Method for continuously synthesizing DNR through microchannel

Abstract

The invention relates to the field of synthesis of PBO fiber monomer aromatic dinitro compounds, and discloses a microchannel continuous synthesis method of DNR, which comprises the following steps: respectively pumping raw materials resorcinol and a mixed acid nitrating agent consisting of sulfuric acid and nitric acid into a microchannel reactor for nitration reaction by taking DMSO as a solvent; feeding a crude product output by the micro-channel reactor into ice water to obtain a DNR crude crystal product; wherein the micro-channel reactors are fluid splitting combined type micro-channel reactors with heat exchange channels, such as series groove type reactors, Kanning heart type reactors or branch type distributors, and single nitration and double nitration of resorcinol are realized through the two sets of micro-channel reactors; the flow and the temperature of cooling circulating water of heat exchange channels of the two sets of micro-channel reactors are controlled, and the selectivity and the yield of step-by-step nitration of resorcinol are regulated and controlled.

Description

Technical Field

[0001] The invention relates to the field of synthesis of poly(p-phenylene benzobisoxazole) (PBO) fiber monomer aromatic dinitro compounds, and in particular to a method for continuously synthesizing DNR in a microchannel. Background Art

[0002] Poly(p-phenylene benzobisoxazole) (PBO) fiber is a high-performance synthetic fiber that plays an important role in many cutting-edge fields with its excellent properties such as high strength and high thermal stability. 4,6-Dinitroresorcinol (DNR) is an important intermediate for the synthesis of PBO fiber, which is mainly prepared by three steps of sulfonation, nitration and hydrolysis of resorcinol. At present, the patent reports (such as CN201910853516.3, CN201110257600.2, CN200810054708.X) all adopt the preparation method of Chinese patent ZL00117956.X authorized by Yukihiro Kumamoto in 2004. The SO3H group of the first step sulfonation reaction stabilizes the nitration rate to prevent excessive nitration to trinitration products. Despite this, the strong exothermic effect of the system leads to high selectivity of mononitration and trinitration products of resorcinol, and the preparation process is relatively complex, the reaction cycle is long, and the energy consumption is relatively high.

[0003] ZL201610929583.5 first reported a process for synthesizing 4,6-dinitroresorcinol by hydrolysis using a microchannel reactor combined with an intermittent reactor, with a maximum total yield of DNR of 87%. However, the total reaction time is relatively long, and the loss of raw materials and products in the semi-continuous and semi-intermittent reaction, as well as the energy consumption, are relatively large. Summary of the invention

[0004] The applicant of the present invention further analyzed and studied the nitration mechanism of resorcinol, identified that the thermal effect and water content of the system are the decisive factors affecting the mononitration, dinitration and trinitration of resorcinol, and proposed a method for controlling the thermal effect and water content of the system in microchannel continuous synthesis, thereby regulating the selectivity and yield of the main product (dinitration). Further energy saving and consumption reduction, the green and economic synthesis of PBO monomer intermediates is achieved, and my country's competitiveness in the field of high-performance fiber monomer synthesis is improved.

[0005] The present invention provides a method for continuously synthesizing DNR and improving the selectivity and yield of DNR in a nitration system, wherein the method is carried out in a microchannel reaction system, wherein the microchannel reaction system comprises a heat transfer unit and at least two microchannel reaction units connected in series, wherein the microchannel reaction units are capable of mixing and reacting at least two reaction materials;

[0006] The method comprises: feeding a mixed acid nitrating agent into each microchannel reaction unit, feeding a resorcinol-solvent raw material into a first-stage microchannel reaction unit, wherein the resorcinol-solvent raw material is gradually mixed with the mixed acid nitrating agent fed respectively through at least two microchannel reaction units connected in series to perform a nitration reaction, generating a final nitration product, cooling, and then recrystallizing to obtain a DNR crude crystal product;

[0007] The heat removal unit is used to remove the reaction heat in each of the microchannel reaction units.

[0008] Preferably, the microchannel reaction unit comprises a microchannel reactor having a fluid splitting composite mixing channel, and the heat removal unit comprises a heat exchange channel for removing the reaction heat of each of the microchannels.

