27 The Direct Liquefaction of Wood Using Nickel Catalysts
Thermal Conversion of Solid Wastes and Biomass Downloaded from pubs.acs.org by FUDAN UNIV on 12/24/16. For personal use only.
D. G. B. BOOCOCK, D. MACKAY, and H. FRANCO Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A4
Recent events have again emphasized the precarious nature of imported petroleum. Canada currently imports about 80,000 m3/day (500,000 Bbl/day) into Eastern provinces and exports 9,000 m3/day (56,600 Bbl/day) to the U.S.A. from western Canada. These exports will probably be phased out in the 1980's. At the present time natural gas exports to the U.S.A. result in an overall dollar trade balance for o i l and gas in Canada. The continued development of the o i l sands, the promising o i l discoveries in the Beaufort Sea, and natural gas discoveries in the Arctic Islands and eastern Canada are key factors in Canada's energy future. However, it is evident that Canada for sometime will rely on o i l imports for which the degree of future price escalation is unknown. Renewable sources of energy are a desirable component of energy self sufficiency. The Ontario Ministry of Natural Resources has for some years been investigating plantations of fast-growing hybrid poplars (1). A reasonable average yield for these poplars is about 17,000 kg.ha - 1 .y - 1 (dry weight). We describe here procedures by which o i l containing 10 to 14 per cent oxygen can be obtained from poplar wood in 30-40 per cent yield. This corresponds to about 35 barrels of o i l per hectare per year. It has been calculated that plants producing 106 kg per day of o i l would require a land area of 350 square miles assuming a 60 per cent use factor. To satisfy Canada's present petroleum requirements (1.8 x 106 Bbl/day) would require approximately 100,000 square miles of suitable land. Poplar wood, like other woods, is made up of three major polymeric components which are cellulose, hemicellulose and lignin. Lignin comprises 18-23 per cent of hybrid poplar, and it is the most complex component, being non-linear in nature. The conversion of wood into a high energy liquid fuel requires depolymerization of the components and removal of as much oxygen as possible. The oxygen content of dry poplar is around 45 per cent and ideally this should be reduced to zero. However, we do not believe that the complete elimination of oxygen should be a dominant consideration particularly as the last few per cent of 0-8412-0565-5/80/47-130-363$05.00/0 © 1980 American Chemical Society
THERMAL
364
CONVERSION
OF SOLID WASTES AND
BIOMASS
oxygen may r e q u i r e d i s p r o p o r t i o n a l c o s t s . We suggest that a unique r e f i n i n g procedure would be used to t r e a t the o i l . T r a d i t i o n a l l y thermal l i q u e f a c t i o n s t u d i e s on biomass have been c a r r i e d out i n the presence of one or both of the reducing gases, hydrogen and carbon monoxide (2, _3, 5_ 6). Equation 1, i n which c e l l u l o s e has been used to approximate the elemental composition of wood, shows that t h e o r e t i c a l l y a reducing gas i s not required f o r wood l i q u e f a c t i o n when i n t e r n a l carbon i s used to remove the oxygen. 9
(C Hio0 ) Thermal Conversion of Solid Wastes and Biomass Downloaded from pubs.acs.org by FUDAN UNIV on 12/24/16. For personal use only.
6
5
2 n
> nC H 8
1 6
+ 4nC0
2
+ 2nH 0 2
Equation 1 The removal of oxygen as carbon d i o x i d e i s d e s i r a b l e , but the formation of carbon monoxide i s i n e f f i c i e n t and, t h e r e f o r e , undes i r a b l e . When methane i s not the major product some oxygen must a l s o be removed i n the form of water, but t h i s mode must not be excessive as i t would lead to hydrogen d e p l e t i o n of the products and encourage char formation. In the absence of hydrogen and carbon monoxide from other sources, the g a s i f i c a t i o n of wood f o r the production of these gases i s c o s t l y and should be avoided. The Bechtel Corporation estimated that g a s i f i c a t i o n would account f o r 36 per cent of the c a p i t a l cost of a plant based on the Albany process (7). In most of our studies we have used hydrogen as a reducing agent and employed Raney n i c k e l as c a t a l y s t , but i n view of the low hydrogen uptake observed with mature c a t a l y s t some experiments were performed i n the absence of hydrogen and these have y i e l d e d very encouraging r e s u l t s . In an e a r l i e r paper (8) we described the complete l i q u e f a c t i o n and g a s i f i c a t i o n of fast-growing h y b r i d poplar (1). The wood (< 0.5 mm mesh) was suspended i n water and t r e a t e d with hydrogen i n a w e l l s t i r r e d and sparged autoclave using an i n i t i a l pressure (24°C) of 10.3 MPa and r e a c t i o n temperatures of 325-375°C. In a l l cases Raney-nickel (9) was used as c a t a l y s t . In these s i n g l e batch r e a c t i o n s hydrogen uptake was high and considerable wood g a s i f i c a t i o n occurred. For example, f o r the highest catalyst/wood mass r a t i o of 0.2, 50g of wood at 350°C consumed 3.8g of hydrogen and produced 1.3g of carbon d i o x i d e , 16.Og of methane, 4.4g of saturated C to Ci+ alkanes and 8.0g of o i l . No carbon monoxide was produced. The o i l products contained 10-12 per cent oxygen and had v i s c o s i t i e s of 700-2200 MPa.s at room temperature and heating values of 37-41 M J . k g . We have now examined the b e n e f i c i a l e f f e c t of prolonged use of the c a t a l y s t i n extended batch r e a c t i o n s . We report here some r e s u l t s from these extended batch r e a c t i o n s and from runs i n which hydrogen was not used. We a l s o address the problem of the wood feed system f o r p o s s i b l e commercial a p p l i c a t i o n . 2
-1
27.
