Intrinsic Kinetic Data Research Articles

(Invited) Regimes of Reaction-Diffusion Processes Nearby the Plasma-Liquid Interface

Plasma-liquid systems are usually comprised of an atmospheric-pressure plasma electrode and a liquid surface, which can have a bubbly and irregular, or a smooth surface. When coupled with a metal counter electrode immersed in the liquid, this configuration has been shown to form capable electrochemical systems that can degrade recalcitrant pollutants, conduct organic chemistry and when reactive gases are used, can create unique gas-liquid reaction pathways for important processes such as N2 fixation and CO2 utilization. Up to date, many different types of plasmas with different frequencies, plasma electrode shapes, gas flow rates and applied powers have been utilized in literature. One common aspect of most plasma sources in plasma-liquid systems is that the current density at the interface is much higher than in conventional electrochemical systems. Consequently, the observed rate constants of some of the plasma-assisted processes mentioned above have been found to fall in a rather narrow range of values, despite the vast differences in plasma sources. This is an indication of mass transport playing a crucial role in the observed kinetics. This argument is supported by experimental results obtained through changing current in continuous plasmas and changing frequency in pulsed plasmas.When mass transport rate is of the same order with reaction rate or slower, the observed picture for kinetics requires a mathematical description of the interplay of reaction and diffusion to elucidate intrinsic kinetic data. A phenomenological, yet practical and predictive modeling framework has not yet been established for plasma-liquid systems. Despite new kinetics that arise from the unique species produced at the plasma liquid interface, gas-liquid contacting is a well-established field in chemical engineering. In this talk, early chemical engineering studies on gas-liquid contacting will be summarized and the reaction-diffusion models developed through these studies will be applied to plasma-electrochemical systems. According to the theory, multiple regimes of reaction-diffusion processes must exist, and some of these regimes can be reduced to simpler analytical models that allow compact expressions for the observed rate constant and faradaic efficiency. Examples on applying the modeling framework to published experimental data will be given and the criteria that determine the validity of the model equations will be discussed.

Bulk oxygen conduction kinetics of iron oxides on the chemical looping combustion

Oxygen-ion conduction is generally considered the rate-determining step during the chemical looping combustion process, which is vital for the design of the oxygen carriers. However, the redox reaction is heavily influenced by gas diffusion, making it very difficult to derive convincing intrinsic kinetic data. This work aims to establish a methodology to evaluate the intrinsic kinetics of oxygen carriers for chemical looping combustion by using an ultra-thin oxygen conducting membrane to exclude the influence of gas diffusion. From mass balance and Fick's second law, a mathematical kinetics model describing the intrinsic oxygen conduction performance was established. The intrinsic activation energy took value of 77.84 kJ/mol for pure Fe2O3. The kinetics parameters can be used for the high throughput design and screening of oxygen carriers.

Plasmonic silver nanoparticles decorated surface functionalized Zirconium doped quantum dots - for enhanced photochemical synthesis of lactic acid esters

Lactic acid, or 2-hydroxypropionic acid (CAS 50-21-5), a natural organic acid immensely engaged in agricultural industry, pharmacy, garment and chemical industry with a long history of practice. Lactic acid generated in fermentation necessitates an extra purification step that must be cost-effective. A green and energy derivatization of lactic acid into corresponding esters was carried out under photocatalytic conditions in this study to render them volatile for distillation separation. Esterification reaction was carried out under low energy photocatalytic system under solvent free conditions using a range of Zirconium impregnated-activated Titanium dioxide photocatalysts (1-0.005Ag/1.9-4.4%S-2.5-12.5%Zr@TO). Both physical and chemical events in the reaction grid have been studied and thermodynamic and kinetic parameters have been established expending pseudo-homogeneous (PH), Eley-Rideal (ER) and Langmuir-Hinshelwood-Haugen-Watson (LHHW) models and the different adsorption of components were proposed to fit the intrinsic kinetic data. Reaction mechanism for the process have been proposed based on the kinetic modelling results as well as FT-IR, TGA, Ammonia-TPD and photo-Electrochemical characterizations, as well as radical trapping tests, were also used to effectively support the reaction mechanism. The findings will be beneficial in the design of industrial photo-reactors for low temperature ester synthesis strategies.

