Method for reducing contents of 16 PAHs (Polycyclic Aromatic Hydrocarbons) for USEPA (United Static Eicosapentaenoic Acid)

Abstract

The invention relates to a method for reducing the content of 16 polycyclic aromatic hydrocarbons optimally controlled by the Environmental Protection Agency by modifying coal tar pitch through an alkylation method, which comprises the following steps: reacting coal tar pitch, a modifier 1-dodecene, a catalyst benzenesulfonic acid and a solvent cyclohexane at 130-170 DEG C under a continuous stirring condition for 3-5 hours, cooling to room temperature after the reaction is finished, removing the solvent cyclohexane, and obtaining the polycyclic aromatic hydrocarbons. And drying the residual solid mixture in vacuum to obtain the modified coal pitch. The reactor adopted by the method is simple and easy to operate, the dosage of the alkylation reagent is small, and the solvent can be recycled.

Description

Technical Field

[0001] The invention relates to a method for modifying coal tar pitch, and in particular to a method for preparing modified coal tar pitch with low content of controlled polycyclic aromatic hydrocarbons for road construction. Technical Background

[0002] Coal tar is the residue after the liquid fraction is removed from the distillation of coal tar. It is widely used in fuel, coatings, road construction, building materials, adhesives, asphalt coke, needle coke, carbon fiber, oil felt, activated carbon, carbon black and other fields. However, coal tar contains a large amount of polycyclic aromatic hydrocarbons (PAHs) that are listed as 16 priority controlled polycyclic aromatic hydrocarbons by the United States Environmental Protection Agency (USEPA). The 16 priority controlled polycyclic aromatic hydrocarbons are: naphthalene, acenaphthene, acenaphthylene, anthracene, phenanthrene, fluorene, fluoranthene, pyrene, benz[a]anthracene, (Chrysene), Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Dibenzo[a,h]anthracene, Indeno[1,2,3-c,d]pyrene, Benzo[g,h,i]perylene. In particular, carcinogenic PAHs such as benzopyrene are the most common, which may pose a threat to the health of construction workers and surrounding residents during use, resulting in great restrictions on their application in coatings, road construction, building materials, etc.

[0003] In order to optimize the reduction of the content of polycyclic aromatic hydrocarbons in coal tar, our research group has done a lot of work in the early stage. On the basis of studying the composition, structure and properties of coal tar, by optimizing the modifiers and catalysts, we proposed a research idea for modifying coal tar from a chemical perspective. For example, Chinese patent CN 105238429 B provides a method for preparing low-toxic modified coal tar for road construction by using p-toluenesulfonic acid as a catalyst, terephthalaldehyde as a modifier, and cyclohexane as a solvent to modify coal tar by traditional heating means. Subsequently, our research group further improved the types of catalysts and modifiers, and proposed in Chinese patent CN 106336884B to use potassium hydrogen sulfate as a catalyst, 10-undecenal as a modifier, and cyclohexane as a solvent to modify coal tar by traditional heating means to prepare environmentally friendly modified coal tar with better performance. And in Chinese patent CN108893132B, it is proposed to add crushed coal tar, catalyst, chemical modifier and low-boiling-point easily recyclable non-protonic organic solvent in sequence into a reactor with a stirrer, a microwave heater and a built-in ultraviolet light generator under microwave heating conditions, and modify the coal tar by microwave constant temperature heating and ultraviolet light radiation to obtain modified low-toxic coal tar. Summary of the invention

[0004] On the basis of previous research work, the present invention further discovered a more effective and simple method for reducing the 16 polycyclic aromatic hydrocarbons (PAHs) that are prioritized by the United States Environmental Protection Agency (USEPA). This method uses an alkylation method to modify coal tar by selecting suitable alkylating agents and catalysts, and can selectively reduce the content of 16 polycyclic aromatic hydrocarbons prioritized by USEPA in coal tar, so that the modified coal tar can be used as an intermediate or additive or product, and is more widely used in the fields of coatings, road construction, building materials, asphalt coke, needle coke, carbon fiber, oil felt, activated carbon, and binder preparation.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is as follows.

