Year of publication: 2009
Precise chlorine determination with the new TOX-100
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Placing the sample boat in the instrument
Chlorinated additives are rarely used with modern lubricants and machining fluids. Nevertheless, chlorinated ingredients can still be present in oil samples, in particular used oil from gas or biogas engines and cooling lubricants. The fuel gas in facilities that operate with landfi ll gas or biogas is sometimes contaminated with chlorinated compounds. Chlorine can end up in the oil during combustion. There it poses a high risk to the engine components. In combination with high temperatures and moisture, aggressive acids that cause corrosion and pitting can be formed. In the past, chlorinated compounds were added to some machining oils. Some of these old stocks of chlorinated materials are still being used up. In addition, some special blends still require chlorinated additives.
Another consideration is that mandatory separate collection and disposal are required for used lubricants and emulsions with excessive chlorine contamination (collection category 3 according to the German Waste Oil Ordinance). However, disposal considerations are not the only reason why it is important to know whether an oil is contaminated with chlorine. This can be a very decisive factor in the analysis of damage to biogas facilities. However, precise determination of chlorine content was not possible with the previous instrument, which operated on the principle of energy- dispersive X-ray fl uorescence. With the new TOX-100, OELCHECK now has an instrument for the microcoulometric determination of the chlorine content of oils, fuels and greases, It guarantees very high precision, even with extremely low concentrations. A sample amount of 20 to 100 mg (0.1 g) is sufficient. This corresponds to approximately two drops of oil, which are taken using a Pasteur pipette and placed in the instrument. The lower detection limit is 1 ng of chlorine. The chlorine content is stated with a precision of 1 ppm in the lab report.
The main parts of the instrument are an oven and a titration cell. The oil sample is fed into the oven in a small boat. There it is burned at a temperature of 1,000°C with the addition of oxygen. It is essential to obtain complete oxidation of the sample. This causes all of the chlorine present in the sample to be converted into chloride ions.
The combustion gases are flushed into the titration cell with the gas flow. Among other things, this cell contains a silver electrode in an electrolyte solution. An electric current causes a continual flow of silver ions into the solution. If the combustion gases contain chloride ions, the ions react with the silver ions. This reduces the silver concentration of the solution, and the current must be increased to compensate for the loss of silver ions in the solution. When all of the chlorine present has reacted, no additional current is necessary to produce silver ions and the measurement is complete. The chlorine content of the sample is calculated from the current consumed for the measurement. Now the boat travel back out of the oven to its initial position and is ready for the next measurement.
Chlorine determination is a special test and is not included in any analysis set. It is only available as an economical individual test on request.