JP2943365B2 - Method and apparatus for continuous measurement of aldehyde concentration in gas sample - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for continuously measuring the concentration of aldehyde in the air. INDUSTRIAL APPLICABILITY The present invention can be used for measuring a change in the formaldehyde concentration in the exhaust gas of an automobile due to a change in running conditions.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of preventing air pollution, the necessity of suppressing emission of aldehydes contained in exhaust gas of automobiles has been discussed. In particular, since formaldehyde is known to have high photochemical reactivity, and there is irritation to the human body even at a low concentration, regulation of its emission is desired.

As a method for measuring the concentration of an aldehyde contained in a gas, there are various chromatographic methods, a method in which the aldehyde is captured in a capturing solvent and measured by a titration method or a colorimetric method, or an infrared spectrometer. There are known methods to use. However, in these measurement methods,
The sensitivity is so low that it is not possible to measure in the low concentration range of ppb level,
There are problems such as complicated operation and slow response speed, and it has been difficult to measure continuously. However, in developing a technology for reducing aldehyde emission, it is essential to continuously measure the aldehyde concentration in exhaust gas, and development of such a measurement technology has been desired.

The inventors of the present invention have established a method for continuously measuring the aldehyde concentration using an enzyme, and
No. 847 discloses the measuring device. This measurement method includes a capturing step in which a gas sample is brought into contact with a capturing solvent in a flowing state to continuously absorb the aldehyde contained therein, and the aldehyde present in the capturing solvent in the presence of aldehyde dehydrogenase is converted into nicotinamide adenine. NAD which is continuously reacted with dinucleotide (NAD) to produce reduced nicotinamide adenine dinucleotide (NADH) in an amount corresponding to the concentration of aldehyde in the liquid
An H generation step and an analysis step of generating a light emission according to the concentration of NADH in the liquid, continuously measuring the concentration of NADH in the liquid from the intensity thereof, and obtaining the aldehyde concentration in the gas sample from the value are sequentially performed. It is characterized by:

According to this measuring method, continuous measurement in a low concentration range of ppb level is possible, and a change in aerial aldehyde concentration can be measured with good responsiveness and accurately.

[0006]

However, when the above-mentioned measuring method is applied to the measurement of the aldehyde concentration in the exhaust gas of an automobile, it has been found that the baseline changes and the measured value becomes lower than the actual value. The present invention has been made in view of such circumstances, and is described in Japanese Patent Application Laid-Open No. HEI 2-2648.
In the measurement method described in Japanese Patent No. 47, the object is to eliminate the fluctuation of the baseline and to make the measured value of the aldehyde concentration more accurate.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on the causes of the above-mentioned problems, and as a result, have found that they are caused by the influence of SO ₂ contained in exhaust gas.
That is, SO ₂ becomes highly reactive sulfite ion in the capture solvent and selectively adsorbs to the enzyme active site to inhibit the reaction with the aldehyde, so that negative interference occurs and the measured value is lower than the actual value. It became clear that it became. Then, before the trapped solvent in which the exhaust gas is absorbed comes into contact with the enzyme, SO ₂
The present invention has been completed by recalling that

[0008] That is, the measuring method of the present invention for solving the above-mentioned problems comprises a capturing step in which a gas sample is brought into contact with a capturing solvent in a flow state to continuously absorb the aldehyde contained in the gas sample into the capturing solvent; SO ₂ absorbed in
An oxidizing step of oxidizing aldehydes, and continuously reacting aldehydes present in the capture solvent with nicotinamide adenine dinucleotide (NAD) in the presence of aldehyde dehydrogenase to reduce the amount of reduced nicotinamide adenine according to the concentration of the aldehyde in the liquid A NADH generating step of generating a dinucleotide (NADH), and generating luminescence corresponding to the concentration of NADH in the solution, and measuring the luminescence intensity to obtain NADH.
And measuring the aldehyde concentration in the gas sample from the measured values in the liquid continuously.

Further, a preferred measuring device for carrying out the above-mentioned measuring method comprises a capturing section for bringing a gas sample into contact with a capturing solvent in a flowing state to continuously absorb aldehyde contained in the gas sample into the capturing solvent, and a downstream section of the capturing section. An oxidation catalyst provided on the side of the catalyst to oxidize SO ₂ absorbed in the trapping solvent; a reducing section provided downstream of the oxidation catalyst to react NAD with aldehyde in the trapping solvent to generate NADH; An analyzer that is provided downstream of the analyzer to continuously measure the NADH concentration in the liquid by reacting NADH and the reagent in a flow state, generating luminescence in accordance with the concentration of NADH in the liquid, and measuring the intensity of the luminescence. Wherein the concentration of aldehyde in the gas sample is continuously determined from the concentration of NADH in the liquid.

