Leistungen
Most critical is the question of analysing the quantity of organic silicon compounds in biogas. The objective is to get a standardized and by the manufacturers and suppliers of gas engines accepted method to measure the content of harmful silicone in the biogas.
The developed method concerns the analytical determination of the most common siloxane compounds in biogas such as:
- Hexamethyldisiloxan (M2)
- Hexamethylcyclotrisiloxane (D3)
- Octamethyltrisiloxane (MDM)
- Octamethyltetracyclosiloxane (D4)
- Decamethyltetrasiloxane (MD2M) and
- Decamethylpentasiloxane (D5)
The procedure is as follows:
Tubes are filled with a polymer material that is marked with an internal standard. On site the tubes are flown through by a sampling volume of about 10 litres of biogas. The siloxanes are adsorbed and the tubes are sent without any delay to the laboratory. The siloxanes are desorbed by elution with hexan. 1µl of the extract will be injected in the gas chromatograph coupled with a mass spectrometer. The sum of total-Si will be calculated on the basis of the six single substances.
This analytical method is at present the fastest and simplest way to determine the content of harmful silicon content in biogas resulting from the most common siloxane compounds. With the help of this method, the up-to-date gas quality can be easily determined and controlled.
Landfill Gas:
It is intended to demand this analytical procedure for a standard method related to warranty limits of gas engines suppliers and to get an official approval. During the Congress of German Association of Chemists at Braunschweig in September 2002 results and method have been presented to the Subdivision of Environmental Chemistry and Ecotoxicology. Furthermore at the next meetings of VDI and DIN Committees -concerned with "Prevention of Air Pollution" in connection with the preparation of a new VDI- guideline 3860, regarding the "Analysis of Landfill Gas"- this new analytical method will be put forward.
The most critical question is the question of analysing the quantity of organic silicon compounds in the biogas. Today, no standardized method exists. The difference in the results is mainly caused by the application of different sampling methods. The objective is to get a standardized and method accepted by the manufacturers and suppliers of gas engines to measure the content of harmful silicon in the biogas.
It has been found that the best methods to determine organic silicon compounds in biogas are the adsorption of solid sorbents with subsequent thermodesorption or gas bag sampling combined with gas chromatography - mass spectrometry. The other methods (e.g. adsorption/elution with hexane or direct absorption in hexane) are not capable of detecting trimethylsilanol, a main component of organic silicon compounds in landfill gas.
Nevertheless, the ideal method would be a direct measurement of total Si. The analysis with gas chromatography includes only the measurement of selected organic silicon compounds. Other silicon containing compounds are not recorded. The developed methods are not capable to detect very small amounts of organic silicon compounds in biogas in a satisfying sensitivity. Further work must be done for the development of such a method.
The comparison of the achieved analytical results with other laboratories' results proves that it is absolutely necessary to develop a standard method of organic silicon compounds.
In this connection, the results and the method have been presented to the Sub-division of Environmental Chemistry and Ecotoxicology on the occasion of the Congress of German Association of Chemists at Braunschweig in September 2002.
Furthermore, the results were presented at the meeting of the VDI-committee "Measurement of gas from landfills" (16. 10. 2003, Cochem-Germany). The main duty of this committee is the measurement of pollutants from landfills to protect the environment.
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