Manufacturing Natural Soap
The reaction with follows is called saponification
and results in the formation of soap and glycerin. The equation
for the reaction is:
Animal fat or Vegetable oil + NaOH(aq)' Soap
+ Glycerin
During the reaction, the mixture is boiled and
mixed with steam which escapes from the holes in the steam coil.
In the soap and glycerin mix natural salt is added in a process
called "Salting out". Glycerin dissolves in the salt solution
which is heaver that soap and settles down while the soap keeps
on floating at the top. The salt water-glycerin solution is drained
off from the bottom of the tank from which glycerin is recovered
as a by-product. Soap Drying
The soap mass gained after the completion of saponification
(neat soap) is usually dried nowadays on vacuum spray dryers.
The moisture content of soap is thus abridged from 30-35 percent
in neat soap to 8-18 percent in soap pellets (soap flakes
or chips are produced on APV-type dryers, after milling). A variety
of vacuum spray-dryers, from single-stage to multi-stage designs,
are accessible from several manufacturers. The operation of a
single-stage vacuum spray-dryer involves the pumping of
neat soap at 80-85°C through a shell-and-tube heat exchanger
where the soap is heated by high-pressure (6-10 bar) steam
passing through the outside tube in a countercurrent manner.
The soap is preheated to 135-155°C and sprayed onto the walls
of a cylindrical vacuum chamber through a revolving nozzle.
The thin layer of dried and partially cooled soap deposited on
the walls of the vacuum chamber is removed by revolving scrapers
and falls to the bottom of the chamber onto a discharge plodder.
This plodder extrudes the dried soap mass in the
form of noodles or pellets.
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