BOOCOCK
ET AL.
Liquefaction of Wood Using Nickel Catalysts
365
Thermal Conversion of Solid Wastes and Biomass Downloaded from pubs.acs.org by FUDAN UNIV on 12/24/16. For personal use only.
Experimental In a t y p i c a l set of runs 150g of a i r - d r i e d poplar, Populus χ Euramericana, clone 1-45/51 (8), which had been ground to l e s s than 0.5 mm mesh, were added to a 2-fL magnedrive packless auto clave (Autoclave Engineering) together with water (750 ml) and c a t a l y s t (20g). The autoclave was f l u s h e d with n i t r o g e n and then hydrogen a f t e r which the hydrogen pressure was r a i s e d to 6.6 or 10.3 MPa. The autoclave temperature was then r a i s e d t o 340-350°C over a p e r i o d of 1 h with s t i r r i n g and sparging and t h i s tempera ture was maintained f o r 1 or 2 h a f t e r which the autoclave was cooled to room temperature over a p e r i o d of 2 h. Carbon d i o x i d e carbon monoxide, methane, ethane, propane and butane i n the gas phase were measured by gas chromatography as described p r e v i o u s l y (8). The autoclave was vented and the volume of the gas i n the head space was measured. The sparging i n the autoclave produced a foam which appeared to be s t a b l e a f t e r the autoclave was opened. Between runs a pipe, extending almost to the bottom of the auto clave, was used to e x t r a c t some of the l i q u i d . T h i s was accom p l i s h e d by p r e s s u r i z i n g the autoclave and f o r c i n g l i q u i d up the pipe. The o i l product had a d e n s i t y greater than water, but because of the foam formation the removed l i q u i d was mostly water. More wood (150g) was added and, i n the r e l e v a n t experiments, more c a t a l y s t was a l s o added. The autoclave was sealed and the contents reacted as described p r e v i o u s l y . A f t e r the f i n a l run of a s e r i e s , the autoclave contents were discharged as before. About 60 ml of l i q u i d remained i n the autoclave because the i n l e t of the discharge pipe was not l o c a t e d a t the base of the lower i n t e r n a l surface due to the presence of the s t i r r e r blades. T h i s r e s i d u a l l i q u i d was extracted s e v e r a l times with acetone, a procedure which a l s o cleaned the inner surface of the autoclave. The acetone f r a c t i o n was kept apart from the bulk l i q u i d . In previous experiments, the product o i l was e x t r a c t e d with chloroform. I n t r o d u c t i o n of a solvent presents many problems and a simple phase s e p a r a t i o n of o i l and water was adopted. C a t a l y s t was removed from the o i l by c e n t r i f u g a t i o n . O i l v i s c o s i t i e s , heating values and elemental analyses were obtained as described p r e v i o u s l y (8). The carbon content of the aqueous phase was measured using a Beckman T o t a l Carbon Analyser. Results and D i s c u s s i o n Table 1 shows r e s u l t s of seven s e q u e n t i a l 2 h runs. A hydrogen pressure of 8 MPa was used i n the f i r s t run to s a t i s f y the demand f o r methane formation. T h e r e a f t e r a lower hydrogen pressure was used. The l i q u i d removed before each run was mostly water and considerably more was removed (except i n run 5) than had been formed i n the previous run. Thus the o i l / w a t e r r a t i o was v a r i e d throughout t h i s s e r i e s . T h i s r a t i o which v a r i e d from 0.3 to 2.0 had no e f f e c t on the course of the r e a c t i o n . Gas
THERMAL
Thermal Conversion of Solid Wastes and Biomass Downloaded from pubs.acs.org by FUDAN UNIV on 12/24/16. For personal use only.
