Ind. Eng. Chem. Res. 2007, 46, 2377-2382
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KINETICS, CATALYSIS, AND REACTION ENGINEERING Oxygenate Conversion over Solid Phosphoric Acid Arno de Klerk,* Reinier J. J. Nel, and Renier Schwarzer† Fischer-Tropsch Refinery Catalysis, Sasol Technology Research and DeVelopment, P.O. Box 1, Sasolburg 1947, South Africa
Conversion of olefins by solid phosphoric acid (SPA) catalysis is a key refining technology for the upgrading of high-temperature Fischer-Tropsch (HTFT) products. Oxygenates present in HTFT material suppress olefin conversion over SPA. A class specific study of SPA catalyzed conversion of alcohols, aldehydes, carboxylic acids, esters, ketones, acetals, and ethers is reported. In addition to well-known acid catalyzed organic reactions, high temperature acid-catalyzed reactions were also observed, such as the conversion of ketones to carboxylic acids and olefins. The following were specifically noted: (a) All of the oxygenates suppressed 1-hexene conversion, and the effect appeared to be related to water production; (b) aldehyde conversion to aromatics, including ethanal to benzene, was observed; (c) tributyl phosphoric acid ester was formed from 1-butanol, but 2-propanol was not converted into tri-isopropyl phosphoric acid ester. Introduction The Fischer-Tropsch conversion of synthesis gas (H2 and CO) into liquid products is invariably accompanied by the production of oxygenates. The nature and concentration of the oxygenates depend not only on the Fischer-Tropsch catalyst, but also on the reactor technology and operating conditions.1 Of the main oxygenate classes found in Fischer-Tropsch syncrude, alcohols, aldehydes, and carboxylic acids are primary Fischer-Tropsch products, while ketones and esters are secondary products. Oxygenate conversion is therefore part and parcel of syncrude refining for the production of transportation fuels and chemicals. Reports dealing with the influence of oxygenates present in Fischer-Tropsch syncrude on acid-catalyzed processes focused mainly on olefin conversion, selectivity, and catalyst deactivation.2-6 A proper understanding of the class specific behavior of oxygenates over solid phosphoric acid (SPA) is therefore still lacking. In syncrude refining, technologies using SPA catalysts are important due to the olefinic nature of the low molecular weight Fischer-Tropsch products and the small environmental footprint of SPA catalysts. (Only natural substances are required during manufacturing of SPA catalysts, and spent SPA is converted into ammonium phosphate fertilizer by neutralization with ammonia.) Despite the importance of SPA catalysis in FischerTropsch refining, little is known about the behavior of oxygenates over SPA, because oxygenates are almost completely converted at industrially relevant conditions, resulting in complicated mixtures of primary and secondary products. This hindered identification of the pathways by which the oxygenates reacted, although some pathways could be identified based on side-product formation. We now report the results of a class specific study aimed at identification of the oxygenate conversion pathways over SPA. * To whom correspondence should be addressed. Tel.: +27 16 9602549. Fax: +27 11 522-3517. E-mail:
[email protected]. † Present address: Department of Chemical Engineering, University of Pretoria, South Africa.
