NL1015183C2 - Method and device for the electrochemical generation of one or more gases. - Google Patents

Description

METHOD AND APPARATUS FOR THE ELECTROCHEMICAL GENERATION OF ONE OR MORE GASES

The present invention relates to a method and apparatus for electrochemically generating one or more gases under high pressure. The invention also relates to an integrated circuit to which a large number of the above devices have been applied and to a method for analyzing the operation of a catalyst.

So-called pressure vessels or "autoclaves" are used for the execution and study of physical or chemical processes under high pressure. The achievable pressure in conventional autoclaves is typically a few hundred to a maximum of several thousand atmospheres. In such autoclaves, a (high) temperature can further be set and controlled.

A drawback of such an autoclave is the necessity to provide far-reaching and expensive safety provisions in connection with the risk of explosion, for instance in the form of a specially equipped free-standing laboratory with a loose roof. There are also 20 stringent safety regulations regarding the construction and use of these autoclaves.

A further drawback is that conventional autoclaves are relatively large and therefore intrinsically slow in variations in pressure, temperature and chemical potential, making the autoclaves difficult to control. Moreover, the amount of material required, for example catalyst, when analyzing a chemical reaction with this catalyst, is relatively large. The above drawbacks make the use of autoclaves relatively laborious and expensive. As a result, in practice only a limited number of measurements can be performed.

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A further drawback of the existing autoclaves is that, since the pressure build-up in the autoclave is slowly established, the occurrence of certain chemical reactions which require a fast pressure build-up is hindered.

It is an object of the present invention to provide an apparatus and a method in which the above drawbacks are obviated.

According to a first aspect of the invention, a device is provided for electrochemically generating one or more gases under high pressure, comprising: - a container comprising one or more chambers to be filled with electrolyte; - a first and a second electrode over which a voltage difference can be applied for effecting electrochemical generation in the holder; the contents of a chamber being of the order of a few milliliters or less and the chamber preferably containing a maximum of 150 microliters of electrolyte. With such a small volume of the chamber or chambers, the forces on the walls of the container are so low that no special safety provisions have to be made and the device is therefore intrinsically safe. Even with a possible explosion of the gases in the container, no significant damage occurs to the container and its surroundings. This provides a device with which safe physical and chemical processes can be carried out and studied under high pressure and with which a (large) number of experiments can be carried out quickly and efficiently in a relatively short time using minimal amounts of material, in particular the high pressure chemical catalyst testing.

The device provides an intrinsically high speed with short relaxation times for adjustment and equalization of parameters such as pressure, temperature and chemical potential.

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In addition, autoclaves of a type are known in which the initial pressure is established by connecting the autoclave reaction chamber to gas bottles or gas lines for supplying gas under relatively high pressure. This has the drawback that the design is complex and extensive. This drawback is obviated in the device according to the invention in that the gases are generated in situ, that is to say in the container itself.

According to a preferred embodiment of the invention, the first electrode is positioned in the first chamber of the container for generating a gas of a first type, for example hydrogen, therein, the second electrode is positioned in the second chamber of the container 15 for generating a gas of a second type, for example oxygen, therein and the two chambers are mutually connected by a connecting channel of such a length that mutual diffusion of the gases is limited. A material 20 is provided in the connecting channels, which is electrically conductive, but hinders the mutual diffusion of the gases in the individual chambers. In this preferred embodiment, the gases generated at each electrode can be generated separately, ie without mixing, and then used in a chemical or physical process.

According to a further preferred embodiment, the device comprises pressure determining means for determining the pressure of the electrochemically generated gases, for instance in the form of a piezo-resistive pressure sensor. This pressure sensor can be mounted directly in (a chamber of) the container, for example by screwing it to one end of the container. In addition to such pressure sensors, other sensors can also be used, for example sensors that detect certain chemical properties, as well as temperature sensors.

