First-order Kinetic Expression Research Articles

Novel simple approaches to modeling composting kinetics

Mathematical models have been developed over the past 40 years to describe the composting process, seeking to ease its implementation, control, and optimization. Due to the complex nature of composting, the ability to simulate the processes kinetics in a simple and generalizable manner has proven to be elusive, acting as a significant limitation to effective environmental, model-assisted, decision-making. Current simple models are ungeneralizable, while generalizable models lack simplicity, requiring information on many operating variables, such as temperature, moisture content, and oxygen content. The aim of this work is therefore to explore the use of novel modeling approaches to produce generalizable and simple composting models that do not require any of this data, while providing a more accurate representation of degradation than current simple models. Four modeling methods are assessed in this study, all based on a first-order kinetic expression. These novel modeling approaches split the degradation into three separate phases and only require two parameters: a degradation rate and an estimation of the ratio between the duration of the mesophilic and thermophilic phases. The models were assessed through their normalized root mean square error and validated over three independent datasets sourced from the literature, covering a wide range of waste types and characteristics. The novel methods achieved errors varying between 1.13% and 6.32% and outperformed a traditional first-order model in every case, as well as more complex models in certain cases. Scenario analyses also demonstrated the resilience of the proposed approaches to uncertainty.

ReaxFF reactive force field development and application for molecular dynamics simulations of heptafluoroisobutyronitrile thermal decomposition

Heptafluoroisobutyronitrile (i-C3F7CN, C4) has obtained widely attention accounts for its good dielectric property and low GWP as a potential alternative gas. To investigate the thermal decomposition characteristics of C4, new reactive force field (ReaxFF) parameters were developed by training against QM-derived calculations with Monte Carlo Annealing (MC) method. The reliability of new parameters was verified not only by the deviations between QM-based calculations and ReaxFF predictions but also by good agreement between molecular dynamics (MD) simulations and experimental results. Hence, various NVT-MD simulations were employed to determine the reaction mechanisms, rate constants and product distributions. Our simulation results showed that the C4 decay was fitted with first-order kinetic expression, and the apparent activation energy was predicted to be 33.9 ± 1.67 kcal/mol. The main products of C4 decomposition were CF4, C2F6, C3F6, FCN, CF3CN, C2F5CN, which were in accordance with experimental and theoretical results. As for the initial reactions, we noted that C-CF3 bond was revealed to be the weakest bond and followed by C-F and C-CN bonds in C4 as reported in previous work. Similar MD simulation was conducted with C4/CO2 mixture system, which suggested that CO2 could consume F and CF3 radicals, resulting in significant impacts for CF4 and FCN. Noteworthy, new products (CO, COF2) were also seen as observed experimentally. To investigate the C4/CO2 system under the moisture condition, C4/CO2 with 1% H2O content was performed and new toxic gas HF was observed as a characteristic product, indicating an unnegligible impact by water content.

Modelling photocatalytic detoxification of aflatoxin B1 in peanut oil on TiO2 layer in a closed-loop reactor

Aflatoxin B1 (AFB1) is the most common and toxic among the aflatoxin group. Improper storage of both raw and processed peanut oil makes it susceptible to AFB1 production. Here, a closed-loop photocatalytic reactor consisting of a glass tube coated with TiO2 as a catalyst has been developed to study the photocatalytic detoxification of AFB1 in peanut oil. The removal rates of AFB1 in the photocatalytic process were apparently higher than that of the photolysis process. It is inappropriate to approximate Langmuir–Hinshelwood kinetics by a first-order kinetic expression based on the experimental kinetic data for the photocatalytic process. The newly proposed Weibull distribution model provides a good description of the kinetics of the photocatalytic process over the ranges of initial AFB1 concentrations and light intensities studied. The key parameters affecting the detoxification efficiency in terms of the reliable life of this model are described.

