DETERGENT MANUFACTURING (COMMERCIAL GRADE)
The most of the active organic materials, commonly known as the synthetic detergents are either in the liquid form or in the paste form and are converted into powders by combining them with inorganic material commonly known as the 'builders' or the 'fillers'. The addition of these builders make the finished powder non-sticky, dry to the touch and do not tend to convert into lump. The common builders employed are of the following groups :
- Oxygen-releasing compounds, and
- Others as whitening agents, enzymes and anti-redeposition agents, insoluble inorganic fillers, colloidal silica and bleaching agent.
Sodium sulphate had been known as the inert fillers since quite a long time back. During the process of neutralisation of the excess of sulphuric acid with caustic soda, which is present in the dodecyl benzene sulphonate acid during sulphonation, sodium sulphate increases the foaming properties of sodium salt of dodecyl benzene sulphonic acid. Sodium sulphate retards the detergency of sodium dodecyl benzene sulphonate, but the addition of carboxy methyl cellulose overcomes this difficulty.
Here are some of the common compounds of each group generally used in the detergent industry.
Out of the four types of carbonates sodium carbonate or soda ash (NO2CO3), modified soda (NO2CO3 NaHCO3 2H2O) sodium bicarbonate (NaHCO3) and potassium carbonate (K2CO3), soda ash is the most important one as a source of alkalinity in detergent powders, absorbent and neutralising agent.
The most commonly employed phosphates in the detergent industry are :
Trisodium phosphates Na3PO4, 12H2O, disodium phosphates Na2HPO4, 12H2O, chlorinated trisodium phosphates (Na2PO4 12H2O)2 NaOCl, trisodium pyrophosphate Na4P2O7, sodium tripoly-phosphate Na5P3O10, sodium tetraphosphate Na6P4O13, and sodium hexametaphosphate (NaPO3)6. Of these, sodium tripolyphosphate is the most commonly used one and constitutes 30 to 50 per cent of the all modern synthetic detergent powders because :
- It adds to the washing powder of the detergent powder
- Its addition helps prevent greying of white clothes on repezted washings
- It equally works in hard water
- It enhances the dirt removing and soil suspending properties
- Its addition helps in the bead formation when the powder is made by conventional drying method.
These are of primary importance in the formulations of dish-washing powders. The commonly available silicates are of the three types :
Sodium metasilicate Na6Si2O7, Sodium metasilicate Na2SiO3, and Sodium orthosilicate Na4SiO4.
The use of potassium silicates in the detergent industry is also very common. SIlicates are added into the detergent powder with following specific purposes in view :
- Suspension of soil in solution and prevention of redeposition on cloth,
- As wetting and emulsifying agents,
- Good buffering action, and
- Inhibit corrosion of stainless steel and aluminium wares.
For getting all-round best result, the quality of silicates added should vary from 160 to 240 percent of the total weight of active detergent material.
Oxygen Releasing Compounds
Sodium perborate NaBO3. 4H2O is the most important compound of this class. When it is in the solution form, it is used as a bleaching agent. Its action is very mild and does not harm animal, vegetable and synthetic fibres.
(a) Whitening Agents
Compounds under this class are usually derivatives of coumarin or stilbene. The whitening agents are sold under the commercial names Blankophor, Calcofluor, Fluorosol, Fluolite, Fluotex, Leucophor, Photine, Pontamine White, Tinopol, Ultraphor and Uritex.
The action of addition of enzymes in the washing process can be explained that they convert proteinaceous soil in such a form which can easily be removed by the detergents.
Enzymes are very sensitive materials and must have certain preconditions fulfilled for their existence or to avoid their inactivity. These are, the moisture content of the powder should be below 5 percent. The powder containing enzymes should not have oxidising agents and to have the best results the pH of the powder should range between 8 to 9.5.
Enzymes of the following types are of interest to the detergent industry:
- Proteases-these act on protein to form amino acids.
- Amylases-convert starches into dextrin.
- Lipases-attack fats and oils.
(c) Anti-redeposition Agents
Carboxy methyl cellulose (CMC) and polyvinyl pyrolidone (PVP) are the important compounds of this class.
(d) Insoluble Inorganic Fillers
Silics, quartz, and marble dust etc., are the common insoluble inorganic fillers used in the manufacture of scouring powders and abrasive soaps.
(e) Colloidal Silica
It is used in making powders which are not prepared by spray-drying. Its addition makes the powder flow freely and reduce its stickyness. Colloidal calcium silicate may also be used in place of it.
(f) Bleaching Agent
Addition of sodium hypochlorite (NaOCl) during the manufacturing, process itself, results in bleached product of detergent powder.
