1846
Ind. E n g . Chem. Res. 1990, 29, 1846-1855
Kara, M.; Sung, S.;Klinzing, G. E.; Chiang, S.H. Hydrogen Mass Transfer in Liquid Hydrocarbons at Elevated Temperatures and Pressures. Fuel 1983,62, 1492-1498. McPherson, W. P.; Foster, N. R.; Hastings, D. W.; Kalman, J. R.; Gilbert, T. D. Tetralin decomposition in short contact time coal liquefaction. Fuel 1985, 64, 457-460. Murena, F. Cinetica del process0 di donazione di idrogeno nella liquefazione del carbone. Ph.D. Dissertation, Universiti di Napoli, Italy, 1989.
Simnick, J. J.; Lawson, C. C.; Lin, H. M.; Chao, K. C. Vapor-Liquid Equilibrium of Hydrogen/Tetralin System at Elevated Temperatures and Pressures. AIChE J. 1977,23, 469-476. Whitehurst, D. D.; Mitchell, T. 0.;Farcasiu, M. Coal Liquefaction; Academic Press: New York, 1980; p 166. Receiued for reuiew November 1, 1988 Revised manuscript received April 23, 1990 Accepted May 14, 1990
Kinetics of the Pyrolysis of Almond Shells and Almond Shells Impregnated with CoC12in a Fluidized Bed Reactor and in a Pyroprobe 100 Rafael Font,* Antonio Marcilla, Emilio Verdii, and Joaquin Devesa Division of Chemical Engineering, University of Alicante, Apartado 99, Alicante, S p a i n
A fluidized bed reactor and a Pyroprobe 100 have been used in order t o study the kinetics of the flash pyrolysis of almond shells and of almond shells impregnated with CoC1, (14.1 g of CoCl,/lOO total g). Assuming first-order reactions, a good fit of the yields of total gases, total liquids, and solids to the expressions deduced has been obtained for the four kinetic studies carried out. Nevertheless, on considering the components analyzed in each case, some discrepancies have been observed. Kinetic parameters obtained for the four kinetic studies have been compared, and their differences have been discussed. Introduction
pregnated with CoCl,, which causes an increase in the yield of 2-furaldehyde.
By biomass pyrolysis, different chemicals and fuels can be obtained. The kinetics of pyrolysis of lignocellulosic materials has been investigated by several researchers using different techniques: furnace reactors ( S t a ” , 1956; Hajaligol et al., 1980,1982; Antal et al., 1980; Thurner and Mann, 1981; Jegers and Klein, 1985; Nunn et al., 1985a,b), vacuum (Broadbury et al., 1979),DTA and TGA (Browne and Tang, 1963; Chatterjee and Conrad, 1966; Akita and Kase, 1967; Mack and Donaldson, 1967; Maa and Bailie, 1978; Leu, 1975; Tran and Rai, 1979; Antal et al., 1980; Urban and Antal, 1982; Bilbao et al., 1987a,b; Alves and Figueiredo, 1988),and fluidized bed reactor (Barooah and Long, 1976; Kosstrin, 1980; Liden et al., 1988; Scott et al., 1988). A wide variation in the kinetic parameters reported, activation energy and rate constants, can be observed in the literature. This fact is probably due to the diversity of raw materials investigated (cellulose, lignin, different types of wood, biomass), the particle size, the different schemes of reaction considered, the different operating conditions studied (temperature intervals, pressure, heating rate, atmosphere, residence time of the volatiles), the different types of reactors, and the variables considered and analyzed (yields of solids, liquids, tars, gases; yields of the different compounds; etc.). Thus, for example, the different values for the activation energy of the pyrolysis reactions of these types of materials, obtained by following the evolution of the total volatiles or condensable volatiles, range from 14.6 to 227 kJ/mol. Almond shells are an abundant and available agricultural byproduct in moderate climate zones as the Alicante area (southeastern Spain). The scope of the present investigation is to study the kinetics in two experimental equipments (fluidized bed reactor and Pyroprobe 100) with nonimpregnated almond shells and almond shells im0888-5885/90/ 2629-1846$02.50/0
Kinetic Model Different schemes of reaction have been suggested for the pyrolysis of biomass, each one leading to different expressions to correlate the kinetic data (Kosstrin, 1980; Thurner and Mann, 1981; Nunn et al., 1985a,b; Scott et al., 1988). From all of these, we have selected two models for the correlation and discussion of the experimental data obtained in the present work. Biomass decomposes at high temperatures according to a complex scheme of reactions, both in series and in parallel. Furthermore, mass diffusion and heat-transfer phenomena may affect the overall kinetics of the process. Assuming that for a solid the specific decomposition rate (mass reacting by time unit and mass unit) is constant, this rate may be written according to the following equation: -(l/B)(dB/dt) = constant (1) where B is the biomass present at any time (mass or mass fraction with respect to the initial mass). This equation corresponds to a first-order overall reaction for the decomposition of the solid material. A single reaction can be written as B aG + bL + cS (2)
-
where G, L , and S are the different fractions of gases, liquids, and solids produced at a time t and a, b, and c are the yield coefficients, expressed as grams of gas, liquid, and solid per gram of reacted biomass. Applying the kinetic law expressed by eq 1, we can deduce dA/dt = k(A, - A ) (3) where A is the yield of any fraction or compound and A , is the maximum value of A at time infinite. The kinetic 0 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1847 constant k does not depend on the fraction or compound considered. Nevertheless, a superscript is introduced to indicate the experimental data considered; Le., kG is the constant obtained when correlating gas yield data. It can be deduced from material balances that the values of A , coincide with the yield coefficients (i.e., a equals G,, b equals L,, etc.). Equation 3 has been used in many works for correlating the experimental data (Kosstrin, 1980; Jegers and Klein, 1985; Nunn et al., 1985a,b). Another expression equivalent expression to eq 3 used in this work is dD/dt = kD(D, - D) (4) where D is the fraction of volatilized biomass (which equals G + L), D, is the maximum value of D at time infinite, and kD is the corresponding kinetic constant (equal to k). Integrating eqs 3 and 4 within the limits t = to, A = 0, D = 0 and t = t, A = A , D = D, we deduce A = A,[1 - exp(-k(t - t o ) ) ] (5) D = D,[1 - exp(-k(t - t o ) ) ]
(6)
On the other hand, Thurner and Mann (1981) suggested that the complex set of reactions may be simplified to three parallel reactions, each one leading, separately, to the corresponding fraction: G
;f
B - L
\ From the material balances between the initial conditions ( t = to, B = 1, G = L = S = 0) and at time t in a discontinuous process a t constant temperature, we could deduce similar expressions to eq 5 for each fraction, G, L, and S , with the following equivalences: k = k, k2 k3 (8) u =
G,
+ + = k,/(k, + k2 + k3)
(9)
Consequently, both schemes (assuming first-order kinetics) lead to equivalent expressions a t constant temperature. Both schemes are simplifications of the actual process. The advantage of using the Thurner and Mann model is that it is possible to correlate the individual constants k,, k2,and k3 with the temperature and thus obtain the variation of the yield coefficients with respect to the temperature. When the decomposition process takes place with variation of temperature, other expressions to those previously reported must be considered. In this case, probably eq 2 cannot be used because the yield coefficients can depend on the temperature history. In this paper, the experiments have been carried out at a fast heating rate, in order to decrease the induction period where the particle is heated to the set temperature.
