Critical Inhibitor Concentration Research Articles

Adsorption mechanism of quaternary ammonium corrosion inhibitor on carbon steel surface using ToF-SIMS and XPS

ToF-SIMS and XPS are combined to study the adsorption of tetradecyl-benzyldimethyl-ammonium (BDA-C14) bromide corrosion inhibitor on carbon steel surface. BDA-C14 forms a protective layer with N-containing polar head group interacting with carbon steel surface. The adsorbed inhibitor surface coverage strongly depends on immersion time and inhibitor concentration. A maximum and uniform coverage is found for sufficiently long exposure times at a critical inhibitor concentration of about 25 ppmw. The uniform adsorbed inhibitor layer formed on the surface mitigates the formation of iron chloride/hydroxide intermediates and thus enhances the corrosion protection of carbon steel in aggressive environment.

A Laboratory Corrosion Inhibition Study of Carbon Steel Using 2-Mercaptobenzothiazole (MBT) Under Post-Combustion CO2 Capture Conditions

Corrosion mitigation is an important aspect of amine-based post-combustion carbon dioxide (CO2) capture operations due to the desire to use less expensive but corrosion-vulnerable materials such as low carbon steels in the construction of a capture system. In this study, the corrosion behavior of A106 (grade B) carbon steel with an in-house proprietary amine-based solvent was investigated in a laboratory environment at 80°C using an organic corrosion inhibitor, 2-mercaptobenzothiazole (MBT). The corrosion inhibition mechanism was interpreted by electrochemical methods and surface analyses. The results revealed that the corrosion rates of carbon steel were significantly retarded using MBT. The critical inhibitor concentration was determined to be lie between 10 ppm and 50 ppm under the tested conditions.

Characterization of a Pyrethroid-Degrading Pseudomonas fulva Strain P31 and Biochemical Degradation Pathway of D-Phenothrin.

D-phenothrin is one of the most popular pyrethroid insecticides for its broad spectrum and high insecticidal activity. However, continuous use of D-phenothrin has resulted in serious environmental contamination and raised public concern about its impact on human health. Biodegradation of D-phenothrin has never been investigated and its metabolic behaviors remain unknown. Here, a novel bacterial strain P31 was isolated from active sludge, which completely degraded (100%) D-phenothrin at 50 mg⋅L-1 in 72 h. Based on the morphology, 16S rRNA gene and Biolog tests, the strain was identified as Pseudomonas fulva. Biodegradation conditions were optimized as 29.5°C and pH 7.3 by utilizing response surface methodology. Strain P31 depicted high tolerance and strong D-phenothrin degradation ability through hydrolysis pathway. Strain P31 degraded D-phenothrin at inhibition constant (Ki) of 482.1673 mg⋅L-1 and maximum specific degradation constant (qmax) of 0.0455 h-1 whereas critical inhibitor concentration remained as 41.1189 mg⋅L-1. The 3-Phenoxybenzaldehyde and 1,2-benzenedicarboxylic butyl dacyl ester were identified as the major intermediate metabolites of D-phenothrin degradation pathway through high-performance liquid chromatography and gas chromatography-mass spectrometry. Bioaugmentation of D-phenothrin-contaminated soils with strain P31 dramatically enhanced its degradation, and over 75% of D-phenothrin was removed from soils within 10 days. Moreover, the strain illustrated a remarkable capacity to degrade other synthetic pyrethroids, including permethrin, cyhalothrin, β-cypermethrin, deltamethrin, fenpropathrin, and bifenthrin, exhibiting great potential in bioremediation of pyrethroid-contaminated environment.

Predicting tyrosinaemia: a mathematical model of 4-hydroxyphenylpyruvate dioxygenase inhibition by nitisinone in rats.

