Medium for quantitatively removing water from a gas stream containing sulphur and / or sulphur-containing compounds, device for this purpose, and use of said medium

Abstract

The invention relates to a material for quantitatively removing water from a gas stream containing molecular sulphur and / or sulphur-containing compounds, in particular from a gas stream fed to a gas analytics system. Said material contains at least 60 wt.% carrier material designed as granulate, which is inert with respect to sulphur compounds, primarily sulphur dioxide, and between 5 and 35 wt.% magnesium perchlorate. The invention furthermore relates to a device for purifying gas streams, which is used with the material according to the invention, and to the use of the material in the gas analytics system.

Description

[0001] Means for the quantitative removal of water from a gas stream containing sulphur and / or sulphur-containing compounds, as well as device therefor and use thereof

[0002] The invention relates to a mixture for the quantitative removal of water from a gas stream containing sulfur and / or sulfur-containing compounds.

[0003] The removal of components from gases that interfere with downstream process steps is of great importance in many processes. Water removal is particularly crucial, as it is necessary not only in a variety of chemical syntheses but also for most quantitative and / or qualitative gas analyses. Gas analysis requires the quantitative removal of the water contained in the gas. The term "quantitative" in the context of the invention is understood to mean reducing the water content to a value of less than 100 ppm.

[0004] The necessity of such water removal particularly affects all existing analysis modes and systems for the quantitative determination of oxygen, sulfur, nitrogen, and / or carbon. Furthermore, to avoid interactions, the gas stream to be measured for TOC analysis and IRMS analysis must be freed of water. Typically, during such drying, the gas stream to be analyzed is passed through a tube partially filled with the drying agent, forcing the gas to pass through the drying agent, thus removing any water present in the gas.

[0005] One type of desiccant used is a phosphorus pentoxide-based desiccant, primarily known under the name Sicapent®, where the phosphorus pentoxide is applied to an inert carrier material as the actual desiccant. Magnesium perchlorate (Mg(ClO4)2) is also used, primarily in gas analysis. Both options have in common that these desiccants are suitable for quantitatively removing water. The use of these materials therefore requires a high level of occupational safety and appropriate training for the personnel working with them. A further disadvantage of these materials is their highly complex and correspondingly energy-intensive production, which also results in high levels of waste.

[0006] Many other conventional drying agents are not suitable for actually removing water quantitatively and thus preparing the gas stream for quantitative analysis. Other drying agents that would be suitable for quantitative water removal, especially molecular sieves, are not inert to all gas streams. In particular, they are not suitable for ensuring reproducible results with sulfur-containing gas streams, where "sulfur-containing" in the sense of the invention includes both the presence of sulfur and sulfur-containing compounds. For example, the known drying agent silica gel frequently results in side reactions, so that the analysis result is distorted by the pre-drying, since components in the drying agent are either bound or altered.

[0007] As already mentioned, magnesium perchlorate is known in the literature as a possible desiccant. However, it has not yet been used in analytical instruments because magnesium perchlorate dissolves in moisture and can consequently clog or damage the downstream analytical instrument.

[0008] The invention is therefore based on the object of providing a simple and safe material for the quantitative removal of water from a gas stream containing sulfur and / or sulfur-containing compounds, in particular sulfur dioxide (SO2), which is particularly suitable for drying a gas stream prior to downstream gas analysis. To achieve this, the drying agent must not react with the sample gases or interact excessively, as this would lead to a change in the measurement signal.

[0009] The highly acidic gas sulfur dioxide poses a particular challenge. This is especially problematic because in elemental analysis, the sample material is first combusted in a reactor, and the resulting gas stream is then quantitatively analyzed for its components. This combustion of the samples always produces SO2 whenever sulfur and / or sulfur-containing compounds are present. This SO2 is subsequently detected, allowing the amount of sulfur contained in the original sample to be calculated. However, due to the interaction of SO2 with almost all common desiccants, reproducible quantitative statements regarding the sulfur content can no longer be made if the gas stream has to be dried beforehand.This is especially true for measurements with a thermal conductivity detector (TCD), for which a dry gas flow is the basic requirement for precise, linear and repeatable results over the entire measuring range.

[0010] Despite these difficulties, the stated problem is solved with a material according to claim 1.

