Design Of Separation Processes Research Articles

Process Intensification for greenhouse gas separation from biogas: More efficient process schemes based on membrane-integrated systems

The separation of biogas leads to not only recovery and sequestration of CO2, but also to much greater purification and recovery of value-added CH4 able to be used, for example, to directly feed pipelines for domestic or small plants. In this work, an alternative approach for a preliminary design of separation process based on the use of polymeric membranes is proposed. Two different types of polymeric membranes were taken into account, Hyflon AD60 and Matrimid 5218, the first showing a higher permeability with respect to other membranes but a quite low selectivity (12.9), the second exhibiting a higher selectivity with respect to other membranes (41 and 100) even though a lower permeability. Four possible operation schemes using two different types of membranes in multistage configuration system are analysed as functions of the main design parameters, i.e., pressure ratio and permeation number. The achieved results are compared with certain targets and are also discussed in terms of process metrics, according to the Process Intensification Strategy. This latter analysis, coupled with a conventional one, provides an alternative point of view over the evaluation of the plant performance taking into account not only the final characteristics of the streams but also process efficiency, exploitation of raw material and energy, and the footprint occupied by the installation.

Novel approach to the characterization of the pore structure and surface chemistry of porous carbon with Ar, N2, H2O and CH3OH adsorption

Characterization of porous carbon for its pore size distribution is traditionally carried out with simple pore models of well-defined geometry (slit or cylinder) with both ends opened to the gas surroundings. These idealised models do not adequately describe the inherently complex structure of porous carbons. An improved model should be sufficiently simple, not only for characterization, but also for the design of separation and purification processes. The following factors should be included: (1) energetic variation along the pore axis due to constrictions or strong energy sites, (2) connectivity between adjacent pores and (3) the presence of functional groups. In this work, we report results from computer simulations, using argon and nitrogen as non–polar or weakly polar adsorbates and water and methanol as examples of associating fluids. The new model is able to produce all hysteresis loops classified by the IUPAC as well as loop types reported earlier by de Boer [1]. Experimental isotherms are commonly measured at 77 K and 87 K (nitrogen and argon boiling points, respectively), but in recent years cryostats have become increasingly available in characterization laboratories and our simulations show that by measuring isotherms at different temperatures new insights about the porous structure can be gained from the variation of the hysteresis loop with respect to temperature which may change, for example, from a single-loop to a double-loop via a fused-loop as the temperature is varied.

Liquid–liquid equilibria for ternary systems ethanol + heptane + phosphoric-based ionic liquids

This work demonstrates the capabilities of three phosphoric-based ionic liquids (ILs) as solvents for the extraction of ethanol from its mixture with heptane. The knowledge of liquid–liquid equilibria (LLE) of this mixture is essential for the design of the extraction separation process. For this reason, the experimental LLE data were measured for the ternary systems, {ethanol+heptane+1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]), or 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), or 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP])}, at T=298.2K and atmospheric pressure. The thermodynamic nonrandom two-liquid (NRTL) model was used to correlate the experimental results for the studied ternary systems. The extraction capabilities for the studied ILs were evaluated by solute distribution ratios of ethanol and ethanol/heptane selectivities. Moreover, this extraction capability was also compared with other ILs obtained from the literature. The experimental results show that the studied ILs can be suitable to act as solvents for the separation of the ethanol and heptane in the extraction process. The extraction capabilities for the studied ILs decrease in the following order [MMIM][DMP]>[EMIM][DEP]>[BMIM][DBP].

Liquid–Liquid Equilibrium for Ternary System Methanol + Methyl Acetate + 1,3-Dimethylimidazolium Dimethylphosphate at Several Temperatures and Atmospheric Pressure

The azeotrope methanol and methyl acetate is involved in the industrial manufacturing process of vinyl alcohol which is made from vinyl acetate by alcoholysis with methanol. This work focused on a study of ionic liquid as a solvent in the extraction separation for this azeotropic mixture. The knowledge of liquid–liquid equilibrium (LLE) is essential for the design of the extraction separation process. For this reason, LLE data for the ternary system {methanol + methyl acetate + 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP])} were measured at the temperatures T = (298.2, 313.2, and 328.2) K and atmospheric pressure. The consistency of the experimental LLE data was ascertained by using the Othmer-Tobias and Hand equations. Additionally, the experimental LLE data were compared with the correlated values obtained by means of the nonrandom two liquid (NRTL) model. The solute distribution ratios and selectivity values, derived from the experimental LLE data, were calculated and analyzed in order to eva...

