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Novel Route of Reactive Extraction To Recover 1,3-Propanediol from a Dilute Aqueous Solution Jian Hao, Hongjuan Liu, and Dehua Liu* Department of Chemical Engineering, Tsinghua University, Beijing 100084, People’s Republic of China
1,3-Propanediol in aqueous solutions was reacted with propionaldehyde, butyraldehyde, or isobutyraldehyde to form substituted 1,3-dioxane. When excess aldehydes were used, the substituted 1,3-dioxanes were extracted from the aqueous phase to the aldehyde phase; in this step, aldehydes were both reactant and extractant. 1,3-Propanediol was recovered from the extractant through hydrolysis of substituted 1,3-dioxanes in reactive distillation equipment. The reaction equilibrium constants of propionaldehyde, butyraldehyde, and isobutyraldehyde were calculated as 1390-625, 3480-470, and 678-204, respectively, at 7-52 °C. Phase equilibrium measurements showed that the mass distribution coefficients between organic and aqueous phases for 2-ethyl-1,3-dioxane, 2-propyl-1,3-dioxane, and 2-isopropyl-1,3-dioxane were 3.965.40, 27.03-28.08, and 38.51-57.91, respectively, at 15-50 °C. Reactive extraction kinetics studies indicated that the acetalization reactions occurred easily at room temperature. The reactive extraction route present in this work is more effective than the normal distillation route. Introduction 1,3-Propanediol (PDO) is a valuable chemical mainly used as a monomer to synthesize poly(trimethylene terephthalate) (PTT). PTT is a type of biodegradable polyester that exhibits better properties than those produced by 1,2-propanediol, butanediol, or ethylene glycol.1 Nowadays, PDO is produced mainly by two different chemical routes: hydration of acrolein and hydroformylation reaction of ethylene oxide.2 PDO also can be produced by a biotechnological route through the conversion of glycol to PDO using bacteria. This method uses renewable feedstock and appears to be more attractive because of it is economically competitive with synthetic routes.3,4 In the biotechnological route, the final concentration of PDO in broth is low (30-130 g/L).5-7 Because PDO has low volatility and strong hydrophilic characteristics in dilute aqueous solutions, the recovery of PDO from fermentation broth is difficult. The current route consists of a pretreatment of the broth with flocculation and desalination,8 removal of water from the fermentation broth by evaporation and distillation, and further purification of the dewatered PDO by distillation.9,10 In this way, the rate of recovery of PDO is low, while the energy consumption is high. Several other methods including an ion-exchange method11,12 and a molecular sieve adsorption method13 have also been proposed, but they all require the dewatering step and provide few advantages. Compared with evaporation and distillation, extraction is a process of lower energy consumption. However, no appropriate extractant with a higher mass distribution coefficient has been found for the strong hydrophilic character of PDO.14 Combined extraction with reaction can be an alternative method. PDO forms substances without high polar groups (including hydroxylic), then the substance can be extracted from the broth, and PDO * To whom correspondence should be addressed. Tel.: +86-010-62782654. Fax: +86-010-62794742. E-mail: dhliu@ tsinghua.edu.cn.
Figure 1. Scheme of the esterification and acetalization of PDO.
