832
Ind. Eng. Chem. Process Des. Dev. 1085, 2 4 , 832-836
Hydroliquefaction of Ilthols No. 6 Coal Using Iron Pentacarbonyl Toshlmitrw Suzukl, Osamu Yamada, Katwhlsa Fupa, Yoshlnobu Takegaml, and Yoshlhlsa Watanabe Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606 Japan
Hydroliquefaction of Illinois No. 6 coal was carried out by using iron pentacarbonyl (Fe(CO),) as a catalyst, under short contact time at high temperature (>460 "C). About 95% daf coal was converted into THF solubles and about 55% into oil fractions (including gases and water) in the presence of Fe(CO), under the liquefaction condkions of 460 "C, 20 min, in l-methylnaphthalene as a solvent. High conversions were achieved in the liquefaction at 480 "C for an even shorter reaction time (10 min). Little dependence of coal conversion upon temperature was observed; on the other hand, fractions of oil greatly increased at high temperature without excessive coking under lower hydrogen partial pressure. This may entirely be due to the high catalytic activity of Fe(CO),. The catalyst derived from Fe(CO), is considered to be effective for the direct hydrogen-transfer process to coal fragment radicals from molecular hydrogen.
Introduction We have previously reported that iron pentacarbonyl (Fe(C0)5),soluble in common organic solvenb, acted as an excellent catalyst precursor in the hydroliquefaction of coal (Watanabe et al., 1984). Very high catalytic activity was observed in the hydroliquefaction of various coal by using a non-hydrogen donating solvent (Suzuki et al., 1.984). In general, it requires a considerable residence time to obtain lighter fractions (40-60 min) in the coal liquefaction process (EDS, H-coal) currently under development (Zaczepinski, 1982; Eccles et al., 1982). One of the disadvantages in long residence time could mainly be attributed to the loss of hydrogen to give a large amount of gaseous material such as methane. To overcome thm short contact time, a two-stage liquefaction process was proposed (Rosenthal et al., 1982; Derbyshire et al., 1983). To reduce contact time, however, higher reaction temperature must be applied. At higher temperature, a certain amount of coal degrades very quickly to lower molecular weight materials in the presence of hydrogen-donor solvent or hydrogen-rich atmosphere. From ESR studies, Petrakis et al. (1980,1983) have reported that the most important factor to increase a concentration of coal fragment radicals was temperature and that the maximum liquefaction yield was obtained at 480 "C for a residence time of 10 min in the liquefaction of Powhatan No. 5 coal in the presence of a hydrogen-donating solvent, tetralin. To carry out coal liquefaction at higher temperature under moderate hydrogen pressure, a powerful hydrogen-donor solvent must be used. However, coal-derived heavy liquid used for a recycle solvent shows poor hydrogen-donating ability. If such a solvent like coal-derived liquid is used as a vehicle oil, prehydrogenation of the solvent or high hydrogen pressure should be applied. As iron pentacarbonyl is one of the active coal liquefaction catalysts, hydrogen transfer from molecular hydrogen will be promoted under low hydrogen partial pressure, even in a poor hydrogen-donor solvent such as coal-derived recycle solvent. It should be possible to operate coal liquefaction at higher temperature in the presence of an active catalyst without excessive reverse reaction to form coke under lower hydrogen pressure. In this paper, we studied the liquefaction of Illinois No. 6 coal at relatively high temperature to reduce reaction time by using Fe(C0)5as a catalyst precursor in non-hydrogen-donating solvent. The effects of the initial hydrogen pressure, residence time, the amounts of catalyst, 0 196-4305/85/1124-0832$01.50/0
