Recovery of butanol from ABE fermentation broth with hydrophobic

Subscriber access provided by Stockholm University Library

Article

Recovery of butanol from ABE fermentation broth with hydrophobic functionalized ionic liquids as extractant Hui Yu, Ke Cui, Tenghui Li, Zidong Zhang, Zhiyong Zhou, and Zhongqi Ren ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00434 • Publication Date (Web): 30 Apr 2019 Downloaded from http://pubs.acs.org on May 1, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Recovery of butanol from ABE fermentation broth with hydrophobic functionalized ionic liquids as extractant Hui Yu, Ke Cui, Tenghui Li, Zidong Zhang, Zhiyong Zhou*, and Zhongqi Ren* College of Chemical Engineering, Beijing University of Chemical Technology, NO. 15, North 3rd Ring Road East, Beijing 100029, People’s Republic of China *Corresponding author: +86-10-64434925, [email protected] (Zhongqi Ren); [email protected] (Zhiyong Zhou) ABSTRACT: Biobutanol has a high energy density, good miscibility with gasoline and a low environmental impact, and so is a possible substitute or additive for gasoline. Because biobutanol is typically obtained through so-called ABE fermentation, the effective separation of butanol from the product mixture is important. Ionic liquids have been used as extractants, and tailoring the IL structure to promote hydrogen bonding with butanol could improve the extraction performance. In the present work, an amine group

was

added

to

the

imidazole

cation

of

an

IL,

paired

with

bis(trifluoromethylsulfonyl)imide as the anion. Hydroxyl groups were added to the 1,8diazabicyclo-[5.4.0]-undec-7-ene cation, and an imidazolium-based IL was produced by combining hydroxyl with imidazole. The structures of these three ILs were verified by 1H nuclear magnetic resonance and Fourier transform infrared spectroscopic analyses. The binding energies between these substances and butanol, acetone and ethanol were calculated using the Gaussian software package based on density functional theory. The results indicated that the interaction energies between N,N-bis(2hydroxypropyl)octan-1-aminium hydroxide imidazole ([C8DIPA][Im]) and butanol,

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

acetone and ethanol are greater than that with water. These ILs were examined as extractants for the separation of butanol, acetone or ethanol with water, and the [C8DIPA][Im] exhibited the best performance. Effects of extraction time, extraction temperature and IL proportion on extraction rate were assessed, and this IL extracted 78%, 34% and 6% of the three components, respectively. This performance remained stable after ten recycling trials, and [C8DIPA][Im] was also used to separate the products in an actual ABE fermentation mixture. KEYWORDS: Solvent extraction; ABE fermentation; Biobutanol; Interaction energy; Reusability INTRODUCTION Butanol is a colorless, transparent liquid that is miscible with organic solvents like ethyl ether. It is widely employed in the chemical industry, including as a raw material to produce plasticizer, and for the synthesis of butyric acid and butyl acetate.1 Butanol is also often used as a solvent in extraction processes.2 In addition, butanol is a promising biofuel,3 as it has a low vapor pressure and high flash point, and so is relatively safe to transport and use. Butanol is not especially hygroscopic, thus reducing the potential for the corrosion of pipelines and other equipment, and lowering transportation and storage costs. Finally, butanol has been considered as a substitute for or additive to gasoline,4 as it is highly soluble in gasoline and is economically superior to bioethanol. Biobutanol is typically obtained by fermentation, employing renewable biomass as the raw material in conjunction with Clostridium bacteria. Because the end products


Page 2 of 51

Page 3 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


are primarily acetone, butanol and ethanol (in a 3:6:1 mass ratio), this process is known as ABE fermentation.5 As ABE fermentation generates several compounds, the efficient separation of butanol from the product mixture is important, and this has traditionally been accomplished via distillation,6 although methods such as adsorption,7 stripping8 and steam infiltration9 have also been reported. Other techniques that have been investigated include membrane extraction, reverse osmosis and membrane distillation, although the mass transfer coefficients of some of these methods may be relatively low.10-13 These techniques can also lead to environmental pollution as a result of the release of solvents, and can suffer from issues related to pressure loss during the separation. Liquid–liquid extraction, which removes products from an aqueous fermentation broth by employing a solvent in which the desired products have a higher distribution coefficient, is widely used in the chemical industry because it requires minimal energy consumption (due to the low operating temperatures and slow agitation rates) and is cost-effective compared with other extraction processes.14-16 Organic solvents are commonly used for extraction, but have associated risks owing to their volatility and potential for explosion. As a result, there is a need for the development of new types of extraction solvents, potentially based on ionic liquids (ILs). ILs are salts comprising organic cations and organic or inorganic anions and having melting points below 100 °C (sometimes as low as ambient temperature). These substances have been considered for use as substitutes for organic solvents because of their unique properties17-20 and limited environmental impacts. One advantage of ILs is that their physicochemical properties,



such as polarity and viscosity, can be tuned by changing the chemical structures of the cations and anions, allowing for numerous applications.21-23 There have been many reports regarding functional ILs in numerous applications, including separation,24 organic synthesis,25 catalysis,26 and fuel and solar cells,27 as well as their use as lubricants28 and functional materials.29 Because the end product of fermentation is essentially an aqueous solution, hydrophobic ILs are often used in the separation process. If ILs can be synthesized that will interact with butanol via hydrogen bonding, the strength of the interaction between these compounds will be increased and the extraction effect will be enhanced. Several common

