Decrease In Reaction Rate Research Articles

A numerical study on the combustion limits of mesoscale methane jet flames with hydrogen addition

A meso-scale jet flame model was established for the flame ports of domestic gas stoves. The influences of hydrogen addition ratio (β = 0%–25%) on the combustion limits were explored. The results show that with the increase of hydrogen addition ratio, the blow-off limit increases obviously, while the extinction limit decreases slightly, namely, the combustible range expands significantly. Quantitative analysis was carried out in terms of chemical effect and thermal effect. It was found that hydrogen addition will reduce O2 fraction in the pre-mixture for a constant equivalence ratio. Under near-extinction limit condition, since the flame is located at the nozzle exit, the external O2 cannot be entrained into or diffuse into the upstream of the flame, which leads to the decrease of reaction rate. However, for the near-blow-off cases, the external O2 can be entrained and diffuse into the flame, which compensates the difference of O2 content in the pre-mixture. Therefore, the combustion reaction is enhanced by hydrogen addition because more H radicals can be produced. In addition, as the flame is located closer to the tube with the increase of hydrogen addition ratio, heat transfer between flame and tube wall is augmented and the preheating of fresh mixture is strengthened by the inner tube wall. This heat recirculation effect becomes especially notable in low velocity cases. In conclusion, the extension of extinction limit by hydrogen addition is attributed to the thermal effect, while the increase of blow-off limit is mainly due to the intensification of chemical effect.

In-Situ Neutron Imaging and Pore Network Modeling of Counter Current Mass Transfer inside Porous Transport Layers Used for PEMWE

The specific morphology of porous materials, as well as their physical properties, crucially affect their applications, e.g. their use in fuel cells, batteries, or electrolysers. A key point is the correlation of their transport properties with the spatially distributed pore structure. In polymer electrolyte membrane water electrolysers (PEMWE), the drainage of oxygen, counter-currently to the water supply inside the porous anode, can significantly control the performance of the system. More precisely, the temporal and spatially distributed oxygen coverage of the catalyst layer obstructs the water supply towards it, which can result in a decrease of reaction rate. At the same time affects the heterogeneous distribution of liquid water the temperature distribution inside porous electrodes. This can have a severe impact on the performance of the PEMWE as well as on the degradation of the catalyst material.In the presented study, mathematical pore network modeling (PNM) was used to investigate the correlation of the porous transport layer (PTL) pore structure with the distribution of water (wetting) and oxygen (non-wetting). The pore network was reconstructed based on the information about porosity, pore size distribution, pore connectivity and pore shape, which were obtained from micro-computed tomography of commercial materials (Fig. 1a). Compared to existing macroscopic models, PNM is suitable for low capillary numbers, takes local wetting characteristics into account and resolves the invasion process at the pore scale. The quasi-static nature of the model provides an edge over other modelling techniques in terms of computational power and additionally the ease of implementation of locally distributed properties. With the help of PNM, it was studied how a change of structure, i.e. the spatial grading of the pore size distribution and porosity, affects the local oxygen and water distribution, as well as the transport properties. This phenomenon was also analyzed experimentally by the use of a non-electrochemical aluminum cell (Fig. 1b and 1c) which was employed in an in-situ imaging setup installed at ILL, Grenoble, France. The recorded water saturations can be compared to the simulation results with the purpose of model validation and further model development. The outcomes of this study can be useful for the development of structural grading strategies with the target of improved transport properties for the efficient removal of the reactant oxygen and the homogeneous distribution of water. Figure 1

Effect of In-Pore Wettability on Mass Transfer Performance of Fuel Cell Gas Diffusion Layer