[0006] A method for reducing the contents of 16 polycyclic aromatic hydrocarbons controlled by USEPA by modifying coal tar pitch by alkylation, comprising dissolving a certain amount of coal tar pitch with a particle size of 80 mesh and a softening point of ≤98°C in a sufficient amount of cyclohexane solvent, and then adding a modifier 1-dodecene and an appropriate amount of catalyst benzenesulfonic acid, reacting at 130-170°C for 3-5 hours under continuous stirring conditions; cooling to room temperature after the reaction is completed, removing the cyclohexane solvent, and vacuum drying the obtained solid mixture to obtain a modified coal tar pitch with a content of 16 controlled polycyclic aromatic hydrocarbons not higher than 13.4 mg / g.

[0007] Preferably, the amount of the modifier 1-dodecene is 2-6 times the mass of the coal tar pitch.

[0008] Preferably, the amount of the cyclohexane solvent used is 40-80 times the mass of the coal tar pitch.

[0009] A more preferred technical solution is to dissolve a certain amount of coal tar pitch in a sufficient amount of cyclohexane solvent, then add the modifier 1-dodecene and an appropriate amount of catalyst benzenesulfonic acid, and react at 130-170°C for 3-4 hours under continuous stirring conditions; wherein the amount of cyclohexane used is 55-65 times the mass of the coal tar pitch, and the amount of the modifier 1-dodecene used is 4-6 times the mass of the coal tar pitch.

[0010] In the above preferred technical scheme, after the reaction is completed and cooled to room temperature, the cyclohexane solvent is removed, and the obtained solid mixture is vacuum dried to obtain 16 kinds of modified coal tar with a controlled polycyclic aromatic hydrocarbon content not higher than 6 mg / g.

[0011] More preferably, the cyclohexane solvent is removed by any one of rotary evaporation, reduced pressure distillation or suction filtration.

[0012] Further preferably, the cyclohexane solvent is recovered and reused.

[0013] A modified coal tar pitch prepared by the above-mentioned method of reducing the content of 16 PAHs preferentially controlled by USEPA in coal tar pitch, wherein the content of the 16 preferentially controlled polycyclic aromatic hydrocarbons is not higher than 13.4 mg / g, preferably not higher than 6 mg / g.

[0014] The modified coal tar pitch prepared by the method of the present invention can be used as an intermediate, additive or product, and is applied to the fields of coatings, road construction, building materials, asphalt coke, needle coke, carbon fiber, oil felt, activated carbon, adhesive preparation, etc.

[0015] Compared with the prior art, the method of the present invention has the following advantages and positive effects:

[0016] (1) This method uses high-temperature coal tar pitch with a low softening point as raw material. Through a large number of experimental studies, we discovered 1-dodecene, an electrophilic substitution reagent (or alkylation modifier) ​​that has a stronger binding affinity to the 16 PAHs controlled by USEPA in asphalt, as well as the corresponding benzenesulfonic acid catalyst and suitable reaction conditions, thus expanding the types of coal tar pitch modifiers.

[0017] (2) This method uses an ordinary reactor, and can achieve full reaction between the alkylating agent 1-dodecene and the 16 kinds of polycyclic aromatic hydrocarbons in coal tar at 130-170°C, and the amount of alkylating agent used is only 2-6 times the amount of coal tar. After the reaction is completed, the cyclohexane solvent can be recovered and reused by any method such as rotary evaporation, vacuum distillation or suction filtration. It has the advantages of low requirements for reaction equipment, simple process flow, small amount of alkylating agent, recyclable solvent, and low production cost.

[0018] (3) Under the most preferred process conditions, using the alkylating reagent 1-dodecene of the present invention, reacting at 130 - 170 °C for 3 - 4 h under atmospheric pressure can achieve a total reduction rate of 98.24% in the content of 16 PAHs preferentially controlled by USEPA in coal tar pitch. Thus, the modified coal tar pitch can be used as an intermediate, additive or product and be more widely applied in fields such as coatings, road construction, building materials, pitch coke, needle coke, carbon fiber, roofing felt, activated carbon, binder preparation, etc., greatly expanding the application scope of coal tar pitch. Description of the Drawings

[0019] Figure 1 It is a distribution diagram of the content of 16 polycyclic aromatic hydrocarbons preferentially controlled by USEPA in the high-temperature coal tar pitch used in each example of the present invention.

