Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 497-496
49 1
Fluidized-Bed Flash Pyrolysis of Almond Shells Temperature Influence and Catalysts Screening Rafael Font,” Antonlo Marcllla, Emlilo VerdO, and Joaqdn Devesa Departamento de Qdmica Tgcnica, Universidad de Alicante, Alicante, Spain
An experimental system for almond shell pyrolysis has been designed and constructed. The system hydrodynamics has been studied. Temperature and heating rate Influences on the pyrolysis of almond shells in a fluidized-bed reactor have been investigated. Significant increases in liquid yields have been obtained in the 400-600 O C temperature range when flash pyrolysis conditions are employed, reaching 55 wt % (dry basis) in liquids and more than 10% of acetic acid. A Pyroprobe 100 pyrolyzer has been used for ialyst screening, and FeCI, and CoCI, have been selected for testing in the experimental system due to their interesting shifting in the liqvid fractions composition. When 6.4% of CoCI, is used, some 5.2% of furfural and 6.5% of acetic acid have been obtained as compared with 0.9 % and 1 3 % , respectively, when alrnond shells are pyrolyzed without catalysts. Results obtained with the Pyroprobe 100 have proven to be indicative of what would be obtained in the experimental reactor.
Introduction The study of alternative supplies of energ -nd chemicals has an increasing interest due to the well-known “oil-raw materials crisis”. Pyrolysis processes of biomass yield a pyrolytic oil, which is a mixture of organic chemicals with water, a low BTU gas, and charcoal. The study of these processes to obtain better yields in organic chemicals is a very interesting research field. Almond shells are an abundant and available agr: ultural byproduct in some moderate climate zones. In JJi’evious papers (Ruiz et al., 1984a,b) the Department of Chemical Engineering of the University of Alicante, Spain, has studied the utilization of this raw material to obtain activated carbon by ZnC1, activation. The scope of the present investigation of the pyrolysis of almond shells is to obtain a better profit from this abundant byproduct in the Alicante area (southeastern Spain). Flash pyrolysis of lignocellulosic materials leads to an increase in the amount of liquids produced at moderate temperatures. Accordingly, experimental equipment with a sand fluidized bed reactor has been designed, and the hydrodynamic characteristics of the system have been investigated. Temperature and catalyst influence on the amount and composition of the liquids obtained have also been investigated.
hopper (see Figure 1). The inerc ,CIS flow (from an industrial N2source) was set and the oven switched on. Once the react : reached the selected temperature, the exit flow was shifted t o the feed hopper in order to avoid the entrance of air into the reaction chamber from the hopper. After a few minutes, the feeding valve was opened and the samp!e fell into the sand bed iluidized reactor. When the pyrolysis was run at a slow heating rate, the sample was placed inside the reactor together with the sand a t room temperature, air inside the reactor being purged before heating the reactor. Liquids were collected by means of a condensation train formed by water-cooled and salt-ice-cooledcondensers and several cold traps in order to collect all the Condensable volatile compounds. At different times several gas samples were taken. Liquid and gas samples were analyzed by gas liquid chromatography. For the identification of the light liquids analyzed, the following chromatographic columns were used: OV-225, SE-30, and Porapak Q, The amount of each condensable compound was obtained by using propanol as the internal standard with a Porppak Q chromatographic column. Dry residue (constar iveight) at 120 OC (tarry fraction of the liquid) was also determined. Gas composition was determined from all the gas compourr.l/nitrogen ratios obtained by using a silica gel chromatographic column. Yields of the different products obtained were determined by weighing the solid residue (charcoal) and the liquid collected and by integrating the gas evolution molar flow curves of the different compounds with time (Le., molar flow for each component is deduced from the constant inert gaa flow introduced into the system and the gas component/mert gas mole ratios obtained by analysis). In order to test the reproducibility of the experiments we tripled the experiment a t 495 O C . It can be seen from Table I11 that yields higher than 170have low dispersion, whereas lower yields are more disperse. Material balances for all experiments came within 96-10370 of the dry almond shell sample. In addition, a Pyroprobe 100 flash pyrolyzer was used for catalyst screening.
