Accepted Manuscript Title: A Morpholinium Ionic Liquid for Cellulose Dissolution Author: Dilip G. Raut Ola Sundman Weiqing Su Pasi Virtanen Yasuhito Sugano Krisztian Kordas Jyri-Pekka Mikkola PII: DOI: Reference:
S0144-8617(15)00348-3 http://dx.doi.org/doi:10.1016/j.carbpol.2015.04.032 CARP 9863
To appear in: Received date: Revised date: Accepted date:
26-11-2014 17-4-2015 20-4-2015
Please cite this article as: Raut, D. G., Sundman, O., Su, W., Virtanen, P., Sugano, Y., Kordas, K., and Mikkola, J.-P.,A Morpholinium Ionic Liquid for Cellulose Dissolution, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.04.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Highlights
2
Dissolution of cellulose in newly synthesized ionic liquids was studied.
3
At 120 °C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of cellulose
4
with degree of polymerization (DPn) - 789, 1644 and 2082 respectively, in 20 min. Importantly, 25 wt% cellulose with very high DP (2082) could be dissolved.
6
Structure and morphology of regenerated cellulose films were determined.
7
No discernible changes occurred in terms of the degree of polymerization of the
cr
9 10 11
different celluloses after regeneration.
Efficient recovery of [AMMorp][OAc] was demonstrated using water as an antisolvent.
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Page 1 of 19
A Morpholinium Ionic Liquid for Cellulose Dissolution Dilip G. Raut,*a Ola Sundman,a Weiqing Su,a Pasi Virtanen,b Yasuhito Sugano,c Krisztian Kordas,d JyriPekka Mikkola, *ab University, Department of Chemistry, Chemical-Biology Centre, Technical Chemistry, SE-90787 Umeå, Sweden b Åbo Akademi University, Process Chemistry Centre, Laboratory of Industrial Chemistry and Reaction Engineering, FI-20500 Turku/Åbo, Finland c Åbo Akademi University, Laboratory of Analytical Chemistry, ProcessChemsitry Centre, FI-20500 Turku/Åbo, Finland d Microelectronics and Materials Physics Laboratories Department of Electrical Engineering, University of Oulu, P.O. Box 4500, FIN-90014
us
cr
ip t
aUmeå
an
E-mail: [email protected] (Dilip Raut), [email protected] (Jyri-Pekka Mikkola), [email protected] (Weiqing Su), [email protected] (Ola Sundman), [email protected] (Pasi Virtanen), [email protected] (Yasuhito Sugano), [email protected] (Krisztian Kordas) Abstract: A series of substituted morpholinium ionic salts and allyl ammonium acetates were prepared. Amongst those, N-allyl-N-methylmorpholinium acetate ([AMMorp][OAc]) was found to dissolve cellulose readily without any pre-processing of native cellulose. At 120 °C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of cellulose with degree of polymerization (DPn) - 789, 1644 and 2082 respectively, in 20 min. Importantly, SEC analysis indicated that no discernible changes occurred in terms of the degree of polymerization of the different celluloses after regeneration. Furthermore, when comparing the cellulose dissolution capability of these newly synthesized ionic liquids, it is evident that the combination of all three constituents - the morpholinium cation, the existence of an allyl group and choosing the acetate anion are essential for efficient cellulose dissolution. The structure and morphology of the regenerated cellulosic materials were characterized by SEM, XRD, TGA, CP/MAS 13C NMR and FTIR, respectively.
24
Keywords: Cellulose, dissolution, ionic liquid, morpholinium, allyl, acetate
25
1.
