JP3016407B2 - Interference gas removal filter for gas detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for removing a gas such as hydrogen sulfide from a sample gas flowing into a gas detector.

[0002]

2. Description of the Related Art For example, in petrochemical and oil drilling sites, dangerous gases such as hydrogen sulfide (H ₂ S), sulfur dioxide (SO ₂ ), acetylene (CH ₄ ), and carbon monoxide (CO) are high. Since these gases exist at concentrations, it is necessary to constantly monitor the concentrations of these gases. When measuring sulfur dioxide or carbon monoxide among these gases, usually, a constant potential is applied between a working electrode having a boundary surface with the electrolyte and a counter electrode immersed in the electrolyte, A potentiostatic electrochemical sensor utilizing the fact that the electrolytic current changes depending on the gas concentration is used. When a potentiostatic electrochemical sensor is used in such a situation where hydrogen sulfide is present at a high concentration, the influence of hydrogen sulfide interference is large and the target gas cannot be measured. In order to suppress the influence of interference such as hydrogen sulfide and the like and accurately measure SO ₂ and CO, a filter in which copper sulfate crystals are supported on a granular support such as alumina is provided at the gas inlet of the sensor. That is being done.
However, alumina supporting copper sulfate has extremely high water absorption, so when the humidity of the sample gas increases, water droplets adhere to the filter and the flow of the sample gas into the detector is obstructed, causing a large measurement error. In addition, since the filter material is powder, a container for preventing the filter material from being scattered to the outside is required, so that the size of the filter is inevitably increased and the cost is increased.

In order to solve such a problem, it is conceivable to use a filter material utilizing an adsorption phenomenon such as activated carbon. However, the sample gas itself may be adsorbed or, depending on environmental conditions, the adsorbed sulfide may be used. In addition to the problem that hydrogen is released from the filter material, there is also a problem that a container is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas detector which has a small hygroscopicity, is easy to handle, and has a small size. It is an object of the present invention to provide a suitable filter for removing interference gas.

[0004]

According to the present invention, there is provided a sheet-like carrier having gas permeability and capable of absorbing a polyhydric alcohol, wherein the polyhydric alcohol and the polyhydric alcohol are provided. The silver salt dissolved in the dihydric alcohol was retained.

[0005]

Since the silver salt is dissolved in the polyhydric alcohol and held in a free state on the carrier, the silver salt is reduced by reacting quickly and selectively with the interfering gas contained in the sample gas, and the interfering gas is polyvalent. Since the sample gas is taken in the alcohol, the interfering components of the sample gas are reliably removed.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. A filter formed by holding a silver salt dissolved in a polyhydric alcohol on a carrier made of a sheet-like material having gas permeability and absorbing a polyhydric alcohol, such as cellulose that supports a reagent, and a filter. It is cut to fit the shape of the gas inlet of the gas sensor that requires

[0007] The silver salt used in this filter material includes:
A substance which is reduced by a gas serving as an interfering component such as silver nitrate, silver perchlorate, silver p-toluenesulfonate, silver sulfate or the like, for example, hydrogen sulfide, or a hydride gas such as silane or phosphine to produce metallic silver is selected. ing. Also,
As the polyhydric alcohol, those having extremely low volatility at room temperature and having water retention, such as glycerin and ethylene glycol, are selected.

When the amount of the silver salt retained on the carrier increases, the removal ability increases. However, when the concentration exceeds the saturation concentration with respect to the polyhydric alcohol, the air permeability is impeded by the precipitation of the silver salt. Restrictions arise naturally. Also, if the amount of the polyhydric alcohol held on the carrier is increased, the upper limit of the amount of the silver salt that can be held on the carrier can be increased, but the permeability of the carrier is impaired. Restrictions arise.

Since silver salts have extremely low solubility in water or organic solvents such as alcohol and acetone, a mixed solution of a polyhydric alcohol as a solvent and ethanol as a diluent for lowering the viscosity at the time of coating is used. A silver salt is dissolved in the solution to prepare a solution. When the sheet serving as the carrier is immersed in the solution and the solution is sufficiently impregnated, the carrier is pulled up and the alcohol in the solvent is evaporated at room temperature. Thereby, the polyhydric alcohol and the silver salt dissolved in the polyhydric alcohol are supported on the carrier, and become a filter material.

The filter material 1 constructed as described above
Is a schematic diagram of an electrochemical sensor 1 in which a working electrode formed by forming an electrode on a gas-permeable membrane and a counter electrode as shown in FIG. 1 are brought into contact with an electrolytic solution to generate an electrolytic current proportional to the concentration of a target gas. In a state where the protection member 4 of the gas inlet 3 is removed, the gas inlet 3 is arranged close to the working electrode 5 (a in the figure). Since the filter material 1 is extremely thin, the protective member 4 can be mounted thereon, and can be assembled as before (b in the figure). When the concentration of a sample containing 30 ppm of hydrogen sulfide as an interfering gas was measured in this electrochemical sensor incorporating the filter material 1, no output based on the interfering gas was found until about 30 minutes as shown in FIG. At the time the silver salts were all reduced to metallic silver, an interfering gas output appeared.

When two identical filter materials are placed one on top of another, as shown in FIG. 2 (B), there is no output based on the interfering gas until about two and a half hours, and the filter material is used alone (FIG. 2B). It was found that the interfering gas can be effectively removed for about four times longer than A), and even when three sheets are used in a stack, the interfering gas can be completely removed for about six times longer than in the case of single use. By the way, since glycerin, which also functions as a solvent for the silver salt, has water retention and water absorption, the humidity of the sample gas flowing into the main body of the gas detection means can be adjusted to be constant, and the sensitivity is affected by the humidity. When used in a gas sensor of the type, there is an effect that the detection sensitivity can be stabilized. Further, since metallic silver precipitates in proportion to the integrated removal amount of the interfering gas, the degree of blackening increases. Therefore, the life of the filter material can be easily confirmed by determining the color of the filter material.

