Alkaline hydrolysis of cinnamaldehyde to benzaldehyde in the presence of β‐cyclodextrin

A facile, novel, and cost‐effective alkaline hydrolysis process of cinnamaldehyde to benzaldehyde under rather mild conditions has been investigated systematically in the presence of β‐cyclodextrin (β‐CD), with water as the only solvent. β‐CD could form inclusion complex with cinnamaldehyde in water, with molar ratio of 1:1, so as to promote the reaction selectivity. The complex has been investigated experimentally and with computational methods. ¹H‐NMR, ROESY, UV–Vis, and FTIR have been utilized to analyze the inclusion complex. It shows that the equilibrium constant for inclusion (Ka) is 363 M^?1, and the standard Gibbs function for the reaction, ΔγG (298 K), is ?14.6 kJ mol^?1. In addition, the structures of the proposed inclusion compounds were optimized with hybrid ONIOM theory. Benzaldehyde could be obtained at an yield of 42% under optimum conditions [50°C, 18 h, 2% NaOH (w/v), cinnamaldehyde:β‐CD (molar ratio) = 1:1]. To explain the experimental data, NMR, FTIR, and elemental analysis results were used to determine the main reaction by‐product 1‐naphthalenemethanol. A feasible reaction mechanism including the retro‐Aldol condensation of cinnamaldehyde and the Aldol condensation of acetaldehyde and cinnamaldehyde in basic aqueous β‐CD solution has been proposed. The calculated activation energy for the reaction was 45.27 kJ mol^?1 by initial concentrations method. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

The synthetic kinetics and underwater acoustic absorption properties of novel epoxyurethanes and their blends with epoxy resin

Reaction kinetics between isocyanate-terminated prepolyurethane (PPU) and glycidol using dibutyltin dilaurate (DBTDL) as a catalyst was investigated by monitoring the change in the intensity of the absorbance peak of NCO stretching band at 2,270?cm^?1 on Fourier transform infrared spectrum at different temperatures. The results indicated that the reactions of TDI- and IPDI-type PPU with glycidol followed second-order kinetics, and their activation energies could be efficiently reduced by DBTDL. For TDI-type PPU, the reaction activation energies were 80.37?kJ?mol^?1 without catalyst, 49.86?kJ?mol^?1 with 0.1?% of DBTDLs, and 37.85?kJ?mol^?1 with 0.2?% of DBTDLs, respectively. For IPDI-type PPU, the reaction activation energies were 69.16?kJ?mol^?1 without catalyst, 63.05?kJ?mol^?1 with 0.1?% of DBTDLs, and 55.57?kJ?mol^?1 with 0.2?% of DBTDLs, respectively. This corresponding TDI- and IPDI-type epoxyurethane (EPU) were blended with epoxy resins (EPs) and cured by the Michael adduct of ethlylenediamine with butyl acrylate (molar ratio?=?1:1) curing agent, to prepare EPU/EP blend elastomers for underwater acoustic absorption materials. The TDI-type EPUs had good acoustic absorption properties and the average acoustic absorption coefficient of TDI-type EPU was 0.75, the maximum acoustic absorption coefficient was 0.94; the EPUs blended with E-51 EP had better acoustic absorption properties than those from E-44; and the EPU from PPG-2000 had better underwater acoustic absorption properties than that from PPG-1000.     

Influence of preflame reactions on combustion of hydrocarbons in shock-heated air

The reactions leading to the propagation of a flame have been studied in shock-heated air containing small amounts of either (normal) octane or 1,1-dimethyl hexane (isooctane). Preflame reactions, associated with the production of excited hydroxyl radicals, have been shown to occur with both octanes. Such reactions would account for the observed acceleration of the flame with octane and its retardation with isooctane, provided that the products from octane were more reactive (as found here) and the products from isooctane less reactive (as found by Cullis⁹ for heptane) than the parent hydrocarbons. Isooctane, as expected, was more resistant to preflame reactions; nevertheless they were observed at temperatures as low as 1050 K. The temperature coefficients of the reactions governing the growth of chemiluminescent radiation are similar for the two octanes: 330 and 350 kJ mol^?1 for octane and isooctane respectively. The temperature coefficients for the reactions controlling the overall burning are lower, falling to about 190 kJ mol^?1. The marked differences between the growth of pressure in what is essentially a premixed flame, and the growth of pressure in the combustion of droplets of (normal) hexadecane, are noted.     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

