Production of ethanol by continuous fermentation and liquid–liquid extraction

A continuous pilot plant was constructed for fermentation production of ethanol, using liquid–liquid extraction to remove the product and with recycle of the fermented broth raffinate. The plant was operated for up to 18 days with feed glucose concentrations in the range 10·0–45·8% (w/w). The solvent was n-dodecanol and immobilised yeast was used to overcome the problem of emulsification. The concentration of by-products in the fermented broth had no adverse effect on the rate of ethanol production. A mathematical model to predict the time required for achievement of 99% of the steady-state by-products concentrations was shown to be in good agreement with the experimentally determined concentration of the main by-product, glycerol. At a feed glucose concentration of 45·8% (w/w), the aqueous purge was equivalent to 2·8 m³ of effluent per m³ of ethanol produced and represented a 78% reduction in the volume of the aqueous purge compared with using a feed containing 10% (w/w) glucose.     

Optimal moving and fixed grids for the solution of discretized population balances in batch and continuous systems: droplet breakage

The numerical solution of droplet population balance equations (PBEs) by discretization is known to suffer from inherent finite domain errors (FDE). Tow approaches that minimize the total FDE during the solution of discrete droplet PBEs using an approximate optimal moving (for batch) and fixed (for continuous systems) grids are introduced. The optimal grids are found based on the minimization of the total FDE, where analytical expressions are derived for the latter. It is found that the optimal moving grid is very effective for tracking out steeply moving population density with a reasonable number of size intervals. This moving grid exploits all the advantages of its fixed counterpart by preserving any two pre-chosen integral properties of the evolving population. The moving pivot technique of Kumar and Ramkrishna (Chem. Eng. Sci. 51 (1996b) 1333) is extended for unsteady-state continuous flow systems, where it is shown that the equations of the pivots are reduced to that of the batch system for sufficiently fine discretization. It is also shown that for a sufficiently fine grid, the differential equations of the pivots could be decoupled from that of the discrete number density allowing a sequential solution in time. An optimal fixed grid is also developed for continuous systems based on minimizing the time-averaged total FDE. The two grids are tested using several cases, where analytical solutions are available, for batch and continuous droplet breakage in stirred vessels. Significant improvements are achieved in predicting the number densities, zero and first moments of the population.     

Holdup Profile in Multistage Stirred‐Cell Liquid‐Liquid Extraction Column Using Population Balance Model

The drop exit frequency model developed in the literature is modified and simplified to suit the practical situations. An adjusting factor is inserted in the exit frequency model to account for the simplification of the hydrodynamic pattern used in the analysis and the incorrect constants used in the rise velocity model. The holdup profiles calculated in the present analysis are compared with experimental and theoretical results in the literature to evaluate the model. The comparison shows good agreement between the present model and the experimental data. Even for the cases of poor agreement, the breakage and coalescence rates are adjusted, and the stages of quasi‐equilibrium state are determined to improve the results.     

Selective extraction of organic compounds from transesterification reaction mixtures by using ionic liquids

In this article, we describe assays carried out to determine the suitability of 13 ionic liquids based on 1‐n‐alkyl‐3‐methylimidazolium and n‐alkylpyridinium cations and a wide range of anions (hexafluorophophate, bis{(trifluoromethyl)sulfonyl}imide, tetrafluoroborate, methylsulfate, 2(2‐methoxyethoxy)ethylsulfate, ethylsulfate, n‐octylsulfate, dicyanamide, nitrate, tetrafluoroborate and chloride) to carry out the selective separation of the organic compounds involved in a transesterification reaction (butyl butyrate, vinyl butyrate, 1‐butanol, and butyric acid) from hexane solutions. The assayed ionic liquids were shown to be suitable solvents for the selective separation of the target compounds, the extraction process being controlled by the hydrophobicity of the compounds. The anion composition of the ionic liquid was seen to strongly influence the average extraction ratio, the highest value being reached with the chloride‐based ionic liquid. As regards the cation composition of the ionic liquids, it was seen that the average distribution ratio increased with decreasing length of alkyl chain. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Investigation of liquid–liquid phase equilibria for reactive extraction of lactic acid with organophosphorus solvents

