(38h) Assessment of BIO-Ethanol Dehydration Process Alternatives by Process Modeling and Life-Cycle Analysis

Energy
is one of the major driving forces in today's economic and civic development,
fossil fuels burning account for the vast majority of energy produced worldwide.
Burning fossil fuels produces a vast amount of pollutants, this combustion
reaction can release a vast amount of carbon dioxide, sulfur dioxide, carbon
monoxide, radiation and a vast array of polycyclic aromatic hydrocarbons; these
gases are responsible for the pollution that's affecting the planet and life on
it, some of them are responsible for global warming while the others cause
acidification and the rest can cause cancer. The processes used to acquire
these fuels are also a big source of environmental problems; coal mining
releases harmful substances which pollute the air, the earth and the water beds
surrounding the mines, processing petroleum presents similar problems; and last
but not least the fossil fuel reserves are dwindling fast, which affects the
economy, security and the development of all countries on earth. It is then
imperative that new ?cleaner' and more renewable sources of energy are to be
found, studied and implemented. These sources include solar power, wind power
and bio-fuels such as bio-butanol and bio-ethanol, studied in this work.

Whatever the feed
source, a bio-ethanol production process will include a fermentation section
(where the alcohol is formed), a separation section (solid/liquid separation),
a distillation section (where the side products are separated out) and a
dehydration section (where the azeotrope is ?broken' and anhydrous ethanol is
obtained); this work focuses on minimizing the energy requirement of the
dehydration step.

Many
methods exist to separate the ethanol-water azeotrope (also known as ?breaking'
the azeotrope), these methods include:

n  Extractive
distillation:

n  Pressure
swing distillation.

n  Azeotropic
distillation.

n  Pervaporation.

 Azeotropic distillation and pervaporation are
the two separation techniques studied in this work.

This work studies the
energy requirements and the effectiveness of the aforementioned separation
techniques, computer simulations are heavily used. ASPEN PLUS ® is used as the
simulation engine.

Various
configurations utilizing the pervaporation module were designed and analyzed.

The first configuration
consists of a single module with a feed below the azeotrope.

The second
configuration is a ?hybrid? separation train featuring
a distillation to achieve the azeotrope and a pervaporation module to obtain
anhydrous ethanol.

The top product from the tower is the ethanol-water
azeotrope, this is then fed to the pervaporation membrane which separates the
azeotrope yielding a purer ethanol product in the retentate stream, while the
permeate stream containing water and lost ethanol is sent to a flash drum, the
vapor phase containing most of the lost ethanol is recycled to the tower while
the liquid phase containing mostly water is discarded as a waste stream.

The third configuration is
similar to the second, however it divides the separation between two modules,
the first breaks the azeotrope while the second completes the dehydration.

One of the challenges facing this project is that process simulation
engines do not offer a module to simulate membrane processes,
hence a module that could be linked to ASPEN PLUS® has to be developed in order
to study this separation technique. The developed module relies on the FORTRAN®
VB link to transfer data between ASPEN ® and Excel

A Life Cycle Analysis
(LCA) will also be conducted; this analysis will follow the ISO 1400 series.

The
developed module was tested against experimental data for accuracy. The test
showed that the calculations performed by the module yield similar results to
those find by experimentation throughout most of the studied spectrum, the
biggest error found was 13% at an 80mole% feed composition.

The
total energy requirement per moles of ethanol recovered in each of the membrane
processes were calculated and the results were compared, PFD II was found to
require the least amount of energy, these results were then compared to the
ones found for azeotropic distillation at a base case producing 96 mole% pure
ethanol.

Once
all 4 processes are simulated, process optimization techniques will be used to
optimize them, such as:

·        
Heat and energy integration to
design a heat exchanger network that could minimize the plant's dependence on
outside energy sources to accomplish the heating and cooling required.

·        
Various types of membranes
exist, and the effects of these different types on the energy demand of the
pervaporation technique will be investigated.

·        
The effects of different
types of solvents on the azeotropic distillation will also be analyzed.

All
optimizations suggested will undoubtedly affect the LCA,
this effect will also be taken into account.