Showing papers in "Industrial & Engineering Chemistry Research in 1993"

A modified UNIFAC model. 2. Present parameter matrix and results for different thermodynamic properties

Abstract: Several years ago a modified UNIFAC (Dortmund, FRG) method was proposed, which shows various advantages when compared with the group contribution methods UNIFAC or ASOG; the latter are used worldwide for the synthesis and design of rectification processes. These advantages were reached by using a modified combinatorial part and by using a large data base to fit temperature-dependent group interaction parameters simultaneously to vapor-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE), h E , and γ ∞ data. The main advantages of the modified UNIFAC method are a better description of the temperature dependence and the real behavior in the dilute region and that it can be applied more reliably for systems involving molecules very different in size. To increase the range of this applicability, the temperature-dependent group interaction parameters of the modified UNIFAC has been fitted for 45 main groups using phase equilibrium information (VLE, h E , γ ∞, LLE) stored in the Dortmund Data Bank. A comprehensive comparison with the results of other group contribution methods confirms the high reliability of the modified UNIFAC (Dortmund) method

Olefin/paraffin separation technology: a review

Abstract: A significant amount of the light olefins produced during the refining of crude oil is used as refinery fuel. As natural gas supplies in North America decline, the need to conserve and recover these olefins will become critical. Cost-effective separation technologies will be required that can withstand the harsh operating environment of a petroleum refinery. In addition to traditional refinery and olefin plant applications, paraffin dehydrogenation units for the production of olefins from natural gas liquids (NGL) have recently been brought on stream. Recent federal regulations mandate that hydrocarbon emissions from refineries and chemical plants be reduced to low levels. To reduce the economic penalty of environmental compliance, low-cost hydrocarbon separation technologies are required. For streams containing a mixture of paraffinic and olefinic material, economic and process considerations may dictate that the olefin be recovered and recycled. A review of traditional and nontraditional technologies for the separation of light olefins and paraffins is presented. The technologies addressed range from conventional low-temperature distillation to chemical complexation using copper and silver ions.

Model identification and control of solution crystallization processes: a review

Abstract: The modeling of crystal quality (size, shape, and purity) is discussed. Numerical methods for the model solution are reviewed including collocation and Galerkin's method on finite elements. Measurement technologies for on-line crystal size distribution are presented. The difficulties with laser light scattering methods are discussed in detail. Parameter estimation is reviewed and new methods based on nonlinear optimization are presented. Sample calculations of parameters and their uncertainty from experimental data are included. The research literature covering control of continuous and batch crystallization is reviewed, and sample calculations of optimal cooling profiles for batch crystallizers are presented

Concentration and recovery of carbon dioxide from flue gas by pressure swing adsorption

Abstract: The feasibility of recovering CO[sub 2] from flue gas to generate a high-purity product by pressure swing adsorption (PSA) is studied by simulation using a proven predictive PSA model. Two promising sorbents, activated carbon and carbon molecular sieve, are examined. A nonconventional PSA cycle is designed for this purpose. With activated carbon as the sorbent, CO[sub 2] can be concentrated from 17% in the flue gas to a product of 99.997% (at a CO[sub 2] recovery of 68.4% and at a reasonably high feed throughput). Despite the favorable kinetic selectivity for CO[sub 2] in the carbon molecular sieve, separation results using this sorbent are not as good, because the kinetic selectivity (of CO[sub 2]/N[sub 2]) is not high enough and consequently the equilibrium selectivity dominates the separation.

Synthesis of porous-magnetic chitosan beads for removal of cadmium ions from wastewater

Abstract: Chitosan is a glucosamine biopolymer capable of adsorbing transition-metal ions from aqueous solution. Highly porous chitosan beads were prepared by dropwise addition of an acidic chitosan solution into a sodium hydroxide solution precipitation bath. The gelled chitosan beads were cross-linked with glutaraldehyde and then freeze dried. Beads of 1- and 3-mm diameter were prepared. Beads of 1-mm diameter possessed surface areas exceeding 150 m 2 /g and mean pore sizes of 560 A and were insoluble in acid media at pH 2. Well-mixed batch adsorption experiments revealed that both metal and hydronium ions compete for available adsorption sites by a chelation mechanism