Experimental Section Calcinated sand at 900 OC was used as an inert bed. For the fluidization runs a glass tube and the reactor designed were used to obtain the minimum fluidization velocity and the corresponding bed porosity. Almond shells were washed, dried, crushed, and sieved to get a uniform material. Pyrolysis was carried out in an 18/8 stainless steel reactor (Figure 1). Heating was achieved by means of a cylindrical refractory oven. The internal temperature at the fluidized bed was controlled automatically. The temperatures a t the reactor shell and at the top of the reactor were both controlled and recorded (see Figure 2, where the experimental arrangement is shown). Pyrolysis in the experimental system a t constant temperature was run as follows: First, a dried almond shell sample of the selected particle size was placed in the feed
Hydrodynamics of t h e System Several fluidization runs were carried out to determine the minimum fluidization velocity (u& and the corre-
* Author to whom correspondence should be addressed. 01 96-4321 /86/ 1225-0491$01.50/0
0
1986
American Chemical Society
492
Ind. Eng. Chem. Rod. Res. Dev.. Vol. 25, No. 3, 1986 Table 1. Fluidization Results particle material size," temp, OC sand 0.211H0.105 23 0.21IH.105 420 almond shella 0.500.297 23 0.297-0.210 23 0.210-0.105 23
u,cm/s 2.11 1.79 8.71 5.89 3.05
0.471 0.632 0.692 0.710
4
1
7
.
6
-
5 -
4 .
3
-
2
-
;,A FLUIDIZED
BED
WITHOUT H ~ X I N G
FIXED BED
Figure I. Experimental reactor: (1) nitrogen entry; (2) gas diffuser; (3)reaction zone; (4) gas outlet (5) feed tube; (6)feed hopper; (7) feed valve; ( 6 9 ) thermocouple jacket; (10) furnace; (11) insulation.
0.2
0.3
i,
0.4
0.5
(")
Figure 3. Bed hydrodynamic zones.
Figure 2. Experimental system: (I) nitrogen cylinder; (2-9) thermometer; (3) flow meter; (p6) manometers; (7) reactor; (8) furnace; (IO) condensationtrain; (11) ample collector; (12) mndensers;(13) gas sample collector; (14) water trap; (15) temperature recorder and controller.
sponding bed porosity (emf) for sand and almond shells. Sand of 0.1054.210-mm particle size was utilized since this fraction was the most abundant. Table I shows the rqults obtained. Almond shells of 0.063*,105-mm particle size showed a marked tendency to form preferential paths for the gas, and consequently, their umfcould not be determined. For sand particles having diameters less than 2 mm, Pattipati and Wen (1981) showed that the minimum fluidization velocity decreases as a consequence of the changes in density and viscosity. This is in accordance with the results shown in Table I. For an optimal performance of the fluidized bed reactor with sand and almond shells there are three factors that must be considered first, the inert gas flow must fluidize the biomass-and mixture; second, the almond shell par-
ticle density will diminish when the devolatiliition p r w s a takes place during the pyrolysis: and third, the fine particles of charcoal formed can be taken out of the reactor. In order to obtain the optimal conditions, several tests with almond shells of different sizes and charcoal (produced at 500 "C) have been carried out at room temperature. A 1:30 almond shell/sand ratio was used. Figure 3 shows the bed behavior observed: fixed bed, fluidized bed, well-mixed sand and almond shells, and entrainment of charcoal. It can be seen from Figure 3 that the 0.2970.500-nm particle size (mean diameter of 0.398 mm) allows good mixing without entrainment of fme charcoal particles. Consequently, this particle size was selected for the following pyrolysis experiments. Since the pyrolysis process produces gases and the velocity through the bed increases, it is convenient to select a gas velocity differing subtantially from the entrainment velocity but ensuring a good mixing when almond shells are discharged onto the sand fluidized bed. Accordingly, every experiment was performed with the velocity constant at 4.7 cm/s, worked out at reaction conditions. It was teated that this selected value for the velocity led to a good fluidization and mixing conditions without solids entrainment. Pyrolysis Without Catalysts T w o different kinds of experiments were run in order to study the influence of a fast heating rate on the process. First, an experiment at increasing temperature (at 17.5
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 3, 1986 403 Table 11. Yields on Moisture-Free Almond Shell under Increasing Temperature Pyrolysis and Operating Conditions" temp, OC pyrolytic oil water methanol acetaldehyde acetone 2-propanol acetic acid hydroxyacetone propionic acid 3-methyl-1-butanol 1-hydroxy-2-butanone 2-furaldehyde dry residue at 120 OC solid residue gas COP
1305 3.5 1.9 0.15 0.02 0.44 0.02 0.02 0.09 0.72
1350 7.0 3.6 0.25 0.01 0.04
5385 13.6 5.1 0.39 0.01 0.05
1420 9.2 2.8 0.35 0.01 0.05
5475 6.4 2.4 0.23
1710 4.2 2.8 0.07
0.05
0.06
0.56 0.07 0.01 0.07 0.01 0.19 2.0
1.2 0.51 0.05 0.14 0.24 0.20 4.6
0.67 0.42 0.02 0.08 0.33 0.05 3.5
0.36 0.16
0.17 0.04
0.03 0.06 0.03 2.2
0.01 0.03 0.02 0.92
accumd 44.0 18.6 1.4 0.03 0.27 3.4 1.2 0.08 0.36 0.67 0.58 13.8 35.8 20.0 13.2 5.2 1.7 99.8
co
CH, total
" d , = 0.297-0.500 mm; almond shell weight = 64 g; sand weight = 1004 g; heating rate = 17.5 OC/min to 400 "C and then 8 OC/min to 710 "C; velocity of N2= 4.7 cm/s.
