An electrochemical reactor for simultaneously achieving static mixing and electrochemical reaction

Abstract

The application discloses an electrochemical reactor for realizing static mixing and electrochemical reaction simultaneously, which comprises two graphite electrode plates, a planar static mixer and the like. The planar static mixer promotes fluid diversion and generates vortex through obstacles in a pipeline and sharp changes of a pipe diameter, so that the mixing quality is improved. The reactor and the reaction method can make electrochemical oxidation be completed under a small current gradient and without adding electrolyte due to a large surface area of the graphite electrode plate and a small electrode spacing. The electrochemical reactor is used to successfully realize efficient preparation of HNS. A TNT solution and a NaClO solution are fully mixed to form HNS, and a by-product HNBB of HNS is electrochemically dehydrogenated and converted into HNS, so that the yield can reach 50.85% after 30 min of reaction. The device realizes simultaneous static mixing and electrochemical reaction, so that the yield of HNS is improved.

Description

Technical Field

[0001] This invention belongs to the field of energetic materials technology and relates to an electrochemical reactor that simultaneously achieves static mixing and electrochemical reaction. Background Technology

[0002] According to previous reports, Shipp et al. rapidly added sodium hypochlorite solution to a tetrahydrofuran-methanol solution cooled to 0°C and maintained the reaction temperature at 15°C, then washed with acetone to obtain the crude product. This method yielded a relatively low yield, typically only 30-35% (J.Org.Chem.1964,29,2620–2623). Salter et al. added a nitrogen-containing base (hydrochloride of organic amines) to the reaction solution, increasing the yield of HNS to about 45%, but the use of nitrogen-containing bases caused inconvenience in post-processing (DefSci.,Vol 31,1980,4(10):305-308). Golding et al. added calcium oxide to the reaction, which reduced side reactions and achieved a yield of up to 46%. However, the reaction time reached tens of hours and acid treatment was required to obtain the crude product (US patent:5023386,1991-07-11). Therefore, the one-step preparation method has a long preparation time, many reaction byproducts, and low yield. HNBB, a byproduct, constitutes the largest proportion of the total product. Extensive research has been conducted on the oxidation and dehydrogenation of HNBB to produce HNS. EEGilbert et al. experimented with oxidants including divalent copper salts, halogens, oxygen, benzoquinone, and liquid bromine (Propellants and Explosives, 1980, 5, 168-172). Among these, liquid bromine as the oxidant and pyridine as the catalyst yielded the best results, achieving a yield of up to 90%. GPSollott et al. experimented with oxidants including air, transition metal salts, cobalt naphthenate, and N-bromosuccinimide (US patent: 4268696, 1981-05-19). They used catalysts (sodium carbonate, sodium bicarbonate, carboxylates, etc.) in different solvents (DMF, DMSO, HIMPA, acetonitrile, oxane, etc.) to oxidize and dehydrogenate HNBB. However, the solvents used in these oxidation processes are not environmentally friendly, making wastewater treatment a significant challenge.

[0003] Electron, as a cheap, readily available, green, and clean redox agent, has attracted much attention. Here, we attempt to design an electrochemical reactor to electrochemically dehydrogenate the byproduct HNBB to HNS in a one-step preparation process, thereby improving product purity and yield. Summary of the Invention

[0004] The purpose of this invention is to provide an electrochemical reactor that simultaneously achieves static mixing and electrochemical reaction, and to realize the efficient preparation of HNS through the reactor.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] By designing specially structured obstructions in the fluid channel, combined with abrupt changes in pipe diameter, fluid diversion and vortex generation are achieved, improving fluid mixing quality. This ensures that the fluid flowing through the planar static mixer can simultaneously contact the electrode plates to achieve electrochemical oxidation-reduction. Laser-etched deep grooves create static mixing units, and laser-etched through areas create electrochemical units, thus completing the design of the planar static mixer. The planar static mixer is then bonded together, and the electrochemical reactor is assembled using sealing gaskets, sealing screws, and graphite electrode plates. HNS is then prepared through this electrochemical reactor.

[0007] Fluids with different flow rates can be effectively mixed and their concentrations homogenized when passing through a planar static mixer.

[0008] The fluid velocity changes consistently under different Reynolds numbers. Compared to the velocity in the straight pipe, the velocity decreases significantly when flowing through the static mixing unit, allowing sufficient mixing time for the fluid. Furthermore, the higher the flow velocity, the greater the difference between the flow velocity at the static mixing unit and the flow velocity in other parts of the pipeline.

