A method for separating products of a phenol hydroxylation process for the production of dihydric phenols

Abstract

The application discloses a product separation method of phenylenediamine prepared by a phenol hydroxylation method, which comprises the following steps: (1) sending the phenol hydroxylation reaction liquid into a vacuum dehydration tower for dehydration; (2) sending the mixture in the tower kettle of the vacuum dehydration tower into a thin film scraped blade evaporator for coke removal; (3) sending the gas phase mixture collected from the top of the thin film scraped blade evaporator into a phenol removal tower, and separating phenol; (4) sending the mixture in the tower kettle of the phenol removal tower into an o-phenylenediamine rectification tower for product refining, and separating o-phenylenediamine; (5) washing, filtering and removing coke from the p-phenylenediamine crude product solution in the tower kettle of the o-phenylenediamine rectification tower; and (6) decolorizing and crystallizing the p-phenylenediamine solution after the coke removal, and obtaining p-phenylenediamine. By means of the above-mentioned synergistic effect, the phenol hydroxylation reaction liquid is efficiently and high-quality separated.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation technology and relates to a product separation method for producing hydroquinone by phenol hydroxylation. Background Technology

[0002] Hydroquinone, also known as hydroquinone, is a white crystalline powder that readily changes color upon contact with oxygen in the air. As an important chemical raw material and pharmaceutical intermediate, hydroquinone has a wide range of applications. It can be used in photography, as a medical contrast agent, in azo dyes, anthraquinone dyes, as a polymerization inhibitor, as an antioxidant, and as a rubber anti-aging agent. With the rise of artificial intelligence and the increasing popularity of PEEK materials, the market demand for hydroquinone, as a key raw material for PEEK, is further expanding.

[0003] Catechol, also known as catechol, is a white crystalline powder and is an isomer of hydroquinone. As a basic raw material for fine chemical products, catechol is widely used in industries such as pesticides, fragrances, dyes, pharmaceuticals, and polymers.

[0004] The main production processes for hydroquinone include the o-chlorophenol hydrolysis method, the diisopropylbenzene oxidation method, the aniline oxidation method, the benzoquinone reduction method, and the phenol hydroxylation method. Among these, the phenol hydroxylation method has become the mainstream production process for hydroquinone due to its simple process route, low raw material cost, few by-products, and minimal environmental pollution. During the phenol hydroxylation process, the post-reaction solution contains a large amount of solvent / water, unconverted phenol, by-products, and tar. Both catechol and hydroquinone are heat-sensitive substances, and their distillation processes operate at high temperatures, making them highly susceptible to coking and conversion into phenol tar during separation. Furthermore, the presence of p-benzoquinone and tar in the reactor mixture can also promote the coking of the hydroquinone product to some extent.

[0005] The generation of phenolic tar during the separation process not only increases the amount of solid waste but also seriously affects product yield, resulting in wasted production costs. Therefore, how to efficiently and effectively separate hydroquinone and catechol from the mixed solution in the hydroquinone production process using the phenol hydroxylation method is key to reducing the industrial production cost of hydroquinone and is also an important control step in the phenol hydroxylation process.

[0006] Bayer AG of Germany uses a classic separation method to sequentially dehydrate, remove phenols, separate catechol and hydroquinone from the mixed solution produced by the hydroxylation of phenol. The tar is finally removed from the bottom of the hydroquinone tower. The entire separation process involves high operating temperatures, which makes the product prone to coking. Furthermore, the tar has a long residence time, resulting in poor fluidity and easy carbonization or expansion, thus affecting normal operation.

[0007] The separation method used by Rhône-Poulenc in the production of hydroquinone via the hydroxylation of phenol in France involves first dehydrating and removing phenol at atmospheric pressure, then removing tar under reduced pressure, followed by a second phenol removal process. The phenol-removed mixture is then passed through a distillation column, yielding catechol from the top and hydroquinone from the bottom. Although this method removes tar in advance, the primary phenol removal process involves high operating temperatures due to the presence of tar, making the material prone to coking. Furthermore, the phenol requires multiple phase transition separations, resulting in high energy consumption for the unit.

