Observed Reaction Rate Constants Research Articles

Evaluation of photocatalytic activity of heterojunctions between bismuth oxyhalides and hematite in the degradation of organic compounds in liquid phases under visible light

Photocatalysts were synthesized by constructing p-n type heterojunctions between bismuth oxyhalides BiOX (X = I or Br) and hematite (α-Fe2O3) for enhanced visible light photodegradation of pollutants in aqueous medium. BiOX, in this text called precursors, were synthesized using a modified solvothermal method and by coprecipitation. Hematite was added using hydrothermal treatment. Herein the materials prepared using precursors and hematite are being called catalysts. All materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and adsorption assays with N2. The characterization of BiOX revealed that the solvothermal methods synthesized precursors with greater surface area and structural uniformity than those obtained by coprecipitation. The BiOI precursors, had observed reaction rate constant, kap, values for rhodamine between 0.0054 and 0.0167 min−1. The BiOBr precursors provided values between 0.1016, and 0.0515 min−1. In order to synthesizing the catalysts, an experimental planning was carried out. It showed that Fe/Bi ratio was the variable with the greatest impact on activity, followed by temperature. The BiOI catalysts had kap maximum values for rhodamine between 0.0419, and 0.0213 min−1, while BiOBr catalysts between 0.1144 and 0.1082 min−1. BiOI and BiOBr catalysts provided kap at least 2.0 and 1.12 times greater than their precursors, respectively. Also, successfully degraded phenol, confirming photocatalytic activity of the catalyst surface.

New method of kinetic modeling for CO2 absorption into blended amine systems: A case of MEA/EAE/3DEA1P trisolvent blends

AbstractIn order to establish an accurate kinetic model for the aqueous amine blends, monoethanolamine (MEA), 2‐(ethylamino) ethanol (EAE), and 3‐(diethylamino)‐1‐propanol (3DEA1P) have been chosen as a typical CO2 absorption trisolvents. The reaction kinetics of aqueous amine blends with carbon dioxide have been investigated first combining experiments and molecular simulations. The stopped‐flow technology has been used to obtain the observed reaction rate constant of the overall reactions over the temperature range of 293 to 313 K and at different amine concentrations. A theoretical kinetic model, based on the first‐principles quantum‐mechanical simulations, has been put forward to interpret the reactions between CO2 and the aqueous trisolvent amine blends systems. The proposed model, based on the zwitterion mechanism and the base‐catalyzed mechanism, shows good prediction with an acceptable absolute average deviation (AAD) of 6.32%, and has been found to be satisfactory in determining the kinetics of the involved complicated reactions.

Determination of the kinetics of chlorobenzene nitration using a homogeneously continuous microflow

AbstractThe nitration of chlorobenzene with concentrated mixed acids is a fast and highly exothermic process, which suffers from considerable mass transfer resistance and poor heat transfer rates. The reaction kinetics has not been thoroughly reported before. In this work, a continuous‐flow microreactor system and a homogeneous reaction condition were proposed to obtain accurate chlorobenzene nitration kinetics parameters at high mixed acid concentrations. A general model for predicting the observed reaction rate constants was established. With a new method for estimating the equilibria associated with HNO3 in aqueous sulfuric acid, the rate constants based on nitronium ion and activation energies were obtained. Compared with batch reactors, the continuous‐flow microreactor system allows for a sufficient heat transfer efficiency and accurate residence time control, making it possible to study the reaction performance more quickly and sensitively. This work may provide a reliable reference for the kinetic study of similar processes.

Effect of operating conditions and water matrix on the performance of UV combined electrochemical process for treating Chloride-containing solution and its reaction mechanism

The performance of ultraviolet combined electrochemical (EC) process for treating chloride-containing (UV/EC/Cl-) solution was evaluated based on the N, N-Diethyl-m-toluamide (DEET) degradation. The influences of operating conditions and water matrix on the DEET degradation were investigated, and the reaction mechanism of UV/EC/Cl- process was discussed based on the analysis of DEET degradation pathway, the detection of the steady-state concentrations of active free radicals and the analysis of free radicals scavenging. The observed reaction rate constant of DEET degradation in UV/EC/Cl- process (0.093 min−1) is significantly higher than that of UV/Cl2 process (0.036 min−1), and the synergistic effect on the DEET degradation is remarkable in UV/EC/Cl- process. The current and chloride concentration have remarkable impact on the DEET degradation, while the initial pH, reaction temperature, and initial DEET concentration have slight influence on the DEET degradation. The impact of alkalinity on DEET degradation is more significant than that of ammonia, while sulfate and phosphate have slight effect on the DEET degradation. The active points attacked by free radicals on DEET molecule were predicted basing on density functional theory. During the DEET degradation, small molecular products are produced through a series of reactions such as hydrogen abstraction, substitution, dealkylation, and ring-opening. The steady-state concentrations of HO• and Cl• in UV/EC/Cl- process (1.57 × 10-13 M and 2.37 × 10-14 M, respectively) are higher than those of UV/Cl2 process (1.23 × 10-13 M and 1.07 × 10-14 M, respectively), and HO• and Cl• play key roles in the DEET degradation during the UV/EC/Cl- process.