can be obtained by a reverse reaction. One such reaction is the esterification of PDO with acids to form an ester; another reaction is the cyclic acetalization of PDO with aldehydes to form substituted 1,3-dioxane. The reaction schemes are shown in Figure 1. Early in 1951, Tink and Neish15 had reported extraction of polyhydroxy compounds including 2,3-butanediol, some sugars, and sugar alcohols from dilute aqueous solutions by cyclic acetal formation. Robert et al.16 reported the recovery of 1,2-propanediol from a dilute aqueous solution through cyclic acetalization with formaldehyde and acetaldehyde. The acetals obtained in the reaction were separated from the solution by distillation or extraction. Atul et al.17 and Chopade et al.18 reported the recovery of 1,2-propanediol and ethylene glycol from an aqueous solution via reactive distillation; the reaction was also acetalization with formaldehyde or acetaldehyde. Though the boiling points of the acetals that Robert et al., Atul et al., or Chopade et al. obtained are lower than that of water, they are higher than those of formaldehyde and acetaldehyde. Therefore, during distillation, large amounts of formaldehyde or acetaldehyde were also evaporated and mixed with a distillate, reducing the practicality of those methods. Malinowski19 reported the recovery of PDO by cyclic acetalization with acetaldehyde to form 2-methyl-1,3-dioxane; the acetal was recovered by o-xylene, toluene, or ethylbenzene extraction, but the hydrolyzation of the acetal was not studied. The extraction method that Robert et al. reported also used aromatic solvents as the extractant. In aromatic solvent extraction, formaldehyde or acetal-
10.1021/ie049346z CCC: $30.25 © 2005 American Chemical Society Published on Web 05/13/2005
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Figure 2. Flow schematic of the reactive extraction processes: (1) reaction column; (2) reactive extraction column; (3) aldehyde recovery column; (4) acetal hydrolysis distillation column.
dehyde was also extracted to an organic phase to decrease the conversion rate of PDO. Aldehyde and acetals that dissolved in the extractant had to be separated with an extractant through distillation. Moreover, the acetals that formaldehyde or acetaldehyde formed had to be hydrolyzed through reactive distillation. However, the boiling points of formaldehyde and acetaldehyde are -19 and 21 °C, respectively,20 which makes the recovery of formaldehyde and acetaldehyde from the condenser a challenge. Furthermore, acetaldehyde would be polymerized in an aqueous solution, so this method was not desirable. In this paper, a novel reactive extraction route is presented: propionaldehyde, butyraldehyde, or isobutyraldehyde were used to react with PDO to form substituted 1,3-dioxanes, which were extracted to an organic phase that exceeded the aldehyde formed. PDO was obtained through reactive distillation of the extractant, and aldehyde that dissolved in raffinate was recovered through distillation. The whole flow schematic of the processes is shown in Figure 2. Propionaldehyde, butyraldehyde, and isobutyraldehyde were partly miscible with water; when excess aldehyde was used, the aldehyde formed an organic phase. In this reactive extraction, aldehyde was both the reactant and extractant, and no additional extractant was needed; therefore, the step for separation of aldehydes and acetals with an extractant was avoided. Moreover, the concentration of aldehyde in the aqueous phase remained at a higher level and the acetal concentration remained at a lower level, therefore enhancing the conversion rate of PDO. The boiling points of propionaldehyde, butyraldehyde, and isobutyraldehyde are 48, 74.8, and 64.5 °C, respectively; through distillation, they are easily condensed. Compared with the reported routes, this new route is simple and appears to be an additive replacer for the normal distillation route. Materials and Methods Materials. PDO (99.8%) was obtained from Chen Neng Bioengineering Company (Hei Longjiang, China). Propionaldehyde (98.0%) and butyraldehyde (98.5%) were purchased from Chemical Reagent Company of Shanghai (Shanghai, China). Isobutyraldehyde (98.5%) was purchased from Yonghua Fine Chemistry Company (Jiangsu, China). Other chemicals used were purchased from a commercial supplier at the highest available purity.
