Chemical Minimization

7/30/2019 Chemical Minimization

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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

Chemical Minimization

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