I n d . Eng. Chem. Res. 1988,27, 1783-1788
W , = apparent solid concentration of char, g/cm3 x = coordinate in solid, cm Yi = yield of product i, g/g of cellulose
Greek Symbols az = stoichiometric coefficient of reaction 2 a s = stoichiometriccoefficient for gas formation from reaction 3 agr= stoichiometric coefficient for char formation from re-
action 3, =0.35 t
= void fraction
7 = heating rate, OC/s
initial gas density, mol/cm3 cellulose density, =1.4 g/cm3 CJ = Stefan-Boltzmann constant, =1.36 X 7 = optical thickness 13(x) = SI" e - x t / t 3dt
po = pe =
cal/(s.cm2-K4)
Subscripts
0 = initial condition ac = activated cellulose
L = tars c = cellulose f = fiber G = gases s = surface r = char Registry NO.CO, 630-08-0;COZ, 12438-9; Hz, 1333-74-0;CH4, 74-82-8; C2H4,74-85-1; C2Ha,74-84-0; cellulose, 9004-34-6.
Literature Cited Agarwal, R. K.; McCluskey, R. J. Fuel 1985,64,1502. Antal, M. J., Jr. "Biomass Engineering: Thermochemical Conversation Research Needs". Report of the Kona Workshop, June 1984; Hawaii Natural Energy Institute. Antal, M. J., Jr. Fuel 1985,64, 1483.
1783
Bains, M. S. Carbohydr. Res. 1974,34,169. Bradbury, A. G. W.; Sakai, Y.; Shafizadeh, F. J. Appl. Polym. Sci. 1979,23,3271. Broido, A. Symp. Therm. Uses and Properties Carbohydrates and Lignins; Shafizadeh, F., Sarkanen, K. V., Tillman, M., Eds.; Wiley: New York, 1976; Vol. 19. Chan, W. R.; Kelbon, M.; Krieger, B. B. Fuel 1985,64, 1505. Fan, L. S.; Fan, L. T.; Tojo, K.;Walawender, W. P. Can. J. Chem. Eng. 1978,56, 603. Hajaligol, M. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Ind. Eng. Chem. Process Des. Deu. 1982,21,457. Hottel, H. C.; Sarofim, A. F. Radiative Transfer;McGraw-Hil: New York, 1967. Kansa, E. J.; Perlee, H. E.; Chaiken, R. F. Combust. Flame 1977,29, 311. Kanury, A. M. Combust. Flame 1972,18,75. Kim, N. W.; Trautz, J. A.; Miller, D. J. IGT Energy from Biomass and Wastes XI, Orlando, FL, March 16-20, 1987; Paper #40. Kothari, V.; Antal, M. J., Jr. Fuel 1985,64, 1487. Kung, H. C. Combust. Flame 1972,18,185. Madorsky, S.L. Thermal Degradation of Organic Polymers; Interscience: New York, 1964. Mok, W. S.-L.; Antal, M. J., Jr. Thermochem. Acta 1983a,68, 155. Mok, W. S.-L.; Antal, M. J., Jr. Thermochem. Acta 1983b,68,165. Perry, R. H., Chilton, C. H. Eds. Chemical Engineer's Handbook, 5th ed.; McGraw-Hill: New York, 1973. Prokorov, A. B.; Cergeva, B. H.; Fainber, E. E.; Kalnins, A. R. Chem. Wood Mat. 1978,3,18. Scott, D. S.; Piskorz, J. Can. J. Chem. Eng. 1982,60, 666. Shafizadeh, F. J. Appl. Polymer Sci.: Appl. Polymer Symp. 1983, 37,723; Adu. Carbohydr. Chem. 1968,23,419. Shafizadeh, F.; Fu, Y. L. Carbohydr. Res. 1973,29,133. Sincovec, R. F.; Madsen, N. K. ACM Trans. Math. Software 1975, 1 (3), 232. Smith, J. M. Chemical Engineering Kinetics, 3rd ed.; McGraw-Hill: New York, 1981. Woodside, W.; Messmer, J. H., Jr. J. Appl. Phys. 1961,32, 1688.