[0009] The pressure changes are consistent under different Reynolds numbers. The pressure gradually decreases in the direction of fluid flow, and the greater the Reynolds number, the greater the pressure drop.

[0010] In the above experimental method, when the peristaltic pump head is YZ1515X-A and the silicone tube is 14#, the feed flow rate of TNT solution is 7 ml / min and the feed flow rate of NaClO aqueous solution is 4 ml / min.

[0011] In the above experimental method, the prepared solution was placed in an ice-water bath during the HNS preparation process, the reaction temperature was the normal room temperature of 26℃, the reaction time was 30 min, and the pH range of the solution was adjusted to 9.5-10.5.

[0012] In the above experimental method, triethylenediamine (DABCO) was used as the dehydrogenating agent in the preparation of HNS, and the molar ratio of n(TNT):n(DABCO) was 1:0.036.

[0013] In the above experimental method, tetrabutylammonium tetrafluoroborate (THN) is used in the preparation of HNS. n Bu4NBF4) is an electrolyte, and the molar ratio of n(TNT):n( n Bu4NBF4)=1∶0.012

[0014] The present invention designs an electrochemical reactor that simultaneously realizes static mixing and electrochemical reaction. The planar static mixer is laser-treated to form a channel with a special structure, so that the fluid flowing through the mixer can simultaneously achieve static mixing and contact with the electrode plate.

[0015] The efficient preparation of HNS was achieved by designing an electrochemical reactor. While TNT and NaClO solution were fully mixed, the byproduct HNBB was electrochemically oxidized to HNS. Using parallel graphite plates as electrodes, a small amount of electrolyte and dehydrogenating agent were added, and the reaction was carried out under a constant current of 8-10 mA for 30 min. The yield reached 50.38% and the purity was >99%.

[0016] The advantages of this invention are: (1) The electrochemical reactor has a stable structure, is easy to disassemble and install, and has a high selectivity for static mixers and electrodes. It can simultaneously achieve static mixing and electrochemical oxidation-reduction. Mixing does not require any power source, and electrochemical oxidation-reduction can be achieved under a small gradient current. (2) It achieves efficient preparation of HNS. The method is simple, easy to implement, green and mild. The amount of electrolyte and dehydrogenating agent used is greatly reduced. The yield can reach 50.38% after 30 minutes of reaction, which is conducive to the preparation of HNS at the hundred-gram level and industrial production. Attached Figure Description

[0017] Figure 1 This is a structural diagram of a planar static mixer.

[0018] Figure 2 This is a structural diagram of an electrochemical reactor.

[0019] Figure 3 Mass fraction distribution of liquid in a planar static mixer.

[0020] Figure 4 A graph showing the velocity distribution of liquid in a planar static mixer as a function of Reynolds number.

[0021] Figure 5 A graph showing the pressure of a liquid in a planar static mixer as a function of the Reynolds number.

[0022] Figure 6 Graph showing the change in reaction yield with current.

[0023] Figure 7 Graph showing the change in reaction yield over reaction time.

[0024] Figure 8 The graph shows the change in reaction yield with the amount of nBu4NBF4 added.

[0025] Figure 9 The graph shows the change in reaction yield with the amount of DABCO added.

[0026] Figure 10 The graph shows the change in reaction yield with the feed flow rate of sodium hypochlorite solution.

[0027] Figure 2In the diagram, 1 is a cylindrical head screw, 2 is a washer, 3 is a stainless steel plate, 4 is a heat insulation layer, 5 is a fixing screw, 6 is a graphite electrode plate, 7 is a copper stud for power connection, 8 is a fixing cylinder, 9 is a sealing washer, 10 is a planar static mixer, 11 is a bonding plate, and 12 is a cap nut. Detailed Implementation

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] In the electrochemical reactor of this invention, static mixing is achieved through a designed planar static mixer. Mixing pipes are designed on a planar plate, and the fluid is diverted by a sharp change in pipe diameter and obstructions with special structures on the pipes, resulting in a rapid decrease in velocity and the generation of vortices, thereby improving the mixing quality. Figure 1 Structure ①.

[0030] Electrochemical reactions depend on the contact between the fluid and the electrode plates, which necessitates that the pipes on the planar static mixer be etched through, structure ① ( Figure 1 This creates a hollowed-out structure, which is impossible in actual manufacturing. Therefore, we will use structure ① ( Figure 1 Laser etching is used to create deep grooves, promoting fluid mixing. The next structure is ② ( Figure 1 Laser etching triggers an electrochemical reaction, thus enabling the simultaneous realization of static mixing and electrochemical reaction.

