Catalytic Dehydration of 2-Butene-1,4-diol Hanwant Bir Singh, George E. Klinzing,* and James Coull Chemical and Petroleum Engineering Department, Cniversity of Pittsburgh, Pittsburgh, Pa. 15213
The objective of the present work was to study the catalytic dehydration of 2-butene-1,4-diol (cis) with emphasis on the preferential formation of 2,5dihydrofuran. In the catalyst screening study performed it was possible to search for a catalyst that could find efficient industrial use. Alumina-1 404 was found as the best catalyst for the reaction because of its selectivity against the formation of crotonaldehyde.
T h e dehydration of 2-butene-1,4-diol (B), the products of which find extensive use in fungicides, lubricants, solvents, drugs, etc., has not been studied sufficiently to permit a rational reactor design. I n the present study advantage was taken of t,lie rapid screening methods involved in the use of a microcatalyt,ic reactor in series with a gas chromatographic (gc) unit. Several commercially available dehydration catalysts n-ere sbudied aiid their performances were evaluated in terms of the preferential formation of 2,5-diliydrofuran (D5). I n each case a temperature range was important because of the complexity of the dehydration process. An attempt was made to obtain kinetic data as well as to trace the reaction steps in order to provide a better understanding of the present dehydration reaction. Previous Work
The work reported on the dehydration of H is by no means complete or conclusive. Ahderson (1971) conducted experiments on the homogeneous pyrolysis of I3 and showed from the of activation the reactions with one exception to be first order. In order t,o introduce reaction selectivity it was decided to study a number of solid catalysts in the heterogeneous system. Reppe and Schnabel (1939) were t'he first' to report the dehydration on a laboratory scale experiment in which sulfuric acid was used as a homogeneous catalyst and reported the formation of D5. Friedlin and Sharf (1961), Friedlin, et al. (1966), and Sliarf, et al. (1968), conducted systematic experiments using a steady-state reactor filled with alumina aiid tricalcium phosphate catalysts. It was reported that D5 converted to crotonaldeliyde (C2) a t a negligible rate and C2 was being formed from l3 through an intermediate y-hydroxybutyraldehyde (G). Valette (1946) had concluded that C2 was produced only by the trans isomer of H while the cis isomer yielded D 5 exclusively. However, Friedlin, et al. (1961), disputed this conclusion and observed that both cis and trans isomers of B dehydrated directly to D5 and in both cases the presence of intermediate G for the formation of C2 was indicated. Wellington and Walters (1961) reported the vapor-phase decomposition of D5 to furan (F) by dehydrogenation between 242 and 409' and a t lorn pressures (5-46 mm). They also iiot,ed the absence of any aldehyde in the products. Experimental Setup and Procedure
Xn Inconel-x tubing rnicrocatalytic reactor (8.75 cm long, 5.6-mm i d . ) , the outside of which could bc electrically heated, was attached to the flash vaporizer of a gc unit' (Burrell Kromot,og, Model KD) . A chromel-alumel thermocouple was 184 Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 2 , No. 3, 1973
spot-welded on the reactor wall and a variable-step transformer was used for input pori-er control. The column was an 8 f t long, 3 / ~ & . 0.d. stainless steel tubing packed with 80-100 mesh Poropak Q. Both helium aiid hydrogen were available for use as carrier gases and were purified by passing bhrough 13 molecular sieve beds before entering the gc unit. look a t the axial temperature profiles in the reactor showed a flat maximum of about 1-cm length where the catalyst n-as located to ensure isothermal conditions. The catalyst was crushed and sieved to t,he required particle size aiid a small amount of weighed catalyst (*0.0001 g) was then held in position by two Pyrex glass wool plugs. The reactant was injected near the catalyst bed in the st,ream of carrier gas and the products passed through the gc unit for resolution. The details of the setup have been provided by Singh (1972) aiid Retzloff (1967). Identification of Compounds
