J. Japan. Assoc. Min. Pety. Econ. Geol. 78, 190-193, 1983

Synthesis of graphite from bituminous coal at 0.5-2 kb water pressure and 300-600°C

MICHIo TAGIRI

Department of Earth Sciences, Ibaraki University, Mito 310, Japan.

AND TAKANOBU OBA*

Department of Geology and Mineralogy, Faculty of Science, Hokkaido University, Sapporo 060, Japan.

Graphite (dooz=3.37 A) was synthesized from bituminous coal in the presence of 1% Li2COa or 2% Ni catalyst using cold-seal pressure vessels. Because catalyst concentrations are similar to that found in shales, the results may be applicable to the graphitization process in natural systems. The temperature of transformation of coal into graphite increases sharply from 0.5 to I kb, and then decreases with increasing pressure above 1 kb. The experimental results suggest that graphitization in natural rocks cannot take place at P-T conditions of diagenesis.

The synthesis of graphite can be easily 1.07%) from the Carboniferous Pittsburg done at very high temperatures above Formation of Pennsylvania, U.S.A. Bitum- 2000°C, but is very difficult at low tem- inous coal was ground in an agate mortor peratures below 1000°C. No experiment together with a catalyst; crystallinity was has been done from the viewpoint of geo- determined employing an X-ray powder logical significances. From investigation on diffractometer. The dooa-spacing and the graphitization in rocks (French, 1964; crystallite size of this material are 3.71A Landis, 1971), it is well known that graph- and 10 A, respectively. The starting itization depends on geotherm. On the material does not show a sharp diffraction other hand, as the duration of diagenesis pattern, but contains a trace of quartz, is one of the important factors involved in feldspar and clay minerals as ash com- coalification, it has been thought that graph- ponents. itization also greatly depends on duration of Two kinds of most powerful catalyst heating. The experimental study on graph- were selected for the experiments on the itization will make clear these problems. basis of the previous works (Mackee,1974; The experimental apparatus used in Mackee and Chatterji, 1978; Macak et al., this study was externally heated cold-seal 1978). In one series of experiments, the pressure vessels; water, the pressure medium, starting material contained about 2 wt% was supplied by an external pumping system. Ni metal and in the other, the starting Starting material was bituminous coal (C= material had about 1 wt% Li2CO3. As will 80.84%, H=4.54%, 0=13.55%, others= be discussed later, the concentration of

(Manuscript received January 20, 1983) * Present address: Depatrtment of Eanth Science , Monash University, ;Clayton, Victoria 3168, Australia Synthesis of graphite from bituminous coal 191 catalysts are geologically reasonable values compared with the ratio of Ni or Li to -C in the average shale (Krauskopf, 1967). Samples (about 6 mg) were enclosed in small sealed Ag-Pd capsules together with an adequate amount of water (about 8 mg). In these sealed-tube experiments, oxygen "buffering" was established by the presence of graphite or amorphous carbon during the experiments (French and Eugster, 1965). The duration of individual runs varied from 0.1 hrs to 8 weeks.

Crystallinity of carbonaceous products Fig. 1. Transformation of bituminous coal to was determined by means of the X-ray graphite. powder diffractometer and represented in terms of do,,-spacing and Lc(002)of the crys so that we can easily distinguish graphite tallites (Tagiri, 1981). In this way, fully- from disordered graphite at this point. ordered graphite may be defined by a do, This nomenclature is used in the later sec of 3.35-3.36A and an Lctoo2)of over 500 A. tions of this paper. Temperature and A d002and an Le(O02)of disordered graphite pressure conditions of formation of graphite range from 3.43 to 3.35 A and from 30 to are given in Table 1 and illustrated in 500 A, respectively, and it gradually trans- Fig. 1. forms to fully-ordered graphite with increas- In experiments containing no catalysts, ing temperature (Tagiri, 1981). On the graphite could not be obtained at tem- other hand, carbonaceous material in rocks peratures of 300-600•Ž. In the experi abruptly changes its crystallinity at doo2= ments catalyzed by 1% Li2CO3, Li2C2 co- 3.37 A and L,(002)=100A (Tagiri, 1981), existed with graphite at temperatures ex-

Table 1. Temperatures and pressures of formation of graphite

* The quoted values of P and T are only nominal, and

uncertainties of +20 bars and +2•Ž, respectively, exist.

