Energy & Fuels 1995,9, 67-70
67
Effect of Preheat Treatment on Coal Liquefaction Yoshinari Inukai," Seiji Arita,? and Hideharu Hirosue Kyushu National Industrial Research Institute, Shuku-Machi, Tosu-Shi, Saga-Ken 841, Japan Received June 9, 1994. Revised Manuscript Received October 4, 1994@
For the catalytic and noncatalytic liquefaction of Wandoan and Illinois No. 6 coals with anthracene oil and hydrogenated anthracene oil a t 450 "C, the two-stage liquefaction with in situ preheat treatment at 250,350, and 400 "C for 15 min gave higher yields of toluene solubles (TS) and hexane solubles (HS) than the one-stage liquefaction without in situ preheat treatment. The effect of preheat treatment at low temperature on the yields of TS and HS is believed to result from the swelling of coal in the solvent. The two-stage liquefaction is also advantageous from the viewpoint of using a lower preheat temperature than the liquefaction temperature, compared with the one-stage liquefaction for the same reaction time.
Introduction We r e p ~ r t e d l -that ~ the initial reactions of coal liquefaction, such as the conversion of coal t o preasphaltenes and the swelling of coal in solvents, occurred a t the preheat stage during liquefaction process. Therefore, we have recognized that the preheat treatment is important for coal liquefaction and that the utilization of the swelling phenomena during the preheat treatment has the possibility of improvement of coal conversion and product quality considering the penetration of solvent molecules into the interior of coal particle. Pretreatment of coal has been studied to enhance the coal conversion of liquefaction for many years. The first type of pretreatment methods is heat treatment.5-8 The preheat treatment at 200 "C5 and 277-322 "C6 increased conversions for the noncatalytic liquefaction of bituminous coals, and the preheat treatment at 350 "C gave high liquid yields for the catalytic hydroliquefacAlso, the tion of subbituminous and bituminous catalytic hydroliquefaction procedure after two-step heat soaking a t 350 and 400 "C in the absence of a catalyst was proposed.* The second type of pretreatment methods is preswelling with swelling agentsag-14 Coals t Present address: Nagasaki University, 1-14Bunkyo-Machi, Nagasaki-Shi 852,Japan. Abstract published in Advance ACS Abstracts, November 15,1994. (1)Shibata. M.: Sakaki. T.; Adachi, Y.;Miki, T.; Arita, S. J.Fuel SOC.Jpn. 1989,68,55. (2)Shibata, M.; Sakaki, T.; Adachi, Y.; Miki, T.; Hirosue, H.; Arita, S. J. Jpn. Znst. Energy 1993,72,1161. (3)(a)Nakada, M.; Sakaki, T.; Arita, S. Prepr. 23rd Conf. Coal Sci. (Jpn.)1986,163. (b) Nakada, M.; Matsumoto, S. J. Jpn. Inst. Energy 1993,72,370. (4)Sakaki, T.;Shibata, M.; Hirosue, H. Energy Fuels, to be submitted for publication. ( 5 ) Narain, N. K. Fuel Process. Technol. 1986,11, 13. (6)Wham,R. M. Fuel 1987,66,283. (7) Derbyshire, F.J.; Davis, A.; Epstein, M.; S t a n s b e q , P. G. Fuel 1986,65,1233. (8)Nishioka, M.; Laird, W.; Bendale, P. G.; Zeli, R. A. Energy Fuels 1994. - -, 8.643. (9) Rincon, J. M.; Cruz,S. Fuel 1988,67,1162. (10)Joseph, J. T.Fuel 1991,70,139. (11)Joseph, J. T.Fuel 1991, 70,459. (12)Artok, L.; Davis, A.; Michell, G. D.; Schobert, H. H. Fuel 1992, 71,981. (13)Artok, L.;Davis, A.; Michell, G. D.; Schobert, H. H. Energy Fuels 1993,7,67. @
- 7
~
~~
preswollen with tetrahydr~furan,~-l~ tetrabutylammonium hydroxide,1°-13 methan01,lO-l~pyridine,12J3and acetone14 were liquefied after removal of swelling agents, and the preswelling was found to improve coal conversion and product quality. The third type of pretreatment methods is chemical reactions such as alkylation, oxidation, and hydrolysis.14J5 It is considered that the preheat treatment is the simplest and the most practical in the above-mentioned pretreatment methods, because it can be done in situ for practical catalytic hydroliquefaction processes. However, in the two cases516 of the preheat treatment, a catalyst was not employed and therefore the coal conversions were