A method for fractionally extracting phenolic compounds from coal tar

Abstract

The present invention discloses a method for extracting phenolic compounds from coal tar in stages, which relates to the technical field of chemical separation. The method comprises the following steps: extractant II is mixed with coal tar through an extraction device to obtain coal tar I and extraction phase II; the extraction phase II is sequentially subjected to deep acidification with CO2 and oil-water separation to obtain a low-grade crude phenol oil product and aqueous phase II; the aqueous phase II enters a regeneration device for regeneration by heating, the obtained CO2 gas is recycled to the deep acidification device, and the regenerated extractant is mixed with supplemented fresh extractant to serve as extractant I. Extractant I is mixed with coal tar I through an extraction device to obtain extraction phase I and a dephenolized oil product; the extraction phase I is subjected to acidification and oil-water separation to obtain extractant II and a high-grade crude phenol oil. The present invention utilizes the selectivity difference of different extractants for different types of phenolic compounds in coal tar to realize the efficient extraction of phenolic compounds in coal tar and the preliminary separation of crude phenol oil, and significantly reduces the cost of subsequent treatment of dephenolized oil and crude phenol oil.

Description

Technical Field

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

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

[0003] The alkali washing method long adopted in the industry has obvious technical defects: the process route of generating sodium phenolate by the acid-base neutralization of caustic alkali solution (sodium hydroxide solution) and phenolic compounds in coal tar, and then recovering crude phenol oil by sulfuric acid acidification not only consumes a large amount of acid and alkali reagents (0.42 tons of 98% sulfuric acid is consumed per ton of phenol), but also generates environmental pollutants such as high-phenol saline wastewater (COD>5000 mg / L). In recent years, many researchers have carried out a large number of studies on new methods for extracting phenols from coal tar. For example, Chinese Patent Application CN116410766A proposes a method for extracting phenolic compounds from phenol-containing oil by secondary extraction with an aqueous solution of a composite organic amine, and obtaining a crude phenol oil product by acidifying the phenol-rich extraction phase with an acidifying agent, and the phenolic extraction rate can reach more than 92%. Chinese Patent Application CN118480370A provides a method for selectively separating phenols, aromatics and alkanes in the phenol oil fraction of coal tar. In this method, a polar deep eutectic solvent and a non-polar extractant are simultaneously added to the phenol oil, and after standing and separating, two phases are formed; an anti-extraction agent A is added to the polar phase to back-extract phenols to achieve the enrichment of phenols; and the separation of the anti-extraction agent and phenolic compounds is achieved by distillation operation. However, although the above methods can all achieve the efficient extraction of phenolic compounds in coal tar and have the possibility of replacing traditional industrial phenol extraction methods, they all fail to achieve the selective separation of C6-C9 low-grade phenols and high-grade phenols in the crude phenol oil, resulting in a steam energy consumption as high as 3.2 GJ / ton of product in the subsequent rectification process.

[0004] The technical solution of the present invention utilizes the selective differences of different phenolic compounds in coal tar between an aqueous solution of an organic amine and an aqueous solution of ammonium carbonate formed by partial or balanced acidification of the aqueous solution of the organic amine to achieve the deep extraction and staged separation of phenolic compounds in coal tar, and greatly reduce the energy consumption for the separation and purification of C6-C9 low-grade phenolic compounds in the 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-level phenols and high-level phenols in crude phenol oil and the subsequent refining energy consumption is high, the present invention provides a method for extracting phenolic compounds from coal tar in stages, realizing the deep extraction and staged separation of phenolic compounds in coal tar.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for extracting phenolic compounds from coal tar in stages, comprising the following steps:

[0008] S1. The extractant II is transported to the first extraction device and contacts the raw coal tar countercurrently to selectively extract low-level phenolic compounds (such as phenol, o-cresol, etc.), and the extraction phase II and coal tar I are separated. The extraction phase II is a mixed phase containing phenol-extractant, and the coal tar I is the residual oil phase after removing low-level phenols;

[0009] S2. The extraction phase II enters the deep acidification device and reacts with the acidic gas CO2 to obtain the acidified liquid II; the acidified liquid II is allowed to stand and layer in a phase separator to obtain low-level crude phenol oil (main product) and aqueous phase II. The low-level crude phenol oil is an organic phase, and the aqueous phase II is a pressurized acidified amine salt solution;

[0010] S3. The aqueous phase II is thermally desorbed of CO2 in a regeneration device to obtain a regenerated extractant and recycled CO2 gas. The main component of the regenerated extractant is an aqueous organic amine solution, and the CO2 gas is returned to the deep acidification device for reuse; the regenerated extractant is mixed with a fresh added extractant or the regenerated extractant directly serves as the extractant I. The extractant I is pumped into the second extraction device to extract high-level phenolic compounds (such as ethyl methyl phenol, β-naphthol) in the coal tar I, and the extraction phase I and dephenolized oil (end product) are separated. The extraction phase I is a mixed phase containing high-level phenol-extractant;

[0011] 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-level crude phenol oil (main product) and aqueous phase I; the high-level crude phenol oil is an organic phase, and the aqueous phase I is a partially acidified or atmospheric pressure equilibrium acidified amine salt solution. The aqueous phase I is recycled to the first extraction device as the extractant II to complete the process closed-loop.