[0009] More preferably, the microchannel reactor is selected from at least one of a series tank reactor, a Corning heart-type reactor or a branch-type distributor.

[0010] Through the above technical scheme, based on the step-by-step nitration mechanism and reaction characteristics of resorcinol, the present invention finds that controlling the amount of nitration active intermediate phase generated in nitric-sulfuric mixed acid can effectively control the step-by-step nitration rate of resorcinol, thereby effectively regulating the dinitration selectivity and yield of resorcinol, thereby simplifying the reaction process from the traditional three-step sulfonation, nitration, and hydrolysis reaction to a one-step direct nitration reaction, shortening the production cycle, and improving operational safety. At the same time, the acidic solvent can be directly recovered and reused after dehydration, which is conducive to industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic flow diagram of a method for continuously synthesizing DNR in a microchannel according to an embodiment of the present invention;

[0012] Figure 2 yes Figure 1 Schematic diagram of the structure of the microchannel reactor.

[0013] Description of Reference Numerals

[0014] 1 and 2 are constant temperature baths; 6 and 7 are circulation pumps; 3 is a DMSO solution of resorcinol; 4 and 5 are a DMSO solution of a mixture of concentrated sulfuric acid and concentrated nitric acid; 8, 9 and 10 are horizontal flow pumps; 11 and 12 are heat exchangers; 13 and 14 are microchannel reactors; and 15 is an ice water crystallizer. DETAILED DESCRIPTION

[0015] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0016] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0017] In the present invention, unless otherwise specified, directional words such as "up, down, left, right" generally refer to up, down, left, right as shown in the reference drawings; "inside and outside" refer to inside and outside relative to the outline of each component itself.

[0018] It should be noted that 4,6-dinitroresorcinol (DNR) is an important intermediate for the synthesis of PBO fiber. It is mainly prepared from resorcinol through three steps of sulfonation, nitration and hydrolysis. At present, sulfonation, nitration and hydrolysis reactions are all carried out in intermittent reactors. However, sulfonation and nitration reactions are both highly exothermic reactions. Traditional intermittent operations cannot achieve precise temperature control and it is difficult to achieve uniform mixing of materials. Not only is the safety poor, the reaction yield is not high, and the product quality between batches is also unstable.

[0019] To solve the above problems, Figure 1-Figure 2 As shown, the present invention provides a method for continuously synthesizing DNR in a microchannel, the method is carried out in a microchannel reaction system, the microchannel reaction system includes a heat transfer unit and at least two microchannel reaction units connected in series, the microchannel reaction unit can make at least two reaction materials mix and react;

[0020] The method comprises: feeding a mixed acid nitrating agent into each microchannel reaction unit, feeding a resorcinol-solvent raw material into a first-stage microchannel reaction unit, wherein the resorcinol-solvent raw material is gradually mixed with the mixed acid nitrating agents fed respectively through at least two microchannel reaction units connected in series to perform a nitration reaction, generating a final nitration product, cooling, and then recrystallizing to obtain a DNR crude crystal product; wherein a heat removal unit is used to forcibly remove the reaction heat in each microchannel reaction unit.

[0021] In the present invention, the goal of removing the reaction heat is to control the system temperature rise to less than 5-10°C.

[0022] In the traditional method, due to the violent nitration of resorcinol, the huge heat release is very likely to induce side reactions, so the sulfonic acid group is used as a protective group to weaken the nitration reaction rate, but at the same time, it leads to the need for an alkaline reagent to neutralize the acidity of the system in the subsequent hydrolysis and product collection. The overall process is relatively complex, the reaction cycle is long, and the acid consumption is serious. Based on the step-by-step nitration mechanism and reaction characteristics of resorcinol, the present invention finds that controlling the amount of nitration active intermediate phase generated in nitric and sulfuric acid mixed acid can effectively control the step-by-step nitration rate of resorcinol, thereby effectively regulating the dinitration selectivity and yield of resorcinol, thereby simplifying the reaction process from the traditional three-step sulfonation, nitration, and hydrolysis reaction to a one-step direct nitration reaction, shortening the production cycle, and improving operational safety. At the same time, the acidic solvent can be directly recovered and reused after dehydration, which is conducive to industrial-scale production.

