First-order Chemical Kinetics Research Articles

Biosynthesis of NiFe2O4 nanoparticles using Murayya koenigii for photocatalytic dye degradation and antibacterial application

Biosynthesis of nickel ferrite (NiFe2O4) nanoparticles (NPs) using an aqueous extract of Murraya koenigii (M. koenigii) leaves is a novel, environmentally benign and cost effective method. NiFe2O4 NPs were characterized by different spectroscopic and microscopic techniques, including Ultraviolet–Visible (UV–Vis) spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, Thermogravimetric Analysis (TGA), Transmission Electron Microscopy (TEM), High-Resolution Scanning Electron Microscopy (HRSEM), Energy-dispersive X-ray spectrometry (EDX) and Vibrating-Sample Magnetometer (VSM). The observed results revealed that prepared NiFe2O4 NPs are highly pure, crystalline, partially spherical with an average size of 2–6 nm and attribute magnetic properties. The magnetization of the obtained biosynthesized nanoparticles is noticed ∼5.2 emu/g at 10 K Oe. The NiFe2O4 NPs exhibited a heterogeneous photo Fenton's catalytic feature in the presence of oxalic acid at ambient conditions. The effects of pH, dosage of NiFe2O4 catalyst and doses of oxalic acid on the degradation efficiency of 10 mg/L MB dye were assessed. The optimal degradation efficiency of ⁓ 98.5% was achieved within 70 min, and the observed results elucidated that the photocatalytic reactions follow first-order chemical kinetics. Thermodynamic parameters such as activation energy (Ea), enthalpy of activation (ΔH‡), entropy of activation (ΔS‡), and free energy of activation (ΔG‡) were evaluated, applying Arrhenius and activated complex theory ascertained the endothermic, less random and nonspontaneous features of photocatalytic process. NiFe2O4 NPs were also tested against different bacteria and found to have antibacterial properties. Hence, magnetic NiFe2O4 NPs can be exploited for its multifunctional applications, and specifically for the remediation of dye-contaminated wastewater.

Thermodynamic Characterization of Grease Oxidation–Thermal Stability via Pressure Differential Scanning Calorimetry

This study investigates and characterizes, via thermodynamic laws, a widely employed standard for measuring oxidation-thermal stability of lubricating greases—ASTM 5483—based on first-order chemical kinetics, using pressure differential scanning calorimetry (PDSC). Steps and active mechanisms in the controlled test are analyzed and modeled using energy and entropy transformations. Applying the degradation-entropy generation (DEG) theorem, oxidation induction time is related to accumulated oxidation entropy and entropy transfer by mass flow to obtain characteristic degradation coefficients. These DEG coefficients are calibrated using available measured data from the literature and subsequently used to predict induction times at various temperatures. DEG elements—trajectories, planes, and domain—presented here consistently characterized all greases studied. Results show that the high-pressure entropy transfer by oxygen mass flow in the final step of the ASTM 5483 procedure is the primary contributor to oxidation induction time, verifying the significance of this process in accelerating antioxidant depletion, which would otherwise take months to years under atmospheric conditions. DEG-predicted induction times at various temperatures are compared to induction times predicted by the first-order chemical kinetics model, revealing a close match. The new DEG model is also herein used to predict induction times at atmospheric pressure, whereas the first-order kinetics model is independent of pressure and limited to the specific conditions in ASTM 5483. The DEG approach has useful implications for the accelerated and unaccelerated evaluation of grease oxidation stability and grease useful life.