Experimental Section Details of the fluidized bed reactor are shown in a previous paper (Font et al., 1986). Liquids were collected by means of a condensation train formed by water-cooled and salt-ice-cooled condensers and several cold traps in order
to collect all the condensable compounds. Most of the liquids condense in the first condensers (parts 9 and 10 in Figure 2 of the previous paper (Font et al., 1986)). Replacing the sample collector (number 11 in Figure 2 of the previous paper) made it possible to obtain data on the liquid production. Several gas sample collectors at the end of the experimental system have been used to obtain data on the composition of the outlet gas. Considering the inlet nitrogen flow and the composition of the outlet gas, the yields of gases were obtained a t different times. In the fluidized bed reactor, a sample of almond shells is poured on a hot sand bed fluidized by a nitrogen stream, when the reactor has reached the set temperature. This time was considered the origen of the reaction time. The diameter of the sand particles used in the bed was 0.105-0.210 mm, the diameter of the almond shell particles was 0.297-0.500 mm, the velocity of the nitrogen worked out at the reaction conditions was 4.7 cm/s, the ratio almond shells mass/sand mass was around 1/30, and the amount of almond shells pyrolyzed was around 30 g. The value of 4.7 cm/s for the velocity of nitrogen was selected to obtain a good mixture between the sample of almond shells poured onto the fluidized sand bed and the sand particles. In a set of previous runs, we tested that the volume of the reactor from the top of the fluidized sand bed to the reactor head was great enough to allow the volatiles evolved to be cracked in the gas phase. Porapak Q and silica gel chromatographic columns were used to analyze the compounds of liquids and gases, respectively. The dry residue a t 120 “C (tarry fraction of the liquid) was also determined. More details on the experimental equipment, procedure, and analytical methods can be found elsewhere (Font et al., 1986). CoC1, was selected to study the catalytic pyrolysis of almond shells as a consequence of a previous work, mainly due to the following reasons: (a) it is an acidic catalyst which causes a remarkable increase in the 2-furaldehyde yield; (b) the blue color acquired by the almond shell particles allowed one to test the uniform distribution of the catalyst in different particles and inside each particle. The high percentage of CoCl2,around 14.1%, was selected for two reasons: (a) at this high percentage, the 2-furaldehyde yield was greater than that obtained a t lower percentages; (b) the influence of the catalyst on the kinetics can be observed more clearly at a high impregnation ratio. The impregnation was carried out as follows: five batches of 60 g of washed almond shells mixed with catalyst solutions of known concentrations were prepared in a “rotavaporn Buchi, providing agitation and a 60 mmHg vacuum for 2 h. Afterwards, the samples were dried at 110 “C for 20 h. Once the five samples were prepared they were mixed well. For the kinetic study carried out in the Pyroprobe 100, the operating conditions were the following: diameter of almond shells particles, 0.297-0.500 mm; sample amount, 2 mg; “nominal heating rate”, 20 OC/ms; chamber temperature prior to analysis, 200 O C ; chromatographic columns, Porapak Q and silica gel. Several runs were carried out in a 1-20-s pyrolysis time range. Actual temperatures of the sample probe were tested by melting different inorganic compounds. The results obtained were in good agreement with the calibrated temperatures of the probes where the samples are introduced. In this case, it was possible to follow the evolution of yields corresponding to gaseous compounds and liquid compounds. The overall decomposition (gases + liquids) was determined by weighing the residue. The selection of the temperature ranges and pyrolysis time was carried out according to the possibilities of each experimental equipment.
1848 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990
-r4
-
u
-- 0 7
---
>o, 'II
I
zoo
:or
and gas Figure 1. Liquids (0) reactor. 7' = 425 O C .
( 0 ) yields
9
irc
t
S I
9
vs time. Fluidized bed
Figure 3. CH4 (0) and H2 ( 0 )yields vs time. Fluidized bed reactor. T = 425 OC.
3.0
7
Figure 2. CO ( 0 )and C02 (0) yields vs time. Fluidized bed reactor. T = 425 "C.
Results and Kinetic Parameters in the Fluidized Bed Reactor with Almond Shells without Impregnation Table I shows the total yields obtained in the six experiments, carried out at five temperatures (400,420,425, 440, and 460 " C ) for the kinetic study of the pyrolysis of almond shells without catalyst in the fluidized bed reactor. Yields of the gas components (COz, CO, CHI, and H,) and the total liquids have been measured as functions of time. Figure 1 shows the variation of the total gases and the total liquids vs time, Figure 2 shows the yields of CO and CO, vs time, and Figure 3 shows the variation of CHI and H, vs time for the experiment carried out at 425 "C. To test the kinetic law expressed by eq 5, the following linear equation has been used: (12) In (A,/(A, - A ) ) = k ( t - t o ) Figure 4 shows the In (A,/(A, - A ) ) vs time plots corresponding to the different fractions and compounds for the experiment carried out at 425 "C. We observe that there is an initial period where the experimental points are not on the straight line that can be drawn taking into account the experimental data obtained at higher values of reaction time. In order to determine the optimum values of k and t o and their corresponding confidence intervals, the Gauss-Siedel method (Himmenblau, 1970) was used to minimize the objective function (OF) defined as follows:
where n is the number of data. The size of the almond shells particles (0.2974.500 mm) was limited to the range used in order to obtain a good mixture between almond shells and sand. With the same
U
25
50
75
100
125
150 t ( S )
Figure 4. Values of In ( A , / ( A , - A ) ) vs time. Fluidized bed reactor. T = 425 "C. Total liquids (m);total gases (0);C02 (0); CO (A); CH, ( 0 ) ;Hz (A).
