Ozone-containing nitrogen gas and method for producing ozone-containing nitrogen gas

Abstract

To obtain an ozone-containing nitrogen gas that contains sufficient ozone without adding an inert gas and has a small oxygen content.SOLUTION: An ozone-containing nitrogen gas contains 5 vol.% or less of an oxygen gas, a nitrogen gas, and 0.1 ppm or more of an ozone gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to ozone-containing nitrogen gas and a method for producing ozone-containing nitrogen gas. [Background technology]

[0002] Ozone (O3) has strong oxidizing power and is suitable for decolorization, deodorization, oxidation treatment, etc. In addition, ozone is approved for use as a food additive and a sterilizing disinfectant under the Food Sanitation Act, and has been widely used as a safe method for sterilizing food.

[0003] For example, Japanese Patent Application Laid-Open No. 2000-106856 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2000-93078 (Patent Document 2) disclose a method for sterilizing food by contacting the food with a mixed gas containing ozone and an inert gas such as nitrogen or carbon dioxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-106856 A [Patent Document 2] JP 2000-93078 A Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Documents 1 and 2, the raw material for the generated ozone is oxygen or air. The amount of ozone obtained by using oxygen as the raw material is about 6 to 7% by volume relative to the amount of raw oxygen, so the generated ozone is contaminated with high concentrations of oxygen. Since oxygen promotes the oxidation of food, it has been necessary to dilute the oxygen by supplying an inert gas such as nitrogen or carbon dioxide gas from the outside to suppress the oxidation of food.

[0006] The present disclosure has been made in consideration of the above problems, and has an object to obtain an ozone-containing nitrogen gas that contains a sufficient amount of ozone and has a low oxygen content without adding an inert gas. [Means for solving the problem]

[0007] The ozone-containing nitrogen gas according to the present disclosure contains 5 volume % or less of oxygen gas, nitrogen gas, and 0.1 ppm or more of ozone gas.

[0008] The method for producing ozone-containing nitrogen gas according to the present disclosure includes a step of generating 0.1 ppm or more of ozone gas in a raw material gas containing 5 vol % or less of oxygen gas and nitrogen gas. Effect of the Invention

[0009] According to the present disclosure, it is possible to obtain an ozone-containing nitrogen gas that contains a sufficient amount of ozone and has a low oxygen content without adding an inert gas. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of an apparatus configuration for producing ozone-containing nitrogen gas. [Diagram 2] FIG. 2 is a graph showing the relationship between the oxygen gas concentration in the raw material gas and the ozone gas concentration in the ozone-containing nitrogen gas. [Diagram 3] FIG. 3 is a graph showing the relationship between the oxygen gas concentration in the source gas and the ozone gas concentration in the ozone-containing nitrogen gas. [Figure 4] FIG. 4 is a graph showing the relationship between the pressure of the source gas and the ozone gas concentration in the ozone-containing nitrogen gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described. However, the following description does not limit the scope of the claims.

[0012] <Ozone-containing nitrogen gas> The ozone-containing nitrogen gas in the present disclosure includes 5% by volume or less of oxygen gas, nitrogen gas, and 0.1 ppm or more of ozone gas. Ozone gas is safely used for sterilization and disinfection of food, etc. However, ozone gas alone is harmful. In addition, oxygen gas promotes the oxidation of food.

[0013] In order to solve the above-mentioned problems, the present inventors have discovered that by using a gas containing 5% by volume or less of oxygen gas and nitrogen gas as raw materials, it is possible to obtain ozone-containing nitrogen gas that is suitable for use in food sterilization and the like from low-concentration oxygen gas without adding inert gases such as nitrogen or carbon dioxide gas.

[0014] The ozone gas concentration in the ozone-containing nitrogen gas is 0.1 ppm or more and 500 ppm or less, preferably 0.1 ppm or more and 50 ppm or less, more preferably 0.1 ppm or more and 10 ppm or less. When the ozone gas concentration in the ozone-containing nitrogen gas is 0.1 ppm or more and 500 ppm or less, it is sufficient as an effective amount for sterilization, disinfection, etc. of food, etc.

[0015] The ozone gas concentration in the ozone-containing nitrogen gas is measured, for example, by an ozone concentration measuring device, a gas detector, etc. The nitrogen gas concentration in the ozone-containing nitrogen gas is measured, for example, by a gas analyzer such as a gas chromatograph.

