Apparent Order Research Articles

Continuous Production of Biodiesel from Soybean Oil and Methanol in an Enforced Mass Transfer Reactor

Biodiesel made from vegetable or animal fats is a renewable substitute fuel for petroleum diesel. Continuous production of biodiesel fuel from soybean oil and methanol in an enforced mass transfer reactor without using any catalyst has been investigated. The effects of reaction temperature and molar ratio of methanol to soybean oil on the conversion of transesterification have been discussed. The optimal operational parameters were 360°C and a molar ratio of 40 in this study. Transesterification of soybean oil could reach the expected conversion in shorter reaction time and lower pressure compared with the supercritical methanol method. The new process could reduce the investment cost of equipment. In addition, the apparent reaction order and activation energy of transesterification was 1.66 and 29.34 kJ/mol, respectively. Transesterification in an enforced mass transfer reactor could be a good alternative to the supercritical methanol method and could be more suitable for industrial production.

Mechanism of acetic acid esterification over sulfonic acid-functionalized mesoporous silica

The kinetics of acetic acid esterification with methanol using a propylsulfonic acid-functionalized SBA-15 catalyst were investigated. To determine whether a different mechanism was applicable for heterogeneous or homogeneous catalyzed esterification, propane sulfonic acid was also examined as this homogeneous acid has the same structure as the functional groups tethered onto SBA-15. In isothermal experiments at 323K, the apparent reaction orders using the heterogeneous catalyst were determined to be 0.72 for methanol and 0.87 for acetic acid. Reactant adsorption studies showed that pre-adsorption of acetic acid hindered the reaction rate, while pre-adsorption of methanol or acetic acid with methanol increased the reaction rate, indicating that acetic acid adsorbs more strongly than methanol over the heterogeneous acid catalyst. The experimental results demonstrated that acetic acid esterification with methanol followed a dual-site Langmuir–Hinshelwood type reaction mechanism, which required both the adsorption of acetic acid and methanol over propylsulfonic acid-functionalized SBA-15. In contrast, esterification reaction with the homogeneous catalyst followed an Eley–Rideal mechanism. The kinetic data were successfully fit with a model in which the surface reaction was the rate-limiting step.

Catalytic combustion kinetics of acetone and toluene over Cu 0.13Ce 0.87O y catalyst

Catalytic combustion kinetics of acetone and toluene at low concentrations in air over the previous Cu 0.13Ce 0.87O y catalysts calcined at different temperatures was investigated in order to gain more insight into their catalytic behaviors. A differential packed-bed tubular reactor operated at atmospheric pressure was used to obtain the kinetic data. Reactions were carried out at temperatures between 423 and 483 K and organic compound partial pressures ranging from 10 to 101 Pa. Results showed that the simple power-law model was not enough to represent the kinetics of acetone or toluene combustion over the catalyst. The apparent reaction order and the apparent activation energy for acetone or toluene combustion over the catalyst varied with inlet compound partial pressure and reaction temperature, respectively. Based on the experimental evidence and available information in literature, a kinetic expression assuming reaction between adsorbed acetone and lattice oxygen was proposed to describe acetone combustion and a Langmuir–Hinshelwood (LH) equation assuming reaction between adsorbed toluene and adsorbed oxygen on different adsorption sites was used to account for toluene combustion. It was found that the kinetic equation derived from the mechanistic considerations provided fairly good fits to the kinetic data for catalytic combustion of acetone or toluene over the Cu 0.13Ce 0.87O y catalyst. The estimated kinetic parameters of the Cu 0.13Ce 0.87O y catalysts calcined at different temperatures were compared and the main difference among the three catalysts for acetone and toluene combustion was revealed.

Vibronic line shapes of PTCDA oligomers in helium nanodroplets

Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C(24)H(8)O(6) (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitude larger than the width of the monomer lines. Using a simple theoretical model for the oligomer, in which a Frenkel exciton couples to internal vibrational modes of the monomers, these experimental findings are nicely reproduced. The three peaks present in the oligomer spectrum can already be obtained taking only one effective vibrational mode of the PTCDA molecule into account. The inclusion of more vibrational modes leads to quasicontinuous spectra, resembling the broad oligomer spectra.