Received for reuiew November 3, 1987 Revised manuscript received May 24, 1988 Accepted June 27, 1988
Catalytic Hydrotreatment of Vacuum Pyrolysis Oils from Wood Jean Gagnon and Serge Kaliaguine* Department of Chemical Engineering, Uniuersit6 Laval, Ste-Foy, Quebec G1K 7P4, Canada
T h e effects of a mild hydrogenating pretreatment in the presence of a Ru catalyst over the hydrodeoxygenation (HDO) of wood-derived vacuum pyrolysis oil have been investigated. The optimal conditions found for this pretreatment are a temperature as low as 80 "C and a pressure of 600 psig. T h e results indicate t h a t the yield of HDO is correlated with the average molecular weight of the products determined from gel permeation chromatograms. This suggests t h a t polymerization/ hydrogenolysis reactions are occurring in HDO conditions. It is also found that some hydrogenolysis is produced during the hydrogenating pretreatment. Upgrading of biomass pyrolytic oils involves essentially the removal of oxygen from a variety of organic compounds, and this can be performed by hydrodeoxygenation (HDO). This type of process has been the object of much less work than the related reactions of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN). Early works on HDO were reviewed by Weisser and Landa (1973). More recently, Furimsky (1978,1979,1983a-c) studied HDO of various feedstocks and reported kinetics and mechanisms for the HDO of furan and tetrahydrofuran. The deoxygenation of dibenzofuran was examined by Badilla-Ohl-
* To whom correspondence
should be addressed.
0888-5S85/88/2627-1~83$01.50/0
baum et al. (1979) and Krishnamurthy et al. (1981). Ternan and Brown (1982) performed HDO of coal distillate liquids, with high oxygen contents. High rates were observed although only the smaller oxygenated compounds (for example, phenols) were reacted. Bredenberg et al. (1982) hydrotreated lignin degradation liquids. They report that only phenols and cresols are completely converted, whereas higher molecular weight compounds are almost not reacting. Chum and her group (Johnson et al., 1986) investigated recently the conversion of lignin into phenols and hydrocarbons by mild HDO and the hydrotreatment of lignin model compounds such as 4-propylguaiacol (Ratcliff et al., 1987). Train (1986) developed a 0 1988 American Chemical Society
1784 Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988
Monte-Carlo simulation of the HDO of lignin, utilizing kinetic constants derived through HDO experiments conducted with various lignin model compounds. Wood-derived liquids from various processes have been successfully hydrodeoxygenated by Soltes and Lin (1984) and by Elliot (1983a). Preliminary experiments performed in our laboratory (Gagnon, 1987) have confirmed the difficulty already reported by Elliot (1983b) in performing HDO of wood-derived pyrolysis oils. In our tests, vacuum pyrolysis oils could not be heated over 200 "C without heavy polymerization or coking. Similar difficulties were also met by Baker and Elliot (1987) in hydrotreating Georgia Tech pyrolysis oils. Before HDO could be performed at typical conditions (350 "C, 2000 psig, CoMo/ 7-A1203),a first hydrogenation step was performed a t milder conditions (250-270 "C, low pressure, CoMo/rA1,OJ to prevent heavy coking. It thus seems that among wood-derived liquids vacuum pyrolysis oils are the most difficult to treat by HDO. The reason for this must be associated with peculiarities of the chemical composition of vacuum pyrolysis oils. They are known (Pakdel and Roy, 1987) to contain very high amounts of carboxylic acids. Moreover, it was shown recently that the total content of monosaccharides obtained by acid hydrolysis (pH 1.3-1.5,lOO "C) of a typical vacuum pyrolysis oil (Roy et al., 1987) suggests that these oils may contain up to 7-8 wt % of oligo- and monosaccharides. Coking may thus be visualized as the polymerization and condensation of these saccharides and other compounds with aldehyde functions such as furfural, under the catalytic action of carboxylic acids. In such a case, coking might be prevented by mild hydrogen treatment of aldehydic functions. Such reactions have been intensively studied over the years. Wisniak et al. (1974) and Wisniak and Simon (1979) for example compared rhodium, nickel, and ruthenium catalysts in the hydrogenation of glucose and fructose and found ruthenium to be the most active catalyst. Bizhanov and Drozdova (1982) studied the kinetics of the hydrogenation of glucose to sorbitol over 5% Ru on A1203. Vasyunina et al. (1960, 1964, 1969) studied the activity of Ru catalysts in the hydrogenation of monosaccharides, hydrolyzed cellulose, and wood. In this last case, they report a two-step process. The first step is the hydrogenation of polysaccharides at 160-200 "C and 30-50 atm a t acidic conditions. The second step is the hydrogenation of lignin at 280-320 "C and 50-70 atm in alcoholic media. Ninety-five percent of the saccharides and 35% of the lignin are reacted at these conditions. Vasilakos and Sequera (1983) reported high yields of sorbitol in the hydrogenolysis of cellulose over a ruthenium catalyst. In the present paper we intend to investigate the effect of a mild hydrogen pretreatment of vacuum pyrolysis oils using a ruthenium catalyst on the effectiveness of a subsequent HDO step.
