Vaporization Kinetics Research Articles

Vaporization Kinetics and Vapor Pressures for Petroleum Fractions Using Thermogravimetry Analysis

Thermogravimetric analysis (TGA) was extended to the measurements of vaporization kinetics and vapor pressures for three oil samples. The energies of activation for the vaporization process and the enthalpies of vaporization were obtained through the vaporization rates and the vapor pressure data. The experimental data from TGA and comparative ebulliometry are distributed in the same linear trends and are in reasonable agreement. The TGA method is a rapid and practical one for constructing vapor pressure curves, especially at low pressure range, for petroleum fractions. Combination of the TGA and the embulliometry, the vapor pressures in a wide temperature range can be obtained.

Kinetics and vaporization of anil in nitrogen atmosphere – Non-isothermal condition

The thermal vaporization kinetics of Schiff’s base was studied by thermogravimetry (TG) and differential thermal analysis (DTA) techniques using non-isothermal conditions. The kinetic parameters were calculated under model-free (Friedman’s, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods) and model-fitting (Coats–Redfern, CR) methods. The results of the Friedman’s isoconversional analysis of the TG data suggest that the investigated vaporization process follows a single-step reaction. Based on the obtained results, the mass loss is caused mainly by vaporizations and not by decomposition. The most probable kinetic model for vaporization of the compound is P2 (power law).

Modeling Kinetics of Cd, Pb, and Zn Vaporization during Municipal Solid Waste Bed Incineration

The fate of heavy metals contained in municipal solid waste is of major concern in the incineration process. This study is the first attempt to analyze the kinetic behavior of Cd, Pb, and Zn in a waste bed burning on the grate of an incinerator. The vaporization rates of the three heavy metals were derived from laboratory experiments. The kinetic law was then introduced into Garbed-ss, a mathematical model of the on-grate incineration of a refuse bed. Results show that the calculated vaporization of the three metals is fast, proceeds to nearly full completion, occurs at the pyrolysis front, and is indeed controlled by the thermal degradation of the waste. Alhough in agreement with thermodynamic calculations, the vaporization of lead and zinc seems to be overestimated. The model would be improved by accounting for the initial physical and chemical speciation of the heavy metals in the waste feed.

The influence of the supramolecular structure of water on the kinetics of vaporization

The kinetics of water vaporization was studied gravimetrically using a Q-1500 D derivatograph with an accuracy of ±5 × 10−5 g under atmospheric conditions. Various supramolecular structures were created in liquid water using solutions of K, Na, Ba, and Zn chlorides with various concentrations. The kinetic dependences of weight P loss caused by the vaporization of solutions were compared with the data on pure water used to prepare the solutions. The dependence of the rate of vaporization V on the concentration of hydrated ions in solutions was used to show that the rate V is the sum of the rates of vaporization of particles of two types, (a) H2O molecules and (b) supramolecular formations (H2O clusters) with H-bonds. As a consequence, a nonlinear (piecewise linear) dependence of the kinetics of vaporization P = f(τ) of water and solutions is observed. The rate of vaporization (V1) along the initial P = f(τ) curve portions is substantially (by ∼30%) higher than its stationary value (V).

Kinetics of heavy metal vaporization from coal in a fluidized bed by an inverse model

AbstractThis study addresses the kinetics of heavy metal vaporization during fluidized bed thermal treatment of coal. Both direct and inverse models were developed in transient conditions. The direct model predicts the time course of the metal concentration in the gas from the vaporization rate profile. The inverse model was developed and validated to predict the metal's vaporization rate from its concentration in the outlet gas. A method to derive the kinetic law of heavy metal vaporization during fluidized bed thermal treatment of coal from the global model and the experimental measurements is derived and illustrated. A first‐order law was fitted for the mineral matrix and a second‐order law was fitted for coal. This method can be applied to any matrix, whether it is mineral matrix or organic matrix. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Kinetic Rate Laws of Cd, Pb, and Zn Vaporization during Municipal Solid Waste Incineration