Gas absorption studies in microporous hollow fiber membrane modules

Abstract: A comprehensive experimental investigation of gas-liquid absorption in a shell-and-tube type microporous hydrophobic hollow fiber device in a parallel flow configuration was carried out. Two modes of countercurrent gas-liquid contacting were studied, the wetted mode (absorbent liquid filled pores) and the nonwetted mode (gas-filled pores). The absorbent flowed through the fiber bore in most of the experiments. The systems studied include pure CO[sub 2], pure SO[sub 2], CO[sub 2] - N[sub 2] mixtures and SO[sub 2] - air mixtures. The absorbent was pure water. The absorption process was simulated for each case with a numerical model for species transport with and without chemical reaction. Laminar parabolic velocity profile was used for the tube-side flow, and Happel's free surface model was used to characterize the shell-side flow. The model simulations agreed well with the experimental observations in most cases. SO[sub 2] removals as high as 99% were obtained in small compact contactors. High K[sub L]a and low height of transfer unit (HTU) values were obtained with hollow fiber contactors when compared to those of conventional contactors. The applications of direct interest here are those for acid gas cleanup.

A phase-separation kinetic model for coke formation

Abstract: Coke formation during the thermolysis of petroleum residua is postulated to occur by a mechanism that involves the liquid-liquid phase separation of reacted asphaltenes to form a phase that is lean in abstractable hydrogen. This mechanism provides the basis of a model that quantitatively describes the kinetics for the thermolysis of Cold Lake vacuum residuum and its deasphalted oil in an open-tube reactor at 400 C. The previously unreacted asphaltenes were found to be the fraction with the highest rate of thermal reaction but with the least extent of reaction. This not only described the appearance and disappearance of asphaltenes but also quantitatively described the variation in molecular weight and hydrogen content of the asphaltenes with reaction time. Further evidence of the liquid-liquid phase separation was the observation of spherical particles of liquid crystalline coke and the preferential conversion of the most associated asphaltenes to coke.

Distillation columns containing structured packings: a comprehensive model for their performance. 1. Hydraulic models

Abstract: A mechanistically-based model has been developed to aid the analysis and design of distillation columns containing structured packings of the corrugated plate type. The model encompasses the important, and related, parameters of liquid holdup, pressure drop, flooding, and mass-transfer efficiency. Since it deals with the countercurrent contacting of liquid with gas or vapor, the model may also be applied to absorption or stripping processes. The model is developed from a consideration of the interaction of falling liquid films with upflowing vapors and thus takes into account the flow and physical property characteristics of the systems as well as geometric variables such as corrugation angle and surface enhancement. In this paper (part 1) the model is developed and applied to several sets of liquid holdup and pressure drop experimental data, including new data provided by the authors. The second paper in the series will deal with mass-transfer characteristics, with the model being shown to be dependent on the hydraulic aspects described in part 1. The information provided in these papers should have direct application to new designs, retrofits, or optimization of existing equipment.

Adsorption of metal ions on polyaminated highly porous chitosan chelating resin

Abstract: Highly porous chelating resin was fabricated from the natural polysaccharide chitosan. The adsorption capacity was increased by polyamination with poly(ethylene imine) (MW = 10,000). The capacity was about 1-2 times larger than that of commercial chelate resins. The selectivity for adsorption of metal ions on the resin, which was determined for a single solute at pH [approx equal] 7, was Hg(II) > UO[sub 2](II) > Cd(II) > Zn(II) > Cu(II) > Ni(II). Mg(II), Ca(II), Ga(III), As(III), and Sr(II) were not adsorbed on the resin at all. The selectivity depended on the pH of each metal solution. The equilibrium isotherms for adsorption of HgCl[sub 2] were correlated by the Langmuir equation. The saturation capacities were close to the concentration of amino group fixed on the resin. When HCl or NaCl coexisted in HgCl[sub 2] solution and their concentrations were lower than 100 mol/m[sup 3], the saturation capacity of HgCl[sub 2] was little affected by them. When 500 mol/m[sup 3] H[sub 2]SO[sub 4] coexisted in HgCl[sub 2] solution, extremely low pH inhibited the adsorption of Hg(II) at all.

Chemical processing in high-pressure aqueous environments. 2. Development of catalysts for gasification

Abstract: A liquid water processing environment was used at 20 MPa and 350 C to convert organic compounds to methane and carbon dioxide in the presence of catalysts. This paper describes the evaluation of various types of base and noble metal catalysts and numerous support compositions for the process. The feedstock used in these tests was a mixture of p-cresol and water. Nickel, ruthenium, and rhodium were identified as active metals for the reaction. Other metals from groups VIII, VIB, IB, and IIB were inactive or readily oxidized and lost activity. Stable supports in the processing environment included [alpha]-alumina and zirconia. Silica and titania did not react chemically, but the tablet forms lost their physical integrity. Alumina forms, other than [alpha]-alumina, reacted with water to form boehmite ([gamma]-AlOOH) with significant loss of surface area and physical strength.