Table 111. Constant Temperature Pyrolysis Results"
pyrolytic oil water methanol acetaldehyde acetone 2-propanol acetic acid hydroxyacetone propionic acid 3-methyl-1-butanol 1-hydroxy-2-butanone 2-furalde hyde dry residue at 120 "C solid residue gas
coz
co
CH,
H2
total a Yields
on moisture-free almond shell.
0.67 0.59 0.77 7.9 69.2 5.3 4.4 0.90 0.04
420 57.0 18.7 0.92 0.06 0.12 0.06 10.3 2.1 0.49 0.44 1.1 0.91 24.1 29.4 13.1 9.0 3.8 0.37
495 58.5 16.7 0.56 0.10 0.08 0.05 10.0 1.9 0.10 0.41 1.4 0.75 27.0 26.4 14.4 10.2 3.6 0.61
temp, OC 495 57.2 17.7 1.1 0.21 0.07 0.06 9.6 1.9 0.17 0.90 1.3 0.57 23.0 26.3 15.7 10.3 4.7 0.70
95.6
99.6
99.2
99.2
365 21.1 10.6 0.33 0.04 0.01 0.42 0.79
Acetone
495 59.3 16.7 1.2 0.24 0.06 0.04 9.9 1.7 0.15 0.78 1.2 0.40 26.1 26.4 14.3 10.0 3.8 0.50
610 65.1 16.5 0.70 0.10 0.25b
710 43.2 14.2 0.58 0.16 0.17 0.04 7.7 1.4 0.26 0.22 0.66 0.67 18.1 6.7 53.2 13.3 34.5 5.4 0.23 103
10.4 1.8 0.18 0.46 1.3 0.85 34.5 11.3 22.9 10.6 10.7 1.6
100
99.2
+ 2-propanol.
"C/min up to 400 "C and 8 "C/min up to 710 "C) was run, and then five experiments a t constant temperature were carried out. Table I1 shows the operating conditions and accumulated yields obtained of the different products analyzed for the experiment at increasing temperature up to 710 "C. Figure 4 shows the accumulated gas yields vs. the temperature for this experiment. It can be seen that CO evolution starts around 300 "C, whereas CHI a t evolution starts a t 400 "C. At temperatures within the 360-400 "C range, a marked increase in the gas evolution is attained. I t can be seen from Table I1 that the maximum liquid evolution corresponds to the 350-385 "C temperature range. Liquids collected a t lower temperatures are rich in light volatile compounds, whereas those collected a t higher temperatures have a larger percentage of high molecular weight compounds (i.e., higher dry residue a t 120 "C). These results are similar to those obtained by other researchers (Shafizadeh, 1975; Goldstein, 1981; Beaumont and Schwob, 1984). First, the light compounds are devolatilized at low temperatures, mainly from cellulose and hemicellulose, which are the first components to un-
20
15
E 10
5 5
0
200
300
400
500
600
700
rrci
Figure 4. Accumulated gas yields in slow pyrolysis vs. temperature: (A)total gas yield; (V)C 0 2 yield; (m) CO yield; ( 0 )CHI yield.
dergo decomposition. At higher temperatures, heavy compounds of higher boiling point are obtained mainly from the lignin fraction of the raw material. Five experiments a t 365, 420, 495, 610, and 710 "C, respectively, have been run in order to study the temperature influence on the constant-temperature almond
494
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 3, 1986
2ot 15
300
400
500
600
700
T ('GI
300
400
500
600
700
T ('C)
Figure 5. Total liquids vs. temperature. Comparison between slow (m) and fast ( 0 )pyrolysis.