Moment method for the Boltzmann equation of reactive quaternary gaseous mixture

We are interested in solving the Boltzmann equation of chemically reacting rarefied gas flows using the Grad’s-14 moment method. We first propose a novel mathematical model that describes the collision dynamics of chemically reacting hard spheres. Using the collision model, we present an algorithm to compute the moments of the Boltzmann collision operator. Our algorithm is general in the sense that it can be used to compute arbitrary order moments of the collision operator and not just the moments included in the Grad’s-14 moment system. For a first-order chemical kinetics, we derive reaction rates for a chemical reaction outside of equilibrium thereby, extending the Arrhenius law that is valid only in equilibrium. We show that the derived reaction rates (i) are consistent in the sense that at equilibrium, we recover the Arrhenius law and (ii) have an explicit dependence on the scalar fourteenth moment, highlighting the importance of considering a fourteen moment system rather than a thirteen one. Through numerical experiments we study the relaxation of the Grad’s-14 moment system to the equilibrium state.

Dissipation Behavior and Residue Distribution of Famoxadone and Cymoxanil in Cucumber and Soil Ecosystem Under Open-Field Conditions

In this study, a practical and excellent method was used to determine the famoxadone and cymoxanil via high-performance liquid chromatography equipped utilizing ultraviolet detector lamp (HPLC-UV) for investigating the dissipation behavior and residue distribution of famoxadone and cymoxanil in cucumber and soil ecosystem. The limit of quantification (LOQS) of famoxadone and cymoxanil in cucumber were 0.50, 1.00, 2.00 and 0.05, 0.50, 1.00 mg kg−1 in soil, respectively. The limit of detection (LODS) of both famoxadone and cymoxanil were 8.0 ng. The average recoveries (n = 5) of the fungicide ranged from 84.10 to 108.02% with the relative standard deviations (RSDs) typically < 9.23%. The fungicide was applied to cucumber and soil at the range of doses (275.6–413.4 g a.i.ha−1) three or four times. The half-lives of famoxadone and cymoxanil in cucumber and soil were 1.34–16.12 days, which followed the first-order chemical reaction kinetics equation Ct = C0 × e-kt. The residues of famoxadone and cymoxanil in cucumber at the pre-harvest interval (PHI, 3 days) were below 8.0 × 10−8 g and 8.0 × 10−9 g, respectively. Overall, this study evaluated the food safety and the environmental fate of famoxadone and cymoxanil in cucumber and soil ecosystem. In addition, this study would promote the series of work on the pesticide exposure assessment of these fungicides as well.

Preferential alkaline leaching of amphoteric elements from super-stoichiometric hydrogen storage alloy

Long-lasting charge/discharge cycling (−0.5C/+0.5C) of a super-stoichiometric hydrogen storage alloy with LaNi4.5Co0.5Al0.32Sn0.34Zn0.10 composition has been carried out in a 6 M KOH solution to evaluate the role of selective dissolution of amphoteric elements (Al, Sn and Zn) in electrochemical hydrogenation properties and corrosion behaviour of the hydride electrode. Among alloy constituents, leaching efficiency is the most evident for Sn and Zn additions. Rates of Ni and Co leaching are 2 orders of magnitude lower whereas La is not leached at all. Selective leaching of Al, Sn and Zn is prone to improved material activation and has a minor effect on material passivation and capacity fade. Selective leaching of amphoteric elements as a result of alkaline cycling follows a first-order chemical kinetics law.

Universal Algorithm for Simulating and Evaluating Cyclic Voltammetry at Macroporous Electrodes by Considering Random Arrays of Microelectrodes.

An algorithm for the simulation and evaluation of cyclic voltammetry (CV) at macroporous electrodes such as felts, foams, and layered structures is presented. By considering 1D, 2D, and 3D arrays of electrode sheets, cylindrical microelectrodes, hollow‐cylindrical microelectrodes, and hollow‐spherical microelectrodes the internal diffusion domains of the macroporous structures are approximated. A universal algorithm providing the time‐dependent surface concentrations of the electrochemically active species, required for simulating cyclic voltammetry responses of the individual planar, cylindrical, and spherical microelectrodes, is presented as well. An essential ingredient of the algorithm, which is based on Laplace integral transformation techniques, is the use of a modified Talbot contour for the inverse Laplace transformation. It is demonstrated that first‐order homogeneous chemical kinetics preceding and/or following the electrochemical reaction and electrochemically active species with non‐equal diffusion coefficients can be included in all diffusion models as well. The proposed theory is supported by experimental data acquired for a reference reaction, the oxidation of [Fe(CN)6]4− at platinum electrodes as well as for a technically relevant reaction, the oxidation of VO2 + at carbon felt electrodes. Based on our calculation strategy, we provide a powerful open source tool for simulating and evaluating CV data implemented into a Python graphical user interface (GUI).

