Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 496-499
496
influence of the heating rate
on
Literature Cited
these types of processes.
Gases obtained in flash pyrolysis are richer in methane and
Beaumont, O.; Schwob, Y. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 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 Hydrocarbons”, 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, 20,
carbon monoxide. 4. Acid catalysts produce a significant shifting in liquids composition. Almond shells impregnated with 6.4% CoCl2 yield 5.17% furfural and 6.54% acetic acid. When 3% FeCl3 was used, the corresponding yields were 3.33% and 2.15%, 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.
·,
705-708.
Ruiz Beviá, F,; Prats Rico, D.; Martilla Gomls, A. F. Ind. Eng. Chem. Prod.
Res. Dev. 1984a, 23, 266.
Ruiz Beviá, F.; Prats Rico, D.; Martilla Gomis, A. F. Ind. Eng. Chem. Prod.
Res. Dev. 1984b, 23, 269. Sass, A. Chem. Eng. Prog. 1974, 70, 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.
Registry No. FeClg, 7705-08-0; CoCl2, 7646-79-9; CO, 630-08-0; CH4, 74-82-8; acetic acid, 64-19-7; methanol, 67-56-1; 2-furaldehyde, 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.
for review June 24, 1985 Accepted February 14, 1986
Received,
Catalytic Dehydrochlorination of 3,4-Dichloro-1-butene Supported on Silica Gel
over
CsCI
Isao Mochlda,*1 Tatsuro Miyazaki,1 and Hiroshi Fujitsu1 Research Institute of Industrial Science and the Department of Molecular Engineering, Graduate School of Engineering Science, Kyushu University, Kasuga 816, Fukuoka, Japan
CsCI supported on silica gel dried at 120 °C was found to exhibit high activity for the selective dehydrochlorination of 3,4-dichloro-l-butene into chloroprene in the pulse reactor after calcination at around 500 °C. Although the conversion and the selectivity for chloroprene decreased in subsequent pulses at the expense of increasing 1,4-dichloro-2-butene, the catalyst regeneration and HCI recovery can be achieved by heat treatment above 400 °C 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
Table I. Silica and Silica Alumina Supports and Their Properties
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 CsCI supported on a silica gel after calcination exhibited a very high activity for the selective dehydrochlorination of 1,1,2-trichloroethane into 1,1-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 CsCI 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.
surface area,c m2
silica gel
MB-3A MB-4A MB-5D
Fuji-Davison Chem. Co.
A-200“ A-380“
Nihon Aerosil Inc.
PG-686 SA (silica
Electron Nucleonics, Inc. Shokubai Kasei
280 650 500 280 200 380 70 550
pore size,c’d
Á
25 64 160
1.2
Aerosil. 6 Porous glass. c BET. d Mean diameter. Surface and pore size were both calculated from the N2 adsorption.
area
under reduced pressure gave white powders of CsCI impregnated on Si02 (CsCI 11 wt %). 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-lbutene over CsCl/MB-3A was investivated in the temperature range 110-250 °C by a pulse reactor (carrier gas and flow rate, H2 and 60 cm3 min™1, respectively; catalyst, 0.3 g; pulse size, 2 pL; analyzing column, Ucon oil (4 m, 60 °C)). The interval between pulses was usually 1 h. The catalytic dehydrochlorination of 1,1,2-trichloroethane,
Research Institute of Industrial Science.
Department of Molecular Engineering. 0196-4321/86/1225-0496301.50/0
Wako Junyaku Co.
g™1
alumina)
A microbead silica gel dried at 120 °C was added to a solution of CsCI in dry methanol. Removing the solvent 1
C-200
0
Experimental Section
1
source
©
1986 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 3, 1986
497
Table II. Catalytic Dehydrochlorination of 3,4-Dichloro-l-butene at Variable Reaction Temperatures0 selectivity,6 %
reactn temp, °C 110
pulse 1
2 3
150
1
2 3
4 5 6
T 8d
200
1
2 3
250
1
2 3
no.
