Electrochemical process measuring device

Abstract

The invention relates to an electrochemical process measuring device (10) having a process sensor unit (30), the sensor unit (30) comprising a reference electrolyte tank (50) having a reference electrolyte and a reference electrode (54), and a measurement electrolyte tank (60) having a measurement electrolyte liquid (62), a measurement electrode (64), a gas selective membrane (90) separating the reference electrolyte (52) from the sample (13 '), and a pressure equalization channel (84) fluidly connecting the tank interior (56) to the atmosphere (11). The pressure equalization channel (84) is defined by an equalization channel body (80) made of a hydrophobic material having a contact angle Theta higher than 90 DEG. This allows a very narrow pressure balance channel to be achieved without the risk of clogging by electrolyte droplets, thereby significantly reducing the evaporation loss of measuring the electrolyte.

Description

Technical Field

[0001] The invention relates to an electrochemical process measuring device comprising an electrochemical process sensor unit. Background Art

[0002] A typical electrochemical process measurement device is provided for quasi-continuously determining an analyte (e.g., ammonium concentration) in water and includes a pH electrode assembly having a pH electrode portion and a reference electrode portion. The pH electrode portion includes a measuring electrolyte tank containing a measuring electrolyte liquid, a measuring electrode immersed in the measuring electrolyte liquid, and a pH glass membrane separating the measuring electrolyte from a reference electrolyte. The reference electrode portion includes a reference electrolyte tank containing a reference electrolyte liquid and a reference electrode immersed in the reference electrolyte liquid, and a gas-selective membrane separating the reference electrolyte liquid from the sample liquid.

[0003] Gas-selective membranes are very thin and therefore very sensitive to pressure differences between the proximal and distal sides of the membrane (i.e., the pressure difference between the sample liquid inside the reference electrolyte tank and the sample liquid adjacent to the gas-selective membrane on the membrane's exterior). The thinner the gas-selective membrane and the more vulnerable it is to the pressure difference across the membrane, the higher its permeability should be for the gas ions in question. High-precision gas-selective membranes can be disrupted or damaged at pressure differences above 1.0 mbar.

[0004] Therefore, the reference electrode portion is provided with a pressure equalization channel that fluidly connects the gas volume within the reference electrolyte tank with the surrounding atmosphere. However, the cross-sectional area of the pressure equalization channel needs to be large enough to avoid complete blockage of the cross-sectional area of the pressure equalization channel by droplets. The droplets are caused by condensation of humidity from the external atmosphere or the reference electrolyte liquid within the reference electrolyte tank.

[0005] The reference electrolyte liquid evaporates continuously through the pressure equalization channel, so that the reference electrolyte liquid is typically depleted after a depletion interval of several weeks. This effect is even stronger if the process sensor unit is equipped with an electrical heating device for continuously tempering the electrolyte liquid at, for example, 45°C, thereby ensuring relatively short reaction times and constant basic conditions regardless of the ambient temperature. Summary of the Invention

[0006] It is an object of the present invention to provide an electrochemical process measuring device with reduced evaporation of the reference electrolyte liquid.

[0007] This object is achieved by an electrochemical process measuring device having the features of claim 1 .

[0008] The electrochemical process measuring device according to the present invention is provided with an electrochemical process sensor cell comprising a measuring electrolyte liquid, a measuring electrode at least partially immersed in the measuring electrolyte liquid, and a pH glass membrane separating the measuring electrolyte liquid from a reference electrolyte liquid.

[0009] The process sensor also includes a separate reference electrolyte tank containing a reference electrolyte liquid, a reference electrode partially immersed in the reference electrolyte liquid, and a gas-selective membrane separating the reference electrolyte liquid within the reference electrolyte tank from the sample liquid outside the reference electrolyte tank. Preferably, the gas-selective membrane is defined by a membrane body having a thickness of less than 250 μm. A gas-selective membrane having a thickness of less than 250 μm is highly permeable to the gas ions in question, resulting in a very fast response time for the process sensor unit.

