Abstract
This review will discuss, under the Circular Economy and Biorefinery concepts, the performance of the alternative solvents in the downstream process to recover natural pigments in a more sustainable way. Conventionally, pigments marketed on an industrial scale are produced through chemical synthesis by using petroleum derivatives as the main raw material. Also, the current production chain of the synthetic dyes is linear, with no solvent recycling and waste generation. Thus, the most promising processes of extraction and purification of natural pigments and strategies on the polishing of the solvents are here reviewed. In this review, the use of alternative solvents, namely, ionic liquids, eutectic solvents, aqueous solutions of surfactants, and edible oils, for recovering natural pigments was reviewed. Works discussing higher extraction yields and selectivity, while maintaining the stability of the target pigments, were reported. Also, a panorama between Sustainability and Circular Economy prospection was discussed for better comprehension of the main advances in the field. Behind the analysis of the works published so far on the theme, the most important lacunas to overcome in the next years on the field were pointed out and discussed. Also, the future trends and new perspectives to achieve the economic viability and sustainability of the processes using alternative solvents will be scrutinized.
Highlights
Pigments are responsible for assigning a specific color to a product like paints, plastics, textiles, cosmetics, foods, and others
Based on the results reviewed on this work, it seems that ILs, eutectic solvents, and more recently, edible oils and surfactants may be good candidates to replace, or at least, reduce the use of conventional organic solvents, in the extraction of natural pigments from different biomass matrices
The data available highlight the advantages of the alternative over the conventional organic solvents, improving the physicochemical quality of the extracted pigments, ensuring better extraction yields, the thermal stability of the target compounds, and in some cases, increasing the safety of the process, by decreasing the environmental impact caused by the solvents
Summary
Pigments are responsible for assigning a specific color to a product like paints, plastics, textiles, cosmetics, foods, and others. The possible combination of the starting materials to synthesize the ILs and to prepare the eutectic solvents is virtually countless, and numerous combinations can be produced, with different chemical and biological properties (Kalhor & Ghandi, 2019; Passos, Freire, & Coutinho, 2014; Ventura et al, 2017) Supported by their “design solvent” credential, these have been applied as efficient solvents. Because the extractions usually have low yields (from μg to mg), and the amounts of colorants present in the biomass are not too high, there is a demand for the development of more efficient and integrated downstream processes In this sense, the use of alternative solvents has gained increased attention in the most recent years. This section will be analyzed by class/type of pigments
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