Preparation and characterization of a composite palladium-ceramic membrane

Abstract: Composite palladium--ceramic membranes with palladium films ranging from 11.4 to 20 [mu]m were made by depositing palladium on the inside surface of asymmetric tubular ceramic membranes. Electroless plating was used to deposit the palladium film. Membranes were characterized by conducting permeability experiments with hydrogen, nitrogen, and helium at temperatures from 723 to 913 K and feed pressures from 160 to 2,445 kPa. The membranes had both a high hydrogen permeability and selectivity. The hydrogen permeability for a composite membrane with an 11.4-[mu]m palladium film was 3.23 [times] 10[sup [minus]9] mol [center dot] m/(m[sup 2] [center dot] s [center dot] Pa[sup 0.602]) at 823 K. Hydrogen/nitrogen selectivity for this membrane sealing should further increase the hydrogen selectivity. Results of this study demonstrate the potential for using composite metal-ceramic membranes in membrane reactors including applications that require operation at relatively high temperatures and transmembrane pressure differences. Some of the many potential applications include steam reforming of methane, water gas shift, and dehydrogenation of various hydrocarbons including cyclohexane, ethylbenzene, ethane, propane, and butane. Another promising application is the decomposition of hydrogen sulfide and ammonia impurities in synthesis gas produced at coal gasification plants.

Solubility of naproxen in supercritical carbon dioxide with and without cosolvents

Abstract: The solubility of naproxen ((S)-6-methoxy-α-methyl-2-naphthaleneacetic acid) in supercritical CO 2 was determined at 313.1, 323.1, and 333.1 K. The influence of six polar cosolvents, ethyl acetate, acetone, methanol, ethanol, 1-propanol, and 2-propanol, was studied at concentrations of 1.75, 3.5, and 5.25 mol%. The solubility enhancement with these cosolvents is considerable, and the cosolvent effect increases in the order ethyl acetate, acetone, methanol, ethanol, 2-propanol, 1-propanol. A nonlinear increase in solubility is observed with an increase in cosolvent concentration. The use of the Peng-Robinson and Soave-Redlich-Kwong equations of state to correlate these ternary systems requires the use of negative binary interaction parameters indicating strong interactions between naproxen and the cosolvents. The cosolvent effects cannot be explained by any one physical property of the cosolvents but appear to be influenced by hydrogen bonding ability as determined from solvatochromic parameters as well as the relative distance from the CO 2 -cosolvent binary critical point

Kinetics of the Fischer-Tropsch reaction on a precipitated promoted iron catalyst. 2. Kinetic modeling

Abstract: A detailed kinetic model is derived using Hougen-Watson rate expressions for the Fischer-Tropsch reactions and the water gas shift reaction on a precipitated promoted iron catalyst. The model discrimination and the parameter estimation are performed according to the integral method of kinetic analysis on experiments described in part 1 of this series. In the construction of the kinetic model, the information gained from in situ catalyst characterization is used. The model proposed assumes different active sites for the water gas shift reaction on one side and for the reactions leading to n-paraffins and 1-olefins on the other side. The rate expressions for the hydrocarbon-forming reactions are based on elementary reactions corresponding to the carbide mechanism, in the assumption that two kinds of elementary reactions, the ones describing the adsorption of carbon monoxide and these describing the desorption of the hydrocarbon products, are not at equilibrium. The assumption that the active sites are almost completely occupied with surface hydrocarbon intermediates greatly simplified the kinetic expressions. The rate expression for the water gas shift reaction is based on elementary reactions involving a formate surface intermediate. The two-site reaction describing the formation of the formate intermediate is proposed to be rate determining. Themore » values of the activation energies derived correspond well with data reported in the literature.« less

Modeling of supercritical fluid extraction from herbaceous matrices

Abstract: Experimental results of supercritical fluid extraction from various herbaceous matrices are presented. In optimal extraction conditions, the use of a fractional separation technique allows a nearly complete separation of the extract in cuticular waxes and essential oil. The modeling of these results is proposed starting from the description of the mass transfer from a single spherical particle. The simultaneous extraction of two pseudocompounds is assumed to simulate the two compound families obtained by fractionation. The model is then extended to simulate the whole extractor. The yields of essential oil and cuticular waxes obtained from rosemary, basil, and marjoram leaves are fairly simulated by the model. Intraparticle mass transfer resulted as the controlling stage in supercritical extraction of essential oils.