A kinetic model of standard selective catalytic reduction of NO by NH3 on single sites

Reduction of NO by NH3 in the presence of O2 may occur on single Fe or Cu atoms or dimers incorporated into the inner walls of zeolite. One of the likely schemes of this reaction implies the formation of N2 and H2O through the reaction of gas-phase NO and adsorbed NH3. The steady-state kinetics corresponding to this scheme was recently analyzed by the author assuming that the reaction runs on single metal atoms. In this work, the author presents a model including two metal atoms. Under the practically important conditions, the kinetics predicted by the one- and two-site models are demonstrated to be similar. In particular, both models allow one to interpret the apparent reaction orders observed experimentally.

Significant Role of Ru-Oxide Present in the Pt-Ru Alloy Catalyst for Ethanol Electro-Oxidation in Acid Medium

This work relates to the search for optimum Pt-Ru catalyst composition for electro-oxidation of ethanol. The structure, morphology, and composition of the synthesized Pt-Ru catalysts were investigated through techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) while cyclic-voltammetry, polarization, chronoamperometry, impedance spectroscopy were employed to study the electrocatalytic behavior of the catalyst. XPS spectrum of the binary sample suggests that the facile oxygen transfer from Ru to Pt site occurs, depending upon the respective valency state and the relative amount of oxide species present in the catalyst. The temperature dependence of ethanol oxidation afforded the determination of the activation energies of catalysts. The apparent reaction order with respect to ethanol was determined with the help of linear sweep voltammetry. The pronounced catalytic activity was observed for at around 12 at% Ru containing electrodes.

Quantifying Regeneration in Dye-Sensitized Solar Cells

We propose and apply a new experimental pro-tocol for determining the kinetics of the oxidation of iodide (aka dye regeneration) in dye sensitized solar cells (DSSCs) using measurements on full cells under operating conditions. Transient absorption (TA) decays of the oxidized dye after a laser pulse are correlated with the short circuit current (Jsc) and electron concentration in the TiO2, measured during the TA experiment. Results for a series of cells with N719 [(Bu4N)2][Ru(dcbpyH)2(NCS)2] (dcbpy = 4,4′-dicarboxy-2,2′-bipyridyl), a standard electrolyte, and varying iodide concentration allow us to fit for the fundamental regeneration rate constant (krg = 7.8 × 105 M−1 s−1) and to determine that the order in iodide, in these cells, is near 1 (0.98 ± 0.16) and clearly not 2. The rate and order allow us to rank various reaction mechanisms and to discuss possible rate-limiting steps that could be catalyzed to improve regeneration. The method can also give estimates of the fundamental rate constant for electron dye recombination (EDR) and the apparent reaction order in total electron concentration.

Crystal growth investigations of ice/water interfaces from molecular dynamics simulations: Profile functions and average properties

Attempts to simulate crystal growth of ice from liquid water and to provide a consistent microscopic description of this process have been challenging tasks. In this paper we have adapted our previously developed molecular dynamics simulation methodology to enable the investigation of steady-state directional crystal growth∕melting of ice. Specifically, we examine ice∕water systems of the (001), (110), and (111) faces of ice Ic and the (0001), (1010), and (1120) faces of ice Ih, where the TIP4P, TIP4P-Ew, and SPC∕E water models have been utilized. The influence of different growth∕melting conditions (temperature gradients and growth velocities) is investigated. Profile functions of properties of interest across the interface are obtained from nonequilibrium steady-state simulations and provide consistent descriptions of ice∕water interfaces. The widths of the various crystallographic faces are found to increase in the apparent order Ic111, Ih0001 < Ih1010 < Ih1120 < Ic001 < Ic110. The observed growth rates were in agreement with experimental values and the possible dependence on the various faces is explored. The melting temperatures obtained with the present methodology for the different models are in good agreement with estimates from other work.