[0016] <Method of producing ozone-containing nitrogen gas> The method for producing an ozone-containing nitrogen gas according to the present disclosure includes a step of generating 0.1 ppm or more of ozone gas in the raw material gas containing 5 vol % or less of oxygen gas and nitrogen gas.

[0017] (raw gas) The raw material gas used to generate the ozone-containing nitrogen gas is a gas containing 5% by volume or less of oxygen gas and nitrogen gas. By containing 5% by volume or less of oxygen gas, ozone gas can be generated efficiently. Furthermore, by containing nitrogen gas, sufficient ozone gas can be generated without adding an inert gas such as nitrogen or carbon dioxide gas.

[0018] The oxygen gas concentration in the raw material gas is preferably 0.01% by volume or less, more preferably 0.02% by volume or less. The nitrogen gas concentration in the raw material gas is 50% by volume or more, preferably 99.99% by volume or more, more preferably 99.98% by volume or more. The oxygen gas concentration in the raw material gas is measured, for example, by an oxygen concentration meter.

[0019] (Production process of raw gas) The source gas is produced from a precursor gas. The precursor gas is a gas containing more than 5% by volume of oxygen gas and nitrogen gas. The oxygen gas concentration in the precursor gas is preferably 10% by volume or more, more preferably 15% by volume or more. The nitrogen gas concentration in the precursor gas is preferably 50% by volume or more, more preferably 70% by volume or more. Furthermore, the precursor gas is more preferably air. By using air as the precursor gas, handling becomes easier and the manufacturing costs can be reduced.

[0020] The source gas is produced by removing at least a part of the oxygen gas in the precursor gas. Methods for removing at least a part of the oxygen gas include a method using an adsorbent and a method using a membrane, but the method using an adsorbent is preferred. This is because the use of an adsorbent makes it possible to produce nitrogen gas with a higher purity (for example, 99.9% by volume or more).

[0021] In addition, when removing at least a part of the oxygen gas with the adsorbent, it is preferable to carry out the process under pressure. This is because the oxygen gas can be removed efficiently by carrying out the process under pressure. In addition, the transport of the produced raw material gas can also be carried out efficiently. As a method for removing at least a part of the oxygen gas under pressure with the adsorbent, for example, PSA (Pressure Swage Accompanying) is known. Examples include the Swing Adsorption (pressure swing adsorption) method and membrane separation method.

[0022] (Ozone-containing nitrogen gas manufacturing process) The ozone-containing nitrogen gas is produced from the raw material gas. Examples of methods for producing the ozone-containing nitrogen gas from the raw material gas include ultraviolet irradiation of oxygen gas in the raw material gas and silent discharge. Ozone is generally obtained by collisions between high-energy electrons and oxygen molecules, such as ultraviolet irradiation in air and silent discharge in oxygen. Ozone is mainly generated by the reaction shown in the following formula (1).

[0023] 3O2→2O3…Equation (1) The ozone gas in the ozone-containing nitrogen gas is preferably generated by irradiating the oxygen gas in the raw material gas with ultraviolet light. When ultraviolet light is used, it is difficult to dissociate the nitrogen bond, and harmful nitrogen oxides (NO x In addition, when ultraviolet irradiation is performed, it is preferable to perform the irradiation under pressure.

[0024] As mentioned above, the process of generating ozone gas produces harmful NO x may be generated, but NO x In particular, there are legal standards for nitrogen dioxide (NO2) emissions, as follows: (i) Environmental standards: Standard values ​​based on Article 16, Paragraph 1 of the Basic Law for the Environment. Daily average values ​​are within the range of 0.04 ppm to 0.06 ppm. (ii) Emission standards: Standard values ​​based on the Air Pollution Control Act. Standards vary depending on the facility and are in the range of 10 ppm to 1000 ppm. (iii) Work standard: Standard value based on the Industrial Safety and Health Act. 0.2 ppm (the value at which no long-term health damage occurs even if exposed to the environment for 8 hours a day, 40 hours a week).

[0025] According to the above criteria, the NO generated by the ultraviolet irradiation in this disclosure x The concentration is preferably 0.04 ppm or less.