26 27 28 29 30 31 32 33 34 35
Cellulose is the most copious and replenishable bio-resource generated on earth (Azizi Samir et al., 2004; Heinze et al., 2008). Cellulose and its derivatives have been utilized for various purposes in our day-to-day life viz. fibers, papers, membranes, tissues, polymers, paints and importantly, in the manufacture of various biofuels by fermentation of hydrolyzed cellulose (Edgar et al., 2001; Husar, Iborra, & Corma, 2006; Moutos, Freed, & Guilak, 2007). Due to strong inter and intramolecular hydrogen bonding between the hydroxyl groups of cellulose, it is extremely difficult to dissolve cellulose in water and in commonly used organic solvents. During last decades, various derivatizing and non-derivatizing methods have been developed to dissolve cellulose, such as application of the so called viscose process (Cross, Bevan & Beadle, 1982), the N-methylmorpholineN-oxide (NMMO) process (Johnson, 1969; Johnson, 1970), various processes involving the use of
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13 14 15 16 17 18 19 20 21 22 23
Introduction
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Page 2 of 19
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cellulose acetate (Phillip et al., 1990; Schuetzenberger, 1865), the cellulose formate route (Fujikoto, 1986), a route involving a transition metal and an amine or an ammonium component (Ahlrichs, 1998), the route taking advantage of an aqueous NaOH solution (Isogai, & Atalla, 1998; Roy, Budtova, & Navard, 2003) or an aqueous solution of poly(ethylene glycol) (PEG) and NaOH (Yan, & Gao, 2008), the use of aqueous solutions of NaOH-Urea (7 wt % NaOH /urea 12 wt %) (Cai et al., 2008), the use of aqueous non-alkali bases (Klemm, Philipp, Heinze, Heinze, & Wagenknecht, 1998), the use of N,N-dimethylacetamide (DMAc)/LiCl (McCormick, & Lichatowich, 1979) as well as methods relying on the application of various aqueous inorganic salts and molten salt hydrates (Chen, 1991; Weimarn, 1912) or the route utilizing DMSO/TBAF (Heinze, Dicke, Koschella, Kull and Koch, 2000). More or less, all of these methods suffer from various drawbacks such as the necessity of pre-treatment steps, high toxicity of reagents and volatility of solvents, as well as high costs related to the need of complicated safety measures, thus limiting their application on an industrial scale. In this context, ionic liquids (ILs) are considered to present a potentially sustainable alternative for the dissolution of cellulose. ILs are fused organic salts with melting points under 100 °C (Johnson, 2007). These salts frequently possess many desirable properties like negligible vapour pressure, low toxicity, high thermal stability, high dissolving power and recyclability (Carter et al., 2004; Ngo, LeCompte, Hargens, & McEwen, 2000). Various cellulose dissolving ionic liquids synthesized so far, mainly consist of an aromatic planar 1,3-dialkylimidazolium, 1-allyl-3alkylimidazolium or pyridinium species. Alternatively, they are built of a non-aromatic cyclic or acyclic onium species like ammonium, piperidinium, sulfonium, pyrrolidinium, morpholinium, thiophenium cations. These cations are, in turn, coupled with a halide or an oxygenated anion such as Cl, OAc, HCOO, Me2PO4, Et2PO4, MePO3H, or MePO3Me (Abe, Fukaya, & Ohno, 2010; Graenacher, & Sallman, 1939; Gräsvik, Raut, & Mikkola; 2012; Liebert, & Heinze, 1998; Liebert, 2010, Pinkert, Marsh, & Pang, 2010; Rinaldi , 2011; Swatloski, Spear, Holbrey, & Rogers, 2002; Wang, Gurau, & Rogers, 2012; Zhu et al., 2006). Lately, many researchers have shown a lot of interest in morpholinium based ILs. These ILs have been used in various applications such as components of ionic liquid crystals, reaction media, corrosion inhibitors, catalysts, heat stabilizers and lubricants (Brigouleix et al., 2010; Choi, Kim, Lee, Oh, & Lee, 2005, Galinski, & Stepniak, 2009; Kim et al., 2004; Kim, Park, Yeon, & Lee, 2005). Apart from offering traditional useful properties of ionic liquids, morpholinium based ILs possess lower toxicity than imidazolium, pyridinium or cyclic and acyclic ammonium ionic liquids (Pernak et al., 2011). These authors reported the use of 4-benzyl-4-methylmorpholinium salts for dissolution of 1 wt% cellulose at 100 °C. The present work depicts the synthesis of different morpholinium and ammonium based ionic liquids under normal bench-top experimental conditions in order to investigate their efficacy in dissolution of cellulose. A systematic study of the dissolution of cellulose in these ionic liquids was carried out. Structure and properties of regenerated cellulose were characterized by using various techniques. Further, the recovery of the ionic liquid was also investigated.
