Showing papers in "Industrial & Engineering Chemistry Research in 2000"
TL;DR: In this paper, microcrystalline cellulose decomposition experiments were conducted in subcritical and supercritical water (25 MPa, 320−400 °C, and 0.05−10.0 s).
Abstract: Decomposition experiments of microcrystalline cellulose were conducted in subcritical and supercritical water (25 MPa, 320−400 °C, and 0.05−10.0 s). At 400 °C hydrolysis products were mainly obtained, while in 320−350 °C water, aqueous decomposition products of glucose were the main products. Kinetic studies of cellulose, cellobiose, and glucose at these conditions showed that below 350 °C the cellulose decomposition rate was slower than the glucose and cellobiose decomposition rates, while above 350 °C, the cellulose hydrolysis rate drastically increased and became higher than the glucose and cellobiose decomposition rates. Direct observation of the cellulose reaction in high-temperature water at high-pressure conditions by using a diamond anvil cell (DAC) showed that, below 280 °C, cellulose particles became gradually smaller with increasing reaction time but, at high temperatures (300−320 °C), cellulose particles disappeared with increasing transparency and much more rapidly than expected from the lowe...
665 citations
TL;DR: In this article, the crown ethers were used as extractants in RTIL-based liquid/liquid separations, and the resulting metal ion partitioning depends on the hydrophobicity of the crown and also on the composition of the aqueous phase (e.g., concentration of HNO3 vs Al(NO3)3).
Abstract: The crown ethers 18-crown-6 (18C6), dicyclohexano-18-crown-6 (DCH18C6), and 4,4‘-(5‘)-di-(tert-butylcyclohexano)-18-crown-6 (Dtb18C6) were dissolved in 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6], n = 4, 6, 8) room-temperature ionic liquids (RTILs) and studied for the extraction of Na+, Cs+, and Sr2+ from aqueous solutions. In the absence of extractant, the distribution ratios for the metal ions indicate a strong preference for the aqueous phase. With the crown ethers as extractants in RTIL-based liquid/liquid separations, the resulting metal ion partitioning depends on the hydrophobicity of the crown ether and also on the composition of the aqueous phase (e.g., concentration of HNO3 vs Al(NO3)3). Aqueous solutions of HCl, Na3 citrate, NaNO3, and HNO3 (the latter at low concentrations) decrease the metal ion distribution ratios and also decrease the water content of the RTIL phase. High concentrations of HNO3 decompose PF6- and increase both the water content and the water solubility of ...
601 citations
TL;DR: In this paper, three different tubular flow reactors were used to produce high yields of gas with a high content of hydrogen (57 mol %) at the highest temperatures employed in this work, and all three reactors plugged after 1−2 h of use with feedstocks.
Abstract: Biomass feedstocks, including corn- and potato-starch gels, wood sawdust suspended in a cornstarch gel, and potato wastes, were delivered to three different tubular flow reactors by means of a “cement” pump. When rapidly heated to temperatures above 650 °C at pressures above the critical pressure of water (22 MPa), the organic content of these feedstocks vaporized. A packed bed of carbon within the reactor catalyzed the gasification of these organic vapors in the water; consequently, the water effluent of the reactor was clean. The gas was composed of hydrogen, carbon dioxide, methane, carbon monoxide, and traces of ethane. Its composition was strongly influenced by the peak temperature of the reactor and the condition of the reactor's wall. Extraordinary yields (>2 L/g) of gas with a high content of hydrogen (57 mol %) were realized at the highest temperatures employed in this work. Irrespective of the reactor geometry and method of heating, all three reactors plugged after 1−2 h of use with feedstocks t...
592 citations
TL;DR: In this article, a laboratory-scale packed-bed reactor system is used to screen sorbents for their capability to remove elemental mercury from various carrier gases when the carrier gas is argon, an on-line atomic fluorescence spectrophotometer (AFS), used in a continuous mode, monitors the elemental mercury concentration in the inlet and outlet streams of the packed bed reactor.
