Method for explosion-proof storage of nitrous oxide

Abstract

Disclosed is a method for explosion-proof storage of nitrous oxide in a liquid phase in a container, the method comprising filling the container with nitrous oxide and an inert component selected from the group consisting of nitrogen, oxygen, carbon dioxide, water, argon, helium, krypton, xenon and mixtures thereof, and maintaining it at a temperature of 190 K to 273 K, wherein (i) the container has an internal distance > = 10 cm between two opposing inner walls in all three spatial directions, (ii) the concentration of the inert components in total is 2 to 20 wt.-%, based on nitrous oxide in the liquid phase, and (iii) a compound selected from the group consisting of a gas having a flammable range with air at a pressure of 293.15 K and 101.3 kPa abs, a gas having a flammable range with air at a pressure of 293.15 K and 101.3 kPa abs, and a gas having a flammable range with air at a pressure of 293.15 K and 101.3 kPa abs. A liquid having a flash point of < = 366.15 K at a pressure of 101.3 kPa absolute, and the mixture thereof being held at 0 to 2 wt.-% based on the total amount of nitrous oxide in the liquid phase.

Description

[0001] The invention relates to a method for explosion-proof storage of nitrous oxide in a container, wherein the nitrous oxide is kept together with an inert gas in a liquid phase at 190 K to 273 K.

[0002] Nitrous oxide, chemically N2O and commonly known as laughing gas, is a versatile chemical compound used in various applications. It is mainly used for medical purposes, especially in surgery and dentistry due to its anesthetic and pain-relieving properties, in food technology as a propellant due to its good fat solubility (e.g. for frothing cream), and as an oxidant, for example in rocket engines or vehicles to increase the performance of the engine, in the electronics industry as an oxidizing agent for the production of thin oxide films, or even in chemical synthesis production facilities as a mild oxidizing agent instead of oxygen, such as for the selective oxidation of olefins directly to ketones in one step.

[0003] Depending on its intended use, nitrous oxide is commercially available in different purities and in containers of different sizes. The so-called domestic cream frothing balloon is typically a small metal bottle with an outer diameter of about 2 cm, in which the nitrous oxide is present as a compressed gas. Nitrous oxide for industrial use is typically available in gas cylinders with a size of 2, 5, 10 or 50 L or even large containers (like standard ISO tank containers), which usually contain between 17.5 and 26.0 m 3 or even higher. Among them, nitrous oxide is usually present in liquid form, with typical purity ranging from 99% (corresponding to purity grade 2.0) to 99.999% (corresponding to purity grade 5.0). Nitrous oxide for medical use is typically distributed in 10L cylinders at a purity of 98% or as a 50% / 50% mixture with oxygen.

[0004] Nitrous oxide can be easily produced on a commercial scale by thermal decomposition of ammonium nitrate. US 3,656,899 describes a method in which ammonium nitrate is heated to a temperature of 100°C to 160°C in an aqueous nitric acid solution containing chloride ions while maintaining an ammonia-containing atmosphere above the solution. The ammonia-containing atmosphere neutralizes the acidic vapors in the gas phase containing nitrous oxide. The gas phase containing nitrous oxide is then directed to a scrubbing column, in which water vapor and excess ammonia are scrubbed off, and a crude gaseous nitrous oxide having a purity of about 98 wt.-% is obtained, which can then be further purified.

[0005] In addition, nitrous oxide can also be produced on a commercial scale by catalytic oxidation of ammonia. WO 98 / 25,698 describes a process in which a gaseous mixture containing ammonia and oxygen is passed over a multimetallic oxide catalyst containing MnO2, Bi2O3 and Al2O3 at about 300° C. to 350° C. After removal of water and unconverted ammonia, a crude product stream is obtained which contains 79.6% to 84.9% nitrous oxide in addition to nitrogen oxide and oxygen.

[0006] Another method for preparing nitrous oxide is to recover it as is from nitrous oxide-containing waste gases, which are produced, for example, by the catalytic oxidation of ammonia to nitric acid or by the non-catalytic oxidation of cyclohexanol / cyclohexanone with nitric acid to adipic acid.

[0007] US 4,177,645 describes the separation of a stream rich in dinitrogen monoxide from a dinitrogen monoxide-containing waste gas stream, the separation being carried out by compressing the waste gas stream to reach a pressure of 15 to 300 bar, cooling it stepwise in a cascade of heat exchangers connected in series to a temperature as low as -88°C (185.15K) to condense a liquid rich in dinitrogen monoxide, directing the condensed liquid through a collecting vessel and expanding it into a distillation column, where the dinitrogen monoxide is separated from oxygen and nitrogen. The examples illustrate the purification of a dinitrogen monoxide-containing waste gas stream of a defined amount of 78 to 100 kg to obtain pure dinitrogen monoxide (Example 1) or dinitrogen monoxide with 1,7 wt.-% nitrogen oxides and 5 wt.-% carbon dioxide (Example 3).

[0008] US 8,449,655 discloses separating the stream rich in nitrous oxide from the waste gas stream containing nitrous oxide by dual absorption / desorption process, wherein in the first stage, waste gas is absorbed in the water-based solvent with 3.5 to 8.0 pH value and desorbed subsequently to release the gas mixture rich in nitrous oxide, then in the second stage, this gas mixture is absorbed in another water-based solvent with 2.0 to 8.0 pH value, and desorbed subsequently to release the gas mixture richer in nitrous oxide. Mention that the purified gas stream obtained in this way preferably contains 50 to even up to 99.0wt.-% nitrous oxide and as carbon dioxide, oxygen, nitrogen or nitrogen oxides of other components. In order to remove trace water, US 8,449,655 proposes that purified gas stream is compressed to 1 to 35 bar and is cooled to 1 ℃ to 25 ℃ (274.15K to 298.15K). In addition, it is mentioned that the gas stream obtained can also be liquefied by compressing it and cooling it to a temperature as low as -70°C (203.15K), and that such a liquefied gas mixture can be directly used in an oxidation process in which nitrous oxide serves as an oxidant. According to an example, the two desorbers are operated at a temperature of 35°C (308.15K), and the purified gas stream thus obtained at this temperature has a nitrous oxide content in the range of 54.9 wt.-% (Example 1) up to 81.5 wt.-% (Example 5).

[0009] US 8,808,430 discloses separating the stream rich in nitrous oxide from the waste gas stream containing nitrous oxide, and this separation is carried out by absorption / desorption process and subsequently making the desorption stream condensation rich in nitrous oxide. Mention that the gas stream rich in nitrous oxide obtained preferably contains 50 to even up to 99.0wt.-% nitrous oxide and as carbon dioxide, oxygen, nitrogen or nitrogen oxides of other components.Condensation is described as preferably carrying out at a temperature of 1 to 35 bar pressure and 10 ℃ (283.15K) as low as -70 ℃ (203.15K). According to Example 1, the nitrous oxide of the offgas from a nitric acid production facility is concentrated by an absorption / desorption process, and the concentrated stream is liquefied at -12°C (261.15K) in a vertical tube bundle heat exchanger operated with a water / ethylene glycol coolant to a liquid stream containing 87.9 vol.-% nitrous oxide, 11.4 vol.-% carbon dioxide, 0.3 vol.-% water, 0.3 vol.-% nitrogen and 0.14 vol.-% oxygen. The obtained stream is then subsequently purified in a stripping column containing structured metal packing and operated with a countercurrent nitrogen flow, and a liquid stream containing 86.7 vol.-% nitrous oxide, 11.1 vol.-% carbon dioxide, 1.9 vol.-% nitrogen and 0.01 vol.-% oxygen is obtained.