and the reaction temperature on the liquefaction reaction are described in detail. Experimental Section Materials. In all experiments, Illinois No. 6 (Peabody) high-volatile bituminous coal was employed. The analytical data for the coal are listed as follows: C, 76.8, H, 5.6 (daf %); ash, 11.2; volatile matter, 42.2; fixed carbon, 46.6; totalsulfur, 4.0 (% d). The coal was ground to pass 100-mesh (JIS) screen and stored under an argon atmosphere. Reagents used were commercially available materials and used without further purification. Apparatus and Procedure. The hydroliquefaction experiments were conducted in a batch-rocking 50-mL microautoclave (24 mm i.d. X 110 mm) made of Hasteroy C. A stainless steel heat block with a sheathed heater equipped with a rocking-type shaker was used for heating, and the autoclave was shaken at 110 cycles/min. In a typical experiment, 2.0 g of coal and 4.0 mL of l-methylnaphthalene were placed into the autoclave, and then a certain amount of catalyst was added. A steel ball (diameter 10 mm) was added into the reaction mixture to help agitation. The autoclave was then purged and pressurized with hydrogen to a prescribed pressure (50-100 kg/cmz, corresponding to 11-22 w t % H2gas to coal). The autoclave was heated to a reaction temperature with the heat block preheated at about 450 "C. The reaction temperature was monitored by a sheathed Cromel-Alumel thermocouple inserted directly into the reaction mixture. Typical temperature and pressure profiles against reaction time are illustrated in Figure 1. Nominal reaction time was estimated from the time when the temperature of the reaction mixture reached 20 "C below the prescribed temperature. After a certain reaction time, the autoclave was cooled by air blowing. The reaction mixture was transferred from the autoclave into a thimble filter of Soxhlet extractor with tetrahydrofuran (THF) and then extracted with THF for 10 h. The extract was concentrated to 10 g, and it was poured into a large amount of pentane to separate oil and insoluble matter (AS + PA). Asphaltene was separated by extracting the AS + PA by benzene. The conversion of coal was calculated by using the following equation, assuming that Fe(CO), remained as Fe metal after liquefaction reaction. conversion (%) = (1 - (THF insolubles(g) - ash(g) catalyst(g))/dry-ash-free coal(g)) X 100 Fractions of asphaltene (AS) and preasphaltene (PA) are 0 1985 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 3, 1985 833 Table I. Hydroliqufaction of Illinois No. 6 Coal Using Iron Pentacarbony14 Hz press! run catalystb SOW kg/cm2 temp, "C time, min conv: % 1 none MN 50 460 20 54.9 2 Fe(CO), MN 50 460 20 84.2 3 Fe(C0l6 MN 50 460 40 83.9 4 none MN 80 460 20 69.7 5 Fe(C0)6 MN 80 460 20 95.0 6 Fe(CO), DL 80 460 20 94.8 I none MN 80 480 10 61.2 8 FezOB MN 80 480 10 83.7 9 Fe(CO), MN 80 480 10 93.9
oil (gas)', % 31.5 (4.2) 40.9 (5.2) 47.3 (6.7) 37.2 (6.4) 53.1 (5.6) 56.2 (4.6) 34.9 (5.3) 43.4 (6.3) 50.4 (6.4)
AS: %
PA! %
Hz to coal,' mg (wt % )
15.8 25.5 23.3 20.4 30.5 26.2 16.2 25.4 29.5
7.6 17.8 13.3 12.1 11.4 10.2 10.1 14.9 14.0
15.4 (0.8) 37.8 (2.0) 44.7 (2.4) 25.7 (1.4) 54.6 (3.0) 49.2 (2.7) 22.0 (1.2) 41.7 (2.2) 52.1 (2.8)
"Coal, 2.0 g, solvent, 4.0 mL. bFe, 0.4 mmol (1.1w t % coal). 'MN: 1-methylnaphthalene. DL decalin. dInital pressure. 'THF soluble fraction. f o i l ( % ) = Conv(%) - pentane insolubles(%); ( 1, C1-C.I hydrocarbon gases(%). #Benzene soluble, pentane insoluble fraction. h T H F soluble, benzene insoluble fraction. 'The amount of hydrogen transferred to coal; ( ), wt % daf coal. The values were not used to calculate coal conversion.