Abstract: A laboratory-scale packed-bed reactor system is used to screen sorbents for their capability to remove elemental mercury from various carrier gases When the carrier gas is argon, an on-line atomic fluorescence spectrophotometer (AFS), used in a continuous mode, monitors the elemental mercury concentration in the inlet and outlet streams of the packed-bed reactor The mercury concentration in the reactor inlet gas and the reactor temperature are held constant during a test For more complex carrier gases, the capacity is determined off-line by analyzing the spent sorbent with either a cold vapor atomic absorption spectrophotometer (CVAAS) or an inductively coupled argon plasma atomic emission spectrophotometer (ICP-AES) The capacities and breakthrough times of several commercially available activated carbons as well as novel sorbents were determined as a function of various parameters The mechanisms of mercury removal by the sorbents are suggested by combining the results of the packed-bed testing with
521 citations
TL;DR: In this paper, a new paradigm is recommended for matrix phase selection, guided by the need to optimize both the transport properties of the interfacial region and the matrix material selection criteria noted above, which leads to the formation of mixed-matrix membranes with an appropriate polymer and sieve.
Abstract: Prior work has suggested simple guidelines for matching transport characteristics of materials to form high-performance mixed-matrix materials for gas separation. Such materials comprise a dispersion of molecular sieving particles in a properly selected matrix polymer phase. Recent work has shown that these simple criteria are necessary but not sufficient to achieve the desired properties. The analysis presented here shows the need to optimize the transport properties of the interfacial region, i.e., the region between the bulk polymer and dispersed sieve phases. Guided by the need to optimize both the transport properties of the interfacial region and the matrix material selection criteria noted above, a new paradigm is recommended for matrix phase selection. The practicality of the paradigm is validated by the formation of mixed-matrix membranes with an appropriate polymer and sieve. These materials lead to the attractive predicted performances at low loading. For success at higher loading a zeolite “pr...
485 citations
TL;DR: In this article, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high gravity conditions, is presented for the massive production of nanoparticles.
Abstract: On the basis of the analysis of key engineering factors predominating in a reactive precipitation process, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high-gravity conditions, is presented here for the massive production of nanoparticles. A rotating packed-bed reactor was designed to generate acceleration higher than the gravitational acceleration on Earth. The syntheses of nanoparticles of CaCO3, aluminum hydroxide, and SrCO3 were employed to demonstrate the advantages and industrial potentials of this technology, where the typical gas−liquid−solid, gas−liquid, and liquid−liquid multiphase reaction systems were involved. Experimental results show that the mean size of CaCO3 particles can be controlled and adjusted in the range of 17−36 nm through the change of operation conditions such as high-gravity levels, fluid flow rates, and reactant concentrations. Nanofibrils of aluminum hydroxide of 1−10 nm in diameter and 50−300 nm in le...
414 citations
TL;DR: In this article, a supercritical water-light gas (O 2, H 2, etc) system and reaction equilibrium/rate can be varied to synthesize new materials or define particle morphologies.
Abstract: Supercritical water can provide an excellent reaction environment for hydrothermal crystallization of metal oxide particles. Because of the drastic change of properties of water around the critical point, density, dielectric constant, and ionic product, the phase behavior for the supercritical water-light gas (O 2 , H 2 , etc) system and reaction equilibrium/rate can be varied to synthesize new materials or define particle morphologies. In this work, hydrothermal crystallization experiments were performed with several types of flow apparatuses that allow convenient manipulation of variables such as temperature, pressure, and residence time. The proposed supercritical hydrothermal synthesis method has the following desirable features: (1) ultrafine particles can be produced, (2) morphology of the produced particles can be controlled with small changes in pressure or temperature, and (3) a reducing or oxidizing atmosphere can be applied by introducing oxygen, hydrogen, or other gases. An overview of this method is given for functional material synthesis of significant industrial interest including barium hexaferrite magnetic particles, YAG/Tb phosphor fine particles, and lithium cobalt fine crystals.
378 citations
TL;DR: In this article, the authors present a number of applications of supercritical fluids that are either under investigation or already at commercial scale in various areas, such as supercritical fluid extraction and fractionation.
Abstract: After 2 decades of development of extraction/fractionation processes mainly dedicated to natural products, many “new” applications of supercritical fluids are now either under investigation or already at commercial scale in various areas.
362 citations
TL;DR: In this article, the role of mass transfer in the rate of reaction and selectivity for the desired product is discussed, and different types of reactors that are used, including bubble-column and mechanically agitated, are analyzed, and a simple basis is provided for selection of reactors.