Nitisinone or 2-(2-nitro-4-trifluoromethylbenzoyl)cyclohexane-1,3-dione is a reversible inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme important in tyrosine catabolism. Today, nitisinone is successfully used to treat Hereditary Tyrosinaemia type 1, although its original expected role was as a herbicide. In laboratory animals, treatment with nitisinone leads to the elevation of plasma tyrosine (tyrosinaemia). In rats and Beagle dogs, repeat low-dose exposure to nitisinone leads to corneal opacities whilst similar studies in the mouse and Rhesus monkey showed no comparable toxicities or other treatment related findings. The differences in toxicological sensitivities have been related to the upper limit of the concentration of tyrosine that accumulates in plasma, which is driven by the amount/activity of tyrosine aminotransferase. A physiologically based, pharmacodynamics ordinary differential equation model of HPPD inhibition to bolus exposure of nitisinone in vivo is presented. Going beyond traditional approaches, asymptotic analysis is used to separate the different timescales of events involved in HPPD inhibition and tyrosinaemia. This analysis elucidates, in terms of the model parameters, a critical inhibitor concentration (at which tyrosine concentration starts to rise) and highlights the contribution of in vitro measured parameters to events in an in vivo system. Furthermore, using parameter-fitting methods, a systematically derived reduced model is shown to fit well to rat data, making explicit how the parameters are informed by such data. This model in combination with in vitro descriptors has potential as a surrogate for animal experimentation to predict tyrosinaemia, and further development can extend its application to other related medical scenarios.

Evaluation of Performance of an Amine Based and an Imidazoline Based Gas Condensate Inhibitor Tested with a High Velocity Laboratory Test Rig

An amine based CO2 corrosion inhibitor and an imidazoline based CO2 corrosion inhibitor have been tested in a two-phase laboratory flow loop system under conditions of a gas condensate well in Austria. After a detailed description of the experimental setups, degradation rates of material API L-80 (UNS G41300) as function of flow velocity and inhibitor dosage are presented. Further, the influence of chloride addition on inhibitor performance has been investigated. All results are discussed with respect to critical inhibitor concentration to reach nearly 100 % inhibitor efficiency. Inhibitor A exhibits alkylamine as an active ingredient dissolved in ethylene glycol and different alcohols, and the effect of inhibitor B is based on imidazoline dissolved in different alcohols. Results demonstrate that the test rig delivers reasonable results with respect to inhibitor protection rates. Independent of superficial flow velocities (tested between 3 and 35 m/s), both inhibitors exhibit a good performance as long as dosed above their critical concentration. The critical concentration is clearly below 100 ppm to the liquid phase. The addition of chlorides affects the performance of the alkylamine based inhibitor significantly more than in case of the imidazoline.

Kinetics and Mechanism of Fenpropathrin Biodegradation by a Newly Isolated Pseudomonas aeruginosa sp. Strain JQ-41.

A soil bacterium designated strain JQ-41, capable of growth on fenpropathrin as the sole carbon source and energy source, was isolated from a long-term pyrethroid insecticide-treated orchard. Based on the morphology, physio-biochemical characteristics, and 16S rDNA gene analysis, as well as the G+C content of the genomic DNA, the strain JQ-41 was identified as Pseudomonas aeruginosa. Up to 92.3% of 50 mg l(-1) fenpropathrin was degraded by P. aeruginosa strain at 30°C and pH 7 within 7 days. The kinetic parameters q max, K s, and K i were established to be 1.14 day(-1), 38.41 mg l(-1), and 137.67 mg l(-1), respectively, and the critical inhibitor concentration was determined to be 72.72 mg l(-1). Cell surface hydrophobicity of P. aeruginosa strain was enhanced during growth on fenpropathrin. Three metabolites from fenpropathrin degradation were identified by gas chromatography mass spectrometry, and then a possible degradation pathway was proposed. In addition, this isolate was also able to degrade a wide range of synthetic pyrethroid insecticides including cypermethrin, deltamethrin, bifenthrin, and cyhalothrin with the degradation process following the first-order kinetic model. Taken together, our results provide insights into the kinetics and mechanism of fenpropathrin degradation by P. aeruginosa strain and also highlight its promising potential in bioremediation of pyrethroid-contaminated environment.

Statistical Evaluation of the Mathematical Modelling on the Molybdenum Reduction Kinetics of a Molybdenum-reducing Bacterium

