scispace - formally typeset
Search or ask a question

Showing papers in "Industrial & Engineering Chemistry Research in 1996"


Journal ArticleDOI
TL;DR: In this article, an equation of state (EoS) suitable for describing associating fluids is presented, which combines the simplicity of the Soave−Redlich−Kwong equation for the physical part and the theoretical background of the perturbation theory employed for the chemical part.
Abstract: An equation of state (EoS) suitable for describing associating fluids is presented. The equation combines the simplicity of a cubic equation of state (the Soave−Redlich−Kwong), which is used for the physical part and the theoretical background of the perturbation theory employed for the chemical (or association) part. The resulting EoS (Cubic Plus Association) is not cubic with respect to volume and contains five pure compound parameters which are determined using vapor pressures and saturated liquid densities. Excellent correlations of both vapor pressures and saturated liquid volumes are obtained for primary-alcohols (from methanol up to 1-tridecanol), phenol, tert-butyl alcohol, triethylene glycol, and water. Moreover, excellent prediction of saturated liquid volumes may be obtained from parameters which have been estimated by regressing only vapor pressures. Finally, we suggest a method for reducing the number of adjustable parameters for alcohols to three while maintaining the good correlation of vap...

834 citations


Journal ArticleDOI
TL;DR: In this paper, the equivalence ratio (from 0.20 to 0.45), temperatures of the gasifier bed (750−850 °C) and of its freeboard (500−600 °C), H/C ratio in the feed, use of secondary air (10% of the overall) in the freeboard, and addition (2−5 wt %) of a calcined dolomite mixed with the biomass used as the feedstock.
Abstract: Biomass gasification with air in a bubbling fluidized bed is studied in a small pilot plant. Variables analyzed are equivalence ratio (from 0.20 to 0.45), temperatures of the gasifier bed (750−850 °C) and of its freeboard (500−600 °C), H/C ratio in the feed, use of secondary air (10% of the overall) in the freeboard, and addition (2−5 wt %) of a calcined dolomite mixed with the biomass used as the feedstock. Using advanced tar and gas sampling and analysis methods, the gas composition and tar content in the gas are determined and their variation with the operation parameters is given. A statistical analysis of the effects of the gasification variables is also here presented.

617 citations


Journal ArticleDOI
TL;DR: A comprehensive overview of recent advances in the field of MCM-41 molecular sieves is presented in this article, with a focus on the chemistry of surfactant/silicate solutions.
Abstract: The discovery of mesoporous molecular sieves, MCM-41, which possesses a regular hexagonal array of uniform pore openings, aroused a worldwide resurgence in this field. This is not only because it has brought about a series of novel mesoporous materials with various compositions which may find applications in catalysis, adsorption, and guest-host chemistry, but also it has opened a new avenue for creating zeotype materials. This paper presents a comprehensive overview of recent advances in the field of MCM-41. Beginning with the chemistry of surfactant/silicate solutions, progresses made in design and synthesis, characterization, and physicochemical property evaluation of MCM-41 are enumerated. Proposed formation mechanisms are presented, discussed, and identified. Potential applications are reviewed and projected. More than 100 references are cited.

556 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of temperature, pressure, reactant concentration, weight hourly space velocity, and the type of catalyst on the gasification of glucose are reported, and complete conversion of glucose (22% by weight in water) to a hydrogen-rich synthesis gas was realized at a weight hourly velocity (WHSV) of 22.2 h-1 in supercritical water at 600 °C, 34.5 MPa.
Abstract: Spruce wood charcoal, macadamia shell charcoal, coal activated carbon, and coconut shell activated carbon catalyze the gasification of organic compounds in supercritical water. Feedstocks studied in this paper include glycerol, glucose, cellobiose, whole biomass feedstocks (depithed bagasse liquid extract and sewage sludge), and representative Department of Defense (DoD) wastes (methanol, methyl ethyl ketone, ethylene glycol, acetic acid, and phenol). The effects of temperature, pressure, reactant concentration, weight hourly space velocity, and the type of catalyst on the gasification of glucose are reported. Complete conversion of glucose (22% by weight in water) to a hydrogen-rich synthesis gas was realized at a weight hourly space velocity (WHSV) of 22.2 h-1 in supercritical water at 600 °C, 34.5 MPa. Complete conversions of the whole biomass feeds were also achieved at the same temperature and pressure. The destruction efficiencies for the representative DoD wastes were also high. Deactivation of the...

