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Acetalization reaction between glycerol and n-butyraldehyde using an acidic ion exchange resin. Kinetic modelling
Chemical Engineering Journal 228 (2013) 300–307
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Acetalization reaction between glycerol and n-butyraldehyde using an acidic ion exchange resin. Kinetic modelling M. Belen Güemez ⇑, Jesus Requies, Ion Agirre, Pedro L. Arias, V. Laura Barrio, Jose F. Cambra Department of Chemical and Environmental Engineering, Engineering School of the University of the Basque Country (UPV/EHU), c/Alameda Urquijo s/n, Bilbao 48013, Spain
h i g h l i g h t s Reached results are useful for engineering process design for a sustainable glycerol valorization. Mixtures of cyclic acetals are the main products obtained in acetalization reaction. Amberlysts 47 acidic ion exchange resin is highly active and stable in acetals production.
a r t i c l e
i n f o
Article history: Received 5 January 2013 Received in revised form 25 April 2013 Accepted 29 April 2013 Available online 7 May 2013 Keywords: Cyclic acetals Glycerol n-Butyraldehyde Acidic ionic exchange resin Kinetic parameters
a b s t r a c t The acetalization reaction between glycerol and n-butyraldehyde using Amberlyst 47, an acidic ion exchange resin catalyst, was studied. These acetals can be obtained from renewable sources and seem to be good candidates for different applications such as oxygenated diesel additives. Amberlyst 47 acidic ion exchange showed good activity and stability after five consecutive cycles of reuse. Therefore, 100% of selectivity towards the formation of acetals and butyraldehyde conversions between 92% and 98% were obtained for different molar feed ratios of glycerol:aldehyde. For glycerol:aldehyde molar ratios lower than the stoichiometric one, 2,4,6-tripropyl-1,2,3-trioxane is also detected as product when glycerol is almost totally consumed. Moreover, a pseudo-homogeneous kinetic model able to explain the reaction mechanism was adjusted and the corresponding overall reaction order was determined. The addition of around 15 wt% of water in the feed produces only a slight decrease in the butyraldehyde conversion, and it improves the mixing and transport properties of the reaction mixture. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Acetals have their main application in the chemical industry and fine chemicals – cosmetics, pharmaceutical – , as intermediates or final compounds. However, as in recent years governments have increased restrictions on environmental pollution, the use of some types of acetals and ketals, derived from biomass, as potential oxygenated additives to fuels is being researched. For example, nowadays acetals can be used to reduce particulate emissions [1,2], to increase octane number in gasoline [3], to improve the properties of biodiesel (viscosity, oxidation stability, flash point, etc.) [4–7], or as antifreezing agents of biodiesel [6]. Acetals are obtained typically by the reaction of carbonyl compounds (aldehydes, ketones) and alcohols with or without solvent and in the presence of strong mineral acids as catalysts like H2SO4, HF, HCl, H3PO4 or p-toluenesulphonic acids [2,8–11]. These catalysts also cause corrosion and environmental problems and make the separation and purification process of the products more difficult. These ⇑ Corresponding author. Tel.: +34 946014273; fax: +34 946014179. E-mail address: [email protected] (M.B. Güemez). 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.04.107
disadvantages could be solved using solid catalysts, and in this sense, efforts are being made to develop adequate solid acids. In the literature several types of heterogeneous acid catalysts like ion exchange resins [7,9–17], zeolites [11,18,19], montmorillonites [11,14,18] and MoO3/SiO2 [20] are reported to be used for acetalization reactions. Capeletti et al. [11] concluded that Amberlyst ion exchange resins are the best ones. The process for acetals synthesis could be considered a sustainable process if raw materials from renewable sources are used, as bio-alcohols and aldehydes derived from bio-alcohols. Not all acetals can be used as additives for diesel fuels. Some of them show low flash points and are not useful as additives [2,17]. Those acetals derived from polyols and short chain aldehydes, such as acetaldehyde and butyraldehyde, present flash points close to the diesel specifications, while those derived from ethanol, require long chain aldehydes to produce acetals with an acceptable flash point. Among bioalcohols, glycerol, the main by-product of biodiesel production (transesterification of vegetable oils or animal fats) is the alcohol that have gained more attention in recent years [21– 24] due to its increasing production, associated to the increase of biodiesel world production. Therefore, to valorise its potential uses,
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M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307
and to improve the economic balance of the biodiesel production process, new applications are being developed [21,23], including the use of its acetals as diesel fuel additives. Most of the studies reported in the literature for acetalization reactions are focused on analysing and comparing the activity of the solid catalysts. Moreover, some authors also explained the possible reaction mechanism [9,10,25–30], but a few proposed a reaction kinetic model [9,10,12,16,17,26–29,31–33]. In the case of the synthesis of cyclic acetals obtained from the reaction between a polyol and an aldehyde or ketone, Sharma and Chopade [10] described the mechanism of acetalization of ethylene glycol and formaldehyde as a two-step reversible process. The first stage involves the formation of an hemiacetal, an intermediate compound formed by the addition of an alcohol molecule to the carbonyl group, and in the second stage, the hemiacetal hydroxyl group reacts with another OH group to give the 1,3-dioxolane, releasing a water molecule. For the reaction of glycerol and acetaldehyde, Da Silva Ferreira et al. [28] showed in more detail the stages of possible re-organization of the hemiacetal that lead to the formation of mixed cyclic acetals. Fig. 1 shows the reaction mechanism proposed by Sharma and Chopade [10] adapted to the reaction of glycerol and alkyl-aldehydes. In this case, depending on which hemiacetal OH reacts to form the acetal, 4-hydroxy-2-alkyl-1,3-dioxolane (cis and trans) or 5-hydroxy-2alkyl-1,3-dioxane (cis and trans) are formed. The four isomers tend towards equilibrium between them through reorganization of the corresponding hemiacetal structure [28]. In this work, the acetalization reaction of n-butyraldehyde and glycerol has been studied in a batch reaction system. The ion exchange resin Amberlyst 47 (A47) has been used as heterogeneous catalyst since its mechanical resistance makes this resin, a priori, the most suitable one for its use in slurry reactors or in structured packings. Moreover, Agirre et al. [16] compared the activity of three Amberlyst ion exchange resins (A15wet, A47 and A35wet) obtaining similar results in activity for the acetalization reaction of ethanol and n-butyraldehyde. The experimental data have been extensively treated in order to propose a pseudo-homogeneous kinetic model for the overall reaction. Kinetic parameters have also been estimated. Catalyst reuse and the effect of water in the feed have also been studied.
2.1. Materials and analysis Glycerol (G) (Panreac, 99 wt%) and n-butyraldehyde (B) (Merck, 99 wt%), both of quality for synthesis, were used as reagents. Amberlyst 47 (A47) catalyst was kindly supplied by Rohm & Haas. Both, reactants, glycerol and n-butyraldehyde, and reaction products, 5-hydroxy-2-propyl-1,3-dioxane (cis and trans isomers) (AC1) and 4-methanol-2-propyl-1,3-dioxolane (cis and trans isomers) (AC2) were analyzed by gas chromatography (Agilent 6890 N) using a flame ionization detector (FID) and the water (W) produced was analyzed using a thermal conductivity detector (TCD). An Agilent DB-1 (60 m 0.53 mm 5 lm) capillary column was used with helium as the carrier gas. The elution order of these organic products reported in the literature is [15,29,34]: cis-5-hydroxy-2-alkil-1,3-dioxane, cis-4methanol-2-alkil-1,3-dioxolane, trans-4-methanol-2-alkil-1,3dioxolane and trans-5-hydroxy-2-alkil-1,3-dioxane. In this study, reaction products were identified analyzing their mass spectra obtained by GC/MS and verifying that their MS-spectra included the expected molecular fragments. 2.2. Activity test The reaction tests were carried out in a 1 L glass batch stirred tank reactor (BSTR). The reaction temperature was controlled by an external thermostat (Lauda RE 304). This thermostat contains a thermocouple placed inside the reacting mixture that allows controlling the reaction temperature with an accuracy of ±0.05 K. The reactor is also connected to a condenser in order to condense and reflux all the vapours keeping the reaction volume approximately constant. In a typical experiment, the reactor was first charged with 0.5 L of the reaction mixture, then the system was closed, the agitation speed was fixed and, after the system stabilization at the desired temperature, the catalyst was added. This moment was considered as the initial time for the reaction. Before adding the catalyst sample, its moisture was modified waiting until it reached equilibrium with the room one. Therefore the weight could be controlled. All
OH
O
OH HO
2. Materials and methods
R
OH
C
HO
H
OH
O R
alkyl aldehyde
glycerol
1,2-propanediol-3-(1-hydroxy-alkoxy) (hemiacetal) H2C
OH
OH HO
OH
O
+
O
O R
R
(1)
H2O
(2a)
H
4-hydroxymethyl-2-alkyl-1,3-dioxolane OH OH HO
OH
O R
+
R
H2O
(2b)
O
O H
5-hydroxy-2-alkyl-1,3-dioxane Fig. 1. Generalized reaction mechanism of glycerol and alkyl–adehyde adapted from proposed by Chopade and Sharma [10].
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 100%
3,0 2,5
80%
2,0 60% 1,5 40% 1,0
Conversion
experiments were carried out using 0.5 wt% of A47 with respect to total weight of reactants feed. Moreover, some glass wool was placed in the sampling output in order to keep the catalysts amount constant in the reactor. At specific time intervals, small samples (1.5 mL of volume and a maximum of 15 samples by run) were withdrawn in order to analyze them by GC. To establish the temperature range of operation, an analysis of the physical properties of fed mixture using the UNIFAC-LL thermodynamic method was carried out. Table 1 shows the mixture boiling temperature for different G:B (glycerol to n-butyraldehyde) molar ratios and the mixture viscosity at those temperatures.
