Use of an ester as pressure transmission fluid, pressure transmission fluid composition and pressure measuring device

Abstract

The invention relates to the use of an ester as a pressure transmission fluid, wherein the ester is formed from the esterification of glycerin with one to three carboxylic acids with a chain length of 2-5 carbon atoms at a molar ratio of 1:3, or from the esterification of citric acid with one to three alcohols with a chain length of 2-4 carbon atoms in a molar ratio of 1:3. Further, the invention relates to a pressure transmission fluid composition and to a pressure measuring device.

Description

[0001] Use of an ester as a pressure transmission fluid, pressure transmission fluid composition and pressure measuring device

[0002] The invention relates to a use of an ester as a pressure transmission fluid, a pressure transmission fluid composition and a pressure measuring device for determining and / or monitoring a pressure of a medium.

[0003] In pressure measurement technology, absolute pressure, differential pressure, and gauge pressure sensors are known. Absolute pressure sensors determine the prevailing pressure of a process medium absolutely, i.e., relative to a vacuum, while differential pressure sensors determine the difference between two different pressures of the process medium or media. With gauge pressure sensors, the pressure of the process medium to be measured is determined relative to a reference pressure, with the atmospheric pressure prevailing in the vicinity of the gauge pressure sensor serving as the reference pressure.

[0004] Pressure transducers have a pressure-sensitive measuring element, the so-called pressure sensor, with a pressure applied to its first and second surfaces. In the case of relative or absolute pressure transducers, the pressure of the process medium to be determined acts on the first surface of the pressure sensor, while an absolute or reference pressure acts on the second surface. In the case of differential pressure transducers, a first pressure and a second pressure of a process medium are applied to both surfaces. The measuring element bends depending on the existing relative pressure, which is calculated from the difference between the pressures applied to the two surfaces. This bending is converted by an electronic unit into an electrical signal dependent on the relative pressure, which is then available for further processing or evaluation. A distinction is made between capacitive and piezoresistive pressure sensors, among others.A variety of such pressure transducers are manufactured and distributed by companies in the Endress+Hauser Group. A silicon chip, typically bonded to a silicon substrate, is often used as the pressure sensor. The pressure transducer is typically separated from the medium by a separating diaphragm, which is designed to transmit the pressure of the medium applied to the separating diaphragm to the pressure sensor. For this purpose, the separating diaphragm, usually disc-shaped, has only a small thickness. A pressure transmission path filled with a hydraulic pressure transmission fluid is used to transmit the pressure from the separating diaphragm to the pressure sensor. Conventional pressure transmission fluids include silicone, vegetable, paraffin, medical white oil, or inert halogenated oils.

[0005] Pressure transmission fluids must meet various requirements: They must be liquid within the temperature range used, which can range from -20°C to +250°C, for example, and possess a suitable coefficient of volume expansion. Likewise, the pressure transmission fluid should, if possible, be a pure substance or a mixture with a defined composition. White oils, for example, can vary in composition depending on the manufacturer, so the physical and chemical properties of the white oil vary, making it difficult to use as a pressure transmission fluid.

[0006] Another aspect to consider is a potential leakage of the separating diaphragm and the associated escape of the pressure transmission fluid into a process. In pharmaceutical and food processing applications, only pressure transmission fluids with appropriate approval may be used, such as approval under the US Food & Drug Administration's "21 CFR Part 184" standard, which regulates which substances may be added to food.

[0007] It is therefore the object of the present invention to provide a pressure-transmitting fluid that particularly meets pharmaceutical and food-related requirements. According to the invention, this object is achieved by a use according to claim 1, a pressure-transmitting fluid composition according to claim 6, and a pressure measuring device according to claim 13.

[0008] With regard to the use, the object is achieved according to the invention by using an ester as a pressure transmission fluid, wherein the ester is formed from the esterification of glycerol with one to three carboxylic acids having a chain length of 2-5 carbon atoms in a molar ratio of 1:3, or from the esterification of citric acid with one to three alcohols having a chain length of 2-4 carbon atoms in a molar ratio of 1:3.

[0009] In chemistry, esters form a group of chemical compounds that are formally or de facto formed by the reaction of an acid and an alcohol or phenol with the elimination of water. Glycerol (CsHsOs) is the common name for propane-1,2,3-triol and is a trihydric alcohol. By esterifying glycerol with one to three carboxylic acids in a molar ratio of 1:3, all three alcohol groups of the glycerol form an ester bond, regardless of how many different carboxylic acids are used. The molar ratio of glycerol to carboxylic acid is always 1:3. The proportion of carboxylic acids can be up to three different carboxylic acids. The carboxylic acids are each characterized by a chain length of 2-5 carbon atoms.Likewise, the esterification of citric acid (CeH2O3) with one to three alcohols in a molar ratio of 1:3 results in each of the three acid groups of citric acid forming an ester bond. The molar ratio of citric acid to alcohol(s) is always 1:3. The alcohol content can be up to three, each with a chain length of 2-4 carbon atoms. The esters obtained in this way are characterized by physical and chemical properties that are optimal for pressure transfer. The esters are liquid at atmospheric pressure in the temperature range of -40°C to +240°C and predominantly exhibit compression moduli in the range of 1.5 to 2.4 GPa at a temperature of 20°C. The volume expansion coefficient of the esters is typically (700 - 900) - 10. 6 °CT The viscosity of the esters at 20°C is approximately between 5 and 40 mPas.

