I n d . Eng. C h e m . Res. 1990,29, 204-208
204
Literature Cited Anderson, R. B. Catalyst for the Fischer-Tropsch Synthesis. In Catalysis; Emmett, P. H., Ed.; Van Nostrand-Reinhold: New York, 1956; Vol. IV, pp 29-255. Anderson, R. B.; Seligman, B.; Schultz, J. F.; Elliot, M. A. FischerTropsch Synthesis. Some imp.ortant variables of the synthesis on iron catalyst. Znd. Eng. Chem. 1952,44,391-397. Arakawa, H.; Bell, A. T. Effect of potassium promotion on the activity and selectivity of iron Fischer-Tropsch Catalyst. Znd. Eng. Chem. Process Des. Dev. 1983,22,97-103. Benziger, J.; Madix, R. The Effects of Carbon, Oxygen, Sulfur and Potassium adlayers on CO and Hz adsorption on Fe (100). Surf. S C ~1980, . 94,119-153. Bonzel, H. P.; Krebs, H. Enhanced Rate of Carbon Deposition during Fischer-Tropsch Synthesis on K Promoted Fe. Surf. Sci. 1981,109, L527-L531. Bukur, D. B.; Lang, X.; Rossin, J. A.; Zimmerman, W. H.; Rosynek, M. P.; Yeh, E. B.; Li, C. Activation Studies with a Promoted Precipitated Iron Fischer-Tropsch Catalyst. Ind. Eng. Chem. Res. 1989,28,1130-1140. Deckwer, W.-D.; Serpemen, Y.; Ralek, M.; Schmidt, B. FischerTropsch Synthesis in the Slurry Phase on Mn/Fe Catalysts. Znd. Eng. Chem. Process Des. Dev. 1982,21,222-231. Dictor, R. A,; Bell, A. Fischer-Tropsch Synthesis over Reduced and Unreduced Iron Oxide Catalysts. J . Catal. 1986,97, 121-136. Donnelly, T. J.; Satterfield, C. N. Product Distributions of the Fischer-Tropsch Synthesis on Precipitated Iron Catalysts. Appl. Catal. 1989,52,93-114. Donnelly, T. J.; Yates, I. C.; Satterfield, C. N. Analysis and Prediction of Product Distributions of the Fischer-Tropsch Synthesis. Energy Fuels 1988,2, 734-739. Dry, M. E. The Fischer-Tropsch Synthesis. In Catalysis Science and Technology I ; Anderson, J. R., Boudart, M., Eds.; SpringerVerlag: New York, 1981; pp 159-255. Dry, M. E.; Oosthuizen, G. J. The Correlation between Catalyst Surface Basicity and Hydrocarbon Selectivity in the FischerTropsch Synthesis. J . Catal. 1968,II,18-24. Dry, M. E.; Shingles, T.; Boshoff, L.; Oosthuizen, G. J. Heat of Chemisorption on Promoted Fe Surfaces and the Role of Alkali in Fischer-Tropsch Synthesis. J. Catal. 1969,15, 190-199. Hanlon, R. T.; Satterfield, C. N. Reactions of Selected l-Olefins and Ethanol Added during the Fischer-Tropsch Synthesis. Energy Fuels 1988,2,196-204. Herzog, K.; Gaube, J. Kinetic Studies for Elucidation of the Promoter Effect of Alkali in Fischer-Tropsch Synthesis. J. Catal. 1989,115, 337-346. Huff, G. A.; Satterfield, C. N. Evidence for Two Chain Growth Probabilities on Iron Catalysts in the Fischer-Tropsch Synthesis. J . Catal. 1984, 85,370-379. Itoh, H.; Hosaka, H.; Ono, T.; Kikuchi, E. Properties and Product
