This invention relates to a rectification process by which an aqueous organic solvent is recovered in at least two fractions having different concentrations and the soluble component is recovered from the solution as an aqueous solution free of the organic component. More particularly, this invention is concerned with the recovery of aqueous alcohol solutions of at least two different alcohol concentrations, from a solution or miscella made by extracting carbohydrates and other components from soybeans or other oil seeds.
There is increasing commercial interest in the production of food products from soybeans that are suitable for human consumption. In conventional extraction of oil seeds, such as soybeans, with hexane for the production of animal feed the soybeans are flaked, extracted with hexane and the spent flakes cooked with moist heat (toasted). It has been long recognized that such a toasted product is not well suited for human consumption. The spent flakes prior to toasting are called white flakes, which when ground become the present soy flour of commerce. This too is not a product well suited for human consumption because it has an unpleasant beany taste and causes flatulence.
The major ingredients of hulled soybeans are protein, carbohydrates and sugars, glyceride oils, and numerous non-oil lipids, such as phosphatides. In present commercial practice in the manufacture of toasted meal and soy flour, only the oil and some of the phosphatides are extracted with hexane. The beany flavor of hexane extracted meal and flour is attributed to unextracted non-oil lipids. Flatulence is attributed to unextracted carbohydrates.
It is known that aqueous solutions of methanol, ethanol, and isopropranol in concentrations between 50 and 70% dissolve a substantial portion of the carbohydrates including those that cause flatulence. It is also known that soybean oil has a limited, but useful, solubility in strong alcohols, i.e., hot 95 volume percent ethanol, and that non-oil lipids are very soluble in aqueous alcohol solutions. When carbohydrates are extracted from full-fat flakes with 50 to 70% aqueous alcohol, we have found that almost all of the non-oil lipids are also extracted. We expect that these solubilities will become the basis for the commercial production of soybean products for human consumption.
There are numerous instances in the literature where relatively strong alcohol solutions used for extraction of soybeans are diluted in the process and need to be rectified for recovery of the strong alcohol for reuse. One of us in several applications assigned to the same assignee of the present invention has shown several cases where miscellas resulting from extraction of carbohydrates and other components have to be rectified for reuse.
In U.S. Letters Pat. No. 3,970,764, an alcohol vapor stronger in alcohol than the solvent used for extraction is used to increase the concentration of alcohol in the vapor recirculating in a vapor or flash desolventizer. As disclosed in co-pending application Ser. No. 549,434, now abandoned strong alcohol is advantageously used to displace relatively weak alcohol, prior to desolventizing, from spent flakes which have been extracted with weak alcohol. In the processes disclosed in U.S. Pat. Nos. 4,144,229 and 4,129,470, full-fat soybean flakes are treated successively with dilute and strong alcohols. These processes produce bland soy products which may be essentially free of glyceride oil, deleterious carbohydrates and non-oil lipids.
U.S. Pat. No. 3,993,533, assigned to the same assignee, discloses a distillation process suitable for recovering weak and strong alcohol solvents from a miscella containing whey (the extract containing carbohydrates and non-oil lipids and a minor amount of protein) while recovering whey as a concentrated aqueous solution stripped free of alcohol. In said process, the miscella flows through a series of rectification and stripping steps to obtain the desired result. Although said process meets the claims that by its practice the distillation can be carried out with the least expenditure of heat, it has been our experience that whey solutions often foam to the extent that they cannot be distilled in conventional distillation equipment. Herein is disclosed a new distillation process by which, with minimum additional heat as compared with the said process, the same result is accomplished and the foaming managed.