Energy Fuels 2010, 24, 2733–2736 Published on Web 03/22/2010
: DOI:10.1021/ef9015735
Glycerin Derivatives as Fuel Additives: The Addition of Glycerol/Acetone Ketal (Solketal) in Gasolines Claudio J. A. Mota,*,†,‡ Carolina X. A. da Silva,†,‡ Nilton Rosenbach, Jr.,†,‡ Jair Costa,† and Flavia da Silva† †
Instituto de Quı´mica and ‡Instituto Nacional de Ci^ encia e Tecnologia (INCT) de Energia e Ambiente, Universidade Federal do Rio de Janeiro (UFRJ), Cidade Universit aria CT Bloco A, 21941-909, Rio de Janeiro, Brazil Received December 21, 2009. Revised Manuscript Received March 8, 2010
Glycerin was reacted with acetone and formaldehyde to produce the correspondent ketal (solketal) and acetal, respectively. These compounds were blended in 1, 3, and 5 vol % with gasoline containing 0 and 25 vol % ethanol. The addition of the glycerin derivatives did not significantly change the distillation curve of the gasolines. The solketal reduced the gum formation in both gasolines (with and without ethanol) and increased the octane number up to 2.5 points in the gasoline without ethanol. The glycerin/formaldehyde acetal was only soluble in the gasoline containing ethanol and led to an increase in gum formation and a slight reduction (up to -0.75 points) in the octane number. These results indicate that solketal has a potential for blending with regular gasoline and may be an alternative for the glycerin produced from biodiesel.
industrial process in the coming years. Dehydration10 to acrolein is also a potential application, because acrolein is used in the synthesis11,12 of acrylic acid. The production of glycerol ethers,13-15 esters,16 and ketals and acetals17 is also of great interest, because some of these compounds have potential as fuel additives. The fuel degradation promotes the formation of gum, which causes deposits in filters and distribution lines.18 The tert-butylation of glycerol affords the tert-butyl-glyceryl ethers, which have been blended19 with biodiesel to improve its properties. Triacetin, the glycerol triacetate, improves the cold-flow properties of biodiesel.5 However, all these applications are related to the replacement of some other chemical. For instance, the use of glycerol in the production of acrolein and propylene glycol would replace propene as the raw material for the manufacture of these chemicals. Thus, these actions are not fast, and even if there is a technology available, only the new plants might be considered for using glycerol as the raw material, because of investment and capital costs. Hence, the rapid and large-scale use of glycerol will only be possible if there is a window of opportunity for the replacement of a chemical.
Introduction Biodiesel is becoming an important biofuel worldwide.1-3 It is normally produced from the transesterification of vegetable oil or animal fat with methanol, under base catalysis conditions.4 The reaction affords a mixture of fatty acid methyl esters, the biodiesel themselves, and glycerol or glycerin as a byproduct in approximately 10 wt % mass balance.5 The world forecast of glycerol production from biodiesel points to an increasing supply, with net global production around 1.2 million tons by 2012.6 In Brazil, biodiesel is presently blended in 5 vol % with petrodiesel, yielding approximately 200 000 tons of glycerin per year. The traditional glycerin market is related to the soap, cosmetic, food, and personal-care sectors, which cannot drain these huge amounts of glycerin produced by the biodiesel industry. Glycerol is a good platform for other chemicals, especially oxygenated compounds, and several reviews on glycerol transformation have appeared in the literature in the past few years.6-8 Hydrogenolysis of glycerol to propylene glycol is widely studied9 and might become an important *To whom correspondence should be addressed. E-mail: cmota@ iq.ufrj.br. (1) Hill, J.; Nelson, E.; Tilman, D.; Polasky, S.; Tiffany, D. Proc. Natl. Acad. Sci. U.S.A. 2006, 103 (30), 11206–11210. (2) Ma, F. R.; Hanna, M. A. Bioresour. Technol. 