Effects of coal pretreatment and catalyst recovery on the liquefaction

Coal Science

J.A. Pajares and J.M.D. Tasc6n (Editors) 9 1995 Elsevier Science B.V. All rights reserved.

1375

Effects of coal p r e t r e a t m e n t and catalyst r e c o v e r y on the liquefaction K.Sakanishi a, H.Hasuo a, H.Taniguchi ", I.Mochida a, and O. Okuma b ~lnstitute of Advanced Material Study, Kyushu University,Kasuga, Fukuoka 816, Japan hPolymer & Chemical Technology Lab., Kobe Steel,Ltd., Kobe, Hyogo 651-22, Japan Liquefaction reactivities of Yalloum, Tanitoharum, and Wyoming coals are examined with or without coal pretreatment using sulfided Fe3AI and NiMo supported on carbon blacks, which have functions for recovery. The combined effects of coal pretreatment and Mo salt impregnation are suggested to be marked probably due to the liberations of coal macromolecules through the pretreatment, improving the affinity to the catalyst species and the dispersion of Mo active species into the liberated coal macromolecules. The liquefaction behaviors of the coals are compared in terms of pretreatment effects, liquefaction conditions, and catalyst recovery. 1. I N T R O D U C T I O N Coal liquefaction processes, which have been developing to substitute petroleum crude for next century, are required to break through the economical bamer for their commercialization. One of the economical breakthroughs is to develop a higly active catalyst with functions for recovery to increase distillate yield as well as to get rid of the waste derived from disposable catalysts. The present authors proposed that design of recoverable catalysts for the primary liquefaction stage can improve the economy of coal liquefaction process la~. The basic idea is to recover the catalyst from the inorganic residues which are originated from the feed coal. According to the natures of inorganic residue, three approaches can be designed, 1) removal of inorganic residues such as carbonates and chlorides, 2) recovery of the ferromagnetic catalysts from the diamagnetic residue, and 3) gravimetrical recovery of the catalysts supported on carbon black particles 3~. A multi-stage approach 4~, which consists of coal pretreatment, hydrogentransfer dissolution, and catalytic steps, may facilitate the catalyst recovery by reducing both inorganic and organic residues. The organic residue has been recycled with the catalyst and minerals to the primary liquefaction stage as the bottom recycle ~. Its favorable results have been reported, although the accumulation of inorganic solids requires a fixed rate of purging. In the present study, combinations of coal pretreatment and catalyst dispersion or recovery procedures are examined to accelerate coal depolymerization as well as to increase oil yield with a smaller amount of catalyst. Such combinations have advantages for the catalyst recovery

1376 through the complete conversion of coal with the least yield of inorganic and organic residues.

2. EXPERIMENTAL Three coals of Yallourn (Australian brown), Tanitoharum (Indonesian subbituminous), and Wyoming(American subbituminous) were used for the liquefaction reactions. Their elemental analyses are summarized in Table 1. Tetralin of guaranteed grade was used as a hydrogenTable 1 Elemental analysesof coals Coals wt%, daf basis C H N (O+S)diff. Wyoming 68.9 5.4 1.0 24.7 Tanitohahn 76.3 5.6 1.4 16.7 Yallourn 66.9 4.7 0.5 27.7

Table 2 Someproperties of catalysts and supports Surfacearea Specificgravity H/C Ash Catalysts Particle s i z e (wt%) ( /1 m ) (m2/g) (-, I-t20=1) (-) 3.7 FeS2 1-16(78.4wt%) < 20 0.94 4.8 Fe3A1 7.2(<500mesh) 0.5 6.5 - 7.9 0.87 1.6 KB-JD 30 x 10.3 1270 0.115 0.84

donor solvent. The coals were pretreated in 10% CH3COOH aqueous solution or ammonium tetrathiomolybdate(ATTM) solution in 10% methanol/H20 at room temperature for prescribed hours, followed by the filtration and drying at 60~ 60~

or the evaporation of solvent and drying at

respectively. Three types of the catalysts(see Table 2), sulfided Fe3Al(ferromagnetic),

NiMo / Ketjen Blacks, and a synthetic pyrite, were used for the liquefaction reactions. The liquefaction was carried out in an autoclave (50ml volume) with. The ground coal (< 60 or < 200 mesh, 3.0g), the solvent (4.5g) and catalyst (0.09 - 0.10 g) were charged into the autoclave. After the liquefaction reactions, the product remaining in the autoclave was extracted with THF, acetone, and hexane. The hexane soluble, hexane insoluble-acetone soluble, acetone insoluble-THF soluble, and THF insoluble fractions were defined as oil(O), asphaltene(A), preasphaltene (P), and residue(R), respectively. The gas yield was calculated by the difference between the initial and recovered residual weights. 3. RESULTS AND DISCUSSIONS 3.1 Effects of Coal Pretreatment and Catalyst Dispersion on the Liquefaction Figure 1 shows the liquefactionresults of Wyoming and Morwell coals with sulfided Fe3A1 at 440~

60 rain, and 13 MPa H2, before and after the coal pretreatment. The pretreatment

with 10% CH3COOH at room temperature for 24 hr improved the products slates, increasing oil and asphaltene with decreased yields of gas and heavy products. The pretreatmentwas more effective for Morwell coal than for Wyoming coal, reflecting its higher content of bridging ion-exchangeablecations such as C~ + and M ~ + through the oxygen functional groups 6). Figure 2 illustrates the liquefaction results of Tanitoharum coal at 450~

60 min, and 10

MPa H2 pressure before and after the coal pretreatment and/or ATTM impregnation. The combination of coal pretreatment and Mo impregnation increased the oil yield to 58% with decreasing asphaltene yield. It is noted that a smaller amount(0.5 wt% based on coal) of ATTM impregnation into coal exhibited the high activity, especially higher for the deashed coal.