Acetals (mol/L)
302
20%
0,5 150 rpm
500 rpm
1000 rpm
180
270
360
1250 rpm
0,0 0
90
450
0% 540
Time (min)
3. Results and discussion In order to study the catalytic activity of the ion exchange resin Amberlyst 47 in the acetalization reaction of glycerol and n-butyraldehyde, different parameters were studied: agitation speed, reaction temperature, G:B molar ratio fed, presence of water in the feed mixture and catalyst reuse. When the G:B molar ratio used was greater than 1, activity tests showed that the products obtained were just a mixture of cyclic acetals and water. 3.1. Effect of stirring speed High temperatures, low stirring speeds and viscous liquid mixtures are the most unfavorable conditions in which resistance to external mass transport may occur. Therefore, the effect of the stirring rate on n-butyraldehyde conversion and acetal concentrations was studied within a wide range of agitation speeds, 150 rpm (minimum speed that the available stirring system is able to provide) and 1250 rpm, at 353 K and 3:1 G:B molar ratio. The results are shown in Fig. 2. No external mass transfer limitations were observed even at the lowest stirring speed, (150 rpm). However, it was observed that initial vigorous stirring was necessary to achieve a homogeneous mixture of the reagents due to difficult mixing between glycerol and n-butyraldehyde. Because of this reason, the rest of the experiments were carried out at 1000 rpm. 3.2. Effect of reaction temperature The temperature effect on the reaction of glycerol and n-butyraldehyde was carried out in the temperature range of 323–353 K using the stoichiometric feed ratio. As expected, an increase in
Table 1 Physical properties of the mixture fed at the operating conditions used for the kinetic study (the physical properties were estimated using the UNIFAC-LL thermodynamic method). Molar ratio G:B
Boiling point (K)
Temperature (K)
Density (g/cc)
Viscosity (cPo)
0.2
351
338 346 353
0.87 0.86 –
0.70 0.62 –
0.5
358
338 346 353
0.95 0.94 0.93
1.66 1.39 1.21
1
366
338 346 353
1.03 1.02 1.01
3.93 3.12 2.60
2
376
338 346 353
1.10 1.10 1.09
9.27 7.00 5.70
3
383
338 346 353
1.14 1.14 1.13
14.2 10.5 8.16
Fig. 2. Effect of the stirring rate on n-butyraldehyde conversion and acetal concentration (AC1 - empty, AC2-fulled) (3:1 G:B molar ratio, 353 K and 0.5 wt% catalyst).
temperature increased the overall reaction rate (see Fig. 3a). In the presence of catalyst and after 100 min of reaction time the conversion of n-butyraldehyde increased from 69% to 90% when the temperature was increased from 323 K to 353 K. In the absence of catalyst and at the highest temperature used, the conversion did not exceed 62% after 3 h of reaction time. It was also observed that over the range studied, a temperature increase had practically no influence on the final equilibrium conversion. This can be related to a near zero overall heat of reaction involved in this process (Fig. 3b). A similar behaviour in the overall heat of reaction was also observed in other studies of open-chain acetal synthesis reactions carried out in batch systems with solid catalysts and molar feed ratios alcohol:aldehyde higher than the stoichiometric ones [9,25,27]. In the open literature about the synthesis of open-chain acetals with heterogeneous catalysis, published results indicate that the reaction rate is strongly limited by thermodynamics. Therefore, alcohol:aldehyde molar ratios higher than the stoichiometric ones are required in order to achieve high conversions. Higher catalyst loadings than the ones used in this study were also reported in order to get high reaction rates [9,11,16,25,26]. For example, Agirre et al. studied the reaction between ethanol and n-butyraldehyde using a 0.5 wt% of Amberlyst 47 [16]. They obtained an equilibrium conversion of 48% at 313 K for a stoichiometric feed molar ratio (2:1 of ethanol to butyraldehyde). When this molar ratio was multiplied by a factor of two an equilibrium conversion of 72% was reported. The main difference in the reaction rate and in the existence or not of thermodynamic limitations between open chain acetal synthesis (using monoalcohols) and cyclic acetal synthesis (using polyalcohols) may be related to different reaction mechanisms. In the first case two alcohol molecules and one aldehyde molecule are required in order to get the acetal. The reaction of the hemiacetal, which is formed when one alcohol molecule reacts with one aldehyde molecule, with the second alcohol molecule, uses to be the rate limiting step and accounts for the larger thermodynamic limitations. In the second case, the synthesis of cyclic acetals, the polyalcohol (e.g. glycerol) reacts with the aldehyde giving the hemiacetal and finally this intermediate molecule rearranges itself through the reaction of two of its hydroxyl groups forming the cyclic acetal. According to the results that can be seen below, it seems that this second step in the formation of cyclic acetals is easier than the second step when open chain acetals are formed. Regarding the type of acetal formed (see Fig. 3b), the results indicate that theAC2 mixture of isomers (dioxolane) was formed more rapidly than AC1 (dioxane). When the concentration of AC2 in the reaction mixture was high enough, the isomerisation reaction converting AC2–AC1 acetals became more important. Agirre
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307
(a)
100%
Conversion
80%
60%
40% 323 K 338 K 346 K 353 K 353 K, without catalyst
20%
0% 0
90
180
270
360
450
540
Time (min) 353 K
(b)
346 K
338 K
323 K
353 K, without catalyst
5
Acetals (mol/L)
4
3
2
1
0 0
90
180
270
360
450
540
Time (min) Fig. 3. Effect of the temperature on n-butyraldehyde conversion (a) and acetal concentration (b) (AC1 - empty, and AC2-filled, +) (1:1 G:B molar ratio, 1000 rpm and 0.5 wt% of catalyst).
et al. observed a similar behaviour in the reaction of glycerol and acetaldehyde using Amberlyst 47 as catalyst [35]. Previously, Aksnes et al. (1965) made the same observations in their study of the equilibrium mixture of acetals obtained from the reaction of glycerol and acetaldehyde [34]. In this same reaction, Da Silva et al. studied the evolution of the different isomers in aging wines of Porto and Madeira [28]. They described a similar behaviour to that observed in this study for wines under two years of age, but in older wines, the proportion of 1,3-dioxane was greater than
24h 5
80%
4
60%
3
40%
2 Conversion
20%
1
4-methanol-2-propyl-1,3-dioxolane
Concentration (mol/L)
Conversion
7h 100%
5-hydroxy-2-propyl-1,3-dioxane 0%
0 0
360
720
1080
1440
1800
Time (min) Fig. 4. Evolution of the concentration of mixed acetals and n-butyraldehyde conversion to long reaction times (1:1 G:B molar ratio, 338 K, 1000 rpm and 0.5 wt% of catalyst).
303
the one of 1.3 dioxolane proving that these isomerisations take place at very slow rates (at room temperature in the absence of any added catalysts). In the study of the glycerol reaction with different alkylaldehydes (C4–C12), with dimethylsulphoxide (DMSO) as solvent and Amberlyst 15 as heterogeneous catalyst, Silva et al. obtained a higher selectivity towards the formation of 1,3-dioxolane [7]. However, in the case of the reaction with decanal, the ratio of dioxane to dioxolane was practically one, especially for long reaction times. This was attributed to the low conversion obtained and the higher stability of six-member ring acetals. In the reaction of glycerol and trioxane, as formaldehyde source, and using both homogeneous and heterogeneous catalysts, Ruiz et al. indicated that the isomerisation reaction proceeds toward the formation acetals of the five-member ring [30], while the ratio dioxane:dioxolane was less than unity for the reaction of glycerol, n-heptanal and trioxane (solvent) with homogeneous catalysts. Agirre et al. in the reaction of glycerol and formaldehyde using Amberlyst 47 as catalyst found that the ratio dioxane:dioxolane was initially less than unity, but it increased with reaction time [17]. In order to check the different observations reported in the literature about the evolution of the distribution of five/six-member acetals, an experiment of 30 h was performed. Under the experimental conditions used in this work, Fig. 4 shows that the dioxane:dioxolane ratio is 0.80 after 7 h of reaction and a value slightly higher than 1.02 after 24 h of reaction. If the reaction time had been longer, higher values of the dioxane:dioxolane ratio would have been measured. Thus, these results support the general mechanism shown in Fig. 1 (simplified diagram) for the acetalization reaction between glycerol and alkylaldehydes and, published in detail by Da Silva Ferreira et al. for the reaction of glycerol and acetaldehyde [28]. The reaction of formation of cyclic acetals proceeds preferentially through two parallel pathways formation of 1,3-dioxolane (reaction 2a, Fig. 1) and 1,3-dioxane formation (reaction 2b, Fig. 1), being the first faster than the second. In addition, an isomerisation reaction occurs towards the more stable acetal structure (six-member ring) through the formation of the corresponding hemiacetal. The results of this work and others reported in the literature suggest that the alkylaldehyde type used in the process, the operating conditions and the catalyst used may influence the isomerisation reaction rate and therefore, the ratio dioxane:dioxalane finally obtained is a function of time unless equilibrium is reached.
3.3. Effect of the G:B molar ratio The effect of the initial G:B molar ratio on the n-butyraldehyde conversion was studied at a temperature of 353 K, except for the case of the molar ratio of 0.2 where a temperature of 338 K was used to ensure that the reaction was carried out in liquid phase. (The bubble point of this mixture is estimated to be 351 K, see Table 1). Fig. 5 shows that when an excess of alcohol was used – molar ratio greater than the stoichiometric (1:1) – the reaction shifted towards the products formation increasing the conversion of n-butyraldehyde, as expected. Thus, for a reaction time of 100 min, the conversion of n-butyraldehyde increased from 88% to 98% when the initial G:B molar ratio increased from the stoichiometric ratio (1:1) to the highest molar ratio studied (3:1). The conversion of glycerol (only indicated in Fig. 5) was 100% after 40 min of reaction time when the G:B molar ratio is 0.2, whereas in the studied reaction time period, it varies between 93% and 98% when the G:B molar ratio is 0.5. Experiments showed that when glycerol is the limiting reagent and it is almost totally exhausted in the reaction medium, small amounts of another compound are detected. This compound was identified by GC/MS as the 2,4,6-tripropyl-1,3,5-trioxane and it is formed by cyclotrimerization of n-butyraldehyde:
304
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 Ratio* 0.2:1
Ratio 0.5:1
Ratio 1:1
Ratio 2:1
Ratio 3:1
100%
(a)
100%
80%
Conversion
Conversion
80%
60%
[93-98] % glycerol conversion
60%
40%
40% 20% ratio 3:1, with catalyst ratio 3:1, without catalyst
20%
ratio 1:1, with catalyst ratio 1:1, without catalyst
0%
100% glycerol conversion
0
90
180
90
180
270
360
450
540
Time (min) Fig. 5. Effect of molar ratio G:B on n-butyraldehyde conversion at 353 K (338 K to ratio molar G:B 0.2:1), 1000 rpm and 0.5 wt% of catalyst.