391 citations


Journal ArticleDOI
TL;DR: In this paper, a mass transfer model was proposed for a variety of commercial structured packings for distillation column service with distillation pressures ranging from 0.33 to 20.4 bar.
Abstract: This is the second part of a two-part paper dealing with the fluid mechanics and mass transfer in structured packings for distillation column service. The first part elucidated pressure drop, flooding, and liquid holdup. The second part covers the generation of effective interfacial area and provides a general correlation for predicting the mass-transfer efficiency as a function of surface type, packing geometry, phase flow conditions, and fluid properties. The mass-transfer model has been tested against a variety of commercial structured packings, for distillation pressures ranging from 0.33 to 20.4 bar. In all cases the fit of the data is excellent, with the possible exception of the highest pressures, where additional factors of axial mixing appear to have an effect.

374 citations


Journal ArticleDOI
TL;DR: In this article, a mixed-integer optimization model is developed which relies on time discretization to solve the problem of inventory management of a refinery that imports several types of crude oil which are delivered by different vessels.
Abstract: This paper addresses the problem of inventory management of a refinery that imports several types of crude oil which are delivered by different vessels. This problem involves optimal operation of crude oil unloading, its transfer from storage tanks to charging tanks, and the charging schedule for each crude oil distillation unit. A mixed-integer optimization model is developed which relies on time discretization. The problem involves bilinear equations due to mixing operations. However, the linearity in the form of a mixed-integer linear program (MILP) is maintained by replacing bilinear terms with individual component flows. The LP-based branch and bound method is applied to solve the model, and several techniques, such as priority branching and bounding, and special ordered sets are implemented to reduce the computation time. This formulation and solution method was applied to an industrial-size problem involving 3 vessels, 6 storage tanks, 4 charging tanks, and 3 crude oil distillation units over 15 time intervals. The MILP model contained 105 binary variables, 991 continuous variables, and 2154 constraints and was effectively solved with the proposed solution approach.

313 citations


Journal ArticleDOI
TL;DR: In this paper, a novel combustor without flame is proposed by employing chemical-looping reactions, where NiO particles mixed with YSZ (yttria-stabilized zirconia) have very good properties for the oxygen carrier in the loop.
Abstract: A novel combustor without flame is proposed by employing chemical-looping reactions. Here we report the promising results on the novel combustor by kinetic and crystallographic study. We found that the NiO particles mixed with YSZ (yttria-stabilized zirconia) have very good properties for the oxygen carrier in the loop with respect to the reaction rate, conversion, and physical strength; especially the rate of oxidation of Ni is increased significantly. Furthermore, we observed that NOx was not generated in this combustor. Another significant feature, concerning the greenhouse impact, is that CO2 can easily be recovered.

313 citations


Journal ArticleDOI
TL;DR: In this paper, the thermochemistry of cellulose pyrolysis has been studied by a combination of differential scanning calorimetry and thermogravimetric analysis, and the vapor pressure and heat of vaporization of levoglucosan have been determined by an effusion method.
Abstract: The thermochemistry of cellulose pyrolysis has been studied by a combination of differential scanning calorimetry and thermogravimetric analysis. Additionally, the vapor pressure and heat of vaporization of levoglucosan have been determined by an effusion method. The cellulose pyrolysis has been carried out under inert gas at heating rates from 0.1 to 60 K/min. The main cellulose thermal degradation pathway is endothermic, in the absence of mass transfer limitations that promote char formation. The endothermicity is estimated to be about 538 J/g of volatiles evolved. It is concluded that this endothermicity mainly reflects a latent heat requirement for vaporizing the primary tar decomposition products. Pyrolysis can be driven in the exothermic direction by char-forming processes that compete with tar-forming processes. The formation of char is estimated to be exothermic to the extent of about 2 kJ/g of char formed. Low heating rates, in concert with mass transfer limitations, serve to drive the pyrolysis ...

