Deactivation Rate Constants Research Articles

Spectroscopic and photophysical properties of mono- and dithiosubstituted BODIPY dyes

A series of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes, substituted at the 3 and 5 positions was synthesized and their spectral and photophysical properties were investigated in solvents of different polarity and polarizability. All compounds are characterized by strong absorption bands at 500–580 nm, corresponding to S0 → S1 transition, the typical for the BODIPY chromophore. Emission spectra are mirror images to absorption with maxima at 520–600 nm. Substitution of the BODIPY chromophore by Cl or thioalkyl substituents induces batochromic shifts in both absorption and emission spectra for 50–60 nm and induces higher quantum yields of fluorescence (Φf = 0.1–0.7). The findings were rationalized by TD-DFT computations. The dyes exhibit weak solvatochromic properties which could not be correlated to solvent polarizability, contrary to majority of BODIPY derivatives. Furthermore, estimated singlet excited state lifetimes (τ = 2–6 ns) reveal that radiative and non-radiative rate constants for deactivation from S1 do not vary with changes in solvent polarity/polarizability. However, the highest values of Φf and τ are generally found in solvents of high polarizability. Presented spectroscopic and photophysical study is important for the use of dyes as chemodosimeters for thiols and cystein, as well as for the rational design of new molecular probes.

Luminescence and Geometric and Electronic Structures of Porphyrazines with Annelated 1,4-Diazepine Rings

Absorption, fluorescence, and phosphorescence spectra of metal complexes of 4-tert-butylphenyl-substituted tetra(1,4-diazepino)porphyrazine MPADz4Ph8′ (M = Mg, Zn; PA = porphyrazine; Dz = diazepine; Ph = phenyl; Ph′ = 4-tert-butylphenyl) were recorded in DMF at 293 and 77 K. The Q(0–0) absorption bands of MgPADz4Ph8′ and ZnPADz4Ph8′ did not show signs of splitting, i.e., corresponded to the monomeric form. Singlet–triplet gaps of 4700 cm–1 for the Mg complex and 4800 cm–1 for the Zn complex were determined from fluorescence and phosphorescence spectra. Fluorescence quantum yields and lifetimes were measured. Rate constants of S1,2 → S0 radiative transitions and total rate constants of nonradiative deactivation of the S1,2 states were determined. Internal conversion rate constants were estimated. Conformer geometries of MgPADz4Ph8 (in the 6H tautomeric form) were calculated by density functional theory in the PBE/TZVP version. The conformer of symmetry S4v (D2d ) had the lowest energy. Nonplanar diazepine rings induced small but perceptible out-of-plane distortions in the central porphyrazine ring of MgPADz4Ph8. This feature correlated with the observed Stokes shifts of 400 and 350 cm–1 (at 293 K) for MgPADz4Ph8′ and ZnPADz4Ph8′ whereas the metal phthalocyanines had shifts of ~50 cm–1. Excited electronic states of MgPADz4Ph8 were calculated using INDO/Sm. The Q-state energy of 15,200 cm–1 agreed well with the observed value of 14,800 cm–1. Strong featureless absorption in the range 330–450 nm (Soret band analog) with maxima at ~25,000 and ~29,000 cm–1 was due mainly to two strong electronic transitions with calculated energies of 24,100 and 31,500 cm–1; a shoulder on the long-wavelength side of the Soret band at ~23,000 cm–1, to a transition of calculated energy 23,800 cm–1.

Stability and Thermodynamic Attributes of Starch Hydrolyzing α‐Amylase of Anoxybacillus rupiensis TS‐4

AbstractThe physicochemical conditions influencing α‐amylase secretion by a thermophilic bacterium, Anoxybacillus rupiensis TS‐4 (Genbank number, KU360725) are optimized by the response surface methodology, using Plackett Burman design, followed by Box—Behnken design to enhance amylase production by threefold as compared to the one variable at a time approach. The amylase is purified by ion exchange chromatography, followed by size exclusion chromatography with fold purification and yield of 17.85% and 34.72%, respectively. The molecular weight, Km, and Vmax of the purified amylase are 48 kDa, 0.58 mg mL−1, and 3124 µmol mL−1 min−1, respectively. It catalyzes starch over a broader range of temperature and pH, having optima as 80 °C and 8, respectively. The enzyme is stable at a broad range of temperatures and pH, displaying higher half‐life and reduced deactivation rate constant. The feasibility of the starch catalysis reaction mediated by the studied amylase is substantiated by determining the thermodynamic parameters, such as alterations in the enthalpy, entropy, activation energy, and Gibb's free energy. The attributes of the amylase such as calcium independence, alkali‐tolerance, and stability in presence of various chelators and surfactants aid uniqueness, novelty, and commercial promise.

