Values Of Kinetic Constants Research Articles

A numerical approach for detecting switch-like bistability in mass action chemical reaction networks with conservation laws

BackgroundTheoretical analysis of signaling pathways can provide a substantial amount of insight into their function. One particular area of research considers signaling pathways capable of assuming two or more stable states given the same amount of signaling ligand. This phenomenon of bistability can give rise to switch-like behavior, a mechanism that governs cellular decision making. Investigation of whether or not a signaling pathway can confer bistability and switch-like behavior, without knowledge of specific kinetic rate constant values, is a mathematically challenging problem. Recently a technique based on optimization has been introduced, which is capable of finding example parameter values that confer switch-like behavior for a given pathway. Although this approach has made it possible to analyze moderately sized pathways, it is limited to reaction networks that presume a uniterminal structure. It is this limited structure we address by developing a general technique that applies to any mass action reaction network with conservation laws.ResultsIn this paper we developed a generalized method for detecting switch-like bistable behavior in any mass action reaction network with conservation laws. The method involves (1) construction of a constrained optimization problem using the determinant of the Jacobian of the underlying rate equations, (2) minimization of the objective function to search for conditions resulting in a zero eigenvalue, (3) computation of a confidence level that describes if the global minimum has been found and (4) evaluation of optimization values, using either numerical continuation or directly simulating the ODE system, to verify that a bistability region exists. The generalized method has been tested on three motifs known to be capable of bistability.ConclusionsWe have developed a variation of an optimization-based method for the discovery of bistability, which is not limited to uniterminal chemical reaction networks. Successful completion of the method provides an S-shaped bifurcation diagram, which indicates that the network acts as a bistable switch for the given optimization parameters.

The Effect of the plant Adiantum philippense Extracts on Biofilms Formation and Adhesion to Shigella flexneri: A Predictive Modelling Approach

In the quest for novel bioactive metabolites, which can also be used as therapeutic agents, Adiantum philippense (A. philippense), an ethnomedically important fern, has become a fascinating herb. In this study, the predictive mathematical modelling of A. philippense crude extract was tested against Shigella flexneri, a common food pathogen for its phytochemical constituents, antagonistic ability, and effect on bacterial adhesion and biofilm formation was calculated. Various kinetics models such as Von Bertalanffy, Baranyi-Roberts, modified Schnute, Modified Richards, Modified Gompertz, Modified Logistics and latest Huang were used to get values for the above kinetic constants or parameters. modified Gompertz of the entire model was found to be the best model with the highest adjusted R2 value and lowest RMSE value. The accuracy and bias factors values were close to unity (1.0). The maximum specific growth rate (mmax (h-1) for S. flexneri treatment with A. philippense extract was significantly much lower (p<0.05) with a value of 0.292 (95% confidence interval of 0.254 to 0.331) compared to control with a value of 0.540 (95% confidence interval of 0.481 to 0.599) indicating potential biofilm inhibition.

Stability Testing of Amoxicillin Nano-suspension as Promising Tool for Drug Delivery System

While nano-suspension amoxicillin is one of the approaches for improving dissolution rate of amoxicillinan antibiotic used widely. Stabilizing these nanodosage forms is always a challenge. The present study utilizes nanoprecipitation solvent evaporation technique for preparation of amoxicillin nanoparticles andproposed stability study approach of the same. The methodology was based on investigating stability of amoxicillin nano suspension in vitro, the optimized drug(polymer ratio re-formulated into nano-suspensions) and we compared our results with marketed suspensions. Samples were initially characterized and then subjected to stability testing at ambient temperature and relative humidity up to 6 months assayed using a validated HPLC method. During initial characterization, increase in saturation solubility and dissolution rate observed in all samples. During stability testing, there was gradual decrease in saturation solubility and dissolution rate of the samples, over the period of 3 months. This study considers long-term isothermal measurements, consistent with short-term non-isothermal (accelerating) measurements, providing predictive model to calculate the isothermal degradation periods. As per our results, we agree with the possibility to calculate the value of kinetic constants based on a fixed degradation limit, regardless of the shape of the curve. The accuracy of the prediction would be assessed by comparison of estimated shelf life versus data coming from traditional stability studies.

