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Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 394-397
Hydroliquefaction of Coal with Tin Oxide Catalyst Mamoru Mlzumoto, Hlsao Yamashlta, and Shlmpel Matsuda Hitachi Research Laboratow, Hitachi LM., Hitachl-shi, Ibaraki-ken, 3 19- 12 Japan
Liquefaction of coal was studied by using three kinds of coals in the presence of various metal oxide catalysts under conditions of 7-15 MPa of hydrogen and 380-450 'C. Tin oxide catalyst showed the highest activity on the hydroliquefaction of a Japanese bituminous coal. The conversion of coal reached loo%, and the yield of n-hexanasoluble oil fraction was about 80%. Using three kinds of coals, it was found that the conversion of coal decreased as the amount of fmed carbon increased. Under the liquefaction condiions tin oxide catalyst was reduced to metallic tin. Metallic tin particles were molten and mixed with coal ash. Recovered ash that contained metallic tin particles showed almost the same activity as fresh tin oxide catalyst.
Introduction The mechanism of coal liquefaction has been a subject of many studies for the last decade. A mechanism including the following steps has been proposed (Neavel, 1976; Han and Wen, 1979): Initiation reaction is the formation of free radicals via thermal cleavage of bonds in coal (depolymerization). Reactive free radicals are stabilized by (a) autogenous hydrogen transfer, (b) hydrogen transfer from donor solvent, or (c) repolymerization. In the early stages of reaction, process a is predominant (Neavel, 1976). If solvent that has poor hydrogen-donating activity is used, process c becomes predominant, forming carbonaceous solids. Catalysts employed function on the hydrogenation of intermediates as well as regeneration of hydrogen-donor solvent (Han and Wen, 1979). Many kinds of catalysts have been tested in hydroliquefaction processes in order to improve the efficiency of coal conversion. Hydrotreating catalysts such as CoMo/A1203have been well-known as active catalysts for hydroliquefactionof coal. Bertolacini et al. (1977) screened activity of hydrotreating catalysts on liquefaction of coal using approximately 150 different kinds of catalysts. They reported that the conversion of coal was 90% at most. On the other hand, it is also well-known that tin compounds are active on coal liquefaction. In the 19209, a tinned-plate catalyst was patented in England (Strong, 1929). Weller et al. (1950) examined the catalytic activity of tin chloride, tin oxide, and metallic tin and reported that tin compounds showed high activity on coal liquefaction in combination with chlorine. Recently it was reported that tin oxide catalyst showed high activity on hydroliquefactionof Australian brown coal (Cochran et al., 1982) and Japanese bituminous coal (Mizumoto et al., 1983). The catalytic activity of tin oxide catalyst was higher than that of hydrotreating catalysts in both studies. Cochran et al. (1982) reported that gaseous hydrogen directly interacts with coal in the presence of tin oxide catalyst. In this paper we examine the catalytic activity of tin oxide on hydroliquefaction of coals. Three kinds of coals were used in order to examine the effect of fixed-carbon contents on coal conversion. The function and the working state of tin oxide catalyst are discussed. In view of practical application, the catalytic activity of used catalyst was also investigated. Experimental Section Materials. Two Japanese bituminous coals, Taiheiyo and Mi-ike, and one Chinese coal, Da-tong, were used in this study. Table I shows the composition of the three kinds of coals. Proximate analysis was performed by JIS 0196-4321/85/1224-0394$01.50/0
method. C, H, N, and S were measured by combustion. The metallic components in ash content is shown in Table 11. Coals were pulverized (0.1-0.4 mm) and used without drying. Catalysts were prepared by the following procedures. Fe203,MnO, and ZnO were prepared by precipitation from the corresponding metal nitrates. Co-Mo/A1203 was obtained from CCI Far East. Ni-Mo/Ti02 was prepared by impregnation. Titania support was obtained from Sakai Chemical Industry (CS 224). Tin oxide and titanium oxide were prepared by calcination of metastannic acid and metatitanic acid, respectively. Mixed oxide catalysts, Fe203-Ti02 and ZnO-Ti02, were prepared by mixing corresponding metal hydroxides with metatitanic acid. All catalysts were ground to pass a 200-mesh sieve (C74 ym) before use. Procedure. The experimental apparatus used in this study is shown in Figure 1. Reactions were carried out in a 300-mL autoclave made of stainless steel (SUS 316). Reactants were stirred during the reaction period. The autoclave reactor was operated