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In an effort to develop a novel hydrogen production process in which coal is gasified with highpressure steam in the presence of CO 2 sorbents, the fundamental CO 2 sorption characteristics of Ca-based sorbents during repetitive carbonation-calcination reactions at different pressures were investigated using a conventional TG/DTA analyzer and a laboratory-scale horizontaltube reactor. The results revealed that, as a result of sintering and crystal growth, Ca-based sorbents were significantly deactivated by high-temperature calcination treatment. As a consequence, the CO 2 uptake capacity of the sorbents decreased with cycle number under both atmospheric and pressurized conditions. An intermediate hydration treatment was found to enhance the reactivity and durability of the sorbents for multicycle CO 2 sorption. Because of the presence of eutectics in the CaO-Ca(OH) 2 -CaCO 3 ternary system, the formation of sorbent melts was observed in repetitive calcination-hydration-carbonation reactions at elevated pressures at 923 and 973 K. Even under eutectic conditions, the sorbents retained their high reactivity for CO 2 sorption.

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Oil palm biomass, namely empty fruit bunch and frond fiber, were pretreated using a planetary ball mill. Particle sizes and crystallinity index values of the oil palm biomass were significantly reduced with extended ball mill processing time. The treatment efficiency was evaluated by the generation of glucose, xylose, and total sugar conversion yields from the pretreatment process compared to the amount of sugars from raw materials. Glucose and xylose contents were determined using high-performance liquid chromatography. An increasing trend in glucose and xylose yield as well as total sugar conversion yield was observed with decreasing particle size and crystallinity index. Oil palm frond fiber exhibited the best material yields using ball milling pretreatment with generated glucose, xylose, and total sugar conversion yields of 87.0, 81.6, and 85.4%, respectively. In contrast, oil palm empty fruit bunch afforded glucose and xylose of 70.0 and 82.3%, respectively. The results obtained in this study showed that ball mill-treated oil palm biomass is a suitable pretreatment method for high conversion of glucose and xylose.

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Deactivation of Ca-based sorbents by coal-derived minerals during multicycle CO2 sorption reactions at elevated temperature and pressure was investigated using a laboratory-scale horizontal-tube reactor. The sorbents tended to undergo a solid−solid reaction with coal-derived ash components such as silicon (Si) and aluminum (Al) during multicycle CO2 sorption with an intermediate hydration stage. This reaction formed complex inorganics, such as mayenite (Ca12Al14O33), calcium silicate (Ca2SiO4), and spurrite (Ca5(SiO4)2CO3), and substantially decreased the sorbents' CO2 sorption ability. Interaction with the coal-derived minerals was significant during the multicycle calcination−carbonation reaction only when the sorbents were subjected to the intermediate hydration treatment. This result suggests that steam enhanced the solid−solid interaction between the minerals and the sorbents at elevated temperature (>873 K) and pressure (6.0 MPa) and that the interaction should be avoided by selecting proper reaction conditions for efficient utilization of the Ca-based sorbents.