Application of Sulfonated Carbon-Based Catalyst for Reactive

Oct 28, 2010 - of Technology Thonburi, Bangkok 10140, Thailand, and Department of Chemical Engineering, Faculty of. Engineering and Industrial ...
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Application of Sulfonated Carbon-Based Catalyst for Reactive Extraction of 1,3-Propanediol from Model Fermentation Mixture Panatpong Boonoun,† Navadol Laosiripojana,‡ Chirakarn Muangnapoh,† Bunjerd Jongsomjit,† Joongjai Panpranot,† Okorn Mekasuwandumrong,§ and Artiwan Shotipruk*,† Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn UniVersity, Phayathai Road, Bangkok 10330, Thailand, The Joint Graduate School of Energy and EnVironment, King Mongkut’s UniVersity of Technology Thonburi, Bangkok 10140, Thailand, and Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn UniVersity, Nakorn Pathom 73000, Thailand

This study deals with the possibility of the application of a low-cost sulfonated carbon-based catalyst for reactive extraction to separate 1,3-propanediol (1,3-PDO) from a model solution of 1,3-PDO biologically derived from glycerol. The catalyst was synthesized by incomplete carbonization of naphthalene in sulfuric acid, and was demonstrated to be active for the acetalization of 1,3-PDO with acetaldehyde in aqueous solution. The performance of the reactive extraction process by using a sulfonated carbon-based catalyst was proven to be excellent based on the percent recovery rate of 1,3-PDO. These results along with those on the catalyst reactivity demonstrate that the carbon-based catalyst can be used to replace expensive commercial catalysts currently used such as Dowex 50-WX4-200 and Amberlite IR120. 1. Introduction As the most promising first-generation alternative fuel, a large amount of biodiesel is being produced industrially worldwide. Biodiesel production is typically carried out via a transesterification process, in which plant oils or animal fats are reacted with alcohols and converted into biodiesel. The process produces glycerol as a major byproduct, thus resulting in a large amount of glycerol produced. This leads to significant research interest in trying to convert abundant and low-cost glycerol into other value-added products. One of the most promising glycerolderived products is 1,3-propanediol (1,3-PDO) due to its wide range of applications in various chemical, textile, and fiber industries. The production of 1,3-PDO from glycerol can indeed be achieved either by chemical and biological processes; however, the latter is considered to be more environmentally benign and is gaining considerable interest. In the biological process, glycerol conversion to 1,3-PDO takes place in an aqueous system with the use of various types of microorganisms such as Klebsiella pneumoniae, Citobacter frundii, Enterobacter agglomerans, and Clostridium butyricum.1 Despite the abovementioned advantage, the separation of 1,3-PDO from aqueous solution is a major drawback of the biological process due to the low volatility and highly hydrophilic characteristics of 1,3PDO. Various separation methods have been employed such as evaporation and distillation,2 liquid-liquid extraction,3 pervaporation,4 and chromatography;5,6 nevertheless, these processes require large amounts of energy and give uneconomically low 1,3-PDO recovery. Alternatively, the separation of 1,3-PDO can be carried out by reactive extraction, in which acetalization of 1,3-PDO and a carbonyl compound such as ketone or aldehyde takes place to form dioxane (as shown in Figure 1), which would be extracted simultaneously with an organic solvent.7 Compared with all existing separation processes, reactive extraction is easy, is energy efficient, and gives a relatively high 1,3-PDO yield.7,8 * To whom correspondence should be addressed. Tel.: 662-218-6868. Fax: 662-218-6877. E-mail: [email protected]. † Chulalongkorn University. ‡ King Mongkut’s University of Technology Thonburi. § Silpakorn University.