A new test for the thermodynamic consistency of vapor-liquid equilibrium

Abstract: A new thermodynamic consistency test of vapor-liquid equilibrium data at low pressure has been proposed based on the equation that describes the bubble point of the mixture. The test can be used in a point-to-point or area manner and requires knowledge or estimation of the heat of vaporization of the pure components. The point-to-point mode is applicable to binary and multicomponent data and simplifies the locating of experimental errors

Supercritical fuel deposition mechanisms

Abstract: Jet fuel is the primary coolant used in high-speed aircraft. A decrease in surface deposition (fouling) is often seen as jet fuels and pure hydrocarbons are heated above approximately 370 C, as measured by the wetted wall or film temperature. This temperature is near the critical temperature of most jet fuels. Two explanations have been offered for this decrease in deposition under supercritical conditions. One explanation is that the decrease reflects the temperature where hydroperoxide precursors to solids formation are depleted by thermal decomposition, interrupting the radical chain reactions forming solids. Another explanation is that the solvent properties of the fuel become enhanced under supercritical conditions, with the surface deposition reduced essentially by keeping the solids in solution. In single-tube heat exchanger tests with pure hydrocarbons and jet fuels of widely varying critical temperature, it was found that the deposition decrease is insensitive to fuel critical temperature but very sensitive to residence time/heating rate, indicating that the deposition decrease is a fuel chemistry effect rather than an effect of the supercritical nature of the fuel.

Model of the selective laser sintering of bisphenol-A polycarbonate

Abstract: Selective laser sintering (SLS) is a new additive process for rapidly preparing prototype parts by selectively fusing portions of layers of polymer powder with a rastered, modulated, CO 2 laser beam. Layer to layer fusion is important for achieving good mechanics properties. Generally, the fusion depth is found to be a function of laser beam overlap on adjacent scans, scan speed, and intensity. It is also a function of the kinetic rates of powder sintering and of heat transfer. A one-dimensional model of the SLS thermal process is presented that can accurately predict, to within 20%, the effect of these process and material parameters on experimentally observed fusion depths in bisphenol-A polycarbonate powders

Monitoring and diagnosing process control performance: the single-loop case

Abstract: We present a hierarchical method for monitoring and diagnosing the performance of single-loop control systems based primarily on typical operating plant data. It identifies significant deviations from control objectives, determines the best achievable performance with the current control structure, and identifies steps to improve the current performance. Within the last point, the method can isolate whether poor performance is due to the feedforward loop or the feedback loop. If in the feedback loop, it is sometimes possible to determine whether the cause of poor performance is plant/model mismatch or poor tuning. The methods are based on simple but rigorous statistical analysis of plant time series data using autocorrelation and cross correlation functions. The theoretical basis of the method is developed, and it is applied to simulation studies which clarify the principles. Then, results of studies on two industrial processes are reported. The first is a heat exchanger feedback temperature controller, and the second is a feedforward-feedback tray temperature controller in a 50-tray distillation column. The initial diagnosis and subsequent control performance improvements are reported for both cases

Hollow fiber solvent extraction removal of toxic heavy metals from aqueous waste streams

Abstract: This study is concerned with the applications of the immobilized interface-based techniques to reversible chemical complexation-based solvent extraction of toxic heavy metals from industrial wastewaters using microporous hydrophobic hollow fiber (MHF) modules. Toxic heavy metals studied were copper and chromium(VI). Each metal was individually removed in separate once-through experiments from a synthetic wastewater by organic extractants flowing in the shell-side countercurrent to wastewater flowing in the fiber bore. The organic extractant used for copper extraction was 5-20 % v/v LIX 84 diluted in n-heptane, and that for chromium extraction was 30 % v/v TOA (tri-n-octylamine) diluted in xylene. A mathematical model was developed to predict the extent of copper extraction from the aqueous synthetic wastewater by the MHF module. The equilibrium constant for copper was determined to be 1.7 from experimental partitioning data. The experimental data on copper extraction in the MHF module are described well by the model if the forward interfacial chemical reaction rate constant is 9.0 X 10[sup [minus]6] cm/s.