hydrophobic

ILs,

including

bis(trifluoromethylsulfonyl)imide bis(trifluoromethylsulfonyl)imide

1-butyl-1-methylpyrrolidone

salts, salts

1-butyl-3-methylimidazolium and

1-hexyl-3-methylimidazolium

hexafluorophosphate, were assessed as extractants for the separation of simulated fermentation products by Kamiński et al.30 In addition, 1-hexyl-3-methylimidazolium tetracyanoborate was investigated with regard to the separation of products by Królikowski et al.31 This prior work demonstrated that the introduction of phosphino groups improved the extraction efficiency. Cascon et al.32 studied extraction with amine- and phosphino-based ILs, and found that the former exhibited better efficiency than the latter. There have also been rare instances in which hydrophilic ILs have been used as extractants for the separation of products. In the present work, three hydrophobic ILs, 1-(2-hydroxyethyl)-2,3,4,6,7,8,9,10octahydropyrimido[1,2-ɑ]azepim-1-ium

bis(trifluoromethylsulfonyl)imide


Page 4 of 51

Page 5 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


([HeDBU][NTf2]),

3-(3-(dimethylamino)propyl)-1-methyl-1H-imidazol-3-ium

bis(trifluoromethylsulfonyl)imide hydroxypropyl)octan-1-aminium

([DPAIm][NTf2]) hydroxide

imidazole

and

N,N-bis(2-

([C8DIPA][Im]),

were

synthesized using a two-step method, based on initial calculations with Gaussian software using density functional theory. These substances were characterized via Fourier transform infrared (FT-IR) spectroscopy and 1H nuclear magnetic resonance (NMR), and the associated binding energies were determined to ensure that these ILs would be able to separate specific compounds. The effects of extraction temperature, extraction time, IL concentration and recycling on extraction performance were subsequently studied. Finally, the optimal IL was applied to the separation of an actual fermentation broth. EXPERIMENTAL SECTION Reagents. Butanol, acetone, hydrochloric acid, acetonitrile, petroleum ether, copper sulfate and acetic acid were all supplied by Beijing Chemical Works (Beijing, China). Anhydrous ethanol, tert-butanol and ethyl acetate were supplied by the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), while bromo-n-hexane, bromo-n-octane,

3-dimethylamino-1-propanol,

bromododecane

and

hexadecyl

bromide were acquired from the Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). DBU was obtained from the Accela ChemBio Co., Ltd. (Shanghai, China) and 2-bromoethanol was obtained from Energy Chemical (Shanghai, China). Ion exchange resin was supplied by Alfa Aesar (Shanghai, China), imidazole was supplied by Adamas Reagent Home (Shanghai, China), and diisopropanolamine was



acquired from the Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). Each of the above reagents was analytical reagent purity, except for the tert-butanol, which was chromatographic reagent purity. All trials used deionized water produced in our own laboratory. Preparations of model fermentation products and ILs. Preparation of model fermentation products. First, the model binary solution was prepared by dissolving certain amount of butanol (1.2% wt), acetone (0.6% wt) or ethanol (0.2% wt) in water. Second, the model fermentation product solution was prepared by dissolving butanol, acetone and ethanol simultaneously in water with the corresponding concentrations of 1.2% wt, 0.6% wt and 0.2% wt, respectively. Synthesis of [HeDBU][NTf2]. This IL was synthesized using a two-step method. First, 0.1 mol DBU was transferred into a three-necked flask, after which a small amount of an ethyl acetate/ acetonitrile mixture (volume ratio of 1:1) was added as the solvent. A 0.11 mol quantity of bromoethanol was added dropwise and the mixture was refluxed for 8 h. Following this, cold ethyl acetate (-8 °C) was added dropwise to the reaction mixture. The resulting solid precipitate appeared, and subsequently it was filtered to recrystallize, followed by drying under vacuum at 85 °C for 48 h to obtain the [HeDBU][Br]. Following this, an aqueous solution containing equimolar amounts of [HeDBU][Br] and LiNTf2 was stirred at room temperature for 12 h, after which the aqueous phase was removed and the remaining organic phase was washed with deionized water. Residual water was removed from the product at 80 °C, followed by drying under vacuum at 80 °C for 24 h to obtain [HeDBU][NTf2] with a purity of 89.9%


Page 6 of 51

Page 7 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and yield of 25.9%. The synthetic pathway is summarized in Fig. 1. Synthesis of [DPAIm][NTf2]. The synthesis of the amine-based IL was complicated. First, a 0.1 mol quantity of 3-dimethylamino-1-propanol was transferred into a three-necked flask, after which a quantity of acetic acid was slowly added as the solvent, followed by stirring. This solution was placed in an ice bath and 0.1 mol of 32% hydrochloric acid solution was slowly added. Subsequently, the mixture was refluxed by heating in an oil bath, after which the acetic acid was removed at 100 °C and the solid product was purified by recrystallization from acetone. Equimolar amounts of this crystalline product and N-methylimidazole were dissolved in acetone and the solution was stirred at 70 °C for 8 h, following which the acetone was evaporated at 50 °C to obtain the intermediate product. This compound was then stirred at room temperature for 12 h with an equimolar amount of LiNTf2 aqueous solution, followed by removal of the aqueous phase. The organic phase was washed with deionized water and residual water was removed. Finally, the product was dried under vacuum to obtain [DPAIm][NTf2] with a purity of 78.5% and yield of 36.7%. The synthetic pathway is shown in Fig. 2. Synthesis of [C8DIPA][Im]. The IL [C8DIPA][Im] was prepared by ion exchange. First, 0.1 mol diisopropanolamine was placed in a three-necked flask, after which 0.12 mol brominated n-octane was added dropwise, together with a small amount of ethanol as the solvent. The mixture was refluxed at 60 °C for 72 h, following which the ethanol was removed at 60 °C and the product washed several times with petroleum ether. Subsequently, the petroleum ether was removed at 50 °C and the product dried under



