177
Ind. Eng. Chem. Prod. Res. Dev. 1984, 23,177-182
obtained. Since the degree of deuteration is dependent on how much deuterium is available for exchange, changing the ratio for deuterated to nondeuterated solvents in the generator would change the deuterium content in the final product. The system is therefore capable of producing linear and varying degrees of branched deuteriopolymethylenes having different physical and mechanical properties. Gram quantities of the deuterated polymer are obtained safely and conveniently in several hours with the semibatch bench-scale system described, with the potential for controlling molecular weight and percent deuteration. Acknowledgment
The authors are grateful to glass technologist S. Mezynski and acknowledge the financial support provided by W. 0. Doggett and W. H. Bennett of Plasma Physics Research at NCSU.
Bamberger, E.; Tschlrner, F. Ber. 1900, 33. 955. de Boer, T. J.; Backer, H. J. Org. Syn. 1883, 4 . 943. Basted. H. S. The Indlcetw JUM 1989, 24. Buckley, G. D.; Cross, L. H.; Ray, N. H. J . Chem. Soc. 1950, 2714. Davles, A. G.;Hare, D. 0.; Khan, 0. R.; Slkera, J. J . Chem. Soc.1983, 85, 4481. Feltzln, J.; Restlano, A. J.; Mesroblan, R. 8. J . Am. Chem. Soc. 1955, 77, 206. Intematbnal Technlcal Information Instkute, "Toxlc and Hazardous IndusM a1 Chemicals Safety Manual for Handling and Disposal with Toxlchy and Hazard Data", New York. 1975; p 157. Krakovyak, M.; Anufriyeva, Ye.; Skorokhodov, S. Vysokomol. Soedin 1888, 8, 1681. McKay, A. F. J . Am. Chem. Soc. 1948, 70, 1974. Moore, J. A.; Reed, D. E. Org. Syn. 1981, 4 7 , 16. Mucha, M.; Wunderllch, 6. J . poly" Scl. 1974, 72, 1993. von Pechmann, H. Ber. 1894, 2 7 , 1888. von Pechmann, H. Ber. 1898, 31, 2640. Redemann. C.: Rlce, F.; Roberts, R.; Ward, H. Org. Syn. 1955, 3 , 244. Relmllnger, H. Chem. Ber. 1981, 94, 2547. Sax, N. lrvlng "Dangerous Properties of Industrlal Materlals", 5th ed.; Van Nostrand Reinhold Co.: New York, 1979. Staudlnger, H.; Kupfer, 0. Ber. 1912, 45, 505. Wunderllch. 6. "Macromolecular Physlcs", Academlc Press: New York, 1973; Vol. 1.
L i t e r a t u r e Cited
Received for review May 9, 1983 Accepted September 28,1983
Adamson, D.; Kenner. J. J . Chem. Soc.1935. 286. Ardt, F. Org. Syn. Coll. 1943. 2 , 461.
Supercritical Gas Extraction of Wood with Methanol R. Labrecque,+S. Kallagulne,' and J. L. Grandmairon Department of Chemlcal Englneerlng, Lava1 University, StsFoy, Qc, Canad
A semi-continuous spinning basket type reactor has been designed and built for the supercritical gas extraction of wood in a flowing solvent. Two factorial plans of experiments have been performed to study the extraction of fopulus tremu/okfes in methanol. The temperature range extended up to 350 O C and the pressure range to 17.01 MPa. Results for oil yield and wood conversion were obtained as functions of solvent flow rates, rate of agitation, nature of the reactor iining, wood chips size, and rate of temperature rise. The most important factors were identiRed as temperature, presswe, and solvent flow rate, the size of the wood particles being mainly significant at low pressure. These results are discussed in light of current knowledge on wood pyrolysis.
Among the various processes currently under study for the direct liquefaction of biomass (Klass, 1982), supercritical gas extraction (SGE) is related to pyrolysis (Roy et al., 1982) as well as to the organosolve process (Hansen and April, 1982). Indeed, unlike the thermochemical liquefaction techniques (Brown et al., 1980; Beckman and Boocock, 1983; Eager et al., 1983; Elliott, 1982; Thigpen and Berry, 1982), SGE uses neither a gaseous reducing reactant nor a catalyst. Furthermore, unlike hydrolysis it does not utilize an acidic reactant. Therefore, SGE is a mere pyrolysis conducted in a supercritical solvent, which exerta a favorable effect, possibly owing to the swelling of the wood structure (Hansen and April, 1982),solubilization of the breakdown products of lignin and carbohydrates pyrolysis, and the caging effect of the solvent molecules surrounding the mid-size fragments, protecting them from secondary reactions (Labrecque et al., 1982). Previous works on SGE of pyrolytic oils from wood have been reported by (hhdiand Olcay (1978),utilizing various organic solvents, Modell (1982), with supercritical water, and McDonald and Howard (1981),who utilized methanol and acetone. Institut de Recherche de l'Hydro-Qugbec, Varennes, QC, Canada.
