FINAL REPORT. Participants in the reported tasks 1. Ravi Subramanian 2. Manoranjan Misra 3. Kent Hoekman

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1 FINAL REPORT Subtask 2.2.1: Solar thermal hydrogen production Duration of the Project: October Dec 31, 2010 Date of Final Report Submission: January 24, 2011 Primary Lead contact Vaidyanathan (Ravi) Subramanian Assistant Professor Chemical and Materials Engineering Department University of Nevada, Reno LME 310, MS NV Ph (775) , Fax (775) : Low Cost, High Efficient Flexible Solar Cells (PI: Manoranjan Misra, UNR) Participants in the reported tasks 1. Ravi Subramanian 2. Manoranjan Misra 3. Kent Hoekman 1 Nevada Renewable Energy Consortium Quarterly Progress Report

2 Table of Contents Final Report... 1 Subtask 2.2.1: Solar thermal hydrogen production... 1 Primary Lead contact... 1 Participants in the reported tasks... 1 Table of Contents... 2 Table of Figures Executive Summary Goal and Objectives Project Activity Details Literature review Experiments GC method development Application of GC Methods Other analysis Project Conclusions Patents Publications / Presentations Network / Collaborations References Nevada Renewable Energy Consortium Quarterly Progress Report

3 Table of Figures Figure 1. Apparatus Setup... 6 Figure 2. Crucible with eutectic LiCl/KCl and 5 wt% Ni... 7 Figure 3. Gas chromatograph of hydrogen-methane-nitrogen mixture Figure 4. Calibration curves developed using single-column method with TCD for (a) H 2 and (b) CH Figure 5. UNR approach to gas analysis using GC Figure 6. GC plumbing diagrams for load and injection modes Figure 7. Gas chromatogram for gas mixture (30% standard gas, 70% helium). (Standard gas: 50% hydrogen, 20% carbon monoxide, 20% carbon dioxide, 10% methane.)... 9 Figure 8. Gas chromatogram for gas mixture (~5% ethane, ~5% ethylene, ~90% nitrogen) Figure 9. Callibration curves developed using 2-column method with TCD for (a) H 2, (b) CH 4, (c) CO, and (d) CO Figure 10. Diagram of the canister system for sampling gaseous products from methane cracking Figure 11. HP 6890 Plus Figure 12. A representative chromatogram obtained after injecting exhaust gas from the box furnace in LiCl/KCl and 5 wt% Ni Figure 13. Salt Pour Figure 14. XRD of the product formed after methane injection in LiCl/KCl and 5 wt% Ni Nevada Renewable Energy Consortium Quarterly Progress Report

4 1. Executive Summary The application of solar energy to produce clean fuels is a key requirement to be explored for renewable and sustainable means of offsetting our dependence on oil for energy. Solar radiation contains a significant amount of thermal energy in the form of infra-red radiation. There are very limited efforts currently in progress to harvest this energy. The task for this project stems from the need to exploit the heat content of solar radiation in a reliable, economical, and productive manner. It was proposed to evaluate the possibility of producing hydrogen by thermal cracking of a hydrocarbon at low temperatures using a saltmixture and an appropriate catalyst. The following are the key research highlights from this work: Setting up of a proof-of-concept experimental approach for examining hydrogen production by high temperature cracking of a hydrocarbon Preparing mixtures of salt and a metal catalyst to evaluate the possibility of hydrocarbon cracking at reduced temperatures. Performing analysis of the gas products using gas chromatography Post-doctoral researchers and undergraduates participated in the different tasks listed above. This task was focused on the development of materials for (i) high temperature cracking of hydrocarbon, (ii) examining the solid and gas products of the cracking process. 4 Nevada Renewable Energy Consortium Quarterly Progress Report

