Znd. Eng. Chem. Res. 1988,27, 1143-1149
1143
Gaseous Hydrocarbons from Flash Pyrolysis of Almond Shells Rafael Font,* Antonio Mamilla, Joaquin Devesa, and Emilio Verdii Division de Zngenieria Q u h i c a , Universidad de Alicante, Apartado 99,Alicante, Spain
By use of a sand fluidized bed reactor, yields from major products from almond shells pyrolysis were measured in the 745-950 "C temperature range. A Pyroprobe 100 pyrolyzer was also used to study the influence of particle size temperature and catalysts impregnated in the almond shell samples. The highest yield of gas was obtained in the sand fluidized bed reactor, without catalyst impregnated in the almond shells, a t a temperature of 890 "C and at a residence time of volatiles of ca. 2.3 s. Under these conditions, the yields of the major products are the following: 1.5% Hz, 8.3% C H I , 4% CzH4, 45% CO, 28% COz, 0.7% CZH&0.5% C3H6(weight dry basis). From the different set of experiments, it has been deduced that the production of the gaseous hydrocarbons can be explained taking into account the CO yield. The yields obtained with the fluidized bed reactor were greater than those from the Pyroprobe 100. This is due t o the cracking reactions of the volatilized tars. In addition, a better heat transfer in the fluidized bed reactor has probably a certain influence. Pyrolysis is one of the alternatives to be considered for conversion of biomass to activated carbon, fuels, and chemicals. Almond shells are an abundant agricultural subproduct in regions with a moderate climate. This biomass has already been studied by the Chemical Engineering Division of Alicante University, as raw material for activated carbon preparation (Ruiz et al., 1984a,b),and for organic chemicals (Font et al., 1986). In the latter paper, we studied the flash pyrolysis of almond shells in a sand fluidized bed at temperatures between 305 and 710 "C. The hydrodynamics of the reactor was studied in order to obtain a good mixing between almond shells and sand particles, avoiding the entrainment of fine particles. As a consequence of this research, it was shown that flash pyrolysis (i.e., discharging the almond shells on the sand fluidized bed at 400-500 "C) yields greater amounts of organic liquids than increasing temperature pyrolysis. The interest in high-temperature pyrolysis of biomass is evident, when considering the papers published on this subject in recent years. Here, the results of these publications are compared with those obtained in this study of almond shells flash pyrolysis, carried out at temperatures within the 745-950 "C range. Particular attention is paid to the light hydrocarbons produced, as a consequence of the thermal degradation of the raw material or intermediates. The experiments carried out at lower temperatures (Font et al., 1986) have been useful to explain some of the results obtained at higher temperatures.
Experimental Section The inert bed was sand of 0.105-0.210-mm particle size. The sand was calcinated at 900 "C and washed with HCl. Almond shells were washed with water, dried, crushed, and sieved to obtain an uniform material of 0.297-0.500-mm particle size. The composition of the almond shells is the following: 0.2% ash, 50.7% lignin, 29.8% cellulose, and 19.3% hemicellulose (weight dry basis). Experiments have been carried out at constant temperature in a fluidized bed reactor (66-mm internal diameter) described elsewhere (Font et al., 1986 (Figure 1)). Heating was produced by means of a cylindrical refractory oven. The internal temperature of the fluidized bed was controlled automatically. The temperatures at the reactor shell and at the top of the reactor were also controlled and recorded. Iron-nickel thermocouples were used. Liquids were collected by means of a condensation train formed by water-cooled and salt ice-cooled condensers and
