On approximate mathematical modeling of the vapor–liquid coexistence curves by the Van der Waals equation of state and non-classical value of the critical exponent

Van der Waals equation of state as well as power laws and critical exponent theories are prototypes to study the cubic shape, asymmetries and “flatness” of the vapor–liquid equilibrium curves near the critical point. In this work we study two similar methods to determine the phase curves in analytical form, which differ from each other by simplicity of mathematical calculation. We analyze temperature dependence of the coexistence curves asymptotically close to the vapor–liquid critical point. We explain the novelty of our method with respect to the standard thermodynamic limit discussed in the literature. Therefore we show that the shape of the coexistence curves can strongly influence the accepted value of the critical exponent. The results of theoretical studies have been compared with the ones obtained by experimental methods.     

Calorimetry in testing waste materials from the brown coal combustion

The calorimetric measurements were applied in testing the wastes collected from different furnaces in electric power plants as materials to be used in civil engineering. The fly ash materials were collected from two power stations based on different brown coal deposits and working with conventional and fluidized bed installation. The reactivity of high calcium fly ash from sub-bituminous coal combustion has been proved in calorimetric, conductometric, chemical shrinkage, and rheological measurements before their practical implementation on larger scale. Highly soluble components of fly ash contribute to the hydration products and structure formation, followed by setting and hardening of fly ash–cement mixture. These results have been the base of research project aimed in the innovative solutions dealing with the management of deposits of wastes generated as a result of coal combustion. The standardization and potential use on larger scale of these materials, necessary from the environmental point of view, seems to be the question of nearest future.     

Sustainable Drying and Torrefaction Processes of Miscanthus for Use as a Pelletized Solid Biofuel and Biocarbon-Carrier for Fertilizers

Miscanthus is resistant to dry, frosty winters in Poland and most European Union countries. Miscanthus gives higher yields compared to native species. Farmers can produce Miscanthus pellets after drying it for their own heating purposes. From the third year, the most efficient plant development begins, resulting in a yield of 25–30 tons of dry matter from an area of 1 hectare. Laboratory scale tests were carried out on the processes of drying, compacting, and torrefaction of this biomass type. The analysis of the drying process was conducted at three temperature levels of the drying agent (60, 100, and 140 °C). Compaction on a hydraulic press was carried out in the pressure range characteristic of a pressure agglomeration (130.8–457.8 MPa) at different moisture contents of the raw material (0.5% and 10%). The main interest in this part was to assess the influence of drying temperature, moisture content, and compaction pressure on the specific densities (DE) and the mechanical durability of the pellets (DU). In the next step, laboratory analyses of the torrefaction process were carried out, initially using the Thermogravimetric Analysis TGA and Differential Scaning Calorimeter DSC techniques (to assess activation energy (EA)), followed by a flow reactor operating at five temperature levels (225, 250, 275, 300, and 525 °C). A SEM analysis of Miscanthus after torrefaction processes at three different temperatures was performed. Both the parameters of biochar (proximate and ultimate analysis) and the quality of the torgas (volatile organic content (VOC)) were analyzed. The results show that both drying temperature and moisture level will affect the quality of the pellets. Analysis of the torrefaction process shows clearly that the optimum process temperature would be around 300–340 °C from a mass loss ratio and economical perspective.     

17O and 33S nuclear magnetic shielding of sulfur trioxides from the experimental measurements and theoretical calculations

In a recent ¹⁷O NMR spectra of liquid sulfur trioxide, several unexpected peaks appeared with the temperature‐dependent integrated peak ratio. In order to interpret NMR spectra and assign peaks to possible molecular structures, the theoretical quantum mechanical density functional theory and Møller–Plesset second‐order perturbation theory calculations were performed. It is suggested that in the liquid sulfur trioxide, apart from monomeric SO₃, a significant amount of (SO₃)₃ cyclic trimers should appear. No theoretical data support hypothesis on (SO₃)₂ dimers formation. Copyright © 2014 John Wiley & Sons, Ltd.