[0020] Figure 2 It is a comparison diagram of the content of 16 polycyclic aromatic hydrocarbons preferentially controlled by USEPA in coal tar pitch before and after modification in Example 1 of the present invention; in the figure, coal tar pitch represents the high-temperature coal tar pitch before modification, and modified pitch represents the coal tar pitch after modification. Detailed Embodiments

[0021] The following further describes the detailed embodiments of the present invention.

[0022] The coal tar pitch used in each embodiment of this method is high-temperature coal tar pitch (required softening point between 95 - 120 °C), with a particle size passing through an 80-mesh sieve. The content distribution of 16 polycyclic aromatic hydrocarbons preferentially controlled by USEPA is shown in Figure 1 . The alkylating reagent is 1-dodecene, the catalyst is benzenesulfonic acid, and the solvent is cyclohexane. The content of polycyclic aromatic hydrocarbons in coal tar pitch is detected by gas chromatography. Among them, the content of naphthalene is too low to reach the detection limit of gas chromatography and is thus ignored, and benzo[b]fluoranthene and benzo[k]fluoranthene are isomers and cannot be effectively separated, so they are calculated together.

[0023]

Example 1

[0024] Weigh 2.5 g of coal tar pitch, the amount of cyclohexane used is 60 times the mass of coal tar pitch, the amount of alkylating reagent 1-dodecene used is 4 times the mass of coal tar pitch, and a catalytic amount of benzenesulfonic acid. React at 170 °C for 4 h. After the reaction, cool and filter to obtain a modified pitch sample. The content of polycyclic aromatic hydrocarbons in the pitch samples before and after modification is as follows in the table:

[0025]

[0026]

[0027] Convert the data of coal tar pitch before and after modification in Table 1 into a bar chart comparison diagram (see Figure 2), it can be seen more intuitively that the method of the present invention, by selecting suitable alkylating agents and catalysts and utilizing the alkylation method to modify coal tar, is very effective in reducing the content of 16 polycyclic aromatic hydrocarbons controlled by USEPA in coal tar.

[0028] [Example 2]

[0029] Weigh 2.5g coal tar, the amount of cyclohexane used is 60 times the mass of coal tar, the amount of alkylating agent 1-dodecene used is 2 times the mass of coal tar, and the catalytic amount of benzenesulfonic acid is reacted at 170℃ for 4h. After the reaction is completed, cool and filter to obtain a modified asphalt sample. The content of polycyclic aromatic hydrocarbons in the asphalt sample before and after modification is as follows:

[0030]

[0031] [Example 3]

[0032] Weigh 2.5g coal tar, the amount of cyclohexane used is 60 times the mass of coal tar, the amount of alkylating agent 1-dodecene used is 6 times the mass of coal tar, and the catalytic amount of benzenesulfonic acid is used. React at 170℃ for 4h. After the reaction is completed, cool and filter to obtain a modified asphalt sample. The content of polycyclic aromatic hydrocarbons in the asphalt sample before and after modification is as follows:

[0033]

[0034]

[0035] [Example 4]

[0036] Weigh 2.5g coal tar, the amount of cyclohexane used is 60 times the mass of coal tar, the amount of alkylating agent 1-dodecene used is 4 times the mass of coal tar, and the catalytic amount of benzenesulfonic acid is used. React at 140℃ for 4h. After the reaction is completed, cool and filter to obtain a modified asphalt sample. The content of polycyclic aromatic hydrocarbons in the asphalt sample before and after modification is as follows:

[0037]

[0038]

[0039] [Example 5]

[0040] Weigh 2.5g coal tar, the amount of cyclohexane used is 60 times the mass of coal tar, the amount of alkylating agent 1-dodecene used is 4 times the mass of coal tar, and the catalytic amount of benzenesulfonic acid is used. React at 140℃ for 5h. After the reaction is completed, cool and filter to obtain a modified asphalt sample. The content of polycyclic aromatic hydrocarbons in the asphalt sample before and after modification is as follows:

[0041]

[0042] [Example 6]

