Prashant S. Kulkarni

Deep desulfurization of diesel fuel using ionic liquids: current status and future challenges

Deep desulfurization of diesel fuel has attracted the attention of a growing number of scientists and engineers due to the stringent regulations imposed on the presence of sulfur in fuel (10 ppm). To bring down the concentration of sulfur compounds to less than 10 ppm is very challenging and demands newer technologies. Novel processes are being proposed for this purpose. It is observed that ionic liquids as class of green solvents can play a major role in the deep desulfurization of diesel fuel. For this reason, this review focuses on the current status in application of ionic liquids for achieving ultra-low-sulfur diesel (ULSD). To get a comprehensive perspective about the topic, other techniques of desulfurization are also discussed in brief in the introduction. Here we propose that the appropriate removal method should be selected according to different systems. To achieve deep desulfurization using ionic liquids, a better understanding regarding the regeneration of ionic liquids is vitally important.

Studies on membrane stability and recovery of uranium (VI) from aqueous solutions using a liquid emulsion membrane process

An extensive study on separation and recovery of uranium (VI) from dilute aqueous solutions using a liquid emulsion membrane (LEM) technique is presented. The study has highlighted the importance of emulsion stability for maximizing uranium recovery. The emulsion constitutes tri-n-octylphosphine oxide (TOPO) as a carrier, paraffin as organic diluent, an emulsifying agent, and stripping phase. The residence time required for adequate pertraction of uranium has been evaluated. The important variables affecting the LEM permeation process such as the concentrations of surfactant, extractant, internal strip phase, and effect of speed of agitation, aqueous feed phase pH, and the presence of iron were systematically investigated. Using suitable values, an attempt was made to recover uranium from a synthetic process plant stream. It was found that strip phase sodium carbonate concentration of 0.5 M gives maximum recovery of uranium. The feed phase pH has been found to be critical for uranium recovery by this technique.

Toxicological evaluation on human colon carcinoma cell line (CaCo-2) of ionic liquids based on imidazolium, guanidinium, ammonium, phosphonium, pyridinium and pyrrolidinium cations

Toxicological evaluation of a new group of ionic liquids was performed on human colon cancerous cells—CaCo-2. They belong to different classes of cations: imidazolium (IM), dimethyl-guanidinium (dmg) and tetramethyl-guanidinium (tmg), methyl-pyrrolidinium (MPyr), 2-methyl-1-ethyl-pyridinium (2-MEPy), quaternary ammonium (benzyltriethyl-ammonium–BzTEA; phenyltrimethyl-ammonium–PhTMA; tri-n-octyl-methylammonium-Aliquat) and tri-n-hexyl-tetra-n-decylphosphonium (P6,6,6,14). The new results were compared with data obtained in previous reported studies performed in our lab, and we clearly saw that toxicity can vary significantly with the type of anion. Dicyanoamide-[DCA] and bis(trifluoromethanesulfonyl)amide-[NTf2] were seen to visibly change the impact of some cations. Some were considerably less harmful for CaCo-2 monolayer when the anion was [DCA] or [NTf2], while others induced an abnormal increase of cellular metabolism when [NTf2] was present and therefore, they were considered toxic. However, some cations induced similar responses in the presence of a broad number of anions as (1-butyl-3-methylimidazolium)-[C4MIM] (with the exception of [FeCl4]), (1-(2-hydroxyethyl)-3-methylimidazolium)-[C2OHMIM] and [C4MPyr] and did not cause toxicity. Consequently, they are considered promising cations for building human friendlier solvents. But, a reasonable number of other combinations involving different classes of cations were also seen to not significantly affect viability of the CaCo-2 monolayer.

