Method for segmentally extracting phenolic compounds from coal tar

Abstract

The invention discloses a method for segmentally extracting phenolic compounds from coal tar, and relates to the technical field of chemical separation. The method comprises the following steps: mixing an extraction agent II with coal tar through an extraction device to obtain coal tar I and an extraction phase II; the extraction phase II is sequentially subjected to CO2 deep acidification and oil-water separation, and a low-grade crude carbolic oil product and a water phase II are obtained; the water phase II enters a regeneration device to be regenerated through heating, obtained CO2 gas is circulated to a deep acidification device, and a regenerated extraction agent and a supplemented fresh extraction agent are mixed to serve as an extraction agent I; mixing the extraction agent I with coal tar I through an extraction device to obtain an extraction phase I and a dephenolized oil product; and carrying out acidification and oil-water separation on the extract phase I to obtain an extractant II and high-grade crude carbolic oil. According to the method, the high-efficiency extraction of the phenolic compounds in the coal tar and the preliminary separation of the crude carbolic oil are realized by utilizing the selectivity difference of different extraction agents on different types of phenolic compounds in the coal tar, and the subsequent treatment cost of the dephenolized oil and the crude carbolic oil is obviously reduced.

Description

Technical Field

[0001] The invention relates to the technical field of chemical separation, and in particular to a method for extracting phenolic compounds from coal tar in sections. Background Art

[0002] Coal tar, as an important by-product of coal pyrolysis, liquefaction or gasification, has significant resource utilization value. Phenolic compounds account for 10%-30% of its chemical composition. The presence of such substances not only significantly increases the hydrogen consumption of the subsequent hydrogenation process for producing fuel oil, but also causes problems such as the deterioration of catalyst active sites and shortened service life. More importantly, the existing process fails to effectively recover high-value-added phenolic compounds, resulting in the waste of high-value phenolic compounds and restricting the economic efficiency of coal tar deep processing.

[0003] The alkali washing method used by the industry for a long time has obvious technical defects: the process route of acid-base neutralization of phenolic compounds in coal tar with caustic soda solution (sodium hydroxide solution) to generate sodium phenol salt, and then recovering crude phenol oil through sulfuric acid acidification, not only consumes a large amount of acid-base reagents (0.42 tons of 98% sulfuric acid is consumed per ton of phenol), but also produces environmental pollutants such as phenol-containing high-salt wastewater (COD>5000 mg / L). In recent years, many researchers have conducted extensive research on new methods for extracting phenol from coal tar. For example, Chinese invention patent application CN116410766A proposed a method for extracting phenolic compounds from phenol-containing oil by secondary extraction with a composite organic amine aqueous solution, and acidifying the phenol-rich extraction phase with an acidifier to obtain a crude phenol oil product, and its phenol extraction rate can reach more than 92%. Chinese invention patent application CN118480370A provides a method for selectively separating phenols, aromatic hydrocarbons and alkanes from coal tar phenol oil fractions, wherein a polar low eutectic solvent and a non-polar extractant are added to the phenol oil at the same time, and the two phases are formed by static stratification; a stripping agent A is added to the polar phase to strip phenols to achieve phenol enrichment; and the stripping agent and phenol compounds are separated by distillation. However, although the above methods can achieve efficient extraction of phenol compounds in coal tar and have the potential to replace traditional industrial phenol extraction methods, they fail to achieve selective separation of C6-C9 low-grade phenols and high-grade phenols in crude phenol oil, resulting in a subsequent distillation process with steam energy consumption as high as 3.2 GJ / ton of product.

[0004] The technical solution of the present invention utilizes the selectivity differences of organic amine aqueous solution and ammonium carbonate aqueous solution formed by partial or balanced acidification of organic amine aqueous solution for different phenolic compounds in coal tar, so as to achieve deep extraction and segmented separation of phenolic compounds in coal tar, and greatly reduce the energy consumption of separation and refining of C6-C9 low-level phenolic compounds in crude phenol oil. Summary of the invention

[0005] In view of the technical problems that the above-mentioned prior art fails to achieve the selective separation of C6-C9 low-grade phenols and high-grade phenols in crude phenol oil and the subsequent refining has high energy consumption, the present invention provides a method for extracting phenolic compounds from coal tar in sections, thereby achieving deep extraction and sectioned separation of phenolic compounds in coal tar.

