282354 Assessment of BIO-Ethanol Dehydration Process Alternatives by Process Modeling and Life-Cycle Analysis

Monday, October 29, 2012: 10:36 AM
328 (Convention Center )
Michel Kahwaji Janho1, Jorge E. Gatica2, Fernando Daniel Mele3, María Rosa Hernández4 and Mauricio Colombo3, (1)Chemical And Biomedical Engineering, Cleveland State University, Cleveland, OH, (2)Chemical and Biomedical Engineering, Cleveland State University, Cleveland, OH, (3)Ingenieria de Procesos y Gestion Industrial, Universidad Nacional de Tucuman, Tucuman, Argentina, (4)Chemistry and Chemical Engineering, Universidad Nacional de Tucuman, Tucuman, Argentina

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.

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