JPS63193055A - Method and apparatus for detecting impurity gas - Google Patents

Abstract

PURPOSE:To certainly detect impurity gas, by a method wherein purified hydrogen gas and specimen gas containing impurities are respectively brought into contact with a transition metal catalyst and, thereafter, the heat conductivity difference between both of them is detected. CONSTITUTION:In a chilling adsorptive gas purifying apparatus B, an adsorbing cylinder 10 is immersed in a cooling medium tank 1. Raw material hydrogen is introduced from a supply pipe 14 and impurity gas is adsorbed and removed to purify hydrogen gas, while the purified hydrogen gas is taken out from a withdrawing pipe 15. An impurity gas detection apparatus A is provided and catalyst pipes 7, 8 filled with a transition metal catalyst are provided. Specimen gas is take out from the measuring point 8 of the adsorbing cylinder 10 to be sent to the catalyst pipe 8 through a pipe 20 and brought into contact with the catalyst to be guided to the specimen side 3 of a heat conductivity detector 1. The purified hydrogen gas is taken out from the withdrawing pipe 15 to be guided to the reference side 2 of the detector 1 through the catalyst pipe 7; the heat conductivity difference between the specimen side 3 and the reference side 2 is detected and the impurity gas is measured. Since the hydrogen gas is brought into contact with the catalyst before detection, the impure gas can be accurately measured.

Description

[Detailed Description of the Invention] [Field of Application in the Nitrogen Industry] The present invention relates to a method and apparatus for detecting impure gas, and more particularly to a method for detecting impure gas contained in hydrogen gas being purified by cryogenic adsorption. and regarding equipment.

With the development of the semiconductor industry, nuclear power industry, etc., the demand for various gases such as hydrogen and helium is increasing, but the gases used in these fields are of extremely high purity! !
required. However, these gases that are usually commercially available contain impurity gases such as nitrogen, carbon oxide, and methane, so it is necessary to remove these impurity gases, and various gas purification devices have been introduced. has been done.

One of the most representative of these is a cryogenic adsorption gas purification device that adsorbs and removes impurity gas at extremely low temperatures using an adsorption column filled with an adsorbent.
-7565 and Japanese Unexamined Patent Publication No. 61-38616.

These devices basically consist of an adsorption cylinder, a refrigerant 1, a heat exchanger, a heating device, etc., and perform adsorption purification of gas at extremely low temperatures using liquid nitrogen as a refrigerant, and regeneration of the adsorbent by heating. This is done alternately. In such cryogenic adsorption gas purification equipment, during gas purification, as the adsorption of impure gas progresses, the adsorption zone of impure gas sequentially moves from the upstream side to the downstream side of the adsorption column, and finally the adsorption layer impure gas is mixed into the purified gas discharged from the outlet of the adsorption column. Therefore, it is necessary to take measures such as predicting the breakthrough of the adsorption layer and switching to another adsorption cylinder before the breakthrough occurs. Therefore, it is extremely important to detect an increase in impure gas.

[Conventional technology]

Conventionally, the conventional method for detecting impurity gases contained in gases such as hydrogen and helium is to analyze the sample gas extracted from an adsorption cylinder at predetermined intervals using a mass spectrometer, infrared analyzer, gas chromatograph, etc. It was a target. However, analysis using these analyzers is an intermittent method and has the disadvantage that analysis cannot be performed.In response, the present inventors first used a thermal conductivity detector and used a purified gas and We proposed a method for detecting impure gases by flowing a measuring gas and detecting the difference in thermal conductivity between the two.We conducted further studies and found that by flowing a measuring gas or a purified gas on the opposite side of a thermal conductivity detector, By alternately switching the measurement gas and the purified gas to the sample side, we can monitor the incorporation of impure gas while correcting the zero point deviation between the control side and the sample side. A method for sensitive and rapid detection has been disclosed (Japanese Patent Application Laid-open No. 130864/1986).

