Fatty acid‐based deep eutectic solvents for efficient absorption of VOCs : Hydrophobicity and molecular mechanism study

Hydrophobic deep eutectic solvents as attractive media for low-concentration hydrophobic VOC capture

Volatile organic compounds are a major source of air pollutants. Absorption is an effective solution to treat polluted air loaded with volatile organic compounds, but most actual absorbents are often toxic and non-biodegradable. Here, we tested eutectic solvent mixtures for the absorption of volatile organic compounds for the first time. The affinity of solvent mixtures for toluene, acetaldehyde and dichloromethane was determined by measuring vapour–liquid partition coefficients and liquid phase absorption capacities. Results show that the vapour–liquid partition coefficients vary, at 30 °C, from close to zero for acetaldehyde in the mixtures choline chloride:urea, choline chloride:glycerol and tetrabutylphosphonium bromide:glycerol to 0.124 for dichloromethane in the choline chloride:urea eutectic mixture. These values are similar or even superior to those published for ionic liquids and organic solvents. Solvents based on choline chloride, a food additive, and urea, can solubilize up to 500 times more volatile organic compounds compare to water. Moreover, deep eutectic solvents are easier to prepare and more biodegradable than ionic liquids, which are also toxic. Deep eutectic solvents are more biodegradable than silicone oils, which are also expensive. Furthermore, in terms of recycling, the absorption capacities of the tested solvents remained unchanged during five absorption–desorption cycles. These findings are patented.

Deep eutectic solvents as absorbents for VOC and VOC mixtures in static and dynamic processes

Separation of furfuryl alcohol from water using hydrophobic deep eutectic solvents

Deep eutectic solvents and conventional solvents as VOC absorbents for biogas upgrading: A comparative study

Workers have frequently disregarded long-term dermal exposure to low concentration of gaseous volatile organic compounds (VOCs). To assess dermal exposure risk to gaseous VOCs, equilibrium partitioning coefficients (pc) at the air-sweat interface on human skin surface must be examined. This study analyzed the pc values of hydrophilic iso-propanol (IPA), methyl ethyl ketone (MEK), and hydrophobic benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene (BTEXs) at the air-water and air-sweat interfaces at 27–47°C. The hydrophilic VOCs were dissolved in pure water and artificial human sweat liquors at approximately 10–125 mg/L, and hydrophobic VOCs were at approximately 0.55 mg/L. According to experimental results, the dissolved VOC concentration and salt contents simultaneously have a co-effect on pc during human dermal exposure to gaseous VOCs. The salt effect resulted in increase of pc for hydrophilic and hydrophobic VOCs, and the dissolved VOC concentration effect resulted in a reduction in pc, which is dominant for hydrophilic compounds of high concentrations of aqueous VOCs. The pc data were utilized for further assessment of risk due to dermal exposure to VOCs.

Equivalent Absorption Capacity (EAC) concept applied to the absorption of hydrophobic VOCs in a water/PDMS mixture

Due to increasingly stringent legal regulations as well as increasing social awareness, the removal of odorous volatile organic compounds (VOCs) from air is gaining importance. This paper presents the strategy to compare selected biological methods intended for the removal of different air pollutants, especially of odorous character. Biofiltration, biotrickling filtration and bioscrubbing technologies are evaluated in terms of their suitability for the effective removal of either hydrophilic or hydrophobic VOCs as well as typical inorganic odorous compounds. A pairwise comparison model was used to assess the performance of selected biological processes of air treatment. Process efficiency, economic, technical and environmental aspects of the treatment methods are taken into consideration. The results of the calculations reveal that biotrickling filtration is the most efficient method for the removal of hydrophilic VOCs while biofilters enable the most efficient removal of hydrophobic VOCs. Additionally, a simple approach for preliminary method selection based on a decision tree is proposed. The presented evaluation strategies may be especially helpful when considering the treatment strategy for air polluted with various types of odorous compounds.

Absorption of toluene by vegetable oil–water emulsion in scrubbing tower: Experiments and modeling

