On-site formation of hypochlorite for indigo oxidation – Scale-up and full scale operation of an electrolyser for denim bleach processes

Abstract

On-site production of hypochlorite for denim bleach was investigated using undivided unipolar electrolysers. The current efficiency of the electrolysis process was studied at laboratory scale with up to 20 A cell current and at the technical scale using a 1200 A electrolyser. NaCl solutions in the concentration range 0.236-0.944 M NaCl (13.8-55.2 g l )1 ) were used. Anodic current densities up to 400 A m )2 were used. Hypochlorite solutions with active chlorine concentration c(Cl)=0.10-0.12 M were obtained with current efficiency of 58-70%. For denim bleach processes a concentration of active chlorine up to c(Cl)=0.12 M is required. This corresponds to approximately 30 ml l )1 of commercial hypochlorite solution. Electrical energy consumption calculated per kg of active chlorine formed ranges from 5.7 to 8.6 kWh kg )1 . By coupling the electrolyser to a commercial 30 kg capacity drum washing machine the electrochemically prepared oxidant was successfully used in bleach processes. The technique overcomes problems of insufficient reproducibility of bleach, chemical costs and released wasted water due to the use of commercial NaOCl solution.

Enhancing the electrochemical oxidation of acid-yellow 36 azo dye using boron-doped diamond electrodes by addition of ferrous ion

“…In such cases, addition of specific electrolytes has been suggested as an alternative to enhance the electro-oxidation reaction rate [22,23]. For example, the presence of chloride ions in the reaction mixture has been reported to increase the oxidation initiated by hydroxyl radicals during different dye treatment, avoiding diffusion-limited conditions on these systems [22,[24][25][26]. So far, this effect has not being observed with other ions tested in these works, such as ferrous sulfate [23] and no further studies have been reported dealing with testing the capability of other ions to enhance electro-oxidation using BDD electrodes.…”

Color and COD Removal Using a Three-Dimensional Stacked Pt/Ti Screen Anode

“…The main advantages of adopting an electrochemical technique to treat pollutants are (1) the elimination of the use of redox chemicals, thus avoiding the need to treat spent redox streams, (2) close control of desired reactions by the applied potential or current, (3) the increased possibility of onsite treatment (Simonsson, 1997). Recently, a number of anodic oxidation techniques have been employed for removing the color or COD of dyestuffs (Allen et al, 1995;Vlyssides and Israilides, 1998;Vlyssides et al, 1999;Yang, 1999;Szpyrkowicz et al, 2000;Kim et al, 2002;Wang, 2003;Fernandes et al, 2004;Sanromán et al, 2004;Awad and Galwa, 2005;Bechtold et al, 2006;Hastie et al, 2006;Ammar et al, 2006;Faouzi et al, 2007), organic substances (Comninellis and Nerini, 1995;Do et al, 1997;Vijayaraghavan et al, 1999;Chou et al, 1999;Brillas et al, 2000), landfill leachate (Chiang et al, 1995;Tauchert et al, 2006) and cyanide (Yen et al, 1991;Ögütveren et al, 1999) in the wastewater.…”

“…It is usually achieved by adding salts containing a redox mediator into the solution. The most common redox mediator is Cl Ϫ , which electrochemically generates Cl 2 and ClO Ϫ with high oxidizing powers (Allen et al, 1995, Comninellis andNerini, 1995;Ögütveren et al, 1999;Vlyssides et al, 2002;Wang, 2003;Fernandes et al, 2004;Szpyrkowicz et al, 2005;Bechtold et al, 2006;Rajkumar and Kim, 2006). Another advantage of indirect oxidation is that the added salts can act as supporting electrolytes to increase the electrical conductivity of the solution and thus eliminate the energy consumption during the electrolysis.…”

A novel study on UV protection and antibacterial properties of washed denim garment

“…Essentially the most frequently used denim washing methods are enzyme wash, bleach wash, acid wash, usual wash, stone wash, and so forth. Among the many washing methods, enzymatic methods are essentially the most broadly used procedure in industry as a result of its low damaging nature on clothes floor and eco-friendly nature compared to others [4][5][6][7][8]. In enzyme washing, cellulases attack notably surface of the clothes, leaving the interior of the clothes as it is by doing away with the dye gift in the floor layer of clothes [9].…”