Example 1 Cellulose was prepared by dissolving 2 to 4 g w / v percent of silver perchlorate and 15 v / v percent of glycerin in methanol, respectively.
The tape is immersed, pulled up, and the methanol contained in the tape is evaporated at room temperature. As a result, a filter material holding 1.3 to 2.6 g of silver perchlorate and 25 g of glycerin per square meter can be obtained. Also, 15 v / v percent of ethylene glycol is used as a solvent instead of glycerin, or the total amount is 1%.
It was confirmed that the same performance was exhibited even when a mixture of glycerin and ethylene glycol was used so as to be 5 v / v percent.

Example 2 A cellulose tape is immersed in a solution prepared by dissolving 1 to 2% by weight of silver nitrate and 15% by weight of glycerin in methanol, and the methanol is evaporated at room temperature. As a result, a filter material carrying 0.6 to 1.3 g of silver nitrate and 25 g of glycerin per square meter can be obtained.

Example 3 A cellulose tape was immersed in a solution prepared by dissolving 1 to 2 g w / v percent of silver paratoluenesulfonate and 25 g v / v percent of glycerin in methanol to evaporate the methanol. Thus, a filter material carrying 0.6 to 1.3 g w / v percent of silver paratoluenesulfonate and 25 g of glycerin per square meter can be obtained.

Example 4 A cellulose tape was immersed in a solution prepared by dissolving 0.5 to 1 gram w / v percent of silver sulfate and 25 gram v / v percent of glycerin in methanol to evaporate methanol. 0.3 to 0.6 per square meter
A filter material carrying gram w / v percent and 25 grams of glycerin can be obtained.

Incidentally, silver salts generally have the property of generating metallic silver when receiving light energy.
Considering that the action of removing the interfering gas is the reduction of the silver salt by the interfering gas, if exposure is to be performed for a long period of time or when it is considered to be used in a place exposed to light, exposure Desirably, no metallic silver is formed.

Example 5 Paratoluenesulfonic acid was further added to the preparation solutions shown in the above Examples 1 to 4 at 1 w / v
Add 0.5% w / v cents or nitric acid. The carrier is immersed in the prepared solution to evaporate the organic solvent at room temperature, whereby 1.3 to 2.6 g of silver perchlorate and 0.6 g of paratoluenesulfonic acid per square rice are obtained. Alternatively, 0.3 g of nitric acid and 25 g of glycerin can be impregnated and supported.

According to this filter material, the reduction of silver salt by light energy due to the action of paratoluenesulfonic acid or nitric acid present on the carrier can be suppressed. The ability to remove the interfering gas does not decrease even when exposed to light in the state of being kept.

By the way, from the viewpoint of improving light resistance, silver nitrate and paratoluenesulfonic acid have the same ability, but when cellulose is used as a carrier, silver nitrate has an action of oxidizing cellulose. However, there is a disadvantage that the mechanical strength is reduced. On the other hand, when paratoluenesulfonic acid is used as a light resistance improver, cellulose is not oxidized unlike nitric acid, and thus there is an effect that the mechanical strength of the carrier is not reduced for a long period of time.

In the above embodiment, the case where one type of silver salt is used has been described. However, the same applies when a plurality of types of silver salts are used in combination within a range that does not cause saturation in a polyhydric alcohol. It is obvious that the action of In this embodiment, the case where the present invention is applied to an electrochemical gas sensor has been described. However, it is apparent that the same effect can be obtained when the present invention is applied to another type of gas sensor such as a semiconductor gas sensor.

[0021]

As described above, in the present invention,
A polyhydric alcohol and a silver salt dissolved in the polyhydric alcohol are held on a sheet-shaped carrier with gas permeability, so that the interfering gas can be reliably detected without causing the gas permeability of the sample gas to be impaired by excessive moisture absorption. In addition, a special container for accommodating the filter material is not required, and a light-weight, thin, and low-cost product can be realized.

Furthermore, since the optical density changes in proportion to the integrated removal amount of the interfering gas, it is possible to easily determine the time of replacement by visual observation and not only to prevent the measurement error, but also to prevent the measurement error. The humidity of the sample gas is kept as constant as possible by the moisturizing action of the polyhydric alcohol, so that a change in the detection sensitivity due to a change in the humidity can be prevented.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are cross-sectional views each showing an example in which the filter material of the present invention is applied to an electrochemical gas detector.

FIGS. 2 (A), (B) and (C) are diagrams showing the interfering gas removal characteristics of the filter material of the present invention.

[Explanation of symbols]

 1 Filter material 2 Gas detector

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 1/22 G01N 27/12 G01N 27/28 G01N 27/00

Claims (5)

(57) [Claims] 1. An interfering gas for a gas detector comprising a sheet-like carrier having gas permeability and capable of absorbing a polyhydric alcohol, holding a polyhydric alcohol and a silver salt dissolved in the polyhydric alcohol. Removal filter. 2. The polyhydric alcohol includes glycerins,
2. The filter according to claim 1, wherein said filter is selected from glycols. 3. The filter according to claim 1, wherein the silver salt is at least one selected from silver nitrate, silver perchlorate, silver p-toluenesulfonate, and silver sulfate. 4. The filter according to claim 1, comprising an organic acid and an inorganic acid. 5. The filter according to claim 4, wherein the acid is silver nitrate or p-toluenesulfonic acid.