Degradation Of Ionic Liquids Research Articles

A novel assessment method for the catalytic activity of ionic liquid degradation of PET

Ionic liquids (ILs) have been recognized as environmentally friendly and effective catalysts for poly (ethylene terephthalate) (PET) glycolysis. However, further investigation is required to gain a deeper understanding of the depolymerization mechanism. In this study, a series of experiments are conducted to investigate the impact of metallic and non-metallic ILs, containing diverse anions, on the interaction with PET surfaces. The findings indicate that the catalytic efficiency of IL is strongly correlated to the intensity of the interaction with PET. When the interface adhesion strength is more than twice that of PET/PET, the IL exhibits efficient catalytic properties in PET glycolysis. Therefore, an innovative approach involving the use of AFM for efficiently assessing highly effective IL catalysts is proposed. In addition, attenuated total reflectance Fourier transform-infrared (ATR-FTIR) spectroscopy and density functional theory (DFT) calculations further demonstrate the predominant interaction mechanism between ILs and PET. This research provides guiding significance for understanding the mechanism of PET glycolysis.

Cheap and efficient strategy for photocatalytic degradation of ionic liquids by La/Ce-codoped TiO2@PAM composites.

Ionic liquids are regarded as green solvents mainly due to their non-volatile and easy regeneration and recycling properties. However, ionic liquids have negative effects on the environment and human health, especially alkyl imidazole ionic liquids are more toxic than traditional organic solutions. Studies on the toxicology, ecotoxicology, and degradation of ionic liquids are rarely found in the literature. Here, we prepared the cheap La and Ce-codoped TiO2@PAM (polyacrylamide) composite microspheres with a simple procedure for the first time to degrade three kinds of imidazole ionic liquids with high efficiency. The experimental results show that the composite La (0.25%) and Ce (0.15%)-codoped TiO2@PAM composite microspheres with calcination temperature of 450 °C had a high photocatalytic activity for 1-butyl-3-methyl imidazolium hexafluorophosphate, 1-hexyl-3-methyl imidazolium hexafluorophosphate, and 1-octyl-3-methyl imidazolium hexafluorophosphate with the concentration of 10 mg/L. The photocatalysis degradation extent of the three ionic liquids is 97.4, 91.2, and 88.5% at 90 min. This work opened a new route for the simple preparation of cheap composite microspheres in the photocatalytic degradation of ionic liquids with a high efficiency.

Fenton and photo-assisted advanced oxidative degradation of ionic liquids: a review.

Ionic liquids (ILs) are the class of materials which are purely ionic in nature and liquid at room temperature. Their remarkable properties like very low vapour pressure, non-inflammable and high heat resistance are responsible for their use as a very appealing solvent in a variety of industrial applications in place of regular organic solvents. Because ILs are water soluble to a certain extent, the industrial wastewater effluents are found to contaminate with their traces. The non-biodegradability of ILs attracts the attention of the researchers for their removal or degradation from wastewater. Numbers of methods are available for the treatment of wastewater. However, it is very crucial to use the most efficient method for the degradation of ILs. Advanced oxidation process (AOP) is one of the most important techniques for the treatment of ILs in wastewater which have been investigated during last decades. This review paper covers the cost-effective Fenton, photochemical and photocatalytic AOPs and their combination that could be applied for the degradation of ILs from the wastewater. Theoretical explanations of these AOPs along with experimental conditions and kinetics of degradation or removal of ILs from water and wastewater have been reported and compared. Finally, future perspectives of IL degradation are presented.

