Mutual Solubility of HFC-134a and Synthetic Ester Base Stocks.

Abstract

The solubility behavior of tetraesters of pentaerythritol in HFC-134a was studied by analysis of the three dimensional solubility parameters and 1H-NMR spectra. The three dimensional solubility parameters of HFC-134a were calculated based on: total solubility parameter, δ, 6.8; dispersion parameter, δd, 3.5; hydrogen bonding parameter, δh, 4.6; and polar parameter, δp, 3.6. The characteristics of the solubility parameters of HFC-134a were high δp and δh values, in addition to a low δd value, compared to those of the conventional refrigerants. The poor solubility of HFC-134a in lubricating oils is considered to be well explained by these specific solubility parameters.The solubility of the esters in various solvents was studied and the three dimensional solubility parameters were determined by computer iteration based on the least-squares mehtod. The esters having larger δp and δh values were found to have better solubility in HFC-134a at low temperatures.The proton signals of HFC-134a shifted to a lower magnetic field with an increase in temperature, indicating that the hydrogen bonding was strengthened at high temperatures opposed to the esters. This unique property of HFC-134a could be the reason that HFC-134a had its upper phase separation at high temperatures.