Abstract
Vegetable oils undergo numerous refining steps in order to remove undesirable compounds and produce high quality, stable commercial products. Recovery of vegetable oil from spent bleaching earth is an area where ample opportunities exist for cleaner production and cost saving in the vegetable oil processing industry. Conventional oil extraction and refining processes, which involve multiple unit operations, have several disadvantages. These include complex separation steps, energy-intensive operations, the requirement for large amounts of water and hazardous chemicals and the potential of generating large quantities of wastes. Conventional oil extraction mostly uses hexane. High energy consumption, high temperature operation, the important portion of the nutritional oil components being lost and large amount of water during the process of refining result from the use of hexane. There is a dire need for the development of separation techniques that will facilitate recovery of vegetable oil from spent bleaching earth while sustaining the nutritional components naturally present in the vegetable oils and reducing the negative impact of oil processing on the environment. This paper reviews the state-of-the art technologies for recovery of vegetable oil from spent bleaching earth. It presents the development of the technologies chronologically and compares their relative merits from aspects of capital requirements, resource utilisation, cleaner production, sustainability and economy. The paper ends with a look at supercritical fluid extraction (SFE) as a potentially promising alternative recovery technology that could offer opportunities for process intensification; resulting in a simpler, cleaner and resource-efficient system for oil recovery from bleaching earth.
