Field of the invention

The present invention is in a field of continuous flow reaction device for an electrochemical process.

Background to the invention

Electrochemistry is inherently a surface process. The reagents need to be transported towards the electrode surface in order to react. The number of reagents reacting at the electrode surface corresponds to the amount of electrons, i.e. current, transferred over the electric circuit which contains minimal two electrodes: anode and cathode. A way to obtain a higher reaction rate (or higher productivity) is to increase the voltage difference between the anode and cathode. However, upon increasing voltage differences, the transport of the reagents (i.e. mass transport) towards the electrode surface will reach a limit and the current will reach a constant plateau irrespective of the applied voltage difference.

To further increase mass transport, electrochemical reactors, especially those of the filterpress type, are typically equipped with turbulence promotors, i.e. inert obstructions in the flow channel that increase mass transport towards the electrode surface. Although these turbulence promotors improve the mass transport rate, they shield a part of the electrode surface. Moreover, to have optimal performance, high velocity rates and thus flow rates are typically necessary even with turbulence promotors. As a result, the product concentration obtainable in the outlet stream is limited in a single pass through the reactor, which entails that a semi-batch recirculation method is required to obtain desirable conversion and/or expensive downstream separation is required.

A common issue with reactors for electrochemical processes is the limited current density that can be achieved. Merely increasing the surface area of the electrodes does not lead to a proportionate increase of the current density for the same flow/mixing characteristics. For a given reactor, the limiting current density (i.e., maximum achievable current density in the reactor for a certain application) will remain constant regardless of the size of the electrode (assuming other factors are equal).

EP 0 368 513 A2 describes a flow cell having a plurality of cylinders that induce a vortex turbulence in the flow for a variety of applications; one example contains a electrochemical application for which a single cylindrical pillar was used as an electrode, combined with counter electrodes (not pillars) at the beginning and end of the conduit. WO 2019/224376 A1 describes a flow cell having a plurality of static mixing elements, wherein the device is not suited for an electrochemical process.

The present invention provides a new type of reaction device (100) for an electrochemical process that improves upon low limiting current density, which increases the mass transport rate without increasing the flow rate and avoids the need for recirculation.

Figure legends

FIG. 1 is a schematic plan view of a reaction space (upper), and two lower hight crosssections at positions R1 and R2; all the discrete protrusions have the same polarity.

FIG. 2 shows split and recombine pathways for a part of the reaction space of FIG. 1

FIG. 3 is similar to FIG. 1 , wherein the discrete protrusions are split into to two groups, one group having one polarity (white filled diamonds), another group having the opposing polarity (black filled diamonds).

FIG. 4 is similar to FIG. 1 , wherein the discrete protrusions are split into to two groups, one group having one polarity (white filled diamonds), another group having the opposing polarity (black filled diamonds).

FIG. 5 shows a height cross-section of the reaction space, indicating the walls and height (Ht) and width (W) dimension.

FIG. 6 is a detail of a pair of discrete protrusions.

FIG. 7 is a detail of an intercalating configuration of discrete protrusions of opposing polarity. FIG. 8 shows the discrete protrusions of FIG. 7, provided with a removeable insulation layer. FIG. 9 shows the discrete protrusions of FIG. 7, wherein each free end is coated with an electrically insulative layer.

FIGs. 10 to 13 show formation and assembled view of an intercalating configuration of discrete protrusions of opposing polarity. In FIG. 10 parts are separated; in FIG. 11 parts are inserted; in FIGs. 12 (no gap) and 13 (gap) insertion is complete.

FIG. 14 is a detail of a flat top configuration of discrete protrusions.

FIG. 15 is a detail of an aligned configuration of discrete protrusions.

FIG. 16 is similar to FIG. 14 and includes a semi-permeable layer between opposing electrodes.

FIG. 17 is similar to FIG. 15 and includes a semi-permeable layer between opposing electrodes. FIG. 18 is a height cross-section of a reaction block. Panel A shows an exploded view, Panel B shows an assembled view, Panel C shows an assembled view with heat exchanger.

FIG. 19 is a schematic view of the device (100) with the pumping system and voltage generator (300).

FIG. 20 is a three-dimensional view of a pair of electrode inserts for a reaction block that are upper portion (panel B) and lower portion (panel A) of the reaction space.

FIG. 21 is a three-dimensional view of a pair of electrode inserts (panels A and B) for a reaction block that forms a lower portion (panel C) of the reaction space.

FIG. 22: Graph showing limiting current density curves with and without pulsatile flow (frequency = 2.1 Hz and pulse amplitude = 0.4 ml) in an intercalated (two comb) configuration at varying net flow rates. Panel A: 2 ml/min; and Panel: B 15 ml/min.

FIG. 23: Limiting current density curves with varying pulse amplitudes at a set pulsatile flow pulse frequency. Panel A: 0.3 Hz; Panel B:0.6 Hz; Panel 0:1.5 Hz; Panel D:2.1 Hz.

FIG. 24: Limiting current density curves with varying pulsatile flow pulse frequencies at a fixed pulsatile flow pulse amplitude. Panel A: 0.1 ml; Panel B: 0.2 ml; Panel C: 0.3 ml; Panel D: 0.4 ml.

FIG. 25: Various designs of a continuous flow reaction device for an electrochemical process (not to scale). Diagonal hatching indicate cathode electrode (one hatching direction) and anode electrode (other hatching direction), vertical hatching indicates a gasket, and horizontal hatching represents a protrusion (turbulence promotor) that is not an. Panel A: without protrusions (planar electrodes); Panel B: with protrusions which are not electrodes (planar electrodes); Panel C: with protrusions which are electrodes (presently described device).

Summary of the invention

Described herein is a continuous flow reaction device (100) for an electrochemical process comprising:

- a reaction space (110) having a longitudinal (L) direction and transverse (T) direction, (at one longitudinal end) a fluid inlet end (14) and (at an opposing longitudinal end) a fluid outlet end (16), and a forward direction (F) from the inlet end (14) to the outlet end (16);

- a pumping system (200) configured to generate a flow to the fluid inlet end (14), the flow being a pulsatile flow comprising a steady state flow rate and oscillatory flow rate superimposed on the steady state flow rate; - a plurality of discrete protrusions (120, a: 120, b) in contact with the reaction space (110); wherein each discrete protrusion (120, a: 120,b) is configured such that a flow path (150a- 150c) of the fluid contacting an inlet end (14) side of the discrete protrusion is split at least into two daughter flow paths (150b1 ; 150b2) on the outlet end (16) side of the discrete protrusion (120, a: 120, b); and the discrete protrusions (120, a: 120,b) are arranged so that at least one of the daughter flow paths (150b1) generated by one of the plurality of discrete protrusions (120) combines (152a) with at least one of the daughter flow paths (150a2) generated by another of the plurality of discrete protrusions (120) on the outlet end (16) side of both discrete protrusions (120); each discrete protrusion (120) is an electrode in the electrochemical process.

The plurality of discrete protrusions (120, a: 120, b) in the reaction space (110) may be arranged into a plurality of spatially separated columns (C1-C15), wherein the discrete protrusions (120, a: 120, b) of the same column are spatially separated on a common linear line, and the distance between adjacent discrete protrusions (120, a: 120,b) of the same column is the same.

The columns (C1-C15) may be arranged such that the daughter flow paths (150b1) combine (152a) in the spaces between adjacent columns (C1-C15).

The discrete protrusions (120, a; 120,b) of opposing polarity may be intercalated in the reaction space (110).

By discrete protrusions or electrodes of “opposing polarity” it means that the protrusions or electrodes are connected or connectable to opposite polarities of electrical power. Discrete protrusions or electrodes of opposing polarity are not internally wired together. It is understood that a polarity of a discrete protrusion or electrode may stay the same during the electrochemical process (e.g. always anode or always cathode) or may alternate between anode and cathode during the electrochemical process, for instance where there is a power amplitude variation that crosses zero e.g. +0.05 V to -0.05 or +50 V to -50 V.

Each discrete protrusion (120, a: 120, b) of the plurality may be an electrode, a node electrode, of one polarity having at least two closest adjacent discrete protrusions that are electrodes, satellite electrodes, of the same polarity, wherein the node electrode has an opposing polarity to the satellite electrodes.

