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Sunday, April 29, 2012
Thursday, April 5, 2012
Synthesis of Ammonia is one of the remarkable achievements of Chemical engineering in forties. It is a precursor for Urea, the fertilizer that brought about ‘Green revolution’ in agriculture industry and helped to achieve record food production all over the world. It was a milestone in modern chemistry to synthesis a molecule containing 1 atom of Nitrogen and 3 atoms of Hydrogen, reperesented by NH3 called Ammonia. The Heber-Bosch process for the production of Ammonia is a well established, mature, commercial technology. The process uses a Hydrocarbon source such as Naphtha or Natural gas as the feed stock to generate a synthesis gas composed of Hydrogen and Carbondioxide.The gas mixture is separated into carbon dioxide and Hydrogen using PSA (pressure swing adsorption ) technology. The resulting Hydrogen is used to combine with Nitrogen to synthesize Ammonia. The chemical reaction can be represented by the following equation. N2 + 3H2 ---------- 2 NH3 The above reaction takes place at a pressure of 100-200 bars and temperature of 300-500C in presence of a catalysts. It is an exothermic (heat releasing) reaction and the catalyst bed is cooled and maintained at 400C to be efficient.Buth this process of Hydrogen generation using Hydrocarbon emits greenhouse gases. Alternatively, Hydrogen can be generated using different methods using renewable energy sources using water electrolysis. Such process may be used in the future for this application. Nitrogen is derived from atmospheric air. The air we breathe contains about 79% of Nitrogen and 21% Oxygen. But these two gases can be separated by liquefying the air by cryogenic process and distilling them into two fractions. Alternatively, they can be separated using pressure swing adsorption or membrane separation process, utilizing their density differences. In either way, Nitrogen can be separated from atmospheric air. By combining the above Hydrogen and Nitrogen, it is possible to synthesis Ammonia on a commercial scale. The ammonia can be easily split into Hydrogen and Nitrogen by passing Ammonia through a bed of Nickel catalyst at 200-400C as and when required, to generate onsite Hydrogen. This Hydrogen can be used for power generation or to run our cars using PEM Fuelcell.As we have seen previosulsy, we are now looking for various sources of Hydrogen, and Ammonia is one of the promising sources for couple of reasons. The process and technology of Ammonia production, transportation and usage is well documented and has been practiced for few decades. It does not emit any greenhouse gases.Liquified Ammonia has been widely used in air-conditioning and refrigeration systems. Ammonia can be easily metered into any system directly from the cylinder. It is easier to use Ammonia directly into a convention internal combustion engines in place of Gasoline and this technology has already been practiced in 1880. Ammonia is pungent and any leakage can be easily identified. The advantage of using Ammonia as a fuel in cars, it does not emit any smoke but only water vapour.It can be admixed with Gasoline or used as 100% anhydrous Ammonia. It also helps in reduction of NO2 emission, especially is diesel engines. Ammonia has a great potential as a source of future fuels provided the sources of Hydrogen comes from water using renewable technologies or by photo-electrolysis using sunlight.
Monday, April 2, 2012
One of the wonders of Mother Nature is her ability to sustain life on earth with sun light, water and Carbon dioxide from the atmosphere producing food. No toxic chemicals, no polluting gas emissions and no noise. We can only admire the majesty and power of Nature with our fragile knowledge of science and try to duplicate Nature in order to satisfy our growing energy needs. Nature produces Carbohydrates C6H12O6 using sun’s light, Carbon dioxide from atmosphere and water by a chemical reaction as shown below: 6H2O + 6 CO2 ----------- C6H12O6 + 6O2 The same Carbon dioxide from the atmosphere is now threatening the globe with warming. Can’t we grow more trees so that all the carbon dioxide emissions from our power plants and cars can be converted into more carbohydrates? It sounds very simple and logical but is it feasible? The carbon dioxide in the atmosphere before industrialization was about 280ppm but it has now increased to 392ppm which is almost double. It has grown roughly 2.2% exponentially in the last decade. It is the highest in the past 800 years and likely higher than in the past 20 million years. (Ref: Wikipeadia). Couple of things happened during this period. The industrial and population growth increased rapidly building up carbon dioxide level in the atmosphere and at the same time displacing tropical and rain forests with people and industries; it resulted in the buildup of greenhouse gases to a level, which scientists say are unsustainable. We don’t have enough forest to absorb so much of carbon dioxide. Alternatively, scientists are now trying to interfere with Nature’s photosynthesis process using micro algae called chlamydomonas reinhardtii that will support the production of Hydrogen instead of Oxygen in a normal photosynthesis reaction. This was based on the discovery that if an algae growing culture medium is deprived of Sulfur; it will generate Hydrogen instead of Oxygen. They also found out that such an algae can thrive in a Carbon source such as Carbon dioxide or even in Acetic acid medium. They tested the process using a pilot Photo bioreactor and concluded that the cost of producing Hydrogen by this route will be about $ 42/kg.The cost is high compared to the target cost of Hydrogen by DEO (Department of Energy,USA) at $2.80/kg which is fifteen times lower. However scientists are still working to reduce the cost. Meanwhile scientists are also working on Hydrogen production using Photoelectrolysis.The water electrolysis using Direct current is a known process but the cost of energy in this process is still high. The high cost is due to several stages involved. In the first stage, one has to generate power using PV cells. In the second stage the PV generated electricity will be used to split water electrolyticlly.But scientists are now trying to substitute both the above steps with a single step of utilizing direct sun light to split water into Hydrogen and Oxygen.Thie requires a catalyst known as Photocatalyst which will use light energy instead of electrical energy to split water into elements. Using TIO2 (Titanium dioxide coated electrode) and ultraviolet rays of the sun they believe that a 20m2 PV solar panel can generate about 5m3 of Hydrogen ad 2.5m3 of Oxygen in 24 hours, equival to a power generation capacity of 15kwhrs or roughly about 2.01 gallons of Gasoline from 4 liters of pure water. Scientist are now hoping that light energy, more precisely ultraviolet rays from the sun will come to the rescue of human beings in solving one of the greatest energy crisis in the history of mankind. At last we can hope to see some ‘light’ at the end of the tunnel.