The formation of this trioxane molecule may explain the slight increase of the n-butyraldehyde conversion observed for reaction times exceeding 40 min and at a G:B molar ratio fed of 0.2. In the case of 0.5 feed molar ratio, the overall reaction system reached equilibrium for a glycerol conversion of 98%. However, for reaction times longer than 30 min, part of the butyraldehyde could be consumed due to the cyclotrimerization reaction. For higher reaction times, the peak abundance of trioxane was appreciable. When feed molar ratios greater than the stoichiometric ratio (G:B molar ratio 1:1) were used the trioxane peak was not identified or its contribution was negligible. Fig. 6a shows the n-butyraldehyde conversion when the reaction is carried out with or without solid catalyst for two different G:B molar feed ratios, 1:1 and 3:1, respectively. It can be observed that for the G:B 1:1 feed molar ratio (stoichiometric molar ratio) reaction progresses slowly. After 7 h n-butyraldehyde conversion was 66% versus 93% (approximately equilibrium conversion) obtained when the catalyst was present. However, in the absence of catalyst and when the reaction was carried out with excess of one reactant, in this case glycerol (molar ratio G:B 3:1), the equilibrium conversion was almost reached after 4 h of reaction. Note that in the scientific literature available no published data on non-catalytic acetalization reactions could be found. Regarding the acetal isomer formed, major differences are observed when the catalyst is present in the reaction medium (see Fig. 6b). The results shown were normalized to the initial concentration of aldehyde. The behaviour observed in the presence of catalyst is as described in section 3.2 for both G:B molar ratios. However, an excess of alcohol (molar ratio G:B 3:1) seems to promote the formation of 4-methanol-2-propyl-1,3-dioxolane (AC2), while the initial G:B molar ratio practically does not influence the rate of formation of 5-hydroxy-2-propyl-1,3-dioxane. In the absence of catalyst, the most affected reaction rate is the isomerisation one. As shown in Fig. 6b, the AC2 concentration increased quite rapidly but the formation of AC1, both from direct glycerol acetalization and from AC2 isomerisation took place quite slowly.
(b)
Acetal/fed butyraldehyde molar ratio
0
270
360
450
Time (min)
0%
ratio 3:1, with catalyst ratio 1:1, with catalyst
ratio 3:1, without catalyst ratio 1:1, without catalyst
1,0
0,8
0,6
0,4
0,2
0,0 0
90
180
270
360
450
Time (min) Fig. 6. Comparison between non-catalytic homogeneous reaction and heterogeneous catalytic reaction (0.5 wt% of catalyst): 353 K, 1000 rpm and G:B molar ratio 1:1 and 3:1.
3.4. Modelling of the kinetic data For the kinetic study of the overall acetalization reaction of glycerol and n-butyraldehyde (Eq. (1)) the data obtained using feed molar ratios from 1 to 3 at a temperature of 353 K were used in order to establish the order of reaction. The results obtained in the operating temperature range of 338–353 K allowed estimation of the kinetic constants of the rate law. In all the above mentioned operating conditions, the selectivity to the cyclic acetals mixture was 100%.
ð1Þ
A pseudo-homogeneous model reaction was used for interpreting the experimental data. The order of the reaction for each compound was determined from the experimental data varying the concentration. The best result was achieved for order of one for each compound according to the following equation:
d½Ac ¼ wk1 ½G½B wk2 ½Ac½W dt
ð2Þ
where [ ] is the concentration of compound ‘‘i’’ in mol L1; w the weight of catalyst per unit volume of reaction in gcat L1; and ki is the apparent rate constant velocity in L2 mol1 min1 g1 cat . A fourth-order Runge–Kutta integration method was used to solve the differential equation. Thus, minimizing the sum of squares of the difference between the experimental data and
305
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 Table 2 Kinetic constants at different temperatures and Arrhenius’ parameters estimated for glycerol and n-butyraldehyde reaction.
100%
k1 (L2 mol1 min1 g1 cat )
80%
338 346 353 Ea (kJ mol1) A (L2 mol1 min1 g1 cat ) r2
k2 (L2 mol1 min1 g1 cat )
03
Conversion
Temperature (K)
06
(1.42 ± 0.01) 10 (2.06 ± 0.36) 1003 (3.31 ± 0.43) 1003 55.6 5.33 1005
(4.18 ± 1.20) 10 (9.86 ± 0.28) 1006 (24.0 ± 4.75) 1006 115 2.67 1012
0.986
0.996
Run 1
Run 2
30
60
Run 3
Run 4
Run 5
120
300
420
60%
40%
20%
predicted concentration, the pseudo rate constants, k1 and k2 were estimated. Table 2 shows the apparent kinetic constants obtained as a function of temperature. The corresponding parameters of Arrhenius equation, activation energy (Ea) and pre-exponential factor (A), were determined by lineal regression of ln k versus the inverse of temperature. In order to establish the goodness of the estimation of the kinetic parameters (activation energy and preexponential factor), the apparent kinetic constants, and the overall concentration of acetals were estimated. Fig. 7 shows the agreement between experimental and estimated acetal concentration within the temperature range studied.
3.5. Recycling of the catalysts In order to study the stability of the resin A47 in the reaction of n-butyraldehyde and glycerol, the catalyst was reused five times. Each operating cycle was carried out at the temperature of 353 K and a G:B molar ratio of 1:1 and 120 min of reaction. The catalyst used was recovered by simple filtration, then washed with 150 mL of distilled water and, finally, dried at the laboratory temperature, thus being ready to be reloaded into the reactor. Fig. 8 shows the results of n-butyraldehyde conversion at different reaction times and for each reaction cycle. It is observed that there was no significant deactivation of the catalyst under the conditions studied. The highest fluctuations in the catalytic activity, although no significant (±1.9% standard deviation), were produced for the initial reaction times (30–60 min). This could be due to increased competition by the acid centres of the catalyst when the concentration of reactants in the reaction medium is high. Also, as expected, when the equilibrium conversion was reached, the variations between each run (standard deviation ranges between ±0.7% and ±1.0% for reaction times between 120 and 420 min) decreased. In order to study the possible loss of sulphonated groups, total sulphur was determined for the fresh catalyst and after five runs. The analysis was performed on a total sulphur analyzer TruSpec.
Experimental data (mol/L)
6
5
4
0%
Time (min) Fig. 8. Effect of re-using the catalyst on n-butyraldehyde conversion at different reaction times (1:1 G:B molar ratio, 353 K, 1000 rpm and 0.5 wt% of catalyst).
The fresh catalyst showed a total sulphur content of 12.29 ± 0.26 wt%, while the one for the used catalyst used was 11.39 ± 0.13 wt%. These results show a decrease in total sulphur content slightly above 7% after 600 min of reaction. However, this reduction of the total sulphur content did not seem to affect significantly the activity of the catalyst after five reaction batches under the operating conditions studied.
3.6. Effect of water in the feed mixture The presence of water, one of the acetalization reaction products, in the feed mixture may play a negative role. If water is initially present in the reaction system, the viscosity of the mixture decreases (see Table 3), and as a result both mixture mixing and transportation ends being easier. However the bubble point of the mixture is lowered, so that to carry out the reaction in liquid phase, the operating temperature must be decreased at atmospheric pressure. Therefore, in order to study the effect of initial water concentration on the acetalization process of glycerol and n-butyraldehyde, two mixtures of glycerol and water were prepared: (a) 90 wt% of glycerol and 10 wt% of water and (b) 80 wt% of glycerol and 20 wt% of water. Then, the required amount of nbutyraldehyde was added to obtain B:G molar ratios equal to 2:1, resulting in 15 wt% and 7 wt% of water concentration in the initial mixtures (see Table 3). This molar ratio was selected as an intermediate one within the range studied in this work. The mass composition and physical properties of the final mixtures initially fed to the reactor are shown in Table 3. The maximum percentage of water in the mixture fed was chosen based on the work reported by Agirre et al. [35] for the acetalization reaction of glycerol and acetaldehyde. In this work, the final weight percentage of water in the feed mixture was varied between 12% and 25% depending on the molar ratio alcohol:aldehyde employed. The results reported by them (acetaldehyde conversion of almost 100%) suggest
3
Table 3 Water effect on the physical properties of the feed mixture to the molar ratio G:B 2:1.
2 353 K 346 K 338 K
1
G (wt%) + W (wt%)
0 0
1
2
3
4
5
100 + 0 90 + 10 80 + 20 70 + 30
6
Estimate data (mol/L) Fig. 7. Total concentration of acetals. Agreement between experimental and estimated data obtained applying Eq. (1).
a
Mass composition (wt%)
Mixture physical properties
G
B
W
Tboiling (K)
q (g/cc)a
l (cPo)a
71.9 66.6 60.9 54.9
28.1 26.0 23.9 21.5
0.0 7.4 15.2 23.6
376 368 362 358
1.09 1.09 1.08 1.07
5.7 2.9 1.7 1.2
Physical properties at 353 K.
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 1,0
100%
0,8
80%
0,6
60%
0,4
40%
AC2 without water
0,2
Conversion
Acetal/fed butyraldehyde molar ratio
306
20%
AC2 (90wt% of G + 10wt% of W) AC2 (80wt% of G + 20wt% of W) 0,0
0% 0
90
180
270
360
450
540
Time (min) Fig. 9. Effect of the water presence in the mixture fed to the acetalization reaction system (60.9 wt% of G, 23.9 wt% B and 15.2 wt% W, 2:1 G:B molar ratio, 353 K, 1000 rpm and 0.5 wt% of catalyst).
that the presence of a certain water concentration does not significantly affect the overall rate of reaction. The activity tests were carried out at 353 K. For the selected operating conditions, the dynamic viscosity of the mixture is reduced between 49% and 70% from the viscosity measured when water is not present en the feed. Fig. 9 shows the molar ratio of acetal:fed butyraldehyde and the conversion of n-butyraldehyde as a function of the reaction time. It was observed that the introduction of 15 wt% water in the feed mixture caused a slight decrease in the final conversion of n-butyraldehyde, from 98% (without water) to 94% (with water) after 8 h reaction. However, the presence of water in the initial mixture fed seems to affect the isomerisation reaction rate (dioxolane (AC2) to dioxane (AC1)), although the differences observed between using a 7 wt% or 15 wt% of water concentrations were not important, particularly at high reaction times. Furthermore, the differences observed along the first 90 min of reaction are practically negligible. In the acetalization reaction of glycerol and acetone, Da Silva and Mota [36] studied the effect of water concentration in the feed. After one hour of reaction and when water was used, the conversion of glycerol decreased from 59% to 10%, depending on the initial water concentration and type of heterogeneous acid catalyst used (Amberlyst 15 or zeolite H-Beta). In the acetalization reaction of ethanol and acetaldehyde, Capeletti et al. also found greater differences in the conversion of ethanol when the solid catalyst (Amberlyst 15) was used dry (at 373 K) or pre-wet standard [11]. Based on the results obtained in this study and those mentioned above, it can be concluded that an initial incorporation of water in the feed mixture may have small effects on the reaction rate of glycerol and short-chain aldehydes, and contributes to improve the mixing and transport properties reducing the viscosity of the reaction mixture.