convn, %
CP
1-CBD
cis-l,4-DCB'-2
trans-l,·4-DCB'-2
96 68 36 100 96
95 97 92
5
0 0
0 0
81 49 22 10 67 100 100 93 67 100 90 62
3
6 9 8 13 10
91
92 86 82 54 38 72 91 85 85 77 77 75 49
0 0 0 0 0 4
7
5 15 9 10 13 12 13 16 14
2
0 0 1
1
8 35 50 11
0
0
0 0
0
1
10 0
7
1
0 0
3
27
5
“Catalyst, CsCl/MB-3A 0.3 g; CsCl impregnated, 11%; pulse size, 2 mL. 6CP, chloroprene; 1-CBD, l-chlorobutadiene; l,4-DCB'-2, 1,4dichloro-2-butene. “Heat treatment at 350 °C before pulse. dHeat treatment at 500 °C before pulse.
1,2-dichloropropane, and 1,2-dichlorobutane over CsCl/ MB-3A was investigated at 150 °C by a pulse reactor under the same conditions described above except for the analyzing column (tricresyl phosphate (4 m, 60 °C)).
Table III. Catalytic Activity of CsCl Supported on Various Silica Gels for Dehydrochlorination of 3,4-Dichloro-1-butene in the First Pulse0 selectivity (%)
Results Dehydrochlorination of 3,4-Dichloro-1-butene. The dehydrochlorination of 3,4-dichloro-l-butene (I) over CsCl/MB-3A produced chloroprene (2-chlorobutadiene),
convn, % catalyst MB-3A 0 7 unsupported CsCl 59 CsCl/C-200
trans- and cis-l-chlorobutadienes, and trans- and cis1.4- dichloro-2-butenes. The selectivity of the products varied with the pulse number as well as the reaction temperature. Table II summarizes the conversion and selectivity in sequential pulses over a catalyst (0.3 g) at 150 °C. In the first pulse, 3,4-dichloro-l-butene was completely
converted into chloroprene and l-chlorobutadiene, the selectivity for chloroprene being as high as 91%. The conversion and the selectivity for chloroprene decreased in successive pulses, slowly in the initial three pulses and then larger changes were observed. Instead, the yield of 1.4- dichloro-2-butene increased markedly in the fifth and sixth pulses, while a constant amount of l-chlorobutadiene was produced. Until the third pulse, 0.22 mol of chloroprene was produced by 1 mol of CsCl on silica gel. No reaction took place on the silica gel alone. Unsupported CsCl converted only 7% of 3,4-dichloro-l-butene. Table III summarizes the catalytic activities of CsCl supported on some silica gels commercially available. The highest activity and selectivity of MB-3A was noted. CsCl supported on silica alumina failed to produce chloroprene at 200 °C, no sharp peak being observable in the chromatogram. The calcination temperature also influenced the catalytic activity and selectivity of the CsCl/MB-3A. The calcination at 250 °C allowed only 30% conversion in the first pulse at 150 °C with the same amount of the catalyst. The heat treatment at 350 °C for 1 h after the seventh pulse or at 500 °C for 1 h after the eighth pulse restored the catalytic activity and selectivity for chloroprene, the latter treatment providing those of the fresh catalyst as shown in Table III. Apparently the catalyst poison, HC1, must be removed. In fact, almost 50% of the hydrogen chloride eliminated was recovered during the repeated pulses at 150 °C, and the rest was completely liberated from the catalyst by the heat treatment at 500 °C. The conversion and the product distributions from 3.4- dichloro-l-butene at several temperatures in the first
cis-1,4-
CsCl/MB-3A CsCl/MB-4B CsCl/MB-5D CsCl/A-200 CsCl/A-380 CsCl/PG-68
100 100 94 86 89 38
CP 1-CBD 72 87 91 86 90 90 90 88
DCB'
25 8 9 14 10 9 10
3
8
1
1
trans-1,
DCB'
4
1
3
CsCl/SA1
“Catalyst, 0.3 g; reaction temperature 150 °C; pulse size, 2 µ ; calcination temperature 500 °C. 6Broad peak; no sharp peak observable in chromatogram.