[0012] Further, the extractant I is an aqueous organic amine solution, that is, a homogeneous solution formed by dissolving an organic amine compound in water. The extractant II is the aqueous phase I obtained by partially acidifying the extractant I with the acidic gas CO2 or reaching atmospheric pressure acidification equilibrium and then allowing it to stand and layer in a phase separator. Its formation mechanism is: CO2 undergoes a protonation reaction with the organic amine to form an amine salt (such as R3NH + HCO3 -), resulting in an increased polarity difference in the system and phase separation. The aqueous phase I is rich in hydrophilic amine salt substances.

[0013] Furthermore, the mass fraction of the organic amine compound in the aqueous solution of organic amine is 10% - 50%, preferably 20% - 40%; the organic amine compound is one or more of organic alkanolamine compounds with 2 - 10 carbon atoms.

[0014] Furthermore, both the first extraction device and the second extraction device are selected from one of the following liquid - liquid contact extraction equipment: extraction tower, centrifugal extractor or mixer - settler. The extraction tower realizes phase separation based on density difference, the centrifugal extractor enhances mass transfer through mechanical force, and the mixer - settler completes the mixing and phase separation processes step by step; the extraction temperature is 20°C - 50°C, the extraction pressure is atmospheric pressure, and the mass ratio of extractant I to coal tar I is 1:2 to 5:1, and the mass ratio of extractant II to coal tar is 1:2 to 5:1.

[0015] 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 for preliminary acidification is 20°C - 70°C, the reaction pressure is atmospheric pressure, and the pH value of the acidified liquid I after preliminary acidification is 8 - 9; the reaction temperature for deep acidification is 20°C - 70°C, the reaction pressure (absolute pressure) is 0.2 MPa - 0.6 MPa, and the pH value of the acidified liquid II after deep acidification is 6 - 8; the tail gases generated during the two - stage acidification process all enter the tail gas treatment system and are discharged up to standard after purification.

[0016] Furthermore, the aqueous phase I is pressurized and transported to the first extraction device; the aqueous phase II is transported through a pipeline to the regeneration device and returns to the extraction system for reuse after regeneration.

[0017] Furthermore, the regeneration device uses a desorption tower to separate the CO₂ - extractant system. The regeneration temperature is 90 - 170°C, optimizing the desorption kinetics and energy consumption balance range. The regeneration pressure is 0.1 - 0.3 MPa (absolute pressure). The high - temperature environment promotes the efficient desorption of CO₂, and the high - pressure environment inhibits water evaporation; the CO₂ gas discharged from the top of the desorption tower is directly or pressurized to 0.2~0.6 MPa (absolute pressure) through a compression unit and returned to the deep acidification device for reuse as an acidifying agent, realizing the closed - loop utilization of carbon resources.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The separation efficiency of phenolic compounds is significantly improved: Through segmented extraction, staged acidification, and differential pressure control, while achieving efficient extraction of phenolic compounds from coal tar, the separation and enrichment of high-value low-grade phenolic compounds and low-value high-grade phenolic compounds are realized. The difficulty of separating and refining low-grade phenolic compounds in crude phenol oil decreases, and the separation energy consumption is reduced by 20% - 30%.

[0020] (2) Resource recycling and pollution reduction: The CO2 closed-loop cycle system combines the regeneration and reuse of organic amine extractants, reducing acid-base consumption by more than 90% and avoiding the pollution of mineral acid-base waste liquid in traditional processes; The resource utilization rate of CO2 reaches more than 85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow block diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following further elaborates on the present invention with specific embodiments, but the present invention is not limited thereto. The process flow block diagram of the present invention is as Figure 1 shown and is specifically described as shown in the following embodiments.