According to a further preferred embodiment, the device comprises voltage control means for regulating voltage between the first and the second electrode and thereby controlling the speed at which the electrochemical generation takes place. In a further preferred embodiment, a pressure build-up speed in the container of at least 8 bar per second or even 20 bar per second or more is thus achieved. In a further preferred embodiment, the voltage control means are connected to control means for controlling the electrochemical generation velocity substantially in real time and, as a result, the pressure in the (chambers of the) container. In the device according to the invention such a rapid build-up of pressure within the container occurs that the control means can control the pressure in the container in substantially real time, i.e. within a few minutes or even seconds.

Despite the high pressure in the container, which can amount to several thousands of bar, no high constructional requirements are imposed on the material of which the container is made. Despite these high pressures, the container can be made of standard, easy-to-process technical material, such as aluminum or plastic. This makes it possible to manufacture the devices in a simple manner, on a large scale and at low cost.

According to another aspect of the invention, there is provided an integrated circuit for simultaneously performing a variety of chemical or physical processes, including a substrate, devices of the aforementioned type applied to the substrate for performing the processes, as well as control means provided on the substrate and connected to the device for controlling the processes carried out in the respective holders. Such an integrated circuit is manufactured by micro-manufacturing techniques known per se, in which, for example, a large number of devices are applied to a silicon substrate, which are made of silicon, glass or a similar material.

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For example, when researching new catalysts or improving existing catalysts, a large number of experiments must be carried out with large series of a certain type of catalyst with always small different material parameters. This approach is known as "high throughput experimentation (ΗΤΕ)" and is characterized by a large number of syntheses and analyzes. According to the invention, by integrating a large number of the devices in an integrated circuit, a large number of analyzes and syntheses can be carried out in parallel and within a very short period of time, and a small amount of catalyst material is also required per catalyst.

According to a further aspect of the invention, there is provided a method for analyzing the operation of a catalyst, comprising: - arranging a first and a second electrode in the holder; - arranging the catalyst in the holder; - filling the container with electrolyte; applying a potential difference across the electrodes for electrochemically generating the electrolyte; - determining, at certain pressures, the compensation flow required to maintain the pressure in the container substantially at this pressure value for analyzing the operation of the catalyst. The operation of the catalyst at a large number of (high) pressures can hereby be determined in a simple and rapid manner.

Further advantages, features and details of the present invention will be elucidated in the following description of preferred embodiments thereof. Reference is made in the description to the figures, in which: figure 1 shows a cross section of a micro-pressure cell according to a first embodiment; 101 51 83 6 - figure 2 shows a cross-section of a micro-pressure cell according to a second embodiment; figure 3 is a graph showing the built-up pressure as a function of time at a current of 20 mA; figure 4 is a graph showing the built-up pressure as a function of time at a current of 50 mA; figure 5 shows a graph of the required flow 10 to compensate for the return reaction (compensation flow) as a function of the pressure; figure 6 shows a cross-section of a further embodiment of a micro-pressure cell for testing chemical catalysts; and Figure 7 is a perspective view of an integrated circuit of micro-pressure cells.

Figure 1 shows an exemplary embodiment of a micro-pressure cell with a chambered aluminum holder 1. A pressure sensor 20 4 is screwed on one end of the chamber, which has a stainless steel housing and an aluminum base plate. Two platinum electrodes 2 are glued in the base plate (127 micrometre platinum wire, glued in a molten silica (fused silica) capillary). A standard O-ring 5 is used as a high-pressure seal. The volume of the chamber created is of the order of a few milliliters or less.

The electrodes 2 are connected via standard voltage cables passed through the holder 1 to a power source 3. After filling the micro-pressure cell with electrolyte, such as for instance water with added salts, and screwing in the pressure sensor 4, an electric current is generated and a number of gases are produced by electrolysis in the container, such as, for example, hydrogen gas (H2) and oxygen gas (02).