three pulses are also included in Table II. The elimination proceeded very selectively at 110 °C, giving chloroprene selectivity as high as 95% at a conversion of 96% in the first pulse. The second pulse showed a considerably lower conversion of 68%, although the selectivity stayed at 95%. The third pulse showed a further decline in conversion (36%). At 200 and 250 °C, the conversion in the first pulses increased to 100%; however, the selectivity to chloroprene decreased with the rising reaction temperature. The yield of l-chlorobutadiene increased to about 12 and 15%, respectively, at 200 and 250 °C regardless of the pulse number. The l,4-dichloro-2-butene selectivity increased to 32% in the third pulse at 250 °C, while the selectivity for chloroprene decreased rapidly. The conversion in the first pulse was almost independent of the reaction temperatures, although the conversion in later pulses showed a strong dependence on the temperature. The strong basicity of the fresh catalyst, which may limit the rate of HC1 liberation in successive pulses, is suggestive. Both l-chlorobutadiene and l,4-dichloro-2-butene were identified to be mainly in their trans forms. Reactivities of Some Chloroalkanes. Tables IV-VI summarize the conversion and product distributions from 1.2- dichlorobutane (II), 1,1,2-trichloroethane (III), and 1.2- dichlorobutane (IV), respectively, over CsCl/MB-3A at 150 °C. Product distributions for these reactants, including the trans/cis ratio of the products, are reminiscent of those observed on typical basic solids such as KOH/Si02
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 3, 1986
498
a ci Ct-C-C-H
Table IV. Catalytic Dehydrochlorination of 1,2-Dichlorobutane0 selectivity,6 % convn, %
cis-l-CB'-l
frans-l-CB'-l
2-CB'-l
82 39
19
2
20
3
18
16
43 44 46
38 36 38
pulse
no.
1
a: 5.8
ppm b:4.0 ppm
H
(a) (b)
Cl Cl
H-C-C-CCH 3 H
a:3.6 ppm b:4.1 ppm
(a) (b)
"Reaction temperature, 150 °C; catalyst, CsCl/MB-3A, 0.3 g; pulse size, 2 µ j. 61-CB'-1, 1-chloro-l-butene; 2-CB'-l, 2-chloro-l-
Cl Cl
butene.
H-C-C-i H
Table V. Catalytic Dehydrochlorination of 1,1,2-Trichloroethane" pulse
no.
1
2 3
convn, %
VDC
99 80 37
94 93 93
(a) (b) Ci Cl
6 selectivity, % cis-DCE trans-DCE
2
4
2
5
4
3
a:3.7 ppm
H-C-C-CH=CH, (i,
b: 5.9 ppm
¿
(a) (b)
Figure
Chemical shift values of protons in the reactants.
1.
"Reaction temperature 150 °C; catalyst, CsCl/MB-3A, 0.3 g; 2 µ .. 6VDC, 1,1-dichloroethylene; DCE, 1,2-dichloro-
pulse size, ethylene.
Table VI. Catalytic Dehydrochlorination of 1,2-Dichloropropane" selectivity,6 % convn, %
2-CP'
cis-l-CP'-l
trans-l-CP'-l
1
69
2
26 13
27 29 29
31 32 32
42 39 39
pulse
no.
3
“Reaction temperature 150 °C; catalyst, CsCl/MB-3A, 0.3 g; 2 µ . 62-CP', 2-chloropropene; l-CP'-l, 1-chloro-l-
pulse size, propene.
(Mochida et al., 1967,1971,1974,1976), suggesting again the strong basicity of CsCl/MB-3A. The product distributions were essentially unchanged in successive pulses in contrast to the case of 3,4-dichloro-l-butene, although the conversion decreased considerably in the following pulses.