VOCs absorption from gas streams using deep eutectic solvents – A review

Abstract. Previous studies have demonstrated volatility-dependent absorption of gas-phase volatile organic compounds (VOCs) to Teflon and other polymers. Polymer–VOC interactions are relevant for atmospheric chemistry sampling, as gas–wall partitioning in polymer tubing can cause delays and biases during measurements. They are also relevant to the study of indoor chemistry, where polymer-based materials are abundant (e.g., carpets and paints). In this work, we quantify the absorptive capacities of multiple tubing materials, including four nonconductive polymers (important for gas sampling and indoor air quality), four electrically conductive polymers and two commercial steel coatings (for gas and particle sampling). We compare their performance to previously characterized materials. To quantify the absorptive capacities, we expose the tubing to a series of ketones in the volatility range 104–109 µg m−3 and monitor transmission. For slow-diffusion polymers (e.g., perfluoroalkoxy alkane (PFA) Teflon and nylon), absorption is limited to a thin surface layer, and a single-layer absorption model can fit the data well. For fast-diffusion polymers (e.g., polyethylene and conductive silicone), a larger depth of the polymer is available for diffusion, and a multilayer absorption model is needed. The multilayer model allows fitting solid-phase diffusion coefficients for different materials, which range from 4×10-9 to 4×10-7 cm2 s−1. These diffusion coefficients are ∼ 8 orders of magnitude larger than literature values for fluorinated ethylene propylene (FEP) Teflon film. This enormous difference explains the differences in VOC absorption measured here. We fit an equivalent absorptive mass (CW, µg m−3) for each absorptive material. We found PFA to be the least absorptive, with CW ∼ 105 µg m−3, and conductive silicone to be the most absorptive, with CW ∼ 1013 µg m−3. PFA transmits VOCs easily and intermediate-volatility species (IVOCs) with quantifiable delays. In contrast, conductive silicone tubing transmits only the most volatile VOCs, denuding all lower-volatility species. Semi-volatile species (SVOCs) are very difficult to sample quantitatively through any tubing material. We demonstrate a system combining several slow- and fast-diffusion tubing materials that can be used to separate a mixture of VOCs into volatility classes. New conductive silicone tubing contaminated the gas stream with siloxanes, but this effect was reduced 10 000-fold for aged tubing, while maintaining the same absorptive properties. SilcoNert (tested in this work) and Silonite (tested in previous work) steel coatings showed gas transmission that was almost as good as PFA, but since they undergo adsorption, their delay times may be humidity- and concentration-dependent.

ABSTRACTMixtures of tetrabutylammonium-chloride-based deep eutectic solvent (DES) and three volatile organic compounds (VOCs) – butanal, ethanol, and toluene – have been investigated using classical molecular dynamics simulations. Various structural analyses like radial and spatial distribution functions reveal the presence of specific interactions between DES components and VOCs. The interaction between the VOC and DES components depends on the nature of the former. Both ethanol and butanal have an H-bond interaction with chloride and ethylene glycol. Tetrabutylammonium cations are present above and below the ring of toluene due to the presence of π electron cloud, and toluene also forms π hydrogen bonds with ethylene glycol. The structure of DES is not significantly affected by the absorption of VOCs, which is reflected in their radial distribution functions. Components of DES become more mobile with the addition of VOCs. The interfacial region was found to be the most favourable location for the presence of VOCs.

The physical/chemical abatement of gas pollutants creates many technical problems, is costly and entails significant environmental impacts. Biological purification of off-gases is a cheap and ecologically safe way of neutralization of gas pollutants. Despite the recent advances, the main technological challenge nowadays is the purification of volatile organic compounds (VOCs) of hydrophobic character due to their low solubility in water. Among all known biological methods of air purification, the most cost-effective biodegradation of hydrophobic VOCs is conducted by biotrickling filters. In this context, fungi have gained an increasing interest in this field based on their ability to biodegrade hydrophobic VOCs. In addition, biotrickling filtration using fungi can support a superior hydrophobic VOC abatement when compared to the bacterial biofilters. This paper aims at reviewing the latest research results concerning biocatalytic activity of fungi and evaluating the possibilities of their practical application in biofiltration systems to remove hydrophobic VOCs.

VOC absorption in supramolecular deep eutectic solvents: Experiment and molecular dynamic studies

Absorption is one of the most important treatment technologies for the removal of volatile organic compounds (VOCs) from tail gases, yet the separation of the absorbents and VOCs remains challenging because of concerns related to environmental impact and large energy requirements. Herein, we explored an absorption and desorption process using N,N-dimethylcyclohexylamine (CyNMe2) as a representative switchable-hydrophilicity solvent (SHS) and toluene as a representative VOC. The results showed that in comparison to common absorbents, CyNMe2 exhibits excellent toluene absorption performance. Desorption efficiencies of toluene from CyNMe2 of up to 94% were achieved by bubbling CO2 at 25 °C, and separation efficiencies of CyNMe2 from water up to 90% were achieved by bubbling N2 at 60 °C. Even after five absorption–desorption cycles, the toluene absorption capacity of CyNMe2 was comparable with that of the fresh absorbent, suggesting that CyNMe2 retains its absorption capacity. We demonstrate an innovative and reversible remediation strategy of VOCs based on SHSs, and the results indicate that SHSs can be used as an alternative to common absorbents for the removal of VOCs to reduce environmental pollution and energy consumption.