Energy & Fuels 1988,2, 684-692
684
CaO
+ 0 (from 02,COz, or HzO) = CaO(0) CaO(0) + Cf = CaO + C(0) C(0) = CO (and/or COO)+ Cf
(2) (3) (4)
Oxygen-containinggas, whatever it is, first adsorbs on fine CaO particles, forming surface oxygen complexes, CaO(0) (reaction 2). This surface oxygen spills over to a free site on the carbon surface, Cf, to form an oxygen complex on carbon, C(0) (reaction 3). Excellent dispersion of the Ca species and good contact with carbon is essential for these steps. In reaction 4,C02and CO would be produced from C(0) through many reaction paths as described in the literat~re.~J~
Conclusions The type and amount of surface comlexes on coal char, after being exposed to oxygen-containing gases at various conditions, were evaluated by TPD measurement using a
slow heating rate. Many types of oxygen complexes, both on mineral matter and carbon, were identified. The features of these complexes are strongly affected by the adsorption conditions and also by the treatment conditions after adsorption. Oxygen can be transferred from carbon to metal and vice versa. The gasification mechanism was discussed in relation to the present TPD results. It is proposed that the solid-state reaction between CaC03and C does not occur during the Ca-catalyzed gasification, but the oxygen transfer from CaO to carbon is the principal function of a Ca catalyst.
Acknowledgment. The partial financial support of a Grant-in-Aidfor Scientific Research on Priority Areas from the Ministry of Education, Science acd Culture, Japan (62603014), is acknowledged. Registry No. 02,7782-44-7; C02, 124-38-9;HzO, 7732-18-5; Ca, 7440-70-2.
Characterization of Titanium in United States Coals Gary L. Steinmetz, Mysore S. Mohan,* and Ralph A. Zingaro Department of Chemistry and the Coal and Lignite Research Laboratory, Texas A&M University, College Station, Texas 77843 Received July 6, 1987. Revised Manuscript Received April 11, 1988
Detailed knowledge of the modes of occurrence of titanium in coals is necessary to understand the mechanism(s) by which the element is deposited on the catalysts in the hydroliquefaction and hydrodesulfurization of coal. The modes of occurrence of titanium in six US.coals (0.28-0.67% Ti) have been investigated. The samples (-100 mesh) were extracted with a variety of solvents (benzene/MeOH, methyl isobutyl ketone, pyridine, and dimethyl sulfoxide). DMSO was found to be the most efficient solvent, extracting up to 6.3% of the titanium in one case. In 70% of the cases, the solvents extracted less than 1% of the total titanium. Extractions with NH,Ac indicate that less than 1% of the titanium was ion-exchangeable. Examination of the coal samples by scanning electron microscopy-energy-dispersive X-ray spectrometry showed that titanium in the coals occurred principally in the following modes: (1)as discrete, elongated grains of Ti02(