Kinetic data analysis and mathematical modeling of intra (wild type vs. engineered) and inter species (Saccharomyces cerevisiae vs. Zymomonas mobilis) dependency for bioethanol production from glucose, xylose or their combination

This study investigates intra (wild type vs engineered) and inter (S. cerevisiae vs Z. mobilis) species kinetic parameters relationship for bioethanol production with glucose, xylose or their combination as a carbon source when the same xylose utilization pathway is engineered in these strains. Kinetic constants of wild type and engineered strains of S. cerevisiae were compared. Through the comparison, and due to the introduction of the xylose pathway in the engineered strain (intra species dependency), a set of correction factors were obtained. The correction factors were then used to determine process parameters in silico (e.g., biomass and product rates) of wild type Z. mobilis from experimental kinetic parameters obtained from an engineered Z. mobilis strain presented in the literature (inter species dependency). The estimated process parameters for wild type Z. mobilis were validated using experimental data generated by the authors and showed good correlation. Results showed a relationship between wild type and engineered strains of the same microorganism. For example, the substrate limitation constants in the engineered strain of xylose (Ks,xyl, Kp,xyl, Kx,xyl) and of glucose (Ks,glu, Kp,glu, Kx,glu) were nine and three times higher in the engineered strain compared with that of the wild type (Ks,glu, Kp,glu, Kx,glu) respectively. This study suggests that these correction factors are conserved and can be used as a guide to estimate kinetic constant values for species or strains for which they are not available.

Enhanced Fluid Dynamics in 3D Monolithic Reactors to Improve the Chemical Performance: Experimental and Numerical Investigation

Three-dimensional (3D) Fe/SiC monoliths with parallel interconnected channels and different cell geometries (square, troncoconical, and triangular) were manufactured by robocasting and used as catalytic reactors in hydroxylation of phenol using hydrogen peroxide to produce dihydroxybenzenes; the reaction was performed at Cphenol,0 = 0.33 M, Cphenol,0:CH2O2,0 = 1:1 M, WR = 3.7 g, T = 80–90 °C, and τ = 0–254 gcat·h·L–1 with water as a solvent. The values of the apparent kinetic rate constants demonstrated the superior performance of the triangular cell monoliths for hydrogen peroxide decomposition, phenol hydroxylation, and dihydroxybenzene production reactions. A computational fluid dynamic model was validated with the experimental results. It demonstrated that the triangular cell monoliths, with a lower channel hydraulic diameter and not-facing interconnections, provided a higher internal macrotortuosity that induced an oscillating flow of the liquid phase inside the channels, leading to an additional transverse flow between adjacent parallel channels. This behavior, not observed in the other two geometries, resulted in a better overall performance.

Discoloration of methylene blue at neutral pH by heterogeneous photo-Fenton-like reactions using crystalline and amorphous iron oxides

Abstract Different iron oxides were evaluated for the discoloration of methylene blue (MB) at neutral pH by heterogeneous photo-Fenton-like reactions with a UV-LED lamp. Fe3O4, α-Fe2O3, and a-FeOOH catalysts were synthesized and characterized by X-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy, and adsorption isotherms of N2. The results show high crystallinity and relatively low surface areas for Fe3O4 and α-Fe2O3, and amorphous structure with high surface area for the case of a-FeOOH. The discoloration of MB by iron oxides as catalysts was studied using UV-Vis spectroscopy. Despite the relative high adsorption of MB for magnetite (12%) compared to the other oxides, it shows a slow discoloration kinetics. Besides, amorphous oxide (named a-FeOOH) shows a higher discoloration kinetics with negligible adsorption capacity. The pseudo first-order kinetic constant values for Fe3O4, α-Fe2O3, and a-FeOOH are 5.31 × 10−3, 6.89 × 10−3, and 13.01 × 10−3 min−1; and the discoloration efficiencies at 120 min were 56, 60, and 82%, respectively. It was testified that low crystallinity iron oxide can be used in the efficient discoloration of MB by photo-Fenton process with a hand UV-A lamp.