Experimental Setup and Procedure The oil feeds used in this work were from the same mixture of vacuum pyrolysis oils produced in one operation of the Process Demonstration Unit described by Roy et al. (1985). They were obtained at typical vacuum pyrolysis conditions, namely, a t a pressure of 10 Torr and hearthes temperatures from 200 to 425 "C. Fractions collected at primary condensers were blended with the ones from secondary condensers which were vacuum evaporated in order to maintain the water content in the final mixture close to 10 wt %. The chemical composition of vacuum pyrolysis oils was described recently by Pakdel and Roy (1987). The hydrogenation and HDO were performed in a batch slurry reactor described in Figure 1. This reactor
U
dl
Figure 1. Experimental setup: 1, reactor; 2, turbine; 3, magnetic stirrer; 4,belt; 5, motor; 6, reactor head; 7, thermowell; 8, heating bands; 9, temperature controller; 10, gas feed; 11, mass flow controller; 12, compressor; 13, gas inlet; 14, pressure gauge, 0-500 psig; 15, pressure gauge, 0-5000 psig; 16, liquid sampling; 17, gas sampling.
is provided with a magnetic stirrer and a turbine mounted on a hollowed shaft allowing gas recirculation through the liquid phase. Provision is also made for gas and liquid sampling at various times in the course of an experiment. The gas feed was pure hydrogen from Linde (research grade). The mild hydrogenation pretreatment was performed in the presence of a 5% Ru/y-A1203commercial catalyst purchased from Aesar, Johnson and Matthey. Copper chromite catalyst, also from Aesar, was also tested for hydrogenation. The HDO catalyst was prepared by successive impregnations of 7-A1203 (Catalytic Products) with ammonium metatungstate (ICN Pharmaceuticals) and cobalt nitrate (Aldrich Chemicals) with calcination at 500 "C after each impregnation. This catalyst contained 3 wt % Co and 13 w t % W. The experimental procedure involved introducing 400 g of vacuum pyrolysis oils and 20 g of Ru catalyst in the reactor and purging with hydrogen a t room temperature. The temperature and hydrogen pressure were raised in order to reach simultaneously within about 20 min the target values chosen for the hydrogenation step. At this time (tho),the gas feed was stopped and the temperature was maintained constant. Gas and liquid were sampled a t hydrogenation times t h = 0, 5, 15, 30, 60, 90, and 120 min. Pressure was read before sampling. After 2 h, heating was stopped and the reactor was allowed to cool down to a temperature just below 100 "C. The autoclave was then opened, and 12 g of NiO-W03/7-A1203catalyst was introduced in the reactor. Then the temperature and pressure were again raised until the standard conditions (325 "C, 2500 psig) were reached simultaneously. This transient process lasted about 20 min. HDO was then performed a t constant temperature and pressure for 2 h with samples taken at HDO times th&, = 0,30,60,90, and 120 min. Liquids were analyzed for C, H, N elemental composition using a F & M CHN 185 system, oxygen being determined by difference. As the liquid samples collected were in the form of an emulsion, a procedure involving vigorous agitation and rapid freezing was developed in order to ensure representativeness of the sample fractions analyzed. Gel permeation chromatography (GPC) of liquid samples was also performed by using a Perkin-Elmer 3B liquid chromatograph fitted with refractive index detector
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1785 Table I. Experimental Conditions and Analytical Results hydrogenation step conditions
expt 1 2 3 4 5 6 7 8 9 10
temp, OC 120 80 140 80 100 120 140 80 140 120
pressure, psig 1000 600 600 1000 1000 1000 1000 1500 1500 1000
w t % H20 a t
catalyst none Ru Ru Ru Ru Ru Ru Ru Ru CuCr
tH
10.5 9.6 12.6 10.9 18.4 13.6 15.7 10.5 10.5 10.2
wt%Cat
t H = 0 min 59.2 56.6 56.0
58.6 61.3 58.5 62.1 57.4 58.9 55.6
t w = 60 min.
