Energy & Fuels 1988,2, 529-534

Mechanism of Semicoke Formation during Coal Liquefaction

Hiroshi Moritomi, Chao-Ran Deng, Hiroshi Nagaishi, Seiji Shimomura, Yuzo Sanada, and Tadatoshi Chiba*

Coal Research Institute, Hokkaido University, N13 W 8 Kita-Ku, Sapporo, Japan 060

Received August 3, 1987. Revised Manuscript Received January 14, 1988

529

Systematic experiments have been carried out to develop a reaction model that considers the formation of semicoke during coal liquefaction. Retrogressively formed semicoke is defined as a lumped product that separates from the pyridine-insoluble fraction in coal liquefaction reaction products by hydrogenation under conditions of abundant external hydrogen. The retrogressive reaction paths have been examined by starting the reaction not only with coal but also with preasphaltenes, as- phaltenes, or oils. It is shown from the results that preasphaltenes play the most important role in retrogressive reactions and that semicoke formation from preasphaltenes occurs via an intermediate which is assumed to be equivalent to the thermal fragments from coal. Coupling these results with those described in our previous paper, we propose a comprehensive reaction model.

Introduction At temperatures above around 650 K, coal produces a

wide range of reactive fragments due to thermal cracking. These fragments are stabilized by hydrogen from various sources, such as more hydroaromatic portions of the coal (shuttling), hydrogen donor compounds in solvent and coal-derived liquids (donation), and the gas phase (direct transfer), resulting in products with lower molecular weights. With less hydrogen gas or hydrogen donor sol- vent, they also may recombine or polymerize into semicoke, which is an undesirable high-molecular-weight product in coal liquefaction. The occurrence of retrogressive reactions that form semicoke has already been suggested from the following facts: the yield of pyridine- or benzene-soluble fraction (PS or BS, respectively) decreases with time after attaining a maximum value when poor hydrogen donor solvents are employed at high temperature for a particular coal,14 and the buildup of coke scale and pseudocrystalline mesophase is observed on the surface of the preheater and reactor walls."' In existing kinetic models, semicoke has usually been considered as a part of the pyridine-insoluble (PI) fraction produced by recombination of the reactive thermal fragments of c0al*9~ or by polymerization of the preasphaltenes, a~phaltenes,~ and oils via the resin frac- tion.2 Farcasiu et al.IO and Walker et al.ll suggested from

Table I. GC-MS Analysis of Lighter Fraction of Creosote Oil

compd naphthalene 2-methylnaphthalene and indole methylbiphenyl and acenaphthene C2-naphthalene 1-methylnaphthalene indene dibenzofuran fluorene indan biphenyl quinoline anthracene and phenanthrene others (by diff)

23.01 17.51 9.22 8.86 7.83 5.55 5.10 3.77 3.45 3.10 2.75 1.96 7.89

Table 11. Properties of Coals and Liquefaction Products Used as Startine Materials

~~

ultimate anal. wt % based on daf coal

coal C H N 0" S ash H/C Taiheiyo 74.47 6.43 1.25 17.80 0.05 15.0 1.036 Akabira 82.53 5.90 2.18 8.59 0.80 5.0 0.858 Yallourn 65.76 4.66 0.60 28.72 0.26 0.7 0.850

ultimate anal. wt % based on daf product

intermediates C H N 0" S ash H/C (1) Neavel, R. C. Fuel 1976,55, 237. (2) Morita, M.; Sato, S.; Hashimoto, T. Prepr. Pup-Am. Chem SOC.,

Diu. Fuel Chem. 1976, 24(2), 270. (3) Whitehurst, D. D.; Mitchell, T. 0.; Farcasiu, M.; Dickert, J. J., Jr.

"The Nature and Origin of Asphaltenes in Processed Coals"; Final Report EPRI AF-1298; EPRI: Palo Alto, CA, Dec 1979; Volume 2, Chapter 9. (4) Squires, M. Appl. Energy 1978, 4, 161. (5) Kang, C. C.; Nongbri, G.; Stewert, N. Prepr. Pap.-Am. Chem.