APLICACIÓN DE LA TEORÍA DE PERCOLACIÓN Y LA GEOMETRÍA FRACTAL EN LA PRODUCCIÓN DE METANO EN RELLENO SANITARIO

The estimation of methane generation in landfill is based mainly on first-order chemical kinetics, which is a good theory for gaseous media or in solution, i.e. a homogeneous media; however in landfill, conversions lower than expected yields are observed. In this paper we propose the consideration of the sanitary landfill heterogeneity, through the classic percolation theory, and introducing a&nbsp; &nbsp;factor in first order models to reduce the error of the methane estimations in the landfill. This percolation factor () only considers the degradation of organic matter in methanogenic zones, which we propose immersed in the percolation clusters (including the infinite cluster), so&nbsp; ={1/4,2/3}. When including &nbsp;in the Hoeks model (Hoeks, 1983), and fractal-like Hoeks model (Meraz et al, 2004), conversions of 22-59% and 12-33% are reached at 30 years of closed site, respectively. These ranges are within what was estimated by Bogner and Spokas (1993), 25-40% conversion for the same time period.

Acoustic Wave Catalyzed Urea Detection Utilizing a Pulsatile Microdroplet Sensor

We observe variations in the electrical resistance across a conducting water microdroplet when it was placed on a glass substrate before being mechanically vibrated at natural frequency with the help of an acoustic source. The reduction in the resistance across the droplet was magnified owing to the formation of vortices in the matrix when the periodic oscillation of the surface was increased. The variation in the resistance could be tuned with the frequency of the sound source, which was found to be maximum when a 10 μL droplet was vibrated at ∼320 Hz. Interestingly, the variation in resistance across the oscillating droplet could follow and distinguish the musical notes in the octaves (“sur”) or rhythmic cycles (“taal”) originating from musical instruments such as flute, harmonium, whistle, and tabla. Further, when a suspension of urease-stabilized gold–cadmium–sulfide nanocomposite was suspended inside the droplet and mixed with an analyte containing urea solution, the change in the resistance during the operational time period was found to monotonically vary with the concentration of urea in the analyte. The enzymatic reaction between urea and urease was found to follow a faster first-order chemical kinetics than the commonly observed Michaelis–Menten pathway owing to the presence of the moving nanocomposites and mixing vortices under the optimal acoustic excitations. The specific lock-and-key enzymatic reaction helped in extending these experimental results to estimate the unknown levels of urea in human blood serum samples.

Guidelines for the Voltammetric Study of Electrode Reactions with Coupled Chemical Kinetics at an Arbitrary Electrode Geometry.

A powerful, unified, and simplifying mathematical approach for the theoretical treatment of first-order chemical kinetics coupled to interfacial charge transfers at electrodes of arbitrary geometry and size, both uniformly accessible and nonuniformly accessible to the electroactive species, is presented. The general CEC mechanism at spherical and disc electrodes is considered to test the validity and benefits of such an approach, based on the application of the so-called kinetic steady state, that enables the reduction of the multivariable problem of kinetic-diffusive differential equations to a single variable problem of a diffusion-only differential equation. This is solved both analytically and numerically, showing how this approach leads to general, simple, and efficient solutions for the study of the influence of coupled chemical kinetics on the voltammetric response. The voltammetry of the CEC mechanism is analyzed as a function of the kinetics and thermodynamics of the preceding and subsequent chemical reactions and of the electrode size (from macroelectrodes to ultramicroelectrodes) and shape (spherical and disc). Comparison with the responses of the CE, EC, and E mechanisms is included, proposing diagnosis criteria and procedures for quantitative analysis of experimental data.

