Search Results (8)

This review describes the different developments in the production of ethylene oxide (EO) by epoxidation of ethylene. EO is an important chemical intermediate for the manufacture of a variety of industrial and consumer products, such as ethylene glycol, plastics, and pharmaceuticals. The conventional gas-phase epoxidation process using silver-based catalysts suffers from major drawbacks, including low selectivity and high carbon dioxide emissions. This review underlines emerging solutions for efficiency and sustainability improvement in EO production. Major developments in catalyst design, including novel silver-based hybrid nanostructures, Mn-N₄GP catalysts, and chemical looping epoxidation processes, are presented. It also discusses developments in reaction kinetics, including catalyst surface optimization and the use of dopants. The article also outlines catalyst deactivation challenges, cost, and scalability and describes future research directions on renewable feedstocks, reducing energy consumption and most importantly environmental impact. These innovations are oriented toward a more sustainable and economical route for large-scale manufacturing of ethylene oxide. Full article

With the acceleration of urbanization, the disposal of dewatered sewage sludge (DSS) has become an urgent environmental issue worldwide. Hydrothermal conversion (HC) of DSS is an important method for sludge sustainable utilization due to its combination of efficiency and economic and environmental advantages. This study investigates the product distribution and composition of products during the HC of DSS under subcritical and supercritical water conditions (200–450 °C, 5–90 min), with a particular focus on the formation and conversion mechanisms of steroid compounds. The results indicate that increasing temperature and reaction time leads to a rise in gas-phase products (GPs) and a corresponding decline in solid-phase products (SPs), with phenolic compounds identified as the predominant constituents. In the water-soluble products (WSPs), nitrogen-containing cyclic compounds are the major products. Saturated nitrogen heterocycles dominate at lower temperatures (200 °C), while at elevated temperatures (300–350 °C), saturated azapolycyclic compounds emerge, ultimately transitioning into unsaturated aromatic nitrogen heterocycles at 450 °C. Steroids are primarily concentrated in the oil-phase products (OPs). The conversion process involves the initial conversion of lipids in the DSS to long-chain olefins at 200 °C, which are then converted to steroids at 250–350 °C. At higher temperatures (400–450 °C), these steroids might decompose into gaseous products or undergo polymerization to form char. This suggests the potential for steroids to act as precursor compounds in the process of char formation. This work could contribute to a deeper understanding of the HC mechanism of DSS and provide valuable technical insights for improving bio-oil quality. Full article

A computational model that can accurately describe the thermodynamics of a hydrocarbon system and its properties under various conditions is a prerequisite for running reservoir and pipeline simulations. Cubic Equations of State (EoS) are mathematical tools used to model the phase and volumetric behavior of reservoir fluids when compositional effects need to be considered. To anticipate uncertainty and enhance the quality of their predictions, EoS models must be adjusted to adequately match the available lab-measured PVT values. This task is challenging given that there are many potential tuning parameters, thus leading to various tuning results of questionable validity. In this paper, we present an automated EoS tuning workflow that employs a Generalized Pattern Search (GPS) optimizer for efficient tuning of a cubic EoS model. Specifically, we focus on the Peng–Robinson (PR) model, which is the oil and gas industry standard, to accurately capture the behavior of diverse multicomponent, complex hydrocarbon mixtures encountered in subsurface reservoirs. This approach surpasses the limitations of conventional gradient-based (GB) methods, which are susceptible to getting trapped in local optima. The proposed technique also allows physical constraints to be imposed on the optimization procedure. A gas condensate and an H₂S-rich oil were used to demonstrate the effectiveness of the GPS algorithm in finding an optimized solution for high-dimensional search spaces, and its superiority over conventional gradient-based optimization was confirmed by automatically tracking globally optimal and physically sound solutions. Full article

Anthropogenic activities and industrialization render continuous human exposure to semi-volatile organic compounds (SVOCs) inevitable. Occupational monitoring and safety implementations consider the inhalation exposure of SVOCs as critically relevant. Due to the inherent properties of SVOCs as gas/particle mixtures, risk assessment strategies should consider particle size-segregated SVOC association and the relevance of released gas phase fractions. We constructed an in vitro air–liquid interface (ALI) exposure system to study the distinct toxic effects of the gas and particle phases of the model SVOC dibutyl phthalate (DBP) in A549 human lung epithelial cells. Cytotoxicity was evaluated and genotoxic effects were measured by the alkaline and enzyme versions of the comet assay. Deposited doses were assessed by model calculations and chemical analysis using liquid chromatography tandem mass spectrometry. The novel ALI exposure system was successfully implemented and revealed the distinct genotoxic effects of the gas and particle phases of DBP. The empirical measurements of cellular deposition and the model calculations of the DBP particle phase were concordant.The model SVOC DBP showed that inferred oxidative DNA damage may be attributed to particle-related effects. While pure gas phase exposure may follow a distinct mechanism of genotoxicity, the contribution of the gas phase to total aerosol was comparably low. Full article