* Author to whom correspondence should be addressed. 0888-5885/88/2627-1~43$01.50/0
several cold traps (Font et al., 1986 (Figure 2)). The procedure was as follows: A 1-3-g sample of dry almond shells was placed in the feeder; the flow of the inert gas (commercial nitrogen) was fixed, and the oven was turned on. When the reactor reached the selected temperature, the exit flow was shifted to the feeder in order to eliminate the oxygen. After a few minutes, the feed valve was opened and the sample was poured on the sand fluidized bed. The gas was collected in a previously calibrated reservoir containing a displacement acid solution. The feeder is far from the reaction chamber, and therefore it stayed cold during the experiment. In initial experiments at high temperatures, it was observed that samples larger than 3 g produced a considerable gas evolution, producing the entrainment of fine particles. This was the reason why samples of 1-3 g were used. Nevertheless, with this small samples, it was very difficult to determine accurately the liquid and solid fractions. Gas samples were analyzed by gas chromatography, using a silica gel column to determine the Hz, CO, CHI, and COz, using Nz as a reference. Hydrocarbons were analyzed in an alumina column taking the previously determined CHI as a reference. The GC peaks were identified by comparison with standards. Experiments have been duplicated in order to observe the reproducibility of the results. As can be observed from the corresponding tables, deviations among the yields of experiments carried out in the same conditions are small. Dry residue at 120 "C (tar) obtained from the liquid fraction, produced when pyrolyzing almond shells at 610 "C, has also been used as the material for high temperature pyrolysis. In this experiment, a small amount of sand was impregnated with the liquids from the experiment at 610 "C and dried at 120 "C. After this treatment, the sample was crushed and sieved to ensure its homogeneity. The amount of tar was determined by the weight loss of tar + sand at 900 "C in an oven at air atmosphere. In this way, all the organic material is either volatilized or gasified, and consequently, the amount of the initial tar can be easily determined. On the other hand, the Pyroprobe 100 was used to study the influence of temperature on the gaseous hydrocarbons produced in the pyrolysis of almond shells, as well as the effect of several catalysts on these gases. Analysis of the gas fraction was carried out in a Porapak Q chromatographic column using the FID detector.
Results with the Pyroprobe 100 In order to test the influence of the particle size, temperature, and catalyss impregnanted in the almond shells, 0 1988 American Chemical Society
1144 Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 Table I. Almond Shells Pyrolysis Using Pyroprobe 100. Influence of Particle Size and Sample Amount. T = 850 O C yields (wt S ) on moisture-free almond shells amount, CZH4 + methanol + sample mg CH, CzHz CzH6 C3H6 C3H8 C4H8 C4H10 formaldehyde 1.84 0.51 0.88 0.02 2.44 small small one particle (0.210-0.297 mm) small 0.08 2.35 1.30 0.38 0.73 0.07 one particle (0.297-0.500 mm) 0.10 0.45 0.19 0.36 2.37 1.14 0.35 0.69 0.07 0.41 one particle (0.297-0.500 mm) 0.10 0.11 0.43 2.54 1.13 0.43 one particle (0.500-0.840 mm) 0.42 0.68 0.08 0.46 0.21 0.61 1.11 0.89 2.49 0.44 0.68 some particles (0.297-0.500 mm) 0.10 0.42 0.13 0.95 Table 11. Pyrolysis Using Pyroprobe 100. Influence of Temperature: 0.297-0.500-mm Almond Shells yields (wt % ) on moisture-free almond shells amount, temp, CzH4 + material "C mg CH4 CzHz CZH6 C3H6 C4H8 C4H10 0.21 0.32 almond shells 770 0.80 1.38 0.46 0.05 0.29 0.33
methanol + formaldehyde
790 790 820 850 850 850 905 905