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Page 3 of 19
Results and Discussion
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2.1 Synthesis of ionic liquids and dissolution of cellulose The presence of an allyl group in an ionic liquid is known to reduce its viscosity (Yim et al., 2007; Zhang, Wu, Zhang, & He, 2005; Zhang et al., 2011; Zhao et al., 2005) and can thus accelerate the velocity of cellulose dissolution. When analysing the current literature, it is clear that halide, acetate, formate and alkyl phosphonate anions have positive impact in terms of cellulose dissolution (Fukaya, Hayashi, Wada, & Ohno, 2008; Pinkert, Marsh, Pang, & Staiger, 2009; Vitz, Erdmenger, Haensch, & Schubert, 2009; Yang et al., 2010). Keeping in mind the success of the NMMO process which involves the use of N-methylmorpholinium oxide (NMMO) with a large amount of water (Johnson, 1969; Johnson, 1970), we envisioned that N-allyl-N-methylmorpholinium acetate ionic liquid could be one of the potential candidates for cellulose dissolution. The synthesis of N-allyl-N-methylmorpholinium acetate [AMMorp][OAc] was achieved in a twostep process (see supporting information S3). N-allyl-N-methylmorpholinium bromide [AMMorp][Br] was synthesized by a simple quaternization reaction. Subsequently, an ion exchange method was exploited for the conversion of [AMMorp][Br] into highly pure (99.99%) [AMMorp][OAc]. The purity of the ionic liquid was determined by ion chromatography (detection limit of Br ions ≥0.1 ppm) and also by 1H NMR (for other organic impurities). From thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies, the decomposition temperature, the glass transition temperature and melting point of [AMMorp][OAc] were determined to be 144 °C, -51 °C, and -56°C respectively. Despite heating the ionic liquid at 60 °C under high vacuum (4 x 10-2 mbar) followed by freeze drying, the amount of water in [AMMorp][OAc] was found to be 3.36 wt% as measured by Karl Fischer titration method. The dissolution of cellulose pulps with different DPn was further probed at different temperatures and the results are shown in Table 1. As expected, inverse correlation was observed between the degree of polymerization and amount of cellulose dissolved. In fact, [AMMorp][OAc] could dissolve 17 wt% MCC, 13 wt% Cell-A and 11 wt% Cell-M, respectively in 20 min at 80 °C forming a transparent gel. An increase in the temperature led to a positive effect in terms of celllulose solubility. At 120 °C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of MCC, Cell-A and Cell-M, respectively, in 20 min. It is noteworthy to mention that the cellulose dissolving capability of [AMMorp][OAc] is at par to that of imidazolium based ionic liquids at 100 °C (Table 1). To the best of our knowledge, none of the previously described non-aromatic, cyclic ionic liquids could dissolve such high amounts of cellulose (25 wt%) with high a degree of polymerization (DPn=2082).
