Low Transition Temperature Mixtures Research Articles

Different extractive distillation processes for isopropanol dehydration using low transition temperature mixtures as entrainers

Low transition temperature mixtures (LTTMs) are effective and environmental-friendly entrainers for extractive distillation. However, process intensification for the LTTMs extractive distillation process is less studied. This paper provides a techno-economic study for the separation of isopropanol and water by extractive distillation using ChCl/EG1:2 as entrainer. Firstly, the σ-profiles based on the COSMO-SAC model, the residue curve maps and univolatility lines are used to investigate the advantages of ChCl/EG1:2 over ethylene glycol. Then, the conventional extractive distillation (CED) system with EG or ChCl/EG1:2 entrainers are simulated and optimized by non-dominated sorting genetic algorithm-II (NSGA-II) method with targets of minimum total annual cost (TAC), minimum CO2 emissions and minimum global energy consumption (GEC). The TAC of the CED process using ChCl/EG1:2 as entrainer is reduced by 13.75% than that of the process using ethylene glycol as entrainer. Finally, in order to reduce energy consumption, the processes of extractive dividing wall column (EDWC) and the side-stream extractive distillation system (SED) with ChCl/EG1:2 as entrainer are simulated and optimized. The results show that the EDWC with ChCl/EG1:2 can save 23.83% of TAC, 23.43% of CO2 emissions and 22.66% of GEC compared with the CED process using EG as entrainer.

Comparative study on organic solvents and green solvents in separation of aromatic hydrocarbons/low-carbon alcohols azeotrope by structure–activity relationship

Organic solvents, deep eutectic solvents, low transition temperature mixtures and ionic liquids show excellent performance in the separation of azeotropes by extractive distillation. However, the functions and characteristics of four kind of solvents in azeotropic system are not clear. The interaction between solvent molecules and p-xylene and pentanol was studied by quantum chemical calculation, and the separation mechanism was studied at the molecular level. Electrostatic interaction and van der Waals interaction are the key interactions in the complexes. They are quantitatively studied based on the energy decomposition analysis of molecular force field. The electron density difference is used to explain the weak interaction generated by electrostatic interaction. On this basis, the van der Waals potential between solvent and azeotrope molecules is intuitively displayed by using van der Waals potential. The van der Waals potential is suitable for the molecular configuration in which van der Waals interaction plays a key role, which can be regarded as a supplement to the analysis of electrostatic interaction. In addition, since the optimal molecular structure is bound to be accompanied by orbital overlap, the orbital interaction is analyzed by using Natural Bond Orbital; Use the Interaction Region Indicator function to clearly show all types of interactions in one picture. The results of quantum chemical calculation show that the introduction of solvent has a significant effect on the molecular interaction of azeotropes, which is the main factor for the solvent to reduce the relative volatility between azeotropes. This study provides important information for understanding the role of organic solvents, deep eutectic solvents, low transition temperature mixtures and ionic liquids in the separation of azeotropic systems, and has important reference value for the development of new solvents.

An effect of choline lactate based low transition temperature mixtures on the lipase catalytic properties

A new series of low transition temperature mixures (LTTM) based on choline lactate quaternary ammonium salt and various hydrogen bond donors was prepared and characterized towards their physicochemical properties and usability as an enzymatic reaction mixture for lipase-catalyzed transesterification reactions. Studies of low transition temperature mixtures have shown a long-term stabilizing effect for lipase as well as a positive influence on lipase thermal stability. In the case of Ch[Lac]:Gly: EthGly increasing the stability of lipase by 8 °C (up to 55.2 °C) compared to the control sample. Conducted transesterification reactions were characterized by high yields – up to 98% – and high purity of the obtained products.

