Effect of reaction conditions on the catalytic performance of H3PW12O40 heteropolyacid catalyst in the direct preparation of dichloropropanol from glycerol in a liquid-phase batch reactor

Direct chlorination of glycerol to dichloropropanol (DCP) was conducted in a liquid-phase batch rector using homogeneous H₃PW₁₂O₄₀ heteropolyacid (HPA) catalyst. The effect of reaction conditions (reaction time, reaction pressure, reaction temperature, and catalyst amount) on the catalytic performance of H₃PW₁₂O₄₀ in the direct preparation of DCP from glycerol was examined. The optimum reaction pressure and reaction temperature were found to be 10 bar and 130 °C, respectively. The reaction temperature was more crucial than the reaction pressure in improving the selectivity to DCP. Selectivity to DCP increased with increasing reaction time and with increasing catalyst amount. Acid sites of H₃PW₁₂O₄₀ catalyst favorably devoted to the chlorination of glycerol. H₃PW₁₂O₄₀ served as an efficient catalyst in the direct preparation of DCP from glycerol under the mild reaction conditions.     

The polymerization mechanism and kinetics of DGEBA with BF3-MEA

The diglycidyl ether of bisphenol-A (DGEBA) and boron trifluoride monoethylamine (BF₃-MEA) were used in a model system to investigate the chemical and physical changes that occur during polymerization. Experiments using ¹⁹F and ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) showed that BF₃-MEA breaks down rapidly into HBF₄ and an amine salt at 85°C and above. The HBF₄ complexes with the epoxy groups, producing an activated monomer that reacts with epoxy in an etherification reaction. A mechanism is proposed whereby activated epoxy sites (complexes) continuously add epoxy throughout the reaction, but where unactivated epoxies (monomer molecules) are unable to react with each other. The reaction rate and mode (kinetic vs. diffusion control) therefore are strongly influenced by the BF₃-MEA concentration and the reaction temperature. © 1993 John Wiley & Sons, Inc.     

Al Surface Modification by a Facile Route

A facile route was used to modify Al particle surfaces by putting Al particles into an Al(OH)₃ suspension, which was produced by the reaction of Al powder with water under vacuum at a mild temperature, then drying and heat‐treating under vacuum at elevated temperature. The modified Al powder has a good reaction activity with water to generate hydrogen, and its reaction rate depends on the sizes of Al particles used to produce Al(OH)₃ suspension. The reaction induction time of the modified Al powder prepared using the Al(OH)₃ suspension produced by the reaction of Al with water is obviously shorter than that prepared using the Al(OH)₃ suspension formed by the direct addition of a commercial Al(OH)₃ powder, because the in situ formed Al(OH)₃ has a finer microstructure. As the present method has no complicated processing procedure and the Al‐water reaction byproduct can be reused to modify Al, it is an economically viable way to fabricate the activated Al powder for commercial applications.     

Characterization of transient response curves in heterogeneous catalysis—II Estimation of the reaction mechanism in the oxidation of ethylene over a silver catalyst from the mode of the transient response curves

The reaction mechanism and the kinetic structure of the oxidation of ethylene over a silver catalyst at 91°C have roughly been elucidated from the mode of the transient response curves of ethylene oxide, carbon dioxide and water, due to the concentration jump of reactants. The typical overshoot mode with an instantaneous maximum for C₂H₄O clearly indicates two things. First that the surface reaction controlling in the reaction between adsorbed diatomic oxygen species and gaseous C₂H₄ (an Eley—Rideal type mechanism) with the rapid desorption of C₂H₄O formed and, second, that the slower regeneration of the adsorbed oxygen species. The typical S-shape mode with an overshoot for CO₂ strongly suggests the existence of an intermediate (In) and, the presence of the (In) has been actually confirmed by the transient response of its decomposition in an O₂-He stream. The (In) can desorb as acetic acid only when the surface is reduced by H₂. Much transient data seems to suggest that the (In) is formed from the reaction of adsorbed monoatomic oxygen species with C₂H₄ and, is decomposed by the reaction with diatomic oxygen species. The false start mode for the response curve of (In) decomposition indicates the inhibitory effect of adsorbed ethylene on the reaction.     