Disinfection of municipal wastewater by TiO2 photocatalysis with UV-A, visible and solar irradiation and BDD electrolysis

The efficiency of TiO2 photocatalysis induced by ultraviolet and visible irradiation and salt-free
 electrolysis over boron-doped diamond electrodes to inactivate total (TC) and fecal (FC)
 coliforms in secondary treated municipal wastewater was evaluated. Photocatalytic
 experiments were conducted with two types of titania (Degussa P25 and sulfur-doped
 catalyst) at loadings in the range 0.1-0.5 g l-1 and three types of irradiation, i.e. artificial UV-A,
 artificial visible and solar. Electrolysis was conducted in a flow-through cell at anodic current
 densities of 14.3 and 28.6 mA cm-2 without the addition of auxiliary chemicals. Inactivation
 followed a first-order kinetic expression with regard to bacteria population and the rate was
 dependent of the experimental conditions in question. In general, electrochemical disinfection
 was up to about two orders of magnitude faster than photocatalysis; for instance, TC
 population decreased to less than 5% of the initial population after 9 and 4 min at 14.3 mA
 cm-2 and 28.6 mA cm-2 respectively. Similar efficiencies with TiO2 photocatalysis would
 require at least 30 min of contact time. Interestingly, energy consumption for the
 electrochemical process was computed to about 0.5 kWh per m3 of treated effluent, well
 below the respective value for photocatalysis.

Anaerobic Degradation of Protein: Simplified Kinetic Modelling and Microbial Dynamics

Data on the influence of substrate composition on the anaerobic degradation of peptone in a bench-scale packed-bed reactor are presented and discussed. The experiments were conducted in a horizontal-flow anaerobic immobilised biomass reactor operated with a hydraulic detention time of 4 h. Peptone was the sole carbon source in the first experiment (E1). In the second experiment (E2), the reactor was fed with peptone and carbohydrates, and in the third experiment (E3), lipids were also added. At end of each experiment, the samples were collected to obtain spatial profiles of the substrates and intermediary metabolites. A modified first-order kinetic expression fits well with the chemical oxygen demand data, allowing kinetic parameter inference in both E1 and E2. The presence of lipids in the E3 influent clearly disturbed the equilibrium of the process, which could be better represented by two first-order kinetic expressions in series. A kinetic model of irreversible first-order reactions (in series and in parallel) with two intermediate products was proposed for representing the entire process. Several modifications of the metabolic routes were clearly represented by the values of the model parameters. It was also possible to conclude that the adsorption of lipids in the fixed bed caused a decrease in the consumption rate of proteins and acetate. Microscopy examinations and fluorescence in situ hybridisation analyses corroborated the conclusions from the kinetic study. The frequencies of the microorganisms changed as the substrate composition was modified, indicating the capability of the microorganisms to adapt.

Virus inactivation by high frequency ultrasound in combination with visible light

In this study, the effects of high frequency ultrasound (US) and visible light (VL) on virus inactivation were investigated. The bacteriophages ΦX174 and MS2 were used as model viruses. The experiments were performed at room temperature at three different, relatively high US frequencies (i.e., 582, 862, and 1142kHz) with and without the use of VL, and different initial virus concentrations. The two bacteriophages were diluted in phosphate-buffered saline solution to a titer of 103–104pfu/mL. The experimental virus inactivation data were satisfactorily represented by a simple first-order kinetic expression. Virus inactivation was faster at the lower frequencies (582 and 862kHz). Furthermore, it was observed that MS2 was inactivated faster than ΦX174. The simultaneous use of US and VL was found to be more effective than US alone for MS2 inactivation, indicating the existence of a synergistic effect. However, the use of VL in conjunction with high frequency US hindered the inactivation of ΦX174.