[0043] Weigh 2.5g coal tar, the amount of cyclohexane used is 40 times the mass of coal tar, the amount of alkylating agent 1-dodecene used is 4 times the mass of coal tar, and the catalytic amount of benzenesulfonic acid is used. React at 130℃ for 3h. After the reaction is completed, cool and filter to obtain a modified asphalt sample. The content of polycyclic aromatic hydrocarbons in the asphalt sample before and after modification is as follows:

[0044]

[0045]

[0046] [Example 7]

[0047] Weigh 2.5g coal tar, the amount of cyclohexane used is 80 times the mass of coal tar, the amount of alkylating agent 1-dodecene used is 4 times the mass of coal tar, and the catalytic amount of benzenesulfonic acid is used. React at 130℃ for 3h. After the reaction is completed, cool and filter to obtain a modified asphalt sample. The content of polycyclic aromatic hydrocarbons in the asphalt sample before and after modification is as follows:

[0048]

[0049] In this example, the reduction rate of the content of 16 types of polycyclic aromatic hydrocarbons in coal tar pitch that were prioritized by USEPA reached a maximum of 98.24%, among which the reduction rate of benzo[a]pyrene, the most carcinogenic, reached 97.11%.

[0050] The present invention can be summarized in other specific forms that do not violate the spirit or main features of the present invention. Therefore, the above content is only a basic description of the concept of the present invention, and any equivalent exchange made according to the technical solution of the present invention belongs to the protection scope of the present invention.

Claims

1. A method for reducing the content of 16 PAHs controlled by USEPA in coal tar, characterized in that: A certain amount of coal tar pitch with a particle size of 80 mesh and a softening point of ≤98°C was dissolved in a sufficient amount of cyclohexane solvent, and then the modifier 1-dodecene and an appropriate amount of catalyst benzenesulfonic acid were added, and the mixture was reacted at 130-170°C for 3-5 hours under continuous stirring. After the reaction was completed, the mixture was cooled to room temperature, the cyclohexane solvent was removed, and the obtained solid mixture was vacuum dried to obtain 16 kinds of modified coal tar pitch with a controlled polycyclic aromatic hydrocarbon content not higher than 13.4 mg / g.

2. The method for reducing the content of 16 PAHs controlled by USEPA in coal tar as claimed in claim 1, characterized in that: The amount of the modifier 1-dodecene used is 2-6 times the mass of the coal tar pitch.

3. The method for reducing the content of 16 PAHs controlled by USEPA in coal tar as claimed in claim 1, characterized in that: The amount of the cyclohexane solvent used is 40-80 times the mass of the coal tar pitch.

4. The method for reducing the content of 16 PAHs controlled by USEPA in coal tar as claimed in any one of claims 1 to 3, characterized in that: A certain amount of coal tar pitch is dissolved in a sufficient amount of cyclohexane solvent, and then the modifier 1-dodecene and an appropriate amount of catalyst benzenesulfonic acid are added, and the reaction is carried out at 130-170°C for 3-4 hours under continuous stirring conditions; wherein the amount of cyclohexane used is 55-65 times the mass of the coal tar pitch, and the amount of the modifier 1-dodecene used is 4-6 times the mass of the coal tar pitch.

5. The method for reducing the content of 16 PAHs controlled by USEPA in coal tar as claimed in claim 4, characterized in that: After the reaction was completed and cooled to room temperature, the cyclohexane solvent was removed, and the obtained solid mixture was vacuum dried to obtain 16 kinds of modified coal tar pitch with a controlled polycyclic aromatic hydrocarbon content not higher than 6 mg / g.

6. The method for reducing the content of 16 PAHs controlled by USEPA in coal tar as claimed in claim 5, characterized in that: The cyclohexane solvent is removed by any one of rotary evaporation, reduced pressure distillation or suction filtration.

7. The method for reducing the content of 16 PAHs controlled by USEPA in coal tar as claimed in claim 6, characterized in that: The cyclohexane solvent is recovered and reused.

8. A modified coal tar pitch prepared by the method for reducing the contents of 16 PAHs controlled by USEPA in coal tar pitch according to any one of claims 1 to 7.

9. Use of the modified coal tar pitch according to claim 8 as an intermediate or additive or product for the preparation of coatings, road construction, building materials, asphalt coke, needle coke, carbon fiber, oil felt, activated carbon, and adhesives.

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