Accuracy of visual estimation in classifying effort during a lifting task

The objective was to determine if visual estimation of effort (VEE) during lifting tasks is accurate in classifying relative levels of exertion or distinguishing between incomplete lifts that may be potentially unsafe and incomplete lifts of "actors" feigning weakness. A convenience sample of 117 health professionals and lay subjects participated in the study. Four actors were videoed performing four complete dynamic lifts (sets of five repetitions) of varying levels of exertion (relative to subjects' physical maximum). Subjects viewed the videoed performances, presented in no apparent order, attempting to properly classify the lifting tasks. For the four levels of exertion, participants were to judge if the lifts were 25%, 50%, 75% and 100% of each actor's maximum lifting capacity and to distinguish between an incomplete (failed) lift of 110% of maximum and a feigned failure of a lift of 25% of maximum. Accuracy for in classifying all lifting activities was marginally higher than chance. There were no differences in the accuracy of health professionals or lay subjects. The VEE does not accurately classify relative levels of exertion or distinguish between incomplete feigned effort lifts and lifts that are potentially too heavy to safely lift.

DRIFTS studies on the photosensitized transformation of gallic acid by iron(iii) chloride as a model for HULIS in atmospheric aerosols

Little is known about the interfacial photochemistry of transition metal cations and chromophores relevant to atmospheric aerosols. We report herein water uptake and in situ surface-sensitive spectroscopic studies on the photosensitized transformation of solid gallic acid (GA), externally mixed with FeCl(3) as a photosensitizer, under dry and humid conditions of <1% and 30% relative humidity (RH), respectively. GA is a hydrolysis product of tannic acid, a model macromolecule for humic-like substances (HULIS) in aerosols and aged polyaromatic hydrocarbons (PAH). Water uptake on GA and GA/FeCl(3) mixture films was quantified using a quartz crystal microbalance (QCM) as a function of %RH (<1-60%). Results indicate continuous multilayer formation of adsorbed water with no phase transitions, with a monolayer of adsorbed water forming around 30 and 12%RH, respectively. Photochemical studies were conducted using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Spectra were collected as a function of irradiation time (4 h), mass fraction of FeCl(3) (0.5-3%) using irradiance of simulated solar light equivalent to 120 Wm(-2) at 555 nm. Difference absorbance spectra show changes to GA functional groups suggesting the formation of organochlorine compounds in the condensed phase with their signature v(C=C) at 1601 cm(-1), and release of CO(2). Potential halogenation pathways of GA in the presence of Fe(3+) are discussed based on well-known aqueous phase chemistry. These pathways along with our results also suggest the release of volatile organochlorine compounds and Cl(2) gas. Apparent first order rate constants, k(s), of the photosensitized reactions were derived from kinetic curves of the most intense positive and negative spectral features at 1601 and 1381 cm(-1), respectively. Values of k(s) at 120 Wm(-2) are found to be higher than those reported from UV photo-Fenton reactions of GA in bulk aqueous phases containing H(2)O(2), Fe(2+) or Fe(3+). The implication of our studies on the aging of multicomponent aerosols containing organic matter, transition metals and halide ions due to heterogeneous photochemistry is discussed.

Thermal degradation of piperazine and its structural analogs

Abstract The resistance of concentrated, aqueous piperazine (PZ) to thermal degradation is a critical characteristic that recommends PZ as a solvent for amine based absorption/stripping for CO 2 capture from coal fired flue gas. Seven structural analogs of PZ were thermally degraded in an effort to discover the structural reasons for the enhanced resistance of PZ. Four comparisons are developed that look at the effect of changing heteroatoms (PZ, piperidine (PD), and morpholine (Mor)), ring size in monoamines (pyrrolidine (Pyr), PD, and hexamethyleneimine (HMI)), ring size in diamines (PZ and homopiperazine (HomoPZ)), and methyl substitution (PZ, 1methylpiperazine (1-MPZ), and 2-methylpiperazine (2-MPZ)). In 6-member heterocycles with one amino function, both Mor and PD had decreased degradation rates compared to PZ, likely because the additional amino function in PZ enhances nucleophilic attack reactions. In monoamines, the expected chemical stability predicted for 5-, 6-, and 7-membered alkane rings closely predicted the thermal degradation rates of these heterocycles. Both Pyr and HMI were degraded quickly producing polymers while the 6membered PD was stable. Increasing the size of the PZ ring by the addition of one methylene group greatly enhanced the thermal degradation rate. HomoPZ loss 99% of its initial concentration after 4 weeks at 175 °C while PZ lost only 30%. Methyl substitution increased the rate of amine degradation as both 1-MPZ and 2-MPZ degraded faster than PZ at 150 °C. Unexpectedly, a methyl on the amino group (1-MPZ) enhanced degradation more than a methyl on the carbon in the α−position to the amino group (2-MPZ). An apparent first order rate constant was calculated for the thermal degradation of these structural analogs and compared to other amines of interest in CO 2 capture.

