Products for Selective Catalytic Reduction (SCR) Systems

Recent testing of DuPont™ Vamac® ultra ethylene acrylic elastomers (AEM) and new grades of DuPont™ Zytel® nylon resins and semi aromatic DuPont™ Zytel® HTN in aggressive AdBlue* aqueous urea solution has demonstrated the effectiveness of these products for selective catalytic reduction (SCR) systems used to reduce NOx emissions from diesel engines.

The results of recent compatibility testing of DuPont polymers in aggressive AdBlue* aqueous urea solution have demonstrated the effectiveness of latest “Ultra” grades of DuPont™ Vamac® ethylene acrylic elastomers (AEM) and new grades of DuPont™ Zytel® nylon resins and high performance polyamides for selective catalytic reduction (SCR) systems, used to reduce NOx emissions from diesel engines.

AdBlue* is a registered trademark of the German Association of the Automobile Industry (VDA) for a 32.5% aqueous urea/demineralized water solution (currently termed diesel exhaust fluid (DEF) in North America). The technology has already been successfully used in commercial vehicles equipped with SCR systems, which carry AdBlue* onboard in specially designed tanks ready for dosing into the SCR system at a rate of 3-5% of diesel consumption.

New to Automobiles - Tough on Polymers
Now, the first applications in the automotive sector are set to follow. Audi has recently started to provide the same beneficial technology for one of its production-series vehicles, the Q7 3.0 TDI Clean Diesel. Other automotive manufacturers are currently preparing similar models, or have already launched them to market.
Along with these developments, there is a growing requirement for polymer components able to resist the corrosive liquid, which must be stored and transported in separate tanks. For elastomeric and plastic materials which are used in contact with AdBlue*, additional resistance to diesel or engine oils is generally required. This eliminates non-polar materials like EPDM.

Important issues when selecting a suitable material for use in AdBlue* systems relate to the interaction between the polymer and the solution. On the one hand, the selected material must be able to resist the chemically-aggressive urea contained within the solution as well as the potential swell effect of the water. On the other hand, the effect of the material on the urea solution must remain below very low, industry-defined limits in order to prevent the release of substances from the polymer which could impair the catalytic effect, or even go as far as significantly affecting the catalyst. Additional requirements are made regarding the high stiffness and strength of the material, and in the case of elastomers — its flexibility — due to the fact that AdBlue* will freeze at -11 °C, causing it to expand.

Suitability of DuPont™ Zytel® Nylon Resin
Recent independent testing indicates that new grades of Zytel® PA and Zytel® HTN PPA, specially-stabilized for use with this technology, are highly effective for use in demanding AdBlue* applications such as pumps, feed units, sensors or quick connectors. Moreover, the molder stands to benefit from the very good processability of the respective grades.

Resin Performance at Different Temperatures

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Zytel® 70G35NOX BK309 and Zytel® HTN 51G35NOX BK420 are two recent temperature and hydrolysis-resistant polymers, each reinforced with 35 wt. % glass fibers, which have been specifically developed by DPP. Tests involving 28 and 56 days of exposure to hot AdBlue* (60 °C and 80 °C) have consistently shown that both grades meet specifications as laid out by in-house standards such as DBL 54191 (Daimler) (see Figure 1.). This is both in terms of their effect on the urea solution (the elution of constituents from its composition, ion extraction) and as a result of the very good hydrolysis resistance – the effect of the urea solution on the polymers.

DuPont offers several additional nylon grades for a range of applications in the area of selective catalytic reduction (SCR). These include Zytel® HTN 54G35EF (GF35, heat- and hydrolysis-stabilized PPA), Zytel® FE5382 (PA 612, GF33, heat-stabilized) as well as the impact-resistant PA 612, renewably-sourced extrusion grade Zytel® LC6200 BK385.

Suitability of DuPont™ Vamac® Elastomer
Tests to determine the aging performance of Vamac® AEM in AdBlue* were similarly successful. A range of Vamac® grades, from standard Vamac® G and GLS, to latest Vamac® Ultra grades — Vamac® Ultra IP and VMX-3038 — were immersed in AdBlue* for 168 hrs at 120°C.

The tests indicated that Vamac® Ultra and VMX-3038 maintained most of their elastomeric properties in AdBlue* (see Figure 2.), and offer an excellent price/performance ratio compared with HNBR or FKM. As a result, the Vamac® Ultra grades have opened the window for new applications for AEM, and can be considered as alternative materials for flexible sealing components in contact with AdBlue*.

Vamac® has long-term proven functionality in automotive hoses and seals, and meets automotive low and high temperature requirements from -40°C to 170°C, with peaks up to 200°C, and exhibits good resistance to engine oil and diesel fuel.

Thermoplastics and Elastomers for AdBlue* Service
As supported by the test results, DuPont Performance Polymers is able to offer the automotive industry a range of thermoplastics and elastomers with good mechanical properties and high compatibility with urea solutions. By doing so, the company is not only contributing to enabling emissions reductions, but also promoting the extended use of the AdBlue* technology.