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.     

Kinetics of the hydrogenation of NBR by hydrazine and oxygen,using selenium as a catalyst

The kinetics of hydrogenation of the acrylonitrile‐polybutadiene (NBR) rubber by the action of hydrazine in the presence of selenium and oxygen was studied by varying reaction parameters such as latex and catalyst concentrations. The method of initial rates gives a reaction order of 0.91 and a rate constant of 3.2 × 10¹ L mol^?1 h^?1 in relation to the NBR latex concentration, and an order of 0.86 and a rate constant of 3.3 × 10¹ L mol^?1 h^?1 in relation to the catalyst concentration. Based on these values, a first‐order mechanism with the formation of a diimide intermediate is suggested, which is formed through the oxidation of hydrazine in an oxygen atmosphere in the presence of selenium catalyst. This diimine species reacts rapidly, reducing the carbon–carbon double bonds of NBR resulting in the formation of HNBR rubber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

Kinetics of polymerization of dimer fatty acids with ethylenediamine

A generally applicable stoichiometric and kinetic model was developed for the polymerization of dimer fatty acids with ethylenediamine. The rate equations were second‐order before 90% conversion and were used between 405 and 475 K. The parameters of the rate equations were determined with nonlinear regression analysis. A comparison of the model predictions and the experimental data showed that the approach was useful in predicting the polymerization kinetics. The equilibrium constant changed from 3.175 to 7.311. The frequency factor and activation energy for the forward rate constant before 90% conversion were 2,716,894 kg mol^?1 min^?1 and 66.7 kJ mol^?1, respectively. The equilibrium constant was independent of the temperature at frequency factor and activation energy values of 74.4 and 9.7 kJ mol^?1, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2504–2513, 2004     

The hydrogenation of HO-terminated telechelic polybutadienes in the presence of a homogeneous hydrogenation catalyst based on tris(triphenylphosphine)rhodium chloride

The hydrogenation kinetics of multiple bonds in HO-terminated telechelic polybutadienes was investigated using two types of these prepolymers prepared by the anionic and radical polymerization. The rate of addition of hydrogen to the π-bonds of these polydienes in the presence of tris(triphenylphosphine) rhodium chloride as a homogeneous hydrogenation catalyst was determined by the chemical structures of the starting polydienes, their concentration in the solvent, the partial hydrogen pressure, the concentration of the catalyst, and the temperature. The effect of kinetic parameters given above on the rate of hydrogenation reaction can be interpreted in the sense of Wilkinson's reaction mechanism of the hydrogenation of alkenes in the presence of the Rh(I)-complex. Due to the predominant 1,2-structural units, the anionic prepolymer reacted twice as quickly with hydrogen (k = 0.093 mol^?1 dm³ s^?1) compared with the radical prepolymer (k = 0.045 mol^?1 dm³ s^?1). During the hydrogenation of multiple bonds there is a partial loss of hydroxy groups in modified telechelic prepolymers; the extent of this reaction depends on reaction conditions of the hydrogenation reaction.     

Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120–140 °C in a closed batch reactor. The particle size ranging from 50 to 512.5 µm and the reaction time 60 to 150 min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120 °C) and 100% (at 130 and 140 °C) for the optimal reaction time of 120 min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150 °C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140 °C. The methanolysis rate constant of the reaction at 140 °C (10.3 atm) was 1.4 × 10^?3 g PET mol^?1 min^?1. The activation energy and the frequency factor for methanolysis of PETW were 95.31 kJ mol^?1 and 107.1 g PET mol^?1 min^?1, respectively. © 2003 Society of Chemical Industry     

Vanadia loaded hierarchical ZSM-5 zeolite: a promising catalyst for epoxidation of cyclohexene under solvent free condition

