Method for preparing benzenediol through phenol hydroxylation by using microreactor

Abstract

The invention discloses a method for preparing benzenediol through phenol hydroxylation by using a microreactor, which comprises the following steps: taking phenol and hydrogen peroxide as raw materials, taking a titanium silicalite molecular sieve as a catalyst, and carrying out phenol hydroxylation reaction in the microreactor; wherein phenol enters the microchannel of the microreactor through radial flow perpendicular to the microchannel in the microreactor, is in contact with hydrogen peroxide axially flowing in the microchannel of the microreactor, and rapidly reacts under the action of a catalyst packaged in the microreactor, and obtained reaction liquid flows out of a tube pass outlet of the microreactor. The method has the advantages of high mass transfer efficiency, short overall reaction time and almost no side reaction. The method for preparing benzenediol through phenol hydroxylation by using the microreactor provided by the invention also comprises the step of separating and purifying phenol and benzenediol in the reaction liquid by using a hollow fiber updated liquid membrane technology, so that low-energy-consumption separation and purification of hydroquinone and catechol can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing dihydric phenol by hydroxylation of phenol using a microreactor. BACKGROUND

[0002] Dihydric phenol (mainly including hydroquinone and catechol) is an important organic synthesis intermediate, mainly used in rubber, dyes, antioxidants, pharmaceuticals, pesticides and other fields, and has a wide range of uses. The traditional production process mainly includes aniline oxidation method, p-diisopropylbenzene oxidation method, bisphenol A method, etc. However, due to the problems of excessive waste, high production cost, low safety, etc. in the production process, the application of the above production methods is limited. The phenol hydroxylation method using phenol and hydrogen peroxide as raw materials has gradually become the preferred process for producing dihydric phenol due to the characteristics of easy availability of raw materials, mild reaction conditions, less by-products, less waste, low production cost, etc.

[0003] The Enichem method is the currently widely used industrial production method. However, if a traditional tank reactor is used, due to the serious back mixing, the excessive hydrogen peroxide existing in the local area is easy to contact with the product dihydric phenol, forming tar and other by-products, thereby reducing the selectivity of dihydric phenol, and the product post-treatment is difficult, further increasing the energy consumption of separation. The intermittent flow addition method can alleviate the over-oxidation of dihydric phenol to generate by-products. For example, CN1410406A uses a hydrogen peroxide flow addition method, achieving a dihydric phenol selectivity of 90.4%-93.7%. However, the hydrogen peroxide flow addition time is long (3h-5h), the equipment utilization rate is low, and the local concentration of hydrogen peroxide cannot be completely avoided, and there are problems of side reactions (i.e. the selectivity cannot reach 100%).

[0004] CN202078886U discloses a circulating reactor for phenol hydroxylation to produce dihydric phenol, which is provided with a plurality of double-layer reaction tubes in the main reactor. The outer layer is a reaction material channel (for feeding phenol, catalyst, etc.) with an inner diameter of 30mm-50mm, and the inner layer is a straight pipe with holes with an inner diameter of 10mm-30mm and a hole diameter of 2mm-8mm, which is used for circulating hydrogen peroxide. The phenol hydroxylation reaction is carried out in the outer layer, and the total reaction time is 30min-60min. Although this reactor can realize continuous reaction, there is still back mixing of the material, and the reaction selectivity is 91.5%-92.8%, i.e. a large amount of by-product is still formed. CN114988986B discloses a rotating multi-stage radial reactor for preparing ortho-benzene diol and para-benzene diol, which makes the reaction proceed in a state closer to plug flow, and to a certain extent, improves the selectivity of the reaction. However, this method uses acetone as the solvent, and the concentrations of the reaction materials phenol and hydrogen peroxide are reduced, which can further reduce the over-oxidation of dihydric phenol, but the lower concentration of the reaction materials will also reduce the reaction rate, so that the dihydric phenol selectivity of 92.27%-93.57% is achieved at a residence time of 94min, and there are still by-products and the problem of low equipment utilization rate.