As a first step the reaction of different oxygenates was studied in isolation and in the presence of olefins, the most abundant compound class in Fischer-Tropsch syncrude. This is only a first step, because under industrially relevant condition interactions between different oxygenate classes are also possible. The contact time was deliberately limited to ensure only partial conversion of the oxygenates. The study focused on the main oxygenate classes present in syncrude, namely, alcohols, aldehydes, carboxylic acids, esters, and ketones. In addition to these, two minor oxygenate classes were also included in the study, namely, acetals and ethers. Experimental Section Materials. The catalyst used for the test work was a commercial C84/3 SPA obtained from Su¨d-Chemie Sasol, Sasolburg. The catalyst, consisting of phosphoric acid on Eagle Pitcher kieselguhr, was prepared following a procedure described previously.7 The SPA catalyst consists of a layer of phosphoric acid on the kieselguhr that has partially reacted with the phosphoric acid to produce silicon phosphates. The pore structure of the catalyst is defined by the nature of the kieselguhr, which is not completely destroyed by reaction with the phosphoric acid. The catalyst was characterized (Table 1) and used as received. The following substances were used without further purification: propanal (97%, Aldrich), methanol (99.9%, Aldrich), 2-propanol (99%, Saarchem), 1-butanol (99.8%, Aldrich), butanoic acid (99%, Aldrich), 2-pentanone (99%, Aldrich), ethyl ethanoate (99.5%, Promark), 1,1-dimethoxyethane (95%, Aldrich), ethoxyethane (99.5%, Aldrich), and 1-hexene (97%, Aldrich). The reactions were carried out in n-pentane (99.5%, Aldrich) as solvent. Purity of all chemicals was confirmed by gas chromatographic analysis. Equipment and Procedure. The experiments were carried out in small 316 stainless steel reaction vessels, 0.1 m in length and 0.01 m in internal diameter. After charging the reaction vessels with uncrushed 6 mm catalyst extrudates (0.8 g), oxygenates (2.5 g), and n-pentane as solvent (2.5 g), the vessels
10.1021/ie061522b CCC: $37.00 © 2007 American Chemical Society Published on Web 03/23/2007
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Table 1. Characterization of the Su1 d-Chemie Sasol C84/3 SPA Catalyst description
value
free acid (%) total acid (%) ortho:pyro ratio pore volume (cm3 g-1)
25 76 344:156 0.12
Main Metal Impurities Fe (mass %) Al (mass %)
Figure 1. Acid-catalyzed conversion of methanol over SPA at 140 °C.
0.4 0.1
were placed in a constant temperature oven at 140 °C for a predetermined time (20 h). The reaction took place under autogenous pressure (1-1.5 MPa). The reaction was quenched by cooling the reaction vessels in a water bath at 5 °C, before being analyzed. The inertness of the solvent was verified by loading some reaction vessels with only n-pentane and SPA catalyst. The thermal stability of the oxygenates in the absence of SPA was verified by loading the reaction vessels with mixtures of the various oxygenates in n-pentane and omitting the catalyst. Additional experiments with oxygenates in the presence of olefins were performed with 1:1 mixtures of the respective oxygenates (1.3 g) and 1-hexene (1.3 g) as reagents. All experiments were carried out in duplicate. Analyses. The feed materials and products were subjected to quantitative analysis using an Agilent 6890N gas chromatograph with flame ionization detector (GC-FID). The products were separated on a 50 m HP-Pona methyl siloxane column with 200 µm internal diameter and 0.5 µm film thickness. Identity of compounds was established using a similarly configured Agilent 6890N with Agilent 5973 mass selective detector (GC-MS). The following temperature program was used: 40 °C for 5 min, then ramping at 8 °C/min to 300 °C, and then keeping it at 300 °C for 5 min. The carrier gas was hydrogen, and a 100:1 split ratio was used. Small quantities of compounds showing a poor FID response8 could be readily detected by the GC-MS. The GC-MS was used in the 10-500 atomic mass unit range to allow identification of low molecular weight products. It should be noted that conversion and selectivity values reported are only semiquantitative. Oxygenates have FID response factors that are less than unity, and quantitative analysis would require calibration of the GC-FID. Furthermore, a different method of sample transfer than that used in the present investigation would have to be employed to ensure that volatile components are not lost. Results and Discussion Blank Experiments. The inertness of the reaction vessels and the thermal stability of the oxygenates were established. Thus, the solvent, 2-propanol (isopropanol), 1-butanol, butanoic acid (butyric acid), 2-pentanone, ethoxyethane (diethyl ether), and 1-hexene were recovered unreacted after 20 h at 140 °C. Only trace amounts of products were formed in the case of propanal (propionaldehyde), ethyl ethanoate, and 1,1-dimethoxyethane. Propanal formed some aldol condensation products. Hydrolysis of the ethyl ethanoate gave ethanol and ethanoic acid (acetic acid), and hydrolysis of the 1,1-dimethoxyethane resulted in methanol, methoxymethane (dimethyl ether), and ethanal (acetaldehyde) being formed. This is possibly due to trace amounts of water present in the reagents that were not dried before use. Alcohol Conversion. Methanol was dehydrated to form methoxymethane (Figure 1), which has a boiling point of -25 °C, and even after cooling of the reaction vessel, it was still under considerable pressure. Decomposition of this ether to
Figure 2. Acid-catalyzed conversion of 2-propanol over SPA at 140 °C.