Removal of Cadmium, Nickel, and Zinc from aqueous solutions by activated carbon prepared from corncob - waste agricultural materials

Adsorption of zinc (Zn), cadmium (Cd), and nickel (Ni) from aqueous solutions by corncob (CC) and granular activated carbon prepared from corncob (GACC) were carried out. Synthetic solutions of Cd, Ni, and Zn at 3.0 ppm each were used to perform the adsorption process. A batch pattern was used to determine the kinetics as well as the adsorption isotherm parameters. The obtained results using either both the CC and GACC separately were found to be matched with the Langmuir isotherm model. Furthermore, the breakthrough study was conducted using GACC. The overall results indicated that the breakthrough curve for Cd, Ni, and Zn is the reverse of their adsorption, as demonstrated by R2 and kinetic constant (K) values.

Photocatalytic inactivation of dual- and mono-species biofilms by immobilized TiO2.

Biofilms formed by different bacterial species are likely to play key roles in photocatalytic resistance. This study aims to evaluate the efficacy of a photocatalytic immobilized nanotube system (TiO2-NT) (IS) and suspended nanoparticles (TiO2-NP) (SS) against mono- and dual-species biofilms developed by Gram-negative and Gram-positive strains. Two main factors were corroborated to significantly affect the biofilm resistance during photocatalytic inactivation, i.e., the biofilm-growth conditions and biofilm-forming surfaces. Gram-positive bacteria showed great photosensitivity when forming dual-species biofilms in comparison with the Gram-positive bacteria in single communities. When grown onto TiO2-NT (IS) surfaces for immobilized photocatalytic systems, mono- and dual-species biofilms did not exhibit differences in photocatalytic inactivation according to kinetic constant values (p>0.05) but led to a reduction of ca. 3-4 log10. However, TiO2-NT (IS) surfaces did affect biofilm colonization as the growth of mono-species biofilms of Gram-negative and Gram-positive bacteria is significantly (p≤0.05) favored compared to co-culturing; although, the photocatalytic inactivation rate did not show initial bacterial concentration dependence. The biofilm growth surface (which depends on the photocatalytic configuration) also favored resistance of mono-species biofilms of Gram-positive bacteria compared to that of Gram-negative in immobilized photocatalytic systems, but opposite behavior was confirmed with suspended TiO2 (p≤0.05). Successful efficacy of immobilized TiO2 for inactivation of mono- and dual-species biofilms was accomplished, making it feasible to transfer this technology into real scenarios in water treatment and food processing.

Immobilization of a peroxidase from Moringa oleifera Lam. roots (MoPOX) on chitosan beads enhanced the decolorization of textile dyes

The textile industry is essential, but it is also responsible for causing environmental problems, particularly the discharge of dyes. In this context, this study aimed to immobilize a previously purified peroxidase, called MoPOX, on glutaraldehyde-activated chitosan beads in order to improve the potential for textile dye decolorization. The chitosan beads were activated with 8% glutaraldehyde for 1 h, and the immobilization was performed at 30 °C, pH 5.2 for 4 h. Scanning Electron Microscopy (SEM) analyses were used to observe the differences in the chitosan beads after immobilization. The optimum temperature dropped from 70 °C to 30 °C after immobilization, but immobilized MoPOX demonstrated excellent heat stability. The optimum pH remained 5.2, while the apparent kinetic constant value (Km) of immobilized MoPOX (14.67 mM) was lower in comparison to free MoPOX (46.8 mM). The immobilized enzyme showed improved activity after long storage times, and it could retain 40 % of its original activity even after 5 cycles. The potential for decolorization of different textile dyes was considerably enhanced after immobilization, reaching more than 80 %. Also, MoPOX showed no toxicity towards Artemia salina. Overall, the findings point to the promising potential of using immobilized MoPOX as a biocatalyst in a variety of biotechnological applications.