Abstract: Liquid-phase air oxidation of hydrocarbons, notably p-xylene, cumene, ethylbenzene/isobutane, cyclohexane, and n-butane, is of great scientific, technological, and commercial importance. This state-of-the-art paper covers the chemistry and engineering science aspects of these reactions. The role of uncatalyzed reactions and metal ion and mixed metal ion catalysts with bromide activation is discussed. An analysis is presented for the role of mass transfer in influencing the rate of reaction and selectivity for the desired product. Different types of reactors that are used, notably bubble-column reactors and mechanically agitated reactors, are analyzed, and a simple basis is provided for selection of reactors. Some emerging oxidation systems, notably oxidation of cycloalkenes (cyclohexene/cyclooctene/cyclododecene) and oxidation of isobutane under supercritical conditions, are presented. New strategies for conducting air oxidations, such as in biphasic systems (including fluorous biphasic systems), biocatalysis, photocatalysis, etc., are emerging and illustrate the considerable tailoring of the reaction microenvironment that is becoming possible. In some cases, it may be possible to manipulate chemo-, regio-, and enantioselectivity in these reactions.
334 citations
TL;DR: The reaction kinetics and chemical equilibrium of the reversible esterification of methanol with acetic acid were investigated in this article, where a simple power-law model was proposed to describe the reaction.
Abstract: The reaction kinetics and chemical equilibrium of the reversible esterification of methanol with acetic acid were investigated. This system is of major importance as a model reaction for reactive distillation. The reaction has been catalyzed both homogeneously by acetic acid itself and heterogeneously by an acidic ion-exchange resin (Amberlyst 15). The chemical equilibrium composition was measured for various temperatures and starting compositions of the reactants and products. Kinetic information was obtained at temperatures between 303.15 and 343.15 K at various starting compositions covering concentration ranges from the stoichiometric regime to the dilute regions. Both the esterification and the hydrolysis reaction were investigated to yield a model which is applicable for any starting composition. The homogeneous reaction has been described with a simple power-law model. The use of activities in the kinetic model instead of mole fractions results in a much smaller residual error. To compare pseudohom...
320 citations
TL;DR: In this paper, the molar masses of Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO).
Abstract: Molar masses of both n-pentane-extracted and n-heptane-extracted Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO). The initial asphaltene ...
TL;DR: In this paper, a classical thermodynamic model for the equilibrium pressures of different guests of structure I and II gas hydrates is proposed that removes the need for reference energy parameters used in the van der Waals and Platteeuw (vdWP) type models.
Abstract: A classical thermodynamic model for the equilibrium pressures of different guests of structure I and II gas hydrates is proposed that removes the need for reference energy parameters used in the van der Waals and Platteeuw (vdWP) type models. The assumption of a constant crystal lattice for different guests within a structure, which is not in agreement with quantum chemistry calculations, is removed. This model uses published Kihara cell potential parameters determined from viscosity and second virial coefficient data, unlike previous models that fit these parameters to hydrate data. Quantum mechanical calculations were used to reduce the number of fitted parameters in the new model. This model greatly improves upon the accuracy of previous models and is applicable over a wide temperature range. Percent absolute average deviations in the predicted equilibrium pressures is 3.27% with two or three guest-hydrate specific parameters compared to more than 11% with three adjustable parameters in the vdWP type m...
TL;DR: In this article, the dissolution rate of racemic ibuprofen in supercritical CO2 was measured using a dynamic apparatus at pressures between 80 and 220 bar and temperatures of 35, 40, and 45 °C.
Abstract: The dissolution of a drug into the biological environment can be enhanced by reducing the particle size of the drug. In this study the rapid expansion of supercritical solutions (RESS) process was employed to micronize racemic ibuprofen, and the dissolution rate of the micronized product in a buffered solution was examined. The chiral nonsteroidal antiinflammatory, racemic ibuprofen, was used as a model drug because its dissolution rate is limited by its poor solubility in water. The phase behavior of the ibuprofen−CO2 binary system was investigated prior to the solubility measurements being undertaken. The solubility of racemic ibuprofen in supercritical CO2 was measured using a dynamic apparatus at pressures between 80 and 220 bar and temperatures of 35, 40, and 45 °C. The solubility data was modeled using the Peng−Robinson equation of state with van der Waals mixing rules. The ratio of R and S isomers in the extract was found to be the same as that in the original material. The solubility of pure optic...
