A method for extracting thiophene from coal tar and application thereof

Abstract

The application discloses a method for extracting thiophene from coal tar and application, and relates to the field of coal chemical industry. When the thiophene is extracted from the coal tar, a eutectic solvent composed of tetraethylammonium chloride and propionic acid is used as a selective extractant, light distillate of the coal tar is extracted through a multistage countercurrent extraction tower, and the extraction phase is subjected to reduced pressure distillation to recover the selective extractant and obtain a crude thiophene product; and then the crude thiophene product is subjected to rectification to obtain the thiophene. The process is green and environmentally friendly, the solvent can be recycled, no three wastes are discharged, and the thiophene with high purity and high yield is obtained. The method for extracting the thiophene from the coal tar is simple to operate, easy to be industrialized, and realizes high-value utilization of the thiophene in the coal tar.

Description

Technical Field

[0001] This invention relates to the field of coal chemical industry, specifically to a method and application for extracting thiophene from coal tar. Background Technology

[0002] Coal tar is a liquid product generated during the dry distillation of coal under high temperature and oxygen-deficient conditions. This black or dark brown viscous liquid has a pungent odor and is an important raw material for the production of value-added chemicals and carbon materials. It contains abundant thiophene and its derivatives. Thiophene is an important chemical intermediate that can be used to synthesize benzothiophene, thiophene dyes, pharmaceuticals, etc.

[0003] However, coal tar has a very complex composition. Besides sulfur-containing heterocyclic compounds, currently identified neutral components include benzene, toluene, xylene, naphthalene, acenaphthene, anthracene, and fluorene; acidic components include phenol, cresol, and xylenol; and basic components include pyridine, indole, quinoline, and isoquinoline. Thiophene and benzene have similar boiling points and form an azeotrope, making direct separation difficult using traditional distillation methods.

[0004] Existing technologies mainly employ concentrated sulfuric acid sulfonation or N-methylpyrrolidone extractive distillation. The former generates large amounts of waste acid, which corrodes equipment; while the latter produces products with high purity, NMP is highly toxic, energy-intensive, and difficult to recover the solvent. Therefore, this invention provides a green and efficient method for extracting thiophene from coal tar. Summary of the Invention

[0005] The purpose of this invention is to provide a method and application for extracting thiophene from coal tar, so as to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for extracting thiophene from coal tar, wherein the thiophene is obtained by distillation of crude thiophene.

[0008] As an optimization, the crude thiophene is obtained by vacuum distillation of the extract phase after extraction of light fractions with a eutectic solvent.

[0009] As an optimization, the light fraction is obtained by pre-distillation of coal tar.

[0010] As an optimization, the eutectic solvent is obtained by mixing tetraethylammonium chloride and propionic acid.

[0011] A method for extracting thiophene includes the following preparation steps:

[0012] (1) Take the number of trays to mix tetraethylammonium chloride and propionic acid, stir at 75~85℃ and 600~800rpm for 25~35min to obtain a eutectic solvent;

[0013] (2) Pre-distill the coal tar under normal pressure and collect the light fraction rich in thiophene;

[0014] (3) The light fraction and the eutectic solvent are mixed at a volume ratio of 1:(1~2), and the mixture is subjected to multi-stage countercurrent extraction at 20~60℃ for 5~30 min under ultrasonic assistance to obtain the extract phase and the raffinate phase.

[0015] (4) The extract phase is subjected to vacuum distillation to recover the extractant and obtain crude thiophene.

[0016] (5) The crude thiophene is distilled and the fraction is collected to obtain thiophene.

[0017] As an optimization, the mixing of tetraethylammonium chloride and propionic acid in step (1) is performed at a molar ratio of 1:(1.9~2.1).

[0018] As an optimization, the coal tar in step (2) is high-temperature coal tar or medium-temperature coal tar, and its thiophene content is 0.5%~5%.

[0019] As an optimization, the collection temperature of the pre-distilled light fraction in step (2) is 80~120℃.

[0020] As an optimization, the ultrasound-assisted conditions in step (3) are 100~500 W and 20~40 kHz.

[0021] As an optimization, the multi-stage countercurrent extraction 3~5 plate extraction tower described in step (3) is used.

[0022] As an optimization, the conditions for vacuum distillation in step (4) are 1~10 kPa and 50~90℃.

[0023] As an optimization, the collection temperature of the fraction in step (5) is 84~85℃.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0025] In this invention, when extracting thiophene from coal tar, a eutectic solvent composed of tetraethylammonium chloride and propionic acid is used as a selective extractant. The light fraction of coal tar is extracted by a multi-stage countercurrent extraction tower. The extract phase is then subjected to vacuum distillation to recover the selective extractant and obtain crude thiophene. The crude thiophene is then purified by distillation to obtain thiophene.