size of almond shells particles, some runs were carried out with the Pyroprobe 100, indicating that there is no induction period corresponding to a heat-transfer resistance (values of to close to zero). This indicates that there are no significant gradients of temperature inside the particles. Consequently, an external heat transfer must be considered in the fluidized bed reactor, which provokes the appearance of an induction period. Thus, the experimental points that are close to the straight line obtained when values In (A,/(A, - A)) are plotted vs time have been considered in the numerical fit. The experimental points corresponding to the induction period are not considered. Table I1 shows the kinetic parameters obtained and their 90% confidence intervals, for all the experiments carried out. The variation coefficient (VC) was calculated by the equation VC = 100(OF/(n number of parameters))1/2/meanvalue of A (14) Rate constants for gases and liquids are plotted vs the inverse of the temperature in Figure 5. A coincidence between the kinetic constants obtained for total gases and total liquids as well as a linear variation of the k values with 1/T can be observed. From Table 11, it is apparent that the variation coefficients and the confidence intervals for the kinetic constants for liquids increase with temperature. We have observed that the plots of In (A,/(A, - A)) vs time show linear
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1849 Table I. Overall Yieldsa Obtained in the Kinetic Study of the Pyrolysis of Almond 400 OC 420 "C 425 "C 54.2 47.0 46.8 solids 36.3 41.4 41.6 liauids water 16.6 16.4 16.7 methanol + formaldehyde 1.4 1.0 1.5 acetaldehyde acetone 0.06b 0.14b 0.16* 2-propanol acetic acid 3.2 3.5 4.0 hydroxyacetone 0.88 0.92 0.85 propionic acid 0.10 0.13 0.15 3-methyl-1-butanol 0.26 0.33 0.41 1-hydroxy-2-butanone 0.40 0.52 0.50 2-furaldehyde 0.45 0.46 0.55 13.0 18.0 16.4 dry residue at 120 O C gases 8.1 8.3 8.6 COZ 6.0 4.8 4.9 co 1.9 2.9 3.1 0.13 0.36 0.44 CHI 0.09 0.15 0.15 H2 total a Weight
97.3
96.7
95.1
percentage on moisture-free almond shells basis. *Acetone
Shells in the Fluidized Bed Reactor 440 "C 440 OC 460 "C 29.4 30.6 27.5 57.0 52.0 56.0 18.7 16.4 17.7 0.92 1.1 1.3 0.01 0.06 0.12 0.26 0.25 0.06 0.18 0.33 9.0 9.0 10.3 1.4 1.5 2.1 0.28 0.33 0.49 0.77 0.44 0.81 1.1 1.1 1.2 0.91 0.64 0.67 20.6 22.3 24.1 13.1 13.3 14.2 9.0 9.0 9.9 3.8 3.7 3.6 0.47 0.37 0.61 0.09 0.10 99.6
95.9
97.7
+ 2-propanol.
Table 11. Parameters for Total Liquids, Total Gases, and Components of the Gases for Pyrolysis of Almond Shells without Catalyst in the Fluidized Bed Reactora temp, "C k , s-l A, to, to19 s to29 s vc Total Gases 400 0.013 97 f 0.001 17 8.11 34.8 f 2.8 20 14 5.8 420 0.018 32 f 0.000 76 8.31 27.8 i 1.0 14 13.8 2.7 425 0.013 72 f 0.000 57 8.67 23.9 f 1.6 9 14.9 2.1 440 0.018 23 f 0.000 55 13.26 27.6 f 1.0 8 19.6 1.5 440 0.02091 f 0.001 73 13.17 27.9 f 1.9 8 19.9 3.7 460 0.033 39 f 0.002 93 14.22 27.0 f 1.7 4 23 3.6 Total Liquids 33.0 62.3 f 2.1 37.6 43.8 f 2.7 37.8 41.1 f 3.2 47.2 27.4 f 7.2 50.8 26.1 f 5.2
400 420 425 440 440 460
0.007 64 f 0.000 26 0.009 86 f 0.000 59 0.011 19 f 0.000 83 0.01400 f 0.002 24 0.017 01 f 0.002 42
400 420 425 440 440 460
0.01273 f 0.001 38 0.01403 f 0.00071 0.00943 f 0.00088 0.01561 f 0.00051 0.01660 f 0.000 90 0.029 99 f 0.005 30
6.0 4.9 4.9 9.0 8.9 9.9
400 420 425 440 440 460
0.020 74 f 0.001 65 0.043 11 f 0.007 07 0.027 31 f 0.002 81 0.043 00 f 0.003 65 0.03980 f 0.014 30 0.060 25 f 0.002 86
1.90 2.92 3.10 3.70 3.80 3.60
400 420 425 440 440 460
0.006 34 f O.OO0 88 0.010 44 f 0.000 75 0.00881 f 0.00070 0.01044 f 0.00049 0.01995 i 0.001 82 0.013 93 f 0.001 12
0.13 0.36 0.44 0.47 0.37 0.61
400 420 425 440 440 460
0.022 32 i O.OO0 83 0.033 15 f 0.003 31 0.026 47 f 0.002 74 0.034 10 f 0.005 59
0.09 0.15 0.22 0.09
0.042 19 f 0.003 11
0.11
COZ
co
CH4
H2
48.3 30.0 26.2 7.8 6.2
14.0 13.8 14.9 19.6 19.9
3.3 5.7 7.4 8.6 8.0
34.6 f 3.8 31.5 f 1.6 25.8 f 3.5 31.3 f 1.0 28.3 f 1.4 26.0 f 3.9
8.0 3.6 8.5 2.0 2.7 7.9
34.5 f 2.0 31.1 f 2.1 23.9 f 2.0 29.9 f 1.5 29.8 f 5.1 30.6 f 0.5
4.6 6.8 6.2 2.7 11.9 1.7
44.0 f 6.7 35.2 f 2.8 30.4 f 2.8 33.7 f 1.9 31.7 f 1.9 32.1 f 2.3
17.5 6.5 8.3 3.8 5.1 5.8
29.3 f 1.0 28.2 f 1.8 24.5 f 2.0 29.5 f 3.3
3.9 6.2 6.0
29.0 f 1.1
3 .O
"VC = variation coefficient (YO).The range of the parameters k and t o corresponds to 90% confidence intervals.
1.8
1850 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990
0 - ,005
dMhi ( W S
1
-.010
-,
015
- ,020
100
200
300 400 500 T
600
700
800
(OCi
Figure 7. TGA of almond shells a t 40 "C/min heating rate. U T
(K-l)
Figure 5. Values of k vs 1 T.Fluidized bed reactor: kc (A);kL (A). Pyroprobe 100 kC (0); k (0).
6
0
50
100
150
t
200
150
(s)
Figure 6. Values of In ( A , / ( A , - A ) ) vs time for the fluidized bed reactor without catalyst a t 440 "C (A)and fluidized bed reactor with catalyst a t 445 OC (A).
