While conducting composition measurements on helium-hydrogen mixtures using a Varian gas chromatograph at WSU’s Analytical Chemistry Service Center, I discovered that the ratio of orthohydrogen–parahydrogen has a significant effect on the measurements. An in depth discussion of the allotropic forms of hydrogen can be found in the previous post “Why equilibrium hydrogen doesn’t exist”. In my system, gaseous hydrogen is condensed in a copper test cell at 20 K. An ortho-para catalyst is placed in the bottom of the test cell to ensure all of the hydrogen is converted to parahydrogen. Helium gas is then introduced into the test cell to the desired pressure. The amount of helium that dissolves into the liquid is measured by extracting a liquid sample through a tube at the bottom of the test cell where it is vaporized and collected in a gas sampling bag. The composition of the sample is then analyzed using gas chromatography. The total composition of the first helium-hydrogen measurements were only totaling between 80% – 90% instead of the expected 100%. The GC column was packed with a hydrogen compatible material so it was unlikely the equipment was causing the discrepancy. We double checked that the primary standard gas mixtures were still obtaining correct measurements, they were. The only difference was that the gas standards contained normal hydrogen (since they were maintained at room temperature) and the samples being collected were parahydrogen. By adding an ortho-para catalyst just before the mixture was collected in the sampling bag, I was able to convert the hydrogen back to the normal composition. After this was implemented, every gas sample measurement was within the uncertainty of the equipment. Once again, the subtle differences between orthohydrogen and parahydrogen cannot be overlooked even in a process as standardized as gas chromatography.
Rubotherm IsoSORP instruments utilize a Magnetic Suspension Balance to provide highly accurate fluid density and sorption measurements. The system utilizes Archimedes’ principle to determine fluid density by suspending a sinker of known mass and volume in a fluid and measuring the weight with a precision balance. The applied force is transmitted to the balance by the magnetic suspension which decouples the testing fluid from the balance. The Rubotherm IsoSORP at Washington State University has recently been retrofitted for cryogenic temperatures and pressure up to 4000 psi. By placing the test cell in a vacuum chamber and thermally connecting it to a Cryomech cryocooler I have been able to achieve temperatures down to 15 K. A system diagram is provided in Figure 1 showing the key components. Sorption measurements are conducted by replacing the bottom sinker with a weighing basket filled with the sorption material and measuring the change in mass. The system is currently set up to conduct density measurements with a single quartz sinker.
The system’s operation and accuracy has been validated by conducting initial density measurements of liquid nitrogen and liquid hydrogen. Initial liquid nitrogen density measurements conducted from 79.6 K to 83.7 K had a maximum deviation of 0.08% from the equation of state. Initial normal liquid hydrogen density measurements were conducted from 16 K to 32 K with a maximum deviation of 0.3% from the equation of state. High density (> 52 kg/m3) gaseous hydrogen measurements were conducted from 34 K to 45 K and pressure up to 1090 psi with a maximum deviation of 0.3%.
The Rubotherm system at WSU is capable of conducting pure fluid density and sorption measurements from 15 K to 293 K at pressure up to 4000 psi. We are in the process of modifying the system to have the ability to conduct measurement on binary mixtures using mass spectroscopy to determine fluid composition. The accuracy of this system increases with fluid density. The current system configuration is not intended for low density gaseous measurements.
The award winning hydrogen fuel station designed by Ian Richardson, Jake Fisher and Dr. Jake Leachman was mentioned in the latest version of Alaska Airline’s Magazine. The excerpt is available here on page 34 or is provided bellow.
“In May, a team comprising WSU students and one University of Idaho student-involved in academic tracks ranging from mechanical engineering to economics and public policy-won first place in an international student competition to design a transportable, stand-alone, economical refueling station for hydrogen fuel cell-power cars, whose use may help reduce carbon dioxide emissions.”