[0010] The reference electrolyte tank is also provided with a pressure-equalizing channel that fluidically connects the interior of the reference electrolyte tank to the surrounding atmosphere. The pressure-equalizing channel ensures that the fluid pressure inside the reference tank is at atmospheric pressure. As a result, the pressure differential across the gas-selective membrane is very low, preventing the gas-selective membrane from being disturbed or damaged by excessive pressure differentials across the membrane.

[0011] The pressure balancing channel is defined by a balancing channel body made of a hydrophobic material having a water contact angle Theta greater than 90°, preferably a water contact angle Theta greater than 150°. Preferably, the balancing channel body is made of a flour-based polymer, such as FEP or PTFE, also known as Teflon.

[0012] The inner balancing channel wall, defined by the balancing channel body, has a hydrophobic surface, significantly reducing the specific adhesion force of liquid droplets within the pressure balancing channel compared to hydrophilic channel surfaces. Consequently, the cross-sectional area of the pressure balancing channel can be designed to be very small, preferably less than 1.0 mm². The effective evaporation loss of the reference electrolyte liquid is substantially dependent on the cross-sectional area of the pressure balancing channel. Due to the very small cross-sectional area of the pressure balancing channel, effective evaporation through the pressure balancing channel is significantly reduced. Consequently, the depletion interval of the reference electrolyte liquid is significantly extended by up to 2.0 times, or even more.

[0013] According to a preferred embodiment, the ratio R of the balance channel length to the balance channel cross-sectional area of the pressure balance channel is greater than 2.5, preferably greater than 5.0. In other words, the balance channel is relatively long relative to its cross-sectional area. The use of a hydrophobic material for the pressure balance channel allows the cross-sectional area of the balance channel to be minimized. As a result, relatively small temperature changes in the gas volume within the reference electrolyte tank will cause relatively large oscillatory gas movements in the pressure balance channel, so that even small temperature changes will cause humidity to be discharged from the reference electrolyte tank to the atmosphere. The longer the pressure channel, the smaller the effective evaporation losses, so increasing the longitudinal extension of the pressure balance channel will compensate for the negative effects of a very small cross-sectional area.

[0014] Preferably, a sample container is provided with a sample liquid, wherein the process sensor unit extends into the interior of the sample container such that the gas-selective membrane is immersed in the sample liquid. Preferably, the level of the sample liquid in the sample container is at substantially the same vertical height as the level of the reference electrolyte liquid in the reference electrolyte tank such that the hydraulic pressure difference across the gas-selective membrane is substantially close to zero.

[0015] Preferably, the sample container is arranged to be fluidly open to the atmosphere such that the gas pressure at the surface of the sample liquid and at the surface of the reference electrolyte liquid are the same.

[0016] Preferably, the sensor cell heating device is configured to heat the process sensor cell. More preferably, the sensor cell is provided with a temperature sensor and a temperature controller including a set temperature memory. The temperature controller controls the temperature of the process sensor cell, in particular the temperature of the electrolyte liquid, to provide substantially constant conditions for determining the analyte concentration.

[0017] Preferably, the set temperature stored in the set temperature memory is at least 40° C., more preferably about 45° C. The relatively high process sensor temperature ensures a relatively fast reaction time and also ensures that the process sensor temperature does not rise above the process sensor set temperature in an environment where ambient temperatures exceeding 30° C. may occasionally occur. A cooling device for occasionally cooling the process sensor unit is not required.

[0018] Preferably, the sensor cell heating device is directly attached to the sample container so that the housing of the sample container and / or the reference electrolyte tank and / or the measuring electrolyte tank are directly heated by the sensor cell heating device. This allows for reasonable and precise control of the process sensor cell temperature.

