434
Energy & Fuels 1993, 7, 434-435
Flash Pyrolysis of Coal Swollen by Tetralin Vapor Kouichi Miura,' Kazuhiro Mae, Kiyoyasu Sakurada, and Kenji Hashimotof Research Laboratory of Carbonaceous Resources Conversion Technology and Department of Chemical Engineering, Kyoto University, Kyoto, 606 Japan Received December 7, 1992. Revised Manuscript Received January 19, 1993 We have previously presented a new coal flash pyrolysis method to increase dramatically the total volatiles and the tar yield, in which the coal preswollen by several solvents at 100-250 "C was pyrolyzed in an atmospheric pressure of He.'V2 When 10 coals were swollen by tetralin at 100 OC under 1 MPa of N2, tetralin was retained intimately in micropores of the coals. On pyrolyzingthese swollen coals in a Curie-point pyrolyzer at 764 "C in a helium stream, the total volatiles and the tar yield increased for all the coals. The maximum tar yield reached surprisingly up to 42 kg/lOO kg of coal for an Australian brown coal (Morwell, MW). These effecta were brought about by two types of hydrogen transfer: one is effective hydrogen transfer from hydrogen donor solvent to coal fragments, and the other is intramolecular hydrogen transfer caused by the breakage of noncovalent bondings in coal through the solvent swelling.2 The proposed pyrolysis method was found to be effective to increase the total volatiles as well as the tar yield, but it may be difficult to apply this method to practical coal conversion processes, because the procedure required for the solvent swelling is rather tedious. In this paper, we propose to swell coal with vapors of atmospheric pressure rather than the pressurized liquids. The coal swelling with vapor can be performed easily and continuously while the coal is traveling in the feeder, for example, in practical processes. To examine the validity of this swelling method, MW coal was swollen by both tetralin vapor and liquid tetralin and was pyrolyzed in a free-fall pyrolyzer. Swelling of MW coal (C 67.1, H 4.9, N 0.6, S 0.3, 0 27.1 7% on dry and ash-freebasis) was performed by passing a nitrogen stream containing saturated tetralin at 100 OC. The swollen coal was purged by nitrogen gas at 25 OC for 30 min to prepare samples stable at room temperature, although this treatment is not necessary in practical applications. The stable samples are essential to establish reliable mass balance during pyrolysis. The swelling time ranged from 20 to 60 min. The flash pyrolysis of the swollen coal was performed using a continuous free-fall pyrolyzer, the detail of which was given in a previous paper.3 The coal particles were fed via a screw feeder to the reactor at the rate of 0.10 kg/h with nitrogen gas of 1.5 Wmin. The coal residencetime was estimated to be around 2 s. The product yields of char, tar,BTX (sum of benzene, toluene,and xylene yields),hydrocarbon gases (HCG;CH4, C2H4, C&, C3H6, C3Ha, C4H8, c4Hi0, and c5 and c6
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Figure 1. Change of the tetralin content and the swelling ratio during the pretreatmentof MW coal by tetralin vapor at 100 O C .