vacuum at 60 °C for 24 h to obtain [C8DIPA][Br]. This material was ion-exchanged using an anion resin to give [C8DIPA][OH]. An aqueous solution of [C8DIPA][Im] was then obtained by stirring a [C8DIPA][OH] aqueous solution with an equimolar amount of imidazole at room temperature for 24 h, followed by drying under vacuum at 60 °C for 48 h. The purity and yield of [C8DIPA][Im] are 84.5% and 54.8%. The associated synthetic pathway is provided in Fig. 3. Extraction procedure. All the extraction experiments were conducted in 100 mL conical flasks. Equal volume of model binary solution, model fermentation product solution or actual fermentation system and IL were added into flask, which was continuously stirred for 30 min at 25 °C. Following this, the complete separation of two phases was obtained by settling the flask for 30 min. An aqueous solution sample was taken out from the upper phase for determination of residual fermentation product concentration. The concentration of fermentation product in the IL phase could be obtained by material balance calculating. Stripping of the IL phase in previous experiments demonstrated that the calculated values deviations of fermentation product concentrations were within ± 3%. In addition, the solubilities of the three ILs used in this work in water are 0.09% wt for [HeDBU][NTf2], 0.39% wt for [DPAIm][NTf2] and 0.32% wt for [C8DIPA][Im], respectively. Analytical method. Gas chromatography (GC) employing tert-butanol as an internal standard was used for analyzing the fermentation product concentration. An Agilent 7890A GC, in conjunction with a flame ionization detector and a 0.25 mm × 30 m DB-FFAP capillary column were used for analysis. The injector and detector


Page 8 of 51

Page 9 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


temperatures were 220 and 250 °C, respectively. The temperature of the column was increased from 60 to 150 °C at 15 °C/min and N2 was used as the carrier gas at a flow of 40 mL/min. The column, H2 and air flow rates were 0.8, 30 and 300 mL/min, respectively, equating to a split ratio of 60:1. The extraction percentages, E, of butanol and other substances were used to determine the performance of each IL. This value was calculated as E (%) 

Co  Ce  100 , Co

(1)

where Co and Ce refer to the initial concentration and equilibrium concentration, respectively, of the analyte. RESULTS AND DISCUSSION Characterization of ILs. The composition of [HeDBU][NTf2] was confirmed based on the 1H-NMR spectrum (400 MHz, CDCl3), 13C-NMR spectrum (400 MHz, CDCl3), FT-IR spectrum, elemental analysis and ES-MS, as shown in Figs. 4, 5 and 6. The 1H-NMR spectrum contains peaks at δ values of 3.79 (s, 1H, OH), 3.53-3.59 (s, 6H, 9,10,11-H), 3.38 (s, 4H, 6,7-H), 2.65 (s, 2H, 2-H), 2.06 (s, 2H, 8-H) and 1.73 (s, 6H, 3,4,5-H). The 13C-NMR δ 167.40 (s), 166.29 (s), 124.54 (s), 121.35 (s), 118.15 (s), 114.96 (s), 77.44 (d, J = 12.1 Hz), 77.18 (s), 76.86 (s), 59.17 (s), 55.55 (s), 55.22 (s), 54.73 (s), 49.09 (s), 48.59 (s), 47.27 (s), 38.45 (s), 33.20 (s), 28.68 (s), 28.40 (d, J = 8.7 Hz), 26.23 (s), 25.70 (s), 23.52 (s), 22.60 (s), 19.60 (s), 19.10 (s). The FT-IR spectrum shows a peak attributed to O-H bond stretching at 3546 cm-1, primarily due to a small amount of residual water. The peak at 3355 cm-1 corresponds to the stretching vibration of O-H bonds in ethanol, while the peaks from 3156 to 2865 cm-1 are stretching



vibrations of C-H bonds. The peaks from 1650 to 1452 cm-1 are ascribed to C=N bond stretching, while that at 1351 cm-1 corresponds to the asymmetric and symmetric stretching of O=S=O groups. The peaks at 1270 and 1191 cm-1 are attributed to C-N bond stretching, while those between 990 cm-1 and 662 cm-1 are caused by the bending vibrations of C-H bonds. Elemental analysis: calcd for [HeDBU][NTf2]: C, 32.70; H, 4.43; N, 8.80; S, 13.43. Found: C, 31.06; H, 3.84; N, 10.13; S, 14.78. ES-MS: ES+ m/z 197.1655 [HeDBU]+, ES- m/z 279.9181 [NTf2]-. Thus, the prepared IL had the expected structure. The composition of the [DPAIm][NTf2] was confirmed based on the 1H-NMR spectrum (400 MHz, DMSO-d6) in Fig. 7, 13C-NMR spectrum (400 MHz, CDCl3) in Fig. 8, FT-IR spectrum in Fig. 9, elemental analysis and ES-MS. The 1H-NMR spectrum contains peaks at δ values of 7.95 (s, 1H, CH-2), 7.22 (s, 1H, CH-3), 7.09 (s, 1H, CH-4), 3.71 (s, 3H, CH-1), 3.52 (s, 2H, CH-5), 3.13 (s, 3H, CH-7), 2.79 (s, 6H, CH-8, CH-9) and 1.79 (s, 2H, CH-6). The 13C-NMR δ 170.23 (s), 136.28 (s), 124.24 (s), 123.47 – 120.96 (m), 121.04 (s), 121.04 (s), 117.84 (s), 114.65 (s), 60.76 (s), 57.84 (s), 55.07 (s), 54.04 (s), 42.77 – 42.08 (m), 39.83 (d, J = 17.4 Hz), 39.74 (s), 39.78– 39.20 (m), 39.08 (s), 38.89 (s), 38.77 (d, J = 21.0 Hz), 34.50 (s), 26.85 (d, J = 10.1 Hz), 23.36 (s), 20.28 (s). In the FT-IR spectrum, the O-H bond stretching vibration appears at 3554 cm-1, indicating that the IL was not completely dry. The peaks at 3158 and 2969 cm-1 are ascribed to methylene C-H stretching, while that at 1736 cm-1 is due to C=N stretching. The peaks at 1588 and 1553 cm-1 are ascribed to C=C stretching and the imidazole ring skeleton generates peaks at 1473 and 1530 cm-1. The peak at 1351 cm-1