Preparation of Dioxanes. A. 2-Ethyl-1,3-dioxane. A total of 45 g (0.57 mol) of PDO and 30 g (0.52 mol) of propionaldehyde were mixed in a 250-mL shaken flask, and then 0.5 mL of 12 mol/L HCl was added to the mixture as a catalyzer. A total of 12 g of MgSO4 was added to absorb the water produced in the reaction. After 4 h of shaking, 2 g of Na2CO3 was added to neutralize the HCl. Then the mixture was centrifuged, and the supernatant liquor was distilled. The distillate in the range of 100-140 °C was collected; it was a colorless liquid with a characteristic odor. The distillate was analyzed with a GC-14B gas chromatograph (GC; Shimadzu Corp., Kyoto, Japan), which was equipped with a flame ionization detector and a FFAP-CB column (0.32 mm × 25 m × 0.3 µm film thickness). The temperatures of the injector and detector were set at 250 and 270 °C, respectively. The oven temperature was programmed from 40 to 200 °C. Nitrogen was used as a carrier gas. The purity of the distillate was analyzed as 97%, the boiling point of the distillate was measured as 110 °C, and the density was 1.03 g/mL. Its structure was truly 2-ethyl-1,3-dioxane, which was tested by an electron ionization mass spectrometer. B. 2-Propyl-1,3-dioxane. A total of 50 g (0.64 mol) of PDO and 35 g (0.48 mol) of butyraldehyde were mixed in a 250-mL shaken flask. Other conditions and operations were the same as the method described in section A. After the reaction, the mixture was separated into two layers. All solids were in the bottom layer, and the upper layer was a clear liquid. The two layers were separated by a funnel. GC analysis shows that the upper layer was 2-propyl-1,3-dioxane of 98% purity and was also a colorless liquid with a characteristic odor. Its boiling point was 149 °C, and the density was 0.999 g/mL. C. 2-Isopropyl-1,3-dioxane. Operation conditions were the same as the method described in section B. 2-Isopropyl-1,3-dioxane obtained was also a colorless liquid with a special odor like chocolate. Its boiling point was 138 °C, and the density was 0.994 g/mL. Chemical Equilibrium Measurements. Various concentrations of PDO and aldehyde mixtures were prepared. HCl was added to adjust the solution to pH ) 1. A total of 1 mL of the mixtures was placed in 1.5mL tubes; the tubes were shaken at various temperatures for 4 h to make sure that the reactions reached equilibrium; the concentrations of PDO, aldehydes, and acetals were measured by a GC. The activities of PDO, aldehydes, and acetals were calculated using a UNIFAC (UNIQUAC functional-group activity coefficients) group contribution method, and the equilibrium constants were calculated. Phase Equilibrium Measurements. A total of 0.5 mL of acetal-aldehyde solutions at different concentrations and 0.5 mL of water were mixed in a 1.5-mL tube at temperatures 15, 30, and 50 °C, and a liquid-liquid system appeared. The mixture was vigorously shaken for 2 min to ensure that phase equilibrium was reached, and then no shaking occurred for 10 min to allow for the separation of the organic and aqueous phases. Then the concentrations of acetals at two phases were measured by a GC, and the mass distribution coefficient was calculated. The temperature range was selected at around room temperature, and for the exothermic reactions, the high temperature was selected at around 50 °C.
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Table 1. Chemical Reaction Equilibrium Constant (K) for Acetalization Reactions aldehyde
temp (°C)
K
propionaldehyde
7 24 52 7 21 51 7 21 51
1390 ( 16 690 ( 47 625 ( 77 3480 ( 498 1459 ( 94 470 ( 57 678 ( 143 616 ( 177 204 ( 32
butyraldehyde isobutyraldehyde
Reactive Extraction Kinetics Measurements. A 60 g/L PDO aqueous solution was adjusted to pH ) 1.22, 1.53, and 1.90. A total of 0.5 mL of the PDO solutions and 0.5 mL of aldehydes were added to 1.5-mL tubes; the tubes were placed in a shaker at 20 °C and 140 rpm. Samples were taken, and the changes of PDO and acetals at the two phases were analyzed. Acetal Hydrolysis. A total of 10 mL of the extractant that was obtained from reactive extraction of propionaldehyde acetalization was placed in the distillation equipment. A total of 0.5 mL of water and 1 g of a H+type ion-exchange resin were added. The reaction was performed at 90 °C for 20 min. The hydrolysis products were analyzed by a GC. Acetals obtained from butyraldehyde and isobutyraldehyde were hydrolyzed following the same methods. Results and Discussion Chemical Equilibrium. The reaction equilibrium constant was calculated from the equilibrium activities
K)
[acetal][water] [1,3-propanediol][aldehyde]
(1)
where K is the equilibrium constant, [acetal] is the activity of acetal, [water] is the activity of water, [1,3propanediol] is the activity of PDO, and [aldehyde] is the activity of aldehyde. For each acetalization reaction, experiments were performed on five different initial reactant concentrations at each temperature. The activities were calculated, and the values of K are shown in Table 1. All of the values of K were very large, indicating that all of the reactions were complete. The values of K changed with temperature, so enthalpy and entropy changes of the reactions could be obtained from the relationship
ln(K) ) ∆H
(TR1 ) + ∆S(R1 )
(2)
in which T is the temperature (K), R is the mole gas
Figure 3. Relationship of ln(K) and 1/T for the acetalization reaction: (0) propionaldehyde acetalization reaction (solid line); (O) butyraldehyde acetalization reaction (dashed line); (4) isobutyraldehyde acetalization (dotted line).
