Automated gas burette system for evolved hydrogen measurements
The US Department of Energy has issued a Grand Challenge in Hydrogen Storage for Fuel Cell powered vehicles. New breakthroughs in materials and approaches are needed to facilitate the transition from an energy economy based upon fossil fuels to an energy economy based upon hydrogen. Consequently there is a need for readily accessible instrumentation to evaluate and quantify the potential of condensed phase hydrogen storage materials. Both the total system storage capacity (90 gm H2/kg system and 81 gm of H2/liter system) and rate of hydrogen gas desorption (2 gm H2/sec/100KW) are critical parameters specified by the experts in the automobile and energy industries that can be obtained with volumetric methods . In bench scale studies for material screening, gas burette systems have been routinely used to determine hydrogen gas release kinetics of sodium borohydride 1-14 and ammonia borane systems 15-23. Simple gas burettes with manual measurements at intervals are easy to set up but are not adequate to study fast kinetics or to carry out high throughput testing. Automated gas burettes of various designs have been reported in the literature 23-30. Piston-cylinder type burette systems can measure gas volume changes at constant pressure if they are equipped with a linear actuator that is driven by a pressure controller. The response time of the actuator motors does impose a limit on the rate of volume change allowed. Due to the response time limit and the complexity of such systems, gas burettes with constant pressure device have not found wide spread use in hydrogen storage studies 29,31. Some designs of automated gas burettes relied on measurements of the electrical resistance of the burette liquid to determine gas volume 23,27. In these systems, it is necessary to use special working fluids such as mercury or certain electrolyte solutions, requiring careful considerations of possible interactions among reaction compounds, electrode materials, and the burette fluid. The use of mass flow meters for evolved gas measurements was also reported in the literature, 6-9,15,32,33 but this method is typically only suitable for test systems using a large batch of reactants, where the gas flow rate is high and relatively constant. In bench-scale reaction kinetics studies, the batch size is often small and the overall gas evolution rate is small, but it needs to be measured over a fairly large dynamic range. This requires switching between multiple mass flow meters with added cost and complexity. Thus a simpler system capable of automated fast measurement of volume change is very useful. Here we report on details of a gas burette system using only pressure and temperature sensors and capable of continuous recording of gas evolution rate to a computer. In this system, the moles of gas generated are calculated from the volume, pressure, and temperature change of the gas phase assuming ideal gas P-V-T behavior. While the burette pressure and all process temperatures were measured directly, the volume of the gas in the burette can be calculated by relating the burette pressure to the liquid level difference between the burette and the reservoir. The pressure in the reactor can also be calculated similarly. Thus, at any moment the amount of gas released was simply the difference between the number of the moles of gas in the system and the moles of gas before the reaction. All measurements and computations were carried out in real time using a standard PC, portable data acquisition hardware, and LabVIEW® software. We have used this system successfully to collect hydrogen release rate data on thermolysis of various ammonia borane solids and solutions.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 947474
- Report Number(s):
- PNNL-SA-60596; RSINAK; EB4202000; TRN: US200909%%221
- Journal Information:
- Review of Scientific Instruments, 79(8):Article no: 084103, Vol. 79, Issue 8; ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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