Figure 6. Light organic liquid yields vs. temperature. Comparison between slow (m) and fast ( 0 )pyrolysis.
shell pyrolysis process. The residence time of the vapors inside the reactor is considered to be lower than 0.5 s. The heating rate, according to Scott and Piskorz (1984), has been estimated a t 500 "CIS. Table I11 shows the results obtained and operating conditions used in each experiment. One can deduce the following: The solid residue (charcoal a t high temperature) decreases at increasing temperature due to a greater decomposition of the raw material. At higher temperatures (610 and 710 "C) the charcoal undergoes gasification reactions by the action of the water and carbon dioxide produced by the primary reactions of pyrolysis and the cracking and reforming reactions of the volatile products. A progressive increase in gas yields due to the following conditions. (1)A greater solid decomposition at increasing temperature. Carbon monoxide concentration increases with the temperature, partly due to the CO formation by the lignin pyrolysis, which is greater at high temperatures. (2) Cracking and reforming in the gas phase of the volatiles evolved (610-710 "C). Methane is mainly formed in this way. (3) Charcoal gasification (710 "C), giving hydrogen and mainly carbon monoxide. Liquid fractions present a maximum within the 420-610 "C temperature range, decreasing from 610 "C due to their cracking and reforming. It must be pointed out that the maximum liquid production is achieved at around 610 "C. This temperature is somewhat higher than the optimal range of temperature reported by Kosstrin (1980) (fluidized-bed pyrolysis of biomass). In the present work the gas residence time is significantly lower, and consequently, the liquid yield can be greater a t higher temperatures. The high yields in liquids obtained (about 65% dry basis) are similar to those obtained by other researchers studying flash pyrolysis in fluidized bed (Beaumont and Schwob, 1984) or in solid entrainment reactor (Finney, 1974; Sass, 1974). Acetic acid yield is greater than 10% (dry basis) within the 400-600 "Ctemperature range. This yield is significantly higher than those reported by other authors working with other biomass, typically around 7 % from hardwood (Goldstein, 1981) and 7.84% from beechwood (Beaumont and Schwob, 1984). The other components are in smaller but significant amounts. From a comparison of the two types of experiments at increasing temperature (slow pyrolysis) and at constant temperature (fast pyrolysis), it can be concluded that not only the temperature but also the heating rate plays a decisive role in the reaction. Figure 5 shows the total liquid yields for both types of experiment vs. temperature. Rapid heating rate pyrolysis produces some 20% more liquids than slow pyrolysis does a t 420-610 "C. Figure 6 shows
the total low molecular weight analyzed organic yields for both conditions as functions of temperature. It can be seen that much higher yields can be obtained by fast pyrolysis as compared with slow pyrolysis. Beaumont and Schwob (1984) studied the fluidized-bed slow pyrolysis and fast pyrolysis of beechwood. Their results show around 21 % yield increasing in light organic chemicals under flash pyrolysis conditions. In the present work some 110% yield increasing in light organic chemicals can be obtained. Analysis of the behavior of each component show that only the methanol is produced in higher quantities in slow pyrolysis than in the fast pyrolysis. This is due to a more complete breakdown of the intermediate compounds under these conditions. Concerning the gases, it can be observed that up to 500 "C the behavior is almost similar in both slow and fast pyrolysis (see Tables I1 and 111). But at higher temperatures there is a marked increase in the carbon monoxide and methane evolution in fast pyrolysis, which is not present in slow pyrolysis conditions, where carbon dioxide is always the main component in the whole temperature range studied. It can be concluded that fast pyrolysis at 600 'C leads to a more interesting gas, from the point of view of energy, without significantly decreasing the liquid yields.