The gas diffusion layer (GDL), as the main mass transfer carrier in a hydrogen fuel cell, transports fuel and discharges water, the only by-product of the electrochemical reaction. The dispersion process of water in the pore will hinder the diffusion of gas, thus reducing the concentration of fuel gas at the catalytic site, resulting in the decrease of the electrochemical reaction rate. In this paper, the effect of wettability in the GDL hole on the water transport process is studied. When the pore wall is hydrophilic, the liquid phase is affected by the gas phase eddy current velocity field, and the particles at the center advance to the edge, forming a liquid phase interface with a thin center and thick edge. With the increase of the wall contact angle, the curvature of the three-phase interface increases, the wall adhesion decreases, and the liquid phase is more likely to be discharged. When the contact angle is 130°, the liquid phase almost does not shift in the hole with a radius of 5 μm. With the increase of the radius or inlet pressure difference, the liquid phase is discharged gradually, and the discharge rate of the liquid phase is only related to the wettability of the wall.

Macromolecular Crowding Effects on Citrate Synthase Kinetics are Concentration‐Dependent

Enzyme studies are usually conducted in dilute, in‐vitro conditions; however, enzymes operate within extremely crowded intracellular environments, where macromolecules such as proteins, carbohydrates, and lipids occupy up to 40 % of the available volume. This macromolecular crowding slows diffusion, alters protein structure, and has erratic consequences on enzyme kinetics. To study the potential impacts of crowding on enzyme behavior, Michaelis‐Menten kinetics were employed to monitor citrate synthase reaction rates under crowded conditions. The synthetic polymer dextran was used to mimic the crowded cell interior, and assays were conducted in the presence and absence of dextran at various sizes (10 kDa ‐ 550 kDa) and concentrations (25 g/L ‐ 300 g/L). Crowding decreased the maximum reaction rate, Vmax, for all dextran conditions; however, the severity of this decrease in reaction rate depended on the concentration of dextran. For dextrans at concentrations below their overlap concentrations (c*), crowding resulted in a 10% ‐ 20% decrease in Vmax. However, the reaction rate dropped 30% ‐ 50% at dextran concentrations above c*. The impact of mixtures of dextran sizes on citrate synthase kinetics is also being studied. Taken together, these results indicate that citrate synthase activity is sensitive to the overlap concentration of these dextran solutions.

Experimental and Numerical Investigation of the Dehydration of Ca(OH)2 at Low Steam Pressures

The CaO/Ca(OH)2 system can be the basis for cost-efficient long-term energy storage, as the chemically stored energy is not affected by heat losses, and the raw material is cheap and abundantly available. While the hydration (thermal discharge) has already been addressed by several studies, for the dehydration (thermal charge) at low partial steam pressures, there is a lack of numerical studies validated at different conditions and operation modes. However, the operation at low steam pressures is important, as it decreases the dehydration temperature, which can enable the use of waste heat. Even if higher charging temperatures are available, for example by incorporating electrical energy, the reaction rate can be increased by lowering the steam pressure. At low pressures and temperatures, the limiting steps in a reactor might change compared to previous studies. In particular, the reaction kinetics might become limiting due to a decreased reaction rate at lower temperatures, or the reduced steam density at low pressures could result in high velocities, causing a gas transport limitation. Therefore, we conducted new measurements with a thermogravimetric analyzer only for the specific steam partial pressure range between 0.8 and 5.5 kPa. Based on these measurements, we derived a new mathematical fit for the reaction rate for the temperature range between 375 and 440 °C. Additionally, we performed experiments in an indirectly heated fixed bed reactor with two different operation modes in a pressure range between 2.8 and 4.8 kPa and set up a numerical model. The numerical results show that the model appropriately describes the reactor behavior and is validated within the measurement uncertainty. Moreover, our study revealed an important impact of the operation condition itself: the permeability of the reactive bulk is significantly increased if the dehydration is initiated by a rapid pressure reduction compared to an isobaric dehydration by a temperature increase. We conclude that the pressure reduction leads to structural changes in the bulk, such as channeling, which enhances the gas transport. This finding could reduce the complexity of future reactor designs. Finally, the presented model can assist the design of thermochemical reactors in the validated pressure and temperature range.