4. Conclusions In the acetalization reaction of glycerol and n-butyraldehyde, Amberlyst 47 was found to be highly active and stable after five consecutive cycles. Mixtures of cyclic acetals are the main products obtained when initial glycerol:butyraldehyde molar ratio fed is greater than the stoichiometric one. Moreover, water addition improves handling and transport characteristics of the reactant mixture without any significant effect on the process performance. The
studied reaction system can be described using a pseudo-homogeneous kinetic model. The reported results could be of interest for future developments dealing with process engineering for bioglycerol valorisation through the production of cyclic acetals. The great advantage of the reaction under study is that, contrary to other acetals, its synthesis presents small thermodynamic limitations and, in principle, the industrial production of these acetals for their use as biodiesel additives could be carried out in conventional reaction systems with a simple downstream separation train.
Acknowledgements This work was supported by funds from the Spanish Ministry of Science and Innovation (Ref. ENE2009-12743-C04-04), the Basque Government and the University of the Basque Country (UPV/EHU). The authors also gratefully acknowledge Rohm & Haas for kindly supplying Amberlyst catalysts.
References [1] B. Delfort, I. Durant, A. Jaecker, T. Lacome, X. Montagne, F. Paille, Diesel fuel compounds containing glycerol acetals, Patent US 6,890,364, 2005. [2] F. Frusteri, L. Spadaro, C. Beatrice, C. Guido, Oxygenated additives production for diesel engine emission improvement, Chem. Eng. Sci. 134 (2007) 239– 245. [3] G.A. Nikiforov, V.B. Volieva, G.G. Makarov, L.I. Trusov, Agent for increasing the octane number of gasoline automovile fuel, Patent EP 2 298 851, 2009. [4] E. García, M. Laca, E. Perez, A. Garrido, J. Peinado, New class of acetal derived from glycerin as a biodiesel fuel component, Energy and Fuel 22 (2008) 4274– 4280. [5] J.A. Melero, G. Vicente, G. Morales, M. Paniagua, J. Bustamante, Oxygenated compound derived from glycerol for biodiesel formulations: influence on EN 14214 quality parameters, Fuel 89 (2010) 2011–2018. [6] M. de Torres, G. Jiménez-Oses, J.A. Mayoral, E. Pires, M. de los Santos, Glycerol ketals: syntheys and profits in biodiesel blends, Fuel 94 (2012) 614–616. [7] P.H.R. Silva, V.L.C. Goncalves, C.J.A. Mota, Glycerol acetals as antifreezing additives for biodiesel, Bioresour. Technol. 101 (2010) 6229–6255. [8] J.P. Diebold, A review of the chemical and physical mechanism of the storage stability of fast pyrolysis bio-oils, Thermalchemie Inc., 1999. http:// home.rmi.net/~dieboljc. [9] S.P. Chopade, M.M. Sharma, Reaction of ethanol and formaldehyde: use of versatile cation-exchange resins as catalyst in batch reactors and reactive distillation column, React. Funct. Polym. 32 (1997) 53–64. [10] S.P. Chopade, M.M. Sharma, Acetalization of ethylene glycol with formaldehyde using cation-exchange resins as catalysts: batch versus reactive distillation, React. Funct. Polym. 34 (1997) 37–45.
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 [11] M.R. Capeletti, L. Balzano, G. de la Puente, M. Laborde, U. Sedran, Synthesis of acetal (1,1-diethoxyethane) from ethanol and acetaldehyde over acidic catalysts, Appl. Catal. A: Gen. 198 (2000) L1–L4. [12] A.D. Dhale, L.K. Myrant, S.P. Chopade, J.E. Jackson, D.J. Millera, Propylene glycol and ethylene glycol recovery from aqueous solution via reactive distillation, Chem. Eng. Sci. 59 (2004) 2881–2890. [13] G. Hillion, B. Delfort, I. Durand, Methods for producing biofuels, transforming triglycerides into at least two biofuel families: fatty acid monoesters and/or soluble glycerol acetals, Patent WO 2005/093015. [14] J. Deutsch, A. Martin, H. Lieske, Investigations on heterogeneously catalysed condensations of glycerol to cyclic acetals, J. Catal. 245 (2007) 428–435. [15] X. Hong, O. McGiveron, C.T. Lira, A. Orjuela, L. Peereboom, D.J. Miller, A reactive distillation process to produce 5-Hydroxy-2-methyl-1,3-dioxane from mixed glycerol acetal isomers, Org. Process Res. Dev. 16 (2012) 1141–1145. [16] I. Agirre, V.L. Barrio, B. Güemez, J.F. Cambra, P.L. Arias, Bioenergy II: the development of a reactive distillation process for the production of 1,1 diethoxy butane from bioalcohol: kinetic study and simulation model, Int. J. Chem. React. Eng. 8 (2010) A86. [17] I. Agirre, I. García, J. Requies, V.L. Barrio, M.B. Güemez, J.F. Cambra, P.L. Arias, Glycerol acetals, kinetic study of the reaction between glycerol and formaldehyde, Biomass Bioenergy 35 (2011) 3636–3642. [18] B. Thomas, V.G. Ramu, S. Gopinath, J. George, M. Kurian, G. Laurent, G.L. Drisko, S. Sugunan, Catalytic acetalization of carbonyl compounds over cation (Ce3+, Fe3+ and Al3+) exchanged montmorillonites and Ce3+-exchanged Y zeolitas, Appl. Clay Sci. 53 (2011) 227–235. [19] H. Serafim, I.M. Fonseca, A.M. Ramos, J. Vital, J.E. Castanheiro, Valorization of glycerol into fuel additives over zeolitas as catalysts, Chem. Eng. J. 178 (2011) 291–296. [20] S.B. Umbarkar, T.V. Kotbagi, A.V. Biradar, R. Pasricha, J. Chanale, M.K. Dongare, A.-S. Mamedec, C. Lancelot, E. Payen, Acetalization of glycerol using mesoporous MoO3/SiO2 solid acid catalyst, J. Mol. Catal. A: Chem. 310 (2009) 150–158. [21] N. Rahmat, A.Z. Abdullah, A.R. Mohamed, Recent progress on innovative and potential technologies for glycerol transformation into fuel additives: a critical review, Renew. Sustain. Energ. Rev. 14 (2010) 987–1000. [22] M. Ayoub, A.Z. Abdullah, Critical review on the current scenario and significance of crude glycerol resulting from biodiesel industry towards more sustainable renewable energy industry, Renew. Sustain. Energ. Rev. 16 (2012) 2671–2686.
307
[23] A.B. Leoneti, V. Aragão-Leoneti, S. Valle Walter Borges de Oliveira, Glycerol as a by-product of biodiesel production in Brazil: alternatives for the use of unrefined glycerol, Renew Energ 45 (2012) 138–145. [24] C. Perego, D. Bianchi, Biomass upgrading through acid–base catalysis, Chem. Eng. J. 161 (2010) 314–322. [25] S.M. Mahajani, A.K. Kolah, M.M. Sharma, Extractive reactions with cationic exchange resins as catalysts (acetalization of aldehydes with alcohols), React. Funct. Polym. 28 (1995) 29–38. [26] G.D. Yadav, A.A. Pujari, Kinetics of acetalization of perfumery aldehydes with alkanols over solid acid catalysts, Canadian J. Chem. Eng. 77 (1999) 489– 496. [27] V.M.T.M. Silva, A.E. Rodrigues, Synthesis of diethylacetal: thermodynamic and kinetic studies, Chem. Eng. Sci. 56 (2001) 1255–1263. [28] A.C. Da Silva Ferreira, J.-C. Barbe, A. Bertrand, Heterocyclic acetals from glycerol and acetaldehyde in port wines: evolution with aging, J. Agric. Food Chem. 50 (2002) 2560–2564. [29] B.R. Jermy, A. Pandurangan, Al–MCM–41 as an efficient heterogeneous catalyst in the acetalization of cyclohexanone with methanol, ethylene glycol an pentaerythritol, J. Mol. Catal.: A Chem. 256 (2006) 84–192. [30] V.R. Ruiz, A. Velty, L.L. Santos, A. Leyva-Pérez, M.J. Sabater, Gold catalysts and solid catalysts for biomass transformations: valorization of glycerol and glycerol-water mixtures through formation of cyclic acetals, J. Catal. 271 (2010) 351–357. [31] G.K. Gandi, V.M.T.M. Silva, A.E. Rodrigues, Acetaldehyde dimethylacetal synthesis with Smopex 101 fibres as catalyst/adsorbent, Chem. Eng. Sci. 62 (2007) 907–918. [32] A. C. Hasabnis and S. M Mahajani, Transacetalisation of glycerol with methylal by reactive distillation, Ind. Eng. Chemi. Res. 51 (2012) 13021–13036. [33] X. Hong, O. McGiveron, A.K. Kolah, Alvaro Orjuela, L. Peereboom, C.T. Lira, D.J. Miller, Reaction kinetics of glycerol acetal formation via transacetalization with 1,1-diethoxyethane, Chem. Eng. J. 222 (2013) 374–381. [34] G. Aksnes, P. Albrikten, P. Juvvik, Studies of cyclic acetal anketal isomers of glycerol, Acta Chem. Scand. 19 (1965) 920–930. [35] I. Agirre, V.L. Barrio, M.B. Güemez, A. J.F. Cambra, P.L. Arias, Cap 16: acetals as possible diesel additives, in: Economic Effects of biofuel production, Dos Santos B., M.A. Ed., Intech, 2011. [36] X.A. Da Silva, C.J.A. Mota, The influence of impurities on the acid-catalyzed reaction of glycerol with acetone, Biomass Energy 35 (2011) 3547–3551.