The plurality of discrete protrusions (120, a; 120, b) is disposed on both a longitudinal upper portion (142) of the reaction space (110) and on a longitudinal lower portion (146) of the reaction space (110), and the discrete protrusions (120, a; 120,b) intercalate when the upper portion (142) and the lower portion (146) are brought together.

Some of discrete protrusions (120, a) of the plurality may be provided on a first support (149a) containing a plurality of through-apertures (147) located between the discrete protrusions (120, a), and some of discrete protrusions (120,b) of the plurality are provided on a second support (149b), wherein the discrete protrusions (120, b) of the second support (149b) are arranged to pass through the through-apertures of the first support (149a), thereby providing the discrete protrusions (120, a; 120, b) of opposing polarity intercalated in the reaction space (110).

The first support (149a) and second support (149b) may form a lower portion (146) of the reaction space (110) and an upper portion (142) of the reaction space (110) is at least partially light-transparent.

Each discrete protrusion (120, a; 120, b) may comprise:

- a base end (126, a) attached to a longitudinal upper base wall (144) or to a longitudinal lower base wall (148) of the reaction space (110);

- a free end (122, a, b) opposing the base end (126, a); and

- the discrete protrusions (120, a; 120, b) of the plurality may be arranged into two groups of opposing polarity, and disposed in the reaction space such that the free ends (122, a) of one group are aligned with the free ends (122, b) of the other group.

Each discrete protrusion (120, a; 120,b) may comprise:

- a base end (126, a) attached to a longitudinal upper base wall (144) or to a longitudinal lower base wall (148) of the reaction space (110);

- a free end (122, a, b) opposing the base end (126, a); and - all the discrete protrusions (120, a; 120, b) of the plurality have the same polarity, and are attached to only one of the longitudinal upper base wall (144) or the longitudinal lower base wall (148).

The reaction space (110) may be provided in a reaction block (102), the reaction block (102) comprising a supporting block (170) comprising a longitudinal well (172) for containment and stacking of a plurality of removeable longitudinal inserts (174, 176, 178, 182), wherein a pair of a longitudinal inserts from the plurality are electrode inserts (176, 178), wherein one or both electrode inserts (176, 178) is disposed with the plurality of discrete protrusions (120, a: 120, b).

One of the longitudinal inserts from the plurality is a spacing/sealing insert (178) providing longitudinal side walls (131 , 132) and first (134) and second (136) end walls (134) of the reaction space.

The reaction block (102) may further comprise a heat exchanger (186).

The device (100) may further comprising a voltage generator (300) for generation of a voltage potential applied across electrodes of opposing polarity, wherein the voltage generator is configured for:

- generation of a voltage, a fixed voltage, at a fixed and continuous level, and/or

- generation of a voltage, a variable voltage, generated at two or more different levels over time, optionally, wherein the variable voltage regularly varies between two or more values, optionally wherein the variable voltage regularly varies between high and low value, and/or between a positive and negative value, and or between a positive/negative value and to zero.

One or both electrode surfaces of opposing polarity may be formed at least partially from an electrocatalyst, and/or may be at least partially coated with an electrocatalyst, and/or

- one or both electrode surfaces of opposing polarity may be formed at least partially from a photocatalyst, and/or may be at least partially coated with a photocatalyst, and/or - one or both electrode surfaces of opposing polarity is/are each partially coated with an electrically insulative layer.

Detailed description

Before the present system and method of the invention are described, it is to be understood that this invention is not limited to particular systems and methods or combinations described, since such systems and methods and combinations may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of', "consists" and "consists of".

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

The term "about" or “approximately” as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/-10% or less, preferably +/-5% or less, more preferably +/-1 % or less, and still more preferably +/-0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" or “approximately” refers is itself also specifically, and preferably, disclosed.

Whereas the terms “one or more” or “at least one”, such as one or more or at least one member(s) of a group of members, is clear perse, by means of further exemplification, the term encompasses inter alia a reference to any one of said members, or to any two or more of said members, such as, e.g., any >3, >4, >5, >6 or >7 etc. of said members, and up to all said members. All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination.

In the present description of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration only of specific embodiments in which the invention may be practiced. Parenthesized or emboldened reference numerals affixed to respective elements merely exemplify the elements by way of example, with which it is not intended to limit the respective elements. Unless otherwise indicated, all figures and drawings in this document are not to scale and are chosen for the purpose of illustrating different embodiments of the invention. In particular the dimensions of the various components are depicted in illustrative terms only, and no relationship between the dimensions of the various components should be inferred from the drawings, unless so indicated.

It is to be understood that other embodiments may be utilised and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

Presently provided is a continuous flow reaction device (100) for an electrochemical process. An exemplary reaction device (100) is shown in FIGs. 1 to 5 and 18. The continuous flow reaction device (100) comprises a reaction space (110) having a longitudinal (L) direction and transverse (T) direction, (at one longitudinal end) a fluid inlet end (14) and (at an opposing longitudinal end) a fluid outlet end (16), and a forward direction (F) from the inlet end (14) to the outlet end (16). It further comprises a plurality of discrete protrusions (120, a: 120, b) in contact with the reaction space (110). Each discrete protrusion (120, a: 120, b) (in a majority of the plurality) is configured such that a flow path (150a-150c) of the fluid contacting an inlet end (14) side of the discrete protrusion is split at least into at least two daughter flow paths (150b1 ; 150b2) on the outlet end (16) side of the discrete protrusion (120, a: 120, b). At least one of the daughter flow paths (150b1) generated by one of the plurality of discrete protrusions (120) combines (152a) with at least one of the daughter flow paths (150a2) generated by another of the plurality of discrete protrusions (120) on the outlet end (16) side of both discrete protrusions (120). This is known as split and recombine, and leads to an efficient mixing. Preferably a majority or all of the discrete protrusions each split the flow path (150a-150c) into at least two daughter flow paths (150b1 ; 150b2) at least one of which combines with another daughter flow path (150a2) as mentioned earlier. When a majority or all of the discrete protrusions (120) in contact with the reaction space (110) are configured for a split and recombine, mixing is amplified in a longitudinal (L) direction as a function of distance from the fluid inlet end (14). The fluid flowing in the forward direction (F) is preferably a liquid.

Each (and every) discrete protrusion (120) is an electrode (cathode (120, a) or anode (120, b)) in the electrochemical process, having a polarity and being separated by a distance from at least one closest electrode of an opposing polarity. The continuous flow reaction device (100) may include a pumping system (200) configured to generate a flow to the fluid inlet end (14). The flow is preferably a pulsatile flow comprising a steady state flow rate and an oscillatory flow rate superimposed on the steady state flow rate. The is a net flow in the forward direction (F) from the inlet end (14) to the outlet end (16). For some types of reaction (e.g. photo-electrochemistry), good results can be achieved with a steady state flow rate without the oscillatory flow rate component.

As exemplified in FIGs. 1 and 3, the reaction space (110) has a longitudinal (L) direction and transverse (T) direction, (at one longitudinal end) a fluid inlet end (14) and (at an opposing longitudinal end) a fluid outlet end (16), and a forward direction (F) from the inlet end (14) to the outlet end (16). The reaction space (110) also have a height direction (H), and the directions H, L, T are mutually perpendicular. In use, the transverse (T) direction may be horizontal and the height (H) direction may be vertical.

The reaction space (110) is defined by a longitudinal upper portion (142) containing a longitudinal upper base wall (144), optionally from which discrete protrusions (120, a: 120, b) project into the reaction space (110). It has a longitudinal lower portion (146) containing a longitudinal lower base wall (148), optionally from which discrete protrusions (120, a: 120, b) project into the reaction space (110). The base walls (144, 148) are typically planar.

The reaction space (110) is further defined by longitudinal side walls (131 , 132) connecting the longitudinal sides of the upper portion (142) and lower portion (146). The reaction space (110) is further defined a first end wall (134) at the inlet side (14), and a second end wall (136) at the outlet side (16); they connect the transverse sides of the upper portion (142) and lower portion (146). As described elsewhere herein, the longitudinal side walls (131 , 132) and first (134) and second (136) end walls (134) may be provided in a closed-loop shaped spacing/sealing insert (178).

