Decrease In Reaction Rate Research Articles

Oxidation mechanism of sulfur-containing compounds and antioxidant depletion dynamics: Insights into interactions

Sulfur-containing compounds (SCCs) are the most abundant heteroatomic organic species (HOS) in petroleum fuels. This study investigates the dynamics of SCCs in surrogate fuel systems, focusing on their oxidation stability, reactivity, and interactions. An analysis of eleven selected SCCs, spanning both reactive (thiols, sulfides, and disulfides) and nonreactive (thiophenes and benzothiazole) species, was conducted at 140 °C. The investigation delves into reaction and degradation mechanisms, exploring resulting products, binary mixtures of reactive SCCs for potential interactions, and multicomponent SCC systems to understand nuanced interaction. Findings reveal unique reaction pathways in single-component SCCs, synergetic and antagonistic effects in binary mixtures, and substantial decreases in reaction rates in all multicomponent systems. Moreover, SCCs expedited antioxidant consumption, highlighting their pivotal role in fuel stability and degradation. The study contributes valuable insights into SCC dynamics, advocating further exploration of HOS’s interactions for enhanced fuel formulation and stability testing strategies.

An experimental study of fire development under varying ventilation conditions during the depressurization process in pressurized buildings

Hermetic pressurized buildings are a new type of building in high-altitude areas that efficiently addresses issues such as high-altitude reactions. The indoor pressure is higher than the external pressure under working conditions, and pressure relief must be carried out first during emergencies. The emergency pressure relief process during a fire may lead to complex fire behavior that is different from that in regular buildings. In this study, we focus on the impact of ventilation conditions and the status of doors in such buildings on fire evolution and smoke plume characteristics through experiments. The temperature variation in the fire room and corridor is measured under different ventilation power, ventilation time, and door opening width conditions. This shows that the width of the door has the greatest impact on fire development. A smaller gap in the door opening restricts air circulation between the interior and exterior of the room, resulting in a rapid decrease in the oxygen concentration within the fire room and a decrease in the combustion reaction rate of wood fires. The ventilation power exerts the most significant influence on the temperature variation in the corridor. These findings provide empirical data and a basis for fire science studies in high-altitude hermetic pressurized buildings and can guide existing fire protection design and management for improved safety.

Modifying the second coordination spheres of Fe active sites for electrocatalytic nitric oxide reduction in realistic electrochemical environment

The first and second coordination spheres in the coordination microenvironment may regulate the electronic structure of single-metal atoms supported on carbon matrix, which in turn modulates the catalyst’s catalytic activity. Simulating the kinetic process of electrocatalytic nitric oxide reduction reaction (NORR) by the theoretical modeling of electrochemical microenvironments helps understand the theoretical structure–activity relationship and guides a more rational design of electrocatalysts. In this study, density functional theory calculations combined with a constant-potential/hybrid-solvent model and microkinetic modeling are employed to study NORR mechanism on the carbon-based FeN4, FeN4-O and FeN4-B catalysts with different electronegativity atoms in the second coordination spheres under −1.00 ∼ 0.40 V vs. RHE. The free energy changes of all elementary reactions for NORR on the catalysts reveal that the optimal pathways for NORR on FeN4 produce both ammonia and hydroxylamine, proceeding through the reaction intermediates *NHOH. Within −1.00 ∼ -0.37 V vs. RHE, the kinetic barriers of the rate-determining steps for NORR increase sequentially on FeN4, FeN4-O, and FeN4-B, corresponding to the sequentially decreasing reaction rate constants. At −6.00 mA∙cm−2, the electrode potential for ammonia production on FeN4 catalyst is the lowest among the catalysts at −0.70 V vs. RHE, indicating it has higher electrocatalytic activity.