Page 10 of 51

Page 11 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is due to the asymmetric and symmetric stretching vibrations of O=S=O bonds. The peaks resulting from C-N stretching are present at 1228 and 1194 cm-1, while those at 1137 and 1057 cm-1 result from C-F stretching and those between 950 and 662 cm-1 are attributed to C-H bending. Elemental analysis: calcd for [DPAIm][NTf2]: C, 29.47; H, 4.05; N, 12.50; S, 14.30. Found: C, 23.70; H, 2.75; N, 10.56; S, 16.24. ES-MS: ES+ m/z 169.0107 [DPAIm]+, ES- m/z 279.9180 [NTf2]-. These data confirm the expected structure. The composition of the [C8DIPA][Im] was determined based on the 1H-NMR (400 MHz, CDCl3) spectrum in Fig. 10, 13C-NMR spectrum (400 MHz, CDCl3) in Fig. 11, FT-IR spectrum in Fig. 12, elemental analysis and ES-MS. The 1H-NMR spectra for [C8DIPA][Im] contains peaks at δ values of 7.46 (s, 1H, 17-H), 6.86 (s, 2H, 15,16-H), 3.80 (s, 2H, OH), 3.67 (s, 2H, 2,5-H), 2.36 (s, 2H, 7-H), 2.24 (s, 4H, 3,4-H), 1.28 (m, 2H, 8-H), 1.12 (t, 10H, 9,10,11,12,13-H), 0.97 (s, 6H, 1-H, 6-H) and 0.71 (s, 3H, 14H). The 13C-NMR (400 MHz, CDCl3) δ 136.61 (s), 134.97 (s), 128.14 (s), 121.42 (s), 119.02 (s), 77.81 (d, J = 11.7 Hz), 77.55 (s), 77.23 (s), 64.85 (d, J = 11.8 Hz), 64.07 – 63.60 (m), 63.33 (d, J = 16.8 Hz), 63.24 – 62.54 (m), 62.33 (d, J = 39.5 Hz), 56.87 (s), 56.54 (d, J = 15.5 Hz), 55.53 (d, J = 4.8 Hz), 55.16 (s), 54.83 (d, J = 10.1 Hz), 46.94 (s), 31.72 – 31.23 (m), 30.77 (s), 29.32 (s), 29.08 (s), 28.78 (t, J = 9.2 Hz), 27.00 (dd, J = 37.6, 30.1 Hz), 26.35 (s), 26.30 (d, J = 4.0 Hz), 26.15 – 25.64 (m), 22.41 (d, J = 4.8 Hz), 21.12 (t, J = 7.5 Hz), 20.65 (s), 20.37 (d, J = 12.9 Hz), 18.14 (s), 13.89 (d, J = 3.8 Hz). In the FT-IR spectrum of [C8DIPA][Im], a peak appears at 3188 cm-1 corresponding to O-H stretching. Peaks at 2855, 2927 and 2960 cm-1 are attributed to



C-H, while those at 1533 and 1458 cm-1 are ascribed to the imidazole ring skeleton. The peaks generated by C-C stretching appear at 1375 and 1329 cm-1. The peaks at 1135 and 1257 cm-1 are due to C-N stretching and those from 950 to 662 cm-1 result from the bending vibration of C-H bonds. Elemental analysis: calcd for [C8DIPA][Im]: C, 65.13; H, 11.25; N, 13.40. Found: C, 62.68; H, 11.04; N, 13.17. ES-MS: ES+ m/z 246.2441 [C8DIPA]+, ES- m/z 67.4575 [Im]-. Thus, the structure of the IL was as expected. Screening of ionic liquids. Because ILs are costly, it is crucial to employ the lowest possible quantity so as to reduce expenses in industrial processes. However, it is more important to extract butanol at a greater proportion relative to the amounts of acetone and ethanol extracted. Thus, the effects of the ratio of the IL to the feed volume were studied and the results are showed in Figs. 13, 14 and 15. These data indicate that the proportion of butanol extraction using all three ILs was significantly higher than that of ethanol. However, using either [HeDBU][NTf2] or [DPAIm][NTf2] as the extractant, the difference between the extraction amounts of butanol and acetone was less than that obtained using [C8DIPA][Im]. As the volumebased proportion of each IL in the extraction solutions was increased, the extraction percentages also gradually increased, although this effect plateaued at ratios greater than 1:1. Therefore, the optimal IL to solution volume ratio was 1:1. To better understand the interactions between the three ILs and the fermentation products, the binding energies between the ILs and acetone, butanol, ethanol and water were calculated. The ChemBiodraw software program was used to draw the structures


Page 12 of 51

Page 13 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of each compound, after which these structures were optimized with the Chem3D program. These structures were further optimized using the GaussianView09 software so as to obtain the lowest interaction energy values. The binding energies were then calculated via DFT using the B3LYP/6-311G** functional. The optimized geometric structures of the three ILs and of butanol, acetone, ethanol and water are presented in Fig. 16, while Table 1 lists the interaction energies between the products and the ILs. It is evident that the binding of [C8DIPA][Im] to the products decreases in the order butanol>acetone>ethanol>H2O, which is in agreement with the experimental results. Because the interaction energies between [C8DIPA][Im] and butanol, acetone and ethanol were all greater than the value for water, this IL could potentially be used as an extractant. The above results demonstrate that [C8DIPA][Im] is an extremely effective extractant. Because this material is relatively inexpensive and attains extraction equilibrium within a short time span, it could be used for separating ABE fermentation products.33 The extraction efficiency is determined partly by the hydrophobic character of the IL. The relative polarity of the IL is also important, because the dissolution behavior of a solvent is related to its relative polarity. More highly relative polar ILs will have greater dielectric constants, which in turn reduces the extraction effect, and so less polar ILs are better-suited to extraction processes.34 A comparison of the three ILs shows that the [C8DIPA][Im] was the best extractant, likely because hydrogen bonds can be formed between hydrogen atoms of the imidazole