[0011] Such a material according to the invention comprises a mixture containing a carrier material and magnesium perchlorate, wherein the proportion of the carrier material, based on the total mixture, is at least 60 wt. %, preferably 70 to 80 wt. %, and that of the magnesium perchlorate is between 5 and 35 wt. %, preferably between 10 and 20 wt. %. The two components, carrier material and magnesium perchlorate, can be the only two components in the mixture and their proportions add up to 100 wt. %, or other additives can be provided. Magnesium perchlorate is known as an inert drying material. By mixing it with the carrier material, preferably in a ratio of at least 1:2, preferably 1:3, the previously known disadvantageous clumping during the enrichment of water and, above all, the discharge of the material into downstream process steps or devices can be prevented.

[0012] With regard to the carrier material, it is essential that it is inert to sulfur and sulfur-containing compounds, especially sulfur dioxide. Furthermore, it has proven advantageous for the carrier material to be manufactured in the form of spheres, hollow spheres, or cylinders, as this allows the gas flow to pass through without excessive pressure loss. Hollow spheres with a diameter of 0.5–5.0 mm, preferably 1.0–3.0 mm, have proven particularly suitable for gas analysis systems, as this minimizes pressure loss under the parameters of this application, especially the flow velocities used.

[0013] In principle, any material that is inert with respect to sulfur and sulfur-containing compounds, is available in granular form, and is inert to the gases flowing through it during application. Support materials such as those already known from heterogeneous catalysis, especially ceramic materials with inert behavior, are conceivable. This offers the advantage of being able to use existing and readily available granules.

[0014] Alternatively, it has proven very advantageous to use corundum as the carrier material. Corundum is a relatively common mineral from the mineral class of aluminum oxides and hydroxides. It crystallizes in the trigonal crystal system with the chemical composition Al2O3. Corundum is particularly suitable as a carrier material in this case because it not only exhibits high temperature resistance and, due to its high hardness, also offers great abrasion resistance, but is also inert to almost all compounds. A reaction with sulfur-containing compounds, especially SO2, can therefore be ruled out.

[0015] Another advantage of using corundum, especially hollow corundum spheres, is that the bulk densities of the individual components are close to each other. This allows the material to be produced and filled using simple mixing processes and prevents segregation during transport.

[0016] Another preferred embodiment provides that the carrier material is at least partially coated with the magnesium perchlorate, which can further reduce the risk of clumping. The coating can be applied with only a portion of the magnesium perchlorate or with the entire amount.

[0017] Once again, the use of materials known from heterogeneous catalysis, such as zirconium oxide and, in some cases, particularly inert zeolites, is recommended, as these are typically coated with the catalyst and therefore have suitable surface areas. The same advantages also apply to aluminum oxide corundum, which has a large surface area to which the gel formed from the magnesium perchlorate in humid conditions adheres. This ensures that liquid fractions do not clog or flush away the device, which could lead to the interruption of measurements, premature replacement of the drying tube, or damage to the device.

[0018] It has also proven advantageous to add calcium chloride to the material as an additional desiccant, preferably in an amount of 5 to 35 wt.%, most preferably 5 to 10 wt.%. Calcium chloride is also inert to virtually all gas streams to be measured. This addition can achieve primary drying and reduce the required amount of magnesium perchlorate.

[0019] Additionally or alternatively, an indicator can be added to the mixture to detect when the desiccant's water absorption capacity is exhausted. The indicators used, which indicate a color change depending on the humidity in the surrounding medium, can be inorganic and / or organic substances.

[0020] Inorganic indicators are often available at lower prices on the market. Among inorganic indicators, copper(II) sulfate (Cu(II)SO4) is particularly preferred. Copper(II) chloride can also be used effectively. Its advantage is its safety. When used in conjunction with calcium chloride, the color changes from colorless to blue as soon as the primary drying agent, the molecular sieve, is no longer suitable for quantitatively removing the water.

[0021] Organic substances often exhibit very clearly recognizable color differences. Phenolphthalein is a particularly suitable organic substance. Phenolphthalein has the particular advantage that when the molecular sieve's capacity is exhausted, as its pores fill completely with water, it changes color to white. This "front" shifts further and further in the direction of flow toward the gas outlet over the course of the measurements. As soon as this color change reaches the gas outlet, there is no longer a sufficient amount of desiccant suitable for completely removing the water. However, if the mixture according to the invention is stored for an extended period in such a way that it is exposed to atmospheric humidity, so that the water is not carried through by a gas stream, this changes the reactions that lead to the indicator's color change.The indicator (In) then does not have the structure FLIn, which leads to an orange color, but is present as In. 2- and thus turns white. This color clearly indicates that moisture has slowly diffused in. This also makes it easier to detect the cause of the exhaustion of a column's absorption capacity, particularly storage errors.