Kinetics of elemental sulfur reduction by petroleum hydrocarbons and the implications for hydrocarbon thermal chemical alteration

Abstract Although sulfur-containing compounds are known to play a significant role in the diagenic and catagenic processes that generate oil and gas, relatively little is known about the kinetics of reactions between elemental S and petroleum hydrocarbons. To investigate this subject, a series of closed-system pyrolysis experiments using paraffin, a low-sulfur oil, and a high-sulfur oil with and without elemental S were conducted, and first-order chemical kinetics were fit to the experimental results. The average value for the activation energy required to reduce elemental S to H2S and to thermochemically alter higher molecular weight hydrocarbons to methane was calculated to be 193 kJ mol−1 (46 kcal mol−1). The results of this study demonstrate that under typical geologic conditions the rate of reduction of elemental S to H2S by petroleum hydrocarbons is quite rapid. The maximum time for substantial amounts of elemental S to persist in contact with petroleum hydrocarbons is estimated to be no more than a few million years in cool reservoirs (e.g., 120 °C) the half-life of elemental S may be as short as hundreds of years. Additionally, the presence of elemental S substantially lowers the onset temperature of hydrocarbon thermal chemical alteration (TCA). The activation energy for TCA of a low-sulfur oil to generate methane is estimated to be lowered by 92 kJ mol−1 (22 kcal mol−1) due to the presence of elemental sulfur. Consequently, the presence of elemental S in petroleum reservoirs is expected to lower the thermal stability of oil and decrease the maximum depth at which oil occurs within a basin (thermal deadline). The observed acceleration of hydrocarbon TCA is possibly due to organic sulfur compounds (e.g., thiols and sulfides) that form through the reaction of H2S or polysulfides with hydrocarbons and subsequently thermally degrade leading to the formation of sulfur radicals that in turn enhance TCA reactions.

Evaluation of the bioaccumulation potential of selected alternative brominated flame retardants in marine fish using in vitro metabolic transformation rates

The global consumption of alternative brominated flame retardants (BFRs) has increased with the restriction of the first generation BFRs such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). However, many alternative BFRs are suspected to be persistent in the environment and possibly bioaccumulative after their release into the environment because of their chemical properties, which are similar to those of the already banned BFRs. In this study, the bioaccumulation potential of selected alternative BFRs (1,2-bis(2,4,6‑tribromophenoxy)ethane (BTBPE), 1,2,3,4,5,6‑hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), 2,3,4,5,6‑pentabromotoluene (PBT), 2‑ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and 2,3,4,5‑tetrabromo-6-chlorotoluene (TBCT)) was evaluated. The in vitro depletion rate constants (kdepl) were measured for the alternative BFRs using liver S9 fractions isolated from five marine fish species (Epinephelus septemfasciatus, Konosirus punctatus, Lateolabrax japonicus, Mugil cephalus, and Sebastes schlegelii) that inhabit the oceans off the Korean coast. The measured kdepl values were converted to in vitro intrinsic clearance rate constants (CLin vitro) to estimate whole-body metabolic rate constants (kMET) using an in vitro to in vivo extrapolation (IVIVE) model. Finally, the bioconcentration factors (BCF) were determined using a one-compartment model. The transformation kinetics for obtaining kdepl agreed well with first-order chemical kinetics, regardless of initial BFR concentrations. The values of CLin vitro were lower in the selected marine fish species than those in freshwater fish species, implying slower metabolic transformation. The derived BCF values based on the total concentration in water (BCFTOT) ranged from 16 (TBB in M. cephalus) to 27,000 (HBB in K. punctatus). The BCF values for HBB and PBT were >2000 except for those in M. cephalus suggesting further investigation of BCF values of BFRs whose log KOW is between 6 and 7.