TL;DR: In this paper, pyrocatechol is used as a model compound for lignin in biomass and for aromatic compounds in wastewaters, and experiments were carried out in two different reactor types, a batch and a tubular reactor, to achieve long reaction times at low temperatures as well as short reaction time at high temperatures.
Abstract: The results presented are fundamental investigations with regard to developing a process for hydrogen production from high moisture biomass and wastewater. Pyrocatechol is used as a model compound for lignin in biomass and for aromatic compounds in wastewaters. The experiments of pyrocatechol gasification provides knowledge of the chemical reactions occurring during gasification and their dependence on reaction conditions. The experiments were carried out in two different reactor types, a batch and a tubular reactor, to achieve long reaction times at low temperatures as well as short reaction times at high temperatures. The pressure, temperature, concentration, and reaction time dependence of the gasification is presented and compared with calculated equilibrium data. The influence of potassium hydroxide addition to improve the hydrogen yield was studied and the effect of different catalysts is discussed.
TL;DR: A new method is presented that closes the gap considerably in early SHE assessment because of the lack of substance data and process information, especially when batch processes are considered.
Abstract: During chemical process development, potential safety, health, and environmental (SHE) hazards must be identified, analyzed, and managed as early as possible to avoid negative consequences (higher risks, higher costs, longer development times). The main problem of early SHE assessment is the lack of substance data and process information, especially when batch processes are considered. A new method is presented that closes this gap considerably. SHE aspects are assessed in 11 effect categories. For each substance of a given chemical process and each effect category, the most reliable data are selected out of a variety of different substance databases or estimation methods. After identifying SHE problems as dangerous properties, their magnitude is analyzed as potential of danger and can be reduced by technological measures. In this paper, first the goal and scope of the method is outlined. Then the detailed definitions of all categories as well as the exact way of combining information is presented and dis...
TL;DR: In this paper, the authors show that for some biomass species, the yield of carbon produced by this process effectively attains the theoretical value predicted to exist when thermochemical equilibrium is realized.
Abstract: Previous work has shown that very high yields of charcoal are obtained when pyrolysis of the biomass feedstock is conducted at elevated pressure in a closed vessel, wherein the pyrolytic vapors are held captive and in contact with the solid products of pyrolysis In this paper, we show that, for some biomass species, the yield of carbon produced by this process effectively attains the theoretical value predicted to exist when thermochemical equilibrium is realized Various agricultural wastes (eg, kukui nut, macadamia nut, and pecan shells) and tropical species (eg, eucalyptus, leucaena, and bamboo) offer higher yields of carbon than the hardwoods traditionally employed by industry in the US and Europe Moreover, the yields of carbon from oat and rice hulls and from sunflower seed hulls are nearly as high as the yields of carbon from hardwoods There is a correlation between the yield of carbon and the acid-insoluble lignin content of the feed Charcoal briquettes made from agricultural wastes and lump charcoal from tropical species are promising sources of renewable carbon for use in the smelting of metal ores
TL;DR: Subcolloidal (<0.1 μm) iron−silver (1% Ag) particles were synthesized for the transformation of chlorinated benzenes in aqueous solution as mentioned in this paper.
Abstract: Subcolloidal (<0.1 μm) iron−silver (1% Ag) particles were synthesized for the transformation of chlorinated benzenes in aqueous solution. Hexachlorobenzene (HCB) (4 mg/L) was dechlorinated to tetra...
TL;DR: In this paper, the pore-opening properties of both types of membranes were modeled, and the observed behavior for the auxetic membrane is consistent with the model, which confirms that the dominant deformation mechanism is flexure of the honeycomb ribs.
Abstract: Micromachined polymeric honeycomb membranes having conventional and re-entrant cell geometries have been fabricated using femtosecond laser ablation. Mechanical properties characterization confirms that the re-entrant membrane is auxetic (possesses negative Poisson's ratios: νxy = −1.82 ± 0.05 and νyx = −0.51 ± 0.01) whereas the conventional membrane possesses positive Poisson's ratios (νxy = +0.86 ± 0.06 and νyx = +0.6 ± 0.1). Comparison with honeycomb theory confirms that the dominant deformation mechanism is flexure of the honeycomb ribs. The auxetic membrane has been challenged with single-sized glass chromatography beads such that the beads were initially resting on the re-entrant cells. Subsequent tensile loading of the membrane showed the auxetic cells opening during deformation, enabling the beads to pass through the membrane. We have modeled the pore-opening properties of both types of membranes, and the observed behavior for the auxetic membrane is consistent with the model. This is a clear pro...
TL;DR: In this paper, the decomposition behavior of three types of wood, namely, bamboo, chinquapin, and Japan cedar, in hot-compressed water (HCW) was examined using a flow-type HCW flow type reactor to achieve the maximum utilization of plant biomass.
Abstract: Decomposition behaviors of bamboo, chinquapin (hardwood), and Japan cedar (softwood) in hot-compressed water (HCW) were examined using a HCW flow type reactor to achieve the maximum utilization of plant biomass. HCW was passed through the reactor (3.6 mL) loaded with the biomass sample powder (177−250 μm) at a flow rate of 10 mL/min under 9.8 MPa. The temperature of HCW was maintained at 180 °C for 20 min, after which it was raised to about 285 °C at a rate of 5 °C /min and maintained at 285 °C for about 7 min. By these operations, free sugars, some of lignin and most of hemicellulose, were first solubilized in water and flowed out during the initial 20 min flow of HCW. Cellulose started to decompose when the temperature of HCW was over 230 °C. The orders of elution of these components were common for three biomass samples, although the amount of products obtained during the heat-up period up to 180 °C and that of residue which finally remained in the reactor differed with the samples.
TL;DR: In this paper, the performance of a conical spouted bed reactor for flash pyrolysis of sawdust with an inert gas in the 350−700 °C range and with 50 ms of average gas residence time was studied.
Abstract: The performance of original equipment provided with a conical spouted bed reactor has been studied in flash pyrolysis of sawdust with an inert gas (N2) in the 350−700 °C range and with 50 ms of average gas residence time. The effect of pyrolysis temperature on the yields of gas, liquid, and char on gas and liquid composition and on char properties has been studied. The maximum yield of liquid (corresponding to 70 wt %) is obtained at 450 °C and its composition determined by GC/MS is similar to that reported in the literature for bubbling fluidized beds. Although temperatures above 600 °C are required for the development of the char porous structure, the yield of CO2 obtained under these conditions is unacceptable.
TL;DR: In this paper, the catalytic degradation of high-density polyethylene to hydrocarbons was studied over different zeolites, and the product range was typically between C3 and C15 hydrocarbon.
Abstract: The catalytic degradation of high-density polyethylene to hydrocarbons was studied over different zeolites. The product range was typically between C3 and C15 hydrocarbons. Distinctive patterns of product distribution were found with different zeolitic structures. Over large-pore ultrastable Y, Y, and β zeolites, alkanes were the main products with less alkenes and aromatics and only very small amounts of cycloalkanes and cycloalkenes. Medium-pore mordenite and ZSM-5 gave significantly more olefins. In the medium-pore zeolites secondary bimolecular reactions were sterically hindered, resulting in higher amounts of alkenes as primary products. The hydrocarbons formed with medium-pore zeolites were lighter than those formed with large-pore zeolites. The following order was found regarding the carbon number distribution: (lighter products) ZSM-5 < mordenite < β < Y < US-Y (heavier products). A similar order was found regarding the bond saturation: (more alkenes) ZSM-5 < mordenite < β < Y < US-Y (more alkan...
TL;DR: In this paper, a dielectric-barrier discharge (DBD) with zeolite catalysts is presented for direct higher hydrocarbon formation from the greenhouse gases methane and carbon dioxide.
Abstract: Direct higher hydrocarbon formation from the greenhouse gases methane and carbon dioxide using a dielectric-barrier discharge (DBD) with zeolite catalysts is presented. This catalytic DBD can be operated at ambient conditions and leads to direct hydrocarbon formation. The products include alkanes, alkenes, oxygenates, and syngas (CO + H{sub 2}). The product distribution depends on the pressure, the input power, the flow rate, the CH{sub 4}/CO{sub 2} feed ratio, and the catalyst used. It is not sensitive to gas temperature in the range from room temperature to 150 C. From the experiments it can be concluded that a cogeneration of syngas and higher hydrocarbons can be achieved using the catalytic DBD. The optimum CH{sub 4}/CO{sub 2} ratio in the feed for such cogeneration is in the range 2/1 to 3/1. The energy efficiency of CO{sub 2} and CH{sub 4} conversion increases substantially at higher discharge powers.