Solar photo-Fenton process on the abatement of antibiotics at a pilot scale: Degradation kinetics, ecotoxicity and phytotoxicity assessment and removal of antibiotic resistant enterococci

This work investigated the application of a solar driven advanced oxidation process (solar photo-Fenton), for the degradation of antibiotics at low concentration level (μg L−1) in secondary treated domestic effluents at a pilot-scale. The examined antibiotics were ofloxacin (OFX) and trimethoprim (TMP). A compound parabolic collector (CPC) pilot plant was used for the photocatalytic experiments. The process was mainly evaluated by a fast and reliable analytical method based on a UPLC-MS/MS system. Solar photo-Fenton process using low iron and hydrogen peroxide doses ([Fe2+]0 = 5 mg L−1; [H2O2]0 = 75 mg L−1) was proved to be an efficient method for the elimination of these compounds with relatively high degradation rates. The photocatalytic degradation of OFX and TMP with the solar photo-Fenton process followed apparent first-order kinetics. A modification of the first-order kinetic expression was proposed and has been successfully used to explain the degradation kinetics of the compounds during the solar photo-Fenton treatment. The results demonstrated the capacity of the applied advanced process to reduce the initial wastewater toxicity against the examined plant species (Sorghum saccharatum, Lepidium sativum, Sinapis alba) and the water flea Daphnia magna. The phytotoxicity of the treated samples, expressed as root growth inhibition, was higher compared to that observed on the inhibition of seed germination. Enterococci, including those resistant to OFX and TMP, were completely eliminated at the end of the treatment. The total cost of the full scale unit for the treatment of 150 m3 day−1 of secondary wastewater effluent was found to be 0.85 € m−3.

Mesoporous zirconia nanobelts: Preparation, characterization and applications in catalytical methane combustion

Mesoporous ZrO 2 nanobelts (MZNs) have been prepared by a calcination route of ZrS 3 nanobelts in air. The nanobelts prepared at 400–600 °C are the mixtures of tetragonal and monoclinic phases, and have well-distributed mesopores (pore diameter of about 3.4–3.6 nm). As the calcination temperature increased from 400 to 1200 °C, the structures changed from tetragonal to monoclinic phase, while the morphologies turned from regular nanobelts to bead-like nanowires, and the mesopores disappeared bit by bit. Fe-doped and Fe 2O 3-loaded MZNs have been prepared to compare the catalytic activities of Fe-doped, Fe 2O 3-loaded, and pure MZNs for methane combustion. The results showed that Fe 2O 3-loaded MZNs have rather high catalytic activity, suggesting its potential application in practice. Methane combustion data over the catalysts are well fitted by a first-order kinetic expression.

Kinetic study of the liquid-phase selective hydrogenation of 1-butyne in presence of 1-butene over a commercial palladium-based catalyst

A kinetic investigation of the liquid-phase selective hydrogenation of 1-butyne in presence of 1-butene was performed over a commercial palladium-based/alumina catalyst of the eggshell type. This investigation is aimed at validating a kinetic expression to describe 1-butyne hydrogenation under experimental conditions around the typical operating conditions of industrial C 4 cuts hydrorefining processes. Seven levels of temperature between 27 °C and 62 °C were explored. 1-Butyne and n-butene initial mole fractions amounted to ca. 8% and 9% and hydrogen partial pressure was set between 0.85 atm and 7.82 atm. Experimental data and data analysis were extended to 1-butyne total conversion. Palladium proved to be quite selective towards 1-butyne hydrogenation. However, the intrinsic palladium selectivity is impaired by the presence in our experiments of severe intracatalyst diffusion limitations. This result turns the attention to the crucial influence of hydrogen partial pressure level on selectivity because unnecessary hydrogen excesses severely lessen selectivity when 1-butyne becomes the limiting reactant inside the catalyst. A kinetic expression of the Langmuir–Hinshelwood–Hougen–Watson type was proposed to describe the hydrogenation of 1-butyne. 1-Butene hydrogenation rate was described by a zero-order and first-order kinetic expression with respect to 1-butene and hydrogen, respectively. The kinetic model predicts experimental data with an average deviation of 17.1%. The relative inference intervals of the kinetic parameter estimates were less than ±14.8%.