In this paper we report the results of a study of SGE in methanol, aiming at the determination of the effects of solid-liquid mass transfer as well as residence time distribution and flow patterns of the solvent and soluble fragments in the reactor. Experimental Setup
Figure 1 shows a diagram of the experimental setup (Labrecque, 1983). Approximately 40 g of wood chips are loaded into a spinning basket located in the 750-mL autoclave (Aminco). The methanol solvent is continuously fed by means of a diaphragm reciprocating pump (Whitey LP-10). The outgoing solvent passes through a filter and two precision expansion valves in series (High Pressure Equipment) allowing a precise control of the pressure. The solvent is then admitted to a condenser, maintained at 5 "C, and liquid fraction is collected. The gaseous fraction, whenever present, passes through a second condenser and and is stored in a floating piston gasometer maintained at atmospheric pressure by a mercury contacholenoid valve on-off controller. The autoclave is heated by an external heating element of 3.9 kW and its temperature is monitored by a controller-programmer (Lindberg M211). Two temperature programs were imposed as shown in Figure 2. In both cases two temperature plateaus at 250 and 350 "C were
0196-4321/84/ 1223-O1778Ol.50/0 0 1984 Amerlcan Chemical Soclety
178
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984
1 2 - -1
-
- 153 1 - 1 0 3
0
Figure 1. Schematic diagram of the experimental setup: (1)feed tank; (2) reciprocating pump; (3) surge tank; (4)pressure gage; (5) preheating; (6) thermocouple; (7) heating element; (8) spinning basket; (9) external magnet; (10)variable speed motor; (11)expansion valve; (12) condensers; (13) liquid fractions collecting device; (14)floating piston gasometer; (15) solenoid valve; (16) mercury contact; (17) filter.
a
250
'0
'1250
'f 350
Time,s
Figure 2. Temperature programs.
maintained, until the oil yield reached a steady value. The two programs differ by the constant rate of temperature rise at which the plateaus are reached, as shown in Figure 2. The liquid fractions collected are evaporated in a Buchi evaporator under dynamic vacuum at 75 "C. The residue recovered after evaporation to dryness will be referred to as the pyrolytic oil. After completion of an experiment, the solvent is expanded out of the autoclave maintained at 350 "C. The solids recovered in the basket after the system has been cooled down to room temperature do not lose weight upon heating to 350 "C under nitrogen. These solids will be referred to as the char. Experimental Conditions and Results All results reported here were obtained by utilizing wood from the stem of a 20 year Populus tremuloides. This wood was cut into small parallelepipeds (5 X 5 X 2 and 7 X 7 X 4 mm) and dried overnight in air at 105 "C. The dependent variables under study were the total oil yield, defined as mass of oil collected at 350 "C RT = mass of dry wood the yield in oil no. 1 mass of oil collected at 250 "C R1 = mass of dry wood and the conversion mass of char obtained at 350 "C X=lmass of dry wood The yield in oil no. 2 could be calculated as R2 = RT - R1.
2
4
6
8
10
I2 Time x ~ ' s
14
16
I8
20
22
Figure 3. Cumulative production of pyrolytic oil as function of time. Experiment no. 6.
