DE10222165A1 - Partial pressure measurement probe for determination of gas concentrations e.g. oxygen and hydrogen in gas mixtures or solutions, has a gas-permeable, liquid-tight plastics membrane supported on a porous carrier - Google Patents

Abstract

Probe for measurement of partial pressure has a body (6) with a permeable wall comprising a porous carrier (4) coated on its inner surface with a liquid-tight, gas-permeable plastics membrane layer (3). The carrier material is selected to have a porosity of 10-80% and a pore size of 1-300 micron, and is preferably inorganic e.g. metal, glass or ceramic in the form of a mesh or sinter. Porosity can be controlled by sintering with e.g. PTFE powder. Typically the carrier is 1-20 mm thick. The permeable membrane is preferably electrostatically sprayed and fused to the carrier, to a thickness of 20-1000 micron. Suitable materials are polyfluoroethylene (PTFE), tetrafluoroethylene- hexafluoropropylene copolymer (FEP), polyetherether ketone (PEEK), and polyamide. To measure partial pressure a carrier gas e.g. nitrogen, is fed via a mass-flow controller (22) to the probe inlet (12) and the permeate plus carrier gas from outlet (13) are led to an electrochemical sensor (12) calibrated for the permeate species. Independent claims are included for (1) apparatus utilizing the probe; (2) process for manufacturing the probe; (3) process for measuring partial pressure; (4) a computer program used in conjunction with the measurement process.

Description

The present invention relates to a measuring probe according to the preamble of Claim 1 for measuring the partial pressure of a gas in a fluid after the permeation Carrier gas method. A particularly preferred application is the measurement of Partial pressure of a gas, such as oxygen or hydrogen, in liquid media or in gaseous or supercritical media, very particularly preferred for high ones Temperatures and / or pressures. The present invention further relates to a method for Production of such a measuring probe, a measuring device and a measuring method with such a measuring probe and a computer program for carrying out a measurement method according to the invention.

In the prior art, the partial pressure of a gas in a fluid is often associated with a Clark type sensor measured that includes a diffusion barrier that holds the fluid from separates an electrolyte reservoir of the sensor. What is passing through the diffusion barrier Gas causes a chemical reaction on the electrolyte side of the sensor that is measured and from the exact concentration or partial pressure of the gas on the fluid side of the sensor can be inferred. As is known, sensors from Clark type not for measurements at high temperatures and pressures. Due to the usually exponentially increasing permeation rate of dissolved components on the On the fluid side, the electrolyte composition on the electrolyte side changes too quickly or the electrolyte is used up in a very short time so that the sensor does not continue is usable. In addition, those commonly used in Clark type sensors are suitable Materials for the diffusion barrier not for measurements at high temperatures and / or Presses as envisaged by the present invention, specifically for Measurements in the temperature range from about 60 to about 160 ° C or beyond and / or at pressures in the range from about 2 to about 100 bar.

The generic US 6,192,737 B1 discloses a measuring device for measuring the CO ₂ concentration in beverages. The beverage sweeps along a membrane unit, on the permeate side of which a purge gas of a given concentration and flow rate flows. At the gas outlet on the permeate side there is a gas sensor for determining the gas concentration in the purge gas. From the known permeability of the membrane unit, the mass flow, the temperature and a known calibration curve, the gas concentration in the purge gas flow can be inferred from the gas concentration in the beverage flow.

This sensor is not suitable for spatially resolved in-situ measurement, for example in one chemical reactor, since fluid has to be diverted from the reactor to the sensor unit. On the whole way to the sensor device, the temperature and / or Pressure conditions of the reactor are maintained, which would be expensive. The Sensor device is also not suitable for use at high temperatures and / or pressures because the membrane decompose, at least deform, and change its permeability strongly would.

US 6,277,329 B1 discloses a device for measuring the partial pressure of dissolved Hydrogen according to the permeation gas method. This measurement method too a membrane unit to be arranged externally, that is to say outside of the measurement location, is used. The membrane unit is a composite hollow fiber membrane unit, such as that made of JP 11-114387 A is known. A large number of membrane tubes are in one casting compound glued close to the end faces and flow-wise on the permeate side connected. This means that a large surface area is available for gas permeation. Fluid with The dissolved gas to be measured is directed past the membrane tubes. permeate is dissolved gas from the fluid by vacuum, which through the walls of the Membrane tubes pass through, are suctioned off and subsequently detected.

Because the measuring device is to be attached externally, it is not suitable for one spatially resolved in-situ measurement. The construction of the sensor is particularly not suitable for one Measurement at high temperatures and / or pressures. Measurements are disclosed especially on tap water, in the temperature range up to a maximum of 100 ° C.

DE 199 25 842 A1 discloses a method for measuring the concentration of gases in Fluids, which in a tubular vessel with a PTFE wall, the is gas permeable, the partial pressure change proportional to the gas concentration on the permeate side is measured. The thermoplastic PTFE wall is not suitable for measurements high temperatures and / or pressures as it deforms. The disclosed measuring vessel is not suitable for the permeation carrier gas method.

The object of the present invention is to develop the generic measuring probe for an internal to further develop situ measurement in chemical reactors or closed containers, especially for measurements at high temperatures and / or pressures. Furthermore, a Method for producing such a measuring probe, a measuring device and a Measuring methods and a computer program for such a measuring method can be created.

This object is achieved by a measuring probe with the features according to claim 1, by a measuring device according to claim 19, by a method for producing the Measuring probe according to claim 29, by a measuring method according to claim 33 and by a Computer program according to claim 38. Advantageous further developments are the subject of back-related subclaims.