Hierarchical ZSM-5 zeolite with composite micro and mesoporous was obtained by alkali treatment of parent ZSM-5 for 60 min. Vanadia was loaded on modified zeolite by wetness impregnation technique (VDZ). The prepared samples were characterized by various techniques including XRD, FTIR, TGA, UV-DRS, TEM, XPS and nitrogen adsorption–desorption. Vanadia loaded sample was found to exhibit excellent catalytic activity for the epoxidation of cyclohexene by tertiary butyl hydroperoxide. A controlled reaction was carried out to demonstrate the utility of hierarchical topology of the catalyst. A free radical mechanism was proposed for the reaction with rate constant of 6.91 × 10^?2 L mol^?1 min^?1 and activation energy of 41.81 kJ mol^?1. The reaction was carried out without the use of any solvent and the catalytic activity of VDZ was retained even after five runs.     

枞酸与甲醇酯化反应的基团贡献法热力学分析

以枞酸为模型化合物、枞酸与甲醇的酯化为探针反应,采用基团贡献法对枞酸与甲醇酯化反应进行了热力学分析,计算了473～653 K、0.1～20 MPa反应体系的反应焓变、反应熵变、反应Gibbs自由能变以及反应平衡常数,探讨了温度与压力对酯化反应的影响。计算结果表明,反应的焓变为-46.31～-10.10 kJ·mol^-1,枞酸与甲醇的甲酯化反应为放热反应;反应Gibbs自由能变为-53.26～-25.49 kJ·mol^-1,反应为自发过程;标准压力下反应平衡常数为136.32～748.89,5～20 MPa下反应平衡常数为(1.1×10⁴)～(3.2×10⁴)。实验结果表明,在无催化剂条件下,超/亚临界甲醇与枞酸酯化反应的转化率分别为85.94%～94.89%、73.80%～81.20%,实验结果与基团贡献法热力学计算值相一致。     

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.     

Thermischer Abbau von Polyacrylnitril unter Luft

Hydrogen cyanide is the most important product during thermal degradation of polyacrylonitrile (PAN) under air at temperatures below 250°C. The amount of HCN evolved is temperature dependent; up to 250°C 17 mol-% and above 250°C only 10 mol-% HCN with regard to all nitrile groups in PAN were found. The energy of activation of this reaction was calculated to 15 kcal mol^?1 between 250 and 300°C. By means of DTA and IR-spectroscopy it could be shown, that a cyclization of the nitrile groups competes with the evolution of HCN. The energy of activation of the cyclization was found to be 29 kcal mol^?1. The decomposition of PAN preferentially starts—as indicated by thermogravimetric measurements—at the isolated double bonds originating from the elimination of HCN. In account of IR-spectra and elemental analysis—great amounts of bonded oxygen in degraded PAN were found—a suggestion for the structure of PAN degraded under air was made.     

Cyclohexane dehydrogenation kinetics on a platinum-rhenium/aluminium oxide catalyst with hydrogen and inert diluents

The dehydrogenation of cyclohexane to benzene on a platinum-rhenium/aluminium oxide (Pt-Re/Al₂O₃) catalyst was investigated using both pulse and continuous flow techniques with hydrogen and inert (N₂, He, Ar) diluents at the following conditions: 1 and 4 atm (1 atm = 101 kPa) total pressure and 432–623 K. Experiments performed with hydrogen as a carrier in the pulse mode showed anomalous behaviour as cyclohexane conversion was observed to increase with pulse size/pulse width and decrease with temperature and contact time. The dehydrogenation reaction was first-order with respect to cyclohexane for both the pulse and continuous flow experiments. Lower activation energies were observed for the inert carriers; activation energies were between 37.7–54.4 kJ mol<^?1 for inert diluents. With a hydrogen carrier, the activation energies were found to be 87.9 and 121.3 kJ mol^?1 for T<553 K and <553 K, respectively. The difference in activation energy between hydrogen and the inert carriers was attributed to a change in mechanism on the coked catalyst surface. Surface conversion of cyclohexane to adsorbed cyclohexane was the slowest step in a hydrogen carrier. For the inert carriers, it was postulated that surface diffusion of adsorbed intermediate for for subsequent conversion was rate determining.     