The reactivities of the present reagents into their respective products were deduced as follows (Roman figures in parentheses designate the reagent): chloroprene (I) —»·
1,1-dichloroethylene (III) 1-chloro-l-propene (II) 21-chloro-l-butene (IV) -* 2-chloro-l-butene (IV) 1,2-dichloropropene (II) -» 1-chlorobutadiene (I) chloroethylene (III). l,4-Dichloro-2-butene is not included because it appears to be a secondary addition product found only in later pulses. -»
—-
—*-
Discussion The reactivity order and the product distributions ob-
served in the present study can be explained by a carbanion mechanism, where the acidic proton is eliminated in the rate-determining step as is often postulated for basic catalysts (Mochida et al., 1967,1974). The chemical shifts of protons in the reactants (Figure 1), which may be measures
for their acidity,
are
approximately correlated
to the product distribution and reactivity order
reported in the elimination reactions on the solid base (Mochida et al., 1971), although the rate of formation of 1,2-dichloroethylene and 1-chlorobutadiene is much lower than would be expected from the chemical shifts. This suggests that the very acidic protons in these reactants may hinder the interaction of the less acidic protons with the surface basic groups.
as
The preferential production of the trans forms from all present reactants observed on CsCl/MB-3A is explained by the trans elimination from more stable geometric iso-
Q: to be eliminated 2. Geometric isomers of 3,4-dichloro-l-butene to be dehydrochlorinated through trans elimination and their products.
Figure
of each reagents. The isomers of 3,4-dichloro-lbutene as an example are illustrated in Figure 2. The upper isomer, which is converted into trans- 1-chlorobutadiene, is more stable. Such a mechanism is common on the basic solids (Misono and Yoneda, 1972; Mochida et al., 1976). The mechanism of formation of l,4-dichloro-2-butene illustrates some interesting mechanistic points. The proposed route is shown in eq 1, where the acidic elimination mers
ch2
CL
-Cl H
/
\
XI
H H
X
0-C.
H
Cl
(I) H
ch2ci
CH2CI
0c=c("
(1)
h
(V)
of chloride by hydrochloric acid adsorbed on the catalyst surface is postulated. The trans form of 3,4-dichloro1- butene (I), which is more stable than the cis form, gives the E allyl cation. Addition of chloride at the terminal carbon of the E allyl cation produces trans-l,4-dichloro2- butene (V). The acidic site and chloride anion are available only in later pulses where a considerable amount of hydrogen chloride was accumulated on the catalyst surface. Thus, the product was produced only in later pulses.
The origin of the strong basicity of CsCl/MB-3A requires more investigation and identification of its surface
Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 499-504
structure. Nevertheless, a significant role of silanol groups on the silica surface should be considered likely since they are the only sites capable of adsorbing hydrogen chloride at the reaction temperatures (Her, 1979). The cooperative role of CsCl and silanol groups may attract further investigation because the support strongly influences the catalytic activity of CsCl. Among the silica gels, a larger surface area appears to give a higher conversion with some exceptions. However, silica alumina of large surface area failed to produce chloroprene. The acid-base nature of surface hydroxyl groups may be also influential. Finally, 1 g of the present CsCl/MB-3A catalyst could produce only 2 X 10~2 g of chloroprene from 3,4-dichloro1-butene before regeneration. Further increase of catalytic capacity is most wanted. Better silica gel of larger surface area should be sought. Registry No. CsCl, 7647-17-8; 3,4-dichloro-l-butene, 760-23-6;
499
dichloropropane, 78-87-5; cis-l-chloro-l-butene, 7611-86-1; trons-l-chloro-l-butene, 7611-87-2; 2-chloro-l-butene, 2211-70-3; 1,1-dichloroethylene, 75-35-4; 2-chloropropene, 557-98-2; ci's-1chloro-l-propene, 16136-84-8; trons-l-chloro-l-propene, 1613685-9; 1 -chlorobutadiene, 627-22-5.