Molybdenum is a global pollutant that has been increasingly found to be toxic tospermatogenesis in several animal model studies. Thus its removal and the studies of its reduction kinetics for removal are very important. In a previous study (1), three kinetic models; i.e. Haldane, Luong and Monod were evaluated to study the reduction kinetics of the molybdenum-reducing bacterium Bacillus sp. strain A.rzi. We revisited the model used in this bacterium and extend the study by incorporating more reduction kinetics models such as Hans- Levenspiel, Yano, Aiba, Webb, Hinshelwood and Teissier. We then evaluated the accuracy of the fitted model using statistical analysis. The best model was Han Levenspiel instead of Luong as proposed previously with the majority of the statistical evaluation such as the lowest values for RMSE, the highest adjusted R2 values and with Bias Factor and Accuracy Factor nearest to unity (1.0) indicated that the model was the best. The calculated values for the Han-Levenspiel constants qmax (the maximum specific substrate reduction rate (h−1), Sm (the critical inhibitor concentration (mM) above which reactions stops), Ks (concentration of substrate giving half maximal reduction rate (mM) and the empirical constants m and n (both dimensionless) were 3.832, 106.16, 48.19, -1.271 and 1.001, respectively. The true qmax value where the gradient forthe slope is zero was 1.107 h-1 at 38 mM molybdate as a substrate. The results indicate that the exhaustive use of mathematical models provides new understanding of the way molybdenum inhibits production into molybdenum blue in bacterium. This can provide new knowledge on ways to predict progress of molybdenum reduction in the laboratory and during bioremediation works.

Isolation of a novel beta-cypermethrin degrading strain Bacillus subtilis BSF01 and its biodegradation pathway.

Continuous use of the pyrethroid insecticide beta-cypermethrin (beta-cp) has resulted in serious environmental contamination problems. We report here that a novel bacterial strain BSF01, which was isolated from activated sludge and identified as Bacillus subtilis (collection number: CCTCC AB 2014103), showed high efficiency in degrading beta-cp. Strain BSF01 was able to utilize beta-cp as the sole carbon source for growth and degraded 89.4 % of 50 mg L(-1) beta-cp within 7 days. The optimal conditions for beta-cp degradation were determined to be 34.5 °C, pH 6.7, and inocula amount 0.11 g dry wt L(-1) using response surface methodology. The kinetic parameters q max, K s, and K i were established to be 2.19 day(-1), 76.37 mg L(-1), and 54.14 mg L(-1), respectively. The critical inhibitor concentration was determined to be 64.30 mg L(-1). Seven metabolites were identified by gas chromatography-mass spectrometry. Furthermore, a novel biodegradation pathway for beta-cp was proposed on the basis of analysis of the metabolites. This strain was also capable of degrading a wide range of pyrethroid insecticides including cypermethrin, deltamethrin, cyhalothrin, and beta-cyfluthrin, which similar to beta-cp are hazardous chemicals. Taken together, our results depict the biodegradation pathway of beta-cp and highlight the promising potentials of strain BSF01 in bioremediation of pyrethroid-contaminated environments.

VC and Cr3C2 doped WC-based nano-cermets prepared by MA and SPS

WC powders with average crystallite size of 10nm were obtained through planetary ball milling of micron sized WC powder. Nanosized-WC powders were then mechanically milled with both 9 and 12wt% Co, and the grain growth inhibitors VC and Cr3C2 in the range 0.2–0.8wt%. Powder mixtures were then consolidated using spark plasma sintering (SPS) at two different temperatures, i.e. 1200 and 1300°C. The microstructure, densification and mechanical properties of the resulting sintered nano-cermets were analyzed as a function of the type and amount of grain growth inhibitors, Co content, and sintering temperature. In general, the addition of VC and Cr3C2 was found to reduce densification. Nevertheless, the effect was found to be lower in Cr3C2 containing compositions with higher Co contents. The grain size variation was found by both a conventional line intersection method on FESEM micrographs, and by using grain analyzer software. VC was found to be comparatively more effective in restricting undesirable grain growth during the sintering processes. Moreover, the micro-hardness (HV30) and fracture toughness were measured using micro-indentation and the results were compared for each composition to comparatively assess the individual effect of the inhibitors. Increasing the concentration of inhibitors was found to restrict grain growth even more and higher hardness values were obtained but only up to a critical inhibitor concentration, beyond which the hardness degrades.

Enhancement of bioleaching of a spent Ni/Mo hydroprocessing catalyst by Penicillium simplicissimum