One of the major contributions to the success of reactive extraction of the biologically derived 1,3-PDO is the acid catalyst employed in the process. The most generally used catalysts are Dowex and Amberlite ion-exchange polymeric resins. These commercial catalysts are rather costly, and thus the replacement with a low-cost solid catalyst would make reactive extraction of 1,3-PDO even more economically attractive. Recently, a new class of low-cost sulfonated catalyst has been developed by incomplete carbonization of simple sugars.9 The catalysts are easy to prepare, and they have been shown to have high acid density and thus high activity for many acid catalyzed reactions such as Beckman reformation, esterification, and hydrolyzation.10 In addition, Gao et al.11 proposed a similar sulfonated catalyst synthesized by incomplete carbonization of naphthalene in sulfuric acid and reported its high reactivity and selectivity for the acetalization of carbonyl compounds. Although the catalyst was tested for the reactions that take place in organic solvent phase, their results suggested potential application of such a catalyst for the reactive extraction of 1,3PDO from the aqueous fermentation mixture. This study therefore aims to investigate the feasibility of the application of sulfonated naphthalene based catalyst for reactive extraction of 1,3-PDO from model fermentation mixture. First, the catalyst was synthesized and the physical properties were characterized. Second, the catalyst was tested for acetalization of 1,3-PDO with acetaldehyde to determine the suitable ratio of the catalyst and 1,3-PDO. In addition, the chemical equilibrium constants at various temperatures were determined, and the reactivity and the reusability of the catalyst for such reactions were evaluated and compared with those of commercial Dowex 50-WX4-200 and Amberlite IR120 (hydrogen form). Third, the catalyst was applied to the reactive extraction in which the 2-methyl-1,3dioxane (2-MD) acetalization product was simultaneously extracted with ethylbenzene as an extractant and the effects of system temperature on the mass distribution coefficient of 2-MD and the percent recovery of 1,3-PDO were determined. Furthermore, the possibility of applying this catalyst to the reverse hydrolysis reaction to convert 2-MD back to 1,3-PDO was also investigated.

10.1021/ie1019003  2010 American Chemical Society Published on Web 10/28/2010

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Figure 1. Mechanism of 1,3-PDO conversion to dioxane.

2. Materials and Methods 2.1. Materials. 1,3-PDO (98% purity) was purchased from Acros Organic Co., Singapore. Acetaldehyde (99% purity), ethylbenzene (99% purity) and Dowex 50-WX4-200 ionexchange resin were obtained from Aldrich (Sigma-Aldrich, Singapore). Amberlite IR120 hydrogen form was purchased from Aldrich (Sigma-Aldrich, Singapore). Sulfuric acid and naphthalene were purchased from Fluka and Merck, Singapore. The standard sample of 2-methyl-1,3-dioxane (2-MD) was prepared following the procedure described by Hao et al.8 Briefly, 45 g (0.57 mol) of 1,3-PDO was mixed with 25.1 g (0.57 mol) of acetaldehyde and 3.5 g of Dowex ion-exchange resin. Then, 12 g of MgSO4 was added to absorb the water produced during the reaction. After 4 h under shaking, 2 g of Na2CO3 was added to neutralize the sample. The ion-exchange resin, Na2CO3, and MgSO4 were then separated from the reaction mixture by filtration, and the supernatant liquor was distilled. The distillate in the range 100-140 °C was collected and analyzed with an HP 5890 gas chromatograph (GC) equipped with a TCD detector and a 30-m HP-1 column (0.53 mm diameter, 0.88 mm film thickness) (Hewlett-Packard). The oven temperature was from 70 to 200 °C, while the injector and detector temperatures were set at 250 and 300 °C, respectively. 2.2. Catalyst Preparation and Characterization. The preparation of the sulfonated naphthalene based catalyst employed in this study was modified from that described by Gao et al.11 Briefly, naphthalene (20 g) in concentrated H2SO4 (>96%, 200 mL) was heated at 250 °C under nitrogen flow in a fourneck round-bottom flask for 15 h. Then the nitrogen flow was switched off and the sample was further heated under vacuum for another 8 h in order to remove the excess H2SO4. The resulting black solid was ground to powder, and was washed repeatedly in boiling water until sulfate ions were no longer detected in the washing water. It should be noted that the roundbottom flask and all the connections are made of PYREX glass. The catalyst was characterized by several techniques. First, the total surface area, pore volume, and pore size of catalysts were determined by N2 physisorption using a Micromeritics system (Model ASAP 2020). In addition, neutralization titration was carried out in order to determine the catalyst acidity. Here, a mixture of isopropyl alcohol (12.5 mL) and toluene (12.5 mL) was placed in a 100 mL flask in which 1 g of sulfonated carbonbased catalysts and 0.5 mL of phenolphthalein were then added. This solution was then titrated with 0.25 M KOH (ASTM D6751). Moreover, the sulfur content of sulfonated carbon-based