olefins, like in the ZSM-5 zeolite catalyzed methanol-to-olefin (MTO) process,9-11 was not observed. This is ascribed to the low operating temperature. In a concurrent process methanol was dehydrated on the catalyst to produce the trimethyl phosphoric acid ester. The reaction with methanol caused the catalyst to totally disintegrate. It is not clear whether this is due to the water produced in the above reaction or whether methanol itself is harmful to catalyst integrity. It is known from commercial operation at the Sasol Synfuels refineries in Secunda that the SPA catalyst can be severely damaged when water is inadvertently introduced. Dehydration of 2-propanol over SPA (Figure 2) occurred with high conversion (>75%) and resulted in the formation of mostly propene. Less than 5% 2-(1-methylethoxy)-propane (diisopropylether) and oligomerization products of propene were produced. A small amount of 2-propoxypropane was also found. The reaction temperature was higher than the decomposition temperature of the tri-isopropyl phosphoric acid ester, which is reportedly around 125 °C12,13 and explains why propene and oligomerization products of propene were found, but no triisopropyl phosphoric acid ester. The catalyst also disintegrated during reaction with 2-propanol. The conversion of 1-butanol (30%) was less than that of 2-propanol and resulted in a more complex product spectrum (Figure 3). In addition to butoxybutane and 2-butoxybutane (90%) over SPA, yielding mainly aldol condensation products (Figure 4), with the main products being 2-methyl2-pentenal (∼40% selectivity) and 1,3,5-trimethylbenzene (∼40% selectivity). Although the GC-MS cannot distinguish between all the possible C3-alkylbenzene isomers, the sample was spiked with the different ethyltoluene and trimethylbenzene isomers to confirm that it is indeed 1,3,5-trimethylbenzene (mesitylene) that was the main aromatic product. The mechanism has been previously discussed for propanone (acetone) condensation,19-22 but this reaction has not been reported for propanal. Small quantities of other condensation products such as dimethyltetrahydrofuran and propyl propanoate were also found in the product. The propyl propanoate probably formed through a Tishchenko-type mechanism. No acids were formed during the reaction. Carboxylic Acid Conversion. Butyric acid was essentially stable in the presence of SPA. At trace level some propene and 4-heptanone could be detected, which may be indicative of acidcatalyzed decarbonylation (Figure 5).23 Decomposition of the carboxylic acid was not expected, despite the presence of some
Figure 6. Acid-catalyzed conversion of ethyl ethanoate over SPA at 140 °C.
metal impurities in the catalyst (Table 1), because decomposition via a metal carboxylate intermediate24 requires higher temperatures than were used in the present study. Ester Conversion. Although the reaction mixture was dry, water was formed by the SPA catalyst to maintain the equilibrium between the phosphoric acid species on the catalyst and the water partial pressure in the reaction vessel.25,26 This resulted in hydrolysis of ethyl ethanoate (60% conversion) to ethanol and ethanoic acid as primary products, which subsequently reacted further to produce secondary products that included ethoxyethane, ethene, and triethyl phosphoric acid ester (Figure 6). No butenes or heavier oligomerization products were detected. Ketone Conversion. The main reaction of 2-pentanone (40% conversion) involved aldol condensation,27 although decomposition to yield a carboxylic acid (∼5% selectivity) and an olefin was significant too (Figure 7). Both ethanoic acid and butanoic acid were found in the product, as well as hexenes and octenes, as would be expected from the mechanism that involves the high-temperature hydrolytic cleavage of the R,β-unsaturated ketone (aldol condensation dimer).28,29 Acid catalyzed aldol condensation reportedly takes place preferentially via the methylene group,28 which implies that butanoic acid and hexene should be the preferred hydrolytic cleavage product. This was not found, and taking the different GC-FID response factors into account,8 the ratio of ethanoic acid to butanoic acid was 1:1.1-1.4, implying that SPA catalyzed aldol condensation by both the methylene and the methyl pathways. The hydrolytic cleavage of R,β-unsaturated carbonyls was not observed with aldehydes. Three isomeric C9-alkylbenzene species were formed during the ketone condensation reaction and are likely to be tripropylbenzene and isomers like methyl-ethyl-dipropylbenzenes. The formation of aromatics by acid-catalyzed selfcondensation of aldol products from ketones is a well-known reaction.30 Ketone rearrangement over SPA has been previously reported,31,32 but the formation of 3-pentanone could not be confirmed. Acetal Conversion. The 1,1-dimethoxyethane decomposed (>95%) to methanol and ethanal as primary products, which reacted further to produce secondary products (Figure 8). Methoxymethane, trimethyl phosphoric acid ester, and aldol condensation products from ethanal were found. Of special significance is the formation of benzene and methylcyclopentenone (most likely 4-methyl-2-cyclopentenone) as condensation products, because these products give some indication of the mechanism of aldehyde condensation over SPA. The formation of benzene from ethanal has previously been found in reaction over TiO2 and has tentatively been ascribed to the self-condensation of the hexa-2,4-dienal.33 A small amount of methyl ethanoate was detected in the product. This could have
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Figure 7. Main products from acid-catalyzed conversion of 2-pentanone over SPA at 140 °C.
