Riview of Determination Para Hydrogen Content during Liquefaction Process

Hydrogen molecule consists of two states: ortho and para hydrogen which are in equilibrium at a certain ratio in any temperature. The conversion process in the catalytic beds takes place in order to prevent a slow exothermic conversion of ortho to para hydrogen in the liquid hydrogen storage tanks and to avoid evaporation of liquid hydrogen. Ortho and para hydrogen differs in physical properties such as thermal conductivity, vapor pressure, enthalpy, as well as Raman spectroscopy, nuclear magnetic resonance and gas chromatography. The percentages of para hydrogen content can be determined in each stage of hydrogen liquefaction process using such differences in these properties. Given the importance of determining the amount of para hydrogen in the quality control test of produced liquefied hydrogen, various percentage measurement methods based on differences in the physical properties of para hydrogen content has been expressed in this paper. As the surveys shows, the thermal conductivity is the most applicable method to determine the percentage of para hydrogen.