ISSN 09655441, Petroleum Chemistry, 2015, Vol. 55, No. 2, pp. 140–145. © Pleiades Publishing, Ltd., 2014. Original Russian Text © D.N. Ramazanov, A. Dzhumbe, A.I. Nekhaev, V.O. Samoilov, A.L. Maximov, E.V. Egorova, 2015, published in Neftekhimiya, 2015, Vol. 55, No. 2, pp. 148–153.
Reaction between Glycerol and Acetone in the Presence of Ethylene Glycol D. N. Ramazanova, A. Dzhumbeb, A. I. Nekhaeva, V. O. Samoilova, A. L. Maximova, and E. V. Egorovab aTopchiev
Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia Lomonosov Moscow State University of Fine Chemical Technology, Moscow, Russia email: ramazanov
[email protected]
b
Received June 4, 2014
Abstract—The acetalization of glycerol with acetone in the presence of ethylene glycol over KU2 and Amberlyst 70 cationexchange resins and β and Y zeolites has been studied. It has been shown that the rates of conversion of glycerol and ethylene glycol over the cationexchange resins are significantly lower than over the zeolites. The rates of conversion of the polyols over the β zeolite are lower than over the Y zeolite. Condi tions for the complete conversion of glycerol to acetal have been found. The turnover number (TON) per acid site have been determined; for example, TON = 640 min–1 for glycerol over the Y zeolite. The activation energy is 19.9 and 46.2 kJ/mol for ethylene glycol and glycerol, respectively. Keywords: acetalization, glycerol, ethylene glycol, zeolites, cationexchange resins DOI: 10.1134/S0965544115020152
Production of motor fuel components with improved environmental characteristics from biologi cal feedstock is one of the possible directions of expanding the rawmaterial base of modern fuel industry [1, 2]. The products of reactions between alcohols and carbonyl compounds—acetals—are ethers that are commonly used in organic synthesis (for the protec tion of the carbonyl groups of organic molecules from the action of bases, Grignard reagents, lithium alumi num hydride, and oxidants [3, 4]) and as fragrances in perfumery [5], additives for beverages and foodstuffs (emulsifiers) [6], and solvents in pharmaceutics [7]. Recently, acetals of polyols—glycerol and sugars— have been proposed as additives to improve the prop erties of motor fuels [8–18]. In many aspects, ethers are more advantageous fuel components than alcohols. The main advantages are higher oxidative stability and heat of combustion as well as more favorable partition in the water–fuel sys tem. An important property of acetals is that these ethers can be produced from renewable sources (bio mass; agricultural, forestry, and foodindustry wastes, etc.). The presence of oxygen in the composition of ethers provides a significant improvement of the envi ronmental performance of engines using these alter native motor fuels. It should be noted that some ethers have fairly high octane and cetane numbers [19] and low pour points, exhibit good lubricating properties, and reduce harmful emissions during the combustion of motor fuels [20].
A convenient alcohol for the production of acetals is glycerol. The amount of glycerol formed as a byproduct (10% by weight) in the production of biodiesel by transesterification of vegetable oils with methanol is superabundant in the world market. Therefore, new spheres of application of glycerol are being searched for [21], in particular the production of glycerolbased fuel additives [22]. The conversion of glycerol to solketal—acetal of glycerol and acetone—in excess acetone has been studied previously [23]. It is known that glycerol and acetone do not readily mix; therefore, the acetaliza tion of glycerol with acetone presents certain difficul ties. In this study, the reaction between glycerol and acetone in the presence of ethylene glycol has been examined to overcome mass transfer limitations. EXPERIMENTAL Materials The reactants were special purity grade glycerol and acetone and analytical grade ethylene glycol (Khimmed, Russia). The catalysts were cation exchange resins KU28 (Poliflok, Russia) and Amberlyst 70 (A70) (Rohm & Haas) and zeolites β (Zeolyst CP811Tl) and Y (Zeolyst CBV 760). All the catalysts were used in the acid form. The characteris tics of most of the catalysts are given in [23].