0.64 0.57 0.95 0.89 0.10 0.10 1.11 1.03
1.28 1.65 2.29 2.49 2.35 2.37 2.86 2.42
0.51 0.71 0.98 1.11 1.30 1.14 1.70 1.42
0.18 0.23 0.38 0.44 0.38 0.35 0.57 0.40
0.31 0.41 0.61 0.68 0.73 0.69 0.85 0.64
0.04 0.05 0.08 0.10 0.07 0.07 0.10 0.07
0.20 0.26 0.39 0.42 0.45 0.41 0.57 0.43
0.08 0.09 0.19 0.13 0.19 0.11 0.27 0.14
0.73 0.63 0.70 0.71 0.95 0.36 0.43 0.74 0.76
tar
850 905
0.73 0.90
2.30 2.51
0.60 0.73
0.52 0.49
0.36 0.41
0.11 0.11
0.31 0.36
0.12 0.14
0.41 0.39
lignin
850
0.68
3.29
0.17
0.23
0.09
0.03
0.06
0.01
2.17
Table 111. Almond Shells Pyrolysis Using Pyroprobe 100. Influence of Catalysts. T = 850 "C, Sample Amount = 0.5-1.0 mg, 0.297-0.500-mm Almond Shells yields (wt % ) on moisture-free almond shells C2H4 + methanol + catalyst, wt YO CH4 CzHz C2H6 C3H6 C3H8 C4Hs C4H10 formaldehyde 1.11 0.44 none 2.49 0.68 0.10 0.42 0.13 0.95 0.73 NaOH (13.3) 0.42 1.76 0.32 0.24 0.25 0.23 1.09 0.27 0.65 1.58 0.33 0.05 0.26 NaCl (5.7) 0.11 0.83 0.23 0.51 1.33 0.25 KC1 (4.8) 0.07 0.04 0.20 0.80 0.13 0.50 0.06 1.28 0.30 CdClz (4.6) 0.22 0.59 0.18 0.57 CaCl, (4.6) 1.40 0.28 0.21 0.06 0.49 BaC1, (4.4) 0.23 0.67 1.58 0.36 0.04 0.24 0.08 0.59 0.16 0.28 0.15 MnClz (14.0) 0.03 0.84 0.14 0.49 0.17 MnCl, (14.0) 0.10 0.06 0.02 0.65 0.10 0.49 0.11 ZnClz (4.9) 1.17 0.16 0.30 0.04 0.18 0.65 0.09 0.98 0.16 0.30 0.20 CUClZ (4.7) 0.04 0.70 0.16 1.45 0.60 0.47 0.03 NiClz (4.7) 0.31 0.09 0.60 0.09 0.99 COC12 (5.0) 0.15 0.27 0.04 0.19 0.57 0.15 1.33 CrC13 (4.6) 0.25 0.47 0.07 0.33 0.58 0.14 1.26 NiS04 (3.4) 0.07 0.24 0.57 0.37 0.57
three series of experiments were run using the Pyroprobe 100 with the following conditions: nominal heating rate, 20 OC/ms; pyrolysis time, 20 s. Table I shows the results obtained when varying the particle size and the weight of the sample. No significant effect is observed on the hydrocarbons yields, within the range studied. This fact indicates that the heat transmission is very fast in samples of small particle size. Table I1 shows the results obtained when studying the effect of temperature on the hydrocarbons yields. A common tendency can be observed with all the hydrocarbons, especially for the lighter ones (see Figure 1). The higher the temperature, the greater the yields. Table I1 also shows the results of the tar pyrolysis (the tar was previously obtained by almond shell pyrolysis at 610 "C). The hydrocarbons mixture produced is very similar to that obtained from almond shells, although the CzH4 + C2H2, C2Hs, C3H8, and methanol + formaldehyde yields are lower. The results of the pyrolysis of a lignin fraction (obtained from almond shells) are also shown in Table 11. In this case, a noticeable increase can be observed in the CH, yield, together with a decrease in the yields of the remaining hydrocarbons analyzed. This fact agrees with
the results obtained by other authors (Nunn et al., 1985a,b). In a previous work (Font et al., 1986), we showed that the presence of certain catalysts in the pyrolysis of almond shells at 350-500 "C modified considerably the yields of the different condensables and markedly increased the solid fraction. These results agreed with those obtained by other researchers (Beaumont and Schwob, 1984). In order to study the influence of different catalysts on the hydrocarbon yields from pyrolysis, a set of experiments with almond shells impregnated with different inorganic chemicals were carried out. Results obtained are shown in Table 111. A general decrease can be observed in hydrocarbon yields with respect to the pyrolysis of almond shells without catalysts. On the other hand, no significant change has been observed in the composition of the hydrocarbon fraction. Consequently, it was decided to perform a study of the pyrolysis using nonimpregnated almond shells in the fluidized bed reactor.
Pyrolysis in the Fluidized Bed Reactor In a fluidized bed reactor, the heat transfer between a hot bed and a cold solid being discharged on it increases
Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 1145 Table IV. Almond Shells Pyrolysis Using the Reactor. Influence of Temperature. Sand Amount = 1000 g, Nitrogen Velocity = 3.6 cm/s 3.29 3.16 amond shells sample, g 3.20 3.35 3.13 3.17 3.20 3.26 745 800 temp, OC 745 850 850 890 850 890 yields, wt % 0.83 0.67 0.67 0.68 0.77 H2 0.29 0.38 0.45 24.8 28.7 33.4 31.8 19.9 22.8 25.8 co 16.0 11.2 13.7 17.6 15.0 14.0 15.9 17.5 COP 15.8 5.1 5.0 5.1 5.3 5.3 3.2 4.0 CHI 2.9 0.69 0.71 0.80 0.51 0.67 0.72 0.80 cPH6 0.45 2.8 2.3 2.8 1.4 1.8 2.3 2.7 CZH, 1.3 0.06 0.06 0.08 0.12 0.09 0.09 0.06 C3H.9 0.07 1.1 1.1 0.92 1.2 1.1 1.2 0.85 C3H6 0.74 0.19 0.21 0.14 0.16 0.11 0.08 0.07 C2H2 0.06 0.48 0.44 0.47 0.60 0.45 0.40 0.51 c4 0.34 62.6 53.7 58.3 40.9 47.5 52.6 53.5 total gas 37.9 0.7 0.7 0.7 0.6 0.6 0.9 0.8 estd residence time of volatiles, s 1.1 3.0
I-
= 1.5
-
u?
2.93 950
0.95 36.5 16.7 6.4 0.74 3.3 0.06 0.92 0.26 0.33 66.2 0.6
0.92 34.5 15.6 6.1 0.69 3.1 0.06 0.85 0.22 0.32 62.4 0.6
I
:. .,---;
C2Hq
-
i
>
2.87 950
1.0
0.5
7%
m
8% T
m
('C)
Figure 1. Pyroprobe 100 almond shells pyrolysis. Effect of temperature on hydrocarbons yields.
with the gas flow rate. Nevertheless, there is an upper limit for the gas velocity, in order to avoid the entrainment of fine particles. When studying the hydrodynamics of the system (with similar characteristics to the study carried out a t moderate temperatures, i.e., at 500 "C (Font et al., 1986)), it was impossible to estimate the gas velocity through the bed reactor. This was due to the considerable amount of volatiles instantaneously evolved when the cold sample was poured on the fluidized sand bed at temperatures higher than 750 OC. Consequently, three experimenta were carried out at different nitrogen flows, in order to determine the most adequate gas velocity. At 4.7 cm/s (nitrogen superficial velocity), a considerable entrainment of fine particles was observed, which could be the reason for the decreasing yields obtained. At 3.6 cm/s, there was almost no entrainment of fine particles and the yields are greater than at 2.5 cm/s. This could be due to a better heat transfer a t greater gas flows. Consequently, all experiments were carried out at 3.6 cm/s nitrogen superficial velocity. was Experimentally, it was observed that moat of the produced nearly instantaneously after the discharge of the almond shells sample. The "residence time" wm e s h M accordingly to the following: VT is the empty volume of reaction (zone 2) shown in Figure 2. In the reactor head (zone 3), the temperature was always lower than 500 "C. V is the volume of the gas produced (calculated according to the average molecular weight of the gases evolved and the bed temperature). In all experiments, V was greater than V., Consequently, a volume of gas, V - VT, left the reactor instantaneously (residence time equals zero). It is assumed that the remaining volume VT circulates upward with plug flow, and its average residence time equals VT/2QNpwhere QN, is the volumetric flow rate of nitrogen.
U
66
mm
Figure 2. Residence time estimation. (1) Sand fluidized bed. (2) Empty portion of the reactor. (3) Head of the reactor.
Therefore, the mean residence time of the gaa produced can be estimated as follows:
This is an approximation which permits the comparison of the results on a residence time basis. Before pyrolysis, the residence time of the falling solids in the empty volume of the reactor (zone 2) was lower than 0.05 s. Consequently, the heat transferred to the falling particles is small, and therefore, pyrolysis takes place in the fluidized bed.
