Emissions Catalyst Design using GT-SUITE. Dr. Chaitanya Sampara Mr. Dominik Artukovic

Transcription

1 Emissions Catalyst Design using GT-SUITE Dr. Chaitanya Sampara Mr. Dominik Artukovic

2 Viridis Chemicals Background Specialize in developing catalyst specific reaction kinetics Chemistries Gasoline TWC Diesel DOC, DPF, SCR, SCRF, LNT Customer List SCR, SCRF SCR TWC TWC SCR, SCRF, DOC LNT, SCR, GPF

3 Customer Specific Chemistry Development Viridis bench scale reactor to develop customer specific reaction kinetics Utilize customer s experimental data to generate catalyst specific reaction kinetics Integrate GT s reactor model with optimization routines to develop thermodynamically consistent kinetics

4 Why Emissions Modeling? India a follower for emissions regulations until Euro-V Bharat-VI regulations April 2020 Same as Euro-VI Develop catalyst models at par with engine development Simulate exhaust aftertreatment performance for verification Be involved with catalyst suppliers to optimize costs Develop catalyst specific chemistry Understand the catalyst surface chemistry to develop reaction kinetics E.g. --- Three-way catalyst (Petrol) Pt/Rh vs. Pd/Rh vs. Pt/Pd/Rh Pt/Pd/Rh Pd/Rh Pt/Rh

5 Concentration [ppm] Modeling Methodology Conventional Kinetics Global Kinetics (fast reactions) r CO (1 K CO k c CO CO c ) CO 2 co2 1 K Microkinetics (slow reactions) Modern Kinetics Semi Global mechanisms r CO NO c NO CO + Pt CO-Pt O 2 + 2Pt 2Pt-O CO-Pt + O-Pt CO 2 -Pt + Pt (1 K CO k c CO CO c ) CO 2 c 1 K O2 * NO c NO NH 3 Kinetics Development Define objective function specific to the problem NH 3 - in NH 3 out - sim NH 3 out - expt Temperature Time [s] F = 0.3*f *f2 x 10 4 Scale optimization parameters (A s and E s) Impose thermodynamic constraints

6 Example 1: Modeling the effect of SO 2 on DOC

7 DOC Kinetics GT model Sampara and Bissett (2007) kinetics r = k i c i c O2 1 + K CO c CO K NO c NO i = CO, C 3 H 6, DF, H 2 Strong inhibition due to CO and NO on Pt-Pd catalysts Binding Energy (ev) CO NO C 3 H 6 Pt Pd Sulfur effects Address the effect of Sulfur on CO and NO reactions» Assume other oxidation reactions follow CO and NO

8 SO 2 adsorption/desorption Mechanism Hamzehlouyan and Sampara (2016 and 2014) SO 2 oxidation to SO 3 is small under DOC conditions SO 2 interaction with Al 2 O 3 and Pt/ Al 2 O 3 1. Acid sites (Al n+ ) Weak (S1) Stable up to 200 C 2. Basic sites (exposed O atoms) Strong (Surface sulfite/sulfate) (S2 and S3) Stable up to 500 C 3. Bulk Al 2 (SO 4 ) 3 forms at T>400 C Thermally decompose at o C (S4)

9 SO 2 adsorption/desorption Kinetics Al 2 O 3 adsorbs non-trivial amount of SO 2 No Pt-S bond seen in DRIFTS studies Pt enhances formation of stable sulfate species on the surface

10 SO 2 adsorption/desorption Kinetics (2) S1, S2 50 ppm SO 2, adsorption at 157 C S3 S4 Kinetics for SO 2 ads/des on Pt/Al 2 O 3 1,2 SO S1 SO2 2 S 3,4 SO S2 SO2 2 S S 2 5,6 O2 S2 S3 SO S3 S2 7,8 O2 S3 S4 SO S4 S3 1 S 2 2 Pt catalyzes formation of surface sulfate Pt enhances formation of bulk sulfate from surface sulfate

11 Integrating the effect of SO 2 on DOC reactions Introduce the interaction of Pt De-convoluted peaks during TPD (S 3 = area under peak S 3 etc.) S 3 (S 2 + S 3 ) = 0.42 r i = r i 0.42 θ SO2 S3 (Where r i is the oxidation rate as given in Sampara and Bissett GT DOC)

12 Model Validation CO oxidation Experimental Protocol Expose catalyst to 50ppm SO 2 at 200 o C for 3 hours Ramp down temperature to 60 o C Ramp up to 200 o C in the presence of CO/NO + O 2 TPD to 1190 o C to remove sulfur» New sample used for each run w/o SO 2 r CO = k i c CO c O2 1 + K CO c CO K NO c NO 0.42 θ SO2 S3 w SO 2

