Search Results (110)

Feedstock quality has been proven to be the single variable that most affects fluid catalytic cracking (FCC) unit performance, but catalyst characteristics have also been reported in the literature to have a considerable effect on cracking process performance. How these two main variables of the FCC process complement each other in the search for ways to optimize the performance of the FCC unit is the subject of current research. Twenty-one feedstocks with K_W-characterizing factors ranging from 11.08 to 12.06, Conradson carbon contents ranging from 0.05 to 12.8 wt.%, and nitrogen contents ranging from 800 to 3590 ppm (wt/wt) (basic nitrogen from 172 to 1125 ppm (wt/wt)) were cracked on 21 catalysts with micro-activity between 67% and 76% (wt/wt) in a laboratory-based advanced catalytic evaluation (ACE) unit at a reaction temperature of 527 °C, catalyst–to-oil ratios between 3.5 and 12.0 wt/wt, and a catalyst time on stream of 30 s. Some of the feeds and catalysts tested in the laboratory FCC ACE unit were also examined in a commercial short-contact-time FCC unit resembling a UOP side-by-side design. It was found that conversion can be very well predicted in both the laboratory ACE and the commercial FCC units using multiple linear correlations developed in this work from information about the following feed properties: K_W-characterizing factor, nitrogen content, and micro-activity of the catalyst. The coke on the catalyst that controls the catalyst-to-oil ratio and the regenerator temperature in the commercial FCC unit could be calculated using the correlations developed in this work for the laboratory ACE and commercial FCC units, based on feed characteristics and catalyst micro-activity. Due to the greater slope of the Δ coke/Δ micro-activity dependence observed in the ACE FCC unit, the more active catalysts show weaker results compared to the less active catalysts at a constant coke yield. In contrast, catalysts with higher activity are preferable for operation in the commercial FCC plant because they provide higher conversion at the same coke yield due to the lower slope of the Δ coke/Δ micro-activity relationship. Full article

Ferrocenium catalysis is a growing field of research. This study investigates the catalytic activity of different ferrocenium salts in propargylic substitution reactions to afford propargylic ethers. Four different ferrocenium catalysts were employed in the title reaction, which was monitored over time. The rate of the disappearance of the starting material can be fitted to a first order rate law and observed rate constants were determined. The catalyzed propargylic substitution reactions display a moderate but discernible dependence on the ferrocenium counterion. The lack of an induction period for the reaction indicates that the ferrocenium cation itself is catalytically active, and not just a decomposition product thereof, which would result in an induction period. The presence of a carboxylic acid substituent on one of the cyclopentadienyl rings enhances catalytic activity. The Meyer–Schuster rearrangement of the propargylic alcohol to the corresponding conjugated enone played only a minor role in the ferrocenium-catalyzed reactions. Catalyst decomposition moderately retards the reaction but does not suppress product formation, as demonstrated by experiments with aged FcBF₄. In contrast, the presence of TEMPO as a radical scavenger completely inhibits product formation, while not causing detectable catalyst decomposition at room temperature. In turn, FeCl₃ catalyzes both the propargylic substitution and the Meyer–Schuster rearrangement equally and decomposes the catalysis product over time. These findings reinforce the notion that strong Lewis acids readily promote the rearrangement of propargylic alcohols and that Lewis acidity plays a crucial role in finding a balance between the substitution reactions of propargylic alcohols and their rearrangement to unsaturated aldehydes. Full article

We here present a novel and sensitive methodology for determining the melting point (MP) of Bovine Serum Albumin (BSA) from micromolar to picomolar concentration levels under label-free conditions. At 1 pM we could model the melting with a sharp Gaussian. However, from the transient state observed during the melting process by using a simple exponential decay model, we determined a time constant of 67 s. We applied this methodology by studying a 3.3 pM sample of a botulinum toxin A (BoNT-A) (stabilized with 2.8 nanomolar denatured Human Serum Albumin (HSA)). We were able to determine the Tm of BoNT-A in the presence of approximately 1000-fold more concentrated HSA. This method enables the detection of protein melting transitions at picomolar concentrations without the use of a fluorescence dye. Its sensitivity and simplicity make it a valuable analytical tool for studying protein stability in diluted pharmaceutical formulations. This method is useful for correlating thermal conformational changes with catalytic function. Full article