5 2. Goal and Objectives Goals: The main goal was to examine chloride-based salts with transition n group metal as a catalyst for reducing the temperature of methane cracking and produce hydrogen. Preliminary experiments was planned to explore if the cracking temperature could be reduced by the addition of a catalyst. Objective: The objective was to pursue study of the literature, develop an experimental setup, and, method for analysis of products of reaction. Specifically: 1. We started with a literature search on the different type s materials that can be used as a salt base for trapping the thermal energy. 2. In parallel, we also custom fabricated manifolds for delivering methane and an inert gas to a furnace that simulated the temperatures required in solar thermal cracking reactions. 3. We also developed methods for product gas analysis using gas chromatograph. 3. Project Activity Details 1. Literature review THydrogen (H 2 ) is considered to be a very promising alternative energy carrier and clean fuel. For many years, steam reforming has been the dominant method for H 2 production. However, the significant CO 2 emissions that result from steam reforming force researchers to look for different ways to produce H 2 from natural gas. Two of the most promising technologies involve direct thermal cracking of methane and thermocatalytic decomposition, both of which proceed with little or no concomitant production of CO 2. CH 4 and H 2 are present as the main components in gas products from thermal cracking reactions. In the experiments conducted as part of this project, the reaction zone in the oven was flushed with a continuous flow of N 2. As there was no seal between the ceramic cup and the quartz tube used to deliver the reactant gas, N 2 could also be entrained in the gaseous products. Therefore, it is necessary to measure both H 2 and CH 4 in the presence of N 2. Accurate GC quantification of H 2 utilizing thermal conductivity detection (TCD) is known to be problematic, since the peak shape is dependent upon both H 2 concentration and GC conditions. Hence, it is necessary to develop a simple, reliable method to identify and quantify H 2 and CH 4 in the product stream. At the same time, it is desirable to develop a more comprehensive GC method to simultaneously analyze additional gases, including CO, CO 2, and C 2 hydrocarbons (ethane, ethene, and acetylene). 2. Experiments a. Experimental system setup The apparatus to deliver the methane to the molten salt was also constructed in consulatation with DRI from a variety of materials purchased. The following materials was purchased; copper pipe and fittings to allow easy collection of gas samples, quartz tube for the delivery of methane to the salt, a flow meter to regulate the rate of methane delivery, a final switch to stop/start methane flow, porcelain crucibles to contain the molten salt and catalyst, LiCl and KCl to act as an energy medium for the catalytic decomposition of methane, and Ni/Fe/Co powder to act as catalysts for methane decomposition. The apparatus setup, with all components, is shown in Figure 1 below. 5 Nevada Renewable Energy Consortium Quarterly Progress Report

6 Gas Removal Pipe Quartz Pipe On/Off Septa Furnace Flow Meter Porcelain Figure 1. Apparatus Setup It is to be noted that the present working setup was a result of at-least three iterations in the design of the setup before any successful experiments could be performed. b. Salt mixture and metal LiCl/KCl mixture was identified as the test mixture. The main reason for using this mixture were (i) it is reported to have a good miscibility with metals such as Fe, Co, and Ni, (ii) it can be stable in the temperature range of interest for methane cracking, and (iii) it resembles the actual solar thermal heat transfer media characteristics. The LiCl/KCl and Ni mixture before a run is shown in Figure 2. With the GC in working order, all that was needed is the method to be used for sensitive Hydrogen detection along with the corresponding column information from DRI. Once this information was obtained, the GC was set up and programmed accordingly. After this was completed, trials began and the initial data was collected. The Iron catalyst was tested first and then Nickel. 6 Nevada Renewable Energy Consortium Quarterly Progress Report

7 3. GC method development Figure 2. Crucible with eutectic LiCl/KCl and 5 wt% Ni Single-Column Method The GC (SRI model 8610 C) with a thermal conductivity detector (TCD) was configured to provide separation and analysis of CH 4, H 2, and N 2. The GC method utilizes a 0.5 ml sample loop and a 6 x 1/8 Molecular Sieve 13X column for separation of CH 4, H 2 and N 2. Helium is used as the carrier gas at a constant flow rate of 11 ml/min. The column temperature is held constant at 90 C. An example GC chromatogram is shown in Figure 3. The retention times for H 2, N 2, and CH 4 are approximately 1.72, 2.58 and 4.84 min., respectively. Figure 3. Gas chromatograph of hydrogen-methane-nitrogen mixture. To determine a concentration range for reliable quantification of H 2, a variety of calibration gas mixtures were prepared using a manifold device in DRI s Organic Analytical Laboratory (OAL). The H 2 concentrations in these mixtures ranged from 2% to 20%. An excellent linear GC 7 Nevada Renewable Energy Consortium Quarterly Progress Report

