Pressure–Volume–Temperature Relationships of Tetraethyl, Tetrapropyl, and Tetrabutyl Orthosilicates

High Resolution Image Download MS PowerPoint Slide The physicochemical properties of substances─such as density, kinematic viscosity, and vapor–liquid equilibrium─are essential information for the design of chemical processes. However, since their measurements require specialized equipment and are time-consuming, reported experimental data are often insufficient. One class of materials whose physicochemical properties have not been reported is silicon alkoxide. Among them are tetraalkyl orthosilicates, a family of compounds with different alkyl chain lengths. This difference in their molecular structure has been reported to affect the sol–gel reaction, although there has been little discourse surrounding its effect on the basic thermodynamic properties of these compounds. The pressure–volume–temperature ( PVT ) relationships of tetraethyl orthosilicate ((C 2 H 5 O) 4 Si), tetrapropyl orthosilicate ((C 3 H 7 O) 4 Si), and tetrabutyl orthosilicate ((C 4 H 9 O) 4 Si) were measured at temperatures ranging from 303.15 to 363.15 K and pressures up 160 MPa, whereas densities were measured with an apparatus based on the variable-volume method. The PVT relationships thus obtained were correlated using the Tait equation and the Sanchez–Lacombe equation of state to determine the characteristic parameters of pure components. This was followed by a discussion on the effect of the molecular structure of the substance on its PVT relationship and vapor–liquid equilibrium.