Selectivities of Iron Ultrafine Particles as a’Catalyst for Liquid Phase Hydrogenation of Carbon Monoxide. Appl. Catal. 1988,40, 53-66. Kolbel, H. Kalium als Strucktureller und Energetischer Promotor in Eisenkatalysatoren. In Actes du Deuxieme Congres Znternational de Catalyse; Technip: Paris, 1960; Vol. 11, pp 2075-2099. Kolbel, H.; Giehring, H. Zur Wirkung von Alkali-Promotoren auf Eisenkatalysatoren. Brennstojj-Chem. 1963,44,343-369. Kolbel, H.; Ralek, M. The Fischer-Tropsch Synthesis in Liquid Phase. Catal. Rev. Sci. Eng. 1980,21,225-274. Kolbel, H.; Ackermann, P.; Ruschenburg, E.; Langheim, R.; Engelhardt, F. Beitrag zur Fischer-Tropsch Synthese on Eisenkontak1951,23,153-157. ten. Chem.-Ing.--Tech. Konig, L.; Gaube, J. Fischer-Tropsch-Synthese. Chem.--Zng.-Tech. 1983,55,14-22. Kuo, J. C. W. Two Stage Process for Conversion of Synthesis Gas to High Quality Transportation Fuels. Final Report DOE Contract DE-AC22-83PC 60019; Mobil Research and Development Co.: Paulsboro, NJ, 1985; pp vi-3. Li, C. Effect of Potassium and Copper Promoters on Reduction Behavior of Precipitated Iron Catalysts. Ph.D. Dissertation, Texas A&M University, College Station, 1988. Malessa, R.; Baerns, M. Iron/Manganese Oxide Catalysts for Fischer-Tropsch Synthesis Activity and Selectivity. Ind. Eng. Chem. Res. 1988,27,279-283. Murata, Y.;Sawada, Y.; Takezaki, Y.; Yasuda, M. J. SOC.Chem. Ind. Jpn. (Suppl. Binding) 1942,45,288. Pichler, H. Twenty-five Years of Synthesis of Gasoline by Catalytic Conversion of Carbon monoxide and Hydrogen. In Advances in Catalysis; Frankenburg,W. G., Komarewsky, V. I., Rideal, E. K., Eds.; Academic: New York, 1952; Vol. 4, pp 271-341. Schliebs, B.; Gaube, J. The Influence of the Promoter K2C03in Iron Catalysts on the Carbon Number Distribution of Fischer-Tropsch Products. Ber. Bunsenges Phys. Chem. 1985,89,68-73. Schulz, H.; Gokcebay, H. Fischer-Tropsch CO-Hydrogenation as a Means for Linear Olefins Production. In Catalysis of Organic Reactions; Kosak, J. R., Ed.; Marcel Dekker: New York, 1984; pp 153-169. Schulz, H.; Rosch, S.; Gokcebay, H. Selectivity of the FischerTropsch CO-Hydrogenation. In Coal, Phoenix of ’809, Proc. 64th C. I. C. Coal Symp.; A1 Taweel, A. M., Ed.; Canadian Society for Chemical Engineering: Ottawa, 1982; pp 486-493. Sudheimer, G.; Gaube, J. Fischer-Tropsch-Synthesis: Kinetic Investigation and Process Design for Straight chain l-alkenes. Ger. Chem. Eng. 1985,8,195-202. Wachs, I. E.; Duyer, D. J.; Iglesia, E. Characterization of Fe, Fe-Cu, and Fe-Ag Fischer-Tropsch Catalysts. Appl. Catal. 1984,12, 201-217.
Received for review June 9, 1989 Accepted October 16, 1989
Hydrogenolysis of Dimethyl Succinate over Raney Copper Catalyst: A Correction Daniel J. Thomas, Marc R. Stammbach, Noel W. Cant, Mark S. Wainwright, and David L. Trimm* School of Chemical Engineering and Industrial Chemistry, University of NSW, P.O.Box I , Kensington, NSW 2033, Australia
Previous studies of the hydrogenolysis of dimethyl succinate over Raney copper (Kohler et al., 1987) appeared to show that 1,Cbutanediol could be produced in high yields and with high selectivity. Improved thermodynamic data showed that this reaction was improbable, and the system has been reexamined. I t is found that y-butyrolactone (GBL) and tetrahydrofuran (THF) are the main products of reaction. New experimental data are presented, and the kinetics of hydrogenolysis have been examined. Succinic acid, produced by reaction of traces of water with dimethyl succinate, has been found to inhibit the reaction.