behavior at 400 "C, but with increasing temperature a second linear behavior progressively appears. In Figure 6, where the experimental results a t 440 "C are plotted, we can observe the presence of two straight lines. We have presented the slope of the plots as if all the points fitted only one straight line at each temperature, and thus they represent the average kinetic constants of the two processes observed. This fact could be explained if one considers that the biomass is formed, a t least, by two fractions (Le., cellulose and lignin) which decompose a t different temperatures (cellulose at lower temperatures than lignin) and different rates. Figure 7 shows a TG analysis of almond shells at a 40 "C/min heating rate, proving the existence of two peaks corresponding at least to two decomposition processes. Considering the kinetic constants for the gaseous components, it can be deduced that the formation of CO is faster than the formation of COz and CHI. In order to analyze and compare the values of to in Table
11, we have to consider that toincludes two different times. One is the time required to collect the first amounts of liquids and gases (tol),and obviously this time tor decreases with temperature (since the gas and liquid evolutions are faster at increasing temperatures). Due to the configuration of the collection trains, and the different flow behavior of gases and liquids, the time required to collect the first amounts of gases is lower than that corresponding to liquids (consider that it is necessary to obtain a certain amount of liquids to collect the first drop in the collector, whereas gases are readily detected). The other time considered (toz)in Table I1 is the "induction time", which is the time required to heat the sample to the reaction temperature. This time must be the same for gases and liquids and must increase with temperature. Table I1 shows the values of to obtained from the correlations for gases. For gases, values of tol have been estimated from the plots of A vs time (period between discharging sample and detection of gaseous products), and tO2values have been obtained by subtracting to, from t,. It can be observed that the values of tO2 obtained increase with temperature whereas the tol values decrease with temperature. For liquids, it was impossible to estimate tO1,and we have considered that tozmust be equal for both gases and liquids; thus we have obtained tol by subtracting t , for gases from tofor liquids. The resulting values (toll decrease with temperature as could be expected. The values of tofor the components of the gas fraction are very similar to that of the total gases, and the same considerations must apply for the components. Table I1 only shows the values of to obtained from the fits for the gas components.
Results and Kinetic Parameters in the Pyroprobe 100 with Almond Shells without Impregnation For the kinetic study in the Pyroprobe 100 equipment, experiments a t 460, 480, 510, 530, 560, and 605 "C have been carried out as described in the Experimental Section. Table I11 shows the kinetic parameters obtained. It can also be observed that the kinetic constants for the individual components are quite different. But again, the constants corresponding to the total gases and kD,corresponding to the overall decomposition (gases + liquids), are very similar, following the reaction schemes proposed.
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1851 Table 111. Kinetic Parameters for Total Gases, Overall Decomposition, Components of Liquids, and Components of Gases for the Pyrolysis of Almond Shells without Catalyst in the Pyroprobe 100' temp, "C
k, s-'
460 480 510 530 560 605
0.046 f 0.019 0.092 f 0.018 0.132 f 0.036 0.208 f 0.045 0.402 f 0.163 0.432 f 0.028
460 480 510 530 560 605
0.052 f 0.021 0.102 f 0.020 0.150 f 0.106 0.246 f 0.055 0.466 f 0.244 0.515 f 0.051
460 480 530 560
0.046 0.110 0.213 0.258
460 480 510 530 560 605
f f f f
A, Total Gases
0.011 0.038 0.055 0.098
4.7 f 1.0 5.7 f 0.4 6.7 f 0.5 6.6 f 0.3 9.4 f 0.7 11.2 f 0.1
CO:,
3.6 4.3 4.8 4.8 6.7 7.5
H20 5.0 4.6 5.5 6.9
vc
t,, s
0.7 0.8 -0.9 0.2 0.5 -0.2
f 0.9 f 0.6 f 0.9 f 0.5 f 0.4 f 0.1
5.3 3.7 1.8 2.7 5.9 0.9
0.5 0.8 -1.2 0.4 0.5 -0.2
f f f f f f
1.0 0.6 2.4 0.5 0.5 0.2
5.5 3.7 4.4 2.8 6.9 1.2
f 0.6
1.1 f 0.6
f 0.5 f 0.2 f 0.7
1.5 f 0.9 -1.0 f 0.9 -0.1 f 0.7
2.2 7.5 2.3 8.3
f 0.7 f 0.3 f 0.7
f 0.2 f 0.6 f 0.1
Overall Decomposition (Gases + Liquids) 0.031 f 0.007 64.4 f 9.5 0.0 f 0.6 0.083 f 0.021 0.183 f 0.010 0.187 f 0.028 0.381 f 0.105 0.525 f 0.157
50.5 f 4.8 65.3 f 0.8 67.0 f 1.9 78.7 f 4.2 83.0 f 2.5
f 0.5
1.5 4.4 0.4 1.3 4.0 2.8
2.0 f 0.9 1.4 f 0.6 0.3 f 2.1 -0.4 f 2.1 0.7 f 0.3 0.1 f 0.2
6.5 4.2 7.8 7.6 5.4 2.2
2.1 1.7 -1.5 -0.2
1.0 0.7 0.6 0.5
6.1 6.1 1.2 4.7
0.5 f 1.9 1.1 f 2.1 -3.1 f 3.2 -0.9 f 1.0
6.3 13.3 4.5 7.6
2.7 f 2.5 -0.5 f 1.4 0.4 f 0.5
10.4 1.2 8.9
2.8 f 2.6 0.1 f 1.2 0.4 f 0.6
10.4 5.1 8.9
1.0 f 0.8
18.6
0.7 -0.2 -1.2 0.4 -0.5
f 0.8 f 0.2 f 0.6 f
0.3
co 460 480 510 530 560 605
0.028 0.063 0.106 0.129 0.303 0.336
f f f f f f
460 480 530 560
0.074 0.118 0.187 0.327
f f f f
460 480 530 560
0.058 0.065 0.100 0.128
f 0.036 f 0.051
480 530 560
0.142 f 0.116 0.083 f 0.011 0.235 f 0.078
480 530 560
0.142 f 0.116 0.126 f 0.055 0.235 f 0.078
560
0.213 f 0.121
0.017 0.015 0.103 0.094 0.088 0.039
1.3 f 0.6 1.5 f 0.2 1.9 f 0.7 1.9 f 0.4 2.7 f 0.2 3.8 f 0.1
Acetic Acid 0.030 6.0 f 1.0 0.031 0.027 0.086
6.8 f 0.6 7.6 f 0.2 8.7 f 0.5
f f f f
Methanol f
0.070
f 0.049
Acetone
0.40 0.82 0.56 0.78
f f f f
0.10 0.29 0.11 0.11
+ 2-Propanol 0.30 f 0.05 0.83 f 0.05 0.80 f 0.0
Acetaldehyde 0.30 f 0.06 0.67 f 0.09 0.78 f 0.08
l-Hydroxy-2-butanone
460 480 530 560
1.12 f 0.21
2-Furaldehyde 0.125 f 0.114 0.23 f 0.06 0.162 f 0.104 0.182 f 0.043 0.176 f 0.071
0.26 f 0.04 0.33 f 0.01 0.35 f 0.03
4.5 2.9 -1.2 -1.8
2.1 1.9 0.9 1.3
12.3 8.2 2.1 6.0
1.8 f 2.8 -2.9 f 0.6 0.2 f 0.6
8.3 2.5 8.5
3.5 f 1.3 1.1 f 1.7 1.2 f 0.7
7.3 9.9 18.3
f f f f
3-Methyl- 1 -butanol 480 530 560
0.079 f 0.062 0.192 f 0.041 0.231 f 0.076
480 530 560
0.124 f 0.060 0.068 f 0.067 0.159 f 0.079
0.42 f 0.12 0.53 f 0.02 0.71 f 0.07
Hydroxyacetone 0.39 f 0.05 1.73 f 0.93 1.93 f 0.42
"VC = variation coefficient (%). The range of the parameters k, A,, and t o corresponds to 90% confidence intervals.
