Comparison of alternative solvents for oils extraction

Abstract

A B S T R A C TA comprehensive review of the literature about use of solvents for extraction of oilseeds is presented. Mention has been found of over 70 solvents. Currently, hexane is the major solvent in use, but recent price increases and safety, environmental and health concerns, have generated interest in alternatives. Solvents vary considerably in chemical and physical properties which affect their performance in oil extraction. The choice of solvent depends upon the primary end product desired (oil or meal). Recent research on alternative solvents has focused on ethanol, isopropanol, methylene chloride, aqueous acetone, and hexane/acetone/water mixtures. I N T R O D U C T I O NSolvent extraction has been defined as a process for transporting materials from one phase to another for the purpose of separating one or more compounds from mixtures. In the case of oilseed extraction, crude vegetable oil is separated by solvent from meal comprising proteins and carbohydrates. Various solvents have been used commercially, and others have been proposed, based on encouraging laboratory results; but currently, hexane is the solvent of choice by oilseed processors. Operating losses of solvent range between 0.2 and 2.0 gallons per ton of seed processed, and a 6-to 8-fold increase in price during the last decade, has made hexane costs a major factor in oilseed milling. Occasional scarcities of hexane, toxicological and environmental concerns, and several catastrophic explosions and fires have motivated searches for alternative solvents. Listings of references for various solvents and their usage were published on two occasions in this journal (1,2); and Hron et al.(3) recently discussed biorenewable solvents. However, a comprehensive review of alternative solvents for oilseeds extraction has not been published. D I S S O L U T I O N T H E O R YSolvent extraction dissolution theory, based on the laws of thermodynamics, has been explained by Sedine and Hasegawa (4). During dissolution, two separate substances, the solute and the solvent, form a molecular mixture. Dissolution is always accompanied by a negative free energy change. Free energy (AG) is related by the Gibbs equation to enthalpy (or heat content (AH)), absolute temperature (T), and entropy (or amount of disorder (AS)) as: z~G=~H-TASBecause dissolution involves mixing of two substances and an increase in their disorder, a positive entropy change, oecu IS.Dissolution involves two endothermic processes and one exothermic. First, solute molecules (whether solid or liquid) separate into isolated molecules. This is an endothermic process. Its energy is called "lattice energy," "heat of sublimation," or "heat of vaporization," and is small when the solute molecules are nonpolar. The separated solute molecules are next dispersed into the solvent. Energy is required to dissociate the solvent molecules, in preparation to accommodate the solute molecules. The energy required increases with increasing intermolecular interactions in the pure solvent in the following order: n...

Kinetics and thermodynamics of cottonseed oil extraction

“…The dehulled seeds were dried in a vacuum oven at 318K (Johnson and Lusas, 1983;Becker, 1978). It is listed as a hazardous air pollutant by the US Clean Air Act since it can react with other pollutants to produce ozone and photochemical oxidants (Wan et al, 1995a;Hanmoungjai et al, 2000) and its use in oilseed extraction plants can adversely affect workers' central nervous system (Becker, 1978;Johnson and Lusas, 1983;Lusas et al, 1991;Gandhi et al, 2003). The control of its emission levels in extraction plants requires the installation of additional control equipment at additional costs (Conkerton, et al, 1995).…”

An original approach for lipophilic natural products extraction: Use of liquefied n-butane as alternative solvent to n-hexane

“…The wide use of n-hexane is due to its physico-chemical parameters e.g. low boiling point, low polarity, and chemical stability (Johnson & Lusas, 1983). However, residual content in raw material, non-total recovery of hexane observed in industrial processes, growing environmental and health concerns are major constraints (Mikkelsen & Miljøstyrelsen, 2014).…”

Alternative Solvents for Moringa oleifera Seeds Extraction

“…Although solvent extraction is relatively faster and less expensive compared to mechanical extraction process. Generally, the higher the temperature of the extraction process, the higher the rate of oil extracted and this is due to increased oil solubility in the solvent medium (Johnson and Lusas, 1983). In order to meet the world's rising demand for vegetable oils for domestic and industrial applications, it becomes imperative to source for suitable solvents which are readily available in the country at relatively cheaper costs so as to replace hexane.…”