Reaction mechanism investigation on the esterification of rosin with glycerol over annealed Fe3O4/MOF-5 via kinetics and TGA-FTIR analysis

Reaction mechanism was investigated on the esterification of rosin with glycerol over annealed Fe3O4/MOF-5 with the annealing temperature of room temperature, 300, 500, 700 and 900 °C via the kinetics and TGA-FTIR analysis. Chemical equilibrium constant was employed in kinetic models due to reversible esterification reaction, and thermodynamic parameters were calculated. Kinetic models that considered three kinds of rate-determining steps of single reactant adsorption, single product desorption and surface reaction as well as the reaction mechanism of pseudo-homogeneous (PH), Eley-Rideal (ER) and Langmuir-Hinshelwood-Haugen-Watson (LHHW) and the different adsorption of components were proposed to fit the intrinsic kinetic data obtained by eliminating the effects of external and internal mass transfer resistance. Based on the results of linear regression and nonlinear regression, model discrimination among 38 possible kinetic models lead to the conclusion ER model with the surface reaction of adsorbed glycerol is the best appropriate to experimental results, affording a correlation coefficient above 0.981 and the F values much greater than the F0.05 values. The activation energies reduce with increasing of annealing temperature of the catalyst, from 103.28 to 89.55 kJ mol−1. Furthermore, results from TGA-FTIR characterizations further reveal that this esterification involves the exclusive adsorption of glycerol.

Kinetics of catalytic oxidation of sodium ethyl mercaptide

Catalytic oxidation of mercaptide is a significant way to eliminate waste emission of spent caustic and recycle the resource of caustic. However, the kinetics of mercaptide oxidation for spent caustic regeneration is still unclear, which hinders the reactor design. In this work, mechanism analyses and kinetics experiments were conducted to investigate the kinetics of homogeneous catalytic oxidation of sodium ethyl mercaptide. Ultraviolet visual spectra show that mercaptide ion is superior to oxygen molecule adsorbed on the catalyst, which is in accord with the simulations. Reaction mechanism of two-layer adsorption structure was proposed by density functional theory calculations. By applying the method of decoupling macroscopic kinetics and making pseudo-first-order fast reaction hypothesis, the rate expression of the intrinsic kinetics for the oxidation reaction of sodium ethyl mercaptide was proposed as -dCAdt=6.84×1010exp(-29584RT)CACB. A statistical test was carried out to verify the intrinsic kinetics data, showing that the kinetics data were overall reasonable.

Using modeling to select catalyst dilution methods for mass transfer intensification in lab gas–liquid fixed-bed reactors

Heterogeneous catalyst testing methodology at the lab scale must provide intrinsic kinetics data for reactor design purposes as well as the intrinsic activity ranking during catalyst screening in the field of refining and petrochemistry. The significant downscaling of the past century coupled with the increasingly active catalytic formulations may introduce considerable momentum, mass and heat effects in experiments at small scale. Catalyst dilution has emerged as one versatile and robust way to reduce the impact of momentum and heat effects on heterogeneous catalyst testing. This paper presents a methodology based on global phenomena and catalyst dilution modeling to assess and optimize reactor loading techniques for specific problems. More particularly, the aim is to provide catalysts developers and kinetics experts with concrete guidelines for intensifying gas-liquid mass transfer in lab gas–liquid fixed-bed reactors through catalyst dilution. The methodology is applied to the kinetics determination of the oil residue Hydrodemetallation (HDM) and to the screening of catalysts for benzene hydrogenation. Layered dilution, consisting on the split of the catalyst in two beds separated by an intermediate bed containing an inert material of the same size as the catalyst, poorly improves gas–liquid mass transfer. Uniform dilution, based on the direct mixture of catalyst and inert material of the same size, significantly enhances gas–liquid mass transfer as the reactant local consumption per reactor unit volume is strongly reduced. Combinations of both abovementioned dilution techniques can be used with fast and/or high stoichiometric factor chemical systems operated at conversions higher than 70%. A new criterion is proposed to calculate the minimum dilution factor to guarantee negligible gas–liquid mass transfer limitations as a function of conversion, external mass transfer and global pseudo second-order kinetics.