[0005] Microreactors, as one of the core devices in microchemical systems, generally refer to microreactors with characteristic dimensions ranging from micrometers to hundreds of micrometers, sometimes also called microchannel reactors. Compared with traditional batch reactors, they have excellent mass transfer performance and ideal plug flow characteristics with no backmixing, enabling precise control of material ratios. At the same time, by reducing mass transfer time, they greatly shorten the residence time of reactants and reduce the formation of by-products. However, the current configurations of microreactors are not suitable for systems with high solids content. CN117105747A discloses a method for preparing hydroquinone using phenol as a reactant, through oxidation to obtain p-benzoquinone, followed by hydrogenation reduction to obtain hydroquinone. Both steps employ a microreactor system, where the microchannel reactor is either a tubular reactor with an inner diameter of 3mm-8mm or a fixed-bed plate reactor with an inner diameter of 20mm-30mm. Compared to traditional batch reactors, this significantly shortens the reaction time (2-8 minutes using a microchannel reactor). However, the step in this method to generate benzoquinone is precisely the step after phenol forms hydroquinone, aiming to avoid over-oxidation. It does not address the issue of reducing the formation of phenol hydroxylation byproducts in microreactors. The two-step reaction of oxidation to quinone followed by reduction, compared to the one-step formation of hydroquinone from phenol, increases production costs and process complexity. Moreover, general literature suggests that the characteristic size of microchannel reactors should be from micrometers to hundreds of micrometers. Whether the characteristic size of this patent can achieve the performance unique to microreactors lacks practical and theoretical support.

[0006] Hydroquinone and catechol, the products of phenol hydroxylation, are isomers with similar physicochemical properties, making their separation difficult. Currently, distillation is commonly used to separate hydroquinone and catechol products from the phenol hydroxylation reaction solution, but this method is energy-intensive.

[0007] In the methods described above, the fed-batch method can reduce the concentration of excess hydrogen peroxide in the system, mitigating the excessive oxidation of hydroquinone upon contact with hydrogen peroxide and the generation of byproducts. However, the long feeding cycle leads to low equipment utilization and cannot prevent hydroquinone over-oxidation caused by excessively high local hydrogen peroxide concentrations. While the solvent addition method can reduce reactant concentrations and alleviate the problem of byproduct formation due to over-oxidation, it reduces reaction efficiency and cannot completely eliminate side reactions. Currently, the distillation methods commonly used to separate hydroquinone and catechol products have high energy consumption, resulting in high separation costs. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a method for preparing and separating hydroquinone and catechol using a microreactor and a solvent-free method, further combined with hollow fiber renewable liquid membrane technology. The method provided by this invention achieves near 100% reaction selectivity for preparing hydroquinone and catechol, and avoids the high energy consumption problem associated with distillation for product separation, thereby reducing separation costs.

[0009] This invention discloses a method for preparing hydroquinone by hydroxylation of phenol using microfluidic technology and hollow fiber renewing liquid membrane technology. The method includes: conducting a phenol hydroxylation reaction in a microreactor with a flow channel characteristic size of less than 2000 μm and a hydraulic diameter of less than 500 μm after being filled with a catalyst to obtain a reaction solution containing phenol, hydroquinone, and catechol; and treating the reaction solution using hollow fiber renewing liquid membrane technology to separate and purify hydroquinone. The microreactor used in this invention is composed of hollow fiber ultrafiltration membrane fibers with a characteristic size of less than 2000 μm, wherein the catalyst is encapsulated in the reactor. Phenol enters the microchannels of the microreactor through radial flow perpendicular to the microchannels, contacts hydrogen peroxide flowing axially in the microchannels, and reacts under the action of the catalyst. The reaction solution flows out from the reactor outlet. The hollow fiber renewing liquid membrane process used in this invention is carried out in a hollow fiber membrane device, wherein the outflowing reaction solution is separated by a multi-stage hollow fiber renewing liquid membrane to separate phenol, catechol, and hydroquinone. The method of the present invention can not only achieve a reaction selectivity of nearly 100%, effectively avoiding the problems of long hydrogen peroxide flow cycle and long subsequent solvent separation process in the traditional batch phenol hydroxylation reaction, but also avoid the high energy consumption caused by distillation separation of hydroquinone products, thereby reducing separation costs.