13 Model Validation NO Oxidation w/o SO 2 w SO 2 r NO = k NO c NO c O2 c NO2 c ref Keq 1 + K CO c CO K NO c NO 0.42 θ SO2 S3

14 Parametric Study Property Value V 3L Cpsi 400 w 40 g/s Species Concentration CO 900 ppm C 3 H ppm DF1 (adsorbable) 25 ppm (C 12 ) DF2 (non-adsorbable) 25 ppm (C 12 ) Temperature [ o C] Typical cycle Time [s] H ppm NO 200 ppm SO 2 5 ppm O 2 10% Run 125 cycles

15 Parametric Studies Light Duty Diesel Heavy Duty Diesel Temp Temp SO 2 SO 2

16 Conclusions Sulfur Work Transient SO 2 adsorption/desorption incorporated in GT s DOC model SO 2 effects validated for highly influential CO and NO oxidation reactions Parametric studies using 5ppm SO 2 in catalyst feed (Bharat VI) Heavy Duty (T peak ~ 500 o C) is worse than Light Duty (T peak ~ 350 o C) Significant Sulfur emissions beyond inlet Optimize insulation and location to optimize Sulfur impact on DOC

17 Example 2: Platinum Oxide Hysteresis Modeling

18 Problem Statement and Modeling Goal Measurement data has shown an apparent inverse hysteresis behavior for platinum-based flow-through catalysts and catalyzed wall-flow filters The hysteresis will appear as a higher conversion of NO to NO 2 at a given temperature during warm-up vs. cool-down The theory is that there is oxygen stored on the surface in the form of platinum oxide, and this platinum oxide promotes the conversion of NO to NO 2 The goal is for the model to capture this effect, without negatively affecting the computation time

19 Example of Inverse Hysteresis for NO Oxidation Reversible Activation/Deactivation Effects, Votsmeier, M., CLEERS Workshop 2014.

20 Modeling Approaches Literature primarily uses micro-kinetic modeling approaches Two fast global modeling approaches are proposed 1) Coverage dependent activation energy of NO oxidation K Ae Ea 1 1 RT 0.5 NO O NO 2 2 / K eq 2) 2 nd order coverage dependency of NO oxidation theoretically derived from Langmuir-Hinshelwood type mechanism approach K Where: Ae E a RT» θ = coverage of vacant platinum sites Pt, (1-coverge of PtOx)» β = calibration factor NO O NO K 2 2 / eq

21 Modeling Approach 1 Coverage Dependent Activation Energy Coverage dependent activation energy Activation energy moved to the G(5) general function PtOx is a single stored O coverage Calibrated pre-exponent multipliers, activation temperatures, and beta=0.5 term above correspond to the reactor data test results, which will be shown in later slides

22 Modeling Approach 2 2 nd Order Coverage Dependency 2 nd order coverage dependency PtOx is a single stored O coverage Calibrated pre-exponent multipliers and activation temperatures above correspond to the reactor data test results, which will be shown in later slides

23 Votsmeier CLEERS 2014 Presentation NO Conv. Votsmeier et al. NO Conversion results using: GT-SUITE NO Conversion results using coverage dependent activation energy Good match, first pass and second pass agree, and match the published results

24 Votsmeier CLEERS 2014 Presentation - Coverage Votsmeier et al coverage results using: θ Pt_Ox GT-SUITE coverage results using coverage dependent activation energy Good, first pass and second pass agree, magnitude of coverage agrees reasonably well with published data θ Pt_Ox

25 Votsmeier CLEERS 2014 Presentation NO Conv. Votsmeier et al NO Conversion results using: GT-SUITE NO Conversion results using 2 nd order coverage dependency First pass is good, but not repeatable for second pass (see next slide for explanation)

26 Votsmeier CLEERS 2014 Presentation - Coverage Votsmeier et al coverage results using: θ Pt_Ox GT-SUITE coverage results using 2 nd order coverage dependency First pass is good, but not repeatable for second pass, coverage accumulates, needs additional degree of freedom? θ Pt_Ox

27 Hauff et al Comparison to Figure 4 of Hauff et al 2013 Additional reaction Pt_Ox + O 2 activated at high temp. 2 nd order coverage dependency Match is good for single pass

28 Conclusions for Platinum Oxide Hysteresis Two different approaches presented for modeling hysteresis effects observed on Pt/Al 2 O 3 catalyst towards NO oxidation Coverage dependent activation energy showed better promise in modeling the data over wide operation User is advised to try both approaches when modeling