SOC., Diu. Fuel Chem. 1976, 21(5), 19. (6) Cronauer, D. C.; Ruberto, R. G. "Investigation of Mechanism of

Reaction Involving oxygen-Containing Compounds in Coal Hydrogenation"; Final Report EPRI AF-913 713; EPRI Palo Alto, CA, March 1979. (7) Exxon Research and Engineering Co. "EDS Coal Liquefaction

Process Development Phase V. 1982"; Annual Report EPRI AP-3128;

(8) Shinn, J. H.; Vermeulen, T. Prepr. Pup-Am. Chem. SOC., Diu. Fuel Chem. 1976, 24(2), 80.

(9) Han, K. W.; Wen, C.Y. Fuel 1979,58, 779. (10) Farcasiu, M.; Mitchell, 0.; Whitehurst, D. D. Prepr. Pup.-Am.

Chem. SOC., Diu. Fuel Chem. 1976, 21(7), 11.

EPRI Pal0 Alto, CA, July 1983; pp 212-216.

preasphaltenes 83.77 5.44 3.83 6.50 0.46 0.5 0.779 asphaltenes 85.37 6.38 2.18 5.85 0.22 0.0 0.896

" By differences.

the coking propensity of SRC components that the preasphaltenes (asphaltols) tend to produce less oil and more PI fraction than asphaltenes.

The PI fraction in liquefaction products generally con- sists of the unreacted coal, the inherently inert component of coal, the semicoke formed during the reaction, and the reactive thermal fragments. The distribution of these

(11) Walker, P. L., Jr.b Spackman, W.; Given, P. H.; Davis, A.; Jekins, R. G.: Painter. P. C. "Characterization of Mineral Matter in Coals and Coal Liquefaction Residues"; Final Report EPRI AP-1634; EPRI: Palo Alto, CA, Nov 1980.

0887-0624/88/2502-05295O1.50 /O I , , 0 1988 American Chemical Society

530 Energy & Fuels, Vol. 2, No. 4, 1988

Pi Fraction Rehydrogenation

Table 111. Chemical Composition of Coal Ash (wt %)

Tetraiin HZ 10.1 MPa

parent coal

Moritomi et al.

1 .o

Taiheiyo Akabira Yallourn Si02 A1203 Fe203 CaO MgO Ti02 p205 so3 K20 Na20 MnO others & unknowna

a By difference.

55.1 25.7 3.8 6.2 1.1 1.2 0.7 1.8 1.6 1.1 0.1 1.7

45.0 25.4 7.0 6.5 3.5 1.2 2.6 4.7 2.0 0.8 0.1 1.2

10.8 4.6

31.7 8.5

23.9 0.5 0.4

14.2 0.4 2.6 0.3 2.1

species seems to depend on the nature of the coal and the solvent as well as on the operating conditions such as the reaction time, temperature, and pressure. Nonetheless, semicoke has never been quantified experimentally. Therefore, the mechanism and the rate of semicoke for- mation have been evaluated on the basis of this ambiguous definition by fitting a kinetic model to the observed yields of preasphaltenes, asphaltenes, or oils with time. This paper proposes an experimental method for separating the semicoke from the unreacted coal and the inherently inert component in the PI fraction and develops a general model for coal liquefaction accompanied by semicoke formation.

Experimental Section Experiments were conducted by using a 55 cm3 autoclave re-

actor.12 Coal slurry in the reactor was agitated a t about 500 rpm by a magnetically driven stirrer. The reactor was heated a t ca. 150 K/min in an infrared image furnace and cooled a t ca. 100 K/min by blowing air. The experimental procedure was almost the same as in the previous work.1213 In most of the experimental runs, the temperature and gas pressure were kept invariable a t 723 K and 10.1 MPa, respectively. Tetralin was employed as a hydrogen donor solvent and naphthalene as a nondonor solvent. A light (under 588 K) fraction of creosote oil was used as a practical process solvent. The results of a GC-MS analysis of the creosote oil are shown in Table I. Taiheiyo, Akabira, and Yallourn coals were used to examine the effect of coal properties on semicoke formation. Some relevant properties of these are shown in Tables I1 and 111.