[0008] Patent document CN101830780A discloses a method for separating and purifying phenol, catechol / hydroquinone, and an aqueous tar solution. This method employs a six-tower continuous vacuum distillation process, sequentially performing dehydration, phenol removal, secondary phenol removal, tar removal, catechol separation, and hydroquinone separation. The dehydration and primary phenol removal in this method are performed using vacuum distillation, which lowers the operating temperature of the separation process. Furthermore, by replacing tar removal with secondary phenol removal, multiple vaporization of phenol is avoided, saving energy consumption. However, the later placement of tar removal prolongs the overall residence time of the material under high-temperature conditions and increases the operating temperature of the tar removal process; therefore, the coking problem of the material remains unresolved.

[0009] Patent application CN119977763A discloses a method for separating and purifying a phenol hydroxylation reaction solution. The method involves first dehydrating the phenol hydroxylation solution, then removing tar, and subsequently subjecting the resulting material to phenol removal, catechol separation, and hydroquinone separation. This method performs tar removal immediately after dehydration, reducing the temperature of subsequent separation operations. However, the phenol content in the reaction solution is very high, and the multiple vaporization separations of phenol result in excessively high energy consumption and poor process economy. Summary of the Invention

[0010] To improve the above-mentioned technical problems, the present invention provides a separation method for the reaction solution of phenol hydroxylation to produce hydroquinone. The separation method of the present invention can reduce product coking, increase product yield, and reduce equipment energy consumption, thereby improving the economic efficiency of the equipment.

[0011] This invention provides a method for separating the reaction solution in the preparation of hydroquinone by phenol hydroxylation, comprising the following steps: (1) The phenol hydroxylation reaction solution is sent to a vacuum dehydration tower for dehydration; (2) The mixture in the bottom of the vacuum dehydration tower is fed into the thin film scraper evaporator for decoking; (3) The gas mixture collected from the top of the thin-film scraped evaporator is sent to the dephenolization tower to separate phenol; (4) The mixture in the bottom of the dephenolization tower is fed into the catechol distillation tower for product purification and separation of catechol; (5) Wash and filter the crude hydroquinone solution in the bottom of the catechol distillation column to remove tar; (6) The hydroquinone solution after tar removal is decolorized and crystallized to obtain hydroquinone.

[0012] According to an embodiment of the present invention, in step (1), the process parameters of the depressurization dehydration tower include: the tower top operating pressure is 30 kPa to 50 kPa; the total tower pressure drop is 3 to 5 kPa; the tower bottom temperature is 125 to 160°C; the tower top temperature is 65 to 85°C, preferably 65 to 75°C; and the reflux ratio is 0.5 to 4.

[0013] According to an embodiment of the present invention, in step (1), the chemical composition of the phenol hydroxylation reaction solution includes: water, phenol, catechol, hydroquinone, and tar; wherein, by mass fraction, the content of water is 10% to 40%, the content of phenol is 25% to 70%, the content of catechol is 5% to 25%, the content of hydroquinone is 7% to 25%, and the content of tar is 1% to 5%.

[0014] According to an embodiment of the present invention, in step (2), the process parameters of the thin-film scraped evaporator include: operating pressure of 1~10 kPa, preferably 2~6 kPa; hot oil temperature of 230~270℃, preferably 250~260℃; and material temperature of 220~240℃.

[0015] According to an embodiment of the present invention, in step (3), the process parameters of the dephenolization tower include: the tower top operating pressure is 10 kPa to 25 kPa; the total tower pressure drop is 2 to 4 kPa; the tower bottom temperature is 170 to 200°C; the tower top temperature is 115 to 130°C; and the reflux ratio is 0.5 to 4.