in semibatch mode. Pressurized hydrogen was flowed through the autoclave during the reaction period. Coal (20 g) and creosote oil (40 g) were mixed with catalyst powder (1g) and put into the autoclave. In order to confirm gas sealing, the autoclave was filled with pressurized nitrogen. The nitrogen was then replaced by pressurized hydrogen. The autoclave was heated at a rate of 5 "C/min and maintained at the reaction temperature for 30 min. Effluent gas was sampled periodically and analyzed by a gas chromatograph. After cooling, the autoclave was depressurized and the contents were removed. The contents, which were a mixture of products and residue, were washed by n-hexane before filtration. Filtered cake was extracted by n-hexane and then by toluene with Soxhlet's extractor. The liquid fraction that was soluble in n-hexane was denoted as oil. The n-hexane-insoluble and toluene-soluble fraction was denoted as asphaltene. The conversion of coal and the yields of oil and asphaltene were defined by eq 1-3. (All quantities were weighed in conversion of coal (70)= [toluene-insoluble] x 100 (1) [input coal] [toluene-soluble] x 100 (2) [input coal] [ n-hexane-soluble] yield of oil ( % I = [input x 100 (3)
yield of asphaltene (%) =
dry, ash-free basis.) 0 1985 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24,
No. 3, 1985 395
Table I. ComDosition of Coal ~~~
~
coal Taiheiyo Mi-ike Da-tong
ash 13.9 16.2 9.7
proximate analysis, % moisture vm 5.1 43.8 2.6 37.2 1.9 28.9
Table 11. Metallic Components in Ash, % coal Si A1 Taiheiyo 23.9 19.8 Mi-ike 14.8 14.0 Da-tong 22.3 12.8
Fe 3.15 8.98 11.7
ultimate analysis, 70 fc 37.2 44.0 59.5
Ti 0.88 0.80 0.44
C
H
N
0
63.9 68.8 77.5
5.6 5.0 4.6
1.1 1.1 0.9
14.6 6.5 6.6
Ca 2.32 5.74 1.32
ME 0.98 1.21 0.29
S 0.25 1.93 0.42
K
Na 0.75 2.47 0.31
0.84 0.64 1.07
autoclave
.$
v
$ 60-
u
electric furmce
oil
+ 0
pv-4
U
Figure 1. Diagram of experimental apparatus. -0 none
temperature(0C)
0
Figure 3. Effect of reaction temperature on conversion of coal. Pressure of hydrogen, 15 MPa.
Fe203
Fez03-Ti 02 Ti02
MnO CoMolAl2O3
NI-MolTi02
ZnO -Ti 02 Sn02
";L * e . \ . 8
0
20 40 60 80 100 conversion of coal (%,daf)
Figure 2. Activity of catalysts for liquefaction of coal. Taiheiyo coal; reaction temperature, 450 OC; pressure of hydrogen, 15 MPa; reaction time, 30 min.
Toluene-insoluble residual solid was analyzed by electron micrography and X-ray diffractometer in order to observe used catalyst that was mixed with coal ash.
Results and Discussion Catalytic activity was measured at 450 "C under 15 MPa of hydrogen for Taiheiyo coal. Figure 2 shows the activity of catalysts tested. Fe203,Fe203-Ti02,Ti02, and MnO were less active catalysts, the conversion of coal being about 60%. Hydrotreating catalysts, Co-Mo/A1203 and Ni-Mo/Ti02, showed higher activity than the abovementioned catalysts. The titania-supported Ni-Mo catalyst was more active than the commercially available alumina-supported Co-Mo catalyst. In the case of Sn02,the conversion of coal reached loo%,and the yield of oil was 80%. The following section of this paper describes the effects of reaction temperature, hydrogen pressure, and coal type on the conversion of coal investigated by using tin oxide catalyst. Taiheiyo coal was employed as standard. The effect of reaction temperature on the conversion of coal is shown in Figure 3. The yields of gas, oil, and
10
12
14
pressure(MPa)
Figure 4. Effect of hydrogen pressure on conversion of coal. Reaction temp, 450 OC.
asphaltene are shown in the figure. The reaction temperature ranges from 380 to 450 "C under 15 MPa of pressurized hydrogen. The yield of asphaltene increased by 3 times while the conversion of coal decreased slightly when the reaction temperature was lowered below 400 "C. Conversion of asphaltene to oil and gas seems to become faster as the reaction temperature rises from 380 to 450 "C. Figure 4 shows the effect of hydrogen pressure on the conversion and the yield of each product. The pressure of hydrogen was increased from 7 to 15 MPa at a constant temperature at 450 OC. Figure 4 indicates that the conversion of coal decreased markedly when the pressure of hydrogen was reduced below 10 MPa. It is found that the conversion of coal is strongly affected by the pressure of hydrogen. On the other hand, lowered temperature has a large effect on the yield of asphaltene and has a little effect on the conversion of coal, as shown in Figure 3. The optimum conditions for liquefaction of coal with tin oxide catalyst are temperatures from 420 to 450 OC and pressures above 10 MPa. The effect of coal type was examined by using two Japanese and one Chinese bituminous coals. Figure 5 shows the conversion of coal as a function of fixed carbon.