307 citations


Journal ArticleDOI
TL;DR: In this article, a detailed reaction mechanism for the formation of crystalline elemental sulfur from aqueous sulfide by oxidation with transition-metal ions like VV, FeIII, CuII, etc.
Abstract: A detailed reaction mechanism is proposed for the formation of crystalline elemental sulfur from aqueous sulfide by oxidation with transition-metal ions like VV, FeIII, CuII, etc. The first step is the formation of HS• radicals by one-electron oxidation of HS- ions. These radicals exist at pH values near 7 mainly as S•-. Their spontaneous decay results in the formation of the disulfide ion S22-. The further oxidation of disulfide either by S•- radicals or by the transition-metal ions yields higher polysulfide ions from which the homocyclic sulfur molecules S6, S7, and S8 are formed. In water these hydrophobic molecules form clusters which grow to droplets of liquid sulfur (sulfur sol). Depending on the composition of the aqueous phase, crystallization of the liquid sulfur as either α- or β-S8 is rapid or delayed. Surfactants delay this solidification, while certain cations promote it. All these reactions are proposed to take place in desulfurization plants working by the Stretford, Sulfolin, Lo-Cat, SulFe...

284 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe experiments with hydrogen extraction membranes made of palladium-coated niobium and tantalum heat-exchanger tubes, and the fluxes were as high as 0.001 47 mol/m2 s Pa1/2 at 420 °C.
Abstract: Palladium-based membranes have been used for decades in hydrogen extraction because of their high permeability and good surface properties and because palladium, like all metals, is 100% selective for hydrogen transport. We describe experiments with hydrogen-extraction membranes made of palladium-coated niobium and tantalum heat-exchanger tubes. The cost was about $45/ft of 3/8 in. tubular membrane, and the fluxes were as high as 0.001 47 mol/m2 s Pa1/2 at 420 °C. The main transport resistance is in the refractory metal substrate. Durability tests showed a 15% reduction in flux for 31 days of continuous membrane operation. Assuming durability is maintained for at least 1 year, this price and flux should allow competitive application for hydrogen recovery in petrochemical plants and for membrane reactors.

266 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the performance of a vacuum pyrolysis and an inert purging method on a polyimide precursor material and found that the purging process produced more selective but less productive carbon molecular sieve membranes.
Abstract: In previous research, carbon molecular sieve (CMS) membranes for gas separations have been produced using either a vacuum pyrolysis or an inert purge pyrolysis technique on a precursor which is often polymeric. This study compares both techniques using the same polyimide precursor material. Additional pyrolysis variables included the type of “inert” purge gas (argon, helium, and carbon dioxide), purge flow rate, and temperature. Vacuum pyrolysis produced more selective but less productive CMS membranes than the inert purge pyrolyzed membranes. “High” purge gas flow rates (i.e., 200 standard cubic centimeters per minute or cm3(STP)/min) produced a much higher permeability, but lower selectivity membrane compared to those produced in a “low” purge flow rate (20 cm3(STP)/min). By raising the pyrolysis temperature from 550 to 800 °C, the effective pore size was reduced, thereby making the CMS membranes more selective but less productive. Mixed gas tests using oxygen/nitrogen and hydrogen/nitrogen mixtures wer...

Journal ArticleDOI
TL;DR: A combinatorial library of catalyst candidates, each consisting of a different metal element supported on γ-alumina, is screened for hydrogen oxidation catalytic activity by noninvasive IR thermography as mentioned in this paper.
Abstract: A combinatorial library of catalyst candidates, each consisting of a different metal element supported on γ-alumina, is screened for hydrogen oxidation catalytic activity Heat liberated on the surface of active catalysts by the catalyzed reaction is detected by noninvasive IR thermography A 16-candidate library identifies four distinctly active pellets, which correspond to active formulations known from the literature A higher density library shows similar results, but heat and mass transport effects influence the pellet temperatures This method may be used to screen and optimize catalyst formulations more efficiently and quickly than current methods and may also be useful for study of operational lifetime, resistance to poisons, and regenerability