[0023] Example 1

[0024] A method for segmented extraction of phenolic compounds from coal tar, comprising the following steps:

[0025] (1) Using an aqueous solution of 30 wt% monoethanolamine partially acidified with CO2 to obtain an amine salt aqueous solution (pH = 8.4) as extractant II. The extractant II is transported to the first extraction device (extraction tower) and countercurrently contacts with coal tar with a phenol content of 25 wt% as the raw material to selectively extract low-grade phenolic compounds (such as phenol, o-cresol, etc.), and the extraction phase II (a mixed phase containing phenol and extractant) and coal tar I (residual oil phase after removing low-grade phenols) are separated;

[0026] (2) The extraction phase II enters the deep acidification device and reacts with the acidic gas CO2. The reaction temperature for deep acidification is 50°C, and the reaction pressure (absolute pressure) is 0.3 MPa to obtain acidified liquid II with a pH of about 7; The acidified liquid II is allowed to stand and separate in a phase separator to obtain low-grade crude phenol oil (organic phase, main product) and aqueous phase II (pressurized acidified amine salt solution);

[0027] S3. The aqueous phase II is heated and desorbed of CO2 by a regeneration device (desorption column) at a regeneration temperature of 130 °C and a regeneration pressure of 0.3 MPa to obtain a regenerated extractant (mainly an aqueous solution of organic amine) and recycled CO2 gas (returned to the deep acidification device for reuse); the regenerated extractant is mixed with a fresh extractant, an aqueous solution of 30 wt% monoethanolamine, as extractant I, and extractant I is pumped into a second extraction device (extraction column) to extract the high - grade phenolic compounds (such as ethyl methylphenol, β - naphthol) in coal tar I, and an extraction phase I (a mixed phase containing high - grade phenol - extractant) and dephenolized oil (end - product) are separated;

[0028] S4. The extraction phase I is preliminarily acidified in a preliminary acidification device (absorption column) with industrial tail gas containing CO2 or industrial - grade CO2 gas. The reaction temperature for preliminary acidification is 40 °C, the reaction pressure is atmospheric pressure, and an acidified liquid I with a pH of about 8 is formed; 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 normal - pressure equilibrium acidified amine salt solution); aqueous phase I is recycled to the first extraction device as extractant II to complete the process closed - loop.

[0029] Comparative Example 1

[0030] The rest is the same as in Example 1, except that: both extractant I and extractant II are amine salt solutions (pH = 8.4) obtained by partial acidification of 30 wt% aqueous monoethanolamine solution with CO2.

[0031] Comparative Example 2

[0032] The rest is the same as in Example 1, except that: both extractant I and extractant II are 30 wt% aqueous monoethanolamine solutions.

[0033] Comparative Example 3

[0034] Using the traditional industrial method (caustic washing method), with 15 wt% sodium hydroxide solution and 70 wt% sulfuric acid aqueous solution as extractant and acidifying agent respectively, phenolic compounds are extracted from coal tar with a phenol content of 25 wt%, and through extraction, stripping, acidification and phase separation in sequence, one ton of crude phenol oil product is obtained.

[0035] Comparative Example 4

[0036] Using the improved traditional industrial method, with CO2 and 70 wt% sulfuric acid aqueous solution as acidifying agents; the extraction phase obtained by extracting phenols with 15 wt% sodium hydroxide aqueous solution is acidified with CO2, the precipitated sodium bicarbonate solid is filtered, heated and decomposed and causticized, and part of the caustic soda solution is recovered, and the other conditions are the same as in Comparative Example 3.

[0037] The experimental results of the examples and comparative examples are shown in Table 1.

[0038] Table 1 Experimental results of examples and comparative examples

[0039]

[0040] Note: t / t crude phenol oil represents the mass of substances consumed or produced per ton of crude phenol oil produced, with the unit of ton / ton; GJ / t crude phenol oil represents the energy consumed per ton of crude phenol oil produced in gigajoules, with the unit of gigajoule / ton.

[0041] It can be seen from Table 1 that compared with Comparative Example 3 and Comparative Example 4, Example 1 of the present invention hardly consumes extractant and acidifying agent on the premise of ensuring a high extraction yield of crude phenol oil, and hardly produces wastewater and waste residue while achieving the preliminary separation of crude phenol. Compared with Comparative Example 1 and Comparative Example 2, Example 1 of the present invention not only realizes the preliminary 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 extraction phase II enters the deep acidification device and reacts with the acidic gas CO2 to obtain the acidified liquid II. 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; the acidified liquid II is placed in a phase separator for stratification to obtain low-grade crude phenol oil and 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 the preliminary acidification device with industrial tail gas containing CO2 or industrial-grade CO2 gas to form an acidified liquid I. The reaction temperature of the preliminary acidification is 20°C - 70°C, the reaction pressure is normal pressure, and the pH value of the acidified liquid I after the preliminary acidification is 8 - 9; the acidified liquid I is phase-separated in the phase separator to obtain high-grade crude phenol oil and aqueous phase I; the aqueous phase I is circulated to the first extraction device as the 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 unit and the deep acidification unit use an absorption tower or a Venturi reactor as the core reaction unit.

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 II 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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