Purification of equine chorionic gonadotropin (eCG) using magnetic ion exchange adsorbents in combination with high-gradient magnetic separation.

Current purification of the glycoprotein equine chorionic gonadotropin (eCG) from horse serum includes consecutive precipitation steps beginning with metaphosphoric acid pH fractionation, two ethanol precipitation steps, and dialysis followed by a numerous of fixed-bed chromatography steps up to the specific activity required. A promising procedure for a more economic purification procedure represents a simplified precipitation process requiring only onethird of the solvent, followed by the usage of magnetic ion exchange adsorbents employed together with a newly designed 'rotor-stator' type High Gradient Magnetic Fishing (HGMF) system for large-scale application, currently up to 100 g of magnetic adsorbents. Initially, the separation process design was optimized for binding and elution conditions for the target protein in mL scale. Subsequently, the magnetic filter for particle separation was characterized. Based on these results, a purification process for eCG was designed consisting of (i) pretreatment of the horse serum; (ii) binding of the target protein to magnetic ion exchange adsorbents in a batch reactor; (iii) recovery of loaded functionalized adsorbents from the pretreated solution using HGMF; (iv) washing of loaded adsorbents to remove unbound proteins; (v) elution of the target protein. Finally, the complete HGMF process was automated and conducted with either multiple single-cycles or multicycle operation of four sequential cycles, using batches of pretreated serum of up to 20 L. eCG purification with yields of approximately 53% from single HGMF cycles and up to 80% from multicycle experiments were reached, with purification and concentration factors of around 2,500 and 6.7, respectively.

Unified design of chromatographic separation processes

A unified method is developed for the designing preparative chromatographic processes of various types. The method allows, for example, generalizing the established triangle theory of counter-current simulated moving bed technique for other single and multi-column chromatographic schemes including (1) classical batch chromatography, (2) mixed-recycle steady state recycling chromatography, (3) cross-current chromatography, and (4) mixed-recycle cross-current recycling chromatography. The approach allows direct prediction of the range of feasible dimensionless operating parameters that lead to complete separation of a binary feed mixture. By using the equilibrium theory of chromatography, explicit design equations are derived for systems that follow linear or competitive Langmuir isotherm model. It is shown that under ideal conditions the boundaries of the dimensionless operating parameters are identical for all studied process concepts, except for the upper limit of a parameter that is related to the regeneration of the fluid phase in the case of Langmuir isotherm. The practical relevance of the unified design method is demonstrated with numerical simulations. It is shown that even under non-ideal conditions the counter-current SMB can be designed with good accuracy based on a single pulse injection to a batch column, especially for relatively low purity requirements.

Liquid–liquid equilibria for ternary system water + toluene + benzaldehyde at (303.2–343.2) K

Liquid–liquid equilibrium (LLE) data for the ternary system of water+benzaldehyde+toluene have been determined at (303.2–343.2)K under atmospheric pressure. The Othmer–Tobias and the Hand correlations were used to check the reliability of the experimental data. The obtained LLE data were correlated by both the NRTL and UNIQUAC activity coefficient models. The relevant interaction parameters were extracted by the regression of the experimental data. The calculated values by these two models show good consistency with the measured data. The relative-mean-standard deviations obtained is 0.82% by the NRTL model and 0.12% by the UNIQUAC model. The obtained interaction parameters might be used in the calculation of LLE for the ternary system water+benzaldehyde+toluene as well as for the design and optimization of the related separation process.

A study on the liquid–liquid equilibrium of 1-alkyl-3-methylimidazolium dialkylphosphate with methanol and dimethyl carbonate

Methanol and dimethyl carbonate (DMC) mixture is present in the industrial manufacturing process of DMC, which is made from the catalytic oxidative carbonylation of methanol. The separation of methanol and DMC is important but difficult due to the formation of an azeotropic mixture. This work has been focused on a study of phosphoric-based ionic liquids (ILs) as green solvents for the separation of methanol and DMC in the extraction process. The knowledge of liquid–liquid equilibrium (LLE) of this mixture is essential for the design of the extraction separation process. For this reason, LLE data for the ternary systems {methanol+DMC+1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP])} and {methanol+DMC+1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP])} were measured at T=(298.2 and 313.2)K and atmospheric pressure. The solute distribution ratio and selectivity of the methanol, derived from the tie-lines data, were calculated and analyzed in order to evaluate the capacity of the studied ILs as solvents in liquid extraction process. The experimental results show that the values of selectivity for the studied ILs follow this order: [MMIM][DMP]>[EMIM][DEP]. Finally, the experimental LLE data for the studied ternary systems were compared with the calculated values obtained by means of the non-random two liquid (NRTL) model. The NRTL model was verified to accurately correlate the experimental LLE data.