The reaction space (110) is served by one or more inlets (114) providing a (net) in flow into the reaction space (110). The one or more inlets (114) are typically connected to the pumping system. The reaction space (110) is further served by one or more outlets (116) providing a (net) outflow flow from the reaction space (110).

The electrochemical process may be any that uses an application of a voltage potential to induce a chemical reaction. The electrochemical process may or may not be accompanied by one or more additional energy-consuming reactions such as light (additional photochemical process), heat (additional thermochemical process), other electromagnetic radiation, vibration. In the case of an additional photochemical process, one or more side of the upper portion (142) and lower portion (146) may be at least partially light transparent. The light transparency further gives the opportunity to visually inspect the reaction space during operation and perform photo-electrochemical synthesis protocols by illuminating the flow channel while maintaining the beneficial mass transfer enhancement. This significantly increases the feasibility of different reactions and applications, by additional photo excitation of photocatalysts, reagents or intermediates in the solution or specifically coated (photo)anodes and/or (photo)cathodes.

The electrochemical process may be an electrosynthesis. The electrosynthesis reaction may be any, including, but not limited to Kolbe electrolysis, Shono oxidation, electrochemical sulfoxidation, synthesis of adiponitrile via cathodic hydrodimerization, Birch reduction, electrochemical carboxylations, electrochemical decarboxylations, and the like.

Discrete protrusions (120, a; 120, b) of opposing polarity may intercalate. This is shown for instance in FIGs. 3, 7 to 9 and 10 to 13, 20 and 21. FIGs. 7 to 9 and 20 show a two comb variation, in which the upper portion (142) carries some of the discrete protrusions (120, a: 120, b) of the plurality of the same polarity (e.g. cathode), and the lower portion (146) carries the remaining discrete protrusions (120, a: 120, b) of the plurality of the same polarity (e.g. anode) which opposite to the polarity of the upper portion (142). FIGs. 10 to 13 and 21 show an inserted variation, in which the lower portion (146) carries all of the discrete protrusions (120, a: 120, b) of the plurality of the both polarities (anode and cathode), and the upper portion (142) is non-conductive (e.g. contains a light transparent window). In an intercalated design, each (and every) discrete protrusion (120, a: 120, b) of the plurality may be an electrode, a node electrode, of one polarity (e.g. anode) having at least two closest adjacent discrete protrusions (in a transverse and/or longitudinal direction, but not height direction) that are electrodes, satellite electrodes, of the same opposing polarity (e.g. all cathode). The protrusion (162, a; 162, b) free ends (122, a; 122, b) and base wall (144, 148) may be separated by one or more of: a gap (162, a; 162, b) (FIG. 7), an electrically insulative layer (124a, 124b) (FIG. 8), an electrically insulative coating (e.g. on the free end (122, a; 122, b)) (128a, 128b) (FIG. 9) to prevent undesirable electrical short-circuit.

One node electrode may have 2 satellite electrodes when the node electrode is located along the outer edges of the plurality of discrete protrusion (120, a: 120, b). An example is C1 R3(+) (node electrode) and C2R2(-) C2R4(-) (satellite electrodes) in FIG. 3. One node electrode may have 4 satellite electrodes when the node electrode is located in a central region of the plurality of discrete protrusion (120, a: 120, b). An example is C3R3(+) (node electrode) and C2R2(-) C4R2(-) C2R4(-) C4R4(-) (satellite electrodes). The central region is a region usually central in the reaction space in FIG. 3.

One node electrode may have 3 satellite electrodes when the node electrode is located in a transition region between the outer edges and central region of the plurality of discrete protrusion (120, a: 120, b). An example is C2R2(-) (node electrode) and C1 R3(+) C3R1(+) C3R3(+) (satellite electrodes) in FIG. 3. A transition region is a region is usually located at each of the longitudinal ends of the reaction space.

The separation distance between a node electrode and each of its satellite electrodes may be the same.

In one configuration, the discrete protrusions (120, a; 120, b) of the plurality may be arranged into two groups of opposing polarity, arranged in the reaction space such that the free ends (122, a, b) of one group are aligned (122, a; 120, b) with the free ends of the other group. This is exemplified in FIGs. 1 , 15 and 17, in which the upper portion (142) carries one (first) group of the discrete protrusions (120, a: 120, b) having one polarity (e.g. cathode), and the lower portion (146) carries the other (second) group discrete protrusions (120, a: 120,b) having an opposite to the polarity of the first group. The number of discrete protrusions in both groups is preferably the same, or may vary by no more than 10 %. The protrusion (162, a; 162, b) free ends (122, a; 122, b) may be separated by one or more of: a gap (162, a; 162, b) (FIG. 15), an electrically insulative layer (160) (FIG. 17), an electrically insulative coating (e.g. on the free end (122, a; 122, b)) to prevent undesirable electrical short-circuit.

In the aligned configuration, each (and every) discrete protrusion (120, a: 120, b) of the plurality is an electrode of one polarity having only one closest adjacent discrete protrusion that is an electrode of an opposing polarity (e.g. all cathode). The separation distance between each pair of free ends aligned (122, a; 1220, b) may be the same. When the free ends are aligned (122, a; 122,b), projections of the free ends in a height direction substantially overlap. When the free ends are aligned (122, a; 122, b), the central longitudinal axes of the respective discrete protrusions (120, a: 120, b) may also be aligned. Each (and every) discrete protrusion (120, a: 120,b) of the plurality is an electrode of the same polarity {e.g. anode) may be separated from a common planar electrode of an opposing polarity {e.g. cathode). It may be called a flat-top design. This is exemplified in FIGs. 1 , 14 and 16, in which the upper portion (142) is the common planar electrode e.g. cathode), and the lower portion (146) carries all the discrete protrusions (120, a: 120, b) of the plurality of the same polarity {e.g. anode). The protrusion (162, a; 162,b) free ends (122, a; 122, b) and base wall (144) may be separated by one or more of: a gap (162, a; 162, b) (FIG. 14), an electrically insulative layer (160) (FIG. 16), an electrically insulative coating {e.g. on the free end (122, a; 122, b)), to prevent undesirable electrical short-circuit. Separation distance between each (and every) discrete protrusion (120, a: 120,b) and the common planar electrode of the opposing polarity (e.g. cathode) may be the same. In particular, separation distance between each (and every) discrete protrusion (120, a: 120,b) and the common planar electrode of the opposing polarity (e.g. cathode) may be the same.

The upper portion (142) may form an electrode of one plurality and the lower portion (146) may form an electrode of the opposing polarity. This is exemplified in FIGs. 7-9 and 14-17, 18, 20 and 21. The plurality of discrete protrusions (120, a; 120,b) disposed on both the upper portion (142) and lower portion (146) may intercalate when the upper portion (142) and the lower portion (146) are brought together; this way discrete protrusions (120, a; 120,b) of opposing polarity are brought together side by side (FIGs. 7-9, 20).

Alternatively, the plurality of discrete protrusions (120, a; 120, b) disposed on both the upper portion (142) and lower portion (146) may mutually align (free ends (122) mutually contact) when the upper portion (142) and the lower portion (142) are brought together; this way discrete protrusions (120, a; 120, b) of opposing polarity are brought together in upper and lower alignment (FIGs. 15-17).

Alternatively, all of the plurality of discrete protrusions (120, a; 120, b) may be disposed on one of the upper portion (142) and lower portion (146) as part of an electrode of one polarity, and the other portion being planar may form part of part an electrode of the opposing polarity (FIG. 14, 21)

One (only) of the upper portion (142) or lower portion (142) may contain all of the plurality of discrete protrusions (120, a: 120, b). The plurality of discrete protrusions (120, a; 120, b) of opposing polarity may be mutually intercalated on one of the upper portion (142) or lower portion (146) (FIGs. 10 to 13, 21). This is achieved by providing some of discrete protrusions (120, a) of the plurality on a first support (149a) containing a plurality of through- apertures (147) located between the discrete protrusions (120, a) (FIG. 10 and FIG. 21 panel B), and providing some of discrete protrusions (120, b) of the plurality on a second support (149b) (FIG. 10 and FIG. 21 panel A), wherein the discrete protrusions (120, b) of the second support (149b) are arranged to pass through the through-apertures of the first support (149a) (when the first is placed over the second support) (FIG. 11 and FIG. 21 panel C). Parts of the first and/or second support are electrically insulated to prevent electrical short-circuit. This configuration allows operation with a transparent lid e.g. for performing photo-electrochemical reactions, or electrochemical reactions with the possibility to incorporate non-invasive (through glass) process analytical technologies for real-time analysis/monitoring of the process.