According to the invention, a measuring probe is created for the aforementioned purposes, comprising a probe body with a wall, which is a sealed, for the gas to be measured permeable plastic layer comprises, the outside with the fluid and the dissolved therein or contained gas to be measured can be brought into contact, the wall additionally comprises a porous support material which is on the inside of the dense, permeable Plastic layer is arranged and at least in sections connected to this to the Support plastic layer, the carrier material with a the measuring probe flowing carrier gas can be brought into contact.

The present invention provides a measuring probe in a surprisingly simple manner on the one hand, the advantageous permeation properties of dense, permeable (for the measuring gas permeable) plastic layers, usually at high Temperatures and / or pressures soften and, on the other hand, due to the connection the dense, permeable plastic layer with a suitable carrier material for a has sufficient mechanical support of the plastic layer so that the measuring probe can also be used without problems even at high temperatures and / or pressures. According to the invention, the carrier material is porous for this purpose and is therefore sufficient gas permeable, so that the permeation rate of the gas to be measured through the dense, permeable Plastic layer in the carrier gas is at most insignificant for the intended measurement purposes is affected. The material of a measuring probe according to the invention is advantageous as Composite material formed, which can be easily molded to an in-situ Measurement, for example in chemical reactors or closed containers, also at to allow high temperatures and / or pressures.

According to the invention, the material of the measuring probe is essentially closed Shaped shape so that the measuring probe is easily in the fluid to be measured can be immersed. With "closed form" is in the sense of the present application in particular meant that essentially the entire outer surface of the measuring probe in the immersion area in the fluid, d. H. the entire permeation zone, from the dense, permeable plastic layer, so that according to the invention a relatively large Permeation surface for gas passage is available. Essentially, this is preferably filled the entire inside of the measuring probe with the porous support material on which the Permeation gas can pass freely. The porosity of the carrier material is selected according to the invention so as to achieve an essentially unhindered mass transfer between carrier gas and the gas permeated by the plastic with sufficient To enable mechanical stability, so that a high measurement sensitivity in a simple manner can be achieved.

A measuring probe according to the invention can in the aforementioned closed form in be made comparatively small in a simple manner, so that a spatially resolved measurement is possible. In particular, there is also a spatially resolved one Gradient measurement for the determination of gas concentration gradients in chemical reactors or closed containers, especially at high temperatures and / or pressures possible.

For this purpose, the measuring probe can also be placed in the container containing the fluid be movable and positionable.

The carrier material is preferably a channel-free porous carrier material with a connected porosity for the essentially unhindered passage of permitted Gas to a flow interior within the measuring probe through which the carrier gas for the permeation carrier gas method flows through. For the purposes of the present Invention is to be understood by the term "connected" in particular that across porous carrier material is an essentially through-connected gas column for the permitted Gas exists locally, but it is not linear (channel-shaped), but meandering or randomly across the substrate from the contact surface with the dense, permeable Plastic layer runs to the gas flow interior of the measuring probe. It is advantageous that by varying the parameter of the porosity of the carrier material in an advantageously simpler manner Way on the one hand a sufficient gas passage for the gas to be measured from the dense, permeable plastic layer to the gas flow interior can be created and on the other hand, a high mechanical stability of the measuring probe can be created can, because the meandering or randomly extending across the carrier material Cavities in the carrier material for high dimensional stability even at high external pressures to care. At the same time, the porous carrier material also ensures an optimally large one Gas exchange surface for the passage of the permitted gas in the carrier gas stream in Gas flow interior of the measuring probe.

The outer surface of the porous carrier material offers in a surprising way advantageous connection properties. Similar applications in other areas - z. B. corrosion protection of a surface by a plastic layer - to be observed Blistering, d. H. a partial detachment of the plastic layer from a non-porous one Carrier at high temperatures surprisingly does not take place. morphological Studies have shown that in the manufacturing process (described below) the partially melted or applied plastic into the pores of the porous carrier penetrates and thereby hooks the plastic layer in the carrier material. This will achieved a much better adhesion of the plastic layer on the carrier material than was expected. In addition, permeating substances through the carrier gas flow transported away, so that there are no closed gas cavities between the carrier material and Can form plastic layer. Even when melting or applying the Plastic layer is such a removal of gas through the porous carrier is advantageous however, this results in the embedding of bubbles at the interface between the carrier and Plastic layer advantageously prevented, so that the plastic layer optimally on the Carrier is liable.

The carrier material preferably has a porosity permeable to gases in the range of about 10 to about 80%, more preferably in the range of about 15 to about 80% and even more more preferably in the range of about 15 to about 60%. The porous carrier material preferably has a medium one at least at the interface between the plastic layer and the carrier material Pore size in the range of about 1 to about 300 microns, more preferably in the range of about 2 to about 150 microns, and more preferably in the range of about 5 to about 100 microns.

The porous carrier material preferably consists of an inorganic material which is a sufficient temperature stability and pressure resistance enables. This is preferred inorganic material a material or a combination of materials selected from a group, comprehensive: stainless steel, metal, metal alloys, glass and ceramics. The carrier material is appropriately formed to provide sufficient porosity. This can basically the carrier material also as a comparatively fine-knit or mesh-like structure to be formed into a substantially closed shape. All the porous carrier material made of a sintered powder is particularly preferred, in particular made of a sintered metallic or ceramic powder. Basically can sintering is also carried out with an organic powder, in particular PTFE powder. The porosity of the carrier material can advantageously be achieved in a simple manner by sintering can be varied over a wide range and can be essentially one closed form can be formed for the measuring probe.

The porous carrier material with the dense, permeable is particularly preferred Plastic layer cohesively connected, in particular by melting onto the porous Surface of the carrier material.