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Ind. Eng. GI".Rod. Res. Dev.. Vol. 24, No. 3. 1985
I
"
100,
0
'0
-
0,
40
30
70 amount of fixed-carbonPI.)
A0
50
60
80
Figure 5. Effect of fixed carbon on conversion of mal. o Sn02
(a)
10008,
Figure I . Electron micrograph of toluene-soluble residue.
fresh used - 1 used -2
0
I 10
I 20
I
.I
30
40
50
60
2 e (degree) Figure 6. X-ray diffraction pattems of (a) fresh and (b) used catalysts (Cu Ko. A = 1.54 A).
The conversion of coal decreased as the amount of fixed carbon increased. It is reasonable that coalwhich contains more fixed carbon has lower reactivity on liquefaction, because the content of fixed carbon increases as carbonization of coal proceeds in general. The effect of coal type on conversion of coal has been studied extensively. Yarznb et al. (1980)measured the conversion of 104 kinds of coals and found that the amount of volatile matter had the largest correlation coefficient with the conversion of coal. The reaction conditions of hydroliquefaction are so reductive that many kinds of catalytic components exist in reduced state in a reactor. In order to examine the state of catalyst components, observations by electron micrography and X-ray diffractometer were performed. Figure 6a shows the X-ray diffraction pattern of fresh tin oxide catalyst, and Figure 6b shows that of residue which contained used catalyst. The diffraction pattern of Figure 6a shows the existence of rutile-type SnO, only. It is found in Figure 6b that diffraction peaks axribed to metallic tin were observed. Therefore it is clear that tin oxide is completely reduced to metallic tin under the reaction conditions. It is considered that added tin oxide catalyst exists in the molten-metal state under the liquefaction conditions because the melting point of tin is 232 OC. Figure I shows an electron micrograph of toluene-insoluble residue after hydroliquefaction with tin oxide catalyst. Metallic tin particles were dispersed on coal ash, and the radius of the tin particles was a few hundred A. Tin particles were not gathered into a large agglomerate during the reaction period, despite the tin particles being molten. I t is of practical as well as scientific interest to know whether the used tin catalyst dispersed on coal ash has an activity on the hydroliquefaction. In the first experiment 1g of coal ash that contained about 0.22 g of the used tin catalyst was mixed with coal slurry and hydroliquefaction
I
LO €0 80 loo conversion d coalPl..daf)
20
Figure 8. Activity of fresh and used tin oxide catalysts. U d - 1 and -2 catdyxts were taken from the tolueneinsoluble residue produced after the reaction with fresh and uaed-1 catalysts, reapectively. Tsiheiyo mal: weight of catalyst. 1 g: reaction temperature, 450 "C; pressure of hydrogen, 15 MPa; reaction time. 30 mi".
was carried out. In the second experiment 1g of coal ash that was obtained in the first experiment was employed as a catalyst. In the latter case the catalyst contained about 0.05 g of tin (tinfcoal = 0.003). The experimental results are shown in Figure 8. The conversion of coal was 100% and 98% in the first and second experiments, respectively. Thus it is found that the tin catalyst which is mixed with coal ash can be used repeatedly on the coal liquefaction. The used tin catalyst has an especially high activity, since the conversion of coal is 98% even a t the tin/coal ratio of 0.003. I t has been proposed that a hydroliquefaction catalyst functions in two ways (Han and Wen, 1979): (a) hydrogenation of intermediates formed in thermal cleavage of coal and (b) regeneration of solvent with hydrogen-donor nature. It is well-known that the elements of groups 6.16, and 18 in the periodic table, for example Mo,W, Co, and Ni, have a high activity for hydrogenation. [In this paper the periodic group notation is in accord with recent actions by IUPAC and ACS nomenclature committees. A and B notation is eliminated because of wide confusion. Groups Ia and IIA become groups 1and 2. The d-transition elements comprise groups 3 through 12, and the p-block elements comprise groups 13 through 18. (Note that the former Roman number designation is preserved in the last digit of the new numbering.)] Therefore hydrotreating catalysts are frequently tested in liquefaction of coal from the viewpoint of their hydrogenation activity (Bertolacini et al., 1977). It is also well-known that tin compounds are less active for hydrogenation of unsaturated hydrocarbons in general. On the other hand, tin chloride has been known as a good catalyst for coal liquefaction, and recently tin compounds such as tin oxide, metallic tin, and tin chloride have been shown to have an excellent activity on liquefaction of brown coal (Cochran et al., 1982). In this study it has been found that the tin oxide catalyst has much higher activity on coal liquefaction than ZnOTiO,, Ni-MofTiO,, Co-Mo/Al,O,, and Fe,O* The converison of Japanese bituminous coal (Taiheiyo) reached 100%. of which the yield of oil was 80%under the present
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 397-401
FRAGMENTS
MOLTEN Sn
/""V
repolymerization U'
"
COKE
sta bil i zat ion
4 hydrogenat ion
1 OIL , ASPHALTENE
Figure 9. Reaction scheme of hydroliquefaction of coal with tin oxide catalyst.