The reaction space (110) has height (Ht), width (W) and length (Ln) dimensions. See, for instance, FIGs. 3 and 5.

The height (Ht) of the reaction space (110) means the average distance between the lower base wall (148) and the upper base wall (144) of the reaction space (110). The length (Ln) of the reaction space (110) means the average distance between the first end wall (134) and the second end wall (136) of the reaction space (110). The width (W) of the reaction space (110)” means the average distance between the longitudinal side walls (131 , 132) of the reaction space (110).

The reaction space (110) may have a cross-section with a high aspect ratio (e.g. at least 3, in particular at least 5 and more in particular at least 10), where the aspect ratio is the ratio of the width to the height of the reaction space (110).

The height (Ht) of the reaction space (110) may be at least 0.1 mm. The height (Ht) may be at most 100 mm. The height (Ht) may be preferably at least 0.5 mm, more preferably at least 1 mm and most preferably at least 2 mm. Said height (Ht) may preferably be at most 10 mm, preferably at most 7.5 mm, more preferably at most 5 mm and most preferably at most 3 mm. A limited height (Ht) is advantageous for photo-electrochemistry to allow radiation to penetrate to the lower base wall (148) thus irradiating sufficiently all of the fluid within the reaction space (110). The height (Ht) may be constant along the longitudinal length (L) of the reaction space (10). The length (Ln) of the reaction space (110) may be at least 1 cm. The length (Ln) may be at most 10 m. The length (Lt) may be preferably at least 5 cm, more preferably at least 10 cm, advantageously at least 25 cm and most advantageously at least 50 cm. Said length may be be at most 10 m, preferably at most 5 m, more preferably at most 2 m and most preferably at most 1 m. Such a range of lengths ensures that both long residence times and short residence times are feasible depending on the reaction and/or process in combination with low net flow rates which are known to have a lower pressure drop along the length of the reaction space (110). The length (Ln) may or may not be constant along the transverse (T) width (W) of the reaction space (10).

The width (W) of the reaction space (110) is typically decided based on the desired production capacity, i.e. the wider the reaction space (110), the larger the internal volume thereof and the larger the volume of the product stream. In other words, the width (W) of the reaction space (110) may cover several orders of magnitude in size range. For example, the width (W) may be at least 5 mm. The width (W) may be at most 10 m. The width (W) may be preferably at least 1 cm and more preferably at least 2 cm and at most 10 m, preferably at most 1 m, more preferably at most 50 cm and most preferably at most 10 cm. It will be appreciated that when the width (W) of the reaction space (110) is increased, the number of inlets (114) and outlets (116) may be increased. Such an increase in the number of inlets (114) and outlets (116) is advantageous as there could otherwise i.e. when providing a wide reaction space (110) with a single inlet (114) and a single outlet (116) that are located centrally on respective ones of the first end wall (134) and second end wall (136)) occur dead volumes near the corners of the reaction space (110) which naturally decrease the performance of the flow reaction device (100) and, in particular, result in an residence time distribution (RTD) having a long tail with a premature breakthrough, which is undesired. The length (Ln) may or may not be constant along the longitudinal (L) width (W) of the reaction space (10).

There may at least one inlet (114) and at least one outlet (116) in the reaction space (110).

Where there are two or more inlets (114), distance between adjacent inlets (114) in the same reaction space may be at most 10 cm, preferably at most 5 cm and more preferably at most 2 cm. Where there are two or more outlets (116), The distance between adjacent outlets (116) in the same reaction space may be at most 10 cm, preferably at most 5 cm and more preferably at most 2 cm. Such a small distance aids in avoiding dead volumes between the inlets (114) and outlets (116). As a non-limiting guidance, an exemplary device (100) may have a reaction space (110) height (Ht) of 1 to 3 mm, length (Ln) of 20 to 25 cm, and a width of 1 to 5 cm.

The local height (h) of the reaction space (110) is the distance between the lower base wall (148) and the upper base wall (144) in the location of the discrete protrusion (120, a: 120, b) being measured.

Each discrete protrusion (120, a: 120,b) is a static mixing element that at least partially, preferably completely locally occludes the reaction space (110), obstructing the flow path of the fluid. A discrete protrusion (120, a: 120, b) has an inlet end (14) side facing the inlet end (14) of the reaction space (110), and has an outlet end (16) side facing the outlet end (16) of the reaction space (110). A discrete protrusion (120, a: 120, b) further has a base end (126, a) attached, preferably non-removeably, to one base wall (e.g. upper base wall (144) of the upper portion (142), or lower base wall (148)) of the lower portion (146)). The discrete protrusion (120, a: 120, b) further has a free end (122, a, 122b) opposing the base end (126, a). The free end (122, a, 122b) is not attached to the upper base wall (144) or the lower base wall (148).

The free end (122, a, 122b) faces the opposing portion (e.g. lower base wall (148)) of the lower portion (146), or upper base wall (144) of the upper portion (142)), or other opposing free ends (122, a, 122b)).

Each and every discrete protrusion (120, a: 120,b) is configured as an electrode in the electrochemical process. All the discrete protrusions may be of the same polarity (e.g. all anode or all cathode). Some the discrete protrusions may be of the same first polarity (e.g. all anode or all cathode), and a remainder of discrete protrusions may be of the same second polarity different from the first polarity (e.g. all cathode or all anode).

Each discrete protrusion (120) is preferably electrically connected to an electrical connector for inlet of electrical power. Each discrete protrusion (120) is preferably electrically connected to one of two electrical connectors for electrical power supplying one polarity (e.g. the anode) or another polarity (e.g. the cathode). An electrical connector for one polarity and an electrical connector for the other is preferably comprised in the continuous flow reaction device. The electrical connector is a device that mechanically and electrically attaches to an external cable, optionally via a connector on the external cable. The electrical connector may be any, including: a binding post, terminal block, socket, and the like. The discrete protrusion (120, a: 120, b) at its inlet end (14) side causes the split of the fluid flow path in the forward (F) direction by contact of the fluid flow with the inlet end (14) side of the discrete protrusion (120, a: 120, b). The fluid flow path is split into at least into at least two daughter flow paths, which daughter flow paths form on the outlet end (16) side of the discrete protrusion (120, a: 120, b). The majority of the flow in the forward (F) direction may be split by the discrete protrusion (120, a: 120,b) into only two daughter flow paths, both advancing in the net forward (F) direction. This is illustrated in FIGs. 2 and 4. The fluid flow path (150a, 150b, 150c) encountered by each discrete protrusion is split into at least into at least two daughter flow paths (e.g. 150b is split into 150b1 and 150b2).

The presence of several discrete protrusion (120, a: 120, b) in the same column (C1 to C15) and a space between adjacent columns leads to a combination of the daughter flow paths. At least one of the daughter flow paths (150a2) generated by one of the plurality of discrete protrusions combines (152a) with at least one of the daughter flow paths (150b1) generated by another of the plurality of discrete protrusions (120) on the outlet end (16) side of both discrete protrusions (120). The splitting phenomenon arises for each (and every) discrete protrusion (120, a: 120,b). The combine phenomenon (152a, 152b, 154a) arises for daughter flows generated by adjacent pairs of discrete protrusion (120, a: 120, b) occupying the same column (any one of C1 to C15). The columns (01-015) are arranged such that the daughter flow paths (150b1) combine (152a) in the spaces between adjacent columns (01-015). The location of the combine event is at the inlet end (14) side discrete protrusions (120) in the next adjacent column (which is located at outlet end (16) side of the column that split the flow).

