Ionic‐liquid‐assisted mixed alkali system for reactive dye fixation in a batch process – optimisation through response surface methodology

Abstract

An ionic liquid, choline hydroxide, was synthesised and used in a mixed alkali system for fixation of homobifunctional reactive dyes. Its molecular structure was confirmed using FTIR, 1H NMR, and 13C NMR spectroscopy. Response surface methodology was employed to optimise the dyeing conditions for reactive dyes using a sodium carbonate–choline hydroxide mixed alkali system. A Box–Behnken design with three variables, namely sodium carbonate concentration, choline hydroxide concentration, and fixation time, was used to design the experimental runs. Analysis of variance was used to estimate the statistical parameters and to evaluate the quality of the statistical model fit. The quality and model terms were evaluated using Fisher's F‐test, the coefficient of determination, and probability values. The interactive effect of operating variables on the response (K/S) was studied using three‐dimensional response surface plots. The results obtained from the solutions of highest desirability were found to be comparable with conventionally used alkali systems, namely sodium carbonate alone and sodium carbonate–sodium hydroxide mixed alkali. The ionic liquid choline hydroxide could be effectively used along with sodium carbonate for fixation of reactive dyes, with the advantage of reductions in pollution load, total dissolved solids, and chemical oxygen demand.