Extraction of 5-Hydroxymethylfurfural and Furfural in Aqueous Biphasic Systems: A COSMO-RS Guided Approach to Greener Solvent Selection

5-Hydroxymethylfurfural (HMF) and furfural (Fur) are promising biobased platform chemicals, derived from the dehydration of carbohydrate feedstocks, normally conducted in an aqueous phase. Plagued by side-reactions in such phase, such as the rehydration to levulinic acid (LA) and formic acid (FA) or self-condensation to humins, HMF and Fur necessitates diversification from monophasic aqueous reaction systems toward biphasic systems to mitigate undesired side-reactions. Here, a methodology based on the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) method was used to screen solvent candidates based on the predicted partition coefficients (Ki). Hansen solubility parameters in conjunction with excess thermodynamic quantities determined by COSMO-RS were employed to assess solvent compatibility. Experimental validation of the COSMO-RS values highlighted only minor deviations from the predictions with root-mean-square-error (RMSE) values of HMF and Fur at 0.76 and 5.32, respectively, at 298 K. The combined effort suggested cyclohexanone, isophorone, and methyl isobutyl ketone (MIBK) as the best candidates. Finally, extraction solvent reuse demonstrated cyclohexanone suitability for HMF extraction with KHMF of 3.66 and MIBK for Fur with KFur 7.80 with consistent partitioning across four total runs. Both solvents are classified as recommended by the CHEM21 solvent selection guide, hence adding to the sustainability of the process.

Recovery of Phenolic Compounds from Orange Peel Waste by Conventional and Assisted Extraction Techniques Using Sustainable Solvents

BACKGROUND

The valorization of orange peel waste (OPW) through the extraction of bioactive compounds is a clear example of the circular economy. OPW contains many value-added compounds, among which bioactive phenolic compounds (flavonoids and phenolic acids) could be extracted and used for industrial applications, such as pharmaceuticals or cosmetics.

METHODS

In this work, the extraction of phenolic compounds from orange peel was carried out by conventional (orbital shaker) and assisted (ultrasound and microwave) extraction techniques using deionized water, 80% (v/v) ethanol in water, and ethyl acetate as solvents. The effect of temperature, extraction time, and type of technique was evaluated and discussed following spectrophotometric (total phenolic content and total flavonoid content) and high-performance liquid chromatography (HPLC) analyses of the extracts.

RESULTS

The most effective extraction in terms of efficiency was achieved by microwave-assisted extraction using 80% (v/v) ethanol in water as the extraction solvent, at 373 K for 6 min, which obtained 7.2 ± 0.1 mg gallic acid equivalent (GAE)/g OPW and 13.3 ± 0.1 mg quercetin equivalent (QE)/g OPW, with the main bioactive compound extracted being hesperidin (58.2 ± 0.2 mg/g OPW). The most effective extraction in terms of energy consumption was achieved using ultrasound-probe-assisted extraction, yielding 8.8 ± 0.0 mg GAE/g OPW; 17.1 ± 0.1 mg QE/g OPW; 40.0 ± 0.2 mg hesperidin/g OPW, with an energy consumption of 18 kJ.

CONCLUSIONS

Ultrasound and microwave-assisted extractions can be considered efficient extraction technologies for the valorization of OPW as they reduce extraction time and energy consumption and increase extraction yield.

Green solvents extraction-based detoxification to enhance the enzymatic hydrolysis of steam-exploded lignocellulosic biomass and recover bioactive compounds

A novel strategy for pre-treated biomass detoxification combining emerging green solvents and low environmental impact extraction technologies was evaluated. Steam-exploded biomass was subjected to microwave-assisted or orbital shaking extraction using bio-based or eutectic solvents. The extracted biomass was enzymatically hydrolysed. The potential of this detoxification methodology was studied in terms of phenolic inhibitors extraction and sugar production improvement. The effect of adding a post-extraction water washing step before hydrolysis was also evaluated. Excellent results were achieved when steam-exploded biomass was subjected to the microwave-assisted extraction combined with the washing step. The highest sugar production was achieved when ethyl lactate was used as extraction agent (49.80 ± 3.10 g total sugar/L) over the control (30.43 ± 0.34 g total sugar/L). Results suggested that a detoxification step based on green solvents would be a promising option to extract phenolic inhibitors, which can be revalorized as antioxidants, and improve the sugar production from the extracted pre-treated biomass.

Enhanced Recovery of Natural Antioxidants from Grape Waste Using Natural Eutectic Solvents-Based Microwave-Assisted Extraction

The evaluation of sustainable solvents as alternatives to more harmful conventional solvents combined with intensification techniques to recover phenolic compounds from agri-food waste is in the spotlight. The wine industry generates large amounts of waste as a consequence of grape processing operations, which can be revalued by solvent extraction of valuable antioxidants for food and fine chemical applications. Therefore, the present study focuses on the use of natural eutectic solvents (NAESs) with benign environmental, health, and safety profiles, for valorization of grape waste in the context of a circular economy. Herein, up to 15 NAESs consisting of combinations of three hydrogen bond acceptors (choline chloride, L-proline, and betaine) and four hydrogen bond donors (1,2-propanediol, glycerol, and 1,2- and 1,3-butanediol) were evaluated for antioxidant recovery. After an initial screening of the performance of NAESs by conventional extraction, the process was intensified by microwave-assisted extraction (MAE). The extracts were analyzed by UV/VIS spectrophotometric and HPLC methods. Promising results were obtained with the solvent betaine, 1,2-butanediol [1:4], using MAE at 100 °C for 3 min. Overall, the proposed NAESs-based MAE method was successfully applied to recover target compounds from grape waste, with great prospects for the antioxidants market and sustainable development for the winery sector.

Sustainable joint solventless coproduction of glycerol carbonate and ethylene glycol via thermal transesterification of glycerol

Valuable glycerol carbonate and ethylene glycol can simultaneously be obtained from glycerol in solventless operation by means of a thermal reaction in the absence of a catalyst.