Chemical Kinetic Approach Research Articles

Temperature- and pressure-dependent branching ratios for 1,4 dimethylcyclohexyl (cy-C8H15) + O2 reaction: A key cyclic component of novel biofuels, and fossil fuels

Alkyl cyclohexanes are a key component in novel biodiesel and jet fuel, which are of central focus to next-generation strategies for low-temperature combustion. The state-of-the-art chemical kinetics approach has been employed in the reaction of an oxygen molecule to the three isomers of 1,4-dimethylcyclohexyl radicals (cy-C8H15) to predict the temperature- and pressure-dependent branching ratios. The reaction energies were computed using quantum composite methods, i.e., CBS-QB3 and rate constants, and branching was calculated using Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulations in the temperature range of 400 to 1000 K and pressure range of 0.001 to 100 bar. The RRKM/ME simulation reveals the addition of O2 to the primary radical, cy-C8H15 + O2 reaction (ROO-1), the formation of five-membered cyclic ether P7p (4-methyl-6-oxabicyclo[3.2.1]octane) and six-membered cyclic ether P10p (1-methyl-2-oxabicyclo[2.2.2]octane) are highly pressure-dependent below 0.01 bar and kinetically favorable pathway < 700 K. For tertiary cy-C8H15 + O2 (ROO-2), the formation of P5t (1,4-dimethyl-6-oxabicyclo[3.1.1]heptane), and P8t (1-methoxy-1,4-dimethylcyclohexane) are highly pressure-dependent and kinetically favorable pathway in the temperature range of 600 K to 750 K. On secondary cy-C8H15 + O2 (ROO-3) reaction, the formation of P4s (1,4-dimethyl-6-oxabicyclo[3.1.1]heptane), and P6s (1,4-dimethyl-7-oxabicyclo[4.1.0]heptane) competes with the stabilization of ROO-3 at a pressure lower than 0.01 bar. The updated energies and rate constants may also serve as general prototypes for low-temperature oxidation of alkyl cyclohexanes of next-generation fuels such as bisabolane and jet fuel.

Assessment of combustion development and pollutant emissions of a spark ignition engine fueled by ammonia and ammonia-hydrogen blends

Ammonia is a promising carbon-free fuel for internal combustion engines, but its combustion properties are very poor if compared with conventional fuels. Thus, hydrogen enrichment can be the proper solution in order to overtake the issues related to neat ammonia fueling. In this paper, the authors use a 3D numerical model coupled with a chemical kinetic approach to assess the operation of a light-duty spark-ignition engine fueled by neat ammonia and ammonia-hydrogen blends (up to 15% of hydrogen by volume). The proposed model reproduces the analyzed experimental operating points with a good accuracy. As example, considering the in-cylinder pressure peak, the difference between the calculated maximum pressure and the mean measured one ranges between 1.6% and 6.8% for the examined cases. The 3D approach enables an in-depth analysis of flame development that also allows to detect the effect of hydrogen enrichment on both combustion development and emissions. Unburned ammonia trends are captured, reproducing the measured decrease of ammonia emissions for increasing hydrogen enrichment. The emissions of NOx are also well reproduced. Simulations also highlighted that dissociation of ammonia produces H2, which is detected in the combustion chamber also if neat ammonia is burned and, at least according to the chemical mechanism used, not all the produced hydrogen oxidizes. Only very small quantities of intermediates related to ammonia combustion are calculated at exhaust valve opening, decreasing for an increasing hydrogen content in the fuel mixture.

