Control questions
Which kinds of cake detergents you know?
What is soap?
Which kinds of surface-active substances are used in soaps?
List soap kinds. What is a difference between them?
Basic raw material and auxiliary components at soap production, their purposes.
Standard compositions of toilet and household soaps.
4.3 Chemistry and technology of soap production
In the basis of soap production from fats two basic reactions lay: 1) saponification of acylglycerines and 2) neutralization of alkylcarbon acids.
Formation of alkaline salts from fats (saponification) proceeds in two stages.
The first stage: neutralization of acids by water solution of sodium carbonate. The sodium carbonate - salt of a weak acid and a strong basis, in water medium this salt is exposed to hydrolysis with formation of sodium hydrocarbonate and sodium hydroxide. Sodium hydroxide cooperates with alkyl carbon acids with formation of sodium salt, i.e. soap:
RCOOH + NaOH = RCOONa + H2O
Soap
At rise of temperature higher 600С there is a decomposition of sodium hydrocarbonate to formation of sodium carbonate, carbonic gas and water:
2NaHCO3 = Na2CO3 + CO2 + H2O
The formed sodium carbonate again enters in reaction with acids, and carbonic gas is deleted at 900С.
The second stage consists in neutralization of residue of fat acids by sodium hydroxide and saponification of acyl glycerines, i.e. fats.
3RCOOH + 3NaOH = 3RCOONa + H2O
Hydrolysis of complex ethers is the limiting stage of process. Due to the described reaction hydrolysis of complex ethers of carbon acids has received the term "saponification".
Production of soap can be conducted in periodic and continuous ways.
At periodic way organic raw material is preliminary improved by repeated salting out and bleaching by hydrogen hydroperoxide. The clarified raw material is loaded into soap pan, where saponification and neutralization of acids are carried out. For neutralization the 28-30% solution of sodium carbonate (soda ash) is used. Acids are given with speed about 2 t/h. The mixture is mixed by steam and air within 1 hour. Saponification is considered finished at the content in stock no more than 0,5 % (weights) of sodium carbonate, thus the content of alkyl carbonates makes 56 %. For complete saponification of neutral fats at boiling and agitation in the pan 42 % solution of sodium hydroxide is entered in such quantity, that its surplus did not exceed 0,3 % (weights). Then the stock is settled within 8 hours. The obtaining soap contains more than 60 % of active substance. Ready mass is filtered and fed on vacuum-drying installation.
Continuous way circuit of manufacture of soap active basis is resulted on fig. 4.1. A fatty composition from a tank 1 by pump 5 through heat exchanger 4 at temperature 105-1150С is fed to the device for saponification 6. In the same device from tank 3 the solution of sodium hydrocarbonate is given. The mixture in the first cylindrical part of device 6 is mixed and blown by steam. Allocated carbon dioxide is released from water and fed in gas-holder 8 and then - on clearing and compression.
The stock from the first cylinder of device 6 flows in the second cylinder, where it is also mixed. Allocated gas is given in gas-holder, and the stock is mixed with sodium hydroxide and through a vertical branch pipe flows in the third cylinder. In the third section saponification of neutral fats and neutralization of residue of fat acids occurs. The mixture on reducing pipe flows in the fourth section, where reaction comes to the end. A ready product is collected in reception reservoir 7 and directed on preparation of cake soap.
In manufacture of soap the methods of continuous processing with use of the vacuum-drying chamber and screw-presses are used. The given technological circuit is resulted on fig.4.2. The active mass of toilet soap from soap collector by pump 1 through filter 2 is fed in reservoir 3, from it by dosing pump 4 under pressure 0,5 MPa the mass moves in heater 5, in which it is warmed up to 120-1600С. Further the soap is fed inside of shaft of the vacuum-drying chamber 6 and is sprayed through an atomizer in space, where the vacuum makes 2-6 kPa. Particles of dried and cooled soap settle as a thin layer on the internal surface of chamber, whence they are removed by knifes as chip with thickness of 1 mm. The soap chip is given in two-chambered screw-press 7, located in the bottom part of the chamber. In the first chamber of press the soap chip is condensed, plasticizated, pressed through the lattice and cut on fine granules. Granules are in addition dried in the intermediate vacuum chamber, and then they are fed in the second chamber of screw-press, which works similarly as the first. From the second section of press soap as scales is given in noria 8 and further by screw 14 goes in bunker15.
Vapours of moisture and soap dust are fed in cyclones 9 and 11. Settled particles are pressed and removed as vermicelli by screw-press 10.
The soap chip from the bunker 15 is fed in mixing screw-press 16, where by the dosing pump a mixture of necessary additives is given. The soap mass, feeding from screw-press, is cut and as vermicelli or tablets given on the conveyor 17, which give the mixture in screw-press 18. In this press the soap mass is dried in vacuum, cooled, pressed and of it the bars are formed at temperature 40-600С. The bars are given on conveyor of the automatic cutting machine 19. The received pieces on conveyor are fed in a tunnel 20, where are blown by cold air. Then the hardened soap is fed on a stamp-press 21 and wrapping automatic devices 22.
Keys: 1 – composition tank; 2 – NaOH reservoir; 3 – Na2CO3 reservoir; 4 – heat exchangers; 5 – pumps; 6 – saponification device; 7 – reception reservoir; 8 – gas-holder.
Fig.4.1 – Technological scheme of soap active base production by continuous way.
Keys: 1 – pump; 2 – filter; 3 – feed reservoir; 4 – pump-weigher; 5 – heater; 6 – vacuum-drying chamber; 7, 10 – screw extruder; 8 – noria; 9, 11 – cyclones; 12 – barometric condensator with drop separator;13 – vacuum pump; 14 – screw of soap chips; 15 – bunker; 16 – mixing screw extruder; 17, 23 – conveyers; 18 – vacuum screw extruder; 19 – automatic cutting machine; 20 – forced air cooling tunnel; 21 – stamping press; 22 – wrapping device.
Fig.4.2 – Technological scheme of toilet soap production
Capital equipment of soap manufacture: soap pans, vacuum-drying installations and presses.
A soap pan represents a reservoir in volume up to 200 m3, which is supplied 1) pipelines for submission of initial raw material; 2) a hinge pipe for removal of settled mass; 3) coils for heating and agitation of stock live steam.
A vacuum-drying installation for production of high concentrative soaps with the content of alkyl carboxylates up to 85% consists of a vacuum chamber, representing the vertical cylinder in height of 4 m and diameter of 1,5 m. On the axis of chamber passes a hollow shaft, to which two atomizers and scrapers are attached. The clearance between the wall of chamber and scrapers makes 0,1 mm. Productivity of installations makes 2-6 t/h.