tH
= 120 min 59.4 52.6 60.0 56.9 65.8 61.7 63.7 58.0 62.1 52.0
tHW
8.0 5.0 17.8
= 120 min 25.5" 11.0b 26.4b 13.0 10.9 17.7 20.4" 2Mb
11.1
19.9 17.1 20.9 5.0 24.1 3.6
O F
wt%Hat tHD0
expt 1 2 3 4 5 6 7 8 9 10
t H = 120 min
= 0 min
=
120 min 85.5" 72.0b 88.6b 75.9 75.6 74.3 73.3" 72.76
t~ = 0 min 5.8 5.0 5.3 6.1
tH
2.8 4.4 6.4 4.8 6.1 7.7
= 120 min
tmo = 120 min
2.9 5.5 6.0 5.2 5.1 5.5 2.7 5.6 3.7 5.1
tH
= 0 min
tH
0.44 0.50 0.52 0.45 0.44 0.48 0.38 0.49 0.43 0.50
5.2" 5.6b 5.6b 3.3 7.2 6.1 4.1" 8.6b
tHM) = 120 min
= 120 min
0.48 0.59 0.42 0.50 0.33 0.40 0.39 0.47 0.41 0.62
0.08' 0.23b 0.Ofib 0.21 0.17 0.20 0.23" 0.196
tmo = 90 min.
LC-25 using p-styragel columns of 100, 300, lo3, and lo4 A. The solvent used for these analyses was distilled THF fed a t a flow rate of 1.5 cm3/min. The calibration curve was obtained using polyethylene glycol standards (Gagnon, 1987). The water content in the liquid samples was determined using a Karl-Fisher Automat Model Dosimat 655 from Metrohom and Hydranal-5 (or Hydranal-2) as the reactant. Gas analyses were obtained by using two gas chromatographs. A chromalyzer 100 system equipped with molecular sieve 5-A columns with argon as the carrier gas was used for hydrogen analysis. A Perkin-Elmer Sigma 115 GC equipped with a Porapak Q column and hot wire as well as FID detectors, with helium carrier gas, allowed analysis of the gaseous constituents. Results The experimental conditions for experiments 1-10 are reported in Table I, along with analytical results for the liquid phase taken at nominal times tH = 0, tH = 120 min, and t H D o = 120 min. Experiment 1is a blank performed in the absence of any catalyst during the hydrogenation step. No results are reported after the end of the HDO step because heavy polymerization occurred during this step. The same situation happened in experiment 10 where the hydrogenation catalyst was copper chromite. The water content of liquid samples collected a t the nominal times mentioned is also given in Table I. These data were used to calculate the elemental composition of the organic content of the reactor from the composition of the samples collected. This composition is shown in Table I a t initial time tH = 0 and at the end of both hydrogenation and HDO steps. More complete data for the evolution of this composition with time are shown for experiment 2 in Figure 2. Obviously, whereas the global elemental composition of the organic content of the reactor is not affected by the hydrogenation step, a rather fast deoxygenation is effectively taking place during the HDO step. In this particular case, the hydrotreatment had to be stopped after 60 min because hydrogen in the gas phase was almost entirely converted. The other main components in the gas phase were carbon monoxide, methane,
/i-
901
=
60
.\" 50 c
I
Carbon
c 0
o Oaygen
5
+ Hydrogen
._
20 101 ++-+-+-+-+
-, ++
++-,
+
Figure 2. Carbon, oxygen, and hydrogen concentration of the liquid versus time (experiment 2).
.
-
r ,
I
Erprimenl # 8 I
Experiment #
9
1000
I
g
800
Experiment # 2
e
=
200
0
10
20
30
40
50
1,
60
70
80
90
100
110
120
(mid
Figure 3. Typical hydrogen partial pressure variation versus time during pretreatment step.
ethane, propane, butane, and pentane. Figures 3 and 4 show typical curves for the evolution of the hydrogen partial pressure during hydrogenation and HDO steps, respectively.
