Transient operation of a catalytic liquid-liquid plug flow reactor for kinetics measurements

A centrifugal partition chromatograph (CPC) was used as a liquid-liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid-liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented.     

Polymerization kinetics for the preparation of poly(p-divinylbenzene) via a miniemulsion polymerization process

The polymerization kinetics for the preparation of poly(p-divinylbenzene (p-DVB)) via a miniemulsion polymerization process was studied by the gravimetric analysis and the transmission electron microscopy (TEM) analysis. The influence of the variation of both initiator concentration and polymerization temperature on the polymerization rate was investigated and also the activation energy of p-divinylbenzene was estimated. The evolution of polymer particles was observed by the electronmicrographs and the relatively large size of polymer particles without the formation of coagulum was obtained in the miniemulsion polymerization process.     

Solution and solid-state polymerizations of substituted p-quinodimethanes and p-quinone methides

This article describes the polymerization behavior of electron-accepting and electron-donating p-quinonoid monomers such as substituted p-quinodimethanes and p-quinone methides in solutions and solid states. In the solution polymerizations, the electron-accepting substituted p-quinodimethanes and p-quinone methides with same substituents such as cyano, ester, and sulfonyl groups at the exocyclic positions are not homopolymerizable, but copolymerizable with donor monomers like styrene in an alternating fashion. Their spontaneous polymerizations with donor monomers have been explained with the bond-forming initiation mechanism. The substituted p-quinodimethanes with ester groups are a first example to show an amphoteric behavior in alternating copolymerizations. Some electron-accepting substituted p-quinodimethanes and p-quinone methides with different substituents such as cyano, ester, acyl, alkylthio, and/or phenyl groups are homopolymerizable, and an anionic polymerization initiated with a butyllithium initiator proceeded in a living manner. Equilibrium polymerization behavior have been found in their radical homopolymerizations, and on the basis of the thermodynamic parameters determined for their polymerizations, it has been concluded that homopolymerizabilities of the electron-accepting substituted p-quinodimethanes and p-quinone methides are determined exclusively by a steric hindrance effect arising from the substituents at the exocyclic positions. A new concept for the radical alternating copolymerization have been proposed on the basis of the change in modes (random and alternating copolymerizations) for their copolymerizations with styrene and the cross-propagation step analysis by linear free energy relationship. The polymerizations of the electron-donating substituted p-quinodimethanes take place only in the presence of oxygen molecules. In the solid-state polymerizations, some electron-accepting substituted p-quinodimethanes with same ester substituents polymerized topochemically in vacuo, and the strict requirements of topochemical polymerization for substituted p-quinodimethane and p-quinone methide monomers have been determined on the basis of their crystallographic data. Topochemical alternating copolymerization with molecular oxygen in solid state was discovered for the first time.     

Competitive electrochemical oxidation of p-chlorophenol and p-nitrophenol on Bi-doped PbO2

The initial stages of oxidation of aqueous solutions of p-chlorophenol (pcp) and p-nitrophenol (pnp) on Bi-doped PbO₂ electrodes have been studied. From deconvolution and analysis of UV-Vis spectra of the solutions obtained during electrochemical oxidation, benzoquinone and aliphatic acids were identified as the primary oxidation intermediates; oxidation of benzoquinone was found to be the slow step during the early stages of the electrochemical combustion process. The effect of competing adsorption of pcp and pnp on Bi-PbO₂ was also examined, and the presence of pnp in solution was found to inhibit the rate of oxidation of pcp during concurrent oxidation of both phenols.     

Solution properties and kinetics of aggregation of an alkyl-substituted poly(p-phenylene)

Freshly prepared solutions of poly(2,5-di-n-dodecyl-1,4-phenylene) (PPP 12) in toluene are metastable at room temperature with regard to a process which leads to the formation of aggregates composed of up to 100 individual macromolecules. This aggregation process has an induction period of more than 10 h at room temperature. The kinetics of aggregation was investigated by making use of a fast capillary membrane osmometer. Aggregation follows an Avrami-Evans type formalism and suggests that clusters of a lyotropic liquid crystalline phase of the polymer are formed of the same type as observed in the melt. The long induction period of aggregate formation in dilute solution in toluene allows to apply conventional techniques of molar mass determination like membrane osmometry and size-exclusion chromatography (SEC). A relationship [η] = 1.94 × 10⁻³ M^0.94 was found for PPP 12 in toluene at 20 °C and a persistence length of 15.6 nm was derived applying the Bohdanecky-formalism. This gives evidence of the worm-like nature of the non-aggregated PPP 12 in dilute solution.     