In this case, the variation of the data is much lower than in the fluidized bed reactor. The constant corresponding to COzis, as in the case of the fludized bed reactor, very close to kG and kL. The values to are around zero, so we can deduce that the small sample introduced in the Pyroprobe reaches the set temperature very quickly, and the heat transfer is very fast in this equipment. The values A, in this case have also been calculated by correlation, due to the fact that their determination would require pyrolysis times greater than 20 s, which is the maximum possible pyrolysis time in this equipment. These values A, for gases are much lower than those obtained in the fludized bed reactor, probably due to cracking of the volatiles in the top part of the fluidized bed reactor (something which does not takes place in the Pyroprobe 100 equipment, where the residence time of the volatiles at the reaction temperature is negligible). The values of A, corresponding to the overall decomposition (total volatiles) in the Pyroprobe and the sum of A, for gases and liquids (total volatiles) in the fluidized bed reactor compare very well. On the other hand, the plots of In (A,/(A, - A)) vs time in the Pyroprobe, contrary to the fluidized bed reactor, only show one straight line. This could be due to the overlaping of the processes of decomposition of the different components (celluloseand lignin) as a consequence of the fast heat transfer and a high temperature. In this case, the values t o are very close to zero for all components, proving that the heat transfer is much better than in the fluidized bed reactor. Figure 5 shows the logarithms of kc and kD values obtained in the Pyroprobe 100, together with the logarithms of kG and kL values obtained in the fluidized bed reactor, vs 1/T. A linear behavior can be observed with the following fitting parameters: k, = 1.885 X lo6 s-l and E = 108 kJ/mol, with a correlation coefficient of 0.975. This fact proves that on average the kinetic constants obtained in the Pyroprobe and in the fluidized bed reactor are quite coherent, despite the differences inherent to both techniques. The values k and E obtained are in the range of values given in the literature (see Table IV, where the parameters obtained can be compared with others proposed in the literature).
Results and Kinetic Parameters in the Fluidized Bed with Almond Shells Impregnated with CoClz Five experiments a t 410,425,445,470,and 500 OC have been carried out for this kinetic study. Table V shows the results obtained for the total yields produced in each experiment. Yields of COz,CO, CH,, and Hz, and the total of liquids have been measured at different times. For gases, the plot of In (A,/(A, - A)) vs time is very similar to that obtained without catalyst, showing a linear behavior in the entire range, and thus it is possible to obtain rate constants according to the suggested model. These constants are shown in Table VI. A very low activation energy can be observed (since the rate coefficients are almost constant with temperature), proving a behavior very different to that observed without catalyst and probably more influenced by the heat transfer. Table VI also shows the rate constants for the gas components. Different kinetic constants for each temperature can be observed, proving that the reaction pathway for each component is different. Figure 6 shows the plots of In (A,/(A, - A)) vs time for evolution of liquids for two experiments, one at 440 OC without catalyst and the other at 445 "C with CoC1,. It is evident that the experiments with catalyst do not ?allow the same mechanisms as that without catalyst. On considering the previous comments,
1852 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 Table IV. Kinetic Parameters from the Literature experimental temp researcher system range, OC dynamic TGA 100-800 Tran and Rai (1979) Thurner and Mann (1981) tubular reactor 300-400 100-1000 Hajaligol et al. (1982) screen heater Anta1 et al. (1980) dynamic TGA 110-600 327-1127 Nunn et al. (1985a) screen heater Nunn et al. (1985b) screen heater 327-1127 AIves and Figueiredo (1988) isothermal TGA 265-650 fluidized bed 400-460 present work Pyroprobe 100 460-605 Table V. Overall Yieldsa Obtained in the Kinetic Study of the Pyrolysis of Almond Shells Impregnated with 14.1 wt % CoCl, in the Fluidized Bed Reactor 410 "C 425 "C 445 "C 470 "C 500 "C solids 57.0 46.3 45.2 44.7 41.3 42.8 42.3 liquids 34.6 42.1 46.1 water 19.4 22.7 23.2 24.2 23.3 methanol + 0.61 1.3 1.0 0.69 1.4 formaldehyde acetaldehyde acetone 0.13 0.14* 0.18 0.19 2-propanol 0.07 0.08 0.17 acetic acid 3.7 5.8 5.5 5.5 7.2 hydroxyacetone propionic acid 0.07 0.42 3-methyl-1-butanol 0.09 1-hydroxy-2butanone i.i 6.9 6.9* 7.5 2-furaldehyde 6.1 dry residue at 4.8 5.1 4.2 4.5 5.7 120 "C 4.4 6.7 7.5 /,I 12.4 gases 5.3 5.0 4.8 9.3 coz 4.1 co 0.23 1.1 2.0 2.3 2.4 0.33 0.41 0.45 0.60 CH, 0.05 0.03 0.02 0.09 0.14 0.16 H2
--
I-
total
96.0
95.8
95.0
94.5
!)9.8
Weight percent on moisture-free almond shells basis. bAcetone
+ 2-propanol.
we deduce that CoCl, probably retards the biomass decomposition. In the plot corresponding to CoC1, in Figure 6, we can consider two lines. The first one corresponds to around 25 % biomass decomposition. On considering the points at higher times, which are nearly a straight line, we can obtain the corresponding kinetic constants (kL and to), which are presented in Table VI. The high values of to calculated also indicate the retardation suffered by the process. As these values of to are very far from those corresponding to gases, we deduce that the schemes presented previously are not appropriate for interpreting the experimental results with catalyst. In this case, only the pseudo-first-order reaction dA/dt = k ( A , - A) can be appropriate for consideration of the evolution of each fraction or compound (notice that the t o values obtained for each fraction are very different, which makes the suggested model not applicable). We observe that the values of kL obtained a t different temperatures are very similar, showing an apparent activation energy around zero and, therefore, a great influence of the heat transfer.