Determination of Crystal Growth Rate and Morphology of Barium Carbonate Crystals in a Semi-batch Crystallizer

A semi-batch crystallization system is used to determine growth kinetics and morphology of barium carbonate crystals, under a constant pH value and constant temperature in the various relative supersaturations. Results show that crystal growth rate satisfies a first-order kinetic expression at high relative supersaturation, while at relative supersaturation values lower than 3, the kinetic expression is second order. The crystal growth of barium carbonate follows the Burton, Cabera, and Frank mechanism by the kinetic expression G=ασ 2 tanh (β /σ). The kinetic parameters obtained from low to high supersaturation ratio by using a numerical methods are α=9.5×10 -7 ms -1 and β=1.35×10 -2 . The investigations show that the pH values and relative supersaturation of solutions have an important role on the crystal morphology of barium carbonate and the forms of observed crystals are floc, candy-like, pillar-like, olivary and olivary with end dendrite with respect to operating condition.

Studies on combustion catalytic activity of some pure and doped lanthanum cobaltites

The aim of this work is to compare the catalytic activity of some pure and doped lanthanum cobaltites, prepared by solution combustion technique, with a Pt/Al2O3 commercial catalyst. As test reaction we used the combustion of lean methane mixtures. The experimental data evidenced a significantly better catalytic activity of a cerium-doped lanthanum cobaltite, prepared by using α-alanine as fuel. The combustion data, for the lean methane mixtures we tested, are well fitted by a first-order kinetic expression. The calculated activation energy values are in good agreement with the published data.

Analysis of volatile species kinetics during typical medical waste materials pyrolysis using a distributed activation energy model

The complex reactions of typical medical waste materials pyrolysis and the evolution of different volatile species can be well represented by a Distributed Activation Energy Model (DAEM). In this study, A thermogravimetric analyser (TGA), coupled with Fourier transform infrared analysis of evolving products (TG-FTIR), were used to perform kinetic analysis of typical medical waste materials pyrolysis. A simple direct search method was used for the determination of DAEM kinetic parameters and the yield of individual pyrolysis products under any given heating condition. The agreement between the model prediction and the experimental data was generally good. The results can be used as inputs to a pyrolysis model based on first-order kinetic expression with a Gaussian Distribution of Activation Energies as a sub-model to CFD code.

Anaerobic Corrosion Reaction Kinetics of Nanosized Iron

Nanosized Fe0 exhibits markedly different anaerobic corrosion rates in water compared to that disseminated in moist quartz sand. In water, hydrogen production from corrosion exhibits an autocatalytic style, attaining a maximum rate of 1.9 mol kg(-1) d(-1) within 2 d of reaction. The rate then drops sharply over the next 20 d and enters a period of uniformly decreasing rate, represented equally well by first-order or diffusion-controlled kinetic expressions. In quartz sand, hydrogen production exhibits a double maximum over the first 20 d, similar to the hydration reaction of Portland cement, and the highest rate attained is less than 0.5 mol kg(-1) d(-1). We ascribe this difference in early time corrosion behavior to the ability of the released hydrogen gas to convect both water and iron particles in an iron/water system and to its inability to do so when the iron particles are disseminated in sand. By 30 d, the hydrogen production rate of iron in quartz sand exhibits a uniform decrease as in the iron/water system, which also can be described by first-order or diffusion-controlled kinetic expressions. However, the corrosion resistance of the iron in moist sand is 4 times greater than in pure water (viz. t1/2 of 365 d vs 78 d, respectively). The lower rate for iron in sand is likely due to the effect of dissolved silica sorbing onto iron reaction sites and acting as an anodic inhibitor, which reduces the iron's susceptibility to oxidation by water. This study indicates that short-term laboratory corrosion tests of nanosized Fe0/water slurries will substantially underestimate both the material's longevity as an electron source and its potential as a long-term source of hydrogen gas in groundwater remediation applications.