Highly selective monitoring of metals by using ion-imprinted polymers

AbstractIon imprinting technology is one of the most promising tools in separation and purification sciences because of its high selectivity, good stability, simplicity and low cost. It has been mainly used for selective removal, preconcentration, sensing and few miscellaneous fields. In this review article, recent methodologies in the synthesis of IIPs have been discussed. For several applications, different parameters of IIP including complexing and leaching agent, pH, relative selectivity coefficient, detection limit and adsorption capacity have been evaluated and an attempt has been made to generalize. Biomedical applications mostly include selective removal of toxic metals from human blood plasma and urine samples. Wastewater treatment involves selective removal of highly toxic metal ions like Hg(II), Pb(II), Cd(II), As(V), etc. Preconcentration covers recovery of economically important metal ions such as gold, silver, platinum and palladium. It also includes selective preconcentration of lanthanides and actinides. In sensing, various IIP-based sensors have been fabricated for detection of toxic metal ions. This review article includes almost all metal ions based on the ion-imprinted polymer. At the end, the future outlook section presents the discussion on the advancement, corresponding merits and the need of continued research in few specific areas. Graphical AbstractIIPs for the selective monitoring of metals

Shear‐induced lamellar phase of an ionic liquid crystal at room temperature

The phase behaviour of a number of N‐alkylimidazolium salts was studied using polarizing optical microscopy, differential scanning calorimetry and X‐ray diffraction. Two of these compounds exhibit lamellar mesophases at temperatures above 50°C. In these systems, the liquid crystalline behaviour may be induced at room temperature by shear. Sheared films of these materials, observed between crossed polarisers, have a morphology that is typical of (wet) liquid foams: they partition into dark domains separated by brighter (birefringent) walls, which are approximately arcs of circle and meet at “Plateau borders” with three or more sides. Where walls meet three at a time, they do so at approximately 120° angles. These patterns coarsen with time and both T1 and T2 processes have been observed, as in foams. The time evolution of domains is also consistent with von Neumanns law. We conjecture that the bright walls are regions of high concentration of defects produced by shear, and that the system is dominated by the interfacial tension between these walls and the uniform domains. The control of self‐organised monodomains, as observed in these systems, is expected to play an important role in potential applications.

Supported ionic liquid membranes for removal of dioxins from high-temperature vapor streams.

Dioxins and dioxin-like chemicals are predominantly produced by thermal processes such as incineration and combustion at concentrations in the range of 10-100 ng of I-TEQ/kg (I-TEQ = international toxic equivalents). In this work, a new approach for the removal of dioxins from high-temperature vapor streams using facilitated supported ionic liquid membranes (SILMs) is proposed. The use of ceramic membranes containing specific ionic liquids, with extremely low volatility, for dioxin removal from incineration sources is proposed owing to their stability at very high temperatures. Supported liquid membranes were prepared by successfully immobilizing the ionic liquids tri-C(8)-C(10)-alkylmethylammonium dicyanamide ([Aliquat][DCA]) and 1-n-octyl-3-methylimidazolium dicyanamide ([Omim][DCA]) inside the porous structure of ceramic membranes. The porous inorganic membranes tested were made of titanium oxide (TiO(2)), with a nominal pore size of 30 nm, and aluminum oxide (Al(2)O(3)), with a nominal pore size of 100 nm. The ionic liquids were characterized, and the membrane performance was assessed for the removal of dioxins. Different materials (membrane pore size, type of ionic liquid, and dioxin) and different operating conditions (temperature and flow rate) were tested to evaluate the efficiency of SILMs for dioxin removal. All membranes prepared were stable at temperatures up to 200 °C. Experiments with model incineration gas were also carried out, and the results obtained validate the potential of using ceramic membranes with immobilized ionic liquids for the removal of dioxins from high-temperature vapor sources.

Selective extraction of natural products with benign solvents and recovery by organophilic pervaporation: fractionation of D-limonene from orange peels

There has been a growing awareness of the need to replace volatile organic compounds (VOCs) by benign solvents aiming to implement more sustainable processes. Accordingly, this work aims at evaluating a new and more friendly process based on the use of benign solvents with different hydrophobicities, namely common alimentary oil, polypropylene glycol and polyethylene glycol, for the selective recovery of natural products, followed by pervaporation. Particularly, the extraction and fractionation of limonene from orange peels was studied and optimised, where a high value product is obtained from a highly abundant material that is mostly disposed. Firstly, the best benign solvents were selected, in order to obtain high yields of extraction, and then pervaporation and vacuum distillation were compared after the extraction process, in order to obtain high yields of global recovery of limonene with the least contaminants possible. The integrated process selected was the extraction of limonene from orange peels using polypropylene glycol 240 (PPG), followed by organophilic pervaporation, providing the selective recovery of limonene free of solvent.