The dense, permeable plastic layer very particularly preferably consists of a thermoplastically processable plastic with a sufficient permeation rate for the measuring gas in the intended temperature and / or pressure range. Most notably the material of the dense, permeable plastic layer is preferred by Powder coating is applied to the porous carrier material and then heated over the Melting point or softening point of the plastic applied to the carrier material and cohesively connected at least in sections to the porous carrier material.

Of great importance for the adhesion of the plastic layer on the porous Carrier material is the penetration of the molten plastic powder into the pores of the Carrier material through capillary forces. The microscopic, meandering depressions on the Surface of the porous carrier material are filled with plastic and form after Cooling down a penetrating bond between the substrate and the plastic layer. This ensures that the applied plastic layer is well anchored in the carrier material is and cannot come off. The plastic layer produced in this way can exposed to high pressures and temperatures without deforming.

The powder coating of the porous carrier material is preferably carried out with the Plastic powder particles by electrostatic spraying onto the porous support, in which the Plastic powder particles first automatically on the surface of the porous Maintain the greatest possible mutual distance. When softening afterwards the plastic particle combines the advantageously evenly applied Plastic layer with the porous support, whose pores any gas bubbles from the boundary layer between the carrier and the plastic layer to create an intimate connection between Promote carrier and plastic layer.

In the case of a measuring device according to the invention, one is in the fluid with the one to be measured Gas-immersed probe tip is essentially closed, the dense, permeable plastic layer the porous carrier material to the outside essentially completely encloses. The porous carrier material is with a base body Probe tip preferably integrally connected, in particular by welding, soldering or Glue. Even when the porous carrier material is pressed onto the base body, it can be too a sufficiently mechanically stable connection with the base body. In principle, conventional mechanical connections, e.g. B. screw connections for Connection of the porous carrier material to the base body can be used. The probe tip is particularly preferably essentially cylindrical, for example rod-shaped, and can thus be easily through an opening in a wall at the measuring location, for example a wall of a chemical reactor or a closed one Container to be introduced to save space. The comparatively small external dimensions and the essentially cylindrical shape in particular also enables a spatially resolved one Concentration gradient measurement in situ.

The measuring device preferably comprises a on the outside of the probe tip Connection section for gas-tight and / or pressure-tight connection of the measuring probe with a Wall at the measurement site, for example a chemical reactor or a closed one Container that contains the fluid with the gas to be measured. The temperature resistance and / or Compressive strength of the connecting section is predominant in the usual way Operating conditions designed and can in particular for measurements in the range of about 2 up to at least about 100 bar and temperatures in the range from about 60 to at least about 160 ° C and beyond.

Is preferred in the measuring probe or probe tip, for example in the Gas flow interior, which is swept by the carrier gas flow, a humidity and / or gas sensor arranged, which responds to leaks in the measuring probe, for example for Gas concentration measurements in liquids on moisture due to liquid penetration through the measuring probe or for gas concentration measurements in gaseous media responds to a gas passage of a gas other than the carrier gas through the measuring probe.

Preferably, a signal from the humidity and / or gas sensor is wireless or wired a control means arranged, for example, outside the measuring location is forwarded, that in the case of a detected humidity or gas concentration that a predetermined Exceeds the threshold value, indicates a leak in the measuring probe and in Responding automatically in a gas inlet and / or gas outlet for the device purging carrier gas arranged valve means, in particular check valves, actuated and locks to further leakage of fluid from the measuring location, in particular from the bottom high pressure and / or high temperature standing measuring location to prevent. Is preferred the valve means, for example the check valve, to the operating conditions at the measuring location adapted, for example pressure-tight up to about 20 bar, more preferably up to about 100 bar, and still more preferably pressure-tight up to about 250 bar.

According to the invention, a computer program is therefore also provided that a Processor means, particularly a computer or microprocessor, instructs the output signal to monitor the humidity and / or gas sensor and if a predeterminable value is exceeded Threshold value to actuate a valve means, in particular a check valve. The Computer program can in particular also calculate calibration data and measurement data and the Current measured values can be displayed to the user by means of appropriate aids. The computer program can be on a computer-readable data carrier, for example one Diskette or other magnetic or optical data carrier, be stored or be downloadable via a network, including the Internet.

The invention is illustrated below by way of example with reference to FIG attached drawings, in which:

Fig. 1 in a schematic cross section of a measuring probe of the invention illustrating that measures in situ in a closed container according to the carrier gas permeation measurement method the partial pressure of a gas in a fluid;

Fig. 2 schematically illustrates a measuring method according to the present invention; and

Fig. 3 represents an enlarged part section of a further embodiment of a measuring probe according to the invention with a protective device.

In the figures, identical reference symbols designate identical or essentially equivalent components or functional units.

Fig. 1 shows a schematic cross section of a measuring probe 1 of the invention, which protrudes through a wall 20 of a schematically illustrated chemical reactor or closed vessel 2 and measures the partial pressure of a gas in the fluid 21. The measuring probe 1 is designed for the permeation of carrier gas measuring method and comprises a substantially cylindrical basic body 6 with a carrier gas inlet 12 and a carrier gas inlet 13 and a substantially cylindrical flow inner chamber 7, flows through the carrier gas from the inlet 12 to the outlet. 13 The permeation zone 5 is located at the tip of the probe at the front end of the measuring probe 1 . In this, a porous carrier 4 is provided, which is enclosed by a dense, permeable plastic layer 3 . The porous carrier 4 is in contact with the carrier gas stream and preferably forms the front end of the flow interior 7 completely, so that there is a large contact area with the carrier gas stream. The protective device shown by way of example in FIG. 3 can be arranged on the probe tip.