BACKGROUND: Lactic acid is a versatile commodity chemical with a variety of applications. Synthesis of lactic acid either through fermentation of carbohydrates or through chemical synthesis is state of the art. Separation from dilute aqueous solution is complex and accounts for the major part of production costs. Reactive extraction based on reversible adduct formation is a promising alternative for the separation of lactic acid. RESULTS: Extraction was carried out with the organophosphorus solvents tri‐n‐butyl phosphate, tri‐n‐octylphosphine oxide and Cyanex 923. Shellsol T was used as diluent. Partition coefficients increase with increasing extractant content and decreasing temperature. Cyanex 923 has several advantages compared with tri‐n‐butyl phosphate and tri‐n‐octylphosphine oxide with respect to lactic acid distribution and hydrodynamic properties. Liquid‐liquid phase equilibria for lactic acid extraction with Cyanex 923 were modeled. Selectivity of lactic acid extraction with respect to glycolic acid and formic acid was discussed. CONCLUSION: The organophosphorus extractant Cyanex 923 was found to be an appropriate solvent for lactic acid extraction from aqueous solutions. Experimental data and model data based on the Law of Mass Action showed good agreement. Lactic acid extraction from multi‐acid solution showed good selectivity compared with glycolic acid. Lactic acid selectivity is low with respect to formic acid. © 2012 Society of Chemical Industry     

Determination of ternary solutions concentration in liquid–liquid extraction by the use of attenuated total reflectance‐Fourier transform infrared spectroscopy and multivariate data analysis

A simple and rapid Fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) spectroscopic chemometric method was developed to determine the concentration of solute and solvent in the raffinate layer in a liquid–liquid extraction (LLE) process using partial least squares (PLS) regression. Five type I extraction systems were used with different solute–solvent affinity. The developed model (correlation coefficient from 0.91 to 0.99) was validated with known concentration samples, and in all cases the difference was not larger than 0.5%w. The LLE for the five extraction systems was carried out in a three‐stage crosscurrent extraction process, quantifying the solute and solvent with the chemometric model developed. The results were used to calculate the stage and overall stage efficiencies for the five systems. This method showed to be fast and precise for the quantification of ternary systems in LLE.     

Dearomatization of pyrolysis gasoline with an ionic liquid mixture: Experimental study and process simulation

The pyrolysis gasoline is the main source of benzene, toluene, and xylenes. The dearomatization of this stream is currently performed by liquid – liquid extraction using sulfolane. However, the sulfolane process has high operating costs that could be minimized by employing ionic liquids as solvents because of their non‐volatile character. In this work, we proposed a novel process to perform the dearomatization of pyrolysis gasoline using a binary mixture of 1‐ethyl‐3‐methylimidazolium tricyanomethanide ([emim][TCM]) and 1‐ethyl‐4‐methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf₂N]) ILs. The composition in the IL mixture was optimized considering their extractive and thermophysical properties. The Kremser method was applied using the experimental data to determine the number of equilibrium stages in the liquid – liquid extractor which provides the same extraction yields of aromatics using the IL mixture that those of the sulfolane process. The recovery section was designed and simulated from the experimental vapor – liquid equilibrium between the hydrocarbons and the IL mixture. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4054–4065, 2017     

Mean drop size correlations and population balance models for liquid—liquid dispersion

Reliable models are required for accurate estimation of drop sizes which govern the interfacial area and rate of mass transfer in a system where various correlations and models have been improved for better accuracy and wider application breath. In this article, relevant semiempirical equations and population balance equation (PBE) models are reviewed. Semiempirical correlations are highly system dependent and limited to prediction of steady‐state drop size while PBE models could estimate transient drop size with considerations of inhomogeineity and flow spatial variation during drop size evolution. With appropriate model parameters determination, different PBE models can be used to reproduce experimental data for a similar system. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1129–1145, 2015     

Enantioseparation with liquid membranes

Chiral resolution of racemic products is a challenging and important task in the pharmaceutical, agrochemical, flavor, polymer and fragrances industries. One of the options for these challenging separations is to use liquid membranes. Although liquid membranes have been known for almost four decades and have been used for optical resolutions, no comprehensive review has been published about the use of this technology for enantioseparations. In this review, the various liquid membrane‐related technologies are described and compared, including bulk liquid membranes, emulsion liquid membranes, micelle‐extraction and micellar enhanced ultrafiltration, as well as supported liquid membranes. Next to technological advances, an overview of recent developments in chiral recognition chemistry in liquid–liquid equilibria is presented. The following extractant classes have recently been reported in conjunction with chiral separation: cyclodextrines, BINOL's, calixarenes, crown ethers, BINAP's, tartaric acids and ionic liquids. The use of two supported (non‐liquid) membranes with an inner loop of extract phase appears to be the most stable liquid membrane configuration, allowing for a large degree of freedom in operational conditions such as solvent to feed ratio. The library of solvents still needs broadening to make the technology more versatile and based on the variety of successes with catalytically active organometallic complexes, development of new chiral selector systems based on asymmetric catalysis literature is suggested for future selector screening studies. © 2017 Society of Chemical Industry     

Characterization of liquid‐liquid dispersions with variable viscosity by coupled computational fluid dynamics and population balances

Sustaining stable liquid‐liquid dispersion with the desired drop size still relies on experimental correlations, which do not reflect our understanding of the underlying physics and have a limited prediction capability. The complex behavior of liquid‐liquid dispersions inside a stirred tank, which is equipped with a Rushton turbine, was characterized by a combination of computational fluid dynamics and population balance equations (PBE). PBE took into account both the drop coalescence and breakup. With the increasing drop viscosity, the resistance to drop breakage also increases, which was introduced by the local criteria for drop breakup in the form of the local critical Webber number (We_c). The dependency of We_c on the drop viscosity was derived from the experimental data available in the literature. Predictions of Sauter mean diameter agree well with the experimentally measured values allowing prediction of mean drop size as a function of variable viscosity, interfacial tension, and stirring speed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2403–2414, 2015     

A Critical Review of the Application of Drop-Population Balances for the Design of Solvent Extraction Columns: I. Concept of Solving Drop-Population Balances and Modelling Breakage and Coalescence

Population-balances are a powerful method to predict the population behavior of drops in chemical-engineering equipment such as solvent extraction columns. In such columns a complex interaction of different phenomena, namely drop sedimentation, mass transfer, drop breakage and coalescence as well as axial dispersion occurs. In this article the concept of drop-population balances is discussed in detail as well as possible solution methods. Also, a critical review of existing models accounting for breakage and coalescence taking place in extraction columns is presented. Future parts of this series will be devoted to modelling mass-transfer and sedimentation as well as on application of single-drop based modelling.     

Liquid–liquid extraction of a recombinant protein with reverse micelles

Recombinant cytochrome b₅ was extracted into the reversed micelle phase of an anionic surfactant (AOT) in octane and back-extracted to a final aqueous phase. The extraction of the protein was controlled by an electrostatic mechanism, since it was dependent on the global charge of the protein. This was directly demonstrated by experiments with native and mutant cytochromes obtained by site directed mutagenesis. The back-extraction of cytochrome b₅ to a fresh aqueous phase was decreased by factors that reduced the size of the water pool of the organic phase, such as high salt concentrations (1–2 mol dm^?3 NaCl) and low temperatures (4°C), probably because of an increase in a favourable interaction of this protein with the surfactant at closer distances.     

Terminal and transient drop rise velocity of single toluene droplets in water

The knowledge of the drop rise velocity in dispersed systems is of fundamental importance. Especially, the residence time is needed for calculation of mass transfer rates in extraction columns. This work deals with fluid dynamic measurements of toluene droplets rising in water ranging from 1.0 to 7.0 mm, with the premise of high purity of the used chemicals. The toluene/water‐system is widely used as a test system with high interfacial tension. A semiempirical correlation for pure systems to predict the terminal velocity of single rising/falling droplets based on experimental data is presented. Results show that a distinction between maximum and characteristic mean values of the drop rise velocity is necessary, especially in the diameter range 2.4–3.0 mm where unexpected velocity fluctuations occur. Two distinct terminal rise velocities were observed for 3 mm droplets. Furthermore, comparisons of the Weber‐Reynolds‐correlation and the drag coefficient with correlations from literature show good agreement. © 2009 American Institute of Chemical Engineers AIChE J, 2009