Project conducted under DOE award DE-FC36-03GO13104

Transcription

1 Lawrence Shore Engelhard Corporation Spring AIChE Meeting, April 27, 2004 Precious Metal Recovery from Fuel Cell MEA's Project conducted under DOE award DE-FC36-03GO13104

2 Pt Recycling is Crucial to Successful Implementation of Fuel Cells Recycling will supply the bulk of Pt required in 2050 Refiners, like Engelhard, become miners

3 Complete MEA (Membrane electrode assembly) (Adapted from W.L. Gore website) Gasket Gas diffusion layer Cathode catalyst Nafion membrane Anode catalyst Anode has ~0.5mg Pt/cm 2 (transportation) Stationary application has ~0.3mg Ru/cm 2, too.

4 Nafion Cost is an Important Factor in PEMFC Growth Chart from E.I. Dupont website

5 Current PEMFC Membrane Recovery Current technology based on burning off organic matter MEA is heavily loaded with fluorine HF is a decomposition product of fluoropolymer ignition HF is a regulated emission Alkaline scrubbing is not quantitative in HF removal A new method of preparation is required FT-IR will be used for environmental process compliance.

6 PTFE vs. Nafion PTFE Nafion Extracted from Dupont Nafion MSDS

7 Nafion Degradation Products Compound Evolution T, o C Mg/g Sample SO CO HF 400 High CO RCOF COF COS 400 Trace ROH 400 Trace Extracted from Dupont Nafion MSDS

8 Simple Selective Sprectrophometric Method for the Determination of Ruthenium in Carbon Supported Pt-Ru-GE Catalyst Ruthenium complexed with thiourea at 640 nm. Sample heated at 70 o C for 15 minutes Applied to sample with 0.5% Ru 20% Pt (40:1 excess) does not interfere in Ru measurement Precision in lit. is poor (mean =0.49%, sd = 0.07%) May represent product variation 6 to 1 HCl/HNO 3 used Balcerzak, Swiecicka and Bystronska Analytical Letters, 32, 1799, 1999.

9 Determination of Platinum and ruthenium in Pt and Pt-Ru catalysts with carbon support by direct and derivative spectrophotometry Precious metals recovered using 6:1 HCl/HNO 3 Complexed with stannous chloride Complexation performed at ~90 o C for 45 minutes The value of the first derivative at 377 nm is used to quantify Pt The value of the second derivative at 495 nm is used to quantify Ru Precision good rsd = 1% Higher Ru yield and better precision with 6:1 acid mixture compared to aqua regia Balcerzk, Swiecicka and Balukiewicz, Talanta, 48, 39, 1999

10 Rapid Derivative Spectrophotometric Method for the Determination of Platinum in Pt-Ru/C Catalyst Using Iodide Media Precious metals recovered using aqua regia Complex with potassium iodide Complexation performed at room temperature Pt quantified by determination of the value of the 4 th derivative at a wavelength of 411nm At this wavelength, ruthenium has a value of 0 for the fourth derivative. RSD = 1% for Pt Balcerzk, and Kaczmarcyzj, Analytical Science, 17, 1321, 2001

11 Improvements in the sample Preparation for the Determination of Ruthenium in Catalysts by Different Spectrometric Techniques Fuse sample with KOH/KNO3 mixture at 450 o C After cooling, dissolve melt in KOH solution and add K 2 S 2 O 8 to stabilize oxidation state of Ru Measure the Ru absorbance at the isosbestic point of 415 nm Influence of Pt not determined RSD = 1.3% at 5% Ru level Taddia and Sternini, Annali di Chimica, 91, 239, 2001

12 Isosbestic Point for Mixed Ru Species

13 Flow Cell Arrangement 1. No contact with sample solution 2. Minimal waste 3. Ability to standardize duration of complexation prior to measurement

14 Electronics for Pump Interface

15 Leaching Method Greatly Affects Pt Recovery from Fuel Cell Catalyst Pre-treatment : Post treatment HCl : HNO3 % Pt found Ignited at 300c: filtered 6 to No ignition: filtered 6 to No ignition: filtered 3 to No ignition: filtered 3 to c: no filtering 6 to c: no filtering 6 to

16 Conclusion There are a range of UV-visible spectrophotometric methods for measuring Pt and Ru Depending on method, simultaneous or concurrent determination may be achieved Because of the high level of ruthenium, the method of preparation becomes more important than the measurement method