GB2578292A

GB2578292A - Flow reactor

Info

Publication number: GB2578292A
Application number: GB1816908.6A
Authority: GB
Inventors: Guthrie Duncan
Original assignee: Vapourtec Ltd
Current assignee: Vapourtec Ltd
Priority date: 2018-10-17
Filing date: 2018-10-17
Publication date: 2020-05-06
Also published as: GB201816908D0

Abstract

An electrochemical flow reactor 30 comprising: first and second housings 31, 32, each having a protruding seal 33 forming a closed loop on an inner face thereof; a fluid inlet 42 and a fluid outlet 42; first and second electrode plates 34, 35; a substantially planar membrane 36 having a cut-out pattern formed therein; wherein the first and second housings cooperate to releasably sandwich the membrane between the electrode plates and between the respective seals such that the cut-out pattern forms a reaction chamber between the electrodes and in fluid communication with the fluid inlet and the fluid outlet, and such that the seals and membrane form a fluid-tight seal. The cut-out pattern may form a convoluted path. The electrochemical reactor may allow electrochemical reactions to be conducted at pressures above atmospheric. The electrochemical reactor may ensure that any reagents which leak from the reaction chamber are only in contact with a single electrode to avoid unwanted reaction away from the reaction chamber. A method of conducting an electrochemical flow reaction is also provided.

Description

FLOW REACTOR

Field of the Invention

The present invention relates to a flow reactor. It is particularly, but not exclusively, concerned with flow reactors that can be used to carry out electrochemical reactions.

Background of the Invention

Electrosynthesis is performed by passing an electric current through a reagent solution, causing oxidation and reduction of organic molecules by addition or removal of electrons.

Electrosynthesis has a number of advantages compared to other forms of synthesis. In particular: it is possible to generate reactive species without the need for hazardous oxidising and reducing agents; electrochemical reactions can be highly selective; and electrochemical reactions can be carried out using relatively mild conditions of temperature and pressure (i.e. close to room temperature and atmospheric pressure).

Electrochemistry can also define the electron energy directly via over-potential, helping to avoid the formation of undesired by-products. Accordingly, under the principles of 'Green Chemistry", electrochemistry has high atom economy and low waste.

However, electrochemistry is not a technique which is routinely used in the organic chemistry lab. Mainly this is because equipment has never been available in an easy-to-use format, and because batch electrosynthesis generally requires high concentrations of electrolytes.

During the past 10 years there has been increased interest in electrochemistry particularly as a result of the drive towards green, atom-efficient chemistry. Integrating electrochemistry with continuous flow potentially offers a powerful combination. The requirement for electrolytes can be eliminated because the electrodes can be maintained with a spacing of a fraction of a millimetre. Further, under continuous flow conditions reactions have improved selectivity because the reaction products are removed from the reactor and are not allowed to mix with unreacted starting materials.

However, there are still only a few commercially-available electrochemical flow reactors such as the Asia Flux made by Syrris Ltd. of Royston, UK and the Ammonite family of electrolysis cells made by Cambridge Reactor Design of Cottenham, UK.

Existing electrochemical flow reactors suffer from a number of disadvantages. In particular, in many products, the reactor chamber is machined into one of the electrode plates. This limits the material that this electrode plate can be manufactured from, normally to either stainless steel or a carbon loaded polymer, for example polyviitylidene fluoride (EVE*/ As different electrochemical reactions can require, or are preferably performed with, specific electrodes, this limits the utility of such reactors.

Further, in many products, it is not possible to maintain a pressure much greater than atmospheric pressure in the reactor chamber. In many products, a complex arrangement of several bolts is used to secure the components of the reactor together and thereby seal the reactor chamber. However, a slight unevenness in the tightness of any of these bolts can result in a weaker seal on one side of the reactor which is vulnerable to leakage if the reactor chamber is pressurised more than slightly above atmospheric pressure. Further, in many products, the seal around the reactor is formed, at least in part, by one or both of the electrodes. This means that if reagents are able to escape the defined reactor chamber, they may continue reacting outside the reactor chamber because reagents in this region are able to contact both anode and cathode simultaneously.