[0010] As one aspect of the present invention, a method for preparing hydroquinone by hydroxylation of phenol using a microreactor is provided, comprising the following steps:

[0011] Phenol and hydrogen peroxide were used as raw materials, and titanium-silicon molecular sieves were used as catalysts to carry out the hydroxylation reaction of phenol in a microreactor. Phenol entered the microchannel of the microreactor through radial flow perpendicular to the microchannel, came into contact with hydrogen peroxide flowing axially in the microchannel, and reacted under the action of the catalyst encapsulated in the microreactor. The resulting reaction solution flowed out from the outlet of the microreactor.

[0012] In a specific implementation, the method for preparing hydroquinone by hydroxylation of phenol using a microreactor further includes a separation and purification step:

[0013] The reaction solution flowing out of the microreactor outlet is used to separate and purify phenol, catechol, and hydroquinone using hollow fiber renewable liquid membrane technology: the reaction solution is passed into the shell side of the hollow fiber membrane, the back-extraction phase and the liquid membrane phase mixture is passed into the tube side of the hollow fiber membrane, the treated low-phenol content aqueous solution flows out from the shell side outlet of the hollow fiber membrane, and the enriched solution flows out from the tube side outlet of the hollow fiber membrane.

[0014] In a specific implementation, in the above separation and purification steps, the reaction solution is passed through several hollow fiber membrane devices connected in series to separate sodium phenolate solution, sodium catechol solution and sodium hydroquinone solution. Acid is added to the sodium phenolate solution to cause phenol to separate into phases. The resulting phenol-enriched solution is recycled to the reaction section for reuse, and the hydroquinone-enriched solution enters the subsequent purification process.

[0015] In a specific implementation, the molar ratio of phenol to hydrogen peroxide is (1-5):1.

[0016] In a specific implementation, the reaction temperature inside the microreactor is 60℃~90℃.

[0017] In a specific implementation, the residence time of the hydrogen peroxide and the phenol in the microreactor is 50s to 12min.

[0018] In a specific implementation, the hydraulic equivalent diameter of the microreactor is 100–500 μm.

[0019] In a specific implementation, both the hollow fiber membrane device and the microreactor are made of hollow fiber membrane fibers, and the catalyst is encapsulated in the hollow fiber membrane fibers.

[0020] In a specific implementation, the liquid film phase is a mixture of a carrier and a diluent, wherein the flow carrier is one or more of trioctyl phosphate, tributyl phosphate, and methyl isobutyl ketone, and the diluent is kerosene, sulfonated kerosene, benzene, toluene, n-heptane, or other alkanes.

[0021] In a specific implementation, the back-extraction phase is an alkaline aqueous solution with a pH value of 10-14, and the alkali is sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, or other inorganic alkali.

[0022] As another aspect of the present invention, it relates to the application of the above-described method for preparing hydroquinone by hydroxylation of phenol using a microreactor in the hydroquinone production process.

[0023] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0024] (1) The method for preparing hydroquinone by hydroxylation of phenol using a microreactor provided by the present invention can greatly reduce the diffusion distance of reactant molecules due to the channel characteristic size of the microreactor being only micrometers to hundreds of micrometers. Radial mixing can be completed in a very short time, improving mass transfer efficiency, realizing rapid mixing of reactants, rapid reaction, and precise control of material ratio, thereby shortening the reaction time.

[0025] (2) The axial fluid flow in the microreactor used in the method of the present invention can avoid back mixing, thereby avoiding the formation of by-products such as tar by oxidation and improving the selectivity of hydroquinone.