366
CONVERSION OF SOLID WASTES AND BIOMASS
consumption, gas production and product gas composition were the same f o r runs 3 through 7. At the end of each run only an o i l and water phase were present and no char was formed. The pH of the aqueous phase was i n the range 3 to 4 due to cleavage of the acetate groups i n the poplar h e m i c e l l u l o s e and perhaps a l s o due to phenol formation. The e f f e c t s of prolonging c a t a l y s t use were a l l b e n e f i c i a l . Hydrogen consumption decreased and carbon d i o x i d e production increased from run 1 to run 3. The organic product was an o i l which contained 13 per cent oxygen and was 95 per cent benzene s o l u b l e . Approximately 55g of water was formed i n each run. Thus the molar r a t i o of carbon d i o x i d e product to water product was about 1:6 compared to an i d e a l r a t i o of c l o s e to 2:1. The o i l y i e l d appeared to be 38 per cent but subsequent d i s t i l l a t i o n showed that the product contained about 9 per cent by weight of water. Table 1 RESULTS OF SEVEN SEQUENTIAL RUNS, REACTION TEMPERATURE 350°C, INITIAL PRESSURE 10.7 MPa RUN 1 AND 8 MPa IN SUBSEQUENT RUNS, 2 h REACTION TIME, 740 ml WATER, 150g WOOD ADDED AT EACH STEP LIQUIDS REMOVED (ml)
H (g) CONSUMED
C0
Nil 200 200 200 0 100 200
11.6 3.1 2.0 2.0 2.2 1.9 2.1
9.7 13.1 23.0 22.0 20.1 22.3 23.3
2
OIL YIELD OIL ANALYSIS RESIDUE OIL HEATING VALUE OIL VISCOSITY (24°C) AQUEOUS PHASE AQUEOUS PHASE CARBON
2
(s)
PRODUCT GASES CH C -Cz+ (8) (g) 4
36.0 2.4 0.4 0.4 0.3 0.4 0.4
2
2.9 1.4 0.7 0.8 0.6 0.7 0.8
CO
(g) 0 0.2 0.4 0.5 0.4 0.1 0.6
398g (37.9%) C, 77.7; H, 8.4; 0, 0.5% 35.8 MJ.kg" 5075 mPa.s 390g 41. Og
13.3
1
The aromatic content of the o i l was 33 per cent (10) as measured by carbon-13 nmr. Crude d i s t i l l a t i o n at atmospheric pressure y i e l d e d a major f r a c t i o n (42 per cent) which b o i l e d i n the range 190-350°C and u n l i k e the crude product was completely m i s c i b l e with d i e s e l f u e l . A d u p l i c a t e of t h i s seven run s e r i e s was carried out and i t y i e l d e d very s i m i l a r r e s u l t s . Results f o r shorter s e r i e s i n which d i f f e r e n t amounts of c a t a l y s t were added w i l l be reported elsewhere (11). The r e l a t i v e l y low consumption of hydrogen i n t h i s f i r s t
27.
BOOCOCK
ET
AL.
Liquefaction of Wood Using Nickel Catalysts
367
s e r i e s prompted a s e r i e s of runs i n which no hydrogen was used, and except i n the f i r s t and l a s t runs the r e a c t i o n was blanketed with n i t r o g e n . The r e s u l t s of t h i s s e r i e s are shown i n Table 2. Table 2 RESULTS OF SIX SEQUENTIAL RUNS REACTION TEMPERATURE 350°C, NITROGEN BLANKET (ATMOSPHERIC PRESSURE EXCEPT RUN 6 (4.7 MPa H ) ) , 2 h REACTION TIME, 750 ml WATER, 150g WOOD ADDED AT EACH STEP EXCEPT RUN 6, NO CARBON MONOXIDE DETECTED IN ANY RUNS Thermal Conversion of Solid Wastes and Biomass Downloaded from pubs.acs.org by FUDAN UNIV on 12/24/16. For personal use only.
