The actual amount is affected by the caustic concentration in half - spent lye. The lye added is known as "half spent lye" and is the lye discharged from the washing column see below.
This lye already contains some glycerine, but it is further enriched by that formed in the saponification reaction. Step 2 - Lye separation The wet soap is pumped to a "static separator" - a settling vessel which does not use any mechanical action. The spent lye settles to the bottom from where it is piped off to the glycerine recovery unit, while the soap rises to the top and is piped away for further processing. Step 3 - Soap washing The soap still contains most of its glycerine at this stage, and this is removed with fresh lye in a washing column.
The column has rings fixed on its inside surface. The soap solution is added near the bottom of the column and the lye near the top. This creates enough turbulence to ensure good mixing between the two solutions. The soap is allowed to overflow from the top of the column and the lye "half spent lye" is pumped away from the bottom at a controlled rate and added to the reactor.
Step 4 - Lye separation The lye is added at the top of the washing column, and the soap removed from the column as overflow. Separating off the lye lowers the electrolyte levels to acceptable limits. The soap and lye are separated in a centrifuge, leaving a soap which is 0. The lye removed is used as fresh lye. Step 5 - Neutralisation Although the caustic levels are quite low, they are still unacceptably high for toilet and laundry soap.
The NaOH is removed by reaction with a weak acid such as coconut oil which contains significant levels of free fatty acids , coconut oil fatty acids, citric acid or phosphoric acid, with the choice of acid being made largely on economic grounds. Some preservative is also added at this stage.
This is done by heating the soap to about oC under pressure to prevent the water from boiling off while the soap is still in the pipes and then spraying it into an evacuated chamber at 40 mm Hg 5. The soap chips are scraped off the walls and "plodded" i.
The soap is now known as base or neat soap chip, and can be converted into a variety of different soaps in the finishing stages. The moisture evaporated off the wet soap is transported to a barometric condensor, which recondenses the vapour without the system losing vacuum. Base soap can also be made by a batch process such as that used by Lever Rexona. Step 1 - Oil preparation The oils used most commonly are, as in the Colgate-Palmolive process, tallow and coconut oil.
These are blended together and dried in a vacuum chamber. Once the oils are dry, bleaching earth is sucked by the vacuum into the chamber to remove any coloured impurities.
The spent earth is landfilled and the oils stored ready for saponification. Step 2 - Saponification The mixture of bleached oils is mixed with spent lye from the washing stage see below and a caustic soda solution. The mix is heated and then left to settle into two layers. The neutral lye which is now rich in glycerine is pumped off and the mixture of soap and unreacted oils which has risen to the top is left in the pan.
More caustic liquor is added to this and the mix reheated to saponify the remaining free oils. Step 3 - Washing The crude soap is then pumped to a divided pan unit DPU where it is washed by a counter- current of lye.
This lye is a mixture of fresh brine solution and nigre lye see below. The washed soap comes out the far end of the DPU and is sent to the fitting pans, while the lye comes out the near end and is pumped back into one of the saponification pans.
Step 4 - Fitting Here the remaining unwanted glycerine is removed from the soap by reboiling with water, NaCl and a small amount of NaOH solution. The electrolyte concentration in the water is such that the soap and water to separate out into two layers.
The top layer is 'neat' wet soap, which is pumped off to be dried. The bottom layer is known as the 'nigre' layer, and consists of a solution of soap, glycerine and NaCl. This is left in the pan, reboiled with further salt and left to stand, forming a soap crust over a lower layer of nigre lye salt and glycerine.
This soap is left in the pan and is mixed with the next intake of washed soap, while the nigre lye is pumped back to the DPUs to wash the next batch of crude soap. Step 5 - Drying Moisture is flashed off under vacuum in the same manner as was described above for the Colgate-Palmolive process. Perfume is then added and the mixture plodded then extruded into a continuous bar.
This, in turn, is cut into billets and stamped out into tablets ready for packaging. Toilet soap manufacture Toilet soap has less water and more fatty material fatty acids and soap than laundry soap. For this reason base soap intended for toilet soap manufacture usually has extra fatty acids added with the preservatives before it is vacuum dried.
These ensure that there is no unreacted caustic left in the soap by the time it reaches the consumer, and also make the soap softer. Perfume, dye and opacifier are then added to the dried soap and the mixture milled to ensure even mixing.