This work investigates the coordination compound [Zn(2,2-bpy)₃](BF₄)₂ as a catalyst for the molecular reduction of CO₂. The synthesis and characterization of the complex are reported, along with electrochemical studies conducted both in the presence and absence of CO₂. In the absence of CO₂, reduction of the 2,2′-bipyridine ligands was observed (Epa(I) = −1.84 V vs. Fc/Fc⁺ and Epa(II) = −2.18 V vs. Fc/Fc⁺). In contrast, under a CO₂ atmosphere, catalytic molecular activity toward CO₂ reduction was detected (Epk(I) = −1.90 V vs. Fc/Fc⁺ and Epk(II) = −2.18 V vs. Fc/Fc⁺). Foot of the wave analysis (FOWA) was employed to determine the catalytic rate constant (k = 1.352 × 10³ M⁻¹ s⁻¹) for CO₂ reduction. Spectroelectrochemical experiments were also carried out in both the presence and absence of CO₂. Density functional theory (DFT) calculations were conducted to understand the interaction of the complex with CO₂. Bulk electrolysis and FTIR analysis suggest that oxalate is the product of the CO₂ reduction. Full article

In the polyurethane industry, catalytically generated carbodiimides can modify the properties of isocyanate and, thus, the resulting foams. In this work, a kinetic reaction study was carried out to investigate the formation of a simple, bifunctional carbodiimide from a widely used polyurethane raw material: 4,4′-methylenediphenyl diisocyanate (MDI). The experimental section outlines a catalytic process, using a 3-methyl-1-phenyl-2-phospholene-1-oxide (MPPO) catalyst in ortho-dichlorobenzene (ODCB) solvent, to model industrial circumstances. The reaction produces carbon dioxide, which was observed using gas volumetry at between 50 and 80 °C to obtain kinetic data. A detailed regression analysis with linear and novel nonlinear fits showed that the initial stage of the reaction is second-order, and the temperature dependence of the rate constant is $k(T)=(3.4\pm 3.8)\mathrm{‧}{10}^6\cdot e^{{\displaystyle \frac{-7192\pm 389}{T}}}$. However, the other isocyanate group of MDI reacts with new isocyanate groups and the reaction deviates from the second-order due to oligomer (polycarbodiimide) formation and other side reactions. A linearized Arrhenius equation was used to determine the activation energy of the reaction, which was E_a = 60.4 ± 3.0 kJ mol⁻¹ at the applied temperature range, differing by only 4.6 kJ mol⁻¹ from a monoisocyanate-based carbodiimide. In addition to experimental results, computationally derived thermochemical data (from simplified DFT and IRC calculations) were applied in transition state theory (TST) for a comprehensive prediction of rate constants and Arrhenius parameters. As a result, it was found that the activation energy of the carbodiimide bond formation reaction from theoretical and experimental results was independent of the number and position of isocyanate groups, which is consistent with the principle of equal reactivity of functional groups. Full article

It has been proven that the performance of fluid catalytic cracking (FCC), as the most important oil refining process for converting low-value heavy oils into high-value transportation fuels, light olefins, and feedstocks for petrochemicals, depends strongly on the quality of the feedstock. For this reason, characterization of feedstocks and their relationships to FCC performance are issues deserving special attention. This study systematically reviews various publications dealing with the influence of feedstock characteristics on FCC performance, with the aim of identifying the best characteristic descriptors allowing prediction of FCC feedstock cracking capability. These characteristics were obtained by mass spectrometry, SARA analysis, elemental analysis, and various empirical methods. This study also reviews published research dedicated to the catalytic cracking of biomass and waste oils, as well as blends of petroleum-derived feedstocks with sustainable oils, with the aim of searching for quantitative relationships allowing prediction of FCC performance during co-processing. Correlation analysis of the various FCC feed characteristics was carried out, and regression techniques were used to develop correlations predicting the conversion at maximum gasoline yield and that obtained under constant operating conditions. Artificial neural network (ANN) analysis and nonlinear regression techniques were applied to predict FCC conversion from feed characteristics at maximum gasoline yield, with the aim of distinguishing which technique provided the more accurate model. It was found that the correlation developed in this work based on the empirically determined aromatic carbon content according to the n-d-M method and the hydrogen content calculated via the Dhulesia correlation demonstrated highly accurate calculation of conversion at maximum gasoline yield (standard error of 1.3%) compared with that based on the gasoline precursor content determined by mass spectrometry (standard error of 1.5%). Using other data from 88 FCC feedstocks characterized by hydrogen content, saturates, aromatics, and polars contents to develop the ANN model and the nonlinear regression model, it was found that the ANN model demonstrated more accurate prediction of conversion at maximum gasoline yield, with a standard error of 1.4% versus 2.3% for the nonlinear regression model. During the co-processing of petroleum-derived feedstocks with sustainable oils, it was observed that FCC conversion and yields may obey the linear mixing rule or synergism, leading to higher yields of desirable products than those calculated according to the linear mixing rule. The exact reason for this observation has not yet been thoroughly investigated. Full article