Study of the oxidation of solutions of p-chlorophenol and p-nitrophenol on Bi-doped PbO2 electrodes by UV-Vis and FTIR in situ spectroscopy

The oxidation of p-chlorophenol (pcp) and p-nitrophenol (pnp) was studied at Bi-doped PbO₂ (Bi-PbO₂) electrodes. The mass balance between solution composition and flowing charge was obtained from deconvolution of UV-Vis spectra recorded during electrolysis at constant potential. It is shown that the time-dependent production of CO₂ is different for the oxidation of pcp and pnp, indicating different reaction mechanisms for the oxidation of each of these compounds. The reaction kinetics was also followed under thin layer conditions by SNIFTIRS; the similarly increasing signals associated to the generation of CO₂ obtained during oxidation of both compounds indicates that under conditions of restricted mass transfer the mineralization rates of pcp and pnp are similar. The results show that benzoquinone (bq) formed from oxidation of phenols desorbs prior to further oxidation to yield maleic acid (ma), in turn oxidizing further to CO₂.     

Electrosynthesis and characterization of a poly(paraphenylene) deriving from p-fluoroanisole

The electrochemical oxidation of p-fluoroanisole (p-FA) in the solvent acetonitrile leads to oligomers and polymers of poly(paraphenylene) type. The electropolymerization process involves coupling reactions of the cation radicals intermediates. The obtained polymers are separated according to their chain length by selective precipitation in cyclohexane and ether. The corresponding structures are characterized by NMR, MS, FTIR, UV and XR diffraction. A preliminary physical study shows that the polymers are photoluminescent with a maximum emission in the near infrared.     

Radical copolymerization of N-vinylcarbazole and p-bromostyrene: determination of monomer reactivity ratios by SEC-multidetection

N-Vinylcarbazole (A)/p-bromostyrene (B) copolymers were prepared by radical copolymerization. Size exclusion chromatography (SEC) equipped with a refractometer and UV-vis spectrophotometer was found to be a very convenient technique to follow copolymerizations and to determine monomer conversions, copolymer composition, average molecular weights, polydispersity indexes versus time. The monomer reactivity ratios r_A (N-vinylcarbazole) and r_B (p-bromostyrene) were determined by using the Finemann-Ross (FR), the inverted Finemann-Ross (IFR), the Kelen-Tüdos (KT), and the fitting curve graphical methods. The four methods were in good agreement and led to very different values for r_A (0.55) and r_B (12.3) which induces a preference for the incorporation of B in the copolymer structure. Eventually, with these results the influence of initial feed on the microstructure of the copolymer has been predicted.     

Demixing kinetics of phase systems employed for liquid-liquid extraction and correlation with system properties

The kinetics of phase demixing in liquid-liquid extraction for model systems comprising PEG 4000/potassium phosphate and t-butanol/ammonium sulfate was studied. The kinetics of demixing depicts the entire demixing pattern of phases of the phase system during and after extraction and hence the study is essential prior to design of large scale gravity phase separators. With an increase in composition, both the systems showed increase in demixing rate (decrease in demixing time). At high tie line length (TLL) and phase volume ratio <1, with salt rich phase as continuous phase, both PEG 4000/potassium phosphate and t-butanol/ammonium sulfate systems showed reduction in demixing time by 59% and 50%, respectively as compared to that at low TLL. An empirical equation proposed in the literature for rate of phase demixing was used to correlate the experimental data. The agreement was better for t-butanol/ammonium sulfate system when compared to PEG 4000/potassium phosphate system.     

Concomitant use of liquid–liquid batch and continuous plug flow reactors for kinetic model discrimination. Application to the Rh/TPPTS catalysed reduction of the C–C double bond in dimethylitaconate

The biphasic catalytic reduction of the C–C double bond of dimethylitaconate with a water soluble rhodium/triphenylphosphinetrisulphonated sodium salt (TPPTS) complex is investigated. Kinetic studies in a well-mixed batch reactor provide kinetics parameters and an activation energy of 71 kJ mol⁻¹ but cannot discriminate between a first order or a complex kinetic model within the range of substrate concentration where the approximation of linear liquid/liquid partition is respected. Catalytic tests in the centrifugal partition chromatograph (CPC) reactor under steady-state operations in chemical regime and plug flow mode allow discriminating the kinetic models, the complex kinetic rate law being preferred.     