In all cases, the gases in the gasometer (typically less than 1 L) contained mostly air introduced while changing flasks for the collection of a nepr fraction of solution. Only minor amounts of CHI and C02were found in the gasometer (typicallyless than 0.1 g in total). Most of the volatile products of pyrolysis, including water, are therfore in the solution and they are entrained by the gaseous steam leaving the evaporator. In this work, no effort was made to analyze this stream. It was felt that the mass balance could not be completed in this manner, owing to the fact that methanol, which is likely to appear among the products, could not have been distinguished from the solvent. One may only speculate that in addition to the main volatile compounds CHI, GO,, and H,O some minor amounts of CO, H2, CzH6,and C3H, may also have been produce4 during the pyrolysis. Two factorial plans of experiments were designed in order to study the effect of the following variables on R1, RT,and X. (a) Pressure. Three levels were selected at 3.40,10.20, and 17.01 MPa (500, 1500, and 2500 psig, respectively). Since the critical pressure of methanol is 8.0 MPa and its critical temperature is 240 "C, in tests at 3.40 MPa, the initial rise in temperature was performed at 10.20 MPa until the temperature of 250 "C was reached, at which time the pressure was set to 3.40 MPa. This procedure was adopted in order to avoid phase separation during a test. (b) Methanol Flow Rate. Two nominal values of 0.22 and 0.75 g/s were selected, but some additional tests were also run at intermediate values. (c) Size of the Wood Chips. The two sizes mentioned earlier, namely 5 X 5 X 2 and 7 X 7 X 4 mm were employed. These two sizes correspond to a volume ratio close to 4 and an external surface ratio close to 2. (d) Rate of Temperature Rise. The two temperature programs shown in Figure 2 are designed to vary this parameter. They will be labeled as maximum and minimum in the remainder of this text. (e) Rate of Agitation. Two levels were selected for the rate of rotation of the basket, namely 60 and 500 rpm. (f) Lining of the Reactor. As a test for the possibility of a catalytic effect of the reactor wall, some experiments were performed while covering the internal wall of the reactor with a very thin shell of quartz or graphite. Thus a third level is obtained by using the bare wall of the autoclave (SS316). Figure 3 shows the results for a typical experiment, expressed as the mass of pyrolytic oil collected as a function of time. It shows that a first series of reactions
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984 170 Table I. Analysis of Oils and Char,Experiment No. 29 products from expt no. 29 oil no. 1 oil no. 2 char
mass %
atomic ratio
% water
N
C
H
0
H/C
OlC
0.19
0.60 0.60 0.15
60.25 55.42 76.70
9.17 7.21 5.18
29.98 36.77 17.97
1.826 1.561 0.810
0.373 0.497 0.176
0.22
-
Table 11. Oil Yields and Wood Conversion for Experimental Plan No. l a oil yields expt no.
reactor lining
solvent flow rate, g/s
R,
R2
bare bare graphite graphite quartz quartz
500 60 500 60 500 60
0.222 0.214 0.213 0.212 0.215 0.218
0.28 0.32 0.26 0.32 0.28 0.28
0.27 0.24 0.30 0.29 0.30 0.25
RT 0.55 0.56 0.56 0.61 0.58 0.53
conversion, X
2 7 9 8 6 5 14 16 21 19 13 15
bare bare graphite graphite quartz quartz
500 60 500 60 500 60
0.0755 0.0775 0.0705 0.0750 0.0760 0.0725
0.19 0.19 0.20 0.19 0.19 0.16
0.21 0.21 0.24 0.16 0.21 0.20
0.40 0.40 0.44 0.35 0.40 0.36
0.84 0.81 0.85 0.84 0.82 0.83
Mass of wood: 4 0 g; chips size: 5
X 5 X 2
0.93 0.88 0.90 0.88 0.90 0.89
mm; pressure: 10.20 MPa; rate of temperature rise: maximum.
Table 111. Oil Yields and Wood Conversion for Experimental Plan No. 2 a oil yields
a
expt no.
pressure. MPa
rate of t orise
R,
Rz
RT
conversion, X
33 34 25 28
3.40 3.40 3.40 3.40
chips size. mm 5 5 7 7
x x X x
5 x 2 5 x 2 7 X 4 7x 4
min max min max
0.13 0.13 0.10 0.08
0.23 0.25 0.22 0.20
0.36 0.38 0.32 0.28
0.80 0.79 0.78 0.76
26 29 32 24
10.20 10.20 10.20 10.20
5 5 7 7
x x X x
5 5 7 7
2 2 4 4
min max min max
0.22 0.23 0.20 0.21
0.30 0.30 0.32 0.26
0.52 0.53 0.52 0.47
0.89 0.88 0.87 0.87
27 30 31 23
17.01 17.01 17.01 17.01
5 5 7 7
x x x x
5 x 2 5x 2 7 x 4 7x 4
min max min max
0.25 0.25 0.22 0.21
0.38 0.37 0.41 0.42
0.63 0.62 0.63 0.63
0.95 0.95 0.95 0.94
x x X x
Mass of wood: 40 g; reactor lining: graphite; rate of agitation: 60 rpm; nominal solvent flow rate: 0.16 g/s.