RETRACTED: Numerical simulation of combustion process in different heating furnaces

The physical field of different heating furnaces and its related aspects were studied by numerical simulation method. Firstly, by studying the heating furnaces of different shapes, namely triangle furnace, square furnace and cylindrical furnace, it was found that: square furnace and cylinder furnace combustion was more full, high temperature range was larger, different furnace tube heat intensity distribution was more uniform, the amount of heat loss was lower, the outlet NOx emission was higher. By studying the cylindrical furnaces with different dip angles of 95°, 93°, 90°, 87° and 85°, it was found that with the decrease of the dip angle, the inner reflux decreases, the reaction rate decreases, the range of higher temperature increases, the heat absorption of the furnace tube was larger, and the NOx concentration at the outlet was lower.

Modeling of hydration products and strength development for high-volume fly ash binders

Partial replacement of cement using fly ash, as an environmentally friendly approach, has gained increased attention in construction practice. The realistic prediction of microstructure and mechanical properties of fly ash blended cement paste is therefore noteworthy for many practical applications including selection of construction material and their appraisal of design. In this research work, an integrated framework is proposed and demonstrated for predicting the hydration products and compressive strength of high-volume fly ash binders. The prediction framework is designed to have multiple stages. For computing the hydrates of blended cement paste, a coupled hydration model with thermodynamic modelling is developed. A hierarchical model that captures the development of the paste via multiple levels (from C-S-H globules to blended cement paste) is used subsequently to predict the compressive strength as a function of hydration period. Here, unlike previous works, the formation of C–S–H is realistically modelled by distinguishing it into low- and high-density C–S–H. A series of experiments (including XRD Rietveld analysis, thermo gravimetric analysis, selective dissolution, mercury intrusion porosimetry and compression tests) are performed; hence the predictability of the developed work is assessed by comparing the predicted results with experimental data. A very good agreement is seen between the predicted results (hydration products, pore volume and compressive strength) and experimental results, indicating that the proposed model can be applicable to the high-volume fly ash cement paste to reliably capture the hydrates and compressive strength. It is further noted that with an increase in fly ash replacement ratio, the capillary porosity increases, while the reaction rate and compressive strength decrease.

Liquid zinc assisted electro-extraction of molybdenum

• Co-deposition of Mo and Zn were investigated which lead Mo ions to deposit under a less cathodic potential. • Electrolytic cell was designed utilizing liquid zinc as cathode arranged according to the density. • Pure molybdenum was obtained by removing zinc in Zn-Mo alloy, where Zn-Mo alloy was produced through liquid zinc assisted electro-extraction. Improvements of the direct electro-desulfurization of molybdenum disulfide in NaCl-KCl eutectic molten salt by employing a liquid zinc electrode was studied in this work. According to the previous studies, one of the rate controlling step of the MoS 2 desulfurization process is the sulfur ions’ diffusion through solid MoS 2 pellet, and a decreasing reaction rate is considered to result from the poor conductivity between the loosely connected partial reduced molybdenum particles. Based on these facts, liquid zinc electrode, along with a graphite crucible as the container, was employed to collect the reduced molybdenum particles as long as keep providing a fresh three-phase interline (3PI) as the current collector. Transient electrochemical technologies were introduced to study the electrochemical behavior of molybdenum ions with and without the appearance of zinc ions. Zn-Mo alloy was obtained through the potentiostatic electrolysis process, and molybdenum powders mainly sank into the bottom of liquid zinc due to the gravity. Metallic molybdenum shall be obtained by distilling the electrolysis product.

Investigation of Co3O4 Activity and Stability in Amidation of Fatty Acid Methyl Esters

AbstractCo3O4 activity in amidation reaction between fatty acid methyl esters and 3‐(Dimethylamino)‐1‐propylamine was investigated for the first time. The catalytic effect was approved by comparison of non‐catalyzed and catalyzed reactions activation energies and connected with the unique structure of Co3O4. Using of Co3O4 allows decreasing of activation energy of amidation reaction up to 1.5 times (from 90 to 59 kJ/mol). During the recycling test no significant decrease in reaction rate and product yield was detected even after 5 cycles. Using various analysis methods (XRD, FTIR, EDS‐SEM) of fresh and spent catalyst it was fixed that Co3O4 has no transformation throughout the synthesis.