[0016] According to an embodiment of the present invention, in step (4), the process parameters of the catechol distillation column include: the top operating pressure is 5 kPa to 20 kPa, preferably 10 to 15 kPa; the overall pressure drop is 2 to 4 kPa; the bottom temperature is 210 to 230°C, preferably 215 to 225°C; the top temperature is 160 to 180°C; and the reflux ratio is 0.5 to 4.

[0017] According to an embodiment of the present invention, in step (5), the washing is carried out in a washing tank, and the washing solvent is water. Preferably, the washing temperature is 60~100℃, and the mass ratio of water added to crude hydroquinone solution is 1~6.

[0018] According to an embodiment of the present invention, in step (5), the filtration first involves coarse filtration through a centrifuge, followed by fine filtration through a membrane filter. The centrifuge removes most of the tar, preventing excessive tar from clogging the membrane filter; the remaining mother liquor containing a small amount of tar is then further filtered through the membrane filter for tar filtration. Preferably, the centrifuge operates at a speed of 600-1200 rpm, the filter cloth of the centrifuge has a mesh size of 500-1000 mesh, and the membrane filter has a pore size of 0.01-1 μm.

[0019] According to an embodiment of the present invention, in step (6), the decolorization is performed by a resin adsorption tower, the operating temperature of which is 60~100℃.

[0020] According to an embodiment of the present invention, in step (6), the crystallization is carried out by cooling in a crystallizer. Preferably, the crystallization temperature is 10~35°C.

[0021] According to an embodiment of the present invention, the separation method further includes centrifuging and drying the mixture from which crystals have precipitated to obtain hydroquinone product. The filtrate containing trace amounts of catechol and other impurities obtained by centrifugation is returned to the washing tank for reuse, and the solid hydroquinone is dried in a dryer and then packaged to obtain the hydroquinone product.

[0022] According to an embodiment of the present invention, the separation method of the phenol hydroxylation reaction solution specifically includes the following steps: (1) The hydroxylation reaction solution is sent to a vacuum dehydration tower for dehydration. The phenol-containing wastewater separated at the top of the tower is sent to the phenol water treatment process, and the mixture at the bottom of the tower is sent to a thin-film scraped evaporator. The phenol mass fraction in the wastewater collected at the top of the tower is 5~10 wt%. (2) The mixture from the vacuum dehydration tower enters the thin-film scraped evaporator for decoking. The mixed gas phase of phenol and hydroquinone collected from the top is directly fed into the phenol removal tower, and the concentrated tar after light removal is collected from the bottom. After cooling, it is treated as solid waste. The concentrated tar collected from the bottom contains 5-10 wt% hydroquinone. (3) The mixed gas phase material collected from the top of the thin-film scraped evaporator enters the dephenolization tower to separate phenol. The phenol collected from the top of the tower with a mass fraction ≥99wt% is returned to the reactor feed for recycling. The hydroquinone mixture collected from the bottom of the tower enters the catechol distillation tower. The mass fraction of phenol in the hydroquinone mixture collected from the bottom of the tower is <0.2wt%. (4) The mixture from the bottom of the dephenolization tower is fed into the catechol distillation tower for product purification, and catechol is separated; the catechol solution with a mass fraction of ≥99wt% is collected from the top of the tower and sent to the slicer for cooling and slicing before packaging; the crude hydroquinone product collected from the bottom of the tower is sent to the washing tank for washing; the mass fraction of hydroquinone in the catechol collected from the top of the tower is <0.1wt%; (5) The crude hydroquinone solution is washed in a washing tank with water at a controlled temperature of 60-100℃. The ratio of water to crude solution mass is preferably 1-6. After washing, the solution is first coarsely filtered by a centrifuge to remove tar. The tar is discharged from the bottom and treated as solid waste. The filtered mother liquor is then further filtered by a membrane filter to remove the remaining tar. The centrifuge speed is preferably 600-1200 rpm, the filter cloth mesh size is preferably 500-1000 mesh, and the membrane pore size of the membrane filter is preferably 0.01-1 μm. (6) The hydroquinone solution after tar removal by the membrane filter enters the resin adsorption tower for decolorization, and the operating temperature is 60~100℃; (7) The decolorized hydroquinone solution is placed in a crystallizer for cooling and crystallization, with an operating temperature of 10~35℃; (8) The mixture of precipitated crystals is centrifuged in a centrifuge. The filtrate containing trace amounts of catechol and other impurities is returned to the washing tank for reuse. When the catechol concentration in the filtrate is saturated, it is returned to the dehydration tower. The solid hydroquinone containing trace amounts of moisture is dried in a dryer and then packaged to obtain the hydroquinone product.

