Ah&act
-Phase equilibria in the system H,JCOs have been studied experimentally using a vapor-recirculating apparatus. Measurements of vapor and liquid phase compositions were made for ten temperatures ranging from 220 to 290 K and pressures to 172 MPa. The mixture critical line and the pressure-temperature trace of the three-phase region solid-liquid-vapor have been located. The three-phase region and the critical line intersect at T -234.8 K and P = 1% MPa to form an upper critical end point. Experimental results have been compared with previous studies and with predictions of three equations of state, Peng-Robinson, Redlich-Kwong and Dciters. Expressions have been derived for temperature dependent critical parameters that account for quantum effects in Ha. in calculations for Ha/X systems using the Pent-Robinson equation. tNTRODtJ~ON In previous papers we presented experimental results on the vapor-liquid phase behavior of H,/N2[1], HJAr[2], Hz/CH1[3] and H&O[4]. This study of HJCOz is a continuation of research on Hz/X systems designed to explore patterns of phase behavior in fluid systems at high pressures and to obtain accurate data for testing empirical and theoretical methods of data prediction. Literature search revealed that data for this system are scarce and limited to pressures below 30MPa-a small portion of the vapor-liquid coexistence region. In this paper we present P-T-X data over virtually the entire region of vapor-liquid phase separation. These data are compared with earlier experimental results and with the predictions of three equations of state: Peng-Robinson[5], Redlich-Kwong[6] and Deiters[7].