[0022] As mentioned, the use of pure calcium chloride as the sole drying agent would not be sufficient to ensure quantitative removal of water, which is particularly important for gas analysis. Since calcium chloride also dissolves in water, its use as a carrier material is excluded. However, due to its colorless, opaque crystals, calcium chloride is well suited to visualizing a distinct color change when the calcium chloride contains an indicator. Due to the ability of calcium chloride to absorb large amounts of water and then dissolve itself in the water of crystallization, the color change caused by exposure to water is particularly visible. The indicator thus allows the water absorption to be visually monitored.

[0023] Furthermore, the calcium chloride (CaCl2) containing the indicator can be coated with the indicator so that the indicator lies on the surface of the calcium chloride acting as the carrier material. Applying it to magnesium perchlorate, however, is significantly more complex than the comparatively simple coating of calcium chloride. In a particularly preferred embodiment, the calcium chloride is therefore coated with at least one indicator. Alternatively, it is also possible to mix the indicator with the calcium chloride and form it into granules or beads, for example by pressing. The latter is less complex to manufacture than the aforementioned coating, but depending on the type of indicator used, the color change with a coating is sometimes more visible due to the higher local concentration on the surface.

[0024] Furthermore, the use of calcium chloride as the indicator carrier also has the advantage that, as already mentioned, calcium chloride acts as a desiccant, meaning that the incorporation of an indicator onto a carrier material does not dilute the desiccant material itself. This, in turn, means that the total amount of mixtures can remain the same when compared to the material without an indicator, which plays a role in, among other things, pressure drop, dead volume, and storage time.

[0025] In summary, the advantage of the new invention is that it provides a way to use a new desiccant for C, N, S, and O determinations in the presence of sulfur using simple chemicals available in large volumes. This desiccant simultaneously indicates desiccant exhaustion. Furthermore, the hazard potential of the material has been significantly reduced, making processing, preparation, and use safer and easier. Due to the excellent absorption capacity per volume, the operating time could be maintained while maintaining the same container volume.

[0026] This ensures highly efficient drying even with any form of sulfur present and, at the same time, a clearly visible color change when the drying capacity is exhausted.

[0027] The invention further encompasses a device for drying gases in the sense of quantitatively removing the water, particularly in preparation of a gas stream for subsequent analysis. Such a device comprises a gas-tight housing and a gas inlet and a gas outlet. The volume defined by this housing is at least partially filled with the material according to the invention according to at least one of claims 1 to 10. The material according to the invention can be used directly in any gas analysis, particularly in any elemental analysis, without modifying the system. A filled tubular reactor represents a particularly simple embodiment of such a device.

[0028] The device can in principle be made from any material that is inert to the gas stream to be analyzed and is gas-tight. Furthermore, it must be at least partially transparent. Metals, glass, and plastic are particularly conceivable as base materials. When metals and opaque plastics are used, a viewing window made of glass or a correspondingly transparent plastic must be provided so that the indicator changes color and the exhaustion of the drying agent's service life is visible. Glass, and sometimes plastic, as the base material, has the advantage that such viewing windows are not necessary. When a color change is shifted along the length of the container, especially the tube, this has the advantage that the effect is clearly visible. Glass is particularly preferred as a housing material due to its inert properties.

[0029] In principle, it is also conceivable to fill the device according to the invention sequentially with a series of materials, for example to provide the flow direction first a carbon dioxide absorbing material and then the drying agent according to the invention from the mixture.

[0030] Finally, the invention also relates to the use of the material according to the invention according to any one of claims 1 to 10 and / or a device according to the invention according to claim 11 or 12 for the quantitative removal of water in a gas analysis system. In particular, this relates to gas analysis systems for the determination of nitrogen, carbon, hydrogen, sulfur, and oxygen (CHNSO). The material according to the invention is particularly suitable for completely removing water from the gas stream head without changing the flow behavior and, at the same time, reliably indicates the exhaustion of its drying capacity through the indicator it contains. The use of the material is not limited to specific devices but can be used in all applications that identify non-acidic, dry gas streams. Other conceivable areas of analysis include TOC analysis and IRMS analysis.Even with a thermal conductivity detector (TCD), a dry gas flow is the basic requirement for precise, linear and repeatable results across the entire measuring range.