By providing a plurality of spatially separated columns of discrete protrusions (120), the number of split and combine events is multiplied along the length. When the flow is split, it offers two daughter path each of which can be mixed with another daughter path of the same column in combine event. This combined flow is split again by the next column. A multiplication effect caused by consecutive columns causes thorough mixing of the flow.

It is noted that split and recombine flow pattern results in more turbulence as compared to an induced vortex flow. A vortex flow is more orderly (/.e. circular motion of the fluid), while the split and (re)combine flow pattern presently described introduces more points of chaotic and disorderly turbulence. In the present split and (re)combine flow pattern, the fluid undergoes many more changes of direction which causes more chaos/turbulence in the flow. Additionally, upon the recombination of 2 split streams, said streams collide with each other which introduces a high level of turbulence, while in the vortex flow, the fluid undergoes the more orderly circular mixing motion.

As a result of this “split and (re)combine” locally convective streaming in lateral (L), transverse (T) and height (h) directions occurs, locally homogenising species concentrations. Due to this locally convective streaming, a concentration boundary layer at the protrusion’s surface is reduced, increasing mass the transport rate towards the discrete protrusion surfaces (120).

A discrete protrusion (120, a: 120,b) causes at least a partial local occlusion of the reaction space (110). By local occlusion, it is meant that at the location of the discrete protrusion (120, a: 120,b), there is an at least partial blockage of fluid flow caused by a body of the discrete protrusion (120, a: 120,b). Outside a boundary of the discrete protrusion (120, a: 120, b), the blockage to flow ends.

A discrete protrusion (120, a: 120, b) may completely locally occlude the reaction space (110); in other words there may be no gap between the discrete protrusion (120, a: 120, b) free end (122, a: 122, b) and the opposing portion (142 or 146) (e.g. the adjacent base wall (144, 148)). This is illustrated, for instance, in FIGs. 8, 9, 12, 16, 17. The absence of gap may be caused by a direct contact between the discrete protrusion (120, a: 120, b) free end (122, a: 122, b), and the opposing base wall (144, 148). Where the upper portion (142) is formed from a compression-resistant material such as metal or polymer, there may be no gap, and hence the discrete protrusion (120, a: 120, b) completely locally occludes the reaction space (110) by direct contact of the discrete protrusion (120, a: 120, b) free end (122, a: 122, b) and the adjacent base wall (144, 148).

Where opposing electrode polarities form the upper portion (142) or lower portion (146), an intervening electrical insulation layer (124, a; 124,b) may be provided to prevent electrical short circuit caused by the local occlusion of the reaction space (110). This is illustrated, for instance, in FIGs. 8, 9, 16, 17. The electrical insulation may be any that prevents a short- circuit flow of current. Examples of materials for an electrical insulation layer include polycarbonate, polypropylene, fluorinated ethylene propylene, perfluoroalkoxy alkane, (fluoro)elastomers and ceramics One or both base walls (144, 148) that comes into contact with the free end (122, a; 122b) of a upper portion (142) or lower portion (146), may comprise a removable or nonremovable insulative layer (124,a;124,b). A non-removable insulative layer may be a coating of an electrically insulative material disposed between the plurality of discrete protrusions (120, a: 120,b). A removable insulative layer may be a sheet of electrically insulative material containing cut-outs for the plurality of discrete protrusions (120, a: 120,b); this is illustrated, for instance, in FIG. 8.

Alternatively or in addition, each discrete protrusion (120, a: 120, b) free end may be coated with an electrically insulative layer (128,a;128,b); this is illustrated, for instance, in FIG. 9..

Where discrete protrusions (120, a: 120, b) are disposed on both the upper portion (142) having one polarity and lower portion (146) having another polarity, and where the respective free ends (122, a; 122b) are aligned (do not intercalate), the electrically insulative layer may be provided as a layer (160) that is permeable (162); this is illustrated, for instance, in FIGs. 16 and 17.

As mentioned, a discrete protrusion (120, a: 120, b) may partially locally occlude the reaction space (110). A partial occlusion is caused by the presence of a gap (162) e.g. between the discrete protrusion (120, a: 120, b) free end (122, a: 122, b) and the adjacent base wall (144, 148). A partial occlusion is shown, for instance, in FIGs. 7, 13, 14, 15.

Whether a complete or partial occlusion is employed may depend on the material compatibility or fragility of material forming the upper or lower portion (142, 146) contacting the free end of a discrete protrusion (120, a: 120, b). For instance, if the upper portion (142) made from glass or quartz, a gap may be provided to prevent damage caused by compression forces from discrete protrusions (120, a: 120,b) projecting from the lower portion (146) (FIG. 13).

Where the upper or lower portion (142, 146) is an opposing electrode, the gap is introduced to prevent an undesirable electrical short-circuit between the discrete protrusion (120, a: 120, b) free end (122, a: 122, b) and the adjacent base wall (144, 148) (FIGs. 7, 14, 15).

While electrical short-circuit can be prevented by the presence of the insulating layer mentioned elsewhere herein (allowing the gap to be avoided leading to a complete local occlusion), the insulating layer in some circumstance may not be used, for instance, because of incompatibility of the reaction with the material of the insulating layer. The size of the gap is small enough to avoid creating a significant flow path that bypasses the splitting effect of the discrete protrusion. A discrete protrusion may occupy at least 80 %, preferably at least 90 % of a local height (h) of the reaction space (110). The local height of the reaction space (110) is the distance between the upper base wall (144) and the lower base wall (148) in the location of the discrete protrusion being measured. Each and every discrete protrusion may occupy the same portion of the local height (h) of the reaction space (110).

It will be readily appreciated that the discrete protrusions (120, a: 120,b) may exist in various shapes and/or sizes.

A discrete protrusion (120, a: 120,b) may have a base footprint (transverse cross-sectional profile where it contacts the lower base wall (148)) that is triangular (e.g. equilateral, isosceles, scalene, acute, right), rectangular (square or oblong), polygonal (regular, irregular), circular, oval, elliptical. Where the discrete protrusion (120, a: 120, b) footprint has one or more corners, one of the corners may be orientated to face the on-coming fluid flow.

A discrete protrusion (120, a: 120, b) may have a base footprint area of 0.01 to 100 mm ² .

A discrete protrusion (120, a: 120,b) may have surfaces perpendicular with respect to the lower base wall (148). In particular, side surfaces of a discrete protrusion (120, a: 120, b) may be perpendicular with respect to the lower base wall (148). Side surfaces of the each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may be mutually parallel. Having mutually parallel surfaces is beneficial in electrochemical reaction to avoid voltage potential gradients along a height of the discrete protrusion (120, a: 120, b).

Each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120,b) may have the same shape. Alternatively, two or more discrete protrusions (120, a: 120,b) in the plurality of discrete protrusion (120, a: 120,b) may have a different shape.

Each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may have the same size. Alternatively, two or more discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may have a different size. Each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120,b) may have the same orientation. Alternatively, two or more discrete protrusions (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may have a different orientation.

Preferably, the discrete protrusions in the plurality are set up in a periodic pattern, i.e. a repeating pattern along the longitudinal direction (L) of the reaction space (110).

Furthermore, it is advantageous when the discrete protrusions are set up in a symmetrically ordered periodic pattern, meaning that the discrete protrusions are mirrored with respect to the vertical longitudinal centre plane of the reaction space (110). Such patterns typically result in repeating flow patterns which improve the RTD.

Each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may be solid. Each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120,b) may be hollow. Some of the discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may be solid, and some may be hollow.