PROCEDURAL DETAILS OF MANUFACTURING 'COMMERCIAL' DETERGENT POWDERS
Compounding of all the above mentioned additives or yield homogeneous dry products with lesser tendency to segregate, or to have these products in the granular form, is not done by the same method. Different percentage composition of all the constituents and the techniques employed result in such products. Some of the important techniques employed are:
- Absorption and neutralisation
- Spray drying (pressure jet)
- Drum drying
- Drying mixture of powders.
Ordinary ribbon mixers, plough mixers, and screw mixers are usually employed in this process. A typical formula suitable for preparation of detergent powder by this method is given below:
|Sodium dodecyl benzene sulphonate (four percent active matter)
|Sodium metasilicate pentahydrate
As is clear from the above formulation, the quality of active detergent matter is very limited, therefore, the powders made by this process has limited applications for household use. However, this process is quite suitable for preparation of powders used as industrial cleaners. In this process only those anhydrous in organic salts are used which can easily by hydrated.
In this method the inorganic compounds are first charged into the mixer. The mixer is then set in motion electrically. To this is then added sodium salt of dodecyl benzene sulphonic acid slowly and stirred continuously. When all of the sodium dodecyl benzene sulphonate has been added, the mixer is continued to be in motion for further 15 minutes and then pine oil is added to it. When all the pine oil has been added the mixer is further kept in motion for a minute or two and then spread on the floor for ageing and the powder is ready for use.
Absorption and Neutralisation
The plant is used in this method is also the same as in absorption method such as plough mixers, ribbon mixes, incorporators and screw mixers but no heating is required in this process. The materials are first dried and charged into the mixer and the mixer set in motion. The dodecyl benzene sulphonic acid is then added in small amount while the mixer is running. When the colour of powder has changed bluish, small amount of water (about two percent of the total weight of powder) is added which renders sulphonic acid more reactive and the colour is changed to light yellow. To this solution silicate and optical brightener are then added.
After completion of reaction which takes about 10 minutes for a batch of 200 to 250 lbs., the powder is spread on a concrete floor and left in position overnight for ageing.
However, if necessary, the powder may be charged into the hammer mill for breaking up lumps. The perfume may be added at this stage by spraying and the powder is ready for packing. This process is fruitful for production of cheap, heavy-duty household powder.
The powder obtained by this method is generally of cream to light yellow colour, which may be bleached by adding 2 percent solution (based on final weight of powder) of sodium hypochlorite.
All the powdered ingredients except optical whitening agent and perfume are fed into the mixer started. When sulphonic acid has mixed up well, the two percent solution (already prepared) of sodium hyphchlorite is added. When bleaching has completed, sodium silicate is added. Finally, qualitative tests for active chlorine is performed. Optical whitener and perfume are added only when the test for chlorine is negative, otherwise the presence of chlorine may cause harm to the fabric. However, if the presence of chlorine is indicated by the qualitative tests, andanti-chlor' such as sodium bisulphate, sodium sulphite or sodium thiosulphite (20gm/250lbs.) is added. Mixing is continued for 2-3 minutes and then optical whitener and perfume can be added safely.
This method is of particular importance for manufacturing cheap, heavy-duty household products.
Spray Drying (pressure-jet)
Essentially this technique involves the separation of water from solids by vapourisation, which can be accomplished by exposing the water carrying solid suspension or slurry to hot air under pressure, making the large surface area of the droplet in contact with hot air possible and thereby resulting in a high rate of vapourisation.
The equipment generally used and commonly known as 'Spray Drier' is essentially a cylinder with spray nozzle at one end fitted with an arrangement that the feed (slurry) is made to pass through this nozzle under pressure which meets hot air and turns these drops of suspended solids into fine granules of the desired size. The design of the spray drier is specific to the requirements of individual plant. The height and diameter of the drier, the temperature of the drying air, the amount of water to be dried per hour, size of the detergent granules required and some of the factors which must be paid attention to while designing a drier for a particular plant. Economically it is not advisable to use the same drier for a particular purpose in an other plant for a different purpose.
There are two types of driers, one involving the parallel current while the other making advantage of counter-current principal. In parallel current process the path direction of material and hot air is the same. While in case of counter-current process, the two have their opposite direction of movement. The exhaust air should not be allowed to go off. It is neither in confirmation with the public regulators nor economical because the powder quantities carried along with would amount to several tons per hour. It therefore, should be cleaned with filters and the deposited detergent dust recycled into the spraying zone.
The slurry (feed) for the spray drier may be produced either batch wise or continuously. The batch wise preparation is more commonly used as it facilitates the preparation, control, check and adjust the constituents, if necessary. It requires at least two tanks, from one of these the slurry is being pumped into the tower, while the fresh batch is being prepared in the other. The tanks should be of sufficient capacity so that one batch prepared is sufficient to feed during the time the other batch is ready for use. In continuous process, the labour reduction to the minimum is possible, but at the cost of comprehensive careful control at the feeding units.