A study by Kohler et al. (1987) has focused on the production of 1,4-butanediol by the hydrogenolysis of dimethyl succinate (DMS) over copper-basedcatalysts. At *To whom all correspondence should be addressed. 0888-5885/90/2629-0204$02.50/0
that time, full thermodynamic data were not available but have been obtained from Simulation Sciences (1987). Heats and free energies of formation for all reactants and products were obtained and used to calculate equilibrium constants for possible reactions. These calculations show 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 205 Table I. Catalyst Characterization composition, wt%
catalyst Raney Cu
A1 1.5
cu 98.5
bulk density, g cm-3 1.12
that 1,4-butanediol is unlikely to be formed in any significant amounts a t pressures less than 5000 kPa. The most favorable reactions thermodynamically are suggested to be CH,OOC(CH3)2COOCH, + 2H2 DMS CH 0 &dL
2
C4H602 + 2CH3OH GBL
+ 2H2 z C4H80+ H 2 0 THF
In light of these findings, reexamination of the hydrogenolysis of DMS has been undertaken.
Experimental Section Catalysts. Most of the experimental work was carried out using a Raney copper catalyst. It was prepared by leaching CuA1, with NaOH, as described by Marsden et al. (1980). The catalyst composition was determined by atomic absorption spectrometry. The pore volumes and mean pore radius were measured with a mercury porosimeter (Micromeritics 9200). The BET surface areas were determined by nitrogen adsorption at 77.5 K. The copper surface areas were determined by static N20 titration a t 363 K, in a similar manner to that described by Dell et al. (1953). The conversion from nitrous oxide uptake to copper area assumed 1 adsorbed oxygen atom for each 2 copper atoms and 1.46 X 1019 copper atoms/m2. The catalyst characteristics are given in Table I. A copper chromite catalyst (Harshaw 0203) and a copper/silica catalyst identical with those used by Kohler et al. (1987) were also tested to confirm that the same product species were produced over different copper catalysts. Apparatus. The catalyst sample (0.2-10.0 g) was placed in a 6-mm4.d. stainless steel U-tube reactor with an internal thermocouple. The reactor was immersed in a well-stirred molten salt bath. The catalyst was reduced in flowing hydrogen, with the temperature being slowly increased to 573 K. This temperature was maintained for approximately 12 h to ensure complete reduction. Following catalyst reduction, the salt bath temperature was reset to the desired reaction temperature (513 K unless otherwise stated) and the reactants were admitted. The liquid feed was dimethyl succinate (Merck-Schuchardt, synthesis grade, 97% minimum) and was fed by a 250-cm3 Isco HPLC syringe pump. The liquid was mixed with the gas feed and vaporized in a stainless steel preheater at 553 K. The gases used were hydrogen (CIG, 99.570, as a reactant) and helium (CIG, 99.99% as a diluent when required). The gas flow rates were regulated by means of Brooks mass flow controllers. The flow rates were controlled to within 2% over a range of 10-2000 mL min-' (101.3 kPa, 273 K). The reactor pressure was maintained at 500 kPa by means of an electrically heated needle valve at 473 K. All lines were heated to approximately 520 K, and the partial pressure of the liquid in the gas was kept less than 0.5 times its vapor pressure, to avoid condensation. The hydrogen pressure used was always in excess of stoichiometric
pore vol, cm3 g-' 0.385
pore radius, nm 22.9
surface area, m2 g-' BET cu 17.5 17.0
Table 11. Heats and Free Energies of Formation at and 298 K AHf, k J name formula mol-' dimethyl CH,OOC(CH2)2COOCH3 -792 succinate -379 y-butyrolactone (CH&COO -427 1,4-butanediol HO(CH2)40H -182 tetrahydrofuran (CH,J40 -201 methanol CHSOH methyl HO(CH,)&OOCH, -610 4-hydroxybutanoate -242 water H2O methane CHI -75
1 atm AGf, kJ mol-' -598'
-285' -278' -78' -162"~~ -438' -229",b -510,b
