PREDICTION OF MOLAR VOLUMES, VAPOR PRESSURES AND SUPERCRITICAL SOLUBILITIES OF ALKANES BY EQUATIONS OF STATE

A generalized cubic equation of state which can represent all the cubic equations is introduced and thermodynamic property relations for it are presented. Five cubic equations of states with respective mixing rules are used to predict molar volumes and vapor pressures of pure alkanes (from methane till n-tritriacontane) and solubilities of solid wax components (high molecular weight alkanes) in supercritical solvents. They are the RK (Redlich-Kwong), MMM (Mohsennia-Modarress-Mansoori), RM (Riazi-Mansoori), PR (Peng-Robinson), and SRK (Soave-Redlich-Kwon) equations of state. The experimental data necessary to compare the equations of state are taken from the literature. It is demonstrated that the SRK equation of state is more accurate for predicting vapor pressures of alkanes. The RM equation of state is shown to be more accurate for predicting molar volumes of saturated and sub-cooled liquid alkanes as well as molar volumes of alkanes in their supercritical condition. For the solubility of wax components in supercritical solvents it is shown that the MMM equation of state gives the least AAD% for the 270 data points of 10 binary systems studied consisting of a high molecular weight alkane and supercritical ethane and carbon dioxide.     

Effect of NaBF4 addition on the anodic synthesis of TiO2 nanotube arrays photocatalyst for production of hydrogen from glycerol–water solution

Addition of NaBF₄ during anodic synthesis of TiO₂ nanotube arrays (TNTAs) photocatalyst and its application for generating hydrogen from glycerol–water solution has been investigated. The TNTAs were synthesized by anodic oxidation of titanium metal in glycerol electrolyte solution containing NH₄F. During the process, the NaBF₄ with different concentrations were added to the solution. Annealing of the formatted TNTAs were performed at 500 °C for 3 h under 20% H₂ in argon atmosphere, to produce crystalline phase photocatalyst. FESEM analysis showed that self-organized and well ordered TNTAs have range of inner diameters, wall thicknesses and lengths approximately 62–130 nm, 27 nm and 1.53 μm, respectively. FTIR analysis indicated that carbon, nitrogen and boron were incorporated into the TNTAs lattice. Refer to UV–Vis DRS and XRD analysis, the TNTAs photocatalysts prepared have the band gap range of 2.70–3.10 eV, with mostly have anatase phase. The NaBF₄ addition during synthesis, resulted modified TNTAs that can reduce the recombination of photo-induced electrons-holes. Photocatalytic hydrogen production test, from glycerol–water solution, indicated that TNTAs with the addition of NaBF₄ during anodic synthesis process showed higher hydrogen production comparing to the one without NaBF₄ addition. Among them the TNTAs,b (with the addition 5 mM of NaBF₄) showed up to 32% improvement in the hydrogen production and can be considered as the optimum condition.