Effect of dichloromethane and toluene on the structure, property, and Al electrodeposition in 1-butyl-3-methylimidazolium chloroaluminate ionic liquid

The electrodeposition of aluminum in ionic liquid has broad application prospects, and additives are an effective way to improve the performance of the aluminum coating. However, the relevant mechanism behind this remains to be clarified. In the present work, the effects of dichloromethane (DCM) and toluene (C7H8) on the microstructure, physicochemical properties, and aluminum electrodeposition with 1-butyl-3-methylimidazolium chloride/aluminum chloride ([BMIM]Cl/AlCl3) were studied using quantum chemistry and molecular dynamics simulation. It is found that DCM easily forms hydrogen bonds with anions and cations of ionic liquids. Since DCM is distributed between anion and cation, the distance between the anion and cation increases, and the interaction energy decreases. As a result, the diffusion ability of anions and cations is enhanced, and the aluminum complex anions tend to exist in the form of \begin{document}${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $\end{document} . The viscosity of the system decreases, and the conductivity increases, so the electrochemical properties of the system are significantly improved, which are in good agreement with the experimental values. C7H8 is adsorbed on the protruding part of the electrode surface in a flat way, which plays a leveling role and results in a flat white coating. Alternatively, DCM easily interacts with the electroactive ion \begin{document}${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $\end{document} , which makes it difficult to reduce this electroactive ion. At the same time, the concentration of the electroactive ion decreases as the concentration of the additive is increased, which leads to a large overpotential in the electrochemical process, resulting in a decrease in the electrode reaction rate that plays a role in grain refinement. Moreover, the interaction between DCM and cations is also strong, and they can be adsorbed on the protruding part of the electrode surface during the electrochemical process, playing a certain leveling role. Therefore, the addition of DCM can obtain specular gloss deposits. The effect of C7H8 on the interaction between anions and cations is not as good as DCM, which consequently results in inferior electrochemical properties compared to DCM. Therefore, DCM is more favorable for the electrodeposition of aluminum than the aromatic hydrocarbon C7H8.

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

The chemical continuous time random walk framework for upscaling transport limitations in fluid–solid reactions

Fluid-solid reactions play a key role in a large range of biogeochemical processes. Transport limitations at the pore scale limit the amount of solute available for reaction, so that reaction rates measured under well-mixed conditions tend to strongly overestimate rates occurring in natural and engineered systems. Although different models have been proposed to capture this phenomenon, linking pore-scale structure, flow heterogeneity, and local reaction kinetics to upscaled effective kinetics remains a challenging problem. We present a new theoretical framework to quantify these dynamics based on the chemical continuous time random walk framework. We study a fluid–solid reaction with the fluid phase undergoing advective–diffusive transport. We consider a catalytic degradation reaction, AF+BS→BS, where AF is in fluid phase and BS is in solid phase and homogeneous over the fluid–solid interface, allowing us to focus on the role of transport limitations and medium structure. Our approach is based on the concept of inter-reaction times, which result from the times between contacts of transported reactants with the solid phase. We use this formulation to quantify the global kinetics of fluid-reactant mass and test our predictions against numerical simulations of advective–diffusive transport in stratified channel flow and Stokes flow through a beadpack. The theory captures the decrease of effective reaction rates compared to the well-mixed prediction with increasing Damköhler number due to transport limitations. Although we consider simple kinetics and media, these findings will contribute to the understanding and modeling of the effect of transport limitations in more complex reactive transport problems.