The major compounds involved, namely, 2-butene-1,4-diol (cis), 2,5-dihydrofuraii, crotonaldehyde, furan, and tetrahydrofuran, were available from standard sources with purit'ies exceeding 98.5%. Peaks were identified by their retention times, using pure compounds. The relative position of peaks was also in qualitative agreement with the results of Friedlin, et al. (1966). I n the presence of the catalyst, the retention times were virtually unchanged aiid there was no change in the relat,ive positions of the identified peaks. This was further tested by mixing the reactant with a product and observing the corresponding increase in peak area. Another test for the identification of peaks n-as accomplished by connecting the catalytic reactor directly to a combined gc and mass spectroscopic uiiit. This, together with the product spectrum presented by Friedlin (1966), confirmed the identification of 2,3dihydrofuran (D3) and buteii-1-a1 (C3). Catalysts
Several acid-t,ype catalysts were considered. -111 were commercially available. The following is a list' of catalysts that were st,udied. (A) Alumina Catalyst (Al-1404). ;1tableted ('/g-in size) high-activity alumina containing 96% A l I 0 3 (HarshaJv Chemical Co., Clereland, Ohio) was recommended for use as a catalyst support, as a drying agent, and in dehydratioli reactions. It had a prface area of 190-200 m2;/g and a pore volume (pores -
I
n
-
5
0
T
- -
1.94
1.98
2.02
2.06
2.1
Temp, 'C
(a) A1-1404 (deactivated) (b) K-10 (c) KSF (d) W-0602 (e) W-0801 (f) w-0101 (g) W-0801 (h) A1-1404
Injection
i
223.2
B
1
268 3 381 2 381 0 268.6 328.3 301 7 315 2
D5 D5
2 2 2 2 2 3 3
D5 D5 D5 c2 C2
1 0 3 / ~ * ~
Figure 3. Butenediol dehydration on catalyst AI-1 4 0 4 (deactivated). Conditions: 2-butene-l,4-diol injection, catalyst AI-1 404 (deactivated), carrier gas helium
Since total conversion was obtained on all catalysts, deactivation of catalyst A1-1404 was carried out by allowing a steady stream of B to react with a bed of catalyst held a t 300'. This was accomplished by disconnecting the reactor from the gc and passing the reactant through it in a constant stream of helium that was bubbled through 200 ml of B heated to 100". The deactivation was extremely slow and reaction had to be carried over several days to accomplish a noticeable change in the catalyst characteristics. Table I clearly shows the presence of C2 in the product spectrum, even a t 207" when the deactivated catalyst was employed. Figure 2 shows the formation of C2 upon continuous reaction of B on catalyst K-10. This trend is comparable to the trend observed on catalyst A-1404 even though i t was a much slower process with the latter catalyst. The kinetic parameter ( k K ) mcould be easily evaluated for the X1-1404 deactivated catalyst from Figure 3. The overall reaction is first order in nature as was evidenced by the plot shown in Figure 4. The first-order rate constant ( k K ) ~ isl listed in Table I1 and has a low activation energy of 5.4 kcal/ ) 1/T are shown in mol. Linear plots of In ( ( k K ) l / ( k R ) z us. 186 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
Figure 1. A value of ( k K ) l / ( k K ) of z about 2.7 for the deactivated X1-1404 can be compared with the fresh catalyst where no C2 was observed ( ( k K ) , = 0). The activity of catalysts in the order of decreasing selectivity for D5 can be arranged as 41-1404 (also W-0801) > W-0101 > K-10 > W-0602 > A1-1404 (deactivated) > KSF. The dehydration reactions were completely irreversible. Mixtures of D5 and C2 with water showed no signs of formation of B in the product stream as thermodynamics predicts. This is further confirmed by the 100% decomposition of B on all fresh catalysts. The narrow temperature range of the study of deactivated A1-1404 (207-248') was due to its ability to reactivate quickly. I n fact, almost complete reactivation could be accomplished by heating the deactivated catalyst between 450 and 500" for less than 0.5 hr in a stream of helium. (B) 2,SDihydrofuran Reactions. Typical product distributions are listed in Table 111. The reactant conversion varied from a minimum of 87, on catalyst Al-1404 a t 342" to a maximum of 73y0 on catalyst K-10 a t 348'. The major product a t lower temperatureq was F formed due to the dehydrogenation reaction of D5, with traces of C3, D3, and T 4 occurring on specific catalysts as the temperature was T4) was observed only on raised. Compound T 4 (D5 Hz+. catalysts K-10 and W-0602 a t relatively higher temperatures (348' and above) and in amounts that never exceeded 1%. The other important product was C2 and its amount increased
+
Table 1. Representative Product Distributions of the Dehydration of 2-Butene-l,4-diol on Various Catalysts.