[0019] Preferably, the sensor unit is provided with a reference electrolyte tank cover, wherein the balancing channel body defining the pressure balancing channel is a separate but integral part of the reference electrolyte tank cover. More preferably, the reference electrolyte tank cover is defined by a tank cover body made of a non-hydrophobic plastic. In other words, the reference electrolyte tank cover is made of two different materials, so that the main tank cover body material can be perfectly adapted to its mechanical function. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An embodiment of the present invention is described with reference to the accompanying drawings, in which:

[0021] Figure 1 schematically shows an electrochemical process measuring device with a process sensor unit,

[0022] Figure 2 The schematic diagram of the vertical cross section shows in detail the electrochemical measuring probe and the sample container. Figure 1 process sensor unit, and

[0023] Figure 3 Shown including pressure balance channel and covering Figure 1 and Figure 2 An enlarged view of the electrolyte tank cover body of the reference electrolyte tank of the process sensor unit. DETAILED DESCRIPTION

[0024] Figure 1 An electrochemical process measurement device 10 is shown including a stationary sample water reservoir 12 having sample water 13 and including a land-based process analyzer station 20. Process analyzer station 20 includes a sample pump 22, a process sensor unit 30, and an analyzer controller 24 including a sensor unit temperature controller 28 within an analyzer housing 20'.

[0025] The sample water reservoir 12 can be part of a water treatment plant, and the process sensor unit 30 can be adapted to determine the ammonium concentration of the sample water 13. A sample pump 22 continuously pumps the sample water 13 from the sample water reservoir 12 to the process sensor unit 30 via a supply line 25. The sample water 13 flows into a sample container 32 of the process sensor unit 30 through a sample inlet opening 25' and continuously flows from the sample container 32 back into the sample water reservoir 12 through an outlet opening 26' and via a return line 26, thereby continuously mixing the container sample water 13' with the fresh pool sample water 13. The sample container 32 is essentially defined by a sample container housing 32'. The interior of the sample container is vented to the atmosphere 11 via a sample container vent 34, so that the pressure of the air cushion 35 above the sample container water 13' is always equal to the ambient atmospheric pressure.

[0026] Figure 2, the process sensor unit 30 is shown in more detail: the process sensor unit 30 comprises an electrochemical measuring probe 40 , which comprises an annular reference electrolyte tank 50 and a central measuring electrolyte tank 60 surrounded by the reference electrolyte tank 50 .

[0027] The measuring electrolyte tank 60 is defined by a substantially cylindrical main tank housing 60 ′ made of glass. The main tank housing 60 ′ is closed at the bottom by a pH glass membrane 91 .

[0028] The reference electrolyte tank 50 is defined by a reference tank housing 50' that encloses an annular tank interior containing a reference electrolyte liquid 52 and a reference electrode 54 partially immersed in the reference electrolyte solution 52. The reference electrolyte tank 50 is closed at the bottom by a gas-selective membrane 90 and at the top by a separate reference electrolyte tank cover 70. The gas-selective membrane 90 is defined by a thin film body 92 having a thickness of less than 200 μm, making the membrane body 92 mechanically very fragile. The interior 56 of the reference electrolyte tank 50 is filled with a suitable reference electrolyte liquid 52, while a gas cushion exists above the surface of the reference electrolyte liquid 52.

[0029] The electrochemical measurement probe 40 defines a typical pH probe and is used in this embodiment to determine the concentration of ammonium in the sample water 13 ′.

[0030] The reference electrolyte tank cover 70 includes a main tank cover body 70' made of a non-hydrophobic plastic and a separate hollow cylindrical balancing channel body 80 defining a vertical pressure balancing channel 84. The balancing channel body 80 is made of PTFE (polytetrafluoroethylene) so that a channel surface 80' of the pressure balancing channel 84 is hydrophobic and has a contact angle Theta with water of approximately 126°.

[0031] The cylindrical pressure balancing channel 84 has a diameter of 1.0 mm, a cross-sectional area A84 of about 0.80 mm², and a length L84 of 7.5 mm. The ratio R of the length L84 to the cross-sectional area A84 is about 9.5.

