Volatiles lost during coalification

Losses of CO, H2O, and CH4 during coalification are modeled by calculating possible combinations of the quantities of these Volatiles that must be rel eased to account for the changes in the atomic H/C and O/C ratios that occu r during the transition from the beginning to the end of each of the follow ing coal ranks: high-Volatile bituminous; (combined) medium- and low-volati le bituminous; semi-anthracite; and anthracite. Lower coal ranks were not m odeled because plots of atomic H/C and O/C vs. % volatile matter (dry, mine ral matter free) reveal a lack of equilibration of coal with more than 31% Volatile matter (dmmf). The model uses atomic H/C and O/C ratios, and % vol atile matter (dmmf) values calculated for 2693 coal samples contained in th e US Geological Survey Coal Quality Database. The greatest losses of volati les occur during the transition from the beginning to the end of the high-v olatile bituminous rank. During this transition some CO must be lost. Durin g the transition from the beginning to the end of each of the higher ranks some CH4 must be lost. The increase in the quantity of CH4 evolved may help to explain the presence of catagenic methane found at depth. (C) 2000 Else vier Science B.V. All rights reserved.