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Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Acetalization reaction between glycerol and n-butyraldehyde using an acidic ion exchange resin. Kinetic modelling M. Belen Güemez ⇑, Jesus Requies, Ion Agirre, Pedro L. Arias, V. Laura Barrio, Jose F. Cambra Department of Chemical and Environmental Engineering, Engineering School of the University of the Basque Country (UPV/EHU), c/Alameda Urquijo s/n, Bilbao 48013, Spain
h i g h l i g h t s Reached results are useful for engineering process design for a sustainable glycerol valorization. Mixtures of cyclic acetals are the main products obtained in acetalization reaction. Amberlysts 47 acidic ion exchange resin is highly active and stable in acetals production.
a r t i c l e
i n f o
Article history: Received 5 January 2013 Received in revised form 25 April 2013 Accepted 29 April 2013 Available online 7 May 2013 Keywords: Cyclic acetals Glycerol n-Butyraldehyde Acidic ionic exchange resin Kinetic parameters
a b s t r a c t The acetalization reaction between glycerol and n-butyraldehyde using Amberlyst 47, an acidic ion exchange resin catalyst, was studied. These acetals can be obtained from renewable sources and seem to be good candidates for different applications such as oxygenated diesel additives. Amberlyst 47 acidic ion exchange showed good activity and stability after five consecutive cycles of reuse. Therefore, 100% of selectivity towards the formation of acetals and butyraldehyde conversions between 92% and 98% were obtained for different molar feed ratios of glycerol:aldehyde. For glycerol:aldehyde molar ratios lower than the stoichiometric one, 2,4,6-tripropyl-1,2,3-trioxane is also detected as product when glycerol is almost totally consumed. Moreover, a pseudo-homogeneous kinetic model able to explain the reaction mechanism was adjusted and the corresponding overall reaction order was determined. The addition of around 15 wt% of water in the feed produces only a slight decrease in the butyraldehyde conversion, and it improves the mixing and transport properties of the reaction mixture. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Acetals have their main application in the chemical industry and fine chemicals – cosmetics, pharmaceutical – , as intermediates or final compounds. However, as in recent years governments have increased restrictions on environmental pollution, the use of some types of acetals and ketals, derived from biomass, as potential oxygenated additives to fuels is being researched. For example, nowadays acetals can be used to reduce particulate emissions [1,2], to increase octane number in gasoline [3], to improve the properties of biodiesel (viscosity, oxidation stability, flash point, etc.) [4–7], or as antifreezing agents of biodiesel [6]. Acetals are obtained typically by the reaction of carbonyl compounds (aldehydes, ketones) and alcohols with or without solvent and in the presence of strong mineral acids as catalysts like H2SO4, HF, HCl, H3PO4 or p-toluenesulphonic acids [2,8–11]. These catalysts also cause corrosion and environmental problems and make the separation and purification process of the products more difficult. These ⇑ Corresponding author. Tel.: +34 946014273; fax: +34 946014179. E-mail address: [email protected] (M.B. Güemez). 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.04.107
disadvantages could be solved using solid catalysts, and in this sense, efforts are being made to develop adequate solid acids. In the literature several types of heterogeneous acid catalysts like ion exchange resins [7,9–17], zeolites [11,18,19], montmorillonites [11,14,18] and MoO3/SiO2 [20] are reported to be used for acetalization reactions. Capeletti et al. [11] concluded that Amberlyst ion exchange resins are the best ones. The process for acetals synthesis could be considered a sustainable process if raw materials from renewable sources are used, as bio-alcohols and aldehydes derived from bio-alcohols. Not all acetals can be used as additives for diesel fuels. Some of them show low flash points and are not useful as additives [2,17]. Those acetals derived from polyols and short chain aldehydes, such as acetaldehyde and butyraldehyde, present flash points close to the diesel specifications, while those derived from ethanol, require long chain aldehydes to produce acetals with an acceptable flash point. Among bioalcohols, glycerol, the main by-product of biodiesel production (transesterification of vegetable oils or animal fats) is the alcohol that have gained more attention in recent years [21– 24] due to its increasing production, associated to the increase of biodiesel world production. Therefore, to valorise its potential uses,
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and to improve the economic balance of the biodiesel production process, new applications are being developed [21,23], including the use of its acetals as diesel fuel additives. Most of the studies reported in the literature for acetalization reactions are focused on analysing and comparing the activity of the solid catalysts. Moreover, some authors also explained the possible reaction mechanism [9,10,25–30], but a few proposed a reaction kinetic model [9,10,12,16,17,26–29,31–33]. In the case of the synthesis of cyclic acetals obtained from the reaction between a polyol and an aldehyde or ketone, Sharma and Chopade [10] described the mechanism of acetalization of ethylene glycol and formaldehyde as a two-step reversible process. The first stage involves the formation of an hemiacetal, an intermediate compound formed by the addition of an alcohol molecule to the carbonyl group, and in the second stage, the hemiacetal hydroxyl group reacts with another OH group to give the 1,3-dioxolane, releasing a water molecule. For the reaction of glycerol and acetaldehyde, Da Silva Ferreira et al. [28] showed in more detail the stages of possible re-organization of the hemiacetal that lead to the formation of mixed cyclic acetals. Fig. 1 shows the reaction mechanism proposed by Sharma and Chopade [10] adapted to the reaction of glycerol and alkyl-aldehydes. In this case, depending on which hemiacetal OH reacts to form the acetal, 4-hydroxy-2-alkyl-1,3-dioxolane (cis and trans) or 5-hydroxy-2alkyl-1,3-dioxane (cis and trans) are formed. The four isomers tend towards equilibrium between them through reorganization of the corresponding hemiacetal structure [28]. In this work, the acetalization reaction of n-butyraldehyde and glycerol has been studied in a batch reaction system. The ion exchange resin Amberlyst 47 (A47) has been used as heterogeneous catalyst since its mechanical resistance makes this resin, a priori, the most suitable one for its use in slurry reactors or in structured packings. Moreover, Agirre et al. [16] compared the activity of three Amberlyst ion exchange resins (A15wet, A47 and A35wet) obtaining similar results in activity for the acetalization reaction of ethanol and n-butyraldehyde. The experimental data have been extensively treated in order to propose a pseudo-homogeneous kinetic model for the overall reaction. Kinetic parameters have also been estimated. Catalyst reuse and the effect of water in the feed have also been studied.
2.1. Materials and analysis Glycerol (G) (Panreac, 99 wt%) and n-butyraldehyde (B) (Merck, 99 wt%), both of quality for synthesis, were used as reagents. Amberlyst 47 (A47) catalyst was kindly supplied by Rohm & Haas. Both, reactants, glycerol and n-butyraldehyde, and reaction products, 5-hydroxy-2-propyl-1,3-dioxane (cis and trans isomers) (AC1) and 4-methanol-2-propyl-1,3-dioxolane (cis and trans isomers) (AC2) were analyzed by gas chromatography (Agilent 6890 N) using a flame ionization detector (FID) and the water (W) produced was analyzed using a thermal conductivity detector (TCD). An Agilent DB-1 (60 m 0.53 mm 5 lm) capillary column was used with helium as the carrier gas. The elution order of these organic products reported in the literature is [15,29,34]: cis-5-hydroxy-2-alkil-1,3-dioxane, cis-4methanol-2-alkil-1,3-dioxolane, trans-4-methanol-2-alkil-1,3dioxolane and trans-5-hydroxy-2-alkil-1,3-dioxane. In this study, reaction products were identified analyzing their mass spectra obtained by GC/MS and verifying that their MS-spectra included the expected molecular fragments. 2.2. Activity test The reaction tests were carried out in a 1 L glass batch stirred tank reactor (BSTR). The reaction temperature was controlled by an external thermostat (Lauda RE 304). This thermostat contains a thermocouple placed inside the reacting mixture that allows controlling the reaction temperature with an accuracy of ±0.05 K. The reactor is also connected to a condenser in order to condense and reflux all the vapours keeping the reaction volume approximately constant. In a typical experiment, the reactor was first charged with 0.5 L of the reaction mixture, then the system was closed, the agitation speed was fixed and, after the system stabilization at the desired temperature, the catalyst was added. This moment was considered as the initial time for the reaction. Before adding the catalyst sample, its moisture was modified waiting until it reached equilibrium with the room one. Therefore the weight could be controlled. All
OH
O
OH HO
2. Materials and methods
R
OH
C
HO
H
OH
O R
alkyl aldehyde
glycerol
1,2-propanediol-3-(1-hydroxy-alkoxy) (hemiacetal) H2C
OH
OH HO
OH
O
+
O
O R
R
(1)
H2O
(2a)
H
4-hydroxymethyl-2-alkyl-1,3-dioxolane OH OH HO
OH
O R
+
R
H2O
(2b)
O
O H
5-hydroxy-2-alkyl-1,3-dioxane Fig. 1. Generalized reaction mechanism of glycerol and alkyl–adehyde adapted from proposed by Chopade and Sharma [10].
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 100%
3,0 2,5
80%
2,0 60% 1,5 40% 1,0
Conversion
experiments were carried out using 0.5 wt% of A47 with respect to total weight of reactants feed. Moreover, some glass wool was placed in the sampling output in order to keep the catalysts amount constant in the reactor. At specific time intervals, small samples (1.5 mL of volume and a maximum of 15 samples by run) were withdrawn in order to analyze them by GC. To establish the temperature range of operation, an analysis of the physical properties of fed mixture using the UNIFAC-LL thermodynamic method was carried out. Table 1 shows the mixture boiling temperature for different G:B (glycerol to n-butyraldehyde) molar ratios and the mixture viscosity at those temperatures.
