3 Sequeestering Agents

8/2/2019 3 Sequeestering Agents

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Sequestering agentsSequestering agents

Spring 2010Spring 2010

Why??Why??

Water supplies have metal particles.Water supplies have metal particles.

Rusting of vesselsRusting of vessels

Micro/Micro/ nanonano particles of metal onparticles of metal on

fabric.fabric.

Make Unstable chemical systemMake Unstable chemical system

Iron spots and Pin holesIron spots and Pin holes


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multivalent transition-metal cationscatalyse the decomposition ofhydrogen peroxide (althoughdivalent calcium and magnesium ionshave a stabilising effect)

and localised staining or tendering ofthe fibre may occur

COLORATION

trace-metal ions can react withcertain dyes, giving rise to

precipitation,

discoloration,

unlevel dyeing and

reduced fastness.


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Solution??Solution??

Water treatment ???Water treatment ???

NoNo the overzealous treatment ofwater can actually lead to thepresence of troublesome aluminiumions that were not originally present!

We need special kind of chemicals

our title

What they do !!??What they do !!??

preventing Metal ions frominterfering with the mainstreamreaction or process.

Two terms are used sequesteringagents and Complexing agents.

complexing does cover a wider fieldthan just metalion chelation


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How they do that ?How they do that ?

Make complex formation with metals. InMake complex formation with metals. Inthe formthe form chelationchelation

A chelating agent contains substituentssuitably located to form one or morechelate rings by electron donation to themetal ion

the resulting complex remaining soluble

and innocuous under the conditions ofprocessing.


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The most useful donating atoms are

nitrogen, as found in amines orsubstituted amines

oxygen in the form of carboxyl,phosphate or ionised hydroxy groups

4 types mainly4 types mainly

aminopolycarboxylates and theiranalogues, e.g.hydroxyaminocarboxylates

phosphates and phosphonates

hydroxycarboxylates

polyacrylic acids and derivatives.


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Aminopolycarboxylates and their

analogues

ethylenediaminetetra-acetic acidEDTA

diethylenetriaminepenta-acetic acidDTPA

nitrilotriacetic acid

NTA


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NTA degrades easily, the most stableNTA degrades easily, the most stable

is EDTA at long range of pHis EDTA at long range of pH

EDTA makes 5 member ring withEDTA makes 5 member ring with

metal complexmetal complex


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EDTAEDTA complexingcomplexing with metalwith metal

Phosphates and phosphonates


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All of these polyanions function bywithdrawing the troublesome metalcation into an innocuous and water-soluble complex anion by a processof ion exchange


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Consumptions of these chemicals is less,Consumptions of these chemicals is less,aminopolyphosphonates are used indetergent formulation

Environmentally, phosphates generallyhave been a sensitive issue, not leastbecause they can cause eutrophication ofwatercourses, and the situation is still notresolved completely.

No aerobic or anaerobic bacterium hasbeen found to date that will biodegradeaminopolyphosphonates under thetreatment conditions used today, yetthese products are not biologicallypersistent.


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Action of Sequestering agentAction of Sequestering agent

Used in very less quantity 0.5Used in very less quantity 0.5--11 g/lg/l

EDTA.EDTA.

High constant => good agentHigh constant => good agent

NTA < HEDTA < EDTA < DTPA.

Metals can also be listed in order ofincreasing stability constant:

Mg2+ < Ca2+ < Mn2+ < Al3+

3 Sequeestering Agents

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