The kinetic rate laws of heavy metal (HM) vaporization from municipal solid waste during its incineration were studied. Realistic artificial waste (RAW) samples spiked with Pb, Zn, and Cd were injected into a fluidized bed reactor. Metal vaporization wastracked by continuous measure ofthe above metals in exhaust gases. An inverse model of the reactor was used to calculate the metal vaporization rates from the concentration vs time profiles in the outlet gas. For each metal, experiments were carried out at several temperatures in order to determine the kinetic parameters and to obtain specific rate laws as functions of temperature. Temperature has a strong influence on the HM vaporization dynamics, especially on the vaporization kinetics profile. This phenomenon was attributed to internal diffusion control of the HM release. Two types of kinetic rate laws were established based on temperature: a fourth- or fifth-order polynomial rate law (r(x) = k0e(-E(A)/RT)p(x)) for temperatures lower than 740 degrees C and a first-order polynomial (r(x) = k0e(-E(A)/ RT(q-q(f) for temperatures higher than 740 degrees C.

Computerized simulation of solute–particle vaporization in an inductively coupled plasma

Recent experiments involving aerosol introduction into the inductively coupled plasma have shown that intact droplets and solute particles cause enormous fluctuations in analyte emission and mass-spectral signals. Here, particle-vaporization kinetics are simulated as a detailed function of the operating conditions, fundamental properties and spatial location in the inductively coupled plasma, and as a function of several of the properties of the particles themselves: diameter, chemical composition and size distribution. These simulations portray the particle vaporization as proceeding nominally linearly with respect to the particle radius when the particles are small, but roughly quadratically with radius when the particles are very large. Further, the heat- and mass-transfer-limited rates of vaporization are roughly equal for the typical gas-temperature range in the plasma tail flame, so that at any height either process might limit the rate of vaporization. This similarity gives rise to a dynamic, competitive picture of plasma vaporization kinetics.

Transient Cathode Spot Operation at a Microprotrusion in a Vacuum Arc

A physical model and system of equations was formulated to describe transient cathode spot evolution at a single protrusion. The model considered the self-consistent processes including protrusion heating, kinetics of cathode vaporization, plasma generation, and current continuity. The time dependencies of spot current, current density, and protrusion size were calculated, taking into account the heat flux from the plasma (surface heat source) and Joule energy (volume source). The plasma density, temperature, degree of vapor ionization, electron current fraction, and cathode erosion rate were calculated as functions of the protrusion size, which reduced in time during the spot operation. It was shown that the spot operation on the protrusion was limited by the disappearance of the protrusion due to cathode erosion. The protrusion disappearance time determined the duration of the transient arc spot at a single protrusion. It was calculated that 1-5 mum protrusions reduce their size significantly due to evaporation in 0.5-10 mus, respectively. The smaller time of protrusion destruction occurs due to it relatively high heating, which was mostly by the heat flux from the surrounding plasma.

The Effect of Film Thickness on Thermal Aerosol Generation

Rapid heating of thin films of pharmaceutical compounds can vaporize the molecules, which leads to formation of aerosol particles of optimal size for pulmonary drug delivery. The aim of this work was to assess the effect of coated film thickness on the purity of a thermally generated (condensation) drug aerosol. Pharmaceuticals in their free base form were spray-coated onto stainless steel foils and subsequently heated and vaporized in airflow via a rapid resistive heating of the foil. Aerosol particles were collected on filters, extracted, and analyzed using reverse phase HPLC to assess the amount of degradation induced during the vaporization process. Condensation aerosols of five pharmaceuticals were formed from a wide range of film coating thicknesses. All five showed a roughly linear trend of increasing aerosol purity with decreasing film thickness, although with quite different slopes. These findings are consistent with a model based on general vaporization and degradation kinetics. Small non-uniformities in the film do not significantly alter aerosol purity. Rapid vaporization of pharmaceuticals coated as thin films on substrates is an efficient way of generating drug aerosols. By controlling the film thickness, the amount of aerosol decomposition can be minimized to produce high purity aerosols.

