ÇEVRE TEKNOLOJİLERİJENVIRONMENml TECHNOLOGIES MAKA��� I A new approach is here investigated. it consists in the following sequence: t a nanofiltration step is performed in order to concentrate reactive dyes as retentate, t nanofiltration produces as permeate a mineral salt solution, which is directly reused tor further dyeing in the cases in which it is concentrated enough. Otherwise, it is concentrated by reverse osmosis betore recycling. t in these cases, reverse osmosis produces pure water as permeate which can be used either in the nanofiltration step or in a new dyeing, t the mineral salt solution and the pure water are reused tor new dyeing without difference on the dye efficiency (kinetic, colour and intensity), This is the first process presented, which enables a sufficient reducing of the volume of ultimate chemical used and recycles at once water and mineral salts for new dyeing. The main goal of the re-use (water and mineral salts) is not only to avoid additional consumption of pure water and salts, but also to ensure the mass balance of the whole dyeing process together with real protection of environment. The process developed in this study is divided into four steps: pre-filtration, neutralisation, nanofiltration and reverse osmosis (Figure 1 ). --·-······-· i ........... ---ı 1 HCI 1 Purified \ Concentrated water I 1 1 l Pre Dye Clear Nanofiltration � 1 Reverse ı effluents Filtration coloured osmosıs solution l i� 1 ı jConcentrated dye\ i .,_____,. ....... ··-----·-........... ' ......... ,----········· -. ' ______ ........ Step A Step B Step C Step D Pre - filtration Neutral Nanofiltration Reverse osmosis ➔ Fibrils ➔ Concentradted ➔ Pure water ➔ Clear coloured dye ➔ Concentrated solution ➔socluotiloonrless salt salts \ Figııre I. New process of trecıt111e11ı cınd vcıloriscıtioıı of dye ej]lııeıııs. \ MATERIALS AND METHODS 1. Solutions The study has been conducted with industrial effluents coming from bulk dyeings carried out in a big dyehouse in France. Different type of reactive dyes were used belonging to following groups : t vinylsulfone t difluoromonochloropyrimidine t trichloropyrimidine t monochlorotriazine and vinylsulfone (bireactive dyes) The effluents were containing from 0.1 g.L" 1 to 2g.L" 1 of hydrolysed dyes, 60 to 100g.L" 1 sodium chloride, 5 to 15g.L"1 soda ash. in any cases we have worked with reconstituted effluents. lf necessary, it is possible to concentrate nanofiltration permeate and thus to recover pure water and a concentrated brine to a new dyeing. Dyeings with the brines recovered at the exit of our process were performed with several type of reactive dyes. There were no differences between these dyeings and dyeings carried out the same way with the lab water, same depth of shade, same fastenesses, same dyeing kinetics. 2. Membranes The choice of available membranes is restricted by the upper temperature recommended by the suppliers (usually around 50°C) and the chemical characteristics of the effluent (Molecular weight): t A DESAL 5-OSMONICS membrane, of the spiral wound type was used for the nanofiltration step. Characteristic molecular weight cut off is given as 200-300 Da and the active surface area is 2.5 m2 . With this membrane the electrolyte, which is usually sodium chloride, passes through the membrane meanwhile high retention values are obtained tor hydrolysed reactive dyes. t The reverse osmosis membrane chosen is the AD 2540FOSMONICS with a 2.3 m2 surface. The advantages of !his reverse osmosis membrane include: ability to resist high transmembrane pressure (and high osmotic pressure) and somewhat high temperature ; high retention of sodium chloride is usually observed even when the concentration in the retentate increases. 3. Pre-filtration and Neutralisation steps The pre-filtration step is necessary to remove the cotton fibres present in the rough industrial solutions. These fibres might block the nanofiltration membrane and damage it irreversibly. A specific filler has been designed to fulfill the following requirements: efficient retention of all type of fibres; suitable up to ?0°C; no reduction of the machine drainage time; easy to clean manually and robust The effluents contain a high concentration of carbonates (soda ash alone or soda ash mixed with caustic soda). These carbonates are introduced during the dyeing but not at the beginning because they might disturb the colour unison. in order to recuperate the water of the dyeing bath together with the salt for a new dyeing it is obligatory to neutralise these alcalis. Moreover, carbonates are divalent ionic groups and thus stronglyease the permeate flux during nanofiltration. The carbonates are neutralised using hydrochloric acid and the dissolved carbon dioxide formed is easily removed by gentle air bubbling. ENERJi DÜNYASI EKiM 2006 67
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