1786 Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988
7 7 7000
\
tHoO ( m i d
Figure 4. Typical hydrogen partial pressure variation versus time during HDO step. 16
18
Time (min) 20 22 24
-
26
28
102
13
I
0
I
630
118
60
90
120
1, (min)
M W (g/mole)
70000 11000 1220
30
30
,,,t
I
1
60 90 (mid
Figure 6. Molecular weight versus time for experiment 7. Table 11. Average Molecular Weight (g mol-') of the Liquid Samples (Nontreated Oil: 1775 g mol-') expt t H = 0 min t H = 120 min tHnn = 120 min 1 2490 2940 2 1290 3030" 1040 1990 3 3100b 1150 1830 4 26606 5 1670 1190 4790 6 2160 1070 2900 7 1520 3310 2860 2010 8 2760 5120" 9 4220b 2790 2940 3040 10 2580 (I
2- 1, = 5 min
3- I, = 30 min 4- 1, = 90 min 5 - t H : 120 min 6- IHm = 0 min 7-IHoo:30min 8 - tHDO: 60 min 9- iHDO: 120 min
6 to 9 lscole 1/10)
Figure 5. GPC spectra for the liquid samples of experiment 7.
These data are not considered precise enough to be used for quantitative kinetic analyses of the two processes. The major sources of imprecisions are as follows: The volume of the gas phase is not precisely known, and it may vary during the reaction. The gas and liquid sampling is made manually so that the associated changes in the volume of the two phases are not precisely controlled. Errors on the measurements of the total pressure and the gas-phase molar fractions are both affecting the precision of partial pressure data. Nevertheless, the following qualitative features can be deduced from the variations reported in Figures 3 and 4 and from the oil analytical data in Table I: (1) Hydrogen consumption during the hydrogenation step is more important in experiments 3 and 9 than during experiments 2 and 8, respectively, indicating that this total consumption is increasing with hydrogenation temperature and pressure. At a temperature as low as 80 "C (experiments 2 and 81, a small but significant hydrogen consumption is still observed during the pretreatment. (2) Hydrogen consumption during the HDO step is much faster when the hydrogenation step is performed at 80 "C (experiments 2 and 8) than at 140 "C (experiments
tHD0
= 60 min.
tHD0
= 90 min.
3 and 9). In all cases, an acceleration in hydrogen consumption is observed after 30-40 min of hydrodeoxygenation. (3) The most efficient HDO treatment as revealed by the organic O/C ratio in the liquid phase (Table I) is obtained when both hydrogenation temperature and pressure are at their lowest (experiments 2 and 4). Figure 5 represents the GPC spectra from the liquid samples collected during experiment 7, both for the hydrogenation (curves 1-5) and the HDO steps (curves 6-9). Frpm such chromatograms, an average molecular weight (M,) can be calculated for each liquid sample as -
M, =
~
CM,Ai CAi
where Ai is a surface area increment under the chromatographic curve. The curves for M,,, as a function of sampling time during experiment 7 are reported in Figure 6. A steady increase in M , during the hydrogenation step indicates that some oligomerization of carbohydrates is taking place at a temperature as low as 140 "C in spite of the hydrogenation reactions. These polymerization reactions are accelerated during the heating period which brings the reactor a t the HDO temperature of 325 "C, as a steep increase in Mw is observed a t time tHDo = 0. However the average molecular weight again decreases during the HDO treatment to reach a value slightly higher than the one a t the end of the hydrogenation step. Characteristic values for MWare given in Table 11. A t the end of the HDO step, rather high values of Mw are observed in all cases which indicates that the drastic polymerization effect observed in the absence of hydrogen-
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1787 ation pretreatment is still operative but a t a much less significant level. As experiments conducted a t hydrogenation pressure of 600 psig (experiments 2 and 3) yield Mw values, at the end of the HDO step, significantly smaller than the ones at 1500 psig (experiments 8 and 9), it seems that the low-pressure hydrogenation pretreatment allows a better control of the polymerization in HDO conditions.
:
101
I
I
v2
Discussion The hydrogenation of glucose to sorbitol H
I
H
I
01 2500
OHH
I
I
CHlOH-C-C-C-C-CHO
+
-
H2
I I HI OH I H
OHH
I I I I CH2OH-CC-C-C-C-CHpOH I
I
OH OH
I
1
3500
I
I
4500
I
I
I
-M W 5500 (glmole)
I
6500
I
I
7500
I
Li
8500
Figure 7. Oxygen concentration versus molecular weight of the liquid samples.
