Membrane Processes and Surface Chemistry Modification

Joseph Imbrogno-Department of Chemical and Biological Engineering-CBIS

Talked to us about the different characteristics of membranes, and how those characteristics affect the purpose and function of the membrane.  The Achilles heel of membranes is excessive fouling-Joe was trying to prevent and/or find ways to correct the fouling of a membrane.   Later, we went into the lab and found that it is fairly easy to make a membrane, with basic chemistry of polymers, solvents and non-solvents (phase inversion).

Uses:

Desalination—removing salt (and other minerals) from water

Food Production—purifies and concentrates food components; ultrafiltration of milk yields cheese

Reverse osmosis—treats and purifies drinking water

Types:

Symmetric vs. Asymmetric—pores are all the same size for symmetric membranes and pores are varying sizes for asymmetric membranes

Organic vs. Inorganic—depends on the material:

Organic—natural polymers, Teflon PTFE (polytetrafluoroethylene), rubber, wool, cellulose and polyamide-imide (PAI)

                Inorganic—metallic powders, and ceramics

Hydrophilic vs. Hydrophobic—for protein separations, hydrophilic surfaces perform the best

Fouling—irreversible build-up of solute at or in the membrane and will eventually lead to stop of flow completely

Occurs 3 ways:

Pore blockages-particles block the pores of the membrane

Pore constriction—particles “stick” to the inner walls of the pores of the membrane and cause a decrease in flow of the solution

Cake formation—solute lays down and forms thick layers on top of membrane and complete blocks pores and membrane surface

Two Types of Flow:

Cross Flow—solution flows tangential to the membrane and only the particles that can fit through pores are able to pass through membrane—much more effective

Dead-End Flow—solution flows head on into the membrane—results in more fouling

Ternary Diagram:

Don't worry too much about this for the quiz: A graph/diagram with 3 variables and axis’s: membrane type, pore size and type, and casting composition.  Phase 1 is the solvent and polymer before the membrane is produced, Phase 2 is the result of the three variables and how they will affect each other.  The variables will add up to a constant, K, usually 1.0 or 100%.  The graph shows the ideal efficiency and one could find the actual efficiency, using the actual values of each variable.       

Connections:

Dr. Koratkar—dropped material in water (non-solvent) and an entirely different outcome was produced

Dr. Ullal and Palermo—characteristics and properties of materials determine the results yielded by that material