[0010] In a further development, the one to three carboxylic acids include acetic acid and / or butyric acid. Acetic acid is the common name for ethanoic acid, and butyric acid is that for butanoic acid. One molecule of glycerol can be esterified with one to three molecules of acetic acid, whereby the up to two additional carboxylic acids can be propanoic acid, butyric acid, or pentanoic acid. One molecule of glycerol can also be esterified with one to three molecules of butyric acid, whereby the up to two additional carboxylic acids can be acetic acid, propanoic acid, or pentanoic acid.

[0011] Acetic acid or butyric acid are preferably used as the one to three carboxylic acids. This esterification yields glycerol tributary acid esters (also known as tributyrin) or glycerol triacetate (also known as triacetin). These two compounds are approved, for example, under the US Food and Drug Administration's 21 CFR Part 184 standard and can be used in pharmaceutical or food applications.

[0012] In a further development, the one to three alcohols include ethanol. One molecule of glycerol is then esterified with at least one molecule of ethanol and up to two other alcohols, such as propanol or butanol.

[0013] Ethanol is preferably used as the one to three alcohols. Esterification produces triethyl citrate (also known as triethyl citrate). This compound is approved under 21 CFR Part 184 of the U.S. Food and Drug Administration and can be used in pharmaceutical or food applications.

[0014] The object underlying the present application is further achieved by a pressure transmission fluid composition with at least 50 vol% of an ester which is formed from the esterification of glycerol with one to three carboxylic acids having a chain length of 2-5 carbon atoms in a molar ratio of 1:3, or from the esterification of citric acid with one to three alcohols having a chain length of 2-4 carbon atoms in a molar ratio of 1:3.

[0015] To maintain the previously described advantageous properties of the ester, it is used in the pressure transmission fluid composition at a minimum of 50 vol% (volume percent). In addition to the ester, other substances such as glycols, such as ethylene glycol and propylene glycol, or their derivatives, can be used.

[0016] In a further development, the pressure transmission fluid composition contains at least 70 vol% of the ester. A higher proportion of the ester in the pressure transmission fluid composition ensures that the physical and chemical properties of the ester dominate over those of the other substances.

[0017] In an alternative embodiment, the pressure transmission fluid composition contains at least 90 vol% of the ester. The high proportion of the ester in the pressure transmission fluid composition ensures that the physical and chemical properties of the ester dominate.

[0018] In a further development, the one to three carboxylic acids include acetic acid and / or butyric acid. Acetic acid is the common name for ethanoic acid, and butyric acid is that for butanoic acid. One molecule of glycerol can be esterified with one to three molecules of acetic acid, whereby the up to two additional carboxylic acids can be propanoic acid, butyric acid, or pentanoic acid. One molecule of glycerol can also be esterified with one to three molecules of butyric acid, whereby the up to two additional carboxylic acids can be acetic acid, propanoic acid, or pentanoic acid.

[0019] Acetic acid or butyric acid are preferably used as the one to three carboxylic acids. This esterification yields glycerol tributary acid esters (also known as tributyrin) or glycerol triacetate (also known as triacetin). These two compounds are approved, for example, under the US Food and Drug Administration's 21 CFR Part 184 standard and can be used in pharmaceutical or food applications.

[0020] In a further development, the one to three alcohols include ethanol. One molecule of glycerol is then esterified with at least one molecule of ethanol and up to two other alcohols, such as propanol or butanol.

[0021] Ethanol is preferably used as the one to three alcohols. Esterification produces triethyl citrate (also known as triethyl citrate). This compound is approved under 21 CFR Part 184 of the U.S. Food and Drug Administration and can be used in pharmaceutical or food applications.

[0022] The object underlying the present application is further achieved by a pressure measuring device for determining and / or monitoring a pressure of a medium, with

[0023] - a pressure sensor,

[0024] - a pressure-sensitive separating membrane, and

[0025] - a pressure transmission fluid composition according to one of the preceding embodiments, wherein the pressure measuring device is designed such that the pressure is transmitted from the separating membrane to the pressure sensor by means of the pressure transmission fluid composition.

[0026] For example, the pressure measuring device can have a pressure transmission path designed to transmit the pressure from the separating membrane to the pressure sensor using the pressure transmission fluid composition. In particular, the pressure transmission path connects the separating membrane to a surface of the pressure sensor. Typically, the pressure sensor has two opposing surfaces, one of which is subjected to the pressure of the medium and the second to a reference pressure, for example, to an ambient pressure, an absolute pressure, or another pressure of the medium. With the aid of the pressure transmission fluid composition, the pressure measuring device can be used in a wide temperature range. Furthermore, it can also be used in pharmaceutical and food processing plants and processes.