[0023] The present invention also provides a separation system for a phenol hydroxylation reaction solution, comprising a vacuum dehydration tower, a thin-film scraped evaporator, a phenol removal tower, a catechol distillation tower, a washing tank, a first centrifuge, a membrane filter, a resin adsorption tower, a crystallizer, and a dryer connected in series.

[0024] According to an embodiment of the present invention, the outlet of the depressurization dehydration tower is connected to the inlet of the thin-film scraped evaporator.

[0025] According to an embodiment of the present invention, the top gas phase outlet of the thin-film scraped evaporator is connected to the inlet of the dephenolization tower.

[0026] According to an embodiment of the present invention, the bottom outlet of the dephenolization tower is connected to the inlet of the catechol distillation tower, and the top outlet of the dephenolization tower is connected to the phenol hydroxylation reactor.

[0027] According to an embodiment of the present invention, the bottom outlet of the catechol distillation column is connected to the inlet of the washing tank.

[0028] According to an embodiment of the present invention, the outlet of the washing tank is connected to the inlet of the first centrifuge.

[0029] According to an embodiment of the present invention, the outlet of the first centrifuge is connected to the inlet of the membrane filter.

[0030] According to an embodiment of the present invention, the outlet of the membrane filter is connected to the inlet of the crystallizer.

[0031] According to an embodiment of the present invention, the separation system further includes a second centrifuge, wherein the outlet of the crystallizer is connected to the inlet of the second centrifuge.

[0032] According to an embodiment of the present invention, the separation system further includes a dryer, wherein the outlet of the second centrifuge is connected to the inlet of the dryer.

[0033] The beneficial effects of this invention are: The phenol hydroxylation reaction liquid separation method of this invention first dehydrates the product using a vacuum dehydration tower and then directly removes tar using a thin-film scraped evaporator. This reduces the operating temperature of the subsequent distillation process, thereby reducing product coking, increasing product yield, and avoiding operational problems caused by prolonged carbonization and expansion of tar in the system. Simultaneously, the thin-film scraped evaporator is used for tar removal, allowing the separated light components to directly enter the subsequent distillation process in gaseous form, avoiding repeated vaporization of phenol and thus reducing energy consumption. Furthermore, the crude hydroquinone from the catechol distillation column is recrystallized in conjunction with membrane filtration and resin adsorption to obtain high-purity hydroquinone. Compared with traditional distillation purification methods, this invention's method does not involve phase changes, thus reducing energy consumption. It also operates at a low temperature, produces no new tar, and achieves a high product yield. This invention achieves efficient and high-quality separation of the phenol hydroxylation reaction liquid by first dehydrating the phenol hydroxylation reaction liquid, then directly removing tar using a thin-film scraped evaporator, and finally refining it by recrystallization. Through the synergistic effect of these methods, it achieves efficient and high-quality separation of the phenol hydroxylation reaction liquid. Attached Figure Description

[0034] Figure 1 This is a flow chart illustrating the separation process of the phenol hydroxylation reaction solution of the present invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0036] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0037] In the following embodiments and comparative examples of the present invention, the mass fraction of the substances was determined by liquid chromatography.

