Abstract A feed solution containing a solute and a solvent is concentrated by reverse osmosis. The feed solution is subjected to a given working pressure and is first forced through a series of high rejection membranes. The diluted solution which permeates the high rejection membranes is discarded and the product solution leaving the high rejection membranes is then passed as a feed solution through a series of low rejection membranes. The dilute solution which permeates through the low rejection membranes is preferably recycled to the starting feed solution, but can be discarded, if desired. The product comprises the concentrated solution which does not permeate the low rejection membranes. The working pressure of the solution fed to both the high rejection membrane and the low rejection membranes should exceed R2 pi '' where: R is the rejection ratio of the membrane and pi '' is the osmotic pressure of the solution being fed to the membrane.
The method of claim 1, in which the dilute solution which passes through the second series of membranes is recycled to the high rejection membrane as part of the feed solution,
Claim 2
Dependent Claim
13 words
The method of claim 2 wherein the feed solution is a sugar solution.
Claim 3
Dependent Claim
14 words
The method of claim 2 wherein the feed solution is a fruit juice solution.
Claim 4
Dependent Claim
13 words
The method of claim 1 wherein the membrane is a cellulose acetate membrane.
Claim 5
Independent Claim
148 words
An apparatus for concentrating a feed solution comprising: A high rejection membrane which receives the feed solution and separates the feed solution into a concentrated feed solution which does not pass through the membrane, a low rejection membrane which receives the concentrated feed solution that does not pass through the high rejection membrane and separates the concentrated feed solution into a product solution which does not pass through the second membrane, and a diluted solution which does not pass through the second membrane; means for applying and for adjusting the working pressure within said membranes; supply means for forwarding the feed solution to said high rejection membrane; means for passing the concentrated feed solution to the low rejection membrane product collection means connected to the high pressure side of said low rejection membranes; and removal means for discharging the diluted solution which permeates through the high rejection membranes.
Claim 6
Dependent Claim
28 words
The apparatus of claim 6 including means for recycling to the supply means the solution permeating through the low rejection membranes to prevent loss of valuable dissolved solids.