Effects of sodium persulfate and hydrogen peroxide on imidazolium ionic liquid degradation by simulated solar light in aqueous ZnO suspension

AbstractThe degradation of an ionic liquid: hexyl methyl imidazolium chloride (HMImCl) in the systems of simulated solar light/ZnO and simulated solar light/ZnO/oxidant (i.e., H2O2 and S2O82−) were investigated in aqueous solution. The influences of different variables such as catalyst concentration, hydrogen peroxide, and persulfate dosage on HMImCl photocatalytic degradation were determined. It was found that the adsorption of HMImCl on the catalyst surface was insignificant. The photocatalytic degradation of HMImCl followed pseudo first‐order kinetics, and the rate constant at natural pH (pH 7.2) was 11.8 × 10−2 min−1. The addition of hydrogen peroxide to the process not only does not enhance the degradation rate of HMImCl but also decreases kapp significantly with [HMImCl] = 3×10−5 mol L−1, oxidant concentration (in the range of 5 × 10−5–10−1 mol L−1), and catalyst concentration of 1 g L−1. The results elucidated that the use of Na2S2O8 (in the range of 10−4–10−2 mol L−1) strongly enhances the degradation rate of HMImCl compared with photocatalytic process of the catalyst.

Investigations of potential ionic liquid phases for chromatographic processes using spectroscopic and thermal techniques

The thermal degradation of ionic liquids 1-octyl-3-methyl imidazolium trifluoromethanesulfonate ([OMIM][TfO]) and 1-octyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([OMIM][Tf2N]) were investigated using spectroscopic and thermal techniques to predict gas chromatographic phase stability. For differential scanning calorimetry, lowering the heating rate from 10 to 2 °C/min decreased the decomposition temperature of the ionic liquids ∼ 23 °C for [OMIM][TfO] and ∼ 13 °C for [OMIM][Tf2N]. In addition, lowering the heating rate gave better resolution and showed anion thermal decomposition occurred several degrees before cation decomposition for the ionic liquids. Experimental measurements showed that decomposition of the ionic liquids was indicated at lower temperatures when using spectroscopic methods compared to thermal scanning methods. Total synchronous fluorescence spectroscopy was used to monitor the formation of ionic liquid degradation products during thermal stress experiments. Decomposition temperatures determined by differential scanning calorimetry were approximately 140 °C higher compared to measurements by fluorescence spectroscopy.

Acid Catalysis with Alkane/Water Microdroplets in Ionic Liquids.

Ionic liquids are composed of an organic cation and a highly delocalized perfluorinated anion, which remain tight to each other and neutral across the extended liquid framework. Here we show that n-alkanes in millimolar amounts enable a sufficient ion charge separation to release the innate acidity of the ionic liquid and catalyze the industrially relevant alkylation of phenol, after generating homogeneous, self-stabilized, and surfactant-free microdroplets (1–5 μm). This extremely mild and simple protocol circumvents any external additive or potential ionic liquid degradation and can be extended to water, which spontaneously generates microdroplets (ca. 3 μm) and catalyzes Brönsted rather than Lewis acid reactions. These results open new avenues not only in the use of ionic liquids as acid catalysts/solvents but also in the preparation of surfactant-free, well-defined ionic liquid microemulsions.

Influence of ionic liquids on mechanical and thermal properties of polyethylene from renewable resources

Polyethylene from renewable resources produced using sugarcane as raw material was modified with phosphonium ionic liquids. Tensile properties and thermal behavior of modified biopolyethylene in air and nitrogen atmosphere were studied. The thermal degradation of ionic liquids and their influence on thermal degradation of polyethylene from renewable resources were studied by thermogravimetric analysis (TGA). In general, modification of biopolyethylene with phosphonium ionic liquids resulted in improvement of tensile properties, i.e., tensile strength and Young’s modulus. Thermal degradation of biopolyethylene modified with phosphonium ILs proceeds in one step in the range of 400–500 °C in nitrogen atmosphere. Modification of polyethylene with trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate ionic liquid resulted in increase in DTGpeaks and T10% temperatures toward higher temperature for modified polyethylene in comparison with unfilled PE sample both in air and nitrogen atmosphere.