Strategies for improved production of phycobiliproteins (PBPs) by Oscillatoria sp. BTA170 and evaluation of its thermodynamic and kinetic stability

In the present study, cyanobacterium BTA 170 was isolated from Manipur, India and was phylogenetically related to Oscillatoria sp. The biomass of BTA 170 contained 6.5% of ash, 32.25% of carbohydrate, 37.44% of protein, 22.31% of lipid and 1.5% of moisture. 0.3 M of glycine and 5 mM of sodium glutamate were required for BTA 170 as supplements in BG 11 media for maximum yield of cell biomass and PBPs production. However, 6k Lux of light intensity and 14:10 (Light: Dark) of photoperiod were found as optimum for higher productivity. The specific growth rate was found to be 0.228 day−1 and production of PBPs was found to be growth associated. The first-order kinetic model was used to investigate the deactivation process of PBPs and the deactivation rate constant (kd) was found to be minimum in the temperature range from 10 to 40 °C and pH 7. The maximum deactivation of PBPs was found at pH 12 and 80 °C. Gibb’s free energy for PE, PC and APC were found to be 109.38–117.34; 108.10–115.21 and 108.74–116.48 kJ/mol respectively at pH 7. The pH and thermal tolerances of PBPs suggested that they may have potential for use as pigments in industry.

The Promotional Effects of ZrO2 and Au on the CuZnO Catalyst Regarding the Durability and Activity of the Partial Oxidation of Methanol

The promoter ZrO2 was applied to prevent Cu crystallites from sintering over CZ (ca. Cu 30 wt.% and Zn 70 wt.%) under partial oxidation of the methanol (POM) reaction. Gold was selected to promote the performance of CZrZ (ca. Cu 31 wt.%, Zr 16 wt.%, and Zn 53 wt.%) catalyst to overcome a high ignition temperature of 175 °C and CO selectivity (SCO) (>10% at T. > 200 °C). Experimentally, the deactivation rate constant of A5CZrZ (ca. Au 5 wt.%, Cu 31 wt.%, Zr 17 wt.%, and Zn 47 wt.%) and CZrZ was 1.7 times better than A5CZ (ca. Au 5 wt.%, Cu 31 wt.%, and Zn 64 wt.%) and CZ. The methanol conversion of CZrZ and A5CZrZ catalysts was kept higher than 70% for 12 h in an accelerated aging process. Meanwhile, the Au prompted more methoxy species oxidizing to formate on Cu+-rich A5CZrZ surface at lower temperature, and also improved CO transfer from formate reacting with moveable oxygen to form CO2. The SCO can lower to ca. 6% at 200 °C after adding 3–5% of gold promoter. These features all prove that the CZ catalyst with ZrO2 and Au promoters could enhance catalytic activity, lower the SCO and ignition temperature, and maintain good durability in the POM reaction.

The Chain Length Distribution of an Ideal Reversible Deactivation Radical Polymerization.

The chain length distribution (CLD) of a reversible deactivation radical polymerization at full conversion is shown to be a negative binomial distribution with parameters that are simple functions of the number-average degree of polymerization and either the chain transfer constant (in the case of polymerizations that incorporate a reversible chain transfer step) or the concentrations of dormant polymer chains and deactivating agent and the rate constants of propagation and deactivation (other types of RDRP). Expressions for the CLD at intermediate conversions are also derived, and shown to be consistent with known expressions for the number-average degree of polymerization and dispersity. It is further demonstrated that these CLDs are well-approximated by negative binomial distributions with appropriate choice of parameters. The negative binomial distribution is thus a useful model for CLDs of reversible deactivation radical polymerizations.