1999, 70 (1), 1–15. (3) Pinto, A. C.; Guarieiro, L. L. N.; Rezende, M. J. C.; Ribeiro, N. M.; Torres, E. A.; Lopes, W. A.; Pereira, P. A. D.; de Andrade, J. B. J. Braz. Chem. Soc. 2005, 16 (6B), 1313–1330. (4) Meher, L. C.; Sagar, D. V.; Naik, S. N. Renewable Sustainable Energy Rev. 2006, 10 (3), 248–268. (5) Garcia, E.; Laca, M.; Perez, E.; Garrido, A.; Peinado, J. Energy Fuels 2008, 22 (6), 4274–4280. (6) Zhou, C. H. C.; Beltramini, J. N.; Fan, Y. X.; Lu, G. Q. M. Chem. Soc. Rev. 2008, 37 (3), 527–549. (7) Behr, A.; Eilting, J.; Irawadi, K.; Leschinski, J.; Lindner, F. Green Chem. 2008, 10 (1), 13–30. (8) Pagliaro, M.; Ciriminna, R.; Kimura, H.; Rossi, M.; Della Pina, C. Angew. Chem., Int. Ed. 2007, 46 (24), 4434–4440. (9) Dasari, M.; Kiatsimkul, P. P.; Sutterlin, W. R.; Suppes, G. J. Appl. Catal., A 2005, 281, 225–231. (10) Ramayya, S.; Brittain, A.; DeAlmeida, C.; Mok, W.; Antal, M. J., Jr. Fuel 1987, 66 (10), 1364–1371. r 2010 American Chemical Society
(11) Giebeler, L.; Kampe, P.; Wirth, A.; Adams, A. H.; Kunert, J.; Fuess, H.; Vogel, H. J. Mol. Catal. A: Chem. 2006, 259 (1-2), 309–318. (12) Kampe, P.; Giebeler, L.; Samuelis, D.; Kunert, J.; Drochner, A.; Haass, F.; Adams, A. H.; Ott, J.; Endres, S.; Schimanke, G.; Buhrmester, T.; Martin, M.; Fuess, H.; Vogel, H. Phys. Chem. Chem. Phys. 2007, 9 (27), 3577–3589. (13) Gu, Y.; Azzouzi, A.; Pouilloux, Y.; Jerome, F.; Barrault, J. Green Chem. 2008, 10 (2), 164–167. (14) Karinen, R. S.; Krause, A. O. I. Appl. Catal., A 2006, 306, 128– 133. (15) Klepacova, K.; Mravec, D.; Bajus, M. Appl. Catal., A 2005, 294 (2), 141–147. (16) Gonc-alves, V. L. C.; Pinto, B. P.; Silva, J. C.; Mota, C. J. A. Catal. Today 2008, 133-135, 673–677. (17) Deutsch, J.; Martin, A.; Lieske, H. J. Catal. 2007, 245 (2), 428– 435. (18) Vale, M. C.; Lopes, G. S.; Gouveia, S. T. Fuel 2009, 88, 1955– 1960. (19) Wessendorf, R. Erdoel Kohle, Erdgas, Petrochem. 1995, 48 (3), 138–143.
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: DOI:10.1021/ef9015735
Mota et al. Table 1. Properties of Solketal (GAK) and Glycerol/Formaldehyde Acetals (GFA)
Scheme 1. Reaction of Glycerol with Acetone under Heterogeneous Acid Catalysis
property
method
GAK
GFA
densitya (g/mL) pour point (°C) acidity (mg of KOH/g) flash point (°C) kinematic viscosityb (mm2/s)
ASTM D4052 ASTM D97 ASTM D664 ASTM D93 ASTM D445
1.066 e60 0.19 84.5 5.39
1.216 e60 0.48 96.0 5.14
a
Scheme 2. Reaction of Glycerol with Formaldehyde Solution under Heterogeneous Acid Catalysis
Taken at 20 °C. b Taken at 40 °C.
Gasoline A (without ethanol) and gasoline C (with 25 vol % ethanol) were obtained from RepsolYPF. In Brazil, the regular gasoline contains 25 vol % anhydrous ethanol, and it is denoted gasoline C. The ethanol addition takes place during the distribution by mixing with gasoline A, which normally comes from the catalytic cracking of vacuum gas oil, but may contain fractions of naphtha obtained from oil atmospheric distillation. The glycerol/acetone ketal (solketal), denoted in this work as GAK, and glycerol/formaldehyde acetals, denoted in this work as GFA, were mixed in 1, 3, and 5 vol % with both gasolines. The blends were subjected to analysis of distillation curve, density (ASTM D4052), pour point (ASTM D97), gum formation (ASTM D381), and corrosiveness to copper (ASTM D130). The results were compared to the unblended gasolines. The density (ASTM D4052), pour point (ASTM D97), acidity (ASTM D664), flash point (ASTM D93), and kinematic viscosity (ASTM D445) of the solketal and glycerol/formaldehyde acetals were also determined. The blends of gasoline with the glycerol derivatives were also tested in a stationary CFR motor to measure the octane number, the research octane number (RON) according to ASTM D2700 and the motor octane number (MON) according to ASTM D2699.