First principles based mean field model for oxygen reduction reaction

A first principles-based mean field model was developed for the oxygen reduction reaction (ORR) taking account of the coverage- and material-dependent reversible potentials of the elementary steps. This model was applied to the simulation of single crystal surfaces of Pt, Pt alloy and Pt core-shell catalysts under Ar and O(2) atmospheres. The results are consistent with those shown by past experimental and theoretical studies on surface coverages under Ar atmosphere, the shape of the current-voltage curve for the ORR on Pt(111) and the material-dependence of the ORR activity. This model suggests that the oxygen associative pathway including HO(2)(ads) formation is the main pathway on Pt(111), and that the rate determining step (RDS) is the removal step of O(ads) on Pt(111). This RDS is accelerated on several highly active Pt alloys and core-shell surfaces, and this acceleration decreases the reaction intermediate O(ads). The increase in the partial pressure of O(2)(g) increases the surface coverage with O(ads) and OH(ads), and this coverage increase reduces the apparent reaction order with respect to the partial pressure to less than unity. This model shows details on how the reaction pathway, RDS, surface coverages, Tafel slope, reaction order and material-dependent activity are interrelated.

Modeling of chemical kinetics of elastomer/hydroxyl‐ and carboxyl‐functionalized multiwalled carbon nanotubes nanocomposites' cross‐linking

AbstractSeveral kinds of (hydrogenated) nitrile elastomer ((H)NBR) compounds were prepared by melt compounding of rubbers with carbon nanotubes. Transmission electron microscopy (TEM) showed that the exfoliation degree of nanotubes was high. Multiwalled carbon nanotubes (MWCNT) were either neat or modified by hydroxyl or carboxyl groups. Morphology was also characterized by scanning electron microscopy (SEM). The cure kinetics of (H)NBR and modified multiwalled carbon nanotubes ((m‐)MWCNT/(H)NBR) nanocomposites was studied. It was found that the apparent curing and over‐cure activation energies (EA and EA,1) increased with the increasing amount of (m‐)MWCNT. There was a less obvious change in the apparent orders of curing reactions. The results of n‐th order and autocatalytic kinetic model showed that any studied content of (m‐)MWCNT could increase effective thermal conductivity, but decreased the vulcanization rate of (m‐)MWCNT/(H)NBR nanocomposites. Finally, the effect of (m‐)MWCNT content and functionalization on tensile mechanical properties was presented. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

Modeling and experimental evaluation of vacuum-UV photoreactors for water treatment

Vacuum-UV (VUV) radiation is a promising and effective technology for the oxidation of organic contaminants. The VUV-induced degradation of a model pollutant, Formic Acid (FA), was modeled and experimentally investigated. Experimental work involved an annular flow-through reactor operated in batch mode with complete recycle of the reactants. Ozone-producing low-pressure Hg lamps were used as the source of VUV radiation. FA concentrations of up to 0.55 mmol L −1 were completely degraded after 40 min of irradiation. FA degradation was accompanied by the formation of H 2O 2 at concentrations of about 0.3 mmol L −1. Kinetic and radiation models were combined with the corresponding mass balances to describe the experimental results. The kinetic model accounted for the most important reactions occurring in the system, including photolysis of water and H 2O 2, side reactions between radicals, and degradation of FA. The radiation model, which was solved using the Monte Carlo method, described the propagation of photons in the reactor volume and took into account the optical properties of the solution and the emission power of the lamps, obtained by actimometry. Modeling simulations fit experimental data of FA degradation using VUV, H 2O 2/VUV, and H 2O 2/UV with a root mean square error of 7.4%. According to modeling and experimental results, the VUV-induced degradation of FA followed an apparent zero order kinetics, a fact that may suggest the reaction was limited by the availability of hydroxyl radicals (HO ).