Numerical investigation on the hydrogen removal capability of various catalytic elements in PARs

As an essential part of hydrogen removal system in nuclear power plants, PARs could effectively eliminate released hydrogen and prevent potential hydrogen combustion during severe accidents. Serving as a basic composition in the catalytic section of PARs, catalytic element has a direct influence on the hydrogen removal capability of the PAR device. The CFD software STAR-CCM+ was utilized to develop models of catalytic channels containing three common catalytic elements (including catalytic plates, catalytic cylinders, and catalytic spheres). The elementary reaction mechanism was employed as the reaction kinetics model to define the chemical reaction process. This paper aims to evaluate the hydrogen removal capability of the catalytic elements in same operating conditions and analyze important factors for designing the structure of catalytic elements. All the catalytic surface area of catalytic elements was set to 0.045 m2 and inlet boundary conditions were settled identically. Our findings show that catalytic sphere exhibits the best hydrogen removal capability, which is attributed to the large lower half catalytic surface area of spheres. Catalytic plate with a lower height also demonstrates excellent hydrogen removal capability because of the presence of a larger catalytic area in the leading section. However, the hydrogen removal capability of catalytic cylinder is affected by the boundary layer separation vortex. A noticeable decrease in reaction rate occurs on the lower part of the sidewall surface, especially in the catalytic cylinder with a larger radius. In the structure design of catalytic elements, enlarging the catalytic surface area in the leading section and avoiding boundary layer separation on the catalytic surface are essential to further improve the hydrogen removal capability.

Differential effects of Fe, Ti and Fe + Ti addition on the discontinuous precipitation and properties of cu-Ni-Sn alloys

Controlling discontinuous precipitation is crucial for improving the microstructure and mechanical properties of Cu-Ni-Sn alloys. Through the utilization of various characterization techniques such as transmission electron microscopy, scanning electron microscopy, optical microscopy, and mechanical testing, we have successfully demonstrated that the introduction of either Ti or a combination of Fe and Ti elements effectively inhibits the formation of discontinuous precipitation. Notably, the combined addition of Fe and Ti elements showcases superior suppression of the discontinuous precipitation structure. Consequently, we have developed a novel alloy, namely Cu-15Ni-7.5Sn-0.5Fe-0.5Ti, which exhibits remarkable resistance to over-aging. Our analysis indicates that the mechanism of inhibiting discontinuous precipitation is multifaceted. The main effect is believed to be the reduction in nucleation sites and the pinning effect of the D024-Ni3Ti phase on grain boundaries, resulting in a significant decrease in the nucleation rate and growth of the DP reaction. The secondary impact may be due to the distribution of D024-Ni3Ti phase at grain boundaries, which leads to a decrease in grain boundary energy. Meanwhile, the formation of D019-Ni3Sn phase reduces the chemical driving force required for DP growth.

Catalytic reduction of U(Ⅵ) to U(Ⅳ) using hydrogen as the sole reducing agent

Using hydrogen gas as a sole reducing agent to catalyze the reduction of hexavalent uranium to prepare tetravalent uranium can avoid the problem of pollutant poisoning catalysts caused by hydrazine reducing agents. However, research using only hydrogen as the sole reducing agent is very scarce. Herein, catalyst has been developed for catalytic hydrogen reduction to prepare uranium(Ⅳ) and a systematic study of the influence of process parameters such as catalyst carrier particle size, temperature, pressure, and acidity on the catalytic hydrogen reduction process for the preparation of uranium(Ⅳ) is presented. The effect of catalyst carrier particle size is particularly pronounced due to the differing rates of molecular diffusion. Fine particle-sized catalyst carriers exhibit faster catalytic reaction kinetics. Temperature exhibits an unusual phenomenon in its impact on the reaction process. As temperature increases, the reaction rate decreases, and an upper limit reaction temperature is observed. Furthermore, at excessively high reaction temperatures, an anomalous occurrence of uranium(Ⅳ) formation followed by disappearance was observed. Through an analysis of the reaction mechanism, the underlying reasons for this abnormal phenomenon are elucidated. Additionally, this paper also reveals that reaction rates increase with increasing reaction pressure and decrease with decreasing raw material acidity. Process parameters such as reaction temperature, pressure, and acidity exhibit coupled effects on the reaction process. Different reaction upper limit temperatures are observed under varying pressures and raw material acidities.