500
U
400
v
E
300
3
c
ga 200
ar
E
oil
I2 100
0 0
20
0
40
50
Figure 1. Typical temperature- and pressure-time profiles for the reactor.
also calculated on a dry-ash-free (daf) coal basis. Oil yield was obtained by subtracting the fractions of AS PA from the conversion of coal. Analyses of Gas and Solvent Composition. After liquefaction, whole gaseous materials were collected and analyzed by a gas chromatograph equipped with a Porapak Q column (3 mm i.d. X 2 m; for C1-C4 hydrocarbons) and an active carbon column (3 mm i.d. X 3 m; for CO and COJ. Hydrogen absorbed was calculated from the amount of gas recovered and gas composition. This value was not used to estimate coal conveision data, because material balance of the products from coal cannot be fully evaluated. The solvent composition after liquefaction was analyzed by gas chromatography on Versamide (3 mm i.d. X 3 m) and/or diethylene glycol adipate (3 mm i.d. X 2.25 m) columns with standard samples described in a previous paper (Suzuki et al., 1984). In this study, the amounts of tetralin, 1-methyltetralin, 5-methyltetralin, and naphthalene were determined, since other products formed from 1-methylnaphthalene were negligible (Chien et al., 1983). When the yield of hydrocarbon gases was calculated, the amount of methane formed from the demethylation reaction of 1-methylnaphthalene was estimated by calculating the amounts of tetralin and naphthalene from solvent analyses and was subtracted from a total amount of methane obtained by gas analyses. Among the experimental results, conversion, fractions of asphaltenes and preasphaltenes in the repeated experiments are quite reproducible (within &1.5% absolute). The amounts of hydrogen absorbed and gases produced scatter considerably ( 5 8 % relative to the values observed),
+
100
75
lnitial hydrogen pressure ( kg lcm2)
Reaction lime ( m i n )
Figure 2. Effect of hydrogen pressure on (a) the amount of hydrogen transferred to coal and (b) the yields of products. Reaction conditions: Fe(CO),, 0.4 mmol/2.0 g of coal; 460 "c; 20 min; in THF soluble fraction, (A)benzene soluble I-methylnaphthalene. (0) oil fraction, and ( 0 ) CI-C4 hydrocarbon gases. fraction, (0)
100 1
1 -
4
801 601
0
Y
AS
10
-
20 30 40 50 60 React ion ti me ( m i n )
Figure 3. Effect of reaction time on (a) the amount of hydrogen transferred to coal and (b) the yields of products. Reaction conditions: Fe(C0)6,0.4 mmol/2.0 g of coal, initial hydrogen pressure, 80 kg/cm2; 460 "C; in 1-methylnaphthalene. Keys are the same as Figure 2.
since they were estimated indirectly with several assumptions. Results and Discussion The results of the liquefaction of Illinois No. 6 coal are shown in Table I and Figures 2-5. Marked catalytic effect of iron pentacarbonyl was observed at the temperatures
834
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 3, 1985 3c -
P o N C
I
O
0
1-
20
Oil
;&
_ I _
1 2 3 Iron concentration(wt% of coal)
0
Figure 4. Effect of catalyst level on (a) the amount of hydrogen transferred to coal and (b) the yields of products. Reaction conditions: Fe(CO),, 0-1.0 mmol/2.0 g of coal; initial hydrogen pressure, 80 kg/cm2;460 "C;20 min; in I-methylnaphthalene. Keys are the same as Figure 2.
0
I
: '
--a
I
,.
100
"
0
>-
0
,,i
J
0
420
440
4ao
460
Temperature
('C)
Figure 5. Effect of temperature on (a) the amount of hydrogen transferred to coal and (b) the yields of products. Reaction conditions: Fe(CO),, 0.4 mmol/2.0 g of coal;initial hydrogen pressure, 80 kg/cm2; 10 min; in 1-methylnaphthalene. Keys are the same as Figure 2.
460 and 480 "C, as in the case of the liquefaction at 425 OC (Suzuki et al., 1984). As shown in Table I, runs 1 and 2, coal conversion increased from 54.9 to 84.2% 'and oil yield from 31.5 to 40.9% with an addition of Fe(CO)Sunder an initial hydrogen pressure of 50 kg/cm2. The amount of hydrogen in the gas phase transferred to coal also increased from 0.8 to 2.0% with Fe(CO)& As shown in runs 2 and 3, prolonged reaction time resulted in slight increases in the yield of oil and the amount of hydrogen transferred to coal, but coal conversion did not increase at all. When the initial hydrogen pressure was increased to 80 kg/cm2, coal conversion increased by about 15 and 10% with and without catalyst, respectively. These results suggest that degradation of the coal to fragment radicals occurred rapidly, and consequently gas-phase hydrogen cannot be transferred to coal fragment radicals sufficiently at a lower hydrogen partial pressure. Thus, even in the presence of active iron pentacarbonyl catalyst, considerable hydrogen partial pressure is required to transfer molecular hydrogen to coal fragment radicals at a reasonable rate. The amount of gaseous hydrocarbons, however, did not increase with an increase in hydrogen pressure.