Kinetic study and CFD simulation on multi-stage catalytic removal of the exhaust gases from acrylonitrile plant

The optimal catalyst was selected and the combination sequence of different catalysts for the catalytic combustion of acrylonitrile-containing exhaust gases in a fixed-bed microreactor were detected. The intrinsic kinetic data were obtained, and their reliability were verified. The CFD simulation software established a two-dimensional mathematical model of porous material under real industrial conditions, the catalytic combustions of the exhaust gaseous components were simulated, and the effect of operating parameters on the catalytic combustion characteristics of exhaust gases were analyzed. The optimal operating conditions for the removal of acrylonitrile-containing exhaust were obtained by simulation and data analysis (flow rate: 30000 h−1, inlet temperature: >623 K, composition molar ratio: >10:1, porosity of catalytic bed porosity: ~0.7). Under the optimal operating conditions, the simulation of the two-stage catalytic reactor was carried out to obtain reactor parameters such as pressure drop and adiabatic temperature rise.

Evaluation of the effect of inert support on the carbonation reaction of synthetic CaO-based CO2 sorbents

Calcium oxide has been proved to be a suitable sorbent for high temperature CO2 capture processes based on the cyclic carbonation-calcination reaction. In this work several synthetic sorbents have been prepared with CaO contents between 40 and 95% wt. on to two different inert supports MgO and Ca12Al14O33. The effect of CaO content and inert nature on materials CO2 carrying capacity and reactivity towards carbonation reaction has been assessed. The materials have been texturally characterised. A complete kinetic study has been performed and the Random Pore Model has been applied to determine the intrinsic rate parameters for the carbonation reaction. Suitable particles for operation in fixed bed reactor have been produced from some selected powdered materials, and a complete particle reaction model that incorporate the intrinsic kinetic data has been developed and validated.

Thermodynamic, kinetic, and structural parameterization of human carbonic anhydrase interactions toward enhanced inhibitor design.

The aim of rational drug design is to develop small molecules using a quantitative approach to optimize affinity. This should enhance the development of chemical compounds that would specifically, selectively, reversibly, and with high affinity interact with a target protein. It is not yet possible to develop such compounds using computational (i.e., in silico) approach and instead the lead molecules are discovered in high-throughput screening searches of large compound libraries. The main reason why in silico methods are not capable to deliver is our poor understanding of the compound structure-thermodynamics and structure-kinetics correlations. There is a need for databases of intrinsic binding parameters (e.g., the change upon binding in standard Gibbs energy (ΔGint), enthalpy (ΔHint), entropy (ΔSint), volume (ΔVintr), heat capacity (ΔCp,int), association rate (ka,int), and dissociation rate (kd,int)) between a series of closely related proteins and a chemically diverse, but pharmacophoric group-guided library of compounds together with the co-crystal structures that could help explain the structure-energetics correlations and rationally design novel compounds. Assembly of these data will facilitate attempts to provide correlations and train data for modeling of compound binding. Here, we report large datasets of the intrinsic thermodynamic and kinetic data including over 400 primary sulfonamide compound binding to a family of 12 catalytically active human carbonic anhydrases (CA). Thermodynamic parameters have been determined by the fluorescent thermal shift assay, isothermal titration calorimetry, and by the stopped-flow assay of the inhibition of enzymatic activity. Kinetic measurements were performed using surface plasmon resonance. Intrinsic thermodynamic and kinetic parameters of binding were determined by dissecting the binding-linked protonation reactions of the protein and sulfonamide. The compound structure-thermodynamics and kinetics correlations reported here helped to discover compounds that exhibited picomolar affinities, hour-long residence times, and million-fold selectivities over non-target CA isoforms. Drug-lead compounds are suggested for anticancer target CA IX and CA XII, antiglaucoma CA IV, antiobesity CA VA and CA VB, and other isoforms. Together with 85 X-ray crystallographic structures of 60 compounds bound to six CA isoforms, the database should be of help to continue developing the principles of rational target-based drug design.