low. In the other case7of the preheat treatment, the preheat treatment at 350 "C only was carried out to mainly examine the catalytic prehydrogenation of coal, not the swelling of coal in a solvent, and the other preheat temperatures except for 350 "C were not examined. Also, the heat soakin9 was not performed in the presence of a catalyst and in situ and was mainly aimed a t the physical dissolution of coal. Therefore, there seem t o be few studies investigating systematically the effect of in situ preheat treatment at low temperature and short reaction time on the catalytic hydroliquefaction of coal under various conditions for utilizing swelling phenomena which we pointed out at the beginning. In this paper, the possibilities of high coal conversion, good product quality, and energy saving from the viewpoint of using a lower preheat temperature than the liquefaction temperature a t 450 "C for two-stage liquefaction with in situ preheat treatment for 15 min have been examined under various conditions such as coals (subbituminous and bituminous coals), solvents (anthracene oil and hydrogenated anthracene oil), preheat temperatures (250,350, and 400 "C), and catalyst types (oil-soluble Mo catalysts, NiMo catalyst, and none) in comparison with the corresponding one-stage liquefaction at 450 "C.
Experimental Section Materials. The coal samples were an Australian subbituminous, Wandoan coal and an American low-rank bituminous, (14)Baldwin, R. M.; Kenner, D. R.; Nguanprasert, 0.;Miller, R. L. Fuel 1991,70, 429. (15)Shams, K.; Miller, R. L.; Baldwin, R. M. Fuel 1992,71, 1015.
0 1995 American Chemical Society 0887-0624/95/2509-0067$09.00/0
Inukai et al.
68 Energy & Fuels, Vol. 9,No. 1, 1995 Table 1. Analyses of Coals and Solvents coal and solvent Wandoan coal Illinois No.6 coal anthracene oil (AO) hydrogenated A 0
ultimate analysis (%, da0 C H WC 6.1 0.98 74.1 75.1 5.3 0.83 5.7 0.74 91.2 87.7 6.8 0.92
100
ash (%, dry base)
10.2 5.99 -
-
80 u
8
v
m 6 0
n
3 -
$
40
c
Illinois No. 6 coal, each ground to under 200 mesh. The solvents were anthracene oil (A01 and hydrogenated AO, which was obtained by the hydrogenation of A 0 at 10-15 MPA and 380 "C for 2 h using a presulfided Ni-Mo-alumina catalyst. Table 1 shows the analyses of the coals and the solvents used in this study. The catalysts were oil-soluble molybdenum dithio-2-ethylhexylcarbamate(MoDTC) (21% Mo as metal) and molybdenum dithio-1-methylbutylphosphate (MoDTP)(23% Mo as metal) produced by Asahi Denka Kogyo K. K.,16 and presulfided Shell 324 Ni (2.7%)-Mo (13%)alumina (16-32 mesh size). One- and Two-Stage Liquefaction. The experiments were carried out using a ca. 70 cm3miniautoclave with a n upand-down agitator. The autoclave was loaded with 6 g of coal, 18 g of solvent, and 0.3 g of the oil-soluble Mo catalyst (0.6 g of Ni-Mo catalyst or none), and pressurized to 7.8 MPa with hydrogen at ambient temperature. During the two-stage liquefaction with in situ preheat treatment, the autoclave with agitation a t 40 cycledmin was heated (ca. 200 "C/min) to a preheat temperature of less than 400 "C and kept a t that temperature for 15min using an infrared image furnace. The temperature was again raised (ca. 200 "C/min) to 450 "C and kept a t 450 "C for 15 min. During the one-stage liquefaction without in situ preheat treatment, the autoclave was heated to 450 "C and kept at 450 "C for 15-30 min. In both cases, the autoclave was cooled (ca. 200 "C/min) in water just after the reaction, and the products were removed from the autoclave. The solid and liquid products were extracted with hot solvents and then separated by centrifugation to obtain the yields (daf coal base) of pyridine solubles (PS), toluene solubles (TS), and hexane solubles (HS).In calculating the yields, it was assumed that MoDTC and MoDTP were converted to solvent-insoluble molybdenum disulfide after the reaction. Thus, the weight of molybdenum disulfide produced was reduced from the weight of insoluble residue to determine the weight of solvent insolubles.