Figure 2 shows an alternative embodiment of the micro-pressure cell. In a holder 6, which can be made of plastic, in this case plexiglass, a first chamber 7 and a second chamber 8 are provided. A connecting channel 9 is provided between the two chambers 7 and 8, which ensures an open connection between the chambers. An electrode 10 is arranged in chamber 7 and an electrode 11 in chamber 8. Both electrodes are connected via standard electric wires 14 to a power source 15, which in turn can be controlled with, for example, a computer 16 or the like. The chambers 7 and 8 are respectively closed at their top with sealing caps 10 12 and 13, in which discharge channels 18 and 19 provided with valves 20, 21 are provided. For example, suppose that electrode 10 functions as an anode and electrode 11 functions as cathode, then chamber (7) and chamber 8 generate oxygen (02) and hydrogen (H2), respectively. Both gases can be discharged separately in this embodiment. The connecting channel 9 has in its center a branch to a dotted pressure sensor 17 which can measure the pressure prevailing in the connecting channel 9.

Figure 3 shows the pressure build-up by the gases formed during the electrolysis of a 100 mM KN03 aqueous solution in a pressure cell with a content of 150 μΐ, at a current of 20 mA. The use of this inert electrolyte results in electrolysis reactions known per se. Figure 3 shows how the pressure p (in bar) proceeds as a function of the time t (in seconds) after the power source 3 has been switched on. This shows that the pressure increases almost linearly with time due to the constant production of gas. Already at this relatively low amperage pressure in the container increases rather quickly. After 900 seconds (Mark A), the power is turned off and the pressure drops due to the back reaction: the formation of water from hydrogen gas and oxygen gas.

Figure 4 shows the pressure build-up for the same system at a current of 50 mA (marking C), each time with a 100 bar pressure rise (marks B, B2, ...), the current required to keep the current constant is determined. pressure. This "compensation current" 1015183 8 is a measure of the rate of the reverse reaction. The figure shows that the pressure increases rapidly, whereby high pressure values of approximately 1400 bar can be realized.

In Figure 5, the "compensation flow" 5 is further plotted against the pressure. For pressures above 800 bar, the compensation flow increases exponentially, indicating a drastic increase in the high-pressure return reaction.

Figure 6 shows an exemplary embodiment of a pressure cell for testing chemical catalysts. In a reaction space 22 closed with caps 28, hydrogen gas under high pressure is generated by electrolysis by the platinum electrodes 2. In the pressure cell also a catalyzed hydrogenation action of a compound 15 which has been introduced into the reaction space 22 under the influence of catalyst 27 takes place. From the measured "compensation flow" at a given pressure, the reaction rate of the respective hydrogenation action can be derived, and thus the action (activity) of the catalyst 27 used. In this way, the catalyst can be analyzed and tested.

In addition to generating the aforementioned gases such as hydrogen and oxygen, there is also the possibility of electrochemical in-situ generation of 25 other gases such as Cl2, F2, D2, CO2.12 and Br2.

Due to the small dimensions and when using micro techniques such as thin or thick film technique, abrasive techniques, etching techniques and lithographic techniques for the manufacture, it is possible to manufacture large numbers of parallel operating pressure cells, with which large series of experiments can be carried out in a relatively short time with use of minimal amounts of material.

In a preferred embodiment (not shown) a large number of devices (such as micro-pressure cells) as well as the associated electrical connections, etc., using, for example, abrasive techniques, etching techniques, vacuum technique such as sputtering or evaporation, are then not in combination with lithographic techniques applied to a single substrate in an integrated circuit. This makes it possible to manufacture micro-chemical processing units for use in HTE systems, with which a very large number of analyzes can be performed in a short period of time.

Furthermore, as possible applications we also mention a chemical microreactor, and in particular a micro fuel cell, or a high pressure micro pump.