2
H CONSUMED
(8)
H PRODUCED (g)
-
0.9 0.7 0.6 0.8 0.65
1.3
-
2
2
OIL YIELD OIL ANALYSIS AQUEOUS PHASE CARBON
PRODUCT CASES C2-Cit CHtt (g) (g) (8)
C0
2
37.0 35.8 32.5 33.6 33.6 2.6
12.5 4.5 2.2 1.4 1.2 0.4
2.8 1.4 1.4 2.3 2.0 0.9
253g (33.7%) C, 77.5; H, 7.7; 0, 40g
12.2
Again, no char was formed but, the amounts of carbon d i o x i d e produced were greater than i n the f i r s t s e r i e s , and no carbon monoxide was detected. The o i l product a f t e r each run (and before run 6) j u s t flowed at room temperature. However, hydrogen treatment of t h i s o i l i n run 6 caused s o l i d i f i c a t i o n of the product. This suggested that the o i l contained some alkene linkages which hydrogenated i n the l a s t run. I t t h e r e f o r e appears that some forms of n i c k e l metal have the a b i l i t y to l i q u i f y wood at elevated temperature even i n the absence of hydrogen. Some p r e l i m i n a r y runs using n i c k e l carbonate i n the presence of hydrogen have a l s o y i e l d e d promising r e s u l t s . In these runs the n i c k e l carbonate was reduced i n s i t u to f i n e l y d i v i d e d n i c k e l which presumably functioned as the c a t a l y s t . Commercially a v a i l a b l e n i c k e l powders d i d not appear to be as e f f e c t i v e as Raney n i c k e l or n i c k e l produced i n s i t u . Wood Feed
System
The i n t r o d u c t i o n of s o l i d s i n t o a high pressure system u s u a l l y presents problems p a r t i c u l a r l y i f t h i s i s done on a continuous b a s i s . Reducing wood to small p a r t i c l e s f o r the purpose of producing s l u r r i e s i s not v i a b l e because of the l a r g e energy requirements. However, i t appears that i n the case of wood
Thermal Conversion of Solid Wastes and Biomass Downloaded from pubs.acs.org by FUDAN UNIV on 12/24/16. For personal use only.
368
THERMAL CONVERSION OF SOLID WASTES AND BIOMASS
this problem can be partially solved by a pretreatment of the wood with steam at much lower pressures than those used in the reaction vessel. This weakens the structure of wood by hydrolysis of the hemicellulose, and the treated wood suspended in water is easily macerated to a slurry. Some hydrolysis takes place in the reactor prior to liquefaction, and we have converted 1 cm cubes (size limited by the inlet port) of poplar to o i l directly. No residue remained, and the o i l was slightly more viscous than that formed from slurries of powdered wood. It also appears from previous results that in the reaction, simple sugars liberated by hydrolysis can be incorporated into the o i l . Therefore, prehydrolysis of hemicellulose and even cellulose is not considered a problem in the wood liquefaction process. We are currently constructing a laboratory scale semicontinuous unit which will use the prehydrolysis concept. Acknowledgements We would like to acknowledge financial support from the Department of Energy, Mines and Resources, and the Ontario Ministry of Energy. Current work is also funded by the ENFOR program of Environment Canada. We thank Dr. J. E. McCloskey of Canada Packer's for nmr measurements. Literature Cited 1. Anderson, H.W. and Zsuffa, L., Forest Research Report No. 101, October 1975, Ministry of Natural Resources (Ontario), Division of Forests. 2. Appell, H.R. and Miller, R.D., Conversion of Cellulosic Wastes to Oil, Bureau of Mines Report of Investigation (1975). 3. Appell, H.R., Wender, I., and Miller, R.D., Conversion of Urban Refuse to O i l , Bureau of Mines Technical Progress Report - 25 May 1970. 4. Appell, H.R. and Wender, I., Converting Organic Wastes to Oil, Bureau of Mines Technical Report of Investigation 7560 (1971). 5. Weiss, A.H., Textile Res. J., 1972, 42, 526. 6. Weiss, A.H., Kranich, W.L., and Gupta, D.V., Ind. Eng. Chem., Proc. Des. Dev., 1976, 15, 256. 7. Lindemuth, T., Biomass Liquefaction Program, Experimental Investigation at Albany, Oregon, Second Annual Symposium on Fuels for Biomass, Troy, N.Y., June 1978. 8. Boocock, D.G.B., Mackay, D., McPherson, M., Nadeau, S.J., and Thurier, R., Can. J. Chem. Eng., 1979, 57, 98. 9. Covert, L.W. and Adkins, H., J. Amer. Chem. Soc., 1932, 54, 4116. 10. Schoolry, J.N. and Budde, W.L., Anal. Chem., 1976, 48, 1458. 11. Boocock, D.G.B., Mackay, D., and Franco, Η., "The Production of Synthetic Liquids from Wood Using a Modified Nickel Catalyst", Paper accepted for presentation at 29th Canadian Chemical Engineering Conference, Sarnia, Ontario, 30 Sept. 3 Oct. 1979. RECEIVED November 16, 1979.