Degradation of imidazolium ionic liquids in a thermally activated persulfate system

Thermally activated persulfate (PS) oxidation, a clean source of sulfate radicals (SO4•–), has been used as a promising advanced oxidation method for the treatment of organic contaminants. In this study, the degradation of ionic liquids (ILs) by thermally activated PS was investigated with 1-alkyl-3-methylimidazolium bromides (C4mimBr) as a model compound. The effects of various factors including temperature, initial IL and PS concentrations, solution pH, alkyl chain length of imidazolium cation, and common water constituents such as humic acid (HA), HCO3-and Cl- were evaluated. Results showed that C4mimBr can be completely degraded in 2 h at 60 °C, indicating effective removal of C4mimBr by thermally activated PS oxidation. The oxidation followed a pseudo-first-order kinetics model, and the rate constant increased with increasing temperature, PS concentration and initial solution pH. Alkyl chain length had no effect on the degradation. HA and Cl- had negative effects on C4mimBr removal, while 5 mM HCO3- increased C4mimBr degradation. Multiple intermediate products were identified by HPLC-MS/MS and the degradation pathway and mechanism were proposed. The free radicals generated in the activated PS system (e.g., SO4•– and •OH) showed different effects on the degradation. SO4•– radicals select to attack the substituted side chain of ILs cation, producing more chance for •OH to attack the imidazolium core. Moreover, toxicity tests using bioluminescent bacteria Vibrio Qinghaiensis sp.-Q67 and nematode C. elegans demonstrated efficient detoxification of CnmimBr treatment. These findings may offer an environmentally friendly approach for ILs treatment in aqueous solution.

Quantitative Raman spectroscopy for the Ioncell\xae process: Part 2\u2014quantification of ionic liquid degradation products and improvement of prediction performance through interval PLS

One of the main issues associated with ionic liquids (ILs) is their recyclability. Viable recycling concepts can only be developed if one knows what is in the IL mixtures and solutions. In our previous work, we showed that it is possible to quantify water and 1.5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] IL components in liquid mixtures using Raman spectroscopy. In this regard, we considered Raman spectroscopy as a promising analytical method for the inline monitoring and control of the Ioncell® process. In the present work, we push the limits of this analytical method further by extending it to more complex and realistic liquid mixtures including the hydrolysis product 1-(3-aminopropyl)-2-pyrrolidone (APP) that can be formed upon the reaction of 5-diazabicyclo[4.3.0]non-5-ene (DBN) with water. Quantifying APP is important in order to measure the extent of the hydrolysis reaction and apply the right corrective measures to reverse the reaction and to maintain the process within the optimal working conditions. The simultaneous quantification of the four components (Acetic acid, DBN, APP and H2O) in typical Ioncell® liquid streams is investigated using Raman spectroscopy. The sensitivity of the Raman method in quantifying APP is also highlighted in comparison with refractometry, which is widely applied to measure IL concentration in aqueous mixtures. Finally, we propose simple modifications on the multivariate partial least square regression model based on a variable selection algorithm to enhance the accuracy of the predicted calibration values.

Differential pulse voltammetry as a powerful tool to monitor the electro-Fenton process

This study presents the applicability of differential pulse voltammetry (DPV) technique to carry out in-depth research of electro-Fenton process. To this end, the degradation of the ionic liquid p-xylene-bis(n-pyridinium bromide) was performed, and the main parameters that influence this process were also evaluated. DPV allowed monitoring the evolution of Fe(III) reduction as redox probe, enabling to examine the degradation of ionic liquid and the effect of the potential as well as main intermediates formed throughout the process. By using DPV tool, application of sequential current intensities along the electro-Fenton process was evaluated as alternative to reduce the energy consumption keeping the same efficiency. Based on the profile of the voltammetric curves and the determination of hydroxyl radicals, currents of 50 and 600 mA were chosen for testing a bi-electrical current system. Thus, a current of 600 mA was applied for 30 min followed by 50 mA for 60 min (600, 50), and vice versa (50, 600). Both trials achieved a total organic carbon (TOC) abatement around 60%, being the system (600, 50) less energy consuming (0.24 kWh g−1 TOC) than the other system (50, 600) (5.90 kWh g−1 TOC). Furthermore, chromatographic analyses of inorganic ions allowed validating the attained results. Finally, the feasibility of this bi-electrical current process to a real matrix was successfully carried out, achieving the same TOC abatement when working with synthetic solution. This fact demonstrated the potential of the bi-electrical current electro-Fenton system and its suitability for more complex matrix, as well as the potential of DPV technique to deeply study the electro-Fenton process.