Selection of Catalyst Samples of almond shells impregnated with different catalysts have been pyrolyzed in Pyroprobe 100 pyrolysis equipment. Conditions used were the following: sample amount, 2 mg; pyrolysis temperature, 500 "C; "nominal heating rate", 20 "C/ms; pyrolysis time, 20 s; chromatographic column, Porapak Q; and detector, TCD. Table IV shows the results of the analysis of the volatile fraction obtained. The catalysts have been grouped according to their acidic or basic behavior. Results for liquids are given as relative yields: that is, concentration of the liquid component i divided by the sum of all analyzed liquid component concentration. For gases, similar ratios are given. Results of pyrolysis of almond shells without catalysts are also shown as a reference. Water and methanol could not always be separated in the GC column, thus the figure for water always includes the methanol. It can be seen that basic catalysts increase the CO evolution, probably due to the higher extents of the fission reactions (Shafizadeh, 1975). On the other hand, organic condensables decrease markedly when this type of catalyst is used. These results are in accordance with the results of other authors (Beaumont and Schwob, 1984; Shafizadeh, 1975). Acidic catalysts produce a significant shifting in the liquid composition. High concentrations of furfural are
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 3, 1986 495
Table IV. Catalysts Screening" almond shells K2CO3 oil waterb acetaldehyde acetone 2-propanol acetic acid hydroxyacetone propionic acid 3-methyl-1-butanol 1-hydroxy-2-butanone 2-furaldehyde gas COP
co
52.2 0.09 1.5 31.9 5.6 0.26 2.3 4.7 1.4 88.6 11.4
" Liquids and gases relative percentages.
basic catalysts, 3% NaOH KOH
Yields on moisture-free almond shell.
H3B03
ZnCl,
acidic catalysts, 3% FeCl, SnC12 Ni(N03)2
70.1 2.4 0.14 0.50 15.2 5.7 2.5 0.86 2.5 0.19
71.9 2.7 0.10 0.44 15.3 4.8 2.8 0.36 1.4 0.12
67.8 1.8 0.42 1.4 15.0 5.6 2.9 0.74 3.4 0.92
68.4
65.3
0.19 0.57 24.5 0.95 0.33 0.91 2.3 1.9
0.35 2.1 24.4 0.78 0.07 1.2 0.95 4.8
11.8
14.6
77.8
78.5 21.5
77.6 22.4
85.8 14.2
87.8 12.2
88.6 11.4
89.4 10.6
22.2
82.5
72.2
78.5
2.0 3.6 6.4 0.63 0.38 0.05
5.6
CoC1, 69.4
7.7
54.6 2.8 1.0 0.95 28.5 3.2 1.6 2.2 3.6 1.6
89.8 10.2
91.3 8.7
89.8 10.2
0.62 3.8 8.2 1.1 0.03
19.0 0.02 1.0 10.6
Including methanol.
Table V. Catalytic Almond Shells Pyrolysis Results" catalyst (temp, "C) 6.4% none 3% FeCl, 3% CoClz CoCl, (495Ib (500) (500) (500) pyrolytic oil 58.3 46.9 54.6 45.9 water 17.0 21.1 17.8 23.6 methanol 0.54 0.95 0.50 0.70 acetaldehyde 0.18 acetone 0.11 0.36 0.15 0.07 2-propanol 0.19 0.78 0.37 0.05 2.2 acetic acid 7.4 9.9 6.5 hydroxyacetone 1.9 0.09 0.13 propionic acid 0.14 0.13 0.01 0.04 3-methyl-l-buta0.69 no1 1-hydroxy-2-but1.3 anone 2-furaldehyde 0.57 3.3 3.3 5.2 22.0 15.4 dry residue at 26.0 120 oc solid residue 26.3 43.0 28.1 37.9 14.8 10.4 13.9 12.7 gas 10.2 6.1 9.1 8.1 COZ co 4.0 3.3 4.0 4.1 0.60 0.93 0.80 0.54 CH, total 100 99.5 96.6 96.5 (I
borax
Mean values.
observed. Both types of catalysts, acidic and basic, favor water formation in accordance with the literature. From these results FeC1, and CoC1, have been selected for study in the experimental system.
