Optimizing solvent selection for separation and reaction

Solvent selection is an important factor in chemical process efficiency, profitability, and environmental impact. Prediction of solvent phase behavior will allow for the identification of novel solvent systems that could offer some economic or environmental advantage. A modified cohesive energy density model is used to predict the solid-liquid-equilibria for multifunctional solids in pure and mixed solvents for rapid identification of process solvents for design of crystallization processes. Some solubility data at several temperatures are also measured to further test the general applicability of the model. Gas-expanded liquids have potential environmentally advantageous applications as pressure tunable solvents for homogeneous and heterogeneous catalytic reactions and as novel solvent media for anti-solvent crystallizations. The phase behavior of some carbon dioxide/organic binary systems is measured to provide basic process design information. Solvent selection is also an important factor in the anti-solvent precipitation of solid compounds. The influence of organic solvent on the solid-liquid equilibria for two solid pharmaceutical compounds in several carbon dioxide expanded solvents is explored. A novel solvent system is also developed that allows for homogeneous catalytic reaction and subsequent catalyst sequestration by using carbon dioxide as a miscibility switch. The fundamental biphasic solution behavior of some polar organics with water and carbon dioxide are investigated.Ph.D.Committee Chair: Charles A. Eckert; Committee Co-Chair: Charles L. Liotta; Committee Member: Amyn S. Teja; Committee Member: J. Carson Meredith; Committee Member: Rigoberto Hernande

Measurement and correlation of liquid - Liquid equilibria of three imidazolium ionic liquids with acetone and cyclohexane

Ionic liquids (ILs) can be recycled as extractants for their low vapor pressure and volatility. More and more applications are applied to the separation of industrial organic matter. The industrial production of ILs has gradually been realized, which also widens the way for the application of ILs. In this work, the liquid-liquid extraction of cyclohexane-acetone azeotropic mixture with different ILs {1-butyl-3-methylimidazolium bis(trifluormethylsulfonyl), 1-butyl-3-methylimidazolium trifluoromethansulfonate and 1-butyl-3-methylimidazolium dicyanamide} is studied. The extraction mechanism is discussed based on the molecular scale. The relationship between hydrogen bond donor and acceptor between ILs and acetone is analyzed by COSMO-SAC. The interaction between molecules is optimized and calculated by Materials Studio 7.0. The extraction ability of ILs is analyzed by radial distribution function, and the experimental results are verified. The liquid-liquid equilibrium test is carried out at 298.15 K. Distribution and selectivity are indices used to judge the extraction efficiency of ILs. The NRTL model and UNIQUAC model are adopted to correlate the liquid-liquid equilibrium data. The results show that all of the two models can well correlate the experimental.This work is supported by the National Natural Science Foundation of China (No. 21776145), National Natural Science Foundation of China (No. 21676152)

An overview process analysis of the aromatic-aliphatic separation by liquid–liquid extraction with ionic liquids

There is a lack of knowledge on comprehensive studies when dealing with ionic liquids and extraction processes. In this work, the computational COSMO-based/Aspen multiscale methodology is applied to perform a comprehensive process analysis over a wide set of 100 common ILs after properly validating against all reliable data published, in the representative field of the aromatic/aliphatic separation. The analysis describes: i) the evolution from extractive properties to extractor behavior; ii) the influence of the rigor of the model -binary (n-heptane + toluene) or multicomponent (pyrolysis gasoline) and the process description, namely extractor or complete process with recycling streams; iii) the role of the IL at commercial specifications; iv) the role of the separation train. Main results highlight: i) leading role of mass-based distribution ratio to reduce energy consumption to assess a commercial recovery; ii) selecting an IL with a minimum selectivity required within the more efficient separation train to achieve specifications at the lower energy consumption. Therefore, this work presented a clear guide to properly select the IL extractive properties at process scale and commercial specifications, together with the development of an efficient separation train, as the best approac

Phase equilibrium studies of NFM and toluene with heavy hydrocarbons and the conceptual process design of an aromatics recovery unit.