[0010] The three patents US 4,177,645, US 8,449,655 and US 8,808,430 mentioned above relate to the separation of a nitrous oxide-rich stream from a nitrous oxide-containing exhaust gas stream, wherein the nitrous oxide-rich stream according to US 4,177,645 is a stream containing 90 to 99 wt.-% or even pure nitrous oxide, while according to US 8,449,655 and US 8,808,430 it is a stream containing 50 to 99.0 wt.-% nitrous oxide and has been liquefied by cooling to a temperature of up to -88°C (185.15K) (according to US 4,177,645) and to a temperature of up to -70°C (203.15K) (according to US 8,449,655 and US 8,808,430). All three patents make no mention of safety issues regarding handling liquefied nitrous oxide, despite at least one incident of nitrous oxide-induced explosion described in the prior art.

[0011] The explosion accident induced by nitrous oxide is described and discussed by A.Lange, and is disclosed in "Zeitschrift für angewandte Chemie [applied chemistry]" 29 (1902) 725-731. According to the paper, in August 1900, a factory worker was busy filling 850g of nitrous oxide into several vials from a storage bottle initially filled with 17kg of liquid nitrous oxide. The storage bottle was fixed upside down, connected via a flexible copper pipe between the valve of the storage bottle and the valve of the vial, and the storage bottle was heated steadily with an open flame. After filling the 14th vial and closing the two valves, the storage bottle exploded violently for unknown reasons, killing the factory worker. In the long discussion, A.Lange ruled out the excessive pressure caused by material defects and steady heating in the storage bottle, and finally assumed that it was a chemical explosion because nitrous oxide is a heat-absorbing and energy-absorbing compound. The chemical explosion is assumed to be induced by a sudden initiation (e.g. by additional energy input, such as by friction when closing the valve) or by impurities which suddenly trigger a catalytically induced spontaneous decomposition as the required temperature is reached by heating under an open flame. As a conclusion, A. Lange teaches to avoid temperatures above 40° C. and to install safety valves which open automatically if the pressure rises unexpectedly.

[0012] However, in the context of the present invention it was surprisingly recognized that even in the absence of catalytic impurities and direct ignition sources, liquid nitrous oxide is generally not explosion-proof even at temperatures below 40°C.

[0013] The object of the present invention is to find a method for the explosion-proof treatment of liquid nitrous oxide on an industrial scale, such as during its production and purification or for its storage, whether for its subsequent filling into gas cylinders or bottles, its use in chemical production facilities for the selective oxidation of organic compounds, or for any other application. The method should be easy to carry out, preferably using standard equipment or equipment that is only slightly modified.

[0014] We have surprisingly found a method for the explosion-proof storage of nitrous oxide in a container in the liquid phase, which method comprises filling the container with nitrous oxide and an inert component selected from nitrogen, oxygen, carbon dioxide, water, argon, helium, krypton, xenon and mixtures thereof, and maintaining it at a temperature of 190 K to 273 K, wherein

[0015] (i) the container has an internal distance between two opposing inner walls of ≥ 10 cm in all three spatial directions,

[0016] (ii) the concentration of the inert components amounts to 2 to 20 wt.-%, based on the nitrous oxide in the liquid phase, and

[0017] (iii) a compound selected from the group consisting of

[0018] - Gases that have a flammable range with air at 293.15K and 101.3kPa absolute pressure,

[0019] - liquids having a flash point of ≤ 366.15 K at 101.3 kPa absolute pressure, and

[0020] - mixtures thereof

[0021] A total of 0 to 2 wt.-% based on nitrous oxide in the liquid phase is maintained.

[0022] Even if gas such as nitrous oxide can also be carried out explosion-proof storage in gaseous form as pressurized gas, the present invention still relates to storage in liquid phase intentionally, because liquid phase has the great advantage of much higher density, and therefore per unit volume can store significantly more gas.According to the phase diagram of nitrous oxide, liquid nitrous oxide can in principle exist under the pressure above the critical point (36.42 ℃ (309.57K) and 7.245MPa absolute pressure) and the temperature between triple point (-90.82 ℃ (182.33K) and 0.08785MPa absolute pressure) and gas / liquid curve but below the liquid / solid curve.As can be easily drawn from the above-mentioned value, liquid nitrous oxide needs the pressure greater than 7.2MPa absolute pressure to keep liquid at the temperature just below the critical point temperature, and at the temperature slightly above the triple point temperature, the low pressure of 0.088MPa absolute pressure is enough.The lower the temperature of liquid nitrous oxide is, the lower the pressure required for keeping nitrous oxide liquid is. Low pressure is advantageous in several aspects, because for example less compression energy is needed and the design of storage system about material requirements and safety issues becomes easier.According to the teaching in the journal " Zeitschrift fürangewandte Chemie [applied chemistry] " 29 (1902) 725-731 mentioned above by A.Lange, it is suggested to handle liquid nitrous oxide in conjunction with safety valve below 40 ℃, to minimize or even avoid the risk of sudden and accidental explosion.The document implies that the risk of explosion continues to reduce as the temperature further decreases.Therefore, it was originally expected that the risk of liquid nitrous oxide explosion at only -0.15 ℃ (273K) and the following temperature would be very low or even completely absent.

[0023] Contrary to all expectations, in-depth studies during the course of the present invention have revealed that, despite or more precisely due to the low temperatures of ≤273 K (≤-0.15° C.), liquid nitrous oxide is still explosively sensitive if it is handled in a container in which the internal distance between two opposing inner walls is much greater than 5 cm in all three specific directions. However, such containers are particularly relevant for the storage of technically relevant quantities of liquid nitrous oxide.

[0024] It was then unexpectedly discovered that even at temperatures between 190 K (-83.15 ° C) and 273 K (-0.15 ° C), nitrous oxide can still be stored explosion-proof in technically relevant quantities in liquid form in containers which:

[0025] (i) has an internal distance of ≥ 10 cm between two opposing inner walls in all three spatial directions, if

[0026] (ii) additionally contains inert components selected from nitrogen, oxygen, carbon dioxide, water, argon, helium, krypton, xenon and mixtures thereof, and such inert components constitute in total 2 to 20 wt.-%, based on the nitrous oxide in the liquid phase, and

[0027] (iii) a compound selected from the group consisting of

[0028] - Gases that have a flammable range with air at 293.15K (20°C) and 101.3 kPa absolute pressure,

[0029] - liquids having a flash point of ≤366.15 K (≤93° C.) at 101.3 kPa absolute pressure, and

[0030] - mixtures thereof

[0031] A total of 0 to 2 wt.-% based on nitrous oxide in the liquid phase is maintained.

[0032] For convenience, the temperature is sometimes given in two different units (i.e. in K and ° C), with one unit given in brackets, as shown, for example, above. For the conversion of these two units, the following equation applies: T [K] = T [° C] + 273.15. In case of inconsistency, the value not mentioned in brackets shall prevail.

[0033] The present invention is explained in more detail below.

[0034] Container to be used according to the invention

[0035] (i) have an internal distance of ≥ 10 cm between two opposing inner walls in all three spatial directions, and

[0036] Advantageously for practical and safety reasons

[0037] - is chemically inert towards liquid nitrous oxide and possible further compounds contained in the liquid phase to which the inner wall is exposed during storage at the temperatures and pressures expected to be applied, and

[0038] - Be mechanically stable at the temperatures and pressures expected to be applied during storage.

[0039] Therefore, the container preferably contains a shell made of steel of appropriate thickness to achieve the required mechanical stability. As an example of a suitable type of steel, austenitic steels are mentioned, such as 1.4306, 1.4401, 1.4436, 1.4404, 1.4435, 1.4432, 1.4541 and 1.4571. The container may contain an inner liner, such as an inner jacket of an inert material, or may be coated with an inert material on the inside. Depending on the material of the container and the temperature and pressure expected to be applied during storage, the geometry of the container and its wall thickness typically vary from a few millimeters to a few centimeters.

[0040] The container to be used according to the invention can in principle have any geometric shape and size, but is characterized in that it has an internal distance of ≥10 cm between two opposing inner walls in all three spatial directions. However, in terms of pressure stability, the container advantageously has at least predominantly circular walls. As suitable shapes, cylinders, spheres and three-dimensional ellipses with flat or preferably curved covering surfaces are mentioned as examples. For filling and emptying, the container has at least one connecting branch or facility, whereby at least two separate connecting branches or facilities are preferred because they provide greater flexibility.

[0041] As already mentioned above, the container to be used according to the invention has an internal distance between two opposing inner walls of ≥10 cm in all three spatial directions. In other words, this means that there is at least one point in the container from which no inner wall is less than 5 cm. Preferably, the container has an internal distance between two opposing inner walls of ≥12 cm, more preferably ≥15 cm, particularly preferably ≥18 cm, very particularly preferably ≥21 cm and most preferably ≥25 cm, preferably ≤500 cm, more preferably ≤400 cm and particularly preferably ≤350 cm in all three spatial directions.

[0042] Typically, the container used in the process of the present invention has a volume of 8 L to 250 m 3 , preferably ≥15 L, more preferably ≥25 L, particularly preferably ≥55 L, very particularly preferably ≥105 L and most preferably ≥500 L, and preferably ≤200 m 3 , preferably ≤100m 3 , especially preferably ≤75m 3 And very particularly preferably ≤50 m 3 internal volume.

[0043] In the method for the present invention, the container is filled with nitrous oxide and an inert component selected from nitrogen, oxygen, carbon dioxide, water, argon, helium, krypton, xenon and mixtures thereof totaling 2 to 15wt.-% based on the nitrous oxide concentration in the liquid phase. Filling means that the mentioned component nitrous oxide and an inert component or multiple inert components (as the case may be) are fed into the container, and has nothing to do with the liquid level in the container. Basically, the container can only be filled to very low liquid levels and up to extreme liquid levels, and for safety reasons, it is recommended that the filling level is preferably maintained at ≤99.9vol.-%, more preferably at ≤99.5vol.-%, particularly preferably at ≤99vol.-% and very particularly preferably at ≤98vol.-%.

[0044] If the temperature of the liquid phase in the container is below 273 K, although in principle it is possible to feed nitrous oxide and the inert component separately and sequentially, it is preferred to feed nitrous oxide and the one or more inert components simultaneously, or alternatively, to feed nitrous oxide and the one or more inert components sequentially but at least in such a way that the concentration of the one or more inert components in total does not fall below a lower limit of 2 wt.-%, based on the nitrous oxide in the liquid phase.

[0045] As already mentioned above,

[0046] (ii) The concentration of the inert components in the process according to the invention and in total, based on the dinitrogen monoxide in the liquid phase, is from 2 to 20 wt.-%.

[0047] The concentration is preferably ≥2.1 wt.-%, more preferably ≥2.2 wt.-%, particularly preferably ≥2.3 wt.-%, very particularly preferably ≥2.5 wt.-% and most preferably ≥3 wt.-%, and preferably ≤18 wt.-%, more preferably ≤15 wt.-%, particularly preferably ≤13 wt.-%, very particularly preferably ≤11 wt.-% and most preferably ≤10 wt.-%. In terms of specific ranges, the concentration of the inert components preferably accounts for 2.1 to 15 wt.-% and more preferably 2.1 to 10 wt.-%.

[0048] As inert components, nitrogen, oxygen, carbon dioxide, water, argon, helium, krypton, xenon and mixtures thereof are mentioned. The liquid phase may contain only one specific inert component or a mixture of two or more different inert components. However, the plural form "inert components" used for language simplification should also include the presence of only one inert component, unless the circumstances clearly indicate that a mixture of two or more inert components is specifically intended. In addition, it is clear that the term water in the list generally means H2O as a chemical compound.

[0049] In general, the inert component may be specifically added to the nitrous oxide (e.g. before or when filling the container), may already be present in the nitrous oxide to be stored (e.g. by its preparation or its recovery from a source containing nitrous oxide), or may already be present in the container when the nitrous oxide is filled into the container.

[0050] Although all listed inert components have explosion suppression effect, for practical reasons, nitrogen, carbon dioxide and mixtures thereof are preferred, because they are usually typical by-products when producing nitrous oxide, or are accompanying compounds in processes where nitrous oxide is formed as a by-product. In addition, nitrogen and carbon dioxide are easily available in large quantities.

[0051] Based on the solubility data of the mentioned inert gases regarding their solubility in liquid nitrous oxide at different temperatures and pressures (which a person skilled in the art can determine by himself or by looking up in relevant literature or databases), a person skilled in the art can easily estimate how much of the respective inert gas or gases is needed at a specific pressure and temperature to achieve the desired concentration in the liquid phase.

[0052] Based on the concentration of inert components and possible other compounds in the liquid phase, the concentration of dinitrogen monoxide is generally 82 to 98 wt.-%, based on the liquid phase. The concentration is preferably ≥83.3 wt.-%, more preferably ≥85.5 wt.-%, particularly preferably ≥87.0 wt.-%, very particularly preferably ≥88.5 wt.-% and most preferably ≥89.3 wt.-%, and preferably ≤97.9 wt.-%, more preferably ≤97.8 wt.-%, particularly preferably ≤97.6 wt.-%, very particularly preferably ≤97.6 wt.-% and most preferably ≤97.1 wt.-%.

[0053] The concentration of nitrous oxide, inert compounds and possibly other compounds in the liquid phase of the container can be easily determined by taking a sample of the liquid phase and analyzing it, for example, by gas chromatography. A person skilled in the art knows how to perform such analytical measurements and how to quantitatively evaluate the results.

[0054] Although it has been found that a certain minimum concentration of inert components in the liquid phase is necessary for suppressing the sudden explosion of nitrous oxide in a container with an internal distance of ≥10 cm between two opposite inner walls in all three spatial directions at 190K to 273K, it turns out that this is not enough to actually avoid such sudden explosions, and a certain concentration of other compounds (which can be described as extremely flammable compounds on the surface) still produces a potentially explosive mixture. Therefore, the composition of the liquid phase to be stored according to the present invention is further specified by the upper limit of the range of such possible other compounds. More specifically, and as already mentioned above, these other compounds

[0055] (iii) Selected from

[0056] - Gases that have a flammable range with air at 293.15K (20°C) and 101.3 kPa absolute pressure,

[0057] - liquids having a flash point of ≤366.15 K (≤93° C.) at 101.3 kPa absolute pressure, and

[0058] - mixtures thereof, and

[0059] A total of 0 to 2 wt.-% based on nitrous oxide in the liquid phase is to be maintained.

