Effluent Treatment- Kerosene Recovery from Pigment Printing
In India about 46% of the total printing is done using pigment printing method, 27% using reactive dyes, 15% Disperse dyes, 2% napthol, 3% acid and 7% using vat colors.
In a typical pigment printing paste, 75% is keorsene, 10% is binder, 5% each is gum and water, 2% urea and 1% each of DAP and emulsifier. Kerosene water emulsion acts as a thinkner is pigment printing. Its use is prohibitied in most of the developed countries. Alternatives to kerosene are synthetic thickners but they make the printed fabric stiff.
In India alone, about 140 thousand kiloliters of kerosene per annum is consumed during the process of printing and drying. Out of the total kerosene applied, about 22% is lost at various points during this process( 1 % is left out on the fabric, 12% screen printing and wastage, 5% is before dryer, 4% is at curing machine and 78% is released or evaporated in the atmosphere during the process of drying at 120-150 deg C). It signifies a loss of precious kerosene as well as pollution in the environment.
Apart from the effluents generated during wet processing, there is a substantial amount of kerosene vapour that is released in the air in the process of pigment printing.
Any kerosene recovery process should be based on the fact that kerosene is liquid at room temperature and immiscible with water. The kerosene vapour are at 120 deg C and they have to be cooled below 40 deg Celcius. The kerosene and water will separate out in two layers, with top layer can be skimmed for reuse.
An excellent effluent treatment plant is proposed by BTRA. Average recovery is 58% whereas maximum recovery can be 85%. Read more about it here
To view the pigment printing process and alternative to kerosene, please find the link here.
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