Applications of Choline Chloride-Based Deep Eutectic Solvents as Sustainable Media and Catalyst in the Synthesis of Heterocyclic Scaffolds

Abstract:Deep eutectic solvents (DESs), also referred to as low transition temperature mixtures (LTTMs), have emerged as sustainable and cheap alternatives to conventional organic solvents in organic synthesis. This is attributed to their exceptional characteristics viz. easy preparation with readily available cheap materials, water compatibility, non-flammability, non-toxicity, biocompatibility, biodegradability, etc. All these properties label them as versatile and cost-effective green solvents. The first reported DES, choline chloride urea mixture has appeared as an innocuous solvent and catalyst in many organic transformations. This prospective DES combination has been applied extensively to the synthesis of a wide range of heterocyclic compounds including quinolones, spirooxindoles, etc. The conditions employed are relatively mild and do not require additional acid catalysts or organic solvents. This ecofriendly blend for the synthesis of heterocycles reports excellent yields of products with shorter reaction times and a simple workup procedure. Evaluating these merits, this review focuses on the recent literature published on the use of choline chloride-based DESs in the synthesis of a few important heterocyclic compounds.

Delignification of hemp stalk using a low transition temperature mixture composed of choline chloride and lactic acid

This work used a literature search to select the most suitable system for the delignification process of annual plants. This process was evaluated in terms of lignin removal from plant biomass. Based on previous experiments, a low transition temperature mixture (LTTM) was used, which was a mixture of choline chloride and lactic acid in a molar ratio of 1:2. Samples of hemp fibers were examined. The delignification of biomass was monitored by changing the content of the main components. After application of the solvent at a temperature of 100, 120, or 140 °C and a delignification time of 2 or 4 h, the lignin content expressed by Kappa number decreased to the level of 22 to 13.7. Yields of hemp fibers sown after LTTM application ranged from 72.5 to 90.6%. The results confirmed that the use of LTTM (choline chloride/lactic acid) is a suitable system for the extraction of lignin from biomass. The findings showed that LTTM was an effective delignifying agent for hemp, as a relatively low Kappa number of 13.7 and a yield of 75.9% were achieved after only 2 h and at 140 °C.

An Expedient Synthesis of 2-Aryl-substituted 2,3-Dihydroquinazolin-4(1H)-ones in Low Transition Temperature Mixture (LTTM) containing SnCl2 and L-Proline

2,3-Dihydroquinazolin-4(1H)-ones were synthesized in excellent yield in a prepared low transition temperature mixture (LTTM) containing SnCl2 and L-proline using either direct one-pot two-component cyclocondensation of anthranilamide and aldehydes or one-pot three-component cyclocondensation of isatoic anhydride, ammonium acetate and aldehydes. The prepared LTTM is a green solvent, inexpensive, non-toxic and serves a dual function as reusable catalyst and solvent with excellent reaction endorsing medium. The current protocol has several advantages including an easy work up, shorter reaction time, high yield with a higher atom economy and maximum reaction efficiency with excellent green chemistry metrics.

Is it correct to name DESs deep eutectic solvents?

Recent years of research and development have brought frequently used terms for new types of green solvents to the lexicon of scientists. This can lead to terminological inaccuracies. In particular, different names are being used for the same types of solvents: Deep Eutectic Solvents (DES); Natural Deep Eutectic Solvents; Low-Transition Temperature Mixtures; Low-Melting Mixtures. It would, therefore, be appropriate to eliminate certain inaccuracies and to use simplification, which means using the general term “Low-Temperature Transition Mixtures” or introducing the term “DES-like mixtures”.

Valorization of birch bark using a low transition temperature mixture composed of choline chloride and lactic acid

Abstract This article presents the results obtained in the extraction of birch bark with a green solvent. A low transition temperature mixture (LTTM) consisting of choline chloride (ChCl) and lactic acid in a molar ratio of 1:1 was used as the solvent. Extraction was performed at 60°C and 80°C. At both temperatures, the effect of extraction time on the yield of the extracted substances was monitored. The yields reached were compared with those obtained in studies using common solvents such as ethanol, methanol, d-limonene, ethyl acetate, and others. The extract was quantitatively analyzed by HPLC-UV to determine betulin and betulinic acid (0.491–1.788 mg/g dry bark and 0.106–0.316 mg/g dry bark, respectively). Total phenolic content was determined spectrometrically using Folin–Ciocalteu reagent and expressed as Gallic acid equivalents (GAE; 18.6–56.8 mg GAE/g dry bark). This study has shown that extraction with a green solvent composed of ChCl and lactic acid can be an effective method for extracting polyphenolic compounds from birch bark. The process for extracting triterpenes (betulin and betulinic acid) is less suitable compared to conventional methods using the mentioned organic extractants.