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Equipment and Experimental Procedures The experiments on the acetalization of glycerol and ethylene glycol with acetone were conducted using a setup comprising a 30mL temperaturecon trolled glass reactor, a reflux condenser, and a variable speed magnetic stirrer. The reaction was conducted at temperatures of 35–65°С under vigorous stirring (N = 6 rps) at atmospheric pressure for 60 min. The con centration of ethylene glycol and acetone was 1.12 and 12.75 mol/L, respectively; the amount of the catalyst was 5.0 × 10–3 g (0.037 wt %). In experiments on the joint acetalization of ethylene glycol and glycerol, the concentration of glycerol, ethylene glycol, and ace tone was 0.81, 1.05, and 12.00 mol/L, respectively. Concurrent reaction conditions: concentration of glycerol and ethylene glycol, 0.82 mol/L each; ace tone content, 12.00 mol/L; and temperature, 40°С. Analysis of Products
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Khimmed), and then analyzed by gas chromatogra phy–mass spectrometry. RESULTS AND DISCUSSION It is known that glycerol and acetone do not mix; therefore, the acetalization of glycerol with acetone (hereinafter, acetalization) presents certain difficul ties. Ethylene glycol was used to solve this problem. A heterogeneous system composed of glycerol (0.014 mol) and acetone (0.204 mol) becomes homo geneous after the introduction of 0.018 mol of ethyl ene glycol. Under our conditions, ethylene glycol acts as both a solvent and a reactant. While ethylene glycol undergoes conversion during reaction, the products of acetalization of ethylene glycol (I) and glycerol (II) act as solvents. Therefore, the absence of a solvent, which should be removed after reaction, makes the acetaliza tion process attractive in terms of “green” chemistry. The reaction products are shown in the scheme: OH
The quantitative analysis of the acetalization reac tion products was conducted on a Kristallyuks 4000 M chromatograph equipped with a flame ionization detector using a 30 m × 0.25 mm Supelcowax column and helium as a carrier gas (a split ratio of 1 : 90). Tem perature programming: holding at 70°C for 3 min; rise from 70 to 250°C at a rate of 10°C/min; and holding at 250°C for 9 min. The quantitative analysis was con ducted using calibration mixtures with an exactly known acetal content. The structure of the reaction products was deter mined by gas chromatography–mass spectrometry using a Finnigan MAT 95 XL instrument (a 30 m × 0.25 mm Varian VF5ms capillary column; phase thickness, 0.25 μm; carrier gas, helium; operation mode: injector temperature, 270°С; initial chromato graph oven temperature, 30°С; then a 5min isotherm followed by heating to 300°C at a rate of 10°C/min; operation mode of the mass spectrometer: ionization energy, 70 eV; source temperature, 230°С; scan range, 20–800 Da at a rate of 1 s/decade of mass; and resolu tion, 1000). The components were identified using the reference mass spectra from the NIST/EPA/NIH 11 database. The component content was calculated from the chromatographic peak areas in the chromatogram for the total ion current without corrections for ioniza tion efficiency. The structure of the components whose mass spec tra were absent in the mass spectral database was determined by trimethylsilylation. Derivatization was conducted using commercially available bis(trimeth ylsilyl)trifluoroacetamide containing 1% trimethyl chlorosilane as an additive (BSTFA, Aldrich, United States). For the reaction, 10 μL of the original mixture was admixed to 100 μL of a derivatizing agent. The resulting mixture was heated to 100°С, cooled, diluted with 1 mL of methylene chloride (analytical grade, PETROLEUM CHEMISTRY
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O I
OH A
O
III
O
Cat
–H2O
OH I OH
O
HO
B
O
OH
IV O
III O
OH OH II
O HO V
O
Schematic of acetalization of polyols.
Acetalization of Ethylene Glycol with Acetone (Reaction A) The effect of the catalyst nature on the acetaliza tion of I was studied. To this end, a number of catalysts were tested: a CP811Tl β zeolite, a CBV 760 Y zeolite, A70, and KU28. Zeolites are convenient heteroge neous acid catalysts. Their acidity is confirmed, in particular, by the fact that, in 1H NMR spectra, com mercial zeolites give a signal of about 4 ppm corre sponding to the protons that form Brönsted acid sites [24, 25]. Under the given conditions, the reaction between I and acetone yields a single reaction product—ethyl ene glycol acetal (2,2dimethyl1,3dioxolane) (III). A temperature of 50–55°С was optimum for the con version of I. The activity series of acetalization catalysts is as follows: KU28 < A70 < β zeolite < Y zeolite. The
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Table 1. Conversion and TON (min–1) in the joint acetalization of I and II with acetone over different catalysts* Catalyst Conversion, %; O, min –1 Conversion (I) Conversion (II) O (I) O (II)
β zeolite
Y zeolite
KU2
A70
30.0 18.0 249.6 109.4
38.0 28.0 1122.1 640.8
6.0 7.1 13.5 12.2
1.6 3.0 7.7 12.0
* Experimental conditions: reactant concentration (mol/L): II, 0.81; I, 1.05; and acetone, 12.00; catalyst content, 5.0 × 10–3 g; temper ature, 40°C; and reaction time, 5 min.
conversion of I over the Y zeolite at 50°С exceeds 90% even after 5 min and is 93% within 1 h; over the β zeo lite, the conversion does not exceed 90% within the same time, while over the cationexchange resins it surpasses a 60% level only by the 30th min. By the 60th min, the reaction rates over all the catalysts decrease compared to the initial rate and become almost the same. By the 60th min, the rate of acetalization of I over the β and Y zeolites decreases by 11.8 and 11.3 times, respectively, compared to the initial rate; for 70 A2 and KU, the reaction rate does not signifi cantly change over time. The Y zeolite exhibited high activity in the acylation of thiophene [26] and benzo furan [27]. The decrease in the rate is attributed to both a decrease in the reactant concentration and the release of water, which is a byproduct of the reaction that can, first, block the active sites of catalysts [28] and, sec ond, be involved in a reverse reaction. The Latvian researchers have shown that wet Amberlyst is inactive in the etherification of glycerol with alcohols [29]. The number of catalytic cycles per acid site was estimated by calculating the turnover number (TON), i.e., the number of molecules converted per acid site per unit time, with allowance for the acid site concen tration for the different catalysts. The data on the acid site concentration for most of the catalysts were taken from [23]; for the CBV 760 Y zeolite, from [30]; and for the A70 cationexchange resin, from [31]. Although not all of the acid sites of catalysts are involved in the reaction, the TON values are used for the rough estimation of the activity of various catalysts in liquidphase reactions [32]. Joint Acetalization of Ethylene Glycol and Glycerol with Acetone (Reaction B) Reaction products: III, glycerol acetal, i.e., solketal (2,2dimethyl4hydroxymethyl1,3diox olane) (IV), and the solketal isomer (2,2dimethyl5 hydroxy1,3dioxane) (V); other reaction products were not detected. The selectivity for V over all the studied catalysts did not exceed 9%.