Q) K
E
20
v)
0 250-450
350-450
400-450
450(30min) 450(22min) 450(15min)
Preheat Treatment -Liquefaction Temp. ("C) (Time) PS
0
TS
Figure 1. Hydroliquefaction of Wandoan coal with A 0 using MoDTC catalyst. 100
G=
80
U
8
v
m
n -3
a 40
Y
Q) C
'0
20
v)
0 250-450
350-450
400-450
450(30min) 450(22min) 450(15min)
Preheat Treatment - Liquefaction Temp. ("C) (Time) PS
0 TS
Figure 2. Hydroliquefaction of Illinois coal with A 0 using MoDTP catalyst.
Results and Discussion Hydroliquefaction with A 0 Using Oil-Soluble Mo Catalysts. Figures 1 and 2 show the results for the one- and two-stage hydroliquefaction of Wandoan and Illinois coals, respectively, with A 0 using the oilsoluble Mo catalysts. For the two-stage hydroliquefaction with heating a t 450 "C for 15 min after preheating at 250-400 "C for 15 min, the yields of PS were at the same level as those for the one-stage hydroliquefaction at 450 "C for 15,22, and 30 min. Since coals were easily converted to PS and it was almost completed during the hydroliquefaction a t 450 "C for 15 min, the preheat treatment had no effect on the yield of PS. The yields of TS for the two-stage hydroliquefaction with preheat treatment were higher than those for the one-stage hydroliquefaction without preheat treatment. On the other hand, the conversion to TS was not observed after the heat treatment of Wandoan and Illinois coals with A 0 using the catalysts a t 250 "C for 15 min alone as shown in Figure 3. Therefore, this effect of preheat treatment at 250 "C on the yields of TS for the twostage hydroliquefaction is believed to result from the (16)Kato, H.Petrotech 1984, 7, 66.
raw (wan.) 250°C(wan.) raw( IIli.)
250'C( II Ii.)
Preheat Treatment Temp. (Coal)
t3 PS 0 TS Figure 3. Preheat treatment of Wandoan coal using MoDTC catalyst and Illinois coal using MoDTP catalyst with A 0 at 250 "C for 15 min.
swelling of coal in the solvent. That is, the preheat treatment enables the solvent to be around the reactive sites of coal due to the swelling of coal prior to hydroliquefaction and leads to promoting the conversion to TS during the subsequent hydroliquefaction a t 450 0C.5*6 Also, during preheating a t 350 and 400 "C, weaker bonds might be broken and stabilized by hydrogen transfer7 besides the effect of the swelling of coal as already described, minimizing condensation reactions during the subsequent hydroliquefaction a t 450 "C. During the one-stage hydroliquefactionwithout preheat treatment, however, the solvent does not fully penetrate into the coal because of the rapid heating rate, and thus
Energy & Fuels, Vol. 9,No. 1, 1995 69
Effect of Preheat Treatment of Coal Liquefaction 100 I
I
100 I
250-450
350-450
450(30min) 450(15min)
MoDTc(0.3~) MoDTP(0.39)
Preheat Treatment - LiquefactionTemp. ('C) Crime) PS
0
TS
Figure 4. Hydroliquefaction of Wandoan coal with A 0 using Ni-Mo catalyst.