Heat transfer and kinetics in the pyrolysis of shrinking biomass particle

The impact of shrinkage on pyrolysis of biomass particles is studied employing a kinetic model coupled with heat transfer model using a practically significant kinetic scheme consisting of physically measurable parameters. The numerical model is used to examine the impact of shrinkage on particle size, pyrolysis time, product yields, specific heat capacity and Biot number considering cylindrical geometry. Finite difference pure implicit scheme utilizing tri-diagonal matrix algorithm (TDMA) is employed for solving heat transfer model equation. Runge-Kutta fourth-order method is used for chemical kinetics model equations. Simulations are carried out for radius ranging from 0.0000125 to , temperature ranging from 303 to and shrinkage factors ranging from 0.0 to 1.0. The results obtained using the model used in the present study are in excellent agreement with many experimental studies, much better than the agreement with the earlier models reported in the literature. Shrinkage affects both the pyrolysis time and the product yield in thermally thick regime. However, it is found that shrinkage has negligible affect on pyrolysis in the thermally thin regime. The impact of shrinkage reflects on pyrolysis in several ways. It includes reduction of the residence time of gases within the particle, cooling of the char layer due to higher mass flux rates of pyrolysis products and thinning the pyrolysis reaction region.     

Acylation of p-xylene over zeolites

Zeolites differing in structure and acidity were tested in liquid phase acylation of p-xylene. Hexanoyl chloride, propionic anhydride and isobutyric anhydride were used as acylating agents. The highest conversions of acylating agent were achieved over large pore zeolites USY (66.3%) and Beta (58.2%). It was found that acylation of p-xylene proceeds only over large pore zeolites Beta and USY. Selectivities to monoacylated p-xylene obtained over USY zeolite decreased in the order: propionic anhydride 78.0% > hexanoyl chloride 67.2% > isobutyric anhydride 33.1%. Diacylated product was formed over zeolite USY with all acylating agents tested but only with hexanoyl chloride over zeolite Beta. It was found that the optimum Si/Al ratio of zeolite Beta for p-xylene acylation with propionic anhydride is 25, while for isobutyric anhydride is 19. Conversion of isobutyric anhydride decreased with increasing isobutyric anhydride concentration and increased with increasing amount of catalyst.     

Novelties of liquid–liquid–liquid phase transfer catalysis Alkoxylation of p-chloronitrobenzene

Liquid–liquid–liquid phase transfer catalysis (L–L–L PTC) offers orders of magnitude intensification of rates of reaction and better selectivities than the biphasic PTC. The catalyst-rich middle phase is the main reaction phase. The etherification or alkoxylation of p-chloronitrobenzene (PCNB) was conducted by using alkanol and alkali instead of the metal alkoxide. A kinetic model is presented and validated.     

Fabrication of tridoped p-ZnO thin film and homojunction by RF magnetron sputtering

Tridoping (Al–As–N) into ZnO has been proposed to realize low resistive and stable p-ZnO thin film for the fabrication of ZnO homojunction by RF magnetron sputtering. The tridoped films have been grown by sputtering the AlN mixed ZnO ceramic targets (0, 0.5, 1 and 2 mol%) on GaAs substrate at 450 °C. Here, Al and N from the target, and As from the GaAs substrate (back diffusion) takes part into tridoping. The grown films have been characterized by Hall measurement, X-ray diffraction, photoluminescence, time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. It has been found that all the films showed p-conductivity except for 2 mol% AlN doped film. The obtained resistivity (8.6×10⁻² Ω cm) and hole concentration (4.7×10²⁰ cm⁻³) for the best tridoped film (1 mol% AlN) is much better than that of monodoped and codoped ZnO films. It has been predicted that [(As_Zn−2V_Zn)+N_O] acceptor complex is responsible for the p-conduction. The homojunction fabricated using the best tridoped ZnO film showed typical rectifying characteristics of a diode. The junction parameters have been determined for the fabricated homojunction by Norde's and Cheung's method.     

相转移条件下亚烃基丙二酸亚异丙酯的钯催化还原反应

５－取代丙二酸亚异丙酯可由亚烃基丙二酸亚异丙酯与甲酸钠在相转移条件下进行钯催化还原反应制得,反应条件温和,产率较高。     

Some novel polymer-supported optically active phase transfer catalysts: 2. Use in displacement,reduction, epoxidation and addition reactions

The performance of 27 novel polymer-supported chiral phase transfer catalysts in a range of phase separated reactions has been studied. The later include a number of displacement reactions, sodium borohydride reductions of prochiral ketones, the epoxidation of chalcone, the addition of nitromethane to chalcone and the addition of thiophenol to cyclohexenone. Some of the reactions were performed under liquid/liquid conditions and others using solid/liquid. No systematic difference emerged between these. In general many of the catalysts provided fast reactions and good chemical yields of products. However, in no case was any significant enantiomeric excess achieved. The latter observation is discussed in the light of the reported behaviour of analogous non-supported catalytic systems, and suggestions proposed to explain these differences.     

