December 23, 2014
Solvent extraction and alcohol washing are similar in many ways. Using hexane to dissolve fats, and then pressing the liquid from oil seeds (corn germ, canola, sunflower seeds, peanuts), is an application where Vincent has not ventured. However, pressing aqueous alcohol solution from organic fiber, in factories which remove sugars by washing, is a forte.
Our vapor-tight presses are used to squeeze alcohol with dissolved sugars in the production of food ingredients such as pectin and soybean protein concentrate (SPC). The alcohol is recovered from the press liquor in solvent recovery units. A by-product from this system is a molasses made by evaporating the water in the process.
A few years ago this experience led to Vincent participating in the development of a new alcohol-wash system which was patented by CP Kelco. This system was designed for washing the sugars from fresh lime and lemon peel. Currently the industry practice is to use water to diffuse the sugars from the peel. The "washed" peel is then dried and used at factories which extract the pectin food ingredient.
Since the peel normally has a sugar content of at least 7 Brix, washing puts many tons per day of sugar into the wastewater treatment plant. This severe load can result in noxious odor if the WWTP is not sufficiently large. The investment required in wastewater treatment can rival the cost of the rest of the plant.
The process developed by CP Kelco involves using aqueous alcohol, instead of water, to wash the peel of its sugars. The alcohol wash proved more effective than the traditional water wash. And, since the used alcohol (and sugar) goes to a solvent recovery unit, the plant can become "zero effluent". Environmental problems are thus addressed very effectively.
The process was patented in multiple countries. However, to date no full scale installations have been announced, reportedly because of the large investment required. Vapor-tight wash tanks, screens, and presses are required, along with the alcohol recovery system.
Molasses, a valuable feed ingredient, would be a by-product.
There is an alternate technology. Currently several peel washing plants using water (not alcohol) are studying the possibility of using a TASTE evaporator to concentrate their used wash water. In this manner load would be taken off the WWTP, and the molasses by-product would be produced. Since the used wash water has relatively low dissolved solids, typically up to 3 Brix, a large evaporator is required. The system was employed by Azucitrus in Paysandu, Uruguay, using a spare, small TASTE.