[0023] Compared with intermittent reactors, microchannel reactors adopt a continuous operation mode, have a tiny reaction space and a large heat transfer area, and can accurately control the material concentration during the reaction process. Therefore, it can not only achieve stable and safe operation, but also greatly improve the product yield.

[0024] In the present invention, each microchannel reaction unit includes a microchannel reactor with a fluid splitting composite mixing channel. This microchannel reactor allows the mixed fluid to be continuously split, composited, stretched and broken, increases the contact area, improves the fluid uniformity, and thus achieves rapid mixing and efficient reaction. In some embodiments of the present invention, the heat exchange channels of the microchannel reaction unit and the heat transfer unit are combined in the microchannel reactor. The microchannel reactor has the following features: Figure 2 The tandem slot microchannel tube 16 shown in the left figure has multiple parallel and spaced heat exchange channels for circulating heat exchange medium on both sides of the tandem slot microchannel tube 16. The inlet and outlet of the heat exchange channel are connected to a thermostatic tank filled with heat exchange medium, and the heat exchange medium is transported by a circulating pump; Figure 1 As shown, two sets of the above-mentioned microchannel reactors are connected in series to realize the mononitration and dinitration of resorcinol, and the flow rate and temperature of the cooling circulating water in the heat exchange flow channels of the two sets of microchannel reactors are controlled to achieve the selectivity and yield of the step-by-step nitration of resorcinol.

[0025] In the present invention, the microchannel reactor is preferably selected from at least one of a series tank reactor (eg, ZL202110500782.5), a Corning heart-shaped reactor or a branch-shaped distributor (eg, ZL 202110500297.8).

[0026] In order to improve the selectivity and yield of dinitration of resorcinol, according to a preferred embodiment of the present invention, the flow rate of the heat exchange medium in the heat exchange channel is F>(500-2500)f / Ke, in mL / min; wherein f is the total flow rate of the fluid in the microchannel of the microreactor, in mL / min; Ke is the effective heat transfer coefficient of the heat exchange channel, in W m -2 K -1 In the present invention, the material of the heat exchange channel is selected from stainless steel, alloy or glass. The microchannel reactor has an internal structure of fluid splitting-compounding action. If the external covering heat exchange channel is mainly made of glass material, the heat exchange medium flow rate F in the heat exchange channel is greater than (2000-2500) f / Ke; if it is mainly made of stainless steel and alloy material, the heat exchange medium flow rate F in the heat exchange channel is greater than (500-1000) f / Ke.

[0027] The present invention has no special requirements for the flow direction of the heat exchange medium. The following exemplary description is not intended to limit the scope of the present invention. According to one embodiment of the present invention, the flow direction of the reaction material in the microchannel reactor is opposite to the flow direction of the heat exchange medium in the heat exchange channel of the microchannel reactor.

[0028] In the present invention, conventional heat exchange media are applicable to the present invention. The following exemplary description is given, but the scope of the present invention is not limited thereto. According to one embodiment of the present invention, the heat exchange medium is selected from at least one of water, cooling brine or ethylene glycol aqueous solution.

[0029] According to a preferred embodiment of the present invention, the liquid holding capacity of each splitting and compounding module of the single-stage microchannel reactor is 0.1 to 0.5 mL. The splitting and compounding module in the present invention refers to, for example, Figure 2 A single mixing tank in the series tank reactor (ZL202110500782.5) shown; or the last-stage bifurcation structure of the fluid mixing channel in a branch-type distributor (e.g. ZL 202110500297.8).

[0030] In order to improve the dinitration selectivity and yield of resorcinol, according to a preferred embodiment of the present invention, the liquid holdup in the volume of the microchannel reactor is >6 ml.