Ozone application in water sources: effects of operational parameters and water quality variables on ozone residual profiles and decay rates

Systematic ozonation tests were conducted by means of a mobile pilot plant. Water source 1 was a low turbidity stream with very low solids content and very low turbidity, apparent color and alkalinity. Water source 2 was reservoir water with higher turbidity, solids content and alkalinity than source 1. The ozone plant was a counter-current contactor composed of four columns in series. Variations in contact time, in the feed gas concentration (in terms of percent by weight of ozone) and in splitting of the total applied ozone dosage between columns 1 and 2 were tested. Concentration - time (CT) products were calculated and decay coefficients K were estimated from experimental data. The relative importance of water quality and certain operational parameters with regard to CT products and ozone decay was assessed. Total CT values seemed to increase with: (a) total applied ozone dosage, (b) percent by weight of ozone in the feed gas to the bubble contactor, (c) increasing contact time and (d) higher water quality, with regard to turbidity, apparent color, total organic carbon and particle counts. As the total applied ozone dosage was increased, the more important the contact time and ozone dosage configuration became for the total CT value. The apparent first order ozone decay rate constant (K) decreased with increasing total applied ozone dosage. The contact time appeared to exert a much stronger influence on total CT values than on K values, particularly so as the total applied ozone dosage was increased.

Catalytic removal of nitrates from waters in a continuous flow process: The remarkable effect of liquid flow rate and gas feed composition

The selective catalytic reduction of nitrates (NO3−) in water mediums towards N2 formation by the use of H2 and in the presence of O2 (air) in the gas feed has been investigated under a continuous flow process over Pd–Cu supported on various mixed metal oxides, xwt.% MxOy/γ-Al2O3 (MxOy=CeO2, MgO, Mn2O3, Cr2O3, Y2O3, MoO2, Fe2O3 and TiO2). It is demonstrated for the first time that a remarkable improvement of both catalysts activity and N2 reaction selectivity can be achieved when increasing the liquid flow rate in the continuous flow process. In particular, it was found that NO3− reduction rates up to more than two times higher and NH4+ selectivity values up to twenty times lower can be obtained when increasing the liquid flow rate from 2 to 6mL/min. Moreover, it was proven for the first time, in a continuous flow process, that the presence of oxygen (or air) has a remarkable positive effect on the reaction's selectivity towards nitrogen. The reaction's selectivity towards NH4+ can be decreased by up to three times when 20vol.% air is added in the gas feed of the NO3−/H2 continuous flow reaction. The Pd–Cu clusters supported on TiO2-, CeO2- and MgO-coated γ-Al2O3 spheres showed the best catalytic behaviour compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. In addition, it was found that the initial concentration of nitrates in the liquid feed can significantly affect catalysts activity and reaction's selectivity. A positive apparent reaction order towards nitrates of 0.9 was calculated on Pd–Cu/TiO2/Al2O3.

Curing Reaction and Kinetic Parameters of Diallyl Orthophthalate Resin with Initiator Dicumyl Peroxide

The curing reaction of diallyl orthophthalate(DAOP) resin, which was initiated by dicumyl peroxide(DCP), was studied by Fourier transform infrared spectroscopy(FTIR). Differential scanning calorimetry(DSC) was used to determine the curing behavior and kinetic parameters of dicumyl peroxide (DCP) / diallyl orthophthalate (DAOP) system. The results clarified that the curing reaction of DAOP resin could be initiated by DCP at 150-180°C and the reaction heat diffused slowly in curing process. The gel-temperature, curing temperature and thermal treatment temperature of the DCP(3%)/DAOP system were 145.46°C, 166.03°C and 173.83°C. The apparent activation energy, frequency factor and reaction order were 130.200kJ/mol, 5.231×1010 and 0.9455, respectively.

