Extraction and solvent recovery process for phenolic wastewater in coal chemical industry

Abstract

The invention discloses a coal chemical phenolic wastewater extraction and solvent recovery process which comprises the following steps: extracting and separating phenolic wastewater through an extraction tower, separating light oil, heavy aromatics and crude phenol from an extract through an extract separation tower, refluxing one part of the light oil to the extract separation tower, and washing the other part of the light oil through a water washing tower to obtain a light oil product; one part of the crude phenol flows back to the extract separation tower, and the other part is directly used as a crude phenol product; extracting the raffinate wastewater through a water tower and separating the raffinate wastewater through an oil-water separator, recovering an extracting solvent, and conveying the treated wastewater to a biochemical device for further treatment or direct reuse. According to the process, the content of phenols and homologues in the crude phenol can be increased, the content of neutral oil can be reduced, and the crude phenol product meets the standard requirement; meanwhile, by utilizing the process, impurities such as light oil in the extraction solvent can be removed in time, so that the quality of the recovered extraction solvent is improved, the extraction treatment effect of wastewater can be improved, and the treatment load of a biochemical device is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and specifically relates to a coal chemical industry phenol-containing wastewater extraction and solvent recovery process. Through the process, phenolic substances in the wastewater are recovered and purified into qualified crude phenol that meets standard requirements while further improving the effluent quality and solving the wastewater pollution problem. Background Art

[0002] my country is rich in coal resources, of which more than 50% is low-rank coal. The processing and utilization of low-rank coal is of great significance to ensuring my country's energy security and promoting economic development. When low-rank coal is processed by gasification and dry distillation (pyrolysis), a large amount of high-concentration phenol-containing wastewater will be produced, with a phenol content of up to 5000-25000 mg / L. On the one hand, phenols have strong biological toxicity and huge environmental risks. On the other hand, phenols are important chemical products and raw materials with high economic value. Therefore, it is a common practice in the current coal chemical industry to use phenol recovery equipment and liquid-liquid extraction technology to extract phenols from wastewater as crude phenol by-products, while reducing the biological toxicity of wastewater and improving its biodegradability. The crude phenol obtained by extraction is required to meet the requirements of standard YB / T 5079-2012, that is, the content of phenol and homologues in crude phenol is not less than 83%, and the content of neutral oil is not higher than 0.8%. The extraction solvents currently used mainly include methyl isobutyl ketone, diisopropyl ether, methyl pentenone, etc.

[0003] Since the composition of coal chemical wastewater is very complex, in addition to various types of phenols, aliphatic hydrocarbons, triphenyls, naphthalenes and other organic substances are extracted at the same time and enter the extract during the extraction process. In the current phenol recovery device, binary distillation is used to separate the extract to recover the solvent, that is, the extract is distilled into solvent and crude phenol. With such a configuration, for the conversion process with a high temperature in the dry distillation section, or when coal with a high degree of coalification is used as the raw material, the COD of the treated wastewater can generally be reduced to below 3000 mg / L, and the quality of crude phenol can also meet the requirements of standard YB / T 5079-2012. However, when lignite with a low degree of coalification is used as the raw material and medium-low temperature dry distillation is used to produce blue charcoal, the above-mentioned solvent recovery process often results in high oil content and COD in the effluent, and the content of homologues in crude phenol is far below 83%, and the neutral oil content in crude phenol is often far beyond the standard value. By analyzing the composition of the extracts, we found that the extracts in the production process of blue coke are more complex in composition than gasification wastewater, especially the components with distillation ranges between 130 and 160 °C and above 210 °C are much higher than those in gasification wastewater. When binary distillation is used for solvent recovery, the content of neutral oil represented by naphthalene in crude phenol is often as high as 1.5% or more, and the content of oil components in the solvent can also reach 1% to 2%, resulting in reduced extraction effect. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent. This process can increase the content of phenol and homologues in crude phenol, and can also increase the purity of recovered extraction solvent, thereby improving the wastewater treatment effect.