Imidazolium-urea low transition temperature mixtures for the UHP-promoted oxidation of boron compounds

Different carboxy-functionalized imidazolium salts have been considered as components of low transition temperature mixtures (LTTMs) in combination with urea. Among them, a novel LTTM based on 1-(methoxycarbonyl)methyl-3-methylimidazolium chloride and urea has been prepared and characterized by differential scanning calorimetry throughout its entire composition range. This LTTM has been employed for the oxidation of boron reagents using urea-hydrogen peroxide adduct (UHP) as the oxidizer, thus avoiding the use of aqueous H2O2, which is dangerous to handle. This metal-free protocol affords the corresponding alcohols in good to quantitative yields in up to 5 mmol scale without the need of further purification. The broad composition range of the LTTM allows for the reaction to be carried out up to three consecutive times with a single imidazolium salt loading offering remarkable sustainability with an E-factor of 7.9, which can be reduced to 3.2 by the threefold reuse of the system.

Process of separating acetonitrile and water using LTTMs as entrainer

Abstract New extractive distillation configurations, which use low transition temperature mixtures (LTTMs) as entrainers, have attracted widespread attention among scholars due to their green processes. Furthermore, the design and comparison of different processes can promote the application of new solvents in the future. In this study, two extractive distillation processes, the extractive distillation column (ED) and the extraction dividing wall column (EDW), were selected from previous work. The separation process of acetonitrile (ACN)-water ternary mixtures was studied, and GC3:1(choline chloride/glycolic acid mixture (molar mass 1:3)) and EC2:1((choline chloride/ethylene glycol 1:2 molar mass) were used as entrainers. Minimum consumption energy and the purity of ACN and water were set as the goals, and our sensitivity analysis and economic evaluation results showed that both ED and EDW were effective. As a result, LTTMs can be used in extractive distillation for azeotrope separation.

Development of a green catalyst for production of synthetic banana flavoring based on low transition temperature mixture through numerical optimization, LCA assessment and sustainability metrics

The transition to cleaner production of chemicals to abate the prolonged environmental impairment has been an emerging concern worldwide, calling for alternative cost effective and greener process routes. The present study witnesses the ecofriendly preparation of synthetic banana flavoring or Isoamyl acetate (IAA) catalyzed by a low transition temperature mixture (LTTM) comprised of abundantly available natural resources. The chosen LTTM exhibited bifunctional properties of highly active acidic catalyst as well as an excellent solvent media which could phase out the product as an independent layer after the reaction assuring simpler downstream processing and direct recycle of the catalytic media for subsequent runs. Numerical optimization, executed to obtain the optimal process parameters using the Box-Behnken design yielded a maximum conversion of 99.81%. The LTTM catalyzed reaction kinetics is deciphered through the pseudo-homogeneous model inclusive of the system non-ideality estimated through the UNIFAC model and the thermodynamic functions of the reaction were also evaluated to aid the realistic process design. A comparison of the proposed route and that using sulfuric acid as catalyst has been performed through a cradle to gate life cycle assessment (LCA) using the Simapro 9.1 software for the laboratory production of 1 kg IAA which revealed that the adopted green approach decreased the damage to ecosystem and resource availability by 48.8% and 30.2% respectively. Furthermore, the environment profiling of the conventional and intensified reaction pathways using green metrics also indicated the LTTM mediated production of IAA to be extremely promising that paves the path for sustainable chemical industries.

Sustainable production and purification of furfural from waste agricultural residue: An insight into integrated biorefinery