Temp., OC
Catalysts
F
D3
c2
c3
T4
Unknowns
Fractional reactant (B) conversion
0.00 0.08 0.00 0.00 0.02 0.04 0.13 0.00 0.00 0.01 0.03 0.06 0.28 0.02 0.05
0.00 0.00 0.25 0.27 0.22 0.39 0.18 0.56 0.75 0.39 0.61 0.00 0.00 0.18 0.35
0.00 0.00 0.00 0.00 0.00 0.00 0.26 0.00 0.00 0.00 0.02 0.00 0.41 0.00 0.02
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Traces 0.00 0.00 0.00 0.08 0.00 0.00
1.00 1.00 0.82 0.92 1.00 1.00 1.00 1 .oo 1 .oo 1.00 1 .oo 1 .oo 1.00 1.00 1 .oo
D5
190.1 A1-1404 0.00 1.00 326.7 (fresh) 0.07 0.85 207.2 A1-1404 0.02 0.73 248.8 (deactivated) 0.04 0.69 235.5 Montmorillonite 0.12 0.64 271.1 K-10 0.16 0.41 336.7 0.25 0.18 216.1 Montmorillonite Traces 0.44 334.4 KSF 0.04 0.21 216.1 W-0602 0.02 0.58 337.7 0.09 0.25 243.3 W-0801 0.08 0.86 351.6 0.20 0.03 202.2 W-0101 0.03 0.77 0.08 0.50 318.3 a All product distributions are on a reactant-free basis.
t a b l e II. Kinetic Parameters (kK)Ti
Catalysts
Al- 1404 (fresh) -41-1404 (deactivated) Montmorillonite K-10 Montmorillonite
(kK)i/(kK)n
(kK)Tz
(kKh
EC a
( ( k K ) z = 0)
SARb
0.248 exp( -91 10/RT)
0.097 exp( - 5400/RT)
1 , O l exp(977/RT)
NAR
SAR
EC
See product distribution 0.0057 exp(4750/RT)
184 exp( - 16,58O/RT)
NAR
2.77 exp( -20,46O/RT)
NAR
0 . 3 1 5 exp(-lO,420/RT) 481 exp(-18,270/RT) 4.47 exp( - 13,370/RT)
NAR 161 exp (- 14 840/RT)
EC
KSF W-0602 EC 0.0125 exp(4770/RT) W-0801 EC = 0) w-0 101 EC 0.0117 exp(516O/RT) a Equilibrium conversion. No appreciable reaction.
((a?)*
~
NAR
Table 111. Representative Product Distributions of the Reaction of 2,5-Dihydrofuran on Various Catalysts
Temp, 'C
Catalysts
F
D3
c2
c3
T4
Unknowns
215.6 342.2 238.9 348.3 286.1 444.0 285.0 380.2 216.1 344.2 251,6 368.3
A1-1404 (fresh) Moiitmorillonite K-10 Montmorillonite
1 .oo 0.73 1.00 0.76 1.00 0.38 1.0 0.76 1 .oo 0.61 1.00 0.59
0.00 0.27 0.00 0.19 0.00 0.03 0.00 0.09 0.00 0.16 0.00 0.17
0.00 0.00 0.00 0.04 0.00 0.59 0.00 0.14 0.00 0.00 0.00 0.24
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.20 0.00 0.00
0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03
KSF W-0602 W-0801
w-0101
with increasing temperature. On catalyst KSF, the C2 fraction in the product stream increased from 0 to 59% as the temperature was increased from 286 to 444'. The decomposition reaction of D 5 was first order and this was established from the flow rate variation as shown in Figure 4. The decomposition kinetic constant ( l i K ) was ~~ evaluated for various catalysts from Figure 5 and the results are listed in Table 11. The range of apparent activation energies was 10-21 kcal/mol depending upon the catalyst used. Two particle sizes (120 and 200 mesh) were used to evaluate the effect of external resistances. .Is is clear from
0.00 0.00
Fractional reactant (D5) conversion
0.01 0.08 0.09 0.73 0.01 0.54 0.12 0.43 0.02 0.29 0.04 0.34
Figure 5, no change in the conversion of the reactant mas observed, arid hence it could be assumed that the reaction was controlling (effectiveness factor 1). The activity of various catalysts in the order of decreasing dehydrogenation ability was K-10 > W-0801 > W-0602 > JJ7-O101> KSF > X1-1404. Crotonaldehyde Reactions
On catalysts KSF, K-10, W-0602, and W-0101 virtually no reaction was observed. Total conversion was less than 5% for the above catalysts up to temperatures approaching 350". On catalyst W-0602 no reaction was observed up to 400'. The Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
187
Table IV. Representative Product Distribution of Crotonaldehyde Reaction on Various Catalysts
Temp, OC
Catalyst
D5
D3
c3
Unknowns
Fractional reactant IC21 conversion
206.6 342,2 221.1 296.1
-41-1404
0.57 0.36 0.57 0.09
0.00 0.14 0.09 0.15
0.00 0.17 0.17 0.30
0.43 0.33 0.17 0.46
