WO2019168480A1

WO2019168480A1 - Electrochemical meter for measuring ethanol content in liquids with metal catalyst electrodes

Info

Publication number: WO2019168480A1
Application number: PCT/SI2019/000004
Authority: WO
Inventors: Andrej KAVCIC
Original assignee: Kavcic Andrej
Priority date: 2018-02-28
Filing date: 2019-02-27
Publication date: 2019-09-06
Also published as: SI25400A

Abstract

Electrochemical meter of ethanol content in liquid with metal catalysts solves the problem of simple measurement of the level of ethanol in the liquid, especially in beverages. The major advantage of the meter according to this invention is the high selectivity to ethanol versus sugar and the digital form of the output signal with all the data for further processing. This patent defines the performance of the meter by blowing the humid air to both electrodes of the measuring cell. In this way, the humid air (6), which is oxygen for the chemical process and the water for wetting dielectric, is supplied to the upper electrode, of the in liquid immersed gauge. The air is drawn down to the nozzle (9), which is located in the measured sample of liquid (20) at an appropriate distance below the lower electrode (14). The nozzle generates bubbles. After gravity, the bubbles rise and expand and absorb volatiles of highly volatile ethanol. Bubbles containing ethanol, water vapor and oxygen are rising to the lower electrode (14). A molecular sieve (15) is located between the lower electrode and the measured sample, which separates vapors and air to liquid on the principle of cohesion. Consequently, only the vapors and gases arrive up to the lower electrode, what enables stable operation of the cell. The molecular filter (15) also eliminates the adverse effects of solid material solutions in the sample to protect the lower electrode (14).

Description

ELECTROCHEMICAL METER FOR MEASURING ETHANOL CONTENT IN LIQUIDS WITH METAL CATALYST ELECTRODES

This invention solves the measurement of the concentration of ethanol in water. The same principle can be used at all gauges of ethanol - water solutions, which are of such embodiments, to be partially or completely immersed in liquid.

Today's state of the art of measuring the concentration of ethanol in water offers two options. If the ethanol content of the liquid is not consumed at the time of measurement, then the meter can be dipped in a measured sample. These are for example: refractometer, areometer and optical sensor. Such measurements are largely based on sample measurement. In procedures where the alcohol content in the liquid is consumed at the time of measurement, then merely submerging the meter into an alcoholic solution is not sufficient. Such a gauge is, for example, a biosensor. The simple design is that the liquid flows from the tank, where the measured sample is led along the tube to the meter, and the sample is analyzed. After this measurement, the liquid is waste and, as such, is guided through the drainage pipe into the waste tank. Another possibility is that gauge is immersed in the liquid to be measured and is constantly and steady moved through the fluid. The exchange of liquid can also be provided by means of a mechanical mixer that ensures liquid exchange. All these measurement procedures are impractical and not effective. The supply of the measuring sample to the gauge, according to the present invention is such that the meter is stationary after immersion in the liquid and the air is blown below the measuring point in the liquid. The resulting air bubbles rise along the gauge and cause the measured sample to be changed. This solution has no moving mechanical parts; the exchange of the measuring pattern is quick and reliable. In this way, in addition to the need of exchange the measuring sample, we still solve several essential requirements for proper operation of the device:

• We deliver oxygen by air to electrodes, where oxygen is required to oxidize alcohol, as can be seen from the formula: oxidation of ethanol in water : compound C2 Hs OH + H2O + 302 oxidized to 4H02 + 2CO2 + E

• Due to the different specific gravity of the liquid opposite to the air and ethanol vapor, cavitation separation occurs. Vapors and gases are rising to the sensor, and they exit from the liquid into the bubbles.

• In the bubbles there are vapors of ethanol and water and air. In the aqueous solution of ethanol, strong bipolar bonds operate between the ethanol and water molecules. Consequently, the measurement of the ethanol content directly in aqueous solution is difficult. By introducing energy, we move the measuring sample to a higher aggregate state and accelerate the chemical process. The molecules of water and alcohol are in the bubbles separated from the polar bonds in contrast to these molecules in the liquid.

• In front of the metering point is a molecular filter that on the principle of cohesion forces separates vapors and air from the liquid. In this way no liquid reaches measuring point. A measurement process is therefore faster, because gas-shaped components arrive faster to the catalyst, enabled by the air blown below the measuring point and caviatation.

• By incorporating a molecular filter, the harmful effects of solutions of solids in the measured sample, such as tartar KC4 Hs Ob and the salt NaCI, are excluded.