Physicochemical and kinetic properties of collagenase, native and adsorbed on chitosan

One of the modern research areas in biotechnology and medicine is the development of highly stable biopreparations based on immobilized enzymes. Using the method of sorption immobilization, heterogeneous biocatalysts were obtained based on collagenase (EC 3.4.24.3) from Clostridium histolyticum and from medium molecular weight (200 kDa) and high molecular weight (350 kDa) chitosans. The goal of the work was to study the physicochemical and kinetic properties of free and immobilized collagenase from Clostridium histolyticum on a chitosan matrix. The physicochemical and kinetic properties of the enzyme were studied in soluble and immobilized states using classical biophysical and biochemical methods. It was shown that the maximum activity of native collagenase was observed at 37ºС, while in case of the enzyme immobilized on medium and high molecular weight chitosan it was observed at 40ºС. Sorption immobilization of the biocatalyst on a chitosan matrix allowed increasing its stability during incubation within the temperature range of 40-70°C. After incubation at 80 and 90°C, no significant differences in the activity of soluble and immobilized collagenase were found. When studying the dependence of the protease activity of the enzyme on the medium acidity in the pH range from 5.0 to 9.0, it was established that the maximum catalytic ability of soluble collagenase was observed at a pH value of 7.5. The biocatalyst immobilized on medium and high molecular weight chitosans was highly active at pH 6.0-7.5. The catalytic ability of the enzyme in free and in adsorbed states noticeably decreased at pH 8.0, while at pH 9.0 soluble collagenase immobilized on medium and high molecular weight chitosans was completely inactive. The maximum rate of the enzymatic reaction of native and chitosan-immobilized biocatalysts was observed at a substrate concentration of 0.04 mM. Apparent values of V´max и K´m were calculated. The immobilization of collagenase on medium and high molecular weight chitosans did not result in a decrease of the maximum reaction rate or a change in the degree of affinity of the enzyme to the substrate. Using dynamic light scattering, we confirmed that the structure of collagenase in solution was most stable at pH 7.0-8.0, as exactly in this range of [H+] values we discovered the highest content of particles corresponding to the size of native collagenase and the lowest content of its aggregates. The optimal temperature for the best stability value of collagenase (no autolysis processes and minimal particle aggregation) can be considered as being 46°C.

Experimental study on combustion stability of a gas turbine model combustor under oxygen-lean conditions

Flue gas recirculation has emerged as a promising low-NOx emission technology in advanced gas turbines, while the slower oxidation rate induced by the low oxygen content could potentially cause combustion instability. We conducted an experimental investigation in a single-nozzle swirl combustor to examine the impact of oxygen content, inlet flow rate as well as temperature on combustion instability under oxygen-lean conditions. The results show that reducing oxygen content from 23.3% to 21% leads to reduced amplitudes of pressure pulsation and exothermic pulsation, indicating improved combustion stability. However, further reduction in oxygen content to 18.6% causes a decrease in the combustion reaction rate, resulting in an increase in the amplitude of pressure pulsation. As the oxygen content drops to below 18.6%, the exothermic intensity decreases, which results in a decrease in the amplitude of pressure pulsation. Besides, under oxygen-lean conditions, increasing the inlet temperature is conducive to reducing the amplitude of pressure pulsation and enhancing combustion stability. Additionally, as the incoming flow rate increases from 7.4 to 9.9 m/s, the refined fuel atomization and improved uniformity of oil-gas mixing contributed to decreased pressure pulsation amplitude. Nonetheless, when the incoming flow rate further increases to 12 m/s, the amplitude of exothermic and pressure pulsation increases.

Polyphenol oxidase mediates (−)-epigallocatechin gallate to inhibit endogenous cathepsin activity in Apostichopus japonicus

Apostichopus japonicus (A. japonicus) has rich nutritional value and is an important economic crop. Due to its rich endogenous enzyme system, fresh A. japonicus is prone to autolysis during market circulation and storage, resulting in economic losses. In order to alleviate this phenomenon, we investigated the effect of polyphenol oxidase (PPO) mediated (−)-epigallocatechin gallate (EGCG) on the activity and structure of endogenous cathepsin series protein (CEP) from A. japonicus. Research on cathepsin activity showed that PPO mediated EGCG could significantly reduce enzyme activity, resulting in a decrease in enzymatic reaction rate. SDS-PAGE and scanning electron microscopy results showed that PPO mediates EGCG could induce CEP aggregation to form protein aggregates. Various spectral results indicated that EGCG caused changes in the structure of CEP. Meanwhile, the conjugates formed by PPO mediated EGCG had lower thermal stability. In conclusion, PPO mediated EGCG was an effective method to inhibit the endogenous enzyme activity.