In run 6, decalin (decahydronaphthalene) was used as a solvent instead of 1-methylnaphthalene, Decalin cannot be converted into aromatic or hydrodromatic compounds which serve as a hydrogen-shuttling substance or hydrogen-donating one. In fact, more thap 99% of the decalin used was recovered after the hydroliquefaction reaction. No evidence was observed that the hydrogen-transfer reaction from decalin occurred. Quite simihr results of coal conversion and oil yield were obtained both in decalin and 1-methylnaphthalene solvents. The fact that the nature of the solvent scarcely affects the liquefaction results strongly supports the direct hydrogen-transfer process to coal fragment radicals from molecular hydrogen as suggested in previous papers (Watanabe et al., 1984; Suzuki et al., 1984). Figure 2 shows the effects of initial hydrogen pressure on the liquefaction reaction in the presence of iron pentacarbonyl at 460 "C for 20 min. Coal conversion to THF solubles and oil fraction increased with a rise in the initial hydrogen pressure from 50 to 80 &/an2.Further increase in the hydrogen pressure to 100 kg/cm2, however, resulted in slight increases in coal conversion. The amount of hydrogen transferred to coal also showed a similar tendency. On the other hand, yields of hydrocarbon gases, asphaltene, and preasphaltene are less sensitive to the initial hydrogen pressure. Figure 3 shows the coal conversions, yields of preasphaltene, asphaltene, oil (excluding hydrocarbon gases), and gaseous products against reaction time together with the amount of hydrogen transferred to coal. The conversion to THF soluble materials reached 93 % within 10 min and was constant even with extended reaction time. The amount of oil fraction, hydrocarbon gases, and hydrogen transferred to coal, however, increased gradually with increasing reaction time. " s f e r of hydrogen to the fragment radicals proceeded smoothly in the presence of Fe(CO)& In addition, the most remarkable feature of the reaction in the presence of Fe(C0)6at 460 OC is that almost 70% coal has been converted to asphaltene (33%) and oil (39%)fractions within 10 min. This seem to indicate that a certain part of this coal can be converted to asphaltene and oil fractions directly at 460 OC, without passing through the initial preasphaltene stage. Further hydrocracking of preasphaltene to asphaltene or oil and asphaltene to oil requires much time. The amount of preasphaltene decreased gradually, but the amount of asphaltene does not change with extended reaction time. This indicates that conversion of preasphaltene into asphaltene and conversion of asphaltene into oil occurred in series at a similar reaction rate. The typical composition of gaseous materials produced during liquefaction was shown in Table 11. The main product in the gas phase was methane (corrected for the demethylation from 1-methylnaphthalene). Formation of methane was greatly influenced by temperature compared with that of CO and C02in the reaction time of 10 min. As shown in Figure 3, during the reaction time from 10 to 60 min, the amounts of C1-CI hydrocarbon gases increased twice as much as the amount at 460 "C. Especially, increases in C2-C4gases were remarkable, indicating the further degradation of liquid products. Therefore the reaction must be limited to a certain short contact time in order to reduce loes of hydrogen. On the other hand, formation of CO and C02 is considered to be quite a rapid reaction, and the amounts of CO + CO, are almost constant within the reaction time studied. The effect of catalyst concentrgtion was studied, and the results are shown in Figure 4. The coal conversion in-
Ind. Eng. Chem. Process Des. Dev., Vol. 24, No. 3, 1985 835
Table 11. Composition of Gases after Liquefaction" amount of gases, mg run 10 4e 11 5 12 13 9