Modeling of nitromethane flame structure and burning behavior

Nitromethane was investigated in this study due to the push for higher performance and reduced toxicity monopropellant. A comprehensive detailed model for its flame structure and linear regression rate was developed and validated with experimental data. The model considered one-dimensional behavior with surface vaporization and detailed gas-phase kinetics based on the RDX mechanism of Yetter et al. combined with the nitromethane decomposition mechanism of Glarborg, Bendtsen, and Miller, resulting in a mechanism consisting of 47 species and 250 elementary reactions. The predictive model was implemented using a custom FORTRAN code wrapping the CHEMKIN 4 PREMIX gas-phase solver coupled with the condensed-phase solution. Predicted burning rates using the model showed good agreement with measured rates up to 15 MPa. Calculated species and temperature profiles showed three distinct regions based upon the appearance and consumption of certain species. The first region was marked by decomposition of nitromethane, the second region by consumption of all intermediate species except CH 4 and NO, and the third region by the rise to final temperature and species concentrations near the equilibrium values. Among the intermediate species, CH 4 and NO had higher concentrations than those of CH 2O, N 2O, HNO, and HONO. CH 4 served as fuel species and NO provided a portion of the oxidizer for the third-region reactions to reach equilibrium composition. Sensitivity analysis identified the importance of two elementary reactions involving HNO to the temperature profile, and therefore the burning rate. Although the absolute level of NH and HCO were low, they served as an important intermediate species transporting nitrogen and carbon, respectively, between other higher-concentration species. The calculated flame zone thickness is consistent with that measured by microthermocouples.

Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline ice films

Fast thermal desorption spectroscopy was used to investigate the vaporization kinetics of thin (50-100 nm) H(2)O(18) and HDO tracer layers from 2-5 microm thick polycrystalline H(2)O(16) ice films at temperatures ranging from -15 to -2 degrees C. The isothermal desorption spectra of tracer species demonstrate two distinct peaks, alpha and beta, which we attribute to the vaporization of H(2)O(18) initially trapped at or near the grain boundaries and in the crystallites of the polycrystalline ice, respectively. We show that the diffusive transport of the H(2)O(18) and HDO tracer molecules in the bulk of the H(2)O(16) film is slow as compared to the film vaporization. Thus, the two peaks in the isothermal spectra are due to unequal vaporization rates of H(2)O(18) from grain boundary grooves and from the crystallites and, therefore, can be used to determine independently the vaporization rate of the single crystal part of the film and rate of thermal etching of the film. Our analysis of the tracer vaporization kinetics demonstrates that the vaporization coefficient of single crystal ice is significantly greater than those predicted by the classical vaporization mechanism at temperatures near ice melting point. We discuss surface morphological dynamics and the bulk transport phenomena in single crystal and polycrystalline ice near 0 degrees C.

Development of an inverse method to identify the kinetics of heavy metal release during waste incineration in fluidized bed

This paper deals with the emission of heavy metals (HM) during the incineration of municipal solid waste in a fluidized bed reactor. This study focused on the development of a general method to identify the kinetics of vaporization of heavy metals from the on-line analysis of exhaust gas. This method is an inverse method, which requires only the time evolution of the HM concentration in exhaust gases (experimental data) and a global bubbling bed model developed for transient conditions at the reactor scale. First, a lab-scale fluidized bed incinerator was set-up to simulate the HM release during the thermal treatment of metal-spiked model wastes. A specific on-line analysis system based on ICP-OES was developed to measure in real time the variation of the relative concentration of HM in exhaust gases. Then, a two-phase flow bubbling bed model was developed and validated to calculate the kinetics of vaporization of HM from its measured concentration time profile in the outlet gas. The technique was first validated with model waste (metal-spiked mineral matrices), thus enabling at each time both solid sampling for measuring the HM vaporization kinetic and on-line analysis for measuring the HM concentration in the outlet gas. The inverse method was then applied to realistic artificial wastes (derived from real wastes) to identify the HM vaporization kinetics from the on-line analysis results.