The discrete protrusions (120, a: 120, b) may be provided in the reaction space (110) in a density of at least 0.1 discrete protrusion per cm ² , more preferably with at least 1 discrete protrusion per cm ² and most preferably with at least 5 discrete protrusions per cm ² and with a density of at most 100 discrete protrusions per cm ² , more preferably with at most 50 discrete protrusions per cm ² and most preferably with at most 10 discrete protrusions per cm ² . Moreover, the reaction space (110) may have an internal volume, i.e. a volume without any discrete protrusions being disposed within the reaction space (110). The discrete protrusions may fill up at least 5% of said internal volume, preferably at least 10% of said internal volume and more preferably at least 15% of said internal volume and at most 60% of said internal volume, preferably at most 50% of said internal volume, more preferably at most 40% of said internal volume, most preferably at most 30% of said internal volume and advantageously at most 20% of said internal volume. It has experimentally been found that such a distribution of discrete protrusions within the reaction space (110) enables to provide a desired mixing level for a whole range of Reynolds numbers for different reactions and/or processes. Furthermore, it is advantageous, especially at very low net Reynolds numbers, i.e. very low net flow rates, to provide smaller openings between adjacent discrete protrusions. As such, it has been found that it is beneficial when the discrete protrusions are separated by a shortest distance from an adjacent discrete protrusion of at least 0.1 mm, preferably at least 0.5 mm, more preferably at least 1 mm and most preferably at least 1.5 mm, said shortest distance being preferably less than 8 mm, more preferably less than 5 mm, advantageously less than 3 mm and more advantageously less than 2.5 mm.

The plurality of discrete protrusions (120, a: 120, b) in the reaction space (110) may be arranged separated into a plurality of spatially separated columns (C1-C15) (separated in a longitudinal (L) direction) as shown for instance in FIGs. 1 and 3. The columns are evident in a plan view of the reaction space (110). Discrete protrusions (120, a: 120, b) of the same column are spatially separated on a common linear line or axis. The distance between adjacent discrete protrusions (120, a: 120,b) of the same column may be the same. The daughter paths generated by adjacent pairs of the plurality of discrete protrusions (120) of the same column combine on the outlet end side (16) of the column. A column distance (longitudinal) between each adjacent pair of columns may be the same. The number of discrete protrusions (120) in each column may be the same in a central region.

The discrete protrusions (120, a: 120, b) within a pair of adjacent columns (e.g. C6 and C7) may be arranged so that discrete protrusions (120, a: 120, b) on one of the pair of columns each has a different transverse (T) position compared with that of the discrete protrusions (120, a: 120,b) on the other of the pair of columns. Preferably, the discrete protrusions (120, a: 120, b) within a pair of adjacent columns (e.g. C6 and C7) may be arranged so that discrete protrusions (120, a: 120, b) on one of the pair of columns each has a transverse (T) position corresponding to a midpoint of a space between adjacent pairs of discrete protrusions (120, a: 120, b) on the other of the pair of columns.

The plurality of discrete protrusions (120, a: 120, b) may be further arranged into a plurality of spatially separated rows (R1-R5) (separated in a transverse (T) direction) as shown for instance in FIGs. 1 and 3. The columns are evident in a plan view of the reaction space (110). Discrete protrusions (120, a: 120, b) of the same row are spatially separated on a common linear line or axis. The distance between adjacent discrete protrusions (120, a: 120, b) of the same row may be the same. The daughter paths generated by the plurality of discrete protrusions (120) of the same (1st) row may combine with the daughter paths generated by the plurality of discrete protrusions (120) of an adjacent (2nd) row. A row (transverse) distance between each adjacent pair of rows may the same.

A column (transverse) distance between each adjacent pair of columns may be the same. A row distance between each adjacent pair of rows may be the same. The row distance may be equal to the column distance.

An inter-electrode distance between each anode and cathode pair is preferably the same across all pairs of anodes and cathodes. Each anode and cathode pair comprises one anode and one cathode, each anode and/or cathode being a protrusion, and which are separated by the shortest distance. For instance, in the arrangement of FIG. 7, each and every anode and cathode pair is separated (horizontally) by the same distance. For instance, in the arrangement of FIGs. 14 and 15, each and every anode and cathode pair is separated (vertically) by the same distance.

The uniform distances between multiple anode and cathode pairs provides a uniform electric field

One or both electrode surfaces of opposing polarity may be an electrocatalyst, or may be (/.e. formed at least partially from) an electrocatalyst, and/or may be at least partially coated (e.g. partially or fully coated on a fluid contact side) with an electrocatalyst. For instance, one or both of the upper (142) and lower (146) portions may be an electrocatalyst or may be at least partially coated with an electrocatalyst. For instance, the discrete protrusions (120, a; 120, b) of one polarity or of both polarities may be electrocatalyst or coated with an electrocatalyst. The electrocatalyst of electrode surfaces of opposing polarity may be the same or different. The electrocatalyst may increase kinetic activity and/or selectivity. Examples of electrocatalysts include but are not limited to platinum, gold, carbon, nitrogen doped carbon, diamond doped carbon, iridium, silver, nickel, tin, tin oxide, ruthenium, iron, iron oxide, copper, copper oxide, ion-exchange polymers.

One or both electrode surfaces of opposing polarity may be a photocatalyst, or may be (/.e. formed at least partially from) a photocatalyst, and/or may be at least partially coated (e.g. partially or fully coated on a fluid contact side) with a photocatalyst. For instance, one or both of the upper (142) and lower (146) portions may be a photocatalyst may be at least partially coated with a photocatalyst. For instance, the discrete protrusions (120, a; 120, b) of one polarity or of both polarities may be a photocatalyst or coated with a photocatalyst. The photocatalyst of electrode surfaces of opposing polarity may be the same or different. The photocatalyst may increase kinetic activity and/or selectivity. Examples of photocatalysts include but are not limited to:

- transition metal based (including its oxide and/or complex configurations): platinum, palladium, nickel, gold, silver, copper, tin, iridium, rhodium, cobalt, ruthenium, iron, titanium, bismuth, tungsten, cerium;

- non-metallic dyes: fluorescein, Eosin Y, Eosin B, rose bengal, rhodamine B, nile red, anthracene, naphtalenes, phenoxazines, dihydrophenazines, benzoperylenes, riboflavines, mesityl acridinium salts, 2,3-Dichloro-5,6-dicyano-1 ,4-benzoquinone, 1 , 2,3,5- tetrakis(carbazol-9-yl)-4,6-dicyanobenzene .

It is appreciated that the device may be provided with both an electrocatalyst and a photocatalyst. The electrocatalyst and a photocatalyst may be provided as part of an electrode of the same polarity. The electrocatalyst and a photocatalyst may each be provided as part of electrode of the opposing polarity. One of both of the electrocatalyst and a photocatalyst may be provided as a coating, and/or form a material of the electrode.

One or both of the upper (142) and lower (146) portions may be impermeable (to gas). For instance, each (and every) discrete protrusion (120, a: 120,b) in the plurality of discrete protrusion (120, a: 120,b) may be impermeable (to gas).

One or both of the upper (142) and lower (146) portions may be permeable (to gas). Each (and every) discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120,b) may be permeable (to gas).

One the upper (142) and lower (146) portions may be permeable (to gas), and the other portion may be impermeable (to gas). Some of the discrete protrusion (120, a: 120, b) in the plurality of discrete protrusion (120, a: 120, b) may be impermeable, and some may be permeable.

Gas permeability may be achieved by using porous structures such as paper, fabrics, felts, expanded foams, 3D printed structures, made from or containing electrically conductive substances such as carbon, titanium, nickel. One example is carbon paper made by Sigracell. By providing gas permeability, gaseous reagents may be added into the reaction space directly at the catalyst surface. Using the gas diffusion electrode material, in combination with discrete protrusions (120, a: 120, b) and implementation of pulsatile flow, the three- phase boundary between the gaseous reagent, the liquid electrolyte and the catalyst is optimized, such that the distance the dissolved reagent has to cross in the electrolyte towards the electrode surface is limited to the pm-range, while maintaining the mass transfer enhancement obtained by the oscillatory flow and/or (pulsed) voltage in combination with static mixing elements. Despite the low solubility, gas can be supplied constantly over the whole channel length, keeping either a constant supply of intermediates originating from gas reactions at electrodes or keeping the solution saturated for reactions with gases in the process matrix.

The device (100) may further comprise a voltage potential generator (300), for generation of a voltage potential applied across electrodes of opposing polarity for a reaction session. The voltage generator (300) is shown schematically in FIG. 19.