A Comparative Study on Photocatalytic Degradation of Pyridinium – Based Ionic Liquid by TiO2 and ZnO in Aqueous Solution

Abstract The photocatalytic degradation of hexylpyridinium bromide (HPyBr) from an aqueous solution was studied by focusing on comparison of the photoactivity of ZnO and TiO2 P25. The process was carried out under different experimental conditions. The results showed that there is no adsorption of pollutant by both catalysts in the dark. The efficiency of P25 Degussa and ZnO photocatalysts were compared, and the photocatalytic kinetics study showed that ZnO is more efficient than TiO2 P25. The HPyBr photodegradation was found to follow a pseudo-first order kinetics, and the higher rates constants were obtained at the alkaline medium for ZnO (pH = 11, kapp = 9.61 × 10–2 min−1) and at acidic medium for TiO2 P25 (pH = 3, kapp = 1.28 × 10–2 min−1). The Langmuir–Hinshelwood model was found suitable to explain the rate constant data for the ionic liquid degradation by both catalysts. The presence of carbonate ions at alkaline medium was found to reduce the HPyBr degradation for ZnO and to enhance the HPyBr degradation for TiO2, this enhancement in TiO2/CO32-/UV system was confirmed by the addition of •OH and hvb+ scavengers. According to TOC and COD results, HPyBr mineralization was faster in ZnO/UV system than in TiO2/UV system.

Coupling electro-Fenton process to a biological treatment, a new methodology for the removal of ionic liquids?

This work proposes a hybrid system for the remediation of toxic and/or refractory pollutants, such as the ionic liquid 1-butyl-1-methylpyrrolidinium chloride, which cannot be degraded by conventional methods such as biological oxidation. Therefore, the electro-Fenton process was evaluated as a pre-treatment stage, since it is a powerful technology capable of degrading complex organic pollutants. First, the key operating parameters (anodic material, iron dosage, current applied and initial pollutant concentration) were evaluated to reach complete ionic liquid degradation (98% total organic carbon abatement). The electro-Fenton treatment target pollutant was accompanied by an increase of its biodegradability, tested from average oxidation state and carbon oxidation state parameters. Based on these values, 30 min of pre-treatment by electron-Fenton process was selected and then the solution thus treated was subjected to biological treatment using bacteria and fungi consortiums. The evolution of TOC and carboxylic acids were followed during assays, attaining an overall abatement of 78% and 67% for bacteria and fungi cultures, respectively. Conversely, a control test of ionic liquid performed without pre-treatment was showed no variation in TOC and no formation of carboxylic acids. Therefore, the feasibility at laboratory scale of the coupling between electro-Fenton and biological treatment has been demonstrated.

In vitro toxicological evaluation of ionic liquids and development of effective bioremediation process for their removal

The present study deals with the cyto-genotoxicological impact of ionic liquids, 1-butyl-3-methylimidazolium bromide, trihexyl tetradecylphosphonium dicyanamide, 1-decyl-3-methylimidazolium tetrafluoroborate, benzyldimethyltetradecylammonium chloride, and 1-butyl-4-methylpyridinium chloride, on animal cells and their biodegradation. The long alkyl chain containing ionic liquids were found to be more toxic whereas benzene functional group in benzyldimethyltetradecylammonium chloride enhances its toxicity. Aerobic bacterial granules, a bacterial consortium, were developed that have promising ability to break down these organic pollutants. These aerobic bacterial granules have been applied for the biodegradation of ionic liquids. The biological oxygen demand (5 days) and chemical oxygen demand parameters confirmed that the biodegradation was solely due to aerobic bacterial granules which further decreased the time period needed for regular biodegradation by biological oxygen demand (28 days). The high resolution mass spectrometry analysis further approved that the degradation of ionic liquids was mainly via removal of the methyl group. Elevated N-demethylase enzyme activity supports the ionic liquids degradation which may be occurring through demethylation mechanism. The amplicon sequencing of aerobic bacterial granules gives insight into the involvement of the bacterial community in the biodegradation process.