Journal ArticleDOI
TL;DR: In this article, the coupled effects of particle size and external heating conditions (reactor heating rate and final temperature) on cellulose pyrolysis were investigated by means of a computer model accounting for all main transport phenomena, variable thermophysical properties and primary, and secondary reaction processes.
Abstract: The coupled effects of particle size and external heating conditions (reactor heating rate and final temperature) on cellulose pyrolysis are investigated by means of a computer model accounting for all main transport phenomena, variable thermophysical properties and primary, and secondary reaction processes. The dynamics of particle conversion are predicted, and final product distributions are favorably compared with experimental measurements. A map is constructed, in terms of particle size as a function of the reactor temperature, to identify the transition from a kinetically controlled conversion to a heat transfer controlled conversion (thermally thin and thermally thick regimes) and from flash to slow-conventional pyrolysis. Conditions for maximizing oil, gas, or char yields are also discussed.

Journal ArticleDOI
TL;DR: In this article, the authors reviewed catalytic enhancement and technology as related to supercritical water oxidation (SCWO) and analyzed the effects of SCW on catalysts and catalytic SCWO processes.
Abstract: Recently, catalytic oxidation in supercritical water (SCW) has received considerable research attention. The major thrust of this current research effort is attributable to the rapid development of supercritical water oxidation (SCWO) as an innovative wastewater treatment technology. The incentives of catalyst-enhanced processes may include increased reaction rates, reduced residence times and temperatures, and optimized reaction pathways that are otherwise difficult to achieve through noncatalytic processes. However, the databases associated with the use of catalysts in SCWO are limited. The purpose of this paper is to (1) review catalytic enhancement and technology as related to SCWO; (2) analyze effects of SCW on catalysts and catalytic SCWO processes; and (3) present a catalyst development strategy for SCWO-related applications. Catalyst activity and stability (in terms of reaction kinetics, surface phenomena, and phase behavior of catalysts in SCW) are emphasized. The paper presents a useful database...

Journal ArticleDOI
TL;DR: It is shown that multiway principal component analysis (MPCA) can be used to identify major sources of variability in the processing steps and correlations between the variations in theprocessing steps and the final product properties are found, and recommendations to reduce the sources of variations are discussed.
Abstract: Producing a uniform polymer by batch processing is important for the following reasons: to improve the downstream processing performance, to enable material produced at one site to be used by another, and to remain competitive Eliminating the sources of batch-to-batch variability and tightening the control of key variables are but two ways to accomplish these objectives In this work, it is shown that multiway principal component analysis (MPCA) can be used to identify major sources of variability in the processing steps The results show that the major source of batch-to-batch variability is due to reactor temperature variations arising from disturbances in the heating system and other heat-transfer limitations Correlations between the variations in the processing steps and the final product properties are found, and recommendations to reduce the sources of variations are discussed

Journal ArticleDOI
TL;DR: In this article, a high-gravity vapor−liquid contactor (Higee) was studied under distillation conditions using a semi-works scale system, where the cyclohexane/nheptane test mixture was used at operating pressures of 166 and 414 kPa and under total reflux conditions.
Abstract: A high-gravity vapor−liquid contactor (“Higee”) was studied under distillation conditions using a semiworks scale system. The cyclohexane/n-heptane test mixture was used at operating pressures of 166 and 414 kPa and under total reflux conditions. Rotational speeds ranged from 400 to 1200 rpm. Data were collected on mass transfer efficiency, pressure drop, and hydraulic capacity. As many as six transfer units were achieved in a bed depth of 21 cm, with efficiency being directly proportional to speed of rotation. Models were developed for mass transfer and pressure drop, and the earlier packed bed flooding model of Sherwood, which includes a gravity term, was found to represent the vapor capacity of the contactor. Sufficient information is given to enable the preliminary design of a system containing a high-gravity vapor−liquid contactor. Because the test mixture has been widely used for conventional contactor studies, means for comparing high-gravity contacting with other methods are now available.