8 response was demonstrated within the range of 2-15% (see Figure 4). For CH 4, a linear GC response was demonstrated over an even wider concentration range. Peak area y = x R² = Peak area y = x R² = Hydrogen molar concentration (%) Methane molar concentration (%) (a) (b) Figure 4. Calibration curves developed using single-column method with TCD for (a) H 2 and (b) CH 4. a. Dual-Column Method It is not possible to separate all gases of interest (H 2, CH 4, N 2, CO, CO 2, C 2 H 6 and C 2 H 4 ) using a single column and operating condition. Therefore, the SRI GC was re-configured to use two columns that enable analysis of all gases from a single injection. The Molecular Sieve column is placed in the valve oven, where it is maintained at a constant temperature of 90 C. The Silica Gel column is placed in the column oven, where the temperature can be programmed. A column temperature of 40 C is maintained for 9 min, followed by an increase to 200 C at the rate of 15 C/min. A final hold time of 5 min is used. Figure 5. UNR approach to gas analysis using GC. GC plumbing diagrams for load and inject modes are shown in Figure 6. At the start of the chromatographic run, the valve is set to the inject mode, sending the loop components into the carrier stream and directing them into the two columns. The sample is carried first into the Silica Gel column at 40 C in the column oven, where CO 2 and the C 2 hydrocarbons are retained, while H 2, N 2, CO, and CH 4 continue on to the Molecular Sieve column, where they are separated at 90 C within a period of 9 min. At 9 min, the valve is actuated back into the load mode and immediately the column temperature is increased to 200 C at 15 C/min. The gases that had been retained on the Silica Gel column now elute through the column and into the detector. 8 Nevada Renewable Energy Consortium Quarterly Progress Report

9 Figure 6. GC plumbing diagrams for load and injection modes. Examples of GC chromatograms are shown in Figures 7 and 8. The retention times for H 2, N 2, CO, CH 4, C 2 H 6, CO 2 and C 2 H 4 are approximately 2.33, 4.06, 5.54, 6.77, 12.50, and minutes, respectively. Excellent linear detector responses were demonstrated for all gases of interest, as shown in Figure 9. Figure 7. Gas chromatogram for gas mixture (30% standard gas, 70% helium). (Standard gas: 50% hydrogen, 20% carbon monoxide, 20% carbon dioxide, 10% methane.) Figure 8. Gas chromatogram for gas mixture (~5% ethane, ~5% ethylene, ~90% nitrogen). 9 Nevada Renewable Energy Consortium Quarterly Progress Report

10 Peak area y = x R² = H2 molar percentage (%) Peak area y = x R² = CH4 molar percentage (%) (a) (b) Peak area y = x R² = CO molar percentage (%) Peak area y = x R² = CO2 molar percentage (%) (c) (d) Figure 9. Callibration curves developed using 2-column method with TCD for (a) H 2, (b) CH 4, (c) CO, and (d) CO Application of GC Methods Gas sampling methods A sampling system was constructed at DRI, and deployed at UNR for collecting gas products from methane cracking reactions. This system includes an gas canister under vacuum, metal orifice, pressure gauge (vacuum), ball valve, and check valve (see Figure 10). Before use, the gas canister was cleaned and evacuated at DRI. With a vacuum on the outlet side of an orifice, and atmospheric pressure on the inlet side, the velocity and mass flow rate become choked (limited) once sonic velocity is reached. Hence, a constant flow rate is achieved, as long as the pressure in the canister is less than atm. After sample collection at UNR, the gas canisters were transported to DRI for analysis. 10 Nevada Renewable Energy Consortium Quarterly Progress Report

11 Figure 10. Diagram of the canister system for sampling gaseous products from methane cracking. b. Analysis results Gas samples that had been collected in evacuated canisters at UNR were delivered to DRI, where they were diluted with helium to bring the canister pressure to just above atmospheric pressure. Samples were then introduced into the GC sample loop, and were analyzed using the methods described above. All samples analyzed showed only CH 4 and N 2, with no detectable amounts of H 2. These results demonstrate that under the experimental conditions used at UNR, minimal thermal cracking of CH 4 occurred c. GC analysis at UNR A parallel effort for product analysis was also pursued at UNR. An existing gas chromatograph was customized initially to test the gas samples. Consumables (i.e. glass liners, septa, chemical traps, o-rings, and ext.) were purchased along with a kit to connect the TCD with the FID in series. The connection kit was installed. The GC that was configured, an HP 6890, is shown below in Figure 11. Figure 11. HP 6890 Plus 11 Nevada Renewable Energy Consortium Quarterly Progress Report