The front end 8 of the base body 6 can, as shown, also be stepped, so that the dense plastic layer 3 is essentially flush with the outside of the cylindrical base body 6 . As shown, the dense plastic layer 3 can protrude beyond the rear end of the porous carrier 4 to the carrier gas inlet / outlet 12 , 13 and can be connected to the base body 6 at the protrusion in particular in a cohesive manner, for example by melting or gluing.

The porous carrier material 4 is connected to the front end 8 of the cylindrical base body 6 via the connecting section 9 . On the outer section of the cylindrical base body 6 there is a connecting section 11 , for example a screw thread with a sealing section or a circumferentially extending flange with a seal, so that the measuring probe can be used pressure and / or temperature resistant against the wall 20 of the closed container 2 . The measuring probe 1 enables an in-situ measurement of the gas concentration or the partial pressure in the fluid 21 . In order to be able to measure concentration gradients in the container 2 in a spatially resolved manner, the connecting section 11 can also be designed such that the measuring probe 1 can be moved in the container 2 , so that the probe tip with the permeation zone 5 can be positioned at different locations in the fluid ,

The fluid 21 can be liquid, gaseous or supercritical. The gas to be measured in the fluid 21 can in particular be oxygen or hydrogen. Typical operating conditions of the container 2 are a temperature in the range from approximately 60 to at least approximately 160 ° C. and an internal pressure in the container in the range from approximately 2 to at least approximately 100 bar, wherein the fluid can be neutral, basic or acidic or can be a solvent. However, the present invention is not limited to the aforementioned areas of use.

The dense, permeable plastic layer has a suitable permeation rate for the gas to be measured under the intended operating conditions. The dense, permeable plastic layer 3 is connected to the porous carrier material 4 at least in sections. The interconnected porosity of the carrier material is selected sufficiently so that the gas passage of the permitted gas into the carrier gas stream is not impaired, or only to an insignificant extent. The porous carrier material 4 serves to mechanically support the plastic layer 3 and at the same time ensures sufficient gas exchange of the permeated gas with the carrier gas stream. The measuring probe 1 is at least in the area of the permeation zone 5 (cf. FIG. 2) in an axially symmetrical or point symmetrical manner, so that the pressures prevailing in the container 2 can be absorbed by the measuring probe 1 with a particularly low stress.

Sensors can be provided in the flow interior 7 , preferably at the front end, for example a moisture sensor 18 , a temperature sensor 19 or a gas sensor (not shown). The sensor signals are wired or wirelessly forwarded to a control or regulation arranged outside the measuring location. The temperature sensor measures the temperature in situ. Another temperature sensor is arranged at a suitable point in the container 2 , but can also be arranged on the outside of the measuring probe 1 . The moisture sensor 18 measures moisture or liquid that enters the flow interior 7 in the event of leaks in the measuring probe 1 . The gas sensor, not shown, responds to a gas other than the carrier gas, which passes through the interior 21 of the container 2 in the event of a leak in the measuring probe into the flow interior 7 .

Fig. 2 shows schematically a permeation carrier gas measuring method according to the present invention. The mass flow of a carrier gas, for example nitrogen, is set with the aid of a mass flow controller 22 . The carrier gas flows through the interior 7 of the measuring probe 1 and accumulates at the tip of the probe with the gas passing through the dense, permeable plastic layer 3 and the porous carrier material 4 in the region of the permeation zone 5 . The carrier gas enriched in this way passes from the outlet 13 to a sensor or measuring instrument 23 and its composition is examined in a known manner. If, for example, oxygen or hydrogen is measured, the sensor 23 can be a known electrochemical sensor. The sensor 23 may be preceded by a gas scrubber 24, which prevents substances that impair or even destroy the sensor 23, to be forwarded. A check valve 17 is provided both in the gas inlet and in the gas outlet. In any case, up to the shut-off valves, the flow connections are sufficiently temperature and / or pressure resistant, corresponding to the operating conditions in the container 2 .

If the permeation of the gas to be examined through the plastic layer 3 as a function of the temperature and specific medium influences is known, for which a calibration may be necessary, then the partial pressure of the gas in the fluid 21 can be determined in a known manner with this measuring method. Typical mass flows are in the range of about 0.01 to 0.1 l / min at standard conditions (atmospheric pressure, room temperature). By switching valves (not shown), the carrier gas or a calibration gas can optionally be passed through the measuring probe 1 to the sensor 23 . The measuring probe 1 can be constantly rinsed in the measuring insert in order to be ready for immediate use. Typical response times can be in the range of <10 minutes (90% response accuracy). In addition to the signal from the sensor 23 , the temperature of the fluid 21 is available as an external measurement signal. Software calculates the current partial pressure of the gas in the fluid 21 from the measurement signals and calibration data, which are determined in the manner specified below.

If the moisture and / or gas sensors 18 arranged in the measuring probe 1 respond or if other measuring signals can be used to infer a potential leak in the measuring probe 1 , the electronics, which executes a software according to the invention, automatically actuates the shut-off valves 17 to prevent uncontrolled escape of the fluid 21 from the container 2 .

The calibration of the measuring device takes place in the following way: With a fixed mass flow and known partial pressure of the gas to be measured in the fluid 21 , the sensor signal is measured as a function of the temperature. Care is taken to ensure that gases and medium are in thermodynamic equilibrium. Since the permeation rate through the plastic layer 3 depends not only on the temperature but also on the medium used (e.g. partial pressure of water as fluid 21 ), the calibration should always be carried out in the same medium in which the subsequent measurement is to take place , Each probe should therefore be measured at least once under these conditions without the gas in the fluid being consumed by chemical reactions. The measuring probe 1 should then be stored in these or similar fluids and used only for measurement in such fluids.