gaseous compounds), and inorganic gases (H2, CO, CO2, H20)were obtained by the procedure shown in the previous paper.3 Figure 1shows the change of swelling ratio of MW coal and the amount of tetralin retained by the coal with the time exposed to tetralin vapor at 100 "C. Both values increased gradually with the exposure time and then saturated at around 60 min. This shows that 1 h of exposure is enough to swell and to incorporate tetralin. The volume of tetralin retained in the coal, which can be calculated from the amount of tetralii retained, was almost equal to the volume increase of the swollen coal. This indicates that tetralin retained in the coal swelled the coal through penetrating the coal matrix. Figure 2 showsthe effectof the swellingby tetralin vapor on the product distribution during the flash pyrolysis in the free-fallpyrolyzer. Each yield represents the net yield which was obtained by subtracting the pyrolysis yield of tetralin vapor from the correspondingyield of the swollen coal. The total volatiles of the tetralin swollen coal was larger than that of raw coal by 8.7 kg/lOO kg of coal at above750OC. At750OCthetaryieldofthetetralinswollen coal reached up to 23.1 kg/100 kg of coal, which was 1.7 times larger than that of the raw coal. Correspondingto these changes, the H2O yield of the tetralin swollen coal decreased by 2.6 kg/100 kg of coal as compared with that + Department of Chemical Engineering. of the raw coal. This indicates that the tetralin swelling (1) Miura, K.; Mae, K.; Asaoka, S.; Yoshimura, T.; Haahimoto, K. causes the suppressionof the cross-linkingreaction forming Energy Fuels 1991,5, 340-346. (2) Miura, K.; Mae, K.; Yoahimura, T.; Masuda, K.; Hashimoto, K. H2O as stated in detail in the previous paper.2 The Energy Fuels 1991,5,803-808. (3) Miura,K.;Mae,K.;Murata,A.;Sato,A.;Sakurada,K.;Hashimoto,hydrocarbon gas (HCG) and BTX yields of the tetralinswollen coal also increased at above 750 "C as compared K.Energy Fuels 1992,6, 179-184. 0887-0624/93/2507-0434$04.00/0
0 1993 American Chemical Society
Energy & Fuels, Vol. 7, No.3, 1993 435
Communications 60 -
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MW Coal swoiien by tetraiin vapor (S.lSkg/lOOkg-coal) mw coal
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Tetralin swollen coal 750'C
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Figure 2. Effect of the swelling by tetralin vapor on the product distribution during the flash pyrolysis of MW coal.
with those of the raw coal. These increases were brought about through the gas phase cracking reaction of the tar produced significantlythrough the swelling of coal. Thus, it was clarified that the swelling by tetralin vapor also brings about the dramatic increase in the total volatiles and the tar yield. Figure 3 shows the effect of the tetralin content in the swollen coal on the product distribution. The swollen coals whose tetralin content was below 10 kg/100 kg-coal were prepared by the swelling with vapor. On the other hand, the swollen coals containing more than 10 kg/100 kg-coal of tetralin were prepared by the swellingwith liquid tetralin by the procedure described in the previous paper.' The total volatiles, the tar, the HCG, and the BTX yields increased rapidly with the increase in tetralin content up to around 10 kg of tetralin/100 kg of coal and then almost leveled off. On the contrary, the H20yield decreased with the increase in tetralin content and then leveled off also at above 10 kg of tetralin/100 kg of coal. These results show that the yields obtained from the coal swollen with (4) Matsui, H.; Yamauchi, S. R o c . Int. Conf. Coal Sci. 1989,543-546.
Figure 3. Change of the product distributionwith the increase in tetralin content.
tetralin vapor, whose tetralin content was 8 kg/100 kg of coal, was almost comparable to those obtained from the coal swollen with liquid tetralin. This means that the amount of tetralin required to swell the coal by 10% or so in volume is enough to obtain almostmaximum increase in the total volatiles and the tar yield. Thus, the proposed method, in which the coal swollen with tetralin vapor was pyrolyzed in an atmosphericinert gas stream, was found to be valid to dramatically increase the total volatiles. Since the swelling of coal with vapors is easily performed at temperatures as low as 100 "C under atmospheric pressure, this method is expected to be realized rather easily in industrial scale processes. In comparison with the conventional flash hydropyrolysis,'6 the proposed method gives much larger tar yield under milder pyrolysis conditions.
Acknowledgment. This work was financially supported by the Ministry of Education, Culture and Science of Japan through the Grant-in-Aid on Priority-Area Research (Grant No. 02203112 and 03203111). (5) Miura, K.; Mae, K.; Nakagawa, H.; Uchiyama, M.; Hashimoto, K. Nihon Energy Gakkai-shi 1992,107-115.
