chemical minimization
TRANSCRIPT
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PriyanshuB-Tech (Textile
Chemistry)
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Introduction The textile dyeing and processing sector uses substantial
quantities of complex chemicals. The majority of chemicals applied to the fabric are washed
off and sent to the drain.
Therefore reduction in the chemical usage can lead toreduction in effluent strength.
This presentation aims to elaborate the measures for theminimization of chemical usage in the textile processes.
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Understanding the Process
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Chemical Usage at Different Stages of
Processing
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Affecting human health
Carcinogenic
Toxic to Reproduction
Allergenic
Environmental harms
toxic to aquatic organisms Persistant
Bioaccumulative
causing long-term problems
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Options for reducing Chemical usage
1. Controlling the quantity of each chemical used.
2. Replacing more pollutant chemicals with less pollutant
substances.
Quantity Control :
Recipe optimisation
The chemical recipes used in wet processing are often fail-safe
under extreme conditions resulting in the overuse of
chemicals and increased effluent strength. So to avoid this,
Mix the recipes to specification.
20 - 50% chemical reduction by reviewing recipes
correspondingly reduce effluent BOD by 30 - 50%.
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Dosing control
If recipes mixed manually,check how operators measure and
control dosing.
If automatic, check whether they are properly calibrated.
Overuse will result in,
a higher strength effluent and will increase effluent disposal
costs.
also increases chemical costs.
Reducing MLR of Dyeing
Since dosing of auxiliaries is done on the basis of MLR (g/l of
liquor) hence by reducing the MLR it will significantly reducesthe quantities of chemicals and finally the effluent load.
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RFT aproach
One should carefully follow the dyestuff manufacturersrecommendations for,
Alkali Salt
Temp
Time
Ph
CCM can be used regarding this.
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Substituting chemicals used with less
pollutant substances
Substitution of ,
Conventional surfactants with high toxicity (e.g.
Polyaromatic hydrocarbons APEO, NPE) by biodegradable surfactants.
Complexing agents by biodegradable compounds that do not
contain Nitrogen or Phosphor in their molecules.
Conventional printing paste with less harmful compounds,
based in polyacrylic cid or polyethilenglycol.
Conventional dispersing agents by optimised products
based on fatty acid esters.
Sodium hypochlorite by Hydrogen peroxide in bleaching
processes, in order to reduce AOX.
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Environmental friendly processes
Desizing (Enzymetic)
Enzyme concentration 3-5%
Wetting agent 1-2%
pH 6-7
Temp 50-600
C
Time 1 hr
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Scouring (Bioscouring)
The conventional scouring operation consists of treating the cottongoods with 1- 2% of NaOH solution at high pressure andtemperature (121C) for4-5 hours.
The above treatment is not only energy intensive but also leads to
environmental pollution.
Recipe for bioscouring - pectinase and
cutinase
Enzymes 1%
Wetting agent 0.5%
Temperature 50-600C
Time 1 Hour
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Bleaching (peracetic acid)Peracetic acid bleaching is ecofriendly since it
decomposes to acetic acid and oxygen and
dont form any toxic product.
CH3COOOH CH3COOH + [O]
Recipe
Peracetic acid concentration 1-2.5 gpl
Sequestering agent 0.5-1%
pH 6-7
Temp 50-80 oC
Time 20-60 min
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Combined Pretreatment processes
In order to minimise the energy consumption
(time,temp) and reduction of chemicals,combined
pretreatment processes are used.
Combined desizing and scouring
Potassium persulphate 0.2%
Sodium hydroxide 4%
pH 8-9
Temp 95 oC
Time 85 min
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Combined Scouring and Bleaching
H2O2(50%) 1.5%
NaOH 1.5%
Sodium Silicate 1%
Wetting agent 0.1%
Emulsifying agent 0.5%
Temp 60 oC
Time 12 hours
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Dyeing
Ecofriendly Disperse dyeing:
Do not use banned Azo/Anthraquinone dyes.
Some disperse dyes like C.I Disperse orange
76, C.I. Disperse orange 37 were found to bepotentially allergic.
So, They are replaced by C.I. Disperse orange29, 30, 44, 61.
Do not use chlorinated carriers.Use of low liquor dyeing (1:3)
Continuous ranges for dyeing whenever possible.
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Ecofriendly Reactive dyeing
Options are:
Shift the production from exhaust to pad process toreduce salt concenration.
Bifunctional
low salt Cibacron LS dyes have beenintroduced which require 20 g/l salt whereas in normalexhaust dyeing salt used is 80 g/l.
Recycling of dye bath.
Separation of salts by reverse osmosis. Use of quaternary ammonium compounds to increase
the affinity.
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DYEING WITH SUPERCRITICAL CO2
Dyeing with supercritical CO2 is an
inexpensive,non-toxic,environmental friendly
technique.
No salt and auxiliaries required.
Thus reducing the cost of effluent treatment
drastically.
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Critical point : Temperature & Pressure above which CO2
have both properties of gas and liquid.
Dyeing with CO2
Theory:
Dissolution of dye in supercritical CO2
Transport of dye to fibre surface.
Adsorption.
Diffusion.
Supercritical CO2also acts like a carrier.
At 300 bar, Tg (Glass transition temperature) of polyester is reduced
by 30 oC.
Thus it will reduce the usage of water and other
chemicals required during dyeing.
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Finishing
Formaldehyde free cross-linking agents shouldbe used for finishing processes.
Glyoxal
Polycarboxylic acids (PCA) for eg. Citric acid.As Formaldehyde based cross-linking agents such as
(DMDHEU) are carcinogenic in nature.
Biopolishing method should be used as it isecofriendly.
Low MLR processes should be used.
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E-Control Process
First, fabric is padded with the recipe.
Then E-control fixation is done @ temp -120-
130 oC and steam content-27%.
Thus reducing the time to 2-4 min.
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Thank you