An object of the present invention is to provide a flow reactor suitable for electrochemistry which allows the electrodes used to be freely selected.

A further object of the present invention is to provide a flow reactor suitable for electrochemistry which allows electrochemical reactions to be conducted under pressure without risk of reagents or reaction products leaking from the reactor.

A further object of the present invention is to provide a flow reactor suitable for electrochemistry which can be simply and efficiently assembled and disassembled to permit cleaning and interchange of electrodes.

Aspects of the present invention aim to provide a flow reactor suitable for electrochemistry which satisfies one or more of the above objects.

Summary of the Invention

At their broadest, aspects of the present invention provide an electrochemical flow reactor and a method of conducting an electrochemical flow reaction in which the reactor chamber is defined in a membrane which is sealed between the housings which encompass the chamber.

A first aspect of the present invention provides an electrochemical flow reactor including: first and second housings, each having a protruding seal forming a closed loop on an inner face thereof; a fluid inlet and a fluid outlet; first and second electrode plates; a substantially planar membrane having a cut-out pattern formed therein; wherein the first and second housings cooperate to releasably sandwich the membrane between the electrode plates and between the respective seals such that the cut-out pattern forms a reaction chamber between the electrodes and in fluid communication with the fluid inlet and the fluid outlet, and such that the seals and membrane form a fluid-tight seal.

By sandwiching the membrane between the seals, most, preferably all, reagents that may leak from the reaction chamber are retained within the reactor. Furthermore, as the membrane is between the electrode plates and extends to the edge of the sealed volume (and potentially beyond), most, preferably all, reagents that may leak from the reaction chamber are only ever in contact with one of the electrode plates as they are insulated from the other electrode plate by the membrane.

Preferably the membrane is an insulator. k particular embodiments the membrane may be made from poi yteirafl uoroethylene (PTFE) or a perfluoitalkoxy alkane (PEA).

The reactor may further include a clamp arranged to releasably clamp the first and second housings together. By clamping the housings together a strong seal can be formed between the seals and the membrane.

The clamp preferably involves a single moving part which is operable to clamp the housings together and to release them. This can enable a strong and secure seal of the reactor to be obtained in a consistent manner and without significant time and effort.

Sealing the reactor can allow electrochemical reactions to be conducted in the reaction chamber at pressures above atmospheric. Preferably the seal is such that reactions can be conducted at pressures of 2 bar or above, more preferably 5 bar or above. There are three potential benefits from carrying out electrochemical reactions at higher pressure: 1) it allows solvents to be raised to temperatures well above their normal boiling points (e.g. using methanol in electrochemical reactions at 100°C); 2) pressurised reaction conditions give the ability to control the volume of any gaseous reagents within the reactor; and 3) an electrochemical reaction step can be "telescoped" with a subsequent reaction step that may require significant pressure to operate efficiently. For example, a subsequent reaction step may require a mixing intensive step generating significant back pressure or a thermal reaction step where operation at high pressure is required to prevent boiling of solvents.

In some embodiments the clamp includes: a frame, the frame having a planar member disposed on one side and arranged to engage with a face of the first housing opposite the inner face of said housing; and a moveable member arranged opposite the planar member and movable to impart a clamping force on the face of the second housing opposite the inner face of said housing.

Clamping in this manner provides a simple, single-point clamping operation which can provide a strong and consistent seal.

The moveable member may have a screw-thread which engages with the frame such that rotation of the moveable member causes the clamping force on the second housing to increase or decrease. This allows the clamp to be tightened or loosened by turning the moveable member and can provide for easy securing and release of the reactor.

Preferably the first and second electrode plates are removable from the reactor. By having removable electrode plates, the reactor can be easily cleaned. Preferably the electrode plates are also exchangeable. Different electrochemical reactions require (or work better with) particular types of electrodes. By providing exchangeable reactor plates, the range of electrochemical reactions that can be performed in the reactor is significantly increased.