[0038] Example 1 Table 1 Composition of the phenol hydroxylation reaction solution

[0039] The phenol hydroxylation reaction solution with the composition shown in Table 1 was fed into a vacuum dehydration tower using CY700 packing material. The flow rate was 500 kg / h, the operating pressure at the top of the tower was maintained at 30 kPa, the condensate reflux ratio was 1.5, the overall pressure drop was 4 kPa, the top temperature was 67℃, and the bottom temperature was 125℃. The phenol mass fraction in the wastewater collected from the top of the tower was 7.8 wt%.

[0040] The mixture from the bottom of the dehydration tower is fed into a thin-film scraped evaporator at a flow rate of 300 kg / h, an operating pressure of 6 kPa, a heat transfer oil temperature of 260℃, and a material temperature of 235℃. The top-collected gas mixture contains 60 wt% phenol, 14.7 wt% catechol, and 25.3 wt% hydroquinone, while the bottom-collected concentrated tar contains 12.3 wt% hydroquinone.

[0041] The mixed gas phase material collected from the top of the thin-film scraped evaporator is fed into the phenol removal tower to separate phenol. CY700 packing is used, the tower top operating pressure is 20 kPa, the condensate reflux ratio is 4, the overall tower pressure drop is 3 kPa, the tower top temperature is 127℃, the tower bottom temperature is 198℃, the phenol mass fraction collected from the tower top is 99.5 wt%, and the phenol mass fraction in the tower bottom is 0.1 wt%.

[0042] The mixture from the bottom of the dephenolization column is fed into a catechol distillation column for product purification. The column uses CY700 packing, with a flow rate of 95 kg / h, a top operating pressure of 15 kPa, a condensate reflux ratio of 4, a total pressure drop of 3 kPa, a top temperature of 167℃, and a bottom temperature of 223℃. The catechol content at the top of the column is 99.5 wt%.

[0043] The crude hydroquinone solution from the bottom of the catechol distillation column is washed with water in a washing tank at 85°C, with a water-to-crude-solution mass ratio of 3. After washing, the solution is first coarsely filtered by centrifugation to remove tar, and the filtered mother liquor is then finely filtered through a membrane filter to remove tar. The centrifuge speed is 800 rpm, the filter cloth mesh is 500 mesh, and the membrane filter pore size is 0.1 μm.

[0044] The hydroquinone solution, after tar removal by a membrane filter, is fed into a resin adsorption tower for decolorization at an operating temperature of 85℃.

[0045] The decolorized hydroquinone solution was cooled and crystallized in a crystallizer at an operating temperature of 25°C. The resulting mixture of precipitated crystals was centrifuged and then dried to obtain hydroquinone with a mass fraction of 99.2 wt%.

[0046] The yield of catechol was 99.7% (where: product yield = product flow rate × mass fraction ÷ (reactor discharge flow rate × mass fraction of the product in the reactor discharge)), and the yield of hydroquinone was 96.4%.

[0047] Example 2 Table 2 Composition of the phenol hydroxylation reaction solution

[0048] The phenol hydroxylation reaction solution with the composition shown in Table 2 was fed into a vacuum dehydration tower using CY700 packing material. The flow rate was 200 kg / h, the operating pressure at the top of the tower was maintained at 50 kPa, the condensate reflux ratio was 1.5, the overall pressure drop was 4 kPa, the top temperature was 83℃, and the bottom temperature was 145℃. The phenol mass fraction in the wastewater collected from the top of the tower was 8.3 wt%.

[0049] The mixture from the bottom of the dehydration tower is fed into a thin-film scraped evaporator at a flow rate of 120 kg / h, an operating pressure of 2 kPa, a heat transfer oil temperature of 255℃, and a material temperature of 228℃. The top-collected gas mixture contains 70 wt% phenol, 10.5 wt% catechol, and 19.5 wt% hydroquinone, while the bottom-collected concentrated tar contains 9.4 wt% hydroquinone.