[0060] In the context of the present invention, a gas is defined as a compound that is gaseous at a pressure of 101.3 kPa absolute and a temperature of 293.15 K. Thus, a liquid is a compound that is liquid at a pressure of 101.3 kPa absolute and a temperature of 293.15 K.

[0061] Gases that have a flammable range with air at 293.15 K and 101.3 kPa absolute pressure are referred to below as "flammable gases". The property of whether a gas is a flammable gas can be easily determined experimentally, for example, by the experimental method described in DIN EN ISO 10156:2017, entitled "Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets". This DIN EN ISO method is particularly cited in "Globally Harmonized System of classification and labeling of chemicals (GHS)", 9th revised edition, United Nations, New York and Geneva, 2021, Chapter 2.2, in which the criteria for classifying flammable gases into GHS categories 1A (extremely flammable gases, GHS pictogram), 1B (flammable gases, GHS pictogram) and 2 (flammable gases, no GHS pictogram) are specified. In DIN EN ISO 10156:2017, two test methods are described. The first method involves determining whether the corresponding gas is indeed flammable, and the second method involves determining the flammability limit. For determining whether the corresponding gas has a flammable range with air at 293.15°C and 101.3 kPa absolute pressure as specified in the method according to the invention, the first method is sufficient, since the flammability limit is not relevant.

[0062] This determination is operated in such a way that a mixture of the respective gas with different, gradually increasing concentrations in air is successively fed into a thick glass upright cylinder with a diameter of ≥50 mm and a height of ≥300 mm and, once a measuring temperature of 293.15 K is reached at a pressure of 101.3 kPa absolute, a spark is generated by a high-voltage spark generator. If a flame detachment and an upward propagation of ≥100 mm are observed, the respective gas is classified as flammable. A person skilled in the art knows how to make such a determination.

[0063] As examples of flammable gases, mention is made of hydrogen, carbon monoxide, ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, methane, ethane, propane, n-butane, 2-methylpropane, 2,2-dimethylpropane, ethylene, propylene, but-1-ene, but-2-ene, 2-methylprop-1-ene, acetylene, methylacetylene, 1-butyne, methyl chloride, methyl bromide, ethyl chloride, vinyl chloride, dimethyl ether, methyl ethyl ether, methyl vinyl ether, formaldehyde, hydrogen sulfide, methyl mercaptan, phosphine, methylphosphine, diborane and stibine.

[0064] Liquids having a flash point of ≤366.15 K at 101.3 kPa absolute pressure are referred to hereinafter as "flammable liquids". The property of whether a liquid is a flammable liquid can be easily determined experimentally, for example, by the experimental method described in ASTM D 3828-07a entitled "Standard test method for flash point by small scale closed cup tester". This ASTM method is referenced in "Globally Harmonized System of classification and labeling of chemicals (GHS)", 9th revised edition, United Nations, New York and Geneva, 2021, Chapter 2.6, which specifies the criteria for classifying flammable liquids into GHS categories 1 (extremely flammable liquids and vapors, GHS pictogram), 2 (highly flammable liquids and vapors, GHS pictogram), 3 (flammable liquids and vapors, GHS pictogram) and 4 (flammable liquids, no GHS pictogram). In ASTM D 3828-07a, two experimental methods are described. The first method involves determining whether the corresponding liquid does have a flash point of ≤366.15K at 101.3 kPa absolute pressure, and the second method involves determining the temperature of the flash point. The first method is sufficient for determining whether the corresponding liquid does have a flash point of ≤366.15K at 101.3 kPa absolute pressure, since the actual flash point is not required for the present discovery.

[0065] In principle, the determination operates in such a way that the test compound is filled into a so-called cup cell and once the desired measuring temperature has been reached, an attempt is made to ignite it with a test flame at an absolute pressure of 101.3 kPa. The cup cell can be roughly described as a cylindrical heatable and coolable metal block made of an aluminum alloy with a block diameter of approximately 62 mm, a cylindrical recess at the top with a diameter of approximately 49.55 mm and a depth of approximately 9.85 mm, a sealable filling orifice above the cylindrical recess and an approximately 95 mm 2A cover with an additional opening having a shutter mechanism and a test flame jet above the shutter opening is provided. At the start of the measurement, the cup unit is brought to the desired test temperature by heating or cooling, and a small amount (2 mL) of the corresponding liquid is filled into the cylindrical recess through the filling orifice (e.g., via a syringe), and the orifice is then sealed. As a next step, a test flame is ignited at the test flame jet installed above the additional opening with the mentioned shutter mechanism (which is closed by default). The shutter is then briefly opened for about 2.5 seconds and the behavior of the system is observed. If a large flame appears during the brief opening and propagates itself instantaneously above the surface, the liquid is considered to have flashed. A person skilled in the art knows how to make such a determination.

[0066] As examples of flammable liquids, mention

[0067] - methylethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, ethylenediamine, pyrrolidine, piperidine and other alkylamines, alkylenediamines and heterocyclic aliphatic amines having a flash point of ≤366.15 K at an absolute pressure of 101.3 kPa,

[0068] - n-pentane, 2-methylbutane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, cyclopentane, cyclohexane and other saturated alkanes and saturated cycloalkanes having a flash point of ≤366.15 K at 101.3 kPa absolute pressure,

[0069] 1,3-butadiene, 2-butyne, 1-pentene, 2-pentene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2-methyl-1,3-butadiene, 1-octene, cyclopentene, cyclopentadiene, cyclohexene, 1,4-cyclohexadiene and other unsaturated alkanes and unsaturated cycloalkanes having a flash point of ≤366.15 K at 101.3 kPa absolute pressure,

[0070] - benzene, toluene, xylene, ethylbenzene, furan, pyrrole and other aromatic compounds having a flash point of ≤ 366.15 K at 101.3 kPa absolute pressure,

[0071] - 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, chlorobenzene and other halogenated hydrocarbons having a flash point of ≤ 366.15 K at an absolute pressure of 101.3 kPa,

[0072] - ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, tert-butanol, amyl alcohol and further alcohols having a flash point of ≤366.15 K at 101.3 kPa absolute pressure,

[0073] - diethyl ether, 2,3-dihydrofuran, 2,5-dihydrofuran, tetrahydrofuran and further saturated or unsaturated alkyl ethers and saturated or unsaturated cycloalkyl ethers having a flash point of ≤366.15 K at 101.3 kPa absolute pressure,

[0074] - acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, acetone, 2-butanone, 2-pentanone, 3-pentanone, crotonaldehyde and other saturated or unsaturated aldehydes and saturated or unsaturated ketones having a flash point of ≤366.15 K at 101.3 kPa absolute pressure,

[0075] - methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate and further saturated or unsaturated alkyl esters having a flash point of ≤366.15 K at an absolute pressure of 101.3 kPa.

[0076] As already mentioned above, the concentration of flammable gases and liquids is to be maintained at a total of 0 to 2 wt.-% based on the nitrous oxide in the liquid phase. "Total" means that the total concentration of all flammable gases and liquids together and present in the liquid phase is within the specified range. In addition, "0 to 2 wt.-%" means that the concentration of all flammable gases and liquids present in the liquid phase can even be 0 wt.-%, which is equivalent to the absence of flammable gases and liquids.