Pharmacological inhibition of α-synuclein aggregation within liquid condensates

Aggregated forms of α-synuclein constitute the major component of Lewy bodies, the proteinaceous aggregates characteristic of Parkinson’s disease. Emerging evidence suggests that α-synuclein aggregation may occur within liquid condensates formed through phase separation. This mechanism of aggregation creates new challenges and opportunities for drug discovery for Parkinson’s disease, which is otherwise still incurable. Here we show that the condensation-driven aggregation pathway of α-synuclein can be inhibited using small molecules. We report that the aminosterol claramine stabilizes α-synuclein condensates and inhibits α-synuclein aggregation within the condensates both in vitro and in a Caenorhabditis elegans model of Parkinson’s disease. By using a chemical kinetics approach, we show that the mechanism of action of claramine is to inhibit primary nucleation within the condensates. These results illustrate a possible therapeutic route based on the inhibition of protein aggregation within condensates, a phenomenon likely to be relevant in other neurodegenerative disorders.

Influence of the hydrogen transverse injection mode in a scramjet combustor performance

This paper focuses on the numerical investigation of the transverse hydrogen injection technique in the supersonic airflow on the combustor performance of a scramjet technological demonstrator developed at Universidade Federal do Rio Grande do Norte (UFRN). The UFRN's scramjet vehicle was designed to be fully operational at a hypersonic velocity of 2050 m/s (Mach number 6.8), at 30 km of altitude, which provided a temperature of 1156.95 K and supersonic velocity of 1414.39 m/s (Mach number 2.1), at the combustion chamber entrance. Hydrogen was transversally injected into supersonic airflow at a sonic speed of 1318.46 m/s. A set of 2D-RANS simulations of the reactive flow was performed in combination with a simplified chemical kinetics approach based on the finite-rate chemistry model, defined by a one-step global reaction based on Arrhenius expression to combustion modeling. The turbulence was modeled by the k-kl-ω transition model. Different transverse fuel injections with different dimensions and positioning of injectors were evaluated keeping the same inlet conditions: single-injection versus dual-injection modes. A detailed visualization of several flow phenomena, such as the formation of shock waves, and the performance combustion parameters on the combustor surface were discussed. The analyses indicated hydrogen combustion with a predominantly supersonic flow regime. The transversal injection caused the detachment of the boundary layer as indicated by the recirculation flow structures in the neighboring region next to the injectors. Flow analyses indicate that the purely oblique shock trains were established tending to redirect the airflow over the mixing layer and accelerate the hydrogen burning. Nevertheless, the results showed that this was a local effect since the downstream both mixing and combustion efficiency increased. The dual-injection mode proved to be a promising injection method due to the higher global fuel penetration, elevated from 27,9% to 33,8%, and higher combustion efficiency, increased from 10,33% to 21,99%, with reduced addition of total pressure loss, concerning the single-injection case. Additionally, the growth behavior of performance curves showed that an extension of the combustor downstream length can be indicated to maximize combustor performance.

CALCULATION OF THE ELECTRODE REACTION RATE ON A GRAPHITE CATHODE OF ALUMINUM-ION BATTERY WITH 1-ETHYL-3-METHYLIMIDAZOLIUM CHLORIDE

A method for determining the rate of sorption of chloraluminate complexes on graphite material as the main cathode reaction in aluminum-ion batteries with an ionic liquid as an electrolyte is proposed in terms of classic chemical kinetics approach. The method is applied to the description of the rate of a one-electron cathode reaction that is in the case the sorption/desorption of complexes on the electrode surface with no migration in the interlayer space of graphite taken into account. The experimental part is based on the selection and providing of measurement conditions and the ratio of the components of the cell to ensure that the rate of the cathode process sets the rate of current generation of the cell. The rate of supply/removal of electrons, as participants in the reaction, thus can be directly related to the reaction rate on graphite. The point of reaching the limiting current on the polarization curve in that case corresponds the limiting rate of the chemical sorption reaction. The approach takes into account the effect of other limiting processes, such as the rate of removal/supply of electrons, the rate of removal/supply of ions to/from the electrolyte volume, and the rate of anodic dissolution/deposition of aluminum. The calculated value of the reaction rate for graphite material grade EC-02 and low-temperature ionic liquid 1-ethyl-3-methylimidazole chloride in a mixture with aluminum chloride (1 : 1.3) was calculated to be 46 µmol/cm2 · s.

