Standard Article

Bleaching

  1. Dennis R. Taylor1,2

Published Online: 15 JUL 2005

DOI: 10.1002/047167849X.bio003

Bailey's Industrial Oil and Fat Products

Bailey's Industrial Oil and Fat Products

How to Cite

Taylor, D. R. 2005. Bleaching. Bailey's Industrial Oil and Fat Products. 5:7.

Author Information

  1. 1

    DR Taylor Consulting, Port Barrington, Illinois

  2. 2

    Formerly of Oil-Dri Corporation of America, Vernon Hills, Illinois

Publication History

  1. Published Online: 15 JUL 2005

Abstract

Traditionally, bleaching refers to that process by which colored pigments are removed from fats and oils by adsorption onto bleaching earth. Of course, certain noncolored constituents are also removed as well. In fact, the removal of particular colored and noncolored constituents during bleaching is necessary if high-quality oil is to be produced. In this chapter, the idea of bleaching as primarily an adsorptive purification process is developed. Four key aspects are addressed: (1) the use of adsorptive purification agents, (2) the adsorptive removal of targeted constituents, (3) practical means and methods for achieving optimal efficiency and efficacy from the bleaching process, and (4) approaches for dealing with spent adsorbents.

The properties and preparation of the main adsorptive purification agents used in the bleaching process (activated carbon, bleaching earth, and silica hydrogel) are discussed; differences between acid-activated and natural bleaching earths and the types of clays used in their manufacture are delineated. The effects of various trace constituents (and contaminants) on oil quality, and the nature and specificity of their interaction with surface-active (adsorption) sites are described. In particular, the control that noncolored constituents (phospholipids, soaps, free fatty acids, peroxides) exert over the adsorption of colored pigments (carotenoids, chlorophyll, pheophytins) is elucidated. Optimal bleaching practices and filtration conditions (“press bleach effect”) as well as processes and equipment for achieving maximum efficiency from the bleaching process are described. Finally, various tactics regarding spent filter cake, including utilization/disposal, best methods to recover retained oils, and control over smoldering, are examined.

Keywords:

  • adsorptive purification;
  • adsorption;
  • bleaching;
  • acid-activated;
  • natural;
  • bleaching earth;
  • bleaching clay;
  • activated carbon;
  • silica hydrogel;
  • surface-active site;
  • phospholipids;
  • soaps;
  • free fatty acids;
  • peroxides;
  • pigments;
  • carotene;
  • carotenoids;
  • chlorophyll;
  • pheophytins;
  • filtration;
  • press bleach effect;
  • spent filter cake;
  • oil retention;
  • oil recovery;
  • smoldering