Saturated Vapor Pressure Measurements for Tetraethyl, Tetrapropyl, and Tetrabutyl Orthosilicates up to 473 K

Abstract

The saturated vapor pressures of tetraethyl orthosilicate (TEOS, (CH₃CH₂O)₄Si), tetrapropyl orthosilicate (TPOS, (CH₃CH₂CH₂O)₄Si), and tetrabutyl orthosilicate (TBOS, (CH₃CH₂CH₂CH₂O)₄Si) were measured at temperatures up to 473 K using an apparatus based on the general static method. The standard uncertainties (u_s) were u_s (T) = 0.029 K and u_s (p) = 0.015 kPa, and the maximum combined expanded uncertainties U (0.95 level of confidence) were U(T) = (0.52, 8.60, and 1.64 K) and U(p^sat) = (2.81, 3.09, and 0.82 kPa) for TEOS, TPOS, and TBOS, respectively. Furthermore, the saturated vapor pressure was correlated using the Antoine equation to determine its parameters. The measured saturated vapor pressures were correlated with previously reported pressure–volume-temperature data using the PC-SAFT equation of state (EoS), followed by optimizing the pure component parameters of the PC-SAFT EoS. A relationship between the molecular structure and component parameters was identified, and the occupied volumes were determined according to the Sanchez–Lacombe and PC-SAFT EoS, revealing significant differences. Our findings highlight the potential of using the molecular structure to predict pure component parameters. In addition to providing accurate vapor pressure data for these orthosilicates, this study offers insights into correlation methods, emphasizing the importance of parameter determination in equation of state modeling.