[0026] As described above, by using the method for producing ozone-containing nitrogen gas according to the present disclosure, ozone-containing nitrogen gas is produced.

[0027] (Ozone-containing nitrogen gas production equipment) 1 is a schematic diagram showing an example of an apparatus configuration for producing ozone-containing nitrogen gas according to the present disclosure. The ozone-containing nitrogen gas production apparatus 100 includes a raw air compressor 10, a PSA nitrogen generator 20, and an ozone gas generator 30.

[0028] The precursor gas is compressed by a raw material compressor 10 and flows into a PSA type nitrogen generator 20. The precursor gas that has flowed into the PSA type nitrogen generator 20 flows under pressure into an adsorption tower 21 containing an adsorbent. In the adsorption tower 21, a part of the oxygen gas is removed by the adsorbent, and the oxygen gas and nitrogen gas (raw material gas) are separated. Although one adsorption tower 21 is shown in FIG. 1, it is preferable to install two adsorption towers 21 in parallel. In this case, the precursor gas is passed through one adsorption tower while the other adsorption tower is simultaneously regenerated, whereby the oxygen gas removal process can be performed continuously.

[0029] The separated raw material gas flows into nitrogen tank 22. The concentrations of oxygen gas and nitrogen gas in the raw material gas can be adjusted by pressure gauge 24a, flow rate control valve 25a, flow rate control valve 25b, and flow rate control valve 25c. The oxygen gas concentration in the raw material gas is measured by oxygen concentration meter 23a and oxygen concentration meter 23b.

[0030] The raw material gas that has flowed into the nitrogen tank 22 flows into the ozone generator 30. The oxygen gas in the raw material gas that has flowed into the ozone generator 30 is irradiated with ultraviolet light under pressure to generate ozone gas.

[0031] As described above, ozone-containing nitrogen gas is generated by using the ozone-containing nitrogen gas production apparatus 100. The concentration of ozone gas in the ozone-containing nitrogen gas can be adjusted by the pressure gauge 24b and the flow rate control valve 25c. The concentration of ozone gas in the generated ozone-containing nitrogen gas is measured by the ozone concentration meter 40. The concentration of ozone gas in the generated ozone-containing nitrogen gas can also be measured by a gas detector tube (not shown). EXAMPLES

[0032] The following examples are provided to illustrate, but not to limit, the scope of the claims.

[0033] In the present examples (Tests 1 and 2 below), ozone-containing nitrogen gas was produced using the above-mentioned ozone-containing nitrogen gas production apparatus 100. The ozone-containing nitrogen gas production apparatus 100 includes the following devices. [Details of the ozone-containing nitrogen gas production equipment] Air compressor 10: Thomas 2688-CS32-273 manufactured by Gardner Denver Co., Ltd. PSA type nitrogen generator 20: TN4-06-2 manufactured by Air Water Bellpearl Co., Ltd. Oxygen concentration meter 23a: FCX-MP-F-AC manufactured by Fujikura Co., Ltd. Oxygen concentration meter 23b: Toray Engineering Co., Ltd. LC-450A Ozone generator 30: UV lamp type manufactured by Iwamoto Kiko Co., Ltd. Ozone concentration meter 40: Aprix Co., Ltd. OZG-EB-02 <Test 1> In Test 1, the oxygen gas concentration in the raw material gas and the flow rate of the raw material gas (flow rate control valve 26b) were changed as shown in Table 1 below, and ozone-containing nitrogen gas was produced by the above-mentioned device. The ozone gas concentration in the obtained ozone-containing nitrogen gas was measured by the above-mentioned ozone concentration meter 40. Air was used as the precursor gas. The raw material gas was a gas consisting of oxygen gas and nitrogen gas. The results are shown in Table 1 and FIG. 2. [Test 1 Conditions] Raw gas pressure: atmospheric pressure Environmental temperature: 20℃~28℃ Flow rate of raw gas (flow meter 26a): 10L / min

[0034] [Table 1]

[0035] As shown in Table 1 and Figure 2, if the oxygen gas concentration in the raw gas is about 500 ppm, 0.05 ppm of ozone gas is generated, and if the oxygen gas concentration in the raw gas is 600 ppm or more, an effective amount (about 0.1 ppm) of ozone gas is generated. It was also confirmed that if the oxygen gas concentration in the raw gas is increased, the ozone gas concentration in the ozone-containing nitrogen gas also increases proportionally.