constant [8.314 J/(K mol)], ∆H is the enthalpy change (J/mol), and ∆S is the entropy change [J/(K mol)]. The relationship of ln(K) and 1/T is shown in Figure 3. The changes were linear, and ∆H and ∆S were calculated using the origin. The results are given in Table 2. The results showed that all of the values of K decreased when the temperature increased. Phase Equilibrium. Experiments were performed on different concentrations of acetals at 15, 30, and 50 °C. The concentrations in the aqueous and organic phases are shown in Figure 4. The data fit was linear, and the mass distribution coefficients are shown in Table 3. 2-Propyl-1,3-dioxane and 2-isopropyl-1,3-dioxane, which were formed from butyraldehyde and isobutyraldehyde, had high mass distribution coefficients. They were suitable candidates for the extraction operation. The mass distribution coefficients of acetals varied with temperature, but the changes were very slight and not very regular. Reactive Extraction Kinetics. Acetal reactions were catalyzed by H+ in the solution, and the velocity of the reactions was influenced by the pH of the solution. When a wider range of the solution pH was tested, it was found that the reactions were very slow when the pH of the solution was higher than 2. The kinetics of propionaldehyde acetalization reactions at pH ) 1.22, 1.53, and 1.90 are shown in Figure 5. With reactive extraction going on, the concentration of PDO in the aqueous phase decreased and the concentration of 2-propyl-1,3-dioxane in the organic phase
Table 2. Acetalization Reaction Equations and ∆H and ∆S aldehyde
regressed equation
∆H (J/mol)
∆S [J/(K mol)]
propionaldehyde butyraldehyde isobutyraldehyde
ln(K) ) 1654 (1/T) + 1.2 ln(K) ) 4077(1/T) - 6.5 ln(K) ) 2583(1/T) - 2.6
-13 751 ( 3442 -33 896 ( 2560 -21 475 ( 4290
10 ( 11.6 -53.9 ( 8.3 -22 ( 14.4
Table 3. Acetal Mass Distribution Coefficients of the the Aqueous and Organic Phases mass distribution coefficients temp (°C)
2-ethyl-1,3-dioxane
2-propyl-1,3-dioxane
2-isopropyl-1,3-dioxane
15 30 50
3.96 ( 0.03 5.40 ( 0.10 4.13 ( 0.12
28.08 ( 1.11 27.48 ( 2.41 27.03 ( 1.38
40.42 ( 0.57 57.91 ( 1.77 38.51 ( 1.81
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Figure 4. Acetal mass distribution of the aqueous and organic phases: (A) 2-ethyl-1,3-dioxane; (B) 2-propyl-1,3-dioxane; (C) 2-isopropyl1,3-dioxane; (0) 15 °C (solid line) linear fit; (O) 30 °C (dashed line) linear fit; (4) 50 °C (dotted line) linear fit.
Figure 5. Propionaldehyde acetalization reactive extraction kinetics: (A) pH ) 1.22; (B) pH ) 1.53; (C) pH ) 1.90; (b) 2-propyl-1,3dioxane in the aqueous phase; (O) 2-propyl-1,3-dioxane in the propionaldehyde phase; (2) PDO in the aqueous phase; (4) PDO in the propionaldehyde phase.