Results and Kinetic Parameters in the Pyroprobe 100 with Almond Shells Impregnated with CoCl, Runs have been carried out a t 410,430, 460, 500, and 540 "C, as described in the Experimental Section. Table VI1 shows the kinetic parameters obtained for evolution
raw material fir bark wood cellulose cellulose lignin sweet gum hardwood pine bark almond shells almond shells
conversion degree 0.70 0.70 0.94 0.90 0.84 0.93 0.68 0.72 0.84
EA9
FF, s-l 2.13 X lo* 2.47 X lo6 1.99 x 108 7.0 x 109 3.39 x 106 3.38 x 104 550-1.35 X 1.88 X lo6
lOI5
kJ/mol 202 107 133 153 82 69 52-319 108
Table VI. Kinetic Parameters for Total Gases, Total Liquids, and Components of the Gases for the Pyrolysis of Almond Shells Impregnated with 14.1 wt % CoCI, in the Fluidized Bed Reactora temp, "C k , s-l A, to, 9 vc Total Gases 410 4.60 32.4 f 8.2 14.4 0.0074 f 0.0010 425 0.0128 f 0.0004 22.3 f 1.2 6.84 2.3 7.18 445 0.0093 f 0.0012 33.4 f 7.3 9.6 0.0115 f 0.0008 33.5 f 3.2 7.44 470 3.9 24.2 f 4.0 8.51 0.0099 f 0.0008 500 5.8 410 425 445 470 500
COP 0.0072 f 0.0010 4.02 0.0094 f 0.0008 3.87 4.72 0.0087 f 0.0013 0.0102 f 0.0008 4.70 5.59 0.0086 f 0.0010
33.7 f 8.4 26.8 f 3.3 38.3 f 7.7 36.6 f 4.0 28.7 f 5.9
14.0 7.5 11.8 5.4 9.2
410 425 445 470 500
CHI 0.0068 f 0.0018 0.04 0.0084 f 0.0005 0.43 0.0066 f 0.0005 0.37 0.45 0.0093 f 0.0009 0.0106 f 0.0007 0.45
73.9 f 19.0 33.6 f 2.7 28.8 f 5.0 37.6 f 5.1 25.0 f 3.1
18.3 6.0 5.8 6.9 4.6
410 425 445 470 500
Total Liquids 0.0135 f 0.0012 31.4 0.0125 f 0.0009 38.9 0.0120 f 0.0005 38.4
142 f 5 81 f 3 161 f 2
3.1 5.9 3.2
0.0119 f 0.0007
110 f 3
3.5
41.9
co 410 425 445 470 500
0.0397 f 0.0031 0.0311 f 0.0028 0.0119 f 0.0019 0.0170 f 0.0014 0.0156 f 0.0013
410 425 445 470 500
0.0205 f 0.0019 0.0258 f 0.0014 0.0118 f 0.0010 0.0096 f 0.0006 0.0091 f 0.0005
H2
0.23 2.31 2.00 2.15 2.35
30.9 f 1.1 25.0 f 1.5 26.4 f 8.4 31.2 f 3.1 20.7 f 2.7
2.5 5.3 8.9 3.9 3.9
0.032 0.224 0.090 0.140 0.118
24.9 f 2.3 25.5 f 1.2 16.6 f 5.1 18.0 f 4.2 7.2 f 3.4
5.1 2.6 3.7 3.2 3.0
VC = variation coefficient ('70 1. The range of the parameters k and t o corresponds to 90% confidence intervals.
of gases and overall decomposition (liquids + gases). Liquids do not follow the suggested model, as can be observed from the wide confidence intervals of kL, thus, these values are only orientative. The values to for water, acetic acid, and 2-furaldehyde (Table VII) are negative, whereas these values for the experiments without catalyst in the pyroprobe are near zero. Furthermore, the kinetic constants obtained for 2-furaldehyde are much higher when using CoC12as compared with the experiments without catalyst, proving the marked effect of the CoC1, on the evolution of this compound. This fact may be due to the action of the CoC1, favoring the dehydration reactions. The values of kC are much higher than those obtained in the fluidized bed re-
Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990 1853 Table VII. Kinetic Parameters for Total Gases, Overall Decomposition, Components of the Liquids, and Components of the Gases for the Pyrolysis of Almond Shells Impregnated with 14.1 wt % CoClz in the Pyroprobe 1000
temp,
to, s
A.
k, s-'
O C
vc
Total Gases
200
600
400
800
1(OC)
430 460 500 540
0.148 0.200 0.193 0.207
f 0.093
430 460 500 540
0.144 f 0.104 0.205 f 0.108 0.210 f 0.076 0.220 f 0.080
430 460 500 540
0.086 0.082 0.116 0.164
f 0.094 f 0.065 f 0.078
f f f f
0.025 0.024 0.012 0.022
Figure 8. DTA of almond shells (without impregnation).
3.1 f 0.4 3.2 f 0.4 4.2 f 0.4 5.3 f 0.4
coz
2.5 2.6 3.3 4.0
f f f f
0.3 0.3 0.3 0.3
HZO
17.1 f 1.0 18.8 f 1.1 20.0 f 0.5 20.6 f 0.7
-1.8 -0.4 -0.4 -1.0
f 2.2 f 0.9
-2.2 -0.5 -0.5 -1.2
f 2.8
-9.2 -9.6 -4.7 -1.6
f 2.3 f 2.3 f 0.6
f 0.7 f 1.0
f 1.1 f 0.8
f 1.0
7.8 5.3 5.1 4.7 8.3 5.6 5.2 4.1
f 0.4
0.8 0.7 0.7 1.5
-7.2 f 2.8 -4.0 f 0.8 -2.1 f 0.6 -1.1 f 0.4
1.3 0.9 0.8 1.8
-4.7 -3.8 -1.9 -3.3
f 2.4 f 2.9
3.4 4.8 3.1 2.8
-0.4 f 0.7 0.2 f 0.8 -0.1 f 0.5 -0.2 f 0.9
4.9 7.3 4.2 7.8
-6.3 -2.4 -2.4 -0.6
1.8 4.2 0.6 1.7
2-Furaldehyde 430 460 500 540
0.109 0.170 0.390 0.216
430 460 500 540
0.161 f 0.103 0.215 f 0.254 0.369 f 0.286 0.308 f 0.200
430 460 500 540
0.165 f 0.049 0.183 f 0.096 0.141 f 0.035 0.182 f 0.084
430 460 500 540
0.0678 0.0918 0.1207 0.1328
f f f f
0.044 0.030 0.075 0.034
7.1 f 0.5 7.1 f 0.2 7.0 f 0.1 7.5 f 0.2
Overall Decomposition I
rl
39.6 41.0 43.3 51.1
f f f f
3.3 5.4 2.8 2.6
co
x 1 L.
f
I
0
0.56 f 0.04 0.61 f 0.09 0.92 f 0.07 1.31 f 0.17
f 3.8 f 5.6
Acetic Acid
Y
, 700
,
, 400
,
,
,
, eo0
GOO T
(OC
1
f f f f
0.034 0.055 0.007 0.015
6.1 f 1.0 6.5 f 1.4 6.6 f 0.1 7.4 f 0.3
f 2.5 f 1.8
f 0.2 f 0.3
"VC = variation coefficient (%). The range of the parameters k, A,, and t o corresponds to 90% confidence intervals.