When the liquefaction experiments were performed with coal, the initial contents in the autoclave were 3 g of coal and 7 g of solvent. Preasphaltenes and asphaltenes were also employed as initial reactants to examine their contribution to semicoke for- mation. In these experiments, 2 g of each and 5 g of the solvent were loaded together with 0.2 g of PI fraction (containing 69.7 wt % mineral matter) and 0.02 g of sulfur, to simulate liquefaction in the presence of their catalytic effects.14 The asphaltenes, preasphaltenes, and PI fraction were prepared from Taiheiyo coal liquefaction with tetralin in a 500 cm3 autoclave a t 723 K under a 50.1 MPa of nitrogen atmosphere. The products were frac- tionated with pyridine, benzene, and n-hexane in a shaking-type extractor for 24 h at room temperature. Off-the-shelf creosote oil was used as an initial reactant in the reaction with the oil fraction.

After the reaction, gas was vented and all liquid and solid products were recovered and transferred to an extractor. The products were analyzed by a sequential extraction with benzene, pyridine, and n-hexane for 3 h at their boiling point temperatures. Details of the extraction were described elsewhere.12 The weight

(12) Nagaishi, H.; Moritomi, H.; Sanada, Y.; Chiba, T. Energy Fuels,

(13) Moritomi, H.; Nagaishi, H.; Naruse, M.; Sanada, Y.; Chiba, T.

(14) Nagaishi, H.; Konishi, H.; Moritomi, H.; Sanada, Y.; Chiba, T. J.

submitted. Preceding paper in this issue.

Roc.-Int. Conf. Coal Sci., 1983 1983, 134.

Fuel SOC. Jpn. 1984, 63, 380.

0.8

I 0.6

v)

=a 0.4

1 Semicoke I

I

I F e h y drogenation of

A

1 Semicoke I

I

I F e h y drogenation of

A

Pi

0 723 K 10.1 MPa-Hz Tetralln A 723 K 10.1 MPa-NZ Naphthalene

0.0 1 I 1 1 I I A I

0 20 40 60 80 100 “ 600

t h e , mm

Figure 1. Changes of pyridine-soluble yields with time for Ta- iheiyo coal liquefaction under extreme conditions.

Liquefaction

Bi BS

Pyridine Extraction

n-Hexane Extraction

I

inherent

Semkoke

PS

Figure 2. Experimental procedures for lumping liquefaction products and for separating semicoke from the pyridine-insoluble fraction.

of each ihsoluble fraction was determined after drying a t 353 K for a t least 3 h in a vacuum oven. Yields of the fractions soluble in the solvents, yps, ym, and ym, were calculated from the weight of the corresponding insoluble fraction. Consequently, gaseous products and water were lumped into the HS fraction. These yields were defied on the basis of the initial weight of dry ash-free (daf) coal when coal was employed as initial reactant. On the other hand, for cases where preasphaltenes or asphaltenes were initial reactants, the yields were based on their initial daf weight.

Results and Discussion Figure 1 shows typical

changes of the pyridine-soluble yield (yps) with time for Taiheiyo coal that was liquefied (i) with an “excess amount of tetralin”13 under a hydrogen gas atmosphere and (ii) with naphthalene under nitrogen. The condition in case i is of the highest reaction severity for hydrogenation in the present experiments. In this case, the yield increases rapidly with time and levels off before a complete con- version of the coal. The level-off yield is about 0.92 and seems invariable to 600 min. As discussed in detail in our previous paper,12 this indicates that the PI fraction after the lefel off is an inherently inert component, Io, of the coal.

In case ii, where no external hydrogen is supplied, the yield decreases gradually after attaining its maximum at about 10 min. This implies the occurrence of retrogressive

Definition of Semicoke.