Kinetics of Particulate Organic Matter Removal as a Response to Bioflocculation in Aerobic Biofilm Reactors

Recent research has identified that the major fraction of chemical oxygen demand in domestic wastewaters is in particulate form. The research presented herein develops the kinetics of particle removal as a response to bioflocculation at the surface of aerobic biofilms. This study focuses on the removal of particles that are maintained in aqueous suspension after 30 minutes of gravity settling. It is helpful to consider the particulate organics removal process in biofilms as the sum of four steps, namely (1) external transport of the particles to the biofilm surface, (2) bioflocculation, (3) organic particulate hydrolysis, and (4) diffusion and reaction of the solubilized organics by the bacterial cells comprising the biofilm. Organic (native corn starch) and inorganic particle (Min-U-Sil 10 [U.S. Silica Company, Berkeley Springs, West Virginia]) suspensions, with micronutrients, were continuously fed to a rotating disc biofilm reactor to verify a first-order kinetic expression that has been used to describe bioflocculation and to demonstrate that bioflocculation is the primary particle removal mechanism. Extracellular polymeric substances were extracted and quantified to describe the role they play in the bioflocculation process.

A Model for Simultaneous Particulate and Dissolved Substrate Removal in a Biofilm Reactor

The present kinetic study develops a model describing zero-order soluble substrate (methanol) diffusion and biochemical reaction inside the porous biofilm matrix with simultaneous particle removal by bioflocculation at the surface of aerobic biological films. Methanol (CH3OH) served as the dissolved substrate and native corn starch served as the organic particulates; 95% of the particles were less than a 23.9-micron equivalent spherical diameter, the median particle diameter was 14.1 microns, and only 5% of the particles were less than 1.4 microns. A bench-scale completely mixed rotating disc biofilm reactor was used to grow and experimentally measure substrate removal, both dissolved and particulate, as a function of the ratio of external biofilm area to bulk liquid volumetric flow rate, A/Q. A curve-fitting routine revealed that within the range of concentrations used in this research, internal diffusion and consumption of methanol was predicted by a zero-order reaction, and the removal of organic particulates was described by a first-order bioflocculation kinetic expression. A significant effect of the influent concentration of methanol and corn starch on the numerical value of the kinetic constants could be observed.

Constrain in solving Langmuir–Hinshelwood kinetic expression for the photocatalytic degradation of Auramine O aqueous solutions by ZnO catalyst

Langmuir–Hinshelwood (L–H) and first-order expressions are the most widely used expressions to explain the kinetics of heterogeneous catalytic system. Previously lot of researchers approximated the L–H kinetic expression to first-order expression just to easily obtain the parameters involved in the L–H expression. However, it is inappropriate to alter a kinetic model, which is having definite assumptions behind it without any validation. This study reports the constrain in approximating the L–H kinetic expression to first-order kinetic expression using the experimental kinetic data of photocatalytic degradation of Auramine O aqueous solution in the presence of ZnO catalyst. Further, the present investigation showed that it is not appropriate to approximate the Langmuir–Hinshelwood kinetics to first-order kinetics. In addition, a second-order kinetic model is proposed and is found to well represent the experimental data of Auramine O degradation by ZnO catalyst for the range of initial dye concentration studied.

Evaluation of Catalyst Deactivation during Catalytic Steam Reforming of Biomass-Derived Syngas