additional condensation reactions can occur during the heat-up period and the early heating period a t 450 "C. The two-stage hydroliquefaction is also more advantageous than the one-stage hydroliquefactionfor the same reaction time from the viewpoint of energy saving, because a lower reaction temperature can be used in preheat treatment. The differences of the yields of TS in the two-stage hydroliquefaction of Wandoan coal a t preheat temperatures of 250, 350, and 400 "C were not clear, but the preheat temperature a t 350 "C gave the highest yield of TS for the two-stage hydroliquefaction of Illinois coal. When comparing the hydroliquefactionof Wandoan coal with that of Illinois coal, the yields of TS for Wandoan coal were higher than those for Illinois coal. As similar results were obtained for the noncatalytic liquefaction of Wandoan and Illinois coals using hydrogenated A 0 and tetralin solvent,17 it is considered that Wandoan coal is more reactive than Illinois coal for the liquefaction under these conditions. For the differences of the yields of TS between the one- and two-stage hydroliquefaction, Illinois coal showed larger differences (maximum 18%)than Wandoan coal (maximum 10%). These results may be due to that the conversion to TS during the catalytic hydroliquefaction of Illinois coal was not as easy as that of Wandoan coal. Hydroliquefaction with A 0 Using Ni-Mo Catalyst. Figure 4 shows the results for the one- and twostage hydroliquefaction of Wandoan coal with A 0 using the Ni-Mo catalyst. For the two-stage hydroliquefaction at 450 "C for 15 min after preheating a t 250 and 350 "C for 15 min, the yield of TS was higher than those for the one-stage hydroliquefaction a t 450 "C for 15 and 30 min. Similar results were also obtained for Illinois coal. These results using the Ni-Mo catalyst were similar to those using the oil-solubleMo catalysts shown in Figures 1 and 2. Therefore, the effect of preheat treatment on the yield of TS for the two-stage hydroliquefaction was found not to depend on the catalyst types used. Figure 5 shows the influence of catalyst types on the hydroliquefaction of Wandoan coal with A 0 a t 400 "C for 30 min. When both oil-soluble Mo catalysts are compared, MoDTP gives a slightly higher yield of TS than MoDTC. This may be due to the dispersible power of the phosphate in MoDTP as one can understand from the ability of phosphate used as a surface-active agent, (17) Inukai, Y.; Sakaki, T.; Shibata, M.; Miki, T.; Arita, S. Rep. Gou. Ind. Res. Inst. Kyushu 1990, 2805.
Ni-Mo(O.6g)
Catalyst PS 0 TS Figure 5. Influence of catalyst types on hydroliquefaction of Wandoan coal with A 0 at 400 "C for 30 min.
100
80 -0
8
v
u)
n
60
-
3
$
40
c. 0 C
5
20
v)
0 250-450
350-450
450(30min) 450(22mln) 450(15mln)
Preheat Treatment - LiquefactionTemp.
PS
("C) (Time)
TS
Figure 6. Noncatalytic liquefaction of Illinois coal with AO.
besides the slightly higher Mo content of MoDTP than that of MoDTC. When the catalyst was changed from the oil-solubleMo catalysts (0.3g) to the Ni-Mo catalyst (0.6 g), the yield of TS was reduced in spite of a larger amount of Mo. Similar results were also obtained for the hydroliquefaction of Wandoan and Illinois coals with A 0 a t 450 "C for 30 min. These results depend on the small contact area of the particulate Ni-Mo catalyst for the solvent compared with the oil-soluble Mo catalysts. Noncatalytic Liquefaction with AO. The one- and two-stage noncatalytic liquefaction of Illinois coal with A 0 was carried out at the same hydrogen pressure as that used in Figure 2. The results are shown in Figure 6. When comparing Figure 6 with Figure 2, the yields of PS and TS for the noncatalytic liquefaction were lower than those for the catalytic liquefaction, as expected. For the two-stage liquefaction a t 450 "C for 15 min after preheating a t 250 and 350 "C for 15 min, the yields of PS were higher than those for the one-stage liquefaction a t 450 "C for 15, 22, and 30 min, because coal was not easily converted to PS during the noncatalytic liquefaction. The maximum difference of the yields of PS between the one- and two-stage liquefaction was 20%. The yield of TS for the two-stage liquefaction with preheat treatment a t 350 "C was higher than that for the one-stage liquefaction without preheat treatment. The effect of preheat treatment on the yields of PS and TS for the two-stage noncatalytic liquefaction is also believed to result from the swelling of coal in the solvent. During the one-stage liquefaction, the yields of PS decreased and the yields of TS increased with an increase in reaction time. This is considered to be because the condensation of PS and the conversion of
Inukai et al.
70 Energy & Fuels, Vol. 9,No. 1, 1995 100
1
250-450
350-450 450(30mtn) 450(22min) 450(1Smin)
Preheat Treatment -LiquefactionTemp. ('C) (Time) PS
0
TS
HS
Figure 7. Hydroliquefaction of Illinois coal with hydrogenated A 0 using MoDTP catalyst.
