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Showing posts with label Molasses. Show all posts
Showing posts with label Molasses. Show all posts

Friday, April 20, 2012

Energy efficient 'Bioethanol'production

The science and technology of Bioethanol production from starch or sugar is well-established. Brazil leads the world in Bioethanol production with a capacity of 16,500 million liters/yr followed by US with a capacity of 16,230 million liters/yr.India produces merely 300 million liters/yr as the fifth largest producer in the world.US consumes about 873 MM gallons/day of oil of which about 58% is imported. The US forecast for 2025 import of oil is 870MMgal/day and the President wants to replace imported oil from the Middle East by 75% -100MMgal/day.(Ref: US Environmental protection Agency,Cincinnati,Ohio). Currently bulk of the Bioethanol is produced in centralized plants. This is because an economical plant requires a production rate of 40-55 MMgal /day. Transportation of raw materials to long distance is uneconomical. Countries like India can substantially increase their sugar production and encourage small scale distilleries for the sole purpose of replacing imported oil. Large scale Bioetehanol production involves fermentation of molasses; a byproduct of sugar industry.Bioethanol can also be produced directly from cane sugar juice or from starch such as Corn or Tapioca. Molasses is diluted with water and inoculated by addition of yeast and other nutrients. The fermentation takes about 24 to 30 hours till the fermented broth has an alcohol content of 7.5 to 9.5% by volume. The fermented wash is then distilled in a separate distillation column. This alcohol which is 95-96% is known as rectified spirit. The rectified spirit is further passed though a Molecular sieve to remove moisture and to concentrate alcohol to 99.8% by volume. A spent wash of about 8 lits are generated per liters of Bioethanol.The spent wash will have a BOD (biological oxygen demand) value of 45,000ppm.This can be subject to Anaerobic digestion to generate ‘Bio gas’ with about 55% Methane value and the liquid BOD will be reduced to less than 5000ppm. This Biogas can be used to generate power for the process. This process is economical for a production of Bioethanol 40-55MMgal/day. But in countries like India the sugar cane molasses are available in smaller quantities and the sugar plants are scattered. Small scale distillatory can adopt ‘Per-evaporation’ method to concentrate ‘Bioethanol’.The advantage with ‘Perevaporation’ is the process is not limited by thermodynamic vapor-liquid equilibrium. The distilled alcohol with 96% alcohol can be separated by Perevaportion into streams containing Bioethanol 99+% and alcohol depleted water.Perevaporation is a membrane separation process and it serves as an alternative to distillation and molecular sieve and saves energy. The membrane process can be suitably designed for alcohol enrichment as well as dehydration and easily adoptable for smaller production of Bioethanol. Such process allows production of dehydrated Bioethanol which are suitable to use as a fuel in cars as a Gasoline blend without any engine modification. Production of Bioethanol from cane sugar molasses is cheaper than from corn starch. Countries like India should promote Bioethanol as an alternative fuel to gasoline and reduce their oil imports.

Tuesday, March 27, 2012

Hydrogen is the choice of Nature as the source of clean energy

There is so much discussion about Hydrogen as a source of clean energy because, it is the choice of Nature. Nature has provided us with fossil fuels which are Hydrocarbons, chemically represented by CxHy, Carbon and Hydrogen atoms. In the absence of Hydrogen in a Hydrocarbon, it is nothing but Carbon, which is an inert material. The Hydrocarbon gets its heating value only from the presence Hydrogen atom. The natural gas, now considered as the cleanest form of Hydrocarbon is represented by the chemical formula CH4, has 25% Hydrogen by weight basis. It represents the maximum Carbon to Hydrogen ratio at 1:4.This is the highest in any organic chemicals. In aromatic organic compounds such as Benzene, represented by C6H6, the Hydrogen content is only 7.69%.Even in Sugar which is an organic compound from Nature, represented chemically as C12H22O11 has only 8.27% Hydrogen. But Bioethanol, derived from sugar represented by C2H5OH has almost 13% Hydrogen. Ethyl Alcohol known as ‘Bioethanol’ derived from sugar is blended with Gasoline (Hydrocarbon) for using as a fuel in cars in countries like Brazil. Brazil is the only country that does not depend on imported Gasoline for their cars. The same Bioethanol can also be derived from Corn starch. But the starch should first be converted into sugar before alcohol is derived; it is more expensive to produce Bioethanol from corn starch than from cane sugar molasses. The climatic conditions of Brazil are more favorable for growing Cane sugar than corn. Brazil is in a more advantageous position than North America, when it comes to Bioethanol. US is one of the largest consumer of Gasoline.US has imported 11.5 million barrels/day of oil in 2010.It has used 138.5 billion gallons of Gasoline (3.30billion barrels) in 2010) according to EIA. (US Energy Information Administration) It is estimated that Brazil’s sugar based Alcohol is 30% cheaper than US’s corn based Alcohol. Brazil has successfully substituted Gasoline with locally produced alcohol .They also introduced ‘flexible fuel vehicles’ that can use various blends of Alcohol-Gasoline. Most of the Gasoline used in US has 10% Ethanol blend called E10 and E15, representing the percentage of Alcohol content in Gasoline. Brazil is the largest producers of Bioethanol in the world. Both Brazil and US account for 87.8% of Bioethanol production in the world in 2010 and 87.1% in 2011.Brazil is using Bioethanol blends of various proportions such as E20/E25/E100 (anhydrous alcohol) (Ref: Wikipedia). Almost all cars in Brazil use Bioethanol blended Gasoline and even 100% anhydrous Bioethanol is used for cars. Brazil has set an example as a ‘sustainable economy introducing alternative fuel’ to the rest of the world. The 'bagasse' from cane sugar is also used as a fuel as well in the production of ‘Biogas’, which helps Brazil to achieve sustainability on renewable energy and greenhouse gas mitigation. The above example is a clear demonstration of sustainability because natural organic material such as sugar is the basic building block by which we can build our clean energy source of the future. The same Bioethnanol can easily be reformed for the production of Hydrogen gas to generate power and run Fuel cell cars. Many companies are trying to use chemicals such as metal Hydrides as a source of Hydrogen. For example, one company successfully demonstrated using Sodium Borohydride for Hydrogen generation. Many companies are trying to find alternative sources of Hydrogen generation from water, including Photo-electrolysis using direct solar light and special photo catalyst materials. We know Nature produces sugar by using sun’s light, water and carbon dioxide from air by photosynthetic process. Can man duplicate this natural process and generate Hydrogen at the fraction of the cost by simply using water and sun’s light? The race is already on and only time can tell whether our pursuit for cheap and clean Hydrogen can become a commercial reality or just stay as an elusive dream.