Structural and morphological optimization of Ni doped ZnO decorated silicon nanowires for photocatalytic degradation of methylene blue

In the current work, nickel doped zinc oxide decorated silicon nanowires (SiNWs) were elaborated and applied for photocatalytic degradation of organic dyes. Nickel doped zinc oxide (Ni-ZnO) was synthesized via a facile sol-gel process of metal acetates by varying Ni content from 0 to 5% followed by the annealing process. As-prepared Ni-ZnO was subsequently spin-coated on to silicon nanowires to get ZnO-Ni/SiNWs nanohybrids. The effect of Ni doping on structural, morphological and photocatalytic properties of ZnO-Ni/SiNWs was investigated. Fourier Transform InfraRed spectroscopy (FTIR) analysis confirms the complete removal of organic moieties from as-prepared Ni-ZnO after annealing at 300˚ C. X-ray diffraction studies proved the presence of pure phase hexagonal wurtzite structure while showing a decrease of crystalline size with the increase in Ni dopant. Further, SEM and Raman mapping confirm homogeneous distribution of Ni-ZnO on Si nanowires. Photocatalysis studies showed that Ni doping enhances slightly the photocatalytic degradation of methylene blue. Highest degradation efficiency of 97% with best kinetic rate constant value was obtained for Ni-ZnO (5%)/SiNWs with hydrogen peroxide addition. The developed structure stands as promising candidates as efficient, cost-effective and reusable photocatalytic systems for organic dye decomposition.

Parameter Estimation and Kinetic Monte Carlo Simulation of Styrene andn-Butyl Acrylate Copolymerization through ATRP

Controlled polymerization causes the final product to have predictable properties, allowing it to have a more diverse application, in turn, increasing its added value. In the present work, a dynamic Monte Carlo (MC) model is used to describe the copolymerization of styrene and n-butyl acrylate through atom transfer radical polymerization (ATRP). A further investigation was performed to estimate the values of kinetic constants with no explicit value reported in the literature using particle swarm optimization (PSO). The model had excellent performance when compared with the experimental data from the literature. The model also provided access to the molecular weight and chemical composition distributions and the polymer microstructures. The results show that the propagation and termination constants’ difference affected the polymer structure directly and significantly impacted the distribution curves’ broadening. The developed model might be used in the future for monitoring and controlling the average molecular weights and the molecular weight distributions in the chemical process industry.

Exploring the structural and catalytic features of lipase enzymes immobilized on g-C3N4: A novel platform for biocatalytic and photocatalytic reactions

The exploration of multifunctional supporting materials for modern enzyme immobilization is an attractive subject for advanced catalytic applications. In the present study, lipase enzyme types, namely palatase 20,000 L, lipozyme TL100L, and lipozyme CALB, were immobilized on graphitic carbon nitride (g-C3N4) using physical and covalent immobilization methods in order to obtain biohybrids for utilization in biocatalytic and photocatalytic reactions. Characterization tests confirmed successful immobilization of enzymes without changing the crystal phase of g-C3N4. The immobilization yields were calculated as 71.0% and 93.4% for C3N4@PLTS; 81.3% and 95.4% for C3N4@LPZYM; and 79.4% and 91.7% for C3N4@CALB biohybrids using physical adsorption and covalent bonding methods, respectively. The kinetic constant values of Km and Vmax were significantly higher for immobilized lipases than for free forms. The photocatalytic efficiencies of biohybrid catalysts were also greater than raw g-C3N4. Among the lipase types, lipozyme TL100L attached on g-C3N4 exhibited the best catalytic performance in both biocatalytic and photocatalytic experiments, which was attributed to its open lid structure. As a result, this study opens the door to utilizing g-C3N4 as a support material for the immobilization of different enzymes and establishing catalyzed reactions.