Flowthrough Reductive Catalytic Fractionation of Biomass

Summary Reductive catalytic fractionation (RCF) has emerged as a leading biomass fractionation and lignin valorization strategy. Here, flowthrough reactors were used to investigate RCF of poplar. Most RCF studies to date have been conducted in batch, but a flow-based process enables the acquisition of intrinsic kinetic and mechanistic data essential to accelerate the design, optimization, and scale-up of RCF processes. Time-resolved product distributions and yields obtained from experiments with different catalyst loadings were used to identify and deconvolute events during solvolysis and hydrogenolysis. Multi-bed RCF experiments provided unique insights into catalyst deactivation, showing that leaching, sintering, and surface poisoning are causes for decreased catalyst performance. The onset of catalyst deactivation resulted in higher concentrations of unsaturated lignin intermediates and increased occurrence of repolymerization reactions, producing high-molecular-weight species. Overall, this study demonstrates the concept of flowthrough RCF, which will be vital for realistic scale-up of this promising approach.

Anisole Hydrotreatment Kinetics on CoMo Catalyst in the Absence of Sulfur: Experimental Investigation and Model Construction

Anisole hydrodeoxygenation over a nonsulfided CoMo/Al2O3 catalyst was investigated as a model reaction for fast pyrolysis oil upgrading. Intrinsic kinetic data have been acquired in a gas-phase plug-flow reactor at temperatures ranging from 548 to 623 K, a total pressure amounting to 0.5 MPa, a space time between 95 and 400 kgcat s molanisole–1, and a hydrogen to anisole molar ratio from 50 to 400. A minimum of 16 h on stream stable anisole conversion was observed. The catalyst mainly exhibited anisole demethylation and phenol methylation to cresol, rather than hydrogenation or hydrodeoxygenation. Demethylation and isomerization reactions are followed by hydrodeoxygenation. Additionally, cresol is formed via phenol methylation. Rival mechanisms were proposed, and corresponding Langmuir–Hinshelwood–Hougen–Watson elementary step based kinetic models were derived. Each of the proposed models accounted for the interaction of the species with the catalyst surface as well as for the surface reactions. For each ...

Kinetics of bentonite nanoclay-catalyzed sal oil (Shorea robusta) transesterification with methanol

The transesterification of sal oil with methanol using bentonite nanoclay heterogeneous base catalyst was investigated for biodiesel production. A perfectly mixed batch reactor was used to generate intrinsic kinetic data to determine the reaction mechanism and kinetic constants. The influence of temperature (443–493K), the initial molar ratio of methanol to sal oil (4-12) and catalyst loading (5–25g catalyst/100g oil) was investigated over a broad range of sal oil conversion (i.e., 1-98%). High catalyst loading was used to establish the effect of catalyst loading on sal oil conversion to biodiesel. Five heterogeneous kinetic models, namely, Langmuir-Hinshelwood-Hougen-Watson (LHHW), Eley-Rideal (ER-1), modified Eley-Rideal (ER-2), LHHW-ER and Hattori-Shima-Kabashima (HSK) were applied to determine the best reaction mechanism to describe the experimental data over the entire range of operating conditions. Sal oil conversion based on methanol adsorption on the free basic site of bentonite nanoclay was found to be the most reliable rate determining step using the ER-1 model to fit the experimental data based on statistical analysis and mechanistic consideration under different formulation of transesterification feed mixture. Temperature dependent kinetic constants based on ER-1 model with methanol adsorption were determined. Finally, a parametric sensitivity analysis was carried out to know the most sensitive kinetic constants in the input parameter space. Proposed model may be helpful in scale-up studies and implementation of the model-based control strategy in the large-scale transesterification of sal oil.

