Room-temperature ionic liquids (RTILs) are a moderately new class of liquid substances that are characterized by a great variety of possible anion-cation combinations giving each of them different properties. For this reason, they have been termed as designer solvents and, as such, they are particularly promising for liquid-liquid extraction, which has been quite intensely studied over the last decade. This paper concentrates on the recent liquid-liquid extraction studies involving ionic liquids, yet focusing strictly on the separation of n-butanol from model aqueous solutions. Such research is undertaken mainly with the intention of facilitating biological butanol production, which is usually carried out through the ABE fermentation process. So far, various sorts of RTILs have been tested for this purpose while mostly ternary liquid-liquid systems have been investigated. The industrial design of liquid-liquid extraction requires prior knowledge of the state of thermodynamic equilibrium and its relation to the process parameters. Such knowledge can be obtained by performing a series of extraction experiments and employing a certain mathematical model to approximate the equilibrium. There are at least a few models available but this paper concentrates primarily on the NRTL equation, which has proven to be one of the most accurate tools for correlating experimental equilibrium data. Thus, all the presented studies have been selected based on the accepted modeling method. The reader is also shown how the NRTL equation can be used to model liquid-liquid systems containing more than three components as it has been the authors’ recent area of expertise.
In the last decade a growing interest was observed in low-cost adsorbents for heavy metal ions. Clinoptilolite is a mineral sorbent extracted in Poland that is used to remove heavy metal ions from diluted solutions. The experiments in this study were carried out in a laboratory column for multicomponent water solutions of heavy metal ions, i.e. Cu(II), Zn(II) and Ni(II). A mathematical model to calculate the metals' concentration of water solution at the column outlet and the concentration of adsorbed substances in the adsorbent was proposed. It enables determination of breakthrough curves for different process conditions and column dimensions. The model of process dynamics in the column took into account the specificity of sorption described by the Elovich equation (for chemical sorption and ion exchange). Identification of the column dynamics consisted in finding model coefficients β, KE and Deff and comparing the calculated values with experimental data. Searching for coefficients which identify the column operation can involve the use of optimisation methods to find the area of feasible solutions in order to obtain a global extremum. For that purpose our own procedure of genetic algorithm is applied in the study.
The article focuses on multicomponent system separation with the use of an innovative membrane-based technique i.e. pervaporation. Pervaporation is a membrane technique for separation of liquid mixtures on solid nonporous membranes. Pervaporation is used in this study to separate a quaternary system acetone-butanol-ethanol-water. Such a system may be derived from ABE fermentation process, and the resulting product, biobutanol, is a potential biofuel and may be used in internal combustion engines. Experiments in the study involving concentration of butanol by pervaporation were performed using PERVAP 4060 flat-sheet commercial membrane. To describe the PV process a semi-empirical approach was used. As a result of experiments and calculations permeance coefficients were obtained. Separation and permeance factors were calculated to assess the efficiency of the system separation. Beforehand, activity coefficients were determined for all the components of the mixture with the NRTL equation. Separation coefficients for all the components differed depending on process parameters: concentration, feed flow rate and process temperature. The study confirmed the separation effect of the quaternary system. The most interesting results were obtained for the concentration of butanol. Pervaporation allows to concentrate butanol over 10 times. The permeance coefficient reached for butanol an average value of 7.06·10-3 in comparison with the results for ethanol 3.24·10-2 and acetone 1.83·10-2 [kmol(m2h)-1]. The temperature change from 50 to 70°C led to an increased permeance factor and there was no apparent effect on it in the feed flow rate. Due to the hydrophobicity of the membrane water fluxes in the quaternary system were negative.
In order to assess the influence of hydrodynamic effects on the recovery of n-butanol by means of pervaporation, a commercial PERVAP 4060 membrane was investigated. Laboratory pervaporation experiments were carried out providing a comparison of the permeation fluxes and enrichment factors. While the enrichment factors achieved in both modules under the same process conditions were comparable, the permeation fluxes differed from each other. In order to explain the observed differences, hydrodynamic conditions in the membrane module were examined by means of CFD simulation performed with ANSYS Fluent 14.5 software. Two different modules having membrane diameters of 80 mm and 150 mm were analyzed. As a result, different velocity profiles were obtained, which served to estimate the mass transfer coefficients of butanol, ethanol and acetone.