Determination of nitration kinetics of p-Nitrotoluene with a homogeneously continuous microflow

The kinetics of p-nitrotoluene nitration with mixed acid is important to industrial process design and safety control. However, it's difficult to acquire accurate kinetic data and no kinetics study has ever been reported before because of fast, highly exothermic and heterogeneous characteristics. In this work, a continuous-flow microreactor system including a micromixer, a capillary reactor and an online quenching module was designed to carry out the nitration under a homogeneous reaction condition. The homogeneous nitration can completely eliminate mass transfer resistance between phases, and accurately control reaction temperature and residence time in the continuous-flow microreactor system. The observed reaction rate constants separately based on HNO3 and NO2+, pre-exponential factor and activation energy of p-nitrotoluene nitration were obtained and a general method was established to collect kinetics data for such a kind of fast and highly exothermal nitration reactions.

Kinetic Analysis of Ozonation Degree Effect on the Physicochemical Properties of Ozonated Vegetable Oils

ABSTRACT The aim of this investigation was to evaluate the modification of physicochemical properties (viscosity and density) of four vegetable oils (grapeseed, sunflower, avocado, and olive) during ozonation, and to relate such variation with the ozonation kinetics, the ozonation degree, and the ozonation by-products distribution. During ozonation, the monitorization of the double bonds’ decomposition and accumulation of ozonation by-products yields defined the relationship between the ozonation degree and the physicochemical properties of the ozonated oils. The ozonated oils were characterized by FT-IR and 1H NMR. The ozonation degree was determined by the measurement of the total unsaturation (TU); this method quantified the substrate reactive with ozone contained in oils. During the ozonation, the variation of viscosity, density, and ozonation by-products exhibited differences among the studied oils, which was effectively correlated to the corresponding ozonation degree. These were characterized by the observed reaction rate constants obtained by a parametric algorithm based on the application of a nonlinear least mean square method.

Kinetic and Mechanistic Study of Rhodamine B Degradation by H2O2 and Cu/Al2O3/g-C3N4 Composite

The classic Fenton reaction, which is driven by iron species, has been widely explored for pollutant degradation, but is strictly limited to acidic conditions. In this work, a copper-based Fenton-like catalyst Cu/Al2O3/g-C3N4 was proposed that achieves high degradation efficiencies for Rhodamine B (Rh B) in a wide range of pH 4.9–11.0. The Cu/Al2O3 composite was first prepared via a hydrothermal method followed by a calcination process. The obtained Cu/Al2O3 composite was subsequently stabilized on graphitic carbon nitride (g-C3N4) by the formation of C−O−Cu bonds. The obtained composites were characterized through FT-IR, XRD, TEM, XPS, and N2 adsorption/desorption isotherms, and the immobilized Cu+ was proven to be active sites. The effects of Cu content, g-C3N4 content, H2O2 concentration, and pH on Rh B degradation were systematically investigated. The effect of the catalyst dose was confirmed with a specific reaction rate constant of (5.9 ± 0.07) × 10−9 m·s−1 and the activation energy was calculated to be 71.0 kJ/mol. In 100 min 96.4% of Rh B (initial concentration 20 mg/L, unadjusted pH (4.9)) was removed in the presence of 1 g/L of catalyst and 10 mM of H2O2 at 25 °C, with an observed reaction rate constant of 6.47 × 10−4 s−1. High degradation rates are achieved at neutral and alkaline conditions and a low copper leaching (0.55 mg/L) was observed even after four reaction cycles. Hydroxyl radical (HO·) was identified as the reactive oxygen species by using isopropanol as a radical scavenger and by ESR analysis. HPLC-MS revealed that the degradation of Rh B on Cu/Al2O3/CN composite involves N-de-ethylation, hydroxylation, de-carboxylation, chromophore cleavage, ring opening, and the mineralization process. Based on the results above, a tentative mechanism for the catalytic performance of the Cu/Al2O3/g-C3N4 composite was proposed. In summary, the characteristics of high degradation rate constants, low ion leaching, and the excellent applicability in neutral and alkaline conditions prove the Cu/Al2O3/g-C3N4 composite to be a superior Fenton-like catalyst compared to many conventional ones.