Journal ArticleDOI
TL;DR: In this article, the life cycle of calcined dolomites, limstones, and magnesites is studied at different temperatures (800−880 °C), space times (0.08−0.13 kg·h/nm3), particle diameters (1−4 mm), and types of solid.
Abstract: Calcined dolomites, limestones, and magnesites are active and inexpensive solids for cleaning raw hot gas from biomass gasifiers with steam. The variations of their activities with time-on-stream are studied here. Simultaneous coke formation and coke elimination by steam gasification increases the life of these “naturally occurring” catalysts under some circumstances. The lives of these solids are studied at different temperatures (800−880 °C), space times (0.08−0.32 kg of dolomite·h/nm3), particle diameters (1−4 mm), and types of solid. Not much deactivation was observed for tar concentration in the raw gas below 48 g/nm3, particle diameters of less than 1.9 mm, temperatures above 800 °C, and space times above 0.13 kg·h/nm3. The effectiveness of these calcined minerals is compared with that of an inert material (silica sand) and with a commercial steam reforming catalyst (R-67 from Haldor Topsoe).

Journal ArticleDOI
TL;DR: This paper develops a two-stage stochastic programming approach for process planning under uncertainty by extending a deterministic mixed-integer linear programming formulation to account for the presence of discrete random parameters and devise a decomposition algorithm for the solution of the Stochastic model.
Abstract: This paper develops a two-stage stochastic programming approach for process planning under uncertainty. We first extend a deterministic mixed-integer linear programming formulation to account for t...

Journal ArticleDOI
TL;DR: Based on the similarity analysis between the spherical and nonspherical particle packings, a mathematical model, modified from the previous linear packing model for spherical particles, is proposed for predicting the porosity of non-pregnant particle mixtures.
Abstract: Based on the similarity analysis between the spherical and nonspherical particle packings, a mathematical model, modified from the previous linear packing model for spherical particles, is proposed for predicting the porosity of nonspherical particle mixtures. The background for this development is discussed in detail. The applicability of the proposed model is validated by the good agreement between the measured and calculated results for various packing systems including binary, ternary, and multicomponent packing of spherical and/or nonspherical particles.

Journal ArticleDOI
TL;DR: In this paper, a comparison of the gas transport properties of three different classes of materials highlights the importance of ''entropic selectivity'' which has hitherto not been focused on for membrane-based separation of gases.
Abstract: Commercial polymeric gas separation membranes exhibit a trade-off between productivity and selectivity. However, on this same trade-off curve molecular sieving materials like zeolites and carbon molecular sieves (CMS) lie above the upper bound for polymers. A comparison of the gas transport properties of these three different classes of materials highlights the importance of ``entropic selectivity`` which has hitherto not been focused on for membrane-based separation of gases. A whole new generation of polymeric membrane materials may result from enhancement of entropic selectivity of polymeric membrane materials.

Journal ArticleDOI
TL;DR: In this paper, the solubility of the single gases carbon dioxide and hydrogen sulfide in aqueous solutions of 2,2'methyliminodiethanol (N-methyldiethenolamine (MDEA)) at temperatures between 313 and 413 K and total pressures up to 5 MPa are reported.
Abstract: Experimental results for the solubility of the single gases carbon dioxide and hydrogen sulfide in aqueous solutions of 2,2‘-methyliminodiethanol (N-methyldiethanolamine (MDEA)) at temperatures between 313 and 413 K and total pressures up to 5 MPa are reported. A model taking into account chemical reactions as well as physical interactions is used to correlate the new data. The correlation is also used to compare the new experimental data with literature data.

Journal ArticleDOI
TL;DR: In this paper, the phase equilibria of the n-alkanes and the 1-alkanols were calculated with the Lennard-Jones−SAFT (statistical association fluid theory) equation of state of Muller and Gubbins.
Abstract: The phase equilibria of the n-alkanes and the 1-alkanols have been calculated with the Lennard-Jones−SAFT (statistical association fluid theory) equation of state of Muller and Gubbins. This equation includes contributions from a dipole−dipole term, a modified association term, a chain term, and a Lennard-Jones term to account for monomer dispersion and overlap interactions. The influence of electrostatic forces due to the dipole moment has been investigated, and a simple treatment of the polarizability has been tested. It is shown by comparison with some sample calculations based on the renormalized perturbation theory that this approach is reasonable. The calculated phase equilibria are in good agreement with experimental data. The deviation between calculated and experimental data is significantly lower than for the original SAFT equation of state and a recently published chemical theory.

