The composition changes of polar compounds in recycle solvents (S-1-6) derived from liquefaction experiment with Akabira coal are examined by means of HPLCGC/MS method.
Using HPLC equipped with a Zorbax BP-NH
2 column, polar compounds in recycle solvents were separated into three polar compound classes (Fr-B, N and A) in a stepwise elution system with different concentrations of solvents from hexane to chloroform.
Major polar compound classes in hydrogenated anthracene oil (HAO), used as a starting solvent, were Fr-B (basic nitrogen compounds) and N (neutral hetero compounds), and were mainly composed of carbazoles, benzoquinolines and azapyrenes. However, very little Fr-A (acidic oxygen compounds) was contained in HAO.
The amounts of Fr-N and of carbazoles in S-1 increased more than they did in HAO. But after the first recycle, their levels remained approximately constant regardless of recycling. The levels of anilines and indoles, little contained in HAO, increase with recycling. That is, nitrogen compounds with high molecular weight, such as carbazoles and benzoquinolines derived from coal were partially hydrogenated and cleavaged. Then, nitrogen compounds with low molecular weight, such as anilines and indoles, were produced and their levels increased with recycling.
Fr-A accumulated in the recycle solvent in each recycle and was mainly composed of phenols, phenylphenols and indanols/tetrahydronaphthols.
In general, the level of compounds with low-carbon number of alkyl side chains increased with recycling. This means that the reaction of dealkylation occurs in coal liquefaction.
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