Estimation of Polymerization Rate Constants Using Experimental Residence Time Studies in Industrial Pilot Plant Equipment

AbstractEstimation of polymerization rate constants is industrially important for reactor design, reactor control, and evaluation of the productivity and product properties of new catalyst systems. Propagation and catalyst deactivation rate constants are particularly important as they control how a given catalyst system will behave in a given reactor. Pilot scale reactors are used to investigate the kinetics of solution ethylene polymerization of several catalyst systems; a heterogeneous Ziegler–Natta (Ti/MgCl2) and two constrained‐geometry molecular catalysts. A model is developed to estimate the propagation and first order catalyst deactivation rate constants through carefully conducted residence time experiments. D‐optimal experimental design criteria is used to determine the appropriate experimental conditions. Analysis shows that the observed propagation rate constant is confounded by catalyst poisons while the catalyst deactivation rate constant is independent of these factors. This helps explain how to obtain significantly larger propagation rate constants than have been previously reported in the literature.

Analytical Determination of Rational Catalyst Lifetime for Consecutive Reaction in Isothermal Plug Flow Reactor

Background. The urgency of mathematical modeling of continuous chemical-technological processes in non-stationary con­ditions caused by the actions of various destabilizing factors is undoubted. In this case, analytical solutions have undeniable advantages over numerical ones, since they make it possible to clarify the nature of the cause-effect relationships in the properties of the modeling object under consideration and, as a practical result, to give physically grounded recommendations for increasing the efficiency of its functioning. For catalytic processes, the reason for non-stationarity is the deactivation of the solid catalyst (Kt). This leads to a decrease of the conversion degree \[{x_ \bullet } = 1 - {c_{1 \bullet }}\] of the A 1 reagent, and hence to a negative increase of its concentration \[{c_{1 \bullet }}\] in the reaction mixture at the outlet of the plug flow reactor (PFR) of length \[{L_{0 \bullet }},\] which leads to economic losses. Therefore, a rational (maximally expedient) catalyst lifetime \[{\theta _{\max }} > > 1\] has fundamental importance and is a significant part of the individual problem of selecting Kt. Objective . The aim of the paper is analytical calculation of the maximally expedient lifetime \[{\theta _{\max }} = {\tau _{\max }}/{\tau _{L \bullet }}\] of industrial Kt at the point \[{x_{0 \bullet }}\] of maximum of the nominal yield \[{\eta _{02 \bullet }} \equiv \eta _{02}^{\max }\] of the product A 2 for the isothermal system “PFR at the optimum resi­den­ce time \[{\tau _{L \bullet }} = {L_{0 \bullet }}/{u_0}\] of the reactants + consecutive catalytic reaction \[\mathrm{A}_{1}\xrightarrow[\mathrm{Kt},k_{\mathrm{d}1}]{k_{01},n_{1}=1}\alpha _{2}\mathrm{A}_{2}\xrightarrow[\mathrm{Kt},k_{\mathrm{d}2}]{k_{02},n_{2}=1}\alpha _{3}\mathrm{A}_{3}\] under the influence of the Kt deactivation destabilizing factor. Methods . A linearized mathematical model in the form of a system of ordinary differential equations of characteristics for calculating the relatively small Kt deactivation influence on the system operating mode stationarity has been used. Results . In the case of the first-order reaction for the conditions of the industrial Kt deactivation, the relative deviations \[\left | \varepsilon _{x\bullet } \right |=\left | (x_{\bullet }/x_{0\bullet })-1 \right |\sim k_{\mathrm{d}1}\tau _{\mathrm{max}} 0\] are determined by the simplex \[\gamma _{0k}=k_{01}/k_{02}\] of the nominal rate constants and by the simplex \[\gamma _{\mathrm{d}}=k_{\mathrm{d}2}/k_{\mathrm{d}1}\] of the Kt deactivation rate constants of the reaction stages. Conclusions . It is proved that with respect to the yield of A 2 product, there is a self-regulation effect \[({\varepsilon _{\eta 2 \bullet }} \approx 0)\] of the stationary mode at the condition of the equality \[\gamma _{\mathrm{d}}=1\] of the Kt deactivation rate constants. A nomogram for determining \[1 < <\theta _{max}< < (k_{\mathrm{d}1}\tau _{L\bullet })^{-1}\] on the maximum admissible value of \[\left | \varepsilon _{x\bullet } \right |_{max}^{\mathrm{adm}}< < 1.\] is calculated. For example, at a nominal degree of conversion \[{x_{0 \bullet }} = 75\% \Leftrightarrow {\gamma _{0k}} = 2\] of A 1 reagent and \[\left | \varepsilon _{x\bullet } \right |_{max}^{\mathrm{adm}}= 5\%\Rightarrow \theta _{max}\approx 1,1\cdot 10^{3}(k_{\mathrm{d}1}\tau _{L\bullet }=10^{-4}).\] It is shown that the rational catalyst lifetime \[{\theta _{\max }}\] is inversely proportional to the complex \[k_{\mathrm{d}1}\tau _{L\bullet }\] of the Kt deactivation rate constant of the first stage.

Development of a thermo-stable and recyclable magnetic nanobiocatalyst for bioprocessing of fruit processing residues and D-allulose synthesis

The aim of the study was to covalently immobilize Smt3-D-psicose 3-epimerase onto functionalized iron oxide magnetic nanoparticles. After immobilization, Km of the immobilized enzyme increased, however, Vmax was nearly the same as that of its free form, indicating that immobilization has no detrimental effects on its catalytic output. The covalent immobilization caused a reduction in the deactivation rate constant (kd) values leading to 4–5 fold enhancement in its half-life at 50–65°C, indicating significant thermal stability of the iron-enzyme nanobioconjugate. The immobilized enzyme showed excellent storage stability by losing only 20% activity even after 60days of storage at 4°C. The immobilized enzyme retained up to 90% of its initial activity even after 10 consecutive cycles of catalyzing D-fructose epimerization reactions. Thus, after immobilization the enzyme exhibited remarkable improvements in thermal tolerance, storage stability and recycling efficiency, useful for development of industrially exploitable process for D-allulose production.

Kinetics of cellulose hydrolysis by halostable cellulase from a marine Aspergillus niger at different salinities

Abstract Kinetics of cellulose hydrolysis with halostable cellulase from a marine Aspergillus niger was analyzed at different salinities. Cellulase activity in 8% NaCl solution was 1.43 folds higher than that in NaCl free solution. Half saturation constant, K m (15.6260 g/L) and the rate constant of deactivation, K de (0.3369 g/L h) in 8% NaCl solution was lower than that (18.6364 g/L), 0.3754 (g/L h) in NaCl free solution. The maximum initial hydrolysis velocity, V max (25.5295 g/L h), in 8% NaCl solution was higher than that in NaCl free solution (25.0153 g/L h). High salinity increased affinity to the cellulase to the substrate and thermostability. Halostable cellulase from a marine Aspergillus niger was valuable for cellulose hydrolysis under high salinity conditions.

Triplet states of 3,3′-alkylsubstituted thiacarbocyanine dimers and dimeric complexes with cucurbit[8]uril in water

Alkylsubstituted thiacarbocyanines (3,3′-diethylthiacarbocyanine, D1, and 3,3′-disulfopropylthiacarbocyanine, D2), existing in water as monomers and dimers, manifest the ability to transition to the triplet state. The spectrum of triplet-triplet (T–T) absorption of the D2 dimers is shifted in the range higher than 590 nm by 20 nm to the red in comparison with the T–T spectrum of monomers. The D1 dimers in the presence of cucurbit[8]uril form a dimeric complex with two bands in the differential absorption spectrum. The band at 550 nm belongs to the triplet-triplet absorption of the dimeric complexes, and the band in the range of 620–700 nm is the result of charge transfer in the triplet state. The rate constants of deactivation for these triplet states coincide.