Effective kinetics driven by dynamic concentration gradients under coupled transport and reaction

Biogeochemical reaction kinetics are generally established from batch reactors where concentrations are uniform. In natural systems, many biogeochemical processes are characterized by spatially and temporally variable concentration gradients that often occur at scales which are not resolved by field measurements or biogeochemical and reactive transport models. Yet, it is not clear how these sub-scale chemical gradients affect reaction kinetics compared to batch kinetics. Here we investigate this question by studying the paradigmatic case of localized pulses of solute reacting with a solid or a dissolved species in excess. We consider non-linear biogeochemical reactions, representative of mineral dissolution, adsorption and redox reactions, which we quantify using simplified power-law kinetics. The combined effect of diffusion and reaction leads to effective kinetics that differ quantitatively and qualitatively from the batch kinetics. Depending on the nonlinearity (reaction order) of the local kinetics, these effects lead to either enhancement or decrease of the overall reaction rate, and result in a rich variety of reaction dynamics. We derive analytical results for the effective kinetics, which are validated by comparison to direct numerical simulations for a broad range of Damköhler numbers and reaction order. Our findings provide new insights into the interpretation of imperfectly mixed lab experiments, the effective kinetics of field systems characterized by intermittent reactant release and the integration of sub-scale concentration gradients in reactive transport models.

Kinetic Analysis of a Suicidal DNA‐crosslinking Uracil DNA Glycosylase in UDG Superfamily

Uracil DNA glycosylase (UDG) is an enzyme to initiate base excision repair (BER) of DNA by removing the damaged base from the strand and forming an apurinic/apyrimidinic site (AP site). There are at least six families of enzymes found in UDG superfamily. All the UDGs contain three motifs in their catalytic centers, and the sequences of the motifs are conserved, guaranteeing the glycosylase activity. UDGX was a newly discovered protein of the UDG superfamily from Mycobacterium smegmatis, which was confirmed to be closer to the Family 4 UDGs (UDGa) than the other members by studying its structure and sequence. However, different with the Family 4 UDGs, an obvious loop was inserted in the motif 3 of UDGX. In addition, UDGX was the first reported UDG which can covalently crosslink to the AP site formed by base excision via its His109 on the inserted loop. Several mutants were generated by substituting the key residues in the motif 1 and motif 3 of the MsmUDGX. Uracil DNA glycosylase activity assays as well as uracil DNA crosslinking activity assays were performed with these mutants. It was observed that the E52A and D56A mutants retained both the uracil DNA glycosylase and DNA crosslinking activities, however the H109A, H109N and H109Q only retained the uracil DNA glycosylase activity but lost the DNA crosslinking activity due to the substitution of the His109. Moreover, the loss of both activities of the D59A and R107A mutants were observed. Followed by the activity assays, kinetic analyses were performed on the mutants and the UDGX wild type. The k2/Km of the wild type MsmUDGX on the G/U substrate was determined to be 1.8 ± 0.2 × 104 s-1M-1, which was 10-fold lower than the k2/Km of the Family 4 UDG (TthUDGa) reported. Compared to the wild type, E52A, H109A, H109N and H109Q mutants exhibited a significant decrease of the catalytic reaction rate, suggesting that not only the key residue Glu52 in the motif 1 but His109 may also play an important role in the uracil excision process. The Asp56 and Asp59 in the motif 1 were confirmed to form salt bridges with the Arg107 on the inserted loop in the motif 3, which were hypothesized to stabilize the loop during the interaction between the enzyme and the DNA substrates. Consistent with the hypothesis, the mutations on Asp59 and Arg107 caused the loss of both activities, but the D56A mutant retained both activities, and the kinetic analysis indicated only slight decrease of the reaction rate, which may suggest the Asp56 was not the key residue to stabilize the loop in the salt bridges. In conclusion, the kinetic analysis provides a quantitative assessment on the roles of key catalytic residues on uracil excision activity and DNA-crosslinking activity.

