(136g) Simultaneous Reduction of NOx, Solid, and Semi-Volatile Particles Using 4-Way Catalyzed Filtration Systems | AIChE

(136g) Simultaneous Reduction of NOx, Solid, and Semi-Volatile Particles Using 4-Way Catalyzed Filtration Systems

Authors 

Swanson, J. J. - Presenter, University of Minnesota
Sweeney, J. R. - Presenter, University of Minnesota
Larson, C. - Presenter, University of Minnesota
Kittelson, D. B. - Presenter, University of Minnesota
Newman, R. A. - Presenter, The Dow Chemical Company
Ziebarth, R. P. - Presenter, The Dow Chemical Company


Diesel engines are widely used in
automotive, transportation, construction equipment, stand-by power generators,
and marine engines and off road applications. In 2007, the U.S. Environmental
Protection Agency (EPA) reduced the diesel particulate matter emission (DPM)
standard for heavy-duty diesel engines used on-road to 0.0134 g/kWh and in
2010, the emission standard for NOx (NO + NO2) was reduced to 0.27
g/kWh, roughly a 10-fold reduction over previous standards. To meet the on- and
off-road DPM standards most manufacturers rely on exhaust emission control
devices such as diesel particulate filters (DPF), a wall-flow filter in which
alternate channels are blocked forcing filtration to take place as the exhaust
gases pass through the channel walls while the DPM is retained in the filter
[1, 2].

The next generation of emission
control devices includes 4-way catalyzed filtration systems (4WCFS) that
include both NOx and DPM removal technology. Toyota Motor Corporation introduced
the first successful 4WCFS concept in the early 2000s that they referred to as
a ?diesel particulate ? NOx reduction? system or DPNR [3]. In brief, this
version of a 4WCFS consists of a bare DPF substrate that has been washcoated
with a NOx storage catalyst. Thus, DPM and NOx are reduced simultaneously by a
single control device. The bare DPF used in this study is made from an advanced
ceramic material (ACM). The ACM manufacturing process is controlled so that the
microstructure, total porosity, and pore size distribution are tailored to meet
requirements for DPM emission control. Additionally, ACM is suitable for
catalyzed applications. By increasing the porosity of the ACM filters, it was
hypothesized that larger amounts of NOx storage catalyst could be loaded onto
the filters. Previous studies have shown that ACM DPFs demonstrate high
filtration efficiency, low-pressure drop, high-temperature handling capability,
and excellent mechanical integrity at a porosity of 60% or higher [4, 5, 6, 7].

The focus of this work is twofold.
The first objective was to develop a methodology to
simultaneously evaluate the NOx and DPM control performance of mini
4WCFS that are challenged with diesel exhaust from a 2005 John Deere off-road
diesel engine. The experimental mini filters evaluated were 1.9 x 1.9 x 7.5 cm
square prisms. Thus, the method differs from traditional tests where full-sized
aftertreatment exhaust systems are evaluated. It is a cost effective method to
evaluate prototype filters rapidly and consistently with control of
temperature, flow rate, and face velocity. The second objective was to evaluate
the impact of catalyst loading and substrate porosity on (1) back pressure, (2)
catalytic performance, (3) the particle filtration performance of catalyst-coated
standard (STD) and high porosity (HP) test filters as stand-alone 4-way
catalyzed filtration systems. The catalyst coatings used in this study were
basic research coatings and were used due to availability
within the project timeframe to test the catalyst loading capacity of the STD
and HP test filters and are not intended for production applications.
Further work would be needed with commercial automotive catalyst companies to
optimize for their commercial coatings.

Experimental measurements included
simultaneous and time resolved total and solid particle filtration efficiency
(FE), size resolved FE, pressure drop (ΔP), and NOx removal performance.
Preliminary results indicated that the use of HP ACM 4WCFS results in 98%
reductions in NOx and 95% reductions in solid and semi-volatile particulate
matter averaged over 10 regeneration cycles. Similarly, STD ACM 4WCFS exhibited
high filtration efficiencies but slightly reduced NOx control performance. The
rich / lean cycling that is used to regenerate the filter has almost no impact
on solid particle filtration efficiency, but impacts NOx removal efficiencies.
Shorter lean times (more frequent regeneration) lead to higher removal
efficiencies but more reductant is consumed. Overall, the new methodology for
simultaneously evaluating the FE and NOx removal performance of small scale emission control devices has proven to be a
valuable developmental tool. Future work includes optimization and evaluation
of additional filters and catalysts and scaling up the system to evaluate
larger prototypes.

References:

[1] T.V. Johnson, Platinum
Metals Rev.
52(1):23-37, 2008.

[2] T.V. Johnson, 2010.Platinum
Metals Rev.
54(1):37-41, 2010.

[3] K. Nakatani, S. Hirota, S. Takeshima, K. Itoh, SAE Technical
Paper
2002-01-0957, 2002.

[4] A.J. Pyzik, C.G. Li, Int.
J. Appl. Ceram. Technol
. 2(6):440?451, 2005.

[5] A.J. Pyzik, C.S. Todd, C. Han, J. European Ceramic Society 28:383?391, 2008.

[6] C.G. Li, H. Koelman, R. Ramanathan, U. Baretzky, G. Forbriger, T. Meunier, SAE Int. J. Fuels Lubr.
1(1): 1307-1312, 2008.

[7] J. Swanson, M.
Schumacher, W. Watts. D. Kittelson, R. Newman, R. Ziebarth, 29th AAAR Conference,
Portland, OR, October 25 ? 29, 2010.