[0010] The capture step refers to a step in which the aldehyde is absorbed by the capture solvent, and is carried out by bringing the continuous flow of the capture solvent into contact with a gas sample. As the trapping solvent, a solvent capable of absorbing aldehyde is used. In the case of formaldehyde (hereinafter, referred to as HCHO), water is generally used. In order to bring the trapping solvent into contact with the gaseous sample, the gaseous sample may be bubbled in the trapping solvent. However, it is preferable that the trapping solvent and the gas sample be brought into contact with each other via a molecule permeable membrane in terms of sealing properties and operability. This capturing step is performed in the capturing section. In addition, it is also preferable to heat the entire capturing unit to improve the absorption performance.

The scavenging solution contains SO together with aldehyde.
₂ has also been absorbed. Therefore, an oxidation step which is a feature of the present invention is performed. That is, for example, when the trapping solvent is water, S
O ₂ is absorbed to form a sulfite ion (SO ₃ ²⁻ ), and the existing trapping solvent is brought into contact with an oxidation catalyst to convert the sulfite ion into an inert sulfate ion (SO ₄ ²⁻ ). Thus, interference of SO ₂ in the next step of generating NADH can be prevented. Here, as the oxidation catalyst, P
Noble metal catalysts such as t, Pd, and Rh and transition metal catalysts such as Cu, Ni, and Fe can be used. In addition, since this catalytic reaction is promoted as the temperature increases, it is preferable to perform the reaction under heating. Although there is a possibility that a part of the aldehyde may be oxidized together with the SO ₂ , for example, as shown in FIG.
Since the oxidation reaction of O ₂ precedes the oxidation reaction of HCHO,
By reacting in the shaded region in FIG. 3, oxidation of HCHO can be prevented.

In the NADH producing step performed in the reducing section, the aldehyde present in the capturing solvent is continuously reacted with NAD in the presence of an enzyme (aldehyde dehydrogenase), and the aldehyde present in the solution is determined according to the following equation according to the concentration of the aldehyde in the liquid. NA of quantity
Generate DH. At this time, the aldehyde is oxidized and changes to a corresponding acid. The aldehyde dehydrogenase is preferably immobilized. As a result, the sample solution can be continuously reacted in the flow state.

In the RCHO + NAD + H ₂ O → RCOOH + NADH + H ⁺ analysis step, the luminescence corresponding to the NADH concentration in the liquid is generated and its intensity is measured, whereby the NADH concentration in the liquid is continuously measured, and the gas is determined from the value. In this step, the aldehyde concentration in the sample is determined. The fluorescence of NADH itself may be used, or the luminescence may be used by using a reagent that emits light by reacting with NADH. According to the method for measuring the emission intensity, the sensitivity becomes extremely high as compared with a conventional colorimetric method or the like, and even a small amount of aldehyde can be measured at high speed.

[0014]

According to the measurement method of the present invention, SO ₂ in the trapping solvent is oxidized in the oxidation step.
Avoids the interference of SO ₂ on aldehyde measurements,
Measurement accuracy is improved. Therefore, according to the measuring method and the measuring device of the present invention, since the concentration of aldehyde in the air can be measured continuously and accurately, the continuous quantitative analysis of aldehyde in the exhaust gas of automobiles becomes possible. It can greatly contribute to technology for reducing aldehyde emissions.

[0015]

The present invention will be specifically described below with reference to examples. (Measuring Apparatus) FIG. 1 is a schematic block diagram of a measuring apparatus according to one embodiment of the present invention. This measuring device includes a capturing unit 1, an oxidation catalyst 2, a reducing unit 3, and an analyzing unit 4.

As shown in detail in FIG. 2, the capturing section 1 is composed of a cylindrical gas sample conducting section 10 and an aldehyde transmitting section 11. The gas sample conducting part 10 is an inlet 10
a and an outlet 10b, and the inlet 10a is communicated with an exhaust passage 12 of the vehicle via a pump 13. A three-way valve 14 is provided between the pump 13 and the inlet 10a.
The nitrogen gas supply pipe 15 is connected via the. Further, a pressure valve 16 is provided at the exhaust port 10b so that the discharge amount can be adjusted. That is, one of the exhaust gas and the nitrogen gas can be selectively passed through the gas sample conducting section 10 by switching the three-way valve 14 and the flow rate can be controlled. Further, by controlling the pressure in the gas sample conducting section 10 by the pressure valve 16, the aldehyde trapping rate can be controlled.