Liquid–liquid equilibria for ternary system water + acetic acid + cyclohexanone at (293.2–323.2) K

Liquid–liquid equilibria (LLE) for the ternary system water+acetic acid+cyclohexanone was studied at (293.2–323.2)K and at atmospheric pressure. The immiscibility region was found to be relatively small and not sensitive to the change of temperature. The Othmer–Tobias equation and the Bachman equation were both used to check the reliability of the obtained experimental tie-line data. The experimental results were correlated with both the NRTL and the UNIQUAC activity coefficient models. The calculated results showed good agreement with the experimentally determined ternary LLE data. The root mean square deviations (RMSD) obtained by comparing the calculated and experimental two-phase compositions are 0.72% for the UNIQUAC model and 0.40% for the NRTL model. The obtained interaction parameters can be used in the calculation of LLE for the ternary system water+acetic acid+cyclohexanone as well as for the design and optimization of the related separation process.

Testing solubility data of H2S and SO2 in ionic liquids for sulfur-removal processes

Solubility data of mixtures containing hydrogen sulfide in ionic liquids and sulfur dioxide in ionic liquids at several temperatures and pressures have been tested for thermodynamic consistency. Accurate and consistent data of these mixtures are needed for the design of separation processes for removing sulfur compounds from industrial gases, processes in which ionic liquids present tremendous potential as solvents and extracting agents. The study considers data of twelve binary hydrogen sulfide+ionic liquids mixtures and three binary sulfur dioxide+ionic liquid mixtures. The modified Peng–Robinson equation of state proposed by Kwak and Mansoori is used for correlating the solubility data and a flexible thermodynamic consistency method is applied to analyze 80 isothermal P-x data sets including 630 data points available in the open literature. Modeling is found acceptable in all cases and the thermodynamic consistency method gives a clear conclusion about consistency or inconsistency of each set of data.

Thermodynamics of Coupled Protein Adsorption and Stability Using Hybrid Monte Carlo Simulations

A better understanding of changes in protein stability upon adsorption can improve the design of protein separation processes. In this study, we examine the coupling of the folding and the adsorption of a model protein, the B1 domain of streptococcal protein G, as a function of surface attraction using a hybrid Monte Carlo (HMC) approach with temperature replica exchange and umbrella sampling. In our HMC implementation, we are able to use a molecular dynamics (MD) time step that is an order of magnitude larger than in a traditional MD simulation protocol and observe a factor of 2 enhancement in the folding and unfolding rate. To demonstrate the convergence of our systems, we measure the travel of our order parameter the fraction of native contacts between folded and unfolded states throughout the length of our simulations. Thermodynamic quantities are extracted with minimum statistical variance using multistate reweighting between simulations at different temperatures and harmonic distance restraints from the surface. The resultant free energies, enthalpies, and entropies of the coupled unfolding and absorption processes are in qualitative agreement with previous experimental and computational observations, including entropic stabilization of the adsorbed, folded state relative to the bulk on surfaces with low attraction.

Efficient optimization-based design for the separation of heterogeneous azeotropic mixtures

Model-based design of separation processes for heterogeneous azeotropic mixtures is a challenging task. The multiplicity of the solutions of equilibrium calculations and the discontinuity due to the potential switching between homogeneous and heterogeneous mixtures on a tray severely complicate the application of deterministic optimization. This paper presents a novel computational approach to reliably determine phase stability and the correct equilibrium solutions in every iteration of the optimization. The approach builds on the decomposition of the optimization problem into a generic superstructure model and an implicit model for equilibrium and enthalpy calculations, which is integrated into the optimization problem by means of an external function. The phase states and equilibrium solutions are determined by means of a reliable homotopy continuation algorithm. An additional reformulation of equilibrium solutions and enthalpy calculations allows overcoming the discontinuity problems. Different case studies illustrate the applicability and show the potential of the proposed method.

