Samara State Technical University

The global transition to low-carbon energy systems drives the need for continuous efficiency improvements in fossil-fuel-based power generation. Combined cycle power plants (CCPPs) represent the state-of-the-art in commercial thermal power generation, yet further efficiency gains through conventional methods face diminishing returns. This paper presents a comprehensive thermodynamic analysis of a combined cycle power plant integrated with a chemically recuperated gas turbine (CCPP-CRGT) based on a modern high-temperature gas turbine with turbine inlet temperature of 1600 °C. Unlike conventional recuperation that transfers sensible heat, thermochemical recuperation utilizes exhaust heat to drive endothermic steam methane reforming, converting exhaust heat into chemical energy stored in hydrogen-rich syngas. The performance of the CCPP-CRGT is benchmarked against a conventional CCPP across a range of steam-to-methane molar ratios (S/C = 1.0–3.0). The results demonstrate that thermochemical recuperation shifts the power generation from the steam turbine cycle towards the more efficient gas turbine cycle, increasing the gas turbine net work from 465MW in the conventional case to 598MW at S/C = 3.0, while reducing condenser heat rejection from 327MW to only 117 MW. The overall combined cycle efficiency improves from 62.49% to 65.42%, representing a gain of 2.93 percentage points. The temperature-heat transfer profiles reveal that the reformer consumes up to 28% of the available exhaust heat, displacing the superheater section of the heat recovery steam generator. The material balance shows a progressive reduction in air mass flow rate from 2680t/h to 2463t/h as S/C increases, while the syngas flow grows correspondingly to 323.3t/h. These findings confirm that the CCPP-CRGT configuration offers a viable pathway to surpass the efficiency ceiling of conventional CCPPs by leveraging the high-temperature end of the exhaust heat cascade for thermochemical recuperation rather than for steam generation, thereby reducing the heat rejected in the bottoming cycle by redirecting a portion of the exhaust heat.

Liquid organic hydrogen carriers (LOHCs) based on alpha,w-alkanediol/lactone systems offer significantly lower dehydrogenation enthalpies than conventional aromatic carriers. This study investigates how the chain length and branching of alkyl substituents on the lactone ring influence the thermodynamic equilibrium of reversible hydrogen storage. Using a hybrid approach combining experimental thermochemistry and high-level quantum-chemical calculations (G3MP2), the reaction enthalpies, entropies, and Gibbs energies for both liquid and gas phases have been determined. Results reveal that extending the chain and increasing the branching of the alkyl group substantially reduce the Gibbs reaction energy. For instance, 2-tert-butyl-gamma-butyrolactone exhibits a negative Gibbs reaction energy (-5.3 kJ & sdot;mol-1 at 298.15 K), indicating that thermodynamically spontaneous hydrogen release is possible at room temperature, provided suitable catalysts are available. However, while highly branched substituents greatly facilitate hydrogen release, they reduce volumetric hydrogen storage density and make the reverse hydrogenation step more challenging. Ultimately, a structure-property analysis demonstrates that tuning the size and branching of alkyl substituents provides a versatile strategy to balance the competing thermodynamic demands of hydrogen storage and release, enabling the rational design of tailored diol/lactone LOHCs.

To make a hydrogen economy feasible, it is crucial to identify efficient hydrogen storage technologies. While storing hydrogen by hydrogenation of aromatic and dehydrogenation of alicyclic hydrocarbons is technically feasible, it is associated with a high energy demand for hydrogen release that limits the energetic efficiency of the storage cycle if no suitable source of waste heat is available. This study investigates whether the release of hydrogen through the cyclization of diols forming lactones is energetically more favorable. To this end, equilibrium constants for the dehydrogenation reactions at 298.15 K, 400 K, and 500 K were determined using a combination of combustion calorimetry, vapor pressure measurements, and quantum chemical calculations. The results reveal that, compared to aromatic hydrocarbons, the equilibrium position for the dehydrogenation of diols is significantly more favorable for hydrogen release, and the reaction enthalpies are markedly lower. The most advantageous properties were observed for the 1,4-butanediol/gamma-butyrolactone system. The reaction enthalpy per mole of hydrogen for the dehydrogenation at 298.15 K is exceptionally low, at 42.5 kJ & sdot;mol-1. High hydrogen yields can already be expected at temperatures below 400 K at ambient pressure. Under such conditions, hydrogen release from 1,4-butanediol can be carried out with low energy input for heating the hydrogen carrier and for providing the enthalpy of reaction. This reduced thermal demand contributes to a higher prospective energy efficiency of the respective hydrogen storage cycle, which may represent in some application scenarios a significant economic advantage. Thermodynamics of reversible hydrogen storage with LOHC systems: 1,4-butanediol/gamma-butyrolactone, 1,5-pentanediol/delta-valerolactone and 1,6-hexanediol/s-caprolactone was studied in this work.

Within the framework of the stereoatomic model of crystal structure, a crystal-chemical analysis of compounds containing coordination polyhedra of Tc(IV)Hal6 (Hal = F, Cl, Br, or I) and Tc(II)Br4 was carried out. A linear correlation was established between the solid angles of the faces of Voronoi–Dirichlet polyhedra corresponding to valence and non-valence Tc–Hal contacts and the corresponding internuclear distances. It was shown that technetium halide complexes form structural fragments in the form of isolated Tc(II)Br4 tetrahedra and isolated Tc(IV)Hal3 octahedra (Hal = F, Cl, Br, or I), as well as chains formed by edge-sharing Tc(IV)Hal6 octahedra, which can be described by three crystal-chemical formulas. In total, 35 structures containing Tc(IV)Hal6 (Hal = F, Cl, Br, or I) and Tc(II)Br4 fragments were found to be representable by thirteen topologically distinct types of 3-, 2-, and 1-periodic underlying nets.

Organic compounds have the widest practical application, and the methodology of their synthesis is often developed specifically to solve applied problems in medicinal chemistry, catalysis, materials chemistry, agriculture, food industry, and the creation of electronic and sensor devices. This is due to the huge variety of properties and functional capabilities of organic substances, as well as the ability to fine-tune their structure to impart certain practically useful characteristics. Currently, the number of organic compounds used in various fields of industry, medicine, and agriculture is in the hundreds of thousands, and their number continues to grow steadily due to the rapid development of synthetic organic chemistry and predictive methods for determining properties, including using artificial intelligence. This collective review is devoted to the achievements of Russian chemists in the field of practically oriented organic chemistry over the past 5–10 years. The review presents the achievements of leading research teams representing both RAS institutes and Russian universities, from Kaliningrad to Siberia.