How is coal converted to oil and gasoline? --- Al, S Prairie, Wash.
Marshall Brain Answers:
If you look at gasoline at the molecular level, you find that it is made up of carbon chains with hydrogen atoms attached to the carbons (hence the name "hydrocarbon"). A typical carbon chain is 8 to 10 carbons long in gasoline. See How Gasoline Works for details.
If you look at coal, it also contains carbon and hydrogen atoms, but they are in the wrong form. The carbons need to chained together to have the right number of carbons in the chain and the right number of hydrogens attached to the carbons. This video demonstrates how that happens in two steps: 1) coal gasification to create a "producer gas", and 2) creation of the liquid fuel from the producer gas:
The producer gas is relatively easy to make from coal: you heat coal to drive off all the volatiles, producing things like methane and carbon monoxide. Then you scrub the producer gas to get rid of things like sulfur and mercury. Once you have the producer gas, you convert it to carbon monoxide and hydrogen. Then you feed the producer gas into a Fischer–Tropsch reaction.
Not everyone is happy about the idea of turning coal into liquid fuels, as described here:
The main thing the video points out is that if you take coal, turn it into electricity and then use the electricity to power electric cars, it would be a much more efficient use of coal. But coal-to-electricity has a number of problems as well, including ash lagoons and carbon emissions.