[Problems to be Solved] This method using a thermal conductivity detector can be widely applied to the detection of impure gases contained in hydrogen gas, helium, and the like. However, in the purification of hydrogen gas using the cryogenic adsorption gas purification method described above, if the sample hydrogen gas derived from the purification system is directly passed through the thermal conductivity detector, impurity gas may be present in the hydrogen gas. Not only does it show a value different from the thermal conductivity of normal hydrogen gas even when it is not contained, but there is also a phenomenon in which the thermal conductivity changes depending on the gas flow rate fluctuation in the purification system, the extraction position of the sample gas, etc. Occur. For this reason, even if the thermal conductivity changes due to the mixing of impure gas into hydrogen gas, it is difficult to distinguish whether the change is due to the impure gas or not, and especially when the concentration of impure gas is low, it cannot be detected at all. There was a problem.

[Means for solving problems]

The inventors of the present invention have conducted extensive research in order to solve these problems and reliably detect impurity gas in hydrogen gas in cryogenic adsorption gas purification in the same manner as in the case of other gases. The present inventors have discovered that the above-mentioned change in thermal conductivity can be prevented by contacting a sample hydrogen gas derived from a hydrogen gas with a hydrogenation catalyst containing a transition metal element.

That is, the present invention provides a method for detecting nonconducting gas contained in hydrogen gas being purified in a cryogenic adsorption gas purification device, in which the purified hydrogen gas and the measurement gas derived from the measurement point of the adsorption column in the device are respectively transitioned. Impure gas detection method and cryogenic adsorption gas characterized by detecting impure gas in a measurement gas by bringing it into contact with a hydrogenation catalyst containing a metal element and then detecting a difference in thermal conductivity between the two. A device for detecting impurity gas contained in hydrogen gas being purified in a purification device, the thermal conductivity detector being disposed in the cryogenic adsorption gas purification device and having a gas flow path on a control side and a sample side. , one end of which is connected to each of the gas inlets on the control side and the sample side, and the other end of the catalyst tube is filled with a hydrogenation catalyst containing a transition metal element. Each of these is an impure gas detection device characterized in that it is connected to a sample tube for purified hydrogen gas and a measurement gas led from a measurement point of an adsorption column in a purification device.

The present invention is applied to the detection of impurity gases such as nitrogen, oxygen, carbon oxide, carbon dioxide, and methane contained in hydrogen gas being purified by a cryogenic adsorption gas purification device. and hydrogenation catalysts are used.

The cryogenic adsorption gas purification device to which the present invention is applied is equipped with an adsorption cylinder, a refrigerant tank, a heat exchanger, a heating device, etc., and usually has two series of adsorption cylinders, one in which adsorption purification is performed. On the other hand, the adsorbent is regenerated by heating. The adsorption cylinder is composed of one or more cylinders, and the inside thereof is filled with an adsorbent such as activated carbon or molecular sieve. When refining hydrogen gas, it is cooled with liquid nitrogen, and impurity gas is adsorbed and removed by flowing the raw hydrogen gas at an extremely low temperature of about -196°C to obtain purified gas, but as the adsorption of impure gas progresses, the adsorption zone The impurity gas gradually moves from the upstream side to the downstream side of the adsorption cylinder, and finally breaks through the adsorption layer, and the impure gas is mixed into the purified gas. For this reason,
Before breakthrough, it is necessary to complete regeneration of the adsorbent and to switch to an adsorption column.

In the present invention, the adsorption column in the purification device is provided with a measurement point for extracting the measurement gas. Usually, the measuring point is located upstream from the outlet of the adsorption cylinder, at a position where impurity gas detection can provide enough time for switching to another adsorption cylinder before the adsorption layer breaks through. Furthermore, in the case of an adsorption cylinder in which a large number of cylinders are connected in series through connecting pipes, the measurement point can be provided at the connecting pipe connecting the most downstream cylinder and its upstream cylinder.

The thermal conductivity detector used in the present invention basically has a bridge circuit made of metal wire resistance and has two gas flow paths.
One side is the control side, and the other side is the sample side. Usually, a gas containing no impurity gas is flowed into the control side, and a test gas is flowed into the sample side, to calculate the difference in thermal conductivity between the two. The impure gas in the sample gas is detected by extracting the potential difference due to the difference in electrical resistance of the platinum wire.

In the present invention, purified hydrogen gas is normally flowed to the control side, and measurement gas led from the measurement point of the adsorption cylinder is flowed to the sample side, and impure gas is detected by a change in the thermal conductivity difference between the two.