12 5. Other analysis Figure 12. A representative chromatogram obtained after injecting exhaust gas from the box furnace in LiCl/KCl and 5 wt% Ni. At 700⁰C, a peak becomes barely detectable where hydrogen appears. The peak next to it is an oxygen peak, which is due to minor oxygen leakage into the system (Figure 12). Note that the relative areas of the peaks do not correspond to the relative amounts of each gas. The general temperature range where hydrogen was detected in the absence of the metal was ⁰C. The addition of Fe indicated that the hydrogen generation temperature reduced to below 600⁰C. At best we noted that hydrogen could be evolved at 400⁰C. While this was qualitative result, quantitative results are much more desired and reliable. It is proposed that an online analysis system be developed to ensure both reproducibility, minimize interference (such as oxygen leakage), and obtain quantitative results. d.1. Optical evidence of possible value-added product When the molten salt mixture was poured from the crucible after methane bubbling, there was a noticeable color difference between the upper and lower areas of the mixture. In the upper area, the mixture was extremely light gray, whereas the bottom area was rater dark. This pour with the noticeable difference is shown in Figure 13 below. 12 Nevada Renewable Energy Consortium Quarterly Progress Report

13 Top Area Bottom Area Figure 13. Salt Pour One possibility of this color difference is that while the mixture was liquid, the Nickel catalyst settled to the bottom of the crucible due to inadequate mixing of the particles. This could also mean that carbon may have formed due to cracking of the methane. This result was an interesting observation. 13 Nevada Renewable Energy Consortium Quarterly Progress Report

14 d.2 XRD Figure 14. XRD of the product formed after methane injection in LiCl/KCl and 5 wt% Ni. To test if the colored material was indeed carbon-based, XRD analysis was performed (Figure 14). The solidified salt/catalyst mixture was dissolved in water and the residue was filtered from the salt solution. This residue contains both the iron catalyst and the possible carbon. From there, the solid residue was dissolved in hydrochloric acid. The hydrochloric acid will dissolve any iron or iron oxide compounds and only leave possible carbon. The residue leftover (possible carbon) was filtered from the acid and washed. There were three characteristic peaks from the residue leftover. These peaks seem to be consistent with peaks from CNT from literature and from samples analyzed by XRD. 4. Project Conclusions The key conclusions from the project are listed below: A setup that included a customized gas methane delivery assembly, gas collection assembly, and gas cracking methodology was put together inside a conventional box furnace. Preliminary tests with LiCl-KCl mixture showed that hydrogen could be generated in the presence of Fe at lower temperatures There is evidence of possible high value product such as carbon nanotube formation from the cracking process but further analysis is needed for confirmation. 14 Nevada Renewable Energy Consortium Quarterly Progress Report

15 A single-column GC method was developed and shown to be suitable for measurement of the main gas products (H 2 and CH 4 ) from methane cracking reactions. In addition, a dualcolumn method was developed to permit analysis of multiple gases, including H 2, O 2, N 2, CH 4, CO, CO 2, and C 2 hydrocarbons with a single sample injection. Excellent linear detector responses were demonstrated for all species of interest. The dual-column method has proven to be very useful in support of other DOE-funded R&D projects, such as characterizing syngas and gaseous products produced by hydrothermal pre-treatment of cellulosic biomass. In addition, a gas sampling system was built at DRI and used at UNR to collect gas products from methane thermal cracking experiments. GC analysis of collected samples showed that minimal thermal cracking had occurred under the experimental conditions employed at UNR. 5. Patents None 6. Publications / Presentations 1. Annual merit review, 2010, Washington, D.C nd Annual Nevada Renewable Energy Consortium Meeting Aug Network / Collaborations None 8. References None 15 Nevada Renewable Energy Consortium Quarterly Progress Report