[0026] (3) The solvent-free method used in the present invention can achieve a higher reactant concentration, thereby improving the reaction efficiency and reducing the reactor volume.

[0027] (4) The hollow fiber renewal liquid membrane technology used in this invention can achieve low-energy separation and purification of hydroquinone and catechol in the phenol hydroxylation reaction solution. Attached Figure Description

[0028] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 This is a schematic diagram of the process for the continuous synthesis of hydroquinone and catechol using a microreactor according to the present invention. Detailed Implementation

[0030] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0031] The present invention provides a method for preparing hydroquinone by hydroxylation of phenol using a microreactor:

[0032] Phenol and hydrogen peroxide were used as raw materials, and titanium-silicon molecular sieves were used as catalysts to carry out the hydroxylation reaction of phenol in a microreactor. Phenol entered the microchannel of the microreactor through radial flow perpendicular to the microchannel, came into contact with hydrogen peroxide flowing axially in the microchannel, and reacted rapidly under the action of the catalyst encapsulated in the microreactor. After consuming the hydrogen peroxide, the resulting reaction solution flowed out from the tube outlet of the microreactor.

[0033] Separation and purification steps: This invention utilizes hollow fiber regenerated liquid membrane technology to separate and purify phenol and hydroquinone from the reaction solution flowing out of the tube side outlet of the microreactor. The reaction solution is passed through the shell side of a hollow fiber membrane, while a mixture of the back-extraction phase and the liquid membrane phase is passed through the tube side. Hydroquinone aqueous solution flows out from the shell side outlet of the hollow fiber membrane, and phenol base solution flows out from the tube side outlet. In this separation and purification step, the reaction solution is passed through multiple hollow fiber membranes connected in series to separate phenol base solution, catechol base solution, and hydroquinone base solution. The phenol base solution is adjusted at pH to allow phenol to separate into phases. The resulting phenol-enriched solution is recycled back to the reaction section for reuse.

[0034] Both the hollow fiber membrane device and the microreactor use hollow fiber membrane filaments of 0.2–2 mm. The catalyst is encapsulated within the hollow fiber membrane filaments.

[0035] A schematic diagram of the microreactor continuous synthesis apparatus for hydroquinone and catechol according to an embodiment of the present invention is shown below. Figure 1 As shown.

[0036] In the embodiments of the present invention, the catalyst is a titanium-silicon molecular sieve, and the titanium-silicon molecular sieve used in the embodiments is the TS-1 type titanium-silicon molecular sieve.

[0037] Unless otherwise specified, the percentages referred to in this application are mass percentages.

[0038] Example 1:

[0039] Hydroxylation of phenol to prepare hydroquinone:

[0040] Microreactor parameters: hydraulic equivalent diameter of 100μm, encapsulated with 4.73g of titanium-silicon molecular sieve.

[0041] The reaction raw materials are: a phenol aqueous solution with a mass fraction of 5 wt.% and a hydrogen peroxide aqueous solution with a mass fraction of 5 wt.% for H2O2.

[0042] Phenol aqueous solution and hydrogen peroxide aqueous solution were introduced into the microreactor at rates of 19.6 mL / min and 7.0 mL / min, respectively, corresponding to a phenol:H2O2 molar ratio of 1:1; the reaction temperature of the microreactor was 60℃, and the residence time of the phenol and hydrogen peroxide in the microreactor was 50 s; the resulting reaction solution was collected at the tube outlet of the microreactor.

[0043] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, hydroquinone and catechol was 1:4:6, and the reaction selectivity of this embodiment was 99.5%.

[0044] Example 2:

[0045] The only difference between Example 2 and Example 1 is that:

[0046] The reaction temperature of the microreactor in Example 2 was 75°C, and the residence time of the phenol and hydrogen peroxide in the microreactor was 1.5 min.

[0047] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, hydroquinone and catechol was 1:5:7, and the reaction selectivity of this embodiment was 99.3%.