Figure 6. Butyraldehyde acetalization reactive extraction kinetics: (A) pH ) 1.22; (B) pH ) 1.53; (C) pH ) 1.90; (b) 2-propyl-1,3dioxane in the aqueous phase; (O) 2-propyl-1,3-dioxane in the butyraldehyde phase; (2) PDO in the aqueous phase; (4) PDO in the butyraldehyde phase.
increased. The velocity of reactive extraction was faster at lower pH than at high pH. The 2-propyl-1,3-dioxane concentration in the aqueous phase increased at the beginning and then decreased, which was exhibited by the 2-propyl-1,3-dioxane forming and extracting velocities. 2-Propyl-1,3-dioxane formed in the aqueous phase,
and after it formed, it was extracted to the organic phase. At the beginning, the forming velocity was faster than the extracting velocity, so the 2-propyl-1,3-dioxane concentration increased. With a decrease in the reactant concentration and an increase in the product concentration, the forming velocity of 2-propyl-1,3-dioxane de-
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Figure 7. Isobutyraldehyde acetalization reactive extraction kinetics: (A) pH ) 1.22; (B) pH ) 1.53; (C) pH ) 1.90; (b) 2-isopropyl-1,3dioxane in the aqueous phase; (O) 2-isopropyl-1,3-dioxane in the isobutyraldehyde phase; (2) PDO in the aqueous phase; (4) PDO in the isobutyraldehyde phase of 2-ethyl-1,3-dioxane hydrolysis.
creased at the same time as more 2-propyl-1,3-dioxane was extracted to the organic phase, so its concentration in the aqueous phase decreased. In the equilibrium state, there were still 0.1 mol/L of PDO and 0.2 mol/L of 2-ethyl-1,3-dioxane in the aqueous phase, and the recovery rate of PDO in this unit experiment was about 65%. A similar behavior for butyraldehyde and isobutyraldehyde acetalization reactive extraction was found, as shown in Figures 6 and 7. The solubilities of butyraldehyde (7 g/100 g) and isobutyraldehyde (11 g/100 g) in the aqueous phase were much lower than that of propionaldehyde (30 g/100 g).20 Therefore, the energy consumption in the recovery of butyraldehyde and isobutyraldehyde from the broth was lower than that of propionaldehyde. In equilibrium, the concentrations of PDO and 2propyl-1,3-dioxane in the aqueous phase were 0.01 and 0.06 mol/L, respectively, and the recovery rate of PDO in the unit experiment could reach 85%. In the isobutyraldehyde acetalization reaction, the aqueous phase concentration of 2-isopropyl-1,3-dioxane was about 0.05 mol/L and the PDO concentration was close to 0 mol/L. The recovery rate of PDO could reach 87%. Propionaldehyde was distilled out during the hydrolysis reaction. A small amount of liquid was obtained (volume not measured) after 10 mL of the extractant was distilled, in which the concentration of PDO was 980 g/L. The reaction temperature was 90 °C because the reaction temperature must be higher than the boiling point of propionaldehyde and lower than that of water. The 2-propyl-1,3-dioxane and 2-isopropyl-1,3-dioxane hydrolysis experiments exhibited similar results, except that the reaction temperature could be varied in the ranges of 80-100 and 70-100 °C, respectively. Conclusions The recovery of PDO from a dilute aqueous solution by reactive extraction with propionaldehyde, butyraldehyde, and isobutyraldehyde was studied in this paper. The strong hydrophobic properties of the acetals make it possible to extract the acetals into organic solutions. Propionaldehyde, butyraldehyde, and isobutyraldehyde themselves are used both as the reactant and as the
