Petrochemicals | NOx reducing agents AUS 32/DEF: Refractometric Analysis
AdBlue®, also known as AUS 32 or DEF is an aqueous urea solution and lowers nitrogen oxides in diesel emissions. Measurement of refractive index in order to determine true urea concentration in AdBlue® is demanded by international standards.
Nitrogen oxides (NOx) are formed in engine cylinders from nitrogen and oxygen under high pressure and temperature. They consist mainly of nitric oxide (NO) and a smaller proportion of nitrogen dioxide (NO2). NOx play a role in smog formation and ozone depletion, making emissions a serious environmental concern. In order to lower NOx emissions from diesel engines, AdBlue® was developed. In North America it is also referred to as diesel exhaust fluid (DEF). AdBlue® is the brand name for an aqueous urea solution with a concentration of 32.5 % that is used in selective catalytic reduction (SCR) converters to break down NOx to nitrogen and water according to the following reaction:
(NH2)2CO + H2O --> 2 NH3 + CO2
4 NH3 + 4 NO + O2 --> 4 N2 + 6 H2O
By adding urea to diesel exhausts, NOx emissions can be reduced by up to 90 %. This reduced NOx release may lead to a reduction in the tax and toll of vehicles, as in many countries these are graduated according to the emissions of the vehicle.
The addition of AdBlue® to diesel emissions is also followed by a reduction in fuel consumption of 3 % to 8 %. per 100 L diesel approximately 1.7 L AdBlue® are consumed. As AdBlue® costs approximately half the price of diesel, the "blue motion" technology is very efficient in saving mileage as well as costs.
The international standard ISO 22241 demands the determination of AdBlue® with several methods. ISO 22241-2 Annex C specifies the determination of urea content in AdBlue® solutions with refractive index measurements.
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