Since a high pressure is available in this system, certain reactions which are normally carried out at a reasonably high pressure and at an elevated temperature at a lower temperature or even at room temperature can be carried out. An example of such a reaction is the hydrogenation of benzene to cyclohexane. This reaction, which has hitherto been carried out with the "normal" means at an elevated pressure and an elevated temperature, can be carried out according to the invention cell 20 at room temperature.

In addition, the use of short high pressure pulses can influence the kinetics of the reaction. This is due to differences in how the reaction comes about. If the reaction is effected by colliding two or more molecules, the diffusion rate of the molecules will mainly be important for the speed at which the reaction proceeds and not a parameter such as the pressure on the reaction mixture.

If the reaction is unimolecular (as in a rearrangement) then the amount of energy that the molecule is supplied by the system is important for the speed at which the reaction proceeds. This depends on the pressure on the reaction mixture.

If both reactions mentioned above can occur in a reaction mixture, the unimolecular reaction will be favored by a pressure pulse. Thus, the specificity of the reaction can be influenced.

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In order to carry out more reactions, a number of additional "agents" can be used that affect the reaction conditions. These agents aim to give the molecules just the extra energy they need to react. These methods can also influence the molecules in such a way that this reaction proceeds more specifically. For example, a reaction in which two stereoisomers can be formed proceeds such that more of one stereoisomer is formed than of the other. Thus, a so-called enantiomeric excess occurs in the reaction.

These means can be: heating means for increasing the temperature in the container, preferably by integrating a heating element in the form of an electrical resistance in the cell 15. This resistance can be easily implemented in thin film technology by applying a metal film. By passing current through this metal film, it becomes warm and thereby heats its environment. The heating means may be arranged along the walls of the chamber so that the contents of the chamber are heated from the outside, but also along an electrode or catalyst on the contents of the chamber from which it is heated.

25 - means for applying an electric field over the reaction mixture. This can be done by arranging two metal plates parallel to the chamber in which the reaction takes place, which function as capacitor plates over which a voltage can be applied. Applying a voltage (a few tens to thousands of volts) creates an electric field over the reaction mixture, which causes a change in the molecules in the reaction mixture. This can cause a change in the orientation of the atoms in the molecules, so that certain reactions will run better than other reactions. This includes stereochemical reactions in which one stereoisomer will be formed more than the other.

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The electric field can be continuous (caused by a DC voltage) or alternating (caused by an alternating voltage across the capacitor plates).

- means for applying a magnetic field over the reaction mixture. This can be done through a coil to make the reaction mixture over which a DC voltage or AC voltage is applied. Also in this case, both continuous fields and alternating fields can be used.

- means for irradiating the reaction mixture with optical or electromagnetic radiation, in particular radiation from the deep infrared spectrum into the gamma region. Another purpose of the irradiation may be to record a photo spectrum of the reaction mixture to see which reaction products are formed.

- means for supplying acoustic energy, for example ultrasonic energy, to the contents of the container.

In addition, catalysts can be added to the reaction mixture to see which reaction products are being formed or to allow a given reaction to proceed "catalytically".

The use of means for introducing high-energy electrons into the reaction chamber can influence the reaction of components of the reaction mixture as desired.

An example of a reaction which has significant advantages when performed at high pressure is the Diels-Alder reaction of butadiene with di- (R) -menthyl fumarate. This reaction gives two possible stereoisomers. When the reaction is run at high pressure, 10 times as much of the S isomer is produced as when the reaction is run under one atmosphere. Moreover, due to the rapid build-up of pressure in the present pressure cell, preferred reactions occur, whereby other, less preferred reactions are counteracted or even omitted.

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Furthermore, figure 7 shows a schematic perspective view of an integrated circuit on which a number of micro-pressure sensors are arranged. The circuit comprises a substrate 29 on which fifteen to five micro-pressure cells are arranged. Each micro-pressure cell comprises a first chamber 30, a second chamber 31 and a connecting channel 32. By means of a control unit 33, liquid and electricity lines 34 are connected which are connected to each of the pressure cells (shown only schematically in the figure). The voltage values required to operate the micro pressure cells can be in the order of magnitude of the voltage values for operating electronic switches (not shown) applied to the substrate, such as transistors, diodes, resistors, etc. turn into. This has created a hybrid chip, in which an integration of electronic circuits and micro-pressure cells on a substrate has been realized.