1146 Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 Table V. Almond Shells Pyrolysis Using the Reactor. Influence Nitrogen Velocity = 3.6 cm/s sand amount, g 300 300 300 300 almond shells samde. e 3.15 3.26 3.03 3.05 1.0 0.9 estd residence time of Golatiles, s 1.0 0.9 yields, w t % 1.1 1.2 HZ 0.88 0.96
co
32.3 25.6 7.2 0.66 3.4 0.03 0.52 0.18 0.15 70.9
COP CHI CzH6 C2H4
C3HB CSH6 CZH2
c4
total gas a
33.7 25.0 7.6 0.64 3.5 0.03 0.54 0.18 0.24 72.4
38.8 21.3 6.7 0.67 3.0 0.06 0.68 0.13 0.27 72.7
42.0 20.7 7.3 0.73 3.2 0.06 0.68 0.13 0.27 76.3
of Volatiles Residence Time. T = 890 "C, 300 0.99 2.4
300 1.12 2.2
1000 3.17 0.5
1000 3.25 0.6
1800 2.75 0.2
1800 2.63 0.2
300a 2.73 1.6
300° 2.73 1.5
1.6 46.4 27.3 8.6 0.68 4.2 0.02 0.57 0.12 0.25 89.7
1.4 43.3 28.5 8.0 0.71 3.8 0.02 0.50 0.10 0.22 86.5
0.83 33.4 17.6 5.3 0.77 2.8 0.06 1.1 0.19 0.48 62.6
0.77 31.8 15.0 5.3 0.80 2.8 0.06 1.1 0.21 0.45 58.3
0.83 30.7 19.4 5.3 0.71 2.4 0.07 1.0 0.21 0.44 61.1
0.85 30.0 18.1 5.3 0.68 2.4 0.07 1.0 0.21 0.36 58.9
0.69 19.4 23.1 5.3 0.38 2.8 0.01 0.40 0.17 0.18 52.4
0.88 20.9 22.8 6.1 0.37 3.0 0.02 0.37 0.18 0.10 54.7
Experiments carried out with tar as raw material.
2
1 R t S I D C N C E
Y'
TIM!,
s
--
/* Y
750
?sa
8%
4xI
9%
T ('C1
0
I Q F \ ' r i E Y C t
7
-INc
'r
,
5
Figure 3. Fluidized bed almond shells pyrolysis. Effect of temperature on (a) total gas, CO, and COz yields; and (b) CHI, CzH4,H,, and CzHByields.
Figure 4. Fluidized bed almond shells pyrolysis. Effect of residence time on (a) total gas, CO, and CO, yields; and (b) CHI, CzH4,C,H6, C3H6,and C4 hydrocarbons yields.
In order to study the influence of the temperature, a set of experiments at 745, 800, 850, 890, and 950 "C was carried out. Table IV shows the operating conditions and the results obtained from this set of experiments. Figure 3 shows the yields of some compounds vs temperature. An increase in the yields of Hz, CO, CHI, C2H2,CzH4, and C2H6 with temperature can be observed. the COzyield remains almost constant within the temperature range studied, and C3H6,C3H8,and C4 hydrocarbons show a maximum. On the other hand, another set of experiments at 890 "C was carried out to study the influence of the residence time. Table V shows the experimental conditions and the
results obtained. Figure 4 shows the variation of the yields of the different gases with the residence time. An increase in total gas yield can be observed, as well as an increase in the amount of the major compounds: H2,CO, COP,CHI, and C2H4. Yields of the CzHz, C3H6, and C4 fractions decrease as the residence time increases. At 2.3-9 residence time, the total gas yield was around 85-90% with a CH, yield of ca. 8% and a CzH4yield of ca. 4% (weight basis). Table V also shows the results of two experiments of pyrolysis of tar (dry residue at 120 "C from almond shells pyrolysis at 610 "C). Comparing the results obtained from the almond shells with similar operating conditions, it can
Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 1147 0.30
0.20
0.10
/
*I
n
P
1.0
2 I
I
j"
50
10
100
I
0.04
10
I c0
I
IO
100
50
50
cc
100
0
100
a cc
I
a c:
rn
10
,0,
0.2
10
I GO
50
IO
IO0
50
10
I cc
.?
GO
100
10
50 1 c0
Figure 5. Fluidized bed almond shells pyrolysis. ( 0 )Data from temperature study; (0) data from residence time study. Yields of different compounds vs CO yield: (a) CH4 (m) data from a previous paper (Font et al., 1986). (b) COz. (c) CzHz. (d) CzHB. (e) C3He (f) C3Hs. (g) C4. (h) Hz. (i) CzH4. (j) Total hydrocarbons - CH, + H2.