Reaction kinetics and mass transfer studies of biomass char gasification with CO2

Gasification kinetics of wheat straw char with CO₂ was investigated using Thermogravimetric apparatus (TGA). The main objective was to identify the diffusional and surface reaction phenomena that may occur during biomass char gasification experiments with CO₂. The effects of temperature (750–900 °C) and particle size (<60–925 μm) on gasification rate of char-CO₂ reaction were determined. The 50% conversion (r₅₀) rate showed that the reactivity increases with temperature, and it decreases as the particle size increases. The important diffusional parameters such as effective diffusivity, effectiveness factor and Thiele modulus were calculated based on the experimental data and the results showed that the impact of physical factors is prominent at high temperatures and large particle sizes. It was found that char gasification within the temperature range studied followed the chemically controlled reaction regime and the influence of pore diffusion was negligible for fine powder particles.     

Acceleration or retardation to crystallization if liquid-liquid phase separation occurs: Studies on a polyolefin blend by SAXS/WAXD, DSC and TEM

Blends of statistical copolymers containing ethylene/hexene (PEH) and ethylene/butene (PEB) exhibited the behavior of upper critical solution temperature (UCST). The interplay between the early and intermediate stage liquid-liquid phase separation (LLPS) and crystallization of the PEH/PEB 50/50 blend was studied by time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. Samples were treated by two different quench procedures: in single quench, the sample was directly quenched from 160 °C to isothermal crystallization temperature of 114 °C; while in double quench, the sample was firstly quenched to 130 °C for 20 min annealing, where LLPS occurred, and then to 114 °C. It was found that in the early stage of crystallization, the integrated values of Iq² and crystallinity, X_c, in the double quench procedure were consistently higher than those in the single quench procedure, which could be attributed to accelerated nucleation induced by enhanced concentration fluctuations and interfacial tension. In the late stage of crystallization, some morphological parameters were found to crossover and then reverse, which could be explained by retardation of lamellar growth due to phase separation formed during the double quench procedure. This phenomenon was also confirmed by DSC measurements in blends of different compositions at varying isothermal crystallization temperatures. The crystal lamellar thickness determined by SAXS showed a good agreement with TEM observation. Results indicated that the early stage LLPS in the PEH/PEB blend prior to crystallization indeed dictated the resulting lamellar structures, including the average size of lamellar stack and the stack distribution. There seemed to be little variation of lamellar thickness and long period between the two quenching procedures (i.e., single quench versus double quench).     

Synthesis and gas permeability of ester substituted poly(p-phenylene)s

Polymerizations of various ester substituted 2,5-dichlorobenzoates [substituent: linear alkyl groups (1a-f), branched alkyl groups (1g-l), cyclohexyl groups (1m-o), phenyl groups (1p-r), and oxyethylene units (1s-v)] were investigated with Ni-catalyzed/Zn-mediated system in 1-methyl-2-pyrrolidone (NMP) at 80 °C. Most of monomers bearing linear and branched alkyl groups successfully polymerized to give relatively high-molecular-weight polymers (M_n = 10,000-20,800). However, the molecular weight of the polymer having eicocyl groups was low because of steric hindrance of long alkyl chain. The polymerizations of cyclohexyl 2,5-dichlorobenzoate and phenyl 2,5-dichlorobenzoate produced low-molecular-weight polymers, while the polymerizations of monomers with alkyl cyclohexyl and alkyl phenyl groups proceeded to afford polymers with relatively high-molecular-weights. The polymers possessing oxyethylene units were obtained, but the molecular weights were low when the oxyethylene chains were long. The gas permeability of membranes of poly(p-phenylene)s with alkyl chains increased as increasing the length of alkyl chain. The membranes of poly(p-phenylene)s with phenyl groups and oxyethylene units exhibited high densities and relatively low gas permeability. However, the CO₂/N₂ separation factor of membrane of poly(p-phenylene) having oxyethylene units was as large as 73.6.     

液-液体系界面相厚度与接触角的可视化测量

利用自行设计的微型可视化反应器研究了液体石蜡-水、乙苯-水体系的界面性质。实验测得静置的液体石蜡-水体系的界面相厚度为9.5μm,界面与器壁的接触角为36.97°;静置与扰动过的乙苯-水体系的界面相厚度分别为45.68μm、73.27μm。为液液界面相厚度与接触角的可视化测量提供了一种新的测量方法。