Masters of Science in Chemical Engineering. University of KwaZulu-Natal. Durban, 2017.Distillation and extraction are commonly employed phase separation techniques, and improved efficiency and cost reduction in these large-scale processes are motivating factors behind thermodynamic equilibrium investigations. This first objective of the research undertaken was phase equilibrium studies of two ternary systems comprising of a heavy hydrocarbon and toluene, with the suitability of NFM as an extraction solvent investigated, due to its good selectivity and heat stability (Xia et al., 2008). The other objective was the development and simulation of a conceptual process design using Aspen Plus V8.4 to demonstrate the separation and recovery of aromatics using NFM, and to make a comparison to an existing process in terms of energy and cost efficiency. Ternary liquid-liquid equilibrium (LLE) phase compositions were generated for the systems n-nonane (1) + toluene (2) + NFM (3), as well as n-decane (1) + toluene (2) + NFM (3). The measurements were conducted at 303.15 K, 323.15 K, and 343.15 K for each system. The modified apparatus of Raal and Brouckaert (1992) was used, with the latest modifications to the cell incorporating an adjustable temperature sleeve and magnetic stirrer (Narasigadu et al., 2014). The uncertainty in temperature of each cell was 0.02 and 0.01 respectively. Composition uncertainty was minimized by ensuring that phase composition samples were within 1% of the repeatability error for the average absolute deviation of at least 3 samples taken. Samples were analysed using gas chromatography. The ternary systems measured in this work were modelled in terms of the NRTL model (Renon and Prausnitz, 1968) and the UNIQUAC model (Abrams and Prausnitz, 1975). Calculated RMSD values were between 0.002 and 0.02 for both models, indicating that the models represented the data satisfactorily, with the NRTL model displaying superior representation due to lower RMSD values compared to UNIQUAC. The effectiveness of using NFM an alternative solvent to extract toluene from a mixture containing n-nonane and n-decane was evaluated by determining the distribution coefficient, selectivity, and separation factor. A process design simulation was developed using Aspen Plus V8.4 for the separation of benzene, toluene, ethylbenzene and xylene (BTEX) isomers from a hydrocarbon mixture using NFM as the ABSTRACT ii solvent. Process conditions and column specifications were optimized by investigating numerous unit configurations and running sensitivity analyses on these parameters. The aim was to target a recovery of at least 99% aromatics, which was achieved. A sequence of columns was used to effect the aromatics recovery, consisting of a counter-current liquid-liquid extraction column, followed by four distillation columns in series. The simulation results indicated that the process would consume at least 11 kcal/kg extract less energy than the sulfolane process. This manifests as lower heating and steam requirements, resulting in reduced costs of at least R19 million per annum

A universal segment approach for the prediction of the activity coefficient.