Reactions which require sacrificial electrodes can also be readily performed as the sacrificial electrode can be removed and replaced.

The reactor may further include a locating pin on one of the housings and a corresponding recess on the other of the housings. The locator pin may assist in ensuring a consistent and accurate location of one of more of the electrode plates and/or the membrane within the reactor and/or relative to each other. In some embodiments, one or more of the first electrode plate, the second electrode plate and the membrane have a hole through which the locating pin passes.

Preferably the pattern on the membrane forms a convoluted path from a first end which is in fluid communication with the fluid inlet and a second end which is in fluid communication with the fluid outlet. By having a convoluted path, the length of the reactor chamber can be increased and/or maximised whilst retaining the overall size of the reactor reasonably compact.

In certain embodiments the reactor has means for heating and/or cooling the reactor. For example, at least one of the first and second housings may have a heat-conducting element extending from the housing to a heat-exchanger to allow heating and cooling of the flow 25 reactor.

The reactor may also include a temperature sensor. The reactor may include or be connected to a controller which monitors the temperature of the reactor and adjusts the heating/cooling of the reactor accordingly.

The reactor of this aspect may include any combination of some, all or none of the above-described preferred and optional features.

A second aspect of the present invention provides a method of conducting an electrochemical flow reaction, the method including the steps of: forming a reaction chamber by assembling, between first and second housings, first and second electrode plates and a substantially planar membrane having a cut-out pattern formed therein, such that the membrane is sandwiched between the electrode plates and between first and second seals each forming a closed loop on an inner face on a respective one of the first and second housings, and such that the cut-out pattern forms a reaction chamber between the electrodes; and passing reagents through the reactor chamber whilst a potential is applied between the first and second electrodes.

By forming the reaction chamber with the membrane sandwiched between the seals, most, preferably all, reagents that may leak from the reaction chamber are retained within the reactor. Furthermore, as the membrane is between the electrode plates and extends to the edge of the sealed volume (and potentially beyond), most, preferably all, reagents that may leak from the reaction chamber are only ever in contact with one of the electrode plates as they are insulated from the other electrode plate by the membrane.

Preferably the membrane is an insulator. In particular embodiments the membrane may be made from polytetrafluomerhylene (PTFE) or a perfluoroalkoxy alkane (RE A).

The method may further include the step of, prior to forming the reaction chamber, selecting either or both of the electrode plates based on the reaction to be conducted. Different electrochemical reactions require (or work better with) particular types of electrodes. By selecting the appropriate reactor plates before forming the reaction chamber, the range of electrochemical reactions that can be performed in the reactor is significantly increased. Reactions which require sacrificial electrodes can also be readily performed as the sacrificial electrode can be removed and replaced after the reaction is complete.

The reagents in the reactor chamber may be maintained at a pressure in excess of atmospheric pressure. The reactions may be conducted at pressures of 2 bar or above, optionally at 5 bar or above. There are three potential benefits from carrying out electrochemical reactions at higher pressure: 1) it allows solvents to be raised to temperatures well above their normal boiling points (e.g. using methanol in electrochemical reactions at 100°C); 2) pressurised reaction conditions give the ability to control the volume of any gaseous reagents within the reactor; and 3) an electrochemical reaction step can be "telescoped" with a subsequent reaction step that may require significant pressure to operate efficiently. For example, a subsequent reaction step may require a mixing intensive step generating significant back pressure or a thermal reaction step where operation at high pressure is required to prevent boiling of solvents.

The method may further include the step of clamping the first and second housings together to create a fluid-tight seal around the reactor chamber.

The method may further include the step of sensing the temperature of the reagents in the reactor chamber during the reaction. Preferably the method further includes the step of controlling the temperature of the reagents in the reactor chamber during the reaction.

For example, this may include heating and/or cooling the reactor chamber depending on the sensed temperature. The heating or cooling may be achieved by, for example, a hot/cold air flow which acts to cool one or both of the housings, for example, by passing over a heat exchanger which is in thermal communication with the housing(s).

