Esteban A. Brignole

MOLECULAR DESIGN OF SOLVENTS FOR LIQUID EXTRACTION BASED ON UNIFAC

Abstract On the basis of the UNIFAC group contribution method, it is proposed to synthesize molecular structures with specific solvent properties for the separation of aromatic and paraffinic hydrocarbons. The potential solvents were studied with regard to their solvent power, selectivity and binodal curve on the basis of UNIFAC predictions. In this way good potential solvents were found. In general the number of molecular structures that can be obtained from the various groups is very large. An efficient computerized synthesis of compounds for the molecular design of solvents was developed.

A group contribution equation of state for associating mixtures

Abstract In the present work a group contribution-associating-equation of state (GCA-EOS) is developed for the modeling of phase equilibria found in the near critical fluid extraction and dehydration of oxygenated compounds from aqueous solutions. The new equation of state is obtained by the inclusion of a ‘group’ contribution associating term to the GC-EOS model. The definition of a unique hydroxyl group to represent the association effect of hydrogen bonding in water and alcohols, greatly simplifies the extension of the model to multicomponent mixtures. This approach has been applied to determine the parameters for a common hydroxyl group for water, primary and secondary alcohols. On this basis, revised group and binary interaction dispersive parameters for water, primary and secondary alcohols, alkane groups, light hydrocarbons and CO2 have been determined. Model predictions for binary and ternary data are presented.

Phase equilibria in mixtures of fatty oils and derivatives with near critical fluids using the GC-EOS model

Abstract The Group Contribution Equation of State (GC-EOS) is applied to model high-pressure phase equilibria in mixtures of fatty oils and acid alkyl esters with supercritical fluids. The fatty oil is represented by a pseudo-triacylglyceride with the same molecular weight and degree of unsaturation of the natural oil. The critical hard sphere diameter of the oil, i.e. the size-related parameter, is determined from the correlation of infinite dilution activity coefficients of n -alkanes in high molecular weight triacylglicerides and hydrocarbons. Good predictions of vapor–liquid, liquid–liquid and vapor–liquid–liquid equilibria in mixtures of supercritical solvents (propane, ethane and CO 2 ) with pure triacylglycerides, natural vegetable oils and fatty acid alkyl esters are obtained. These results show the capability of the GC-EOS model to describe the phase equilibria of size-asymmetric mixtures and its potential for modeling supercritical processes involving oils and derivatives.

A strategy for the design and selection of solvents for separation processes.

Abstract A knowledge based strategy for molecular design and selection of solvents for separation processes is presented. The solvent design problem as formulated by Gani and Brignole (1983) has been extended and revised to include improved procedures for solvent synthesis, solvent evaluation and solvent screening. Examples of industrial application are provided through the use of a computer program based on the proposed strategy.

High pressure phase equilibrium modeling of mixtures containing associating compounds and gases

In the present work, the group contribution-associating-equation of state (GCA-EOS) is applied for modeling high pressure phase equilibrium of mixtures containing gases and associating fluids. The GCA performance is compared with other group contribution local composition EOS. Based on extensive testing, it is concluded that the GCA-EOS is a reliable method for modeling the extraction and dehydration of alcohols from aqueous solutions using gases at near critical conditions as solvents (dehyextract process). The parameter tables for the GCA-EOS model have been revised and extended.

Compressed solvents for the extraction of fermentation products within a hollow fiber membrane contactor

Abstract The feasibility of extracting aqueous ethanol and acetone within a hollow fiber membrane contactor (HFC) has been examined using compressed CO 2 (69 bar), ethane (69 bar), and propane (34.5 bar) at ambient temperature. Ethanol and acetone were chosen as ‘model’ fermentation products to further examine the potential for extractive fermentation with compressed fluids. Aqueous and compressed solvent streams were contacted within a single hydrophobic isotactic polypropylene membrane fiber (0.6 mm ID; 106.7 cm in length; 75% porosity), providing a porous barrier between the two immiscible phases. The amount of solute extracted was determined as a function of the aqueous flowrate (tubeside) and molar solvent to feed ratio. The amount of aqueous ethanol (10 wt.%) and acetone (10 wt.%) extracted from binary feed solutions with compressed propane ranged from 6.4 to 14.3% and 21.8 to 90.6%, respectively, as a function of the aqueous flowrate (0.1 to 2 ml/min) and molar solvent to feed ratio ( S/F =1 to 10). Comparatively, ethanol extraction with compressed CO 2 ranged from 4.7 to 31.9% with similar variations in the aqueous flowrate (0.1 to 1 ml/min) and molar solvent to feed ratio (3 and 10). Acetone extracted with CO 2 ranged from 67.9 to 96.1% when varying the aqueous flowrate (0.1 to 1 ml/min) at a molar solvent to feed ratio of 3. Ternary ethanol/acetone/water mixtures were also examined to determine the effect of multi-solute aqueous solutions. The effect of aqueous and compressed fluid flows on extraction are interpreted based on the equilibrium distributions of the solutes between water and the compressed fluid (estimated using a group contribution association equation of state (GCA–EOS)) and the mass transfer characteristics of the compressed fluid.

Phase equilibrium modelling of triglycerides with near critical solvents

Abstract The Group Contribution Equation of State (GC-EOS) is applied to calculate vapor–liquid and liquid–liquid equilibria of supercritical alkane–vegetable oil mixtures. A new functional group is defined, in order to represent the triglyceride nucleus of vegetable oil molecules. Pure group and binary interaction parameters for this group are given. The size of the high molecular weight triglyceride component is characterized by fitting its critical hard sphere diameter to infinite dilution activity coefficient data of hydrocarbons in the triglyceride.

Mass transfer in laminar liquid jets: Measurement of diffusion coefficients

Abstract Laminar liquid jets used in mass transfer studies have been generally discharged from convergent nozzles or orifices. The use of long straight capillary tubes to discharge the liquid jet is studied in this work and numerical values of the jet diameter and surface velocity are obtained. These computed values are applied to predict the actual absorption rates in the laminar jet for different values of N J = N Re / N Fr , N we and the axial coordinate. The effect of N we is slight and can be disregarded in analysing experimental data. Experimental values of absorption of CO 2 in water and water-glycerol solutions are obtained using a laminar liquid jet discharged from capillary tube and good agreement is found between the computed values and the measured absorption rates. The results are applied to the determination of diffusion coefficient for the CO 2 in water glycerol solutions.

Activity coefficients of associating mixtures by group contribution

Abstract A group contribution model is presented for the prediction of activity coefficients in associating mixtures. An association term has been added to the traditional UNIFAC residual and combinatorial contributions to the activity coefficients. The association term is based on Wertheims theory for fluids with highly directed attractive forces, as applied in the SAFT equation, and it follows the group contribution approach proposed by Gros et al. in the GCA-EOS model. Good predictions of both vapor–liquid and liquid–liquid equilibria are achieved, with a set of group interaction parameters determined from infinite dilution activity coefficients.

Optimal design of supercritical fluid processes

Abstract Optimal schemes and operating conditions are analyzed for the deterpenation of citrus peel oils with supercritical carbon dioxide. The problem is formulated as a mathematical programming model using the group contribution equation of state (GC-EOS) for rigorous phase equilibria predictions. Both thermodynamic predictions and simulation results are found to be in agreement with experimental studies. Optimization results give insight to improve current experimental values of product recovery and purity.