Mechanism of Semicoke Formation Energy & Fuels, Vol. 2, No. 4, 1988 531

Ps { 0.8

OD '1.0 0 20 40 60 80 100

t i e , min

Figure 3. Change with time of semicoke yield for Taiheiyo coal liquefied with naphthalene a t 723 K and 10.1 MPa of Nz.

reactions from the coal and the PS fraction. If all portions of the PI fraction, except I,,, were unreacted coal (C) and the thermal fragments (C*), they would be converted completely into the PS fraction by hydrogenation as undet condition i. However, as shown in the figure, the overall yield obtained by the rehydrogenation of the PI fraction at 60 min was only 0.52, which is much lower than the level-off yield in case i. This suggests that the PI fraction obtained in this case contains not only I,, but also an inert fraction formed during the liquefaction. The inert fraction is defined here as semicoke, I. Figure 2 summarizes dia- grammatically the hydrogenation procedure used to sep- arate the semicoke and the inherent inerts from the PI fraction. The semicoke yields, yI, thus obtained for other reaction times in Figure 1, are shown in Figure 3.. It is noted that moSt of the increase in yI occurs in the first 40 min.

Effects of Coal and Solvent on Semicoke Forma- tion. Tetralin and naphthalene are usually considered as a hydrogen donor and a nondonor solvent, respectively. However, the hydrogen donabilities of most solvents practical for use in liquefaction processes lie between those of tetralin and naphthalene. Hence, to simulate the for- mation of semicoke under such conditions, experiments were carried out by using creosote oil as a process solvent under hydrogen atmosphere. Typical results are shown in Figure 4a-c for Taiheiyo, Akabira, and Yallourn coals, respectively. For Taiheiyo coal, semicoke formation with creosote oil and hydrogen is less than that with naphtha- lene and nitrogen. Among the coals, Taiheiyo coal shows the lowest yI while Yallourn coal shows the highest. This dependency of yI on coal cannot be correlated to the atomic ratio shown in Table 11. Taiheiyo coal has the highest ratio, However, in spite of the ratios of Akabira and Yallourn coals being nearly the same, the former gives a fairly lower yI value than the latter. On the other hand, yI seems to increase with decreasing ash content. The mineral matter in coal ash has a catalytic effect on hy- drogenation of the solvent by dissolved hydrogen.13 Na- gaishi et al.14 examined the effect on the yield of the PS fraction, yps, and showed that iron is the most effective element and sulfur is a promoter that produces iron sul- fides and hydrogen sulfides. According to their results, yps increased with addition of Fe203 and sulfur and reached values of yps obtained using red-mud/sulfur or Co-Mo catalyst when 44.5 mg/g of coal of Fe203 and 10.0 mg/g of coal of sulfur were added. From Tables I1 and 111, the amounts of Fe20s in Taiheiyo, Akabira, and Yallourn coals are 5.7, 3.5, and 2.2 mg/g of coal, respec- tively. These amounts are not sufficient compared to the

1.0

0.8

I 0.6

(I) U

* - .!! 0.4

time , min

I I 0.0 (b) '

I O

I 0 BS

0.0 1 I I ' 11.0 0 60 120 180

time , min

I

0.4 II

0 - - 0.6 *

0.8

I Bs I I t l o 0 PS

I 0 BS

0.0 I 1.0 0 60 120 180

time , min

Figure 4. Semicoke formation for different coals liquefied with creosote oil a t 723 K and 10.1 MPa-H2: (a) Taiheiyo coal; (b) Akabira coal; (c) Yallourn coal.

above. Therefore, further examination is required to confirm the correlation between the ash content and yI.

Changes of yps and y ~ s with time also depend on the original coal. The rate of increase of yps is very rapid for all coals and even faster than in the cases where tetralin was used as the solvent.12 This may be attributed to the synergistic interaction between the coal and the solvent15 or to the direct stabilization of thermal fragments by the solvent. After the rapid initial increase, yps continues to increase slightly for Taiheiyo coal-, whereas it decreases gradually for Akabira and Yallourn coals due to semicoke formation from the preasphaltenes, asphaltenes, and oils in the PS fraction. The contribution of these products to

(15) Derbyshire, F. J.; Odoerfer, G. A.; Varghese, P.; Whitehurst, D. D. Fuel 1982,61,899.

532 Energy & Fuels, Vol. 2, No. 4, 1988 Moritomi et al.

1.2 I I 1 I I

1.0 I

Q, 3

.Y 5 0.8 u) r

0, I

0.6

o Taiheiyo 0 Preasphaltenes

from Taiheiy-o A Akabira A Yallourn

H, 5.1 & 10.1 MP

653 - 723 K

0.4 I I I I I 0 0.2 0.4 0.6 0.8

yield of semicoke, - Figure 5. Relationship between H/C atomic ratio and yield of semicoke.