Furanic chemicals are the most significant renewable bio-chemicals with furfural being the basic platform chemical that can serve as a viable alternative to replace several petroproducts. Industrial furfural production poses several drawbacks such as poor yields, highly toxic effluents, energy intensive operations and accumulation of low value solid residue that restricts its tremendous potential. In this purview, the present research maneuvered a two-step translation strategy of corncobs, an abundant agricultural residue to furfural in a cost effective as well as environmental benign manner. Initially, the corncob is hydrolyzed using an aqueous low transition temperature mixture (LTTM) that selectively converts xylan in the lignocellulose matrix to xylose without disrupting the remaining biopolymers. The obtained xylose solution is enriched through strategic recycle of the hydrolysate with a cumulative yield of 76% after four cycles which is a potential substrate for subsequent xylose dehydration without any additional catalyst. Interestingly, autocatalysis in the LTTM media could yield 70% of theoretical furfural using nitrogen as a stripping media with 44% lower dilution of the furfural condensate. Furfural is further purified through an ecofriendly extraction technique utilizing hydrophobic deep eutectic solvents (HDES) as an effective extractant with the highest distribution coefficient being 66.2 for 1-tetradecanol and thymol based HDES portraying 98.6% recovery. The proposed furfural production process exhibits 13.8% overall yield with respect to corncob and 30% higher recovery of cellulose in the pretreated residue compared to conventional route which presents a high value integrated biorefinery with environmental compatibility.

Therapeutic Liquid Formulations Based on Low Transition Temperature Mixtures for the Incorporation of Anti-Inflammatory Drugs.

Most nonsteroidal anti-inflammatory drugs (NSAIDs) present poor aqueous solubility, impairing their efficiency in physiological media. In this context, Low Transition Temperature Mixtures (LTTMs) are a promising platform to overcome drugs’ poor solubility, forming therapeutic liquid formulations. In this work, the LTTMs of citric acid:L-arginine:water (C:A:W) and glycerol:sorbitol (G:S) were studied in terms of their features and assessed in terms of their ability to increase the solubility of six NSAIDs in physiological media. The physicochemical properties of LTTMs were characterized by state-of-art techniques commonly used for these systems. The cytotoxicity of G:S was also evaluated in L929 mouse fibroblasts and the viscosity, polarity, and pH properties of the studied mixtures were related to the solubility of NSAIDs. The pH and polarity were the parameters that most influenced the drugs’ solubility. Ibuprofen, naproxen, ketoprofen, indomethacin, and flurbiprofen did not present any solubility improvement in the formulations tested. However, concentrated mixtures of C:A:W or G:S in the physiologic-mimicked media (PBS) rendered a celecoxib solubility 4 and 5 times higher than PBS, respectively. These therapeutic liquid formulations of celecoxib in C:A:W or G:S can be a promising tool to increase celecoxib’s therapeutic efficiency in local applications.

Prediction of solvation properties of low transition temperature mixtures (LTTMs) using COSMO-RS and NMR approach

The concept of sustainable and green solvent has always highlighted in the field of energy and environmental science. The synthesis and application of natural-based Low Transition Temperature Mixture (LTTM) as a novel and green solvent for the lignocellulose biomass pre-treatment such as delignification of Oil-Palm Empty Fruit Bunch (EFB) have been greatly emphasized. In this present work, the investigation of LTTM efficiency as green solvent in delignification process was conducted using both theoretical and experimental studies. Initially, screening of solvation properties of different types of hydrogen bond acceptor (HBA) and predicted hydrogen bond donor (HBD) for synthesis of LTTMs was conducted using conductor-like screening model (COSMO-RS) software and formation of hydrogen bonding was evidenced using NMR spectroscopy analysis. Three types of HBA namely sucrose, choline chloride and monosodium glutamate were mixed with malic acids as HBD and their charge density distribution on the surface was determined through sigma profile (σ). The COSMO-RS results determined the σ profile of pure component malic acid to be 11.42, sucrose to be 25.37 and the total value of σ profile for mixtures is 14.19 as the best combination of LTTM composition compared to LTTM from choline chloride and monosodium glutamate (MSG). The reliability of the COSMO-RS predictions data was correlated with Nuclear Magnetic Resonance (NMR) analysis through determination of peaks with chemical shifts hydrogen bonding that suggested existence of potential interaction between malic acids and sucrose has occurred.

