Invented by Philippe Deblay, Cogia SA
The Cogia SA invention works as followsThe invention is a method for at least partial dehydration in an aqueous mixture. This is done by bringing the composition into contact with a microporous, hydrophobic membrane. The receiving phase has a water activity substantially lower than the aqueous component. In this way, the aqueous mixture is at least partially recovered. This invention also includes devices that allow the process to be carried out, particularly continuously.
Background for Process to at least partially dehydrate an aqueous mixture and devices for implementing it
The invention is a process that at least partially dehydrates an aqueous mixture.” It also includes devices that can be used to implement said dehydration process.
The operations of concentration and dehydration, which are required in the manufacture many commodity products, are most commonly encountered in the agrifoodstuffs or biotechnology industries.
The conventional way to increase the solids content is to remove the solvent (generally water) either by thermal or physical routes, such as evaporation or reverse osmosis, or other ultrafiltration techniques.
Conventional membrane processes like ultrafiltration and reverse osmosis are especially advantageous in the biotechnology industry, particularly when it comes to the concentration of sensitive solvents, especially during preparation of enzymes or nucleic acid vaccines.
These processes allow us to reduce the activity loss due to temperature (in contrast to evaporation and distillation) and maintain the structures and, consequently, the biological activity.
These processes have a few drawbacks. The greatest being the inability to select low molecular weight solutes.
The threshold that corresponds to the smallest molecular weight retained by the membrane is 200 in reverse osmosis and 200 in ultrafiltration (Delaunay, et al. Revue generale du froid II, 622-626 (1979)). These conditions allow small molecules such as sugars and amino acids to pass through the membrane with the aqueous solution.
A gradual accumulation is observed along the membranes under pressure. This is the concentration polarization phenomenon, as described in Maurel Techniques de l’Ingenieur chimie-genie chimique [Engineering Techniques chemistry-chemical engineering], volume I, J2790/1?J2795/6 (1989). This causes a reduction in plant performance in terms of solvent flow rate and rejection rate. Deposition losses mean that the concentration operation can’t be quantified.
It is possible to conclude that some sensitive constituents or solutes have been wholly or partially degraded under the effects of pressure (up to 60 bar in the case reverse osmosis).
Concentrating products in the food and agricultural industries has two advantages: It increases the product’s lifespan by reducing chemical, enzymatic, and microbiological degradation, and it reduces storage and transport costs. Particularly in tropical countries, preservation of water-rich foods such as vegetables (from 70% to 90% water) is a critical problem. Water activity (written as wa) is directly linked to the development of microorganisms within food. Water activity is the ratio of the liquid or solid water vapor pressure to pure water at the same temperature. The closer wa is to 1, the greater the development of microorganisms. They cannot reproduce if the concentration is below 0.6 (Botton and al. ; Collection biotechnologies [Biotechnology series], Masson, Paris 223-233 (1985). Food preservation requires that they are subject to a treatment which results in a decrease of their water content.
Osmotic Dehydration using a semipermeable hydrophilic membrane has been used since 1938 to concentrate liquid foods with high water content such as fruit juices. It is one of the possible treatments. No. 2,116,920. This process works on the principle of Osmosis. A semipermeable membrane separates liquids to be concentrated from solutions with a higher osmotic tension. Water moves through the membrane, from the less concentrated to the more concentrated solution. This water transport relies on an Osmotic Pressure gradient, or in other words water activity. These two quantities are linked by the following relationship: aw=e- (?V/RT).
Historically, the first device used to concentrate fruit juices consisted in a cellophane and a sugar syrup or solution of calcium chloride as water-receiving phases (U.S. Patent. No. 2,116,920). This process has the main advantage of concentrating at room temperature or at a lower temperature. The main disadvantage is the nonselective water transportation, such as orange juice concentrations that have shown citric acid diffusion through the cellophane membrane.
Since 1947, “Osmotic Dehydration of Solid Foods” has been contemplated (U.S. Patent. No. 2,420,517). This involves placing the food product into a solution of a hydrophilic, organic product with a lower water activity than the food. The solute component of the receiving phase must not only be insoluble in water but also hygroscopic and nontoxic. It should also be inert towards the flavor, odor, and color of food. These are the most common constituents:
Pure products: sodium chloride or sucrose or glucose
Agricultural raw materials: Cane Molasses or Corn Syrup
Mixtures of these compounds: sodium chloride and glycerol, corn syrup and sucrose.
Dehydration is accompanied with an increase in the food’s content as constituent solutes of the receiving phases; when compared to the initial weight, the water loss in the foodstuffs is compensated for by the gain of solute, according Adambounou et all, Science des aliments 3, 551-587 (1983).
These processes have the main advantage of being able to quickly rehydrate solid food products in order to return it to a state that is closer to its original state than foodstuff that has been dried traditionally.
However, water flow can be accompanied by unwanted diffusion of water-soluble substances such as short organic acids or sugar or salt, which are present in water-receiving phases. The main drawback of this process (especially taste and smell) is the marked changes in organoleptic properties that result.
The invention was therefore made to improve the processes just described.
The present invention aims to provide a process that is highly selective for both the components of the aqueous mixture to be dehydrated as well as the receiving phase.Click here to view the patent on Google Patents.