Mitigation of tars produced during biomass gasification continues to be a technical barrier to developing systems. This effort combined the measurement of tar-reforming catalyst deactivation kinetics and the production of syngas in a pilot-scale biomass gasification system at a single steady-state condition with mixed woods, producing a gas with an H2-to-CO ratio of 2 and 13% methane. A slipstream from this process was introduced into a bench-scale 5.25 cm diameter fluidized-bed catalyst reactor charged with an alkali-promoted Ni-based/Al2O3 catalyst. Catalyst conversion tests were performed at a constant space time and five temperatures from 775 to 875 °C. The initial catalyst-reforming activity for all measured components (benzene, toluene, naphthalene, and total tars) except light hydrocarbons was 100%. The residual steady-state conversion of tar ranged from 96.6% at 875 °C to 70.5% at 775 °C. Residual steady-state conversions at 875 °C for benzene and methane were 81% and 32%, respectively. Catalytic deactivation models with residual activity were developed and evaluated based on experimentally measured changes in conversion efficiencies as a function of time on stream for the catalytic reforming of tars, benzene, methane, and ethane. Both first- and second-order models were evaluated for the reforming reaction and for catalyst deactivation. Comparison of experimental and modeling results showed that the reforming reactions were adequately modeled by either first-order or second-order global kinetic expressions. However, second-order kinetics resulted in negative activation energies for deactivation. Activation energies were determined for first-order reforming reactions and catalyst deactivation. For reforming, the representative activation energies were 32 kJ/g·mol for ethane, 19 kJ/g·mol for tars, 45 kJ/g·mol for tars plus benzene, and 8−9 kJ/g·mol for benzene and toluene. For catalyst deactivation, representative activation energies were 146 kJ/g·mol for ethane, 121 kJ/g·mol for tars plus benzene, 74 kJ/g·mol for benzene, and 19 kJ/g·mol for total tars. Methane was also modeled by a second-order reaction, with an activation energy of 18.6 kJ/g·mol and a catalyst deactivation energy of 5.8 kJ/g·mol.

Modeling the evolution of volatile species during tobacco pyrolysis

A great need exists for comprehensive biomass-pyrolysis models that could predict yields and evolution patterns of selected volatile products as a function of feedstock characteristics and process conditions. Low heating rate data obtained from a thermogravimetric analyzer (TGA), coupled with Fourier transform infrared analysis of evolving products (TG-FTIR), were used to perform kinetic analysis of tobacco pyrolysis. The results were utilized to create input to a biomass-pyrolysis model based on first-order kinetic expressions with a Gaussian distribution of activation energies. Pyrolysis simulations were carried out for high heating rate conditions, and predicted product yields were compared with literature data.

Kinetic study of hydrogen peroxide decomposition by catalase in a flow-mix microcalorimetric system

The kinetics of hydrogen peroxide decomposition by the enzyme catalase was studied at pH 7.4 in the temperature range 10–30 °C. Experiments were performed by the LKB-2277 Thermal Activity Monitor equipped with a flow-mix cylinder. The calorimetric reaction unit was schematised as a tubular reactor operating under plug-flow conditions. A first-order kinetic expression, with respect to both the substrate and the enzyme, was used to describe the rate of hydrogen peroxide decomposition. Regression analysis of calorimetric data provided a molar reaction enthalpy of −87.55 kJ mol −1 and an activation energy of 11 kJ mol −1. Analysis of model residuals and the normal probability plot indicated that the results obtained were statistically significant.

Determination of nucleation and crystal growth kinetics of barium carbonate

A compact apparatus of specific construction is used for nucleation measurements in accordance with Nielsen's method. Experiments are realized by varying the supersaturation ratio from 35 to 280 and temperature from 10 to 50 °C. Barium carbonate is precipitated by mixing equal volumes of sodium carbonate and barium hydroxide solutions. The experimental data have shown that the nucleation rate of barium carbonate in the supersaturation range cited above is characterized by the primary heterogeneous mechanism and can be expressed by the relation r N= A 0 exp(− E/ RT)exp[− B/((ln S) 2)], where A 0=6.4×10 24 m −3 s −1, E=22,065 J mol −1, and B=58.7. An original method, using a high seed charge in a batch crystallizer, is developed for the determination of crystal growth kinetics in a large range of supersaturation variation. At high supersaturation ratio, the crystal growth rate satisfies a first-order kinetic expression, while at supersaturation ratio values lower than 2, the kinetic expression is second order. These results show that the crystal growth of barium carbonate follows the Burton, Cabrera, and Franck mechanism characterized by the kinetic expression G= αs 2 tanh( β/ s). The fitting of this kinetic expression with all experimental data at 25 °C from low to high supersaturation ratio values using a least-squares technique gives α=9.49×10 −7 m 7 mol −2 s −1 and β=1.35×10 −2 mol m −3.