Statistically based experimental designs were applied to screen and optimize the bioleaching of spent hydrocracking catalyst by Penicillium simplicissimum. Eleven factors were examined for their significance on bioleaching using a Plackett–Burman factorial design. Four significant variables (pulp density, sucrose, NaNO 3, and yeast extract concentrations) were selected for the optimization studies. The combined effect of these variables on metal bioleaching was studied using a central composite design (CCD). Second-order polynomials were established to identify the relationship between the recovery percent of the metals and the four significant variables. The optimal values of the variables for maximum metals bioleaching were as follows: pulp density (4.0%, w/v), sucrose (90 g/L), NaNO 3 (2 g/L) and yeast extract (0.36 g/L). The maximum metals recovery percentages from the predicted models were 97.6% Mo, 45.7% Ni, and 14.3% Al. These values were in perfect agreement with the actual experimental values, which were (98.8 ± 0.9)% Mo, (46.5 ± 0.6)% Ni, and (13.7 ± 0.4)% Al. The growth kinetics of the fungus in the presence of the spent catalyst at various pulp densities (2–11%) and optimal condition was modeled using the modified Gompertz model. The kinetic parameters in the system were estimated using MATLAB R2008a. Results showed that the modified Gompertz model fit the experimental data well. The relationship between the specific growth rate and pulp density was found by modifying the Luong inhibition model which gave maximum specific growth rate of 0.034 day −1, optimal pulp density of 3.95% w/v and critical inhibitor concentration of 10.9% w/v.

Fungal bioleaching of incineration fly ash: Metal extraction and modeling growth kinetics

Aspergillus niger is known to be capable of bioleaching heavy metal ions from municipal solid waste (MSW) incineration fly ash. The objective of this study was to investigate the bioleaching kinetics of the fungus in the presence of the fly ash at various pulp densities (1–6%) in a batch system. The growth of the fungus was modeled using the modified Gompertz model. Since the metals present in the fly ash are toxic and inhibit microbial growth, an inhibition kinetic model using the generalized Monod growth kinetics was evaluated. In a two-step bioleaching system where the fly ash was introduced into the culture two days after inoculation, citric acid production and the leaching of the metals aluminium, iron and zinc from the fly ash were examined. The kinetic parameters in the system were estimated using the least square method. Results showed that the modified Gompertz model fit the experimental data well. The specific growth rate decreased with increasing pulp density, with a maximum specific growth rate ( μ max) of 0.115 day −1 for the control. The critical inhibitor (i.e. fly ash) concentration ( C I * ) above which no growth occurred was found to be 6.0%. Results also showed an increase in metal concentration leached with a concomitant increase in the citric acid production at various pulp densities.

Effect of adsorbed impurities on the crystal growth of poorly soluble salts from slightly supersaturated solutions

A model explaining the nonlinear dependence of crystal growth on the concentration of the impurity to be adsorbed in solution, impurity particle size, and surface coverage for poorly soluble salts at low supersaturations is proposed. The hypothesis about the adsorption of impurity particles on the terraces of crystals makes it possible to describe the evolution of growth steps using the model of crystallization at the potential relief. Analysis of the potential relief allows us to determine the critical surface coverage and the critical inhibitor concentration at which the crystallization is completely terminated. When the values of the surface coverage are lower than critical, the model predicts the near-exponential dependence of the crystallization rate on the surface coverage and impurity concentration, which agrees with the experimental data reported in the literature.

Influence of solution chemistry and surface condition on the critical inhibitor concentration for solutions typical of hot potassium carbonate CO2 removal plant

This research studied the influence of steel surface condition and solution chemistry on the critical inhibitor concentration required for spontaneous passivation of carbon steel in solutions typical of hot potassium carbonate plant (HPC). The inhibitor was added to the solution as V2O5. The critical inhibitor concentration depended on solution composition and on the steel surface condition. An inhibitor concentration of 30 g/l may be required to ensure spontaneous passivation under all conditions. The spontaneous passivation of clean polished carbon steel surfaces required a critical inhibitor concentration of 0.5–1.8 g/l. A minimum level of V5+ is required for inhibition, so that monitoring the V5+ concentration may be crucial to successfully managing corrosion protection in plant.

Computational Modeling of Active Corrosion Inhibitor Release from an Al-Co-Ce Metallic Coating: Protection of Exposed AA2024-T3

An alloy coating has been developed for an AA2024-T3 substrate that can serve as barrier, sacrificial anode, and reservoir to supply soluble inhibitor ions to protect any defect sites. In this paper, the chemical throwing power of such an metallic coating under thin electrolyte films representative of atmospheric conditions is modeled. The geometry is that of an surface with the presence of a scratch simulating exposed AA2024-T3. The model calculates the time necessary to accumulate and inhibitors over the scratch when released from the coating under different conditions. The model factors in the pH-dependent passive dissolution rate of an alloy to define the inhibitor release flux. Transport by both electromigration and diffusion are considered together. The effects of scratch size, initial pH, chloride concentration, and electrochemical kinetics of the material involved were studied. Sufficient accumulation of the released inhibitor (i.e., the concentration surpassed the critical inhibitor concentration over AA2024-T3 scratches) was achieved within a few hours (e.g., for scratches of ) when the initial solution pH was 6 and the coating was adjacent to the AA2024-T3.

