Adaro subbituminous coal (AD) from Indonesia was used. The coal
sample was dried, ground, and sieved between 150 and 250 μm.
Tables 1 and 2 show the proximate and ultimate analysis results and
ash composition of the AD coal, respectively.
Commercial CaCO3 (Nacalai Tesque) was used as the catalyst raw
material. The loading of the Ca catalyst was performed as follows: the
AD coal (10 g) was immersed in 200 ml of deionized and distilled
water (theNa and K concentrationswere below10 ppb) containing variousamounts
of CaCO3, and the suspensionwas stirred at 120 rpmusing
a rotary evaporator at 40 °C for 1 h under vacuum. The water was then
evaporated at 60 °C for 1 h under vacuum to yield coal samples with a
Ca content of 0.5–2 wt.%. For reference, Ca(OH)2 (Nacalai Tesque) was
also used as a catalyst raw material. The Ca loading was determined
by inductively coupled plasma–optical emission spectrometry (Seiko
Instruments Inc., SPS5510) after acid leaching at room temperature.
Hereafter, the coals with CaCO3 and Ca(OH)2 were denoted as
Ca(C) and Ca(H), respectively.