A chemical kinetics theory for interpreting the non-monotonic temperature dependence of enzymatic reactions

Abstract. One notable observation of enzymatic chemical reactions is that, for a given abundance of enzymes and substrates, temperature increases cause reaction rates to first increase consistent with the Arrhenius relationship, then plateau, and finally fall off quickly to zero at high temperatures. While many mathematical functions have been used to describe this pattern, we here propose a chemical kinetics theory which successfully replicates this observation and provides insights into the processes responsible for these dynamics. The chemical kinetics theory combines the law of mass action, von Smoluchowski's diffusion-limited chemical reaction theory, and Eyring's transition state theory. This new theory reveals that the thermally reversible enzyme denaturation ensured by the ceaseless thermal motion of molecules and ions in an enzyme solution explains the plateau and subsequent decrease in chemical reaction rates with increasing temperature. The temperature-dependent affinity parameter (K) that relates enzymes and substrates through their binding also affects the shape of the emergent temperature response. We demonstrate that with an increase in substrate availability, K shifts the optimal temperature, where reaction rates plateau, towards higher values. Further, we show that the chemical kinetics theory accurately represents 12 sets of published enzyme assay data and includes the popular mechanistic model by Ratkowsky et al. (2005) as a special case. Given its good performance and solid theoretical underpinning, we believe this new theory will facilitate the construction of more mechanistic-based environmental biogeochemical models.

Synergistic impacts of radiative flow of Maxwell fluid past a rotating disk with reactive conditions: An Arrhenius model analysis

This study presents an analysis of the hydromagnetic radiative flow of a Maxwell fluid past a rotating disk around its own axis with an angular velocity Ω0 which has enormous applications in metal casting (help to optimize the solidification and cooling of molten metals), plastic molding and aerospace engineering (cooling system of aircraft engines). The flow is constrained by boundaries that induce convection and chemical reactions described by the Arrhenius model. By applying similarity transformations, the non-linear partial differential equations, which describe the flow phenomenon, are metamorphosed into the non-dimensional system of ordinary differential equations (ODEs). The obtained ODEs are then solved numerically using ‘Keller box method’, an efficient computational technique, by implementing the finite-difference approach. The influence of different parameters, namely magnetic field strength, radiation parameter, reaction rate constant, and convective heat transfer coefficient, on the flow and heat/mass transfer characteristics are investigated. The findings suggest that the higher activation energy leads to a slower rate of reaction. As the reaction rate decreases, the consumption of reactant molecules and the reduction in their concentration also slow down. The influence of the convective heat transfer coefficient is also examined in terms of its effect on the thermal and concentration boundary layers. As the stretching parameter increases, the Maxwell fluid undergoes greater deformation, leading to greater strain and a consequent slowing of the fluid's radial velocity. Heat transfer is enhanced by thermal radiation and convective condition at the surface of rotating disk. The findings of this study provide valuable insights into the industries dealing with Maxwell fluids, enabling them to enhance process efficiency, optimize resource utilization, and develop sustainable and environmentally friendly solutions.

Mechanisms controlling albite dissolution/precipitation kinetics as a function of chemical affinity: New insights from experiments in 29Si spiked solutions at 150 and 180 °C