PS to TS occurred simultaneously during the noncatalytic liquefaction at the high temperature of 450 "C. Hydroliquefaction with Hydrogenated A 0 Using Oil-Soluble Mo Catalyst. Figure 7 shows the results for the one- and two-stage hydroliquefaction of Illinois coal with hydrogenated A0 using the MoDTP catalyst. When comparing Figure 7 with Figure 2, the yields of PS for the hydroliquefaction with hydrogenated A0 were at the same level as those with AO, because coal was easily converted to PS in both solvents. However, the yields of TS for the hydroliquefactionwith hydrogenated A0 were higher than those with AO. This shows that hydrogenated AO, which has hydrogendonor species,18is more effective for the conversion to TS than AO. Moreover, HS were obtained during the hydroliquefaction with hydrogenated A 0 as shown in Figure 7. For the two-stage hydroliquefaction at 450 "C for 15 min after preheating at 250 and 350 "C for 15 min, the yields of PS were at the same level as those for the onestage hydroliquefaction at 450 "C for 15,22, and 30 min. On the other hand, the yields of TS for the two-stage hydroliquefaction with preheat treatment were higher than those for the one-stage liquefaction without preheat treatment. These results are similar to the results for the hydroliquefaction with A 0 shown in Figure 2. For the differences of the yields of TS between the oneand two-stage hydroliquefaction, hydrogenated A 0 solvent showed smaller differences (maximum 13%)than A 0 solvent shown in Figure 2 (maximum 18%). These results may be because the conversion to TS during the catalytic hydroliquefaction with A 0 was not as easy as (18) Inukai, Y.; Adachi, Y.; Shibata, M.; Arita, S. J . Fuel Soc. Jpn. 1986,65,329.
that with hydrogenated AO. The yields of HS for the two-stage hydroliquefaction were higher than that for the one-stage hydroliquefaction for 15 min, and at the same level as those for 22 and 30 min. Similar results were also obtained for the one- and two-stage hydroliquefaction of Illinois coal with hydrogenated-coalderived recycle 0i1.l~ Therefore, the effect of preheat treatment on the yields of HS is also believed to result from the swelling of coal in the solvent.
Conclusions For the catalytic hydroliquefaction of Wandoan and Illinois coals with A 0 and hydrogenated A 0 at 450 "C using the oil-soluble Mo catalysts and the Ni-Mo catalyst, the two-stage hydroliquefaction with in situ preheat treatment at 250, 350,and 400 "C for 15 min gave higher yields of TS than the one-stage hydroliquefaction for 15-30 min without in situ preheat treatment. For the differences of the yields of TS between the oneand two-stage hydroliquefaction, in general the difference had a tendency to increase as the conversion to TS decreased. Also, for the catalytic hydroliquefaction of Illinois coal with hydrogenated A 0 using the oilsoluble Mo catalyst, the two-stage hydroliquefaction with in situ preheat treatment at 250 and 350 "C gave higher yields of HS than the one-stage hydroliquefaction for 15 min. The effect of preheat treatment a t low temperature on the yields of TS and HS is believed to result from the swelling of coal in the solvent inducing the solvent molecules to penetrate into the interior of coal particle. The two-stage hydroliquefaction is also advantageous from the viewpoint of using a lower preheat temperature than the liquefaction temperature, compared with the one-stage hydroliquefaction for the same reaction time. For the catalytic hydroliquefaction of Wandoan and Illinois coals with A 0 and hydrogenated AO, however, the preheat treatment had no effect on the yield of PS, because coals were easily converted to PS. On the other hand, for the noncatalytic liquefaction of Illinois coal with A 0 at 450 "C, the two-stage liquefaction with in situ preheat treatment at 250 and 350 "C gave higher yields of PS than the one-stage liquefaction, because the conversion to PS during the noncatalytic liquefaction was not as easy as that during the catalytic hydroliquefaction. Acknowledgment. We are grateful to Mr. Hidekatsu &to for providing the oil-soluble catalysts used in this work, and we also thank Dr. Michael A. Wilson (CSIRO, Australia) for his helpful advice. EF9401076 (19) Inukai, Y.;Hirosue, H. Rep. Kyushu Natl. Znd. Res. Inst., to be submitted for publication.