Efficiency of ozonation and O3/H2O2 as enhanced wastewater treatment processes for micropollutant abatement and disinfection with minimized byproduct formation

Ozonation, a viable option for improving wastewater effluent quality, requires process optimization to ensure the organic micropollutants (OMPs) elimination and disinfection under minimized byproduct formation. This study assessed and compared the efficiencies of ozonation (O3) and ozone with hydrogen peroxide (O3/H2O2) for 70 OMPs elimination, inactivation of three bacteria and three viruses, and formation of bromate and biodegradable organics during the bench-scale O3 and O3/H2O2 treatment of municipal wastewater effluent. 39 OMPs were fully eliminated, and 22 OMPs were considerably eliminated (54 ± 14%) at an ozone dosage of 0.5 gO3/gDOC for their high reactivity to ozone or •OH. The chemical kinetics approach accurately predicted the OMP elimination levels based on the rate constants and exposures of ozone and •OH, where the quantum chemical calculation and group contribution method successfully predicted the ozone and •OH rate constants, respectively. Microbial inactivation levels increased with increasing ozone dosage up to ∼3.1 (bacteria) and ∼2.6 (virus) log10 reductions at 0.7 gO3/gDOC. O3/H2O2 minimized bromate formation but significantly decreased bacteria/virus inactivation, whereas its impact on OMP elimination was insignificant. Ozonation produced biodegradable organics that were removed by a post-biodegradation treatment, achieving up to 24% DOM mineralization. These results can be useful for optimizing O3 and O3/H2O2 processes for enhanced wastewater treatment.

Elimination efficiency of synthetic musks during the treatment of drinking water with ozonation and UV-based advanced oxidation processes

This study investigated the reaction kinetics and elimination efficiency of eleven synthetic musks during ozonation and UV254nm-based, advanced oxidation processes. The synthetic musks containing olefin moieties with electron-donating alkyl substituents such as octahydro tetramethyl naphthalenyl ethanone (OTNE) and ambrettolide (AMBT) showed high reactivity toward ozone (k ≥ 3.7 × 105 M−1 s−1) and free available chlorine (FAC) (k = 9.2 – 88 M−1 s−1), while all other synthetic musks were less ozone reactive (k = 0.3 – 560 M−1 s−1) and FAC-refractory. All synthetic musks showed high •OH reactivity (k > 5 × 109 M−1 s−1), except musk ketone (MK) (k = 2.3 × 109 M−1 s−1). In concordance with the kinetic information, OTNE and AMBT were efficiently eliminated (>97%) in simulated ozone treatments of drinking water at a specific ozone dose of 0.5 gO3/gDOC. The elimination levels of the other synthetic musks were below 50% at 0.5 gO3/gDOC. The fluence-based UV photolysis rate constant of the synthetic musks was determined to be (0.2 – 2.7) × 10−3 cm2/mJ. The elimination levels of synthetic musks during UV alone treatment ranged from 7 to 81% at a UV fluence of 500 mJ/cm2. The addition of 10 mg/L H2O2 (UV/H2O2) significantly enhanced the elimination of most synthetic musks (achieving >90% elimination at 500 mJ/cm2), indicating that the •OH reaction was mainly responsible for their elimination. The addition of 10 mg/L FAC (UV/FAC) also significantly enhanced the elimination of olefinic and aromatic synthetic musks (>90%), for which the reaction with ClO• was mainly responsible. For MK and two alkyl synthetic musks, their elimination during UV/FAC treatment was still limited (28 – 64%) and was mainly achieved by UV photolysis or reaction with •OH. In summary, this study substantiates the chemical kinetics approach as a helpful tool for predicting or interpreting the elimination of micropollutants during oxidative water treatment.