Figure 8. Main products from acid-catalyzed conversion of 1,1-dimethoxyethane over SPA at 140 °C.
Figure 9. Acid-catalyzed conversion of ethoxyethane over SPA at 140 °C.
formed by hydrolysis of the acetal to produce the hemiacetal, followed by hydrogen transfer to yield the ester.34 Ether Conversion. The products from ethoxyethane conversion (Figure 9) showed the expected products from acidcatalyzed decomposition to produce the corresponding olefin (ethene) and alcohol (ethanol). Although SPA is commercially used for ethene hydration to ethanol, the equilibrium between dehydration and hydration favors dehydration.35,36 Ethene reacts with the catalyst to form a stable triethyl phosphoric acid ester, which is reportedly stable to about 200 °C.12,37 This shifts the
equilibrium even further toward olefin formation. The stability of the triethyl phosphoric acid ester, which was found in the product, also explained the virtual absence of oligomers, with butenes being present in trace quantities only. Influence of Oxygenates on Olefin Conversion. The acidcatalyzed conversion of 1-hexene yields 2- and 3-hexenes by double bond isomerization, branched hexene isomers by skeletal isomerization, and other olefins by oligomerization and cracking.38 The conversion 1-hexene over SPA is nevertheless slow because of the labile nature of the hexyl phosphoric acid ester and short-lived existence of the polarized intermediate required for reaction.39 The choice of 1-hexene as olefin was therefore deliberate, because it is sensitive to changes in the SPA catalyst and catalytic environment. The SPA catalyzed conversion of 1-hexene in the absence and presence of various oxygenates was determined on the basis of the average observed conversion over a 20-h period (Table 2). These results should be compared on a relative basis only, because the experiments were all done in the same way, but not in such a way that the absence of transport limitations could be guaranteed. Furthermore, comparison is subject to the assumption that transport limitations were similar in all experiments, because they were performed in the same way. It
Table 2. Olefin Distribution and Reaction Rate of 1-Hexene Conversion over SPA at 140 °C in the Presence of Various Oxygenatesa oxygenate added none 1-hexene trans-2-hexene cis-2-hexene 3-hexenes branched hexenes C7 and heavier olefins double bond isomerization skeletal isomerization dimerization
15 16.7 37.7 16.4 6.2 8 0.119 0.010 0.013
2-propanol 98.3 0.4 0.3 0.1 0.9 0 0.001 0.002 0
1-butanol 85.1 6.5 5.8 0.7 1.5 0.4 0.022 0.002 0.001
propanal
butanoic acid
Olefin Distribution 92.6 29.9 3.3 32.6 2 16.1 1.2 13.3 0.9 4.5 0 3.6
ethyl ethanoate 25.5 21.5 13.9 34.6b 0 0
Reaction Rate (g gcat-1 h-1) 0.011 0.104 0.117 0.002 0.007 0 0 0.006 0
2-pentanone 19.2 37.4 18.3 15.6 3.4 6.1 0.120 0.006 0.010
1,1-dimethoxyethane 100 0 0 0 0 0 0 0 0
ethoxyethane 60 18.7 14.1 5.8 1.4 0 0.065 0.002 0
a The observed reaction rates were calculated on the same concentration basis as 1-hexene without oxygenate addition and should only be used for relative comparison. b High value due to overlap of ethyl ethanoate and 3-hexenes during GC-FID analysis.
