During the SCR procedure, NOx emissions that are released from the engine during combustion are treated in a catalytic converter. The SCR catalytic converter consists of transit metal bonds of titanium dioxide (TiO2), mixed oxide of titanium(III) and titanium(IV) (Ti3O5 - often called titanium pentoxide) pentoxide and tungsten oxide, which are fixed on ceramic plates. The transformation of NOx in the catalytic converter depends on the number of active cells and especially on the pore size of the ceramic plates. For this procedure, a reducing agent is required - the so-called AdBlue®, a non-toxic and odourless aqueous solution of highquality urea in a precisely defined concentration.

Why at a specific concentration of 32.5% (+/- 0.7%)?

This mixture gives the best freezing point - about -11Cº, at which the urea and water freeze at the same time. This means that the concentration of the product will not dilute/thicken depending on climate changes as both components freeze and thaw simultaneously.

Product action AdBlue

The AdBlue® reactive agent is injected into the exhaust gas stream and, as a result of the high temperature, AdBlue® is hydrolysed to ammonia (NH3) and carbon dioxide (CO2). With the help of the ammonia and the high temperature (NH3), the nitrogen oxides (NOx) react on the surface of the catalytic converter and are transformed into nitrogen (N2) and water (H2O) - natural components of our atmosphere. The unreacted ammonia is oxidized in the reverse oxidation converter, without a catalyst, to nitrogen and water, which are discharged with the exhaust. This avoids the danger of releasing residual ammonia into the atmosphere. The ammonia content of the product is tested by measuring Alkali as NH3, with a maximum value of 0.2%. Higher values would lead to the release of ammonia into the atmosphere and pollution above the permissible level.

What is BIURET?

Biuret or carbonyl ureate is an impurity of urea solutions, it is a product of the condensation of two molecules of urea. In SCR systems, high levels of biuret create a problem as it is deposited on the active surface of the catalyst, thereby deactivating it. This prevents the removal of NOx and the AdBlue® sensor continuously signals for additional product to be injected into the system, resulting in additional cement-like formations forming and layering on the catalyst and giving excess AdBlue®. In this case, the incoming Nox-nitrogen monoxide will not be fully transformed into nitrogen and water, resulting in a significant exceedance of the emission limits to the atmosphere.

The biuret content should not exceed 0.3%.

The risks of potential contamination of catalysts are high as they are extremely sensitive to certain elements which, even in small quantities, in prolonged contact with the catalyst and its individual components lead to system damage.

Phosphate PO4, in large quantities, leads to serious problems in the operation of SCR systems. Usually high phosphate content is present in the fertilizing urea. The use of an inappropriate type of urea to produce the product is the main problem for high phosphate content.

The maximum permissible level of phosphate in AdBlue is 0,5 mg/kg.

Sodium, Calcium and Magnesium when above the norm in a prolonged cycle also cause problems. These elements are components of processed de-ionized water and their presence, in most cases, is due to poor processing of the raw water. It is possible that the presence of these and other elements is due to contact with materials and liquids during storage of the product immediately prior to use.

Below you will find possible causes of product contamination and the permissible limits of the elements according to the ISO 22241-2 test method: