Kinetics of polyurethane formation between glycidyl azide polymer and a triisocyanate

Kinetics of the polyurethane formation between glycidyl azide polymer (GAP) and a polyisocyanate, Desmodur N‐100, were studied in the bulk state by using quantitative FTIR spectroscopy. The reaction was followed by monitoring the change in intensity of the absorption band at 2270 cm^?1 for NCO stretching in the IR spectrum, and was shown to obey second‐order kinetics up to 50% conversion. The activation parameters were obtained from the evaluation of kinetic data at different temperatures in the range of 50–80°C. The enthalpy and entropy of activation were found to be ΔH^? = 44.1 ± 0.5 kJ · mol^?1 and ΔS^? = ?196 ± 2 J · mol^?1l · K^?1, respectively. Dibutyltin dilaurate (DBTDL) was used as the curing catalyst. The kinetic study of the polyurethane formation between GAP and Desmodur N‐100 showed that the reaction is enormously speeded up in the presence of the catalyst, and the reaction obeys second‐order kinetics, provided that the catalyst concentration is kept constant. An investigation on the rate of the catalysed reaction depending on the catalyst concentration provided the order of the reaction, with respect to the DBTDL catalyst concentration, and the rate constant for the catalytic pathway of the reaction. The rate constant for the catalytic pathway was established to be 4.37 at 60°C, while the uncatalyzed reaction has a rate constant of 3.88 × 10^?6 L · mol^?1 · s^?1 at the same temperature. A rate enhancement factor of 23 was achieved by using 50 ppm catalyst. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 918–923, 2001     

Sorption of caesium by complex hexacyanoferrates iv. ion exchange kinetics and mechanism of sorption by potassium copper ferrocyanide

The kinetics of caesium sorption by potassium copper ferrocyanide have been studied. Liquid film diffusion is rate controlling in very dilute solutions of caesium (3.8 × 10^?6m). The average film diffusion coefficient was found to be 1.465 × 10^?9 m² s^?1 at 20°C and the activation energy for the corresponding process was found to be 15.14 kJ mol^?1. Chemical reaction rate controls the caesium-potassium ion exchange process at a higher caesium concentration of 3.8 × 10^?3m. The shell progressive reaction model was found applicable to the sorption process. The activation energy for the caesium-potassium ion exchange reaction was measured to be 74.85 kJ mol^?1. Finally, a comparison between the theoretical and the experimental sorption profile has been made to demonstrate the validity of the theory.     

Treatment of dyehouse waste‐water by supercritical water oxidation: a case study

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste‐water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L^?1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400–600 °C and residence times of 8–16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste‐water with an activation energy of 104.12 ( ± 2.6) kJ mol^?1 and a pre‐exponential factor of 1.59( ± 0.5) × 10⁵ s^?1. The oxidation reaction rate orders for the TOC and the oxidant were 1.169 ( ± 0.3) and 0.075 ( ± 0.04) with activation energies of 18.194 ( ± 1.09) kJ mol^?1, and pre‐exponential factor of 5.181 ( ± 1.3) L^0.244 mmol^?0.244 s^?1 at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 16 s under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste‐water was removed completely at temperatures of 450 °C and above. Copyright © 2010 Society of Chemical Industry     

High‐Impact Polyamide Composites with Linear Ethylene–Norbornene Anhydride Copolymers from Insertion Polymerization

Toughening of polyamide 66 with novel linear norbornene anhydride functionalized polyethylenes leads to an impact performance in the Charpy‐notch impact testing at 23 °C and ?30 °C as high as a_CN = 18.0 ± 1.0 and 13.7 ± 0.8 kJ m^?2, respectively, which compares favorably to a state of the art functional low density polyethylene (LDPE) from high‐pressure copolymerization with a Charpy‐notch impact strength of a_CN = 16.8 ± 0.0 and 13.8 ± 2.1 kJ m^?2 at 23 and ?30 °C, respectively. The linear copolymers are obtained by insertion polymerization at mild ethylene pressures of 5 to 15 bars with phosphinesulfonato Pd (II) catalysts, to yield linear copolymers with norbornene anhydride incorporations as high as 4.8 mol% along with a polymer molecular weight of >10⁵ g mol^?1. Furthermore, the norbornene anhydride functionality serves as a reaction site for postpolymerization functionalization with alcohols to obtain the respective half‐ and diesters of the anhydride functionality. Notably, the impact performance is improved with the increase of the alkyl chain length and degree of branching of the ester functionality in the order methanol < n‐butanol < 2‐ethyl hexanol from 10.0 to 13.8 kJ m^?2.     

Synthesis,characterization and kinetics of terpolymerization of acrylonitrile,N-vinyl pyrrolidone and styrene

Synthesis of a series of novel terpolymers, consisting of two electron-donating monomers, viz. N-vinyl pyrrolidone (N-VP) (heterocyclic polar monomer) and styrene (Sty) (non-polar monomer), with one electron-accepting polar monomer, i.e. acrylonitrile (AN), using α,α'-azobisisobutyronitrile as radical initiator and benzene as diluent at 60°C, has been extensively surveyed. Besides the synthesis, an attempt has been made to study the kinetics and various properties of the terpolymers, such as softening temperature and chemical resistance. The system follows non-ideal kinetics and the kinetic equation for the present system can be written as This non-ideality can be explained on the basis of significant initiator-dependent termination through primary radicals and degradative chain transfer to acrylonitrile monomer. The overall energy of activation is 72.4 kJ mol^?1 and k_p²/k_t is 0.26 × 10^?3 litre mol^?1 s^?1. The effects of various additives such as imidazolium-p-chlorophenacylide (ICPY) and ZnCl₂ were also studied. ICPY functions as a chain transfer agent (C^tr = 0.43 × 10^?4), whereas ZnCl₂ accelerates the rate of reaction. IR spectroscopy was used to confirm the structure of the terpolymers.     

Condensation polymerization of pyrogallol and benzaldehyde

Novolac-type polycondensation of benzaldehyde (B) and pyrogallol (P) has been carried out at 60°C, 75°C and 90°C and at B/P mole ratios of 1.5 and 3.0 using phosphoric acid as catalyst. The reaction follows a 2nd order rate law. By using GC consumption data of benzaldehyde and pyrogallol, kinetic parameters such as the overall rate constants, activation energies (E_a) and logA values are investigated. The activation energies for 1.5 and 3.0 B/P mole ratios are found as 62.3 kJ mol^?1 and 56.4 kJ mol^?1, respectively. The molecular weights of the resins determined by measuring intrinsic viscosities (25°C, THF) are in the range of 0.03 to 0.07 dL g^?1 at various temperatures and B/P mole ratios.     

Reactive polymers. XX. The preparation of a carrier with aldehyde groups by oxidation of a macroporous glycidyl methacrylate-ethylenedimethacrylate copolymer with periodic acid

The oxidation of a macroporous glycidyl methacrylate-ethylenedimethacrylate copolymer and of a polymer formed by its hydrolysis was investigated at temperatures ranging from 5 to 80°C with various concentrations of periodic acid. The reaction yields (formylmethyl)-methacrylate units bearing free aldehyde groups capable of further reactions. The results allowed to estimate the activation energy of the reaction (60 and 27.5 kJ mol^-1) and to discuss its mechanism. The oxidation of the epoxide group seems to proceed in two steps with vicinal glycol as the intermediate product.     

Kinetics of Denaturation and Effects of Surfactants and Polyethylene Glycol on Soybean Esterase (Glycine max L) Stability

The objective of this work was to evaluate the kinetics and thermodynamics parameters and the effects of anionic, cationic and nonionic surfactants and polyethylene glycol on the activity and stability of a crude esterase extracted from soybeans (Glycine max L.). The activation energy for thermal inactivation was calculated from the Arrhenius plot was found to be 59.4 kJ mol^?1 and the ΔH* 56.82 kJ mol^?1 at 40 °C, which was the optimum temperature for enzyme activity. The ΔS* and ΔG* of the enzyme were found to be 61.67 kJ mol^?1 and 15.50 J mol^?1 K^?1, respectively, at the optimum temperature. The activity was only enhanced by the cationic surfactants cetyltrimethylammonium bromide and tetradecylmethylammonium bromide at a concentration of 3.0 mM. The anionic surfactant showed a positive effect on enzyme activity at the concentrations of 1.5 and 3.0 mM. Aqueous PEG (polyethylene glycols) solutions activated the esterase, and maximum activation (170 %) occurred with the addition of 6 kDa PEG. PEG with molecular weights of 0.4 and 10 kDa enhanced enzyme stability at 40 °C.     

Laboratory-scale coal reactivity testing for entrained gasification

A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO₂ or H₂O. It is shown that gasification reactivity increases with decreasing coal rank. The CO₂ and H₂O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO₂ gasification reaction has an activation energy of about 100 kJ mol^?1 for lignite and 220–230 kJ mol^?1 for bituminous coals and fluid petroleum coke. The activation energies for H₂O gasification are about 100 kJ mol^?1 for lignite, 290–360 kJ mol^?1 for bituminous coals and about 200 kJ mol^?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results.     

TRANSFER RATE AND SEPARATION OF Sr2+ and Cs+ BY SUPPORTED LIQUID MEMBRANES UTILIZING SYNERGIZED CROWN ETHER CARRIERS

ABSTRACT

The rate of the isotopic exchange of Na? and Cs? between hydrous silicon-titanium(IV) oxide in the relevant ionic form and aqueous solution was determined radiochemically. The rate was controlled by the diffusion of the ions in the exchanger particles. The diffusion coefficients at 5 °C are (3.9±0. 1)×10^?11m² s^?1 and (2.4± 0. 1)×10^?11 m² s^?1respectively, for Na? and Cs? in the exchanger equilibrated with solutions at pH 6. The activation energies are 31±5 kJ mol^?1 and 20±5 kJ mol^?1 for Na? and Cs? diffusion, respectively. The diffusion coefficients of the ions decreases with increasing pH of the solutions equilibrated with the exchanger, whereas their activation energy is independent of pH. The results were interpreted in terms of the strength of the electrostatic interaction between the counter ions and the ion-exchange sites.     

A thermal study on the use of immobilized penicillin G acylase in the formation of 7‐amino‐3‐deacetoxy cephalosporanic acid from cephalosporin G

Penicillin G acylase (PGA) is an important enzyme for the industrial production of 7‐amino‐3‐deacetoxy cephalosporanic acid (7‐ADCA) from cephalosporin G (Ceph‐G), and 6‐aminopenicillanic acid (6‐APA) from penicillin G (Pen‐G). These products are used for the manufacture of semi‐synthetic cephalosporins and penicillins. In this study, immobilized PGA was utilized to catalyze the conversion of Ceph‐G to 7‐ADCA. The optimal conditions were found to be an operating temperature of 45 °C, 0.2 M phosphate buffer, a substrate concentration of 30 mg cm^?3 and a catalyst particle concentration of 0.01 g cm^?3 (specific activity of 623.2 U g^?1). Up to 45 °C the reaction was characterized by an activation energy of 38.66 kJ mol^?1. Beyond 57.5 °C there was a sharp decline of activity, characterized by a deactivation energy of 235.88 kJ mol^?1. Copyright © 2004 Society of Chemical Industry     

Kinetics of vinyl polymerization initiated by potassium permanganate/β-hydroxybutyric acid redox system

The aqueous polymerization of acrylamide initiated by potassium permanganate/β-hydroxybutyric acid has been studied volumetrically at 35 ± 0.01°C in an inert medium. The rate of polymerization shows nearly square root dependence on β-hydroxybutyric acid at low concentration (3.12 – 12.5 · 10^?3 mol dm^?3). The order with respect to potassium permanganate has been found to be 0.6 indicating thereby a bimolecular mode of termination. The polymerization rate has been varied linearly at low monomer concentrations i.e. from 2.5 –7.0 · 10^?2 mol dm^?3. The dependence of number average degree of polymerization on the initial rate of polymerization and temperature has been determined. The over-all activation energy has been found to be 51.66 kJ mol^?1. A kinetic reaction scheme is proposed on the basis of experimental results.     

Synthesis and thermal cure of diphenyl ethers terminated with acetylene and phenylacetylene

Two kinds of novel compounds, diphenylacetylene diphenyl ether (DPADPE) and diacetylene diphenyl ether (DADPE), were prepared and polymerized under heating. Raman, DSC and ¹³C CP/MAS NMR analyses were used for studying the polymerization reaction. DPADPE and DADPE have melting points at 190 and 79 °C, with exothermic peaks of the DSC curves at 375 and 215 °C for curing, respectively. Raman and ¹³C CP/MAS NMR spectra show that DPADPE could be cured at a temperature higher than 300 °C and DADPE at a lower temperature of higher than 150 °C. The kinetic parameters for the thermal crosslinking reactions were obtained by the Ozawa method and the results show that the apparent activation energy is 152 kJ mol^?1 for DPADPE and 109 kJ mol^?1 for DADPE. An ene–yne Straus product appears in the cured DADPE, whereas this product has not been identified in the cured DPADPE. The cured DPADPE and DADPE demonstrate good thermal and thermo‐oxidative stability. Copyright © 2006 Society of Chemical Industry     

Sintering and grain growth behaviour of magnesium aluminate spinel: Effect of lithium hydroxide addition

Lithium hydroxide, LiOH, in the amounts ranging from 0.1 to 1.2 wt% has been used as a sintering aid to improve the densification of MgAl₂O₄. The addition of 0.3 wt% LiOH promotes densification and limits grain growth. The activation energy of sintering, calculated using master sintering curve approach, decreases from 790 ± 20 kJ.mol^?1 to 510 ± 20 kJ.mol^?1 with the addition of 0.3 wt% of LiOH. In addition, MgAl₂O₄ was also mixed with 10 wt% of LiOH to amplify the formation of reaction products. High-temperature XRD results showed that secondary phases (MgO and LiAlO₂) are produced above 1040 °C. The secondary phases start to disappear at T > 1200 °C, and MgAl₂O₄ is produced. While adding small amounts of LiOH, up to ca. 0.3 wt%, is beneficial for densification and suppressing grain growth, there exists a critical concentration of Li⁺ that is accounted for by the preferential incorporation of lithium ions into MgAl₂O₄ crystal lattice.     

The pre-exponential factor and its importance in determining mechanism: the bromine electrode

The rate of the reaction 2Br^? = Br₂ + 2 e at Pt electrodes has been studied in the temperature range 0 – 50 °C. Hence the enthalpy of activation was found to be 15 kJ mol^?1. The preexponential factor was calculated using various assumptions and it is shown that the most probable rate-determining step in this reaction is Br^? → Br (ads) + e, the adsorbed bromine atom being in a sparsely filled second layer with the electrode covered completely with a first layer of unreactive bromine atoms.     

Adsorptive removal of anionic and non‐ionic surfactants from aqueous phase using Posidonia oceanica (L.) marine biomass

BACKGROUND: In this study, the capability of low‐cost, renewable and abundant marine biomass Posidonia oceanica (L.) for adsorptive removal of anionic and non‐ionic surfactants from aqueous solutions have been carried out in batch mode. Several experimental key parameters were investigated including exposure time, pH, temperature and initial surfactant concentration. RESULTS: It was found that the highest surfactant adsorption capacities reached at 30 °C were determined as 2.77 mg g^?1 for anionic NaDBS and as 1.81 mg g^?1 for non‐ionic TX‐100, both at pH 2. The biosorption process was revealed as a thermo‐dependent phenomenon. Equilibrium data were well described by the Langmuir isotherm model, suggesting therefore a homogeneous sorption surface with active sites of similar affinities. The thermodynamic constants of the adsorption process (i.e. ΔG°, ΔH° and ΔS°) were respectively evaluated as ? 8.28 kJ mol^?1, 48.07 kJ mol^?1 and ? 42.38 J mol^?1 K^?1 for NaDBS and ? 9.67 kJ mol^?1, 95.13 kJ mol^?1 and ? 174.09 J mol^?1 K^?1 for TX‐100. CONCLUSION: Based on this research, valorization of highly available Posidonia oceanica biomass, as biological adsorbent to remove anionic and non‐ionic surfactants, seems to be a promising technique, since the sorption systems studied were found to be favourable, endothermic and spontaneous. Copyright © 2007 Society of Chemical Industry     

Equilibrium bulk polymerization of 1,3-dioxolan

Cationic bulk polymerization of 1,3-dioxolan has been carried out in sealed ampoules using a high vacuum technique. The polymerization is initiated with triethyl oxonium hexafluorophosphate and the equilibrium between monomer and active polymer is attained within a few hours. Specific volumes of pure monomer and polymer in solution of its own monomer have been measured. Equilibrium measurements have been performed in the 40° to 141·4°C temperature range and the ceiling temperature is estimated to be 144° ± 2°C. The effect of short polymer chains on the equilibrium is discussed briefly. Values of ΔG_lc, the free energy of polymerization of one mole of pure liquid monomer to one base-mole of amorphous polymer, are computed making allowance for the non-ideal mixing. Respective values of ?17.5 ± 0.8 kJ/mol and ?47.9 ± 2.2JK^?1mol^?1 are deduced for the corresponding ΔH_lc and ΔS_lc. ΔG_lc is also computed from published data on equilibrium polymerization of 1,3-dioxolan in various solvents and the combined results for both types of polymerization yield ΔH_lc = ?16.7 ± 0.5kJ/mol and ΔS_lc = ?45.8 ± 1.5JK^?1mol^?1 for the 20° to 140°C range.     

Hydride Transfer: A Dominating Reaction of Ozone with Tertiary Butanol and Formate Ion in Aqueous Solution

This article provides evidences that hydride transfer is an important primary step in ozone reactions of formate and tertiary butanol in aqueous media. In both systems, one argument is the fact that the free hydroxyl radical yields are relative low ((40 ± 4)% and (7 ± 0.8)% for formate and tertiary butanol, respectively). Another hint is the high exergonicity of these reactions: ΔG = –249 kJ mol^?1 for formate/ozone system and ΔG = –114 kJ mol^?1 for hydride transfer followed by a methyl shift in the reaction between tertiary butanol and ozone. In addition, the main product of tertiary butanol ozonolysis is butan-2-one [(89 ± 3)%], a compound that is formed only via hydride transfer. For the reaction of ozone with formate an activation energy of (54.6 ± 1.2) kJ mol^?1 and a pre-exponential term of (2.5 ± 1.2) × 10¹¹ were determined (in the presence of tertiary butanol as ^?OH scavenger) whereas for tertiary butanol the two activation parameters were (68.7 ± 1.9) kJ mol^?1 and (2.0 ± 1.5) × 10⁹, respectively.     

Kinetics of reaction of C36 dimeric fatty acids and ethylenediamine in solution

Kinetic studies were carried out on the reaction between ethylenediamine and C₃₆ dimeric fatty acids using benzyl alcohol as solvent. The reaction was performed at four different temperatures in the range of 160–190°C, and the products were analyzed for acid and amine values intermittently to follow the reaction. The fall in both the values was almost the same throughout the reaction. The kinetics was determined from the fall in acid value, and the reaction was found to be of overall third order and had an activation energy of 30.7 kcal mol^?1 (128.5 kJ mol^?1).     

Kinetic and thermodynamic investigation of Arthrospira (Spirulina) platensis fed‐batch cultivation in a tubular photobioreactor using urea as nitrogen source

BACKGROUND: Fed‐batch culture allows the cultivation of Arthrospira platensis using urea as nitrogen source. Tubular photobioreactors substantially increase cell growth, but the successful use of this cheap nitrogen source requires a knowledge of the kinetic and thermodynamic parameters of the process. This work aims at identifying the effect of two independent variables, temperature (T) and urea daily molar flow‐rate (U), on cell growth, biomass composition and thermodynamic parameters involved in this photosynthetic cultivation. RESULTS: The optimal values obtained were T = 32 °C and U = 1.16 mmol L^?1 d^?1, under which the maximum cell concentration was 4186 ± 39 mg L^?1, cell productivity 541 ± 5 mg L^?1 d^?1 and yield of biomass on nitrogen 14.3 ± 0.1 mg mg^?1. Applying an Arrhenius‐type approach, the thermodynamic parameters of growth (ΔH* = 98.2 kJ mol^?1; ΔS* = ? 0.020 kJ mol^?1 K^?1; ΔG* = 104.1 kJ mol^?1) and its thermal inactivation ( kJ mol^?1; kJ mol^?1 K^?1; kJ mol^?1) were estimated. CONCLUSIONS: To maximize cell growth T and U were simultaneously optimized. Biomass lipid content was not influenced by the experimental conditions, while protein content was dependent on both independent variables. Using urea as nitrogen source prevented the inhibitory effect already observed with ammonium salts. Copyright © 2012 Society of Chemical Industry