[0048] Example 3:

[0049] The only difference between Example 3 and Example 1 is that:

[0050] The reaction temperature of the microreactor in Example 3 was 90°C.

[0051] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, hydroquinone and catechol was 1:10:14, and the reaction selectivity of this embodiment was 99.1%.

[0052] Example 4:

[0053] Hydroxylation of phenol to prepare hydroquinone:

[0054] Microreactor parameters: hydraulic equivalent diameter of 100μm, encapsulated with 4.73g of titanium-silicon molecular sieve.

[0055] The reaction raw materials consist of an aqueous solution of phenol with a mass fraction of 5 wt.% and an aqueous solution of hydrogen peroxide with a mass fraction of 2.4 wt.% H2O2.

[0056] Phenol aqueous solution and hydrogen peroxide were introduced into the microreactor at rates of 20.1 mL / min and 3.0 mL / min, respectively, corresponding to a phenol:H2O2 molar ratio of 5:1. The reaction temperature of the microreactor was 60 °C, and the residence time of phenol and hydrogen peroxide in the microreactor was 50 s. The resulting reaction solution was collected at the tube outlet of the microreactor.

[0057] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, catechol and hydroquinone was 13:1:1.5, and the reaction selectivity of this embodiment was 99.8%.

[0058] Example 5:

[0059] The only difference between Example 5 and Example 4 is that:

[0060] In Example 5, the residence time of the phenol and hydrogen peroxide in the microreactor was 12 minutes.

[0061] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, catechol and hydroquinone was 10:1:1.3, and the reaction selectivity of this embodiment was 99.2%.

[0062] Example 6:

[0063] The only difference between Example 6 and Example 4 is that:

[0064] The parameters of the microreactor in Example 6 are as follows: the hydraulic equivalent diameter of the microreactor is 500 μm, and it contains 1.89 g of titanium-silicon molecular sieve.

[0065] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, catechol and hydroquinone was 20:1:1.6, and the reaction selectivity of this embodiment was 99.1%.

[0066] Example 7:

[0067] The only difference between Example 7 and Example 4 is that:

[0068] The parameters of the microreactor in Example 7 are as follows: the hydraulic equivalent diameter of the microreactor is 200 μm, and it contains 4.10 g of titanium-silicon molecular sieve.

[0069] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, catechol and hydroquinone was 20:1:2.7, and the reaction selectivity of this embodiment was 99.7%.

[0070] Example 8:

[0071] Hydroxylation of phenol to prepare hydroquinone:

[0072] Microreactor parameters: hydraulic equivalent diameter of 100μm, encapsulated with 4.73g of titanium-silicon molecular sieve.

[0073] The reaction raw materials consist of an aqueous solution of phenol with a mass fraction of 5 wt.% and an aqueous solution of hydrogen peroxide with a mass fraction of 1.8 wt.% for H2O2.

[0074] Phenol aqueous solution and hydrogen peroxide were introduced into the microreactor at rates of 7.4 mL / min and 2.7 mL / min, respectively, corresponding to a phenol:H2O2 molar ratio of 3:1. The reaction temperature of the microreactor was 60 °C, and the residence time of phenol and hydrogen peroxide in the microreactor was 50 s. The resulting reaction solution was collected at the tube outlet of the microreactor.

[0075] The reaction solution obtained in this embodiment was analyzed by high performance liquid chromatography. The concentration ratio of phenol, catechol and hydroquinone was 9:1:3.1, and the reaction selectivity of this embodiment was 99.6%.

[0076] Comparative Example 1:

[0077] Hydroxylation of phenol to prepare hydroquinone:

[0078] Reactor parameters: The reactor diameter is 4 mm, and it is encapsulated with 0.31 g of titanium-silicon molecular sieve.

[0079] The reaction raw materials consist of an aqueous solution of phenol with a mass fraction of 12 wt.% and an aqueous solution of hydrogen peroxide with a mass fraction of 5 wt.% H2O2.