[0031] To ensure structure ② ( Figure 1 The ability to contain a certain volume of liquid for electrochemical reactions presents a challenge in terms of material fabrication for planar static mixers. Conventional materials such as glass and PTFE cannot achieve centimeter-level thicknesses, so we chose silicon carbide. Currently available electrochemical reactors do not incorporate static mixing and mostly employ overlapping electrode plates sealed with PTFE gaskets. This structure is unstable, prone to leakage, and only supports small volumes of reaction liquid and short reaction times.

[0032] Specifically, a planar static mixer is provided, comprising: a fluid pipeline frame consisting of alternating peach-shaped channels and straight pipes, with the pipe diameters changing alternately; processing of the peach-shaped channels to form alternating static mixing units and electrochemical units; laser-etched grooves to form static mixing units, with V-shaped diverters and cylinders installed within the static mixing units; and laser-etched through-holes to form electrochemical units.

[0033] The electrochemical reactor is configured in sequence as a stainless steel plate 3, a heat insulation layer 4, a graphite electrode plate 6, a planar static mixer 10, and a bonding plate 11; the graphite electrode plate 6, the heat insulation layer 4, and the stainless steel plate 3 are symmetrically arranged on the other side of the bonding plate 11.

[0034] A cylindrical head screw 1, a washer 2, and a cap screw are installed on one side of the stainless steel plate 3 to fix the entire electrochemical reactor.

[0035] A copper stud 7 for power connection and a fixed cylinder 8 are provided on the graphite electrode plate. The fixed cylinder 8 is used to fix the planar static mixer 10. The heat insulation layer 4 is provided with a groove for placing the copper stud 7 for power connection.

[0036] Sealing gaskets 9 are provided between the graphite electrode plate 6 and the planar static mixer 10, and between the other graphite electrode plate 6 symmetrically arranged and the bonding plate 11.

[0037] The present invention enables the fluid to be effectively mixed when it flows through the planar static mixer 10 and to undergo an electrochemical oxidation-reduction reaction when it comes into contact with the electrode plate.

[0038] In the planar static mixer 10, the static mixing unit improves the mixing quality by promoting fluid diversion and changing the velocity direction, and the cylinder improves the mixing quality by obstructing fluid flow and changing the velocity magnitude; the electrochemical unit ensures that the fluid transports electrons to undergo electrochemical reactions.

[0039] Example 1

[0040] Fluid flow behavior was simulated using CFD based on the Reynolds-averaged Navier-Stokes (RANS) equations. A Mixture multi-component flow model was employed, with the turbulence model set to the standard k-ε model. The three-dimensional reactor model was built using Solidworks 2021, and the computational mesh was created using Fluent's built-in mesh generator. The phase-coupled SIMPLE algorithm was used, with velocity-inlet boundary conditions at the inlet. TNT solution was used as solution 1, and NaClO aqueous solution as solution 2. Changing the feed rate effectively homogenized the fluid mass fraction. Figure 3 The two materials are black at the inlet, turn white and dark gray after initial mixing, and turn gray when fully mixed, with each accounting for 0.5% of the mass fraction.

[0041] Example 2

[0042] Fluid flow behavior was simulated using CFD based on the Reynolds-averaged Navier-Stokes (RANS) equations. A Mixture multi-component flow model was employed, with the standard k-ε turbulence model used. The 3D reactor model was created using Solidworks 2021, and the computational mesh was generated using Fluent's built-in mesh generator. The phase-coupled SIMPLE algorithm was used, with velocity-inlet boundary conditions at the inlet. TNT solution was used as solution 1, and NaClO aqueous solution as solution 2. Simulations were performed under the following four conditions, varying the feed velocity: ① u1 = 0.15 m / s, u2 = 0.05 m / s ② u1 = 0.25 m / s, u2 = 0.15 m / s ③ u1 = 0.35 m / s, u2 = 0.25 m / s ④ u1 = 0.45 m / s, u2 = 0.35 m / s. The fluid velocity distribution is shown below. Figure 4 .