anion and the alcohol and the symmetrical cation is less polar. The combination of these two effects increases the extraction rate significantly.35 Separation of model fermentation products with [C8DIPA][Im]. In subsequent trials, a simulated fermentation product composed of butanol, acetone, ethanol and deionized water in a 1.2:0.6:0.2:98 ratio was extracted. These trials employed only [C8DIPA][Im], as the prior experiments showed it to have the best performance. Effects of carbon chain length, extraction temperature, extraction time, IL concentration and IL recycling on extraction performance were studied. Effect of the carbon chain length of [C8DIPA][Im]. ILs with different carbon chain lengths prepared in this work were used as extractants to separate the simulated products, with the results shown in Fig. 17. The data show that increasing the carbon chain length gradually decreases the butanol and acetone extraction rates, while the data for ethanol show no specific trend, possibly as a result of variations in the residual ethanol concentration in the IL. It also appears that reducing the polarity of the IL slightly increases its hydrophobicity while decreasing the extraction rate. The IL with a six carbon chain was less hydrophobic, and so the version having an eight carbon chain was chosen for use in subsequent experiments. Effect of extraction temperature. Temperature is a significant factor in the extraction process, as it not only affects the extraction efficiency but also the extent of energy consumption. Therefore, effect of temperature on extraction rate was studied. Fig. 18 shows that temperature had nearly no significant effect on extraction rate, possibly because the interaction forces were not greatly affected by temperature. Thus,


Page 14 of 51

Page 15 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


because a higher temperature increases energy requirements and may result in evaporation of the volatile products, ambient temperature was employed in subsequent trials. Effect of extraction time. When the extraction process reached equilibrium, the extraction effect was stable. It was therefore necessary to make system achieve equilibrium. Therefore, effect of extraction time on extraction rate was investigated, to determine at what point the extraction effect plateaued. The results are showed in Fig. 19. These data indicate that the extraction process was rapid, such that equilibrium was achieved within 1 min. This rapid equilibration can likely be attributed to the low viscosity of the IL at room temperature, which increased both the transfer rate and mass transfer coefficient. Effect of the IL proportion. Using a small amount of IL may not produce the desired extraction effect, while using too much will result in excess waste and energy consumption. Therefore, effect of employing varying proportions of the IL on the extraction rate was examined, and the resulting data are shown in Fig. 20. The abscissa of this plot represents the volume ratio of the IL in the solution. These results demonstrate that, when using smaller quantities of the IL, the extraction rate increases along with increasing the amount of the IL. However, the butanol extraction rate was only marginally increased, and so the optimal IL to extraction solution ratio based on limiting energy usage was determined to be 1:1. Effect of IL recycling. Because ILs are difficult to synthesize and costly, they are currently used solely in laboratory environments, and have not been scaled up for



application in industry. If ILs that are readily regenerated and exhibit stable performance, such that they can be recycled to reduce costs, can be identified, these materials could be widely applied. In the present work, the IL was regenerated through rotary evaporation and the extraction abilities of the recycled IL were studied. The results are showed in Fig. 21. These data demonstrate that, as the number of recoveries is increased, the extraction effect remains approximately stable. Thus, the IL maintained its original extraction efficiency after reuse. Application to an actual fermentation system. The above results show that [C8DIPA][Im] works as an effective extractant for the separation of butanol from simulated fermentation products, and so this compound was applied to an actual fermentation system. In subsequent trials, Clostridium acetobutylicum ATCC 824 was cultured in a solution including 5-HMF, acetic acid and lignocellulose to simulate the ABE fermentation process. The substance of culture dish consisted of water containing corn flour at a concentration of 80 g/L. The proliferation medium was a synthetic material containing 40-60 g/L glucose, 2.2 g/L ammonium acetate, 0.001 g/L paminobenzoic acid and 0.0001 g/L biotin in a buffer containing 1 g/L KH2PO4 and 1 g/L K2HPO4 together with 0.2 g/L MgSO4, 0.01 g/L MnSO4 and 0.01 g/L FeSO4. The bacteria was subsequently cultivated in 100 and 150 mL bottles containing glucose solution, after which the Clostridium spores were heated at 80 °C for 10 min and then rapidly cooled in ice water. High purity nitrogen gas was continuously introduced into the medium for more than 15 min to ensure an anaerobic environment. After the


Page 16 of 51

Page 17 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


inoculation was complete, the solution was placed for settling at 60 °C for 60-96 h, following which a fermentation broth was obtained after fermentation lasting for 80 h. In these trials, [C8DIPA][Im] was employed as the extractant, using the optimized extraction conditions obtained from the simulated fermentation experiments. These consisted of an ionic liquid to fermentation broth volume ratio of 1:1, an extraction time of 30 min and a temperature of 25 °C. The concentrations of the fermentation products before and after extraction are summarized in Table 2. From these results, it is apparent that the [C8DIPA][Im] extracted 82%, 38.2% and 1.18% of the butanol, acetone and ethanol, respectively, similar to the performance obtained with the simulated fermentation system. Table 3 lists the comparison of extraction performances of different ionic liquids. The extraction performance obtained in this work was significantly superior to that reported in literatures. Compared with other extractants, [C8DIPA][Im] could extract more butanol and less acetone and ethanol with much less time to reach equilibrium. These results indicate that [C8DIPA][Im] could be used for effective recovery of butanol from ABE fermentation broth. CONCLUSION In this work, three ILs were synthesized, incorporating hydroxyl, amine or imidazole groups. These compounds were characterized, and the results were consistent with the expected structures. The binding energies associated with these ILs were determined with the Gaussian software package based on density functional theory. One of the three, [C8DIPA][Im], showed good extraction performance and was able to



rapidly achieve equilibrium. The performance of this IL was also basically unchanged after recovery and reuse during separation of simulated fermentation products, indicating good stability. Finally, [C8DIPA][Im] was used as the extractant to separate an actual fermentation mixture, and the results suggest that an imidazolium-based IL could be suitable for use in such applications. AUTHOR INFORMATION Corresponding Author * [email protected] * [email protected] ORCID Zhongqi Ren: 0000-0002-2571-5702 Zhiyong Zhou: 0000-0001-6436-1399 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS

We thank Michael D. Judge, MSc, from Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript. We thank the supports by High performance computing platform of Beijing University of Chemical Technology. This work was supported by the National Natural Science Foundation of China (21576010, 21606009, U1607107 and U1862113) and Beijing Natural Science Foundation (2172043). The authors gratefully acknowledge these grants.