Acetals (mol/L)
302
20%
0,5 150 rpm
500 rpm
1000 rpm
180
270
360
1250 rpm
0,0 0
90
450
0% 540
Time (min)
3. Results and discussion In order to study the catalytic activity of the ion exchange resin Amberlyst 47 in the acetalization reaction of glycerol and n-butyraldehyde, different parameters were studied: agitation speed, reaction temperature, G:B molar ratio fed, presence of water in the feed mixture and catalyst reuse. When the G:B molar ratio used was greater than 1, activity tests showed that the products obtained were just a mixture of cyclic acetals and water. 3.1. Effect of stirring speed High temperatures, low stirring speeds and viscous liquid mixtures are the most unfavorable conditions in which resistance to external mass transport may occur. Therefore, the effect of the stirring rate on n-butyraldehyde conversion and acetal concentrations was studied within a wide range of agitation speeds, 150 rpm (minimum speed that the available stirring system is able to provide) and 1250 rpm, at 353 K and 3:1 G:B molar ratio. The results are shown in Fig. 2. No external mass transfer limitations were observed even at the lowest stirring speed, (150 rpm). However, it was observed that initial vigorous stirring was necessary to achieve a homogeneous mixture of the reagents due to difficult mixing between glycerol and n-butyraldehyde. Because of this reason, the rest of the experiments were carried out at 1000 rpm. 3.2. Effect of reaction temperature The temperature effect on the reaction of glycerol and n-butyraldehyde was carried out in the temperature range of 323–353 K using the stoichiometric feed ratio. As expected, an increase in
Table 1 Physical properties of the mixture fed at the operating conditions used for the kinetic study (the physical properties were estimated using the UNIFAC-LL thermodynamic method). Molar ratio G:B
Boiling point (K)
Temperature (K)
Density (g/cc)
Viscosity (cPo)
0.2
351
338 346 353
0.87 0.86 –
0.70 0.62 –
0.5
358
338 346 353
0.95 0.94 0.93
1.66 1.39 1.21
1
366
338 346 353
1.03 1.02 1.01
3.93 3.12 2.60
2
376
338 346 353
1.10 1.10 1.09
9.27 7.00 5.70
3
383
338 346 353
1.14 1.14 1.13
14.2 10.5 8.16
Fig. 2. Effect of the stirring rate on n-butyraldehyde conversion and acetal concentration (AC1 - empty, AC2-fulled) (3:1 G:B molar ratio, 353 K and 0.5 wt% catalyst).
temperature increased the overall reaction rate (see Fig. 3a). In the presence of catalyst and after 100 min of reaction time the conversion of n-butyraldehyde increased from 69% to 90% when the temperature was increased from 323 K to 353 K. In the absence of catalyst and at the highest temperature used, the conversion did not exceed 62% after 3 h of reaction time. It was also observed that over the range studied, a temperature increase had practically no influence on the final equilibrium conversion. This can be related to a near zero overall heat of reaction involved in this process (Fig. 3b). A similar behaviour in the overall heat of reaction was also observed in other studies of open-chain acetal synthesis reactions carried out in batch systems with solid catalysts and molar feed ratios alcohol:aldehyde higher than the stoichiometric ones [9,25,27]. In the open literature about the synthesis of open-chain acetals with heterogeneous catalysis, published results indicate that the reaction rate is strongly limited by thermodynamics. Therefore, alcohol:aldehyde molar ratios higher than the stoichiometric ones are required in order to achieve high conversions. Higher catalyst loadings than the ones used in this study were also reported in order to get high reaction rates [9,11,16,25,26]. For example, Agirre et al. studied the reaction between ethanol and n-butyraldehyde using a 0.5 wt% of Amberlyst 47 [16]. They obtained an equilibrium conversion of 48% at 313 K for a stoichiometric feed molar ratio (2:1 of ethanol to butyraldehyde). When this molar ratio was multiplied by a factor of two an equilibrium conversion of 72% was reported. The main difference in the reaction rate and in the existence or not of thermodynamic limitations between open chain acetal synthesis (using monoalcohols) and cyclic acetal synthesis (using polyalcohols) may be related to different reaction mechanisms. In the first case two alcohol molecules and one aldehyde molecule are required in order to get the acetal. The reaction of the hemiacetal, which is formed when one alcohol molecule reacts with one aldehyde molecule, with the second alcohol molecule, uses to be the rate limiting step and accounts for the larger thermodynamic limitations. In the second case, the synthesis of cyclic acetals, the polyalcohol (e.g. glycerol) reacts with the aldehyde giving the hemiacetal and finally this intermediate molecule rearranges itself through the reaction of two of its hydroxyl groups forming the cyclic acetal. According to the results that can be seen below, it seems that this second step in the formation of cyclic acetals is easier than the second step when open chain acetals are formed. Regarding the type of acetal formed (see Fig. 3b), the results indicate that theAC2 mixture of isomers (dioxolane) was formed more rapidly than AC1 (dioxane). When the concentration of AC2 in the reaction mixture was high enough, the isomerisation reaction converting AC2–AC1 acetals became more important. Agirre
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(a)
100%
Conversion
80%
60%
40% 323 K 338 K 346 K 353 K 353 K, without catalyst
20%
0% 0
90
180
270
360
450
540
Time (min) 353 K
(b)
346 K
338 K
323 K
353 K, without catalyst
5
Acetals (mol/L)
4
3
2
1
0 0
90
180
270
360
450
540
Time (min) Fig. 3. Effect of the temperature on n-butyraldehyde conversion (a) and acetal concentration (b) (AC1 - empty, and AC2-filled, +) (1:1 G:B molar ratio, 1000 rpm and 0.5 wt% of catalyst).
et al. observed a similar behaviour in the reaction of glycerol and acetaldehyde using Amberlyst 47 as catalyst [35]. Previously, Aksnes et al. (1965) made the same observations in their study of the equilibrium mixture of acetals obtained from the reaction of glycerol and acetaldehyde [34]. In this same reaction, Da Silva et al. studied the evolution of the different isomers in aging wines of Porto and Madeira [28]. They described a similar behaviour to that observed in this study for wines under two years of age, but in older wines, the proportion of 1,3-dioxane was greater than
24h 5
80%
4
60%
3
40%
2 Conversion
20%
1
4-methanol-2-propyl-1,3-dioxolane
Concentration (mol/L)
Conversion
7h 100%
5-hydroxy-2-propyl-1,3-dioxane 0%
0 0
360
720
1080
1440
1800
Time (min) Fig. 4. Evolution of the concentration of mixed acetals and n-butyraldehyde conversion to long reaction times (1:1 G:B molar ratio, 338 K, 1000 rpm and 0.5 wt% of catalyst).
303
the one of 1.3 dioxolane proving that these isomerisations take place at very slow rates (at room temperature in the absence of any added catalysts). In the study of the glycerol reaction with different alkylaldehydes (C4–C12), with dimethylsulphoxide (DMSO) as solvent and Amberlyst 15 as heterogeneous catalyst, Silva et al. obtained a higher selectivity towards the formation of 1,3-dioxolane [7]. However, in the case of the reaction with decanal, the ratio of dioxane to dioxolane was practically one, especially for long reaction times. This was attributed to the low conversion obtained and the higher stability of six-member ring acetals. In the reaction of glycerol and trioxane, as formaldehyde source, and using both homogeneous and heterogeneous catalysts, Ruiz et al. indicated that the isomerisation reaction proceeds toward the formation acetals of the five-member ring [30], while the ratio dioxane:dioxolane was less than unity for the reaction of glycerol, n-heptanal and trioxane (solvent) with homogeneous catalysts. Agirre et al. in the reaction of glycerol and formaldehyde using Amberlyst 47 as catalyst found that the ratio dioxane:dioxolane was initially less than unity, but it increased with reaction time [17]. In order to check the different observations reported in the literature about the evolution of the distribution of five/six-member acetals, an experiment of 30 h was performed. Under the experimental conditions used in this work, Fig. 4 shows that the dioxane:dioxolane ratio is 0.80 after 7 h of reaction and a value slightly higher than 1.02 after 24 h of reaction. If the reaction time had been longer, higher values of the dioxane:dioxolane ratio would have been measured. Thus, these results support the general mechanism shown in Fig. 1 (simplified diagram) for the acetalization reaction between glycerol and alkylaldehydes and, published in detail by Da Silva Ferreira et al. for the reaction of glycerol and acetaldehyde [28]. The reaction of formation of cyclic acetals proceeds preferentially through two parallel pathways formation of 1,3-dioxolane (reaction 2a, Fig. 1) and 1,3-dioxane formation (reaction 2b, Fig. 1), being the first faster than the second. In addition, an isomerisation reaction occurs towards the more stable acetal structure (six-member ring) through the formation of the corresponding hemiacetal. The results of this work and others reported in the literature suggest that the alkylaldehyde type used in the process, the operating conditions and the catalyst used may influence the isomerisation reaction rate and therefore, the ratio dioxane:dioxalane finally obtained is a function of time unless equilibrium is reached.
3.3. Effect of the G:B molar ratio The effect of the initial G:B molar ratio on the n-butyraldehyde conversion was studied at a temperature of 353 K, except for the case of the molar ratio of 0.2 where a temperature of 338 K was used to ensure that the reaction was carried out in liquid phase. (The bubble point of this mixture is estimated to be 351 K, see Table 1). Fig. 5 shows that when an excess of alcohol was used – molar ratio greater than the stoichiometric (1:1) – the reaction shifted towards the products formation increasing the conversion of n-butyraldehyde, as expected. Thus, for a reaction time of 100 min, the conversion of n-butyraldehyde increased from 88% to 98% when the initial G:B molar ratio increased from the stoichiometric ratio (1:1) to the highest molar ratio studied (3:1). The conversion of glycerol (only indicated in Fig. 5) was 100% after 40 min of reaction time when the G:B molar ratio is 0.2, whereas in the studied reaction time period, it varies between 93% and 98% when the G:B molar ratio is 0.5. Experiments showed that when glycerol is the limiting reagent and it is almost totally exhausted in the reaction medium, small amounts of another compound are detected. This compound was identified by GC/MS as the 2,4,6-tripropyl-1,3,5-trioxane and it is formed by cyclotrimerization of n-butyraldehyde:
304
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 Ratio* 0.2:1
Ratio 0.5:1
Ratio 1:1
Ratio 2:1
Ratio 3:1
100%
(a)
100%
80%
Conversion
Conversion
80%
60%
[93-98] % glycerol conversion
60%
40%
40% 20% ratio 3:1, with catalyst ratio 3:1, without catalyst
20%
ratio 1:1, with catalyst ratio 1:1, without catalyst
0%
100% glycerol conversion
0
90
180
90
180
270
360
450
540
Time (min) Fig. 5. Effect of molar ratio G:B on n-butyraldehyde conversion at 353 K (338 K to ratio molar G:B 0.2:1), 1000 rpm and 0.5 wt% of catalyst.