Efficient and environmentally sustainable domino protocol for the synthesis of diversified dispiroheterocycles using 1-Butyl-3-methylimidazolium bromide [bmim]Br

An environmentally benign, simple, and efficient procedure has been developed for the construct of some symmetrical dispiroheterocycles derivatives by the reaction of the variety of 6-amino-2-thiouracil/6-aminouracil /2-amino-1,3,4-thiadiazole, isatins and p-toluidine in the presence of 1-Butyl-3-methylimidazolium bromide ([bmim]Br) as a solvent as well as catalyst at room temperature. In this study, a variety of bis-spiro-indoline-chromenes, pyranopyranes, imidazo-pyridines, pyrido-pyrimidines and pyridines were obtained with excellent yields within short reaction time and without chromatographic separation. Furthermore, the green catalytic system can be recycled specific times with no decreases in yields and reaction rates.

Hydrolysis of Aliphatic Bis-isonitriles in the Presence of a Polar Super Aryl-Extended Calix[4]pyrrole Container.

We report binding studies of an octa-pyridinium super aryl-extended calix[4]pyrrole receptor with neutral difunctional aliphatic guests in water. The guests have terminal isonitrile and formamide groups, and the complexes display an inclusion binding geometry and 1:1 stoichiometry. Using 1 H NMR titrations and ITC experiments, we characterized the dissimilar thermodynamic and kinetic properties of the complexes. The bis-isonitriles possess independent reacting groups, however, in the presence of 1 equiv of the receptor the hydrolysis reaction produces mixtures of non-statistical composition and a significant decrease in reaction rates. The selectivity for the mono-formamide product is specially enhanced in the case of the bis-isonitrile having a spacer with five methylene groups. The analysis of the kinetic data suggests that the observed modifications in reaction rates and selectivity are related to the formation of highly stable inclusion complexes in which the isonitrile is hidden from bulk water molecules. The concentration of the reacting substrates in the bulk solution is substantially reduced by binding to the receptor. In turn, the hydrolysis rates of the isonitrile groups for the bound substrates are slower than in the bulk solution. The receptor acts as both a sequestering and supramolecular protecting group.

Hydrolysis of Aliphatic Bis‐isonitriles in the Presence of a Polar Super Aryl‐Extended Calix[4]pyrrole Container

AbstractWe report binding studies of an octa‐pyridinium super aryl‐extended calix[4]pyrrole receptor with neutral difunctional aliphatic guests in water. The guests have terminal isonitrile and formamide groups, and the complexes display an inclusion binding geometry and 1:1 stoichiometry. Using 1H NMR titrations and ITC experiments, we characterized the dissimilar thermodynamic and kinetic properties of the complexes. The bis‐isonitriles possess independent reacting groups, however, in the presence of 1 equiv of the receptor the hydrolysis reaction produces mixtures of non‐statistical composition and a significant decrease in reaction rates. The selectivity for the mono‐formamide product is specially enhanced in the case of the bis‐isonitrile having a spacer with five methylene groups. The analysis of the kinetic data suggests that the observed modifications in reaction rates and selectivity are related to the formation of highly stable inclusion complexes in which the isonitrile is hidden from bulk water molecules. The concentration of the reacting substrates in the bulk solution is substantially reduced by binding to the receptor. In turn, the hydrolysis rates of the isonitrile groups for the bound substrates are slower than in the bulk solution. The receptor acts as both a sequestering and supramolecular protecting group.

Pore-scale numerical study of multiphase reactive transport processes in cathode catalyst layers of proton exchange membrane fuel cells