Doctor of Philosophy in Chemical Engineering. University of KwaZulu-Natal, Durban 2016.This study comprised an investigation into solid-liquid equilibrium prediction, measurement and modelling for active pharmaceutical ingredients, and solvents, employed in the pharmaceutical industry. Available experimental data, new experimental data, and novel measuring techniques, as well as existing predictive thermodynamic activity coefficient model revisions, were investigated. Thereafter, and more centrally, a novel model for the prediction of activity coefficients, at solid-liquid equilibrium, which incorporates global optimization strategies in its training, is presented. The model draws from the segment interaction (via segment surface area), approach in solidliquid equilibrium modelling for molecules, and extends this concept to interactions between functional groups. Ultimately, a group-interaction predictive method is proposed that is based on the popular UNIFAC-type method (Fredenslund et al. 1975). The model is termed the Universal Segment Activity Coefficient (UNISAC) model. A detailed literature review was conducted, with respect to the application of the popular predictive models to solid-liquid phase equilibrium (SLE) problems, involving structurally complex solutes, using experimental data available in the literature (Moodley et al., 2016 (a)). This was undertaken to identify any practical and theoretical limitations in the available models. Activity coefficient predictions by the NRTL-SAC ((Chen and Song 2004), Chen and Crafts, 2006), UNIFAC (Fredenslund et al., 1975), modified UNIFAC (Dortmund) (Weidlich and Gmehling, 1987), COSMO-RS (OL) (Grensemann and Gmehling, 2005), and COSMOSAC (Lin and Sandler, 2002), were carried out, based on available group constants and sigma profiles, in order to evaluate the predictive capabilities of these models. The quality of the models is assessed, based on the percentage deviation between experimental data and model predictions. The NRTL-SAC model is found to provide the best replication of solubility rank, for the cases tested. It, however, was not as widely applicable as the majority of the other models tested, due to the lack of available model parameters in the literature. These results correspond to a comprehensive comparison conducted by Diedrichs and Gmehling (2011). After identifying the limitations of the existing predictive methods, the UNISAC model is proposed (Moodley et al, 2015 (b)). The predictive model was initially applied to solid-liquid systems containing a set of 18 structurally diverse, complex pharmaceuticals, in a variety of solvents, and compared to popular qualitative solubility prediction methods, such as NRTLSAC and the UNIFAC based methods. Furthermore, the Akaike Information Criterion (AIC) (Akaike, 1974) and Focused Information Criterion (FIC) (Claeskens and Hjort, 2003) were used to establish the relative quality of the solubility predictions. The AIC scores recommend the UNISAC model for over 90% of the test cases, while the FIC scores recommend UNISAC in over 75% of the test cases. The sensitivity of the UNISAC model parameters was highlighted during the initial testing phase, which indicated the need to employ a more rigorous method of determining parameters of the model, by optimization to the global minimum. It was decided that the Krill Herd algorithm optimization technique (Gandomi and Alavi, 2012), be employed to accomplish this. To verify the suitability of this decision, the algorithm was applied to phase stability (PS) and phase equilibrium calculations in non-reactive (PE) and reactive (rPE) systems, where global minimization of the total Gibbs energy is necessary. The results were compared to other methods from the literature (Moodley et al., 2015 (c)). The Krill Herd algorithm was found to reliably determine the desired global optima in PS, PE and rPE problems. The algorithm outperformed or matched all other methods considered for comparison, including swarm intelligence and genetic algorithms, with an average success rate of 89.5 %, and with an average number of function evaluations of 1406. The UNISAC model was then reviewed, and extended, to incorporate the significantly more detailed group fragmentation scheme of Moller et al. (2008), to improve the range of application of the model. New UNISAC segment group area parameters that were obtained by data fitting, using the Krill Herd Algorithm as an optimization tool, were calculated. This Extended UNISAC model was then used to predict SLE compositions, or temperatures, of a large volume of experimental binary and ternary system data, available in the literature, (over 4000 data points), and was compared to predictions by the UNIFAC-based and COSMO-based models (Moodley et al., 2016 (d)). The AIC scores suggest that the Extended UNISAC model is superior to the original UNIFAC, modified UNIFAC (Dortmund) (2013), COSMO-RS(OL), and COSMO-SAC models, with relative AIC scores of 1.95, 4.17, 2.17 and 2.09. In terms of percentage deviations alone between experimental and predicted values, the modified UNIFAC (Dortmund) model, and original UNIFAC models, proved superior at 21.03% and 29.03% respectively; however, the Extended UNISAC model was a close third at 32.99%. As a conservative measure to ensure that inter-correlation of the training set did not occur, previously unmeasured data was desired as a test set, to verify the ability of the Extended UNISAC model to estimate data outside of the training set. To accomplish this, SLE measurements were conducted for the systems diosgenin/ estriol/ prednisolone/ hydrocortisone/ betulin and estrone. These measurements were undertaken in over 10 diverse organic solvents, and water, at atmospheric pressure, within the temperature range 293.2-328.2 K, by employing combined digital thermal analysis and thermal gravimetric analysis, to determine compositions at saturation (Moodley et al., 2016 (e), Moodley et al., 2016 (f), Moodley et al., 2016 (g)). This previously unmeasured test set data was compared to predictions by the Extended UNISAC, UNIFAC-based and COSMO-based methods. It was found that the Extended UNISAC model can qualitatively predict the solubility in the systems measured (where applicable), comparably to the other popular methods tested. The desirable advantage is that the number of model parameters required to describe mixture activities is far lower than for the group contribution and COSMO-based methods. Future developments of the Extended UNISAC model were then considered, which included the preliminary testing of alternate combinatorial expressions, to better account for size-shape effects on the activity coefficient. The limitations of the Extended UNISAC model are also discussed

The thermodynamics of liquids in solution at 298 K and 1 atm.