[0006] The technical solution adopted by the present invention is as follows: A method for extracting phenolic compounds from coal tar in sections comprises the following steps: S1. The extractant II is transported to the first extraction device, and is countercurrently contacted with the raw coal tar to selectively extract low-level phenolic compounds (such as phenol, o-cresol, etc.), and the extraction phase II and coal tar I are separated, wherein the extraction phase II is a mixed phase containing phenol-extractant, and the coal tar I is a residual oil phase after the low-level phenol is removed; S2. The extraction phase II enters a deep acidification device and reacts with the acidic gas CO2 to obtain an acidified liquid II; the acidified liquid II is placed in a phase separator for stratification to obtain a low-grade crude phenol oil (main product) and an aqueous phase II, wherein the low-grade crude phenol oil is an organic phase and the aqueous phase II is a pressurized acidified amine salt solution; S3. The aqueous phase II is heated and desorbed CO2 through a regeneration device to obtain a regenerated extractant and a circulating CO2 gas, wherein the main component of the regenerated extractant is an organic amine aqueous solution, and the CO2 gas is returned to the deep acidification device for reuse; the regenerated extractant is mixed with a supplementary fresh extractant or the regenerated extractant is directly used as an extractant I, and the extractant I is pumped into a second extraction device to extract the higher phenolic compounds (such as ethyl methylphenol and β-naphthol) in the coal tar I, and the extraction phase I and the dephenolized oil (end product) are separated, and the extraction phase I is a mixed phase containing higher phenols and the extractant; S4. The extraction phase I is acidified in the preliminary acidification device with industrial tail gas containing CO2 or industrial-grade CO2 gas to form an acidified liquid I; the acidified liquid I is phase-separated in a phase separator to obtain high-grade crude phenol oil (main product) and aqueous phase I; the high-grade crude phenol oil is the organic phase, the aqueous phase I is a partially acidified or atmospheric pressure balanced acidified amine salt solution, and the aqueous phase I is circulated to the first extraction device as the extractant II to complete the process closed loop.

[0007] Furthermore, the extractant I is an aqueous solution of an organic amine, i.e., a homogeneous solution formed by dissolving an organic amine compound in water, and the extractant II is an aqueous phase I obtained by partially acidifying the extractant I with acidic gas CO2 or reaching normal pressure acidification equilibrium, and then standing and stratifying in a phase separator. The formation mechanism is: CO2 and the organic amine undergo a protonation reaction to generate an amine salt (such as R3NH + HCO3 - ), resulting in an increase in the polarity difference of the system and phase separation, and the aqueous phase I is rich in hydrophilic amine salt substances.

[0008] Furthermore, the mass fraction of the organic amine compound in the organic amine aqueous solution is 10%-50%, preferably 20%-40%; the organic amine compound is one or more of organic alcohol amine compounds having carbon atoms of C2-C10.

[0009] Furthermore, the first extraction device and the second extraction device are both selected from one of the following liquid-liquid contact extraction equipment: an extraction tower, a centrifugal extractor or a mixing-clarification tank. The extraction tower realizes phase separation based on density difference, the centrifugal extractor strengthens mass transfer by mechanical force, and the mixing-clarification tank completes the mixing and phase separation process in steps; the extraction temperature is 20°C - 50°C, the extraction pressure is normal pressure, the mass ratio of the extractant I to the coal tar I is 1:2 to 5:1, and the mass ratio of the extractant II to the coal tar is 1:2 to 5:1.

[0010] Furthermore, both the preliminary acidification device and the deep acidification device use an absorption tower or a Venturi reactor as the core reaction unit. The reaction temperature of the preliminary acidification is 20℃ - 70℃, the reaction pressure is normal pressure, and the pH value of the acidified liquid I after the preliminary acidification is 8 - 9; the reaction temperature of the deep acidification is 20℃ - 70℃, the reaction pressure (absolute pressure) is 0.2 MPa - 0.6 MPa, and the pH value of the acidified liquid II after the deep acidification is 6 - 8; the exhaust gas generated in the two-stage acidification process enters the exhaust gas treatment system and meets the emission standards after purification.

[0011] Furthermore, the aqueous phase I is conveyed to the first extraction device under pressure; the aqueous phase II is conveyed to the regeneration device through a pipeline, and after regeneration, it returns to the extraction system for reuse.

[0012] Furthermore, the regeneration device uses a desorption tower to separate the CO2-extractant system. The regeneration temperature is 90-170℃, the desorption kinetics and energy consumption balance range are optimized, and the regeneration pressure is 0.1-0.3 MPa (absolute pressure). The high temperature environment promotes efficient desorption of CO2, and the high pressure environment inhibits water evaporation. The CO2 gas discharged from the top of the desorption tower is pressurized to 0.2~0.6 MPa (absolute pressure) directly or through a compression unit, and returned to the deep acidification device for reuse as an acidifier to achieve closed-loop utilization of carbon resources.

