Solubility study for the purification of hydrogen from high pressure hydrocracker off-gas by an absorption-stripping process

Experiments were carried out to identify a solvent which has a high solubility and selectivity for methane relative to hydrogen at 295 K and pressures from 13.88 to 20.78 MPa. Binary solubilities with pure hydrogen and methane, and ternary solubilities with 73 mol% H-2 and 27 mol% CH4 were measured at 295 K and for pressures from 6.99 to 20.78 MPa in various organic solvents. This gas mixture simulates hydrocracker and hydrotreater off-gases which are candidates for purification with an absorption-stripper. Of the solvents tested, 2,2,4-trimethylpentane (iso-octane), which showed very high methane solubility and a reasonable selectivity, and methylcyclohexane, which showed a very high selectivity and a reasonable solubility, are the best solvents for methane absorption. Correlations for hydrogen and methane as a function of pressure and solvent solubility parameter were developed with the experimental solubilities. Binary interaction parameters for Peng-Robinson (Peng and Robinson, 1976) and Soave-Redlich-Kwong (Soave, 1972) equations of state were calculated with experimental solubility results. Prediction of gas solubility in a ternary system was compared with experimental and found to be satisfactory when experimental binary interaction parameters were used.