[0032] The process sensor unit 30 is provided with an electric sensor unit heater 36 that is directly attached to and directly heats the sample container 32, and is also provided with a temperature sensor 37 that directly senses the temperature of the sample water 13' within the sample container 32. The electric heater 36 and the temperature sensor 37 are electrically connected to the analyzer controller 24, which includes a temperature controller 28, which includes a set temperature memory 28'. The set temperature TS stored in the set temperature memory 28' is 45°C. The temperature controller 28 controls the sensor unit heater 36 to maintain the temperature of the sample water 13', and in particular, the temperature of the probe 40 including the electrolyte liquid 52, 62, constant at the set temperature TS of 45°C. Heating and temperature control may alternatively be implemented in another suitable manner.

Claims

1. An electrochemical process measuring device (10) having a process sensor unit (30), the process sensor unit (30) comprising: a reference electrolyte tank (50) having a reference electrolyte liquid (52) and a reference electrode (54); and a measuring electrolyte tank (60) comprising an electrolyte liquid (62), a measuring electrode (64), a gas selective membrane (90) for separating the reference electrolyte liquid (52) from the sample liquid (13'), and a pressure balancing channel (84) for fluidly connecting the tank interior (56) of the reference electrolyte tank (50) to the atmosphere (11), The pressure balance channel (84) is defined by a balance channel body (80) made of a hydrophobic material having a contact angle Theta greater than 90°.

2. The electrochemical process measuring device (10) according to claim 1, wherein the contact angle Theta is higher than 115°, and preferably higher than 122°.

3. The electrochemical process measurement device (10) according to any one of the preceding claims, wherein the equilibrium channel body (80) is made of a flour-based polymer.

4. The electrochemical process measuring device (10) according to any one of the preceding claims, wherein a ratio R of the equilibrium channel length (l84) to the equilibrium channel cross-sectional area (A84) of the pressure equilibrium channel (84) is greater than 2.5, preferably greater than 5.

0.

5. The electrochemical process measuring device (10) according to any one of the preceding claims, wherein the equilibrium channel cross-sectional area (A84) is less than 1.0 mm².

6. The electrochemical process measurement device (10) according to any one of the preceding claims, wherein the gas-selective membrane (90) is defined by a membrane body (92) having a thickness of less than 250 µm.

7. The electrochemical process measuring device (10) according to any of the preceding claims, comprising a sample container (32) with the sample liquid (13'), wherein the process sensor unit (30) extends into the interior (35) of the sample container (32) such that the gas-selective membrane (90) is immersed in the sample liquid (13').

8. The electrochemical process measuring device (10) according to any one of the preceding claims, wherein a sensor cell heating device (36) is provided for heating the process sensor cell (30).

9. Electrochemical process measuring device (10) according to the preceding claim, wherein the process sensor unit (30) is provided with a temperature sensor (37), and wherein the temperature controller (28) comprises a set temperature memory (28') which is arranged for controlling the sensor unit temperature to a constant set temperature (TS) stored in the set temperature memory (28').

10. The electrochemical process measuring device (10) according to the preceding claim, wherein the set temperature (TS) stored in the set temperature memory (28') is at least +40°C.

11. The electrochemical process measuring device (10) according to any one of the preceding claims 8 to 10, wherein the sensor cell heating device (36) is directly attached to the sample container (32).

12. The electrochemical process measuring device (10) according to any one of the preceding claims 7 to 11, wherein the sample container (32) is arranged to be fluidically accessible to the atmosphere (11).

13. The electrochemical process measurement device (10) according to any one of the preceding claims, wherein the process sensor unit (30) is provided with a reference electrolyte tank cover (70), and wherein the balancing channel body (80) is a separate but integral part of the measuring electrolyte tank cover (70).

14. Electrochemical process measuring device (10) according to the preceding claim, wherein the reference electrolyte tank cover (70) is provided with a tank cover body (70') made of a non-hydrophobic plastic.

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