Thermal stability study of HFO-1234ze(E) for supercritical organic Rankine cycle: Chemical kinetic model approach through decomposition experiments

The supercritical organic Rankine cycle (SORC) is considered as a potential technique for converting heat waste resources to electricity. Owing to its low global warming potential, HFO-1234ze(E) (trans-1,3,3,3-tetrafluoroprop-1-ene) is a suitable working fluid for the SORC system. This paper proposes a simple kinetic method for evaluating the thermal decomposition of HFO-1234ze(E) based on the temperatures and pressures in the SORC loop. A long-term decomposition test conducted at temperatures of 433.15–473.15K under a pressure of 5.0MPa was used to establish a kinetic equation based on the first-order kinetic model. At 423.15K, in the high-temperature region of the SORC loop, the decomposition rate of HFO-1234ze(E) was only 1.25% for the 50-year continuous running cycle. When the temperature of the high-temperature region increased by 20K and 40K, decompositions of HFO-1234ze(E) significantly increased to 5.24% and 18.40%, respectively, which highlights the high sensitivity of the thermal decomposition rate toward the temperature in the SORC loop.

A numerical study on the quasi-steady spray and soot characteristics for soybean methyl ester and its blends with ethanol using CFD-reduced chemical kinetics approach

This work numerically examines the quasi-steady spray combustion and soot development for soybean methyl ester (SME) and SME-ethanol blends (S90E10, S70E30). A validated reduced ethanol mechanism (37 species and 149 reactions) was formulated using a temperature sensitivity analysis under auto-ignition and jet-stirred reactor conditions. At initial pressures between 10.0 bar and 60.0 bar, initial temperatures between 750 K and 1350 K and equivalence ratios between 0.5 and 2.0, the ignition delays and key species profiles (C2H5OH, CO2, O2) of the reduced mechanism deviated by 0.5 order and 40%, respectively as compared to the experimental measurements. Subsequently, the reduced ethanol mechanism was combined with a reduced biodiesel mechanism to form a surrogate mechanism (102 species and 446 reactions) for biodiesel-ethanol blends and integrated into OpenFOAM for spray combustion modelling. Under reacting spray conditions at a constant ambient density of 22.8 kg/m3 and ambient temperatures of 900 K and 1000 K, the spray penetrations for SME-ethanol blends were shortened by 35.5% (maximum difference). Smaller flame areas with 60 K higher local flame temperature were obtained. Due to a 20% decrease in acetylene mass fractions and soot formation rates, the peak soot volume fractions for SME-ethanol blends were 19.6% lower.

Complexity in Lipid Membrane Composition Induces Resilience to Aβ42 Aggregation.

The molecular origins of Alzheimer's disease are associated with the aggregation of the amyloid-β peptide (Aβ). This process is controlled by a complex cellular homeostasis system, which involves a variety of components, including proteins, metabolites, and lipids. It has been shown in particular that certain components of lipid membranes can speed up Aβ aggregation. This observation prompts the question of whether there are protective cellular mechanisms to counterbalance this effect. Here, to address this issue, we investigate the role of the composition of lipid membranes in modulating the aggregation process of Aβ. By adopting a chemical kinetics approach, we first identify a panel of lipids that affect the aggregation of the 42-residue form of Aβ (Aβ42), ranging from enhancement to inhibition. We then show that these effects tend to average out in mixtures of these lipids, as such mixtures buffer extreme aggregation behaviors as the number of components increases. These results indicate that a degree of quality control on protein aggregation can be achieved through a mechanism by which an increase in the molecular complexity of lipid membranes balances opposite effects and creates resilience to aggregation.