[0043] Example 3

[0044] Fluid flow behavior was simulated using CFD based on the Reynolds-averaged Navier-Stokes (RANS) equations. A Mixture multi-component flow model was employed, with the standard k-ε turbulence model used. The 3D reactor model was created using Solidworks 2021, and the computational mesh was generated using Fluent's built-in mesh generator. The phase-coupled SIMPLE algorithm was used, with velocity-inlet boundary conditions at the inlet. TNT solution was used as solution 1, and NaClO aqueous solution as solution 2. Simulations were performed under four conditions with varying feed velocities: ① u1 = 0.15 m / s, u2 = 0.05 m / s ② u1 = 0.25 m / s, u2 = 0.15 m / s ③ u1 = 0.35 m / s, u2 = 0.25 m / s ④ u1 = 0.45 m / s, u2 = 0.35 m / s. The fluid pressure variation trend is shown below. Figure 5 .

[0045] Example 4

[0046] Weigh 0.01 mol TNT and dissolve it in a mixed solvent of 10 ml methanol and 20 ml tetrahydrofuran, and use this as material 1. Measure 10 ml of a 5% NaClO solution, dilute it with 8 ml of water, and use this as material 2. Control the feed flow rate of solution 1 at 7 ml / min, control the feed flow rate of solution 2 at 4 ml / min, control the pH of the reaction solution at 9.5-10.5, and add 0.04 g of [amount missing]. n Bu4NBF4 and 0.04g DABCO were mixed, and the power supply was turned on. The reaction current was adjusted to 6mA, 8mA, 10mA, 12mA, and 15mA, and the reaction was carried out for 30 minutes. The change in reaction yield with current is as follows: Figure 6.

[0047] Example 5

[0048] Weigh 0.01 mol TNT and dissolve it in a mixed solvent of 10 ml methanol and 20 ml tetrahydrofuran, and use this as material 1. Measure 10 ml of a 5% NaClO solution, dilute it with 8 ml of water, and use this as material 2. Control the feed flow rate of solution 1 at 7 ml / min, control the feed flow rate of solution 2 at 4 ml / min, control the pH of the reaction solution at 9.5-10.5, and add 0.04 g of [amount missing]. n Bu4NBF4 and 0.04g DABCO were reacted with a power source and the reaction was carried out at a constant current of 8-10mA. The reaction times were changed to 15min, 20min, 25min, 30min, and 35min. The change in reaction yield with reaction time is shown below. Figure 7 .

[0049] Example 6

[0050] Weigh 0.01 mol TNT and dissolve it in a mixed solvent of 10 ml methanol and 20 ml tetrahydrofuran, and use this as material 1. Measure 10 ml of a 5% NaClO solution, dilute it with 8 ml of water, and use this as material 2. Control the feed flow rate of solution 1 to 7 ml / min, control the feed flow rate of solution 2 to 4 ml / min, control the pH of the reaction solution to 9.5-10.5, add 0.04 g DABCO, and change... n The addition amounts of Bu4NBF4 were 0 g, 0.02 g, 0.04 g, 0.06 g, and 0.08 g, respectively. With the power supply on, the reaction was carried out at a constant current of 8-10 mA for 30 minutes. The reaction yield increased with... n The change in the amount of Bu4NBF4 added is as follows: Figure 8 .

[0051] Example 7

[0052] Weigh 0.01 mol TNT and dissolve it in a mixed solvent of 10 ml methanol and 20 ml tetrahydrofuran, and use this as material 1. Measure 10 ml of a 5% NaClO solution, dilute it with 8 ml of water, and use this as material 2. Control the feed flow rate of solution 1 at 7 ml / min, control the feed flow rate of solution 2 at 4 ml / min, control the pH of the reaction solution at 9.5-10.5, and add 0.04 g of [amount missing]. n Bu4NBF4, with varying amounts of DABCO added (0g, 0.02g, 0.04g, 0.06g, 0.08g), power was connected, and the reaction was carried out at a constant current of 8-10mA for 30 minutes. The reaction yield changed with the amount of DABCO added as follows: Figure 9 .

[0053] Example 8

[0054] Weigh 0.01 mol TNT and dissolve it in a mixed solvent of 10 ml methanol and 20 ml tetrahydrofuran, and use this as material 1. Measure 10 ml of a 5% NaClO solution, dilute it with 8 ml of water, and use this as material 2. Control the pH of the reaction solution to 9.5-10.5, and add 0.04 g of [amount missing]. n Bu4NBF4 and 0.04g DABCO were added, and the power was turned on. The reaction was carried out at a constant current of 8-10mA for 30 minutes. The feed flow rate of sodium hypochlorite solution was controlled at 3ml / min, 4ml / min, 5ml / min, 6ml / min, and 7ml / min. To ensure that both materials were completely fed into the reactor within the same time, the difference in liquid viscosity could be ignored when the pipe inner diameter was 1.6mm. The corresponding feed flow rates of TNT solution were 5ml / min, 7ml / min, 8ml / min, 10ml / min, and 12ml / min. The reaction yield changed with the feed flow rate as follows: Figure 10 The crude product was purified by boiling in nitric acid and acetone, followed by recrystallization. The purity of the product was determined by liquid chromatography and melting point measurement. The purity of the purified product was >99%.

