The Chemicals from Coal
The Coal has been considered as a major component of Americas energy reserves for a long time, and more recently it has become an important raw material for the production of chemicals. The worldwide abundance of coal, as reflected in Table 1, and its proximity to sites where it can be used, have made it an attractive alternative to more costly or less strategically located feedstocks. Most approaches to the conversion of coal to chemicals involve either coal gasification or coal liquefaction, processes that convert solid coal to fluids. The fluids are more easily handled and processed than the original coal; they can be used as fuels site or after pipeline transmission, or they can be converted to chemical intermediates. A secondary but important aspect of these conversion processes is that potentially harmful materials in coal are more easily separated from the fluids produced by gasification or liquefaction than from either the solid coal or the off-gases from its combustion.
The most common coal gasification process involves the reaction of carbon, the primary constituent of coal, with steam to produce carbon monoxide and hydrogen.
C + O2 CO + H2 (1) The carbon monoxide and hydrogen can be separated from the other compounds exiting the gasifier and used
either as a fuel or a feedstock to a chemical manufacturing process. Simultaneously, oxygen fed to the reactor along with steam reacts with carbon to form carbon dioxide.
C + O2 CO2 (2) In addition, there is significant reaction between water and carbon monoxide in the gasifier via the water-gas
shift reaction.
CO + H2O CO2 + H2 (3) Although Reactions 1, 2 and 3 are the primary reactions in coal gasification, there are important secondary
reactions. For example, the hydrogen-rich atmosphere in the gasification reactor causes the formation of hydrogen sulfide from the sulfur usually found in coal and of small amounts of methane.
S + H2 H2S (4)
C + 2H2 CH4…