Carbon Dioxide Uptake by Hydrated Lime Aerosol Particles

The reaction of the greenhouse gas, CO₂, with Ca(OH)₂ was explored using single-particle Raman spectroscopy to track the chemical reaction. Single particles were levitated in an electrodynamic balance (EDB) to maintain the particle in a laser beam. The levitation voltage provided gravimetric data. The humidity in the EDB chamber was varied to determine the effects of humidity on the reaction. It is demonstrated that no appreciable reaction occurs at low relative humidities (RH < 70%). This is evidenced by no disappearance of the Raman peak associated with the [OH]^? vibrational bond, but at high humidities (RH > 70%) the Raman spectrum of CaCO₃ developed as the reaction proceeded. The results are consistent with results from packed-bed studies of the reaction and are in agreement with similar findings for the SO₂/Ca(OH)₂ reaction used for desulfurization, that is, the reaction does not proceed until multiple monolayers of water are adsorbed on the particle surface.     

Kinetics of carbon dioxide reaction with diethylaminoethanol in aqueous solutions

Differential rates of CO₂ adsorption into 0.90, 0.47 and 0.24 M aqueous solutions of 2-(diethylamino)ethanol (DEAE) were measured at 323 K over a wide range of carbonation ratios. A rigorous thermodynamic model was used to define species activities which were coupled with Danckwerts' gas-liquid reaction model to deduce the kinetics. The reaction of CO₂ with this highly basic tertiary amine occurs by two pathways: (1) a minor path via the CO₂ reaction with hydroxide ion and (2) a predominant reaction pathway that can be characterized by its first order dependency on the free amine concentration. The second reaction was proposed to involve an internal salt-like intermediate,.     

Formation of cross-links during prepolymerisation reaction of methylene-bis (4-phenylisocyanate) with poly (tetramethyleneoxide) in N,N-Dimethylacetamide

An attempt was made to investigate the cross-linking reaction which occurs as a side reaction when an excess of methylene-bis(4-phenylisocyanate) (MDI) is reacted with polytetramethyleneoxide (PTMO) (number-average molecular weight 2010) in N,N-dimethylacetamide (DMAc) prepolymerisation reaction) to give an isocyanate-terminated prepolymer having urethane groups. Cross-links existing in the prepolymer were shown to be of the biuret type by high performance liquid chromatography (HPLC) analysis on a product prepared by the raction of excess phenylisocyanate with n-butanol in DMAc. The biuret-forming reaction, as well as the urethane reaction (i.e. the main reaction), is accelerated remarkably by an N,N-dimethyl-N'-phenyl(phenylcarbamoyl)acetamidine derivative formed from a side reaction of MDI with DMAc, and the former reaction is suppressed dratically by neutralising the corresponding amidine with, for ecample, H₂SO₄. A novel kinetic model of the prepolymerisation reaction is proposed and reaction orders and rate constants are derived. Three heterocompetitive reactions are involved: (1) urethane groups formed from MDI with PRMOin the prepolymer, and subsequent formation of (2) biuret type cross-links between isocyanates and urea groups formed from MDI with DMAc as a side reaction, and (3) the corresponding amidine derivative.     

Electrochemical and quantum chemical studies of the reactions of transition metals M (M = Co, Fe and Ni) with LiF and Li2O

It has been a puzzle that transition metals can unexpectedly react with lithium-based matrixes of LiF and Li₂O in the potential versus Li/Li⁺ range from 0.01 to 3.5 V at room temperature. The electrochemical and theoretical investigations on the reactions of transition metals M (M = Co, Fe and Ni) with LiF and Li₂O were carried out. The electrochemical reactivity of metal cobalt with LiF and Li₂O has been examined by the discharge and charge, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. Density functional theoretical calculation results suggested that the stable compounds MLiF and MLi₂O could be formed by the insertion of transition metal (M) in lithium-based matrixes with exothermic as an intermediate. The theoretical calculations provide an understanding in chemical reaction of M with LiF and Li₂O. The small molecular or clusters reaction may play an important role in the electrochemical reaction of metal with transition Li₂O or LiF, which could be used to explain for the unexpectedly reaction of transition metal with LiF and Li₂O.     

Mechanism and kinetics of esterification of adipic acid and ethylene glycol by tetrabutyl titanate catalyst

An eight-step mechanism of esterification reaction between adipic acid (AA) and ethylene glycol (EG) catalyzed by tetrabutyl titanate [Ti(OBu)₄] was studied in detail. The kinetic data for the esterification reaction between AA and EG catalyzed by tetrabutyl titanate [Ti(OBu)₄] were measured in the temperature range of 403 K-433 K. A second-order kinetic model was established, and the model parameters were obtained through an optimization procedure by minimizing the value differences between the simulated component concentrations in the reaction system with the experimental ones. The results demonstrate that the model is suitable for the esterification reaction between AA and EG catalyzed by tetrabutyl titanate [Ti(OBu)₄]. Furthermore, the esterification reaction rate increases with the increase of reaction temperature, concentration of catalyst and the initial reactant ratio of EG to AA.     