Process of Manufacture
The slurry, first prepared is passed through straining drums, magnetic separators, homogenizing mill and forced under high pressure (30 to 40 atm.) through the spray nozzles to the spray towers 30 to 40 meters high. Here, firstly the big droplets are formed which are less prone to heat transfer. When the droplets thus formed, come into contact with hot tower air, the water at its surface evaporates at a fairly fast speed and turns into semi-sold plastic shells. When it further comes in the downward direction, more water from within the plastic shells are evaporates which escapes as steam through small apertures and the plastic shells are changed to hollow spheres (beads). The lower part of the spray tower is made conical, so that the tower-powder can collect there. The powder discharged from the tower is still very hot and needs cooling before further processing can be carried out. To save time and maintain the continuity of the process, cooling is combined with pneumatic conveyance in most of the modern detergent powder making units.
A clear understanding of the process can best be understood through the concurrent spray drying system and the allied flow sheet of detergent manufacture in.
The product (tower-powder) obtained above is not the final detergent powder, rather lack sensitive materials like per borates of alkli metals or the substitutes, enzymes and perfumes oils. As these decompose at the temperature of the tower-powder, therefore, these can not be added prior to spraying or immediately after it, rather their admixture involves further processing as shown in the above diagram.
While making a choice for the perfumes to be added in the detergent powders, following points must be given due consideration.
- The type of perfumes have both an immediate and residual odour and both must be given due weight age
- Effect of contents of powder on perfume on storage
- Its volatile nature under conditions of packing and storage
- Whether any residual smell of the perfume is left on washing.
As the perfume have a positive effect on the consumer, therefore, standard quality perfumes should be added instead of cheaper varieties.
The packing is done mechanically. The dosing in the packets is done volumetrically instead of gravimetrically as the latter one cannot sustain to high filling speeds. The density of the powder should be fairly constant, otherwise it will result in weight deficit on excess of the packets.
To complete with the open market the detergent powders manufactured by you must have the following characteristics:
- It must have good colour properties
- The size of the particle should be desirable one and every spread
- The density of different samples taken from the lot must be same
- It must have the same residual water content in all the samples taken from different lots
- It should not be sticky
- It should have uniform composition and appearance.
Drum drying is convenient for production on small scale. It can easily be started and stopped in a short period as compared to spray drying. It is particularly used for preparing highly concentrated powder of alkyl benzene sulphonate or fatty alcohol sulphates. But inspite of some of the advantages it has over spray drying, it is also not free from some of the disadvantages. The product made by this process is not fluffy, rather is heavily dull in colour and not attractive. Powder made by this method does not dissolve freely in water. The finished products get scorched on storage. It is suggested that the drums used in this method should be of stainless steel to avoid any corrosion.
It is a measure of the quantity of foam formed by adding the detergent to water and is measured by the height of foam rise in a jacketed tube when a given volume of detergent solution falls through a known distance.
Prevention of Soil Deposition
A pure white piece of cloth is added to the detergent solution. A standard solution of the detergent is prepared and divided into four or five parts in different containers. To all of these is then added a piece of white cloth of equal measurements. To each of these containers is then added different soil such as carbon black, iron oxide, manganese oxide etc. The loss in whiteness of the piece of cloth is directly a measure of soil deposition.
It is measured by the time taken to sink a skein of cotton yarn into the detergent solution when placed slowly on its surface.
Although it is one of the most important properties of the detergents, yet it is very difficult to define it specifically and has certain limitations. A test just opposite of the soil deposition provides a sufficient measure of the cleaning property of the detergent. What is done, is that the fabrics are soiled and then after immersing it in detergent solution, its whiteness is increased. The photometric increase in the whiteness of the cloth provides a means for cleaning determination.
The monochromatic light is transmitted through the solution of the detergent. The percentage of light transmitted is found with a calorimeter, which, itself is a measure of colour intensity. The result may also be had by visual compression when the light is passed through a standard solution.
Properties Based on Concentration
Tests based on the concentration properties of detergents include the percentage determination of the active detergent matter and that of builders, measurement of the fluidity and density of the slurries determination of stickiness and tendency of cake formation in humid atmosphere are some of determination of interest to the formulators and manufacturers. However, in case of liquid detergents clarity at low temperatures and stability to hydrolysis are qualities of interest to note.
Some of the detergents which when come in contact with human skin cause irritation. A group of people are asked to immerse their hands in to the solution of the detergent. The average view of the observers is much more near to the actual results and reliable. Besides the above mentioned tests, by far the most important one is the overall assessment of the reaction of the consumers about a product. The consumer is the best judge. He observes all its aspects, its working, its price, and side effects etc., and makes his mind about a particular product, and gives an assessment of the popularity. To assess the consumers reaction about new product, consumer surveys are conducted in limited areas. Such operations are tedious and expensive. Therefore, the true assessment of the consumers reaction is the final evaluation and essential for providing the real value of a new product.