Ethanol C2 Hs OH (Et OH) and water H2 0 have polar molecules, or both fluids have permanent electric dipole. An electrical dipole means that the molecule has a positive ion on one side, and on the other side, a negative ion. Regardless such molecules, viewed as a whole, are without electric charge, there is a strong intermolecular force between alcohol and water. Such polarization plays an important role in connecting the molecules to the chain. This is the reason for complete solubility of ethanol in water and consequently it is a stable solution. This is marked as dipole-dipole interaction. If we want to carry out any chemical reaction on a bipolar molecule, we must first break this interaction, but for this we need a lot of energy. In such a case we need to input more energy versus to ionization. If we want oxidize alcohol in an aqueous solution, we must first dissociate molecules of ethanol from water in prior to oxidation.

The breakdown of the dipole interaction and the ethanol gasification can be carried out by cavitation. Cavitation is a phenomenon when the pressure over liquid is rapidly reduced the and thus forming bubbles of air and steam. This can be done by blowing the air into the liquid. When the air exits from the nozzle, bubbles are quickly formed. As bubbles rise, they expand, and their volume increases. When the volume of bubbles is expanded in the water, a rapid pressure reduction occurs on the surface. A drop in pressure literally knocks the molecule of alcohol and water into the interior of the bubble because the equilibrium vapor pressure is exceeded. Liquid on contact with the air tends to exit the fluid molecules in the air, that is, from the liquid in a gaseous state. In this phenomenon, molecules must overcome the vapor pressure, that is, the pressure applied by steam to the liquid phase. Equilibrium vapor pressure is an indicator of the evaporation of the liquid. The equilibrium vapor pressure for water is 2.3 kPa and for ethanol 5.83 kPa at 20 deg C. It follows that ethanol is 2.54 times more volatile than water .

By blowing the air into the liquid, thus energy is injected, which manifests as intense evaporation. Evaporation is so intense that it has the character of flashy evaporation, such as boiling. Flashy evaporation is an intense evaporation at a temperature below the boiling point of the liquid. Thus free alcohol and water molecules are generated in bubbles from solutions of alcohol in water. When dissociated ethanol and oxygen molecules are fed to the catalyst, the oxidation is very turbulent. Chemical reaction in wine, juice or vinegar is even more demanding due to the presence of a range of third substances. Various substances are present in these liquids that interfere with the measurement of the presence of ethanol. The most harmful substances for the operation of the measuring cell are tartar ( Potasium bitartrate = KC4 H5 Ob ) and a kitchen salt (Sodium chloride = NaCI).

The performance of the ethanol concentration meter in a liquid with metal catalysts is schematically shown in Figure 1. The parts in the figure are intended to illustrate the operation of the device and are not drawn in the scale relative to the actual size. Figure 1 shows a pipe connection, which leads from the capture of ambient air 1, injection of air into water 3 and controlling the humid air from the outlet 4 to the air injection into the gauge at the location 6. The same air is further guided along the pipe from the outlet 7 through the non-return valve 8 to the nozzle 9. The other lines in the figure are electric conductors, mostly polygonal. The components of the meter and the process are numbered:

1 Ambient air coverage.

2 Air pump with control option.

3 Injecting air into water.

4 Output from the humid air generator.

5 Flumid air generator with gas- tightly closed container and partly filled with water.

6 Injecting moist air over protective fabric.

7 Output of moist air under pressure.

8 Non - return valve.

9 Spray nozzle below the measuring point.

10 Moisture and temperature sensor. 11 Protective fabric of micro fiber.

12 Upper electrode with a catalyst.

13 Dielectric, which is at the same time a separation membrane.

14 Lower electrode with a catalyst.

15 Semi-permeable filter which separates the liquid from the gases and vapors.

16 Sensor for measuring the sample temperature.

17 Microprocessor unit, which also includes an analog input for sensor control and sensor signal gain, power for controlling the air pump, and a USB connection.

18 Exit with all data from the gauge in the USB format and the input for the supply of the necessary electricity.

19 The meter housing.

20 Measured sample.

The measuring cell is composed by layers 12, 13 and 14 . In addition to these layers, optional protective layer of fabric 11 and the molecular filter 15 also form a cell.

In figure circles in humid air generator 5 represent bubbles of humidified air, the small circles in the measured sample 20 EtOH + H2O are bubbles filled by air, water vapor and alcoholic beverages.