[0031] In the present invention, the characteristic dimension of the inlet and outlet fluid mixing of the microchannel reactor is less than 1 mm. In the present invention, the characteristic dimension of the inlet and outlet fluid mixing refers to the minimum diameter of the microreactor mixing channel, such as Figure 2 The channel diameter at the neck of the tank reactor is the smallest. In the present invention, the smaller the characteristic size is, the more conducive it is to the generation of the active phase of the nitration reaction, and the more conducive it is to improving the yield and selectivity.

[0032] According to a preferred embodiment of the present invention, the flow rate of the resorcinol-solvent raw material fed to the first-stage microchannel reaction unit is 2-5 mL / min.

[0033] According to a preferred embodiment of the present invention, the concentration of the resorcinol-DMSO raw material solution is preferably 1 to 6 mol / L.

[0034] In the present invention, the mixed acid nitrating agent includes sulfuric acid, nitric acid and DMSO solvent. The present invention has no special restrictions on the sources of sulfuric acid, nitric acid and DMSO solvent. Commercial products of the above substances can be used, or they can be prepared by themselves according to the technical schemes for preparing the above substances well known to those skilled in the art.

[0035] In the present invention, preferably, in the mixed acid nitrating agent, the sulfuric acid is fuming sulfuric acid or concentrated sulfuric acid with a concentration of 70-98 wt%, and the nitric acid is fuming nitric acid or concentrated nitric acid with a concentration of ≥65 wt%.

[0036] In the present invention, preferably, the flow rate of the mixed acid nitrating agent fed to the first-stage microchannel reaction unit is 1-4 mL / min.

[0037] In the present invention, preferably, in the mixed acid nitrating agent fed to the first-stage microchannel reaction unit, the volume ratio of sulfuric acid, nitric acid and DMSO solvent is (1-4):1:(0.4-2).

[0038] According to a preferred embodiment of the present invention, the flow rate of the mixed acid nitrating agent fed into the microchannel reaction unit after the first stage is 2-8 mL / min.

[0039] According to a preferred embodiment of the present invention, in the mixed acid nitrating agent fed into the microchannel reaction unit after the first stage, the volume ratio of sulfuric acid, nitric acid and DMSO solvent is (6-8):1:(1-2).

[0040] According to a preferred embodiment of the present invention, the liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 6 to 8 mL.

[0041] According to a preferred embodiment of the present invention, the feed temperature of the mixed acid nitrating agent and resorcinol-solvent raw material fed to the microchannel reactor in the first-stage microchannel reaction unit is 20-30°C.

[0042] According to a preferred embodiment of the present invention, the temperature of the heat exchange medium flowing in the heat exchange channel of the microchannel reactor of the first-stage microchannel reaction unit is 5-15° C., and the flow rate of the heat exchange medium is 100-120 mL / min.

[0043] According to a preferred embodiment of the present invention, the liquid holdup of the microchannel reactor in the reaction unit after the first stage is 12 to 22 mL.

[0044] According to a preferred embodiment of the present invention, the feed temperature of the mixed acid nitrating agent fed to the microchannel reactor in the reaction unit after the first stage is 45-60°C.

[0045] According to a preferred embodiment of the present invention, the temperature of the heat exchange medium flowing in the heat exchange channel after the first stage is 20-30° C., and the flow rate of the heat exchange medium is 100-150 mL / min.

[0046] The advantages of the present invention will be described below by way of examples, but the present invention is not limited thereto.

[0047] The following examples are Figure 1-Figure 2 The reaction is carried out in the microchannel reaction system shown in the figure, which includes two microchannel reactors connected in series. The microchannel reactor is a series trough microreactor proposed by the applicant of the present invention with authorization ZL202110500782.5, which is named as the first-stage microchannel reactor 13 and the second-stage microchannel reactor 14 along the overall flow direction of the material. The characteristic size of the inlet and outlet fluid mixing of the reaction inlet 1, reaction inlet 2 and reaction outlet of the first-stage microchannel reactor 13 and the second-stage microchannel reactor 14 is 0.8 mm.