[0005] The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent provided by the present invention comprises the following steps:

[0006] Step 1: Extraction

[0007] The phenol-containing wastewater is divided into two parts, most of which enters the extraction tower and contacts with the extraction solvent from the solvent circulation tank to complete the extraction process, and another small part of the phenol-containing wastewater enters the water washing tower; the extract obtained after extraction overflows into the extraction tank, and then is pumped to the extract separation tower for separation of the extract; the residual wastewater after extraction is pumped from the bottom of the extraction tower to the water tower, and the extraction solvent dissolved and entrained in the wastewater is recovered by steam stripping.

[0008] Step 2: Extraction separation

[0009] The extract obtained in step 1 enters the feed port of the extract separation tower, and the extraction solvent is extracted from the top of the extract separation tower; the light oil extracted from the first side line outlet of the extract separation tower enters the light oil tank after cooling, a part of which is refluxed to the extract separation tower, and the other part is sent to the water washing tower for water washing; the crude phenol extracted from the second side line outlet of the extract separation tower enters the crude phenol tank 8 after cooling, a part of which is refluxed to the extract separation tower, and the other part is sent to the crude phenol product tank; the heavy aromatics in the bottom of the tower are cooled and sent to the heavy aromatics product tank.

[0010] Step 3: Solvent Stripping

[0011] The raffinate wastewater obtained in step 1 enters from the top of the water tower. After the produced material at the top of the water tower is condensed, it enters the oil-water separator for oil-water separation. The upper extraction solvent overflows into the solvent circulation tank for recycling, and the lower water phase returns to the water tower for re-stripping; the treated wastewater discharged from the bottom of the water tower is sent to the biochemical for further treatment or directly reused.

[0012] Step 4: Light Oil Wash

[0013] The light oil entering the water washing tower in step 2 is countercurrently contacted with the small part of phenol-containing wastewater entering the water washing tower in step 1 to complete water washing. The light oil after water washing is sent to the light oil product tank, and the extraction solvent entrained in the light oil is eluted into the phenol-containing wastewater. The phenol-containing wastewater is pumped from the bottom of the water washing tower to the extraction tower for extraction treatment.

[0014] Furthermore, in the above step 1, the phenol-containing wastewater is preferably divided into two parts at a split ratio of 1:10 to 24.

[0015] Furthermore, in the above step 1, the extraction solvent is preferably one of methyl isobutyl ketone and methyl pentenone or a mixture of the two.

[0016] Furthermore, in the above step 1, the extraction temperature of the extraction tower is preferably 30 to 80°C.

[0017] Furthermore, in the above step 2, it is preferred that the operating pressure of the extract separation tower is -0.09 to 0.03 MPa, the number of theoretical plates is 20 to 30, and the feed inlet is located at the 8th to 17th theoretical plates.

[0018] Furthermore, in the above step 2, it is preferred that the first side line production outlet is located at the 3rd to 6th theoretical plates downward from the feed inlet, and the temperature of the first side line production outlet is 65 to 185°C. After the light oil is produced, it is cooled to 30 to 60°C and then enters the light oil tank, a part of it is refluxed to the extract separation tower with a reflux ratio of 0.2 to 1.0, and the other part is sent to the water washing tower for water washing.

[0019] Furthermore, in the above step 2, it is preferred that the second side line outlet is located at the 6th to 14th theoretical plates downward from the feed inlet, and the temperature of the second side line outlet is 120 to 215°C. After the crude phenol is taken out, it is cooled to 60 to 80°C and then enters the crude phenol tank, a part of it refluxes to the extract separation tower with a reflux ratio of 0.2 to 0.3, and the other part is sent to the crude phenol product tank.

[0020] Furthermore, in the above step 2, it is preferred that the tower top temperature is 46-115° C., and the extraction solvent is produced from the tower top; the tower bottom temperature is 160-245° C., and the heavy aromatics in the tower bottom are cooled and sent to the heavy aromatics product tank.

[0021] Furthermore, in the above step 4, it is preferred that the theoretical number of stages of the water washing tower is 1 to 4.

