grokstar (Stranger)
02-06-02 01:20
No 265661
      Pervaporation  Bookmark   

I just had this sent to me by a friend.  Pervaporation seems to be good for purifying solvents and removing water,
but there may be some deeper application someone may have some ideas about!! 

Pervaporation Systems

About Pervaporation
Pervaporation and Vapor Permeation are membrane processes for purifying volatile chemicals:
Breaking azeotropes
Dehydration of solvents and other volatile organics
Organic/organic separations (methanol and ethanol removal)

General characteristics of pervaporation:
Uses semi-permeable membrane
Permeate leaves membrane in vapor state
Permeate must be volatile at operating condition
Functions irrespective of vapor/liquid equlibrium
Used to purify volatile chemicals
Permeates water, methanol, ethanol or organics
Separates mixtures that form azeotropes
Replaces traditional separation methods
Low energy consumption
No entrainer required, no contamination

Sulzer Chemtech has the following pervaporation technologies and skid-built equipment available:
1. Continuous pervaporation
Lowest energy consumption
Best with low impurity level feeds
Effective for large capacities
2. Batch pervaporation
Simple system
Maximum flexibility
Requires buffer tanks
3. Vapor permeation
For impure feeds
Can be fed directly from distillation column
Dissolved solids removed by evaporation

Most applications can be evaluated from our experience. For new applications, tests are required:
Bench tests to determine feasibility, select membrane and determine flux and selectivity
Pilot test to demonstrate process and optimize operating parameters.

Bench and pilot test units are available for rental or purchase.

Products separated or purified by pervaporation
Methanol CH4O
Ethanol C2H6O
Propanol (both Isomers) C3H8O
Butanol (all Isomers) C4H10O
Pentanol (all Isomers) C5H12O
Cyclohexanol C6H12O
Benzyl alcohol
Acetone C3H6O
Butanone (MEK) C4H8O
Methyl isobutyl ketone (MIBK)
Benzene C6H6
Toluene C7H8
Triethylamine C6H15N
Pyridine C6H5N
Methyl acetate (MeAc) C3H6O2
Ethyl acetate (EtAc) C4H8O2
Butyl acetate (BuAc)
Methyl tert-butyl ether (MTBE) C5H12O
Ethyl tert-butyl ether (ETBE) C6H14O
Di-isopropyl ether (DIPE) C6H14O
Tetrahydro furan (THF) C4H8O
Organic Acids
Acetic acid

From C3 to C8
Chlorinated hydrocarbons
Dichloro methane CH2Cl2

Solvents routinely dehydrated in SULZER CHEMTECH pervap units
Isopropanol, ethanol: Standard applications for pervaporation, typically dehydrated from their azeotropes to fractions of a percent of water. Debottlenecking of entrainer plants.

Ethyl acetate, butyl acetate: Form azeotropes in the miscibility gap. Pervaporation or vapour permeation is easily the best technique for dehydration.

Acetone: Does not form an azeotrope with water but when distilled, a large reflux is required. Pervaporation is ideal for final dehydration or for debottlenecking existing distillation systems.

Acetonitrile: Forms azeotrope with water, fully miscible with water. Can easily be dehydrated to low water concentrations. Avoid messing with contaminated salt solution and redistillation of salt contaminated organic phase.

Pyridine: Forms fully miscible, water rich azeotrope, easily split by pervaporation or vapor permeation. Final dehydration feasible. Avoids entrainers and messy salt/alkali solutions.
THF: Easily dehydrated by pervaporation down to a few hundred ppm of water. No messy chemicals.

MEK: Distillation is only possible with an entrainer because the azeotropic composition is nearly identical to the miscibility limit. Pervaporation is far superior.

N-butanol, n-propanol: Form azeotropes with high water content so the distillation/phase separation process involves massive recycle streams. Pervaporation plants are less costly to build and easier to operate.

Reaction mixtures: Remove by-product water to shift equilibrium, increase yield, simplify product purification. Pervaporation or vapor permeation.

Acetic Acid: Difficult to remove pure water by distillation. Pervaporation can remove water from acetic acid of any concentration.

Methanol, ethanol: Can be separated out of its mixture with organics. Pervaporation ideal tool for splitting of azeotropes of organics with these alcohols. No water wash, no messy salts.

Can anyone explain how it works??  There are many reactions I`d like to perform in a completely anhydrous environment,  Wouldn`t you?coolcool

02-06-02 02:01
No 265669
      Re: Pervaporation  Bookmark   

Semi-permeable membranes are a rather complicated beast, since there are so many configurations used. The basic principle underlying porous ones is based on the spatial cross section of the permeating species, small molecules permeate faster than larger ones, and linear chain molecules better than those with a globular shape. Most of the time mass transport through non-porous memebranes is caused the by the difference in the free energy of the permeate between upstream and downstream.  There are entire books devoted to this subject, you might want to visit a technical library for a better description smile
02-06-02 07:16
No 265793
      Re: Pervaporation  Bookmark   

Much like a molecular mesh no??

Ahhh this old Dog just wants to remove the water azeotrope
out of ethanol without benzene, 
Or somehow purify freebase oils like this? 

If I think about a molecular mesh then I don`t know how water would be stripped from ethanol,  unless the ??azeotrope compounds?? are whats left in the mesh?

Interesting though,  aint it