[0048] The method comprises: taking a mixed solution of resorcinol and DMSO as a feed 3, and mixing a mixed acid nitrating agent composed of sulfuric acid and nitric acid and a DMSO solvent as another feed 4, and inputting the two feeds to a first-stage microchannel reactor 13 after heat exchange to a reaction temperature through a heat exchanger 11 to perform a primary nitration reaction to generate a primary nitration product, and inputting a cooling medium into the heat exchange channel of the first-stage microchannel reactor 13 through a thermostatic tank 2 to transfer heat;

[0049] The discharge port of the first-stage microchannel reactor 13 is connected to the second-stage microchannel reactor 14, and the other feed is a mixed acid nitrating agent 5. After heat exchanged to the reaction temperature by the heat exchanger 12, it enters the second-stage microchannel reactor 14 and undergoes a secondary nitration reaction with the primary nitration product of the discharge of the first-stage microchannel reactor 13. The cooling medium is input from the thermostatic bath 1 to the heat exchange channel of the second-stage microchannel reactor 14 for heat transfer, and the outlet product of the second-stage microchannel reactor 14 is directly input into the ice water crystallizer 15 filled with ice water for cooling and recrystallization to obtain a crude DNR crystalline product. It should be noted that the crystalline material includes the target substance and by-products (sulfonated products of DNR).

[0050] It should be noted that the fluid flow rate formula of the heat exchange channel of the present invention is limited to the resorcinol nitration reaction conditions proposed in this embodiment, and there is no strict restriction on the structure of the microchannel reactor (the branch-type distributor proposed by the patent ZL202110500297.8 authorized by the applicant of the present invention also has the same effect);

[0051] The calculation method of the mass yield of the crystals is Y = m / (n DNR M DNR +n 副 M 副 ), m is the mass of the crystalline substance, and M is the molar mass;

[0052] The calculation method of DNR selectivity is S DNR =n DNR / (n DNR +n 副 ), n is the molar amount.

[0053] Example 1

[0054] The concentration of the DMSO solution for preparing resorcinol is 3 mol / L, and the flow rate is 5 mL / min. The mixed acid nitrating agent is composed of commercially available 98wt% concentrated sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 1:1:2, and the flow rate is 2 mL / min. The second-stage mixed acid nitrating agent is composed of 20wt% oleum, 80wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 6:1:1, and the flow rate is 4 mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 7 mL, the feed temperature is 25°C, the liquid holding capacity in each split composite mixing module volume is 0.112 mL, the circulating water temperature in the heat exchange channel is 10°C, and the flow rate is 110 mL / min. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 14 mL, the feed temperature is 55°C, the liquid holding capacity in each split composite mixing module volume is 0.224 mL, the circulating water temperature in the heat exchange channel is 25°C, and the flow rate is 140 mL / min. The outlet of the microchannel reactor was connected to an ice water crystallizer, and the mass yield of the crystals was measured to be 94%, and the DNR selectivity was 97%.

[0055] Example 2

[0056] The concentration of the DMSO solution for preparing resorcinol is 1 mol / L, and the flow rate is 2 mL / min. The mixed acid nitrating agent is composed of commercially available 70wt% concentrated sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 4:1:0.4, and the flow rate is 4 mL / min. The second-stage mixed acid nitrating agent is composed of 20wt% oleum, 100wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 8:1:1, and the flow rate is 8 mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 10 mL, the feed temperature is 30°C, the liquid holding capacity in each split composite mixing module volume is 0.112 mL, the circulating water temperature in the heat exchange channel is 15°C, and the flow rate is 120 mL / min. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 22 mL, the feed temperature is 60°C, the liquid holding capacity in each split composite mixing module volume is 0.448 mL, the circulating water temperature in the heat exchange channel is 30°C, and the flow rate is 100 mL / min. The outlet of the microchannel reactor was connected to an ice water crystallizer, and the mass yield of the crystals was measured to be 97%, and the DNR selectivity was 91%.

