The synergetic effect of α-hydroxycarbonyls mixtures used as green reducing agent on the indigo dyeing process

Abstract

Article Highlights• Development of a clean process for indigo dyeing • Substitution of conventional sodium dithionite by green alternatives in reducing indigo• Study of synergy effect of mixture α-hydroxycarbonyls in reducing indigo • Determination of the optimum mixture of α-hydroxycarbonyls for reducing indigo Abstract Textile industries use different chemicals in dyeing processes, consuming large quantities of water and producing large volumes of wastewater. For the particular case of indigo dyeing processes, its reduction is performed chemically by the addition of sodium dithionite. However, this is considered environmentally unfavorable because of the resulting contaminated wastewaters. Therefore, it is important to replace sodium dithionite with other alternatives in order to achieve cleaner processes. α-hydroxycarbonyls have been suggested as possible environmentally friendly alternatives to reduce indigo. However, each one applied alone is unable to attain the dyeing performances offered by the conventional reductant. Thus, the study of the synergy of some selected α-hydroxycarbonyls was proposed. In this paper, a mixture design of experimental (DOE) methods was used to determine the optimum combination of α-hydroxycarbonyls to be applied in the indigo reduction process. Based on the design expert software, quadratic models were established as functions of α-hydroxycarbonyls ratios. The diagnostics of models were investigated by using mixture contour plots. Finally, a model was proposed to predict the optimum conditions leading to dyeing performances exceeding those obtained from the reduction of indigo by the conventional sodium dithionite.Keywords: green reducing agent, α-hydroxycarbonyls, synergetic effect, mixture design, clean process.As a vat dye, indigo is considered the oldest dye known to man. It is an organic compound with a distinctive blue color. Historically, it was naturally extracted from plants, and this was important economically because blue dyes were rare. Nearly all indigo dyes produced today -several thousand tons each year -are synthetic. Indigo and other vat dyes consumption reaches about 33×10 6 kg annually [1]. This

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Electrochemical reduction of indigo by combination of sodium borohydride and copper salt

“…In recent years, some new reduction methods have been studied, including biological reduction (Božič et al, 2009;Shin et al, 2016), electrochemical reduction (Roessler and Jin, 2003), catalytic hydrogenation pre-reduction (Blackburn et al, 2009) and application research of new reducing agents (Buscio and Gutiérrez-Bouz an, 2017). Among these new reducing agents, thiourea dioxide, ascorbic acid (Chavan, 2015), iron complexes (Chavan and Chakraborty, 2001), plant extracts (Hossain et al, 2016) and organic polyhydroxy compounds (such as glucose and a-hydroxy ketones) (Ben et al, 2014;Saikhao et al, 2018) have been studied in depth. NaBH 4 , as a common reducing agent, can achieve selective reduction of aldehydes or ketones, and is stable in alkaline solutions (Santos and Sequeira, 2011;Wang et al, 2016).…”

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