The conversion and number of catalytic cycles TON (min–1) in the joint acetalization of I and II over the different catalysts are shown in Table 1. The most active catalyst with respect to the number of catalytic cycles in the acetalization of polyols was the Y zeolite. For the zeolites, the TON decreases with increas ing reaction time, unlike the A70 and KU2 cation exchange resins, for which the TON value does not significantly change over time and remains low. The decrease in TON over time for the zeolite catalysts is attributed to a change in the equilibrium constant of the reaction (consumption of reagents and accumula tion of products). This relationship is not observed for the sulfonated cation exchangers: the reaction rate over the zeolites is significantly higher; therefore, the establishment of equilibrium in the system over time occurs faster. In addition, the formation of water can have an effect on the process not only in accordance with the law of mass action: the adsorption of water on the active sites of the catalyst can reversibly deactivate the sites and exclude them from the process. It is also known that the surface area and number of Brönsted acid sites of zeolites decrease owing to the blocking of the pores by the reaction products, as shown in [33] using the example of the reaction between II and tert butanol. The difference in the reactivity of I and II over the β and Y zeolites is attributed both to the larger geometrical dimensions of the molecule of II and the larger pore size of the Y zeolite and to the fact that the adsorption of II on zeolites is worse than that of I [34]. In the case of the cationexchange resins, the conclu sion made in [23] is confirmed; that is, zeolites and cationexchange resins are more active at low and higher temperatures, respectively. The considerable difference in the TON values for the zeolite and sulfonated cationexchange resin cata lysts can be attributed to significant differences in the surface properties of the catalysts: the zeolites have high specific surface areas and were used in the form of a fine powder (a pore diameter of about 0.69 and 0.74 m and a surface area of 725 and 629 m2/g for the β and Y zeolites, respectively), whereas the sulfonated cationexchange resin grains have a small surface area on which adsorption and diffusion are hindered (a PETROLEUM CHEMISTRY
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REACTION BETWEEN GLYCEROL AND ACETONE Ethylene glycol conversion, %
80 Glycerol conversion, %
70 60 50 40 30 20 10
80 70 60 50 40 30 20 10 0
0
10
20
30 40 Time, min
50
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10
20
60
30 40 Time, min
50
60
Fig. 1. Effect of the catalyst nature on the conversion of glycerol in a mixture with ethylene glycol. Experimental conditions: reactant concentration (mol/L): glycerol, 0.81; ethylene glycol, 1.05; and acetone, 12.00; T = 40°C; catalyst content, 5.0 × 10 ⎯3 g: (䊉) Y zeolite, (䊊) β zeolite, (䊐) A70, and (䉬) KU2.
Fig. 2. Effect of temperature on the conversion of ethylene glycol in a mixture with glycerol. Experimental conditions: reactant concentration (mol/L): glycerol, 0.81; ethylene glycol, 1.05; and acetone, 12.00; β zeolite catalyst content, 5.0 × 10–3 g; and T of (䉬) 35, (䊏) 40, (䉱) 45, (䊉) 50, (䊊) 55, (䉫) 60, and (䉭) 65°C.
pore diameter of 22 nm, a grain diameter of about 0.5 mm, a specific surface area of 36 and 15 m2/g for A70 and KU2, respectively). Another factor that transfers catalysis over sulfonated cationexchange resins in the diffusion region is the higher hydrophobicity of the styrene–divinylbenzene matrix of the ionexchange resin. The kinetic curves of the conversion of II in the presence of I over the different catalysts show that the zeolite catalysts are more active than the cation exchange resins (Fig. 1). Temperature has a significant effect on the conver sion of I and II (Figs. 2, 3). In the studied temperature range, the conversion of I and II achieves a maximum at 60°С. In addition, after 5 min of reaction, the rate of conversion of I in the presence of II decreases, as in the case of reaction with a single polyol, regardless of temperature. The optimum temperature for the conversion of both I and II in the joint acetaliza tion thereof in the presence of the β zeolite is 60°C (Figs. 2, 3). For the formation of V within 5 min of reaction, the optimum temperature was 50°С, while the selectivity for V was 8.7%. These results suggest that the rate of acetalization is high even at low tem peratures. The highest conversion of II (an initial concentra tion of 0.81 mol/L) is observed at a concentration of I of 1.05 mol/L. Upon the introduction of II, the rate of conversion of I significantly decreases in the entire temperature range (e.g., it decreases fourfold and two fold at 35 and 65°С, respectively). The dependence of the logarithm of the conversion rate of polyols on the reciprocal of temperature in the presence of the β zeolite is shown in Fig. 4; the activa tion energies of the reactions are listed in Table 2.