Analytical solutions for the study of homogeneous first-order chemical kinetics via UV–vis spectroelectrochemistry

Analytical solutions are reported for the identification and study of homogeneous chemical reactions via UV–vis spectroelectrochemistry. Expressions are presented for the concentration profiles and the absorbance response of any the species of the CEC mechanism when applying a potential-pulse perturbation under semi-infinite linear diffusion conditions. With this theory it is possible to relate easily the absorbance transient to the physicochemical dynamics of the redox system. In particular, the influence of the chemical reactions involving the oxidized and/or the reduced species will be investigated both in the normal and parallel beam configurations. Expressions for the reaction schemes CE, EC and E can be deduced as particular cases. The EC solutions are applied to the study of facilitated ion transfers across liquid|liquid interfaces where the likely different diffusivity of the ion in the two phases has been considered.

Air-Parcel Residence Times Within Forest Canopies

We present a theoretical model, based on a simple model of turbulent diffusion and first-order chemical kinetics, to determine air-parcel residence times and the out-of-canopy export of reactive gases emitted within forest canopies under neutral conditions. Theoretical predictions of the air-parcel residence time are compared to values derived from large-eddy simulation for a range of canopy architectures and turbulence levels under neutral stratification. Median air-parcel residence times range from a few sec in the upper canopy to approximately 30 min near the ground and the distribution of residence times is skewed towards longer times in the lower canopy. While the predicted probability density functions from the theoretical model and large-eddy simulation are in good agreement with each other, the theoretical model requires only information on canopy height and eddy diffusivities inside the canopy. The eddy-diffusivity model developed additionally requires the friction velocity at canopy top and a parametrized profile of the standard deviation of vertical velocity. The theoretical model of air-parcel residence times is extended to include first-order chemical reactions over a range of of Damkohler numbers (Da) characteristic of plant-emitted hydrocarbons. The resulting out-of-canopy export fractions range from near 1 for $$Da =10^{-3}$$ to less than 0.3 at $$Da = 10$$ . These results highlight the necessity for dense and tall forests to include the impacts of air-parcel residence times when calculating the out-of-canopy export fraction for reactive trace gases.

Carbon Mineralization in Soils Irrigated with Treated Swine Wastewater

Treated swine wastewater agricultural use can promote environmental and agronomical improvements, however, the inappropiate management of this organic load added on soil can cause unbalances in soil fertility and in availability of nutrients and/or contaminants. Thus, this study aim was evaluate the organic matter biodegradation of treated swine wastewater (WB) and diluted swine wastewater (WBD) applied in Oxisol clayey texture (CS) and in Ultisol (SS) with medium-sandy texture. The treatments studied were: R1 – CS control; R2 – irrigation with WB on CS; R3 – irrigation with WBD on CS; R4 – SS control; R5 – irrigation with WBD on SS; R6 – irrigation with WBD on SS. Three applications were done in flasks containing 500 g of soils sampled from depth of 0-20 cm, the C-CO2 evolutions and degradation fractions were quantified after each application. The results obtained were adjusted to first-order chemical kinetics model. More than half organic matter was biodegraded between 4 and 10 days of incubation, when higher WB amount was applied (33.3 mm). Sucessive WBD use caused degradation of organic matter remaning of previous application. Higher CO2 evolutions were obtained for Oxisol treatments due to higher carbon contents of this soil. SW use caused depletion of Ultisol native organic matter. However, the WB use in Oxisol provided accumulation of organic matter. Soon, the respirometry test evidenced the importance of evaluate the soil depuration capacity before agricultural use, since that this process can affect the contents of organic matter native of these soils and the availabity of nutrient/contaminant for soil-water-plant system.

