30.1 Introduction

Soaps are sodium or potassium salts of fatty acid. Common fatty acids used are oleic acid, stearic acid, palmitic acid, lauric acid and myristic acid. Soaps are used for human comfort, cleanliness and for industrial use.

Soap is a surface active agent or surfactant. The soap molecules contain both hydrophilic part and hydrophobic part. The hydrophilic part of soap is carboxylate head group and hydrophobic part is aliphatic chain. The dirt or grease is cleaned by key mechanism.

Most marketed bar soaps contains TiO₂ as an opacifier or as a whitener. A variety of dyes are also used to produce colour soaps.

Chemical Reactions:

Fat splitting reaction:

Process flow sheet: Illustrated in Figure.

Figure 30.1 Flow sheet of manufacture of soaps, fatty acids and glycerin

 

30.2 Functional role of various processes (Figure 30.1)

(a) Hydrolyser

•  The fat and catalyst are mixed together and enter the hydrolyser. •  Hot water is added here •  Intimate mixing is required for the water oil immiscible phase. •  Water has 10 – 15% solubility in oil and fats. •  Temperature is maintained at 230°C - 250°C and pressure at 40 – 45 atm for reaction between water and organic compound. •  The fatty acids stream is produced as top product while glycerin stream is produced as bottom product .