[0026] First, a eutectic solvent composed of tetraethylammonium chloride and propionic acid is used as a selective extractant. The intermolecular hydrogen bonds formed between the hydrogen bond acceptor tetraethylammonium chloride and the hydrogen bond donor propionic acid can preferentially capture thiophene aromatic sulfides through stronger intermolecular forces, thereby enhancing the extraction selectivity and improving the purity and yield of thiophene.

[0027] Secondly, the light fraction of coal tar is extracted using a multi-stage countercurrent extraction tower. The extract phase is then subjected to vacuum distillation to recover the selective extractant and obtain crude thiophene. The crude thiophene is then further distilled to obtain thiophene. The use of a multi-stage countercurrent extraction tower enables continuous operation, which reduces solvent consumption compared to traditional single-stage extraction. Ultrasonic assistance is introduced to enhance liquid-liquid mass transfer using the cavitation effect, thus shortening the extraction equilibrium time. A non-volatile, non-corrosive eutectic solvent is used as the extractant, which is recovered and reused after vacuum distillation, reducing waste liquid discharge and avoiding secondary pollution. Attached Figure Description

[0028] Figure 1 The infrared spectrum of thiophene described in this invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] The raw materials used in the following examples and comparative examples are all commercially available:

[0031] The coal tar was sourced from Hebei Deri New Materials Technology Co., Ltd.

[0032] Example 1:

[0033] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0034] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0035] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0036] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 3 plates at 40℃, 300 W and 30 kHz with ultrasonic assistance to obtain the extract phase and the raffinate phase.

[0037] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0038] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0039] Example 2:

[0040] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0041] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0042] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0043] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 300 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0044] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0045] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0046] Example 3:

[0047] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0048] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0049] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0050] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 5 plates at 40℃, 300 W and 30 kHz with ultrasonic assistance to obtain the extract phase and the raffinate phase.

[0051] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0052] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0053] Comparative Example 1:

[0054] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0055] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:1 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0056] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0057] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 300 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0058] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0059] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0060] Comparative Example 2:

[0061] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0062] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:1.5 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0063] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0064] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 300 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0065] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0066] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0067] Comparative Example 3:

[0068] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0069] (1) Mix tetraethylammonium chloride and propionic acid at a molar ratio of 1:2.5 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0070] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0071] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 300 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0072] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0073] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0074] Comparative Example 4:

[0075] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0076] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:3 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0077] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0078] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 300 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0079] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0080] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0081] Comparative Example 5:

[0082] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0083] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0084] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0085] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 200W and 30 kHz to obtain the extract phase and the raffinate phase.

[0086] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0087] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0088] Comparative Example 6:

[0089] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0090] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0091] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0092] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates at 40℃, 250 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0093] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0094] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0095] Comparative Example 7:

[0096] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0097] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0098] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0099] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates at 40℃, 350 W and 30 kHz with ultrasonic assistance to obtain the extract phase and the raffinate phase.

[0100] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0101] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0102] Comparative Example 8:

[0103] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0104] (1) Mix tetraethylammonium chloride and propionic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0105] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0106] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates at 40℃, 400 W and 30 kHz with ultrasonic assistance to obtain the extract phase and the raffinate phase.

[0107] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0108] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0109] Comparative Example 9:

[0110] A method for extracting thiophene from coal tar, the method comprising the following preparation steps:

[0111] (1) Mix choline chloride and oxalic acid in a molar ratio of 1:2 and stir at 80°C and 700 rpm for 30 min to obtain a eutectic solvent;

[0112] (2) The coal tar was pre-distilled at atmospheric pressure, and the light fraction rich in thiophene was collected at 100℃;

[0113] (3) The light fraction and the eutectic solvent were mixed at a volume ratio of 1:1.5 and extracted countercurrently for 20 min in a plate extraction column with 4 plates under ultrasonic assistance at 40℃, 300 W and 30 kHz to obtain the extract phase and the raffinate phase.

[0114] (4) The extract phase was subjected to vacuum distillation at 5 kPa and 70℃ to recover the extractant and obtain crude thiophene.

[0115] (5) The crude thiophene is distilled and the fraction at 85°C is collected to obtain thiophene.

[0116] Test Example 1:

[0117] Yield test method: The thiophene obtained from each example and comparative example was measured by gas chromatography using a Celian 456C at a column temperature of 80℃ and a carrier gas flow rate of 50mL / min. The extraction yield was calculated as (actual mass of thiophene obtained / theoretical total mass of thiophene in the raw material) × 100%.

[0118] Purity test method: The thiophene obtained from each example and comparative example was determined by gas chromatography using a Celian 456C at a column temperature of 80℃ and a carrier gas flow rate of 50mL / min. The thiophene purity was calculated as 100% - total impurity content (GC analysis directly gives the peak area percentage).