The voltage potential generator may be configured to output a voltage generated at a fixed and continuous level (fixed voltage) during the reaction session. Alternatively or additionally, the voltage potential generator may be configured to output a voltage (variable voltage) generated at two or more different levels during the reaction session. For instance, voltage potential generator may be configured to output a voltage that regularly varies between two or more values (e.g. high to low to high etc, positive to negative to positive etc, positive to zero to positive etc). The frequency of the variation may range from 1 .Hz to 1 kHz, preferably 0.1 to 10 Hz. The amplitude of the variation may range from 0.11 V (e.g. +0.05 V to -0.05 V) to 100 V (e.g. +50 V to -50 V) , preferably 1 to 10 V . Additionally, the voltage potential generator may be configured to output a fixed voltage or variable voltage intermittently (on-off or pulsed).

The variable and/or intermittent voltage advantageously leads to anti-fouling, and/or antipassivation and/or self of one of both electrodes. It also allows for on-demand control of chemistry (selectivity). It can modulate the thickness of the concentration boundary layer at the electrode surface (i.e. mass transfer factor) and affect the dynamic (time-dependent) coverage of surface species during potential pulsing (i.e. surface adsorption-desorption factor), e.g. formed intermediate species are allowed to migrate away from electrode surface to the bulk section. A combination of pulsatile flow and variable and/or intermittent voltage (dual pulse) can further refine reaction parameters.

The reaction space (110) may be a non-divided reaction space, meaning that there is no layer separating the upper portion (142) and the lower portion (146). Non-divided reaction spaces are shown, for instance, in FIGs. 7-9, 12-13, 14-15.

The reaction space (110) may be a divided reaction space, meaning that there is a permeable layer (160) separating the upper portion (142) and the lower portion (146). Divided reaction spaces are shown, for instance, in FIGs. 16-17. The permeable layer (160) may allow for non-selective passage of species (e.g. ions, molecules) across the layer. The permeable layer (160) may allow for selective passage of species (e.g. ions, molecules) across the layer; selectivity may be based on species size, species charge, species hydrophobicity/hydrophilicity. The permeable layer allows for separate fluid flow across either side of the membrane. The permeable layer allows for separation of gases across either side of the membrane.

As mentioned elsewhere, the device (100) may include a pumping system (200) configured to generate a flow to the fluid inlet end (14). The pumping system (200) is shown schematically in FIG. 19. The pumping system (200) is configured to generate a flow to the fluid inlet end (14). The flow is preferably a pulsatile flow comprising a steady state flow rate an oscillatory flow rate superimposed on the steady state flow rate. In some circumstances, the pumping system (200) configured to generate steady state flow rate (e.g. for some photo-electro chemical reactions).

To achieve the pulsatile flow, the pumping system (200) may include an oscillator configured to generate the oscillating flow component. In particular, said oscillator may be configured to generate said oscillatory flow component with an oscillation frequency of at least 0.01 Hz, preferably at least 0.1 Hz and more preferably at least 0.5 Hz and 20 of at most 400 Hz, preferably at most 100 Hz, more preferably at most 50 Hz and most preferably at most 25 Hz.

The oscillating flow component may have an oscillation centre-to-peak- amplitude of at least 1 pm, preferably at least 10 pm, more preferably at least 0.1 mm and most preferably at least 0.5 mm and at most 100 cm, preferably at most 20 cm, more preferably at most 5 cm, most preferably 25 at most 1 cm, advantageously at most 5 mm and more advantageously 1 at most 2 mm. The centre-to-peak- amplitude is a measure of the distance moved in the reaction space (110) by the fluid in a longitudinal (L) direction during one cycle of the oscillation.

It is advantageous when the generated centre-to-peak amplitude of the oscillatory flow is of at least the same order of magnitude as the distance between discrete protrusions (120, a: 120, b) separate longitudinally (L), i.e. discrete protrusions (120, a: 120, b) which are adjacent to one another along the longitudinal (L) direction. In other words, the centre-to- peak amplitude is ideally at least half of the distance between adjacent discrete protrusions (in the longitudinal (L) direction) as this ensures that, for each periodic oscillation cycle, a fluid parcel is displaced over a distance in the longitudinal direction that it is at least equal to the distance between subsequent discrete protrusions, meaning that, for each periodic oscillation cycle, the fluid parcel normally is split by a discrete protrusion. More in particular, the centre-to-peak amplitude may be equal to or greater than a distance between a pair of adjacent columns (C1 to C15) of discrete protrusions (120, a: 120, b).

The oscillator may be in the form of a modified membrane pump or a piston pump where the check valves have been removed or altered.

Alternatively, a custom made piston or bellows directly connected to the reaction space (110), e.g. the feed stream, is possible too. Furthermore, a first pump, e.g. a membrane pump, may be used to generate the net flow component and a second pump, e.g. a modified membrane pump, may be used to generate the oscillatory flow component.

It will be readily appreciated that, in practice, the pumping system (200) may have different settings, meaning that the pumping system may be capable of generating net flows across a range of flow velocities and/or oscillatory flows across a range of oscillation amplitudes and/or oscillation frequencies.

In general, for a pulsatile flow, the net and oscillatory Reynolds numbers are defined in order to characterise the flow. The net Reynolds number is given by

R _n = (u L) / v where u is the velocity of the net flow component, L is a characteristic length which is typically taken as the hydraulic diameter of the reaction space (110) and v is the kinematic viscosity of the fluid.

The oscillatory Reynolds number is given by Ro = 2(pi) fx ₀ (L /v)

Where f frequency of the oscillatory flow component and xo is the centre-to-peak amplitude of the oscillatory flow component.

Using both Reynolds numbers it is also possible to define the velocity ratio y y = (Ro/Rn) = 2(pi) f (xo/u)

Furthermore, as both Reynolds numbers are dependent on the characteristics of the medium within the reaction space (110) through the kinematic viscosity, it is useful to define normalised Reynolds numbers. Specifically, the normalised net Reynolds number is given by

R _n = _n v = uL, and the normalised oscillatory Reynolds number is given by

Ro = Rov = 2(pi) fx ₀ L

It has been found that a normalised oscillatory Reynolds number that is at least 5v, preferably at least 25v, more preferably at least 50v, advantageously at least 75vand most advantageously at least 100v leads to sufficient turbulence and/or chaotic motions even for relatively low net flow rates as described above. In some embodiments, said pulsatile flow has a velocity ratio of at least 1 , preferably at least 5, more preferably at least 10, advantageously at least 15 and most advantageously preferably at least 20. Similarly, said pulsatile flow has a normalised net Reynolds number that is preferably at most 200v, preferably at most 100v, more preferably at most 50 v, most preferably at most 20 v, advantageously at most 10v, more advantageously at most 5v, and most advantageously at most 0.5v. Such low net Reynolds numbers are advantageous as it enables a long residence time of the fluid within a short reaction space (110), meaning the flow reactor 1 may be very compact and may thus be easily used in a laboratory for example.

In calculating the Reynolds numbers, the hydraulic diameter of the reaction space (110) is used. This hydraulic diameter is typically dependent on the cross-sectional area of the reaction space (110), i.e. its height Ht and its width W, and on the area that is filled by the discrete protrusions (120, a: 120, b).

The reaction space (110) may be provided in a reaction block (102). The device (100) may comprise the reaction block (102). An exemplary reaction block is shown in FIG. 18. Panel A shows an exploded view, Panel B shows an assembled view, Panel C shows an assembled view with heat exchanger. The reaction block (102) may comprise a supporting block (170) comprising a longitudinal well (172) for containment and stacking (in height) of a plurality of removeable longitudinal (flat) inserts (174, 176, 178, 182). The reaction block (102) may further comprise a pair of a longitudinal inserts that are electrode inserts (176, 178).

In one configuration (upper-lower), the one electrode insert (176) of the pair may be a lower portion (146) of the reaction space (110), and the other one electrode insert (180) of the pair may be an upper portion (142) of the reaction space (110) (two comb, teeth, flattop); this configuration may be used to implements the designs of FIGs. 7, 8, 9, 14, 15, 16. Examples of electrode inserts (176, 180) are shown in FIG. 20; a spacing/sealing insert (178) (not shown) - see later below - is disposed between electrode inserts (176, 180) thereby forming the reaction space (110). A longitudinal insert may be provided that is a lower current collector (174) comprising a longitudinal plate of current-conductive material, disposed in electrical contact with the electrode insert (176) of the pair that is the lower portion (146) of the reaction space (110). A longitudinal insert that is an upper current collector (182) comprising a longitudinal plate of current-conductive material, disposed in electrical contact with the electrode insert (178) of the pair that is the upper portion (142) of the reaction space (110).