Modelling of emerging contaminant removal during heterogeneous catalytic ozonation using chemical kinetic approaches

This study evaluated the prediction of emerging contaminant (EC) removal during heterogeneous catalytic ozonation by chemical kinetic models. Six ECs with differing ozone reactivity were spiked in a synthetic water and a groundwater, then treated by conventional ozonation and heterogeneous catalytic ozonation with α- or β-MnO2 catalysts. Results show that catalysts did not considerably influence the removal of ECs with high and intermediate ozone reactivity (diclofenac, gemfibrozil, and bezafibrate), but enhanced the removal efficiencies of ECs with low ozone reactivity (2,4-dichlorophenoxyacetic acid, clofibric acid, and ibuprofen) to varied extent (˜10–30%). The removal efficiencies of ECs could be reasonably predicted using chemical kinetic models based on the ozone (O3) and hydroxyl radical (OH) rate constants of ECs, pseudo-first-order rate constants observed for EC adsorption on the MnO2 catalysts, and O3 and OH exposures observed for catalytic ozonation. Furthermore, the model reveals that ECs are removed mainly by O3 and/or •OH oxidation during heterogeneous catalytic ozonation, while adsorption of ECs on catalysts contributes negligibly. Therefore, the removal efficiencies of ECs could be satisfactorily predicted using a simplified model based only on the O3 and OH rate constant and the O3 and OH exposures.

Elimination efficiency of organic UV filters during ozonation and UV/H2O2 treatment of drinking water and wastewater effluent

The efficiency of elimination of organic UV filters by ozonation and UV254nm/H2O2 processes was assessed and predicted in simulated treatments of sewage-impaired drinking water and wastewater effluent in bench-scale experiments. Second-order rate constants (k) for the reactions of the eight UV filters with ozone and OH were determined by quantum chemical calculations and competition kinetics methods, respectively. The UV filters containing phenolic (ethylhexyl-salicylate, homosalate, and benzophenone-3) and olefinic moieties (4-methylbenzylidene-camphor, benzyl-cinnamate, and 2-ethylhexyl-4-methoxycinnamate) showed high ozone reactivity (k ≥ 8 × 104 M−1s−1 at pH 7), while those without such electron-rich moieties (isoamyl-benzoate and benzophenone) were ozone-refractory. All the UV filters showed high OH reactivity (k ≥ 6.2 × 109 M−1s−1). In concordance with the rate constant information, the phenolic and olefinic UV filters were efficiently eliminated by ozone treatment, requiring specific ozone doses of <0.5 mgO3/mgDOC for ∼100% elimination. The UV filters were eliminated by ≤ 38% at a UV fluence of 1500 mJ/cm2 in the UV254nm-only treatment. Rapid photoisomerisation between the E and Z geometric isomers was observed for the olefinic UV filter, benzyl-cinnamate. The addition of H2O2 (10 mg/L) greatly enhanced the elimination of all UV filters, indicating that OH was the main contributor to their elimination in the UV254nm/H2O2 treatment. A chemical kinetics approach developed previously for ozonation and UV/H2O2 processes was shown to predict the elimination of the UV filters in the tested water matrices reasonably well, demonstrating that the chemical kinetics method can be used for a priori prediction of micropollutant elimination in oxidative treatment processes for potable reuse of municipal wastewater effluents.

Modeling of evaporation and condensation processes: a chemical kinetics approach

The processes of evaporation and condensation are considered in the framework of chemical kinetics. At the phenomenological level, the processes of evaporation and condensation were considered using formal kinetics, and at the molecular level, these processes were considered using collision theory. In the framework of formal kinetics, the rate equations for the processes of evaporation and condensation were obtained. In the framework of collision theory, the equations for the rate of evaporation and condensation and for the condensation coefficient were obtained. A comparison of the calculated and available experimental data for the case of evaporation of water into air and for the case of evaporation of metals in a vacuum was made. From these comparisons, the energy characteristics of the surface of water and some metals and the condensation coefficients for these substances were determined.