The measuring device, which is electrochemical meter of the ethanol content in the liquid with metal catalysts, consists of several sub-assemblies. The basic component part is integrated in the housing 19. This housing is made of electrically non-conductive and of health harmless plastic, resistant to chemically aggressive substances. Housing 19 is designed as waterproof to a depth of 1.5 m according to the IP68 standard.

The ethanol meter in water with the aim of measuring the concentration of ethanol in wine, sweet drinks and vinegar is based on the above description by the means of cavitation , which converts ethanol and water into vapors from the measured sample . The only gasification with the help of cavitation is not enough to completely eliminate the negative influence of the solutions of solids on the measuring site. For the permanently reliable operation of the measuring cell we need a complete selection of steam from the liquid and dissolved harmful substances in it. The consequence of poisoning the measuring cell with these substances is that the sensitivity of the cell to ethanol over time is lower. The essential advantage is, ethanol, as has been proven above, is very volatile. Before measuring cell is filter 15, which separates the steam from the liquid. Filter is made of PTFE (polyetrafluorethylene = (C2 F4)n ) with a commercial name Teflon. Teflon has no cohesion forces up to water and ethanol. It is wrong to believe that due to its hydrophobic properties, Teflon rejects water. It is also wrong to believe that there are adhesive forces. Neither of them exist. In nature there are only forces that attract fluid molecules, or they are not, and there are no solid substances that refuse water or other liquids. When there are no cohesive forces between liquid and the solid, in such a case the effect of bipolar force in the liquids gives the impression, the solid is reflecting the liquid. In the absence of cohesion forces, dipole-dipole interaction forces operate freely in the solution of ethanol in water. These forces, aiming to the center of the liquid have tendency to form droplets. Droplets of water containing ethanol are in the micro-world fairly firm mechanical formations. We cannot easily squeeze them through apertures of 1 pm or less . In order to cross the water in the liquid phase, the openings must be at least 4 pm. Use of Teflon, which has channels transverse to its length in the size class under 1 pm has the nature of the mentioned filter. Such a gap is easily crossed by a steam, but it cannot be crossed by an alcoholic solution.

Dielectric is numbered 13. Its function is translation of ions, but electrons do not translate, therefore it is electrical insulator. Dielectric is a proton-exchangeable membrane (PEM = Polymer Electrolite Membrane or Proton Exchange Membrane). This is completely new and very hygroscopic solid material on the market. In the dielectric, there are 4 to 10 pm channels . If the membrane is dry, it stops working, and if it is over poured with water, oxygen is difficult to get to the catalyst. To the catalyst 12, which is also an electrode, oxygen is to be supplied, and through the porous electrode 12 also water to the dielectric. With the help of the air pump 2, which captures ambient air from the surroundings at the position 1, pressurized air is fed through a tube to a device for humidifying the air 5. The air enters in place 3 and is led into distilled water. The humid air leads to the outlet from the humidifier 4 continue to the place 6, just above the upper electrode measuring cell. Protective fabric 11 is an optional mechanical support for the electrode 12 and disperses air and moisture. When the moist air performs the specified function, it exits from the chamber at place 7 . Next, the air under pressure is lead through a non-return valve 8 to the injection point with nozzle 9 . The air above the nozzle 9 generates cavitation bubbles in the measured liquid H2O + EtOH . Non-return valve 8 has double functions: with its own resistance, as we have to overcome the pressure in the valve, fine and defined overpressure is generated over the measuring cell. Thus cell layers are permanently squeezed. In the event, the sensor is fully immersed in the liquid and air pump does not work, non-return valve prevents reversible intrusion of the measured liquid into the chamber above the dielectric.