PR [ M A R Y TAR
GO
(VAPOR)
CHq
PLMOND SHELLS
1
I PRIMARY TAR (LIO!D)
1
C2Hq. H2. C2H2, CzHg,
h
C3Hg.
WITH
C3Hs.
Cq
C N A C K I N G OF THE
H E A V l C S T HYDROCARBONS
1
be deduced that similar yields, although slightly lower, are obtained. The main difference is with the CO yield.
Discussion In order to correlate the results obtained in this work, the logarithms of the yields of the different compounds vs the logarithm of the CO (major compound) yield have been plotted. Figure 5 shows these graphs and the slopes of the straight lines obtained. Scheme I showing the reactions is suggested based on these graphs, the results obtained in the Pyroprobe 100, and those presented in a previous paper (Font et al., 1986). The plot of CHI also includes the results reported in a previous paper (Font et al., 1986), corresponding to the experiments carried out a t 610 and 710 "C. A linear relationship with the slope close to 1 can be observed between the logarithms of the yields of CHI and CO. Consequently, it may be assumed that their mechanisms of
formation are similar for both compounds. At temperatures ranging from 420 to 495 "C (Font et al., 1986), the CO yield remained almost constant at ca. 4%. From 610 "C onward, the CO yield increased notably. This is probably due to a cracking of the volatiles evolved and that of the lignin fraction. A similar conclusion can be obtained in the case of CHI with a yield of ca. 0.5% within the 420-495 'C temperature range. The fact that the ratio CO yield/CH, yield remains almost constant when varying temperature and/or residence time implies that both the CO generation and the CHI generation pass through cracking reactions, with similar activation energy. On the other hand, the logarithm of the C02yield vs the logarithm of the CO yield showed two different variations. In the experiments at constant residence time but at varying temperature, the COz yield was almost constant. This fact has also been observed by other authors (Funazukuri et al., 1986a). The C02yield increases, however, when the residence time also increases. In the 420-710 "C range, a slight increase in the C 0 2yield from 9% to 13.3% was observed (Font et al., 1986). These results can only be explained if the decarboxylation reactions (of the solids or volatile tar) have a small activation energy. As a result, the C02 generation varies slightly with temperature at constant residence time. On the other hand, the fact that the C 0 2yield increases when the residence time is greater proves that a considerable amount of COz is generated by the vapor-phase cracking reaction.
1148 Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988
With respect to the logarithms of C2H2,C&6, C3H6, C3He,and C4vs the logarithm of CO, different maxima can be observed. This indicates that these compounds, which are formed by cracking reactions of the solid and/or the primary liquid tar,also undergo cracking reactions to lower molecular weight compounds. This would explain the fact that the logarithms of H2and CzH4 vs the logarithm of CO have slopes greater than 1. From the graph of the logarithm of the sum Hz CzH6 + CzH4 + C3H8+ C3H6+ CzHz + C4 vs the logarithm of CO, a straight line is obtained. This proves that the cracking of the heaviest hydrocarbons (C, + C,) causes the Hz and CzH4 fractions to increase. Nevertheless, some elemental carbon and CHI may be formed, which could explain the slope of the straight line (0.7) being lower than 1.0. Comparing the results obtained with the Pyroprobe 100 with those observed in the fluidized bed reactor, it can be observed that the yields of the major hydrocarbons (CHI, CzH4) are somewhat lower in the Pyroprobe 100. Both apparatus (Pyroprobe 100 and fluidized bed reactor) have a very high heat-transfer rate. In the fluidized bed reactor, however, the volatiles evolved pass through a hot zone where they undergo cracking reactions. In the Pyroprobe 100, the volatiles leave the high-temperature zone immediately, and consequently cracking reactions are unlikely to occur at high conversions. Furthermore, the heat transfer in the fluidized bed reactor is probably better than that of the Pyroprobe 100, and this would also explain the difference observed. Taking into consideration the results obtained from the pyrolysis of tar (dry residue at 120 "C, obtained from an experiment at 610 "C), it can be concluded that all the gases (considered in the almond shells pyrolysis) come from the heaviest fractions (tar) as well as from the lightest ones. On the other hand, tar pyrolysis may be considered as a possible application for the residue obtained in the distillation of the mixture produced by biomass pyrolysis. This means that by pyrolysis of almond shells at moderate temperature, chemicals (2-furaldehyde, acetic acid, etc.) can be produced. The tar obtained can be pyrolyzed at high temperatures to obtain a fuel gas orland hydrocarbons. Due to the great number of possible reactions involved in the pyrolysis of biomass (depolymerization, disproportionation, dehydratation, decarboxylation, random scission (Shafizadeh, 1982; Diebold, 1980, Funazukuri, 1986b),and cracking and reforming of the volatiles), it is difficult to define a parameter related to the inensity of the thermal treatment. In the present study, the CO yield was to be extremely useful to correlate the hydrocarbon generations.