[0022] The beneficial effects of the present invention are as follows:

[0023] The present invention extracts and separates phenol-containing wastewater through an extraction tower, and then separates the extract into light oil, heavy aromatics and crude phenol through an extraction separation tower. A portion of the light oil is refluxed to the extraction separation tower, and the other portion is washed by a water washing tower and sent to a light oil product tank; a portion of the crude phenol is refluxed to the extraction separation tower, and the other portion is sent to a crude phenol product tank; the residual wastewater is extracted by a water tower and separated by an oil-water separator, and the extraction solvent is recovered, and the treated wastewater is sent to a biochemical for further treatment or direct reuse. The present invention can increase the content of phenol and homologues in crude phenol after washing by a water washing tower, and can reduce the content of neutral oil, so that the crude phenol product meets the requirements of the standard; at the same time, the quality of the recovered extraction solvent can be improved after washing by a water washing tower, and impurities such as light oil in the extraction solvent can be removed in time, thereby improving the extraction treatment effect of the wastewater and reducing the treatment load of the biochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is an extract tank, 2 is an extraction tower, 3 is a water tower, 4 is an oil-water separator, 5 is an extract separation tower, 6 is a light oil tank, 7 is a water washing tower, 8 is a crude phenol tank, and 9 is a solvent circulation tank. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0026] Example 1

[0027] A coal pyrolysis plant produces 120 tons / hour of phenol-containing wastewater, with a phenol content of 15,000 mg / L. Figure 1 The process flow is to extract and recover the solvent, and the specific steps are as follows:

[0028] Step 1: Extraction

[0029] The phenol-containing wastewater is divided into two parts with a split ratio of 1:10, wherein most of the phenol-containing wastewater enters the extraction tower 2, and another small part of the phenol-containing wastewater enters the water washing tower 7. The phenol-containing wastewater entering the extraction tower 2 contacts with the extraction solvent methyl isobutyl ketone from the solvent circulation tank 9 to complete the extraction process, and the extraction temperature is 30-40°C; the extract obtained after the extraction overflows into the extraction tank 1, and then is pumped to the extraction separation tower 5 for separation of the extract; the residual wastewater after the extraction is pumped from the bottom of the extraction tower 2 to the water tower 3, and the extraction solvent dissolved and entrained in the wastewater is stripped and recovered.

[0030] Step 2: Extraction separation

[0031] The extract obtained in step 1 enters the extract separation tower 5 from the middle and upper part for distillation separation. The operating pressure of the extract separation tower 5 is -0.09MPa, the number of theoretical plates is 20, and the feed port is located at the 8th theoretical plate. The extraction solvent is produced from the top of the extract separation tower 5, and the top temperature is 46-48°C. The first side line production port of the extract separation tower 5 is located at the 3rd theoretical plate downward from the feed port, and the temperature at the first side line production port is 65°C. After the light oil is produced, it is cooled to 30°C and then enters the light oil tank 6. A part of the light oil in the light oil tank 6 is refluxed to the extract separation tower 5, and the reflux ratio is 0.3, and the other part is sent to the water washing tower 7 for water washing. The second side line production port of the extract separation tower 5 is located at the 7th theoretical plate downward from the feed port, and the temperature at the second side line production port is 120-124°C. After the crude phenol is produced, it is cooled to 60-80°C and then enters the crude phenol tank 8. The crude phenol in the crude phenol tank 8 is partially refluxed to the extract separation tower 5 at a reflux ratio of 0.2, and the other part is sent to the crude phenol product tank. The bottom temperature of the extract separation tower 5 is 160-162°C, and the heavy aromatics in the bottom are cooled and sent to the heavy aromatics product tank.

[0032] Step 3: Solvent Stripping

[0033] The raffinate wastewater obtained in step 1 enters from the top of the water tower 3. After the produced material at the top of the water tower 3 is condensed, it enters the oil-water separator 4 for oil-water separation, and the upper layer of the extraction solvent overflows into the solvent circulation tank 9 for recycling; the lower layer of water phase returns to the water tower 3 for re-stripping; the treated wastewater discharged from the bottom of the water tower 3 is sent to the biochemical for further treatment or directly reused.

[0034] Step 4: Light Oil Wash

[0035] The light oil entering the water washing tower 7 in step 2 is countercurrently contacted with a small portion of the phenol-containing wastewater entering the water washing tower 7 in step 1 to complete the water washing. The water washing tower 7 is configured as a liquid-liquid extraction tower, and the theoretical number of stages is 1. The light oil after water washing is sent to the light oil product tank; the extraction solvent entrained in the light oil is eluted into the phenol-containing wastewater, and the phenol-containing wastewater is pumped from the bottom of the water washing tower 7 to the extraction tower 2 for extraction and dephenolization treatment.