Oligomerization of Phenylglycidylether

Reactions taking place between phenylglycidylether (PGE) and pip-eridine (PP), and PGE and 1-(N-piperidinyl)-3-phenoxy-2-propanol (TAA) were followed by means of nuclear magnetic resonance (NMR) spectroscopy. For an equimolar mixture of PGE and PP, reaction was limited to the addition of PP to PGE. The structure of this reaction product (TAA) was determined by ¹H and ¹³C NMR spectroscopy. In the presence of an excess of PGE homopolymerization occurred. Two different oligomers (P₁ and P₂) were obtained as reaction products and their structures were studied. During the progress of the reaction, the molar ratio [P₁]/[P₂] was measured and as a result [P₂] was greater than [P₁] over the entire reaction time. This finding was explained by the importance of the transfer reaction in the homopolymerization of PGE. When an excess of PGE was used in the PGE–TAA reaction, the product was similar to that of the PGE–PP reaction. © of SCI.     

A Highly Efficient Tandem Reaction of 2‐(gem‐Dibromovinyl)phenols(thiophenols) with Organosilanes to 2‐Arylbenzofurans (thiophenes)

2‐Arylbenzofurans(thiophenes) were prepared through an efficient tandem elimination–intramolecular addition–Hiyama cross‐coupling reaction. In the presence of tetra‐(n‐butyl)ammonium fluoride (TBAF), palladium(II) acetate [Pd(OAc)₂] and triphenylphosphine (PPh₃), the reaction of 2‐(gem‐dibromovinyl)phenols(thiophenols) with phenyl(trialkoxy)silanes proceeded smoothly and generated the corresponding products with good yields in one‐pot. It should be noted that TBAF plays an important role in the tandem reaction.     

Comparison among attrition-reaction models of SO2 capture by uncalcined limestone under pressurized fluidized bed combustion conditions

Mathematical models of SO₂ capture by uncalcined limestone (CaCO₃) particles with solid attrition were compared under pressurized fluidized bed combustion conditions. For reaction, we used: (1) a shrinking core model with a distinct border between the product (CaSO₄) layer with a conversion of unity and unreacted core with a conversion of zero, and (2) a distributed reaction model with smooth transition from the unreacted part to the product part with conversion between zero and unity. Continuous attrition and intermittent attrition were compared for attrition. Apparent conversion of the solid was overestimated regardless of the reaction model for continuous attrition. Attrition model plays an important role in determining limestone utilization efficiency, whereas the reaction model played only a minor role.     

Chemical absorption of carbon dioxide into oxirane solution containing ID-CP-MS41 catalyst

CP-MS41 was synthesized by hydrolysis of tetraorthosilicate, as a silicon source, with 3-chloropropyltriethoxysilane as an organosilane using cetyltrimethylammonium bromide as a template. ID-CP-MS41 was synthesized by immobilization of imidazole on the CP-MS41 and was dispersed in organic liquid as a mesoporous catalyst for the reaction between carbon dioxide and oxirane. Phenyl glycidyl ether and glycidyl methacrylate were used as oxiranes. Carbon dioxide was absorbed into the oxirane solution in a stirred batch tank with a planar gas-liquid interface within a range of 0–2.0 kmol/m³ of oxirane and 333–363 K at 101.3 kPa. The measured values of absorption rate were analyzed to obtain the reaction kinetics using the mass transfer mechanism associated with the chemical reactions based on the film theory. The overall reaction of CO₂ with oxirane, which is assumed to consist of two steps-i) a reversible reaction between oxirane (B) and catalyst of ID-CP-MS41 (QX) to form an intermediate complex (C₁), and ii) irreversible reaction between C₁ and CO₂ to form QX and five-membered cyclic carbonate (C)-was used to obtain the reaction kinetics through the pseudo-first-order reaction model. Polar solvents such as N, N-dimethylacetamide, Nmethyl-2-pyrrolidinone, and dimethyl sulfoxide affected the reaction rate constants.     