+
Comparison with Other Results From all experiments carried out, the maximum yields correspond to those at 890 "C and at 2.2- and 2.4-9 residence time. Under such conditions, 8590% gas yields was obtained. Table VI shows the average yields of these experiments compared to the yields obtained by other authors using different raw materials, types of reactor, and operating conditions. It can be observed that, with a fluidized bed reactor at optimum conditions, relative high yields can be obtained. The cracking of the volatiles evolved increases the yields of the different compounds: CO, COP,CH,, CzHz,and HP. Conclusions 1. From the sets of experiments carried out in the Pyroprobe 100,the following conclusions have been deduced
Ind. Eng. Chem. Res. 1988,27, 1149-1152 (a) the particle size does not modify the hydrocarbon yields obtained in the 0.21-0.84-mm-diameter range of almond shells, (b) the hydrocarbon yields increase with temperature in the 770-905 OC range, and (c) the different chemicals impregnated in the almond shell samples do not increase the hydrocarbon yields. 2. High gas yields can be obtained in a sand fluidized bed reactor with the following operating conditions: sand particles of 0.105-0.210-mm diameter, almond shell particles of 0.297-0.500-mm diameter, inert gas flow rate of 3.6 cm/s through the sand fluidized bed, temperature greater than 850 "C, and volatiles residence time of 1-3 9.
3. The higher yields of hydrocarbons obtained in the fluidized bed reactor correspond to the experiments carried out a t a temperature of 890 "C and at a residence time of volatiles of 2.4 s. Under these conditions, the yields (dry basis) of the different compounds are the following: 8.3% CHI, 4% CzH4,1.5% Hz,45% CO, 0.7% CZH6,0.5% C3H6, 0.02% C3H8, 0.1% CZHZ, 0.2% C4, 28% COZ. 4. From the sets of experiments carried out in the fluidized bed reactor, it has been deduced that the production of the different compounds can be explained taking into account the CO yield, CHI and CO are produced mainly from reactions which are similar. The hydrocarbons of three and four carbon atoms undergo cracking reactions, which lead to the increase of the C2H4 and H2 yields. 5. The yields obtained with the fluidized bed reactor are greater than those from the Pyroprobe 100. Cracking reactions of the volatilized tar and probably a better heat transfer in the fluidized bed reactor would explain the difference indicated above. Registry No. NaOH, 1310-73-2; NaCI, 7647-14-5; KC1, 7447-40-7; CdCIz,10108-64-2; CaClz, 10043-52-4; BaClZ,10361-37-2; MnCl,, 7773-01-5; ZnCl,, 7646-85-7; CuCIz, 7447-39-4; NiClZ, 7718-54-9; CoCIz,7646-79-9; CrCl,, 10025-73-7;NiS04, 7786-81-4; Hz, 1333-74-0; CO, 630-08-0; COZ, 124-38-9; CZH6, 74-84-0; C2H4, 74-85-1; C3H8,7498-6; CHI, 7482-8 C,&, 115-07-1;CzH2,74-86-2.