Kinetics of hydrogenation of 4‐chloro‐2‐nitrophenol catalyzed by Pt/carbon catalyst

Hydrogenation of 4‐chloro‐2‐nitrophenol (CNP) was carried out at moderate hydrogen pressures, 7–28 atm, and temperatures in the range 298–313 K using Pt/carbon and Pd/γ‐Al₂O₃ as catalysts in a stirred pressure reactor. Hydrogenation of CNP under the above conditions gave 4‐chloro‐2‐aminophenol (CAP). Dechlorination to form 2‐aminophenol and 2‐nitrophenol is observed when hydrogenation of CNP is carried out above 338 K, particularly with Pd/γ‐Al₂O₃ catalyst. Among the catalysts tested, 1%Pt/C was found to be an effective catalyst for the hydrogenation of CNP to form CAP, exclusively. To confirm the absence of gas–liquid mass transfer effects on the reaction, the effect of stirring speed (200–1000 rpm) and catalyst loading (0.02–0.16 g) on the initial reaction rate at maximum temperature 310 K and substrate concentration (0.25 mole) were thoroughly studied. The kinetics of hydrogenation of CNP carried out using 1%Pt/C indicated that the initial rates of hydrogenation had first order dependence with respect to substrate, catalyst and hydrogen pressure in the range of concentrations varied. From the Arrhenius plot of ln rate vs 1000/T, an apparent activation energy of 22 kJ mol^?1 was estimated. © 2001 Society of Chemical Industry     

Universal one‐pot,one‐step synthesis of core–shell nanocomposites with self‐assembled tannic acid shell and their antibacterial and catalytic activities

Facile synthesis of metal@polymer nanocomposites were achieved using self‐assembled tannic acid (TA) shells without crosslinkers. The TA shell was assembled under mildly alkaline conditions in reaction time of 20 min under constant vortexing. Universal synthesis method was demonstrated by the synthesis of Ag@TA and Au@TA nanocomposites. We propose that the shell formation is due to TA undergoing oxidative self‐polymerization to poly(tannic acid) or a supramolecular aggregate of oxidized TA held together by charge transfer, hydrogen bond, and π–π interactions, similar to dopamine polymerization. Gibbs free energy calculations suggest that polymerization is energetically favorable. Synthesized Ag@TA exhibited antibacterial functionality with Escherichia coli minimum inhibitory concentration of 100 µg mL^?1 up to 48 h. The population of E. coli was also reduced by 99% within 5 h when incubated with 100 µg mL^?1 of Ag@TA nanocomposite. Au@TA also functions as a reduction catalyst. It reduces 4‐nitrophenol to 4‐aminophenol in the presence of NaBH₄ with a rate constant of k = 0.63 min^?1 μmol^?1. For comparison, using Au nanoparticles yields a rate constant of 0.14 min^?1 μmol^?1. The ease of synthesis renders the nanocomposites superior to others, with potential for large‐scale application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45829.     

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.     

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     

Process optimization for selective hydrogenation of <Emphasis Type="Italic">α</Emphasis>-pinene over Ni/AlPO<Subscript>4</Subscript>

A new supported Ni/AlPO₄ catalyst was synthesized and studied for the selective hydrogenation of α-pinene to prepare cis-pinane. The support was flaky morphology with orthorhombic phase and Ni was well dispersed. The surface area of the catalyst was 37.62 m²·g^?1 with a pore size of 2.83 nm. For the hydrogenation reaction, the performance of the catalyst was positively correlated with the surface area of support and loading content of Ni. Effects of hydrogenation condition were determined and the process was optimized by response surface methodology. The result suggested that the conversion was positively correlated to hydrogenation temperature, duration and catalyst dosage, while the selectivity showed a negative correlation to temperature and catalyst dosage. After optimization, 95.1% of selectivity was obtained under 94.8% of conversion at 405 K, 81 min and 2.28 wt% of catalyst.     