beginning at 130 "C comes to completion at 250 "C and that a temperature of 280-290 "C must be reached before a second generation of oil is detected. The second process is terminated at 350 "C. The two oil fractions obtained before and after the end point of the temperature plateau at 250 "C (designated as oil no. 1 and no. 2) were systematically collected and stored separately. The limit of 350 "C is imposed by the thermal cracking of methanol, which was observed at temperatures of 370-380 "C. Raising the end temperature to 400 "C did not cause any significant increase in the oil yield, in agreement with results of Shdizadeh et al. (1979) for the vacuum pyrolysis of cellulose. Table I presents some typical results obtained from the analysis of the two oils and char for experiment no. 29. More complete results have been reported elsewhere (Kaliaguine, 1983). The water content in the oils, determined by the automatic Karl Fischer analysis is very low. The highest value found was 0.50 wt % , showing that the evaporating technique was thorough enough to eliminate nearly all the water formed during pyrolysis. The elemental analysis was performed according to ASTM procedure, that is by independent analysis of N, C, and H, the remainder of the sample being considered as ashes and oxygen. As is typical for the liquid products of pyrolytic processes, the oxygen content is rather high with a noticeable difference between the two oils. Also of interest
is the fact that the H/C ratio of the oils is high and shows a significant difference between the two oils. For reference, the H/C in gasoline is close to 1.9 (Kaliaguine, 1981). In Table 11, the results of oil yields and wood conversion, as well as the experimental conditions corresponding to the set of experiments in plan no. 1, are presented. A statistical error analysis or these data using the Fisher-F test (Snedecor and Cochran, 1967) shows that reactor lining and rpm have no significant effects on R1, RT, or X. A very significant effect of the methanol flow rate, with probabilities higher than 0.999 was found for these three dependent variables. (For R1 and RT a significant interaction was found between flow rate and agitation) (Labrecque, 1983). Figure 4 shows the variation of the three variables R1, RT, and X with methanol flow rate, at a total pressure of 10.20 MPa. Inspection of the graph indicated that the solvent flow rate indeed has a determining importance especially on RT, which varies from 40 to 60% over the range of flow considered. Table I11 presents the experimental conditions and the results of oil yield and wood conversion for experimental plan no. 2. The Fisher-F test method shows, in this case, that pressure has a very significant effect on R1, RT, and X. No effect was found for the rate of temperature rise. The size of the chips, however, has a significant effect on R1, RT, and X,with respective probabilities higher than 0.999, 0.998, and 0.991. Figure 5 shows the effect of
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984
180
I
I 90
80
0
w m d conversion X total oil yield
RT
,
1
I406
Qde
0,12
0,;O
I
0,;4
0.16
0,k
0,:8
Solvent f l o w r a t e , g / s
od2
1
1
717x4
515x2 Woad particle size,rnm
Figure 4. Pyrolytic oil yields and wood conversion as function of the methanol flow rate at pressure 10.20 MPa.
Figure 6. Pyrolytic oil yields and wood conversion as function of wood particle size.
I
I
50
0
I - . 0 wood Conversion total oil yield
X
RT
mi y'eld a t 250 'C
1-
I
5
I
I
10
15
Figure 7. Cumulative production of acetic and formic acids as a function of time. Experiment no. 32.
R~
i
20
Pressure, MPa
Figure 5. Pyrolytic oil yields and wood conversion as function of pressure, at methanol flow rate of 0.16 g/s.
pressure on the yields and conversion. Both the conversion X and total oil yield RT essentially increase with pressure. The difference X - RT,which as a first approximation may be considered the fraction converted to volatile compounds
(including water), decreases significantly over the range of pressure considered. The results for the effect of chips size are shown on Figure 6. A larger size results in smaller values for R1,RT,and X,and this effect is felt mainly at low pressure. One of the main advantages of the continuous flow of solvent is the possibility of collecting and analyzing successive fractions produced at different times and temperatures (Labrecque et al., 1982). Full analysis of the oil fractions will be reported elsewhere. As an illustration of the interest of this procedure, Figure 7 was obtained in the following manner. Upon evaporation of each fraction of solution collected during experiment no. 32, the recondensed methanol was weighed and analyzed by gas chromatography. Two products had appeared in the solvent, namely methyl formate and methyl acetate. These were assumed to be the products of esterification of formic and acetic acids by methanol. Figure 7 shows the calculated
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984
cumulative masses of these acids against time. At the end of experiment no. 32, these two products amounted to 5.7 g, or 14.2 w t % of the initial wood. It is of particular interest to note that whereas acetic acid is mainly formed below 250 "C, most of the formic acid is produced between 250 and 350 "C.