The reformulated gasoline was introduced in the U.S. to improve the air quality in large urban areas. One of the mandatory acts was the inclusion of oxygenated compounds in gasoline. For many years, methyl tert-butyl ether (MTBE) was the main oxygenated compound added to gasoline worldwide.20 Nevertheless, because of environmental and health concerns,21-24 it has been phasing out since the beginning of this century, opening a window of opportunity for substitutes, especially from renewable sources. This gap has been occupied by ethanol, produced from carbohydrate fermentation, but there are concerns if this alcohol can be sustainably and economically produced, especially from corn,25 while its production from cellulosic material is not technologically developed.26 Glycerol is a triol with about 52% of its weight in oxygen atoms, being a good platform for the development of oxygenated molecules for addition in gasoline. Glycerol itself is a polar molecule, not soluble in hydrocarbons, and has a high boiling point. Thus, it is not suitable for blending with gasoline. On the other hand, glycerol ketals and acetals, especially those formed in reactions with acetone (Scheme 1) and formaldehyde (Scheme 2), might be good candidates. We have recently prepared them through a green procedure,27 without using solvents to distill off the water formed. Now, we report the use of glycerol/acetone ketal (solketal) and glycerol/ formaldehyde acetal in mixtures with gasoline.
Results and Discussion In the concentration used in this study, the glycerol/formaldehyde acetals were insoluble in gasoline A, without ethanol, but completely soluble in gasoline C, containing 25 vol % ethanol. In contrast, solketal was soluble in both gasolines, and the results reported refer to blends of solketal with gasolines A and C but only gasoline C in the case of glycerol/formaldehyde. Table 1 shows the results of the analysis of the glycerol derivatives. The density of the glycerol/formaldehyde acetals is significantly higher than the density of solketal. Its acidity, expressed in milligrams of KOH per gram of reagent, is also higher than solketal, but both values are low. The acidity may be associated with the free hydroxyl group. Both glycerol derivatives present a low pour point, below 60 °C. Their kinematic viscosity is similar, and solketal shows a slightly lower flash point than glycerol/formaldehyde acetals. In comparison to MTBE and ethanol, the density and flash point of the glycerin derivatives are significantly higher. MTBE has a density of 0.74 g/mL and a flash point of -10 °C, whereas ethanol has a density of 0.79 g/mL and a flash point of 13 °C. The higher density of the glycerin derivatives reflects their higher oxygen content relative to ethanol and MTBE. The flash point is related to their volatility, and it might be anticipated that the glycerin derivatives would not have a significant effect on the gasoline volatility as ethanol.28 Figures 1-3 show the distillation curves for the gasoline and glycerol derivative blends. Within the amount added in this study, there is no significant difference between the
Experimental Section The reactions of glycerol with acetone and formaldehyde were reported elsewhere.27 The products were distilled from the reaction medium, and their purity was over 98 wt %, as checked by gas chromatography. The reaction with formaldehyde produces two acetals (Scheme 2), which were not separated by distillation and used as a mixture containing approximately 80% of the sixmembered ring acetal. (20) Nadim, F.; Zack, P.; Hoag, G. E.; Liu, S. L. Energy Policy 2001, 29 (1), 1–5. (21) Ahmed, F. E. Toxicol. Lett. 2001, 123 (2-3), 89–113. (22) Mehlman, M. A. In Carcinogenesis Bioassays and Protecting Public Health;Commemorating the Lifework of Cesare Maltoni and Colleagues; Mehlman, M. A., Bingham, E., Landrigan, P. J., Soffritti, M., Belpoggi, F., Melnick, R. L., Eds.; New York Academy of Sciences: New York, 2002; Vol. 982, pp 149-159. (23) Rosell, M.; Lacorte, S.; Barcelo, D. TrAC, Trends Anal. Chem. 2006, 25 (10), 1016–1029. (24) Rudo, K. M. Toxicol. Ind. Health 1995, 11 (2), 167–173. (25) Szklo, A.; Schaeffer, R.; Delgado, F. Energy Policy 2007, 35 (11), 5411–5421. (26) Hamelinck, C. N.; Faaij, A. P. C. Energy Policy 2006, 34 (17), 3268–3283. (27) da Silva, C. X. A.; Goncalves, V. L. C.; Mota, C. J. A. Green Chem. 2009, 11 (1), 38–41.
(28) Muzikova, Z.; Pospisil, M.; Sebor, G. Fuel 2009, 88, 1351–1356.
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blended and the parent gasolines, indicating that the volatility of the glycerol derivatives is compatible with the gasoline components. Table 2 shows the density and gum formation results for the pure gasoline and the blends. As expected, the density increases as the amount of glycerol derivative increases in the
gasoline. The addition of solketal significantly reduced the gum formation of both gasolines, with and without ethanol. In contrast, the addition of the glycerol/formaldehyde acetals significantly increased the gum formation (Figure 4). It is not completely clear why this contradictory behavior occurs, but one hypothesis is associated with the methylene carbon of the glycerol/formaldehyde acetals. It is known29 that gum
Figure 1. Distillation curve for the gasoline A and solketal blend (GA þ GAK): (9) GA, (0) GA þ 1% GAK, (b) GA þ 3% GAK, and (O) GA þ 5% GAK.