OH OH
H
1
I
(
1)
OH
is typical of the hydrogenation of monosaccharides which is performed during the course of the hydrogenation step. As polymerization during subsequent HDO is rather effectively controlled for the hydrogenation temperature as low as 80 "C, it may be concluded that the conversion of the aldehyde function by reaction 1 is achieved in these conditions. The stoichiometry of reaction 1indicates that complete conversion would yield a 2/12 increase in hydrogen content so that assuming arbitrarily a maximum value of 30 wt % content of compounds equivalent to monosaccharides in the oil would imply a maximum increase in hydrogen content by this reaction of 5%. This value is in the order of magnitude for the percentage of error on the determination of the H content by elemental analysis. This explains why the H% value in Figure 2 is almost constant even though the conversion of aldehydes must be close to complete given the good HDO conversion observed in experiment 2. As the hydrogen comsumption during the first step increases with both temperature and pressure, it might be suggested that both factors favor hydrogen consumption by reactions parallel to monosaccharides hydrogenation. For some yet unrevealed reason, it seems that a low hydrogen consumption during the first step yields a faster and more complete HDO (compare Figures 3 and 4), so the best hydrogen pretreatment is obtained at the lowest temperature and the lowest pressure of the experimental plan. The absolute value for the molecular weights determined by GPC might be in error because the GPC retention times depend not only on molecular size but also on the functionalities of the chemical compounds. The standards used in obtaining calibration curves must therefore bear the same chemical groups as the analyzed compounds. As the choice of standards is necessarily arbitrary because wood oils are complex mixtures the components of which are not completely identified, some uncertainty is unavoidable. The data however are a valuable tool for comparison purposes. From experiment 1, for example, it can be concluded that, in the absence of a catalyst, polymerization is already detected a t 100 OC since the data from Table I1 indicate a significant increase in average molecular weight between t H = 0 and tH = 120 min. This polymerization must even start at temperatures below 100 "C, as a difference in MW is even observed between Mw at t H = 0 CMw= 2490) and the value 1775 observed for the unreacted oil. It is interesting to note from Table I1 that very similar Mwvalues are obtained in experiments 10 and 1, suggesting that the
copper chromite catalyst is not active for the reaction under study. Figure 7 shows that the oxygen content in the organic fraction of the liquid in the reactor during the HDO step is correlated with average molecular weight of the liquid samples. Most of the points on this figure correspond to the end of the HDO step, except for those from experiment 7 which correspond to various HDO times during this experiment. This correlation indicates that those oils which have experienced the least polymerization are more efficiently hydrodeoxygenated. It may therefore be suggested that as the molecular weight increases entanglement of linear chains would occur so that oxygen atoms in these chains would be sterically hindered from contacting the active sites on the HDO catalyst surface. Simultaneously these bulkier molecules may absorb on the catalyst particles, thus preventing access of the smaller molecules to the catalyst pores. This plugging effect would also contribute to the decreased catalytic HDO activity when the pretreatment temperature is raised, as observed in Figure 4. Some of the M,,,'s observed during the hydrogenation step are significantly lower than the value for untreated oil (for example experiment 2, Table 11). One may therefore conclude that the ruthenium catalyst can favor hydrogenolysis as well as aldehyde hydrogenation, a t the low temperatures of the hydrogenation step. Moreover hydrogenolysis is also significant during HDO. This is illustrated by the HDO curve in Figure 6 which shows very clearly that the oil average molecular weight decreases significantly as HDO proceeds. This process follows the steep increase in molecular weight observed after the reactor was heated to 325 "C. In both hydrogenation and HDO steps, it may thus be considered that catalytic hydrogenolysis is in competition with thermal polymerization. Since as discussed before the higher molecular weight compounds are the most difficult ones to deoxygenate, the progressive hydrogenolysis would therefore be at the origin of the induction period observed for hydrogen consumption during HDO (see Figure 4). Indeed the acceleration in hydrogen consumption would then occur only when the oil molecules reach a sufficiently low molecular weight for HDO to proceed rapidly. The longer induction period observed after a pretreatment conducted a t 140 "C compared to 80 "C (see Figure 4) would therefore be associated with a more significant thermal polymerization prior to the HDO step. Conclusion A catalytic pretreatment allowing hydrogenation/ hydrogenolysis of mono- and oligosaccharides a t very mild conditions is proposed as a means of controlling the catastrophic polymerization/coking observed when vacuum
Ind. Eng. Chem. Res. 1988,27, 1788-1792
1788
pyrolysis oils derived from wood are heated to the temperature levels necessary for HDO. This treatment involves the use of a supported ruthenium catalyst. I t was shown to be quite effective, as it permitted high HDO conversions to be reached for vacuum pyrolysis oils which, contrary to the other wood-derived liquids, are deemed to be impossible to hydrotreat. Registry No. Ru, 7440-18-8; Co, 7440-48-4; W, 7440-33-7.