It is then plodded and extruded out as a continuous bar, cut into billets and stamped ready for packaging and sale. They are made both in powder and liquid form, and sold as laundry powders, hard surface cleansers, dish washing liquids, fabric conditioners etc. Most detergents have soap in their mixture of ingredients, but it usually functions more as a foam depressant than as a surfactant. Detergent powder manufacture Step 1 - Slurry making The solid and liquid raw ingredients Table 2 are dropped into a large tank known as a slurry mixer.
As the ingredients are added the mixture heats up as a result of two exothermic reactions: the hydration of sodium tripolyphosphate and the reaction between caustic soda and linear alkylbenzenesulphonic acid.
The mixture is then further heated to 85oC and stirred until it forms a homogeneous slurry. These are sprayed into a column of air at oC, where they dry instantaneously. The resultant powder is known as 'base powder', and its exact treatment from this point on depends on the product being made. Step 3 - Post dosing Other ingredients are now added, and the air blown through the mixture in a fluidiser to mix them into a homogeneous powder.
Typical ingredients are listed in Table 3. Sodium sulphate Bulking and free-flowing agent. Soap noodles Causes rapid foam collapse during rinsing. Sodium carboxymethyl cellulose Increases the negative charge on cellulosic fibres such as cotton and rayon, causing them to repel dirt particles which are positively charged.
Coconut diethanolamide or a fatty Nonionic detergent and foam former. Water Dissolves the various ingredients, causing them to mix better. Liquid detergent manufacture Step 1 - Soap premix manufacture Liquid detergent contains soap as well as synthetic surfactants. This is usually made first as a premix, then other ingredients are blended into it. This step simply consists of neutralising fatty acids rather than fats themselves with either caustic soda NaOH or potassium hydroxide.
Step 2 - Ingredient mixing All ingredients except enzymes are added and mixed at high temperature. The ingredients used in liquid detergent manufacture are typically sodium tripolyphosphate, caustic soda, sulphonic acid, perfume and water. The functions of these ingredients has been covered above. Step 3 - Enzyme addition The mixture is cooled and milled, and the enzymes added in powder form.
This ensures optimum detergent function. Also forms insoluble carbonates with Ca and Mg, so acts as a water softener. Bleach Bleaches stains without damaging colour-fast dyes. Bleach activator Catalyses sodium perborate breakdown at low e. Enzymes e. Colour and perfume Create a more asthetically pleasing product. This is done in a three step process. Step 1 - Soap removal The spent lye contains a small quantity of dissolved soap which must be removed before the evaporation process.
This is done by treating the spent lye with ferrous chloride. Step 2 - Salt removal Water is removed from the lye in a vacuum evaporator, causing the salt to crystallise out as the solution becomes supersaturated.
This is removed in a centrifuge, dissolved in hot water and stored for use as fresh lye. Two fractions are taken off - one of pure glycerine and one of glycerine and water. There are two main areas of concern: the safe transport and containment of the raw materials, and the minimisation of losses during manufacture. The three main components of soap by both cost and volume are oils, caustic and perfumes.
Oils and perfume are immiscible in water and if spilled create havoc, although the oils do solidify at room temperature. Transport of these products is by trained carriers, and the systems for pumping from the truck to storage tanks is carefully designed. Perfumes are bought in lined steel drums which are quite robust, and flammable perfumes are not used in soaps.
All storage tanks are surrounded by bunds to catch the contents of a tank should it rupture or a valve fail. Log in with Facebook Log in with Google.
Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Muler Hanita. A short summary of this paper. A soap molecule consists of a long hydrocarbon chain composed of carbons and hydrogen with a carboxylic acid on one end which is ionic bonded to metal ion usually a sodium or potassium. The saponification of the fat is done by boiling the fat with sodium hydroxide solution soda lye in a large cylindrical steel vessel known as Soap Pan or Kettle.
The lower part of the pan is 'funnel shape. This step involves the separation of soap and glycerol, a process known as 'Salting Out'. Use is made of the fact that soap is insoluble in concentrated salt solution Common Ion Effect , while glycerol is readily soluble.
The soap left in the pan is dissolved in water and after boiling for a short time is ;salted out, the lye being removed after settling. Manufacture of Bar Soap. The methods developed for the purpose are continuous and hence more economical. In this process the hydrolysis of fat is carried out with water under pressure and at elevated temperature in the presence of lime or zinc oxide as catalyst.
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