TL;DR: It is demonstrated that near-quantitative yields of glucose from cellulose can indeed be obtained using a bench-scale shrinking-bed percolation reactor in which an internal spring compresses the biomass as the reaction progresses.
Abstract: Previous kinetic modeling and bench-scale demonstration efforts using batch, percolation, or plug-flow reactors for the dilute sulfuric acid hydrolysis of cellulose have concluded that glucose yields above 70% of theoretical were not possible. This has been explained to be a result of reactions involving glucose or the cellulose itself in a destructive manner, as well as hydrolyzed soluble oligomers which have been modified chemically so as not to release glucose. However, recently, we have demonstrated that near-quantitative yields of glucose from cellulose can indeed be obtained using a bench-scale shrinking-bed percolation reactor in which an internal spring compresses the biomass as the reaction progresses. The present study was initiated to gain a fundamental understanding of the kinetic sequences involved in these high yields. Three reactor configurations (batch, percolation, and shrinking-bed percolation) were studied using similar hydrolysis severities to begin addressing chemical, physical, and h...
TL;DR: In this paper, two novel global optimization methods are presented which offer a theoretical guarantee of convergence to the global minimum for a wide range of problems, including the existence of multiple local minima.
Abstract: The estimation of parameters in semiempirical models is essential in numerous areas of engineering and applied science. In many cases these models are represented by a set of nonlinear differential-algebraic equations. This introduces difficulties from both a numerical and an optimization perspective. One such difficulty, which has not been adequately addressed, is the existence of multiple local minima. In this paper, two novel global optimization methods will be presented which offer a theoretical guarantee of convergence to the global minimum for a wide range of problems. The first is based on converting the dynamic system of equations into a set of algebraic constraints through the use of collocation methods. The reformulated problem has interesting mathematical properties which allow for the development of a deterministic branch and bound global optimization approach. The second method is based on the use of integration to solve the dynamic system of equations. Both methods will be applied to the pro...
TL;DR: In this paper, the gas-phase hydrogenation/hydrogenolysis of alcoholic solutions of phenol between 423 and 573 K has been studied using a Y zeolite-supported nickel catalyst (2.2% w/w Ni) and Ni/SiO2 catalysts (1.5−20.3%).
Abstract: The gas-phase hydrogenation/hydrogenolysis of alcoholic solutions of phenol between 423 and 573 K has been studied using a Y zeolite-supported nickel catalyst (2.2% w/w Ni) and Ni/SiO2 catalysts (1.5−20.3% w/w Ni). This is a viable means of treating concentrated phenol streams to generate recyclable raw material. Phenol hydrogenation proceeded in a stepwise fashion with cyclohexanone as a reactive intermediate while a combination of hydrogenolysis and hydrogenation yielded cyclohexane. Hydrogenolysis to benzene is favored by high nickel loadings and elevated temperatures. A catalytic hydrogen treatment of cyclohexanone and cyclohexanol helped to establish the overall reaction network/mechanism. The possible role of thermodynamic limitations is considered and structure sensitivity is addressed; reaction data are subjected to a pseudo-first-order kinetic treatment. Hydrogen temperature-programmed desorption (H2-TPD) has revealed the existence of different forms of surface hydrogen. Selectivity is interprete...
TL;DR: In this article, three commercial, full-size steam-reforming catalysts for naphthas, BASF G1-50, ICI 46-1, and Topsoe R-67, are tested at pilot-scale level for hot gas cleanup in biomass gasification in a fluidized bed.
Abstract: Three selected commercial, full-size steam-reforming catalysts for naphthas, BASF G1-50, ICI 46-1, and Topsoe R-67, are tested at pilot-scale level for hot gas cleanup in biomass gasification in a fluidized bed. Gas composition and tar content in the flue gas are measured before and after the catalytic bed. Variations of the catalytic bed in H2, CO, CO2, CH4, and H2O contents are reported for different operating conditions. Tar conversions and an apparent first-order kinetics constant for the overall tar removal reaction are calculated. Tar contents at the exit of the catalytic reactor as low as 10 mg/mn3 are obtained in a test of 50 h-on-stream without noticeable catalyst deactivation. Important variations in tar conversion with space time in the catalytic bed, with H2O/C* in the flue gas, and with the equivalence ratio in the upstream gasifier are observed. These results obtained at the pilot-scale level and with the use of full-sized commercial catalysts are an important forward step in demonstrating t...