Isoconversional kinetic study of alachlor and metolachlor vaporization by thermal analysis

AbstractThe vaporization kinetics of two acetamide pesticides, namely alachlor and metolachlor, was studied by thermogravimetric analysis under nonisothermal conditions (using heating rates between 1.0 and 10 K min−1). A model‐free isoconversional method of kinetic analysis was proposed, and activation energy dependences on the extent of conversion α for nonisothermal experiments were given. An increase in activation energy is shown for alachlor from 50 to 60 kJ mol−1, while E values do not significantly vary in the range α > 0.1: 63 kJ mol−1 for metolachlor while 60 kJ mol−1 for alachlor. At the end of vaporization (0.9 < α < 1.0), the activation energies are in close agreement with the enthalpies of vaporization calculated from DSC measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 74–80, 2005

The vaporization rate of ice at temperatures near its melting point

The first study of free vaporization kinetics of ice at temperatures near its melting point is reported. The experimental approach employed is based on a unique combination of thermal desorption spectroscopy, microcalorimetry, and time-of-flight mass spectrometry, making it possible to overcome challenges associated with the introduction of volatile solids into a high vacuum environment. Measurements of the vaporization rate of polycrystalline ice demonstrate that the vaporization kinetics deviate dramatically from those predicted by a simple mobile precursor mechanism. The vaporization rate follows Arrhenius behavior from -40 to 0 degrees C with an effective activation energy of 50+/-4 kJ/mol, which is significantly higher than the value predicted by the simple mobile precursor mechanism. Extrapolation of earlier measurements conducted below -40 degrees C yields a value of approximately 0.02 at 0 degrees C for the vaporization coefficient alphav. In contrast, experimentally determined vaporization coefficient is found to be 0.7+/-0.3 and shows a weak dependence on temperature up to the bulk melting point. The role of possible surface phase transitions in the mechanisms of release and uptake of H2O and other chemical species by ice surfaces is discussed.

Debris generation and propagation phenomenology from hypervelocity impacts on aluminum from 6 to 11 km/s

A systematic computational and experimental study is presented on impact generated debris resulting from record-high impact speeds recently achieved on the Sandia three-stage light-gas guns. In these experiments, a targetplate of aluminum is impacted by a titanium-alloy flier plate at speeds ranging from 6.5 to 11 km/s, producing pressures from 1 Mbar to over 2.3 Mbar and temperatures as high as 15000 K (>1 eV). The aluminum plate is totally melted at stresses above 1.6 Mbar. Upon release, the thermodynamic release isentropes will interact with the vapor dome. The amount of vapor generated in the debris cloud will depend on many factors such as the thickness of the aluminum plate, super-cooling, vaporization kinetics, and the distance over which the impact-generated debris is allowed to expand. To characterize the debris cloud, the velocity history produced by stagnation of the aluminum expansion products against an aluminum witness plate is measured using velocity interferometry. X-ray measurements of the debris cloud are also recorded prior to stagnation against the witness plate. Both radiographs and witness-plate velocity measurements suggest that the vaporization process is both time-dependent and heterogeneous when the material is released from shocked states around 230 GPa. Experiments suggest that the threshold for vaporization kinetics in aluminum should become significant when expanded from shocked states over 230 GPa. Numerical simulations are conducted to compare the measured X-ray debris cloud and the time-resolved experimental interferometer record with calculational results using the 3-D hydrodynamic wave-code, CTH. Results of these experiments and calculations are discussed in this paper.

The kinetics of vaporization of a heavy metal from a fluidized waste by an inverse method