Measurements and Correlation of Liquid–Liquid Equilibria for the Ternary System Water + Cyclohexanol + Cyclohexanone

Liquid–liquid equilibrium (LLE) data of the ternary system water + cyclohexanol + cyclohexanone was measured from (303.2 to 333.2) K. The reliability of the experimental tie-line data was confirmed by applying the Othmer–Tobias and the Bachman equations. The equilibrium data were correlated with the nonrandom two-liquid (NRTL) and universal quasichemical activity coefficient (UNIQUAC) models. The calculated LLE data for the ternary system agreed well with the experimental data. The root-mean-square deviations (rmsd’s) obtained comparing calculated and experimental two-phase compositions are 0.46 % for the NRTL model and 0.44 % for the UNIQUAC model. The obtained interaction parameters can be used in the calculation of LLE for the ternary system water + cyclohexanol + cyclohexanone as well as for the design, simulation, and optimization of the related separation process.

Chemometrics for Analytical Data Mining in Separation Process Design for Recovery of Artemisinin from Artemisia annua

The separation process for recovery of natural products from plants very often employs multiple separation techniques, and key to the success of such processes is to find the synergy between different separation techniques. Molecular level understanding of process streams is highly required in order to determine the synergy between unit operations, which can be attained through analysis of process streams using advanced process analyzers such as high performance liquid chromatography (HPLC), liquid chromatography–mass spectrometry (LC-MS), etc. Very often use of such process analyzers generates an enormous amount of data making it difficult to extract useful information. Therefore, application of chemometrics for extracting process information from analytical data of process streams is demonstrated in this work. The multivariate data analysis technique PARAFAC is used to extract chemical information such as number of impurities, their relative concentrations, and finally their identification from rather complex analytical chromatograms of flash column chromatography (flash CC) fractions during purification of artemisinin from the crude extract of Artemisia annua. Crude extract of A. annua leaves obtained from dichloromethane is used in this work. Prior to the application of PARAFAC, the data set is preprocessed to remove baseline drift and peak misalignment caused by retention time shifts due to matrix effects. The process information extracted from analytical chromatograms by using the PARAFAC technique indicated the presence of impurities ranging from coumarins, polyacetylenes, and flavonoids to artemisinin related compounds in the flash CC fractions.

High pressure excess isotherms for adsorption of oxygen and argon in a carbon molecular sieve

Adsorption equilibrium data for oxygen and argon are needed for design of adsorptive separation processes to produce pure oxygen from air and also for adsorptive gas storage applications. Carbon molecular sieves may be used to accomplish a rate-based separation of oxygen and argon and, as we show, may also be useful for gas storage. Given the limited data available, particularly at high pressures, volumetric methods are applied in this paper to measure surface excess isotherms of oxygen and argon on a carbon molecular sieve, Shirasagi MSC-3R Type 172. Temperatures are considered from 25 to 100°C with pressures as high as 100bar. Isotherms are compared at 25°C, including new data measured for nitrogen. Adsorbed-phase excess loadings are high, approaching 10mol/kg at 100bar. The oxygen capacity of the carbon molecular sieve at high pressure is comparable to that of a superactivated carbon on a mass basis, and it is higher on a volumetric basis. The excess adsorption isotherms are modeled using a multi-temperature Toth equation, which provides an excellent description. A carbon molecular sieve is shown to be a promising adsorbent for oxygen storage.

Dynamics of actinyl ions in water: a molecular dynamics simulation study

The dynamics of actinyl ions (AnO2(n+)) in aqueous solutions is important not only for the design of advanced separation processes but also for understanding the fate of actinides in the environment. The hazardous nature of actinides makes it difficult to measure transport and thermodynamic properties experimentally, so predictive simulations are an attractive method for studying these systems. Here, we report the results of atomistic-level molecular dynamics simulations of actinyl ions (of U, Np, Pu, and Am) in their mono- and dication states in aqueous solution. Quantum mechanically derived force field parameters are used to compute self-diffusion coefficients of the actinyl ions, water exchange mechanisms, and residence times of water molecules in the first solvation shell of the actinyl ions. We find that monocation actinyl ions diffuse slightly faster than their dication counterparts. Our simulations suggest that there are two distinct water exchange mechanisms for mono and dications. An associative interchange pathway is observed for water exchange involving dication actinyls, while in monocation actinyls the exchange occurs via a dissociative mechanism. The residence time of water molecules in the first solvation shell depends on the water exchange mechanism. In the case of dications, a stiffer actinyl bond angle results in a longer residence time, while for monocations, a shorter water coordination distance leads to a longer residence time. The simulations predict much faster water exchange for UO2(2+) than what is observed experimentally with NMR, but other properties are consistent with experiments.