Impedance of Mediated Electrochemical Processes: Fenton Reaction

Impedance is a powerful technique that provides a deep insight into the mechanism, kinetics, and thermodynamics of various physicochemical processes. Impedance of electrochemical systems coupled with homogeneous chemical reactions is seldom reported. Catalytic processes governed by the EC′ mechanism are of particular relevance since these processes are widely employed for mediated electrochemical oxidation of persistent environmental pollutants, gas sensing, catalytic hydrogen evolution, carbon dioxide electroreduction, enzyme oxidation, electrochemistry of nucleic acids, amino acids, as well as for numerous other bioanalytical applications. These system has been investigated almost exclusively by using classical transient electrochemical methods. Recently we have developed an analytical expressions describing the faradaic impedance of the catalytic processes governed by (pseudo) first-order chemical kinetics. The solution was obtained in the rigorous treatment and it is applicable to the analysis of the experimental EC’ systems regardless the kinetics of the homogeneous and electrochemical steps.1 We have found that unequal diffusivities of the oxidized and reduced forms of the redox mediator have a strong effect on the impedance characteristics of the catalytic EC’ systems. This behavior is related to the novel impedance element, which reduces to the Gerischer impedance when both diffusion coefficients are equal.1 In this study we demonstrate how to fully characterize EC’ type processes by using impedance spectroscopy and our model. Provided equivalent circuit together with potential dependence of all impedance parameters allow for a rapid and precise determination of all kinetic and thermodynamic parameters of EC’ type reactions. For Fenton reaction, the formal potential, E 0’, heterogeneous, k 0, and homogeneous, k, rate constants, electron transfer coefficients, α, β, and both diffusion coefficient of the redox mediator D ox, D red were precisely determined. Greater part of these parameters have been determined here for the first time while the other are in good agreement with the previous literature reports. [1] R. Jurczakowski and P. Polczynski, J Phys. Chem. C, 2014, 118, 7980-7988.

Effect of TBHQ on avermectin photo-degradation and its synergism on small brown planthopper

To delay avermectin photo-degradation, the paper studied the effects of different concentrations of antioxidant, terliary butyl hydroqulnon (TBHQ), on avermectin photo-degradation. The toxicity of avermectin and TBHQ mixture on small brown planthopper (SBPH) Laodelphax striatellus (Fallen) was also determined via rice-stem-dipping method. The results indicate that avermectin photo-degradation fits into the equation for first-order chemical reaction kinetics. Photolysis rate of avermectin photo-degradation under sunlight is slower than that under UV light. When TBHQ and avermectin ratio is 1︰1, photolysis rate is lowest for avermectin photo-degradation, and its half-life is 11.81 h. This is 167.19% increase compared with treatment without TBHQ. Laboratory bioassay results demonstrate that the synergistic effect of TBHQ and avermectin mixture on SBPH is significantly strong. After 3 h exposure to sunlight and UV light, the toxicity of avermectin and TBHQ mixture on SBPH increases significantly compared to that without TBHQ. The synergism ratio is 2.00 and 2.63, respectively.

CALCULATION OF PESTICIDE RESIDUES ON ROSES USING CALIFORNIA'S TOTAL REPORTING DATA AND FIRST ORDER CHEMICAL KINETICS

Questions may arise as to residual pesticide concentrations on rose plants because of worker health, customer health, or environmental concerns. A case study conducted on roses from the Wasco, CA, USA, area provided a framework for addressing this question through development of experimental data for rose plant surface area, followed by compilation of pesticide application data collected via California's total reporting requirement. Thirteen pesticides were used on the crop, some with multiple applications and up to four different rates. In the modeling portion of the study, pesticide residual concentrations were calculated using degradation rate data and first-order chemical reaction kinetics. Results indicated concentrations of pesticides were small on rose plant surfaces at time of respective applications, and vanishingly small at the time of harvest and subsequent sale. This modeling approach can be used to provide estimates of pesticide concentrations at various times following application, and is a relatively simple yet powerful tool for addressing questions of chemical concentration where residues of pesticides or other agrochemicals are of interest.