Transfer mechanism of temoporfin between liposomal membranes

The transfer kinetics of temoporfin, a classic photosensitizer, was analyzed by investigating the influence of total lipid content, temperature, as well as charge, acyl chain length, and saturation of the lipids in donor vesicles using a mini ion exchange column technique. The obtained results are consistent with an apparent first order kinetics in which the transfer proceeds through both liposome collisions and through the aqueous phase. We present a corresponding theoretical model that accounts for the detailed distribution of drug molecules in donor and acceptor liposomes and predicts the transfer rates as a function of drug concentration and number of donor and acceptor liposomes. The experimentally observed transfer rates depended strongly on the temperature and comply with the Arrhenius equation. Thermodynamic calculations indicate the transfer process to be entropically controlled. In terms of the charge of donor liposomes, positively charged liposomes showed transfer rates faster than negatively charged liposomes whereas the maximum amount transferred was almost the same. A more rigid structure of the donor liposomes increases the transfer rate of temoporfin, which is caused by expelling the drug from the membrane interior, as proposed in former work. In summary, our combined theoretical/experimental approach offers a systematic way to study the mechanism of drug release from liposome-based delivery systems.

EFFECTS OF FEED CONCENTRATION AND WATER VAPOR ON CATALYTIC COMBUSTION OF ETHYL ACETATE AND BENZENE IN AIR OVER CR-ZSM-5 CATALYST

Catalytic combustion of ethyl acetate (EAc) and benzene (Bz) over chromium exchanged ZSM-5 (Si/Al=240) is reported. An 11 mm i.d. fixed-bed catalytic reactor, operated at temperatures between 100 oC and 500 oC, and under excess oxygen condition, was used for the catalytic activity measurement. Apparent order of reaction and apparent activation energy were determined by operating the reactor differentially at a gas hourly space velocity (GHSV) of 78,900 h-1 and feed concentrations between 3,500 ppm to 17,700 ppm and 3,700 to 12,400 ppm for ethyl acetate and benzene, respectively. Ethyl acetate was more reactive than benzene due to highly reactive carbonyl group in the molecule. The combustion process satisfactorily fitted pseudo first-order kinetics with respect to organic concentration and a zero-order dependence on the oxygen concentration. The presence of water vapor (9,000 ppm) in the feed stream was found to weaken the reactivity of these organics which could also be demonstrated with increases in the activation energy from 23.1 kJ/mole to 37.6 kJ/mole for ethyl acetate and from 27.6 kJ/mole to 46.1 kJ/mole for benzene. Water vapor was found to play a positive role in the formation of carbon dioxide yield in ethyl acetate combustion. Deactivation of catalyst by water appeared to be only temporary and the activity reverted back to its original value once the source of water vapor was removed.

A polyethylene chain investigated with replica exchange molecular dynamics simulation: Equilibrium lamellar thickness and melting point, ordering and free energy

In the present work, a polyethylene chain with N=200 CH2 units was simulated using replica exchange molecular dynamics (REMD). Simulations were performed in a broad temperature range and for intra-chain interactions varying from the fully interacting to the ideal spring chain.Our work demonstrates that REMD is a very efficient method to obtain equilibrium data. It is found that the coil-to-globule transition is dominated by the vdW energy, whereas the globule-to-folded chain transition is accompanied by transitional behavior in the torsion and vdW energies. Our data clearly show that for the chain length considered here, the chain folded crystal to globule transition is a continuous transition. Nevertheless, we can establish with good accuracy the equilibrium transition temperature for the chain folded crystal to globule transition.A set of orientational order parameters was used to investigate the order in the polymer chain. At the globule-to-folded chain transition an abrupt change in the value of the order parameter is observed, whereas there is no or almost no change in the value of the order parameter at the coil-to-globule transition temperature. The (apparent) order in the disordered globular and coiled states indicated by some studied order parameters is related to the definition of the order parameter and depends on the chain length of the polymer.Below the equilibrium melting temperature the (largest principal component of the) radius of gyration and the equilibrium lamellar thickness of the folded chain crystal decrease with increasing temperature, which gives support to the theory of Muthukumar but is opposite to the prediction of classical crystallization theories. The agreement between simulations and theory may hint to universal behavior of the relative equilibrium thickness versus the relative super cooling.