In one configuration (lower-lower), both electrode inserts (176, 180) of the pair may form the lower portion (146) of the reaction space (110) (intercalating protrusions, inserted); a transparent block (glass, quartz) may form the upper portion (142) of the reaction space (110). This configuration may be used to implement the designs of FIGs. 12, 13. Examples of electrode inserts (176, 180) are shown in FIG. 21 ; an upper (142) portion (not shown) is provided, and a spacing/sealing insert (178) (not shown) is disposed between upper (142) and lower portions (176, 180) thereby forming the reaction space (110).

The reaction block (102) may further comprise a spacing/sealing insert (178) disposed between upper (142) and lower portions (176, 180). The longitudinal side walls (131 , 132) and first (134) and second (136) end walls (134) may be provided in the closed-loop shaped spacing/sealing insert (178);

The reaction block (102) may further comprise a lid (184). The reaction block (102) may further comprise one or more spacing shims. The reaction block (102) may further comprise a (coolant circulating or Peltier) heat exchanger (186); see for instance FIG. 18. Panel C. The use of a reaction block (102) and a plurality of removeable longitudinal (flat) inserts (174, 176, 178, 182), allows the device (100) to be quickly reconfigured, for instance to change an electrode for one of a different material, to add or change a permeable layer. As a result, the device can be opened, visually inspected and cleaned to prevent crosscontamination between different synthesis protocols.

Moreover, the basic design also allows easy modification between electrochemical reactor set-ups e.g. the change from an undivided to a divided set-up with incorporation of a membrane, inclusion of a transparent window, or porous gas diffusion electrode.

The continuous flow reaction device (100) may include a pumping system (200) configured to generate a flow to the fluid inlet end (14). The flow is preferably a pulsatile flow, however, for some types of reaction (e.g. photo-electrochemistry), good results can be achieved with a steady state flow rate without the oscillatory flow rate component. Hence, the device (100) as described herein may be disposed with a pumping system configured for a steady state flow.

Multiple reaction spaces (110) may be connected in parallel to increase flow rates and reaction yield. The reaction spaces (110) may be connected to a single pumping system (200), and/or to a single voltage generator (200).

Further provided is a method of carrying out an electrochemical reaction using the present device. Further provided is a method of carrying out an electrosynthesis using the present device.

Limiting current density describes the maximum achievable amount of charge per time unit per area unit that can be transferred from/to an electrode for a certain application. A higher limiting current density, the more electrons may by transferred per time unit, thus the electrode can produce more chemical reactions per time unit, and consequently leading to faster reactions and higher productivity.

A primary advantage of the presently-described device is an unexpectedly large increase in limiting current density. This is achieved when combining the (i) split-and-recombine flow pattern, and (ii) each and every protrusion being an electrode, and in the presence of the pulsatile flow. For instance, data presented in Table 1 below for the different flow patterns using the present configuration show an unexpected high limiting current density (up to 60mA/cm ² (Design C)) when compared to all other tested cell configurations (Designs A and B)). Designs A, B and C have the same cell characteristics i.e., identical inter-electrode distance and electrode surface area, yet design C is superior by a significant degree.

This allows a boost of the reaction product obtained in a single pass through the reactor space at the same flow rate, increasing concentration of the end product, facilitating the fully continuous operation of the system. This avoids semi-batch or recirculation methods. Alternatively, the same productivity can be reached at a significant lower overpotential leading to a higher selectivity, less tedious down-stream processing (i.e. purification of the end product) and higher energy efficiency.

By using the discrete protrusions as electrode pairs, the separation between the walls forming reaction space (110) can be large, yet the distance between opposing pairs of protrusions are small enough for efficient catalysis, minimizing voltage potential gradient. The discrete protrusions also serve as efficient heat exchangers.

The limiting current density may be adjusted by means of the pulsation settings (amplitude and frequency) and irrespective of the flow rate, which allows tunability towards the selectivity and/or productivity of the reaction, independent of the required reaction time.

The present device has a superior modularity. The electrodes can be exchanged effortlessly. Additionally, different electrode configurations are possible, including undivided cell, divided cell and an electrochemical cell including a transparent window.

The arrangement of protrusions in combination with pulsation, further provide self-cleaning properties, as fouling/clogging and other possible passivation effects (e.g., due to gas bubble trapping on surface of electrodes) are mitigated.

The “split and (re)combine” flow increases turbulence, disorderly and chaotic flow compared with tradition vortex flow, and additionally results in a better defined and narrower residence time distribution when combined with pulsatile flow.

Examples

Example 1 To demonstrate the beneficial influence of an oscillatory flow regime on the electrochemical behavior, the limiting current method was utilized with the ferri-ferrocyanide redox couple as species of interest in an intercalated (two comb) configuration (see FIGs. 22, 23 and 24). From these results it can be observed that the pulsatile flow regime increases the limiting current density with an order of magnitude (FIG. 22) without affecting the mean residence time. In FIG. 23, the impact of a varying oscillatory flow pulse amplitude on the limiting current density at a given oscillatory flow pulse frequency is shown. For instance, for an oscillatory flow pulse frequency of 2.1 Hz the averaged limiting current density increases in a linear fashion from 32mA/cm ² to 59mA/cm ² when the oscillatory flow pulse volume is varied from 0.1 mL to 0.4mL respectively. This is a near 4 fold increase in current signal compared to the current density measured when operating in a non-pulsed flow regime. The same linear trend can be observed when operating at the other oscillatory flow pulse frequencies. In FIG. 24 the influence of the oscillatory flow pulse frequency on the limiting current density is shown. From these results, it can be seen that an increase in pulse frequency leads to an increase in limiting current density response.

Example 2

The limiting current method as described in D.A. Szanto, S. Cleghorn, C. Ponce-de-L'eon, F.C. Walsh, The limiting current for reduction of ferricyanide ion at nickel: the importance of experimental conditions, AIChE J. 59 (4) (2012) 215-228 was utilized in three different reactor designs A, B, and C schematically (not to scale) shown in FIG. 25 using a ferri- ferrocyanide redox couple as species of interest:

[Fe(CN) ₆ ]’ ⁴ Fe(CN) ₆ ]’ ³ + e’ ¹

In FIG. 25 designs A, B, and C, diagonal hatching indicate cathode electrode (one hatching direction) and anode electrode (other hatching direction), vertical hatching indicates a gasket, and horizontal hatching represents a protrusion (turbulence promotor) that is not an electrode (made from nylon-containing material with a woven mesh pattern, U.S. mesh was 18). FIG. 25 design C corresponds to one of the designs presently described herein. Designs A, B and C have the same cell characteristics i.e. identical inter-electrode distance and electrode surface area. Limiting current densities was measured for the different reactor designs FIG. 25 A, B, and C at 1.0V. 0.1 M equimolar solution of [Fe(CN)e]' ³ /[Fe(CN)e]' ⁴ in deionized water. All experiments were carried out at an ambient temperature (22°C), at a net flow of 5mL/min, and using graphite electrodes. Reactions were performed that utilised pulsatile flow or steady state flow. With pulsatile flow, pulse frequency was 3 Hz, pulsed volume displacement (amplitude) was 0.4mL. The results are shown in Table 1 below.

Reactions were performed that utilised pulsatile flow or steady state flow. With pulsatile flow, pulse frequency was 3 Hz, pulsed volume displacement (amplitude) was 0.4mL. The results are shown in Table 1 below.

Table 1 : Measured limiting current density (A/cm ² ) for different reactor designs, with or without pulsatile flow. The surface area of the electrodes in each experiments was the same.

Unexpectedly high current density of approximately 60 mA/cm ² was obtained for design C with pulsatile flow, resulting in an increase by a factor of 4 as compared to the non-pulsed case, and presents about one order of magnitude increase in current density as compared to the more traditional planar electrode configurations (Design A). This is accredited to the conductive pillar array electrodes and oscillatory flow regime combination. The presence of turbulence promotors that are not electrodes (Design B) does not achieve the same level of limiting current density (A/cm ² ).