Layer‐by‐Layer Assembly of Polyelectrolyte and Nanoparticles, Monitored by Capillary Electrophoresis

Layer-by-layer (LBL) assembly is a versatile nanofabrication technique, and investigation of its kinetics is essential for understanding the assembly mechanism and optimizing the assembly procedure. In this work, the LBL assembly of polyelectrolyte and nanoparticles were monitored in situ by capillary electrophoresis (CE) for the first time. The assembly of poly(diallyldimethylammonium chloride) (PDDA), and gold nanoparticles (AuNPs) on capillary walls causes surface-charge neutralization and resaturation, and thus yields synchronous changes in the electroosmotic flow (EOF). The EOF data show that formation of multilayers follows first-order adsorption kinetics. On the basis of the fit results, influencing factors, including number of layers, concentration of materials, flow rate, and size of AuNPs, were investigated. The stability and robustness of the assembled coatings were also characterized by CE. It was found that degradation of PDDA layers follows first-order chemical kinetics, while desorption of AuNPs takes place in a disorderly manner. The substrate strongly affects assembly of the underlying layer, while this effect is rapidly screened with increasing number of layers. Furthermore, we demonstrate that the EOF measuring step does not disturb LBL assembly, and the proposed method is reliable and rugged. This work not only studies in detail the LBL adsorption/desorption process of polyelectrolyte and nanoparticles, but also offers an alternative tool for monitoring multilayer buildup. It may also reveal the potential of CE in fields other than analytical separation.

The Effect of Flow Rate of Compressed Hot Water on Xylan, Lignin, and Total Mass Removal from Corn Stover

Flowing hot water through cellulosic biomass offers many promising features for advanced pretreatment, and a better understanding of the mechanisms responsible for flowthrough behavior could allow us to capitalize on its key attributes while overcoming its limitations. In this study, extensive data were developed to show the effect of flow on the fate of hemicellulose, lignin, and total mass for hot-water pretreatment of corn stover in a small tubular flowthrough reactor at 180, 200, and 220 °C. Solubilization of hemicellulose increased with flow, especially at high temperatures; a result that is inconsistent with traditional first-order kinetic models. The dissolved xylan in the hydrolyzate was mostly oligomers over this temperature range, and the fraction as oligomers increased with flow rate. Also of importance, lignin removal increased from less than about 30% for batch reactors to about 75% at high flow rates and was nearly linearly related to hemicellulose release for the flowthrough reactor. These observations suggest that mass transfer or other physical factors, and not strictly first-order homogeneous chemical kinetics, impact hemicellulose hydrolysis. In addition, lignin appears to be released throughout hydrolysis, but its fate may be governed by subsequent precipitation reactions unless it is removed first.

Solubilization of α-FeO(OH), ThO2.2H2O and γ-UO3 by hydroxamate and carboxylate Hgands

The ability of five different ligands to solubilize α-FeO(OH) (goethite), ThO2.2H2O and γ-UO3 was investigated at pH 3, 5 and 7: the hydroxamates acetohydroxamate (AHA), glutarodihydroxamate (GDA), rhodotorulate (RA), desferoxamine B (DFO) and the dicarboxylate iminodiacetate (IDA). Solubilization in the absence of ligand and solubilization by DFO (pH 5) as a function of time was also investigated. RA was the most effective at solubilizing α-FeO(OH) at all three pH values and ThO2.2H2O at pH 5 and 7. IDA solubilized most ThO2.2H2O at pH 3. GDA was the least effective ligand for α-FeO(OH) and ThO2.2H2O. Most γ-UO3 was solubilized by DFO (pH 3 and 5) and GDA (pH 7). AHA was the least effective. For dissolution over time, solubilization of α-FeO(OH) appears to be a diffusion-controlled process, whilst for ThO2.2H2O and γ-UO3 it is controlled by first-order chemical kinetics.