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nevertheless gives some indication of the inhibitory effect of the various oxygenates. The 1-hexene, in the absence of oxygenates, reacted as expected, with skeletal isomerization to produce branched hexenes being a prerequisite for oligomerization.39 The cisselective double bond isomerization behavior was similarly expected15 and is typical of SPA catalysis. No olefins heavier than C12 were formed, because the formation of heavier olefins is mechanistically limited.4 Of the oxygenates tested, 2-pentanone and butanoic acid had the least effect on 1-hexene conversion (Table 2). The 2-pentanone reacted in the same way as in the absence of 1-hexene, forming hexenes, octenes, ethanoic acid, butanoic acid, aldol condensation products, and C9-alkylbenzenes, while the butanoic acid did not react. Although 2-pentanone and butanoic acid suppressed skeletal isomerization and dimerization somewhat, the double bond isomerization rate was not really affected, and only the cis-selectivity of SPA was affected. It is speculated that the carboxylic acids contributed to cis-trans double bond isomerization, causing the 2-hexene isomers to reach thermodynamic equilibrium (cis-2-hexene/trans-2-hexene ) 0.5). The other oxygenates, namely, 2-propanol, 1-butanol, propanal, ethyl ethanoate, 1,1-dimethoxyethane, and ethoxyethane, significantly suppressed skeletal isomerization of 1-hexene and, with the exception of 1-butanol, completely suppressed dimerization of 1-hexene (Table 2). Propanal, ethyl ethanoate, and ethoxyethane formed products in the presence of 1-hexene similar to those they formed when reacting on their own. The 1-hexene mostly acted as a diluent, and selectivity to products from consecutive reactions was lower; for example, in the presence of 1-hexene the selectivity of propanal conversion to 2-methyl-2-pentanal was 30%, but the selectivity to 1,3,5trimethylbenzene was only 5%. However, in some instances the 1-hexene participated in the reactions, with ethyl ethanoate forming ethoxyhexanes and hexyl ethanoate, while ethoxyethane formed ethoxyhexanes. The oxygenates capable of producing a significant quantity of water influenced SPA the most. Conversion of 1-hexene was completely suppressed by the decomposition of 1,1-dimethoxyethane, which yielded methanol, methoxymethane, and ethanal, but neither heavy aldol condensation products, nor benzene was found. It is not clear why the latter two reactions only took place in the absence of 1-hexene. The alcohols also produced water, and because it is not clear to what extent the propylene and butene produced during dehydration were responsible for producing branched C6 isomers and C12 olefins, these products could erroneously have been attributed to 1-hexene conversion. In general the 1-hexene did not have a significant effect on oxygenate conversion. This was not surprising, because the oxygenates are more polar than the 1-hexene and were preferentially adsorbed on the polar catalyst surface. The reaction networks were surprisingly complex, despite dealing with only binary mixtures of reagents. This complicated interpretation of the results and calls for a proper kinetic study of each system to resolve the sequence of events leading to the suppression of olefin conversion over SPA. Subsequent work from our laboratories will deal with this topic. Conclusions Class specific oxygenate conversion over a SPA catalyst were investigated for oxygenates produced during high-temperature Fischer-Tropsch synthesis, namely, alcohols, aldehydes, carboxylic acids, esters, ketones, acetals, and ethers. In addition to well-known acid catalyzed organic reactions, some reactions