Note that purified hydrogen gas is usually introduced from the outlet of the adsorption column, but it can also be introduced from other purification equipment, cylinders, etc. In addition, the measurement gas is not diluted with a carrier gas or the impurity gases are separated unlike in a gas chromatograph, and the total concentration of the impurity gases is measured as is, so even trace amounts of impurity gases can be detected with high sensitivity. Although it can be detected,
Similar to the method in Publication No. 1-130864, if a method is used in which measurement gas and purified hydrogen gas are alternately passed through the sample side and the potential difference with drift corrected is detected, impurity gas can be detected with even higher sensitivity and accuracy. Can be detected.

In the present invention, purified hydrogen gas and measurement gas are each brought into contact with a hydrogenation catalyst and then flowed into a thermal conductivity detector. If these hydrogen gases are passed directly to the thermal conductivity detector without going through the contact process with the catalyst, it is assumed that this is due to interaction of the hydrogen gas with the adsorbent in the refinery, as well as fluctuations in temperature and flow rate. Thermal conductivity of the hydrogen gas itself changes, making it impossible to accurately detect impure gas.

The catalyst used in the present invention contains a transition metal element and is a generally known hydrogenation catalyst that can activate and adsorb hydrogen to carry out a hydrogenation reaction. Specifically, V, CrlMn.

F e% Cas N rs Cu% Z ns M as
T cs Ru-Rhs P dsAglW, Re
, Os, Ir%PtlAu, etc.,
The main components are alloys, oxides, sulfides, and mixtures thereof, and include Fe-, CosNr
sCu s几U%Rh%Ir, Pt, etc. are mainly used in elemental parts, and others are often used in the form of oxides and sulfides.

These catalysts are packed into catalyst tubes such as tubes and tubes and connected to the control and sample sides of the thermal conductivity detector, respectively. The catalyst loading amount varies depending on the type of catalyst and the flow rate of the sample gas, and cannot be generally specified, but it is designed so that the contact time of the gas with the catalyst is usually 5 seconds or more, preferably 10 seconds or more in practice. be done. Although the temperature of the catalyst tube may be room temperature, it may be heated as appropriate for the purpose of further increasing the activity of the catalyst.

The impure gas detection device of the present invention is installed in a cryogenic adsorption gas purification device, and the catalyst tubes on the control side and the sample side are connected to sample tubes for purified hydrogen gas and measurement gas, respectively.

Next, the present invention will be specifically illustrated and explained with reference to the drawings.

FIG. 1 is an example of an impure gas detection device of the present invention and a flow sheet in which the same is installed in a cryogenic adsorption gas purification device.

In FIG. 1, %A is the impure gas detection device of the present invention, and B is the gas purification device (only one system is shown).

Regarding A, the thermal conductivity detector 1 is connected to the control side 2 and the sample side 3.
It consists of a detection section 4 having two gas flow paths, a recorder 5 and an alarm 6. The gas inlet side of the detection section 4 is filled with a hydrogenation catalyst, and two catalyst tubes 7 and 8 are provided together with a heating furnace 9 containing the hydrogenation catalyst. The catalyst tubes 7 and 8 are connected to the control side 2 and sample side 3 of the thermal conductivity detector 1 via constant flow valves 2' and 3', respectively, to form an impure gas detection device A, and are arranged in a gas purification device B. It is set up. On the other hand, in the gas purification apparatus B, a refrigerant tank 11 containing an adsorption cylinder 10 filled with adsorbent is housed together with a heat exchanger 12 in a vacuum insulation container 13, and a raw gas supply pipe 14 and a purified gas extraction pipe 15 are connected to the refrigerant tank 11. is introduced into the heat exchanger 12
are respectively connected to the inlet 16 and outlet 17 of the adsorption cylinder 10 via the above, thereby forming one line of the purification system. Even if the measurement point 18 is provided at a position closer to the gas upstream side from the outlet 17 of the adsorption cylinder 10. The measurement point 18 is connected to the catalyst pipe 8r of the impurity gas detection device A by the sample pipe 20,
A sample tube 19 branched from the purified gas extraction tube 15 is connected to the catalyst tube 7. A bypass pipe 21 branched from the sample pipe 19 is led to the catalyst pipe 8 together with the sample pipe 20. Further, valves 22a, 22b and 22c are interposed in the sample tubes 19 and 2.degree. and the bypass tube 21, respectively.