conditions. The tin oxide catalyst is reduced to metallic tin, which is present as small lriolten tin particles dispersed in coal slurry under the liquefaction conditions. A reaction scheme of hydroliquefaction of coal with tin oxide catalyst is shown in Figure 9. Fragment radicals formed by thermal cleavage of coal would be stabilized on the molten tin surface. Repolymerization is strongly suppressed by the stabilization effect of molten tin, probably. Almost all fragment radicals formed are hydrogenated to products such as oil and asphaltene. The tin catalyst used twice repeatedly maintained a high activity, indicating that the catalyst was not deactivated significantly. Deposition of carbonaceous materials on the catalyst surface, which is usually the major cause of deactivation of the hydrotreating catalyst, is insignificant in the case of molten tin catalyst. The high activity exhibited by the used tin catalyst results from the fact that the catalyst is not deactivated during the hydroliquefaction reaction.
397
It is of practical importance that the tin catalyst has a high activity and can be used repeatedly in the liquefaction of coal. The high activity of the tin catalyst brings in a high yield of liquid products, and repeated use of the catalyst reduces the amount of catalyst usage. In order that coal liquefaction with tin catalyst be employed on a commercial scale, a recovery process for tin must be developed, since the tin catalyst in a powder form is always mixed and diluted with coal ash after usage. A study on the hydrogenation of model compounds typical of coal structure, such as dibenzyl ether and bibenzyl, has been undertaken in order to elucidate a reaction mechanism in the presence of tin oxide catalyst. The results will be published shortly. Acknowledgment
We are grateful to R. Kaji of Hitachi Research Laboratory for chemical analysis of ash. Registry No. SnOz, 18282-10-5; Fe203, 1309-37-1; Ti02, 13463-67-7;MnO, 1344-43-0;ZnO, 1314-13-2;Co, 7440-48-4;Mo, 7439-98-7; Ni, 7440-02-0. Literature Cited Bertolacinl, R. J.; Gutberlet, L. C.; Kim, D. K.; Robinson, K. K. EPRl AF-547 Project 408-1, 1977. Cochran, S. J.; Hatswell, M.; Jackson, W. R.; Larkins, F. P. Fuel 1982, 6 1 , 831. Han, K. W.; Wen, C. Y. Fuel 1979, 58, 779. Mizumoto, M.; Yamashita, H.; Matsuda. S. Prepr. P a p . Am. Chem. SOC. Div. Fuel Chem. 1983, 28, 218. Neavel, R. C. Fuel 1976, 55, 237. Strong, H. W. British Patent 335 215, 1929. Weller, S.;Pelipetz, M. G.; Friedman, S.;Storch, H. H. Ind. Eng. Chem. 1950, 42, 330. Yarzab, R. F.; Given, P. H.: Spackman, W.; Davis, A. Fuel 1980, 5 9 , 81.
Received for review September 10, 1984 Accepted March 18, 1985
Kinetics of the Vapor-Phase Hydrogenolysis of Methyl Formate over Copper on Silica Catalysts Danlele M. Montl, Mark S. Walnwrlght," and Davld L. Trimm School of Chemical Engineering and Industrial Chemistty, The University of New South Wales, P.O. Box 1. Kensington, New South Wales, 2033 Australla
Noel W. Cant School of Chemistry, Macquarie University, North Ryde, New South Wales, 21 13 Australia
The kinetics of the hydrogenolysisof methyl formate to methanol on ion-exchanged copper on silica catalysts was studied in a recycle reactor at temperatures from 120 to 190 O C and atmospheric pressure. The rate data were fied by a power law model in which the reaction orders with respect to the reactants, methyl formate and hydrogen, were 0.39 and 0, respectively. Carbon monoxide produced by the decarbonylation of methyl formate was shown to inhibit the hydrogenolysis reaction, and a reaction order of -0.17 with respect to CO was found. At CO concentrations higher than 1-2 % a continuous loss of catalyst activity was observed.
Introduction
Methanol manufacture on an industrial scale is currently based on the hydrogenation of carbon monoxide over Cu/ZnO catalysts containing alumina or chromia at pressures ranging from 90 to 110 bar and temperatures 0196-432 118511 224-0397$01.50/0
around 250 "C. Kung (1980) and Klier (1982) have comprehensively reviewed the catalytic and mechanistic aspects of this conventional route to methanol. An alternative two-stage process for the production of methanol involving the carbonylation of methanol to 0 1985 American
Chemical Society