Thus, the activation energy of acetalization of I with acetone in a temperature range of 308–333 K for 5 min of reaction is Eact = 10.6 kJ/mol. Comparison of the activation energy of the joint acetalization reaction with the values for the reaction in the presence of a sin gle substrate (Table 2) shows that Eact for I in the joint reaction is almost 2 times higher and amounts to 19.9 kJ/mol. In the case of the joint acetalization, Eact for II is 2.3 times higher than that for I.
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Glycerol conversion, %
70 60 50 40 30 20 10 0
10
20
30 40 Time, min
50
60
Fig. 3. Effect of temperature on the conversion of glycerol in a mixture with ethylene glycol. Experimental condi tions: reactant concentration (mol/L): glycerol, 0.81; eth ylene glycol, 1.05; and acetone, 12.00; β zeolite catalyst content, 5.0 × 10–3 g; and T of (䉬) 35, (䊏) 40, (䉱) 45, (䊉) 50, (䊊) 55, (䉫) 60, and (䉭) 65°C.
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100 90
–1.5
80 Conversion, %
ln (WT)
–2.0 –2.5 –3.0 –3.5
60 50 40 30 20
–4.0 –4.5 3.00
70
10 3.05
3.10 3.15 1/T × 10–3, K
3.20
3.25
Fig. 4. Dependence of the logarithm of the conversion rate of the polyol on the reciprocal of temperature in the presence of the β zeolite. β zeolite catalyst content, 5.0 × 10–3 g; reaction time, 5 min: (䉬) for ethylene glycol (eth ylene glycol, 1.12 mol/L; acetone, 12.75 mol/L), (䊏) for ethylene glycol (glycerol, 0.81 mol/L, ethylene glycol, 1.05 mol/L; acetone, 12.00 mol/L), and (䉱) for glyc erol(glycerol, 0.81 mol/L; ethylene glycol, 1.05 mol/L; acetone, 12.00 mol/L).
In a number of studies on the acetalization of II and butanol under conditions excluding internal diffu sion, the obtained Eact values were close to our value for II. For example, for the transacetalization of II with 1,1diethoxyethane over the Amberlyst15 cat ionexchange resin, Eact is 58.6 kJ/mol [35]; for the reaction of II with acetaldehyde over Amberlyst47, 55.4 kJ/mol [36]; for the reaction of butanol with ace taldehyde over Amberlyst15, 51.55 kJ/mol [37]; and for the acetalization of II with acetone in an ethanol solution over Amberlyst35, 55.6 kJ/mol [38]. An increase in Eact of I in the joint reaction is appar ently attributed to a change in the structure of the solution: the addition of II provides the formation of a larger number of hydrogen bonds than in a solution only of I owing to the presence of three hydroxyl groups in the molecule of II. Furthermore, the addi tion of II complicates the mass transfer processes
0
30
60
90 120 Time, min
150
180
Fig. 5. Concurrent reaction. Experimental conditions: reactant concentration (mol/L): glycerol, 0.82; ethylene glycol, 0.82; and acetone, 12.00; T = 40°C: (䊏) 5 mg of β zeolite, ethylene glycol; (䊉) 5 mg of β zeolite, glycerol; (䊊) 15 mg of β zeolite, ethylene glycol; and (䉫) 15 mg of β zeolite, glycerol.