Oxygenated hydrocarbons steam reforming over Ni/CeZrGdO2 catalyst: Kinetics and reactor modeling

The kinetics of the steam reforming of an equimolar mixture of oxygenated hydrocarbons (Oxy-HC) over Ni/Ce0.5Zr0.33Gd0.166O2 catalyst was studied in a packed bed tubular reactor (PBTR) at atmospheric pressure, a temperature range of 550–600°C, and a steam to feed (S/F) molar ratio range of 2–6. Intrinsic kinetic data were collected in the absence of heat and mass transport limitations, which was confirmed by performing relevant kinetic analysis. A new and unique method for estimating the kinetic rate model parameters, which uses conversion error between a 2D axisymmetric PBTR simulation and experimental results, was developed and applied in this study. A modified genetic algorithm was also developed and used as an optimization tool to minimize the model error. Three different kinetic models consisting of an empirical power law model and two mechanistic Eley–Rideal (ER) models were developed and investigated. The developed power law rate model had the form (−rA)=4×104e−(99026)/RTpA0.6pB0.8 for which the reaction orders w.r.t. methanol and steam were 0.6 and 0.8, respectively, with an activation energy of 99kJ mol−1. An ER type mechanism that postulates the dissociative adsorption of Oxy-HCR as the rate-controlling step (RDS) was found to adequately describe the Oxy-HCR with an estimate of activation energy of 103kJmole−1. A comparison between the experimental rate and the corresponding rates obtained using this model yielded an average error of 7%.

Producing high quality carbide-derived carbon from low quality byproducts stemming from SiC production

The utilization of carbide-derived carbons (CDCs) in a wide range of applications is obstructed due to relatively high production costs. In this study a possibility to reduce the costs of CDC synthesis by employing low quality SiC byproducts stemming from the ESK process is presented. While the crystallinity and impurity content differs for the different precursor qualities, the resulting CDC materials possess similar textural characteristics and carbon microstructures. Evaluation of intrinsic kinetic data reveals that the low grade precursors react faster during reactive extraction and can be best described by a power law approach. The CDC materials were further investigated with respect to their performance as electrode materials in Electric Double Layer Capacitors (EDLC). All SiC-CDCs display a comparable and excellent specific capacitance of approx. 115Fg−1. The results are demonstrating the promising utilization of CDC materials synthesized from low valuable SiC feedstock.

ChemInform Abstract: Experimental and Theoretical Methods in Kinetic Studies of Heterogeneously Catalyzed Reactions

AbstractReview: 127 refs.

Kinetics of Thiophene Hydrodesulphurization: Pore Diffusional Effects

AbstractHydrodesulfurization (HDS) of straight‐run naphtha (SRN) reformer feed significantly improves reformer catalyst life, gasoline yield, and its stability. HDS of SRN helps in protecting the expensive platinum‐based reforming catalyst. HDS is usually catalyzed by sulphided Co–Mo/Al2O3 or sometimes Ni–Mo/Al2O3. The design of naphtha HDS units requires the development develop a kinetic model. It is well‐known that among the sulphur types present in naphtha, the most persistent sulphur compound is thiophene. Therefore, the design of naphtha HDS units is governed by thiophene HDS rates. It is essential to have experimental conditions free from intraparticle diffusional limitations in order to obtain intrinsic kinetics data. This Communication discusses the calculation procedures involved in ensuring experimental conditions free from pore diffusional resistances before conducting detailed kinetics studies. The pore diffusional resistance was quantified in terms of Thiele modulus (Φ).

Experimental and theoretical methods in kinetic studies of heterogeneously catalyzed reactions.

This review aims to illustrate the potential of kinetic analysis in general and microkinetic modeling in particular for rational catalyst design. Both ab initio calculations and experiments providing intrinsic kinetic data allow us to assess the effects of catalytic properties and reaction conditions on the activity and selectivity of the targeted reactions. Three complementary approaches for kinetic analysis of complex reaction networks are illustrated, using select examples of acid zeolite-catalyzed reactions from the authors' recent work. Challenges for future research aimed at defining targets for synthesis strategies that enable us to tune zeolite properties are identified.