Autotuning of multiloop proportional-integral controllers using relay feedback

Abstract: In this paper, a simple method for autotuning multiloop PI controllers for multivariable systems is presented. The procedure is a combination of sequential loop closing and relay tuning often used for tuning single-loop PI/PID controllers. The proposed design offers three major advantages. Firstly, overall closed loop stability is guaranteed; secondly, very little knowledge of the process is required; thirdly, it is an autotuning procedure. Set point and load disturbance responses are improved by introducing set point weighting factors. Some simulation and comparative results are shown for distillation column models commonly used to demonstrate multiloop designs.

Solubility of carbon dioxide and hydrogen sulfide in aqueous alkanolamines

Abstract: The Deshmukh-Mather thermodynamic model has been fitted to all available, public, phase-equilibrium data for CO[sub 2] and H[sub 2]S in aqueous solutions of monoethanolamine, diethanolamine, diglycolamine, and N-methyldiethanolamine. The fitting was done for both acid gases simultaneously, and the best numerical values of the most important interaction parameters for each amine were obtained. Although the method used for data regression did not provide a statistical measure of the goodness of fit, the regressed model forms a unified basis for evaluating the large amount of data collected over the past 50 years and it results in a rational approach to performing vapor-liquid equilibrium calculations in a computationally affordable, thermodynamically sound manner.

Multiple solutions in reactive distillation for methyl tert-butyl ether synthesis

Abstract: A reactive distillation column for the synthesis of methyl tert-butyl ether (MTBE) is simulated using a steady-state equilibrium stage model. For identical column and feed specifications, two distinctly different composition profiles are obtained, which correspond to high and low conversion of isobutene. With the aid of residue curve maps for simultaneous physical and chemical equilibrium, it is shown that the high- and low-conversion steady-state composition profiles obtained in the column simulations correspond to residue curves which have their starting points in distinctly different composition regions

Adsorptive separation of propylene-propane mixtures

Abstract: The separation of propylene-propane mixtures is of great commercial importance and is carried out by fractional distillation. It is claimed to be the most energy-intensive distillation practiced in the United States. The purpose of this paper is to describe experimental work that suggests a practical alternative to distillation for separating the C[sub 3] hydrocarbons: adsorption. As studied, the process involves three adsorptive steps: initial separation with molecular sieves with heavy dilution with an inert gas; separation of propylene and propane separately from the inert gas, using activated carbon; and drying of the product streams with any of several available desiccants. The research information presented here deals with the initial step and includes both equilibrium and kinetic data. Isotherms are provided for propylene and propane adsorbed on three zeolites, activated alumina, silica gel, and coconut-based activated carbon. Breakthrough data are provided for both adsorption and regeneration steps for the zeolites, which were found to be superior to the other adsorbents for breakthrough separations. A flow diagram for the complete proposed process is included.

Improved steam gasification of lignocellulosic residues in a fluidized bed with commercial steam reforming catalysts

Abstract: The improved/two-stage steam gasification of biomass or lignocellulosic residues in fluidized bed with steam reforming catalysts placed in a downstream secondary reactor has been studied. Two commercial catalysts, R-67 and RKS-1 from Topsoee, were used at their incipient fluidization conditions. At 720-760 C and space-times of only 0.10-0.20 s, with catalyst sizes under 1.0 mm and with steam/biomass ratios of 1.2-1.6, tar conversions of 99.95% were achieved in the catalytic reactor. In this process, tar and methane in the flue gas can be easily lowered below 5 mg/m[sup 3](NTP) and 0.5 vol %, respectively, without using oxygen. The catalyst deactivation by coke from the tar cracking is the main problem of this process.

Simple activity coefficient model for the prediction of solvent activities in polymer solutions

Abstract: A new simple activity coefficient model for the prediction of solvent activities in polymer solutions is presented. The model consists of two terms, a recently proposed «combined» combinatorial-free-volume term by Elbro et al. and the residual term of UNIFAC. The linear temperature-dependent parameter table for UNIFAC, recently developed by Hansen et al., is used. The ability of the new model to predict solvent activity coefficients at infinite dilution for many different polymer-solvent systems is shown

Influence of Oxygen-containing, Nitrogen-containing, and Sulfur-containing-compounds On the Hydrodeoxygenation of Phenols Over Sulfided Como/gamma-al2o3 and Nimo/gamma-al2o3 Catalysts