Knowledge of the rates of dissolution of rock-forming minerals close to equilibrium and their dependence on ΔGr, the Gibbs free energy of reaction, is essential for describing the temporal and spatial evolution of many environmental and engineering processes involving solid/fluid interactions. In the present study we used the isotope-doping method to quantify albite forward and net dissolution rates. Batch experiments were performed at 150, 180 °C and pH = 9 at near equilibrium and equilibrium conditions (-25 ≤ ΔGr ≤ + 8.2 kJ/mol) in 29Si spiked solutions which were undersaturated with the secondary Al-Si solid phases likely to precipitate.The forward dissolution rates normalized to the initial BET surface area were found to decrease continuously and monotonically with increasing time and ΔGr, achieving values 1.3 to 2.4 orders of magnitude lower at chemical equilibrium than initial far from equilibrium values, with the highest rate decrease for the highest solid to fluid ratio. These rate drops were accompanied by an increase in BET specific surface areas associated with the formation of widespread dissolution features. A decrease of albite forward dissolution rate together with an increase of its BET surface area was also observed as a function of reaction time at far from equilibrium conditions (ΔGr ≤ − 65 kJ/mol). These observations are consistent with a continuous decrease with time and increasing ΔGr of albite effective surface area linked to the formation of unreactive negative crystal facets, in addition to etch pits stopping nucleating above a critical value of ΔGr. Thus, the observed decrease in albite dissolution rate as equilibrium is approached is not linked primarily to the increase in the contribution of the backward reaction but rather to the decrease of the forward reaction rate in conjunction with the decrease in the density of reactive sites at the mineral surface.The results of this study show that the characterization of the effective surface area and its evolution with reaction time and chemical affinity is crucial to deriving robust dissolution rates of well-crystallized minerals like feldspars. Dissolution experiments in 29Si spiked solutions of samples with different history and well-characterized effective surface area and surface morphology should help to better quantify the rate laws controlling silicate minerals weathering.

A kinetic study on the effect of hyperbaric storage on the development of Maillard reaction in glucose-glycine model systems

The effect of pressure (0.1, 15, 50 and 100 MPa) and temperature (43, 53, 63 °C) on the formation rate (k) of Maillard α-dicarbonyls (absorbance at 294) and melanoidins (absorbance at 420 nm), was studied during hyperbaric storage (HS) of glucose-glycine model solutions (pH 6).While increasing storage temperature increased k values according to the Arrhenius equation (Ea ~ 85 kJ mol−1), increasing pressure decreased reaction rates as predicted by the Eyring model (Va ~ 11 mL mol−1). Pressure did not affect reaction temperature sensitivity, indicating no significant mechanism changes under hyperbaric conditions. A combined model predicting the effect of concomitant changes of temperature and pressure on Maillard reaction rate was implemented and validated within and outside (20–25 °C, 20–200 MPa) its building range.Results indicate HS to limit Maillard browning in food, with possible practical applications, and the potential to develop predictive models based on temperature-accelerated HS trials. Industrial relevanceThe capability of hyperbaric storage to impair Maillard reaction rate extends the scope of this multi-tasking technology to the prevention of color alterations due to non-enzymatic browning. The latter is expected to be of industrial relevance in the case of perishable foods affected by this phenomenon, such as thermally-treated milk. In these matrices, the technology could concomitantly guarantee microbiological safety, protein functionalization, and Maillard browning impairment.

In vitro synthesis and biochemical characterization of acyl-homoserine lactone synthase and its deletion mutant.

Quorum sensing can induce density-dependent gene expressions that cause various problems. For quorum-sensing inhibition, fundamental solutions such as gene manipulation are required, and acyl-homoserine lactone synthase (AHL synthase), which synthesizes the universal quorum-sensing signal of gram-negative bacteria, can be used as a target. In this study, researchers synthesized His-tagged AHL synthase and its deletion mutant that lacks the active site and compared their biochemical characteristics. His-YpeI, the 6x His-tagged AHL synthase of Serratia fonticola, and His-ΔYpeI, its deletion mutant, were designed, and their property conservation were examined using in silico projection tools. For in vitro synthesis of enzymes, the His-YpeI CFPS template was synthesized by in vitro gene synthesis, and the His-ΔYpeI CFPS template was obtained by deletion PCR. CFPS was performed and the products were purified with the 6x His-tag. The enzymes' properties were compared using an enzymatic assay. The bioinformatic analysis confirmed the conservation of biochemical properties between 6x His-tagged and untagged enzymes, including helix-turn-helix interactions, hydropathy profiles, and tertiary structure between His-YpeI and YpeI and between His-ΔYpeI and ΔYpeI. His-YpeI and His-ΔYpeI synthesized by CFPS were found to have the expected molecular weights and demonstrated distinct differences in enzyme activity. The analyzed enzymatic constants supported a significant decrease in substrate affinity and reaction rate as a result of YpeI's enzyme active site deletion. This result showed that CFPS could be used for in vitro protein synthesis, and quorum sensing could be inhibited at the enzymatic level due to the enzyme active site's deletion mutation.