Photostability and photocatalytic degradation of ionic liquids in water under solar light.

The aim of this work is to study, (i) the photostability of different imidazolium and pyridinium ionic liquids (ILs) in water under solar light; and (ii) the photocatalytic degradation of those ILs in water with TiO2 under solar light. The effects of the type of cation and anion as well as the length of the cationic chain of the imidazolium ILs have been analyzed. These imidazolium-based ILs show high solar stability, slightly decreasing as the length of the cationic chain increases. The anion plays a main role in the stability of ILs under solar light, decreasing in the case of hydrophobic anions. The kind of head group (pyridinium or imidazolium) or the presence of functional groups (allyl, OH) also influence the solar light stability. DFT calculations on the fundamental and excited electronic states of the ILs were carried out to obtain a deeper insight on their photostability. In the case of the photocatalytic degradation of the ILs, complete conversion was achieved for all the ILS tested but mineralization reached 80% at the most. The rate of degradation increased with the length of the alkyl chain while the anion showed little effect. The pyridinium-based IL tested was the easiest to breakdown.

Electroanalytical techniques applied to monitoring the electro-Fenton degradation of aromatic imidazolium-based ionic liquids

In this study, the degradation of the ionic liquid (IL) 1,3-dicyclohexylbenzimidazolium chloride ([DCy6bim][Cl]) was carried out by applying an heterogeneous electro-Fenton (HEF) treatment using iron alginate spheres (FeAS) as catalyst. Initial trials were performed at current between 50 and 250 mA, different FeAS dosages (1–5 g), and [DCy6bim][Cl] concentrations (70–280 mg L−1) as key parameters for the characterization of the HEF process. Comparative experiments suggest that high current, low FeAS dosage and low [DCy6bim][Cl] concentration are the best conditions to yield near complete total organic carbon decay after 4 h. In order to evaluate the catalyst behaviour and iron leaching during the degradation of [DCy6bim][Cl], differential pulse voltammetry (DPV), a sensitive and selective electroanalytical technique, was used to monitor the IL degradation, by-products and iron evolution into the solution at high concentration levels. The profile of the voltammetric curves obtained by DPV suggests almost complete cleavage of the cation structure of [DCy6bim][Cl] during the first 120 min. At longer treatment times, DPV revealed the generation of iron complex with chloride and carboxylic acids. Finally, chromatographic analysis of these carboxylic acids and inorganic anions permitted to validate the results obtained by DPV and demonstrated the feasibility of the HEF process for IL degradation.

Electro-assisted activation of peroxymonosulfate by iron-based minerals for the degradation of 1-butyl-1-methylpyrrolidinium chloride

Abstract In the present study, the degradation of ionic liquid 1-butyl-1-methylpyrrolidinium chloride has been carried out through sulfate radicals. These radicals were generated by different methods of activation of the commercial peroxymonosulfate (PMS) formulation, Oxone®. Among them, the electro-assisted activation in presence of iron provided the best results in terms of pollutant removal and mineralization. However, radical scavenging takes place at high concentration of catalyst (Fe 2+ ) in solution, that provokes the reduction of the removal rate. In order to control the iron self-regulation in the process, iron-based minerals such as pyrite, goethite and magnetite were studied as catalyst. This process was evaluated in detail and the key factors as catalyst concentration, oxidant dosage and applied current were analyzed. It was confirmed that the removal reaction in the heterogeneous system followed pseudo-first order kinetic model. Pyrite catalyst achieved the best results and its application was optimized. The activation of PMS (10 mM) by pyrite (1 mM) under electric field (150 mA) showed a very high pollutant degradation efficiency (over 80% TOC decay in 300 min) with a low electrical energy consumption per log-unit of pollutant concentration decrease (5.45 kWh m −3 order −1 ). In addition, the use of solid catalyst eased its separation from the reaction medium and its reuse at least 5 cycles, achieving in all cases a degradation efficiency near 100% in 300 min. This fact justifies the developed process as a promising treatment for a novel class of neoteric contaminants such as ionic liquids.

