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23 Cards in this Set
- Front
- Back
- 3rd side (hint)
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property difference:
vapor pressure |
membrane separation technique:
pervaporation, membrane distillation |
conventional separation technique:
distillation |
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property difference:
affinity |
membrane separation technique:
gas separation, reverse osmosis |
conventional separation technique:
extraction, adsorption, absorption |
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property difference:
charge |
membrane separation technique:
electrodialysis |
conventional separation technique:
ion exchange |
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property difference:
chemistry |
membrane separation technique:
carrier-mediated transport |
conventional separation technique:
complexation or precipitation |
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property difference:
size |
membrane separation technique:
microfiltration, ultrafiltration, electrodialysis, molecular sieving |
conventional separation
technique: gravity, bed filtration |
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What is a membrane?
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A membrane is a (typically) thin, discrete interface between phases that moderates the permeation (flux) of chemical species
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What is the general form of the equation for flux?
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J=K∇Φ
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What do Fick's, Fourier's, Darcy's, Ohm's, and Newton's Laws describe?
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Diffusive mass flux, heat flux, volume flux, current flux, shear flux
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Why do all the flux equations have a negative sign before the coefficient of proportionality?
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Because species move down, not up, a gradient (from high to low)
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What are some advantages of using membranes?
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Possibility of hybridization
mild conditions for separations easily scalable modularity can be tailored to application |
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What are some drawbacks of using membranes?
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concentration polarization
fouling and scaling questionable lifetime low selectivity/flux linear scale-up |
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What is the ideal membrane?
Why is it not used in industry? |
The ideal membrane is the lipid bilayer that comprises biological membranes. It is too thin to be practical.
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What is a pore?
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A pore is an open space that is void of the membrane material
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What types of pores exist?
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Through pore
Dead-end pore Closed pore |
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Define percent pore volume
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the total percentage of volume occupied in the pores
also known as "porosity" in quotes because porosity is not a percentage but rather a factor related to the total volume of the membrane which is greater than or equal to zero and less than one |
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Why can porosity not equal one?
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It would mean that there is no membrane material and only "holes" which makes no physical sense
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Define pore size
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the constricted pore diameter (throat) of an "effective pore"
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Define pore diameter
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the distribution of diameters throughout the pore structure
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What is the difference between pore diameter and pore size?
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While pore size refers to the smallest part of a pore, pore diameter gives a more complete picture of the diameters and their frequency of occurrence
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Define tortuosity
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A factor that relates the membrane thickness to the effective pore length
Tortuosity is always greater than or equal to one |
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Define pore interconnectivity
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the degree to which pore space is bicontinuous
bicontinuous: every part of the membrane is connected to every other part of the membrane AND every pore is connected to every other pore quantified as a percentage |
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What is the difference between screen and depth filtration?
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Although both are forms of size exclusion, screen filtration rejects particles at the pore entrance, while depth filtration removes the species within the pore structure
screen filtration uses the mechanism of sieving while depth filtration uses the mechanism of adsorption |
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What is log reduction value?
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A way to quantify selectivity in microfiltration equal to the base-10 logarithm of the ratio of the concentration of feed to permeate
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