A ≥ 200 °C
fraction (CT200F) of low-temperature coal
tar was prepared by a rotary film evaporator. The catalytic conversion
experiments of CT200F and six model compounds were conducted on the
pyrolysis gas chromatography–mass spectrometer. The yields
of catalytic conversion products benzene, toluene, xylene, and naphthalene
(BTXN) were analyzed by semi-quantitative analysis according to the
chromatographic peak areas. Additionally, the possible formation pathways
and mechanisms of the target products BTXN generated over different
catalysts were investigated. The results show that the yield of aromatic
hydrocarbons increases and the yield of acid compounds decreases during
CT200F pyrolysis over ZSM-5, HY, USY, and β-zeolite compared
with that of its non-catalytic pyrolysis, especially the yields of
BTXN obtained over USY and β-zeolite increase by 128 and 108%,
respectively. The pore structure of ZSM-5 is suitable to produce BTX,
while the suitable acidity and pore structure of USY, HY, and β-zeolite
are more beneficial for the selective preparation of naphthalene than
that of ZSM-5. The conversion pathways of six model compounds into
BTXN over zeolites were obtained, and the following conclusions can
be drawn: The dehydroxylation effect of zeolites shows the order of
ZSM-5 > HY > USY > β-zeolite. The catalytic effect
of zeolites
on the cracking and ring opening of PAHs in CT200F shows the order
of β-zeolite > USY > HY > ZSM-5. The catalytic effect
of catalysts
on the cracking and aromatization of aliphatic compounds shows the
order of ZSM-5 > β-zeolite > USY > HY. β-zeolite
has an
outstanding catalytic performance in the conversion of PAHs into naphthalene.
ZSM-5 and HY can effectively remove phenolic hydroxyl groups in phenol
and naphthol. During the catalytic conversion processes of the coal
tar fraction and model compounds, the catalytic effect of the pore
constructions of zeolites is more important than their acidities,
which determines whether large molecules can enter and whether acid sites in non-micropores
can be effectively utilized.