[0050] The mixed gas phase material collected from the top of the thin-film scraped evaporator is fed into the phenol removal tower for phenol separation. CY700 packing is used. The tower top operating pressure is 15 kPa, the condensate reflux ratio is 3, the overall tower pressure drop is 3 kPa, the tower top temperature is 115℃, and the tower bottom temperature is 175℃. The phenol mass fraction collected from the tower top is 99.7 wt%, and the phenol mass fraction in the tower bottom is 0.05 wt%.

[0051] The mixture from the bottom of the dephenolization column is fed into the catechol distillation column for product purification. The column uses CY700 packing, with a flow rate of 31 kg / h, a top operating pressure of 12 kPa, a condensate reflux ratio of 4, a total pressure drop of 3 kPa, a top temperature of 161℃, and a bottom temperature of 218℃. The catechol content at the top of the column is 99.7 wt%.

[0052] The crude hydroquinone solution from the bottom of the catechol distillation column is washed with water in a washing tank at 65°C, with a water-to-crude-solution mass ratio of 4. After washing, the solution is first coarsely filtered by centrifugation to remove tar, and the filtered mother liquor is then finely filtered through a membrane filter to remove tar. The centrifuge operates at 1000 rpm, the filter cloth has a mesh size of 800 mesh, and the membrane filter has a pore size of 0.05 μm.

[0053] The hydroquinone solution, after tar removal by a membrane filter, is fed into a resin adsorption tower for decolorization at an operating temperature of 70°C.

[0054] The decolorized hydroquinone solution was cooled and crystallized in a crystallizer at an operating temperature of 32°C. The resulting mixture of crystals was centrifuged and then dried to obtain hydroquinone with a mass fraction of 99.3 wt%.

[0055] The yield of catechol was 99.5%, and the yield of hydroquinone was 98.1%.

[0056] Comparative Example 1 Based on Example 1, with the initial feed flow rate and composition unchanged, and the operating conditions of each separation process unchanged, the phenol hydroxylation reaction solution with the composition shown in Table 1 was fed into a vacuum dehydration tower for initial dehydration, followed by primary phenol removal, secondary phenol removal, tar removal, catechol distillation, and hydroquinone distillation. Specific conditions were as follows: the vacuum dehydration tower used CY700 packing, with a tower top operating pressure of 30 kPa, a condensate reflux ratio of 1.5, a total tower pressure drop of 4 kPa, a tower top temperature of 67°C, and a tower bottom temperature of 125°C. The material collected from the tower bottom was fed into the phenol removal tower for phenol removal. The primary phenol removal tower had a tower top operating pressure of 20 kPa, a condensate reflux ratio of 1.5, a total tower pressure drop of 2 kPa, a tower top temperature of 126°C, and a tower bottom temperature of 175°C; the secondary phenol removal tower had a tower top operating pressure of 20 kPa, a condensate reflux ratio of 4, a total tower pressure drop of 3 kPa, a tower top temperature of 124°C, and a tower bottom temperature of 198°C. After phenol removal, the bottom product from the distillation column enters a thin-film scraped evaporator, operating at a pressure of 6 kPa, with a heat transfer oil temperature of 260°C and a product temperature of 235°C. The mixed gaseous product collected from the top of the evaporator enters a catechol distillation column, operating at a top pressure of 15 kPa, a condensate reflux ratio of 4, a total pressure drop of 3 kPa, a top temperature of 167°C, and a bottom temperature of 223°C. The hydroquinone distillation column uses CY700 packing, operating at a top pressure of 5 kPa, a condensate reflux ratio of 2, a total pressure drop of 2 kPa, a top temperature of 195°C, and a bottom temperature of 235°C. The final catechol yield is 98.6%, and the hydroquinone yield is 94.3%.

[0057] Comparative Example 2 The phenol hydroxylation reaction solution with the composition shown in Table 1 above was fed into a vacuum dehydration tower using CY700 packing material. The flow rate was 500 kg / h, the operating pressure at the top of the tower was maintained at 30 kPa, the condensate reflux ratio was 1.5, the overall pressure drop was 4 kPa, the top temperature was 67℃, and the bottom temperature was 125℃. The phenol mass fraction in the wastewater collected from the top of the tower was 7.8 wt%.