Heavy Metal Removal and Neutralization of Acid Mine Waste Water ‐ Kinetic Study

The influence of the apatite on the efficiency of neutralization and on heavy metal removal of acid mine waste water has been studied. The analysis of the treated waste water samples with apatite has shown an advanced purification, the concentration of the heavy metals after the treatment of the waste water with apatite being 25 to 1000 times less than the Maximum Concentration Limits admitted by European Norms (NTPA 001/2005). In order to establish the macro‐kinetic mechanism in the neutralization process, the activation energy, Ea, and the kinetic parameters, rate coefficient of reaction, k_r, and k_t were determined from the experimental results obtained in “ceramic ball‐mill” reactor. The obtained values of the activation energy Ea >> 42 kJ mol^?1 (e.g. Ea = 115.50 ± 7.50 kJ mol^?1 for a conversion of sulphuric acid η_H2SO4 = 0.05, Ea = 60.90 ± 9.50 kJ mol^?1 for η ^H2SO4 = 0.10 and Ea = 55.75 ± 10.45 kJ mol^‐1 for η ^H2SO4 = 0.15) suggest that up to a conversion of H2SO4 equal 0.15 the global process is controlled by the transformation process, adsorption followed by reaction, which means surface‐controlled reactions. At a conversion of sulphuric acid η ^H2SO4 > 0.15, the obtained values of activation energy Ea < 42 kJ mol^‐1 (e.g. Ea = 37.55 ± 4.05 kJ mol^‐1 for η ^H2SO4 = 0.2, Ea = 37.54 ± 2.54 kJ mol^‐1 for η ^H2SO4 = 0.3 and Ea = 37.44 ± 2.90 kJ mol^‐1 for η ^H2SO4 = 0.4) indicate diffusion‐controlled processes. This means a combined process model, which involves the transfer in the liquid phase followed by the chemical reaction at the surface of the solid. Kinetic parameters as rate coefficient of reaction, kr with values ranging from (5.02 ± 1.62) 10‐4 to (8.00 ± 1.55) 10‐4 (s^‐1) and transfer coefficient, kt, ranging from (8.40 ± 0.50) 10‐5 to (10.42 ± 0.65) 10‐5 (m s^‐1) were determined.     

Effect of Temperature on Kinetics and Adsorption Profile of Endothermic Chemisorption Process: –Tm(III)–PAN Loaded PUF System

Abstract

The sorption behavior of 3.18×10^?6 mol l^?1 solution of Tm(III) metal ions onto 7.25 mg l^?1 of 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated at different temperatures i.e. 303 K, 313 K, and 323 K. The maximum equilibration time of sorption was 30 minutes from pH 7.5 buffer solution at all temperatures. The various rate parameters of adsorption process have been investigated. The diffusional activation energy (ΔE_ads) and activation entropy (ΔS_ads) of the system were found to be 22.1±2.6 kJ mol^?1 and 52.7±6.2 J mol^?1 K^?1, respectively. The thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were calculated and interpreted. The positive value of ΔH and negative value of ΔG indicate that sorption is endothermic and spontaneous in nature, respectively. The adsorption isotherms such as Freundlich, Langmuir, and Dubinin–Radushkevich isotherm were tested experimentally at different temperatures. The changes in adsorption isotherm constants were discussed. The binding energy constant (b) of Langmuir isotherm increases with temperature. The differential heat of adsorption (ΔH_diff), entropy of adsorption (ΔS_diff) and adsorption free energy (ΔG_ads) at 313 K were determined and found to be 38±2 kJ mol^?1, 249±3 J mol^?1 K^?1 and –40.1±1.1 kJ mol^?1, respectively. The stability of sorbed complex and mechanism involved in adsorption process has been discussed using different thermodynamic parameters and sorption free energy.     