The main objective of this research was to evaluate the development of volatile organic compounds (VOCs) and the accumulation of biogenic amines (BAs) in relation to the dynamic of microbial population composition in fresh and ripened cheese produced from raw milk of ewes fed a diet containing grape pomace (GP+) and fed a standard diet (Ctrl). Genomic DNA was extracted from the cheeses at 2 (T2), 60 (T60), 90 (T90) and 120 (T120) days of ripening and prepared for 16S rRNA-gene sequencing to characterize the cheese microbiota; furthermore, VOCs were determined via solid-phase microextraction combined with gas chromatography-mass spectrometry and biogenic amines by HPLC analyses. Diet did not affect the relative abundance of the main phyla identified, Proteobacteria characterized T2 samples, but the scenario changed during the ripening. At genus level, Pseudomonas, Chryseobacterium and Acinetobacter were the dominant taxa, however, a lower percentage of Pseudomonas was detected in GP+ cheeses. Enterococcus became dominant in ripened cheeses followed in Ctrl cheeses by Lactobacillus and in GP+ cheeses by Lactococcus. The diet affected the development of carboxylic acids and ketones but not of aldehydes. Low levels of esters were identified in all the samples. In total, four biogenic amines were determined in cheeses samples and their levels differed between the two groups and during ripening time. In 60, T90 and T120 GP+ cheeses, a lower amount of 2-phenylethylamine was found compared to Ctrl. Putrescine was detected only in GP+ samples and reached the highest level at 120 days. Conversely, the amount of cadaverine in GP+ samples was invariable during the ripening. The concentration of tyramine in GP+ samples was compared to Ctrl during the ripening. Overall, significant positive correlations between some families of bacteria and the formation of VOCs and BAs were found. Full article

We study quantum double dark-solitons, which give pairs of notches in the density profiles, by constructing corresponding quantum states in the Lieb–Liniger model for the one-dimensional Bose gas. Here, we expect that the Gross–Pitaevskii (GP) equation should play a central role in the long distance mean-field behavior of the 1D Bose gas. We first introduce novel quantum states of a single dark soliton with a nonzero winding number. We show them by exactly evaluating not only the density profile but also the profiles of the square amplitude and phase of the matrix element of the field operator between the N-particle and $(N-1)$-particle states. For elliptic double dark-solitons, the density and phase profiles of the corresponding states almost perfectly agree with those of the classical solutions, respectively, in the weak coupling regime. We then show that the scheme of the mean-field product state is quite effective for the quantum states of double dark solitons. Assigning the ideal Gaussian weights to a sum of the excited states with two particle-hole excitations, we obtain double dark-solitons of distinct narrow notches with different depths. We suggest that the mean-field product state should be well approximated by the ideal Gaussian weighted sum of the low excited states with a pair of particle-hole excitations. The results of double dark-solitons should be fundamental and useful for constructing quantum multiple dark-solitons. Full article

Silicon nitride–zirconia–graphene composites with high graphene content (5 wt.% and 30 wt.%) were sintered by gas pressure sintering (GPS). The effect of the multilayer graphene (MLG) content on microstructure and fracture mechanism is investigated by multi-scale and in-situ microscopy. Multi-scale microscopy confirms that the phases disperse evenly in the microstructure without obvious agglomeration. The MLG flakes well dispersed between ceramic matrix grains slow down the phase transformation from α to β-Si₃N₄, subsequent needle-like growth of β-Si₃N₄ rods and the densification due to the reduction in sintering additives particularly in the case with 30 wt.% MLG. The size distribution of Si₃N₄ phase shifts towards a larger size range with the increase in graphene content from 5 to 30 wt.%, while a higher graphene content (30 wt.%) hinders the growth of the ZrO₂ phase. The composite with 30 wt.% MLG has a porosity of 47%, the one with 5 wt.% exhibits a porosity of approximately 30%. Both Si₃N₄/MLG composites show potential resistance to contact or indentation damage. Crack initiation and propagation, densification of the porous microstructure, and shift of ceramic phases are observed using in-situ transmission electron microscopy. The crack propagates through the ceramic/MLG interface and through both the ceramic and the non-ceramic components in the composite with low graphene content. However, the crack prefers to bypass ceramic phases in the composite with 30 wt.% MLG. Full article

The Si₃N₄ ceramics were prepared in this study by gas pressure sintering (GPS) and spark plasma sintering (SPS) techniques, using 5 wt.% Yb₂O₃–2 wt.% Al₂O₃ and 5 wt.% CeO₂–2 wt.% Al₂O₃ as sintering additives. Based on the difference in sintering methods and sintering additive systems, the relative density, phase composition, phase transition rate, microstructure, mechanical properties, and thermal conductivity were comparatively investigated and analyzed. SPS proved to be more efficient than GPS, producing higher relative density, bending strength, hardness, and thermal conductivity of Si₃N₄ ceramic with both additive systems; however, the phase transition rate and fracture toughness were lower. Similarly, higher bending strength, hardness, and thermal conductivity were achieved with Yb₂O₃–Al₂O₃ than CeO₂–Al₂O₃ in the case of GPS and SPS, and only the relative density, fracture toughness, and phase transition rate were lower. Full article