This study addresses the emission of heavy metals during the incineration of municipal solid waste. A global method was developed to determine the vaporization rate of the metal from the on-line analysis of exhaust gas. This method differs from direct models, which predict the time course of the metal concentration in the gas from the vaporization rate profile, but which are not practicable because this vaporization rate cannot be measured in real incinerators burning real wastes. The method is based on the determination of the global rate of release of heavy metal from the combustion of model wastes in a fluidized bed. It is an inverse method, which involves only the measured concentration of heavy metal in the exhaust gases and a model developed at the reactor scale. The thermal treatment of model wastes spiked with a metal was performed in a laboratory- scale fluidized bed. In fact, a solid matrix derived from real waste was dosed with Cd, Pb, or Zn and burned to simulate the metal’s release during the incineration of municipal solid waste. An on-line analysis system was linked to the gas outlet of the reactor, and the metal’s vaporization was tracked successfully by continuously measuring by inductively coupled plasma optical emission spectroscopy (ICP-OES) the relative concentration of the metal in exhaust gases. On the theoretical front, a bubbling bed model was developed and validated to calculate the metal’s vaporization rate from its concentration-time profile in the outlet gas. The inverse method consists in identifying these vaporization rates at the particle level from only the on-line diagnostic results and using the model, whatever the waste considered. The data obtained may be used in any process, in which wastes are heated rapidly (several hundreds of degrees per second), as in fluidized beds.

On-line heavy metal analysis in the fumes from a laboratory fluid-bed incinerator

An inductively coupled plasma spectrometer was used with a laboratory fluidized-bed reactor and adapted to continuously measure the heavy metal concentrations in exhaust gases. The system is devoted to the thermal treatment of metal-spiked model wastes; on-line analyses were performed to study heavy metal release. This method was used to study the kinetics of heavy metal vaporization from pure mineral and pure organic matrices to determine the roles of temperature, residence time, gas and matrix composition, and initial metal speciation. Then, a more complex metal-spiked matrix, derived from real waste, was burned to simulate metal release during municipal solid-waste incineration. Three metals were considered: Cd, Pb, and Zn. In all cases, the experimental setup was successfully used to monitor the metal evaporation process during fluidized-bed incineration.

Experimental measurement of droplet vaporization kinetics in a fluidized bed

Feedstock injection is an essential step of the fluid catalytic cracking process in which complex phenomena take place, such as droplet formation and dispersion, liquid heat-up and vaporization. These phenomena greatly affect product and coke yields. Several models have been proposed to estimate the vaporization of feed droplets in the riser injection zone. However, depending on the assumptions on which the model is based, completely different vaporization times may be predicted. No experimental validation exists to discriminate between the various models. This paper presents the first method for the accurate measurement of the vaporization kinetics of a liquid spray injected into a hot fluidized bed. The droplet size has a very strong effect on the vaporization. With a droplet size of 60 μm, it takes about 100 ms to vaporize 50% of the liquid; with a droplet size of 30 μm, this time is cut by half.

Kinetics of Heavy Metal Vaporization from Model Wastes in a Fluidized Bed

Metal vaporization experiments were carried out in an atmospheric fluidized bed to study the influence of operating conditions on the extent of heavy metal (HM) release in fumes from municipal solid waste incinerators. Modelwastes spiked with compounds of Pb, Cd, and Zn were used. The parameters studied were temperature, treatment duration, matrix of the model waste (mineral and organic), HM initial speciation, and gas composition (N2, air, air + HCl, gas mixture simulating the incinerators). The extent of vaporization was measured by solid sample analysis and on-line analysis of the gaseous effluent, after customization of the ICP technique for gas analysis. The results indicate the metal vaporization rate is very high initially and then slows. The results with mineral matrices give the decreasing order of volatility Cd > Pb > Zn, but in industrial incinerators Zn volatilizes slightly more than Pb. Temperature (especially for porous alumina) and mineral matrix have a strong influence on the HM vaporization, but HCl concentration and HM initial speciation do not. The gas composition and the initial metal concentration are significant parameters. The matrix influence clearly denoted the mass transfer limitations in the vaporization process from mineral matrix.

Simultaneous thermal analysis of hexahydrophtalic anhydride

Hexahydrophtalic anhydride is studied by means of a simultaneous thermal analyzer (STA) over a temperature range of 20–400°C, at the heating rates of 5, 10, 20, and 40°C/min. All the experiments have been conducted under argon gas environment and then repeated with dried air as the purge gas. All samples show the melting transition followed by the vaporization indicated by the weight loss. The activation energy calculated from the weight loss data has been compared with the enthalpy of vaporization. Although a zero order transition fits well with a reaction order model, the kinetics of vaporization does not follow this model.