[0077] A compound selected from the following

[0078] - Gases that have a flammable range with air at 293.15K and 101.3kPa absolute pressure,

[0079] - liquids having a flash point of ≤ 366.15 K at 101.3 kPa absolute pressure, and

[0080] - mixtures thereof

[0081] Preferably, a total of 0 to 1.8 wt.-%, more preferably 0 to 1.5 wt.-%, particularly preferably 0 to 1 wt.-%, very particularly preferably 0 to 0.5 wt.-%, most preferably 0 to 0.2 wt.-% and in particular 0 to 0.1 wt.-%, based on the nitrous oxide in the liquid phase is maintained.

[0082] The concentration of possible flammable gases and liquids present in the liquid phase of the container can be easily determined by taking a sample of the liquid phase and analyzing it, for example, by gas chromatography. A person skilled in the art knows how to perform such analytical measurements and how to quantitatively evaluate the results.

[0083] The phrase "maintaining" the flammable gas and liquid at a certain concentration level simply means that the nitrous oxide and inert components filled into the container and possible compounds already present in the container contain at most a certain amount of flammable gas and liquid so that the total concentration of flammable gas and liquid in the liquid phase is within the specified range (including the absence of any flammable gas and liquid), and means that no further flammable gas and liquid are added to the container or at most only such an amount of flammable gas and liquid is further added to the container to ensure compliance with the specified range. Preferably, no additional flammable gas and liquid are added to the container, and the amount of flammable gas and liquid (if any) present in the container is based on the amount generated by filling with nitrous oxide and inert components.

[0084] Another class of compounds that should preferably be limited in concentration or even avoided are nitrogen oxides with a ratio of N to O ≤ 1, because they are oxidizing gases and are also corrosive in combination with water, so that the chemical quality of nitrous oxide will be negatively affected by them. This applies to a very wide range of possible applications, such as its use for medical purposes, food technology, as an oxidizing agent for the electronics industry, as an oxidizing agent for rocket engines or as a mild oxidizing agent. Therefore, the nitrous oxide to be stored according to the present invention preferably does not contain or only contains a limited amount of such nitrogen oxides. More precisely, it is preferred that the nitrogen oxides with a ratio of N to O ≤ 1 are maintained at a certain concentration, at which the amount of nitrogen present in these nitrogen oxides is based on the nitrous oxide in the liquid phase. The concentration of nitrogen combined in these nitrogen oxides in the liquid phase can be even 0wt.-%, which is equivalent to the absence of such nitrogen oxides. Regarding the phrase "maintain", the explanations described with respect to flammable gases and liquids are applicable with necessary modifications.

[0085] Specifically, the nitrogen oxides with a N to O ratio of ≤1 are nitrogen monoxide (NO) with an N / O ratio of 1, nitrogen trioxide (N2O3) and trinitroamine (N4O6) with an N / O ratio of 0.67, nitrogen dioxide (NO2) and nitrogen tetroxide (N2O4) with an N / O ratio of 0.5, and nitrogen pentoxide (N2O5) with an N / O ratio of 0.4. More preferably, nitrogen monoxide and nitrogen dioxide are maintained at a concentration at which the amount of nitrogen present in these nitrogen oxides is in the range of 0 to 1000 wt.-ppm based on the nitrogen monoxide in the liquid phase.

[0086] Preferably, the nitrogen oxides having a N to O ratio ≤1 are maintained at a concentration at which the amount of nitrogen present in these nitrogen oxides, based on the total nitrous oxide in the liquid phase, is 0 to 1000 wt.-ppm, more preferably 0 to 100 wt.-ppm, particularly preferably 0 to 10 wt.-ppm, very particularly preferably 0 to 5 wt.-ppm, most preferably 0 to 2 wt.-ppm and in particular 0 to 1 wt.-ppm.

[0087] Nitrogen oxides with a N to O ratio of ≤1 can be easily determined quantitatively, for example, by taking a defined amount of a liquid phase, transferring it to standard conditions for temperature and pressure so that the sample is converted into a gas phase, and adding a sufficient amount of aqueous hydrogen peroxide to the gas phase. All nitrogen oxides with a N to O ratio of ≤1 react with hydrogen peroxide to form nitric acid (HNO 3 ), while nitrous oxide does not react with hydrogen peroxide. The formed nitric acid can then be easily determined quantitatively, for example by ion chromatography. Those skilled in the art know how to perform such analytical measurements and how to quantitatively evaluate the results.

[0088] Although the method of the invention is generally applicable over a wide temperature range of 190K to 273K, there are two opposing effects. One effect relates to the temperature dependence of the pressure. The lower the storage temperature, the lower the pressure inside the container, the lower the evaporation rate in the event of a leak, the easier the operation of the pressure pump (because the temperature is further from the critical point), and, as already explained above, the lower the energy required for compression. Another effect relates to the material properties of the container, which generally become increasingly favorable with increasing temperature, since materials generally tend to become brittle at very low temperatures. Therefore, the liquid phase in the container is preferably maintained at ≥200K, more preferably ≥213K, particularly preferably ≥223K and very particularly preferably ≥233K, and preferably ≤268K, more preferably ≤263K, particularly preferably ≤258K and very particularly preferably ≤253K.

[0089] Cooling can be easily performed, for example, by circulating a cooling medium through cooling coils, and these cooling coils are located in the container or wrapped around the container. Depending on the expected temperature, suitable cooling media may be, for example, ethylene glycol / water mixtures, liquid ammonia or other suitable cooling media known in the prior art and sold under trade names such as or Commercially available. A person skilled in the art knows how to cool such a container.

[0090] The phrase "maintaining it at a temperature of" simply means that the temperature of the nitrous oxide in the liquid phase in the container is maintained within a specified range, although the specific temperature may fluctuate within the specified range over time.

[0091] The method for storing nitrous oxide of the present invention breaks away from any time limit.This means that the time during storage of nitrous oxide in container can be very short to very long, or in other words, can be only a few seconds until several years.More specifically, storage time is normally ≥10 seconds, preferably ≥1 minute, more preferably ≥1 hour, particularly preferably ≥10 hours, very particularly preferably ≥1 day and most preferably ≥1 week.According to the present invention, nitrous oxide can store even very long time, as reach 1 year, reach 10 years or even longer.

[0092] Storage does not require that the liquid phase containing nitrous oxide is fixed in a closed container without any inlet for additional nitrous oxide and inert components and any outlet for nitrous oxide and inert components. Therefore, storage in the sense of the present application does include storage in a closed container and storage in a container for a while, wherein additional nitrous oxide and inert components are added continuously or intermittently and continuously or intermittently withdrawn.

[0093] In a general example of explosion-proof storage of nitrous oxide in the liquid phase, liquid precooled nitrous oxide separated from the offgas of an adipic acid production facility is fed together with nitrogen into a 50 m3 / s flask. 3 In the cylindrical storage tank with external cooling spiral tube, this storage tank is purged with nitrogen in advance, and this storage tank has the internal distance of 300cm between two relative inner walls, and this storage tank is heat-insulated and is additionally provided with external cooling tube to compensate for heat loss and maintain the temperature of 248K.Nitrogen is fed in a pressure-controlled manner as gas.The required pressure of the desired nitrogen concentration in the liquid phase can be determined by the solubility data of nitrogen in liquid nitrous oxide.For example, in order to realize the nitrous oxide based on the liquid phase, the concentration of nitrogen in the liquid phase is about 3wt.-%, and setting total pressure is 3.4MPa absolute pressure.Nitrogen monoxide is stored for two weeks under these conditions, and then extracted from the cylindrical storage tank in liquid form by using a high-pressure membrane pump.