Literature Cited Badilla-Olhbaum, R.; Pratt, K. C.; Trimm, D. L. “A Study of Nickel-Molybdate Coal-Hydrogenation Catalysts Using Model Feedstocks”. Fuel 1979, 58, 309-314. Baker, E. G.; Elliot, D. C. “Catalytic Hydrotreating of Biomass-Derived Oils”. Prepr. Pup.-Am. Chem. SOC.,Diu. Fuel Chem. 1987, 2, 257-263. Bizhanov, F. B.; Drozdova, R. B. “Studies of the Kinetics and Mechanism of Glucose Hydrogenation with Ruthenium Catalyst”. React. Kinet. Catal. Lett. 1982, 1-2, 35-39. Bredenberg, J.; Huuska, M.; Raty, J.; Korpio, M. ”Hydrogenolysis and Hydrocracking of the Carbon-Oxygen Bond”. J . Catal. 1982, 77, 242-247. Elloit, D. C. “Hydrodeoxygenation of Phenolic Components of Wood-Derived Oil”. Symposium on Heavy Oil and Residua Proceeding, Seattle, March 20-25 1983a. Elliot, D. C. Final Report, Vol. 4, IEA Co-operative Project D1, Biomass Liquefaction Project, 198313. Furimsky, E. “Catalytic Deoxygenation of Heavy Gas Oil”. Fuel 1978, Aug, 494-496. Furimsky, E. “Catalytic Removal of Sulfur Nitrogen and Oxygen from Heavy Gas Oil”. AZChE J. 1979, 2, 306-311. Furimsky, E. “Chemistry of Catalytic Hydrogenation”. Catal. Rev. Sci. Eng. 1983a, 3, 421-458. Furimsky, E. “The Mechanism of Catalytic Hydrogenation of Furan”. Appl. Catal. 198313, 6, 159-164. Furimsky, E. “Mechanism of Catalytic Hydrodeoxygenation of Tetrahydrofuran”. Znd. Eng. Chem. Prod. Res. Deu. 1 9 8 3 ~1, 31-34. Gagnon, J. “Hydrotraitement catalytique des huiles pyrolytiques du bois”. Master Thesis, Universit6 Laval, QuBbec, Canada, 1987. Johnson, D. K.; Ratcliff, M.; Black, S.; Posey, F.; Chum, H. L.; Gabeen, D. W.; Cowley, s.;Baldwin, R. “Liquids Fuels from Lignins”. Proceedings of the Biochemical Conversion Program Review Meeting, Golden, CO, 1986; pp 261-281.