[0036] In this embodiment, compared with the prior art, the content of phenol and homologues in the crude phenol in the crude phenol product tank is increased from about 55% to 85%, and the neutral oil content is reduced from more than 2.0% to less than 0.5%; the oil content in the recovered solvent is reduced from about 1.5% to less than 0.05%, the oil content of the treated wastewater discharged from the bottom of the water tower 3 is reduced from 180mg / L to less than 60mg / L, and the COD is reduced from more than 3800mg / L to less than 2800mg / L. The obtained light oil and heavy aromatics also meet the corresponding product quality standards.

[0037] Example 2

[0038] A coal pyrolysis plant produces 80 tons / hour of phenol-containing wastewater with a phenol content of 20,000 mg / L. Figure 1 The process flow is to extract and recover the solvent, and the specific steps are as follows:

[0039] Step 1: Extraction

[0040] The phenol-containing wastewater is divided into two parts with a split ratio of 1:20, wherein most of the phenol-containing wastewater enters the extraction tower 2, and another small part of the phenol-containing wastewater enters the water washing tower 7. The phenol-containing wastewater entering the extraction tower 2 contacts with the extraction solvent methyl isobutyl ketone from the solvent circulation tank 9 to complete the extraction process, and the extraction temperature is 30-40°C; the extract obtained after the extraction overflows into the extraction tank 1, and then is pumped to the extraction separation tower 5 for separation of the extract; the residual wastewater after the extraction is pumped from the bottom of the extraction tower 2 to the water tower 3, and the extraction solvent dissolved and entrained in the wastewater is stripped and recovered.

[0041] Step 2: Extraction separation

[0042] The extract obtained in step 1 enters the extract separation tower 5 from the middle and upper part for distillation separation. The operating pressure of the extract separation tower 5 is 0.02MPa, the number of theoretical plates is 30, and the feed port is located at the 13th theoretical plate. The extraction solvent is produced from the top of the extract separation tower 5, and the top temperature is 110-112°C. The first side line production port of the extract separation tower 5 is located at the 4th theoretical plate downward from the feed port, and the temperature at the first side line production port is 135°C. After the light oil is produced, it is cooled to 40°C and then enters the light oil tank 6. A part of the light oil in the light oil tank 6 is refluxed to the extract separation tower 5, and the reflux ratio is 0.8, and the other part is sent to the water washing tower 7 for water washing. The second side line production port of the extract separation tower 5 is located at the 9th theoretical plate downward from the feed port, and the temperature at the second side line production port is 210-215°C. After the crude phenol is produced, it is cooled to 60-80°C and then enters the crude phenol tank 8. The crude phenol in the crude phenol tank 8 is partially refluxed to the extract separation tower 5 at a reflux ratio of 0.3, and the other part is sent to the crude phenol product tank. The bottom temperature of the extract separation tower 5 is 238-245°C, and the heavy aromatics in the bottom are cooled and sent to the heavy aromatics product tank.

[0043] Step 3: Solvent Stripping

[0044] The raffinate wastewater obtained in step 1 enters from the top of the water tower 3. After the produced material at the top of the water tower 3 is condensed, it enters the oil-water separator 4 for oil-water separation, and the upper layer of the extraction solvent overflows into the solvent circulation tank 9 for recycling; the lower layer of water phase returns to the water tower 3 for re-stripping; the treated wastewater discharged from the bottom of the water tower 3 is sent to the biochemical for further treatment or directly reused.

[0045] Step 4: Light Oil Wash

[0046] The light oil entering the water washing tower 7 in step 2 is countercurrently contacted with a small portion of the phenol-containing wastewater entering the water washing tower 7 in step 1 to complete the water washing. The water washing tower 7 is configured as a liquid-liquid extraction tower with a theoretical number of stages of 4. The light oil after water washing is sent to the light oil product tank; the extraction solvent entrained in the light oil is eluted into the phenol-containing wastewater, and the phenol-containing wastewater is pumped from the bottom of the water washing tower 7 to the extraction tower 2 for extraction and dephenolization treatment.

