FOR DYE MANUFACTURING INDUSTRY
Industry Description and Practices
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=0); carbon (=C=C=); carbon-nitrogen (>C=NH or -CH=N-): nitroso (-NO or N-OH): nitro (-NO 2 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:
Dyes are synthesized in a reactor, filtered,dried, and blended with other additives to produce the final product. The synthesis step involves reactions such as sulfonation, halogenation, amination, diazotization, and coupling, followed by separation processes that may include distillation, precipitation, and crystallization. In general, organic compounds such as naphthalene are reacted with an acid or an alkali along with an intermediate (such as a nitrating or a sulfonating compound) and a solvent to form a dye mixture. The dye is then separated from the mixture and purified. On completion of the manufacture of actual color, finishing operations,including drying, grinding, and standardization, are performed; these are important for maintaining consistent product quality.
The principal air pollutants from dye manufacturing are volatile organic compounds (VOCs), nitrogen oxides (NOx), hydrogen chloride (HCI), and sulfur oxides (SOx).
Liquid effluents resulting from equipment cleaning after batch operation can contain toxic organic residues. Cooling waters are normally recirculated. Wastewater generation rates are of the order of 1-700 liters per kg (1/kg) of product except for vat dyes. The wastewater generation rate for vat dyes can be of the order of 8,000 1/kg of product. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) levels of eactive and azo dyes can be of the order of 25 kg/kg of product and 80 kg/ kg of product, respectively. Values for other dyes are, for example, BOD5, 6 kg/kg; COD, 25 kg/kg; suspending solids, 6 kg/kg; and oil and grease, 30 kg/kg of product.
Major solid wastes of concern include filtration sludges, process and effluent treatment sludges, and container residues. Examples of wastes considered toxic include wastewater treatment sludges, spent acids, and process residues from the manufacture of chrome yellow and orange pigments, molybdate orange pigments, zinc yellow pigments, chrome and chrome oxide green pigments, iron blue pigments, and azo dyes.
Pollution Prevention and Control
Every effort should be made to substitute degradable and less toxic ingredients for highly toxic and persistent ingredients. Recommended pollution prevention measures are to:
Target Pollution Loads
Implementation of cleaner production processes and pollution prevention measures can yield both economic and environmental benefits.
Specific reduction targets for the different processes have not been determined. In the absence of specific pollution reduction targets, new plants should always achieve better than the industry averages cited in "Waste Characteristics," above .
Stack gas scrubbing and/or carbon adsorption (for toxic organics) are applicable and effective technologies for minimizing the release of significant pollutants to air. Combustion is used to destroy toxic organics. Combustion devices should be operated at temperatures above 1,100 C (when required for the effective destruction of toxic organics), with a residence time of at least 0.5 second.
normally includes neutralization, flocculation, coagulation, settling,
Solid Hazardous Wastes
solid wastes are generally incinerated, and the flue gases, when acidic,
The guidelines are expressed as concentrations to facilitate monitoring. Dilution of air emissions or effluents to achieve these guidelines is unacceptable.
All of the maximum levels should be achieved for at least 95% of the time that the plant or unit is operating, to be calculated as a proportion of annual operating hours.
levels presented in Table I should be achieved.
levels presented in Table 2 should be achieved.
Note: Effluent requirements are for direct discharge to surface waters
solid wastes should be incinerated under controlled conditions to reduce
Noise abatement measures should achieve either the levels given below or a maximum increase in background levels of 3 decibels (measured on the A scale) [dB (A)]. Measurements are to be taken at noise receptors located outside the project property boundary.
Maximum allowable log
Monitoring and Reporting
Frequent sampling may be required during startup and upset conditions. Once a record of consistentperformance has been established, sampling for the parameters listed in this document should be as described below.
of air emissions should be done on a continuous basis. Liquid effluents
data should be analyzed and reviewed at regular intervals and compared
The key production and control practices that will lead to compliance with emissions guidelines can be summarized as follows: