Gibbs Free Energy

A thermodynamic equilibrium analysis on the multi-reaction system for carbon dioxide reforming of methane in view of carbon formation was performed with Aspen plus based on direct minimization of Gibbs free energy method. The effects of CO 2 /CH 4 ratio (0.5–3), reaction temperature (573–1473 K) and pressure (1–25 atm) on equilibrium conversions, product compositions and solid carbon were studied. Numerical analysis revealed that the optimal working conditions for syngas production in Fischer–Tropsch synthesis were at temperatures higher than 1173 K for CO 2 /CH 4 ratio being 1 at which about 4 mol of syngas (H 2 /CO = 1) could be produced from 2 mol of reactants with negligible amount of carbon formation. Although temperatures above 973 K had suppressed the carbon formation, the moles of water formed increased especially at higher CO 2 /CH 4 ratios (being 2 and 3). The increment could be attributed to RWGS reaction attested by the enhanced number of CO moles, declined H 2 moles and...

In this study, we use solubility and oxide melt solution calorimetry measurements to determine the thermodynamic properties of the uranyl phosphate phases autunite (abbreviated: CaUP), uranyl hydrogen phosphate (HUP), and uranyl orthophosphate (UP). Solubility measurements from both supersaturated and undersaturated conditions, as well as under different pH conditions, rigorously demonstrate attainment of equilibrium and yield well-constrained solubility product values of

The adsorption of lead onto date palm fibers (palm fibers) and leaf base of palm (petiole) has been examined in aqueous solution by considering the influence of various parameters such as contact time, solution pH, adsorbent dosage, particle sizes, ionic strength, and temperature. The adsorption of Pb(II) increased with an increase of contact time. The optimal range of pH for Pb(II) adsorption is 3.0–4.5. The linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both models fitted well. The monolayer adsorption capacity of Pb(II) on palm fibers and petiole was found as 18.622 and 20.040 mg/g, respectively, at pH 4.5 and 25°C. Dubinin-Radushkevich (D-R) isotherm model was also applied to equilibrium data. The mean free energy of adsorption (2.397 and 4.082 kJ/mol) onto palm fibers and petiole, respectively, may be carried out via physisorption mechanism. Pseudo-first-order rate equation and pseudo-second-order rate equation were applied to study the adsorption kinetics. In comparison to first-order kinetic model, pseudo-second-order model described well the adsorption kinetics of Pb(II) onto palm fibers and petiole from aqueous solution. From the results of the thermodynamic analysis, Gibbs free energy ΔG, enthalpy change ΔH, and entropy ΔS were determined. The positive value of ΔH suggests that interaction of Pb(II) adsorbed by palm fibers is endothermic. In contrast, the negative value of ΔH indicates that interaction of Pb(II) ions by petiole is exothermic. The negative value of ΔG indicates that the adsorption of Pb(II) ions on both palm fibers and petiole is a spontaneous process.

Based on the non-stoichiometric Gibbs free enthalpy minimization algorithm (FEM), an equilibrium physicochemical model of the ferrosilicon FeSi75 smelting process has been elaborated where the influence of process parameters was determined. In the above model in the submerged arc furnace, the basic parameters are temperatures of the upper and lower reactors and a fraction of the reducer in reaction mixture expressed by the molar ratio C/SiO2. In addition, considering the carbon content and the content of admixtures in the metallic phase, small amounts of oxides: Al2O3, CaO, MgO,TiO2 in the simulation calculations were included in the reaction mixture. The following temperature ranges were taken into account: 1630 to 1650 ℃ for the upper reactor and 1920 to 2010 ℃ for the lower one. The presented calculation results show good compliance with the observations of the increased quality ferrosilicon FeSi75 (used in the production of special steels) smelting process under industrial conditions. This concerns in particular the influence of temperature conditions and the fraction of the reducer in the reaction mixture on the silica reduction process efficiency as well as the yields of basic component Si and the trace elements Al, Ca, Mg, Ti.

The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24±0.16×10−5 and 1.54±0.03×10−4 molg−1 for chitin and

Boltwoodite and uranophane are uranyl silicates common in oxidized zones of uranium ore deposits. An understanding of processes that impact uranium transport in the environment, especially pertaining to the distribution of uranium between solid phases and aqueous solutions, ultimately requires determination of thermodynamic parameters for such crystalline materials. We measured formation enthalpies of synthetic boltwoodites, K(UO2)(HSiO4)·H2O and Na(UO2)(HSiO4)·H2O, and uranophane,