Synthesis and catalytic activity of single-site group V alkoxide complexes for the ring-opening polymerization of ε-caprolactone.

The synthesis, characterization, and ring-opening polymerization (ROP) activity of a family of niobium and tantalum alkoxide catalysts was studied. The final catalysts are made in a two-step synthesis, first by reacting the desired homoleptic metal ethoxide with a phenolketoimine ligand to form a series of synthetic intermediates, followed by reaction with catechol to produce a catalytic platform with a single ethoxide initiator. By using two separate ligands, the electronic properties of the catalyst can be tuned, and the molecular weight of the polymer can be increased. It was found that synthetic intermediates adopted a mer geometry both in solution and in the solid state. This mer geometry was retained for the final catechol derivatives, however in one case, where catechol was substituted for 3-methoxycatechol, the molecule adopted a highly distorted fac geometry. Catalytic ROP activity of the synthetic intermediates and final catechol derivatives with ε-caprolactone was studied through a kinetic analysis. In all seven cases studied the reactions proceeded through the expected coordination-insertion mechanism, following pseudo first-order kinetics and increasing in Mn linearly vs. conversion. The single-initiator catechol derivatives increased the Mn by three times compared to that of the three-initiator synthetic intermediates with little decrease in the overall reaction rate. Both the nature of the ligand and metal were found to impact the rate of reaction in these systems. By switching from an electron donating ligand to an electron withdrawing ligand, the rate was found to nearly double. Tantalum species were faster than their niobium counterparts by ∼3 times in the synthetic intermediates and ∼1.5 times in the catechol derivatives. This observed periodicity supports recent literature findings in this area.

Evaluation of the Effects of Some Metal Chlorides on the Initial Reaction Rate of Crude Peroxidase from Watermelon Peels

Aims: This study evaluates the effect of some chloride on the initial reaction rates of crude peroxidase from watermelon peels. Study Design: In vitro enzyme assay. Place and Duration of Study: Department of Biochemistry, Faculty of Life Sciences, Ambrose Alli University, Ekpoma, Edo State, Nigeria between April 2021 and June 2021. Methodology: The kinetics of crude peroxidase catalyzed oxidation of 3,5,3′,5′-tetramethylbenzidine (TMB) in the presence of varying concentrations of different chloride salts and hydrogen peroxidase was determined spectrophotometrically at 655nm. The assay mixture contained 2.3 mL of sodium phosphate buffer of pH 7.0, 0.1 mL of a crude enzyme from the watermelon peels, 0.2 mL of varying concentration of the respective chloride salts, 0.2 mL of 0.02 mM TMB, and 0.2 mL of 2 mM hydrogen peroxidase added last to start the reaction. Results: Results showed that chloride salts of Pb2+ Hg2+ Fe2+ and Na+ had peroxidase activating effects at low salt concentration (1 mM). The activating effect increased proportionately up to their respective optimum salt concentration. Further increment of salt concentration above their respective optimum value lead to a decrease in initial reaction rate of the crude enzyme. Within a chloride concentration range of 0.025 mM to 3 mM, the highest activating effect recorded was in the order Pb2+ > Fe2+ > Na+ > Hg2+.. Results show that Pb2+ had the highest enzyme activating effect at the lowest concentration (0.5 mM) of the salt when compared with other salts within the same concentration range. Conclusion: These findings are of great significance in research to understanding the mechanism of action of peroxidase from the peels of watermelon, especially as the search for cheap and alternative sources of peroxidases continues.