Zn-promoted hydrogen exchange for methane and ethane on Zn/H-BEA zeolite: In situ 1H MAS NMR kinetic study

Hydrogen (H/D) exchange between Brønsted acid sites of both the acidic form of zeolite beta (H-BEA) and Zn-loaded zeolite beta (Zn/H-BEA) and small alkanes (methane and ethane) has been studied by monitoring the kinetics of the exchange in situ with ¹H MAS NMR spectroscopy within the temperature range of 433–563 K. On Zn/H-BEA, the exchange has been found to be more than two orders of magnitude faster compared to that on H-BEA. The decrease of reaction temperature and activation energy of the exchange on Zn/H-BEA (86–88 kJ mol^?1) compared to the acidic form of zeolite H-BEA (138 kJ mol^?1) has been rationalized by the promoting effect of zinc. We propose that the mechanism of the H/D exchange on Zn/H-BEA involves Zn-alkyl species as intermediates.     

Kinetic studies on Victorian brown coal hydroliquefaction

Reaction kinetics of the liquefaction of Victorian brown coal in a process development unit (PDU) having three reactors in series have been studied at temperatures of 430–470°C, and pressures of 15–25 MPa. It is shown that the rate of hydrogen consumption can be expressed as a function of the concentrations of coal and catalyst, hydrogen partial pressure, reaction temperature and residence time, and is controlled by the rates of hydrogenation of polynuclear aromatic components, and the rates of formation and stabilization of radicals. The relative contribution of these reactions, at any temperature, determine the influence of the hydrogen partial pressure on the rate of the hydrogen consumption. The kinetics of the decomposition reactions of brown coal to preasphaltene, asphaltene and to oil also have been studied. The apparent activation energies determined are 25 kJ mol^?1 for the brown coal to preasphaltene, 50 kJ mol^?1 for preasphaltene to asphaltene, 76 kJ mol^?1 for asphaltene to oil, and 184 kJ mole^?1 for oil to gases.     

The conversion of polysaccharides to hydrogen gas. Part II: The catalytic decomposition of formaldehyde in the aqueous phase

The aqueous phase decomposition of formaldehyde, to hydrogen gas, catalysed by platinum—copper chromite, has been carried out in the temperature range 20–60°C, at a solution pH of 12. The production of hydrogen was favoured by intermediate temperatures (40–50°C) and an activation energy of 22.2 kJ mol^?1 (5.3 kcal mol^?1) was recorded. The rate of reaction was first order with respect to OH^? ion concentration at low alkali concentrations and was first order with respect to HCHO concentration at all concentrations. At high alkali concentrations the reaction should become zero order with respect to OH^? ion concentration, but initial rates actually decrease under these conditions having passed through a maximum. The rate of reaction was directly proportional to catalyst weight at low catalyst loading, but the relationship became non-linear at high catalyst loadings. Conversions of formaldehyde to hydrogen gas were substantially less than theoretical. The decomposition reaction has to compete with a number of side reactions such as polymerization of formaldehyde at low temperatures (<40°C) and at higher temperatures with the Cannizzano reaction, aldol condensation, and possibly formaldehyde hydrogenation to methanol. In addition hydrogen loss may occur due to copper chromite reduction. A reaction mechanism is proposed involving a surface formate intermediate.     