catalysts was determined by inductively coupled plasma mass spectrometry (ICP-MS) using a 7500a ICP-MS. Here, the catalyst was digested with 5 mL of HNO3 and made up to 25 mL with ultrapure water at 18.2 mΩ, using an Anton Paar microwave digester for testing. In addition, the sulfonic group on the catalyst was confirmed by a Nicolet NEXUS 670 Fourier transform infrared (FTIR) spectrometer using KBr disks. Last, the thermal behavior of the catalyst was analyzed by a thermogravimetric analyzer (PerkinElmer, Pyris 1 TGA) in which 10 mg of catalyst was used, and an air flow rate of 10 mL/min was employed. The temperature was ramped from room temperature to 1000 °C at the rate of 10 °C/min. The X-ray diffraction (XRD) of sulfonated carbon-based catalyst was identified by a SIEMENS D500 X-ray diffractometer (Germany) using Ni-filtered Cu KR radiation. The measurements were carried out in the 2θ range of 10-80° at the scan step of 0.04°. 2.3. Experimental Procedures. 2.3.1. Test of Catalyst for Acetalization in Aqueous Solution. The catalyst was tested for acetalization of 1,3-PDO with acetaldehyde in an aqueous mixture to replicate the reaction of the aqueous fermentation products. The reaction was carried out by mixing 0.5 mL of 1,3-PDO with 15.7 mL of acetaldehyde solution (containing 3.7 mL of acetaldehyde and 12 mL of water). This assumed that the fermentation process gave 1,3-PDO product of about 40 g/L, a typical concentration obtained experimentally.12 The mixture was then stirred at 150 rpm, and the reaction was allowed to take place up to 120 min at 35 °C in the presence of various amounts of sulfonated carbon-based catalysts, from which experiment the suitable catalyst to 1,3-PDO ratio was determined. After each reaction, the catalyst was immediately separated from the reaction product, which was then kept in a refrigerator (4 °C) until analysis. The effect of the mass ratio of the catalyst and 1,3-PDO in the range 0.1-0.9 was determined on the conversion, calculated based on the molar amount of 2-MD produced with respect to that of the 1,3-PDO reactant. This was equivalent to the range of mass to volume ratio of 4-36 g of catalyst/L of the 40 g/L of 1,3-PDO aqueous solution. The resulting reaction product was analyzed for the amount of 2-MD produced and the unreacted 1,3-PDO. The suitable ratio giving the highest conversion was then selected for subsequent experiments to determine the catalyst reactivity and reusability. The results were then compared with those employing the same amount of commercial Dowex 50-WX4200 and Amberlite IR120 (hydrogen form). Moreover, this catalyst to 1,3-PDO ratio was also used for the experiment to determine the chemical equilibrium constants (K) at 15, 25, and

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Table 1. Physical Properties of Catalysts

catalyst type

BET pore acid surface area volume H+ content site 2 -1 3 -1 -1 (m g ) (cm g ) (mmol g ) (mmol g-1)

sulfonated carbon-based 1.1 catalysta Dowexb 200-300 Amberliteb 1000-1300

0.07

1.44

1.46c

1.2 1.0-1.2

4.0 3.6

4.6d 3.8d

a This work. b Commercial catalysts (Sigma-Aldrich, Singapore). From elemental analysis. d From company data (Sigma-Aldrich, Singapore), reported as mequiv/g. c

Figure 2. FTIR spectrum of sulfonated carbon-based catalyst.

35 °C, whose values were calculated from the activities of the products and the reactants according to eq 1. K)

C2-MDCwater CacetaldehydeC1,3-PDO

(1)

2.3.2. Reactive Extraction of 1,3-PDO from Model Fermentation Mixture. To test the catalyst for reactive extraction of 1,3-PDO from model fermentation mixture, the process was carried out by adding a specified amount of catalyst (determined from previous experiment) to a mixture of equal volumes (15.7 mL) of ethylbenzene and acetaldehyde solution (15.7 mL of solution containing 3.7 mL of acetaldehyde and 12 mL of water). The solutions were mixed in a 125 mL shake flask, and were brought to a desired reaction temperature (15, 25, 35 °C). Then, 0.5 mL of 1,3-PDO was added and stirred vigorously at a constant temperature for various reaction times up to 300 min. The pH of the reaction mixture was measured to be around pH 1. After the reaction, the product was separated using a separation funnel into two phases: the aqueous phase and the extract (ethylbenzene) phase. The analyses of 1,3-PDO and 2-MD were performed on an HP5890 series II gas chromatograph (Hewlett-Packard) equipped with a thermal conductivity detector and a 30-m HP-1 column (0.53 mm diameter, 0.88 µm film thickness). It should be noted that the quantity of 1,3-PDO was measured only in the aqueous phase, while the quantity of 2-MD produced was measured in both phases. The mass distribution coefficients of 2-MD were therefore obtained from the amounts of 2-MD partitioned into the two phases according to eq 2. mass distribution coefficient ) mass of 2-MD in extract phase at equilibrium mass of 2-MD in aqueous phase at equilibrium