[0058] The mixture from the bottom of the dehydration tower is fed into a thin-film scraped evaporator at a flow rate of 300 kg / h, an operating pressure of 6 kPa, a heat transfer oil temperature of 260℃, and a material temperature of 235℃. The top-collected gas mixture contains 60 wt% phenol, 14.7 wt% catechol, and 25.3 wt% hydroquinone, while the bottom-collected concentrated tar contains 12.3 wt% hydroquinone.

[0059] The mixed gas phase material collected from the top of the thin-film scraped evaporator is fed into the phenol removal tower to separate phenol. CY700 packing is used, the tower top operating pressure is 20 kPa, the condensate reflux ratio is 4, the overall tower pressure drop is 3 kPa, the tower top temperature is 127℃, the tower bottom temperature is 198℃, the phenol mass fraction collected from the tower top is 99.5 wt%, and the phenol mass fraction in the tower bottom is 0.1 wt%.

[0060] The mixture from the bottom of the dephenolization column is fed into a catechol distillation column for product purification. The column uses CY700 packing, with a flow rate of 95 kg / h, a top operating pressure of 15 kPa, a condensate reflux ratio of 4, a total pressure drop of 3 kPa, a top temperature of 167℃, and a bottom temperature of 223℃. The catechol content at the top of the column is 99.5 wt%.

[0061] The crude hydroquinone solution from the bottom of the catechol distillation column is fed into the hydroquinone distillation column for purification. The hydroquinone distillation column uses CY700 packing, with a top operating pressure of 7 kPa, a condensate reflux ratio of 1.5, a total pressure drop of 2.2 kPa, a top temperature of 199℃, and a bottom temperature of 240℃.

[0062] Ultimately, the yield of catechol was 99.5%, and the yield of hydroquinone was 95.2%. Furthermore, the reboiler load in the hydroquinone distillation column was 43 kW, which is higher than the energy consumption of the recrystallization process in Example 1.

[0063] Comparative Example 3 The phenol hydroxylation reaction solution with the composition shown in Table 1 above was fed into a vacuum dehydration tower using CY700 packing material. The flow rate was 500 kg / h, the operating pressure at the top of the tower was maintained at 30 kPa, the condensate reflux ratio was 1.5, the overall pressure drop was 4 kPa, the top temperature was 67℃, and the bottom temperature was 125℃. The phenol mass fraction in the wastewater collected from the top of the tower was 7.8 wt%.

[0064] The mixture in the bottom of the dehydration tower was detarted using a detarting tower with CY700 packing. The operating pressure at the top of the tower was 6 kPa, the condensate reflux ratio was 1.2, the overall pressure drop was 3 kPa, the top temperature was 135℃, and the bottom temperature was 231℃. The concentrated tar collected from the bottom contained 12.6 wt% hydroquinone.

[0065] The material collected from the top of the tar removal tower is condensed and then fed into the phenol removal tower for phenol removal. CY700 packing is used. The operating pressure at the top of the tower is 20 kPa, the condensate reflux ratio is 4, the overall pressure drop is 3 kPa, the top temperature is 127℃, the bottom temperature is 198℃, and the phenol mass fraction collected from the top of the tower is 99.6 wt%.

[0066] Ultimately, the heat load of the reboiler in the dephenolization tower was 148 kW, which is about 29% higher than the tower reboiler load of 115 kW when the thin film scraped evaporator was fed with gas phase.