About building a basis surface in inverse kinetic problems for non-break processes of diene polymerization

The work contains a mathematical description of diene polymerization with a neodym-based Ziegler-Natta catalysts. The resulting system of differential equations was reduced from infinite to finite by the method of moments. For this, the basis of nonlinear parametric functions was searched with a method allowing obtain expressions that reflect the kinetics of the polymerization process. The obtained basis of two functions enables us to construct a surface containing local regions of the minimum of the objective function which define the starting points for search of optimum kinetic constant values.

A Versatile Cationic Organic Network Adsorbent for the Highly Efficient Removal of Diverse Water Contaminants

AbstractWater decontamination is of great importance to address the increasing shortage of water resources, ion‐exchange‐driven adsorption being one of the most efficient approaches to this aim. Despite the advances achieved in this field, particularly with the emergence of ionic organic networks as a new class of adsorbents for water treatment, the development of adsorbents with high performance is still highly desired. This paper describes the facile preparation of a new cationic organic network, denoted as CON‐LDU3, via a quaternization reaction between 1,2,4,5‐tetra(pyridin‐4‐yl)benzene and 1,4‐bis(bromomethyl)benzene. The cationic framework and abundant exchangeable Br− anions render CON‐LDU3 as a suitable adsorbent to capture anionic contaminants from water. CON‐LDU3 displays fast kinetics and high capacity for the removal of CrO42−, reaching the kinetic constant and maximum capacity values of 0.0539 g mg−1 min−1 and 232 mg g−1, respectively. Moreover, this adsorbent can be regenerated by simple washing with KBr solution, and it can be recycled for at least eight times. CON‐LDU3 also exhibits excellent performance in the adsorption of some emerging organic water contaminants such as orange G and diclofenac sodium. Therefore, this study demonstrates the high potential of CON‐LDU3 as a versatile adsorbent for water remediation.

Effect of Vernonia amygdalina on phospholipase activity from Naja Mossambica (Cobra)

Background: Phospholipases are one of the numerous enzymes found in the Naja mossambica venom. They play a major role in snakebite envenomation, and also responsible for the hydrolysis of a phospholipid, disrupting the membrane integrity. In this study, we evaluated the effect of Vernonia amygdalina on Phospholipase activity from Naja mossambica (Cobra) Results: Partially purified phospholipase had maximal velocity (Vmax) and Michaelis Menten constant (Km) of 7.6 × 10-5 mol/min and 1.7mg/ml, while the crude phospholipase had Vmax and Km of 9.4 × 10-5mol/min and 2.5mg/ml respectively. Inhibition study of aqueous extracts of Vernonia amygdalina leaf shows that the extract is a potent inhibitor of crude phospholipase in a dose-dependent pattern. The different doses of extract 15 %, 10 % and 5% produced percentage inhibition of 74.04 %, 78.6 % and 86.63% respectively. The kinetic binding constant (Ki) values of crude phospholipase for different concentrations of extracts 5%, 10% and 15% were 0.21mg/ml, 0.29mg/ml and 0.39mg/ml, while the partially purified phospholipase for different concentrations of extracts 5%, 10% and 15% were were 0.48mg/ml, 0.42mg/ml and 0.41mg/ml respectively. It can be deduced from the results that the extract inhibits the phospholipase activity in an uncompetitive manner. Conclusion: Aqueous extract of Vernonia amygdalina leaves may contain some bioactive agents that could serve as potent inhibitors of phospholipase from Naja mossambica venom.

Torrefaction of Short Rotation Coppice Willow. Characterization, hydrophobicity assessment and kinetics of the process

Short Rotation Coppice Willow (SRCW) is one of the newest sources of renewable energy. Torrefaction enhances the initial poorest characteristics of SRCW, such as hygroscopicity or low heating value compared to traditional fuels, to use it as a fuel. Non-oxidative and oxidative torrefaction of SRCW were compared. Torrefaction were conducted within the range 200–240 °C and torrefied SRCW and released gases were characterized (proximate, ultimate, compositional and heating value analysis as well as hydrophobicity assessment, Py-GC/MS and chemical-kinetics parameters). At optimal torrefaction temperature, mass and energy yields were around 88% and 93%, respectively, moisture was reduced up to 1.22–1.28% and H/C and O/C atomic ratios up to 1.4 and 0.6, respectively. Biomass turns hydrophobic since contact angle increase and the amount of water absorb decrease in contact angle and liquid penetration studies, respectively. The global reaction order was 2 and kinetic constant values were in the range 4.6 10−5 s−1–3.6 10−5 s−1.