The method of this aspect may be performed using a flow reactor according to the above-described first aspect, but need not be.

The method of this aspect may include any combination of some, all or none of the above-described preferred and optional features.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 shows an electrochemical flow reactor according to an embodiment of the present invention; Fig. 2 is an exploded view of the electrochemical flow reactor of Fig. 1; Fig. 3 is an exploded view of the main components of the reactor unit of the electrochemical flow reactor of Figs. 1 and 2; and Fig. 4 shows the membrane used in the electrochemical flow reactor of Figs. 1-3.

Detailed Description

Fig. 1 shows an electrochemical flow reactor 1 according to an embodiment of the present invention. Fig. 2 is an exploded view of this flow reactor 1 and the same reference numerals are used for the components which are also visible in Fig. 1.

The electrochemical flow reactor 1 is made up of three main components: a heat exchanger unit 10, a clamp 20 and a reactor unit 30 which is shown in Fig. 1 clamped by the clamp 20 as it would be in use.

The some of the main components of the reactor unit 30 are shown in more detail in the exploded view of Fig. 3. The reactor unit 30 has a first housing element 31 and a second housing element 32 which together form the exterior of the reactor unit. The housing elements 31, 32 are typically machined from 316 grade stainless steel or a carbon loaded polymer such as polyvinylidene fluoride (PVDF).

Each housing element 31, 32 has a seal 33 associated with it, which sits in a groove 41 around the periphery of the inner face of the respective housing element.

The first housing element 31 has a plurality of fluid ports 42 formed in it, including an inlet port and an outlet port, which provide fluid communication for reagents from the exterior of the reactor to the reactor chamber which is formed when the reactor unit is sealed. The fluid ports 42 are in fluid communication with corresponding access points 43 in the exterior of the first housing unit 31. Other access points 43 in the first and second housing elements 31, 32 provide for electrical connection points for the electrode plates 34, 35, for the insertion of, or connection to, a temperature sensor and for additional or alternative fluid connections.

Two electrode plates 34, 35 are provided on the interior of the housing elements. The electrode plates are smaller than the area encompassed by the seals 33 and therefore are seated inside of the seals when the reactor unit 30 is assembled. The electrode plates have through holes 44 which allow fluid to pass from the ports 42 to the interior of the reactor unit.

Between the two electrode plates 34, 35 is an impermeable membrane 36. The membrane is shown in greater detail in Fig. 4. In this embodiment the membrane is formed from either polytetrafluoroethylene (I IFE) or a perfluoroalkoxy aikane (PFA) and has a pattern cut into it by laser machining which defines a convoluted flow path 37 from an inlet point 39 to an outlet point 40. The convoluted path forms a relatively long channel within the overall size of the reactor unit and maintains a narrow residence time distribution. The path narrows adjacent to each of the fluid inlets to create an even pressure on the o-ring seal at the fluid inlet.

The membrane 36 also has a number of locator holes 38 which engage with locator pins (not shown) to fix the lateral position of the membrane 36 relative to the housing elements 31, 32. The arrangement of locator holes shown in Figs. 3 & 4 allows the locator pins to also be used to locate the edges of the electrode plates 34, 35 to assist or ensure correct positioning. In other embodiments, the electrode plates 34, 35 may also be provided with locator holes which engage with the locator pins to assist or ensure correct positioning. It will be appreciated that, whilst the membrane 36 shown in Fig 4 has four such locator holes 38 arranged in pairs near two of the corners of the membrane, the number and location of the locator holes can vary.

The membrane is dimensioned such that it covers an area larger than the area defined by the seals 33. In this way, when the reactor unit 30 is assembled, the membrane 36 is sandwiched between the seals 33, and the housing elements 31, 32 and the seals 33 form a fluid-tight enclosed space in which are disposed the electrode plates 34, 35 either side of the membrane 36. In this configuration, the flow path 37 in the membrane 36 forms an elongate, convoluted reaction chamber which runs from the inlet port, which is in communication with the inlet point 39 to the outlet port which is in communication with the outlet point 40. Except in the area of the flow path 37, the membrane 36 forms a layer of insulation between the two electrode plates 34, 35 thereby reducing or preferably preventing the possibility of unwanted reaction outside the reaction chamber.