Dehydrogenation kinetic model of heavy paraffins

Based on the dehydrogenation mechanism of heavy paraffins under industrial conditions, the intrinsic reaction kinetic model and catalyst deactivation model were established considering the influence of side reactions with different carbon‐number heavy paraffins. Based on the experimental data of dehydrogenation reactions with different carbon‐number paraffins in an axial continuous‐flow isothermal fixed‐bed microreactor, Powell optimization method was used to estimate the model parameters. The results show that there is a liner relationship between the activation energies and pre‐exponential factors of homologous reactions and carbon number of paraffins. A correlation model about the deactivation rate constants under different conditions was established. The validation of kinetic model showed that the model could be used to predict detailed product distribution with different feedstocks under different reaction conditions. © 2017 American Institute of Chemical Engineers AIChE J, 2017

Photonics of 18-crown-6-containing styryl dye and its complexes with metal cations

Using absorption, luminescence, 1H NMR, and laser kinetic spectroscopies, the photophysical processes and photochemical reactions of 4-[(E)-2-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)vinyl]-1-ethylpyridinium perchlorate and its complexes with lithium, sodium, potassium, calcium, barium, silver, and lead perchlorates in MeCN have been studied. The styryl dye and its complexes with metal cations are capable of emitting normal (prompt) and delayed fluorescence and enter into the trans–cis photoisomerization reaction. The dye molecules in the triplet state participate in the processes of degradation of electronic excitation energy. Triplet–triplet absorption is observed only in the presence of lead cations with a maximum at 470 nm and the deactivation rate constant of the triplet state k = 2.5 × 104 s–1 in a deoxygenated solution.

Optimization of CO2Capture Process from Simulated Flue Gas by Dry Regenerable Alkali Metal Carbonate Based Adsorbent Using Response Surface Methodology

The low cost of K2CO3/Al2O3 adsorbent is encouragement to use it for CO2 capture from the flue gas of fossil-fuel power plants. In this study, optimization of the CO2 capture process using a K-based adsorbent in a fixed-bed reactor has been investigated. The sorbent was also characterized by different techniques such as SEM, BET, and XRD analysis before and after the reactions. Response surface methodology (RSM) combined with Box–Behnken design (BBD) was employed to evaluate the effects of the process variables (temperature, mole ratio of H2O/CO2, and vapor pretreatment time) and their interaction on the responses (CO2 capture capacity and deactivation rate constant) to achieve the optimal conditions. In addition to the experiments, the deactivation model in the noncatalytic heterogeneous reaction system was employed to evaluate the kinetic parameters (sorption rate and deactivation rate constants) using nonlinear-least-squares technique. According to the analysis of variance (ANOVA), the vapor pretreatme...

Production, immobilization and thermodynamic studies of free and immobilized Aspergillus awamori amylase

Enzyme cost, stability and its thermodynamic characteristics are the main criteria for industrial use. In this study, Aspergillus awamori amylase was constitutively produced using various agro-industrial wastes. Olive oil cake gave the highest activity (230U/g). The amylase was partially purified to 2.81-fold purification. Immobilization was achieved using different carriers by covalent binding. The novel carrier Ca+2 alginate (Alg) starch (St)/polyethyleneimine (PEI)/glutaraldehyde (GA), showed the highest operational stability and was selected for further studies. The optimum temperature for the free and immobilized form was 50°C and 55–60°C, respectively. The immobilization process had a major role in improving enzyme thermal stability. In comparison to free enzyme, the immobilized form showed the highest optimum temperature, activation energy (Ea) and deactivation rate constants (kd). Also, t1/2, D-values (decimal reduction time), change in enthalpy (ΔH° kJmol−1), and Gibbs free energy (ΔG°) increased and was higher than the native enzyme within 50–80°C. The magnitude of negative value of entropy (ΔS° kJmol−1) for immobilized enzyme was negative for the free and immobilized enzymes revealing that native form of enzyme was in more ordered state. Km and Vmax values were slightly affected by the temperature variations 40–70°C.

Kinetics of the permanent deactivation of the boron-oxygen complex in crystalline silicon as a function of illumination intensity

Based on contactless carrier lifetime measurements performed on p-type boron-doped Czochralski-grown silicon (Cz-Si) wafers, we examine the rate constant Rde of the permanent deactivation process of the boron-oxygen-related defect center as a function of the illumination intensity I at 170°C. While at low illumination intensities, a linear increase of Rde on I is measured, at high illumination intensities, Rde seems to saturate. We are able to explain the saturation by assuming that Rde increases proportionally with the excess carrier concentration Δn and take the fact into account that at sufficiently high illumination intensities, the carrier lifetime decreases with increasing Δn and hence the slope of Δn(I) decreases, leading to an apparent saturation. Importantly, on low-lifetime Cz-Si samples no saturation of the deactivation rate constant is observed for the same illumination intensities, proving that the deactivation is stimulated by the presence of excess electrons and not directly by the photons.

