Coal liquefaction using indene-tetralin and indene-decalin mixtures as solvent

Coal liquefaction using indenetetralin indener’ecalin mixtures as solvent Koji Chiba,

Hideyuki

Tagaya,

Shimio

Sato and Kazuo

Faculty of Engineering, Yamagata University, Johnan, (Received 3 April 7984; revised 23 May I984)

Yonezawa

and

Ito 992, Japan

Indene-tetralin and indene-decalin mixtures were used as the solvent for coal liquefaction. The effect of mixing on conversion for Yallourn coal was observed under nitrogen pressure at 400 and 440°C. Conversion to benzene-soluble material in an indene-decalin mixture (50:50, wt) at 440°C for 1 h was 73.0%and was only 9% lower than that in 100% tetralin. The reaction of indene with tetralin or decalin may provide the active species for coal dissolution. Simultaneously, coal radicals may be scavenged by indene. (Keywords:

coal; liquefaction;

indene-tetralin

mixture;

Solvents for coal liquefaction are very important. They determine the liquefaction efficiency. Their desired characteristics are the ability to donate hydrogen, shuttle hydrogen and to act as a physical solvent’. Several studies have been carried out to correlate model or practical recycle solvents with their characteristics and other parameters 2-5 . However, although several solvents lie within the optimum parameter ranges, they are not always good6. This fact suggests that there are unidentified important characteristics for the solvent. In this work, as an approach to understanding the role of solvent-solvent interactions during coal liquefaction, the coal conversions were carried out in binary solvent systems comprising indene and tetralin or decalin. Tetralin and decalin are well known as donor and non-donor solvents, and creosote oil has been found to contain 2.2 wt% indene7. EXPERIMENTAL Yalloum coal (analysis: C, 64.3; H, 4.6; N, 0.6; 0,30.5 (by diff.) wt%, daf; ash, 1.1 wt%) was ground to pass 100 mesh (149 pm) screen, and dried at 107°C under nitrogen. Liquefaction was carried out using a 100 ml magnedriven autoclave. Coal (6 g) and solvent (18 g) were placed in the autoclave and pressurized to 5MPa with nitrogen or hydrogen. Nominal reaction time was 60min at 400 or 440°C. Materials remaining in the autoclave after liquefaction were extracted with benzene. Benzene insoluble material was further extracted with THF. The liquefaction solvent was recovered from the benzene extract by vacuum distillation, and was analysed by g.c. The distillation residue was weighed as a solvent-refined coal (SRC). Conversions to benzene-soluble material (BC) and to THF-soluble material (TC) were calculated according to the following equation: conversion to BC or TC (wt%, daf coal basis) coal charged - benzene- or THF-insoluble material x 100 daf coal 0016-2361/85/0100684,3$3.00 @ 1985 Butterworth & Co. (Publishers)

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indene-decalin

mixture)

Conversions to BC and TC on repeated runs using tetralin alone were 59.6 and 59.4% for conversion to BC, and 82.1 and 82.0% for conversion to TC. RESULTS AND DISCUSSION Liquefaction results at 400°C using indene-tetralin mixture as the solvent are shown in Figure 1. The results of aromatic solvent-tetralin mixture are also shown in Figure 1. The effects of aromatic solvents, l-methylnaphthalene, naphthalene, fluorene and phenanthrene were almost the same and can be expressed by the same plot. The effect of mixing of indene was pronounced in conversion to TC. The difference in the conversion to TC between indene-tetralin and aromatic solvent-tetralin mixtures reached a maximum at 25% tetralin. Conversions to BC in 78 and 88% tetralin mixtures were 65.2 and 65.6%, respectively. They were slightly higher than the conversion to BC for the aromatic solvent-tetralin mixture, which was x60%. But, in mixtures containing (50% tetmlin, conversion to BC obtained in the indenetetralin mixture was lower than in aromatic solventtetralin mixture. Such a reduction was not observed in conversion to TC. With an increase of indene in the solvent from 22 to 100x, the recovery of solvent decreased from 84 to 36%, and the yield of SRC increased from 56.6 to 199%. In mixture containing more than ~40% indene, the yield of SRC went up beyond the conversion to BC. For example, in 52% indene mixture at 400°C for 1 h, the yield of SRC and the conversion to BC were 98.6 and 50.3x, respectively. Under hydrogen pressure conversions to BC and TC obtained in 78% tetralin mixture were 52.0 and 75.2x, respectively. These values were close to those obtained in the aromatic solvent-tetralin mixture. When indene alone was heated at 400°C for 1 h under the pressure of hydrogen, most of indene was converted to indane. A mixture of indane with 78% tetralin under nitrogen pressure provided conversions to BC and TC of 51.4 and

Solvents

for coal liquefaction:

K. Chiba

et al.

results using indane instead of indene indicate that indane was ineffective in Yallourn coal liquefaction. According to the procedure described by Yokono et d3, hydrogen donating ability of a solvent was estimated by the extent of hydrogen transfer from solvent to anthracene. When a mixture of anthracene and an equal weight of tetralin or indene was heated at 400°C for 1 h, the yields of dihydroanthracene were 56 and 28% in the mixture with tetralin and the indene mixture, respectively. Dihydroanthracene was determined by measuring the peak height at 3.87 ppm in the ‘H n.m.r. spectrum. These results indicated that indene is a poor hydrogen donor, and the effectiveness of indene is not directly related to its donating ability. As noted above, it was suggested from the large apparent TH obtained in indene-tetralin mixture that