0.10 0.69 0.19 0.80
0.011 1.35
w-0801
I
1.45
1.55
1.b5
lo3/ I
1.75
I
I
I
1.85
1.95
2.05
I( __c
Figure 5. Catalytic decomposition of 2,5-dihydrofuran (2,5-dihydrofuran injection carrier gas helium): (a) catalyst K-10; (b) catalyst KSF; (c) catalyst W-0602; (d) catalyst W-0801; (e) catalyst W-0101 j 0 , O, 0, 3,8, 120 mesh; w, a,D, U,n, 200 mesh
overall conversion was however significant on catalysts -411404 and R-0801. The product distributions for these two catalysts are listed in Table IV. The major products were D5 with traces of C3 and D 3 and significant amounts of unknowns (predominantly ethylene). At temperatures beyond 350', extensive cracking took place and a host of u n k n o m products appeared on the spectrum. *Inoverall C2 conversion of 69% a t 342' on catalyst -11-1404 can be compared with a n 80% conversion on IT-0801 a t 296'. The values of ( k K ) m were obtained from linear plates and the results are listed in Table 11, indicating a n apparent activation energy range of 915 kca1,'mol. Furan Reactions
No reaction of F was observed on any catalyst up to a temperature of 320'. At 400' a reactant conversion of more than 3y0 was not observed on any catalyst. Slow cracking began to take place after 450'. The situation up to 400' registered no change when hydrogen was employed as the carrier gas (replacing helium). Discussion and Conclusions
Alumina-1404 catalyst was adjudged as the best catalyst for any commercial product of 2,5-dihydrofuran from 2188 Ind.
Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1 9 7 3
butene-1,4-diol. The ease with which it reactivates and its extremely slow deactivation, together with a favorable product distribution, make it a very desirable catalyst. The dehydration reaction on catalysts A1-1404 (fresh) and W-0801 was marked by the absence of crotonaldehyde. However, when -11-1404 was continuously treated with 2butene-l,4-diol, product distribution changed appreciably and the presence of crotonaldehyde was evident in the product spectrum. The same phenomenon was observed with catalyst K-10 as is clearly shown in Figure 4. It is well known that on various acidic catalysts there are two types of acidic sites, namely, Lewis acid sites (electron acceptors) and Brinsted acid sites (proton donors), with the former changing to the latter in the presence of excess moisture (DeBoer and Visseren, 1971). The initial absorption of moisture, formed due to dehydration, by the catalyst surface leads to the conversion of Lewis acid sites, which seem to favor the formation of 2,5dihydrofuran, to Brgnsted acid sites, which favor the formation of crotonaldehyde. The quick reactivation can also be explained in terms of the quick removal of surface moisture and the reversal to Lewis acid sites (NacIver, et al., 1963). Even though 2,5-dihydrofuran converts to crotonaldehyde, its function as an intermediate for the formation of crotonaldehyde can be easily ruled out. X look a t Tables I and I11 will show that 2-butene-1,4-diol forms crotonaldehyde a t temperatures where 2,s-dihydrofuran shows virtually no conversion to crotonaldehyde. I n the present study no 7-hydroxybutyraldehyde was observed in any product spectrum and hence its function as an intermediate (Friedlin, et al., 1966) could not be confirmed. A view a t Table I11 may suggest the function of 2,3-dihydrofuran as an intermediate for the formation of crotonaldehyde from 2,5-dihydrofuran. I n all the product distributions obtained by injecting 2,5-dihydrofuran it was noted that the presence of crotonaldehyde was always marked with the presence of 2,3-dihydrofuran and the former did not appear until the latter had been detected (Singh, 1972).