[0055] The designed electrochemical reactor enabled the efficient preparation of HNS. Compared to the methods used by Shipp, Salter, and others, this reactor utilizes electric current to convert the byproduct HNBB into the product HNS, thus shortening the reaction time and increasing the yield. Compared to the method used by Zou Jiedong et al., which involves collecting the reaction solution using a tubular mixer and electrochemically dehydrogenating the byproduct using a graphite rod as the anode and a platinum sheet as the cathode, this designed electrochemical reactor can simultaneously perform static mixing and electrochemical reaction, achieving continuous and efficient preparation. This reduces the amount of electrolyte added, shortens the reaction time, improves purity, and saves costs and energy consumption.

Claims

1. A planar static mixer, characterized in that, The planar static mixer includes: a fluid piping framework consisting of alternating peach-shaped channels and straight pipes, with the pipe diameters changing alternately; processing of the peach-shaped channels to form alternating static mixing units and electrochemical units; laser-etched grooves to form static mixing units, with V-shaped diverters and cylinders installed within the static mixing units; and laser-etched through sections to form electrochemical units. The planar static mixer is made of silicon carbide.

2. An electrochemical reactor integrating static mixing and electrochemical reaction based on the planar static mixer of claim 1, characterized in that, The electrochemical reactor is sequentially configured with a stainless steel plate, a heat insulation layer, a graphite electrode plate, a planar static mixer, and a bonding plate. Graphite electrode plates, heat insulation layers, and stainless steel plates are symmetrically arranged on the other side of the bonding plate.

3. The electrochemical reactor according to claim 2, characterized in that, The entire electrochemical reactor is fixed by cylindrical head screws, washers, and cap screws on one side of the stainless steel plate.

4. The electrochemical reactor according to claim 2, characterized in that, The graphite electrode plate is equipped with a copper stud for power connection and a fixed cylinder. The fixed cylinder is used to fix the planar static mixer. The heat insulation layer is provided with grooves for placing the copper stud for power connection.

5. The electrochemical reactor according to claim 2, characterized in that, Sealing gaskets are provided between the graphite electrode plate and the planar static mixer, as well as between the other symmetrically arranged graphite electrode plate and the bonding plate.

6. A reaction method based on an electrochemical reactor according to any one of claims 2-5, characterized in that, Fluids flowing through a planar static mixer can be effectively mixed and come into contact with the electrode plates to undergo electrochemical oxidation-reduction. In the static mixing unit, the mixing quality is improved by promoting fluid diversion and changing the velocity direction, while the cylinder improves the mixing quality by obstructing fluid flow and changing the velocity magnitude. The electrochemical unit ensures that the fluid transports electrons and undergoes an electrochemical reaction.

7. The reaction method of the electrochemical reactor as described in claim 6, characterized in that, The process conditions for preparing HNS using an electrochemical reactor are as follows: TNT is dissolved in a mixture of methanol and tetrahydrofuran as one solution, and a 5% (w / w) NaClO solution with available chlorine is mixed with water to form another liquid stream. The volume ratio of methanol to tetrahydrofuran is 1:2; the molar ratio of TNT to NaClO is 1:1.2; and the volume ratio of NaClO to H2O is 1:

1. The feed flow rate of the TNT solution is 6-7 ml / min, and the feed flow rate of the NaClO aqueous solution is 4-5 ml / min. The constant current of the reaction system is controlled at 8-10 mA, and the reaction is carried out at room temperature (26°C) for 30 min.

8. The reaction method of the electrochemical reactor as described in claim 7, characterized in that, Triethylenediamine (DABCO) was used as a dehydrogenating agent, and the amount added was in molar form, n(TNT):n(DABCO) = 1:0.

036.

9. The reaction method of the electrochemical reactor as described in claim 7, characterized in that, Using tetrabutyltetrafluoroborate ammonium as the electrolyte, the amount added is expressed in moles as n(TNT):n( n Bu4NBF4) = 1:0.012.

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