Energy & Fuels, Vol. 6, No.5,1992 679
Communications
Temperature, K Figure 1. Profiles for the temperatureprogrammedhydrogaeification of Loy Yang coal at 3.5 and 7.0 MPa.
Profiles for the temperature-programed hydrogasification are illustrated in Figure 1, where coal conversion is expressed as wt 9% on a dry, ash- and catalyst-free basis. When the flow rate of Hz was increased from the normal level of 0.5 to 2 L(STP)/min, no significant effects on the gasification profiles were observed, which means that the reaction under the present conditions is free from the gas film diffusion control. Coal devolatilizationin the absence of catalyst was almost complete at temperatures up to 800 K, followed by char gasification. The reaction rate was larger at a higher pressure of 7.0 MPa. The iron-catalyzedgasificationproceeded in two stages: in other words, rapidly between 700 and 800 K and slowly beyond 800 K. The iron catalyst enhanced the reaction rate even in the conversion range up to about 50 % ,namely, the devolatilizationstep. In this region the deposition of carbon (or carbon precursor) from tarry materials evolved and the subsequent hydrogenation may proceed on the catalyst surface, as observed with the nickelcatalyzed gasifi~ation.8*~ As is well known, volatile hydrocarbons are decomposed to form highly reactive carbon
and coke over Fe and Ni metals.1° Another possibility is that the iron may promote the reaction of devolatilizing coal with Hz, the so-called rapid hydrogenation.llJ2 Thus, the iron catalyst seems to greatly promote CH( formation at the expense of tarry materials. Char gasification followed the hydrogenation of deposited carbon, and the gasification rate was larger at a higher iron loading and pressure of H2. The conversion up to 800 K after the completion of the first rapid stage reached 80% at 9 wt % Fe and 7.0 MPa, whereas it was only 40% without iron. The reaction rate in the second slow stage beyond 800 K was rather lower in the presence of catalyst, but the conversion up to lo00 K at 9 wt % Fe, 90%, was much larger than that (75%) without catalyst. The XRD measurements of iron-bearing char after gasification showed that the crystallite size of a-Fe is too large to be determined by XRD. Therefore, the decreased rate in the second stage may be attributable to the catalyst deactivationdue to agglomerationof iron particles. These observationssuggest that the optimumtemperature region for producing CH4 efficiently with an iron catalyst may be below 800 K. The residual iron-rich char after CHI productionmay be burned in a blast furnaceand converted to pig iron. In conclusion, a C1-free, finely dispersed iron catalyst prepared from FeC13 shows a large rate enhancement in the pressurized hydrogasification of brown coal at low temperatures of 700-800 K. Registry No. Fe, 7439-89-6. (8)Tomita, A.; Watanabe, Y.; Takarada, T.; Ohtsuka, Y.; Tamai, Y. Fuel 1986,64,795-800. (9) Takarada,T.; Ohtsuka, Y.; Tomita, A. J. Fuel Soc. Jpn. 1988,67, 683-692. (10) Albright, L. F., Baker, R. T. K., Ede. Coke Formation on Metal Surfaceu; ACS Symposium Series 202; American Chemical Society: Washington, DC, 1982. (11) Johnson, J. L. In Coal Gasification; Msesey, L. G., Ed.;Advances in Chemistry Series 131; American Chemical Society: Washington, DC, 1974; pp 145-178. (12) Anthony, D. B.; Howard, J. B. AZChE J. 1976,22,625-658.
Additions and Corrections Klaus H. Altgelt and Mieczyslaw M. Boduszynski*: Composition of Heavy Petroleums. 3. An Improved Boiling Point-Molecular Weight Relation. 1992,6, 68-72. Page 6 9 Equation 5 is incorrect as printed. The correct equation is MW,m
DF
MW,,
eF[l-
(600 - AEBP)''4 X 10-9 (5)
