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SoapFabrication1.Introduction[1]

Themainusesofsoapincludebathing,washing,cleaningandothertypesofhousekeeping.Soapactsassurfactantbecauseithassurfaceactiveproperties.WhenSoapsaredissolvedinwater,theycanbreakdirtfromthesurfacesandemulsifyoils.Moreover,inindustry,soapsareimportantcomponentsoflubricantsandsometimesusedintextilespinning.Chemically,soapisawater-solublesodiumorpotassiumsaltsoflongchainfattyacids.Whentriglyceridesinfat/oilreactwithaqueousNaOHorKOH,theyareconvertedintosoap.TheformationofsoapiscalledtheSaponification.

2.RawMaterial[2]

Themajorrawmaterialsofmanufacturingsoapsincludefatandlye.

Fat:

• Animalfatarelipidmaterialsderivedfromanimalsandarecomposedoftriglycerides.Physically,animalfatsaresolid.Inthepast,peoplecandirectlyobtaintheanimalfatfromaslaughterhouse.However,modernsoapmakersusefatwhichhasbeenprocessedintofattyacids.Thisnew“fat”eliminatesmanyimpurities,andthebyproductwillbewaterinsteadofglycerin.Inadditiontotheanimalfat,manyvegetablefats,includingcoconutoil,palmkerneloilandoliveoilarealsousedinsoapmakingprocesstoday.

Lye

• Lye,oralkaliarenecessarycomponentsofsoaps.Thereactionbetweenthelyeandthefatiswhatwecallsaponification.Oncethesaponification(thereactionbetweenthelyeandthefat)iscompleted,alllyewillconvertintosoap.Thefinishedsoapbardoesn’tcontainanylye.Therearetwotypesoflye,sodiumhydroxideandpotassiumhydroxide.Sodiumhydroxideisusedformakingsolidsoap.Potassium-basedsoapiscalledsoftsoapsinceitisamorewater-solubleproductthansodium-basedsoap.Thecombinationofsoftandsolidsoapiscommonlyusedinshavingproductsortomakecreamsoaps.

Others:

• Withoutdye,soapwillbedullgreyorbrown.Modernmanufacturerswilladdadditives,abrasives,fragrancestoenhancethecolor,texture,andscentofsoap,makingthesoapmoreenticingtotheconsumer.

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3.TheManufacturingProcess[2]

Theprocessesofsoapsmanufacturingarevarious,includingkettleboilingandcontinuoussaponification.Today,somesmallsoapmanufacturersstillusekettleprocesswhichtakesaroundfourtoelevendaystocomplete.Andthequalityofeachbatchisquiteinconsistentduetothedifferentkindsofoils.Engineersandscientistsdevelopedamoreefficientmethodcalledcontinuousprocessin1940.Thismethodiscommonlyusedbylargesoapmanufacturersallovertheworldnowadays.Soapsaremadecontinuouslyratherthanonebatcheachtimeinthecontinuousprocess.Thereareseveralimprovements.Firstly,itjusttakesaroundsixhourstocompleteonebatchofsoapswhichismuchquickerthanthekettleprocess.Secondly,thetechnicianscaneasilydothequalitycontrolofallthefinishedgoods.3.1TheKettleProcess

Figure1.TheKettleProcess

Boiling• Akettleisasteeltankwhichcanstandashighasthreestories,holdingseveral

thousandpoundsofmaterialsimultaneous.Steamcoilswithinthekettleheatthebatchandthenboilthem.Afterboiling,thefatreactswiththealkalitoproducesoapandglycerin.

Salting

• Thepurposeofthesaltingistodividethesoapandglycerin.Themixtureofsoapandglycerinistreatedwithsoap.Asaresult,thesoapwillrisetothetopandtheglycerinwillsettletotheverybottom.Thenextractingtheglycerinfromthebottomofthekettle.

StrongChange

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• Thestrongcausticsolutionisaddedintothekettleinordertoremovethesmallamountsofunsaponifiedfat.Thenboilingthesaponifiedfatagain.Themanufacturercouldeitherdothesalttreatmentatthistimeorproceedtothenextstep.

Pitching

• Thelaststepiscalled“pitching”.Firstly,theleftsoapinthekettlewillbeboiledforonemoretimewithwater.Thesemi-finishedproductswillseparateintotwodifferentlayers.Thetoplayercontainsabout70%ofsoapand30%water.Wecallit“neatsoap”.Thelowerlayerwhichiscalled“nigre”isalmosttheimpuritiesincludingdirt,saltandwater.Theneatsoapistakenoffandcooledintheend.Thefinishingprocessisthesameforbothkettleandcontinuousprocess.

3.2 Continuous Process

Figure2.TheContinuousProcess

Splitting

• Thefirststepistosplitnaturalfatintofattyacidsandglycerin.Theequipmentiscalledhydrolyzerwhichisverticalstainlesssteelcolumnwithbarrel.Theheightmayupto80feet(24meter).Pumpsandmetersattachedtothecolumnhelptodotheprecisemeasurement.

• Moltenfatispumpedintooneendofthesteelcolumn,meanwhile,attheotherend,boiledwater(266°F[130°C])andpressureareintroduced.Thislargecontainersplitsthefatintotwodifferentcomponents,fattyacidsandglycerin.Duringtheprocess,therearecontinuousfattyacidsandglycerinbeingpumpedoutasmorefatandwaterenter.Thenthefattyacidsaredistilledforpurification.

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Mixing

• Mixingthepurifiedfattyacidswithpreciseamountofalkalitoformsoap.Thesoapmakerscanmixotheringredientssuchasfragranceandabrasivessimultaneouslytomakeattractivescent.Thehotliquidsoapcanthenincorporatewithair.

CoolingandFinishing

• Thesoapmaybepouredintomodesorlargeslabsorbecooledinspecialfreezers.Theslabswillthenbecutintosmallerpieceslikethebarsize.Theentirecontinuousprocess,fromsplittingtofinishing,canbeaccomplishedjustincouplehours.

4.SoapMillandRefiningProcess[3]

Figure3.ThreeRollMill

Additiontothebasicprocess,mostsoapwillundergomilling.Soapmakersusethreerollmilltorefinethesoap.Refiningistogrindallparticlesintosmallsizes.Threerollmillisusedtoimprovethefinenessandhomogeneityoftheoneproduct.Asaresult,themilledbarswillhavefinerconsistencyandthuslatherupbetterthanthenon-milledones.Thecooledsoapiscrushedandkneadedafterbeingfedthroughthreerollmill.Duringthemilling,fragrancesandabrasivescanbebetterincorporatedsincevolatileoilsdon’tevaporateinthecoldmixture.Afterthesoapemergesfromthreerollmill,itbecomes

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moresmoothandextrudes.Thencuttingtheextrudedsoapintobarsize.Thelaststepistostampandwrapthefinishedgoods.

Themostsignificantparameterofathreerollmillisthegapbetweenthelasttworolls.Theadvisablegapshouldbe0.15or0.20mm.Theincreasingordecreasingofthegapmayleadtothedifferenceofproductionrate.

Reference:

1.Saponification-TheprocessofMakingSoap,http://amrita.olabs.edu.in/?sub=73&brch=3&sim=119&cnt=1

2.http://www.madehow.com/Volume-2/Soap.html

3.http://www.soapworld.biz/soap-roll-mill.html