(2)

In addition to the use of the carbon-based catalyst for the acetalization reaction to produce 2-MD, to complete the process of reactive extraction, the possibility of employing the sulfonated carbon-based catalyst for hydrolysis of 2-MD back to 1,3-PDO was also evaluated. For this experiment, equal molar quantities of 2-MD and water were placed in the distillation equipment in which the carbon-based catalyst was added. The reaction was allowed to take place at 90 °C for 20 min, and the hydrolysis products were analyzed by GC.8 3. Results and Discussion 3.1. Catalyst Characterization. The physical properties of the sulfonated naphthalene based catalyst and conventional Dowex 50-WX4-200 and Amberlite IR120 ion-exchange resins such as surface area, pore volume, and catalyst acidity are given in Table 1. The BET measurement indicates that the catalyst shows low specific surface area and pore volume compared with Dowex 50-WX4-200 and Amberlite IR120 hydrogen form. As shown in Table 1, the acidity of the catalyst analyzed by

Figure 3. XRD of sulfonated carbon-based catalyst.

neutralization titration was also lower than those of Dowex 50WX4-200 and Amberlite IR120 hydrogen form and the values of acidity agree closely with the acid site densities calculated in the form of sulfonic acid site (estimated by elemental analysis). The sulfonic group on carbon-based catalyst was confirmed by the Nicolet NEXUS 670 FTIR as shown in Figure 2. The IR spectrum shows strong absorption at 1600-1800 cm-1, which confirms the SdO stretching bands of the catalyst, and a broad band at 2600-3500 cm-1 confirms the presence of OH.10 Furthermore, the XRD of the catalyst shown in Figure 3 confirms that the sulfonated carbon-based catalyst consists of a sulfonated group and carbon (at 2θ ) 12 and 2θ ) 25).13 In addition, the TGA analysis result shown in Figure 4 indicates that the catalyst started to rapidly decompose in the temperature range between 200 and 400 °C, and all catalyst disappeared completely above 600 °C. 3.2. Test of Catalyst for Acetalization in Aqueous Solution. In applying the carbon-based catalyst for acetalization in the model mixture aqueous solution, the suitable amount of catalyst was first determined by varying the mass ratio of catalyst to 1,3-PDO from 0.1 to 0.9. The reaction was carried out at the temperature of 35 °C and the reaction time of 120 min. As shown in Figure 5, the conversion increased with increasing the catalyst to 1,3-PDO ratio from 0.1 to 0.7, in which the maximum value of 92% was achieved. At higher ratios, however, the conversion was not significantly changed; hence all subsequent experiments were carried out with 0.7 g of catalyst to 1 g of 1,3-PDO. In addition, the chemical equilibrium constants at various temperatures were determined and the results are shown in Table 2. These chemical equilibrium data were used for the calculation of enthalpy and entropy changes of the reaction using a graphical method following eq 3.

[ ( RT1 ) - ∆S( R1 )]

ln K ) - ∆H

(3)

Figure 6 shows the plot of ln K versus 1/T, in which the values of enthalpy and the entropy changes of the reaction can be determined by multiplying the gas constant R (8.314 J K-1

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Figure 4. TGA of sulfonated carbon-based catalyst.

Figure 5. Effect of catalyst to 1,3-PDO mass ratio on conversion of acetalization in aqueous solution (reaction temperature 35 °C, reaction time 120 min, and initial concentration 40 g/L 1,3-PDO). Table 2. Equilibrium Constants, Regression Equation, and ∆H and ∆S of Acetalization temp (°C)

15 25 35 a

K

regression equation

250.69 178.82 ln K ) - 4223 - 9.089 RT R 96.40

[( ) (

)]

∆H (kJ mol-1)

∆S (kJ mol-1 K-1)

-35.11a

+0.076

∆H agrees with the previously reported value of -34.7 kJ mol-1.13

Figure 6. Plot of ln K versus 1/T for acetalization of 1,3-PDO in aqueous solution.

mol-1) by the slope and the y-intercept of the graph, respectively. From this, the enthalpy and the entropy change of this reaction were calculated to be -35.11 kJ mol-1 and 0.076 kJ mol-1 K-1,

Figure 7. Conversions of multiple reactions for acetalization in aqueous solution various solid catalysts (reaction temperature 35 °C, catalyst to1,3PDO ratio 0.7 g of catalyst/1 g of 1,3-PDO, and initial 1,3-PDO concentration 40 g/L).