Figure 3. Distillation curve for the gasoline C and glycerol/formaldehyde acetals blend (GC þ GFA): (9) GC, (0) GC þ 1% GFA, (b) GC þ 3% GFA, and (O) GC þ 5% GFA.
Figure 2. Distillation curve for the gasoline C and solketal blend (GC þ GAK): (9) GC, (0) GC þ 1% GAK, (b) GC þ 3% GAK, and (O) GC þ 5% GAK.
Figure 4. Gum formation against the volume percent of glycerol derivative on gasoline: (9) GA þ GAK, (b) GC þ GAK, and (2) GC þ GFA.
Table 2. Analysis of the Gasoline and Glycerol Derivatives Mixtures sample b
GA GA þ GAK GA þ GAK GA þ GAK GCc GC þ GAK GC þ GAK GC þ GAK GC þ GFA GC þ GFA GC þ GFA a
volume percent of ketal/acetal
densitya (g/mL)
gum formation (mg/mL)
0 1 3 5 0 1 3 5 1 3 5
0.741 0.744 0.750 0.756 0.754 0.758 0.764 0.771 0.759 0.769 0.777
4.2 3.6 2.6 2.7 4.2 3.3 2.5 2.6 7.5 10.3 16.4
Taken at 25 °C. b Gasoline A (without ethanol). c Gasoline C (with 25 vol % ethanol).
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number. There is no reported octane value for this compound, but glycerol/acetaldehyde acetals show19 a blend octane number of 86, considerably lower than the value found for solketal. It is well-known that branching increases the anti-knocking properties of gasoline, affecting octane. Thus, it might be possible that the two methyl groups in the solketal molecule contribute to the increased octane number of this compound compared to the glycerol/ formaldehyde acetals. These results show that solketal might be an alternative oxygenated compound for blending with gasoline, reducing gum formation and improving octane. The use of solketal may be particularly important in gasolines produced from catalytic cracking, because of its high olefin content, which induces gum formation and decreases the octane number, compared to alkylated gasoline. In addition, solketal may also be used in gasoline/ethanol blends to reduce the gum formation, without reducing the octane number. Although glycerol is derived from biomass, one may argue that glycerol derivatives, such as solketal, have fossil components, because acetone usually comes from naphtha processing. Nevertheless, acetone can also be produced from biomass, through fermentation of sugar molecules.31 Therefore, solketal might be a potential oxygenated additive for gasoline in replacement of MTBE. It can be used as an alternative to ethanol, to improve octane, or together with this component, to reduce gum formation.
Figure 5. Octane number (average of MON þ RON) against the volume percent of glycerol derivative on gasoline: (9) GA þ GAK, (b) GC þ GAK, and (2) GC þ GFA.
formation may involve radical reactions, especially forming resonance-stabilized species.30 Thus, the hydrogen atoms of the methylene carbon atom may be abstracted, giving rise to reactive radical species, stabilized by resonance with the nonbonded electrons of the adjacent oxygen atoms, inducing polymerization of the olefins present in the gasoline. The pour point and copper corrosiveness did not change with the addition of the glycerin additives. The pour point of the pure and blended gasolines was below -60 °C, and the copper corrosiveness was 1a, indicating that both additives have no appreciable effect in these two properties. Figure 5 shows the average octane number increment of the gasolines, (RON þ MON)/2, with the percent of glycerol derivative added. With gasoline A, the addition of solketal increased the octane number up to 2.5 points. It has been reported19 that solketal has a blend octane number of 98 (average of MON and RON), which might explain these results. However, with gasoline C, the increase in octane was significantly less important. This is because ethanol is also an octane booster. Thus, the addition of a second booster does not necessarily lead to an additive effect. The results of gasoline C and glycerol/formaldehyde acetals blends showed a slight reduction of the octane
Conclusions The addition of glycerol/acetone ketal, solketal, to gasoline (with and without ethanol), in the range of 1-5 vol %, led to a significant decrease in gum formation, indicating a potential antioxidant property of this glycerin derivative. Solketal also improved the octane number of the gasoline. The increment was more significant for the gasoline without ethanol. In contrast, the glycerol/formaldehyde acetals led to an increase in gum formation, probably associated with the presence of a methylene carbon atom, which upon formation of a free radical may induce polymerization. The results indicated the potential of solketal as a gasoline additive, to improve octane and reduce gum formation, especially in gasolines produced from catalytic cracking. Acknowledgment. The authors thank the financial support from RepsolYPF, FINEP, CNPq, FAPERJ, and PRH-ANP.
(29) Nagpal, J. M.; Joshi, G. C.; Singh, J.; Rastogi, S. N. Fuel Sci. Technol. Int. 1994, 12 (6), 873–894. (30) Pereira, R. C. C; Pasa, V. M. D. Fuel 2006, 85, 1860–1865.
(31) Beesch, S. C. Ind. Eng. Chem. 1952, 44 (7), 1677–1682.
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