'Data from Simulation Sciences PROCESS databank. Data from CRC (1981) handbook. Calculated value. The AHf and AGr values for dimethyl succinate were calculated from data for diethyl succinate, diethyl phthalate, and dimethyl phthalate. It was assumed that the difference between A& and AGf for diethyl phthalate and dimethyl phthalate would be very close to that between diethyl succinate and dimethyl succinate, because of the similarity in structure. The A& and AGf values for methyl 4hydroxybutanoate were assumed to be intermediate between those for dimethyl succinate and 1,4-butanediol. and generally set a t 9 times that of dimethyl succinate. The reaction products were sampled with a heated sixport valve and were analyzed by using a gas chromatograph fitted with a thermal conductivity detector and with a 0.6-m X 1/8-in. 0.d. column of Porapak Q (80-100 mesh) maintained at 473 K. The carrier gas was hydrogen with a flow of 20 mL min-'. The elution sequence and retention times (in minutes) were methane (0.30), water (0.48), methanol (0.61), tetrahydrofuran (2.25), y-butyrolactone (9.46), and dimethyl succinate (24.8). The retention times and relative molar response factors for each component were determined using liquid mixtures prepared by accurate weighing. The mass balance for all runs was accurate to within h2.570. Samples of the liquid product were periodically trapped a t 273 K, for confirmatory off-line analysis by GC/MS. The components were separated over an 85-m X 0.5-mm i.d. FFAP-coated capillary column, temperature programmed a t 5 K min-l from 343 to 523 K. The outlet from the column was split and sent to an FID detector and to an AEI MS12 electron impact mass spectrometer. The mass spectrometer ionsource temperature was 473 K, and the accelerating voltage was 8000 V.
Results Heats and free energies of formation for all possible reactants and products were obtained as described in the footnotes to Table I1 and used to calculate equilibrium constants for possible reactions (Figure 1). The thermodynamic data obtained from Simulation Sciences (1987) are based on experimental measurements. Initial experiments showed that four major products were formed by the hydrogenolysis of DMS. These were y-butyrolactone, tetrahydrofuran, methanol, and water. Trace amounts of methane, methyl formate, and C4 aldehydes were also detected. No traces of 1,Cbutanediol or of methyl 4-hydroxybutanoate, as suggested by Kohler et al. (1987), were observed.
206 Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 Table 111. Product Composition as a Function of Residence Time: Reactor Temperature = 513 K, Pressure = 500 kPa, Hydrogen/DMS Ratio = 9:l total flow product composition, mole fraction conversion, rate, mL THF GBL DMS ofDMS.% mass of catalyst, g min-' residence time, s CH4 H2O - MeOH 0.032 0.000 0.010 0.948 1.3 0.21 609 0.05 0.000 0.010 3.5 0.069 0.030 0.899 0.10 0.000 0.001 0.001 1.98 2816 7.3 0.131 0.801 0.002 0.004 0.002 0.060 1.98 1408 0.20 0.711 11.5 0.007 0.005 0.187 0.086 1571 0.003 0.50 5.51 0.714 12.5 0.170 0.001 0.006 0.006 0.104 6.72 1916 0.50 15.2 0.666 0.007 0.007 0.196 0.122 1019 0.002 0.78 5.60 17.1 0.010 0.631 0.009 0.218 0.130 0.002 1.00 958 6.72 0.617 16.5 0.011 0.247 0.111 0.009 0.004 785 5.51 1.00 0.516 25.3 0.272 0.016 0.019 0.174 1.06 0.003 403 3.00 0.469 26.2 0.021 0.015 0.341 0.148 2.01 0.006 140 1.98 0.544 22.8 0.265 0.015 0.012 0.162 0.003 2.35 340 5.60 41.8 0.298 0.448 0.185 0.035 0.020 0.014 56 5.04 1.98 39.7 0.313 0.441 0.035 0.019 0.175 9.90 0.017 29 1.98 0.117 68.8 0.100 0.085 0.500 0.170 19.32 0.028 3:3 4.35
8
7
o
DMS
C
Water mMethanol *Methane
oTHF
08
41 ,
1
06
2
1
3
I/T ( K - ' ) x ~ o ~
Figure 1. Equilibrium constants as a function of temperature. (A) dimethyl succinate 2H2 s y-butyrolactone t Z(methano1); (B) y-butyrolactone + 2H2 s tetrahydrofuran t H20; (C) dimethyl succinate 4H2 s 1,4-butanediol + P(methano1); (D)y-butyrolactone + 2H2 s 1,4-butanediol; (E) 1,4-butanediol s tetrahydrofuran H20; (F) dimethyl succinate t 2H2 s methyl 4-hydroxybutanoate + methanol; (G) methyl 4-hydroxybutanoate zy-butyrolactone + methanol.
