The World Bank

Dye and Pigment Manufacturing Industry - Pollution Prevention Guidelines

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Courtesy of The World Bank

Introduction

Pollution Prevention Guidelines to provide technical advice and guidance to staff and consultants involved in pollution-related projects. The guidelines represent state-of-the-art thinking on how to reduce pollution emissions from the production process. In many cases, the guidelines provide numerical targets for reducing pollution, as well as maximum emissions levels that are normally achievable through a combination of cleaner production and end-of-pipe treatment. The guidelines are designed to protect human health; reduce mass loadings to the environment; draw on commercially proven technologies; be cost-effective; follow current regulatory trends; and promote good industrial practices, which offer greater productivity and increased energy efficiency.

Table of Contents

  • Industry Description and Practices
  • Waste Characteristics
  • Pollution Prevention and Control
  • Target Pollution Loads
  • Treatment Technologies
  • Emissions Guidelines
  • Monitoring and Reporting
  • Key Issues
  • Sources

Industry Description and Practices

This document discusses the synthesis of dyes and pigments used in textiles and other industries. Dyes are soluble at some stage of the application process, whereas pigments, in general, retain essentially their particulate or crystalline form during application. A dye is used to impart color to materials of which it becomes an integral part. An aromatic ring structure coupled with a side chain is usually required for resonance and thus to impart color. (Resonance structures that cause displacement or appearance of absorption bands in the visible spectrum of light are responsible for color.)

Correlation of chemical structure with color has been accomplished in the synthesis of dye using a chromogen-chromophore with auxochrome. Chromogen is the aromatic structure containing benzene, naphthalene, or anthracene rings. A chromophore group is a color giver and is represented by the following radicals, which form a basis for the chemical classification of dyes when coupled with the chromogen: azo (–N=N–); carbonyl (=C=O); carbon (=C=C=); carbon-nitrogen (>C=NH or –CH=N–); nitroso (–NO or N–OH); nitro (–NO2 or =NO–OH); and sulfur (>C=S, and other carbon-sulfur groups). The chromogen-chromophore structure is often not sufficient to impart solubility and cause adherence of dye to fiber. The auxochrome or bonding affinity groups are amine, hydroxyl, carboxyl, and sulfonic radicals, or their derivatives. These auxochromes are important in the use classification of dyes.

A listing of dyes by use classification comprises the following:

  • Acetate rayon dyes: developed for cellulose acetate and some synthetic fibers
  • Acid dyes: used for coloring animal fibers via acidified solution (containing sulfuric acid, acetic acid, sodium sulfate, and surfactants) in combination with amphoteric protein
  • Azoic dyes: contain the azo group (and formic acid, caustic soda, metallic compounds, and sodium nitrate); especially for application to cotton
  • Basic dyes: amino derivatives (and acetic acid and softening agents); used mainly for application on paper
  • Direct dyes: azo dyes, and sodium salts, fixing agents, and metallic (chrome and copper) compounds; used generally on cotton-wool, or cotton- silk combinations
  • Mordant or chrome dyes: metallic salt or lake formed directly on the fiber by the use of aluminum, chromium, or iron salts that cause precipitation in situ
  • Lake or pigment dyes: form insoluble compounds with aluminum, barium, or chromium on molybdenum salts; the precipitates are ground to form pigments used in paint and inks
  • Sulfur or sulfide dyes: contain sulfur or are precipitated from sodium sulfide bath; furnish dull shades with good fastness to light, washing, and acids but susceptible to chlorine and light
  • Vat dyes: impregnated into fiber under reducing conditions and reoxidized to an insoluble color.

 

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