New liquefying technique works for high-grade coal,
a chemical technique that Germany used in World War ii may now help break the spiral of ever-rising oil prices. A team of German scientists has perfected the technology of transforming coal into liquid transportation fuels such as diesel and petrol.
Since the 1940s, chemical engineers have been using iron oxide-based catalysts to break coal's extended network of chemical bonds into smaller hydrocarbon molecules, which can serve as precursors for liquid fuels. But these catalysts work well only with the relatively young, so-called "low-rank" coals that are highly porous, allowing the chemicals to freely percolate. The porosity in coal owes to the presence of impurities; in low-rank coals the impurites may be as high as 40 per cent.
The older, high-rank coal, which is found abundantly the world over, is non-porous. High-grade bituminous and semi-anthracite coals have carbon content as high as 90 per cent.This means that carbon molecules are more densely packed than in low-rank coals. The iron oxide-based catalysts cannot rupture the more stable ring-like hydrocarbon structures found in high-gade coal. But now scientists led by Matthias Haenel at the Max Planck Institute for Coal Research in Mlheim on the Ruhr have found how to weaken these bonds and liquefy the high-rank coals.
The team has identified a new class of soluble catalysts made from boron and iodine that work in two steps. First, the catalysts add hydrogen atoms to the highly stable carbon-carbon double bonds between hydrocarbon rings (in organic compounds) and the chainlike hydrocarbons (aliphatic compounds) that link them, converting them to weaker single carbon-carbon bonds. Next, they break these single carbon-carbon bonds, creating a mixture of hydrocarbon chains of various lengths. Together, these chains can serve as a liquid precursor for making diesel. The findings appeared in an online version of Angewandte Chemie International Edition published in January, 2006.
The German scientists tested the catalyst's ability to transfer the hydrogen atoms to the organic molecules by dissolving the coal in pyridine, an organic solvent. When they stirred medium-volatile bituminous coal found in Germany (German coking coal) with pyridine at 280 0 c and at a pressure 150 times that of normal, the coal's solubility in the liquid increased dramatically from 13 per cent to 91 per cent. They also found that its carbon to hydrogen ratio went up substantially. The scientists said this was due to breaches in carbon-carbon bonds between aromatic and aliphatic parts of the molecules caused by the newly infused hydrogen atoms.
They claimed that this was the firstever high grade coal hydration -- the infusion of additional hydrogen atoms into carbon structures. "This can probably make coal, which is quite abundantly available, a suitable feedstock for liquid fuels and chemicals that are currently sourced from petroleum," Haenel said.
Several countries have been attempting to turn coal into liquid fuels. But all of them target low-grade coal as the attempt is focused on making use of poor quality coal, rather than making coal a viable alternative to petroleum. China is currently setting up a us $2 billion coal liquefaction facility in Inner Mongolia to turn its vast coal reserves into oil and refine it into gasoline, jet fuel, diesel and fuel oil.
Similarly, India, which accounts for 7 per cent of the world's coal reserves, is exploring the possibility of converting some of its low-grade coal into oil. State-owned firms, Coal India Limited and Oil India Limited, are working with a us company to try the latter's proprietary technology on coal with high sulphur content mined by Northeastern Coalfields. Out of a total hard coal reserves of 214 billion tonnes found in India, 84 billion tonnes are proven recoverable reserves of anthracite and bituminous coals.
The coal liquefaction process can make production of oil from coal a more viable process for countries with little or no oil reserves but endowed with vast coal mines. However, the technique still requires fine-tuning, say experts.
The boron and iodine catalysts currently used are moderately expensive and cannot be recovered after the reaction. However, the scientists feel that the work has opened the door to finding low-cost catalysts that can cheaply convert any type of coal into a liquid.
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