Many commercial hydrophilic solvents form azeotropes or have vapor-liquid equilibrium (VLE) pinch points with water, which makes solvent recovery by conventional distillation difficult. Solvents that form such azeotropes or have such pinch points include isopropyl alcohol (IPA), acetone, methyl ethyl ketone (MEK), ethyl acetate, ethanol, butanol and tetrahydrofuran, etc. Molecular sieve drying is possible, but is energy intensive and is generally not economical for situations where the water concentration is more than 2-3 wt%. Pressure swing distillation or extractive distillation is often used for feed streams containing more than a few percent water, but the capital cost of the columns needed is an issue, as well as the high operating cost caused by the high steam consumption of the distillation process.
Our zeolite membrane process offers a simple alternative to distillation technology. Vapor permeation of water through the robust zeolite membrane allows almost complete recovery of dry organic solvent, which can be reused without further processing or treatment. The water content of the solvent is reduced to the 0.1 to 1.0 % range.
|The thin zeolite layer separates water (molecular diameter 2.9Å) from organics|
The feed liquid typically containing 10 to 15 wt% water is evaporated at 120-130 °C in a 3 bar (abs) evaporator. The slightly superheated vapor is then circulated through a bank of tubular zeolite membranes that permeate water as low pressure permeate. The hot dehydrated solvent is condensed to produce product containing 0.1 to 1.0 wt% water depending on the customer need.
The low pressure water permeate is cooled and condensed. Typically, 95-98% of the solvent is recovered in the dry product.
A one million gallon per year ethanol dehydration plant. The system reduces the water content from 10 wt% to 0.5 wt%, 98% recovery of the feed ethanol is achieved.
Depending on the size of the plant, membrane modules containing 7 m2 to 20 m2 are used. If membrane replacement is needed, modules are simply disconnected and replaced with new units.
Membrane modules with different packing areas