Discussion and Conclusions Our observations concerning the effect of temperature on the yield of the oils are in full agreement with current literature. The first step ending at 250 "C is visualized as the simultaneous total thermal decomposition of hemicelluloae and pastial delignification. Aspen wood is known (Poliquin, 1981) to contain about 28% of D-xylose based hemicellulose, which upon pyrolysis yields acetic acid (Elder, 1979). This is therefore in line with the result of acetic acid being mostly produced during this step (Figure 7). According to Elder (1979), the pyrolysis of lignin in an atmosphere of nitrogen takes place between 280 and 500 "C. We believe, however, that in SGE with methanol, the partial delignification described by Hansen and April (1982) in a series of alcohols at temperatures 175 and 205 "C, is also occurring during the first step. According to Shafiideh (1977 and 1979), the initial step in the thermal degradation of cellulose is the rupture of glucosidic links at 300 "C followed by transglucosylation, which produces levoglucosan as the initial compound. Further transformations of the saccharidic units were shown to take place between 300 and 400 "C. The second step observed between 280 and 350 "C is thought to be mostly the thermal degradation of cellulose. Formic acid (Figure 7) would therefore be a product of this reaction. We believe, however, that residual lignin, either unconverted or as recondensed fragments, is also decomposed on the same temperature range. Among the other factors studied in our work, three were not found to have significant effects on either yields or conversion, namely rate of temperature rise, rate of agitation, and the nature of the lining of the reactor. In the case of the first two factors we believe that the ranges covered in our study may not have been broad enough to show a distinct trend. The absence of effect of the nature of the lining of the reactor wall must be linked to the presence of a very thin film of carbonaceous material covering the stainless steel surface during the reaction. This frlm can be clearly seen after completion of a run,and it may passivate the metallic surface. Such an observation casts a serious doubt on the possible use of metallic catalysts in such systems. Although the range covered for the sizes of wood chips is not very large, a distinct effect of this parameter was found especially for the oil conversion at the end of the first step. This is in agreement with the observations of Hansen and April (1982) associating the ease of delignification to the swelling of the wood structure by the solvent. Both would take place during the first step, making internal diffusion of the products easier during the second step. The fact that particle size has a more significant effect on yields at low pressure (Figure 6) would mean also that the ability of methanol to swell the structure increases with pressure. In agreement with the results of McDonald and Howard (1981), an increase in pressure from 3.40 to 17.01 MPa results in very significant increases in both yields and conversion. This beneficial effect may be associated with the normal increase in solubility a t the approach of the critical region of the solvent. In addition the role of the solvent may be to build a cage of molecules around the primary products of pyrolysis, thus protecting them from
181
secondary reactions, either binary collisions or recondensation on the solid structure. Indeed, as can be seen in Figure 5, an increase in pressure not only increases the oil yield RT,but it decreases the yields in char (1 - X)and in light compounds (X- R T ) . The effect of flow rate is of particular interest. As can be seen in Figure 4, raising the methanol flow rate increases the oil yield and diminishes the residual char. This behavior illustrates the existence of a secondary reaction of recondensation and repolymerization of the primary liquid products on the solid residue. A reduction in flow rate means as increase in residence time of the solvent and of the dissolved oil in the reactor. This favor recombination of some fragments in the oil onto the char. This is not only confirmed by an increase in the mass of char recovered but also by structural changes of the char which is then much darker in color and has a lower specific surface area. For example, typical BET nitrogen surface areas of samples obtained at 0.22 g/s were 11.0 m2/g compared to a typical value of 5.3 m2/g at 0.075 g/s and the same pressure of 10.20 MPa. The magnitude of the effect of flow rate on the total oil yield is surprisingly high. By