[0094] In a second general embodiment of explosion-proof storage of nitrous oxide in the liquid phase, liquid pre-cooled nitrous oxide is fed together with carbon dioxide into a 32 m 3 The nitrous oxide was stored in a cylindrical storage tank container with an external cooling spiral tube, which was previously purged with nitrogen, with an internal distance of 235 cm between two opposing inner walls, and which was thermally insulated and additionally provided with an external cooling tube to compensate for heat losses and maintain a temperature of 255 K. Based on the nitrous oxide in the liquid phase (and some trace nitrogen from the previous purging procedure), the amount of carbon dioxide was calculated to provide a carbon dioxide concentration of about 10 wt.-% in the liquid phase. The nitrous oxide was stored under these conditions for two months and then extracted from the cylindrical storage tank in liquid form via a cooled pipeline.

[0095] In a third general embodiment of explosion-proof storage of nitrous oxide in the liquid phase, liquid precooled nitrous oxide from an ammonium nitrate decomposition production facility is fed together with nitrogen into 1 m 3 In the cylindrical storage tank with external cooling spiral tube of , this storage tank is purged with argon in advance, this storage tank has the internal distance of 80cm between two relative inner walls, and this storage tank is heat-insulated and is additionally provided with external cooling tube to compensate for heat loss and maintain the temperature of 263K.Argon is fed as gas in a pressure-controlled manner so that the argon concentration in the liquid phase is about 5wt.-%.The required pressure of realizing desired argon concentration in the liquid phase can be determined by the solubility data of argon in liquid nitrous oxide.Nitrogen monoxide is stored 1 month under these conditions, and then slowly extracted from the cylindrical storage tank in the time period of another month in liquid form by using a high-pressure membrane pump.

[0096] In a fourth general embodiment of explosion-proof intermediate storage of nitrous oxide in the liquid phase, liquid precooled nitrous oxide separated from the offgas of an adipic acid production facility is continuously fed together with nitrogen to a 50 m 3 In the cylindrical storage tank with external cooling spiral pipe, the storage tank is purged with nitrogen in advance, and the storage tank has an internal distance of 300cm between two relative inner walls, and the storage tank is heat-insulated and is additionally provided with an external cooling pipe to compensate for heat loss and maintain a temperature of 248K. Nitrogen is fed as gas in a pressure-controlled manner so that the nitrogen concentration in the liquid phase is about 3wt.-%. The pressure required for the desired nitrogen concentration in the liquid phase can be determined by the solubility data of nitrogen in liquid nitrous oxide. Nitrous oxide is only temporarily stored under these conditions, because the storage tank only serves as a surge tank to absorb the fluctuation in filling and extracting out. Therefore, by using a high-pressure membrane pump, nitrous oxide is continuously extracted out of the cylindrical storage tank in liquid form, and is fed to the chemical production facility in which nitrous oxide is used as a mild oxidizing agent. Depending on the amount filled and extracted per unit time, the average residence time of nitrous oxide in the storage tank is different from a few hours to a few weeks, and wherein typical value is 15 hours.

[0097] The method of the present invention enables to realize explosion-proof treatment of liquid nitrous oxide (such as during its production and purification or for its storage) on an industrial scale, whether for its subsequent filling into gas cylinders or bottles, its use in chemical production facilities for the selective oxidation of organic compounds, or for the use of any other application. It is easy to carry out. First, standard instruments can be easily used, provided that the minimum requirements about the internal distance between two relative inner walls are met, which is usually the case of typical storage containers. Secondly, required inert gas is well-known, easy to obtain, easy to measure, and does not interfere with subsequent applications usually or can be selected accordingly. The third, the temperature below 272K is easily obtained by using standard cooling media such as ethylene glycol solution or liquid ammonia.

[0098] Examples

[0099] Experimental setup and execution

[0100] The experimental apparatus for determining the explosive potential of samples containing liquid nitrous oxide is based on the test entitled "to determine if a substance has explosion properties" commonly known as UN-GAP published in the "Manual of Tests and Criteria", 7th revised edition, United Nations, New York and Geneva, 2019, Part I, Section 11, Test Series 1, but with some adjustments, as described below. The test is designed to determine the sensitivity of a substance or mixture of substances to detonation shock.

[0101] The experimental apparatus used in the following experiments is as follows Figure 1 The meanings of the symbols used therein are summarized for a better overview.

[0102] (A) Cylinders installed in an inverted orientation

[0103] (B) Angle valve

[0104] (C)HPLC pump

[0105] (D) Valve

[0106] (E) Pressure holding valve

[0107] (F) Three-way valve

[0108] (G) Valve

[0109] (H) Explosion-proof wall

[0110] (I) Tube with 8mm Swagelok connection port

[0111] (J) Blasting cap with RDX explosive

[0112] (K) Metal foil (film)

[0113] (L) Detonator

[0114] (M) Shock absorber

[0115] (N) Safety valve

[0116] (O) Remote control pneumatic valve

[0117] (P) Exhaust pipe

[0118] The experiments were performed by using a 2" steel tube with an inner diameter of 2 inches (corresponding to 5.08 cm) and an inner length of about 40 cm, or a 4" steel tube with an inner diameter of 4 inches (corresponding to 10.16 cm) and an inner length of about 50 cm. Such tubes are also commonly called GAP-tubes, but for simplicity they are simply referred to as tubes in the following. For each experiment, a bursting cap (J) containing 160 g of RDX / wax (95 / 5 w / w) was mounted to the tube (I) together with an initiator (L) and separated from the nitrous oxide sample space by a metal foil (K). RDX is a commonly used explosive also known as RDX, or chemically known as 1,3,5-trinitroperhydro-1,3,5-triazine. According to the recommendations of the UN-GAP test manual, hollow glass microspheres with a diameter of approximately 50 μm were added to simulate cavitation. In the case of the 2" tube, 0.25 g of microspheres were added, while in the 4" tube, 2.1 g of microspheres were used. The top of the tube is closed with a threaded closure including inlet and outlet ducts, and a removable cooling coil ( Figure 1 The bottom side of the tube prepared in this way is then placed in a wooden block as a shock absorber (M). The above-mentioned device is located in an explosion-proof shelter and is separated from the feeding equipment by an explosion-proof wall (H).

[0119] Before filling the corresponding nitrous oxide sample, the system is purged to remove air by passing pure gaseous nitrous oxide through the system. After purging, pipe (I) is cooled by circulating a coolant through the cooling coil installed, and the test sample is filled. In the case of pure nitrous oxide, nitrous oxide 5.0 with a nitrous oxide concentration of 99.999% is used. For the experiment carried out with a nitrous oxide / carbon dioxide mixture, a premixed nitrous oxide / carbon dioxide mixture is used. The mixture with ammonia or cyclopentene is prepared by adding nitrous oxide and ammonia or cyclopentene separately, respectively. The method is applicable in principle to a mixture of nitrous oxide and nitrogen, except that nitrogen is added as a gas to reach a predetermined final pressure. The amount filled is determined by weighing.

[0120] Once the tube (I) is filled with the corresponding test sample and cooled to a set temperature of 247K±2K (-26.15°C±2°C), the bursting cap (J) is detonated by the detonator (L). Depending on the severity of the destruction, the test results are classified as negative (non-explosive) or positive (explosive). If the tube breaks into pieces, the test is classified as "positive", and if the tube is at most only broken but mostly remains in one piece, the test is classified as "negative".