[0013] The beneficial effects of the present invention are: (1) The separation efficiency of phenolic compounds is significantly improved: Through segmented extraction, staged acidification and differentiated pressure control, the efficient extraction of phenolic compounds in coal tar is achieved, while the separation and enrichment of high-value-added low-grade phenolic compounds and low-value-added high-grade phenolic compounds are achieved. The difficulty of separation and refining of low-grade phenolic compounds in crude phenol oil is reduced, and the separation energy consumption is reduced by 20% to 30%.

[0014] (2) Resource recycling and pollution reduction: The CO2 closed-loop circulation system is combined with the regeneration and reuse of organic amine extractants, reducing acid and alkali consumption by more than 90%, avoiding the pollution of mineral acid and alkali waste liquid in traditional processes; the CO2 resource utilization rate reaches more than 85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below in conjunction with specific embodiments, but the present invention is not limited thereto. Figure 1 The specific description is shown in the following embodiments.

[0017] Example 1 A method for extracting phenolic compounds from coal tar in sections comprises the following steps: (1) A 30 wt% monoethanolamine aqueous solution is partially acidified with CO2 to obtain an amine salt aqueous solution (pH = 8.4) as an extractant II, and the extractant II is transported to a first extraction device (extraction tower) and countercurrently contacted with a raw material coal tar having a phenol content of 25 wt%, so as to selectively extract low-level phenolic compounds (such as phenol, o-cresol, etc.), and separate to obtain an extract phase II (a mixed phase containing phenol-extractant) and coal tar I (a residual oil phase after removing low-level phenols); (2) The extraction phase II enters the deep acidification device and reacts with the acidic gas CO2. The reaction temperature of the deep acidification is 50°C and the reaction pressure (absolute pressure) is 0.3 MPa to obtain the acidified liquid II with a pH of about 7. The acidified liquid II is placed in a phase separator to separate the layers and obtain low-grade crude phenol oil (organic phase, main product) and aqueous phase II (pressurized acidified amine salt solution). S3. The aqueous phase II is heated to desorb CO2 through a regeneration device (desorption tower), the regeneration temperature is 130°C, the regeneration pressure is 0.3MPa, and a regenerated extractant (mainly an organic amine aqueous solution) and a circulating CO2 gas (returned to the deep acidification device for reuse) are obtained; the regenerated extractant is mixed with a fresh extractant 30 wt% monoethanolamine aqueous solution as extractant I, and the extractant I is pumped into the second extraction device (extraction tower) to extract the higher phenolic compounds (such as ethylmethylphenol and β-naphthol) in the coal tar I, and the extraction phase I (a mixed phase containing higher phenols-extractant) and the dephenolized oil (the terminal product) are separated; S4. The extraction phase I is initially acidified in the preliminary acidification device (absorption tower) by industrial tail gas containing CO2 or industrial-grade CO2 gas. The reaction temperature of the preliminary acidification is 40°C and the reaction pressure is normal pressure to form an acidified liquid I with a pH of about 8. The acidified liquid I is phase-separated in a phase separator to obtain high-grade crude phenol oil (organic phase, main product) and aqueous phase I (partially acidified or atmospheric pressure balanced acidified amine salt solution). The aqueous phase I is circulated to the first extraction device as the extractant II to complete the process closed loop.

[0018] Comparative Example 1 The rest is the same as Example 1, except that: Extractant I and Extractant II both use amine salt aqueous solution (pH = 8.4) obtained by partial acidification of 30 wt% monoethanolamine aqueous solution with CO2.

[0019] Comparative Example 2 The rest is the same as Example 1, except that both extractant I and extractant II use 30 wt % monoethanolamine aqueous solution.

[0020] Comparative Example 3 The traditional industrial method (alkaline washing method) was adopted to extract phenolic compounds from coal tar with a phenol content of 25 wt%. 15 wt% sodium hydroxide solution and 70 wt% sulfuric acid aqueous solution were used as extractant and acidifying agent respectively. After extraction, stripping, acidification and phase separation, one ton of crude phenol oil product was obtained.

[0021] Comparative Example 4 A traditional industrial improved method was adopted, with CO2 and 70 wt% aqueous sulfuric acid solution as acidifying agents; the extract phase obtained by extracting phenol with 15 wt% aqueous sodium hydroxide solution was acidified with CO2, the precipitated sodium bicarbonate solid was filtered, decomposed at elevated temperature and causticized, and part of the caustic solution was recovered, and the other conditions were the same as those in Comparative Example 3.

[0022] The experimental results of the embodiments and comparative examples are shown in Table 1.

[0023] Table 1 Experimental results of embodiments and comparative examples

[0024]

[0025] Note: t / t crude phenol oil means the mass of substances consumed or produced for producing one ton of crude phenol oil, and the unit is ton / ton; GJ / t crude phenol oil means the energy in gigajoules consumed for producing one ton of crude phenol oil, and the unit is gigajoules / ton.