1149
Literature Cited Antal, M., Jr. "Effects of Reactor Severity on the Gas-Phase Pyrolysis of Cellulose and Kraft Lignin-Derived Volatile Matter". Znd. Eng. Chem. Prod. Res. Dev. 1983,22,366-375. Beaumont, O.,; Schwob, Y. "Influence of Physical and Chemical Parameters on Wood Pyrolysis". Znd. Eng. Chem. Prod. Res. Deu. 1984,23, 637-641. Diebold, J. P. Gasoline from Solid Wastes by a Noncatalytic Thermal Process. American Chemical Society: Washington, D.C., 1980; NO. 130, pp 209-226. Font, R.; Marcilla, A.; Verdfi, E.; Devesa J. "Fluidized-Bed Flash Pyrolysis of Almond Shells. Temperature Influence and Catalysts Screening". Znd. Eng. Chem. Prod. Res. Deu. 1986,25,491-496. Funazukuri, T.; Hudgins, R.; Silveston, P. "Product Distribution in Pyrolysis of Ceilulose in a Microfluidized Bed". J . Anal. Appl. Pyrolysis 1986a, 9, 139-158. Funazukuri, T.; Hudgins, R.; Silveston, P. "Correlation of Volatile Produds from Fast Cellulose Pyrolysis". Ind. Eng. Chem. Process Des. Dev. 1986b, 25, 172-181. Hajaligol, M. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. "Product Composition and Kinetics for Rapid Pyrolysis of Cellulose". Znd. Eng. Chem. Process Des. Dev. 1982,21,457-465. Nunn, T.; Howard, J. B.; Longwell, J. P.; Peters, W. "Product Composition and Kinetics in the Rapid Pyrolysis of Sweet Gum Hardwood". Ind. Eng. Chem. Process Des. Dev. 1985a, 24, 836-844. Nunn, T.; Howard, J. B; Longwell, J. P.; Peters, W. "Product Composition and Kinetics in the Rapid Pyrolysis of Milled Wood Lignin". Znd. Eng. Chem. Process Des. Dev. 1985b, 24,844-852. Rolin, A,; Richard, C.; Masson, D.; Deglise, X. "Catalytic Conversion of Biomass by Fast Pyrolysis". J. Anal. Appl. Pyrolysis 1983,5, 151-166. Ruiz, F.; Prats, D.; Marcilla, A,; "Activated Carbon from Almond Shells. Chemical Activation. 1. Activating Reagent Selection and Variables Influence. Znd. Eng. Chem. Prod. Res. Dev. 1984a, 23, 266-269. Ruiz, F.; Prats, D.; Marcilla, A. "Activated Carbon from Almond Shells. Chemical Activation. 2. ZnCll Activation Temperature Influence. Znd. Eng. Chem. Prod. Res. Dev. 1984b, 23,269-271. Shafizadeh, F. "Introduction to Pyrolysis of Biomass". J . Anal. Appl. Pyrolysis 1982, 3, 283-305.
Received for review June 11, 1987 Revised manuscript received February 2 , 1988 Accepted February 12, 1988
The Fate of Hydrazine in Pure, Deoxygenated, Aqueous Solutions at Elevated Temperatures and Pressures? George R. B r u b a k e r * and Michael M. Geoffrey Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
The fate of aqueous hydrazine at temperatures between 373 and 573 K (212-572 OF) a t saturation pressures has been determined. Particular emphasis was placed on high-purity water and careful exclusion of oxygen. At least 97% of the initial hydrazine charge was recovered after up to 3 h in a passivated 316 stainless steel reactor. Statistical analyses indicate that hydrazine recovery is independent of mass fraction of hydrazine in the vapor phase as well as temperature, pressure, and time. The use of dilute aqueous solutions of hydrazine as an oxygen scavenger and passivating agent in boiler feedwater and boiler water treatment for commercial steam generators is widely practiced. Of interest is the extent of hydrazine decomposition at the temperatures and pressures of operation and in a controlled environment. This work was presented in part at the Hydrazine Centennial Conference, Division of Inorganic Chemistry, 193rd National Meeting of the American Chemical Society, April 1987 (INOR 292). This work is also contained in part in the M.S. Thesis of M. M. Geoffrey.
0888-5885/8812627-1149$01.50/0
The concentration of dissolved O2 found in the steam turbine loop of a commercial electric generating station is a function of the efficiency of mechanical deaeration, percent makeup or blowdown used, and the efficiency of chemical O2 removal. Correspondingly, the amount of residual hydrazine found in the steam turbine loop is a function of these same parameters. Residual dissolved O2 in the feedwater of the steam turbine loop may be reduced to less than 0.007 ppm by the use of countercurrent mechanical deaerators (Kesler, 1978). Blowdown or makeup in these systems varies greatly. Schmidt reports 60% makeup for the Olin Chemicals 0 1988 American Chemical Society