Vortex assisted dispersive liquid–liquid microextraction based on low transition temperature mixture solvent for the HPLC determination of pyrethroids in water samples: Experimental study and COSMO-RS

A green, simple, and effective vortex-assisted dispersive liquid–liquid microextraction method that utilizes a menthol-based low transition temperature mixture (menthol-LTTM-VADLLME) was developed to extract and preconcentrate four types of pyrethroids, namely bifenthrin, deltamethrin, fenpropathrin, and permethrin from water samples. In addition, quantum chemical-based conductor-like screening model for realistic solvents (COSMO-RS) software was used to predict the molecular interaction between low transition temperature mixtures (LTTMs) and pyrethroids based on their σ-profile, σ-potentials, and activity coefficient at infinite dilution. High performance liquid chromatography (HPLC) was employed for the further separation of the pyrethroids and their quantification. Several key parameters that affect pyrethroid extraction efficiency are identified as the vortex time, type of LTTM, volume of LTTM, type of dispersive solvent, dispersive solvent volume, type of salt, and amount of salt. The extraction time of 90 s and 150 µL of menthol: sesamol at ratio 1:1 were selected as the best conditions, while ionic strength and type of dispersant solvent were not relevant for the extraction of the target compounds. After optimization, the menthol-LTTM-VADLLME method was found to be able to detect pyrethroids in the range of 0.5–1000.0 μg/L with good linearity (correlation coefficient = 0.9988–0.9995). The method detection limit and quantification limit were found to be in the range of 0.05–0.11 μg/L and 0.18–0.35 μg/L, respectively. The relative standard deviation of inter-day and intra-day precisions were 2.2–5.0% (n = 5) and 1.2–1.9% (n = 7) respectively. The optimized method can successively determine pyrethroids in tap, drinking and river water samples with good recoveries of 73–111%. Hence, this method presents a good approach for determining pyrethroid content in water samples.

Application of a Low Transition Temperature Mixture for the Dispersive Liquid-Liquid Microextraction of Illicit Drugs from Urine Samples.

The use of psychoactive substances is a serious problem in today’s society and reliable methods of analysis are necessary to confirm their occurrence in biological matrices. In this work, a green sample preparation technique prior to HPLC-MS analysis was successfully applied to the extraction of 14 illicit drugs from urine samples. The isolation procedure was a dispersive liquid–liquid microextraction based on the use of a low transition temperature mixture (LTTM), composed of choline chloride and sesamol in a molar ratio 1:3 as the extracting solvent. This mixture was classified as LTTM after a thorough investigation carried out by FTIR and DSC, which recorded a glass transition temperature at −71 °C. The extraction procedure was optimized and validated according to the main Food and Drug Administration (FDA) guidelines for bioanalytical methods, obtaining good figures of merit for all parameters: the estimated lower limit of quantitation (LLOQ) values were between 0.01 µg L−1 (bk-MMBDB) and 0.37 µg L−1 (PMA); recoveries, evaluated at very low spike levels (in the ng-µg L−1 range), spanned from 55% (MBDB) to 100% (bk-MMBDB and MDPV); finally, both within-run and between-run precisions were lower than 20% (LLOQ) and 15% (10xLLOQ).

Optimization and application of green solvent extraction of natural bioactive coumarins from Lamiaceae and Asteraceae herbal plants

Simple coumarins, 2H-1-benzopyran-2-ones, represent group of natural bioactive compounds. They are considered as secondary metabolites in plants of Lamiaceae and Asteraceae families. In this study, heat assisted extraction with low transition temperature mixtures (LTTM) based on choline chloride and L-lactic acid were used for simultaneous extraction of esculin, umbelliferone, scoparone, 4-methylumbelliferone and herniarin from herbal plants prior their determination by HPLC method with fluorescence detection. The effect of LTTM composition on coumarins extraction was verified. Optimal extraction conditions included choline chloride/L-lactic acid/1,3-propanediol (1:2:1) extraction solvent, solid/liquid ratio 1/40 g/mL, treatment time 15 min, rotation speed 20 rpm and temperature 60 °C. Temperature was the most significant parameter affecting extraction efficiency, the extraction time was an important variable for penetration of solvent in the matrix. Proposed HPLC method was applicable in linear concentration ranges from 5 to 100 ng/mL (for esculin, umbelliferone, scoparone, 4-methylumbelliferone) and from 15 ng/mL to 100 ng/mL (for herniarin) (R2 ≥ 0.998). The limits of detection were 0.2–5.0 ng/mL. The recovery of the method was higher than 87.7% (RSD < 5.8%). The content of umbelliferone and herniarin in herbal plants were 11.49–68.38 μg/g. The use of LTTM extraction solvent, application the response surface methodology and Taguchi orthogonal arrays design of experiment for optimization of extraction conditions, were contribute to the green aspect of the developed method.