The reaction chamber is bounded on either side of the membrane by the electrode plates 34, 35 making the reaction chamber suitable for carrying out electrochemical reactions as fluid passes through the reaction chamber from the inlet port to the outlet port.

In the assembled reactor unit 30, any fluid that escapes from the flow path 37 cannot escape from the reactor unit 30 as the seals 33 and the membrane 36 form a fluid-tight seal.

Further, fluid that escapes from the flow path 37 will always be insulated from one of the electrode plates 34, 35 by the membrane 36, thereby reducing or eliminating the possibility of an electrochemical reaction occurring in the escaped fluid.

It can also be seen from Fig. 3 that all of the parts of the reactor unit 30 can be separately removed and cleaned or interchanged with alternative units. This allows, for example, for different electrode plates 34, 35 to be used for the cathode and anode of the electrochemical reactor 1, depending on the reaction which is to be performed. By way of examples: the electrochemical conversion of benzylamine to dibenzylamine requires a platinum anode and a carbon cathode; the oxidation of toluene requires a carbon anode and a stainless steel cathode; the electrochemical nickel catalysis sp2-sp3 cross-electrophile coupling reactions of unactivated alkyl halides have been completed using a carbon cathode and sacrificial anode of either aluminium, magnesium, zinc or iron.

Fig. 2 illustrates how the reactor unit 30 is assembled within the clamp 20. The housing elements 31, 32 cooperate to sandwich the membrane 36 between the seals 33 and thus seal the reaction chamber.

The clamp 20 includes two end plates 21, 22 which are joined by supports 26 in each corner. A rubber 0-ring 25 is positioned on one of the end plates 22. The other end plate 21 has a threaded hole 27 located in the centre of it through which passes a threaded screw 24 to which a securing wheel 23 is attached.

Generally, the end plates 21, 22 and supports 26 are assembled in advance and are not detachable from each other. However, in Fig. 2 these components are show in an exploded view so that their inter-relationship with each other and with the reactor unit 30 can be understood.

Once assembled, the reactor unit 30 slides in between the end plates 21, 22 (in the vertical direction of Fig. 2). The reactor unit is secured in place and securely sealed by rotation of the securing wheel 23 such as to cause the tip of the threaded screw 24 to bear against the outer face of the first housing element 31 and force it into contact with the 0-ring 25.

The action of the threaded screw 24 and the 0-ring 25 against the housing elements 31, 32 of the reactor unit 30 forces the seals 33 and the membrane 36 into tight contact with each other, thereby sealing the reactor unit 30 and preventing fluid in the reactor chamber from escaping from the reactor unit 30 even at pressures significantly above atmospheric, potentially up to 5 bar of internal pressure.

As the threaded screw 24 provides a single force urging the housing elements 31, 32 towards each other, a uniform seal around the periphery of the reactor unit 30 can be achieved. Moreover, using a single securing wheel 23 makes assembly and disassembly of the reactor unit 30 considerably quicker and simpler than arrangements in which a plurality of securing bolts are required to be tightened or released.

When a reaction has been completed, the reactor unit 30 can be released from the clamp 20 by using the securing wheel 23 to loosen the threaded screw. The reactor unit 30 can then be removed from the clamp and taken apart for cleaning and/or exchange of components.

As shown in Figs. 1 and 2, a heat exchanger 10 is connected to the reactor unit 30 by a plurality of heat pipes 11 which run from the first housing element 31 to the heat exchanger 10. In the embodiment shown, there are 4 heat pipes 11 which are thin-walled copper tubes sealed under vacuum containing a small, prescribed amount of working fluid.