[0067] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for separating the reaction solution from the phenol hydroxylation process for preparing hydroquinone, characterized in that, Includes the following steps: (1) The phenol hydroxylation reaction solution is sent to a vacuum dehydration tower for dehydration; (2) The mixture in the bottom of the vacuum dehydration tower is fed into the thin film scraper evaporator for decoking; (3) The gas mixture collected from the top of the thin-film scraped evaporator is sent to the dephenolization tower to separate phenol; (4) The mixture in the bottom of the dephenolization tower is fed into the catechol distillation tower for product purification and separation of catechol; (5) Wash and filter the crude hydroquinone solution in the bottom of the catechol distillation column to remove tar; (6) The hydroquinone solution after tar removal is decolorized and crystallized to obtain hydroquinone.

2. The separation method as described in claim 1, characterized in that, In step (1), the process parameters of the vacuum dehydration tower include: the tower top operating pressure is 30 kPa to 50 kPa; the total tower pressure drop is 3 to 5 kPa; the tower bottom temperature is 125 to 160°C; the tower top temperature is 65 to 85°C; and the reflux ratio is 0.5 to 4.

3. The separation method as described in claim 1 or 2, characterized in that, In step (2), the process parameters of the thin-film scraped evaporator include: operating pressure of 1~10 kPa; hot oil temperature of 230~270℃; and material temperature of 220~240℃.

4. The separation method according to any one of claims 1-3, characterized in that, In step (3), the process parameters of the dephenolization tower include: the operating pressure at the top of the tower is 10 kPa to 25 kPa; the pressure drop across the entire tower is 2 to 4 kPa; the temperature at the bottom of the tower is 170 to 200°C; the temperature at the top of the tower is 115 to 130°C; and the reflux ratio is 0.5 to 4.

5. The separation method according to any one of claims 1-4, characterized in that, In step (4), the process parameters of the catechol distillation column include: the top operating pressure is 5 kPa to 20 kPa; the total pressure drop is 2 to 4 kPa; the bottom temperature is 210 to 230°C; the top temperature is 160 to 180°C; and the reflux ratio is 0.5 to 4.

6. The separation method according to any one of claims 1-5, characterized in that, In step (5), the washing temperature is 60~100℃, and the mass ratio of water added to crude hydroquinone solution is 1~6.

7. The separation method according to any one of claims 1-6, characterized in that, In step (5), the filtration process first involves coarse filtration through a centrifuge, followed by fine filtration through a membrane filter. And / or, the centrifuge has a rotational speed of 600~1200 rpm, the centrifuge filter cloth has a mesh size of 500~1000 mesh, and the membrane filter has a membrane pore size of 0.01~1μm.

8. The separation method according to any one of claims 1-7, characterized in that, In step (6), the decolorization is performed by a resin adsorption tower, and the operating temperature of the resin adsorption tower is 60~100℃. And / or, the crystallization temperature is 10~35℃.

9. A separation system for the phenol hydroxylation reaction solution according to any one of claims 1-8, characterized in that, It includes a vacuum dehydration tower, a thin-film scraped evaporator, a phenol removal tower, a catechol distillation tower, a washing tank, a first centrifuge, a membrane filter, a resin adsorption tower, and a crystallizer connected in series.

10. The separation system as described in claim 9, characterized in that, The outlet of the pressure-reducing dehydration tower is connected to the inlet of the thin-film scraped evaporator; And / or, the top gas phase outlet of the thin-film scraped evaporator is connected to the inlet of the dephenolization tower; And / or, the bottom outlet of the dephenolization tower is connected to the inlet of the catechol distillation tower, and the top outlet of the dephenolization tower is connected to the phenol hydroxylation reactor. And / or, the bottom outlet of the catechol distillation column is connected to the inlet of the washing tank; And / or, the outlet of the washing tank is connected to the inlet of the first centrifuge; And / or, the outlet of the first centrifuge is connected to the inlet of the membrane filter; And / or, the outlet of the membrane filter is connected to the inlet of the crystallizer; And / or, the separation system further includes a second centrifuge, wherein the outlet of the crystallizer is connected to the inlet of the second centrifuge; And / or, the separation system further includes a dryer, wherein the outlet of the second centrifuge is connected to the inlet of the dryer.

Images