Calcium oxide and potassium hydroxide catalysed low temperature methane production from graphite and water Comparison of catalytic mechanisms

An experimental study was carried out to obtain information on the catalytic mechanisms involved in the methanation of graphite using, separately, potassium and calcium as catalysts, and water and/or hydrogen as reactants. The mechanisms for the potassium-catalysed graphite—water reaction appear to be the same in the wide temperature range from 473 to 873 K as indicated by the constant activation energy, 46 kJ mol^?1, found for methane production. The intercalation of potassium into the graphite as a possible step in the methane synthesis has been investigated and ruled out. XPS studies indicate the formation of an active form of more positively charged carbon from graphite when graphite is heated at low temperature in the presence of a calcium catalyst and water vapour. The activation energy for this carbon depolymerization reaction is 68.1 kJ mol^?1. Methane formation occurs only in the presence of hydrogen due to its reaction with the active carbon with an activation energy of 106.6 kJ mol^?1.     

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.     

RAFT polymerization of N‐vinyl pyrrolidone using prop‐2‐ynyl morpholine‐4‐carbodithioate as a new chain transfer agent

RAFT polymerization of N‐vinyl pyrrolidone (NVP) has been investigated in the presence of chain transfer agent (CTA), i.e., prop‐2‐ynyl morpholine‐4‐carbodithioate (PMDC). The influence of reaction parameters such as monomer concentration [NVP], molar ratio of [CTA]/[AIBN, i.e., 2,2′‐azobis (2‐methylpropionitrile)] and [NVP]/[CTA], and temperature have been studied with regard to time and conversion limit. This study evidences the parameters leading to an excellent control of molecular weight and molar mass dispersity. NVP has been polymerized by maintaining molar ratio [NVP]: [PMDC]: [AIBN] = 100 : 1 : 0.2. Kinetics of the reaction was strongly influenced by both temperature and [CTA]/[AIBN] ratio and to a lesser extent by monomer concentration. The activation energy (E_a = 31.02 kJ mol^?1) and enthalpy of activation (ΔH^?= 28.29 kJ mol^?1) was in a good agreement to each other. The negative entropy of activation (ΔS^? = ?210.16 J mol^‐1K^‐1) shows that the movement of reactants are highly restricted at transition state during polymerization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Silane grafting reactions of low-density polyethylene

Reactions of vinyl trimethoxysilane grafting onto low-density polyethylene (LDPE) were investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermal gravimetric analysis. The silane grafting reactions were induced by a fixed amount of dicumyl peroxide at 0.2 part of reagent per hundred parts with respect to LDPE. Fourier transform infrared data demonstrated that the extent of the silane grafting reaction was increased as the amount of silane used, the reaction time, or the reaction temperature was increased. The apparent activation energy of the silane grafting reaction was 9.7 kJ mol⁻¹. Differential scanning calorimetry was used to follow the silane grafting reactions in situ at a heating rate of 20°C per minute. The silane grafting reaction was exothermic starting at about 150°C and ending at about 230°C, indicating a completion of the reaction in 4 min. The grafting reaction heat has linear relations to the amount of silane used. The grafting reaction heat of about 1 J/g of sample was generated during reaction per part of reagent per hundred parts of silane used. The reaction heat of silane grafting onto LDPE per mol of silane used was 14.5 kJ mol⁻¹ silane, and the reaction heat of peroxide that reacted with LDPE was −12 kJ mol⁻¹ peroxide. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 255–261, 1998     

Kinetics of non-catalytic hydrocracking of Athabasca bitumen

The kinetics of non-catalytic hydrocracking of Athabasca bitumen were studied in a batch reactor at 648–693 K and at an initial hydrogen pressure of 7.2 MPa. The reaction products were separated into coke, asphaltenes, resins, aromatics, saturates and gases. Reaction time versus product yield curves were obtained for the above six product groups. Two simple reaction models were proposed. In the first, bitumen is considered to be a single reactant and the hydrocracking reaction a single irreversible reaction. The activation energy for bitumen consumption was found to be 150 kJ mol⁻¹. In the second model, coke, asphaltenes, maltenes and gases are treated as components. Activation energies for the reactions were found to be in the range 142–284 kJ mol⁻¹. Hydrocracking reactions were found to be first order. Activation energies for the hydrocracking reactions are compared with those for thermal cracking reactions.     