[0031] Further embodiments of the invention will become apparent from the examples, as well as the figures and their associated descriptions. Each feature is intended to be disclosed individually or in any combination. Some of the illustrations are slightly simplified and schematic.

[0032] They show:

[0033] Fig. 1 : a schematic design of a device according to the invention and

[0034] Fig. 2: schematically shows the use of a device according to the invention in a gas analysis system

[0035] Figure 1 shows the device 10 according to the invention, which is designed as a preferably cylindrical housing 11 with a gas inlet 12 and a gas outlet 13. Inside there is a filling 14 with the material according to the invention, which is introduced in such a way that the gas stream flowing in through the gas inlet 12 must always pass through the material before it can escape via the gas outlet 13. Figure 2 shows a highly simplified gas analysis system 20, preferably an elemental analysis system, in which the material according to the invention is used for the quantitative removal of water. Via lines 21, 22 and 23, the gas stream is first passed through a carbon dioxide removal device 24 and then through a device 10 according to the invention before being analyzed in the detector 25.

[0036] As an alternative to the graphic representation, the functions of devices 24 and 10, i.e., carbon dioxide removal and drying, can also be arranged in one device such that this device has two segments into which a corresponding material is filled. In particular, this can be a tube, which is filled in a first part with the mixture according to the invention and in a second part, downstream of the gas flow, with a drying agent.

[0037] In addition, pre-drying (not shown) may be provided before the removal of carbon dioxide.

[0038] Example 1

[0039] The following example shows how many measurements can be performed with each type of absorbent for quantitative water removal before the indicator indicates complete water loading. The values ​​given are averages over three lifetime tests. The following example shows that due to the very good drying properties, the service life of a column can at least be maintained.

[0040] List of reference symbols

[0041] 10 Device

[0042] 11 housings

[0043] 12 Gas inlet

[0044] 13 Gas outlet

[0045] 14 Filling with inventive material

[0046] 20 Gas analysis system

[0047] 21 - 23 Line

[0048] 24 Drying device

[0049] 25 detector

Claims

Patent claims 1. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds, characterized in that the material contains at least 60 wt.% of a carrier material in the form of granules, which is inert towards sulfur and sulfur-containing compounds, and between 5 and 35 wt.% magnesium perchlorate, characterized in that the material additionally contains calcium chloride and the proportion of calcium chloride is between 5 and 35 wt.%.

2. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to claim 1, characterized in that the granulated carrier material at least partially comprises granules in the form of spheres, hollow spheres and / or cylinders.

3. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to claim 1 or 2, characterized in that the carrier material is a ceramic material or corundum.

4. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to one of the preceding claims, characterized in that the carrier material is at least partially coated with at least parts of the magnesium perchlorate.

5. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to one of the preceding claims, characterized in that the material additionally contains an indicator.

6. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to claim 5, characterized in that the indicator is an inorganic compound, in particular copper(II) sulfate.

7. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to claim 5, characterized in that the indicator is an organic compound, in particular phenolphthalein.

8. Material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds according to one of the preceding claims, characterized in that the calcium chloride is at least partially coated with the indicator or calcium chloride and indicator are present together in granules.

9. Device (10) for absorbing water with a gas-tight housing (11) which has a gas inlet (12) and a gas outlet (13) and whose volume is at least partially filled with a material according to one of claims 1 to 8.

10. Device (10) according to claim 9, characterized in that the housing is at least partially transparent.

11. Use of a material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds in a gas analysis system (20) for the determination of nitrogen, carbon, hydrogen and / or oxygen, wherein the material contains at least 60 wt.% of a carrier material in the form of granules which is inert to sulfur and sulfur-containing compounds, and between 5 and 35 wt.% of magnesium perchlorate.

12. Use of a material for the quantitative removal of water from a gas stream containing molecular sulfur and / or sulfur-containing compounds in a TOC analysis or an IRMS analysis, wherein the material contains at least 60 wt.% of a carrier material in the form of granules which is inert towards sulfur and sulfur-containing compounds, and between 5 and 35 wt.% magnesium perchlorate.

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