Page 18 of 51

Page 19 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES (1) Oudshoorn, A.; Wielen, L. A. M. V. D.; Straathof, A. J. J. Assessment of options for selective 1-butanol recovery from aqueous solution. Ind. Eng. Chem. Res. 2009, 48, 7325-7336. (2) Wang, Y. R.; Chiang, Y. S.; Chuang, P. J.; Chao, Y. P.; Li, S. Y. Direct in situ butanol recovery inside the packed bed during continuous acetone-butanol-ethanol (abe) fermentation. Appl. Microbiol. Biotechnol. 2016, 100, 7449-7456. (3) Patraşcu, I.; Bîldea, C. S.; Kiss, A. A. Eco-efficient butanol separation in the abe fermentation process. Sep. Purif. Technol. 2017, 177, 49-61. (4) Huang, H. J.; Ramaswamy, S.; Liu, Y. Separation and purification of biobutanol during bioconversion of biomass. Sep. Purif. Technol. 2014, 132, 513-540. (5) Merlet, G.; Uribe, F.; Aravena, C.; Rodríguez, M.; Cabezas, R.; QuijadaMaldonado, E.; Romero, J. Separation of fermentation products from ABE mixtures by perstraction using hydrophobic ionic liquids as extractants. J. Membrane Sci. 2017, 537, 337-343. (6) Diaz, V. H. G.; Tost, G. O. Energy efficiency of acetone, butanol, and ethanol (ABE) recovery by heat-integrated distillation. Bioproc. Biosyst. Eng. 2018, 41, 395-405. (7) Faisal, A.; Zhou, M.; Hedlund, J.; Grahn, M. Recovery of butanol from model ABE fermentation broths using MFI adsorbent: a comparison between traditional beads and a structured adsorbent in the form of a film. Adsorption, 2016, 22, 205-214. (8) Abdehagh, N.; Dai, B.; Thibault, J.; Tezel, F. H. Biobutanol separation from abe



model solutions and fermentation broths using a combined adsorption-gas stripping process. J. Chem. Technol. Biot. 2017, 92, 245-251. (9) Knozowska, K.; Kujawska, A.; Kujawa, J.; Kujawski, W.; Bryjak, M.; Chrzanowska, E.; Kujawski, J. K. Performance of commercial composite hydrophobic membranes applied for pervaporative reclamation of acetone, butanol, and ethanol from aqueous solutions: binary mixtures. Sep. Purif. Technol. 2017, 188, 512-522. (10)Fang, W. J.; Shao, D. B.; Lu, X. X.; Guo, Y. S.; Xu, L. Extraction of aromatics from hydrocarbon fuels using n-alkyl piperazinium-based ionic liquids. Energ. Fuel. 2012, 26, 2154–2160. (11)Zhang, F.; Li, Y.; Zhang, L. L.; Zhou, Z. Y.; Sun, W.; Ren, Z. Q. Benzyl- and vinylfunctionalized imidazoium ionic liquids for selective separating aromatic hydrocarbons from alkanes. Ind. Eng. Chem. Res. 2016, 55, 747-756. (12)Larriba, M.; Navarro, P.; García, J.; Rodríguez, F. Liquid-liquid extraction of btex from reformer gasoline using binary mixtures of [4empy][Tf2N] and [emim][DCA] ionic liquids. Energ. Fuel. 2014, 28, 6666-6676. (13)Zhang, J.; Huang, C. P.; Chen, B. H.; Ren, P. J.; Lei, Z. G. Extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures using chloroaluminate roomtemperature ionic liquids as extractants. Energ. Fuel. 2007, 21, 1724-1730. (14)Bankar, S. B.; Survase, S. A.; Singhal, R. S.; Granström, T. Continuous two stage acetone-butanol-ethanol fermentation with integrated solvent removal using clostridium acetobutylicum b 5313. Bioresource Technol. 2012, 106, 110-116.


Page 20 of 51

Page 21 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15)Yen, H. W.; Wang, Y. C. The enhancement of butanol production by in situ butanol removal using biodiesel extraction in the fermentation of abe (acetone-butanolethanol). Bioresource Technol. 2013, 145, 224-228. (16)Birajdar, S. D.; Rajagopalan, S.; Sawant, J. S.; Padmanabhan, S. Continuous countercurrent liquid–liquid extraction method for the separation of 2,3-butanediol from

fermentation

broth

using

n-butanol

and

phosphate

salt. Process

Biochem. 2015, 50, 1449-1458. (17)Rogers, R. D. Materials science: reflections on ionic liquids. Nature 2007, 447, 917-918. (18)Earle, M. J.; Esperança, J. M.; Gilea, M. A.; Lopes, J. N.; Rebelo, L. P.; Magee, J. W.; Seddon, K. R.; Widegren, J. A. The distillation and volatility of ionic liquids. Nature 2006, 439(7078), 831-834. (19)Maton, C.; De, V. N.; Stevens, C. V. Ionic liquid thermal stabilities: decomposition mechanisms and analysis tools. Chem. Soc. Rev. 2013, 42, 5963-5977. (20)Plaquevent, J.; Levillain, J.; Guillen, F.; Malhiac, C.; Gaumont, A. Cheminform abstract: ionic liquids: new targets and media for α‐amino acid and peptide chemistry. Chem. Rev. 2008, 108, 5035. (21)Giernoth, R. Task-specific ionic liquids. Angew. Chem. Int. Ed. 2010, 49, 28342839. (22)Bates, E. D.; Mayton, R. D.; Ntai, I.; Davis, J. H. CO(2) capture by a task-specific ionic liquid. J. Am. Chem. Soc. 2002, 124, 926-927. (23)Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Mayton, R.; Sheff, S.; Wierzbicki,