The formation of this trioxane molecule may explain the slight increase of the n-butyraldehyde conversion observed for reaction times exceeding 40 min and at a G:B molar ratio fed of 0.2. In the case of 0.5 feed molar ratio, the overall reaction system reached equilibrium for a glycerol conversion of 98%. However, for reaction times longer than 30 min, part of the butyraldehyde could be consumed due to the cyclotrimerization reaction. For higher reaction times, the peak abundance of trioxane was appreciable. When feed molar ratios greater than the stoichiometric ratio (G:B molar ratio 1:1) were used the trioxane peak was not identified or its contribution was negligible. Fig. 6a shows the n-butyraldehyde conversion when the reaction is carried out with or without solid catalyst for two different G:B molar feed ratios, 1:1 and 3:1, respectively. It can be observed that for the G:B 1:1 feed molar ratio (stoichiometric molar ratio) reaction progresses slowly. After 7 h n-butyraldehyde conversion was 66% versus 93% (approximately equilibrium conversion) obtained when the catalyst was present. However, in the absence of catalyst and when the reaction was carried out with excess of one reactant, in this case glycerol (molar ratio G:B 3:1), the equilibrium conversion was almost reached after 4 h of reaction. Note that in the scientific literature available no published data on non-catalytic acetalization reactions could be found. Regarding the acetal isomer formed, major differences are observed when the catalyst is present in the reaction medium (see Fig. 6b). The results shown were normalized to the initial concentration of aldehyde. The behaviour observed in the presence of catalyst is as described in section 3.2 for both G:B molar ratios. However, an excess of alcohol (molar ratio G:B 3:1) seems to promote the formation of 4-methanol-2-propyl-1,3-dioxolane (AC2), while the initial G:B molar ratio practically does not influence the rate of formation of 5-hydroxy-2-propyl-1,3-dioxane. In the absence of catalyst, the most affected reaction rate is the isomerisation one. As shown in Fig. 6b, the AC2 concentration increased quite rapidly but the formation of AC1, both from direct glycerol acetalization and from AC2 isomerisation took place quite slowly.
(b)
Acetal/fed butyraldehyde molar ratio
0
270
360
450
Time (min)
0%
ratio 3:1, with catalyst ratio 1:1, with catalyst
ratio 3:1, without catalyst ratio 1:1, without catalyst
1,0
0,8
0,6
0,4
0,2
0,0 0
90
180
270
360
450
Time (min) Fig. 6. Comparison between non-catalytic homogeneous reaction and heterogeneous catalytic reaction (0.5 wt% of catalyst): 353 K, 1000 rpm and G:B molar ratio 1:1 and 3:1.
3.4. Modelling of the kinetic data For the kinetic study of the overall acetalization reaction of glycerol and n-butyraldehyde (Eq. (1)) the data obtained using feed molar ratios from 1 to 3 at a temperature of 353 K were used in order to establish the order of reaction. The results obtained in the operating temperature range of 338–353 K allowed estimation of the kinetic constants of the rate law. In all the above mentioned operating conditions, the selectivity to the cyclic acetals mixture was 100%.
ð1Þ
A pseudo-homogeneous model reaction was used for interpreting the experimental data. The order of the reaction for each compound was determined from the experimental data varying the concentration. The best result was achieved for order of one for each compound according to the following equation:
d½Ac ¼ wk1 ½G½B wk2 ½Ac½W dt
ð2Þ
where [ ] is the concentration of compound ‘‘i’’ in mol L1; w the weight of catalyst per unit volume of reaction in gcat L1; and ki is the apparent rate constant velocity in L2 mol1 min1 g1 cat . A fourth-order Runge–Kutta integration method was used to solve the differential equation. Thus, minimizing the sum of squares of the difference between the experimental data and
305
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 Table 2 Kinetic constants at different temperatures and Arrhenius’ parameters estimated for glycerol and n-butyraldehyde reaction.
100%
k1 (L2 mol1 min1 g1 cat )
80%
338 346 353 Ea (kJ mol1) A (L2 mol1 min1 g1 cat ) r2
k2 (L2 mol1 min1 g1 cat )
03
Conversion
Temperature (K)
06
(1.42 ± 0.01) 10 (2.06 ± 0.36) 1003 (3.31 ± 0.43) 1003 55.6 5.33 1005
(4.18 ± 1.20) 10 (9.86 ± 0.28) 1006 (24.0 ± 4.75) 1006 115 2.67 1012
0.986
0.996
Run 1
Run 2
30
60
Run 3
Run 4
Run 5
120
300
420
60%
40%
20%
predicted concentration, the pseudo rate constants, k1 and k2 were estimated. Table 2 shows the apparent kinetic constants obtained as a function of temperature. The corresponding parameters of Arrhenius equation, activation energy (Ea) and pre-exponential factor (A), were determined by lineal regression of ln k versus the inverse of temperature. In order to establish the goodness of the estimation of the kinetic parameters (activation energy and preexponential factor), the apparent kinetic constants, and the overall concentration of acetals were estimated. Fig. 7 shows the agreement between experimental and estimated acetal concentration within the temperature range studied.
3.5. Recycling of the catalysts In order to study the stability of the resin A47 in the reaction of n-butyraldehyde and glycerol, the catalyst was reused five times. Each operating cycle was carried out at the temperature of 353 K and a G:B molar ratio of 1:1 and 120 min of reaction. The catalyst used was recovered by simple filtration, then washed with 150 mL of distilled water and, finally, dried at the laboratory temperature, thus being ready to be reloaded into the reactor. Fig. 8 shows the results of n-butyraldehyde conversion at different reaction times and for each reaction cycle. It is observed that there was no significant deactivation of the catalyst under the conditions studied. The highest fluctuations in the catalytic activity, although no significant (±1.9% standard deviation), were produced for the initial reaction times (30–60 min). This could be due to increased competition by the acid centres of the catalyst when the concentration of reactants in the reaction medium is high. Also, as expected, when the equilibrium conversion was reached, the variations between each run (standard deviation ranges between ±0.7% and ±1.0% for reaction times between 120 and 420 min) decreased. In order to study the possible loss of sulphonated groups, total sulphur was determined for the fresh catalyst and after five runs. The analysis was performed on a total sulphur analyzer TruSpec.
Experimental data (mol/L)
6
5
4
0%
Time (min) Fig. 8. Effect of re-using the catalyst on n-butyraldehyde conversion at different reaction times (1:1 G:B molar ratio, 353 K, 1000 rpm and 0.5 wt% of catalyst).
The fresh catalyst showed a total sulphur content of 12.29 ± 0.26 wt%, while the one for the used catalyst used was 11.39 ± 0.13 wt%. These results show a decrease in total sulphur content slightly above 7% after 600 min of reaction. However, this reduction of the total sulphur content did not seem to affect significantly the activity of the catalyst after five reaction batches under the operating conditions studied.
3.6. Effect of water in the feed mixture The presence of water, one of the acetalization reaction products, in the feed mixture may play a negative role. If water is initially present in the reaction system, the viscosity of the mixture decreases (see Table 3), and as a result both mixture mixing and transportation ends being easier. However the bubble point of the mixture is lowered, so that to carry out the reaction in liquid phase, the operating temperature must be decreased at atmospheric pressure. Therefore, in order to study the effect of initial water concentration on the acetalization process of glycerol and n-butyraldehyde, two mixtures of glycerol and water were prepared: (a) 90 wt% of glycerol and 10 wt% of water and (b) 80 wt% of glycerol and 20 wt% of water. Then, the required amount of nbutyraldehyde was added to obtain B:G molar ratios equal to 2:1, resulting in 15 wt% and 7 wt% of water concentration in the initial mixtures (see Table 3). This molar ratio was selected as an intermediate one within the range studied in this work. The mass composition and physical properties of the final mixtures initially fed to the reactor are shown in Table 3. The maximum percentage of water in the mixture fed was chosen based on the work reported by Agirre et al. [35] for the acetalization reaction of glycerol and acetaldehyde. In this work, the final weight percentage of water in the feed mixture was varied between 12% and 25% depending on the molar ratio alcohol:aldehyde employed. The results reported by them (acetaldehyde conversion of almost 100%) suggest
3
Table 3 Water effect on the physical properties of the feed mixture to the molar ratio G:B 2:1.
2 353 K 346 K 338 K
1
G (wt%) + W (wt%)
0 0
1
2
3
4
5
100 + 0 90 + 10 80 + 20 70 + 30
6
Estimate data (mol/L) Fig. 7. Total concentration of acetals. Agreement between experimental and estimated data obtained applying Eq. (1).
a
Mass composition (wt%)
Mixture physical properties
G
B
W
Tboiling (K)
q (g/cc)a
l (cPo)a
71.9 66.6 60.9 54.9
28.1 26.0 23.9 21.5
0.0 7.4 15.2 23.6
376 368 362 358
1.09 1.09 1.08 1.07
5.7 2.9 1.7 1.2
Physical properties at 353 K.
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 1,0
100%
0,8
80%
0,6
60%
0,4
40%
AC2 without water
0,2
Conversion
Acetal/fed butyraldehyde molar ratio
306
20%
AC2 (90wt% of G + 10wt% of W) AC2 (80wt% of G + 20wt% of W) 0,0
0% 0
90
180
270
360
450
540
Time (min) Fig. 9. Effect of the water presence in the mixture fed to the acetalization reaction system (60.9 wt% of G, 23.9 wt% B and 15.2 wt% W, 2:1 G:B molar ratio, 353 K, 1000 rpm and 0.5 wt% of catalyst).
that the presence of a certain water concentration does not significantly affect the overall rate of reaction. The activity tests were carried out at 353 K. For the selected operating conditions, the dynamic viscosity of the mixture is reduced between 49% and 70% from the viscosity measured when water is not present en the feed. Fig. 9 shows the molar ratio of acetal:fed butyraldehyde and the conversion of n-butyraldehyde as a function of the reaction time. It was observed that the introduction of 15 wt% water in the feed mixture caused a slight decrease in the final conversion of n-butyraldehyde, from 98% (without water) to 94% (with water) after 8 h reaction. However, the presence of water in the initial mixture fed seems to affect the isomerisation reaction rate (dioxolane (AC2) to dioxane (AC1)), although the differences observed between using a 7 wt% or 15 wt% of water concentrations were not important, particularly at high reaction times. Furthermore, the differences observed along the first 90 min of reaction are practically negligible. In the acetalization reaction of glycerol and acetone, Da Silva and Mota [36] studied the effect of water concentration in the feed. After one hour of reaction and when water was used, the conversion of glycerol decreased from 59% to 10%, depending on the initial water concentration and type of heterogeneous acid catalyst used (Amberlyst 15 or zeolite H-Beta). In the acetalization reaction of ethanol and acetaldehyde, Capeletti et al. also found greater differences in the conversion of ethanol when the solid catalyst (Amberlyst 15) was used dry (at 373 K) or pre-wet standard [11]. Based on the results obtained in this study and those mentioned above, it can be concluded that an initial incorporation of water in the feed mixture may have small effects on the reaction rate of glycerol and short-chain aldehydes, and contributes to improve the mixing and transport properties reducing the viscosity of the reaction mixture.