The generated air flows from the air pump 2 , via the humid air generator 5 , supplies the necessary moist air to the chamber above the measuring cell . Regardless of the amount of air supplied to the chamber, in any a case supplies enough oxygen for the chemical process in the cell. The amount of moisture input, or water in the gaseous state, depends on several factors. Water is generated on the upper electrode during the ethanol combustion in the cell, and the humidity of the dielectric is also conditioned by the cell activity itself, in addition to the temperature of the cell. In order to control the humidity of the measuring cell, a sensor 10 for measuring humidity up to 100% RH and a temperature gauge up to 60 deg C is in function. The electronic circuit has a backward effect on the amount of inlet air by regulating the speed of air pump 2. Thus controlled conditions are achieved for a stable operation of the measuring cell. This is important because of the accuracy and repeatability of the measurement, and we need to control and stabilize all the changing effects for cell functioning. The temperature of the fluid sample has markedly affect to the measurement result. We have no influence on this effect in the portable version of the device and we must constantly measure it and take into account its impact. At low temperatures, the operation of the measuring cell is not possible, and in this case, we can deviate from the measurement and warn the user at a low temperature. This is particularly true of the measurement samples taken from the refrigerator. Impact of temperature is double. First, evaporation of ethanol and water into bubbles is exponential dependent to temperature. Secondly, temperature also affects the chemical process of catalytic combustion of alcohol in a cell. In order to compensate these effects, two temperature meters are installed. One gauge is located in liquid under cell 16 and another gauge just above the cell 10. Impact of temperature is compensated according to the program of the processor 17. The processor directly controls the air pump 2, data of concentration of alcohol, humidity over the cell and the temperature is further processed via USB output 18. The USB connector is also the power source for processing the processor 17, pump 2 and digital meters 10 and 16. The total energy consumption is less than 7W, which corresponds to the standard of the USB connection capability. Fortunately, the measuring cell is already the source of energy-rich output signal. This property can be used extensively in the construction. The cell may in neutral electrical state, at no electric load, generates output voltage of 0.3V. We must be aware; the cell is current generator and not voltage generator. Output voltage signal is not a function of concentration of ethanol, but the output current is proportional to the ethanol concentration. Cell at open connections, without electrical contact between electrodes, generates an output voltage of about 0.1V already at small concentrations of ethanol. Measurement of the concentration of ethanol is not able at open cell terminals. The electrodes must be connected with an electric conductor and the current between the electrodes is to be measured. The current depends to the concentration of ethanol, what is essential for the measurement. This is also the energy situation logic. If the voltage at open terminals is measured with the voltmeter, no current flows into voltmeter and the measurement is without energy consumption. This means, the voltage at the open terminals is independent of the amount of ethanol oxidation and is energy-independent to the fuel combustion. When we measure the current between the electrodes, the energy generated by oxidation of ethanol is completely consumed by measuring equipment. The energy situation logic is thus confirmed. More ethanol, more oxidation, and consequently higher current of electrons at connection between the electrodes.

The lower the electrical resistance of the connection between the electrodes, the greater is the current between the electrodes, the more stable is the operation of the measuring cell. This is mainly reflected in the time of regeneration of the cell after measurement. During the cell's exposure to ethanol, ions, hydrogen protons, accumulate in the dielectric. Protons are energy carriers. If electrodes are short-circuited, energy is rapidly consumed and protons in the dielectric are neutralized. The better is electrical conductivity of connection between electrodes, the measurement is more accurate and the cell regeneration after the measurement is faster. What electrodes do they need to be? Requirements are worse than expectations. The surface of the electrodes do not affect to the voltage of the open terminals. Measurement of output voltage without electrical load, the voltage at the electrodes are independent to the surface of electrode, it is always close to 0.3 V, also at very low concentration of ethanol. When the electrodes are electrically connected, flow of electric current is proportional to the surface area of the electrodes, and, of course, the concentration of ethanol. What is the required surface area of electrodes for the needs of measurements, the answer is obvious. The required surface depends on the possibility of signal amplification by the electronic circuit. Practice has shown that a surface area of approximately 1 square cm is sufficient. The surface depends to the price of expensive catalyst, the precision of the product and the size of the gauge. These are conditions that influence the fact, in the present state of the art the optimal surface is 1 square cm. We can anticipate that the optimal surface will decrease over time to about half. The electrodes must be porous to allow the flow of gases and steams through them.

Which metal is suitable for the catalyst? The cell works in principle on all platinum metals and their alloys. The choice of metal affects to the efficiency of catalysis and to the price of the cell. Here, too, we find the optimal solution. However, there is one requirement that significantly influences the selection of metals. The measuring device has a fundamental requirement; there should be no signal at the output when there is no presence of measuring sample, in this case ethanol. If electrodes are used by different metals, this may have some positive effects on the cell's functioning, but there are always electro potential differences between different metals. Basically, at different metals we make a galvanic article. Since in our case, there is a well conducting connection between the electrodes, the cell with electrodes done by different metals behave as a short-circuit battery. This eventually leads to the destruction of the cell. A simple solution is that both catalysts are of the same metal and no voltage is present already at the start, in short, output voltage is zero down to microvolt.

