Limiting oxygen concentration of alcohols and ketones in nitrogen and carbon dioxide

Status:

completed 03/2023

Aims:

Expansion of the database is the basis for designing the inertisation of explosive vapours of flammable liquids. Since alcohols and ketones play an important role as solvents in many plants and carbon dioxide typically permits inerting with a lower inert gas content than nitrogen, the addition to the database is of immediate and considerable practical benefit to many businesses. The values were included in the CHEMSAFE database and are also to be included in the Technical Rules for Hazardous Substances (TRGS) 722 when it is revised.

Activities/Methods:

The limiting oxygen concentrations (LOC) of various alcohols and ketones were measured at ambient pressure and, if necessary, at elevated temperatures. The measurement programme included 12 representatives of the class of alcohols with carbon dioxide as inert gas and 6 representatives of the class of ketones with nitrogen and carbon dioxide as inert gas. Within this research project, method T (tube method) of DIN EN 1839 was used. Gas mixtures with a defined composition are produced and ignition tests are carried out in the mixture at rest. By varying the fuel proportion, the composition is sought at which just no more combustion reaction takes place. When determining the LOC, the test substance content of the test mixture and the inert gas content are varied step by step until just no more ignition is detected. For this purpose, at least five non-ignitions in succession must be detected.

Results:

The results show the well-known dependence of the limiting oxygen concentration on the temperature and the type of inert gas. When nitrogen is added to the test mixture, the heat capacity of the mixture changes only slightly. Carbon dioxide, however, has an increased inerting effect compared to nitrogen. This effect is already known and manifests itself in a greater narrowing of the explosion ranges of flammable gases and vapours. ISO 10156 gives a nitrogen equivalence coefficient of 1.5 for carbon dioxide. This is based both on a higher molar heat capacity (cp) compared to nitrogen and on the ability of a triatomic molecule to absorb thermal radiation. When carbon dioxide is added to the test mixtures, the molar heat capacity increases for all unburned test gas mixtures, so that this effect amplifies the dilution effect. The ratio of the measured limiting oxygen concentrations with the two different inert gases is found to be 1.33 ± 0.04.

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