By reversing the gas flow with a zero gas, i.e. H. a gas known Composition, the zero point of the measuring device can be set and by reversing the Gas flow with a calibration gas of known concentration and composition can Calibration of the measuring device can be changed. The software or Adjust the electronics of additional control valves (not shown) appropriately.

If the fluid consists of a liquid and a gaseous phase, the Probe tip also in a gas space, for example in a gas phase Gas space above the liquid phase, in which the partial pressure of the Gases is known in many cases or can be measured in a simple manner. This measurement in Gas space at a known pressure and preferably with a known gas composition can Calibration of the measuring probe can be used and carried out during the measuring process become.

The volume flow of gas that passes through the dense, permeable plastic layer 3 is given by:

F = P (T) .A. (P1 - p2) / L

where P (T) = permeation constant
A = area of the plastic layer
L = thickness of the plastic layer
p1, p1 = partial pressures of the permeate on both sides of the plastic layer
F = volume flow of the permeating gas

The temperature dependence of the permeation constant of gases through a dense, permeable plastic layer is given by:

P = Po.exp (-Ep / RT)

P = permeation constant Po = constant Ep = activation energy for the permeation of a gas molecule R = general gas constant T = temperature in Kelvin.

This type of dependency is known as the Arrhenius law. A temperature sensor 19 integrated in the probe 1 is not absolutely necessary, since the relatively thin plastic layer according to the invention quickly takes on the temperature of the medium anyway. The temperature of the medium is therefore usually measured using a separate temperature sensor which projects into the fluid 21 . The signal from the temperature sensor is available for evaluation.

The permeation rate of a gas at a given temperature also depends on the humidity (e.g. water vapor pressure). Water as an example of the fluid 21 is a polar molecule and also dissolves in the plastic layer, as a result of which it influences the diffusion of the gas to be examined, for example oxygen, through the plastic layer.

For many materials there is no indication of the influence of moisture on permeation physical law available. The permeation rate can vary depending on the plastic be enlarged or reduced. There appears to be a dependence on morphology (crystalline / amorphous) and the type of crosslinking of the dense, permeable polymers To give plastic layer. Therefore only one empirical value can be used for correction become.

Fig. 3 shows a further embodiment of the inventive measuring probe 1 is arranged in a protective device 15 in the area of permeation. 5 The protective device 15 can serve various purposes, for example the mechanical protection of the dense, permeable plastic layer 3 from abrasion by solid particles thrown around in the fluid 21 (which can have a size of 20 to 600 μm, for example, especially when using noble metal catalysts on an aluminum oxide support ) or as a bubble deflector.

The protective device 15 preferably consists of a metal sleeve or a metal net, which is pushed axially over the probe tip and can be attached to the probe body. The fastening zone 16 of the protective device 15 can be designed such that the transition 10 between the probe body 6 and the plastic layer 3 is protected or sealed from the ingress of fluid. For this purpose, a sleeve-like extension or a sleeve extension of the protective device 15 can tightly enclose the transition region 10 . The fastening can be supported by a clamping ring (not shown) or a comparable fastening device.

In addition, the protective device 15 is designed such that the fluid 21 can flow directly around the plastic layer 3 at a speed of, for example, more than 10 cm / second. This ensures that the measurements do not depend, or only insignificantly, on the flow velocity of the fluid 21 .

After the general operation of the measuring probe 1 has been described above, preferred materials and manufacturing methods for the measuring probe 1 according to the present invention are listed below in a non-limiting manner.

Embodiment 1 for the porous support material

Powder particles made of metal or stainless steel, in particular brass, bronze, aluminum, copper, or metal alloys with components made of iron, chrome, nickel, titanium, molybdenum, tungsten, yttrium, cobalt, aluminum, copper, manganese and / or vanadium with an average particle diameter in the range from about 1 to 1000 μm, more preferably from about 2 to about 500 μm and even more preferably from about 5 to about 400 μm, were introduced into a cylindrical shape which has a cylindrical mandrel to form the essentially cylindrical flow interior 7 . The powder was pressed in the mold. The pressed powder was then heated in the mold to a high temperature, for example about 800 ° C., until it sintered into a porous, essentially cylindrical support. The carrier material is characterized by an average pore size at the interface between the plastic layer 3 and the carrier material 4 in the range from approximately 1 to 500 μm, more preferably in the range from approximately 1 to approximately 200 μm and even more preferably in the range from approximately 1 to approximately 100 μm. The porosity for permeation at the interface and in the interior of the carrier material is approximately in the range from 10 to approximately 80%, more preferably in the range from approximately 15 to approximately 80% and even more preferably in the range from approximately 15 to approximately 60%. This gives sufficient mechanical stability under pressure and a well-adhering base due to the surface roughness of the carrier material. Due to the permeable porosity, the permeation is essentially not hindered by the subsequently applied, dense, permeable plastic layer and the removal of the permeated carrier gas through the carrier material to the carrier gas flow.

The carrier material can have a thickness in the range from about 1 to about 20 mm, more preferably in Range from about 1 to about 10 mm, and more preferably in the range from about 1 to about 6 mm exhibit. Adequate mechanical stability is at temperatures from 20 to guaranteed in any case 160 ° C.

Embodiment 2 for the porous support material

It becomes a commercial filter element made of precious metal or other metals, glass or Ceramics used, as for example from GKN Sinter Metals Filters GmbH under the Designation SIKA-R or from Robu Glasfilter GmbH under the designation Vitrapor is commercially available. The average pore size is approximately in the range from 1 to approximately 300 μm, more preferably in the range of about 2 to about 150 microns, and even more preferably in the range from about 5 to 100 µm. The material has a porosity in the range of about 10 to about 80%, more preferably in the range of about 15 to about 80% and even more preferably in the range from about 15 to about 60%.