1377

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Figure 1 Effect of coal pretreatment on the liquefaction at 440~ 60 min, and 13 MPa (a) Wyoming coal (c) Morwell coal

(b) Pretreated Wyoming coal (d) Pretreated Morwell coal

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Figure 2 Effects of coal pretreatment and catalyst impregnation on the liquefaction at 450~ 60 min, and 10 MPa H2

3.2 Recovery and Repeated Use of NiMo/KB Catalyst Figure 3 shows the activity of NiMo/Ketjen Black(KB) catalyst and its recovered one as THFI for the liquefaction of Wyoming coal at 440~ 60 min, and 13 MPa H2 pressure. The recovered catalyst as THFI residue, which contained the used catalyst at the concentration of 20 wt% with organic and inorganic insolubles, appeared to regenerate the acitvity to the similar level of the virgin catalyst by the resulfiding treatment with 5% H2S/H2 at 360~ for 2 h. Figure 4 illustrates the activity of NiMo/KB catalyst and its recovered one as THFI for the liquefaction of Yallourn coal at 440~ 60 min, and 13 MPa H2 pressure. The virgin catalyst exhibited the high activity with 70% of oil and asphaltene yield, while the recovered one gave lower oil and asphaltene yield, although the yield was still much higher than that of non-catalytic liquefaction. Yields/%(d.a.f.) O. (a)

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Fig.3 Activity of Ni-Mo/KB JD and its recovered one as THFI in the liquefaction of Wyoming coal.

(a) no catalyst (b) Ni-Mo/KB JD (c) THF-I(catalyst 0.09g in THFI(0.4g)) Reaction conditions reaction temperature reaction pressure reaction time heating rate catalyst

: 440~ : 13.0MPa : 60min

: 22~ : catalyst M (3wt% addition to coal) solvent(Tetralin)/coal = 1.5

I

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Fig.4 Activity of Ni-Mo/KB JD and its recovered one as THFI in the liquefaction of Yallourn coal.

(a) no catalyst O) Ni-Mo/KB JD (c) THF-I(catalyst 0.0% in THFI(0.2g)) Reaction conditionr reaction temperature reaction pressure reaction time heating rate catalyst

: 4400C : 13.0MPa : 60min : 22~ : catalyst M (3wt% addition to coal)

soivent(Tetralin)/coal = 1.5

1378 KB-supported NiMo catalysts were found to be recovered from the whole product by gravity separation using methanol, hexane and water in this order as illustrated in Figure 5, although the weight of recovered catalyst was gained to some extent due to the inclusion of organic materials on the catalyst. The combination of deashing pretreatment and recoverable catalysts, such as NiMo supported on magnetic supports of Fe3AI and ferrite / carbon or gravimetrically recoverable supports of carbon blacks, may facilitate the catalyst recovery as well as keep the initial catalytic activity in the repeated run.

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Dispersion | b y ultrasonic I~ irradiati~

Figure 5

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Soluble fraction of coal Mineral mailer and insoluble fraction of coal

R e c o v e r y S c h e m e of the K B - s u p p o r t e d Catalyst

4. CONCLUSIONS The present study emphasized that the recovery and recycle of the catalyst are basically possible by using the catalyst supports with the functions for recovery, after the primary coal liquefaction, where the inorganic solid residues are present to contaminate the used catalyst. Although the catalytic activity so far is not super, more elaborate preparation of the catalyst can improve the activity without losing functions for recovery. Smaller particle size, better dispersion of active species, and strengthening favorable catalyst-support interactions are such ways to enhance the activity. Recovered catalysts often lost their initial activity. The loss of sulfur and contamination with inorganic as well as organic poisons cause the deactivation. The multi-stage reaction schemes including coal pretreatment, solvent roles of hydrogen donation and dissolution, and the higher dispersion of active catalytic species should be further developed to achieve the maximum oil yield with the least amount of catalyst.

REFERENCES 1. I.Mochida, K.Sakanishi, M.Kishino, K.Honda, T.Umezawa, S.H.Yoon, ACS Div.Fuel Chem., 1993, 38(1), 93. 2. l.Mochida, K.Sakanishi, R.Sakata, K.Honda, T.Umezawa, Energy & Fuels, 1994, 8, 25. 3. I.Mochida, H.Hasuo, K.Sakanishi, H.Taniguchi, ACS Div.Fuel Chem., 1995, 40, 4. l.Mochida, K.Sakanishi, Y.Korai, H.Fujitsu, Fuel Process.Technol., 1986, 14, 113. 5. l.Mochida, K.Sakanishi, 'Advances in Catalysis(Academic Press)', vol.40, p.39-85 (1994). 6. l.Mochida, A.Yufu, K.Sakanishi, Y.Korai, Fuel, 1988, 67, 114.