A.; Davis Jr., J. H.; Rogers, R. D. Task-specific ionic liquids for the extraction of metal ions from aqueous solutions. Chem. Commun. 2001, 135-136. (24)Manohar, C. V.; Banerjee, T.; Mohanty, K. Co-solvent effects for aromatic extraction with ionic liquids. J. Mol. Liq. 2013, 180, 145-153. (25)Sawant, A. D.; Raut, D. G.; Darvatkar, N. B.; Salunkhe, M. M. Recent developments of task-specific ionic liquids in organic synthesis. Green Chem. Lett. Rev. 2011, 4, 41-54. (26)Lucchini, V.; Noè, M.; Selva, M.; Fabris, M.; Perosa, A. Cooperative nucleophilicelectrophilic organocatalysis by ionic liquids. Chem. Commun. 2012, 48, 51785180. (27)Zhao, J.; Yan, F.; Qiu, L. H.; Zhang, Y. G.; Chen, X. J.; Sun, B. Q. Benzimidazolyl functionalized ionic liquids as an additive for high performance dye-sensitized solar cells. Chem. Commun., 2011, 47, 11516-11518. (28)Zeng, Z.; Phillips, B. S.; Xiao, J. C.; Shreeve, J. M. Polyfluoroalkyl, polyethylene glycol, 1,4-bismethylenebenzene, or 1,4-bismethylene-2,3,5,6-tetrafluorobenzene bridged functionalized dicationic ionic liquids: synthesis and properties as high temperature lubricants. Chem. Mater. 2008, 20, 2719-2726. (29)Zhang, Y. J.; Shen, Y. F.; Yuan, J. H.; Han, D. X.; Wang, Z. J.; Zhang, Q. X.; Niu, L. Design and synthesis of multifunctional materials based on an ionic-liquid backbone. Angew. Chem. Int. Ed. 2010, 45, 5867-5870. (30)Kamiński, W.; Górak, A.; Kubiczek, A. Modeling of liquid–liquid equilibrium in the quinary system of water, acetone, n -butanol, ethanol, and ionic liquid. Fluid


Page 22 of 51

Page 23 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Phase Equilibr. 2014, 384, 114-121. (31)Domańska, U.; Królikowski, M. Extraction of butan-1-ol from water with ionic liquids at t = 308.15 k. J. Chem. Thermodyn. 2012, 53, 108-113. (32)Cascon, H. R.; Choudhari, S. K.; Nisola, G. M.; Vivas, E. L.; Lee, D. J.; Chung, W. J. Partitioning of butanol and other fermentation broth components in phosphonium and ammonium-based ionic liquids and their toxicity to solventogenic clostridia. Sep. Purif. Technol. 2011, 78, 164-174. (33)Roffler, S.; Blanch, H. W.; Wilke, C. R. Extractive fermentation of acetone and butanol: process design and economic evaluation. Biotechnol. Progr. 2010, 3, 131140. (34)Kurkijärvi, A.; Lehtonen, J.; Linnekoski, J. Novel dual extraction process for acetone–butanol–ethanol fermentation. Sep. Purif. Technol. 2014, 124, 18-25. (35)Rabari, D.; Banerjee, T. Biobutanol and n-propanol recovery using a low density phosphonium based ionic liquid at t = 298.15 k and p = 1 atm. Fluid Phase Equilibr. 2013, 355(5), 26-33. (36)Stoffers, M.; Górak, A. Continuous multi-stage extraction of n -butanol from aqueous solutions with 1-hexyl-3-methylimidazolium tetracyanoborate. Sep. Purif. Technol. 2013, 120, 415-422. (37)Fadeev, A. G.; Meagher, M. M. Opportunities for ionic liquids in recovery of biofuels. Chem. Commun. 2001, 3, 295-296.



List of Tables Table 1. Interaction energies between [C8DIPA][Im] and products. Table 2. Concentrations of products. Table 3. Comparison of extraction performances of different ionic liquids.


Page 24 of 51

Page 25 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Interaction energies between [C8DIPA][Im] and products. System

E/hartreea

E/kJ/mol

∆E/kJ/mol

Butanol

-233.74

-613753.03

-

Acetone

-193.22

-507343.45

-

Ethanol

-155.10

-407241.55

-

H2O

-76.46

-200761.22

-

[C8DIPA][Im]

-985.03

-2586450.74

-

[C8DIPA][Im]-butanol

-1218.79

-3200226.83

-22.68

[C8DIPA][Im]-acetone

-1178.26

-3093814.55

-20.36

[C8DIPA][Im]-ethanol

-1140.13

-2993712.20

-19.91

[C8DIPA][Im]-H2O

-1061.50

-278731.31

-19.36

1 Hartree = 27.211 eV = 627.509 kcal/mol = 2625.753 kJ/mol



Page 26 of 51

Table 2. Concentrations of products. Butanol

Acetone

Ethanol

concentration/%

concentration/%

concentration/%

Fermentation liquid

0.931

0.350

0.499

Raffinate phase

0.163

0.216

0.493


Page 27 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3. Comparison of extraction performances of different ionic liquids. Ionic liquid

System

Extraction condition

Extraction rate

[C8DIPA][I

Real system

Extraction time: 30

Butanol: 82%

min

Acetone: 38.2%

Settling time: 30 min

Ethanol: 1.18%

m]

[Ph3t][NTf]