Removal of Tetrachloroethene in Water with Nano Pd/Fe Bimetal Immobilized in Alginate Beads

In this study, nZVI, nPd/Fe and nPd/Fe-B particles were synthesized and used to remove PCE in solution to investigate the effects of several parameters such as the types of metal particles and their mass concentration. From the elemental mapping images of energy dispersive spectrometer (EDS), amorphous Fe and Pd were tightly integrated into the alginate matrix, which cannot be solely exfoliated from the whole composites. The results showed that the removal efficiency (r) and observed reaction rate constants (kobs) was the highest for nPd/Fe, followed by nPd/Fe-B and nZVI particles. Moreover, the larger the reductant dosage, the higher the r of PCE for nZVI, nPd/Fe, and nPd/Fe-B particles is. The pH in solution quickly raised from about 5-6 to 8-9 at the beginning of tests and then maintained at around 8-9 to the end of tests. The ORP in solutions descended to reductive state immediately at the beginning of tests and kept in the range between -730 and -770 mV to the end of tests indicating that the system maintained in a stable reductive state.

Experimental evaluation of nitrate reduction from water using synthesis nanoscale zero-valent iron (NZVI) under aerobic conditions

The aim of this research was to study the potential of synthesized nanoscale zero-valent iron for nitrate reduction in aqueous solution. Batch technique was used to determine the kinetics and effective parameters. The effects of initial pH level, initial nitrate concentration and nanoscale Fe° concentration on nitrate reduction were studied. Nanoscale zero-valent iron was synthesized by chemical reduction method. The TEM image showed that synthesized nano Fe° has a size in the range of 40-120 nm. Experimental results exhibited that reduction efficiency of nitrate decreases with increasing initial pH and increases significantly due to increasing the concentration of zero-valent iron nanoparticles. Also, it was illustrates that initial concentration of nitrate has little effect on the nitrate reduction efficiency. Under acidic and neutral conditions, pH level of the reaction solution increased considerably after 60 min. However, under alkaline conditions, pH level of the reaction solution decreased. The reduction rate of nitrate reached 80% in 60 min with nanoscale Fe° dosage of 1.0 gl -1 and pH in4. The observed reaction rate constant was determined to be 0.0255 in min -1 for nanoscale concentration 1.0 gl -1. The experimental results indicated that the nitrate reduction with zero-valent iron nanoparticles do not comply the first-order reaction model with respect to nitrate concentration.

Kinetics of Carbon Dioxide Absorption into Water-Lean Potassium Prolinate/Ethylene Glycol Solutions

Kinetics of the reaction of carbon dioxide (CO2) with potassium prolinate (ProK) in water-lean ethylene glycol was measured using a stirred cell reactor at temperatures from 283.2 to 313.2 K with ProK concentrations ranging from 0.5 to 2.0 M. Physicochemical properties including Henry’s constant of N2O and CO2 were measured or estimated for the investigated solutions. A proposed correlation was used to calculate the liquid-side physical mass transfer coefficient. The observed reaction rate constants (kobs) were obtained from the measured absorption flux against CO2 partial pressure under the pseudo-first-order regime conditions. Results show that the overall pseudo-first-order rate constant kov increases remarkably as the increasing ProK concentration and temperature. The reaction order with respect to ProK is found to vary between 1.76 and 1.91 over the temperature range, which is quite different from that observed in aqueous ProK systems. The kinetic results were also nonlinearly regressed to fit the mo...

Sorption and desorption of BrF3 on NaF: Studies on thermodynamics and kinetics

Temperature dependence of bromine trifluoride vapor pressure over its adduct with sodium fluoride has been determined; the adduct normal dissociation temperature has been determined. Kinetics of sorption and desorption processes in BrF3(gas)–NaF(solid) system have been studied.The equation was proposed to illustrate the link between forward reaction rate (Ка) described by Arrhenius equation and experimental value (Ki):Ki= Kа⋅ (Pa/Peq)m,where Ki – observed reaction rate constant, Ka – forward reaction rate constant described by Arrhenius equation; Pa – partial pressure of BrF3; Peq – equilibrium pressure of BrF3 above BrF3⋅3NaF; m – factor characterizing the interaction area of BrF3 with NaF. The application of this equation makes possible to determine the true reaction rate values and reaction activation energy in chemisorption terms; it also helps to calculate the degree BrF3 sorption on NaF reaction at different temperatures and adsorbate pressures.The possibility of sorption-desorption separation of bromine trifluoride – uranium hexafluoride – iodine pentafluoride system with use of sodium fluoride was shown.