+
+
+
The original experiments were repeated, using the new and the old analysis system (Kohler et al., 1987). It was found that the columns used in the original system could not separate y-butyrolactone, tetrahydrofuran, and butanediol. GC/mass spectrometry was used to confirm the presence of y-butyrolactone and tetrahydrofuran and the absence of butanediol. It is clear that the original findings are wrong. The conversion of dimethyl succinate was calculated from the mole fractions of the various carbon-containing species in the product by using
X=
4YGBL 6YDM.S
+ 4 Y T H F + YMeOH + YCHl
+ 4YGBL + 4YTHF + YMeOH + YCH,
(1)
where yi denotes the mole fraction of species i in the product. As a check, the conversion was also calculated based on oxygen-containingspecies in the product by using
X=
2YGBL 4YDMS
+
+ Y T H F + YMeOH + YHzO
2YGBL
+ Y T H F + YMeOH + YHPO
(2)
Figure 2 shows a typical graph of product composition as a function of dimethyl succinate conversion, and Table I11 lists the product compositions for a range of residence times a t 513 K and 500 kPa. The primary products are seen to be y-butyrolactone and methanol, formed by reaction A. Tetrahydrofuran and water are formed as secondary products at elevated conversions.
I
04 06 08 Fractional conversion of DMS Figure 2. Product composition as a function of DMS conversion. Reactor pressure = 500 kPa,temperature = 513 K, hydrogen/DMS ratio = 9.1.
00
02
I
z
I
i t I
l
02
04
Fractional conversion
06 of
08
DMS
Figure 3. Molar selectivity of C i s to tetrahydrofuran. Reactor pressure = 500 kPa,temperature = 513 K, hydrogen/DMS ratio = 9.1.
Confirmation of this suggestion was obtained by feeding y-butyrolactone and hydrogen to the reactor to produce tetrahydrofuran and water. Similar experiments with 1,4-butanediol also gave tetrahydrofuran and water. As predicted from the thermodynamics, reactions A and B are seen to be the major reactions. The C4 selectivity to tetrahydrofuran was defined as sc, =
YTHF YTHF
+ YGBL
(3)
Figure 3 shows the C4 selectivity to THF as a function of conversion, at 513 K and 500 kPa. The curves at higher temperatures show a similar shape.
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 207 025O P u r e DMS feed
0200
Water
Residence time (s)
Figure 4. Fractional conversion of DMS versus residence time. (A) Predicted behavior if reaction is zero order overall. (b) Actual behavior. Reactor pressure = 500 kPa, temperature = 513 K, hydrogen/DMS ratio = 9.1.
16
18
20
22
I/T ( K - ' ) ~ ~ O ~
Figure 5. Apparent activation energy plot. Reactor pressure = 500 kPa, hydrogen/DMS ratio = 91.
Study of the kinetics of these reactions was then initiated. The feed concentration of DMS was kept constant (at a DMS partial pressure of 50 P a ) and hydrogen varied between 200 and 3000 kPa under differential reactor conditions (DMS conversion