4. Conclusions In the acetalization reaction of glycerol and n-butyraldehyde, Amberlyst 47 was found to be highly active and stable after five consecutive cycles. Mixtures of cyclic acetals are the main products obtained when initial glycerol:butyraldehyde molar ratio fed is greater than the stoichiometric one. Moreover, water addition improves handling and transport characteristics of the reactant mixture without any significant effect on the process performance. The
studied reaction system can be described using a pseudo-homogeneous kinetic model. The reported results could be of interest for future developments dealing with process engineering for bioglycerol valorisation through the production of cyclic acetals. The great advantage of the reaction under study is that, contrary to other acetals, its synthesis presents small thermodynamic limitations and, in principle, the industrial production of these acetals for their use as biodiesel additives could be carried out in conventional reaction systems with a simple downstream separation train.
Acknowledgements This work was supported by funds from the Spanish Ministry of Science and Innovation (Ref. ENE2009-12743-C04-04), the Basque Government and the University of the Basque Country (UPV/EHU). The authors also gratefully acknowledge Rohm & Haas for kindly supplying Amberlyst catalysts.
References [1] B. Delfort, I. Durant, A. Jaecker, T. Lacome, X. Montagne, F. Paille, Diesel fuel compounds containing glycerol acetals, Patent US 6,890,364, 2005. [2] F. Frusteri, L. Spadaro, C. Beatrice, C. Guido, Oxygenated additives production for diesel engine emission improvement, Chem. Eng. Sci. 134 (2007) 239– 245. [3] G.A. Nikiforov, V.B. Volieva, G.G. Makarov, L.I. Trusov, Agent for increasing the octane number of gasoline automovile fuel, Patent EP 2 298 851, 2009. [4] E. García, M. Laca, E. Perez, A. Garrido, J. Peinado, New class of acetal derived from glycerin as a biodiesel fuel component, Energy and Fuel 22 (2008) 4274– 4280. [5] J.A. Melero, G. Vicente, G. Morales, M. Paniagua, J. Bustamante, Oxygenated compound derived from glycerol for biodiesel formulations: influence on EN 14214 quality parameters, Fuel 89 (2010) 2011–2018. [6] M. de Torres, G. Jiménez-Oses, J.A. Mayoral, E. Pires, M. de los Santos, Glycerol ketals: syntheys and profits in biodiesel blends, Fuel 94 (2012) 614–616. [7] P.H.R. Silva, V.L.C. Goncalves, C.J.A. Mota, Glycerol acetals as antifreezing additives for biodiesel, Bioresour. Technol. 101 (2010) 6229–6255. [8] J.P. Diebold, A review of the chemical and physical mechanism of the storage stability of fast pyrolysis bio-oils, Thermalchemie Inc., 1999. http:// home.rmi.net/~dieboljc. [9] S.P. Chopade, M.M. Sharma, Reaction of ethanol and formaldehyde: use of versatile cation-exchange resins as catalyst in batch reactors and reactive distillation column, React. Funct. Polym. 32 (1997) 53–64. [10] S.P. Chopade, M.M. Sharma, Acetalization of ethylene glycol with formaldehyde using cation-exchange resins as catalysts: batch versus reactive distillation, React. Funct. Polym. 34 (1997) 37–45.
M.B. Güemez et al. / Chemical Engineering Journal 228 (2013) 300–307 [11] M.R. Capeletti, L. Balzano, G. de la Puente, M. Laborde, U. Sedran, Synthesis of acetal (1,1-diethoxyethane) from ethanol and acetaldehyde over acidic catalysts, Appl. Catal. A: Gen. 198 (2000) L1–L4. [12] A.D. Dhale, L.K. Myrant, S.P. Chopade, J.E. Jackson, D.J. Millera, Propylene glycol and ethylene glycol recovery from aqueous solution via reactive distillation, Chem. Eng. Sci. 59 (2004) 2881–2890. [13] G. Hillion, B. Delfort, I. Durand, Methods for producing biofuels, transforming triglycerides into at least two biofuel families: fatty acid monoesters and/or soluble glycerol acetals, Patent WO 2005/093015. [14] J. Deutsch, A. Martin, H. Lieske, Investigations on heterogeneously catalysed condensations of glycerol to cyclic acetals, J. Catal. 245 (2007) 428–435. [15] X. Hong, O. McGiveron, C.T. Lira, A. Orjuela, L. Peereboom, D.J. Miller, A reactive distillation process to produce 5-Hydroxy-2-methyl-1,3-dioxane from mixed glycerol acetal isomers, Org. Process Res. Dev. 16 (2012) 1141–1145. [16] I. Agirre, V.L. Barrio, B. Güemez, J.F. Cambra, P.L. Arias, Bioenergy II: the development of a reactive distillation process for the production of 1,1 diethoxy butane from bioalcohol: kinetic study and simulation model, Int. J. Chem. React. Eng. 8 (2010) A86. [17] I. Agirre, I. García, J. Requies, V.L. Barrio, M.B. Güemez, J.F. Cambra, P.L. Arias, Glycerol acetals, kinetic study of the reaction between glycerol and formaldehyde, Biomass Bioenergy 35 (2011) 3636–3642. [18] B. Thomas, V.G. Ramu, S. Gopinath, J. George, M. Kurian, G. Laurent, G.L. Drisko, S. Sugunan, Catalytic acetalization of carbonyl compounds over cation (Ce3+, Fe3+ and Al3+) exchanged montmorillonites and Ce3+-exchanged Y zeolitas, Appl. Clay Sci. 53 (2011) 227–235. [19] H. Serafim, I.M. Fonseca, A.M. Ramos, J. Vital, J.E. Castanheiro, Valorization of glycerol into fuel additives over zeolitas as catalysts, Chem. Eng. J. 178 (2011) 291–296. [20] S.B. Umbarkar, T.V. Kotbagi, A.V. Biradar, R. Pasricha, J. Chanale, M.K. Dongare, A.-S. Mamedec, C. Lancelot, E. Payen, Acetalization of glycerol using mesoporous MoO3/SiO2 solid acid catalyst, J. Mol. Catal. A: Chem. 310 (2009) 150–158. [21] N. Rahmat, A.Z. Abdullah, A.R. Mohamed, Recent progress on innovative and potential technologies for glycerol transformation into fuel additives: a critical review, Renew. Sustain. Energ. Rev. 14 (2010) 987–1000. [22] M. Ayoub, A.Z. Abdullah, Critical review on the current scenario and significance of crude glycerol resulting from biodiesel industry towards more sustainable renewable energy industry, Renew. Sustain. Energ. Rev. 16 (2012) 2671–2686.
307
[23] A.B. Leoneti, V. Aragão-Leoneti, S. Valle Walter Borges de Oliveira, Glycerol as a by-product of biodiesel production in Brazil: alternatives for the use of unrefined glycerol, Renew Energ 45 (2012) 138–145. [24] C. Perego, D. Bianchi, Biomass upgrading through acid–base catalysis, Chem. Eng. J. 161 (2010) 314–322. [25] S.M. Mahajani, A.K. Kolah, M.M. Sharma, Extractive reactions with cationic exchange resins as catalysts (acetalization of aldehydes with alcohols), React. Funct. Polym. 28 (1995) 29–38. [26] G.D. Yadav, A.A. Pujari, Kinetics of acetalization of perfumery aldehydes with alkanols over solid acid catalysts, Canadian J. Chem. Eng. 77 (1999) 489– 496. [27] V.M.T.M. Silva, A.E. Rodrigues, Synthesis of diethylacetal: thermodynamic and kinetic studies, Chem. Eng. Sci. 56 (2001) 1255–1263. [28] A.C. Da Silva Ferreira, J.-C. Barbe, A. Bertrand, Heterocyclic acetals from glycerol and acetaldehyde in port wines: evolution with aging, J. Agric. Food Chem. 50 (2002) 2560–2564. [29] B.R. Jermy, A. Pandurangan, Al–MCM–41 as an efficient heterogeneous catalyst in the acetalization of cyclohexanone with methanol, ethylene glycol an pentaerythritol, J. Mol. Catal.: A Chem. 256 (2006) 84–192. [30] V.R. Ruiz, A. Velty, L.L. Santos, A. Leyva-Pérez, M.J. Sabater, Gold catalysts and solid catalysts for biomass transformations: valorization of glycerol and glycerol-water mixtures through formation of cyclic acetals, J. Catal. 271 (2010) 351–357. [31] G.K. Gandi, V.M.T.M. Silva, A.E. Rodrigues, Acetaldehyde dimethylacetal synthesis with Smopex 101 fibres as catalyst/adsorbent, Chem. Eng. Sci. 62 (2007) 907–918. [32] A. C. Hasabnis and S. M Mahajani, Transacetalisation of glycerol with methylal by reactive distillation, Ind. Eng. Chemi. Res. 51 (2012) 13021–13036. [33] X. Hong, O. McGiveron, A.K. Kolah, Alvaro Orjuela, L. Peereboom, C.T. Lira, D.J. Miller, Reaction kinetics of glycerol acetal formation via transacetalization with 1,1-diethoxyethane, Chem. Eng. J. 222 (2013) 374–381. [34] G. Aksnes, P. Albrikten, P. Juvvik, Studies of cyclic acetal anketal isomers of glycerol, Acta Chem. Scand. 19 (1965) 920–930. [35] I. Agirre, V.L. Barrio, M.B. Güemez, A. J.F. Cambra, P.L. Arias, Cap 16: acetals as possible diesel additives, in: Economic Effects of biofuel production, Dos Santos B., M.A. Ed., Intech, 2011. [36] X.A. Da Silva, C.J.A. Mota, The influence of impurities on the acid-catalyzed reaction of glycerol with acetone, Biomass Energy 35 (2011) 3547–3551.