Thermolysis of Dibenzyl Ether under Coal Liquefaction Conditionst

Abstract

Thermolysis of dibenzyl ether in tetralin and 1-methylnaphthalene as typical hydrogendonating and -nondonating solvents \was studied at temperature of 380 to 400°C, pressure of 10 to 80 MPa and reaction time of 5 to 40 min by continuous flow reactor. The major products from dibenzyl ether at low initial concentrations was identified as toluene and benzaldehyde with small amounts of benzene and carbon monoxide in both solvents. The product distribution was listed in Table 1. The disappearance of dibenzyl ether obeyed good first order kinetic expression regardless of the changes of solvent used as shown in Figs.2 and 3. The decomposition of dibenzyl ether increased considerably with increasing pressure. Assuming that dibenzyl ether would thermally decompose to afford toluene and benzaldehyde by first-order reaction and benzaldehyde as intermediate decomposes successively to toluene and benzene within our reaction conditions, the rate constant for each of the reaction pathways was estimated by nonlinear regression. These results were summarized in Table 3. Effect of pressure on each step of the reaction was shown in the van't Hoff plot given in Figs.5and 6. The activation volume of dibenzyl ether thermolysis was determined to be 20-30 cm³/mol, such a large negative value suggested fairly polar transition state of the reaction. It may be concluded, therefore, that dibenzyl ether thermolysis under coal liquefaction conditions mainly proceeds by intramolecular hydride-transfer mechanism.