To purify hydrogen gas, the refrigerant tank 11 is filled with liquid nitrogen and the adsorption column 10 is cooled to an extremely low temperature, and then the raw material gas supply pipe 1 is
Hydrogen gas is supplied from 4.

This hydrogen gas is pre-cooled in the heat exchanger 12 and enters the adsorption column 10 from the inlet 16 in the refrigerant tank 11, where impurity gas is removed by adsorption and purified.The purified hydrogen gas is then purified at the outlet 16.
7 and the heat exchanger 12, and is extracted from the purified gas extraction pipe 15.

On the other hand, purified hydrogen gas and measurement gas are passed through sample tubes 19 and 20, respectively, to the impure gas detection device A, and the impurity gas in the hydrogen gas (measurement gas) at the measurement point 18 of the adsorption column 10 is purified. Monitored in comparison to hydrogen gas. That is, detection of impure gas in the measurement gas is performed by the following operation.

First, valve 22a of sample tube 19 and bypass tube 21
and 22c, and flow purified hydrogen gas through the control side 2 and sample side of the thermal conductivity detector 1, respectively, while heating the catalyst tubes 7 and 8 in the heating furnace 9 as required.The potential difference when stabilized is used as the reference. and OmV. Next, the valve 22c of the bypass pipe 21 is closed and the valve 22b of the sample pipe 20 is opened to switch the sample @3 to the measurement gas and continue monitoring the potential difference in this state. As time passes, the impure gas accumulates and the adsorption band reaches the measurement point 18, and when the impurity gas is mixed into the measurement gas, a significant change in potential difference occurs at this point, and the impure gas is detected. Furthermore, when the impurity gas concentration in the raw material gas is particularly low, the change in this potential difference is small, so it is necessary to increase the sensitivity, but in that case, the slight change in potential difference due to the drift of the detector interferes, making identification difficult. For this reason, by alternately switching the measurement gas and purified hydrogen gas to the sample side and detecting the slight change in potential difference before and after switching while correcting the drift, it is possible to detect the presence of a trace amount of impure gas. . Changes in the potential difference are monitored by a recorder 5, an alarm 6, etc., but the switching operation of the gas purification apparatus can also be performed automatically by operating a switching valve or the like using a signal from the alarm 6, for example.

〔Effect of the invention〕

According to the present invention, contamination of impure gas can be accurately detected without being affected by changes in thermal conductivity of hydrogen gas during the cryogenic adsorption gas purification process. In addition, the detection device is small and relatively inexpensive, and can be easily installed in purification equipment, so it can be used to quickly detect impurity gas during hydrogen gas purification, and it can reliably predict adsorption cylinder breakthrough. can.

Furthermore, the operation of the refining equipment can be automated by operating the switching valve of the adsorption cylinder based on the detection signal from the alarm.

〔Example〕

Example 1 The structure is similar to that shown in Fig. 1, but instead of one tube, a cylinder (89,1〆X84.9〆X10X100) filled with activated carbon 2.5KF as an adsorbent (one tube is connected Impurity gas is detected in hydrogen gas being purified at a gas flow rate of 36 t 2 NrrL"/hr at an extremely low temperature of approximately -196°C using a cryogenic adsorption gas purification device having adsorption cylinders connected in series through tubes. The impurities in the raw hydrogen gas and purified hydrogen gas were analyzed by gas chromatography, and the results are shown in Table 1.

Table 1 N2 25 0.01 Below Q2 4 Q, []2++Co
10 0.03 ttCO220,02# CH490,03s The measurement points for extracting the measurement gas are 6 from the upstream side of the adsorption cylinder.
It was provided in the connecting pipe section that connected the first tube and the seventh tube (the most downstream side).

First, as a preliminary experiment, we performed 7 pups without using a catalyst tube.2. Thermal conductivity was measured when the tube was directly connected to a thermal conductivity detector having a detection unit (TCD-7 manufactured by Shimadzu Corporation), a recorder, and an alarm.

First, purified hydrogen gas was flowed through each of the control side and the sample side of the thermal conductivity detector at a rate of 30 l/min, and the potential difference between the two was set to 0. Adjusted to OOmV.

