Nitrogen from coal liquids, removal

Adschiri et al. removed 70 wt.% of the nitrogen from coal-derived pitches by catalytically hydrotreating the pitch in a supercritical toluene-tetralin mixture at 450 °C [67]. These pitches could be used for the production of high-quality electrode carbon. The more conventional process for this reaction involves catalytic hydrotreating of the pitch in the liquid phase. The higher dif-fusivities in the SCF resulted in higher reaction rates. Moreover, catalyst coking could be reduced effectively due to the increased pressure and hence the solvent power of the SCF. 

Typically, liquids derived from coal are lower in hydrogen content and contain more impurities than do petroleum products. These impurities consist of atoms other than hydrogen and carbon, that is, nitrogen, sulfur, oxygen, and inorganic materials. Upgrading of coal liquids to make specification fuels typically involves both hydrogen addition and removal of impurities. 

The character and hydrocarbon-type composition of several syncrudes have been investigated by adaptation of methods developed for heavier fractions of petroleum crude oils. The methods are reviewed briefly, and results are summarized for five coal liquids and a hydrotreated shale oil Refining requirements for removal of heteroatoms, especially nitrogen, and conversion of polynuclear aromatics are discussed in relation to the composition of the syncrudes and the character of refined products to be expected. A preliminary report is given on the preparation of liquid samples from coals of widely different rank to permit more systematic correlation of hydrocarbon character with coal source in relation to refining. 

The ammonia and other volatile nitrogen compounds are then removed from the coal gas by water scrubbing. To assure over 98% sulfur removal and recovery, the trace amounts of COS in the coal gas are converted to H S via catalytic hydrolysis. The HjS is then removed from the coal gas by the conventional Dow GAS/SPEC ST-1 methyldiethanolamine (MDEA) process and the is con-verted to valuable liquid sulfur by the conventional Claus process with MDEA-based tail gas treating. 

In liquid phase oxidations diffusivities are about 1/104 times those existing in the gas phase, and from the pores humic acids and benzenoid acids are removed whose mean diameters are very large compared with the average pore diameter in coal and molecules such as nitrogen and methanol. 

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