extractant in the process, which makes the whole route more simplified. Furthermore, the reactions are reversible at room temperature, and at lower pH, the velocities of those reactions are very quick, so the process is easy to operate. In unit reactive extraction, the recovery rates of PDO are 65%, 85%, and 87% for propionaldehyde, butyraldehyde, and isobutyraldehyde, respectively. Compared with distillation and other routes, this new route is more economical in energy consumption. Literature Cited (1) Witt, U.; Muller, R. J.; Augusta, J.; Widdecke, H.; Deckwer, W. D. Synthesis, properties and biodegradability of polyeasters based on 1,3-propanediol. Makromol. Chem. Phys. 1994, 195, 793802. (2) Miche`le, B.; Pierre, G.; Anne, P.; Scott, R. Development of an improved continuous hydrogenation process for the production of 1,3-propanediol using titania supported ruthenium catalysts. Appl. Catal. A 2003, 250, 117-124. (3) Forsberg, W. C. Production of 1,3-Propanediol from Glycerol by Clostridium acetobutylicum and other Clostridium species. Appl. Environ. Microbiol. 1987, 53, 639-643. (4) Biebl, H. Glycerol fermentation of 1,3-propanediol by Clostridium butyricum. Measurement of product inhibition by use of a pHauxostat. Appl. Microbiol. Biotechnol. 1991, 35, 701-705. (5) Seraphim, P.; Ruiz-Sanchezb, P.; Pariset, B. High production of 1,3-propanediol from industrial glycerol by a newly isolated Clostridium butyricum strain. J. Biotechnol. 2000, 77, 191-208. (6) Himmi, E. H.; Andre, B.; Fabien, B. Nutrient requirements for glycerol conversion to 1,3-propanediol by Clostridium butyricum. Bioresour. Technol. 1999, 67, 123-128. (7) Emptage, M.; Haynie, S. L.; Laffend, L. A.; Pucci, J. P.; Whited, G. Process for the biological production of 1,3-propanediol with high titer. U.S. Patent 6,514,733, 2003. (8) Yan, G.; Yu, T. The possibility of the desalination of actual 1,3-propanediol fermentation broth by electrodialysis. Desalination 2004, 161, 169-178. (9) Kelsey, D. R. Purification of 1,3-propanediol. U.S. Patent 5,527,973, 1996. (10) Ames, T. T. Process for the isolation of 1,3-propanediol from fermentation broth. U.S. Patent 6,361,983, 2002. (11) Roturier, J. M.; Fouache, C.; Berghmans, E. Process for the purification of 1,3-propanediol from a fermentation medium. U.S. Patent 6,428,992, 2002. (12) Hilaly, A. K.; Binder, T. P. Method of recovering 1,3propanediol from fermentation broth. U.S. Patent 6,479,716, 2002. (13) Corbin, D. R.; Norton, T. Process to separate 1,3-propanediol or glycerol, or a mixture thereof from a biological mixture. U.S. Patent 6,603,048, 2003.
Ind. Eng. Chem. Res., Vol. 44, No. 12, 2005 4385 (14) Malinowski, J. J. Evaluation of liquid extraction potentials for downstream separation of 1,3-propanediol. Biotechnol. Tech. 1999, 13, 127-130. (15) Tink, R. R.; Neish, A. C. Extraction of polyhydroxy compounds from dilute aqueous solutions by cyclic acetal formation. I. As investigation of the scope of the process. Can. J. Technol. 1951, 29, 243-249. (16) Robert, R. B.; Lynn, S.; King, C. J. Recovery of Propylene Glycol from Dilute Aqueous Solutions via Reversible Reaction with Aldehydes. Ind. Eng. Chem. Res. 1994, 33, 3230-3237. (17) Atul, D. D.; Laurie, K. M.; Shubham, P. C.; James, E. J.; Dennis, J. M. Propylene glycol and ethylene glycol recovery from aqueous solution via reactive distillation. Chem. Eng. Sci. 2004, 59, 2881-2890.
(18) Chopade, S. P.; Dhale, A. D.; Kiesling, C. W. Process for the recovery a polyol from an aqueous solution. U.S. Patent 6,548,681, 2003. (19) Malinowski, J. J. Reactive Extraction for Downstream Separation of 1,3-Propanediol. Biotechnol. Prog. 2000, 16, 76-79. (20) John, A. D. Lange’s Handbook of Chemistry, 15th ed.; McGraw-Hill Co.: New York, 1998.
Received for review July 24, 2004 Revised manuscript received December 16, 2004 Accepted February 25, 2005 IE049346Z