Figure 9. DTA of almond shells impregnated with CoC12.
actor and probably due to the different heat-transfer conditions in both types of equipment. Due to this, two DTA runs, with samples of almond shells without catalyst and impregnated with CoCl2,have been carried out. The corresponding results are shown in Figures 8 and 9. It can be observed that in the pyrolysis of almond shells without impregnation all processes are exothermic, whereas in the pyrolysis with CoC1, there is a first stage which is endothermic, probably due to the evaporation of the water which the CoC1, retains. Thus, it is possible that a t the beginning of the process the heat transfer in the fluidized bed reactor may not be sufficient for the almond shell particle to reach the bed temperatures. (Consider that in the fluidized bed reactor the C0C12has two molecules of water of hydration, whereas in the Pyroprobe the catalyst is in an anhydrous state since the initial temperature of the sample was 200 OC. Consequently, the catalyst has already lost its hydration water.)
Discussion In the previous sections, the experimental results and a comparison between the different values of kinetic con-
stants have been presented. The following scheme of reactions can facilitate the interpretation of the experimental results with or without catalyst:
e - ]7 primarygas
cellulose
biomass hemicellulose [lignin
primary tar
/
s-ndarygas
secondary liquids
charcoal
In addition, two facts must be taken into account: (1)With the Pyroprobe 100, only the primary products are produced, due to the low residence time of volatiles, which cannot undergo a secondary decomposition. (2) The heat transfer is faster in the Pyroprobe (induction period around zero) than in the fluidized bed (considerable value of the induction period). The heat-transfer effect is greater in the catalytic almond shells pyrolysis due to the presence of the acidic catalyst, which must lose two molecules of water of the hydrated salt. According to the scheme proposed and the two facts previously cited, several considerations can be deduced. Taking into account the total gases and total liquids or overall decomposition, similar values of kinetic constants have been obtained when pyrolyzing almond shells without
1854 Ind. Eng. Chem. Res., Vol. 29, No. 9, 1990
impregnation. This means that the single schemes with pseudo-first-order reactions 8
-
aG
+
bL
+
CS or
/ G
8 -1 1 .
S
can interpret the experimental results. Taking into account the kinetic constants obtained for total gases, total liquids (using the fluidized bed reactor), and total gases and overall decomposition (using the Pyroprobe loo), the following expression for k can be deduced: k = k 4 7 3 . 6 0 ~exp[-13002(1/T - 1/(473.6 + 273.15))] = 5.221 X lo-, exp[-13002(1/T - 1/(473.6 + 273.15))] = 1.885 X lo6 exp(-13002/77 s-l (15) The correlation coefficient of the linealized equation is r = 0.975. The 90% confidence interval obtained from the linealized equation is (for k473,6)4.43 X 10-2-6.15 X lo-, s-'. The activation energy is 94.8-121 kJ/mol. For the pyrolysis of almond shells using the fluidized bed reactor, the corresponding values of kl,k,, and k3 have been obtained from eq 15 and the values of G,, L,, and S , (1 - G, - L,) and by taking into account eqs 9-11. Taking into account that the volume of the reactor from the top of the fluidized bed was great enough to allow the volatiles evolved to be cracked, constant k l in the three parallel reactions scheme (or yield coefficient "a" in the single-reactionscheme) includes the gases proceeding from the initial decomposition (primary gases) and those proceeding from the cracking of the volatiles (secondary gases). The constant k , or yield coefficient "b" refers to the primary liquid volatiles minus the volatiles cracked. These values have been correlated with 1/T, and the corresponding expressions are also presented in Table VIII. For the pyrolysis of almond shells using the Pyroprobe 100, from eq 15 and the values of G,, L , (D,- G,), and S, (1- G, - L J , the corresponding parameters k,, k,, and k3 have been calculated. In Table VIII, the relationships between these constants and 1/T are presented. We deduce that the formation of the gases, liquids, and solids can be interpreted by the three parallel reactions, in accordance with the Thurner and Mann (1981) model. The formation of the volatiles (gases and liquids) is favored when increasing the temperature with respect to the carbonization process, in accordance with the values of the apparent activation energies presented in Table VIII. When almond shells impregnated with CoCl2 are pyrolyzed, the evolution of total gases follows the pseudofirst-order law for the fluidized bed reactor and the Pyroprobe 100. With the Pyroprobe 100, values of to for evolution of gases are around zero, and a good heat transfer, therefore, can be observed. Values of k increase slightly when increasing the temperature, so a small value of apparent activation energy can be deduced. Probably the presence of several pathways for the formation of gases from the different fractions (cellulose,lignin, etc.) causes the overall evolution of gases to have a small apparent energy. Howard (1981) proposed a multiple first order reaction kinetic model, where an activation energy distribution is defined. According to this model, a distribution of activation energy tends to increase the central value of activation energy. It is possible, therefore, that the activation energies obtained for the pyrolysis with and without catalyst were somewhat underestimated, especially in the case of the pyrolysis of almond shells impregnated with CoCl,. Nevertheless, from the data of yields vs time at different temperatures it is evident that the activation energy for
Table VIII. Relations between kl,k,,k,,and the Inverse of the Absolute Temperature for the Pyrolysis of Nonimpregnated Almond Shells parafluidized bed reactoP meter Pyroprobe 100b k , , S" 6.803 x IO8 exp(-18714/T) 1.521 X 10' exp(-16756/T) El. 156 139 kJ/mol rc k,,
s-l
E,, kJ/mol r
ks, s-' E39
0.988 8.229 X lo8 exp(-17863/T) 148
0.998 5.851 X lo6 exp(-14313/T) 119
0.995 2.91 X lo2 exp(-7390/T) 61
0.996 2.981 X lo3 exp(-8828/T) 73
0.933
0.971
kJ/mol r
Temperature range 400-460 "C. Temperature range 460-605 "C. Correlation coefficient.
the case with catalyst is very much lower than in the case without catalyst. With the fluidized bed reactor, values of kG are much lower than those obtained in the Pyroprobe 100 and do not vary with temperature. The influence of the heat transfer is great in this case. The evolution of liquids, at high values of time, in the catalytic almond shells pyrolysis fits to a pseudo-first-order reaction, but the values toare much higher than those obtained for the evolution of gases. We conclude that the formation of each fraction must be considered separately. The evolution of liquids undergoes a delay due to the presence of the catalyst. The CoCl, favors the dehydration reactions which lead to the formation of water, methanol, acetic acid, and 2furaldehyde. With respect to the evolution of the gaseous components (CO, CO,, H,, and CH4) in the four kinetic studies, general statements cannot be deduced. Some conclusions might be obtained from the comparison of the different results, but they are not very relevant.