temp, OC 425 460 460 460 460 460 480
time, min 10 20 10 20 40 60 10
co + cot
CHc
cz
c3
25.9 46.1 37.7 35.2 41.4 36.3 38.9
6.4 57.9 32.9 45.2 54.5 48.1 52.9
8.6 29.7 23.0 29.4 41.1 49.6 33.7
6.2 18.0 15.1 18.7 28.7 33.9 22.2
C4 2.7 7.3 6.0 6.7 12.0 12.9 8.9
tot HC gas: wt % 1.3 6.4 4.3 5.6 7.7 8.1 6.4
"Coal, 2.0 g; Fe(C0)6, 0.4 mmol (1.1 wt % Fe of coal); inital hydrogen, pressure, 80 kg/cm2, in 4.0 mL of 1-methylnaphthalene. *Contribution from Fe(C0)5 was corrected. The amount of CH4 from demethylation of 1-methylnaphthalene was subtracted. dTotal amount of C1-C4 hydrocarbon gases, daf coal basis. eUncatalyzed run. Table 111. Solvent Composition after Liquefaction"
run 10 4 2 11 5 13 7 9
temp, OC 425 460 460 460 460 460 480 480
time, min 10 20 20 10 20 60 10 10
Fe(C0)5
Y N Y Y Y Y N Y
Hz press,b, kg/cm2 80 80 50 80 80 80 80 80
Hz to abs,Cmg 39.8 37.4 53.2 54.3 73.4 110.1 35.1 73.2
TL 0.1 0.9 1.1 0.7 1.8 8.7 0.6 2.1
s o h composition,d % 1-MT 5-MT NAPH 1.7 3.1 1.6 0.9 0.7 15.4 1.1 0.8 20.4 2.4 2.1 11.5 3.0 3.1 15.3 4.1 3.4 32.5 0.6 1.1 17.2 1.9 3.2 19.2
sol," mg 5.4 11.7 15.4 12.8 18.8 41.4 13.1 21.1
Hz to coal!& %
1.9 1.4 2.0 2.3 3.0 3.9 1.2 2.8
"Coal, 2.0 g; Fe(CO)5,0.4 mmol (1.1wt % Fe of coal), solvent; 4.0 mL of 1-methylnaphthalene (more than 99.5% pure). *Initial pressure. The amount of hydrogen absorbed. dTL: tetralin. 1-MT 1-methyltetralin. 5-MT 5-methyltetralin. NAPH naphthalene. OThe amount of hydrogen consumed for hydrogenation of the solvent. fThe amount of hydrogen transferred to coal, daf coal basis.
creased from 70 to 93% when 0.2 mmol of Fe(CO), (0.6% as Fe, coal basis) was used and slightly increased with further addition of the catalyst up to 1.0 mmol (2.8% as Fe). Constant oil and asphaltene yields were observed when more than 1% Fe was added as Fe(CO),. The gas yield was little affected by the catalyst level. The amount of hydrogen transferred to coal shows a similar tendency of the behavior of oil or asphaltene with an increasing amount of the catalyst level. In the liquefaction of North Assam coal using mineral matter constituents in the coal as catalyta, Mukherjee and Chowdhury (1976) reported that coal conversion gradually increased with the amount of catalyst and that about 7% iron waa needed to obtain more than 80% coal conversion. Garg and Givens (1983) recently reported that the addition of a highly dispersed iron catalyst such as impregnated FeS04 or iron naphthenate could reduce the iron concentration to 1% (coal basis) to obtain similar results given by using 3.5% Fe in the form of particulate pyrite. The high dispersion state of the Fe(C0)5-derived active species is suggested from the fact that the catalyst level can be reduced to 1%coal without decreasing the liquefaction yields. In Figure 5, effects of temperature on the conversion of coal into THF solubles, benzene solubles, oil, and hydrocarbon gases are illustrated together with the amount of hydrogen transferred to coal. Even in a very short reaction time (10 min), conversion to THF soluble products was almost constant throughout the temperature range from 425 to 480 "C. On the other hand, conversion to asphaltene and oil required a higher reaction temperature to obtain considerable amounts of them in a short contact time. Remarkable increases in gaseous product were observed at an elevated temperature even in the short contact time. The amount of hydrogen transferred to coal also increased at higher temperature. Figure 5 clearly indicates that liquefaction of Illinois No. 6 coal can be carried out smoothly in the presence of iron pentacarbonyl under low hydrogen partial pressure (80 kg/cm2 cold). Very low conversion of coal was observed without Fe(CO), under