Embodiment 3 for the porous support material

A plastic material is caused by melt spinning and pore formation Extension method made porous. The plastic material is made with regard to a suitable melting point is selected to adapt to the operating conditions Measurement. The plastic material is selected from a non-limiting one Group comprising: crystalline polymers, for example fluorinated polymers, Olefin system polymers, polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1, Polyvinyl fluoride and polyfluoroethylene. For further stiffening, the porous Carrier material can also be applied to a grid. The porous support material typically has a smaller pore size than in the previous exemplary embodiments, for example one average pore size in the range of about 1 to 50 microns, more preferably in the range of about 1.5 to 45 µm and more preferably in the range of about 2 to 40 µm. The mean porosity is typically somewhat less than in the previous exemplary embodiments for example in the range of about 10 to 50%, more preferably in the range of about 15 to 45% and more preferably in the range of about 20 to 40%.

Experiments have shown that this embodiment at higher temperatures of for example above about 100 C is no longer sufficiently stable, so that the preferred application range is in the low temperature range, for example in the range of about 20 C to about 100 C.

Embodiment 4 for the porous support material

A carrier made of a non-expanded sintered porous polytetrafluoroethylene (PTFE) is produced with the help of a sintering process in which PTFE solid particles are placed on a high temperature to form a porous matrix. Such material is available under the trade name ZITEX (Norton Camplast, New Jersey, USA) and comprises fibrous PTFE, whereby PTFE fibers are glued to a porous matrix. Such Materials can be mixed by mixing cellulosic or protein acid materials with PTFE and manufactured by heating in an oxygen atmosphere to high temperatures to burn out the cellulosic or proteinic material carbonize and sinter the PTFE. Such a method is described, for example, in US Pat. No. 3,775,170 the content of which is hereby expressly incorporated by reference Registration included.

In a modified embodiment, a sintered porous PTFE carrier is made PTFE particles are made comprising granular PTFE particles that interact with each other are fused to form a porous, integral network of interconnected particles form. The PTFE particles that are used to form the porous network are essentially entirely or partially made from granular PTFE particles, although other types of PTFE particles may also be included. The The term "sintering" in connection with PTFE means in particular heating over the melting point, which is around 343 ° C for pure, unmodified PTFE. The Granular PTFE can contain homopolymeric tetrafluoroethylene and modified PTFE. Granular Teflon is, for example, from DuPont Specialty Polymers Division, Wilmington, USA, available.

• 1. ungesintertes feinpulvriges PTFE;
• 2. Partikel aus einem thermoplastischen, fluorinierten, organischen Polymer;
• 3. Partikel eines niedermolekularen PTFE-Mikropulvers, das durch Bestrahlung erzeugt wird.

The porous PTFE carrier is characterized by high tensile strength and mechanical strength, the average pore size being smaller than in the aforementioned exemplary embodiments, approximately in the range from approximately 1 to 10 μm, if abrasive particles with an average grain size of 40 μm are added to the aforementioned Network were melted together. According to a modification, the granular PTFE particles used to produce the sintered, porous support consist of a mixture of one or more of the following materials:

• 1. unsintered fine powder PTFE;
• 2. Particles made of a thermoplastic, fluorinated, organic polymer;
• 3. Particles of a low molecular weight PTFE micropowder that is generated by radiation.

Organic or inorganic filler materials can be added to the PTFE particles. especially to increase the average pore size. Examples of such Filler materials include carbon, activated carbon, glass, chromium oxide, titanium oxide, Silicon dioxide and the like. The proportion of filler material can be up to 60% by weight, so that the aforementioned porosities can also be achieved in this exemplary embodiment.

The carrier material according to this exemplary embodiment is preferred in combination with a plastic layer, the material of which has a lower softening point owns as the carrier material. So a stable connection between carrier and Plastic layer can be ensured by softening the material of the plastic layer, wherein the carrier material maintains its consistency and shape.

Experiments have shown that - depending on the choice of starting materials - also this embodiment at higher temperatures, for example above approx. 100 C is no longer sufficiently stable, so that the preferred area of application for Embodiment 4 is in the low temperature range, for example in the range of about 20 C to about 100 C.

Embodiment 5 for the porous support material

By combining suitable plastic material, as enumerated by way of example in Examples 3 and 4 , with the inclusion of suitable inorganic particles to form a dimensionally stable but porous framework structure, a porous composite carrier material could be realized. Examples of inorganic particles that can be mixed into the plastic are: carbon or soot particles, aluminum oxide and silicate. The porosity of the carrier material can be predefined in a simple manner by suitably selecting the size of the inorganic particles added. The mechanical cohesion and the shape and temperature stability of the composite material can be specified in a simpler manner by a suitable choice of the mixing ratios of plastic and inorganic components. The inorganic particles are preferably also electrically conductive, at least on their surface, so that the plastic layer can be applied by means of the electrostatic spraying process described below.

This enables a porous carrier material to be realized, which to a considerable extent based on organic raw materials, which is nevertheless sufficiently form and is temperature stable, even at higher temperatures, especially in the temperature range of about 100 C to about 160 C, can be used.

Characterization of the dense, permeable plastic layer

The is particularly suitable for producing a dense, permeable plastic layer Powder coating, especially after the so-called electrostatic spraying process, the aforementioned metallic porous support material. Then the applied one Powder layer heated above the melting point and onto the porous support material melted. The thickness of the dense, permeable plastic layer is approximately in the range of 20 to 1000 microns, more preferably in the range of about 20 to about 500 microns, and even more preferred in the range of about 30 to about 400 microns.

Adhesive primers can be applied before the powder coating. The Powder coating and melting can be repeated several times until the desired layer thickness is reached. Resin components and other additives are added.