The aldehyde permeable portion 11 is formed of a pipe made of a porous fluororesin film, penetrates the gas sample conducting portion 10 and has one end connected to a pump 17 for supplying pure water. The other end is connected to the oxidation catalyst 2. The aldehyde transmitting section 11 is capable of selectively transmitting aldehyde such as HCHO, and HCHO in the gas in the gas sample conducting section 10 is captured by pure water flowing through the tube wall of the aldehyde transmitting section 11 and flowing inside. It is configured to be.

The oxidation catalyst 2 comprises a 1000-mesh granular catalyst in which an activated alumina layer is formed on the surface of cordierite-based powder and Pt is supported on the activated alumina layer. Enclosed in capacity. One end on the upstream side communicates with the aldehyde permeating section 11, and the other end on the downstream side is connected to the reducing section 3. Note that the capturing unit 1 and the oxidation catalyst 2 are arranged in a constant temperature chamber 5 and can be heated to a predetermined temperature.

The aldehyde-containing water that has passed through the oxidation catalyst 2 is mixed with NAD supplied from the NAD supply pump 6 and flows into the reduction unit 3. The reducing unit 3 is an immobilized enzyme reactor consisting of an immobilized enzyme in which the enzyme formaldehyde dehydrogenase is immobilized by an aminopropyl modification technique and a column packed with the immobilized enzyme. The HCHO contained is oxidized to formic acid, and NAD is equimolar to the HCHO.
H is generated.

After passing through the reducing section 3, formic acid, hydrogen ions and N
The aqueous solution containing ADH is mixed with the phenazine mezosulfate solution and the mixed solution of isoluminol and microperoxidase supplied from the supply pumps 7 and 8, respectively, and goes to the analysis unit 4. At this time, NADH reacts with phenazine mezosulfate to generate hydrogen peroxide. This hydrogen peroxide reacts immediately with the isoluminol: microperoxidase mixture, producing chemiluminescence. The intensity of the chemiluminescence is measured by a chemiluminescence detector provided in the analysis unit 4.

Since the light intensity of the resulting chemiluminescence is proportional to the amount of NADH and the amount of NADH is proportional to the amount of HCHO,
The amount of HCHO in the gas sample can be known by preparing a calibration curve with HCHO of the reference concentration in advance. (Measurement Method) Using the measurement apparatus of the present embodiment configured as described above, the HCHO concentration in the exhaust gas of a running automobile was continuously measured.

First, an exhaust gas is supplied from the exhaust passage 12 to the gas sample conducting section 10 by the pump 13, and pure water is supplied to the aldehyde transmitting section 11 by driving the pump 17. The supply rate of the exhaust gas is 10 l / min, and the supply rate of the pure water is 1 cc / min. In the aldehyde transmitting section 11,
Aldehyde, SO _{2 and the} like permeate through the pipe wall and dissolve in pure water.

The solution that has passed through the aldehyde transmitting section 11 is
It passes through the oxidation catalyst 2 and comes into contact with the Pt-alumina catalyst. Here, the contact time of the solution per unit volume with the catalyst is 1.2 seconds, which is within the range of the shaded area in FIG.
HO oxidation is prevented. Then, by the contact with the catalyst, the sulfite ions generated by dissolving the SO ₂ are efficiently oxidized and changed to sulfate ions. The constant temperature chamber 5 is 8
Since it is heated to 0 ° C., the gas sample conducting part 10, the aldehyde transmitting part 11, and the oxidation catalyst 2 are heated to 80 ° C.,
It is configured to promote aldehyde absorption and oxidation reaction of the catalyst.

The solution passing through the oxidation catalyst 2 is supplied to a pump 6
, An NAD aqueous solution is supplied and mixed, and flows into the reduction unit 3. In the reduction unit 3, the HC contained in the influent solution is
An amount of NAD corresponding to the amount of HO is reduced to NADH. Then, an aqueous solution of phenazine mezosulfate is supplied from the pump 7, and an aqueous solution of a mixture of isoluminol and microperoxidase is supplied from the pump 8, mixed with the solution flowing out of the reducing unit 3, and immediately reacts to generate chemiluminescence.