Scrutiny of the supramolecular structure of bio-sourced fructose/glycerol/water ternary mixtures: Towards green low transition temperature mixtures

This work deals with fully green ternary mixtures composed of three low cost, bio-sourced and safe molecules, namely Fructose (F), Glycerol (G), and Water (W), able to interact to each other by H-bonds. Through an eco-friendly approach, we prepared a series of FGW mixtures differing in their composition in order to identify the combinations exhibiting a long-lasting macroscopic homogeneity. To well understand how water interferes in such as mixtures, we focused on thermal transitions, changes in viscosity and activation energies, and on internal organization at the molecular scale through NOESY and PFG-NMR experiments. It resulted that, as a function of the water content, the FGW mixtures can be defined either i) as a cooperatively H-bonded supramolecular structure in which water is actively involved in the interactions, thus leading to stable solvents designed as low transition temperature mixtures (LTTM), or ii) as aqueous solutions due to the diluting effect of water which disrupts the H-bonded organization and promotes the overall mobility. This comprehensive study is a prerequisite for a further industrial implementation of such eco-designed solvents in various applicative attractive domains, as in cosmetic field.

Air-assisted dispersive liquid phase microextraction coupled chromatography quantification for purification of therapeutic lectin from aloe vera – A potential COVID-19 immune booster

The present research focuses on devising air assisted liquid phase microextraction coupled chromatographic quantification method for purification of therapeutic lectin using switchable low transition temperature mixtures. Four switchable low transition temperature mixtures were formed by mixing benzyl trimethyl ammonium chloride with sodium salts of various heavy chain fatty acids in the molar ratio of 1:1. Thermophysical properties (Density, Refractive index and surface tension) were determined as a function of temperature. Air-assisted dispersive liquid-phase microextraction with switchable solvents was carried out to obtain lectin rich concentrate in top phase with an extraction efficiency of (85% w/w). The purified lectin was quantified by size exclusion chromatography with the retention time of 2.3 min and resolution of 6.2 with NTU of 13.2. The ultrapure fraction of lectin was obtained with anion exchange chromatography yielding antioxidant activity of 40.2 mg GAE/g lectin and haemagglutination activity of 45.36 HU/g in the isolate. The method of dispersive liquid-phase microextraction provides a high selective one-pot extraction and partial purification of the therapeutic lectin from aloe vera.

Dispersive liquid-liquid microextraction using a low transition temperature mixture and liquid chromatography-mass spectrometry analysis of pesticides in urine samples

Biomonitoring is a potent tool to control the health risk of people occupationally and non-occupationally exposed. The latest trend in bioanalytical chemistry is to develop quick, cheap, easy, safe and reliable green analytical procedures to analyse a large number of chemicals in easily accessible biomatrices such as urine. In this paper, a new dispersive liquid–liquid microextraction (DLLME) procedure, conceived to treat urine samples and based on the use of a low transition temperature mixture (LTTM), was developed and validated to analyse twenty pesticides commonly used in farm practises. The LTTM was composed of choline chloride and sesamol in molar ratio 1:3 (ChCl:Ses 1:3); its characterization via differential scanning calorimetry identified it as an LTTM and not as a deep eutectic solvent due to the occurrence of a glass transition at -71 °C. The prepared mixture was used as the extraction solvent in the DLLME procedure, while ethyl acetate as the dispersing solvent. The salting out effect (50 mg mL−1 of NaCl in a diluted urine sample) improved the separation phase and the analyte transfer to the extractant. Due to the high ionic strength and despite the density of ChCl:Ses 1:3 (1.25 g mL−1), the LTTM layer floated on the top of the sample solution after centrifugation. All extracts were analysed by high-performance liquid chromatography coupled to mass spectrometry. After optimization and validation of the whole method, lower limits of quantitation were in the range of 0.02 – 0.76 µg L−1. Extraction recoveries spanned from 50 to 101 % depending on the spike level and analytes. Precision and accuracy ranges were 3-18% and 5-20%, respectively. The extraction procedure was also compared with other methods, showing to be advantageous for rapidity, simplicity, efficiency, and low cost. Finally, urine samples from ten volunteers were effectively analysed using the developed method.