Table 1 Tetralin in solvent (wt%)

Solvent mixed with tetralin

100

-

77 50 88 78 48

400°C I

1

I

I

20

40

60

80

Tetfali n in solvent

(wt

I( i

'10)

Analysis of the recovered

solvent by 9.~. a

THb (wt%, daf)

I-Methylnaphthalene 1-Methylnaphthalene indene indene indene

2.05 1.96 1.57 2.11 2.14 2.28

Liquefaction conditions: 4OO’C. 5 MPa N,, 1 h Transferred hydrogen from tetralin calculated by the amount of naphthalene in the recovered solvent

Figure 1 Liquefaction of Yallourn coal using indene-tetralin mixture as the solvent. -, Conversion to BC with aromatic solvent-tetralin; -O-, conversion to BC with indenetetralin; --.__ , conversion to TC with aromatic solvent-tetralin; --a--, conversion to TC with indenetetralin

73.9x, respectively. They were almost the same as those for indene-tetralin mixture under the pressure of hydrogen. Apparent transferred hydrogen (TH, wt%, daf coal basis) from tetralin to coal and indene was calculated from the amount of naphthalene produced in the recovered solvent. Calculated values are shown in Table 1. The amount of apparent TH was 2.05 in the liquefaction in which tetralin alone was used as the solvent. Amounts of apparent TH in the liquefaction using l-methylnaphthalene (MN) as an aromatic solvent were 1.96 and 1.57 for 23 and 50% MN in the solvent, respectively. When indene was mixed with tetralin in amounts ranging from 12 to 52x, the apparent TH went up to over 2.05; larger values than those predicted. Presumably, hydrogen transfer from tetralin to indene occurred. It was found that the addition of indene was effective also when the partner solvent was an apparently nondonor solvent such as decalin. Figure 2 shows the results of the liquefaction using indenedecalin mixture as the solvent. A synergistic effect on conversion was observed particularly in the conversion to TC. For example, at 440°C conversion to TC for 50% decalin was 73.00/ and was only 9% lower than that for 100% tetralin. Naphthalene was detected by g.c. in the recovered solvent. Bockrath and Noceti5 reported that indane had a larger hydrogen donating ability than tetralin on the basis of the reaction results of model compounds. However, the

Decalin

in solvent (wt%)

Figure 2 Liquefaction of Yallourn coal using indenedecalin mixture as the solvent. Conversion to TC at 0, 400 and A, 440°C. Conversion to BC at 0, 400 and a, 440°C

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Solvents for coal liquefaction: K. Chiba et al.

hydrogen transfer from tetralin to indene occurred. It was confirmed by g.c. ,that the reaction of indene with tetralin at 400°C proceeded easily to produce indane and naphthalene. For example, when a mixture of 22% indene and 78% tetralin was heated at 400°C for 1 h, most of the indene was hydrogenated to indane, and z 8% of tetralin was dehydrogenated to naphthalene. In the course of the reaction of indene with tetralin, the indene mixture appears to have an enhanced activity. When indene alone was heated at 400°C for 1 h under the nitrogen pressure, 76% of indene polymerized to produce a dimer or trimer, which were confirmed by gel permeation chromatography g.p.c. analysis. Most of the remainder was indene monomer. In addition, when a mixture of 50% tetralin and 500/, indene was heated under the same conditions, a new small peak was detected before the indene dimer peak. As tetralin alone did not polymerize under these conditions, the new peak appears to be due to the reaction product of indene and tetralin. These findings suggested that indene might not only polymerize but also bond to coal species. Therefore, the reduced conversion to BC in mixtures containing > 50% indene and tetralin, the low recovery of solvent and abnormally high yield of SRC in > 40% indene mixture is likely to originate in the conversion of indene to benzene-insoluble and nondistillable materials such as polymers or species bonded to

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coal. The polymerization or addition products are probably THF soluble, but benzene insoluble. Two possible reaction mechanisms for the effects of mixed coal solvents are as follows. 1. The biomolecular reaction of indene with tetralin or decalin may provide active intermediates which promote the liquefaction of coal as the active hydrogen donors, hydrogen acceptors or scavengers for coal radicals. 2. Coal radicals are scavenged by indene and stabilized as lower molecular weight substances. It appears that a more effective solvent for coal liquefaction can be prepared by selecting a suitable combination of solvent components.

REFERENCES Whitehurst, D. D., Mitchell, T. 0. and Farcasiu, M., ‘Coal Liquefaction’, Academic Press, NY, 1980 Furlong, L. E., Effron, E., Vernon, L. W., and Wilson, E. L. Chem. Eng. Progr. 1976, 72,69 Yokono, T., Marsh, H., and Yokono, M. Fuel 1981,60,607 Miller, R. L. and Silver, H. F. Energy Sources 1980, 5, 211 Bockrath, B. C. and Noceti, R. P. Am. Chem. Sot. Div. Fuel Chem. Prepr. 1981, 26,94 Curtis, J. W., Guin, J. A., Jeng, J. and Tarrer, A. R. Fuel 1981,60,677 Yao, T. and Kamiya, Y. Nippon Kagaku Kaishi 1980,6,893