Kinetics and mechanism of reaction between carbon disulfide and novel aqueous amines solutions

The mechanism and kinetics of carbon disulfide (CS2) capture by aqueous solutions of well known alkanolamines ([monoethanolamine (MEA) and diethanolamine (DEA)] and novel cyclic mono- and polyamines [morpholine (MRPH), piperazine (PZ), n-methyl piperazine (NMPZ) and n-hydroxyethyl piperazine (NHEPZ)] were investigated by stopped-flow apparatus with conductivity detection. The observed reaction rate constants were obtained for a temperature range of 298.15-313.15 K and it was found that cyclic amines react much faster than others. A modified termolecular reaction mechanism was used to analyse the experimental kinetic data. The activation energies for all systems were also obtained by evaluating the Arrhenius equation.

Kinetics and Mechanism of Reaction between Carbon Disulfide and Novel Aqueous Amines Solutions

The mechanism and kinetics of carbon disulfide (CS2) capture by aqueous solutions of well known alkanolamines ([monoethanolamine (MEA) and diethanolamine (DEA)] and novel cyclic mono- and polyamines [morpholine (MRPH), piperazine (PZ), n-methyl piperazine (NMPZ) and n-hydroxyethyl piperazine (NHEPZ)] were investigated by stopped-flow apparatus with conductivity detection. The observed reaction rate constants were obtained for a temperature range of 298.15-313.15 K and it was found that cyclic amines react much faster than others. A modified termolecular reaction mechanism was used to analyse the experimental kinetic data. The activation energies for all systems were also obtained by evaluating the Arrhenius equation.

Investigation of fixed-bed photocatalytic membrane reactors based on submerged ceramic membranes

Though having been studied for more than four decades, photocatalysis is still hardly applied in large-scale water and wastewater treatment. This is mainly due to the low energy efficiency of conventional photocatalytic reactors. A recently introduced reactor concept, the fixed-bed photocatalytic membrane reactor (FPMR), can potentially overcome this shortcoming. Its performance for the degradation of organic compounds is examined for different modes of operation. For this purpose, FPMRs based on commercial submerged ceramic membranes were used, which are covered by a photocatalytic layer of pyrogenic titania. The FPMRs were performed in two operational modes: closed-loop reactor and continuous-flow reactor. Oxalic acid was used as a model organic compound to conduct photocatalysis. The influence of light intensity and catalyst layer thickness as well as mass transfer inside the layer were thoroughly studied. The evaluation of the reactors was based on the apparent quantum yield, the photocatalytic space–time yield and specific energy consumption. The results demonstrate that the FPMRs are considerably more efficient than other reported reactor concepts. Its apparent quantum yield can reach up to 11.1%. Furthermore, its specific light energy consumption is merely around 0.1 kWh/g (TOC). The results also reveal that closed-loop FPMRs achieve higher efficiencies than continuous-flow FPMRs. Last but not least, a quantitative model for calculating the reaction rate constant of a photocatalytic membrane from observed reaction rate constant of a photocatalytic membrane reactor was developed and experimentally verified.

Mechanisms and Characterization of the Pulsed Electron-Induced Grafting of Styrene onto Poly(tetrafluoroethylene-co-hexafluoropropylene) to Prepare a Polymer Electrolyte Membrane.

During the pulsed-electron beam direct grafting of neat styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) substrate, the radiolytically-produced styryl and carbon-centered FEP radicals undergo various desired and undesired competing reactions. In this study, a high-dose rate is used to impede the undesired free radical homopolymerization of styrene and ensure uniform covalent grafting through 125-μm FEP films. This outweighs the enhancement of the undesired crosslinking reactions of carbon-centered FEP radicals and the dimerization of the styryl radicals. The degree of uniform grafting through 125-μm FEP films increases from ≈8%, immediately after pulsed electron irradiation to 33% with the subsequent thermal treatment exceeding the glass transition temperature of FEP of 39°C. On the contrary, steady-state radiolysis using 60Co gamma radiolysis, shows that the undesired homopolymerization of the styrene has become the predominant reaction with a negligible degree of grafting. Time-resolved fast kinetic measurements on pulsed neat styrene show that the styryl radicals undergo fast decays via propagation homopolymerization and termination reactions at an observed reaction rate constant of 5 × 108 l · mol-1 · s-1. The proton conductivity of 25-μm film at 80°C is 0.29 ± 0.01 s cm-1 and 0.007 s cm-1 at relative humidity of 92% and 28%, respectively. The aims of this work are: 1. electrolyte membranes are prepared via grafting initiated by a pulsed electron beam; 2. postirradiation heat-treated membranes are uniformly grafted, ideal for industry; 3. High dose rate is the primary parameter to promote the desired reactions; 4. measurement of kinetics of undesired radiation-induced styrene homopolymerization; and 5. The conductivity of prepared membranes is on par or higher than industry standards.