Lc contains an estimated +10% error. 192 Michio Tagiri and Takanobu Oba ceeding 470°C. Li2C2 did not, however, centrations of catalysts in the experiments crystallize at temperatures below 450°C. seem to be similar to that in some rocks, and Graphite precipitated on capsule walls in we can apply these results to the process of the 600° and 700°C runs, but was found graphitization in shales, sandstones and inside the charges which were held at tem- carbonaceous metamorphic rocks. The peratures below 500°C. In the experiments graphite isograd is situated on the boundary catalyzed by 2% Ni metal, graphite formed between the chlorite zone and the garnet at temperatures over 500°C. No other zone of the Sanbagawa Metamorphic Belt crystal except Ni3S2 was associated with (Tagiri, 1981), and approximate tem graphite, although Ni8C crystallized only at peratures of 350 to 400°C at 4-6 kb have low temperatures along with disordered been estimated for this boundary from carbonaceous material. In the experiments metamorphic facies analyses (Ernst of al., catalyzed by Ni, graphite only appeared in 1970; Seki, 1973). The estimates are the main part of the charge. The yields of consistent with the extrapolated transition graphite were several percent in all experi of carbonaceous material to graphite ments, and the crystallinity of the coexist- established in this study. It has been ing carbonaceous material was 4402-0.45 A thought that graphite crystallizes in a process and Lc(042)-=20A. The transition tem- of diagenesis, though many diagenetic perature of graphite shifts to higher tem and metamorphic rocks do not contain peratures with increasing pressures to 1 kb, graphite (Tagiri, 1983). The experimental then decreases with increasing pressure over results indicate that graphite does not 1 kb. The following reaction is suggested to crystallize in such rocks during diagenesis. have occurred during graphitization. Sedimentary rocks sometimes includes a Coal (C, H, 0) --s graphite + small trace of graphite (Tagiri, 1983). That amount of gas. graphite is apparently a detrital one. Some kinetic-type experiments on this Acknowledgements:This study was graphitization reaction were performed in supported by a grant from the Ministry of the next study (Tagiri and Oba, in prepara- Education, Japan and by Professor W.G. tion). It was found that graphite crystal- Ernst of University of California,Los An- lization from coal becomes complete in a geles through NSF grant EAR80-17295. week, and the crystallinity of the graphite We thank W.G. Ernst for his supervision product does not change in runs of longer- and critical review of the manuscript; Dr. duration. It is clear that the dependence G. Sen for critical reading of the manu of graphitization on duration is very little. script; Ms.M. McCauleyfor her help regard- The starting material includes 1 wt% ing hydrothermal technique; We also thank Li2COa or 2 wt% Ni metal as a catalyst. ProfessorY. Hariya of Hokkaido University In a sedimentary rock containing 0.5 wt% for allowingus to use his laboratory; Thanks carbon, the content of Li and Ni catalysts are also due to Dr. W.A. Dollase, Dr. J.L. are about 12 ppm Li and 100 ppm Ni, respec Rosenfeldand Mr. R.E. Jones of University tively. The average content of Li and Ni of California, Los Angeles for their discus in shale is 60 ppm and 95 ppm, respectively sions. (Krauskopf, 1967). Accordingly, the con- Synthesis of graphite from bituminous coal 193

Ni from methane-water vapor mixtures. References Carbon, 16, 111-114. Mackee, D.W. (1974), Effect of metallic impurities Ernst, W.G., Seki, Y., Onuki, H. and Gilbert, M.C. on the gasification of graphite in water vapor (1970),Comparative study of low-grade meta- and hydrogen. Carbon, 12, 453-464. morphism in the California Coast Ranges and Mackee, D.W. and Chatterji, D. (1978), The the Outer Metamorphic Belt of Japan. Geol. catalyzed reaction of graphite with water Soc. Amer. Mem., 124, 276p. vapor. Carbon, 16, 53-67. French, B.M. (1964), Graphitization of organic Seki, Y. (1973), Temperature and pressure scale material in a progressively metamorphosed of low-grade metamorphism. J. Geol. Soc. Precambrian iron formation. Science, 146, Japan, 79, 735-743. 917-918. Tagiri, M. (1981), A measurement of the French, B.M. and Eugster, H.P. (1965), Siderite graphitizing-degree by the X-ray powder dif- (FeCOa) : Thermal decomposition in equilib fractometer. J. Japan. Assoc. Min. Petr. rium with graphite. Science, 147, 1283-1284. Econ. Geol., 76, 345-352. Krauskopf, K.B. (1967), Introduction to geo Tagiri, M. (1983), A preliminary study on the chemistry, McGraw-Hill, pp. 638-640. distribution of detrital graphite in DSDP Landis, C.A. (1971), Graphitization of dispersed materials and ancient sedimentary basins. carbonaceous material in metamorphic rocks. J. Geol. Soc. Japan, 89, 1-13. Contrib. Mineral. Petrol., 30, 34-45. Tagiri, M. and Oba, T. (in preparation), Experimen Macak, J., Knilek, P. and Malecha, J. (1978), tal study on graphitization and its validity for Formation of carbonaceous deposits on metallic geothermometry.

0.5-2Kb加 水 圧,300-600℃ の 条 件 で,レ キ 青 炭 を 出 発 物 質 と し た 石 墨 の 合 成

田切美智雄 ・大場 孝信

ター トル型熱 水 合成 装 置 を用 い て,i%Li2CQ3又 は2%Ni触 媒 の 存 在 の も とで,レ キ青 炭 を 出 発物 質 とし て 石墨(d002=3.37A)を 合 成 した 。 触 媒 の含 有 量 は 頁岩 中 の炭 素含 量 に比 較 して ほ ぼ 溝 程度 の量 で あ り,実 験 結 果 を天 然に応 用 す る上 で 障 審 にな らない 。 石 炭 か ら石墨 へ の転 移 温 度 は,0.5Mlkbま で は急 激 に 上 昇 す るが, 1kも を越 え る.と低下 す る。 実 験 結 果 は,続 成 作 用 の 湿 度圧 力範 囲 で は,石 墨 の結 晶化 が 起 らな い こ とを示 して. い る。