What thickness of the catalyst layer is needed? The low electric resistance connection between the electrodes requires a good conductivity of the catalyst. Conductivity is improved by the thickness of the catalyst. The electric current passed over a catalyst at high ethanol concentration may be so high, it can permanently damage catalyst. The weak side of the catalyst thickness is the reduction of porosity and the prolongation of the response time of the cell, as the measuring substances must cross the longer path, and ultimately, the higher price. Since we have here opposite effects and interests, the decision is the subject of the constructor, not theoretically identifiable.

In addition to the electron flow from the catalyst to the electrodes, the ionization from the catalyst to the dielectric, as indicated above, must be ensured in the catalyst. This is ensured by adding to the metal a dielectric solution at a concentration of several percent of the dielectric substance at the time of making the catalyst.

Where are the limits of usability of such a meter? The limits are the lower and upper limits for measuring the concentration. Basically, the cell is extremely sensitive, which reacts sufficiently under concentration of 0.5% ethanol in water. The upper limit of the gauge is conditioned by saturation of the dielectric. Dielectric can translate ions to the above border when saturation occurs. Thus, the process stops at high concentration because the cell capacity cap has been reached. The molecular filter, located under the electrode 14, influences on both sides of sensitivity. In any case, the filter moves both borders upwards. Because the measuring cell is very sensitive, it is advantageous to operation of the device. With the density of the filter, the lower limit becomes critical. If we tend to increase the sensitivity of the gauge , we need the higher filter's permeability despite the high sensitivity of the cell . We are facing an unusual phenomenon here. The measuring cell acts at a molecular level. Otherwise, micro world becomes noticeably large at the measuring cell. Molecular phenomena in the cell are so expressed, almost every ion is felt at the output, and the output signal is not calm, but full of pulses of undefined repetition. This phenomenon is called white noise in electronics. The noise can hide a useful signal and therefore influences to the measurement at low concentrations of ethanol. It follows, it is necessary to search for optimal filter damping according to the needs. We proceed from the requirement for which field of concentration of ethanol we need the device. In any case, the good side of this possibility is that the upper limit can be lifted above 20% of ethanol in water.

How is the meter calibrated? There are two borders here. The lower limit is when we need to have a zero signal at the gauge immersed in distilled water. We can select another measuring point also. Fortunately, we can make etalon by ourselves, because we can precisely and easily mix defined volume of ethanol and water and thus we make standard concentration for calibration.

USB output can be accessed to any digital device with a display. On the screen we can display all the measured data, and above all, the target data, what is concentration of ethanol in the sample. All the necessary measurement instructions may be also displayed on the screen. These are the permission to start the measurement, which is substantially influenced by the humidity of the dielectric, a warning in case of too low temperature of both the measured liquid and the ambient air and other instructions. Important instructions include re- measurement when the device reaches successful regeneration of the cell after the last measurement. Intermediate states, such as the course of the measurement preparation and regeneration after last measurement is also displayed on the screen, with an estimate time of the duration of the intermediate states. The USB connector is also intended for power supply of the meter, which is approximately 5 W. The main energy consumer is an air pump. If we are measuring the meter from the power line, the consumption is negligible. If portable devices are powered by battery, we have to count on spending capacity about 500 mAh per measurement.

Claims

PATENT CLAIMS

1. Electrochemical meter of ethanol content in liquid with metal catalysts, characterized in that ,

for operation over-pressured controlled humidity air is lead to the upper electrode

(12 ) .

2. An electrochemical meter for ethanol content in a liquid with metal catalysts according to claim 1,

characterized in that ,

by blowing the air under pressure into the measured liquid (20) under the lower electrode (14) and thus bubbles are created containing air and vapor of ethanol and water .

3. An electrochemical meter for ethanol content in a liquid with metal catalysts according to claim 1 and 2,

characterized in that ,

a semi-permeable filter (15) is located between the measured sample (20) and the measuring cell, which is impermeable to the substance in the liquid phase.

4. An electrochemical meter for ethanol content in a liquid with metal catalysts according to claim 1, 2 and 3,

characterized in that ,

the humidity and the temperature above the upper electrode of the measuring cell (12) is measured by an electronic meter (10) and data on these magnitudes are lead to the processor.

5. An electrochemical ethanol content meter in a liquid with metal catalysts according to claim 1, 2, 3 and 4,

characterized in that ,

to measure the temperature of the measured sample (20) using a temperature gauge (16) and this information goes to the processor.