Literature Cited Carothers, W. H. U.S. Patent 2 038 538; Chem. Abstr. 1936, 30, 3838. Iler, R. K. The Chemistry of Silica·, Wlley-Interscience : New York, 1979. Malkhasya, A. Ts.; Khachatryan, L. A.; Mirakyan, S. M.; Martirosyan, G. T. Arm. Khim. Zh. 1981, 34, 404. Misono, M.; Yoneda, Y. Bull. Chem. Soc. Jpn. 1972, 45, 1274. Mochida, I.; Take, J.; Salto, Y.; Yoneda, Y. J. Org. Chem. 1967, 32, 3894. Mochida, I.; Anju, Y.; Yamamoto, H.; Kato, A.; Selyama, T. Bull. Chem. Soc. Jpn. 1971, 44, 3305. Mochida, I.; Uchino, A.; Fujitsu, H.; Takeshita, K. J. Catal. 1976, 43, 264. Mochida, I.; Miyazaki, T.; Takagl, T.; Fujitsu, H. Chem. Lett. 1985a, 833. Mochida, I.; Takagi, T.; Fujitsu, H. Appl. Catal. 1985b, 18, 105. Stille, J. K. Industrial Organic Chemistry Prentice-Hall: Englewood Cliffs, NJ, 1968. Tomlnaga, H.; Nakamura, T.; Arai, H.; Kunugl, T. Kogyo Kagaku Kaishi 1971, 74, 199. ·,
Received for review June 4, 1985 Revised manuscript received December 4, 1985 Accepted February 6, 1986
chloroprene, 126-99-8; írcms-1,4-dichloro-2-butene, 110-57-6; 1,2-dichlorobutane, 616-21-7; 1,1,2-trichloroethane, 79-00-5; 1,2-
Model for the Thixotropic Behavior of Cement Pastes Clrlllo Atzenl, Luigi Massidda,* and Ulrlco Sanna Istltuto dl Chlmlca Applicata
e
Metallurgy, University of Cagiyri, 09100 Cagliari, Italy
A model is presented for describing the thixotropic behavior of Portland cement pastes. In defining the model, Tattersall’s energy theory was adopted, but in place of the original assumption that the strength of all the linkages forming the structure is the same, such strength was considered unequal. Experiments were conducted in a rotating viscometer of the Searle type at different solid-phase concentrations, measuring shear stress against time t at constant rate of shear D. In all cases the experimental data were in excellent agreement with the model proposed: =
ß + (Tm
-
rJe-B-'-B.TaV-e-'^
The findings indicate that about 3 min are required for the paste to reach practically steady flow conditions. During the time required by the system to attain equilibrium, the energy output breaks down fractions of linkages of increasingly greater strength. The mode of paste preparation has a marked effect on the observed rheological behavior. In light of the above, the discrepancies between the experimental data reported by different workers are discussed.
Introduction
followed: (a) hysteresis cycle, which measures the behavior of vs. D, the latter varying continuously or stepwise from 0 up to a maximum value (up curve) and back (down curve); and (b) transient, which measures the behavior of r with respect to time t at constant D. The first method enables rapid determinations, and using a standard test procedure, we can find the main rheological coordinates of the system, in particular r0 and , useful in cement technology. The transient approach, on the other hand, seems particularly suitable for interpreting the effect on viscometric flow conditions of the different forces existing between the particles of the systems examined. In this work the latter technique was adopted in experiments on Portland cement suspensions with varying water/cement (w/c) ratios in a coaxial cylinder viscometer, measuring r against t for different rates of shear D. These data were then used to verify the assumption of unequal linkage strength. can be
Cement pastes are solid-liquid dispersions with a high solid concentration, and their rheological behavior is non-Newtonian, time dependent, and generally thixotropic. The solid phase consists of water-active silicates and aluminates to which molecules of the mix water are attached, creating new formations and bridges between the solid particles, the majority of which are smaller than 100 Aim. The amount of water fixed during the first stage of the hydration process is relatively small. Our recent findings (1985) have indicated that in the first few hours of cement-water contact the rheological behavior of cement pastes does not differ substantially from that of other suspensions of industrial importance (clay and polymers). The rheological characterization of cement pastes is usually accomplished by means of experiments with rotating viscometers. Two different types of test procedures 0196-4321Z86/1225-0499S01.50/0
©
1986 American Chemical Society