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.     

Adsorption of BTX compounds from aqueous solutions by water-insoluble starch

The removal of benzene, toluene and p-xylene (BTX) compounds from aqueous solutions with highly crosslinked cationic starch containing tertiary amine groups was investigated. The adsorption process has found to be initial pH- and initial concentration-dependent, endothermic, and follows the Langmuir isothermal adsorption. The heats of adsorption (ΔH) at initial pH = 4 of benzene, toluene and p-xylene compounds are 29.45 kJ mol^?1, 34.41 kJ mol^?1, and 35.58 kJ mol^?1, respectively, those at initial pH = 10 are 30.17 kJ mol^?1, 35.56 kJ mol^?1, and 39.39 kJ mol^?1, respectively. The order of the amount of adsorbed BTX compounds on the adsorbent is benzene > toluene > p-xylene.     

Hydrogenation-dehydrogenation of pyrenes catalysed by sulphided cobalt-molybdate at coal liquefaction conditions

The hydrogenation and dehydrogenation kinetics of pyrene and hydropyrenes were studied in batch microreactors, both with and without catalyst, as a function of time, temperature, pressure and catalyst concentration. Under catalytic conditions at 648 K and 7.2 MPa, 4,5-dihydropyrene and pyrene reached equilibrium in 3 min with a molar ratio of 0.41. The heat of the hydrogenation reaction was —10 ± 1 kcal mol^?1 compared with -12 kcal mol^?1 for the hydrogenation of phenanthrene to 9,10-dihydrophenanthrene. The hydrogenation and dehydrogenation rates were negligible without catalyst. At 648 K with catalyst, 70% of the hydropyrenes reverted to pyrene in 5 min under nitrogen. The rapid pyrene—4.5-dihydropyrene equilibration implies that the equilibrium constant may be of more importance than the hydrogenation rate constant for predicting the amount of hydrogen available for donation by pyrene-like components in coal liquefaction solvents.     

The preparation and sintering of a high area supported nickel oxide catalyst

A detailed study has been made on the preparation and consequent heat treatment of various active nickel oxide—alumina catalysts. The techniques used in this study were surface area measurements, pore size analysis and density determinations. Three methods were employed for catalyst preparation, these being impregnation; co-precipitation and bulk fusion of the metal nitrates. The results indicate that the catalyst prepared by co-precipitation was the most suitable. By following surface area changes with temperature and time as variables two modes of sintering were noted, one occurring in the temperature range 1100 to 1164 K giving an activation energy of 98 kJ mol^?1, and the other occurring in the temperature range 1182 to 1200 K giving an activation energy of 460 kJ mol^?1. It is thought that the mechanism controlling the sintering in the first case is a direct result of surface diffusion, whilst that occurring in the second range is governed by volume diffusion. The decrease in the number of particles as a trend in sintering is calculated for the sample sintered at 1182 K using surface area and density data.     

Bulk polymerization of hydroxyl terminated polybutadiene (HTPB) with tolylene diisocyanate (TDI): A kinetics study using 13C-NMR spectroscopy

The bulk polymerization of hydroxyl-terminated polybutadene with tolylene diisocyanate has been studied in uncatalyzed isothermal reactions. The conversion in urethane was monitored by ¹³C-NMR spectroscopy of the C?O function at level up to 70%. Effects of reagents ratio and temperature were investigated. The experimental data were modeled by a set of two competitive second-order reactions to account for the difference in reactivity of o-NCO and p-NCO groups of tolylene 2,4 diisocyanate. The apparent kinetic constants calculated appeared to be statistically higher than previous results found in literature from work in aromatic solvents. Deviations from second-order law were observed during the last stage of polymerization. Activation energies were estimated at 12.3 kJ. mol^?1 and 42.8 kJ. mol^?1 for the p-NCO and o-NCO groups, respectively. The difference in their reactivity tended to decrease as temperature of reaction was increased. © 1995 John Wiley & Sons, Inc.