Journal ArticleDOI
TL;DR: In this article, a methodology is presented for the study of the void space structure of consolidated calcium carbonate paper-coating formulations and compressible polymer spheres, using mercury porosimetry.
Abstract: A methodology is presented for the study of the void space structure of consolidated calcium carbonate paper-coating formulations and compressible polymer spheres, using mercury porosimetry. Two limitations of mercury porosimetry are addressed: first, that the shrinkage of compressible samples causes an apparent increase in void volume, and, second, that large void spaces shielded by smaller ones are not intruded until anomalously high applied pressures of mercury are reached. The first limitation is overcome by means of a new correction procedure which, uniquely, also allows the measurement of the bulk modulus of the continuous solid phase of a porous sample. Shielding effects are taken into account by means of our software package known as Pore-Cor, which generates a three-dimensional structure which has both a mercury intrusion curve and porosity in close agreement with experiment. The simulated permeabilities provide realistic and useful values, which cannot be measured experimentally.

Journal ArticleDOI
TL;DR: In this article, sugar-cane bagasse and leaves (10−15 g oven-dry basis) were fractionated without size reduction by a rapid (45 s to 4 min), immersed percolation using only hot (190−230 °C), compressed (P > Psat), liquid water (0.6−1.2 kg).
Abstract: Sugar-cane bagasse and leaves (10−15 g oven-dry basis) were fractionated without size reduction by a rapid (45 s to 4 min), immersed percolation using only hot (190−230 °C), compressed (P > Psat), liquid water (0.6−1.2 kg). Over 50% of the biomass could be solubilized. All of the hemicellulose, together with much of the acid-insoluble lignin in the bagasse (>60%), was solubilized, while less than 10% of the cellulose entered the liquid phase. Moreover, recovery of the hemicellulose as monomeric sugars (after a mild posthydrolysis) exceeded 80%. Less than 5% of the hemicellulose was converted to furfural. Percolation beyond that needed to immerse the biomass in hot liquid water did not result in increased solubilization. The yield of lignocellulosic residue was also not sensitive to the form of the sugar cane used (bagasse or leaves) or its moisture content (8−50%). Commercial applications for this fractionation process include the pretreatment of lignocellulosics for bioconversion to ethanol and the produ...

Journal ArticleDOI
TL;DR: In this article, the extraction rate of oil from freeze-dried ginger root with supercritical carbon dioxide was measured as a function of CO2 flow rate, particle size, temperature, and pressure.
Abstract: The extraction rate of oil from freeze-dried ginger root with supercritical carbon dioxide was measured as a function of CO2 flow rate, particle size, temperature, and pressure. The extraction curv...

Journal ArticleDOI
TL;DR: In this paper, a stepwise procedure is proposed to obtain such distillation configurations, and a series of observations are presented which make the task of generating these configurations a little easier. But, for n ≥ 4, some of these configurations are missing from the known superstructures in the literature.
Abstract: Thermally linked distillation column configurations to separate near-ideal multicomponent mixtures containing four or more components are discussed. It is shown that for sharp separation of an n-component mixture using only one reboiler and one condenser the minimum number of rectifying and stripping sections needed is 4n − 6. A stepwise procedure is proposed to obtain such distillation configurations, and a series of observations are presented which make the task of generating these configurations a little easier. It is found that, for n ≥ 4, some of these distillation configurations are missing from the known superstructures in the literature. An alternative method is proposed to obtain an n-component superstructure. The resulting superstructure has all the earlier known configurations embedded within it and contains the substructures incorporating the missing configurations. This provides a more complete superstructure for the optimization task.

