Volume 13: Industry Processes and Controls
6. Rendering
Annex A to Chapter 6: Tallow and its derivatives
Introduction
Tallow derivatives

Introduction

6.73 Tallow is one of the main products of rendering and has a diverse range of uses including candles, soap, chemicals and human cooking materials. The derivatives of tallow are used in a large number of pharmaceuticals, cosmetics and other industrial products.

6.74 This section describes some of the main processes of derivation. The high temperatures used in most of these processes are considered to render the derivatives safe for human use. Indeed, in 1996 the European Agency for the Evaluation of Medicinal Products (EMEA) considered that even raw tallow had no discernible infectivity of BSE. ¹ Volume 11: Scientists after Southwood describes the consideration given by MAFF and SEAC to the possible infectivity of tallow, including tallow derived from SBO.

Tallow derivatives

6.75 The main derivatives of tallow - fatty acids, fatty esters and soaps - are produced by further refinement of tallow by the oleochemical industry. There are three basic processes: hydrolysis, transesterification and saponification. Glycerol is produced in all these. ²

6.76 Hydrolysis, which produces glycerol and fatty acids, combines tallow and water at a high temperature (220-250°C), for between 1.5 and 10 hours. A crude fatty acid and dilute crude glycerol result, which have further high pressures and temperatures applied to them. The fatty acid is then distilled at low pressure at about 200°C to remove impurities. These acids can be further refined to make fatty alcohols, metallic soaps, fatty amines, fatty acid esters and fatty amides. ³

6.77 Transesterification combines tallow and methanol at temperatures over 200°C and under high pressure for longer than 20 minutes. Methyl ester and glycerine are produced. The methyl ester is distilled to remove water and impurities, and then hydrogen is added to it at temperatures in excess of 200°C. This produces tallow fatty alcohol and methanol. The tallow alcohol can be further refined into cetyl and stearyl alcohols. ⁴

6.78 Saponification can occur in one of two ways. In the first method, called continuous saponification, the tallow is heated with sodium hydroxide at temperatures of up to 105°C, and then sent through a saponification reaction column. At this stage, the blend is mixed with more, concentrated sodium hydroxide at a temperature of about 140°C at twice atmospheric pressure for about eight minutes. This produces soap and glycerol. The latter is afterwards washed out of the soap mass. ⁵ In the second method of saponification, called batch saponification, the tallow is placed in a pan with concentrated sodium hydroxide at about 95°C for about three hours. The soap and glycerol which results is kept at this temperature for about five days to complete the washing process and separation of glycerine. ⁶ These processes do not produce high quality glycerol and it must be further refined, by distillation or ion exchange. ⁷