[0080] Phenol aqueous solution and hydrogen peroxide were introduced into the microreactor at rates of 7.4 mL / min and 8.7 mL / min, respectively, corresponding to a phenol:H2O2 molar ratio of 1:1. The reaction temperature was 60 °C, and the residence time of phenol and hydrogen peroxide in the reactor was 20 min. The resulting reaction solution was collected at the tube outlet.

[0081] The reaction solution obtained in this comparative example was analyzed by high performance liquid chromatography. The concentration ratio of phenol, hydroquinone and catechol was 1:3:5, and the reaction selectivity of this comparative example was 88.1%.

[0082] Comparing the above embodiments and comparative examples, it can be seen that the reaction selectivity of the embodiments of the present invention is above 99%, which is better.

[0083] The following specific post-processing example demonstrates the separation of phenol and hydroquinone from the reaction solution of Example 1 using liquid membrane technology.

[0084] Post-processing Example 1:

[0085] The reaction solution obtained in Example 1 contained phenol at a concentration of 1 g / L, catechol at a concentration of 4 g / L, and hydroquinone at a concentration of 6 g / L.

[0086] The liquid film phase was a 30% trioctyl phosphate-kerosene system, and the back-extraction phase was an aqueous sodium hydroxide solution with pH=10.

[0087] The back-extraction phase was mixed with a 5% (v / v) liquid membrane phase, resulting in a 5% (v / v) liquid membrane phase in the back-extraction phase. This mixture (0.2 L) was introduced into the tube side of the hollow fiber membrane unit, while the reaction solution (1 L) was introduced into its shell side. After 6 hours of operation, a hydroquinone-enriched solution flowed out from the shell side outlet of the hollow fiber membrane unit, and a sodium phenolate-enriched solution flowed out from the tube side outlet. The hydroquinone-enriched solution was then introduced into a second hollow fiber membrane unit, and the separation process was the same as described above. Concentrated hydrochloric acid was added to the phenol-based solution exiting both hollow fiber membrane units to cause phase separation of the formed phenol. The resulting phenol-enriched solution was recycled back to the reaction section for reuse.

[0088] The phrase "mixing the back-extraction phase with a liquid film phase of 5% by volume" means that the volume fraction of the liquid film phase in the extraction phase after mixing is 5%.

[0089] High performance liquid chromatography (HPLC) analysis was performed on the hydroquinone enrichment solution flowing out from the second hollow fiber membrane in this post-processing example and the phenol enrichment solution after pH adjustment. The concentration of the phenol enrichment solution was 30 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 1.69 and 0.63, respectively.

[0090] Post-processing Example 2:

[0091] The only difference between post-processing embodiment 2 and processing embodiment 1 is that:

[0092] The back-extraction phase is an aqueous solution of sodium hydroxide with pH=14.

[0093] The hydroquinone enrichment solution flowing from the hollow fiber membrane in this post-processing example and the phenol enrichment solution after pH adjustment were analyzed by high performance liquid chromatography. The concentration of the phenol enrichment solution was 40 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.86 and 0.27, respectively.

[0094] Post-processing Example 3:

[0095] The only difference between post-processing embodiment 3 and processing embodiment 1 is that:

[0096] The back-extraction phase is an aqueous solution of sodium carbonate with pH=14.

[0097] High performance liquid chromatography was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 40 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.86 and 0.27, respectively.

[0098] Post-processing Example 4:

[0099] The only difference between post-processing Example 4 and processing Example 1 is that:

[0100] The back-extraction phase is an aqueous solution of potassium hydroxide with pH=14.

[0101] High performance liquid chromatography was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 40 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.86 and 0.27, respectively.

[0102] Post-processing Example 5:

[0103] The only difference between post-processing Example 5 and processing Example 1 is that:

[0104] The back-extraction phase is an aqueous solution of potassium carbonate with pH=14.

[0105] High performance liquid chromatography was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 40 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.86 and 0.27, respectively.