[0121] Control experiment with water

[0122] As a control experiment for negative test results, a 4" tube was filled with water at room temperature and the bursting cap (J) was detonated. The tube was only deformed.

[0123] Example 1 (Comparison)

[0124] A 2" tube containing 0.25 wt.-% hollow glass microspheres was filled with 400 g of pure nitrous oxide and cooled to the above-mentioned set temperature of 247 K ± 2 K (-26.15 °C ± 2 °C). At this temperature, nitrous oxide has a carbon dioxide content of 1025 kg / m 3 The bursting cap (J) was then detonated and the tube was broken only to a length of about 20 cm. No fragments were formed. The test was classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0125] Example 1 demonstrates that even pure liquid nitrous oxide (with a concentration of 1025 kg / m 3 density) at a temperature of 247K±2K (–26.15℃±2℃) in a 2" tube is not sensitive to detonation by shock waves.

[0126] Example 2 (Comparison)

[0127] Since pure nitrous oxide is not sensitive to detonation by shock waves in a 2" tube at 247K±2K (-26.15℃±2℃), pure nitrous oxide was tested in a 4" tube containing 2.1 wt.-% hollow glass microspheres at the same set temperature. The 4" tube was filled with 3650 g of pure nitrous oxide and cooled to the above-mentioned set temperature of 247K±2K (-26.15℃±2℃). The blasting cap (J) was then detonated and the tube completely ruptured, forming fragments. The test was classified as "positive". A tabular overview including comparisons with other examples is given in Table 1.

[0128] Pure nitrous oxide is sensitive to detonation by shock waves in a 4" tube at a temperature of 247 K ± 2 K (-26.15 °C ± 2 °C) relative to the experimental setup with a 2" tube.

[0129] Example 3 (the present invention)

[0130] Since pure nitrous oxide is sensitive to detonation by shock waves at 247 K ± 2 K (–26.15° C. ± 2° C.) in a 4" tube, it was tested whether a low content of nitrogen in the nitrous oxide would prevent detonation triggered by shock waves. Therefore, a 4" tube containing 2.1 wt.-% hollow glass microspheres was filled with 4215 g of pure nitrous oxide and then pressurized with nitrogen to a pressure of 30.1 bar absolute. The composition thus obtained contained 97.8 wt.-% nitrous oxide and 2.2 wt.-% nitrogen in the liquid phase. The composition was cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15° C. ± 2° C.) and the bursting cap (J) was detonated. The tube broke to a length of approximately 13 cm. No fragments were formed. The test was classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0131] Example 3 shows that even a nitrogen content of only 2.2 wt.-% in nitrous oxide is already sufficient to suppress the detonation sensitivity to shock waves in a 4" tube.

[0132] Example 4 (the present invention)

[0133] Since nitrogen has been shown to be able to suppress the detonation sensitivity of nitrous oxide to shock waves, it was tested whether carbon dioxide could also suppress the detonation sensitivity. Therefore, a 4" tube containing 2.1 wt.-% hollow glass microspheres was used, but filled with 3341 g of pure nitrous oxide and 440 g of carbon dioxide. The composition thus obtained contained 88.4 wt.-% nitrous oxide and 11.6 wt.-% carbon dioxide. The composition was cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15 ° C ± 2 ° C) and the bursting cap (J) was detonated. The tube only bulged and did not rupture. The test was classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0134] Example 4 shows that a content of 11.6 wt.-% carbon dioxide in nitrous oxide suppresses detonation sensitivity to shock waves in a 4" tube.

[0135] Example 5 (the present invention)

[0136] Example 5 is based on Example 4, but is carried out with a lower content of carbon dioxide. A 4" tube containing 2.1 wt.-% hollow glass microspheres is filled with 3350 g of pure nitrous oxide and 320 g of carbon dioxide. The composition thus obtained contains 91.3 wt.-% nitrous oxide and 8,7 wt.-% carbon dioxide. The composition is cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15 ° C ± 2 ° C) and the bursting cap (J) is detonated. The tube only bulges and does not rupture. The test is classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0137] Example 5 shows that a content of 8.7 wt.-% carbon dioxide in nitrous oxide also suppresses detonation sensitivity to shock waves in a 4" tube.

[0138] Example 6 (present invention)

[0139] Example 6 is based on Example 5, but is carried out with a lower content of carbon dioxide. A 4" tube containing 2.1 wt.-% hollow glass microspheres is filled with 3320 g of pure nitrous oxide and 220 g of carbon dioxide. The composition thus obtained contains 93.8 wt.-% nitrous oxide and 6,2 wt.-% carbon dioxide. The composition is cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15 ° C ± 2 ° C) and the bursting cap (J) is detonated. The tube only bulges and does not rupture. The test is classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0140] Example 6 shows that a content of 6.2 wt.-% carbon dioxide in nitrous oxide also suppresses detonation sensitivity to shock waves in a 4" tube.

[0141] Example 7 (present invention)

[0142] Example 7 is based on Example 6, but is carried out with an even lower content of carbon dioxide. A 4" tube containing 2.1 wt.-% hollow glass microspheres is filled with 3615 g of pure nitrous oxide and 110 g of carbon dioxide. The composition thus obtained contains 97.05 wt.-% nitrous oxide and 2.95 wt.-% carbon dioxide. The composition is cooled to the above-mentioned set temperature of 247 K±2 K (–26.15° C.±2° C.) and the bursting cap (J) is detonated. The tube ruptures to a length of approximately 32 cm. The test is classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0143] Example 7 shows that a content of 2.95 wt.-% carbon dioxide in nitrous oxide also suppresses detonation sensitivity to shock waves in a 4" tube.

[0144] Example 8 (Comparison)

[0145] Since nitrogen and carbon dioxide are stable, inert molecules and are therefore not sensitive to oxidation, the behavior of ammonia as an oxidizable molecule was tested in a mixture with nitrous oxide. For this test, a 2" tube containing 0.25 wt.-% hollow glass microspheres was filled with 456 g of pure nitrous oxide and 10 g of ammonia. The composition thus obtained contained 97.9 wt.-% of nitrous oxide and 2.1 wt.-% of ammonia. The composition was cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15 ° C ± 2 ° C) and the bursting cap (J) was detonated. The tube broke to a length of approximately 22.5 cm. The test was classified as "negative". A tabular overview including comparisons with other examples is given in Table 1.

[0146] Example 8 shows that 2.1 wt.-% ammonia in a 2" tube is not sensitive to detonation by shock waves.

[0147] Example 9 (Comparison)

[0148] Example 9 is based on Example 8, but was carried out at a much higher ammonia concentration. For this test, a 2" tube containing 0.25 wt.-% hollow glass microspheres was filled with 275 g of pure nitrous oxide and 180 g of ammonia. The composition thus obtained contained 60.4 wt.-% of nitrous oxide and 39.6 wt.-% of ammonia. The composition was cooled to the above-mentioned set temperature of 247 K±2 K (–26.15°C±2°C) and the bursting cap (J) was detonated. The tube broke completely, forming fragments. The test was classified as "positive". A tabular overview including comparisons with other examples is given in Table 1.

[0149] Example 9 shows that a composition containing a significantly higher concentration of ammonia in nitrous oxide is sensitive to detonation by shock waves even in a 2" tube.