Commercial thermoplastics can be used as plastics. preferred Starting materials include, for example: polytetrafluoroethylene (PTFE), Tetrafluoroethylene / hexafluoropropylene copolymers (FEP), tetrafluoroethylene / ethylene copolymers (E / TFE), Tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride terpolymer (THV), Polytrifluorochloroethylene (PCTFE), polyvinylidene fluoride (PVDF), perfluoroalkoxy copolymer (PFA), Tetrafluoroethylene / Perfluoromethylvinylethercopolymer (MFA), copolymers from Tetrafluoroethylene and fluorinated cyclic ether, thermoplastic fluoroelastomers, Thermoplastic polycondensates, e.g. B. aromatic polyether ether ketones (PEEK), or polyamides (PA).

The melting point of the dense, permeable plastic layer is above 200 ° C. The Plastic layer is due to a water absorption of <0.1 wt .-% in water at 23 ° C. (ASTM D570). The average porosity of the dense, permeable Plastic layer is <0.1%, making the plastic layer gas-tight and essentially non-porous (electrical test). Chemical resistance according to test method ASTM D543 is very good. The plastic layer is therefore without a permanent use temperature mechanical stress above 140 ° C.

The permeation for gases, especially hydrogen and oxygen, is therefore high. At the same time, the plastic layer is for larger molecules, atoms or ions in the fluid are solved, tight. Basically, water can make the plastic layer swell, when water molecules dissolve in it. This could result in shear forces along the adhesive surfaces and lead to the detachment of the plastic layer from the porous carrier material. According to the invention, the water absorption of the plastic layer is only slight.

Claims (39)