Multi-component：

Extraction time: 24 h

Butanol: 52.38%

32

butanol-acetone-

Settling time: 24 h

Acetone: 43.5%

ethanol-water

Ethanol: 9.91%

[THA][DH

Multi-component：


Butanol: 88.76%

SS]32

butanol-acetone-

Settling time: 24 h

Acetone: 44.13%

ethanol-water

Ethanol: 44.13%

[Im6,1][tcb]3

Two-component：


6

butanol-water

Temperature: 35 °C

Butanol: 85%

Volume ratio: 1:1 Settling time: 15 h [P14,6,6,6][TC Two-component：


B]31

Temperature: 35 °C

butanol-water

Butanol: 80%

Volume ratio: 1:1 Settling time: 24 h [OMIM][PF Two-component： 37

6]

butanol-water

Extraction

time: Butanol: 48%

overnight Temperature: 23 °C Volume ratio: 1:1 Settling time: 1-3 d



Figure Captions Figure 1. Synthesis pathway of [HeDBU][NTf2]. Figure 2. Synthesis pathway of [DPAIm][NTf2]. Figure 3. Synthesis pathway of [C8DIPA][Im]. Figure 4. 1H-NMR spectrum of [HeDBU][NTf2]. Figure 5. 13C-NMR spectrum of [HeDBU][NTf2]. Figure 6. FT-IR spectrum of [HeDBU][NTf2]. Figure 7. 1H-NMR spectrum of [DPAIm][NTf2]. Figure 8. 13C-NMR spectrum of [DPAIm][NTf2]. Figure 9. FT-IR spectrum of [DPAIm][NTf2]. Figure 10. 1H-NMR spectrum of [C8DIPA][Im]. Figure 11. 13C-NMR spectrum of [C8DIPA][Im]. Figure 12. FT-IR spectrum of [C8DIPA][Im]. Figure 13. Effect of volume ratio of [HeDBU][NTf2] to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C). Figure 14. Effect of volume ratio of [DPAIm][NTf2] to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C). Figure 15. Effect of volume ratio of [C8DIPA][Im] to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C). Figure 16. Geometries optimizations of (a) cation and antion of [C8DIPA][Im], (b) [C8DIPA][Im] and butanol, (c) [C8DIPA][Im] and acetone, (d) [C8DIPA][Im] and ethanol and (e) [C8DIPA][Im] and H2O.


Page 28 of 51

Page 29 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 17. Effect of carbon chain length of ionic liquid on extraction rate (extraction time: 30 min, extraction temperature: 30 °C, volume ratio of ionic liquid to feed solution: 1:1). Figure 18. Effect of extraction temperature on extraction rate (extraction time: 30 min, volume ratio of ionic liquid to feed solution: 1:1). Figure 19. Effect of extraction time on extraction rate (extraction temperature: 30 °C, volume ratio of ionic liquid to feed solution: 1:1). Figure 20. Effect of volume ratio of ionic liquid to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C). Figure 21. Effect of regeneration times on extraction rate (extraction time: 30 min, extraction temperature: 30 °C, volume ratio of ionic liquid to feed solution: 1:1).



Figure 1. Synthesis pathway of [HeDBU][NTf2].


Page 30 of 51

Page 31 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Synthesis pathway of [DPAIm][NTf2].



Figure 3. Synthesis pathway of [C8DIPA][Im].


Page 32 of 51

Page 33 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. 1H-NMR spectrum of [HeDBU][NTf2].



Figure 5. 13C-NMR spectrum of [HeDBU][NTf2].


Page 34 of 51

Page 35 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. FT-IR spectrum of [HeDBU][NTf2].



Figure 7. 1H-NMR spectrum of [DPAIm][NTf2].


Page 36 of 51

Page 37 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. 13C-NMR spectrum of [DPAIm][NTf2].



Figure 9. FT-IR spectrum of [DPAIm][NTf2].


Page 38 of 51

Page 39 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 10. 1H-NMR spectrum of [C8DIPA][Im].



Figure 11. 13C-NMR spectrum of [C8DIPA][Im].


Page 40 of 51

Page 41 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 12. FT-IR spectrum of [C8DIPA][Im].



Figure 13. Effect of volume ratio of [HeDBU][NTf2] to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C).


Page 42 of 51

Page 43 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 14. Effect of volume ratio of [DPAIm][NTf2] to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C).



Figure 15. Effect of volume ratio of [C8DIPA][Im] to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C).


Page 44 of 51

Page 45 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


b

a

d

c

e

Figure 16. Geometries optimizations of (a) cation and antion of [C8DIPA][Im], (b) [C8DIPA][Im] and butanol, (c) [C8DIPA][Im] and acetone, (d) [C8DIPA][Im] and ethanol and (e) [C8DIPA][Im] and H2O.



Figure 17. Effect of carbon chain length of ionic liquid on extraction rate (extraction time: 30 min, extraction temperature: 30 °C, volume ratio of ionic liquid to feed solution: 1:1).


Page 46 of 51

Page 47 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 18. Effect of extraction temperature on extraction rate (extraction time: 30 min, volume ratio of ionic liquid to feed solution: 1:1).



Figure 19. Effect of extraction time on extraction rate (extraction temperature: 30 °C, volume ratio of ionic liquid to feed solution: 1:1).


Page 48 of 51

Page 49 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 20. Effect of volume ratio of ionic liquid to feed solution on extraction rate (extraction time: 30 min, extraction temperature: 30 °C).



Figure 21. Effect of regeneration times on extraction rate (extraction time: 30 min, extraction temperature: 30 °C, volume ratio of ionic liquid to feed solution: 1:1).


Page 50 of 51

Page 51 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For Table of Contents Use Only

An imidazolium-based hydrophobic functionalized ionic liquid was used as extractant for recovery of butanol from ABE fermentation broth.


Recovery of butanol from ABE fermentation broth with hydrophobic

Recommend Documents