmosphere is nitrogen, carbon dioxide or air, and the temperature control accuracy is ±1°C.

6. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The modifier in step 2 is one or more combinations of terephthalaldehyde, terephthalic alcohol, formaldehyde, benzoic acid, polyethylene glycol, divinylbenzene, and trioxymethylene, and can be recycled.

7. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The catalyst in step three is one or more combinations of concentrated sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, anhydrous aluminum chloride, and cobalt chloride, and can be recycled.

8. The method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The system solvent in step three includes one or more combinations of methanol, toluene, cyclohexane, acetone, ethyl acetate, butyl acetate, and n-butanol, and can be recycled.

9. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: In the step 4, the rotary evaporation temperature is 40-100° C., and the rotary evaporation time is 1-12 hours; the drying temperature is 80-140° C., and the drying time is 1-12 hours.

10. A method for removing trace toxic polycyclic aromatic hydrocarbons from coal-based residues according to claim 1, characterized in that: The modifier in step 2 is terephthalaldehyde, and the catalyst in step 3 is concentrated sulfuric acid; the system solvent in step 3 is toluene, and the amount of terephthalaldehyde added is 0.3 times the mass of the residue powder before modification; the amount of concentrated sulfuric acid added is 0.4 times the mass of the residue powder before modification, and the amount of toluene solvent is 3 times the mass of the residue powder before modification. The chemical reaction in step 3 is carried out at a temperature of 90±3°C, a reaction time of 6h, and a stirring rate of 1000r / min to obtain a modified mixture.

Images