[0026] It can be seen from Table 1 that, compared with Comparative Examples 3 and 4, Example 1 of the present invention consumes almost no extractant and acidulant while ensuring a high extraction yield of crude phenol oil, and produces almost no wastewater and waste residue while achieving the initial separation of crude phenol. Compared with Comparative Examples 1 and 2, Example 1 of the present invention not only achieves the initial separation of crude phenol, but also significantly improves the extraction yield of crude phenol oil.

Claims

1. A method for extracting phenolic compounds from coal tar in sections, characterized in that: The steps include: S1. The extractant II is transported to the first extraction device, and is countercurrently contacted with the raw coal tar to selectively extract the low-level phenolic compounds, and the extract phase II and the coal tar I are separated; S2. The extracted phase II enters a deep acidification device and reacts with the acidic gas CO2 to obtain an acidified liquid II; the acidified liquid II is allowed to stand and separate into layers in a phase separator to obtain a low-grade crude phenol oil and an aqueous phase II; S3. The aqueous phase II is heated and desorbed by the regeneration device to obtain a regenerated extractant and a circulating CO2 gas; the regenerated extractant is mixed with a fresh supplementary extractant or the regenerated extractant is directly used as an extractant I, and the extractant I is pumped into a second extraction device to extract the higher phenolic compounds in the coal tar I, and the extract phase I and the dephenolized oil are separated; S4. The extraction phase I is acidified in a preliminary acidification device with industrial tail gas containing CO2 or industrial-grade CO2 gas to form an acidified liquid I; the acidified liquid I is phase-separated in a phase separator to obtain high-grade crude phenol oil and an aqueous phase I; the aqueous phase I is circulated to the first extraction device as an extractant II to complete the process closed loop.

2. The method for extracting phenolic compounds from coal tar in sections according to claim 1, characterized in that: The extractant I is an organic amine aqueous solution, and the extractant II is an aqueous phase I obtained by partially acidifying the extractant I with acidic gas CO2 or reaching normal pressure acidification equilibrium and then standing and stratifying in a phase separator.

3. The method for extracting phenolic compounds from coal tar in sections according to claim 2, characterized in that: The mass fraction of the organic amine compound in the organic amine aqueous solution is 10%-50%; the organic amine compound is one or more of organic alcohol amine compounds with carbon atoms of C2-C10.

4. The method for extracting phenolic compounds from coal tar in sections according to claim 3, characterized in that: The mass fraction of the organic amine compound in the organic amine aqueous solution is 20%-40%.

5. The method for extracting phenolic compounds from coal tar in sections according to claim 1, characterized in that: The first extraction device and the second extraction device are both selected from one of the following liquid-liquid contact extraction equipment: an extraction tower, a centrifugal extractor or a mixing-clarification tank, the extraction temperature is 20°C - 50°C, the extraction pressure is normal pressure, the mass ratio of the extractant I to the coal tar I is 1:2 to 5:1, and the mass ratio of the extractant II to the coal tar is 1:2 to 5:

1.

6. The method for extracting phenolic compounds from coal tar in sections according to claim 1, characterized in that: Both the preliminary acidification device and the deep acidification device use an absorption tower or a Venturi reactor as the core reaction unit. The reaction temperature of the preliminary acidification is 20℃ - 70℃, the reaction pressure is normal pressure, and the pH value of the acidified liquid I after preliminary acidification is 8 - 9; the reaction temperature of the deep acidification is 20℃ - 70℃, the reaction pressure is 0.2 MPa - 0.6 MPa, and the pH value of the acidified liquid II after deep acidification is 6 - 8.

7. The method for extracting phenolic compounds from coal tar in sections according to claim 6, characterized in that: The exhaust gas generated in the two-stage acidification process enters the exhaust gas treatment system and meets the emission standards after purification.

8. The method for extracting phenolic compounds from coal tar in sections according to claim 1, characterized in that: The aqueous phase I is conveyed to the first extraction device under pressure; the aqueous phase II is conveyed to the regeneration device through a pipeline, and after regeneration, it returns to the extraction system for reuse.

9. The method for extracting phenolic compounds from coal tar in sections according to claim 1, characterized in that: The regeneration device adopts a desorption tower, the regeneration temperature is 90-170℃, and the regeneration pressure is 0.1MPa - 0.3MPa.

10. The method for extracting phenolic compounds from coal tar in sections according to claim 9, characterized in that: The CO2 gas discharged from the top of the desorption tower is pressurized to 0.2 - 0.6 MPa directly or through a compression unit, and returned to the deep acidification device for reuse as an acidifier, realizing closed-loop utilization of carbon resources.

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