In the analysis section 4, the intensity of the chemiluminescence is continuously measured by a photomultiplier tube, and the change is recorded. Next, the three-way valve 14 is operated to cut off the communication between the exhaust passage 12 and the gas sample conducting part 10 and to make the nitrogen gas supply pipe 15 communicate with the gas sample conducting part 10. Then, a nitrogen gas containing a reference concentration of HCHO is supplied to the gas sample unit 10 by a pump (not shown) at the same supply amount as the supply amount of the exhaust gas by the pump 13. Then, the light is passed through the oxidation catalyst 2 and the reduction unit 3 under exactly the same conditions as described above, and the intensity of chemiluminescence generated in the same manner is measured by the analysis unit 4. This operation is similarly performed for nitrogen gas containing HCHO at a plurality of reference concentrations, and a calibration curve is created from the intensity of each chemiluminescence and the HCHO concentration in that case.

By applying the continuous chemiluminescence intensity data obtained above to the obtained calibration curve and converting it into HCHO concentration, the fluctuation of the HCHO amount can be known. (Test Example 1) The vehicle was a "22R Hilux" manufactured by Toyota Motor Corporation, using gasoline as the fuel, and operating under the operating conditions in the LA # 42 mountain mode shown in FIGS. The chemiluminescence intensity was measured under the same conditions as in the example except that the oxidation catalyst 2 was not used. Under this condition, the exhaust gas contains SO ₂ but not HCHO. As a result, as shown in FIG. 4, the measured value decreases as the vehicle speed increases,
There was a difference of about 0.5 ppm at the maximum in terms of HO amount, and the baseline fluctuated. (Test Example 2) The chemiluminescence intensity under the same conditions without HCHO was measured in the same manner as above except that the oxidation catalyst 2 was used. As a result, as shown in FIG. 5, there was no change in the measured value, and the baseline was stable.

From the results of these two tests, it is clear that in the absence of the oxidation catalyst 2, SO ₂ contained in the exhaust gas is not oxidized but affects the reducing section 3 and interferes with the enzyme reaction. . It was also found that the presence of 1 ppm of SO ₂ caused interference corresponding to 0.1 ppm of HCHO in the measurement results. However, the use of the oxidation catalyst 2 makes it possible to disregard the interference of SO ₂ , so that the measuring device and the measuring method of the present invention can accurately measure the amount of HCHO.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a measuring apparatus according to one embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a capturing unit 1 of FIG.

FIG. 3 is a graph showing a relationship between a contact time and an oxidation rate in an oxidation catalyst.

FIG. 4 is a diagram showing a running mode and a baseline in Test Example 1.

FIG. 5 is a diagram showing a running mode and a baseline in Test Example 2.

[Explanation of symbols]

1: Capture unit 2: Oxidation catalyst 3: Reduction unit
4: Analysis unit 5: Constant temperature chamber 6, 7, 8: Pump 10: Gas sample conduction unit 11: Aldehyde transmission unit 12: Exhaust passage

Claims (2)

(57) [Claims] 1. A capturing step of bringing a gas sample into contact with a capturing solvent in a flow state to continuously absorb aldehyde contained in the gas sample into the capturing solvent, and oxidizing SO ₂ absorbed in the capturing solvent. Oxidizing step, and aldehyde present in the capture solvent in the presence of aldehyde dehydrogenase is converted to nicotinamide adenine dinucleotide (NAD)
With the reduced nicotinamide adenine dinucleotide (NA) in an amount corresponding to the concentration of the aldehyde in the liquid.
DH) is produced, and the concentration of the NADH in the liquid is continuously measured by generating luminescence corresponding to the concentration of the NADH in the liquid and measuring the intensity of the luminescence. A method for continuously measuring the concentration of aldehyde in a gas sample, comprising sequentially performing an analysis step for determining the concentration of aldehyde in the gas sample. 2. A capturing section for bringing a gas sample into contact with a capturing solvent in a flow state to continuously absorb aldehyde contained in the gas sample into the capturing solvent; and a capturing solvent provided downstream of the capturing section. an oxidation catalyst for oxidizing SO ₂ absorbed in, the oxidative nicotinamide adenine dinucleotide provided downstream of the catalyst (NAD) and the an aldehyde of the capture in a solvent is reacted with reduced nicotinamide adenine dinucleotide A reducing unit for producing (NADH) and a reagent provided downstream of the reducing unit, the NADH reacting with a reagent in a flow state to generate luminescence corresponding to the concentration of NADH in the liquid, and measure the intensity of the luminescence By doing this NADH
And an analyzer for continuously measuring the concentration of the NA in the liquid.
An apparatus for continuously measuring the concentration of aldehyde in a gas sample, wherein the concentration of aldehyde in the gas sample is continuously determined from the concentration of DH in the liquid.