respectively. It should be noted that the enthalpy of -35.1 kJ/ mol agrees with the previously reported value of -34.7 kJ mol-1,13 and the negative value indicates that the acetalization is an exothermic reaction. Given the suitable catalyst to 1,3-PDO ratio of 0.7 previously determined, the reactivity of the catalyst toward acetalization was compared with the commercial catalysts Dowex 50-WX4200 and Amberlite IR120 for the reactions carried out at 35 °C. The conversions, after reaction times of up to 120 min, are shown in Figure 7. At reaction times of 60 and 90 min, Dowex 50-WX4-200 and Amberlite IR120 hydrogen form were found to have higher reactivities compared with the synthesized carbon-based catalysts. Nevertheless, with the reaction time of 120 min, the reactivity of carbon-based catalyst was comparable to those of the commercial catalysts. The lower reactivity of the synthesized catalyst could be due to lower acid site, pore volume, and surface area as demonstrated in Table 1. Despite this, the lower cost of the carbon-based catalyst compared to the commercial catalysts demonstrates the potential application and suggests possible future development of the carbon-based catalyst for this application. 3.3. Evaluation of Catalyst Reusability. Other than reactivity, deactivation of the carbon-based catalyst was compared with those of commercial catalysts to evaluate the catalyst reusability. Here, acetalization of 1,3-PDO at 35 °C was carried out repeatedly with the reaction time of 120 min for each reaction cycle. As shown in Figure 8, in the second and third reaction cycles, the reactivity decreased for all catalyst. The synthesized carbon-based catalysts deactivated considerably compared to the

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Figure 8. Comparison of deactivation of sulfonated carbon-based and commercial catalysts in aqueous solution (reaction temperature 35 °C, reaction time 120 min, catalyst to1,3-PDO ratio 0.7 g of catalyst/1 g of 1,3-PDO, and initial 1,3-PDO concentration 40 g/L).

commercial catalysts. The above results suggest that despite the potential application of the sulfonated carbon catalyst, improvement in terms of its acidity, surface area, and pore volume, as well as reusability, is still required to improve the performance of the catalyst in order to compete with the existing commercial ion-exchange catalysts. 3.4. Reactive Extraction of 1,3-PDO from Model Fermentation Mixture. The sulfonated carbon-based catalyst was tested at various temperatures (15, 25, 35 °C) for application in reactive extraction system, in which ethylbenzene was used as an extractant. The concentration profiles of 1,3-PDO in aqueous phase and 2-MD in both phases were similar in all cases as shown in Figure 9. At the beginning of the process, a sudden decrease in 1,3-PDO concentration was observed, while the 2-MD concentrations sharply increased in both phases. As the reactive extraction progressed, the concentration of 1,3-PDO in aqueous phase slowly decreased, while the 2-MD concentration in the extract phase increased as it was extracted from the aqueous phase, until equilibrium was reached. The process performance could be evaluated in terms of the percent recovery of 1,3-PDO determined from eq 4. % recovery of 1,3-PDO ) C1,3-PDO,i - (C1,3-PDO,f + C2-MD,f) × 100% C1,3-PDO,i

(4)

where C1,3-PDO,i is the initial molar concentration of 1,3-PDO and C1,3-PDO,f and C2-MD,f are the molar concentrations of 1,3PDO and 2-MD remaining in the aqueous phase at equilibrium. From these calculations, percent recovery values for 1,3-PDO at 15, 25, and 35 °C were 67, 81, and 83%, respectively. Since C1,3-PDO,f values were relatively small, these results indicate that a higher amount of 2-MD was extracted into the extract phase at higher temperature. These results agree with the mass distribution coefficients of 2-MD of 2.4, 6.5, and 11.7 at 15, 25, and 35 °C, respectively, determined according to eq 2, which were found to increase with increasing temperatures. Relatively high percent recovery of 1,3-PDO supports the potential use of sulfonated carbon-based catalyst for the separation of 1,3-PDO from aqueous fermentation solution by reactive extraction. 3.5. Application of Sulfonated Carbon-Based Catalyst for 2-MD Hydrolysis. To examine the feasibility of the application of sulfonated carbon-based catalyst for hydrolysis of 2-MD back to 1,3-PDO, 3 g of 2-MD and 0.53 g of water (equal molar quantities of 2-MD and water) were reacted in the presence of 0.1 g of sulfonated carbon-based catalyst at 90 °C. Immediately at the onset of the reaction, the highly viscous 1,3-PDO reaction product appeared. The GC analysis of the

