Brown coal oxygen functional groups

Figure 2. Distribution of the oxygen-containing functional groups in Rhenish brown coal.

In general, fresh (unweathered) higher-rank (bituminous and anthracite) coals appear to contain little, or no, aliphatic hydroxyl, carboxyl, or methoxyl functions while brown coals are reputed to contain aliphatic hydroxyl groups. Furthermore, there have been suggestions that, except for lignites, virtually all of the oxygen in coal can be accounted for as carboxyl. 

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