Conclusions From the four kinetic studies carried out, (a) fluidized bed reactor with almond shells, (b) Pyroprobe 100 with almond shells, (c) fluidized bed reactor with almond shells impregnated with CoCl,, and (d) Pyroprobe 100 with almond shells impregnated with CoCl,, the following conclusions with respect to the equipment and decomposition have been obtained: The heat transfer is faster in the Pyroprobe 100 than in the fluidized bed reactor. As far as the pyrolysis of almond shells without any impregnation is concerned, the formation of the fractions of gases, liquids, and solids can be considered according to the following two schemes: (1)biomass a(gases) + b(1iquids) c(so1ids) (k);(2) biomass gases (k,),biomass liquids (k,),and biomass solids (k3).Good correlation for the different kinetic constants vs 1/T has been obtained. For the overall decomposition, the activation energy is around 108 kJ/mol. The pyrolysis of almond shells impregnated with CoCl, cannot be simplified to simple schemes. In the fluidized bed reactor, the evolution of liquids is retarded as a consequence of the presence of the acidic catalyst. The primary reactions of dehydration are favored, leading to the increased formation of 2-furaldehyde. With respect to the formation of the particular compounds C02,CO, CHz, Hz, H20,acetic acid, etc., different kinetic constants have been obtained as a consequence of the complicated network of reactions and the different
-
+
-
I n d . Eng. Chem. Res. 1990,29, 1855-1858
reactivity of the fractions cellulose, hemicellulose, and lignin. Registry No. CoClZ,7646-79-9; COz, 124-38-9; CO, 630-08-0; CH,, 74-82-8; Hz, 1333-74-0; water, 7732-18-5; methanol, 67-56-1; formaldehyde, 50-00-0; acetaldehyde, 75-07-0; acetone, 67-64-1; 2-propanol, 67-63-0; acetic acid, 64-19-7; hydroxyacetone, 116-09-6; propionic acid, 79-09-4; 3-methyl-l-butanol, 123-51-3; 2-furaldehyde, 98-01-1.
Literature Cited Akita, K.; Kase, M. J . Polym. Sci., Polym. Chem. Ed. 1967, 5 (4), 833-844. Antal, M. J., Jr.; Friedman, H. L.; Rogers, F. E. Combustion Sci. Technol. 1980, 21, 141-152. Alves, S. S.; Figueiredo, J. L. J . Anal. Appl. Pyrolysis 1988, 13, 123-134. Barooah, J. N.; Long, V. D. Fuel 1976,55, 116-120. Bilbao, R.; Arauzo, J.; Millera, A. Thermochim. Acta 1987a, 120, 121-131. Bilbao, R.; Arauzo, J.; Millera, A. Thermochim. Acta 198713, 120, 133-141. Broadbury, A. G. W.; Sakai, Y.; Shafizadeh, F. J . Appl. . . Polym. Sci. 1979, 23, 3271. Browne. F. L.:, Tane. W. K. Effects of Various Chemicals on TGA of Ponderosa Pine. Forest Products Laboratory Paper 6, Madison, WI, 1963. Chatterjee, P. K.; Conrad, C. M. Textile Res. J . 1966, 36, 487-94. Font, R.; Marcilla, A.; Verdu, E.; Devesa, J. Znd. Eng. Chem. Prod. Res. Deu. 1986,25, 491-496. Hajaligol, M. R.; Peters, W. A.; Howard, J. B.; Longwell, J. P. Proc. Specialists Workshop on Fast Pyrolysis of Biomass; SERIjCP 622-1096, 1980; pp 215-236. "I
1855
Hajaligol, M. R.; Howard, J. B.; Longwell, J. B.; Peters, W. A. Ind. Eng. Chem. Process Des. Deu. 1982,21, 457-465. Himmenblau, D. M. Process Analysis by Statistical Methods; Wiley: New York, 1970; Chapter 6. Howard, J. B. In Chemistry of Coal Utilization-Second Suplementary Volume;Elliot, M. A., Ed.; Willey: New York, 1981; Chapter 12. Jeeers, H. E.: Klein. M. T. Ind. Enn. Chem. Process Des. Dev. 1985, 124, in-183. Kosstrin, H. Proc Specialists Workshop on Fast Pyrolysis of BiomU S S : SERI/CP 622-1096. 1980 PD 105-121. Leu, J. C. Modeling of the'Pyroly& and Ignition of Wood. Ph.D. Thesis, University of Oklahoma, 1975. Liden, A. G.; Berruti, F.; Scott, D. S.Chem. Eng. Commun. 1988,65, 207-221. Maa, P. S.; Bailie, R. C. The 84th National Meeting AIChE, Atlanta, GA, February 1978. Mack, C. H.; Donaldson, D. J. Textile Res. J . 1967,37, 1063-1071. Nunn, T. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Ind. Eng. Chem. Process Des. Dev. 1985a, 24, 836-844. Nunn, T. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Ind. Eng. Chem. Process Des. Deu. 1985b, 24,844-852. Scott, D. S.; Piskorz, M. A,; Bergougnou, R. G.; Overend, R. P. Ind. Eng. Chem. Res. 1988, 27, 8-15. Stamm, A. J. Ind. Eng. Chem. 1956,48,413-417. Thurner, F.; Mann, U. Znd. Eng. Chem. Process Des. Deu. 1981,20, 482-488. Tran, D. Q.; Rai, C. Pyrolytic Gasification of Bark. AIChE Symp. Ser. 1979, 75 (1984), 41-49. Urban, D. L.; Antal, M. J., Jr. Fuel 1982, 61, 799-806.
Received for review February 6, 1989 Revised manuscript received December 7, 1989 Accepted April 16, 1990
MATERIALS AND INTERFACES Polysilahydrocarbon Synthetic Fluids. 1. Synthesis and Characterization of Trisilahydrocarbons Kazimiera J. L. Paciorek,* Joseph G. Shih, and Reinhold H. Kratzer Ultrasystems Defense, Inc., 16775 Von Karman Avenue, Iruine, California 92714'
Bruce B. Randolph Technolube Products Company, 5814 E . 61st Street, Los Angeles, California 90040
Carl E. Snyder, Jr. WRDCIMaterials Laboratory, Wright-Patterson AFB, Ohio 45433
Trisilahydrocarbons, a new class of compounds of the general formula R2Si(C8HI6SiR3)2,were synthesized by reaction of alkyllithium or alkylmagnesium halides with the novel bis[8-(trichlorosilyl)octyl]dichlorosilane precursor. By varying R groups from C6 to Clo and by using a combination of different R groups, we obtained a series of fluids of wide liquid ranges. The 40 "C viscosities ranged from 74 to 133 cSt, and 100 "C viscosities were from 12.6 to 20.4 cSt. The fluid with R = n-C8HI7had a pour point of -54 "C and a vapor pressure a t 125 "C of 1.6 X Torr. The newly developed process allows the preparation of fluids with closely tailored properties for application in environments where extremes of exposure conditions are encountered.
Introduction For space applications, liquid lubricants are required which are capable of performance at extremes of temperature, have adequate viscosities and high viscosity indices, possess good lubricity, and are involatile even 0888-5885/90/2629-1855$02.50/0
under hard vacuum conditions. Specifically, extremely low vapor pressure compositionshaving viscosities between 90 and 150 cSt at 40 "C and pour points below -50 "C are needed. The materials currently available f o r these applications exhibit a number of shortcomings. The Fom0 1990 American Chemical Society