Solid surface-mediated photochemical transformation of decabromodiphenyl ether (BDE-209) in aqueous solution

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants which have received considerable attention due to their global distribution, bioaccumulation potential, environmental persistence, and possible toxic effects. In this work, the photodegradation of decabromodiphenyl ether (BDE-209) in aqueous system was investigated by preloading it on the surface of various solid matrices. After 6 h of Xe lamp irradiation, almost complete degradation of BDE-209 was observed on silica gel (SG), with much slower degradation occurring in other adsorbents. The degradation of BDE-209 on SG sample followed pseudo-first-order kinetics, and the observed reaction rate constant was decreased by lowering pH, adding humic acid and increasing the initial BDE-209 concentration. In addition to direct photolysis, BDE-209 could be oxidized by hydroxyl radicals generated from SG, as confirmed by the electron paramagnetic resonance (EPR) technology. Product analysis showed that BDE-209 was mainly decomposed into lower brominated PBDEs, polybrominated dibenzofurans (PBDFs), hydroxylated PBDEs (OH-PBDEs), hydroxylated PBDFs (OH-PBDFs), bromophenols and bromide ions. Thus, consecutive debromination, intramolecular elimination of HBr, hydroxyl addition and the cleavage of ether bond were proposed as the degradation pathways. This study may help understanding the photochemical transformation of solid surface adsorbed BDE-209 in natural surface waters, which is important to evaluate the environmental fate of PBDEs.

Kinetics of reaction between CO2 and ionic liquid-carbon dioxide binding organic liquid hybrid systems: Analysis of gas-liquid absorption and stopped flow experiments

It is generally accepted that CO2 emissions from point sources – such as thermal power plants – can be controlled by gas-liquid absorption where the process is intensified significantly by introducing a reactantinto solvent. In this work, blends of 1-ethyl-3-methyl imidazolium bis (trifluoromethylsulfonyl) imide ([emim][Tf2N]) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (or 1,1,3,3-tetramethylguanidine (TMG)) in 1-hexanol were studied. Gas absorption experiments were carried out in a gas-liquid mini reactor for the hybrid systems containing different weight concentrations of organic bases while keeping the ionic-liquid weight percentage constant. Total amount of absorbed CO2 was measured as function of time and the absorption (or loading) capacities and the initial absorption rates have been obtained at 313K. It was found that increasing the amount of the organic base increased the loading capacity of CO2. Also, reusability and performance loss of hybrid solutions were investigated by using Fourier transform infrared spectrometry under sequential absorption-desorption cycles. The intrinsic reaction rates were measured in a stopped flow equipment for a temperature range of 283–303K. The empirical power law reaction orders with respect to DBU and TMG were found to be between 1.0 and 2.0 at different temperatures and the kinetic data could be interpreted satisfactorily by a modified termolecular reaction mechanism.Finally, the observed reaction rate constants inferred from heterogeneous gas absorption rates – through estimated solubility and diffusivity – were compared with the homogeneous – intrinsic – reaction rate constants obtained by a rapid mixing technique, namely stopped-flow conductimetry. The observed pseudo first order rate constants at 313K were found to be very similar and the deviations remained within 5–15%. Obtaining relevant data by these two very different techniques in the same laboratory provided pros and cons of each method and clarified – often – biased ambiguities.

Adiabaticity of the proton-coupled electron-transfer step in the reduction of superoxide effected by nickel-containing superoxide dismutase metallopeptide-based mimics.