Kinetics of granular development and the size distribution of latent image centres

The parallel development (with uncharged or strongly adsorbed active species, or without soluble bromide), in particular typical to colour processing, was recently proved to be non-autocatalytic silver growth with a constant rate until silver halide is completely reduced or a critical inhibitor concentration is accumulated. The other kinetic extreme is granular, stop-gamma development (with strong anionic developers and much bromide), being typical of reversal or positive processing. It slowly exhausts instantly reduced grains, providing a quasi-linear after-induction silver growth, which has been derived from the exponential size distribution of developable latent image centres and the first-order bromide replacement from them by slowly penetrating developing anions. The nearly time-cubed toe of common mixed kinetics has been shown to be inconsistent with the common autocatalytic hypothesis and to follow from the two extremes combined. The granular development in principle and the typical mixed development initially occur on the largest latent image centre in grain and cannot give evidence for the concentration principle in latent image formation.

Detailed Mechanism of Phenol‐Inhibited Peroxidase‐Catalyzed Oxidation of Indole‐3‐Acetic Acid at Neutral pH*

ABSTRACTThe inhibition of horseradish peroxidase (HRP)‐cata‐lyzed oxidation of indole‐3‐acetic acid (IAA) by a phenol, caffeic acid (CA), was studied using both a kinetic approach and computer simulation. The presence of CA resulted in a lag period in IAA oxidation. The lag period increased slowly with increasing [CA] until a critical concentration, [CA]cr, was reached, then it increased much faster when [CA] was greater than [CA]cr. The [CA]cr was proportional to [IAA] and did not depend upon [HRP]. Caffeic acid was oxidized by compound I and compound II of HRP with bimolecular rate constants (6.8 ± 107 and 2.1 ± 107M‐1s−l), which were much higher than the corresponding rate constants for IAA oxidation (2.3 ± 103 and 2.0 ± 102M−1s−1). Our experimental data show that CA inhibits IAA oxidation because it is able to compete effectively as a peroxidase substrate. A model based on a detailed mechanism of IAA oxidation was investigated using computer simulation. A rate constant driving nonenzymatic hydroperoxide formation in IAA solution was determined, 3.0 × 10−‐7 s−1. The model quantitatively describes the experimental results of this work and also qualitatively explains data published earlier. The critical inhibitor concentration is approximately equal to twice the concentration of hydroperoxide in IAA solution at the time of inhibitor addition. Therefore hydroperoxide Concentration can be calculated from the determination of critical inhibitor concentration.

Critical stabilizer concentrations in oxidizing polymers

The concept of a critical antioxidant or inhibitor concentration was introduced more than 30 years ago. Since numerous studies seemed to give it considerable theoretical and experimental support, it found rather broad acceptance. In this work it is shown, however, that the theoretical derivations of the concept are not valid. Possible reasons for the ‘no-effect concentration’ sometimes observed with polymer melts and, more often, with high molecular mass antioxidants in polymer solids, are discussed.

Extended monod kinetics for substrate, product, and cell inhibition

A generalized form of Monod kinetics is proposed to account for all kinds of product, cell, and substrate inhibition. This model assumes that there exists a critical inhibitor concentration above which cells cannot grow, and that the constants of the Monod equation are functions of this limiting inhibitor concentration. Methods for evaluating the constants of this rate form are presented. Finally the proposed kinetic form is compared with the available data in the literature, which unfortunately is very sparse. In all cases, this equation form fitted the data very well.

Characteristics of the critical phenomena in the liquid-phase oxidation of hydrocarbons in the presence of inhibitors

1. An analysis was made of the kinetic principles of the oxidation of hydrocarbons at constant, concentration of the inhibitor. Depending on the inhibitor concentration, the oxidation can proceed with autoacceleration or according to a steady-state reaction. The parameters determining the value of the autoacceleration factor of the processϕ were found. 2. The critical inhibitor concentration at which transition from an autoaccelerated to a steady-state process occurs, is determined from the conditionϕ=0. 3. The degree of sharpness of the critical transition in reactions of slow oxidation of hydrocarbons depends on the value of the rate constant of the decomposition of hydroperoxide to radicals.