Krishnamurthy, S.; Panvelker, S.; Shah, Y. T. “Hydrodeoxygenation of Dibenzofuran and Related Compounds”. AZChE J. 1981, 6, 994-1001. Pakdel, H.; Roy, C. “Chemical Characterization of Wood Oils Obtained in a Vacuum Pyrolysis Process Development Unit”. Prepr. Diu. Fuel Chem. 1987,2, 203-214. Pap-Am. Chem. SOC., Ratcliff, M.; Posey, F.; Chum, H. “Catalytic Hydrodeoxygenation and Dealkylation of a Lignin Model Compound”. Prepr. Pap.Am. Chem. SOC.,Diu. Fuel Chem. 1987,2,249-256. Roy, C.; Larouche, J. P.; de Caumia, B. Unpublished data, UniversiG Laval, QuBbec, Canada, 1987. Roy, C.; Lemieux, R.; de Caumia, B.; Pakdel, H. “Vacuum Pyrolysis of Biomass in a Multiple Hearth Furnace”. BiotechnoL Bioeng. 1985, 15,108-113. Soltes, E, J.; Lin, S. C. K. ‘Hydroprocessing of Biomass Tars for Liquid Engine Fuels”. In Progress in Biomass Conversion; Tillman, D. A,, Jahn, E. C., Eds.; Academic: New York, 1984; Vol. V. Ternan, M.; Brown, J. R. “Hydrotreating a Distillate Liquid Derived from Subbituminous Coal Using Sulphided CoO-Mo03-Al203 Catalyst”. Fuel 1982, 1110-1118. Train, P. M. “Chemical and Stochastic Modeling of Lignin Hydrodeoxygenation”. Ph.D. Thesis, University of Delaware, Newark, 1986. Vasilakos, N. P.; Sequera, C. E. “Catalytic Hydrogenolysis of Cellulose”. BiotechnoL Bioeng. Symp. 1983, 13, 65-79. Vasyunina, N. A.; Chepigos, S. V.; Balandin, A. A.; Barysheva, G. S. “Catalytic Hydrogenation of Wood and other Vegetal Materials”. Akad. Nauk SSSR. Otd. Khim. Nauk 1960,8,1419. Vasyunina, N. A.; Barysheva, G. S.; Balandin, A. A.; Chepigos, S. V.; Pogosov, Y. L. “Hydrolytic Hydrogenation of Cotton Cellulose”. Zh. Prikl. Khim. 1964, 12, 2725-2729. (Translation) Vasyunina, N. A.; Barysheva, G. S.; Balandin, A. A. “Catalytic Properties of Ruthenium in the Hydrogenation of Monosaccharides“. Zzu. Akud. Nuuk SSSR, Ser. Khim. 1969, 4, 848-854. (Translation) Weisser, 0.; Landa, S. Sulfide Catalysts, their Properties and Applications; Pergamon: New York, 1973. Wisniak, J.; Hershkowitz, M.; Leibowitz, R.; Stein, S. “Hydrogenation of Xylose to Xylitol”. Znd. Eng. Chem. Prod. Res. Deu. 1974, 1 , 75-79. Wisniak, J.; Simon, R. “Hydrogenation of Glucose, Fructose, and Their Mixtures”. Znd. Eng. Chem., Prod. Res. Dev. 1979,1,5&57. Received for review October 28, 1987 Revised manuscript receiued May 16, 1988 Accepted July 7, 1988
Hydrofining of Heavy Gas Oil on Zeolite-Alumina Supported Nickel-Mol ybdenum Catalyst R. S. Mann,* I. S. Sambi,? and K. C. Khulbe Department of Chemical Engineering, University of Ottawa, Ottawa, Canada K I N 6N5
The hydrotreatment of heavy gas oil derived from Athabasca bitumen was studied in a trickle bed reactor over Ni-Mo supported on zeolite-alumina-silica catalyst at 623-698 K (350-425 “C), LHSV 1-4, and 6.99 MPa. The effects of temperature and liquid flow rates on the product were investigated. The activities of this catalyst for hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) are compared with a commercially available Ni-Mo on y-alumina catalyst. This catalyst was able t o remove as much as 99% S and 86% N present in the oil a t 698 K (425 “ C ) . Activation energies for the HDS and HDN reactions were i0.8 and 25.1 kcal/mol, respectively. The use of zeolites in hydrocracking has been described in great detail (Bolton, 1976). A good hydrocracking catalyst should have a highly acidic cracking component along with a noble metal or a combination of noble metals as a hydrocracking component. Zeolites are highly acidic in nature. But pure zeolites due to its fine pores are not suitable for cracking. Hence, they are usually mixed with Present address: Energy Research Laboratories, CANMET, Energy Mines and Resources, Ottawa, Canada K1A OG1.
0888-5885/88/2627-1788$01.50/0
other amorphous support materials. The rare earth exchanged Y-zeolite (faujasite) dispersed in the matrix of silica-alumina, synthetic or natural clays, is most commonly used as a cracking catalyst (Heinemann, 1981). However, use of such catalysts in hydrocracking is still quite limited. The main objective of this study was to develop a high-efficiency Ni-Mo catalyst using zeolite material and a composite of silica-alumina as support material. In this paper, we report the kinetics of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) 1988 American Chemical Society