Nickel-containing superoxide dismutases (NiSODs) are bacterial metalloenzymes that catalyze the disproportionation of O2(-). These enzymes take advantage of a redox-active nickel cofactor, which cycles between the Ni(II) and Ni(III) oxidation states, to catalytically disprotorptionate O2(-). The Ni(II) center is ligated in a square planar N2S2 coordination environment, which, upon oxidation to Ni(III), becomes five-coordinate following the ligation of an axial imidazole ligand. Previous studies have suggested that metallopeptide-based mimics of NiSOD reduce O2(-) through a proton-coupled electron transfer (PCET) reaction with the electron derived from a reduced Ni(II) center and the proton from a protonated, coordinated Ni(II)-S(H(+))-Cys moiety. The current work focuses on the O2(-) reduction half-reaction of the catalytic cycle. In this study we calculate the vibronic coupling between the reactant and product diabatic surfaces using a semiclassical formalism to determine if the PCET reaction is proceeding through an adiabatic or nonadiabatic proton tunneling process. These results were then used to calculate H/D kinetic isotope effects for the PCET process. We find that as the axial imidazole ligand becomes more strongly associated with the Ni(II) center during the PCET reaction, the reaction becomes more nonadiabatic. This is reflected in the calculated H/D KIEs, which moderately increase as the reaction becomes more nonadiabatic. Furthermore, the results suggest that as the axial ligand becomes less Lewis basic the observed reaction rate constants for O2(-) reduction should become faster because the reaction becomes more adiabatic. These conclusions are in-line with experimental observations. The results thus indicate that variations in the axial donor's ability to coordinate to the nickel center of NiSOD metallopeptide-based mimics will strongly influence the fundamental nature of the O2(-) reduction process.

Insights into the Relationship of Catalytic Activity and Structure: A Comparison Study of Three Carbonic Anhydrase Mimics

ABSTRACTDensity functional theory (DFT) calculations were used to study the mechanism of CO2 hydrolysis by Zn‐(1,5,9‐triazacyclododecane) and Zn‐cyclam and evaluate the associated thermodynamic and kinetic parameters. Microkinetic models were then built based on the kinetics and thermodynamics derived from first principles. Both catalysts showed very similar behavior to Zn‐cyclen, which we have reported previously, but with multiple distinctions. The intrinsic reaction rate constants for Zn‐(1,5,9‐triazacyclododecane) and Zn‐cyclam were calculated to be 2693 and 4623 M−1 s−1, respectively, which is in reasonable agreement with experimental values reported or estimated. The CO2 adsorption step was found to be a rate‐limiting step for all three catalysts. Zn‐cyclam has the lowest barrier for this step due to the highest pKa or nucleophilicity of the Zn‐OH− form, and, therefore, the highest intrinsic activity. However, the observed reaction rate constant also depends on the availability of the catalyst. The decrease in the observed reaction rate constant over 0–12 ms was ascribed to the decrease in the concentration of the catalytic form, Zn‐OH−, which was primarily converted to Zn‐HCO3−. The reaction rate constant of Zn‐cyclam dropped much faster than those of Zn‐cyclen and Zn‐(1,5,9‐triazacyclododecane) due to lower energy of the Zn‐HCO3− form. The conversion of CO2 at 1000 ms as a function of pH was calculated to compare the relative activity of these catalysts, and Zn‐cyclen was found to be the best catalyst.

Observed Kinetic Parameters during the Torrefaction of Red Oak (Quercus rubra) in a Pilot Rotary Kiln Reactor

The torrefaction of red oak (Quercus rubra) was performed in a pilot rotary kiln reactor, and the apparent kinetic results were compared with the results of torrefaction performed in a bench-scale fluidized reactor. Mass loss, gross calorific analyses, ultimate analyses, and proximate analyses were applied to the final torrefied material. The experimental torrefaction temperatures were 250, 275, 300, and 325 °C, and the experimental total torrefaction times were 20, 35, 50, and 80 min. A significant variation of the energy content occurred in the range of temperature between 275 and 300 °C, with the energy yield changing from 97.5% to 83.6%, respectively. The molar ratios H:C:O for the torrefied red oak presented a behavior independent of the experimental equipment when the temperature ranged between 250 and 325 °C. For the torrefaction process of red oak in the pilot rotary kiln reactor, a first-order reaction and one-step kinetic model were fitted with a maximum error of about 7.5% at 325 °C. The observed reaction rate constant (k) for the rotary reactor was 0.072 min−1 at 300 °C, which was 71% lower than the reaction rate constant for torrefied red oak in a bench-scale fluidized reactor. Arrhenius analysis determined an activation energy of 20.4 kJ/mol and a frequency factor of 5.22 min−1. The results suggest significant external heat and mass-transfer resistances in the rotary system.