5-Hydroxymethylfurfural (HMF) is a versatile platform molecule with the potential to replace many fossil fuel derivatives. It can be obtained through the dehydration of carbohydrates. In this study, we present a simple and cost-effective microwave-assisted method for producing HMF. This method involves the use of readily available sucrose as a substrate and glucose-derived bifunctional hydrochars as carbocatalysts. These catalysts were produced via hydrothermal carbonisation using thiourea and urea as nitrogen and sulphur sources, respectively, to introduce Brønsted acidic and basic sites into the materials. Using a microwave reactor, we found that the S, N-doped hydrochars were active in sucrose dehydration in water. Catalytic results showed that HMF yield depended on the balance between acidic and basic sites as well as the types of S and N species present on the surfaces of these hydrochars. The best-performing catalyst achieved an encouraging HMF yield of 37%. The potential of N, S-co-doped biochar as a green solid catalyst for various biorefinery processes was demonstrated. A simple kinetic model was developed to elucidate the kinetics of the main reaction pathways of this cascade process, showing a very good fit with the experimental results. The calculated rate constants revealed that reactions with a 5% sucrose loading exhibited significantly higher fructose dehydration rates and produced fewer side products than reactions using a more diluted substrate. No isomerisation of glucose into fructose was observed in an air atmosphere. On the contrary, a limited rate of isomerisation of glucose into fructose was recorded in an oxygen atmosphere. Therefore, efforts should focus on achieving a high glucose-to-fructose isomerisation rate (an intermediate reaction step) to improve HMF selectivity by reducing humin formation. Full article

Environmental contamination from industrial dyes, particularly Methylene Blue (MB), presents a growing challenge due to their toxicity and persistence in aquatic systems. This study explored the catalytic potential of cellulose acetate-stabilized nickel (CA/Ni) nanoparticles for the degradation of MB in aqueous solutions. CA/Ni was synthesized and characterized using FTIR and SEM, confirming its successful incorporation into the cellulose acetate matrix and uniform distribution across the membrane. UV-Vis spectrophotometry was employed to monitor the catalytic degradation of MB, revealing a significant decrease in absorbance at 665 nm over 28 min, indicating 68% degradation efficiency. Kinetic analysis showed that the degradation followed pseudo-first-order kinetics, with an apparent rate constant of 0.0348 min⁻¹ and an R² value of 0.9851, confirming excellent catalytic performance. The effects of temperature and pH on MB degradation were investigated, with the highest efficiency observed at 35 °C and a pH of 7. A room temperature (25 °C) and acidic conditions (pH 5) reduced the degradation rate to 52%. In comparison, a higher temperature (45 °C) and an alkaline pH (pH 9) resulted in a slight decline to 55%, likely due to changes in catalyst efficiency and MB solubility. These findings highlight the potential of Ni NP-stabilized membranes for wastewater treatment applications, providing a scalable and efficient approach to dye removal. Full article