previously reported for high temperature solid acid-catalyzed processes have also been observed, such as the conversion of ketones to carboxylic acids and olefins. The following were specifically noted: (a) All of the oxygenates studied suppressed the conversion of 1-hexene over SPA. The oxygenates capable of producing a significant quantity of water suppressed 1-hexene conversion the most. Unfortunately the reaction network was too complex even for the binary mixtures studied to resolve the mechanism of suppression without a kinetic study. (b) The acid-catalyzed conversion of ketones to aromatics has been reported previously, but very little has been reported on the analogous reaction for aldehydes. The present study reports the formation of 1,3,5-trimethylbenzene (mesitylene) from propanal (propionaldehyde), as well as benzene from ethanal (acetaldehyde). The latter reaction was observed only in the absence of 1-hexene. (c) Methyl and ethyl phosphoric acid esters were detected in products where methanol, ethanol, or ethene had been present. It was surprising to find the butyl phosphoric acid ester during reaction with 1-butanol, especially because the propyl phosphoric acid ester was not found during reaction with 2-propanol and neither was expected based on previous literature. The observed results can be explained if there is a significant difference in the stability of the phosphoric acid ester bonded to the R-carbon versus β-carbon of the alkyl group, which indicates that the ester is primarily formed from the alcohol, but further work is required to confirm this hypothesis. Acknowledgment All work was done at Sasol Technology Research and Development, and permission to publish the results is appreciated. Literature Cited (1) Steynberg, A. P., Dry, M. E., Eds. Fischer-Tropsch technology; Elsevier: Amsterdam, 2004. (2) de Klerk, A. Deactivation behaviour of Zn/ZSM-5 with a FischerTropsch derived feedstock. In Catalysis in application; Jackson, S. D., Hargreaves, J. S. J., Lennon, D., Eds.; Royal Society of Chemistry: Cambridge, 2003; p 24. (3) Smook, D.; de Klerk, A. Inhibition of etherification and isomerization by oxygenates. Ind. Eng. Chem. Res. 2006, 45, 467. (4) de Klerk, A. Distillate production by oligomerization of FischerTropsch olefins over Solid Phosphoric Acid. Energy Fuels 2006, 20, 439. (5) Cowley, M. Skeletal isomerisation of Fischer-Tropsch derived pentenes: the effect of oxygenates. Energy Fuels 2006, 20, 1771. (6) de Klerk, A. Effect of oxygenates on the oligomerization of FischerTropsch olefins over amorphous silica-alumina. Energy Fuels, published online February 2, 2007, http://dx.doi.org/10.1021/ef060485y. (7) Coetzee, J. H.; Mashapa, T. N.; Prinsloo, N. M.; Rademan, J. D. An improved solid phosphoric acid catalyst for alkene oligomerisation in a Fischer-Tropsch refinery. Appl. Catal. A 2006, 308, 204. (8) Dietz, W. A. Response factors for gas chromatographic analyses. J. Gas Chromatogr. 1967, 5, 68. (9) Chang, C. D. Hydrocarbons from methanol. Catal. ReV.-Sci. Eng. 1983, 25, 1. (10) Haag, W. O.; Lago, R. M.; Rodewald, P. G. Aromatics, light olefins and gasoline from methanol: mechanistic pathways with ZSM-5 zeolite catalyst. J. Mol. Catal. 1982, 17, 161. (11) Keil, F. J. Methanol-to-hydrocarbons: process technology. Microporous Mesoporous Mater. 1999, 29, 49. (12) Ipatieff, V. N. Catalytic polymerization of gaseous olefins by liquid phosphoric acid. I. Propylene. Ind. Eng. Chem. 1935, 27, 1067. (13) Krawietz, T. R.; Lin, P.; Lotterhos, K. E.; Torres, P. D.; Barich, D. H.; Clearfield, A.; Haw, J. F. Solid phosphoric acid catalyst: A multinuclear NMR and theoretical study. J. Am. Chem. Soc. 1998, 120, 8502. (14) Choudhary, V. R. Catalytic isomerization of n-butene to isobutene. Chem. Ind. DeV. 1974, 8, 32.