D5 +D 3 +C2
(9)
h most general reaction scheme of the dehydration of 2butene-l14-diol may be suggested as €3
+D5 + HzO
B + C2
+ HzO
(10) (11)
Reactions 10 and 11 can be best illustrated by observing the product distribution due to 2-butene-1,4-diol injection, from Table I. Tables I11 and IV show the occurrences of reactions 12 and 13. T h e dehydrogenation of 2,Sdihydrofuran to furan representing reaction 14 was studied on all catalysts considered and was completely irreversible. The reaction of 2,5dihydrofuran with the hydrogen evolved due to its dehydrogenation was minimal and only traces of tetrahydrofuran were found as reported in Table 111. Nomenclature
B C2
c3 D3 D5 E'T~
F
FO FR
G
2-Butene-1,4-diol Crotonaldehyde 3-Butene-1-a1 2,3-Dihydrofuran 2,5-Dihydrofuran Apparent activation energy (cal/mol); i = 1-4 Furan Flow rate at 0" and mean reaction pressure Flow rate at room conditions y-hydroxy butyraldehyde Kinetic parameters defined in eq 2 Kinetic parameters defined in eq 2-5 Apparent frequency factor; i = 1-4
R T
Gas constant Temperature Tetrahydrofuran Catalyst weight Mole fraction; i = 1-4
T4 WC
XT i
literature Cited
Anderson. T.. Ph.D. Thesis. Universitv of Pittsburgh. 1971. Bassett, D.W., Habgood, H. W., J . Piys. Chem., 64,76911960). DeBoer, J. H., Visseren, W. J., Catal. Rev., 5, 55 (1971). Friedlin, L. Kh., Sharf, V. Z., Dokl. Akad. A'auk SSSR, 136, 1108 (1461 \-"--,.1 Friedlin, L. Kh., Sharf, V. Z., Kazaryan, A. A., Nejtekhimiya, 6,608 (1966). MacIver, D. S., Tobin, H. H., Barth, R. T., J . Catal., 2, 488 (1963).
R. (to I. G. Farben Industries), British "
8. 258 (1968).
I
I
.
Singh, H.' B., Ph.D. Thesis, University of Pittsburgh, 1972. Valette, A., C. R. Acad. Sci., 223,907 (1946). Wellington, C. A., Walters, W. D., J . Amer. Chem. SOC.,83, 4888 (1961). RECEIVED for review November 20, 1972 ACCEPTEDMarch 2, 1973
Surface Structure of Modified Copper Oxide Catalysts Edward B. Stuart* and Humberto Vainieri Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pa. 15261
The catalytic partial oxidation of isobutylene to methacrolein over pumice-supported copper oxide catalyst was studied. It i s known that the addition of trace amounts of modifiers to the feed increases the selectivity of the reaction for methacrolein formation. The catalyst was modified with bromine and chlorine to investigate the particular effect that the modifier ions have on the surface structure of the catalyst and to propose an explanation for the improved selectivity in terms of the changes in surface structure. It was observed that the addition of modifiers causes a decrease in the surface area of the catalyst and a shift in the pore volume distribution which gives a peak at a larger pore radius. The pore size distribution data show that during 4 hr of operation without an additive to the feed, the pore volume of the catalyst increases about 50%, primarily small pores with about 25-A radii; however, when additives which improve the oxidation selectivity were present, the increase in small pores did not occur. In view of these findings, the increase in selectivity caused by the modifier ions may b e explained by the following hypotheses. (a) The modifier ions become adsorbed on the surface by replacing some of the adsorbed oxygen species. The decrease in the surface concentration of oxygen then decreases the probability of having the methacrolein molecules oxidized any further; thus, the selectivity increases. (b) The observed shift in distribution peak shows that the effective diffusivity has been increased b y the modifier. Various observers have shown that an increase in effective diffusivity can cause an increase in selectivity for the intermediate products of a consecutive reaction.
Heterogeneous catalytic oxidation of hydrocarbons has attracted wide attention in recent years. These reactions can be used to obtain valuable oxygenated carbon compounds or to oxidize organic materials completely to carbon dioxide and water. One type of reaction that has been the object of considerable study is the partial oxidation of olefins and dienes to useful intermediate products. The useful products, ketones
and aldehydes, are usually the intermediates of the reaction sequence olefin
aldehyde or ketone
3-
kr
--t
carbon dioxide and water
The major problem encountered in the partial oxidation of Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
189