[0057] Example 3

[0058] The concentration of the DMSO solution for preparing resorcinol is 6 mol / L, and the flow rate is 4 mL / min. The mixed acid nitrating agent is composed of commercially available 80wt% concentrated sulfuric acid, 100wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 2:1:1, and the flow rate is 1 mL / min. The second-stage mixed acid nitrating agent is composed of 20wt% oleum, 100wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 7:1:2, and the flow rate is 2 mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 6 mL, the feed temperature is 20°C, the liquid holding capacity in each split composite mixing module volume is 0.224 mL, the circulating water temperature in the heat exchange channel is 5°C, and the flow rate is 100 mL / min. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 12 mL, the feed temperature is 45°C, the liquid holding capacity in each split composite mixing module volume is 0.112 mL, the circulating water temperature in the heat exchange channel is 20°C, and the flow rate is 150 mL / min. The outlet of the microchannel reactor was connected to an ice water crystallizer, and the mass yield of the crystals was measured to be 99%, and the DNR selectivity was 94%.

[0059] Example 4

[0060] The concentration of the DMSO solution for preparing resorcinol is 2mol / L, and the flow rate is 3mL / min. The mixed acid nitrating agent is composed of commercially available 20wt% fuming sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 1:1:0.4, and the flow rate is 1mL / min. The second-stage mixed acid nitrating agent is composed of 20wt% fuming sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 6:1:2, and the flow rate is 5mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 8mL, the feed temperature is 20°C, the liquid holding capacity in each split composite mixing module volume is 0.448mL, the circulating water temperature in the heat exchange channel is 10°C, and the flow rate is 100mL / min. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 16mL, the feed temperature is 50°C, the liquid holding capacity in each split composite mixing module volume is 0.112mL, the circulating water temperature in the heat exchange channel is 20°C, and the flow rate is 150mL / min. The outlet of the microchannel reactor was connected to an ice water crystallizer, and the mass yield of the crystals was measured to be 97%, and the DNR selectivity was 95%.

[0061] Example 5

[0062] Different from Example 1, the concentration of the DMSO solution for preparing resorcinol is 3 mol / L, and the flow rate is 10 mL / min. The mixed acid nitrating agent is composed of commercially available 98 wt% concentrated sulfuric acid, 65 wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 6:1:5, and the flow rate is 10 mL / min. The second-stage mixed acid nitrating agent is composed of 20 wt% oleum, 80 wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 2:1:5, and the flow rate is 10 mL / min. The outlet of the microchannel reactor is connected to an ice water crystallizer, and the mass yield of the crystals is determined to be 86%, and the DNR selectivity is 83%.

[0063] Example 6

[0064] Different from Example 1, the liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 4 mL, the feed temperature is 25 ° C, the liquid holding capacity in each split composite mixing module volume is 0.112 mL, the circulating water temperature in the heat exchange channel is 10 ° C, and the flow rate is 80 mL / min. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 20 mL, the feed temperature is 55 ° C, the liquid holding capacity in each split composite mixing module volume is 0.224 mL, the circulating water temperature in the heat exchange channel is 25 ° C, and the flow rate is 180 mL / min. The outlet of the microchannel reactor is connected to an ice water crystallizer, and the mass yield of the crystals is measured to be 92%, and the DNR selectivity is 66%.

[0065] Comparative Example 1

[0066] The concentration of the DMSO solution of resorcinol is 3 mol / L, and the flow rate is 5 mL / min. The mixed acid nitrating agent is composed of commercially available 98 wt% concentrated sulfuric acid, 65 wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 1:1:2, and the flow rate is 2 mL / min. The second-stage mixed acid nitrating agent is composed of 20 wt% oleum, 80 wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 6:1:1, and the flow rate is 4 mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 7 mL, the feed temperature is 25 ° C, and the liquid holding capacity in each split composite mixing module volume is 0.112 mL; the liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 14 mL, the feed temperature is 55 ° C, and the liquid holding capacity in each split composite mixing module volume is 0.224 mL. The outlet of the microchannel reactor is connected to an ice water crystallizer, and the mass yield of the crystals is measured to be 60% (the microchannel reactor is blocked in the late stage of the reaction), and the DNR selectivity is 60%.