[0150] Example 10 (Comparison)

[0151] Since the relatively low content (2.1 wt.-%) of ammonia in nitrous oxide is not sensitive to detonation by shock waves in a 2" tube, the detonation behavior of a similar mixture was tested in a 4" tube. Therefore, a 4" tube containing 2.1 wt.-% hollow glass microspheres was filled with 3300 g of pure nitrous oxide and 80 g of ammonia. The composition thus obtained contained 97.6 wt.-% of nitrous oxide and 2.4 wt.-% of ammonia. The composition was cooled to the above-mentioned set temperature of 247 K±2 K (–26.15°C±2°C) and the bursting cap (J) was detonated. The tube ruptured completely and the test was classified as "positive". A tabular overview including comparison with other examples is given in Table 1.

[0152] Example 10 shows that 2.4 wt.-% ammonia in nitrous oxide in a 4" tube does not suppress detonation sensitivity to shock waves.

[0153] Example 11 (Comparison)

[0154] Since 2.4 wt.-% ammonia in nitrous oxide is detonation-sensitive to shock waves in a 4" tube, it was tested whether the additional presence of carbon dioxide as an inert compound could suppress the detonation sensitivity. Therefore, a 4" tube containing 2.1 wt.-% hollow glass microspheres was filled with 3500 g of pure nitrous oxide, 430 g of carbon dioxide and 90 g of ammonia. The composition thus obtained contained 87.1 wt.-% of nitrous oxide, 10.7 wt.-% of carbon dioxide and 2.2 wt.-% of ammonia. The composition was cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15 ° C ± 2 ° C) and the bursting cap (J) was detonated. The tube broke completely, forming fragments. The test was classified as "positive". A tabular overview including comparisons with other examples is given in Table 1.

[0155] Example 11 shows that a nitrous oxide composition is sensitive to detonation by shock waves in a 4" pipe even in the presence of 10.7 wt.-% carbon dioxide if 2.2 wt.-% ammonia is present.

[0156] Example 12 (Comparison)

[0157] As another oxidizable molecule, cyclopentene was tested in a mixture with nitrous oxide with regard to its influence on the detonation sensitivity of the mixture to shock waves. Therefore, a 4" tube containing 2.1 wt.-% of hollow glass microspheres was filled with 940 g of pure nitrous oxide and 1654 g of cyclopentene. The composition thus obtained contained 36.2 wt.-% of nitrous oxide and 63.8 wt.-% of cyclopentene. The composition was cooled to the above-mentioned set temperature of 247 K ± 2 K (–26.15 ° C ± 2 ° C) and the bursting cap (J) was detonated. The tube broke completely, forming fragments. The test was classified as "positive". A tabular overview including comparisons with other examples is given in Table 1.

[0158] Example 12 shows that 63.8 wt.-% cyclopentene in nitrous oxide does not suppress detonation sensitivity to shock waves in a 4" tube.

[0159]

Claims

1. A method for explosion-proof storage of nitrous oxide in a container in the liquid phase, the method comprising filling the container with nitrous oxide and an inert component selected from nitrogen, oxygen, carbon dioxide, water, argon, helium, krypton, xenon and mixtures thereof, and maintaining the container at a temperature of 190 K to 273 K, wherein (i) the container has an internal distance between two opposing inner walls of ≥ 10 cm in all three spatial directions, (ii) the concentration of the inert components amounts to 2 to 20 wt.-%, based on the nitrous oxide in the liquid phase, and (iii) a compound selected from the group consisting of - Gases that have a flammable range with air at 293.15K and 101.3kPa absolute pressure, - liquids having a flash point of ≤ 366.15 K at 101.3 kPa absolute pressure, and - mixtures thereof In total 0 to 2 wt.-% based on the dinitrogen monoxide in the liquid phase is maintained.

2. The method according to claim 1, wherein: The container has an internal distance of ≥15 cm between two opposing inner walls in all three spatial directions.

3. The method according to any one of claims 1 to 2, wherein: The container has a capacity of 500L to 100m 3 internal volume.

4. The method according to any one of claims 1 to 3, wherein: The concentration of these inert components amounts to 2.1 to 15 wt.-%, based on the nitrous oxide in the liquid phase.

5. The method according to any one of claims 1 to 4, wherein: The inert component is selected from nitrogen, carbon dioxide and mixtures thereof.

6. The method according to any one of claims 1 to 5, wherein: The concentration of nitrous oxide in the liquid phase is from 82 to 98 wt.-%.

7. The method according to any one of claims 1 to 6, wherein: These gases having a flammable range with air at 293.15 K and 101.3 kPa absolute pressure are selected from hydrogen, carbon monoxide, ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, methane, ethane, propane, n-butane, 2-methylpropane, 2,2-dimethylpropane, ethylene, propylene, but-1-ene, but-2-ene, 2-methylprop-1-ene, acetylene, methylacetylene, 1-butyne, methyl chloride, methyl bromide, ethyl chloride, vinyl chloride, dimethyl ether, methyl ethyl ether, methyl vinyl ether, formaldehyde, hydrogen sulfide, methyl mercaptan, monophosphine, methylphosphine, diborane and stibine.

8. The method according to any one of claims 1 to 6, wherein: These liquids having a flash point of ≤366.15 K at 101.3 kPa absolute pressure are selected from methylethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, ethylenediamine, pyrrolidine, piperidine, n-pentane, 2-methylbutane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, cyclopentane, cyclohexane, 1,3-butadiene, 2-butyne, 1-pentene, 2-pentene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2-methyl-1,3-butadiene, 1-octene, cyclopentene , cyclopentadiene, cyclohexene, 1,4-cyclohexadiene, benzene, toluene, xylene, ethylbenzene, furan, pyrrole, 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, chlorobenzene, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, tert-butanol, pentanol, diethyl ether, 2,3-dihydrofuran, 2,5-dihydrofuran, tetrahydrofuran, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, acetone, 2-butanone, 2-pentanone, 3-pentanone, crotonaldehyde, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate and methyl propionate.

9. The method according to any one of claims 1 to 8, wherein: (iii) a compound selected from the group consisting of - Gases that have a flammable range with air at 293.15K and 101.3kPa absolute pressure, - liquids having a flash point of ≤ 366.15 K at 101.3 kPa absolute pressure, and - mixtures thereof In total 0 to 1 wt.-% based on nitrous oxide in the liquid phase is maintained.

10. The method according to any one of claims 1 to 9, wherein: Nitrogen oxides having a N to O ratio ≤ 1 are maintained at a concentration at which the amount of nitrogen present in these nitrogen oxides is from 0 to 1000 wt.-ppm, based on the total nitrous oxide in the liquid phase.

11. The method according to any one of claims 1 to 9, wherein: Nitrogen monoxide and nitrogen dioxide are maintained at a concentration at which the amount of nitrogen present in the nitrogen oxides is from 0 to 1000 wt.-ppm, based on the total of nitrous oxide in the liquid phase.

12. The method according to any one of claims 9 to 11, wherein: The nitrogen oxides having a N to O ratio ≤ 1 are maintained at a concentration at which the amount of nitrogen present in the nitrogen oxides is from 0 to 10 wt.-ppm, based on the total nitrous oxide in the liquid phase.

13. The method according to any one of claims 1 to 12, wherein: The liquid phase in the container is maintained at 223K to 263K.

14. The method according to any one of claims 1 to 13, wherein: The nitrous oxide was stored for ≥ 1 hour.

15. The method according to any one of claims 1 to 13, wherein: The nitrous oxide was stored for ≥ 1 week.

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