The residue conversion processes, coking, visbreaking, and fluid catalytic cracking (FCC), have demonstrated that feedstock quality is the single factor that most affects process performance. While, for the FCC, it is known that the heavy oil conversion at a maximum gasoline yield point can vary between 50 and 85 wt. %, for the vacuum residue hydrocracking, no reports have appeared yet to reveal the dependence of conversion on the quality of vacuum residue being hydrocracked. In order to search for such a dependence, eight vacuum residues derived from medium, heavy, and extra heavy crude oils have been hydrocracked in a laboratory unit at different reaction temperatures. The current study has witnessed that the vacuum residue hydrocracking obeys the same rule as that of the other residue conversion processes, confirming that the feedstock quality has a great influence on the process performance. A conversion variation between 45 and 85 wt. % can be observed when the sediment content in the hydrocracked atmospheric residue is within the acceptable limit, guaranteeing the planned cycle length. An intercriteria analysis was performed, and it revealed that the vacuum residue conversion has negative consonances with the contents of nitrogen and metals. Correlations were developed which predict the conversion at constant operating conditions within the uncertainty of conversion measurement of 1.7 wt. % and correlation coefficient of 0.964. The conversion at constant hydrocracked atmospheric residue (HCAR) sediment content was predicted with a correlation coefficient of 0.985. The correlations developed in this work disclosed that the higher the contents of metals, nitrogen, and asphaltenes, and the lower the content of sulfur, the lower the conversion in the hydrocracking process is. It was also shown that vacuum residues, which have the same reactivity (the same conversion at identical operating conditions), can indicate significant difference in the conversion at the same HCAR sediment content due to their diverse propensity to form sediments in the process of hydrocracking. Full article

The presence of paracetamol (PCT) in aquatic environments has raised environmental concerns due to its incomplete removal in conventional wastewater treatment plants. This study evaluates the degradation kinetics of PCT using an ozonation system enhanced with blast furnace slags (BFSs) as a heterogeneous catalyst under acidic (pH 3), neutral (pH 7), and basic (pH 10) conditions. Experimental results show that a simple ozonation process achieves up to 85% PCT removal within 30 min, with the highest rates being observed at pH 10. The addition of BFSs increases the reaction rate constants by 20–30% across all pH levels, attributed to the catalytic activity of metallic oxides in BFSs, which promote radical-based degradation pathways. Biochemical oxygen demand (BOD5) and HPLC analyses confirm a significant reduction in PCT and its byproducts, while ozone consumption is optimized in the catalytic system. A hybrid kinetic modeling approach, integrating pseudo-first-order kinetics and a long short-term memory (LSTM) neural network, was developed and validated, demonstrating superior predictive accuracy (R² > 0.98) for PCT degradation dynamics compared with traditional models. Full article

The selective chlorination of ethane to 1,2-dichloroethane offers a promising route for upgrading ethane, yet its efficiency remains constrained by limited mechanistic insights into gas-phase chlorine-radical-mediated pathways, which govern target product selectivity and competing dehydrochlorination side reactions. This work systematically decouples the kinetics of ethane chlorination and chloroethane functionalization under varying Cl₂ concentrations, revealing that chlorine radicals govern product distribution through thermodynamically favored pathways. This results in an interesting phenomenon whereby the product ratio between 1,1-C₂H₄Cl₂ and 1,2-C₂H₄Cl₂ maintains a constant 2:1 stoichiometry regardless of Cl₂ concentration variation. A critical observation is that the rate of all chlorination steps remains independent of alkane concentrations, highlighting the dominant role of chlorine radicals in rate-determining steps. Furthermore, ethylene byproducts are demonstrated to originate from the dechlorination of chlorine-radical-induced 2-chloroethyl radicals derived from chloroethane, rather than the direct dehydrochlorination of chloroethane itself. These insights into the dual role of chlorine radicals—mediating both the chlorination and dehydrochlorination pathways—establish a foundational framework for integrating gas-phase radical chemistry with catalytic engineering strategies to suppress undesired side reactions and enable scalable, selective ethane chlorination. Full article

The research literature presents divergent opinions regarding the role of dissipation in living systems, with views ranging from it being useless to it being essential for driving life. The implications of universal thermodynamic evolution are often overlooked or considered controversial. A higher rate of entropy production indicates faster thermodynamic evolution. We calculated enzyme-associated dissipation under steady-state conditions using minimalistic models of enzyme kinetics when all microscopic rate constants are known. We found that dissipation is roughly proportional to the turnover number, and a log-log power-law relationship exists between dissipation and the catalytic efficiency of enzymes. “Perfect” specialized enzymes exhibit the highest dissipation levels and represent the pinnacle of biological evolution. The examples that we analyzed suggested two key points: (a) more evolved enzymes excel in free-energy dissipation, and (b) the proposed evolutionary trajectory from generalist to specialized enzymes should involve increased dissipation for the latter. Introducing stochastic noise in the kinetics of individual enzymes may lead to optimal performance parameters that exceed the observed values. Our findings indicate that biological evolution has opened new channels for dissipation through specialized enzymes. We also discuss the implications of our results concerning scaling laws and the seamless coupling between thermodynamic and biological evolution in living systems immersed in out-of-equilibrium environments. Full article