Experimental study and modeling of oxy-char combustion in a pressurized fluidized bed combustor

Pressurized oxy-coal combustion has received wide attention recently due to its potential of high efficiency and low cost in CO 2 capture. However, there is still a significant knowledge gap on the effects of pressure on the oxy-coal and oxy-char combustion behaviors. In this study, oxy-char combustion experiments were carried out in a pressurized fluidized bed combustor, and the effects of pressure and oxygen concentration on the burnout time, reactivity and temperature of the char particles were investigated. The experimental results showed that the burnout time of the char particles decreased significantly with an increase in pressure from 0.1 MPa to 0.5 MPa. Besides, an increase in either the combustion pressure (within the range of 0.1 – 0.5 MPa) or the oxygen concentration (within the range of 10 – 30% O 2 in CO 2 ) led to increases in the reactivity and temperature of the char particles, while the promotional effects of the pressure increase were weaker at the higher pressures. In order to better interpret the experimental results, a combustion model considering reaction kinetics, mass and heat transfer, and energy balance was developed and validated by the experimental results. The model simulation results showed that an increase in pressure would reduce the burnout time of char particles only when the combustion was kinetically controlled or combined kinetic-diffusion controlled. Once the combustion became diffusion-controlled, a further increase in pressure would have an insignificant effect on the char burnout time. Although the values of kinetic constants were different when different kinetic models, the global power-law model and Langmuir-Hinshelwood model, were adopted, the simulation results of the burnout time of the char particle under the pressurized fluidized bed combustion conditions were almost the same since the char combustion was mainly diffusion-controlled. The elevated combustion pressure accelerated both the char combustion rate and the char-CO 2 gasification rate, while the carbon consumption ratio by gasification increased with pressure. Moreover, the enhanced gasification reaction had a great impact on the particle temperature especially under the higher oxygen concentration combustion conditions.

Bench-Scale Absorption Testing of Aqueous Potassium Lysinate as a New Solvent for CO2 Capture in Natural Gas-Fired Power Plants

This work reports the results of an experimental campaign aiming at the characterization of the CO2 absorption performance for different aqueous solutions of potassium lysinate (LysK). The solvent stands out as a promising amino acid for post-combustion CO2 capture from combustion flue gas and it has been selected based on the high values of the overall kinetic constant (kov) and CO2 absorption flow reported in the literature.Three different LysK concentrations (8.9, 17.4 and 32.9 %w/w) have been compared and benchmarked against aqueous MEA solution (30% w/w), via closed-cycle absorption tests conducted on a bench-scale column (D = 80 mm, Packed Height = 900 mm). Liquid to gas ratios (1.39 mol/mol) and synthetic flue gas conditions (4% CO2 concentration on a molar basis, the remainder being N2) target the solvent application of CO2 capture in natural gas combined cycles, and are consistent with previous tests conducted on MEA and Potassium prolinate (ProK) solutions.Results highlight that LysK attains faster loading increase rates compared to ProK and higher CO2 loadings at saturation (between 0.82 and 0.98 molCO2/molAlk depending on the test case) with respect to MEA (0.52 molCO2/molAlk) and ProK. Finally, according to the capacity trend measured in this work, an aqueous solution with 43.7% w/w LysK has been identified as a promising option to be further investigated, verifying potential savings in the absorber packing requirements (i.e. lower packing height in a full-scale application, due to the better kinetics of LysK) while ensuring the same absorption capacity level of 30% MEA.