understanding interactions between multiphase flow and reactive transport processes in catalyst layers (CL) of proton exchange membrane fuel cells is crucial for obtaining better performance and lower cost. In this study, a pore-scale model is developed to simulate coupled processes occurring in CLs, including oxygen diffusion, electrochemical reaction, and air-liquid two phase flow. Simulation conducted in an idealized local CL structures shows that the pore-scale model successfully captures dynamic behaviors of liquid water including generation, growth and subsequent migration, as well as the interaction between multiphase flow and reactive transport. Pore-scale simulation is then conducted in hydrophobic CLs with complicated structures where carbon, platinum, ionomer and pores are resolved. It is found that filling modes of the liquid water in the CLs are different. Before forming the continuous flow paths in CLs, liquid water presents as tiny droplets in pores surrounding relative large pores. After the continuous flow paths are formed, liquid water dynamic behaviors follow the capillary fingering mechanism. The multiphase flow and reactive transport processes are closely coupled with each other, and as liquid water saturation increases the reaction rate decreases. Increasing the hydrophobicity can alleviate the water flooding, accelerate the water breakthrough, and facilitate the water evaporation.

Homogeneous catalytic oxidation of toluene under the ultrasonic action

The regularities of toluene catalytic oxidation with molecular oxygen catalyzed by cobalt (II) acetate in a liquid phase under the ultrasonic action have been researched. It was found a close relationship between the temperature and pressure of the oxidation process. The relationship determines the reaction rate, the reaction products composition, and the toluene limiting conversion value. It was found that the ratio between a sonochemical reaction rate and a toluene oxidation reaction rate without ultrasonic action increases with increasing the reaction temperature both at the process initial stage and higher values of hydrocarbon conversion. Simultaneously, an increase in the rate of toluene oxidation reaction under the ultrasonic action was detected only at a temperature of 430–438 K and a pressure of 0.4 MPa. Under all other conditions the rate of sonochemical reaction is lower than the toluene oxidation rate without ultrasonic action. An extreme reaction rate dependence of the homogeneous catalytic toluene oxidation on pressure at constant temperature was revealed. It is established that the reaction rate decreases with pressure increasing under the ultrasonic action more significantly the higher the reaction temperature is. In general the sonochemical reaction rate is lower than the rate of catalytic toluene oxidation. It was shown that ultrasound affects the concentrations of all reaction products. The relationship between the product concentrations obtained in the sonochemical reaction and in the toluene oxidation reaction without ultrasonic treatment depends on temperature and pressure. It is established that the main changes in the quantitative composition of oxidation products are to increase/decrease the benzoic acid and benzyl alcohol concentrations under the ultrasonic action. The decrease in the sonochemistry reaction rate of toluene catalytic oxidation at the reaction initial stage and its simultaneous increase at higher values of hydrocarbon conversion, as well as changes in the reaction products selectivities, and the ultrasonic effect on the toluene limiting conversion indicate that the cavitation affects on the changes in the regularities of catalyst-intermediate complexes transformations.

EFFECT OF PORE DIFFUSION ON THE GASIFICATION CHARACTERISTICS OF COAL CHAR UNDER CO2 ATMOSPHERE

The effect of pore diffusion on kinetic parameters is of particular interest to the current study using coal char under CO2 gasification conditions. A high-temperature entrained-flow gasifier was used for the preparation of char through the rapid pyrolysis process. The kinetic study with the char was then carried at temperatures of 973-1473 K under atmospheric pressure. A prediction of carbon conversion for large particle size (100 μm) is reported from the carbon conversion of small particle size (25 μm) considering the diffusion effect. The effect of diffusion caused by temperatures and particle size was reported through activation energy. The apparent activation energy in the chemically controlled region (973-1173 K) was calculated to be 178 kJ/mol, whereas it was 69 kJ/mol in the pore diffusion zone (1373-1473 K) using smaller particle size. The apparent activation energy using large particle size was found to be 186 and 99 kJ/mol in chemically controlled and pore diffusion zone, respectively. The intrinsic activation energy for both particle sizes was almost similar. A variation between apparent and intrinsic reaction rates was depicted mostly at higher temperatures of over 1273 K. The change in the surface area of char particle was crucial in terms of decreasing reaction rates, which was decreased with the progression of the conversion. The predicted carbon conversion for large particle size was in good agreement with the experimentally measured conversion except for little discrepancies at higher temperatures.