UVA-UVB activation of hydrogen peroxide and persulfate for advanced oxidation processes: Efficiency, mechanism and effect of various water constituents

In the present work we investigate the activation efficiency of H2O2 and S2O82− using UVA and UVB radiation. Bisphenol-A (BPA) is used as model pollutants to estimate the oxidative process efficiency in simulated and real sewage treatment plant waters. Particular attention is paid to the BPA removal efficiency and to the radical mechanism involvement considering the effect of typical inorganic water constituents (carbonates and chloride ions) and organic matter. Despite a detrimental effect observed when carbonate ions are in solution using both hydrogen peroxide and persulafate, the presence of high chloride ions concentration was found to improve BPA removal using S2O82− as radical precursor. This enhancement, investigated combining chemical kinetic model approach and laser flash photolysis experiments, is attributed to the formation of hydroxyl radical and chlorine radical species from sulfate radical. Different transformation products are identified by means of GC–MS and HPLC-MS analyses. Moreover, experiments using sewage treatment plant water (STPW) spiked with BPA are performed in order to assess the efficiency of oxidative processes in a simulated treatment systems activated using UVA + UVB radiations.

Numerical Simulations of the flow field and chemical reactions of the Storage/Oxidation process within a NSC Pt - BaO Catalyst

A NOx Storage Catalyst (NSC) has been studied by means of reactive CFD simulations. In the scenario of automotive pollutant emission reduction, due to the stringent regulation, the detailed description of the chemical and physical phenomena within catalysts represents a key point in order to improve their conversion efficiency. The active part of the catalyst has been simulated as a porous medium. In this zone, surface reactions take place, which are modelled by means of an Arrhenius chemical kinetic approach, involving the Pt and BaO sites on the active surface of the matrix. Actually, two chemical mechanisms are considered, the simplest involves only BaO site, the other one includes both BaO and Ptsites. Both models are validated against data available in the literature and then applied to a real automotive catalyst geometry. Thus, a detailed description of the spatial distribution of the species is provided for both models. Lean condition is simulated in order to check the catalyst behaviour according to experimental results.

2017 Leonard Medal for Mark Thiemens

2017 Leonard Medal for Mark Thiemens

Numerical study of CO2 effects on laminar non-premixed biogas flames employing a global kinetic mechanism and the Flamelet-Generated Manifold technique

Numerical simulations of flames employing detailed kinetic mechanisms are computationally demanding problems. For this reason, reduced mechanisms and techniques of chemical kinetic reduction have been developed and used in both research and industrial applications. The objective of the present work is to compare the prediction of a global kinetic mechanism and the Flamelet-Generated Manifold (FGM) reduction technique with a detailed mechanism in numerical simulations of laminar non-premixed flames. The fuel was a biogas-like mixture modelled as methane diluted with carbon dioxide. First, the effect of CO2 addition into fuel stream was studied in one-dimensional counterflow flames. Flame structure and chemical kinetics were investigated for different levels of CO2. A new approach for evaluating the dilution effect is introduced based on the CO2 content in a stoichiometric mixture. With this definition, the effect of pure dilution on major species and temperature peak values tends to be linear. The comparisons among solutions obtained with a detailed, a skeleton and a 4-step global mechanism for different strain rates and dilution levels reveals the capabilities of these chemical kinetic approaches for modelling biogas flames. Then, the 4-step mechanism and the FGM technique were compared with a skeleton kinetic model in two-dimensional coflow flames. It was observed that the 4-step mechanism presented good results for temperature and major chemical species, being a good choice when these fields are desired. On the other hand, the FGM technique presented better quantitative results with the advantage of providing detailed information about the flame composition with lower computational time. For the FGM technique, the capability of different progress variable definitions in reproducing the composition space of CO2 diluted flames is investigated and discussed in detail. The chemical and pure dilution effects of CO2 addition to the fuel stream are also discussed for the two-dimensional results.