Fenton-based processes for the regeneration of catalytic adsorbents

In the present study, natural phyllosilicate clays, Illite and Montmorillonite, were stablished as efficient adsorbents for the removal of the ionic liquid 1-butyl, 2,3-dimethyl imidazolium chloride, achieving, respectively, 14 and 25mg/g of adsorption. In addition, the regeneration of both adsorbents was hereby firstly performed by Fenton-based processes, using the catalytic action of the iron naturally present in clays. Two different reactor configurations, with regard to the ratio of adsorbent to liquid phase, were tested: fluidized and fixed bed reactors. The desorption equilibrium was the main limiting factor for the effective regeneration of the Illite clay by electro-Fenton process in the fluidized bed reactor. On the other hand, the fixed bed reactor, based on electrokinetic-Fenton phenomenon, proved to be suitable for the regeneration of the Montmorillonite clay and it would be an appropriate solution for the implementation of adsorbent regeneration by Fenton-based technology at large adsorbent/solution ratios. Both reactor configurations were suitable for the adsorbents regeneration, and 80% of ionic liquid degradation has been accomplished. Additionally, the adsorption capability of both clays was confirmed after the regeneration process, achieving almost the same initial uptake.

On the interaction of carbon electrodes and non conventional electrolytes in high-voltage electrochemical capacitors

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr14BF4) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr14TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et4NBF4/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation.

Heterogeneous electro-Fenton catalyst for 1-butylpyridinium chloride degradation.

The application of the electro-Fenton process for organic compound mineralisation has been widely reported over the past years. However, operational problems related to the use of soluble iron salt as a homogeneous catalyst involve the development of novel catalysts that are able to operate in a wide pH range. For this purpose, polyvinyl alcohol-alginate beads, containing goethite as iron, were synthesised and evaluated as heterogeneous electro-Fenton catalyst for 1-butylpyridinium chloride mineralisation. The influence of catalyst dosage and pH solution on ionic liquid degradation was analysed, achieving almost total oxidation after 60min under optimal conditions (2g/L catalyst concentration and pH3). The results showed good catalyst stability and reusability, although its effectiveness decreases slightly after three successive cycles. Furthermore, a plausible mineralisation pathway was proposed based on the oxidation byproducts determined by chromatographic techniques. Finally, the Microtox® test revealed notable detoxification after treatment which demonstrates high catalyst ability for pyridinium-based ionic liquid degradation by the electro-Fenton process.

Kinetics of imidazolium-based ionic liquids degradation in aqueous solution by Fenton oxidation.

In the last few years, several works dealing with Fenton oxidation of ionic liquids (ILs) have proved the capability of this technology for their degradation, achieving complete ILs removal and non-toxic effluents. Nevertheless, very little is known about the kinetics of this process, crucial for its potential application. In this work, the effect of several operating conditions, including reaction temperature (50-90°C), catalyst load (10-50mgL-1 Fe3+), initial IL concentration (100-2000mg L-1), and hydrogen peroxide dose (10-200% of the stoichiometric amount for the complete IL mineralization) on 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) oxidation has been investigated. Under the optimum operating conditions (T=90°C; [Fe3+]0=50mgL-1; [H2O2]0=100% of the stoichiometric amount), the complete removal of [C4mim]Cl (1000mgL-1) was achieved at 1.5-min reaction time. From the experimental results, a potential kinetic model capable to describe the removal of imidazolium-based ILs by Fenton oxidation has been developed. By fitting the proposed model to the experimental data, the orders of the reaction with respect to IL initial concentration, Fe3+ amount and H2O2 dose were found to be close to 1, with an apparent activation energy of 43.3kJmol-1. The model resulted in a reasonable fit within the wide range of operating conditions tested in this work.