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Page 4 of 19
OAc
Cell-A (DP= 1644)
[AMMorp][OAc]
Cell-M (DP= 2082)
[AMMorp][OAc]
[BMIm][Cl] (1-butyl-3-methyl imidazolium chloride)
Avicel 398
[AMIm][Cl] (1-Allyl-3-methyl imidazolium chloride)
120
30
80
13
100
24
120
28
80
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100 120
20 min
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Table 1: Comparison of cellulose dissolution capacity for various ionic liquids Weight Temp. Ionic liquid Cellulose Ref. dissolved time °C (wt %) [AMMorp][OAc] 80 17
20 min
Present work
Present work
25
Vitz, Erdmenger, Haensch, Schubert, 2009
15
S0144-8617(15)00348-3 http://dx.doi.org/doi:10.1016/j.carbpol.2015.04.032 CARP 9863
To appear in: Received date: Revised date: Accepted date:
26-11-2014 17-4-2015 20-4-2015
Please cite this article as: Raut, D. G., Sundman, O., Su, W., Virtanen, P., Sugano, Y., Kordas, K., and Mikkola, J.-P.,A Morpholinium Ionic Liquid for Cellulose Dissolution, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.04.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Highlights
2
Dissolution of cellulose in newly synthesized ionic liquids was studied.
3
At 120 °C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of cellulose
4
with degree of polymerization (DPn) - 789, 1644 and 2082 respectively, in 20 min. Importantly, 25 wt% cellulose with very high DP (2082) could be dissolved.
6
Structure and morphology of regenerated cellulose films were determined.
7
No discernible changes occurred in terms of the degree of polymerization of the
cr
9 10 11
different celluloses after regeneration.
Efficient recovery of [AMMorp][OAc] was demonstrated using water as an antisolvent.
us
8
ip t
5
Ac ce
pt
ed
M
an
12
1
Page 1 of 19
A Morpholinium Ionic Liquid for Cellulose Dissolution Dilip G. Raut,*a Ola Sundman,a Weiqing Su,a Pasi Virtanen,b Yasuhito Sugano,c Krisztian Kordas,d JyriPekka Mikkola, *ab University, Department of Chemistry, Chemical-Biology Centre, Technical Chemistry, SE-90787 Umeå, Sweden b Åbo Akademi University, Process Chemistry Centre, Laboratory of Industrial Chemistry and Reaction Engineering, FI-20500 Turku/Åbo, Finland c Åbo Akademi University, Laboratory of Analytical Chemistry, ProcessChemsitry Centre, FI-20500 Turku/Åbo, Finland d Microelectronics and Materials Physics Laboratories Department of Electrical Engineering, University of Oulu, P.O. Box 4500, FIN-90014
us
cr
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aUmeå
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E-mail: [email protected] (Dilip Raut), [email protected] (Jyri-Pekka Mikkola), [email protected] (Weiqing Su), [email protected] (Ola Sundman), [email protected] (Pasi Virtanen), [email protected] (Yasuhito Sugano), [email protected] (Krisztian Kordas) Abstract: A series of substituted morpholinium ionic salts and allyl ammonium acetates were prepared. Amongst those, N-allyl-N-methylmorpholinium acetate ([AMMorp][OAc]) was found to dissolve cellulose readily without any pre-processing of native cellulose. At 120 °C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of cellulose with degree of polymerization (DPn) - 789, 1644 and 2082 respectively, in 20 min. Importantly, SEC analysis indicated that no discernible changes occurred in terms of the degree of polymerization of the different celluloses after regeneration. Furthermore, when comparing the cellulose dissolution capability of these newly synthesized ionic liquids, it is evident that the combination of all three constituents - the morpholinium cation, the existence of an allyl group and choosing the acetate anion are essential for efficient cellulose dissolution. The structure and morphology of the regenerated cellulosic materials were characterized by SEM, XRD, TGA, CP/MAS 13C NMR and FTIR, respectively.
24
Keywords: Cellulose, dissolution, ionic liquid, morpholinium, allyl, acetate
25
1.