[0119] Table 1. Thiophene extraction yield and purity

[0120] Extraction yield % purity% Extraction yield % purity% Example 1 88.62 99.12 Comparative Example 4 86.17 90.74 Example 2 93.24 99.23 Comparative Example 5 81.49 96.38 Example 3 93.39 99.27 Comparative Example 6 88.03 97.51 Comparative Example 1 84.83 91.02 Comparative Example 7 87.28 99.04 Comparative Example 2 90.76 93.68 Comparative Example 8 80.31 99.17 Comparative Example 3 90.55 94.25 Comparative Example 9 71.53 82.59

[0121] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-9 in Table 1 reveals that the thiophene prepared by this invention has good yield and purity.

[0122] The extraction stages in Examples 1-3 are different. By comparison, the extraction yield of Example 2 is higher than that of Examples 1 and 3, indicating that the use of a multi-stage countercurrent extraction tower to achieve continuous operation results in a higher yield than traditional single-stage extraction. The optimal extraction stage is 4 stages.

[0123] Comparative Examples 1-4 had different eutectic solvent ratios, and Comparative Example 9 used choline chloride and oxalic acid to prepare the eutectic solvent. By comparison, Example 2 had a higher extraction yield and purity than Comparative Examples 1-4, indicating that the intermolecular hydrogen bonds formed between the hydrogen bond acceptor tetraethylammonium chloride and the hydrogen bond donor propionic acid can preferentially capture thiophene aromatic sulfides through stronger intermolecular forces, thereby enhancing extraction selectivity and improving the purity and yield of thiophene. The optimal ratio of the eutectic solvent is tetraethylammonium chloride and propionic acid prepared at a molar ratio of 1:2.

[0124] Comparing the ultrasonic powers of Comparative Examples 5-8, Example 2 showed a higher extraction yield than Comparative Examples 5-8. This indicates that introducing ultrasonic assistance and utilizing the cavitation effect to enhance liquid-liquid mass transfer shortens the extraction equilibrium time. Under the same time conditions, the optimal ultrasonic power was selected as 300 W and 30 kHz.

[0125] Test Example 2:

[0126] Extractant recovery efficiency test method: After 10 cycles of testing, the recovery extractant obtained in each Example 2 was measured. The extraction yield of the 10th cycle was 81.54%, which shows that using a non-volatile and non-corrosive eutectic solvent as an extractant, the high extraction yield can still be achieved after vacuum distillation and reuse, reducing waste liquid discharge and avoiding secondary pollution.

[0127] Test Example 3:

[0128] The thiophene obtained in Example 2 was characterized using a Tensor 37 infrared spectrometer from Bruker Spectroscopy Instruments, Germany.

[0129] Depend on Figure 1 It can be seen that there is a distinct aromatic CH stretching vibration peak near 3100 cm⁻¹, a C=C skeleton vibration peak of the thiophene ring appears in the 1400-1600 cm⁻¹ region, and an out-of-plane bending vibration peak of CH in the 700-800 cm⁻¹ region, indicating that the present invention has successfully extracted thiophene.

[0130] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for extracting thiophene from coal tar, characterized in that, The thiophene was obtained by distillation of crude thiophene. The crude thiophene was obtained by vacuum distillation of the extract phase after extraction of light fractions with a eutectic solvent. The light fraction is obtained by pre-distillation of coal tar; The eutectic solvent is obtained by mixing tetraethylammonium chloride and propionic acid.

2. The method for extracting thiophene from coal tar according to claim 1, characterized in that, The preparation steps include the following: (1) Take the number of trays to mix tetraethylammonium chloride and propionic acid, stir at 75~85℃ and 600~800rpm for 25~35min to obtain a eutectic solvent; (2) Pre-distill the coal tar under normal pressure and collect the light fraction rich in thiophene; (3) The light fraction and the eutectic solvent are mixed at a volume ratio of 1:(1~2), and the mixture is subjected to multi-stage countercurrent extraction at 20~60℃ for 5~30 min under ultrasonic assistance to obtain the extract phase and the raffinate phase. (4) The extract phase is subjected to vacuum distillation to recover the extractant and obtain crude thiophene. (5) The crude thiophene is distilled and the fraction is collected to obtain thiophene.

3. The method for extracting thiophene from coal tar according to claim 2, characterized in that, The mixing of tetraethylammonium chloride and propionic acid in step (1) is performed at a molar ratio of 1:(1.9~2.1).

4. The method for extracting thiophene from coal tar according to claim 2, characterized in that, The collection temperature of the pre-distilled light fraction in step (2) is 80~120℃.

5. The method for extracting thiophene from coal tar according to claim 2, characterized in that, The ultrasound-assisted conditions in step (3) are 100~500 W and 20~40 kHz.

6. The method for extracting thiophene from coal tar according to claim 2, characterized in that, Step (3) describes the multi-stage countercurrent extraction 3-5 plate extraction tower.

7. The method for extracting thiophene from coal tar according to claim 2, characterized in that, The conditions for vacuum distillation in step (4) are 1~10 kPa and 50~90℃.

8. The method for extracting thiophene from coal tar according to claim 2, characterized in that, The collection temperature of the fraction in step (5) is 84~85℃.

9. Application of the method for extracting thiophene from coal tar according to any one of claims 1 to 8.

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