I

1 .o

0.8

I 0.6

cn E '5. 0.4

0.0 1 0 20 40 60 80 100

t h e , min

Tetralii Tetralin Naph. Naph 9Omin 90mh 9Omin 60min

Figure 6. Distributions of products from asphaltenes using different solvents with and without PI residue.

the retrogressive reaction is examined in detail later. The separated semicoke was subjected to an ultimate

analysis and a polarized-light microscopic observation. In Figure 5, the atomic ratios, H/C, of ,the semicoke obtained under different conditions from Taiheiyo, Akabira, and Yallourn coals and preasphaltenes from Taiheiyo coal are plotted against the semicoke yield, yI. I t is seen that the ratio decreases with increasing yield. The rate of decrease does not depend appreciably on the temperature and preSsure but does depend strongly on the nature of the coals. For all present cases, the asymptotic value of the ratio seems to be around 0.5. Formation of a mesophase was detected only in the semicoke from Yallourn coal.

Generalized Liquefaction Model. Since the semicoke formed during liquefaction could be quantified from the pyridine-insoluble fraction, the retrogressive reaction paths were experimentally examined by using oils, asphaltenes, and preasphaltenes as initial reactants, with an assumption that their contributions to the Semicoke formation are the same as those where they are reaction intermediates during coal liquefaction. When creosote oil is used as initial reactant, it may produce retrogressively semicoke and asphaltenes. However, no semicoke formation was ob- served, and the yield of asphaltenes was negligible (0.006) at 90 min under a 10.1 MPa of H2 atmosphere even without the residue (the PI residue contained 69.7 wt % mineral matter and sulfur), where the retrogressive reac- tions were expected to occur. Thus, both retrogressive reactions were expected to occur. Thus, both retrogressive reaction paths from oils to the semicoke and asphaltenes can be neglected.

l a O a ]

0.8

I

0.6 -

u)

'0 .!! 0.4 a

PS 6s HS Catalyst

Q 0 A Resldue c) A Residue/S I /

A 1

0.0 I 2' ' I I I 0 20 40 60 80 100

time , min

Figure 7. Semicoke formation from preasphaltenes a t 723 K and 10.1 MPa of Hz, using (a) naphthalene, (b) naphthalene and P I residue, or (c) tetralin and tetralin with P I residue and PI resi- due/sulfur.

Figure 6 compares the distributions of products from asphaltenes treated at 10.1 MPa of H2 with various com- binations of solvents and the residue. Semicoke formation can be seen to occur only when no external hydrogen is supplied by using naphthalene as the solvent without the residue.13 In this case, the yield of preasphaltenes is highest (yp = 0.22), and oils and gases = 0.21) are produced simultaneously with semicoke and preasphalt- enes. This suggests that the retrogressive formation of semicoke and preasphaltenes proceeds through dispro- portionation of asphaltenes and preasphaltenes. Such semicoke and preasphaltenes formation is suppressed by increasing the hydrogen supply, e.g., by replacing naph- thalene with tetralin or partially by adding the PI residue

Mechanism of Semicoke Formation

1.0

0.8

I 0.6

m I a 0.4 .-

0.2

0.0

Energy &Fuels, Vol. 2, No. 4, 1988 533 -

-

-

-

~

- 90 min 90 mln 9omin W-min

Figure 8. Effects of solvent and PI residue on semicoke yield from preasphaltenes.

into naphthalene. These results are easily explained by assuming that the direct path from asphaltenes to the semicoke can be neglected for simplicity and the semicoke is produced from asphaltenes through preasphaltenes.