This study investigates the impact of nickel doping on the thermal and combustion properties of ammonium perchlorate/carboxymethyl cellulose (AP/CMC) composites. Through comprehensive SEM-EDS, FTIR, XRD, DSC, TGA, and burning rate analyses, significant improvements in the structural and functional characteristics of the AP/CMC-Ni composite were observed compared to those of pure AP and AP/CMC composites. The SEM-EDS analysis revealed that nickel incorporation resulted in thicker and more irregular CMC fibers, indicating substantial morphological changes. The FTIR spectroscopy showed shifts in the O-H and C=O stretching bands, pointing to interactions between nickel ions and CMC functional groups. The XRD patterns highlighted a decrease in crystallinity and the presence of NiO phases, confirming the successful integration of nickel into the CMC matrix. The thermal analysis demonstrated that nickel doping significantly lowered the decomposition temperature of the AP/CMC composite, as evidenced by DSC, and enhances the thermal degradation process, as shown by TGA. The AP/CMC-Ni composite exhibited a higher burning rate across all of the tested pressures, highlighting the catalytic effect of nickel in improving the combustion efficiency. The burning rate for AP/CMC follows the power-law expression with constants a = 2.34 and n = 0.499, while for AP/CMC-Ni, the constants are a = 3.35 and n = 0.475. This study highlights the essential role of nickel doping in facilitating the decomposition of AP within the AP/CMC composite. By lowering the decomposition temperature, nickel enhances the overall combustion process, making the AP/CMC-Ni composite more efficient for applications requiring controlled thermal decomposition. These findings provide valuable insights for the design and development of high-performance composite materials in advanced industrial applications. Full article

This study explores the purification, characterization, and application of laccases from Trametes hirsuta CS5 for degrading synthetic dyes as models of emerging contaminants. Purification involved ion exchange chromatography, molecular exclusion, and chromatofocusing, identifying th ree laccase isoforms: ThIa, ThIb, and ThII. Characterization included determining pH and temperature stability, kinetic parameters (K_m, K_cat), and inhibition constants (K_i) for inhibitors like NaN₃, SDS, TGA, EDTA, and DMSO, using 2,6-DMP and guaiacol as substrates. ThII exhibited the highest catalytic efficiency, with the lowest K_m and highest K_cat. Optimal activity was observed at pH 3.5 and 55 °C. Decolorization tests with nine dyes showed that ThII and ThIa were particularly effective against Acid Red 44, Orange II, Indigo Blue, Brilliant Blue R, and Remazol Brilliant Blue R. ThIb displayed higher activity towards Crystal Violet and Acid Green 27. Among substrates, guaiacol showed the highest K_cat, while 2,6-DMP was preferred overall. Inhibitor studies revealed NaN₃ as the most potent inhibitor. These results demonstrate the significant potential of T. hirsuta CS5 laccases, especially ThIa and ThII, as biocatalysts for degrading synthetic dyes and other xenobiotics. Their efficiency and stability under acidic and moderate temperature conditions position them as promising tools for sustainable wastewater treatment and environmental remediation. Full article

In this article, we investigate the encapsulation of K₂[Ni(maleonitriledithiolate)₂] (1) within a host molecule, β-cyclodextrin (β-CD), via single-crystal X-ray analysis. An inclusion complex, K₂{[Ni(maleonitriledithiolate)₂]@(β-CD)₂} (2), was constructed from 1 and two β-CDs. The anion guest Ni complex included a host cavity, constructed using two β-CDs, and the Ni atom of the anion was located between the two hydrophilic primary rims. Ultraviolet-visible absorption spectroscopy revealed that inclusion complex 2 exhibited a 2:1 (host:guest) stoichiometry in the solution, which is consistent with the result obtained from X-ray crystallography. The association of the host and guest occurred in two steps, and the association constants for the first and second steps were 1.1(7) × 10⁴ and 1.8(5) × 10⁴ mol⁻¹ dm³, respectively. The catalytic behavior of 1 and 2 was investigated for electrochemical hydrogen production in the aqueous solution of an acetate buffer (pH = 4.72). During the catalytic reaction, inclusion complex 2 was observed to have a better catalytic reaction rate than 1. The study findings provide insights into the effects of the encapsulation of guest molecules within host structures. Full article