Thesis (M.Sc. Eng)-University of Natal, Durban, 2003.For many years the problem of separating aliphatic and aromatic compounds has been at the forefront of the petroleum and oil refining industries. This separation is often effected using liquid-liquid extraction or extractive distillation. Both of these processes require the addition of a solvent to bring about separation. The aims of this work were to investigate the use of "mixed" solvents, such as those used in the Arosolvan process, for their application in liquid-liquid extraction and extractive distillation as well as to provide related thelmodynamic data for systems containing mixed solvents. In the last part of this work, a computer program was developed to theoretically predict the effectiveness of a number of solvents on a user-defined separation. The solvents used for liquid-liquid extraction were chosen based on their similarities to those in the Arosolvan process and were of the form, {N-methyl-2-pyrollidone (NMP) + glycerol, a glycol or water} where the glycol was either monoethylene glycol (MEG), diethylene glycol (DEG) or triethylene glycol (TEG). The additives were combined in various mixing ratios to NMP to determine a mixing ratio for which the effect of the solvent is possibly optimized (a list of all solvents and mixing ratios used are presented in this work). Solvent selectivity and the range of compositions over which separation could occur determined the effectiveness of the solvents. This work dealt with the separation of n-hexane and toluene. In order to determine the selectivity and range of compositions, the liquid-liquid equilibria (LLE) of systems containing n-hexane + toluene + solvent had to be determined. LLE was measured using a simple equilibrium cell at 298 K and 1 atm. The phase separation boundaries (binodal curves) were determined using a titration method. The results obtained in this work showed an increase in the range of compositions over which the mixture of n-hexane and toluene could be separated (i.e a larger range of mixing ratios over which these components could be separated from each other) from the pure NMP solvent to the mixed solvent cases. This implies that there is a The range of compositions over which separation could be affected is given (for the solvents) in descending order: NMP + 50% glycerol> NMP + 10% water > NMP + 30% MEG > NMP + 5% water > NMP + 30% glycerol> NMP + 10% glycerol > NMP + 10% MEG > NMP + 10% DEG > NMP + 10% TEG > NMP + 5% DEG > 100% NMP. The selectivities of the solvents showed a remarkable increase from the pure NMP case to the mixed solvent cases. The maximum selectivity obtained for the NMP + 10% DEG system was over 1200 compared to a maximum selectivity of just 6 for the pure NMP system. The maximum selectivities obtained in descending order were as follows: NMP + 10% DEG > NMP + 10% TEG > NMP + 10% glycerol > NMP + 10% MEG > NMP + 30% MEG > NMP + 50% glycerol > NMP + 10% water > NMP + 5% water > NMP + 30% glycerol > NMP + 5% DEG > 100% NMP. The binodal curves were modelled using the Hlavaty, ,8-density and log-y functions. The maximum standard deviations obtained were 0.075, 0.078 and 0.05 for each of the functions respectively. The equilibrium data was modelled using the UNIQUAC and NRTL thermodynamic models and showed excellent agreement. This work showed better agreement to the NRTL functions due to the fact that the non-randomness parameter, a ij , may be chosen arbitrarily. The results obtained in this work indicate that the use of mixed solvents greatly increases the effectiveness ofNMP used for the separation of n-hexane and toluene. It is suggested that further studies be performed on a wider range of aliphatic and aromatic compounds in order to determine whether this is a generic behaviour or just true for n-hexane and toluene. The effectiveness of each solvent for extractive distillation was determined by its separation factor. In order to determine separation factors, the activity coefficients at infinite dilution (IDACs) had to be measured. This was done using a gas-liquid chromatography technique. The solvents employed in this study were NMP, Glycerol, MEG, TEG, NMP + 10% glycerol, NMP + 10% MEG, NMP + 10% DEG, NMP + 10% TEG. The solutes used were: pentane, heptane, hexane, toluene and benzene. The separation factors were determined for each alkane/aromatic pair per solvent. The pure solvent cases were then compared to the mixed solvent cases. The mixed solvents did not show results as promising for extractive distillation applications as they did for liquid-liquid extraction. TEG displayed the best selectivities for each of the alkane/aromatic separations except for the heptane/benzene pair, for which NMP + 10% glycerol proved to be the most effective solvent. When compared to the results obtained from the original UNIF AC model, the IDACs obtained in this work showed up to a 99% deviation. This is due to the fact that the model does not work well for all types of molecules and does not predict the equilibrium of "unlike" molecules adequately. It is suggested that other mixing ratios and different solvents be used to further investigate the effectiveness of mixed solvents for extractive distillation applications. It is further recommended that a computer aided data logging system be developed to determine residence times. This would not only provide more accurate results, but also provide a database for future reference. The computer program that was developed using the original UNIF AC method contains a database of 28 commonly used industrial solvents. This program enables the user to compare graphically the effectiveness of each of the solvents on the desired separation. Due to the limitations of the original UNIF AC method, the program does not work well for all types of molecules. However, the model can be changed without altering the prografnming structure to include a modified version of the UNIFAC model depending on the users needs. The program although written from an extractive distillation standpoint can be extended to include liquid-liquid equilibrium predictions. The main benefit of such a program is to eliminate time-consuming experimental work required to narrow down a long list of solvents required for a particular separation by theoretically predicting the best solvents for the job. The solvent database can also be expanded when new solvents become available or the user needs chang

Ionic liquids as solvents in separation processes.

Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.Due to the ever increasing need for sustainable development, the chemical and allied industries have been at the focus of much change. Decreasing tolerances on pollution via waste streams has resulted in a re-examination of many chemical processes. This has ushered in the era of 'green chemistry' which incorporates the synthesis of a process in both a sustainable and economically viable manner. In the petroleum and chemical industries, this has led to the search for alternatives to volatile organic compounds. Ionic liquids provide one such alternative. With a wide liquid phase and no measurable vapour pressure, ionic liquids have been found to be successful as a medium for reactions. Ionic liquids differ from high-temperature molten salts in that they have a significantly lower melting point. This work investigates the use of ionic liquids as solvents in separations. The work focuses on the separation of alpha-olefins from complex mixtures. The ionic liquids used in this study were: • l-methyl-3-octyl-imidazolium chloride • 4-methyl-N-butyl-pyridinium tetrafluoroborate • trihexyl-tetradecyl-phosphonium chloride Three experimental techniques used to evaluate ionic liquids were: • gas-liquid chromatography • liquid-liquid equilibria measurements • vapour-liquid equilibria measurements l-Methyl-3-octyl-imidazolium chloride ((MOIM)C1) was used as a stationary phase in gas-liquid chromatography. The solutes used were: • Alkanes: n-Pentane; n-Hexane; n-Heptane; n-Octane • Alkenes: 1-Hexene; 1-Heptene; l-Octene • Alkynes: l-Hexyne; l-Heptyne; 1-0ctyne • Cycloalkanes: Cyclopentane; Cyclohexane; Cycloheptane • Aromatics: Benzene; Toluene Activity coefficients at infinite dilution were measured at temperatures (298.15, 308.15 and 318.15) K. Values at 298.15 K ranged from 1.99 for benzene to 26.1 for n-octane. From the temperature dependence of the activity coefficients, the partial excess molar enthalpies at infinite dilution were calculated. These range from 2.0 kJ.mol'l for l-octyne to 7.3 kJ.mol·1 for n-pentane. (MOIM)C1 shows reasonable ability to separate 1-hexene from the longer n-alkanes and aromatics. 4-Methyl-N-butyl-pyridinium tetrafluoroborate (BuMePyBF) was used as a solvent in liquid-liquid equilibria measurements. The following systems were measured at 298.2 K: • LLE System 1: BuMePyBF4 + 1-Hexene + Toluene • LLE System 2: BuMePyBF4 + 1-Hexene + Ethanol • LLE System 3: BuMePyBF4 + 1-Hexene + 2-Butanone • LLE System 4: BuMePyBF4 + 1-0ctene + Ethanol LLE System 1 is a type 11 system and the other systems being type I. All systems exhibit a large two-phase region. LLE System 1 shows low distribution. LLE System 3 show almost equal distribution between phases resulting in a distribution ratio of close to 1. LLE Systems 2 and 4 show high distribution ratios at low concentrations of solute. LLE Systems 1 and 3 show low to moderate selectivity of the solvent towards the solute. LLE Systems 2 and 4 show high to moderate selectivity, but decrease exponentially with increasing solute concentration in the organic phase. For all systems investigated, the solvent shows no miscibility with feed solutions of low to medium solute concentration. The binodial curves were correlated to the Hlavaty equation, the beta function and the log gamma function. The correlations yielded acceptable results for LLE Systems 2, 3 and 4. The tie-lines were correlated to the NRTL model, with LLE systems 2 and 4 giving acceptable results and LLE systems 1 and 3 give excellent results. The following binary vapour-liquid equilibrium systems were measured: • Acetone + Methanol at 99,4 kPa • l-Hexene + 2-Butanone at 74.8 kPa The acetone + methanol system exhibits a minimum boiling azeotrope at 0.78 mole fraction acetone. The l-hexene + 2-butanone system exhibits a minimum boiling azeotrope at 0.83 mole fraction l-hexene. Trihexyl-tetradecyl-phosphonium chloride (CJ3C1PhCl was then added to the above systems in order to evaluate it as a solvent in extractive distillation. (CJ3C1PhCI shifts the azeotrope of the acetone + methanol system to a higher acetone concentration, but does not remove it altogether. (CJ3C1PhCI has a negative effect on the relative volatility of the l-hexene + 2-butanone, thus rendering it ineffective as an extractive distillation solvent for this system. Another aspect that was considered in this work was the production of an ionic liquid. Synthesis steps and experimental considerations were discussed. A major factor in the use of ionic liquids is the cost of the ionic liquid itself. The major problem associated with ionic liquids is the general lack of available information that is necessary for them to be implemented in a process. Ionic liquids show potential as solvents in liquid-liquid extraction for a number of systems. Their potential as solvents in extractive distillation is probably limited, due to their miscibility/immiscibility properties, to systems involving slightly polar to highly polar compounds