26 27 28 29 30 31 32 33 34 35
Cellulose is the most copious and replenishable bio-resource generated on earth (Azizi Samir et al., 2004; Heinze et al., 2008). Cellulose and its derivatives have been utilized for various purposes in our day-to-day life viz. fibers, papers, membranes, tissues, polymers, paints and importantly, in the manufacture of various biofuels by fermentation of hydrolyzed cellulose (Edgar et al., 2001; Husar, Iborra, & Corma, 2006; Moutos, Freed, & Guilak, 2007). Due to strong inter and intramolecular hydrogen bonding between the hydroxyl groups of cellulose, it is extremely difficult to dissolve cellulose in water and in commonly used organic solvents. During last decades, various derivatizing and non-derivatizing methods have been developed to dissolve cellulose, such as application of the so called viscose process (Cross, Bevan & Beadle, 1982), the N-methylmorpholineN-oxide (NMMO) process (Johnson, 1969; Johnson, 1970), various processes involving the use of
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13 14 15 16 17 18 19 20 21 22 23
Introduction
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Page 2 of 19
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cellulose acetate (Phillip et al., 1990; Schuetzenberger, 1865), the cellulose formate route (Fujikoto, 1986), a route involving a transition metal and an amine or an ammonium component (Ahlrichs, 1998), the route taking advantage of an aqueous NaOH solution (Isogai, & Atalla, 1998; Roy, Budtova, & Navard, 2003) or an aqueous solution of poly(ethylene glycol) (PEG) and NaOH (Yan, & Gao, 2008), the use of aqueous solutions of NaOH-Urea (7 wt % NaOH /urea 12 wt %) (Cai et al., 2008), the use of aqueous non-alkali bases (Klemm, Philipp, Heinze, Heinze, & Wagenknecht, 1998), the use of N,N-dimethylacetamide (DMAc)/LiCl (McCormick, & Lichatowich, 1979) as well as methods relying on the application of various aqueous inorganic salts and molten salt hydrates (Chen, 1991; Weimarn, 1912) or the route utilizing DMSO/TBAF (Heinze, Dicke, Koschella, Kull and Koch, 2000). More or less, all of these methods suffer from various drawbacks such as the necessity of pre-treatment steps, high toxicity of reagents and volatility of solvents, as well as high costs related to the need of complicated safety measures, thus limiting their application on an industrial scale. In this context, ionic liquids (ILs) are considered to present a potentially sustainable alternative for the dissolution of cellulose. ILs are fused organic salts with melting points under 100 °C (Johnson, 2007). These salts frequently possess many desirable properties like negligible vapour pressure, low toxicity, high thermal stability, high dissolving power and recyclability (Carter et al., 2004; Ngo, LeCompte, Hargens, & McEwen, 2000). Various cellulose dissolving ionic liquids synthesized so far, mainly consist of an aromatic planar 1,3-dialkylimidazolium, 1-allyl-3alkylimidazolium or pyridinium species. Alternatively, they are built of a non-aromatic cyclic or acyclic onium species like ammonium, piperidinium, sulfonium, pyrrolidinium, morpholinium, thiophenium cations. These cations are, in turn, coupled with a halide or an oxygenated anion such as Cl, OAc, HCOO, Me2PO4, Et2PO4, MePO3H, or MePO3Me (Abe, Fukaya, & Ohno, 2010; Graenacher, & Sallman, 1939; Gräsvik, Raut, & Mikkola; 2012; Liebert, & Heinze, 1998; Liebert, 2010, Pinkert, Marsh, & Pang, 2010; Rinaldi , 2011; Swatloski, Spear, Holbrey, & Rogers, 2002; Wang, Gurau, & Rogers, 2012; Zhu et al., 2006). Lately, many researchers have shown a lot of interest in morpholinium based ILs. These ILs have been used in various applications such as components of ionic liquid crystals, reaction media, corrosion inhibitors, catalysts, heat stabilizers and lubricants (Brigouleix et al., 2010; Choi, Kim, Lee, Oh, & Lee, 2005, Galinski, & Stepniak, 2009; Kim et al., 2004; Kim, Park, Yeon, & Lee, 2005). Apart from offering traditional useful properties of ionic liquids, morpholinium based ILs possess lower toxicity than imidazolium, pyridinium or cyclic and acyclic ammonium ionic liquids (Pernak et al., 2011). These authors reported the use of 4-benzyl-4-methylmorpholinium salts for dissolution of 1 wt% cellulose at 100 °C. The present work depicts the synthesis of different morpholinium and ammonium based ionic liquids under normal bench-top experimental conditions in order to investigate their efficacy in dissolution of cellulose. A systematic study of the dissolution of cellulose in these ionic liquids was carried out. Structure and properties of regenerated cellulose were characterized by using various techniques. Further, the recovery of the ionic liquid was also investigated.