1. Measuring probe for measuring the partial pressure of a gas in a fluid according to the permeation carrier gas method, in particular oxygen or hydrogen in a fluid at high temperatures and / or pressures, comprising a probe body ( 6 ) with a wall that a Dense plastic layer ( 3 ) permeable to the gas to be measured, the outside of which can be brought into contact with the fluid ( 21 ), characterized in that the wall additionally comprises a porous carrier material ( 4 ) on the inside of the dense permeable plastic layer ( 3 ) is arranged and at least in sections connected to it in order to support the plastic layer ( 3 ). 2. Measuring probe according to claim 1, wherein the porous carrier material ( 4 ) has a connected porosity. 3. Measuring probe according to one of the preceding claims, in which the porous carrier material ( 4 ) has a porosity which is permeable to the gas to be measured in the range from approximately 10 to approximately 80%, more preferably in the range from approximately 15 to approximately 80% and even more preferably in the range of about 15 to about 60%. 4. Measuring probe according to one of the preceding claims, wherein the porous carrier material ( 4 ) consists of an inorganic material which is selected from a group comprising: stainless steel, metal, glass and ceramic. 5. Measuring probe according to one of the preceding claims, in which the porous carrier material ( 4 ) consists of a sintered powder, in particular of a sintered metallic or ceramic powder. 6. Measuring probe according to one of the preceding claims, in which the porous carrier material ( 4 ) has an average pore size at the interface between the plastic layer and the porous carrier material in the range from about 1 to 300 µm, more preferably in the range from about 2 to 150 µm and even more more preferably in the range of about 5 to 100 microns. 7. Measuring probe according to one of the preceding claims, in which the porous carrier material ( 4 ) has a thickness in the range from about 1 to 20 mm, more preferably in the range from about 1 to 10 mm and even more preferably in the range from about 1 to 6 mm having. 8. Measuring probe according to one of the preceding claims, in which the porous carrier material ( 4 ) is integrally connected to the dense, permeable plastic layer ( 3 ). 9. Measuring probe according to one of the preceding claims, wherein the dense, permeable plastic layer ( 3 ) consists of a thermoplastically processable plastic, which is suitable for powder coating, in particular powder coating by electrostatic spraying onto the porous carrier material ( 4 ). 10. Measuring probe according to the preceding claim, wherein the dense, permeable plastic layer ( 3 ) consists of a plastic which is selected from a group comprising: polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoro / Ethylene copolymer (E / TFE), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride terpolymer (THV), polytrifluorochloroethylene (PCTFE), trifluorochloroethylene / ethylene copolymer (E / TFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), perfluoroalkoxy copolymer, perfluoroalkoxy copolymer, Perfluoromethyl vinyl ether copolymer (MFA), copolymer of tetrafluoroethylene and fluorinated cyclic ethylene, thermoplastic fluoroelastomers, polyamides (PA). 11. Measuring probe according to one of the preceding claims, in which the dense, permeable plastic layer ( 3 ) has a thickness in the range from about 20 to 1000 µm, more preferably in the range from about 20 to 500 µm and even more preferably in the range from about 30 to 400 µm. 12. Measuring probe according to one of the preceding claims, wherein the dense, permeable plastic layer ( 3 ) has a melting point above about 200 ° C. 13. Measuring probe according to one of the preceding claims, wherein the dense, permeable plastic layer ( 3 ) has a porosity of less than about 0.1%. 14. Measuring probe according to one of the preceding claims, in which the dense, permeable plastic layer ( 3 ) is characterized by a water absorption of less than approximately 0.1% by weight in water at 23 ° C. within 24 hours in accordance with test method ASTM D570 is. 15. Measuring probe according to one of the preceding claims, in which the dense, permeable plastic layer ( 3 ) completely surrounds the carrier material on the outside. 16. Measuring probe according to one of the preceding claims, wherein the probe body has a cylindrical base body ( 6 ) with a stepped front end ( 8 ), the outside of the plastic layer ( 3 ) being essentially flush with an outside of the base body ( 6 ) completes. 17. Measuring probe according to one of the preceding claims, in which a temperature ( 19 ) and / or humidity ( 18 ) and / or gas sensor is arranged in an interior ( 7 ) of the measuring probe ( 1 ) through which a carrier gas can flow , 18. Measuring probe according to one of the preceding claims, in which at least one permeation zone, in which the gas to be measured passes through the dense, permeable plastic layer ( 3 ) and the porous carrier material ( 4 ), is cylindrical or spherical. 19. Device for measuring the partial pressure of a gas in a fluid according to the permeation carrier gas method, in particular oxygen or hydrogen in a fluid at high temperatures and / or pressures, characterized by a measuring probe ( 1 ) according to one of the preceding claims , 20. The apparatus according to claim 19, further comprising a connecting section ( 11 ) for the gas-tight and pressure-tight connection of the measuring probe ( 1 ) to a wall ( 20 ) of a chemical reactor or closed container ( 2 ) which connects the fluid ( 21 ) to the contains gas to be measured. 21. The apparatus of claim 20, wherein the connecting section ( 11 ) for a pressure prevailing inside the reactor or container ( 2 ) pressure in the range from about 2 to at least about 100 bar and for a temperature inside the reactor or container ( 2 ) is designed in the range from about 60 to at least about 160 ° C. 22. The device according to any one of claims 19 to 21, wherein the probe body is linearly displaceable to the probe tip at predeterminable locations in the fluid position. 23. The device according to one of claims 19 to 22, which is essentially a has cylindrical outer contour. 24. Device according to one of claims 19 to 23, further comprising a protective body ( 15 ) in order to protect the measuring probe ( 1 ) from abrasion by solid particles present in the fluid and / or to serve as a bubble deflector. 25. The device according to claim 24, wherein the protective body ( 15 ) is designed to ensure a flow velocity when flowing around the measuring probe ( 1 ) of more than about 10 cm / s. 26. The apparatus of claim 24 or 25, wherein the protective body is substantially cylindrical and is axially attachable and attachable to the probe body, wherein the protective body preferably has a sleeve-like extension to a front. Seal the penetration of fluid in a transition area from permeable plastic layer ( 3 ) to the probe body ( 6 ). 27. Device according to one of claims 19 to 26, comprising a shut-off valve ( 17 ) in a gas inlet (IN) and / or gas outlet (OUT) for a carrier gas flushing through the device, the shut-off valve being pressure-tight up to about 20 bar and more preferably pressure-tight up to is lockable at least about 100 bar. 28. The apparatus of claim 27, if indirectly or directly related to claim 18, further comprising a control means to receive a signal of the moisture sensor ( 18 ) or gas sensor arranged in the measuring probe ( 1 ) and to close the shut-off valve ( 17 ) block if a moisture detected in the measuring probe ( 1 ) or the concentration of a gas detected with the gas sensor in the measuring probe, which is not the carrier gas, exceeds a predefinable threshold value. 29. A method for producing the measuring probe according to one of claims 1 to 19, comprising the steps:
Providing a porous support material ( 4 );
Providing a dense plastic layer ( 3 ) permeable to the gas to be measured; and
at least in sections connecting the dense, permeable plastic layer ( 3 ) to the porous carrier material ( 4 ) in order to support the plastic layer arranged on an outside of the carrier material. 30. The method of claim 29, wherein the step of providing the Carrier material a sintering step for sintering the carrier material from a powder, preferably from an inorganic powder, in particular from a metallic or ceramic powder. 31. The method according to claim 29 or 30, wherein the step of providing the dense, permeable plastic layer ( 3 ), a powder coating, in particular by an electrostatic spraying method, and melting a powder layer onto the porous carrier material ( 4 ) by heating the powder layer over the Melting point of the powder layer comprises in order to form the dense, permeable plastic layer ( 3 ), the thickness of the plastic layer being in the range of approximately 20 to 1000 μm, more preferably in the range of approximately 20 to 500 μm and even more preferably in the range of approximately 30 to 400 μm lies. 32. The method according to claim 31, in which an adhesion promoter is introduced between the dense, permeable plastic layer ( 3 ) and the porous carrier material ( 4 ). 33. The method of claim 31, wherein the resin components or additives one Plastic powder can be added. 34. Method for measuring the partial pressure of a gas in a fluid according to the permeation carrier gas method, in particular oxygen or hydrogen in a fluid at high temperatures and / or pressures, by means of the measuring probe ( 1 ) according to claim 17 or 18, when referring back to claim 17, in which method a control means receives a signal of the moisture sensor ( 18 ) or gas sensor arranged in the measuring probe ( 1 ) and a check valve which is in a gas inlet (IN) and / or gas outlet (OUT) for a the carrier gas flushing through the measuring probe ( 1 ) blocks a predeterminable threshold value if a moisture detected in the measuring probe ( 1 ) or the concentration of a gas which is detected by the gas sensor in the measuring probe and which is not the carrier gas exceeds. 35. The method according to claim 34, further comprising the step of zeroing the downstream gas sensor ( 23 ) during a measurement operation by reversing the gas flow of the carrier gas through a downstream gas sensor ( 23 ) and the measuring probe by means of additional control valves. 36. The method according to claim 33 or 34, additionally comprise the step of adjusting the sensitivity of the downstream gas sensor ( 23 ) by means of a gas flow reversal and a calibration gas supply through a downstream gas sensor ( 23 ) and the measuring probe by means of additional control valves. 37. The method according to any one of claims 33 to 35, additionally comprising the Step that by moving the measuring probe out of the fluid in a gas space the measuring probe is calibrated above the fluid. 38. Computer program comprising sections of software code included in the Main memory of a computer can be loaded to perform the method according to one of claims 34 to run 37. 39. Computer program according to the preceding claim, in which the Software code sections are stored on a computer-readable data carrier.