[0047] In this embodiment, compared with the prior art, the content of phenol and homologues in the crude phenol in the crude phenol product tank is increased from about 45% to 85%, and the neutral oil content is reduced from more than 3.0% to less than 0.6%; the oil content in the recovered solvent is reduced from about 2% to less than 0.03%, the oil content of the treated wastewater discharged from the bottom of the water tower 3 is reduced from 260mg / L to less than 80mg / L, and the COD is reduced from more than 4500mg / L to less than 2800mg / L. The obtained light oil and heavy aromatics also meet the corresponding product quality standards.

Claims

1. A process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent, characterized in that: The steps include: Step 1: Extraction The phenol-containing wastewater is divided into two parts, wherein most of the phenol-containing wastewater enters the extraction tower, contacts with the extraction solvent from the solvent circulation tank, and completes the extraction process, and another small part of the phenol-containing wastewater enters the water washing tower; the extract obtained after the extraction overflows into the extraction tank, and then is pumped to the extraction separation tower for separation of the extract; the raffinate wastewater after the extraction is pumped from the bottom of the extraction tower to the water tower, and the extraction solvent dissolved and entrained in the wastewater is stripped and recovered; Step 2: Extraction separation The extract obtained in step 1 enters the feed port of the extract separation tower, and the extraction solvent is extracted from the top of the extract separation tower; the light oil extracted from the first side line extraction port of the extract separation tower enters the light oil tank after cooling, a part of which is refluxed to the extract separation tower, and the other part is sent to the water washing tower for water washing; The crude phenol extracted from the second side line outlet of the extract separation tower enters the crude phenol tank 8 after cooling, a part of which is refluxed to the extract separation tower, and the other part is sent to the crude phenol product tank; the heavy aromatics in the tower bottom are cooled and sent to the heavy aromatics product tank; Step 3: Solvent Stripping The raffinate wastewater obtained in step 1 enters from the top of the water tower. After the produced material at the top of the water tower is condensed, it enters the oil-water separator for oil-water separation. The upper layer of the extraction solvent overflows into the solvent circulation tank for recycling, and the lower layer of the water phase returns to the water tower for re-stripping. The treated wastewater discharged from the bottom of the water tower is sent to the biochemical for further treatment or directly reused; Step 4: Light Oil Wash The light oil entering the water washing tower in step 2 is countercurrently contacted with the small part of phenol-containing wastewater entering the water washing tower in step 1 to complete water washing. The light oil after water washing is sent to the light oil product tank, and the extraction solvent entrained in the light oil is eluted into the phenol-containing wastewater. The phenol-containing wastewater is pumped from the bottom of the water washing tower to the extraction tower for extraction treatment.

2. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 1, the phenol-containing wastewater is divided into two parts at a split ratio of 1:10 to 24.

3. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 1, the extraction solvent is methyl isobutyl ketone, methyl pentenone or a mixture of the two.

4. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 1, the extraction temperature of the extraction tower is 30-80°C.

5. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 2, the operating pressure of the extract separation tower is -0.09 to 0.03 MPa, the number of theoretical plates is 20 to 30, and the feed inlet is located at the 8th to 17th theoretical plates.

6. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 2, the first side line production outlet is located at the 3rd to 6th theoretical plates downward from the feed inlet, and the temperature of the first side line production outlet is 65 to 185°C. After the light oil is produced, it is cooled to 30 to 60°C and then enters the light oil tank. A part of it is refluxed to the extract separation tower with a reflux ratio of 0.2 to 1.0, and the other part is sent to the water washing tower for water washing.

7. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 2, the second side line outlet is located at the 6th to 14th theoretical plates downward from the feed inlet, and the temperature of the second side line outlet is 120 to 215°C. After the crude phenol is taken out, it is cooled to 60 to 80°C and then enters the crude phenol tank. A part of it refluxes to the extract separation tower with a reflux ratio of 0.2 to 0.3, and the other part is sent to the crude phenol product tank.

8. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 2, the tower top temperature is 46-115° C., and the extraction solvent is produced from the tower top; the tower bottom temperature is 160-245° C., and the heavy aromatics in the tower bottom are cooled and sent to the heavy aromatics product tank.

9. The process for extracting phenol-containing wastewater from coal chemical industry and recovering solvent according to claim 1, characterized in that: In step 4, the theoretical number of stages of the water washing tower is 1 to 4.

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