[0036] From the above test results, it was confirmed that the ozone gas concentration in the ozone-containing nitrogen gas increases in proportion to the oxygen gas in the raw material gas, but when the oxygen gas concentration in the raw material gas is 450 ppm or less, the generation of ozone gas could not be confirmed. However, from the results shown in Table 1 and Figure 2 above, it is considered that ozone gas is generated even in the region where the oxygen gas concentration in the raw material gas is lower. Therefore, in order to confirm the presence or absence of ozone gas generation in the region where the oxygen gas concentration in the raw material gas is lower, the ozone gas concentration in the ozone-containing nitrogen gas obtained under the same conditions as those described above was measured using a gas detector tube (Ozone Detector Tube 18L manufactured by Gastec Corporation) that can detect ozone gas at a lower concentration than the ozone concentration meter 40. The results are shown in Table 2 and Figure 3.

[0037] [Table 2]

[0038] As shown in Table 2 and Figure 3, when the oxygen gas concentration in the raw material gas was 194 ppm, ozone gas was not generated, and when the oxygen gas concentration in the raw material gas was 207 ppm, 287 ppm, and 410 ppm, the generated ozone gas concentrations were 0.020 ppm, 0.025 ppm, and 0.045 ppm, respectively. From these results, it was confirmed that ozone gas is generated when the oxygen gas concentration in the raw material gas exceeds 200 ppm. <Test 2> In Test 2, the pressure of the raw material gas was changed as shown in Table 3 below, and ozone-containing nitrogen gas was produced by the above-mentioned device. The ozone gas concentration in the obtained ozone-containing nitrogen gas was measured by the above-mentioned ozone concentration meter 40. Air was used as the precursor gas. The raw material gas was a gas consisting of oxygen gas and nitrogen gas. The results are shown in Table 3 and FIG. 4. [Test 2 Conditions] Environmental temperature: 28℃ Flow rate of raw gas (flow meter 26a): 10L / min

[0039] [Table 3]

[0040] As shown in Table 3 and Figure 4, in Example 1, when the pressure of the raw material gas was 0 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, and 0.3 MPa, the ozone gas concentration in the ozone-containing nitrogen gas was 0.2 ppm, 0.4 ppm, 0.5 ppm, 0.6 ppm, 0.7 ppm, and 0.8 ppm, respectively. In addition, in Example 2, when the pressure of the raw material gas was 0 MPa and 0.3 MPa, the ozone gas concentration in the ozone-containing nitrogen gas was 2.4 ppm and 5.2 ppm. From the results of Test 2, it was confirmed that when the pressure of the raw material gas was increased, the ozone gas concentration in the ozone-containing nitrogen gas was also increased in proportion to the increase in pressure, regardless of the oxygen gas concentration.

[0041] From the results of Test 2 above, it was confirmed that the ozone gas concentration in the ozone-containing nitrogen gas increases in proportion to the pressure of the raw material gas, regardless of the oxygen gas concentration, but it is believed that ozone gas is generated by increasing the pressure of the raw material gas even in the region where the oxygen gas concentration in the raw material gas is lower. Although not shown in Table 3 and Figure 4, it was confirmed that ozone gas is generated if the oxygen gas concentration in the raw material gas is 80 ppm or more when the pressure of the raw material gas is 0.4 MPa.

[0042] The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0043] 10 raw air compressor, 20 PSA type nitrogen generator, 21 adsorption tower, 22 nitrogen tank, 23a, 23b oxygen concentration meter, 24a, 24b pressure gauge, 25a, 25b, 25c flow control valve, 26a, 26b flow meter, 30 ozone generator, 40 ozone concentration meter, 100 ozone-containing nitrogen gas manufacturing device.

Claims

1. An ozone-containing nitrogen gas comprising: oxygen gas of more than 0 volume % and not more than 5 volume %, nitrogen gas; and ozone gas of 0.1 ppm or more and 500 ppm or less.

2. 2. The ozone-containing nitrogen gas according to claim 1, wherein the concentration of nitrogen oxides in the ozone-containing nitrogen gas is 0.04 ppm or less.

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