Next, when I switched the sample side to the measurement gas, it was about 0.24 mV even though there was no impurity gas mixed in the measurement gas.
A phenomenon was observed in which a potential difference appeared and this potential difference caused fluctuations in a width of 04 mVli degrees. The results are shown in FIG. In addition, when the raw material gas supply rate to the adsorption cylinder is increased (point a in Figure 2) or decreased (point in Figure 2), the potential difference changes drastically, causing impurity gas to be present in the measurement gas. It has been shown that it is difficult to identify even if it is mixed in.

Next, fill stainless steel tube (3$ x 2000m
), each filled with hydrogenation catalyst (1411!7), is housed in a heating furnace and connected to the control side and the sample side of the thermal conductivity detector, respectively, to produce an impurity gas measuring device of the present invention. This was placed in a cryogenic adsorption gas purification device, and the catalyst tubes were connected to each sample tube. The hydrogenation catalysts shown in Table 2 were used, and the difference in thermal conductivity was monitored at room temperature (25°C) without heating the catalyst tube under the same conditions as in the preliminary experiment for each catalyst. .

That is, after flowing purified hydrogen gas into the control side and the sample side to zero-adjust the potential difference between the two to O, OOmV, the sample side was switched to the measurement gas.

The results are shown in Figure 2, and no matter which hydrogenation catalyst is filled in the catalyst tube, as long as there is no impurity gas in the measurement gas, the potential difference is 0.00 mN', which is the same as in the preliminary experiment. increase the raw material gas supply rate (second
Even if the voltage was decreased (point in Figure 2), no potential difference was generated. Furthermore, when we continued to monitor the case in which the catalyst tube was filled with nickel catalyst, we found that the potential difference, which had been 0°00 mV, rose to 0.06 mV 842 hours after the start of hydrogen gas purification (Fig. 2C). point). At this point, the gas to be measured was analyzed using a gas chromatograph, and 12 ppm of nitrogen was detected, confirming that the adsorption zone of the adsorption column had reached the measurement point. In addition, when we replaced the catalyst tube filled with a different type of hydrogenation catalyst in the area where this impure gas was mixed and measured the potential difference, the results showed that the potential difference was O, []66
It was confirmed that there was a potential difference of m, indicating that the incorporation of impure gas could be detected. The results are shown in Table 2.

Purification equipment.

Table 2 When there is no impure gas Nickel catalyst after the pot breaks at the measuring point o, oo o
, o6 cobalt no, 00
0.06 steel-zinc/chromium catalyst o, oo
o, o6 chromium/activated carbon catalyst o, oo
o, o6 chromina/alumina catalyst o,
oo o, o6 platinum/alumina catalyst
0. (100,06

[Brief explanation of the drawing]

FIG. 1 shows the impure gas detection device of the present invention and a flow sheet in which the same is installed in a cryogenic adsorption gas purification device, and FIG. 2 shows a potential difference curve appearing in a thermal conductivity detector. The numbers in the figure are as follows. 1 Thermal conductivity detector 2 Control side 3 Sample side
7 and 8 Catalyst tube 1o Adsorption column 18 Measurement point
19.20 and 21 Sample tube A Impure gas detection device B Gas patent applicant Fumio Takasaki, representative of Nippon Bionics Co., Ltd.

Claims (2)

[Claims] (1) In a method for detecting impurity gases contained in hydrogen gas being purified in a cryogenic adsorption gas purification device, the purified hydrogen gas and the measurement gas derived from the measurement point of the adsorption column in the device are each detected as a transition metal element. 1. A method for detecting an impure gas, which comprises: detecting an impure gas in a measurement gas by bringing it into contact with a hydrogenation catalyst containing a hydrogenation catalyst, and then detecting a difference in thermal conductivity between the two. (2) A detection device for impurity gas contained in hydrogen gas being purified in a cryogenic adsorption gas purification device, which is installed in the cryogenic adsorption gas purification device and connects the gas flow path on the control side and the sample side. and a catalyst tube, one end of which is connected to each of the gas inlets on the control side and the sample side, and the inside of which is filled with a hydrogenation catalyst containing a transition metal element. . An impure gas detection device, wherein the other ends of the catalyst tubes are connected to sample tubes for purified hydrogen gas and a measurement gas led from a measurement point of an adsorption column in a purification device.