A Straightforward Estimation of Activation and Deactivation Parameters for ATRP Systems from Actual Polymerization Rate and Molecular Weight Distribution Data

The accuracy of a model prediction relies heavily on the quality of the parameters used. Some of the available methods to estimate the activation and deactivation rate constants in atom transfer radical polymerization (ATRP) are done in the absence of monomer, hence they may not be representative of the polymerization conditions. Others offer great accuracy but requires data that are not commonly measured in experiments. In this study, a simple method is proposed to estimate activation and deactivation rate constants through correlating the recently reported theoretical equations with experimental data of monomer conversion and polymer molecular weight dispersity. The kinetics and dispersity equations used are straightforward and explicit, thus can be easily calculated. Only two parameters (activation and deactivation rate constant) are involved in the correlation of two data sets without any other adjustable parameters. In addition, the experimental data required are some of the most often measured quantities in polymerization, thus no additional experiments or measurements are required. Since the conversion and dispersity are obtained from actual polymerization, the reaction rate constants estimated are representative of the real reaction conditions. The applicability of this method is demonstrated by estimating parameters using reported experimental data of ATRP of methyl methacrylate conducted at various conditions. image

Kinetic modeling for the deactivation of TiO2 during the photocatalytic removal of low concentration SO2

A kinetic model considering the deactivation of a catalyst was developed for the removal of low concentration SO2 with TiO2 as the photocatalyst. For the deactivation caused by poisoning of the reaction products, the catalyst activity which decreased with time was derived based on the Langmuir adsorption assumption. The calculated results of the kinetic model were consistent with the experimental data under various operation conditions, including inlet SO2 concentration, space time, flue gas humidity, and time on stream. The kinetic model can be used to predict the evolution of the outlet SO2 concentration, as well as the catalyst activity, with the operation time and the position of catalyst bed. The influences of water content on the reaction and deactivation processes of the catalyst were discussed based on the obtained kinetic parameters. The reaction and deactivation rate constants both increased with the increase in water content, which means that the presence of water in flue gas will not only promote the photocatalytic reaction of SO2 but also accelerate the deactivation of the TiO2 catalyst.

Influence of Support Structural Characteristics on Long-term Performance of Pd-Ag/α-Al2O3 Catalyst for Tail-end Acetylene Selective Hydrogenation

Abstract The selective hydrogenation of acetylene to ethylene in acetylene/ethylene mixture over Pd-Ag/α-Al2O3 catalysts prepared by sequential impregnation method was studied. The α-Al2O3 support was prepared by thermal treatment of γ-Al2O3 in temperature range of 1,090–1,100 °C. The samples were characterized for their structural properties and coke deposition. They showed egg-shell structure with penetration depth increasing with sintering temperature of the support. A kinetic model based on 1st order in acetylene and 0.5th order in hydrogen for the main reaction and 2nd order independent decay law for catalyst deactivation was used to fit the conversion-time data and to obtain quantitative assessment of catalyst performances. Fair fits were observed from which the reaction and deactivation rate constants were evaluated. The highest selectivity to ethylene, and therefore best performance, was obtained for the highest calcination temperature which was attributed to its lower acidity and larger pore diameters.

Correlations of kinetic parameters with various system operating conditions for CO2 sorption using K2CO3/Al2O3 solid sorbent in a fixed/fluidized bed reactor

The kinetic parameters for carbon dioxide sorption using potassium carbonate supported on an alumina oxide solid sorbent in a fixed/fluidized bed reactor were investigated using a deactivation kinetic model. The initial parameters of the deactivation model were explored by comparison of the obtained results with experimental data. Then, the effects of varying the three key system operating conditions (inlet gas velocity, sorption temperature and water vapor content) on the kinetic parameters were considered. The obtained breakthrough curves were used for calculation of the kinetic parameters. Finally, the relationship between the obtained kinetic parameters and the system operating conditions were summarized. The selected deactivation model was found to fit well with the experimental data. The reaction rate constant was highest in a turbulent fluidization flow pattern and the initial sorption and deactivation rate constant were dependent on the water vapor content except with excess water vapor content.