[0067] Comparative Example 2

[0068] The concentration of the DMSO solution of resorcinol is 6 mol / L, and the flow rate is 4 mL / min. The mixed acid nitrating agent is composed of commercially available 80 wt% concentrated sulfuric acid, 100 wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 2:1:1, and the flow rate is 1 mL / min. The second-stage mixed acid nitrating agent is composed of 20 wt% oleum, 100 wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 7:1:2, and the flow rate is 2 mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 6 mL, the feed temperature is 20 ° C, and the liquid holding capacity in each split composite mixing module volume is 0.224 mL. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 12 mL, the feed temperature is 45 ° C, the liquid holding capacity in each split composite mixing module volume is 0.112 mL, the circulating water temperature in the heat exchange channel is 20 ° C, and the flow rate is 150 mL / min. The outlet of the microchannel reactor is connected to an ice water crystallizer, and the mass yield of the crystals is measured to be 88%, and the DNR selectivity is 74%.

[0069] Comparative Example 3

[0070] The concentration of the DMSO solution for preparing resorcinol is 2mol / L, and the flow rate is 3mL / min. The mixed acid nitrating agent is composed of commercially available 20wt% fuming sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 1:1:0.4, and the flow rate is 1mL / min. The second-stage mixed acid nitrating agent is composed of 20wt% fuming sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 6:1:2, and the flow rate is 5mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 8mL, the feed temperature is 20°C, the liquid holding capacity in each split composite mixing module volume is 0.448mL, the circulating water temperature in the heat exchange channel is 10°C, and the flow rate is 100mL / min. The liquid holding capacity of the microchannel reactor in the second-stage microchannel reaction unit is 16mL, the feed temperature is 50°C, and the liquid holding capacity in each split composite mixing module volume is 0.112mL. The outlet of the microchannel reactor was connected to an ice water crystallizer, and the mass yield of the crystals was measured to be 82%, and the DNR selectivity was 71%.

[0071] Comparative Example 4

[0072] Different from Example 1, only the first-stage microchannel reactor is set, and the concentration of the DMSO solution prepared for resorcinol is 3 mol / L, and the flow rate is 5 mL / min. The mixed acid nitrating agent is composed of commercially available 98% concentrated sulfuric acid, 65wt% concentrated nitric acid and DMSO solvent, the volume ratio of the three is 1:1:2, and the flow rate is 2 mL / min. The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 7 mL, the feed temperature is 25 ° C, the liquid holding capacity in the volume of each split composite mixing module is 0.112 mL, the circulating water temperature in the heat exchange channel is 10 ° C, and the flow rate is 110 mL / min. The outlet of the microchannel reactor is connected to an ice water crystallizer, and the mass yield of the crystals is measured to be 75%, and the DNR selectivity is 98%.

[0073] Comparative Example 5

[0074] An intermittent synthesis reaction is carried out in a reactor with a water jacket, 100 mL of a 3 mol / L resorcinol DMSO solution is added to the reactor, the temperature of the reactor is controlled by the water jacket to maintain at 25°C, 98 wt% concentrated sulfuric acid and 65 wt% concentrated nitric acid are prepared into a mixed acid, wherein the molar ratio of the concentrated sulfuric acid and the concentrated nitric acid to the resorcinol is 2:1:1, the mixed acid is added dropwise to the reactor at a dropping rate of 0.3 mL / min, and stirred at a rate of 500 rpm, and the constant temperature time is 1 hour after the addition is completed. Subsequently, the mixed solution is crystallized in an ice water crystallizer, and the mass yield of the crystals is determined to be 90%, and the DNR selectivity is 15%.

[0075] The present invention realizes the mononitration and dinitration of resorcinol through two sets of microchannel reactors, controls the cooling circulating water flow and temperature of the heat exchange channels of the two sets of microchannel reactors, and regulates the selectivity and yield of the step-by-step nitration of resorcinol. The method according to the present invention can quickly achieve DNR selectivity of up to 98% and yield of up to 99% within a relatively short residence time (3 to 15 minutes), and the present invention is green, economical, safe and efficient.