Numerical study on nonisothermal reactive viscous fingering

The numerical study examines the dynamics of viscous fingering in a miscible flow displacement involving an exothermic reaction between displacing and displaced fluids producing nanoparticles. The exothermic reaction alters fluid properties by producing nanoparticles and/or by releasing heat at the front, both competitive in nature. The front changes from stable to forward (reverse) fingering when the contribution of temperature (concentration) to the viscosity dominates. For a fixed viscous behavior, decreasing reaction rate weakens the forward movement of fingers and reverse fingering is obtained. For a fixed injection rate, the thermal diffusivity can weaken the thermal gradients leading to a stable displacement even when the system is viscously unstable and can also trigger double-diffusive instability in a viscously stable system. Overall, the study suggests that the interplay between the mass and thermal contribution to the fluid properties and chemical reaction rates governs the fingering dynamics.

Drying behavior of solid digestate and reaction kinetics of ammonium degradation during laboratory-scale drying

Fundamental knowledge of the drying behavior and ammonia emission from digestate is required in order to properly design efficient drying processes. In this study, laboratory-scale drying experiments with two different digestates (D1 and D2) were conducted at four different drying temperatures (50, 60, 70, and 80 °C). The solid digestate D1 mainly consisted of plant silage (88.7%), while D2 comprised primarily of manure (55.9%). The drying experiments were performed in a controlled drying chamber using relatively small-sized samples of digestate (30 g for D1, 37 g for D2). These samples were characterized by an initial moisture content of about 74% wb (D1) and 78% wb (D2). This sample size mass was deliberately chosen to ensure homogeneous drying conditions within a thin layer and to facilitate precise laboratory quality measurements of parameters including water content, nitrogen contents (N-total, NH4-N), and pH values before and after the drying process. Both types of digestate exhibited a similar kinetics of drying and ammonium degradation. The first period of constant drying rate was followed by two periods with decreasing rates. Similarly, the ammonium degradation was characterized by three periods with decreasing reaction rates. Considering only the first reaction period herein, ammonium degradation was determined as a first-order reaction. The activation energy for this reaction period was obtained to be 20.00 kJ mol−1 for digestate D1 and 18.44 kJ mol−1 for digestate D2. The results of this study may serve as a basis for the conceptualization and design of optimized, continuous drying processes tailored to digestate materials.

Numerical study of inlet air conditions on methane flameless combustion characteristics

The current study investigates the influence of inlet air momentum and temperature for flameless characteristics. Three-dimensional computations were implemented by ANSYS FLUENT. A small-scale experimental combustor geometry was used for validation study. Turbulence modelling was performed by RNG k- ε model and the GRI-Eddy Dissipation Concept (GRI-EDC) model was used for the combustion modelling. The influence of inlet air velocity was investigated through using different air jet diameters at constant flow rate. Five different air jet diameters (4,6,8,10 and 12 mm) were studied. It was found that decreasing air jet diameter leads to an increase in the exhaust gas recirculation which reserve in mixture dilution (low O2 content mixture) subsequently, the reaction rate decreases which support the flameless mode creation. Also, this recirculated gas participates in heating up of fresh reactants which make the mixture tends to complete combustion. The influence of combustion air preheating temperature on NO and CO emissions were studied. CO and NO concentration were decreased with reducing the temperature of inlet preheated combustion air.

Addressing polar solvent challenges in the heterogenization of palladium catalysed Hayashi-Miyaura reaction on polymer support

The development of recyclable heterogeneous catalysts for the palladium-catalysed additions of arylboronic acids to nitrostyrenes is investigated in this study. Two strategies, direct copolymerization and post-modification, are explored for immobilizing chiral isoquinoline-oxazoline ligands onto polymer matrices. Various copolymer formulations are prepared, and their catalytic activity, recyclability, and reaction kinetics are evaluated. The incorporation of polar functional groups into the polymer matrix enhances catalytic properties, albeit with a decrease in reaction rate compared to the homogeneous system. Post-modification using a polystyrene-polyethylene glycol (PS-PEG) support shows promise, resulting in a moderate decrease in reaction rate and satisfactory performance over multiple reaction cycles. The findings provide valuable insights into the immobilization of chiral ligands and highlight the advantages and limitations of different polymer compositions. These results contribute to the development of advanced catalytic systems for the synthesis of biologically relevant compounds.