[0027] The invention will be explained in more detail below with reference to the following figures 1-2. They show:

[0028] Fig. 1a-c: three esters used according to the invention.

[0029] Fig. 2: a pressure measuring device according to the invention.

[0030] Figures 1a-c show, by way of example, three esters which are used according to the invention as pressure-transmitting fluids. Fig. 1a shows glycerol triacetate, Fig. 1b shows glycerol tributanoate, and Fig. 1c shows triethyl citrate. All three esters have in common that they are approved for pharmaceutical and food applications. All three esters have a liquid aggregate state in the temperature range from -55 to -250°C and exhibit a compression modulus of 1.8 to 2.2 GPa at 20°C. The volume expansion coefficient of the three esters is in the range of (760 - 890) ■ 10 -6 °C -1 . These three esters are therefore particularly well suited as pressure transmission fluids.

[0031] Fig. 2 shows an embodiment of a pressure measuring device 1 according to the invention. The pressure measuring device 1 has a pressure sensor 3 and a separating membrane 4, to which the pressure p of the medium 2 can be applied. The pressure sensor 3 has a first surface 7 and a second surface 8 opposite the first surface. The first surface 7 can be applied to the pressure p of the medium 2 by means of the pressure transmission fluid composition 5. The second surface can be applied to a second pressure, which can be, for example, a relative pressure from the environment of the pressure measuring device. For this purpose, the pressure measuring device has, for example, a relative pressure path 11 and a relative pressure opening 10 in the housing 14, by means of which the second surface 8 can be applied to the relative pressure. Alternatively, the pressure measuring device 1 can be designed as an absolute or differential pressure measuring device.

[0032] Between the separating membrane 4 and a membrane bed 6 assigned to the separating membrane 4 there is a pressure chamber 13 in which the pressure-transmitting fluid composition 5 is present. Furthermore, the pressure chamber 13 is connected to the first surface 7 by means of a pressure transmission path 9, which is also filled with the pressure-transmitting fluid composition 5. In this way, the pressure p of the medium 2 can be transmitted from the separating membrane 4 to the first surface 7 by means of the pressure-transmitting fluid composition 5. The pressure measuring device 1 can further comprise an evaluation unit 12, which determines and / or monitors the pressure p of the medium 2 based on the electrical signals from the pressure sensor 3.

[0033] List of reference symbols

[0034] 1 pressure gauge

[0035] 2 Medium 3 Pressure sensor

[0036] 4 Separation membrane

[0037] 5 Pressure transmission fluid composition

[0038] 6 membrane bed

[0039] 7 first area 8 second area

[0040] 9 Pressure transmission path

[0041] 10 Relative pressure opening

[0042] 11 Relative pressure path

[0043] 12 Evaluation unit 13 Pressure chamber

[0044] 14 housings

Claims

Patent claims 1 . Use of an ester as a pressure transmission fluid, wherein the ester is formed from the esterification of glycerol with one to three carboxylic acids having a chain length of 2-5 carbon atoms in a molar ratio of 1:3, or from the esterification of citric acid with one to three alcohols having a chain length of 2-4 carbon atoms in a molar ratio of 1:

3.

2. Use according to claim 1, wherein the one to three carboxylic acids comprise acetic acid and / or butyric acid.

3. Use according to claim 1, wherein acetic acid or butyric acid are used as the one to three carboxylic acids.

4. Use according to any one of claims 1-3, wherein the one to three alcohols comprise ethanol.

5. Use according to any one of claims 1-3, wherein ethanol is used as the one to three alcohols.

6. Pressure transmission fluid composition (5) with at least 50 vol% of an ester which is formed from the esterification of glycerol with one to three carboxylic acids having a chain length of 2-5 carbon atoms in a molar ratio of 1:3, or from the esterification of citric acid with one to three alcohols having a chain length of 2-4 carbon atoms in a molar ratio of 1:

3.

7. The pressure transmission fluid composition (5) according to claim 6, wherein the pressure transmission fluid composition (5) comprises at least 70 vol% of the ester.

8. The pressure transmission fluid composition (5) according to claim 6, wherein the pressure transmission fluid composition (5) comprises at least 90 vol% of the ester.

9. Pressure transmission fluid composition (5) according to any one of claims 6-8, wherein the one to three carboxylic acids comprise acetic acid and / or butyric acid.

10. Pressure transmission fluid composition (5) according to any one of claims 6-8, wherein acetic acid or butyric acid is used as the one to three carboxylic acids.

11. Pressure transmission fluid composition (5) according to any one of claims 6-8, wherein the one to three alcohols comprise ethanol.

12. Pressure transmission fluid composition (5) according to any one of claims 6-8, wherein ethanol is used as the one to three alcohols.

13. Pressure measuring device (1) for determining and / or monitoring a pressure (p) of a medium (2), with - a pressure sensor (3), - a separating membrane (4) which can be subjected to pressure (p), and - a pressure transmission fluid composition (5) according to any one of claims 6-12, wherein the pressure measuring device (1) is designed such that the pressure (p) is transmitted from the separating membrane (4) to the pressure sensor (3) by means of the pressure transmission fluid composition (5).

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