owing to an increase in the viscosity of the reaction mixture. As the catalyst concentration increases, the rate of conversion of I and II linearly increases at 40°С, while the fraction of V in the reaction products decreases. In the case of I, in the presence of 15 mg of the catalyst, the conversion of I achieves 90% within 5 min and remains constant to 60 min, while the conversion of II achieves 100% within 15 min. By the 60th min, the rate of conversion of I over the Y and β zeolites (a cat alyst content of 5.0 × 10–3 g, 40°С) decreases by 6.2 and 6.3 times, respectively, compared to the initial rate; for II over the Y and β zeolites, it decreases by 5.1 and 4.1 times, respectively. Concurrent Acetalization of an Equimolar Mixture of I and II with Acetone Similar relationships are observed under condi tions of a concurrent reaction. Figure 5 shows results of a concurrent reaction with 5 and 15 mg of the β zeo
Table 2. Experimental values of activation energy Reactant concentration (mol/L) Single polyol: Ethylene glycol I – 1.12 acetone – 12.75 Polyol mixture: Ethylene glycol I – 1.05; glycerol II – 0.81 acetone – 12.00
Polyol
Eact, kJ/mol
I I II
10.6 19.9 46.2
β zeolite content, 5.0 × 10–3 g; reaction time, 5 min. PETROLEUM CHEMISTRY
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lite. Initially, the highest activity is exhibited by I. The conversion of I does not exceed 90%, whereas for II under the same conditions, the process occurs with a 100% conversion. The activity of I at the initial moment of the reac tion is attributed to the sizes the molecules of I (0.68 nm lengthwise and 0.35 nm crosswise) and the pore sizes of the β zeolite (0.69–0.70 nm). At the ini tial moment, the access to the acid sites of larger nearly spherical molecules of II (a diameter of 0.68 nm) is limited to the presence of a fairly high concentration of smaller molecules of I. An interesting fact that I, which is initially more active, does not achieve 100% conversion, unlike II, has not yet been understood. ACKNOWLEDGMENTS We thank I.V. Bakhtin (Dow Water & Process solu tions) for kindly providing the sample of Amberlyst 70 sulfonated cationexchange resin and R.S. Borisov and N.Yu. Polovkov (Topchiev Institute of Petro chemical Synthesis) for conducting the gas chroma tography–mass spectrometry analysis. This work was supported in part by the Presidium of the Russian Academy of Sciences under Program no. 3 “The Energy Aspects of Deep Processing of Fos sil and Renewable CarbonContaining Raw Materi als” (program code 3P, executor code Kh9717). REFERENCES 1. I. I. Moiseev, H. A. Plate, S. D. Varfolomeev, and Vestn. Ross. Akad. Nauk 76, No. 5, 427 (2006). 2. S. D. Varfolomeev, I. I. Moiseev, and B. F. Myasoedov, Vestn. Ross. Akad. Nauk 79, 595 (2009). 3. Yanovskaya, L.A., Yufit, S.S., and Kucherov, V.F., Chemistry of Acetals (Nauka, Moscow, 1975) [in Rus sian]. 4. T. W. Greene and P. G. N. Wuts, Protective Groups in Organic Synthesis (Wiley, New York, 1991), 2nd Ed., vol. 4, p. 212, 5. G. A. Burdock, Fenaroli’s Handbook of Flavour Ingredi ents (CRC, Boca Raton, 1995), 3th Ed., vol. 2. 6. S. V. Ley and H. W. M. Priepke, Angew. Chem. 106, 2412 (1994). 7. R. T. Blickenstaff, S. M. Brandstadter, E. Foster, et al., Ind. Eng. Chem. Res. 32, 2455 (1993). 8. E. García, M. Laca, E. Pérez, et al., Energy Fuels 22, 4274 (2008). 9. S. D. Varfolomeev, G. A. Nikiforov, V. B. Vol’eva, et al., RU Patent No. 2 365 617 (2009). 10. S. D. Varfolomeev, Chem. J., Aug, 36 (2009). 11. A. L. Maksimov, A. I. Nekhaev, D. S. Shlyakhtitsev, et al., Pet. Chem. 50, 325 (2010). 12. C. J. A. Mota, C. X. A. Silva, N. Rosenbach, Jr., et al., Energy Fuels 24, 2733 (2010). 13. P. H. R. Silva, V. L. C. Gonalves, and C. J. A. Mota, Biores. Technol. 101, 6225 (2010). PETROLEUM CHEMISTRY
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