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Results and Discussion
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2.1 Synthesis of ionic liquids and dissolution of cellulose The presence of an allyl group in an ionic liquid is known to reduce its viscosity (Yim et al., 2007; Zhang, Wu, Zhang, & He, 2005; Zhang et al., 2011; Zhao et al., 2005) and can thus accelerate the velocity of cellulose dissolution. When analysing the current literature, it is clear that halide, acetate, formate and alkyl phosphonate anions have positive impact in terms of cellulose dissolution (Fukaya, Hayashi, Wada, & Ohno, 2008; Pinkert, Marsh, Pang, & Staiger, 2009; Vitz, Erdmenger, Haensch, & Schubert, 2009; Yang et al., 2010). Keeping in mind the success of the NMMO process which involves the use of N-methylmorpholinium oxide (NMMO) with a large amount of water (Johnson, 1969; Johnson, 1970), we envisioned that N-allyl-N-methylmorpholinium acetate ionic liquid could be one of the potential candidates for cellulose dissolution. The synthesis of N-allyl-N-methylmorpholinium acetate [AMMorp][OAc] was achieved in a twostep process (see supporting information S3). N-allyl-N-methylmorpholinium bromide [AMMorp][Br] was synthesized by a simple quaternization reaction. Subsequently, an ion exchange method was exploited for the conversion of [AMMorp][Br] into highly pure (99.99%) [AMMorp][OAc]. The purity of the ionic liquid was determined by ion chromatography (detection limit of Br ions ≥0.1 ppm) and also by 1H NMR (for other organic impurities). From thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies, the decomposition temperature, the glass transition temperature and melting point of [AMMorp][OAc] were determined to be 144 °C, -51 °C, and -56°C respectively. Despite heating the ionic liquid at 60 °C under high vacuum (4 x 10-2 mbar) followed by freeze drying, the amount of water in [AMMorp][OAc] was found to be 3.36 wt% as measured by Karl Fischer titration method. The dissolution of cellulose pulps with different DPn was further probed at different temperatures and the results are shown in Table 1. As expected, inverse correlation was observed between the degree of polymerization and amount of cellulose dissolved. In fact, [AMMorp][OAc] could dissolve 17 wt% MCC, 13 wt% Cell-A and 11 wt% Cell-M, respectively in 20 min at 80 °C forming a transparent gel. An increase in the temperature led to a positive effect in terms of celllulose solubility. At 120 °C, [AMMorp][OAc] could dissolve 30 wt%, 28 wt% and 25 wt% of MCC, Cell-A and Cell-M, respectively, in 20 min. It is noteworthy to mention that the cellulose dissolving capability of [AMMorp][OAc] is at par to that of imidazolium based ionic liquids at 100 °C (Table 1). To the best of our knowledge, none of the previously described non-aromatic, cyclic ionic liquids could dissolve such high amounts of cellulose (25 wt%) with high a degree of polymerization (DPn=2082).
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OAc
Cell-A (DP= 1644)
[AMMorp][OAc]
Cell-M (DP= 2082)
[AMMorp][OAc]
[BMIm][Cl] (1-butyl-3-methyl imidazolium chloride)
Avicel 398
[AMIm][Cl] (1-Allyl-3-methyl imidazolium chloride)
120
30
80
13
100
24
120
28
80
11
100 120
20 min
20
Present work
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20 min
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Table 1: Comparison of cellulose dissolution capacity for various ionic liquids Weight Temp. Ionic liquid Cellulose Ref. dissolved time °C (wt %) [AMMorp][OAc] 80 17
20 min
Present work
Present work
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Vitz, Erdmenger, Haensch, Schubert, 2009
15
