Non Soapy Detergent (Nsd) Production Slurry Making

Non-Soapy Detergent (NSD) Production- Slurry Making

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Detergent whose active ingredient is manufactured with materials that are not of biological origin is called Non-Soapy Detergent (NSD). The active ingredient of NSD is called AD paste, AD paste for short and one way to produce it is through the reaction of sulphonic acid with caustic soda. Some of the available NSD products are Omo and Surf, products of Unilever, and Elephant, a product of Patterson Zochonis (PZ).

The facts given in this article including the production technology, processes and conditions are based on my production experience at a particular production plant. To manufacture NSD, the AD paste is mixed with some ingredients to produce what is known as slurry. The slurry is in liquid form and to convert it to powdered detergent, it undergoes the process called spray drying. For the slurry making, the following ingredients are required-

  • AD paste- This is active ingredient of NSD. It is the lathering and foaming agent providing the washing power of the liquor. Technically, it reduces surface tension thereby making it easy for detergent to go into greasy materials.
  • Sodium silicate- It plays two roles. On the process side, due to its slimy and gritty nature, it facilitates slurry flow through pipe work. In addition, it cleans the linings of pipes and aids the scouring action of detergent on sinks, pans etc.
  • Water- It is a diluent.
  • Dye- It is a brightener imparting its color on the detergent. Example is monastral blue.
  • Flourescer- They are brightening agents capable of absorbing invincible or incident UV light and re-emitting visible light at a wider wavelength thus making it possible for dyes to appear brightly on detergent powder. Examples are blancophor and tinopal.
  • Recovered slurry- A water substitute or supplement.
  • Sodium tripolyphosphate (STTP)- A water softener aiding detergency. On the process side if properly hydrated, it helps give powder a crispy appearance provided it is not over dried otherwise what is known as fines would be obtained.
  • Sodium sulphate- It is a filler giving powder weight.
  • Sodium toluene sulphonate (STS)- It is an aerating agent breaking the bonds between the component chemicals and aiding atomization of the slurry into the spraying drying tower in the process.
  • Sodium carboxyl methyl cellulose (SCMC)- if dosed at the right level, it plays the role of a dirt suspender making dirt to be on the lather and not on clothe fabrics. If excess is added, jells are produced and sticky powder is formed.
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    These ingredients are processed under three operations- Solid, liquid and turbo operations.

    1. Solid operations- This entails processing of all solid ingredients required for slurry making into a suitable form. The bulky ones are STTP and sodium sulphate. Others are minor ingredients which are STS, SCMC and flourescer which are of two kinds- tinopal and blancophor. The two bulk solid materials are ground in crushers to reduce them to fines before they are discharged into silos and from there they are conveyed to the turbo mixers. The minor ingredients are pre-weighed at the turbo platform before they are discharged into the slurry making vessel (turbo).

    2. Liquid operation- The liquid materials are AD paste, alkaline sodium silicate, recovered slurry/water and dye. Sodium silicate is glass, therefore before utilization it requires additional handling. This is called silicate digestion. Also recovered slurry is prepared prior to turbo operations.

    Silicate digestion- Silicate is normally received as solid glass material. The process of reducing it to liquid form is known as digestion. For this purpose, Digesters and Diluters are used. The digester is a 3 ton pressurized vessel in which 1 ton (1000 liters) of water is first charged followed by 1.5 tons of silicate. After covering it, steam is opened to it until the pressure gauge reads about 3.5 bars. Then steam is shut. The process is exothermic and pressure continues to build up in the vessel which rises till about 4.5 bars. At this point, a pressure relief bar is activated which triggers off the discharge of steam gradually from the vessel until the pressure reaches zero and on attaining this, the digestion is fully complete. The next stage is the dilution process.

    600 liters of water is run into the diluter and again steam is opened into the digester until steam pressure reaches 2.5 bars. Then the steam is shut off and the vessels transfer valve is cracked open. Under pressure, silicate is lifted and recycled for thoroughly dissolution. A silicate of 132o twaddle is obtained at this stage which is too viscous for pumping purposes and the likelihood of having pipeline blocked is high. So, more dilution is done to bring the twaddle down to 108o, the right value for slurry making. It is pumped to storage tanks.

    The remaining liquid operation is the preparation of recovered slurry normally used in place of water or as a supplement for water at times. Water is run into a dissolving vessel and drums of tailings are added to obtain a moisture content of 60%.

    3. Turbo operations- Turbo mixers or turbo dispensers are used for the turbo operations. Each vessel has a capacity of 2.5 tons. They are fitted with agitators and baffles to create turbulence and in addition there is motorized strainer (filter) at their discharge. All are linked to a single transfer pump thus making it impossible to transfer from more than one turbo at a time.

    The mixing process follows a laid down order of addition and in this regard, liquid materials (AD paste, silicate, water and/or recovered slurry and dye) are added first. The agitator is put on motion for mixing while the minor ingredients are added. This is followed by the addition of the flourescer. Lastly, STTP and sodium sulphate are introduced and because the STTP needs to be properly hydrated, it is added before sodium sulphate. The order of addition could be changed from time to time due to modifications in process conditions.

    Even though the reaction is exothermic, there is still the need to do some heating whilst mixing is being carried out. The working temperature is 70oC because a good slurry structure maintaining a temperature between 75oC and 85oC is obtained by so doing. Although the capacity of the turbos is 2.5 tons each, it is never filled to this level to prevent overflowing of the slurry. In any case, the volume used is 2. 2 tons which provides for thorough mixing and gives room for fluctuations in characteristics. About 40% moisture and 60% solid is expected in the slurry whose specific gravity should be about 1.25 (plus or minus 0.05). The slurry is transferred to a holding vessel (7.5 tons) and the total cycle time for the whole process is 15 minutes. About 5 minutes is however allowed for dissolution of caking materials after mixing before the slurry is transferred and moreover 3 batches can be made within an hour from one turbo.

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    Olumide Bola holds a bachelors degree in Chemistry of the University of Ibadan, Nigeria and he has worked in the production plant of some manufacturing companies in Nigeria. He is pursuing chartered membership of the Computer Professionals Registration Council of Nigeria (CPN) and he is a member of Nigeria Computer Society (NCS). He is currently a Software Developer and the Managing Director/CEO of Victolay Technologies Limited. Official web site: http://www.victolaytechnologies.com

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