When the reactor is not operating, the fluid is contained inside a wick structure that lines the inner diameter of the heat pipe. When the electrochemical reactor generates heat, the fluid vaporizes at evaporator section and the fluid vapour quickly spreads to the other end of the heat pipe, using pressure generated by the temperature difference. When the fluid reaches the opposite end (in the heat exchanger), the fluid condenses, releasing its latent heat to the heat exchanger and the wick structure passively returns the fluid back to the evaporator using capillary action. However, it will be appreciated that heat pipes of different construction can be used and the number, shape and configuration of these can differ from that shown.

The heat exchanger 10 is formed as a box 12 through which a large number of gas passages are provided which, inside the box 12, pass over baffles or fins 13 which are connected to the heat pipes 11. In this manner the passage of hot or cold air through the box 12 can heat or cool the baffles or fins in the heat exchanger, with the heat being conducted to or from the housing element 31 which in turn regulates the temperature of the reactor unit 30 and the reagents inside the reaction chamber.

A fan (not shown) may be arranged to direct air through the box 12 and may be configured in conjunction with a heater or a chiller of any construction to adjust the temperature of the air being supplied. A temperature sensor may be provided in the heat exchanger 10, or in the reactor unit 30 (or both) to provide a sensor feedback to enable temperature control by a controller.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

Claims 1. An electrochemical flow reactor including: first and second housings, each having a protruding seal forming a closed loop on an inner face thereof; a fluid inlet and a fluid outlet; first and second electrode plates; a substantially planar membrane having a cut-out pattern formed therein; wherein the first and second housings cooperate to releasably sandwich the membrane between the electrode plates and between the respective seals such that the cut-out pattern forms a reaction chamber between the electrodes and in fluid communication with the fluid inlet and the fluid outlet, and such that the seals and membrane form a fluid-tight seal.
2. An electrochemical flow reactor according to claim 1 further including a clamp arranged to releasably clamp the first and second housings together.
3. An electrochemical flow reactor according to claim 2 wherein the clamp includes: a frame, the frame having a planar member disposed on one side and arranged to engage with a face of the first housing opposite the inner face of said housing; and a moveable member arranged opposite the planar member and movable to impart a clamping force on a face of the second housing opposite the inner face of said housing.
4. An electrochemical flow reactor according to claim 3 wherein the moveable member has a screw-thread which engages with the frame such that rotation of the 25 moveable member causes the clamping force on the second housing to increase or decrease.
5. An electrochemical flow reactor according to any one of the preceding claims wherein the first and second electrode plates are removable and exchangeable.
6. An electrochemical flow reactor according to any one of the preceding claims further including a locating pin on one of the housings and a corresponding recess on the other of the housings.
7. An electrochemical flow reactor according to claim 6 wherein one or more of the first electrode plate, the second electrode plate and the membrane have a hole through which the locating pin passes.
8. An electrochemical flow reactor according to any one of the preceding claims wherein the pattern on the membrane forms a convoluted path from a first end which is in fluid communication with the fluid inlet and a second end which is in fluid communication with the fluid outlet.
9. An electrochemical flow reactor according to any one of the preceding claims wherein at least one of the first and second housings has a heat-conducting element extending from the housing to a heat-exchanger to allow heating and cooling of the flow reactor.
10. A method of conducting an electrochemical flow reaction, the method including the steps of forming a reaction chamber by assembling, between first and second housings, first and second electrode plates and a substantially planar membrane having a cut-out pattern formed therein, such that the membrane is sandwiched between the electrode plates and between first and second seals each forming a closed loop on an inner face on a respective one of the first and second housings, and such that the cut-out pattern forms a reaction chamber between the electrodes; and passing reagents through the reactor chamber whilst a potential is applied between the first and second electrodes.
11. A method according to claim 10, further including the step of, prior to forming the reaction chamber, selecting either or both of the electrode plates based on the reaction to be conducted.
12. A method according to claim 10 or claim 11, wherein the reagents in the reactor chamber are maintained at a pressure in excess of atmospheric pressure.
13. A method according to any one of claims 10 to 12, further including the step of clamping the first and second housings together to create a fluid-tight seal around the reactor chamber.
14. A method according to any one of claims 10 to 13, further including the step of controlling the temperature of the reagents in the reactor chamber during the reaction.