[0106] Post-processing Example 6:

[0107] The only difference between post-processing embodiment 6 and post-processing embodiment 2 is that:

[0108] The liquid membrane phase is a 30% tributyl phosphate-kerosene system, and the reaction solution enters three hollow fiber membranes connected in series in sequence.

[0109] High performance liquid chromatography (HPLC) analysis was performed on the hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example and the phenol enrichment solution after pH adjustment. The concentration of the phenol enrichment solution was 38 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.89 and 0.29, respectively.

[0110] Post-processing Example 7:

[0111] The only difference between post-processing embodiment 7 and post-processing embodiment 6 is that:

[0112] The liquid film phase is a 30% tributyl phosphate-sulfonated kerosene system.

[0113] High performance liquid chromatography (HPLC) analysis was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 38 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.89 and 0.29, respectively.

[0114] Post-processing Example 8:

[0115] The only difference between post-processing embodiment 8 and post-processing embodiment 6 is that:

[0116] The liquid film phase is a 30% tributyl phosphate-benzene system.

[0117] High performance liquid chromatography (HPLC) analysis was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 38 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.89 and 0.29, respectively.

[0118] Post-processing Example 9:

[0119] The only difference between post-processing Example 9 and post-processing Example 6 is that:

[0120] The liquid film phase is a 30% tributyl phosphate-toluene system.

[0121] High performance liquid chromatography (HPLC) analysis was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 38 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.89 and 0.29, respectively.

[0122] Post-processing Example 10:

[0123] The only difference between post-processing Example 10 and post-processing Example 6 is that:

[0124] The liquid film phase is a 30% tributyl phosphate-n-heptane system.

[0125] High performance liquid chromatography (HPLC) analysis was performed on the hydroquinone enrichment solution and the pH-adjusted hydroquinone enrichment solution flowing out of the hollow fiber membrane in this post-processing example. The concentration of the phenol enrichment solution was 38 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.89 and 0.29, respectively.

[0126] Post-processing Example 4:

[0127] The only difference between post-processing Example 4 and post-processing Example 2 is that:

[0128] The liquid membrane phase is a 30% methyl isobutyl ketone-kerosene system, and the reaction solution enters three hollow fiber membranes connected in series in sequence.

[0129] The hydroquinone enrichment solution flowing from the hollow fiber membrane in this post-processing example and the phenol enrichment solution after pH adjustment were analyzed by high performance liquid chromatography. The concentration of the phenol enrichment solution was 34 wt.%, and the separation factors of catechol and hydroquinone relative to phenol were 0.94 and 0.50, respectively.

[0130] The method for preparing hydroquinone by hydroxylation of phenol using a microreactor according to embodiments of the present invention can be summarized as follows:

[0131] A method for preparing hydroquinone by hydroxylation of phenol using a microreactor includes the following steps:

[0132] Phenol and hydrogen peroxide are used as raw materials, and titanium-silicon molecular sieve is used as catalyst to carry out the hydroxylation reaction of phenol in a microreactor. Phenol enters the microchannel of the microreactor through radial flow perpendicular to the microchannel, comes into contact with hydrogen peroxide flowing axially in the microchannel, and reacts rapidly under the action of the catalyst encapsulated in the microreactor. After consuming the hydrogen peroxide, the resulting reaction solution flows out from the tube outlet of the microreactor.

[0133] The above-mentioned method for preparing hydroquinone by hydroxylation of phenol using a microreactor also includes a separation and purification step:

[0134] The reaction solution flowing out of the microreactor outlet is separated and purified using hollow fiber renewable liquid membrane technology: the reaction solution is passed into the shell side of the hollow fiber membrane, the back-extraction phase and the liquid membrane phase mixture is passed into the tube side of the hollow fiber membrane, the treated low-phenol content aqueous solution flows out from the shell side outlet of the hollow fiber membrane, and the enriched solution flows out from the tube side outlet of the hollow fiber membrane.

