FLOFOAM ™

Defoamer

2.1

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1.Foam is a gas dispersion in a liquid orsolid continuous phase. Foam iscreated by the surfactants which areat the air/liquid interface. Thereforeair bubbles occur and are stabilisedby the surfactants.

Today, silicone antifoams are thebest solution to a foaming problemthanks to a very competitive ratio ofcost/efficiency.Based on a silicone oil and silicaparticles, FLOFOAMTM products workfollowing the outlined principles :

In spreading over the foam,the silicone activeingredient displacessurfactant molecules andthins out the lamellae,leading to destabilisation andcollapse.

Silica particles transportedby the siloxanes onto thefoam lamelle have anadditional destabilizingeffect on the foam.

The foam bubble bursts andthe entrapped air escapes.

Why Foam could be so inconvenient ?Why Foam could be so inconvenient ?A light foam is generally not problematic in mostapplications however heavy foaming can often lead tovarious processing problems. These problems range frominaccurate readings from control and measuringequipment such as temperature, level and densitycontrollers to poor mixing of reactants in chemical reactionvessels and products hanging in the foam,all too often leading to losses in production.Finally the presence of foaming can give a bad imageof the way a process is operated in the eyes of a customer.The presence of foam in discharged effluent can causecomplaints from local people and authorities even ifthe foam is harmless to people and the environment.

How do silicone defoamers work ?How do silicone defoamers work ?H

ow do silicone defoam

ers work ?

1

2

3

Silica particle

Surfactant molecule

Polydimethylsiloxane

Foamdestabilisation mecanism

4.3.Silicone antifoams

Silic

on a

ntifo

ams

Si-O

Silicone antifoamsToday silicone antifoams remain the best solutionto foaming problems because they give betterefficiency/cost compared to organic antifoams.Silicone based products meet perfectly the three cru-cial requirements to make an effective antifoam :

• Low surface tension (approximately 21 mN/m)

• Insoluble in the foaming medium

• Good spreading coefficient

How do we assess antifoam efficiency? How

do we assess antifoam

efficiency ?How do we assess antifoam efficiency ?

CH3 Si

CH3

O OSi CH3

CH3

Si

CH3

n

CH3

CH3

CH3

100<n<10000500

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0

400

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1000

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100 150 200 250 300Time (s)

Foam

hei

ght

(cm

)

AA

BCD

Inefficient productGood defoamer but weak antifoamWeak defoamer but strong antifoamBest product

BCD

Silicone antifoams have other interesting properties :

• They are highly efficient and are therefore oftenmore economical to use than organic defoamers.

• They control almost all types of foam encounteredin any effluent.

• They are chemically inert and therefore resistantto chemical attack.

• They are thermostable.• They make for safe operating conditions.• As they do not produce any undesirable degradation

products, they are environmentally compatible.

A silicone oil namedpolydimethylsiloxane (PDMS) andsilica particles are the two majoringredients of a silicone antifoamagent.

Silicone antifoam can be compound(100% active content), emulsion(variable active content) or powder.

The SNF Floerger range of antifoamagents are in emulsion form. FLOFOAMTM products are of the oil-in-water type, and therefore suitablefor easy dispersion in aqueousmedia. Thanks to their relatively lowviscosity they are easy to pump.

These two parameters can be assessed by several tests.The main test is the bubbling method. A graduated column with a glass frit inthe bottom is required. Foaming water is poured in the column and air atconstant flowrate is introduced through the glass frit in the column. Foam isgenerated by the air and starts to travel up the column. At a determined levelof foam, antifoam is injected. By this method several antifoaming agents canbe tested.A graph reporting foam height vs time is very helpful to establish theknockdown ability and the persistence for each product.The selected antifoam is the product with the best compromise betweenshock effect and durability.

Quality of an antifoam is given by two maincharacteristics :

• Knockdown ability or shock effect :Meaning the speedto destroy an existing foam.

• Persistence or durability :Meaning the efficiencyover time.

Polydimethylsiloxane

Polydimethylsiloxane Bubbling Test

5.Environmental performance

Envi

ronm

enta

l per

form

ance Environmental performance Products Products

Products

Dosage and dilutionSNF Floerger antifoam agents have to be used undiluted formaximum efficiency. Experimental plant trial is the best wayto determine the optimal dosage of the appropriateantifoam, however a preliminary test in the lab oftenindicates suitable products. Generally optimal antifoamdosage is between 10 and 1000 ppm according to theapplication and to the stability of the foam.FLOFOAMTM products can be diluted in water to obtain abetter dispersibility in the foaming medium,but efficiency of the antifoam will be affected.In case of dilution we recommend not to exceed a dilutionratio of 1:10. The diluted product must be used immediately.

Shear stabilityEfficiency of a silicone antifoam is based on the particles size.Therefore shear forces and turbulence have a considerableinfluence on the efficiency of silicone defoamers.This rule particularly applies to products already in dispersedform, such as emulsions. Particles will be split by shear forcesor turbulence and the antifoam efficiency is reduced com-pared to the initial unsheared products.

PumpsSilicone emulsion must be pumped with care. We recom-mend the use of low shear gear pumps as these are able tometer even small amounts very accurately.As mentioned previously turbulence can damage the pro-duct. So the flowrate should be kept relatively low (<1m/s).

StorageWe recommend you store the SNF Floerger antifoam atroom temperature. Product stability is affected by high tem-perature (higher than 30°C) and frost, therefore temperaturefluctuations must be avoided.After opening antifoam containers or drums the lid must bereplaced and tightly closed in order to prevent anymicro-organism contamination.

Silicone antifoams are essentially composed ofpolydimethylsiloxane (PDMS) and silica.Silica is a natural element which can be found in sand.PDMS is a strictly inert compound. Studies haveproved that PDMS does not interfere with any othercompound in a sewage plant. Because of itsinsolubility in water, PDMS has a low COD and BOD*.It does not undergo any chemical reaction in thetreatment process. PDMS has a very high ability toadsorb on sludge and therefore most of the injectedPDMS is attached to the sludge. Later sludge isdisposed to land and abiotic degradation of the PDMSoccurs. Carbon dioxide, water and silicon dioxide arethe only three products generated in this reaction.Any remaining small amount of PDMS(analytical detection limit) tends to bind to solidparticles suspended in the process water phase.These solid particles settle and PDMS is again subjectto abiotic degradation as previously mentioned.

*• COD : Chemical Oxygen Demand• BOD : Biological Oxygen Demand

6.Fate of Polydimethylsiloxane

PDMS

SEWAGETREATMENT

PLANT

PDMS Adsorptionon suspended

solids

CleanWater

PDMS Adsorptionon sludge

Settlingwith sedimentsIncineration Landfill

disposal

SiO2 (Amorphous Silica)CO2H2O

Adsorption on soilSilicaCO2H2O

SNF S.A.41 rue Jean Huss - 42028 Saint Etienne Cedex 1 France

Tel: +33 (0)4 77 47 66 00 - Fax: +33 (0)4 77 47 66 96floerger@snf.fr

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