Emulsion ionic liquid membranes (EILMs) for removal of Pb(II) from aqueous solutions

Ionic liquids (ILs) are playing increasingly important roles in the membrane separation processes. The present manuscript discusses the removal of Pb(II) ions from aqueous solution using an emulsion ionic liquid membrane (EILM) process. Initially, the emulsion liquid membrane (ELM) was prepared by stirring strip phase (sulphuric acid) and organic phase (surfactant: span 80, extractant: D2EHPA, diluent: hexane) together under high speed agitation. Note that, the parameters of the ELM process such as emulsification speed, pH of the feed phase, treat ratio, extractant and surfactant concentrations were studied for the maximum removal of Pb(II) ions. The role of IL was explored by adding hydrophobic IL, octylmethylimidazole hexafluorophosphine ([OMIM][PF6]), in the organic phase. The performance of ELM with and without IL was compared on the basis of stability, enrichment factor and the removal efficiency for Pb(II). The results showed that the percentage of Pb(II) extraction was complete by the emulsion membrane with IL (EILM) in comparison to the 97% achieved by neat ELM. Further, the stability and the enrichment factor of the EILM were found to be 2–3 times greater than that of the ELM. The FT-IR spectroscopic analysis revealed that bond interactions between IL and membrane phase components avoided the coalescence of internal phase droplets and enhanced the emulsion stability. The results obtained in this work support the use of the IL [OMIM][PF6] as both a stabilizer and carrier for the overall improvement of the ELM process.

Ultrafast igniting, imidazolium based hypergolic ionic liquids with enhanced hydrophobicity

Exploring ultrafast igniting and hydrolytically stable ionic liquids (ILs) has a wide scope in hypergolic rocket fuels. The hydrophobicities of ILs, induced by a smart change in alkyl substituents of imidazolium cations with energy-rich cyanoborohydride, [BH3CN]− and dicyanamide, [DCA]− anions were examined for the first time. The physico-chemical properties and performance of ILs were also studied. Consequently, hydrolytic stability in terms of moisture study of all the ILs was thoroughly investigated under standard environmental conditions. The analysis indicates that the IL 14, 1-allyl-3-octyl imidazolium cyanoborohydride is most hydrophobic and hydrolytically stable. Studies evaluating the role of the cationic hydrocarbon chain and the nature of anions of ILs on the properties of hypergolic fuel were carried out. All the ILs are liquid at room temperature and exhibit a positive heat of formation. IL 10, 1,3-diallyl-imidazolium cyanoborohydride exhibited the shortest ignition delay of 1.9 ms with WFNA and IL 11, 1-allyl-3-ethyl imidazolium cyanoborohydride presented the lowest viscosity of 16.62 mPa s. Therefore, these ILs can be suggested as potential candidates for replacing acutely toxic and carcinogenic hydrazine and its methylated derivatives as hypergolic fuels.

Versatility of polyethylene glycol (PEG) in designing solid–solid phase change materials (PCMs) for thermal management and their application to innovative technologies

The research on phase change materials (PCM) has evolved significantly in the last few decades due to the need to manage the demands of energy requirements. Polyethylene glycol (PEG) is established as an organic solid–liquid PCM offering a wide range of enthalpies and phase transition temperatures as a function of its molecular weight. Herein, we have focussed on three aspects including preparation methods, microencapsulation and applications. An attempt has been made to focus on thermal conductivity enhancement methods used in the preparation of PEG based PCMs to give way for the commercial utility of these materials. The concluding remarks address the future directions for investigation, challenges and new possibilities for practical implementation of these materials.