Journal ArticleDOI
TL;DR: In this article, a method for the preparation of macroporous chitosan and chitin membranes, which employs silica particles as porogen, was suggested, and the results showed that the pore sizes of the chitusan membranes can be easily controlled by varying the size of the particles.
Abstract: A novel method for the preparation of macroporous chitosan and chitin membranes is suggested, which employs silica particles as porogen. The macroporous chitosan membranes were prepared by (1) casting an acidic chitosan solution that contains silica particles, (2) removing the solvent by evaporation, and (3) dissolving the silica particles by immersing the membranes into an alkaline solution. This simple method provides chitosan membranes with high porosity and satisfactory mechanical strength, the pore sizes of which can be easily controlled by varying the size of silica particles. The effects of various evaporation conditions and amount of silica on the flow rate of water through the membranes were investigated. In order to prevent their dissolution in acidic solutions, the chitosan membranes were cross-linked under alkaline conditions, using epichlorohydrin as the cross-linking agent. Macroporous chitin membranes were prepared by acetylating the chitosan membranes with acetic anhydride in methanol. In ...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the relationship between the particle growth rate and tetraethylorthosilicate (TEOS) hydrolysis and condensation rate with reaction condition variables, such as temperature, NH3 concentration and H2O concentration.
Abstract: Kinetic studies of the hydrolysis and condensation of tetraethylorthosilicate (TEOS) during the formation of uniform silica particles were performed through determining concentrations of TEOS and silicic acid by means of gas chromatography and a conductometer, respectively. It was shown that both hydrolysis of TEOS and condensation of Si(OH)4 are first order with TEOS and Si(OH)4, respectively, and the relationships of the hydrolysis and condensation rate constants with reaction condition variables, such as temperature, NH3 concentration, and H2O concentration, were determined. In addition, the particle growth rate was investigated with relation to the hydrolysis and condensation kinetics. Experiments showed that, during most of the reaction, the amount of formed particles is less than that of consumed TEOS, indicating that reaction intermediates exist during the process of silica formation. In the early stages of the Stober process, the reaction intermediates include silicic acid and subparticles, while ...

Journal ArticleDOI
TL;DR: In this article, a BPDA-pp'ODA polyimide film was formed on the outer surface of a porous alumina support tube (outside diameter, 2.4 mm; inside diameter, 1.8 mm; void fraction, 0.48; and average pore size, 140 nm) and was then carbonized at an optimized temperature of 700 °C.
Abstract: A BPDA−pp‘ODA polyimide film was formed on the outer surface of a porous alumina support tube (outside diameter, 2.4 mm; inside diameter, 1.8 mm; void fraction, 0.48; and average pore size, 140 nm) and was then carbonized at an optimized temperature of 700 °C. Membranes prepared by repeating this process two and three times respectively exhibited permeances of approximately 1 × 10-8 mol·m-2·s-1·Pa-1 for C2H4 and 2 × 10-9 mol·m-2·s-1·Pa-1 for C2H6 at 100 °C. Permeances to C3H6 and C3H8 at 100 °C were 4 × 10-9 and 1 × 10-10 mol·m-2·s-1·Pa-1, respectively. The selectivities were 4−5 for C2H4/C2H6 systems and 25−29 for C3H6/C3H8 systems. When the permeation temperature was decreased to 65 and 35 °C, permeances decreased and selectivities increased to 5−7 for C2H4/C2H6 systems and 33−56 for C3H6/C3H8 systems. The permeance and selectivity for an equimolar mixture of C3H6 and C3H8 were nearly the same as those for the single-component gases.

Journal ArticleDOI
TL;DR: In this paper, a numerical model for endothermic biomass pyrolysis, which includes both high activation energy kinetics and heat transfer across a boundary layer to the reacting solid particle, is presented.
Abstract: Results from a numerical model for endothermic biomass pyrolysis, which includes both high activation energy kinetics and heat transfer across a boundary layer to the reacting solid particle, are presented. The model accounts for conventional thermocouple thermal lag and unconventional thermal lag due to heat demand by the chemical reaction (which is governed by Arrhenius kinetics). Biomass fusion, first identified quantitatively by Lede and Villermaux, is shown to be a manifestation of severe thermal lag that results from the chemical reaction heat demand. Over the wide range of conditions studied, the true substrate temperature remains almost constant during pyrolysis, as is the case with compounds undergoing fusion or sublimation at constant pressure. A simple algebraic model, whose derivation presupposes the idea that biomass pyrolysis mimics the melting of a block of ice, accurately predicts the maximum value of thermal lag during pyrolysis. Unidentified thermal lag in TGA experiments lowers the valu...