Studies on the adsorption behavior of CO2-CH4 mixtures using activated carbon

Separation of CO2 from CO2-CH4 mixtures is an important issue in natural gas and biogas purification. The design of such separation processes depends on the knowledge of the behavior of multicomponent adsorption, particularly that of CO2-CH4 mixtures. In this study, we present a series of experimental binary equilibrium isotherms for CO2-CH4 mixtures on an activated carbon at 293 K and compare them with predicted values using the Ideal Adsorption Solution Theory (IAST) and the Extended Langmuir (EL) model. Even at concentrations of ca. 20% for all binary isotherms, CO2 already presents higher adsorbed amounts with respect to CH4. A maximum selectivity of around 8.7 was observed for a nearly equimolar mixture at 0.1 MPa. The IAST in conjunction with the Toth equation showed slightly better results than IAST using the Langmuir equation and both showed better results than the EL model.

Non-ideality and Solubility Modeling of Amino Acids and Peptides in Aqueous Solutions: New Physical and Chemical Approach

The estimation of accurate activity coefficients and subsequent solubilities of amino acids/peptides in solution is fundamental for the design and optimization of efficient biotechnological separation and purification processes. In this work a new activity coefficient model is developed for amino acids and peptides in aqueous solution which comprises terms that represent nonidealities arising from short-range and long-range interactions: the former are taken into account by the UNIFAC method, and the latter are computed by the Debye–Huckel equation. The chemical equilibria leading to the formation of the zwitterionic, cationic, and anionic forms of the amino acids and peptides are also part of the new model. In the particular case of zwitterion, notwithstanding its null global charge, long-range contributions are also included due to its electrostatic dipole. The interaction parameters of the new UNIFAC groups are optimized using activity coefficients compiled from the literature. The new model correlates...

Liquid–Liquid Equilibrium for Ternary System Water + Cyclohexane + Acetic Acid at (303.2 to 333.2) K

Liquid–liquid equilibrium (LLE) data for the ternary system water + cyclohexane + acetic acid have been measured at (303.2 to 333.2) K under atmospheric pressure. The Othmer–Tobias and Bachman equations were used to check the reliability of the obtained tie-line data. The experimental data were correlated by NRTL (nonrandom two-liquid) activity coefficient model, and the relevant interaction parameters were regressed with the experimental data. The predicted values by NRTL method show good consistency with the measured data. The obtained interaction parameters can be used in the calculation of LLE for the ternary system water + cyclohexane + acetic acid as well as for the design and optimization of the related separation process.

Permeation of single gases and binary mixtures of hydrogen and helium through a MFI zeolite hollow fibres membrane for application in nuclear fusion

Tritium Extraction Systems (TES) in future nuclear fusion power plants will recover tritium (radioactive hydrogen isotope) from the outlet stream of the breeder blanket, where tritium will be produced and purged out by a high flow rate of helium. This work presents an experimental assessment of the performance of a MFI zeolite hollow fibres membrane for the tritium removal and pre-concentration in the first stage of TES. A set-up was built for the permeation experiments of hydrogen and helium single gases and the separation experiments of binary mixtures of those gases. Numerous assays were performed for binary mixtures of H2 and He under various operating conditions (feed and permeate pressures, temperature, and feed composition) to assess the membrane separation performance. Optimal separations were achieved at the lowest temperatures (around room temperature) and the lowest hydrogen molar fraction (0.22). H2 and He permeances ranged 0.70–2.3 and 0.43–0.74μmolm−2Pa−1s−1, respectively, corresponding to membrane selectivities of H2 over He between 1.2 and 4.0. By regulating the feed pressure, hydrogen recovery factors around 50% were attained without compromising the maximum enrichment factor of 1.5. These preliminary data enable the design of a multi-stage separation process complying with the strict requirements for the tritium recovery and enrichment in a nuclear fusion power plant.