TL;DR: In this article, the authors compared the first-order rate constants of HNCO hydrolysis with the SCR reaction using the integral equation for a plug-flow reactor.
Abstract: The hydrolysis of isocyanic acid (HNCO) was investigated on various oxidic catalysts, including TiO2, V2O5/TiO2, and V2O5−WO3/TiO2. The kinetics were studied using powdered samples in a microreactor. The conversions of HNCO are high even at the high space velocities (106 h-1) and low temperatures (150 °C) used in the tests. The highest rate for the hydrolysis of HNCO was found on pure TiO2 powder, while the addition of vanadia and tungsta decreased the activity slightly. To compare the rate of HNCO hydrolysis with the rate of the SCR reaction, uncorrected first-order rate constants were calculated for both reactions using the integral equation for a plug flow reactor. For a catalyst sample containing both WO3 and V2O5, the rate constant for hydrolysis of HNCO at low temperatures is about 2 orders of magnitude higher than the respective rate constant for the SCR reaction, whereas at high temperatures, the rate constants are of comparable magnitude. The apparent activation energy of the hydrolysis reaction ...
TL;DR: In this article, a new technique is developed to measure the diffusivity of gas in bitumen as a function of composition, which can be easily applied to other nonvolatile liquid systems.
Abstract: A new technique is developed to measure the diffusivity of gas in bitumen as a function of composition. Results are presented for a carbon dioxide−bitumen system, which is of considerable industrial relevance. The technique employs transient pressure data obtained from a nonintrusive pressure decay experiment at constant temperature and volume. The underlying theory is presented along with a computational algorithm to calculate diffusivity. Using experimental pressure decay data in the range 25−90 °C at 4 MPa, the diffusivity of carbon dioxide in bitumen is calculated. The results are compared with the limited data available in the literature. The approach is straightforward and can be easily applied to other nonvolatile liquid systems.
TL;DR: In this article, the structural and acid properties of zeolite samples were investigated in an effort to identify the parameters that decide their structural and acidic characteristics, and it was shown that the structure breakdown of the parent type of Y zeolites is mainly dependent on the degree of dealumination.
Abstract: Dealuminated zeolite samples prepared by different methods are characterized by different techniques, and the structural and acidic characteristics are investigated in an effort to identify the parameters that decide their structural and acidic characteristics. The investigation gave evidence that the structure breakdown of the parent type-Y zeolite is mainly dependent on the degree of dealumination, but the nature of extraframework aluminum (EFAl) species formed is dependent on the type of dealumination procedure. Monomeric Al species and oligomeric Si,Al species were formed by steam treatment at relatively low and high temperatures, respectively. Aluminosilicate phases of Si/Al ratios 2.0−4.0 and 8.0 were found in SiCl4-treated and ammonium hexafluorosilicate (AHFS)-treated samples, respectively. EFAl species of octahedral and tetrahedral coordination were observed by NMR spectra in steam and SiCl4-treated samples. High degrees of dealumination within each type of treatment resulted in loss of microporo...
TL;DR: A two-stage, stochastic programming approach is proposed for incorporating demand uncertainty in multisite midterm supply-chain planning problems and the challenge associated with the expectation evaluation of the inner optimization problem is resolved by obtaining its closed-form solution using linear programming (LP) duality.
Abstract: A two-stage, stochastic programming approach is proposed for incorporating demand uncertainty in multisite midterm supply-chain planning problems. In this bilevel decision-making framework, the production decisions are made “here-and-now” prior to the resolution of uncertainty, while the supply-chain decisions are postponed in a “wait-and-see” mode. The challenge associated with the expectation evaluation of the inner optimization problem is resolved by obtaining its closed-form solution using linear programming (LP) duality. At the expense of imposing the normality assumption for the stochastic product demands, the evaluation of the expected second-stage costs is achieved by analytical integration yielding an equivalent convex mixed-integer nonlinear problem (MINLP). Computational requirements for the proposed methodology are shown to be much smaller than those for Monte Carlo sampling. In addition, the cost savings achieved by modeling uncertainty at the planning stage are quantified on the basis of a r...