Figure 9. Concentration profiles of 1,3-PDO in aqueous phase and 2-MD in both aqueous and organic phases at (a) 15, (b) 25, and (c) at 35 °C.

reaction product indicated that the hydrolysis reaction was completed within 20 min, at which time more than 99% of 2-MD was converted into 1,3-PDO. This result supports the potential application of the low-cost carbon-based catalyst for the entire separation process of 1,3-PDO by reactive extraction. 4. Conclusions Sulfonated carbon-based catalyst was shown to be feasible for reactive extraction recovery of 1,3-PDO from a dilute model aqueous fermentation mixture, using acetaldehyde as a reactant and ethylbenzene as an extractant. The suitable amount of catalyst for acetalization of 1,3-PDO and acetaldehyde was found to be 0.7 g/1 g of 1,3-PDO, giving the conversion of 92% after 120 min at 35 °C. The graphical analysis of chemical equilibrium constants at various temperatures indicated that acetalization was an exothermic reaction. The effectiveness of reactive extraction with the use of this catalyst was confirmed by the high recovery of 1,3-PDO. The catalyst was also proven to be suitable for the hydrolysis reaction in which the extracted 2-MD was converted back into 1,3-PDO, with as high as 99% conversion. Compared with the commercial Dowex 50-WX4200 and Amberlite IR120 (hydrogen form), although the carbonbased sulfonated catalyst required longer reaction time and has

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inferior stability, the low cost of such a catalyst makes it attractive enough for further development to improve its reactivity and stability for such an application. Acknowledgment The authors thank Dr. Veerapat Tantayakom and Dr. Phatthanon Prasitchoke (PTT Chemical Public Co. Ltd.) for helpful discussions. We also thank the Thailand Research Fund (TRF) under Project DBG52-Bunjerd Jongsomjit for financial support. Literature Cited (1) Zeng, A. P.; Biebl, H. Bulk chemicals from biotechnology: the case of 1,3-propanediol production and the new trends. AdV. Biochem. Eng.Biotechnol. 2002, 74, 239–259. (2) Ames, T. T. Process for the isolation of 1,3-propanediol from fermentation broth. U.S. Patent 6,361,983 B1, 2002. (3) Malinowski, J. J. Evaluation of liquid extraction potentials for downstream separation of 1,3-propanediol. Biotechnol. Tech. 1999, 13, 127– 130. (4) Li, S.; Tuan, V. A.; Falconer, J. L.; Noble, R. D. X-type zeolite membranes: preparation, characterization, and pervaporation performance. J. Membr. Sci. 2001, 191, 53–59.

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(5) Roturier, J.; Fouache, C.; Berghmans, E. Process for the purification of 1,3-propanediol from a fermentation medium. U.S. Patent 6,428,992 B1, 2002. (6) Hilaly, A.; Thomas, P. Method of recovering 1,3-propanediol from fermentation broth. U.S. Patent 6,479,716, 2002. (7) Malinowski, J. J. Reactive extraction for downstream separation of 1,3-propanediol. Biotechnol. Prog. 2000, 16, 76–79. (8) Hao, J.; Liu, H. J.; Liu, D. H. Novel Route of Reactive Extraction To Recover 1,3-Propanediol from a Dilute Aqueous Solution. Ind. Eng. Chem. Res. 2005, 44, 4380–4385. (9) Takagaki, A. Esterification of higher fatty acids by a novel strong solid acid. Catal. Today 2006, 116, 157–161. (10) Mo, X. A. Novel Sulfonated Carbon Composite Solid Acid Catalyst for Biodiesel Synthesis. Catal. Lett. 2008, 123, 1–6. (11) Gao, S. High efficient acetalization of carbonyl compounds with diols catalyzed by novel carbon-based solid strong acid catalyst. Chin. Sci. Bull. 2007, 52, 2892–2895. (12) Reimann, A.; Biebl, H.; Deckwer, W. D. Production of 1,3propanediol by Clostridium butyricum in continuous culture with cell recycling. Appl. Microbiol. Biotechnol. 1998, 49, 359–363. (13) Yun-Jin, F.; Peng, Z. Study on reactive extraction kinetics of 1,3propanediol in dilute aqueous solutions. Sep. Sci. Technol. 2006, 41 (2), 329–340.

ReceiVed for reView March 17, 2010 ReVised manuscript receiVed October 8, 2010 Accepted October 12, 2010 IE1019003