comparing Figures 4 and 5 it can be appreciated that a change from 0.075 to 0.22 g/s has almost as much effect as a variation in pressure from 3.40 to 17.01 MPa. This means that by proper control of flow patterns and of residence time distribution of the oil, the pressure of the process can be reduced signficantly. Moreover, since the data in Figure 4 show no levelling trend, it can be hoped that further increase in yield and conversion can be achieved by operating at much lower residence times than those possible with the present setup. It is therefore our view that further work is needed in order to assess the optimal performances of SGE for wood liquefaction. In particular, the effect of a largely decreased residence time would be of special interest since according to our results this should lead to higher oil yield and lower residual char while providing a possibility for reducing the solvent to wood ratio. Another important parameter still to be thoroughly studied is the nature of the solvent. As previously shown by McDonald and Howard (1981) and further illustrated by our findings concerning methyl acetate and methyl formate, methanol is to a certain extent reacting with some of the oil components. The search for a nonreacting solvent would thus be of some importance, as would the systematic study of aqueous solutions of organic solvents. In this respect, the possible use of wet wood in the process would constitute an important technical advantage since the costly and energy consuming preliminary wood drying operation would be avoided. It is also our opinion that a fair and well-documented comparison between the various processes studied for the direct liquefaction of wood will not be possible until systematic comparative studies of the capacity for upgrading of the various oils from these processes have been conducted. The ultimate criterion for the choice of a process will be the production cost for a liter of gasoline from wood and obviously much experimental information in particular on catalytic upgrading is still needed before these costs can be reasonable estimated. Acknowledgment We wish to thank the Natural Science and Engineering Research Council of Canada for a strategic grant, and the Ministry of Energy and Resources of the Province of Quebec and the FCAC fund for two scholarships. Registry No. Quartz, 14808-60-7;graphite, 7782-42-5;methanol, 67-56-1.
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 1, 1984
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Elder,-T. PhD. Thesls, Texas A 8 M Unhwsky, 1979. E M , D. C. “Bench Scale Research In Biomass Dkect Liquefactlon”; Proceedkrgs of the 14th Blomass Thermochemlcal Conversion Contractor’s Meetlng, ArRngton, VA, 1982. Hansen, S. M.; Aprll, G. C. I d . Eng. Chem. Rod. Res. Dev. 1982, 21, 621.
KaUagulne, S. “Etude de falsabillt6 d’un proc6d6 permettant de convertlr les mat6rlaux ll@wcellulosiqws en carburants llquides”. DEN, Mlnlst&re de I’Energle et des Ressources, au8bec, 1983. Kallagukre, S. “Upgrading Pyrolytic OHs from Wood and other Biomasses”; Energy P r o m Offlce, NaHonal Research Councll of Canada, Ottawa, 1981.
Klass. D. L. “Energy from Blomess and Wastes: 1982 Update”; Symposlum papers Energy from Blomass and Wastes VII, Lake Buena Vista, FP, 1982.
Labrecque, R. Masters Thesls, Lava1Unlversky, 1983.
Labrecque, R.; Kallagulne, S.; Grandmalson, J. L. “Supercritical Pyrolysls of Wooci”; Fourth Bloenergy R 8 D Setmlnar, Whnlpeg, 1082. McDonald, E.; Howard. J. "Chemicals from Forest Products by Supercrltlcal Qas Extractlon”; ENFOR ProJect C51, DSS contract No. 41SS.KL 229-04123, Ottawa, 1981. Modell, M. “QasHlcetlon and Liquefaction of Forest Products in Supercrltlcal Water”; Fundamentals of Thermochemlcal Biomass Converslon: an Internatlon Conference, Eastes Park, CO, 1982. Pollquln, J. /’Ing&i8uf 1081, 6(1), 7. Roy, C.; de Caumla, B.; Broulllard, D. “The Pyrolysis under Vacuum of Popu/us bemukM8s and Its Constltuents”; Abstracts, Fundamentals of Thermochemical Blomass Conversion, Eastes Park, CO, 1982. Shaflzadeh, F., et al. J. of Appl. Pokm. Scl. 1970 23(12), 3525. Shaflzadeh, . “Fuels from Wood Waste“ In “Fuels from Wastes”: Anderson, L. L.; TIBman, D. A., Ed., Academlc Press: New York, 1977. Snedecor, G. W.; Cochran, W. G. “Statlstlcal Methods”: The Iowa State Unverstty Press: Ames. IA, 1967. Thigpen, P. L.; Berry, W. L. “Liquid Fuels from Wood by Continuous Operatiin of the Albany, Oregon Blomass Llquefaction Facllky”; Symposlum Papers Energy from Bbmass and Wastes VI, Lake Buena Vista. FP, 1982.
Received for review June 6 , 1983 Accepted August 15, 1983