[0135] In the above separation and purification steps, the reaction solution is passed through several hollow fiber membrane devices connected in series to separate phenol base solution, catechol base solution and hydroquinone enrichment solution; wherein, the phenol base solution is adjusted by pH adjustment to separate the phenol phase, and the obtained phenol enrichment solution is recycled to the reaction unit for reuse.

[0136] In the above method, the molar ratio of phenol to hydrogen peroxide is (1-5):1;

[0137] The reaction temperature of the microreactor is 60℃~90℃;

[0138] The residence time of the hydrogen peroxide and the phenol in the microreactor is 50s to 12min.

[0139] The hydraulic equivalent diameter of the microreactor is 100–500 μm;

[0140] Both the hollow fiber membrane and the microreactor use hollow fiber membrane fibers in their tubular sections, with the catalyst encapsulated within the hollow fiber membrane fibers.

[0141] The liquid film phase is a mixture of a carrier and a diluent. The carrier is one or more of trioctyl phosphate, tributyl phosphate, and methyl isobutyl ketone. The diluent is kerosene, sulfonated kerosene, benzene, toluene, n-heptane, or other alkanes.

[0142] The stripping phase is an alkaline aqueous solution with a pH value of 10-14, and the alkali is sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate or other inorganic alkali.

Claims

1. A method for preparing hydroquinone by hydroxylation of phenol using a microreactor, characterized in that, Includes the following steps: Phenol and hydrogen peroxide are used as raw materials, and titanium-silicon molecular sieve is used as catalyst to carry out the hydroxylation reaction of phenol in a microreactor. Phenol enters the microchannel of the microreactor through radial flow perpendicular to the microchannel, comes into contact with hydrogen peroxide flowing axially in the microchannel, and reacts rapidly under the action of the catalyst encapsulated in the microreactor. The resulting reaction solution flows out from the tube outlet of the microreactor.

2. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 1, characterized in that, It also includes separation and purification steps: The reaction solution flowing out of the microreactor outlet is separated and purified using hollow fiber renewing liquid membrane technology: the reaction solution is passed into the shell side of the hollow fiber membrane, the back-extraction phase and liquid membrane phase mixture is passed into the tube side of the hollow fiber membrane, the low-concentration aqueous solution after phenol extraction flows out from the shell side outlet of the hollow fiber membrane, and the alkaline enrichment solutions of phenol, catechol and hydroquinone flow out from the tube side outlets of each stage of the hollow fiber membrane.

3. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 2, characterized in that, In the separation and purification step, the reaction solution is passed through several hollow fiber membrane devices connected in series to separate phenol base solution, catechol base solution and hydroquinone enrichment solution; wherein, the phenol base solution is adjusted by pH to separate the phenol phase, and the obtained phenol enrichment solution is recycled to the reaction unit for reuse.

4. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 1, characterized in that, The molar ratio of phenol to hydrogen peroxide is (1-5):

1.

5. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 1, characterized in that, The reaction temperature inside the microreactor is 60℃~90℃.

6. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 1, characterized in that, The residence time of the hydrogen peroxide and the phenol in the microreactor is 50s to 12min.

7. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 1, characterized in that, The microreactor has a hydraulic equivalent diameter of 100–500 μm.

8. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor according to any one of claims 1-3, characterized in that, Both the hollow fiber membrane and the microreactor use hollow fiber ultrafiltration membrane fibers, and the catalyst is encapsulated in the hollow fiber membrane fibers.

9. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor according to claim 2, characterized in that, The liquid film phase is a mixture of a carrier and a diluent. The carrier is one or more of trioctyl phosphate, tributyl phosphate, and methyl isobutyl ketone. The diluent is kerosene, sulfonated kerosene, benzene, toluene, n-heptane, or other alkanes.

10. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in claim 2, characterized in that, The stripping phase is an alkaline aqueous solution with a pH value of 10-14, and the alkali is sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate or other inorganic alkali.

11. The method for preparing hydroquinone by hydroxylation of phenol using a microreactor as described in any one of claims 1-10, in the hydroquinone production process.

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