Kinetic study of anionic polymerization of butadiene in a polar solvent

The kinetics of the propagation reaction for the polymerization of butadiene initiated by cumyl potassium in tetrahydrofuran solution at several temperatures have been studied. Kinetic data and electrolytic behaviour indicate that polybutadienyl free ions assume the whole of the propagation reaction. At 0°C, the respective rate constants for ion-pairs and free ions are 1 l mol^?1 s^?1 and 4.8 × 10⁴ l mol^?1 s^?1 respectively. The ionic dissociation constant is 7.8 × 10^?9 mol/l. The activation energy of the propagation reaction for free ions is 6.5 kcal/mol.     

Reactive separation of p-nitro phenol (PNP) from aqueous solution using tri-n-butyl phosphate: equilibrium and COSMO-RS studies

ABSTRACT

The present study is aimed to optimized diluent type, tri-n-butyl phosphate (TBP) composition and temperature for the reactive extraction of p-nitro phenol (PNP) in two different PNP concentration ranges [(0.00036–0.00646) kmol·m^?3 and (0.00646–0.01437) kmol·m^?3] as found in industrial effluents. 1-Octanol is investigated as the best diluent with TBP based on COSMO-RS theory. Equilibrium study based on mass action law is performed to find the insights of extraction mechanisms, equilibrium constant (K = 295.12 k·mol^?1) and stoichiometry (m:n = 1:1) as also confirmed by FTIR. Thermodynamic parameters, enthalpy (ΔH°), and entropy (ΔS°) are determined 27.51 K J mol^?1 and ?50.21 J mol^?1 K^?1, respectively.     

Spectroscopic and Thermodynamic Analysis of Cd2+ Ion Sorption Kinetics by Manganese Dioxide in the Presence of Oxyanions

The present study reports the effect of contact time, nature of electrolyte, and temperature on the sorption kinetics of Cd²⁺ by manganese dioxide, which is the most active oxide in soils and sediments. The sorption kinetics of Cd²⁺ by manganese dioxide is evaluated at pH 6 in different electrolytes in the temperatures range 293-323 K. The solid samples are equilibrated in 0.45 mmol.L^?1 Cd²⁺ and different electrolytes at pH 6. The results indicate that sorption of Cd²⁺ increases with time and temperature and the system attains equilibrium within 60 min in KNO₃ as the electrolyte. However, in the presence of 0.001 M KH2PO₄ sorption of Cd²⁺ increases and the time for equilibrium shifts to 90 min. The data second-order kinetics model and the calculated rate constant k and initial sorption rate h increases with increasing temperature phosphate treatment. Among the calculated thermodynamic activation parameters the positive values of ΔH^? and ΔG^? show the sorption process to be endothermic and nonspontaneous, while the ΔS^? being negative indicates a decrease in randomness of the system during sorption process at the solid-liquid interface. The free energy of activation decreases from 15.95 kJ.mol^?1 in nitrate to 8.76 kJ.mol^?1 in phosphate. These observations suggest that the rate controlling step in Cd²⁺ sorption is diffusionally controlled, a fact that has been proved by application of Fick’s law.     

Raney镍上松香加氢制备二氢和四氢枞酸的本征动力学

采用FYX-2G型高压搅拌釜,以Raney镍为催化剂,在温度423～453K、压力4.0～7.0MPa下进行松香催化加氢反应动力学的研究。利用改进搅拌器类型、提高搅拌速度、加入200#溶剂油和改变催化剂粒径的方法消除内外扩散,使反应处于化学动力学控制区,然后采集动力学数据,经对17种可能的反应机理模型进行筛选,结果表明,Raney镍催化枞酸加氢生成二氢和四氢枞酸是并行反应,最可几反应机理为:松香中的主要成分枞酸分子与催化剂表面上被吸附的氢原子进行反应,氢原子的吸附为控制步骤,生成二氢枞酸和四氢枞酸的活化能分别为47.18kJ.mol-1和106.35kJ.mol-1。