When preasphaltenes are used as the initial reactant, they may produce asphaltenes and oils and gases pro- gressively and semicoke retrogressively. Figure 7a shows changes with time in the yield of products from preas- phaltenes under 10.1 MPa of H2 with naphthalene. In this case, most of the PI fraction obtained from the preas- phaltenes is semicoke and its yield CyI) increases with time, initially rather rapidly and then gradually. In addition, a certain species is seen to be produced from preasphalt- enes, which is apparently a portion of the PI fraction converting to the PS fraction by rehydrogenation. As can be seen, the yield of this species reaches an early maximum in its change with time. This means that the species is an intermediate for semicoke formation from preasphaltenes. However, it is at present impossible to examine any further characteristics of this kinetically defined pyridine-insoluble intermediate. Hence, it is assumed for simplicity that the intermediate can be lumped with another pyridine-insol- uble intermediate, C*, i.e., the thermal fragments from coal.

The semicoke formation from preasphaltenes also de- pends on the solvent and the residue and is suppressed with increasing hydrogen supply. Figure 7b shows the semicoke formation when naphthalene is used with the residue. It is seen that the semicoke yield, yr, is less than about 0.20 and seems to level off within 20 min. A further suppression would be expected if tetralin is substituted for naphthalene, and this is indeed the result shown in Figure 7c, where yI is as low as about 0.10, regardless of the catalyst effect of the PI residue. These results reveal that the semicoke formation can be suppressed by the hydrogen supply, not only from tetralin but also from hydrogen donor compounds produced from the liquid products as well as naphthalene by the catalytic hydro- genati~n. '~ These effects of the solvent and PI residue on yI at 90 min are summarized in Figure 8.

On the basis of the experimental findings for the re- trogressive reaction paths, a generalized reaction model can be deduced

Here, on the basis of the results described in our previous paper,I2 coal is assumed to consist of three different com-

Table IV. Apparent Reaction Rate Constant and Nominal Activation Energy for Semicoke Formation

activation rate const,' lo2 m i d energy,

coal 653K 683 K 723 K kJ/mol Taiheiyo 0.45 1.13 1.61 70.2 Akabira 0.29 0.90 2.20 112.9 Y allourn 3.83

a Integrated mean values for 60 min.

ponents, Io, C1, and C2. C2 is the coal component that produces oils and gases directly without consuming any external hydrogen, and the amount is experimentally given by the level-off yield of the n-hexane-soluble fraction from liquefaction of coal with naphthalene under a nitrogen gas atmosphere.

Rate of Semicoke Formation. The mean rate constant of the semicoke formation, kI, was analyzed according to the reaction model

I 4

I O

BS

This was obtained by simplifying the model in the previous chapter with the following assumptions: (1) The rate of formation of thermal fragments, C*, from the coal com- ponent, C1, is much higher than those of other products and is lumped into C1. (2) The initial values of the coal components, Cl0, Cl0, and C20, and the rate constant, kC2, for direct O&G formation from C2, are the same as those obtained in our previous paper.12 Furthermore, for sim- plicity of analysis, the asphaltenes and oils and gases were lumped as the BS fraction. From the mass balance equation for the semicoke

Cdt) - CI(t0)

LotCc(t) dt

C,(t) = CCl + cc* CI(t0) = CIO

kI =

where

The values of kI, determined from the above equation, are listed in Table IV for the coals in Figure 4a-c at different temperatures. The rate constant at 723 K ranges from 1.61 X to 3.83 X min-'. The table also shows the approximate values of the activation energy for semicoke formation. It is demonstrated that both the rate and its temperature dependency are strongly dependent on the coal nature. These kinetic data might also depend on the heating rate of the coal slurry. The maximum rate at- tainable in the present batch reactor system was ca. 150 K/min, which was still lower than in the continuous li- quefaction reactors.16 Therefore, care must be taken in applying directly these data to continuous liquefaction.

All individual reactions, except the direct formation of oils and gases from C2 in the present model, are more or less affected by the concentration of hydrogen capable of being transferred to the products from the various sources. In the present analysis, the hydrogen concentration is implicitly involved in the rate constants. In this sense, the

(16) Moritomi, H.; Kurouji, Y.; Sanada, Y.; Chiba, T. Liq. Fuels Technol. 1984, 2, 1.

534 Energy & Fuels 1988,2, 534-538

rate constants are apparent and are considered to be a function of the hydrogen concentration. Further work is needed in the future to evaluate the effective hydrogen concentration during liquefaction reactions.