Benefits of n-butanol, as a biofuel, in reducing the levels of soot precursors issued from the combustion of benzene flames

Although oxygenated fuel additives are effective in reducing soot emissions, the extent to which molecular structure of the oxygenate plays a role in soot reduction has remained unclear and controversial. To gain a deeper insight in this field, a detailed chemical kinetic modeling approach was used to examine the phenomenon of suppression of sooting by the addition of oxygenated hydrocarbon species to the fuel. For this task, the PREMIX code in conjunction with Chemkin II and models resulting from the merging of validated kinetic schemes describing the oxidation of the components of the n-butanol-benzene mixtures were used to investigate the effect of n-butanol addition on the formation−depletion of acetylene recognized as soot precursor in flames under fuel-rich conditions. The first part of this study treats the dependence of the soot precursor amounts on n-butanol percentage in the fuel mixture, whereas the second part defines the key reaction mechanisms responsible for the observed reduction in C2H2 and consequently in polycyclic aromatic hydrocarbons and soot amounts induced by the oxygenate additive. The principal objective of the current study was to obtain fundamental understanding of the mechanisms through which the oxygenate compound affects the soot precursor amounts. The modeling results indicated that there was a dramatic decrease in the acetylene peak height with the addition of the oxygenated addtitive. This finding was found to be due to the increase in the C2H2 consumption rates induced by n-butanol addition. Finally, the modeling results provided evidence that n-butanol played a role in changing acetylene formation mechanism by enhancing the role of C3H4P, C3H4 and aC3H5 and by eliminating the role of C6H4, C5H5, C5H6, H2CCCCH, C4H2, C5H4O, C2H, CHCHCHO, H2C4O and C4H4.

Chemical kinetics of octane sensitivity in a spark-ignition engine

This paper uses a chemical kinetic modeling approach to study the influences of fuel molecular structure on Octane Sensitivity (OS) in Spark Ignition (SI) engines. Octane Sensitivity has the potential to identify fuels that can be used in next-generation high compression, turbocharged SI engines to avoid unwanted knocking conditions and extend the range of operating conditions that can be used in such engines. While the concept of octane numbers of different fuels has been familiar for many years, the variations of their values and their role in determining Octane Sensitivity have not been addressed previously in terms of the basic structures of the fuel molecules. In particular, the importance of electron delocalization on low temperature hydrocarbon reactivity and its role in determining OS in engine fuel is described here for the first time. The role of electron delocalization on fuel reactivity and Octane Sensitivity is illustrated for a very wide range of engine fuel types, including n-alkane, 1-olefin, n-alcohol, and n-alkyl benzenes, and the unifying features of these fuels and their common trends, using existing detailed chemical kinetic reaction mechanisms that have been collected and unified to produce an overall model with unprecedented capabilities.

Chemical Kinetics for the Microbial Safety of Foods Treated with High Pressure Processing or Hurdles

The application of chemical kinetics is well known in food engineering, such as the use of Arrhenius plots and D- and z-values to characterize linear microbial inactivation kinetics by thermal processing. The emergence and growing commercialization of nonthermal processing technologies in the past decade provided impetus for the development of nonlinear models to describe nonlinear inactivation kinetics of foodborne microbes. One such model, the enhanced quasi-chemical kinetics (EQCK) model, postulates a mechanistic sequence of reaction steps and uses a chemical kinetics approach to developing a system of rate equations (ordinary differential equations) that provide the mathematical basis for describing an array of complex nonlinear dynamics exhibited by microbes in foods. Specifically, the EQCK model characterizes continuous growth–death–tailing dynamics (or subsets thereof) for pathogens such as Staphylococcus aureus, Listeria monocytogenes, or Escherichia coli in various food matrices (bread, turkey, ham, cheese) controlled by “hurdles” (water activity, pH, temperature, antimicrobials). The EQCK model is also used with high pressure processing (HPP), to characterize nonlinear inactivation kinetics for E. coli (inactivation plots show lag times), baro-resistant L. monocytogenes (inactivation plots show slight lag times and protracted tailing), and Bacillus amyloliquefaciens spores (inactivation plots show protracted tailing; HPP also induces spore activation and spore germination). We invoke further chemical kinetics principles by applying transition-state theory (TST) to the HPP inactivation of L. monocytogenes and develop novel dimensionless secondary models for temperature and pressure (TST temperature and TST pressure) to estimate kinetics parameters (activation energy E a and activation volume ∆V ‡), thereby offering new insights into the inactivation mechanisms of pathogenic organisms by HPP.