[0076] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various specific technical features in any appropriate manner. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations. However, these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for continuously synthesizing DNR in a microchannel, characterized in that: The method is carried out in a microchannel reaction system, wherein the microchannel reaction system comprises a heat transfer unit and at least two microchannel reaction units connected in series, wherein the microchannel reaction units are capable of mixing and reacting at least two reaction materials; The method comprises: feeding a mixed acid nitrating agent into each microchannel reaction unit, feeding a resorcinol-solvent raw material into a first-stage microchannel reaction unit, wherein the resorcinol-solvent raw material is gradually mixed with the mixed acid nitrating agent fed respectively through at least two microchannel reaction units connected in series to perform a nitration reaction, generating a final nitration product, cooling, and then recrystallizing to obtain a DNR crude crystal product; The heat removal unit is used to remove the reaction heat in each of the microchannel reaction units.

2. The method according to claim 1, wherein: The microchannel reaction unit comprises a microchannel reactor having a fluid splitting composite mixing channel; the heat removal unit comprises a heat exchange channel for removing the reaction heat of each microchannel reactor; Preferably, the microchannel reactor is selected from at least one of a series tank reactor, a Corning heart reactor or a branch distributor.

3. The method according to claim 2, wherein: The flow direction of the reaction material in the microchannel reactor is opposite to the flow direction of the heat exchange medium in the heat exchange channel of the microchannel reactor; and / or The heat exchange medium is selected from at least one of water, cooling brine or ethylene glycol aqueous solution.

4. The method according to claim 2 or 3, wherein: The liquid holding capacity in each splitting composite mixing module volume of the single-stage microchannel reactor is 0.1 to 0.5 mL; and / or The total liquid holdup within the volume of the single-stage microchannel reactor is >6 ml.

5. The method according to any one of claims 1 to 4, wherein: The flow rate of the resorcinol-solvent raw material fed to the first-stage microchannel reaction unit is 2 to 5 mL / min; The concentration of the resorcinol-solvent raw material solution is preferably 1 to 6 mol / L.

6. The method according to any one of claims 1 to 5, wherein: Mixed acid nitrating agents include sulfuric acid, nitric acid and DMSO solvent; Preferably, In the mixed acid nitrating agent, the sulfuric acid is fuming sulfuric acid or concentrated sulfuric acid with a concentration of 70-98wt%, and the nitric acid is fuming nitric acid or concentrated nitric acid with a concentration of ≥65wt%.

7. The method according to any one of claims 1 to 6, wherein: The flow rate of the mixed acid nitrating agent fed to the first-stage microchannel reaction unit is 1-4 mL / min; and / or In the mixed acid nitrating agent fed to the first-stage microchannel reaction unit, the volume ratio of sulfuric acid, nitric acid and DMSO solvent is (1-4):1:(0.4-2).

8. The method according to any one of claims 1 to 7, wherein: In the microchannel reaction unit after the first stage: The flow rate of the mixed acid nitrating agent fed is 2 to 8 mL / min; and / or In the mixed acid nitrating agent fed, the volume ratio of sulfuric acid, nitric acid and DMSO solvent is (6-8):1:(1-2).

9. The method according to any one of claims 1 to 8, wherein: The liquid holding capacity of the microchannel reactor in the first-stage microchannel reaction unit is 6 to 8 mL; and / or The feed temperature of the mixed acid nitrating agent and resorcinol-solvent raw materials fed to the microchannel reactor in the first-stage microchannel reaction unit is 20-30° C.; and / or The temperature of the heat exchange medium flowing in the heat exchange channel of the medium microchannel reactor of the first-stage microchannel reaction unit is 5-15° C., and the flow rate of the heat exchange medium is 100-120 mL / min.

10. The method according to any one of claims 1 to 9, wherein: In the microchannel reaction unit after the first stage: The liquid holdup of the microchannel reactor is 12 to 22 mL; and / or The feed temperature of the mixed acid nitrating agent is 45-60°C; and / or The temperature of the heat exchange medium flowing in the heat exchange channel is 20-30° C., and the flow rate of the heat exchange medium is 100-150 mL / min.

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