Kinetics of thermal degradation of renewably prepared amines useful for flue gas treatment

N-ethylmonoethanolamine (EMEA) and N-N-diethylmonoethanolamine (DEMEA) can be prepared from renewable resources and appear to be commercially attractive solvents for post-combustion CO2 capture by absorption/stripping process. In this paper, the thermal degradation of these renewably prepared amines was studied at 423 K and compared with other amines such as monoethanolamine, diethanolamine, triethanolamine, and N-methyl diethanolamine. Furthermore, an investigation of the kinetics of thermal degradation of aqueous EMEA and DEMEA was conducted by using a 600 ml high-temperature high-pressure reactor in the temperature range of 393 to 423 K and amine concentration range of 1 to 3 kmol m−3, respectively. Estimation of the active solvent content of the reaction mixture samples obtained during the degradation experiments was performed using a gas chromatograph (GC) equipped with a Flame Ionization Detector (FID) and a Tenax GC column. The obtained results indicate that the rate of thermal degradation of both aqueous EMEA and DEMEA increases with the increase in the initial amine concentration and temperature. Additionally, the degradation reaction was observed to be first order with respect to the initial amine concentration. Two intrinsic kinetic power law models were formulated to describe the kinetics of the thermal degradation of aqueous EMEA and DEMEA and the kinetic parameters were predicted by using the linear least-squares regression analysis. The kinetic rate constants for the thermal degradation of these renewably prepared amines were determined (both experimentally and by the models) and on the basis of their temperature dependency, the activation energy for the degradation reaction was estimated. This work represents the first attempt towards obtaining the intrinsic kinetic data for thermal degradation of aqueous EMEA and DEMEA and formulating a kinetic model that fits the data based on the initial rate of degradation.

Recommendations for the Production of Silicon Carbide‐derived Carbon Based on Intrinsic Kinetic Data

AbstractRecommendations for mode of operation and critical dimensions regarding inner mass transfer limitation were deduced for the technical extraction of silicon from silicon carbide to produce nanoporous carbon (carbide‐derived carbon, CDC). The recommendations are based on intrinsic kinetics derived from experimental data and reaction engineering simulation of the transient process (shrinking‐core like mechanism). As the reaction takes place at 1000 °C under chlorine atmosphere, kinetic data as well as diffusion coefficients are extracted from integral conversion data in a lab scale reactor. The reaction rate dependency for varying chlorine concentrations is represented best by a Hougen‐Watson type rate approach with dissociative adsorption of a reactant. From the experimental data the effective diffusion coefficient of chlorine in the resulting nanoporous carbon could also be derived to 4 · 10–8 m2s–1 at 1000 °C.

A comparative kinetic study on ultra-deep hydrodesulfurization of pre-treated gas oil over nanosized MoS2, CoMo-sulfide, and commercial CoMo/Al2O3 catalysts

Unsupported nanosized MoS2 and CoMo-sulfide catalysts were synthesized, and their catalytic performances for the deep hydrodesulfurization (HDS) of treated gas oil were investigated as compared with that of a CoMo/Al2O3 catalyst. The HDS reactions were carried out in a batch autoclave reactor at 340°C and 3MPa H2. The CoMo-sulfide catalyst shows the highest activity and can reduce the sulfur content to less than 10ppm. The decrease in total sulfur content as a function of reaction time was found to follow pseudo-second order kinetics (empirical form). The change in the concentration of some individual representative sulfur-containing species in gas oil as a function of time was found to follow pseudo-first-order kinetics. However, the change in combined concentration of these species in the gas oil during HDS with the reaction time was found to corroborate pseudo-second-order kinetics. A kinetic model approach was proposed from which an estimation of the intrinsic kinetic data can be achieved. The model fitted the obtained data reasonably well, suggesting its potential for better assessment of the catalytic activity in the HDS of real feedstock. The study reveals that ranking of catalyst activities using model refractory sulfur-containing compounds does not necessarily imply a typical rank in case of investigating the real feedstocks.