Visible Light Driven Degradation of Terephthalic Acid: Optimization of Energy Demand by Light Modulation Techniques

Aims: The aim of this work was to investigate the impact of light modulation parameters on the degradation of terephthalic acid, an organic model pollutant, within a heterogeneous photocatalytic system under visible light. For this purpose, a fixed bed photocatalytic reactor, irradiated by white-light LEDs matrix controlled by a system for light dimming, was used. The bed consisted of a nitrogen-doped titania photocatalyst deposited on polystyrene pellets. Background: Wastewater containing TPA can be treated into conventional aerobic biological units. However, the mineralization of TPA is slow and inefficient and its presence negatively influences the biodegradation efficiency because this pollutant inhibits microbial growth. Nowadays, innovative technologies named advanced oxidation processes (AOPs), such as heterogeneous photocatalysis with UV and visible light, ozonation, and Fenton oxidation, have gained popularity for effective organic destruction of TPA from wastewater. The heterogeneous photocatalytic oxidation process of the TPA under visible light is the most advantageous process in terms of both fixed and operating costs. Objective: In this work, the successful application of light modulation techniques for degradation of TPA using a photocatalytic system with supported visible active photocatalysts (N-doped TiO2) immobilized on polystyrene pellets is reported. In particular, sinusoidal lighting has been used analyzing the influence of the period of oscillation and the amplitude of light modulation on the reaction kinetics, in such a way as to minimize the times and energy costs for the process. Methods: To evaluate the influence of light modulation on the efficiency of the TPA removal, a discontinuous system composed of a Recirculating Photocatalytic Fixed Bed Reactor (RPFBR) irradiated by a matrix of white light LEDs was used. The flat geometry of the photoreactor guarantees the efficient excitation of the photocatalyst. An amount of 250 mL of aqueous solution with the initial TPA concentration of 12.5 ppm was applied in the photocatalytic tests lasting 180 min of irradiation fixed or sinusoidal modulated. Results: The results show that the variation of the oscillation period of the sinusoidal modulation has a pertinent influence on the photodegradation of TPA and a maximum value of the apparent kinetic constant, 0.0045 min-1 is found when the period of oscillation is 0.24 s. The sinusoidal modulation with optimal amplitude occurs with current between 50-200 mA, that shows the highest value of the apparent kinetic constant equal to 0.0046 min-1. The optimal sinusoidal modulation, as a consequence is with current between 50-200 mA and period of 0.24 s. From the data collected from the tests, it is possible to evaluate the energy cost necessary to obtain the reduction of 90% of the terephthalic acid in 1 m3 of polluted water for each modulation (E E/O), and compare these values with other tests for TPA degradation reported in the literature. The internal comparison with the three systems of literature shows that the optima sinusoidal modulation of LEDs matrix permits a strong reduction in the electrical energy consumption. Conclusion: Photocatalytic tests have demonstrated the improvement of the process energy efficiency using the light modulation technique. A further confirmation of the advantage of light modulation was obtained by comparing the energy costs required for the abatement of 90% of the terephthalic acid in 1m 3 of the photocatalytic system. Finally, a mathematical model for photocatalytic degradation of terephthalic acid within the recirculating fixed bed photocatalytic reactor, irradiated by white-light LEDs was developed.

Kinetics of Polycondensation of Citric Acid with Glycerol Based on a Genetic Algorithm

Poly(glycerol citrate) is a biodegradable aliphatic polyester made of citric acid and glycerol. Because of the high functionality of the reactants, citric acid—4 and glycerol—3, there are many possibilities for creating different polymer chain structures. In this work, the polycondensation of citric acid with glycerol and its kinetics were studied through the kinetic model, allowing for estimation of relevant kinetic constants values for the first time with the employment of a genetic algorithm. The proposed kinetic model is multidimensional and contains eight parameters. The values of kinetic constants of the reaction included in our kinetic model were estimated. Relevant Arrhenius plots justify the applied model because of values of the R2 coefficient of nearly 1.0. Considerations on the competitiveness of various reactionary acts are presented.