The present invention is not limited to the described preferred embodiments thereof; the requested rights are determined by the claims within the scope of which many modifications are conceivable.

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Claims (24)

Device for electrochemically generating one or more gases under high pressure, comprising: - a container comprising one or more chambers to be filled with electrolyte; 5. a first and a second electrode over which a voltage difference can be applied for establishing an electrochemical generation in the holder; wherein the volume of a chamber is of the order of a few milliliters or less. The device of claim 1, wherein the contents of a chamber contain up to 150 microliters of electrolyte. The device of claim 1 or 2, wherein the first electrode is positioned in a first chamber 15 of the container for generating a gas of a first type therein, the second electrode is positioned in a second chamber of the container for generating therein generating a gas of a second type and the two chambers are mutually connected by a connecting channel of such a length that diffusion of the gases is limited. An apparatus according to claim 1, 2 or 3, comprising pressure determining means for determining the pressure of the electrochemically generated gases. 5 is H2, 02, Cl2, F2, D2, CO2, I2, and / or Br2. The device according to claim 4, wherein the pressure determining means comprise a piezo-resistive pressure sensor. 6. Device as claimed in any of the foregoing claims, comprising voltage regulation means for regulating the voltage between the first and second electrode. 1015183 An apparatus according to claim 6, wherein a pressure build-up speed in the container is achievable 8 bar per second or more, or even 20 bar or more. 8. Device as claimed in claim 6 or 7, wherein the voltage regulation means are connected to control means for controlling the pressure in the container in substantially real time. 9. Device as claimed in any of the foregoing claims, comprising heating means for heating the contents of the chamber. Device as claimed in claim 9, wherein the heating means comprise a metal film arranged in the holder and connected to an electric power source. 11. Device as claimed in any of the foregoing claims, provided with means for applying an electric field over the holder. 12. Device as claimed in any of the foregoing claims, provided with means for applying a magnetic field in the holder 20. Device as claimed in any of the foregoing claims, wherein the holder is substantially optically transparent. 14. Device as claimed in claim 13, comprising optical irradiation means for irradiating the contents of the holder. Device as claimed in any of the foregoing claims, provided with means for supplying acoustic energy to the content of the container. An apparatus according to any one of the preceding claims, comprising catalyst fasteners for mounting a catalyst in the container. Device according to any one of the preceding claims, comprising means for providing high energy electrons in the holder 35. Device as claimed in any of the foregoing claims, wherein the holder is made of conventional 1 01 51 83 technical material, such as aluminum, or plastic and in particular plexiglass. The device of any preceding claim, wherein the electrochemically generated gas 20. Integrated circuit for simultaneously carrying out a large number of chemical or physical processes, comprising: - a substrate; A number of devices arranged on the substrate according to any one of the preceding claims for carrying out the processes; control means provided on the substrate and connected to the devices for controlling the processes carried out in the respective holders. Method for the electrochemical generation of one or more gases, comprising: - applying electrolyte in a container; 20. arranging a first and a second electrode in the holder; - applying a potential difference across the electrodes. 22. Method for analyzing the operation of a catalyst, comprising: - placing a first and a second electrode in the holder; - placing the catalyst in the holder; 30. filling the container with electrolyte; applying a potential difference across the electrodes for the electrochemical generation of gas; - analyzing the contents of the container. The method of claim 22, wherein the analyzing step comprises determining the compensation flow required at certain pressures to maintain the pressure in the container at 101 51 83 *. 24. A method according to claim 22 or 23, wherein the device according to any one of claims 1-19 is used. 1 01 51 83