such conditions as shown in Table I (run 7). Catalytic activity of Fe(C0)5 was compared with that of the conventional iron catalyst Fe203at 480 "C for the reaction time of 10 min (Table I, runs 8 and 9). Illinois No. 6 coal contains a relatively large amount of pyrite (16.6% as FezO3in ash) which is known to act as a good catalyst for the liquefaction reaction. The addition of Fe203promoted the liquefaction reaction to some extent. However, higher coal conversion and a larger amount of hydrogen transferred to coal were observed in the presence of Fe(CO)+ Iron pentacarbonyl is considered to d e c o m p e into finely dispersed metallic iron or react with sulfur contained in the coal to produce sulfided iron during the liquefaction reaction. The role of the catalyst appears to promote the rapid hydrogen-transfer process from molecular hydrogen to the thermally cracked fragment radicals of coal. As thermal degradation of coal to fragment radicals may proceed in the same manner with or without catalyst, the low conversion to THF soluble products can be attributed to a retrogressive reaction such as coking. Previously, two processes were proposed on the mechanisms of the hydrogen-transfer process catalyzed by Fe(CO),: (1)production of hydrogen-donor solvent by hydrogenation of the aromatic compounds; (2)a direct hydrogen-transferprocess from activated molecular hydrogen on the catalyst surface. Typical results of solvent composition after liquefaction in 1-methylnaphthalene are listed in Table 111. The fractions of hydrogenated products such as tetralin, 1methyltetralin, and 5-methyltetralin were small even in the presence of Fe(CO), compared with the great increase in the amount of hydrogen absorbed at 425-480 "C for 10 min. When the reaction time was extended, the amounts of hydrogenated products increased, indicating that the hydrogenation reaction proceeded slowly. Since the amounts of hydrogenated products were unexpectedly small, hydrogen transfer from partially hydrogenated solvent may participate slighly for the stabilization of coal fragment radicals in the early stage of liquefaction. The direct hydrogen-transfer process is considered to play a
838
Ind. Eng. Chem.
Process Des. Dev. 1985, 2 4 , 836-844
main role. The fact that little difference in the liquefaction was observed between the results in decalin and 1methylnaphthalene also supports the direct process. On the other hand, the contribution of coal-derived materials which are more easily hydrogenated with Fe(CO), and serve as a hydrogen shuttler cannot be ruled out. Conclusion Fe(C0I5 acted as an excellent catalyst precursor for hydroliquefaction of Illinois No. 6 coal under the conditions of short contact time, high temperature (>460"C), and relatively low hydrogen partial pressure. Optimum conditions to obtain the maximum oil yield in the limited reaction time were 460 "C, 20 min or 480 "C, 10 min by using 1w t % (coal basis) Fe as Fe(C0)5at 80 kg/cm2 (cold) hydrogen. The active species derived from Fe(C0)5 is considered to serve in the direct hydrogen-transfer process
to the coal fragment radicals from molecular hydrogen. Literature Cited Chlen, P. L.; Sellers, G. M.; Weiler, S.W. Fuel Process. Technol. 1983, 7 , 1. Derbyshire, F. J.; Varghese, P.;Whkahurst, D. D.Fuel 1983, 62, 491. Eccles, R. M.; DeVaux, G. R.; Rakow, M. S. Pan-Pac. Synfuels Conf., Prepr. 1982, 388. Garg. D.;Givens, E. N. Fuel Process. Technol. 1983, 7 ,59. Mukherjee, D. K.; Chowdhury, P. B. Fuel 1976, 55, 4. Petrakis, L.; Grandy, D. W. Fuel 1980, 5 9 , 227. Petrakis. L.; Jones, G. L.; Grandy, D.W. Fuel 1983, 62, 671. Rosenthai, J. W.; Dahlberg, A. J.; Kuehler, C. W.; Cash, D.R.; Freedman, W. Fuel lS82, 67, 1045. Suzukl, T.; Yamada, 0.; Fujita, K.; Takegami, Y.; Watanabe. Y. Fuel 1984, 63,1708. Watanabe, Y.; Yamada, 0.; Fujita. K.; Takegami, Y.; Suzuki, T. Fuel 1884, 63,752. Zaczepinski, S. Pan-Pac. Synfuel Conf.. Prepr. 1982, 372.