Gas phase reaction kinetics in boron fibre production

In the production of boron fibres using the chemical vapor deposition (CVD) technique, boron deposition and dichloroborane formation reactions occurs simultaneously. Boron deposition reaction occurs at the surface, whereas the formation of dichloroborane is the result of both gas phase and surface reactions. A continuous stirred tank reactor (CSTR) type of reactor was designed to investigate the reaction kinetics and kinetic parameters in the gas phase reactions of boron trichloride and hydrogen. It was concluded that reaction rate of the product increased with an increase in the inlet concentration of both reactants (BCl₃ and H₂) and with an increase in the reactor temperature. While reaction order with respect to BCl₃ was almost constant at about 0.5 at each temperature, reaction order with respect to hydrogen increased significantly at temperatures lower than 350°C. A general rate expression was derived for BHCl₂ formation from BCl₃ and hydrogen. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Characteristics of magnesium polyphosphate cements derived from ammonium polyphosphate solutions

Magnesium polyphosphate cement pastes prepared by mixing MgO powder and ammonium polyphosphate (AmPP) solutions yielded early strengths of 2000 psi (13.78 MPa) at an age of 1 hr. The major reaction products responsible for the initial strength development at room temperature were found to be ternary phases of NH₄MgPO₄·6H₂O and Mg₃(PO₄)₂·4H₂O. The former exhibited morphological features resembling interlocking crystals composed of thin plates ～ 7 μm in length.The use of sodium tetraborate decahydrate (borax) as an additive to reduce the rate of reaction between MgO and AmPP was demonstrated. The inclusion of 20% borax by weight of AmPP extended the reaction time to 20 min, compared with a reaction time of <3 min for specimens without borax.     

Theoretical study on a kind of cyclization mechanism of boron trichloride and hexamethyldisilazane to form the borazine ring for SiBCN ceramics precursor

Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl₃) and hexamethyldisilazane (HN(SiMe₃)₂) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl₃ and HN(SiMe₃)₂ to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl₃ and HN(SiMe₃)₂ alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl₃ with more heat released compared to that for the introduction of HN(SiMe₃)₂. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions.     

High temperature electrochemical heat pump using water gas shift reaction. Part I: Theoretical considerations

A new electrochemical heat pump using a combination of an electrolytic reaction at lower temperature to absorb low grade thermal energy and a thermochemical reaction at higher temperature to produce more efficient thermal energy is proposed. At a lower temperature, an endothermic reaction which cannot occur thermochemically proceeds with electrolysis. At a higher temperature, an exothermic reaction which is the reverse of the electrolysis reaction occurs thermochemically to produce high grade thermal energy. The water gas shift reaction, CO₂(g) + H₂(g) CO(g) + H₂O(g), in molten carbonate is one possible candidate for the new electrochemical heat pump and can lead to an increase in the temperature of the thermal energy from 1100 to 1200K. A heat pump system using the shift reaction is also considered theoretically.     

Mass Transfer of Ozone to Water: A Fundamental Study

The authors review mass transfer of ozone to water with or without chemical reaction. In order to calculate the dimensions of an ozone-water contactor, it is necessary to know its characteristics without chemical reaction (K_L) and with chemical reaction.     

An Efficient and Facile Synthesis of CL‐20 from TADNO Using HNO3/N2O5 and Optimization of Reaction Parameters by Taguchi Method

Hexanitrohexaazaisowurtzitane (CL‐20) is an outstanding member of a promising new class of energetic compounds, which is applicable in both propellants and explosives. Herein, CL‐20 was synthesized in an efficient method from tetraacetyldinitrosohexaazaisowurtzitane (TADNO) using N₂O₅/HNO₃. The optimization reaction parameters were performed according to the Taguchi OA method. The yield of reaction at the optimized conditions was 97 % with 98.75 % purity.     

Well-Defined Highly Active Heterogeneous Catalyst System for the Coupling Reactions of Carbon Dioxide and Epoxides

The poly(4-vinylpyridine)-supported zinc halide catalysts, prepared from a reaction of ZnX₂ and poly(4-vinylpyridine), exhibit high selectivity and activity for the coupling reaction of CO₂ and ethylene oxide or propylene oxide. Solid NMR characterization of the poly(4-vinylpyridine)-supported ZnBr₂ catalyst and its reaction product with propylene oxide and/or CO₂ show that a pyridinium-alkoxy ion-bridged zinc bromide complex is functioning as an active species, such as in the homogeneous catalysis with L₂ZnBr₂ (L = pyridine or methyl-substituted pyridine).