Catalytic Pyrolysis of Almond Shells Three experiments, 3 wt % FeC13, 3 wt % CoCl,, and 6 wt % CoC1, have been run in the designed reactor at 500 OC. Table V shows the results obtained as well as those obtained without catalyst. A significant variation with respect to liquids composition, similar to that observed in the Pyroprobe 100 equipment, can be observed. Furfural (5.17%) and acetic acid (6.54%) were obtained when 6.4% CoC1, was used as the catalyst, compared to 0.75% and l o % , respectively, when pyrolysis was carried out without a catalyst. A slight increase in water production as well as in acetone and isopropyl alcohol production can also be observed. Concerning the gases, a decrease in carbon dioxide and a change in carbon monoxide and methane can be observed, reaching 4.1% (dry weight basis) of CO when 6.4% CoCl, is used and 0.93% CH, when 3% FeC1, is used. Significant variations in yields of solids, liquids, and gases are obtained when this type of catalyst is used, de-
0.2
0.0
0.6
0.a
PVROPROBE Y I E L D
Figure 7. Comparison between the relative yields of water (e), acetic acid (m), 2-furfuraldehyde (A),hydroxyacetone ( o ) ,and 1hydroxy-2-butanone (0) obtained in the experimental reactor and in the Pyroprobe.
creasing gases and liquids and increasing solids. Tarry fractions were always lower when catalysts were used. This behavior is usual for acidic type catalysts (Yamada, 1959; Smicek and Cerny, 1970). Figure 7 shows the mass fraction of the main components (water, acetic acid, and furfural) with respect to the analyzed liquids obtained in the experimental reactor vs. the corresponding mass fractions obtained in the Pyroprobe 100 equipment. All points lie on the diagonal, which shows that results obtained in the Pyroprobe 100 are indicative of what would be obtained in the experimental reactor. Additionally, it can be concluded that pyrolysis in the experimental reactor is run in conditions very close to actual flash pyrolysis.
Conclusions 1. The hydrodynamic characteristics of the designed experimental reactor have been studied. Calcinated sand of 0.105-0.210-mm particle size, almond shells of 0.2970.500-mm particle size, and 4.7 cm/s gas velocity were selected for the present study, since they ensure a wellmixed bed and no fine charcoal particles entrainment. 2. Liquid yields around 65% (dry basis) at 610 OC have been obtained under fast pyrolysis conditions. Organic yields in this run were 10.4% acetic acid, 1.77% hydroxyacetone, 1.29% 1-hydroxy-Z-butanone,0.85% furfural, 0.46% 3-methyl-1-butanol, and 0.70% methanol. Similar yields are obtained within the 420-610 "C temperature range. 3. Flash pyrolysis a t 610 O C produces around 110% more light liquid than slow pyrolysis, proving the marked
Ind. Eng. Chem. Prod. Res. Dev.
496
influence of the heating rate on these types of processes. Gases obtained in flash pyrolysis are richer in methane and carbon monoxide. 4. Acid catalysts produce a significant shifting in liquids composition. Almond shells impregnated with 6.4% CoC1, yield 5.17% furfural and 6.54% acetic acid. When 3% FeC1, was used, the corresponding yields were 3.3370 and 2.1570, respectively. 5 . Pyroprobe 100 pyrolyzer equipment has proven to be very useful for pyrolysis conditions screening, given the good accordance with the results obtained in the experimental reactor and the simplicity of its handling. Registry No. FeCl,, 7705-08-0; CoC12,7646-79-9; CO, 630-08-0; CH4, 74-82-8; acetic acid, 64-19-7; methanol, 67-56-1; 2-fur-
aldehyde,98-01-1;acetone, 67-64-1; 2-propanol,67-63-0; propionic acid, 79-09-4; acetaldehyde, 75-07-0; hydroxyacetone, 116-09-6; 3-methyl-1-butanol,123-51-3;l-hydroxy-2-butanone,5077-67-8.
1986,2 5 , 496-499
Literature Cited Beaumont, 0.; Schwob, Y. Ind. Eng. Chem. Process Des. Dev. 1984, 2 3 , 637. Finney, C. S.;Garret, D. E. Energy Sources 1974, 1 , 192. Goldstein, I. S. Organic Chemicals from Biomass; CRC: Boca Raton, FL, 1981; Chapter 5. Kosstrin, H. "Direct Formation of Biomass Derived Pyrolytic Vapors to Hydrccarbons", Proceedings of the Specialists' Workshop on Fast Pyrolysis of Biomass; U.S. Government Printing Office: Washington, DC. 1980; p 105. Pattipati, R. R.; Wen, C. Y. Ind. Eng. Chem. Prod. Res. Dev. 1981, 2 0 , 705-708. Ruiz Bevii, F.; Prats Rico, D.; Marcilla Gomis, A. F. Ind. Eng. Chem. Prod. Res. Dev. 1984a, 2 3 , 266. Ruiz Bevii, F.; Prats Rico, D.; Marcilla Gomis, A. F. Ind. f n g . Chem. Prod. Res. Dev. 1984b, 2 3 , 269. Sass, A. Chem. Eng. Prog. 1974, 7 0 , 72. Scott, D. S.; Piskorz, J. Can. J . Chem. Eng. 1984, 62, 404-412. Shafizadeh, F. Appl. Polym. Symp. 1975, 28, 153. Smicek, S.; Cerny, S. Active Carbon; Elsevier: Amsterdam, 1970. Yamada, D. Bull. Fac Eng., Yokohama Natl. Univ. 1959, 8 .
