Solubility prediction of high boiling point impurities in liquid hydrogen by solid-liquid equilibrium methods

Due to the low temperature characteristic of liquid hydrogen (LH 2 ), most of impurities, such as nitrogen (N 2 ) and oxygen (O 2 ), could be dissolved out and converted to solid particles in LH 2 if their amount exceeds their solubility limits . To avoid safety issues such as ice blocking, the impurity solubility and the composition of probable solid air should be accurately predicted. Four different models, including Scatchard-Hildebrand (SH) model, modified SH (MSH) model, PR equation of state (EoS) and SRK EoS, were employed to predict the solubilities of N 2 , O 2 , water (H 2 O), and carbon dioxide (CO 2 ) in LH 2 . For the SH and MSH models, a new approach of dealing with solute-solvent solubility parameters at the solvent's melting temperature was proposed, which could effectively corrected unreasonable prediction by the original models. To improve prediction accuracy, a characteristic parameter of l 12 = −0.058 was suggested in the improved MSH model, and the binary interaction coefficient ( k 12 ) in form of a bivariate linear formula correlated with temperature and pressure was fitted in the EoS models. The results showed that the solubility levels for N 2 , O 2 , CO 2 , and H 2 O were 10 −8 , 10 −12 , 10 −51 , 10 −89 mol fraction in the normal LH 2 at 20 K. Based on differences in solubility levels of N 2 and O 2 , different air existence modes, including complete dissolution of N 2 and O 2 molecules, N 2 dissolution but solid oxygen formation, and solid air formation, could occur successively with the air leakage amount increases. • Activity coefficient model and equation of state model were adopted to predict impurities solubilities in liquid hydrogen . • Different model modifications were performed to execute solubility prediction for near-critical state events. • Solubility levels for N 2 , O 2 , CO 2 , H 2 O are 10 −8 , 10 −12 , 10 −51 , 10 −89 mol fractions. • Air amount affects its phase state in LH 2 and solid oxygen could occur in LH 2 .