Abstract: The hydrodeoxygenation (HDO) of phenols is a key reaction of the hydroprocessing of bio-oils, because phenolic molecules represent an important part of these oils and they are among the most difficult to deoxygenate. This reaction is also a very good reaction test for the characterization of the hydrogenation and hydrogenolysis functions of hydrotreating catalysts. In this work, the influence of competitors on the activity and selectivity of 4-methylphenol HDO over conventional CoMo and NiMo hydrotreating catalysts was evaluated in batch reaction tests. The inhibiting strength followed the order H2O << 2-ethylphenol < H2S < NH3. In all cases, the hydrogenolysis path was more inhibited than the hydrogenation path, indicating a higher adsorption strength and electrophilicity of associated sites. The inhibition was quantified according to a Langmuir adsorption concept. The deviations from this model were attributed to a distribution of the adsorption strength. As opposed to other competitors, hydrogen sulfide slightly promotes the hydrogenation activity of CoMo but not of NiMo. These observations were interpreted as the result of an interconversion of the hydrogenolysis and hydrogenation active sites.

Acid properties of silica-alumina catalysts and catalytic degradation of polyethylene

Abstract: A relationship between the acid strengths and amounts of silica-alumina catalysts and the compositions of products formed by the catalytic degradation of polyethylene at 673 K was studied. The acid strengths and amounts were varied with SiO{sub 2}/Al{sub 2}O{sub 3} weight ratio in the catalysts. Although the resulting products and amounts were varied with SiO{sub 2}/Al{sub 2}O{sub 3} weight ratio in the catalysts. Although the resulting products consisted of gases, oils, and wax, the fraction of gases increased, and, inversely, the fraction of oils decreased, as the acid amounts over the catalysts increased. The fraction of aromatics in the oils was enhanced, however, as the acid amounts over the catalysis increased, which was discussed in terms of the acid types: Broensted and Lewis acids generated on silica-aluminas. Since some inorganic compounds such as MgO, ZnO, TiO{sub 2}, and carbon are incorporated into plastics, the catalytic activities and selectivities of these additives for polyethylene degradation were also discussed.

A new surface oxygen complex on carbon: Toward a unified mechanism for carbon gasification reactions

Abstract: Molecular orbital theory calculations and recent high-temperature TPD experiments revealed the feasibility of a new type of active oxygen complex on graphite. This type of complex is formed by bonding of an oxygen atom to a saturated carbon atom (in the caved-in position) adjacent to the unsaturated edge carbon atom that is already bonded to an oxygen atom. Molecular orbital calculation results also show that this type of complex is substantially more active than the known complexes that have been discussed in the literature, e.g., semiquinones and carbonyls. On the basis of this new type of complex, a unified mechanism is proposed for the gasification reactions of carbon with all oxygen-containing gases. The proposed mechanism can account for all major features of the published experimental results on temperature-programmed desorption, transient kinetic, and steady-state rate studies of the gas-carbon reactions.

Estimating Diffusion Coefficients of Dense Fluids

Abstract: Gas injection (hydrocarbon, nitrogen, or carbon dioxide) into oil and condensate reservoirs may be attempted to recover more in situ hydrocarbons. In some cases, particularly in naturally fractured reservoirs, there has been a need for information on the rate and amount of mass transfer by diffusion. The most important property, to obtain such information, is the diffusion coefficient at reservoir conditions. A simple and generalized correlation in terms of viscosity and molar density is proposed to estimate diffusion coefficients for hydrocarbon systems. The correlation can be used for both gases and liquids up to a pressure of about 400 bar (6,000 psia). It has been shown that the proposed method may also be used to estimate effective diffusion coefficients in multicomponent systems with a reasonable degree of accuracy. Although the proposed correlation is based on experimental data in hydrocarbon systems, preliminary evaluations have shown that it is also satisfactory for non-hydrocarbon systems as well. The proposed equation predicts diffusion coefficients in gases with an absolute average deviation of 8% and in liquid systems with an absolute average deviation of 15%. The input parameters for the correlation are molecular weight, critical properties, and acentric factor of components in the system; mixturemore » molar density; low-pressure gas viscosity; and actual viscosity. The last three properties may be predicted from appropriate correlations.« less

Optimal feed locations and number of trays for distillation columns with multiple feeds

Abstract: MINLP models for finding the optimal locations for the feeds and the number of trays required for a specified separation for a distillation column with multiple feeds are presented. Systems with ideal, Soave-Redlich-Kwong equation of state and UNIQUAC thermodynamic models are considered. This rigorous procedure requires no assumptions concerning the order of the feeds - i.e., the disposition of any feed with respect to other feeds. The optimization step automatically determines the order and the locations