Received for review June 24, 1985 Accepted February 14, 1986
Catatytic Dehydrochlorination of 3,4-Dichloro-l-butene over CsCl Supported on Silica Gel Isao Mochlda,' Tatsuro Mlyazakl,t and Hlroshl Fujitsut Research Institute of Industrial Science and the Department of Molecular Engineering, Graduate School of Engineering Science, Kyushu University, Kasuga 8 16, Fukuoka, Japan
CsCl supported on silica gel dried at 120 OC was found to exhibit high activity for the selective dehydrochlorination of 3,4dichloro-l-butene into chloroprene in the pulse reactor after calcination at around 500 OC. Although the conversion and the selectivity for chloroprene decreased in subsequent pulses at the expense of increasing 1,4dichloro-2-butene, the catalyst regeneration and HCI recovery can be achieved by heat treatment above 400 OC with evolution of HCI. Reactivities and product distributions of some other chloroalkanes over the same catalyst were studied to deduce the base-catalyzed carbanion mechanism.
Introduction
Dehydrochlorination of 3,4-dichloro-l-butene selectively into chloroprene with recovery of hydrogen chloride is a target for its practical production (Stille, 1968). Very few attempts have been reported (Carothers, 1936; Tominaga et al., 1971; Malkhasya et al., 1981) probably because of the high reactivity of chloroprene. We have reported that in pulse reactor tests CsCl supported on a silica gel after calcination exhibited a very high activity for the selective dehydrochlorination of 1,1,2-trichloroethane into 1,l-dichloroethylene (Mochida et al., 1985a,b). The catalyst lost its activity in repeated pulses, but it could be regenerated by heat treatment above 400 "C with the liberation of hydrogen chloride produced on its surface. In the present report, the selective dehydrochlorination of 3,4-dichloro-l-butene over CsCl supported on a silica gel was examined in pulse reactor tests. Some particular features of its reactivity in the catalytic elimination reaction are reported. The reactivities of some chloroalkanes were included for a comparison to discuss the mechanism of the elimination reaction. E x p e r i m e n t a l Section
A microbead silica gel dried a t 120 "C was added to a solution of CsCl in dry methanol. Removing the solvent Research Institute of Industrial Science. Department of Molecular Engineering. 0196-4321/86/1225-0496$01.50/0
Table I. Silica and Silica Alumina Supports and Their Properties surface silica gel
(2-200 MB-3A MB-4A MB-5D A-200" A-380' PG-68* SA (silica alumina) a
area,c m2 g-'
source Wako Junyaku Co. Fuji-Davison Chem. Co.
Nihon Aerosil Inc.
Electron Nucleonics, Inc. Shokubai Kasei
Aerosil. *Porousglass. BET.
280 650 500 280 200 380 70
pore size:d A
25 64 160 1.2
550
Mean diameter. Surface area
and pore size were both calculated from the N2 adsorption.
under reduced pressure gave white powders of CsCl impregnated on SiOz (CsC1 11 wt 70). The catalyst was calcined in the reactor under hydrogen flow at 500 "C for 2 h before the first pulse. Some properties of some silica gels are listed in Table I. The catalytic dehydrochlorination of 3,4-dichloro-1butene over CsCl/MB-3A was investivated in the temperature range 110-250 OC by a pulse reactor (carrier gas and flow rate, H2 and 60 cm3 min-l, respectively; catalyst, 0.3 g; pulse size, 2 pL; analyzing column, Ucon oil (4 m, 60 OC)). The interval between pulses was usually 1 h. The catalytic dehydrochlorination of 1,1,2-trichloroethane, 0 1986 American Chemical Society
