PEROXIDASE-CATALYZED POLYMERIZATION AND DEPOLYMERIZATION OF COAL IN ORGANIC-SOLVENTS

Peroxidases from horseradish roots (HRP) and soybean hulls (SBP) catal yze the efficient polymerization of a 4-kDa dimethylformamide (DMF)-so luble fraction of Mequininza (Spanish) lignite in 50% (v/v) DMF with a n aqueous component consisting of acetate buffer, pH 5.0. Under these conditions, HRP and SBP catalyze the oxidation of free phenolic moieti es in the coal matrix, thereby leading to oxidative polymerization of the low-molecular-weight coal polymers. The high fraction of nonphenol ic aromatic moieties in coal inspired us to examine conditions whereby such coal components could also become oxidized. Oxidation of nonphen olic aromatic compounds was attempted using veratryl alcohol as a mode l substrate. SBP catalyzed the facile oxidation of veratryl alcohol at pH <3. HRP, however, was unable to elicit veratryl alcohol oxidation. The potential for SBP to catalyze interunit bond cleavage on complex polymeric substrates was examined using 1-(3,4-dimethoxyphenyl)-2-(phe noxy)propan-1,3-diol (1) as a substrate. SBP catalyzed the C alpha-C b eta and beta-ether bond cleavage of this compound, suggesting that sim ilar reactions on coal, itself, could lead to depolymerization. Depoly merization of a >50 kDa coal fraction was achieved using SBP in 50% (v /v) DMF with an aqueous component adjusted to pH 2.2. Approximately 15 % of the initial high-molecular-weight lignite fraction was depolymeri zed to polymers <4 kDa in size. Hence, SBP is capable of catalyzing th e depolymerization of coal in organic solvents, and this may have impo rtant ramifications in the generation of liquid fuels from coals.