Received for review January 5, 1984 Revised manuscript receiued November 15, 1984 Accepted November 28, 1984
Product Compositions and Kinetics in the Rapid Pyrolysis of Sweet Gum Hardwood Theodore R. Nunn, Jack B. Howard, John P. Longwell, and WlHlam A. Peters' Energy Laboratory and Department of Chemical Englneerlng, Massachusetts Institute of Technology, CambrMge Massachusetts 02 139
Yields, composition, and rates of evolution of major products from batch pyrolysk of predried sweet gum hardwood were measured for the temperature range 600-1400 K under 5 psig of helium, at heating rates and residence times at final temperature of 1000 K/s and 0 s, respectively. Approximately 100-mg layers of 45-88-pm wood powder, thinly spread on a hot stage, were heated, so that volatiles residence times at elevated temperatures were minimized. Total weight loss increased strongly with temperature to an asymptote of 93% at 1100 K. Tar is the major pyrolysis product above 800 K. I t exhibits a maximum yield of 55 wt % at 900 K and declines to an asymptote of 46 wt % at 1300 K. Secondary cracking of the tar is significant above 900 K and contributes substantially to the yields of CO, CH, C2H4,and other light gases. Carbon monoxide dominates the gas produced above 850 K and attains an asymptote of 17 wt % above 1300 K. A single-reaction first-order decomposition model describes well the global rates of evolution of most major products except tar. However, the data imply that most products are evolved by more complex kinetic pathways.
Introduction The pyrolysis of wood, cellulose, and other biomass materials has been studied extensively. Previous work, including several kinetic investigations, is reviewed by the following: cellulose, Molton and Demmitt (1977);Lewellen et al. (19771, and Hajaligol(1980);lignin, Allan and Mattila (1971), Klein (1981); wood, Roberts (1970) and Wenzl (1970);and different forms of biomass, Peters (1978), Milne (1979), and Antal(1980). There have been very few systematic studies of the independent effects of biomass type, temperature, heating rate, solids residence time, volatiles residence time, pressure, gaseous atmosphere, and sample dimension, on the yields, compositions, and rates of production of pyrolysis gases, liquids, and chars. Quantitative information on the separate contributions to pyrolysis of primary decomposition and volatiles secondary reactions is also lacking. These details are needed to advance basic understanding of biomass thermal conversion pathways and to provide predictive models for existing and future processes for converting renewable resources to clean fuels and chemical feedstocks. A further application is in studies of flammability, flame spread, and related issues in fire research, because pyrolytic decomposition supplies the 0196-4305/85/1124-0836$01.50/0
volatiles that can ignite and support flaming combustion of condensed phase materials (Lewellen et al., 1977). This paper responds to some of the above information deficiencies. It presents recent results from a systematic study of the effect of temperature on the rapid pyrolysis of powdered sweet gum hardwood (Liquidambar styraciflua)under 5 psig of helium, including quantitative data on the yields, composition,and rates of evolution of major products. This work constitutes one fact of an ongoing research program aimed at providing better quantitative understanding of the rapid pyrolysis of whole biomass, and the three major biomass constituents-cellulose, hemicellulose, and lignin. Previous communications (Hajaligol, 1980; Hajaligol et al., 1982) have presented similar information on cellulose. A companion paper (Nunn et al., 1985) discusses our results on milled wood lignin extracted from the same parent sample of sweet gum used in the present study. A similar paper on one form of hemicellulose (xylan) is in preparation (Ghosh et al., 1985). Experimental Section Reactor Description. The measurements were performed in a captive sample electrical screen heater reactor 0 1985 American Chemical Society