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(15) de Klerk, A. Isomerization of 1-butene to isobutene at low temperature. Ind. Eng. Chem. Res. 2004, 43, 6325. (16) Ipatieff, V. N.; Corson, B. B. Catalytic polymerization of gaseous olefins by liquid phosphoric acid. II. Butylenes. Ind. Eng. Chem. 1935, 27, 1069. (17) Ipatieff, V. N.; Schaad, R. E. Mixed polymerization of butenes by solid phosphoric acid catalyst. Ind. Eng. Chem. 1938, 30, 596. (18) de Klerk, A.; Engelbrecht, D. J.; Boikanyo, H. Oligomerization of Fischer-Tropsch olefins: Effect of feed and operating conditions on hydrogenated motor-gasoline quality. Ind. Eng. Chem. Res. 2004, 43, 7449. (19) Neogi, P. Orthophosphoric acid as a dehydrating catalytic agent. Part 1. The condensation of acetone in presence of phosphoric acid. Chem. Soc. ReV. 1911, 99, 1249. (20) Reichle, W. T. Pulse microreactor examination of the vapor-phase aldol condensation of acetone. J. Catal. 1980, 63, 295. (21) Salvapati, G. S.; Ramanamurthy, K. V.; Janardanarao, M. Selective catalytic self-condensation of acetone. J. Mol. Catal. 1989, 54, 9. (22) Xu, T.; Munson, E. J.; Haw, J. F. Towards a systematic chemistry of organic reactions in zeolites: In situ NMR studies of ketones. J. Am. Chem. Soc. 1994, 116, 1962. (23) Ropp, G. A. Isotopic evidence for the mechanisms of decarbonylation of three carboxylic acids in sulfuric acid. J. Am. Chem. Soc. 1958, 80, 6691. (24) Rajadurai, S. Pathways for carboxylic acid decomposition on transition metal oxides. Catal. ReV. Sci. Eng. 1994, 36, 385. (25) Brown, E. H.; Whitt, C. D. Vapor pressure of phosphoric acids. Ind. Eng. Chem. 1952, 44, 615. (26) de Klerk, A.; Leckel, D. O.; Prinsloo, N. M. Butene oligomerisation by phosphoric acid catalysis: Separating the effects of temperature and catalyst hydration on product selectivity. Ind. Eng. Chem. Res. 2006, 45, 6127. (27) Guthrie, J. P. Equilibrium constants for a series of simple aldol condensations, and linear free energy relations with other carbonyl addition reactions. Can. J. Chem. 1978, 56, 962. (28) McAllister, S. H.; Bailey, W. A., Jr.; Bouton, C. M. The catalyzed cleavage of diacetone alcohol and other ketols and unsaturated ketones. J. Am. Chem. Soc. 1940, 62, 3210.
(29) Demorest, M.; Mooberry, D.; Danforth, J. D. Decomposition of ketones and fatty acids by silica-alumina composites. Ind. Eng. Chem. 1951, 43, 2569. (30) Gutsche, C. D. The Chemistry of Carbonyl Compounds; Prentice Hall: Englewood Cliffs, NJ, 1967. (31) Corkern, W. H.; Fry, A. Reactions of ketones and related compounds with solid supported phosphoric acid catalyst. I. The scope and mechanism of ketone rearrangements. J. Am. Chem. Soc. 1967, 89, 5888. (32) Fry, A.; Corkern, W. H. Reactions of ketones and related compounds with solid supported phosphoric acid catalyst. II. A carbon-14 tracer study of the mechanism of the rearrangement of 3-pentanone and 2-pentanone. J. Am. Chem. Soc. 1967, 89, 5894. (33) Luo, S.; Falconer, J. L. Acetone and acetaldehyde oligomerization on TiO2 surfaces. J. Catal. 1999, 185, 393. (34) Inui, K.; Kurabayashi, T.; Sato, S.; Ichikawa, N. Effective formation of ethyl acetate from ethanol over Cu-Zn-Zr-Al-O catalyst. J. Mol. Catal. A 2004, 216, 147. (35) Maki, Y.; Sato, K.; Isobe, A.; Iwasa, N.; Fujita, S.; Shimokawabe, M.; Takezawa, N. Structures of H3PO4/SiO2 catalysts and catalytic performance in the hydration of ethene. Appl. Catal. A 1998, 170, 269. (36) Fougret, C. M.; Atkins, M. P.; Ho¨lderich, W. F. Influence of the carrier on the catalytic performance of impregnated phosphoric acid in the hydration of ethylene. Appl. Catal. A 1999, 181, 145. (37) Ipatieff, V. N.; Pines, H. Polymerization of ethylene under high pressures in the presence of phosphoric acid. Ind. Eng. Chem. 1935, 27, 1364. (38) de Klerk, A. Oligomerization of 1-hexene and 1-octene over solid acid catalysts. Ind. Eng. Chem. Res. 2005, 44, 3887. (39) de Klerk, A. Reactivity differences of octenes over solid phosphoric acid. Ind. Eng. Chem. Res. 2006, 45, 578.
ReceiVed for reView November 28, 2006 ReVised manuscript receiVed January 19, 2007 Accepted February 2, 2007 IE061522B