Conclusions 1. Semicoke formed during liquefaction reactions of coal

is experimentally defined as a lumped product separated from liquefaction products by hydrogenating the PI frac- tion in the products.

2. Preasphaltenes play the most important role in re- trogressive (semicoke-forming) reactions, and semicoke formation from preasphaltenes occurs through an inter- mediate species, C*, corresponding to thermal fragments from coal.

3. On the basis of the above mechanism, a compre- hensive kinetic model for coal liquefaction accompanied by semicoke formation has been developed, and the mean rate constants of semicoke formation for three different coals have been obtained. The rate constants are on the order of 1.61-3.83 X 1C2 min-l and depend on the reaction temperature and coal properties.

Acknowledgment. This work was partially supported by a Grant-in-Aid for the Special Project Research on Energy (Energy(1)-No. 58040001 and No. 59040002) from

the Ministry of Education, Science and Culture, Japan.

Nomenclature Cclo = weight fraction of component C1 in original coal Cczo = weight fraction of component C2 in original coal CIo = weight fraction of component Io in original coal It = apparent rate constant, min-l y = product yield

A BI BS C c1 CZ

C* HI HS I

IO O&G P PI PS

Components asphaltenes (BS-HI) benzene-insoluble fraction benzene-soluble fraction dry ash-free (daf) coal portion of coal forming O&G consequently via P

portion of coal forming directly O&G without

intermediate from C to P or from P to I n-hexane-insoluble fraction n-hexane-soluble fraction semicoke fraction defined as PI fraction from reh-

portion of coal inherently inert for coal liquefaction oils and gases preasphaltenes pyridine-insoluble fraction pyridine-soluble fraction

and A

consuming external hydrogen

ydrogenation of primary PI fraction

Water and Nondonor-Vehicle-Assisted Liquefaction of Illinois Bituminous Coal?

Michael A. Mikita*

Department of Chemistry] University of Colorado at Denver, Denver, Colorado 80202

Bradley C . Bockrath,* Henry M. Davis, Sidney Friedman, and Eugene G. Illig

Pittsburgh Energy Technology Center, U.S. Department of Energy, Pittsburgh, Pennsylvania 15236

Received November 6 , 1987. Revised Manuscript Received January 26, 1988

Through the use of water or other non-hydrogen-donor vehicles as substitute liquefaction media, high conversions of Illinois No. 6 (River King Mine) bituminous coal were obtained in minireactor experiments at modest temperatures with little or no hydrogen-donor solvents. Typical THF con- versions (daf basis) of 67% with water only, 87% with water and SRC 11, and 90%+ with only water and 1000 ppm of Mo were obtained in 30 min at 385 OC with a cold charge of 1200 psig of Hz. A synergism was observed at low ratios (0.5 or less) of donor solvent to coal upon combination of SRC I1 distillate and water. A similar effect was not observed when cyclododecane replaced water. The addition of Mo catalyst precursors to the water allowed complete elimination of donor solvent without loss in conversion. The exclusion of added organic donor solvent permits analysis of the coal-derived liquefaction products without interference. Other experiments were performed for both 20 and 5 min with molecular hydrogen and a donor solvent but with deuterium oxide replacing the water. No isotope effect was found, which suggests that water is not a rate-limiting reactant under the reported conditions.

Introduction For a variety of reasons, water has been used in the past

in the liquefaction or the extraction of coal. When used in combination with carbon monoxide and a suitable catalyst, water was a source of hydrogen for the reduction

'Reference to a brand or company name is made to facilitate understanding and does not imply endorsement by the U.S. De- partment of Energy.

0887-0624/88/2502-0534$01.50/0

of coal.'s2 In this work, an organic solvent was frequently used in combination with water. Liquefaction under carbon monoxide, without an organic solvent, has also been carried out with slurries composed of coal and either water or aqueous b a ~ e . 9 ~ In some cases, water served to carry

(1) Appell, H. R.; Wender, I.; Miller, R. D. Chem. Ind. (London) 1969,

( 2 ) Appell, H. R. Energy (Oxford) 1976, 1 , 24. (3) Ross, D. S.; Blessing, J. E. Fuel 1978, 57, 379.

1703.

0 1988 American Chemical Society