Study of the Interaction between Carbohydrates and Ionic liquids Using AB Initio Calculations

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Study of the behavior of systems containing (Carbohydrate-ILs)

The aim of this chapter is to overcome the lack of experimental data on phase equilibria of biomass carbohydrates in ionic liquids. The solubility of glucose, fructose, sucrose and lactose in ionic liquids was measured within a temperature range from 283 K to 383 K. Solubility data were successfully correlated with local composition thermodynamic models such as NRTL and UNIQUAC. In this work, the possibility of extracting glucose from these ionic liquids using the antisolvent method has been also evaluated. The parameters affecting the extraction process are the ionic liquid type, ethanol / ionic liquid ratio, temperature, water content, and time. Results indicate that ethanol can be successfully used as an antisolvent to separate sugars from ionic liquids.

Introduction

The search for sustainable and alternative energy is of critical importance with the ever-growing energy demands and environmental concerns, together with the decrease of fossil fuel reserves.1,2 Development of a technology platform, which could facilitate the access to natural biopolymers and enable the production of biofuels based on renewable sources, is a major step towards sustainability. Biomass is regarded as a permanent source of renewable feedstock on the planet for both material and energy. Lignocellulosic materials, such as agricultural residues (corn stover and wheat straw), waste paper, wood wastes, and energy crops, have been recognized as a potential sustainable source of sugars for biotransformation into bioethanol and value-added bio-based products.3 Bioethanol production from cellulosic materials usually consists of three steps: (1) pretreatment of lignocellulose to enhance the enzymatic or microbial digestibility of polysaccharide components; (2) hydrolysis of cellulose and hemicellulose to fermentable sugars; and (3) fermentation of the sugars to liquid fuels.4-6 Lignocellulosic biomass primarily consists of a complex mixture of lignin, hemicellulose, and semi crystalline cellulose. This complicated structure makes the production of fermentable sugars from lignocellulosic biomass expensive and inefficient when compared with the production of sugars from starch-based feedstocks. Pretreatment of lignocellulosic biomass is required to disrupt the lignin-carbohydrate complex, decrease cellulose crystallinity and partially remove lignin and hemicelluloses. The pretreated cellulose becomes more accessible to the enzymes that convert the carbohydrate polymers into fermentable sugars.7-9 Ionic liquids (ILs) have recently emerged as promising new solvents capable of disrupting the native cellulose crystalline structure, possibly also breaking structurally important chemical linkages, in a wide range of biomass feedstocks.10-13 Ionic liquids are salts in the liquid state having melting point below some arbitrary temperature, such as 100°C (373 K). They are solvents that facilitate more ecological applications in reactions and separations because of their unique properties, such as negligible vapor pressure14 and high thermal stability.15 Their very low vapor pressure reduces the risk of exposure that is a clear advantage over the use of the classical volatile solvents. They are considered as more environmentally-friendly than their volatile, toxic, and organic counterparts. ILs that are regarded as ‘‘green’’ solvents, have received worldwide attention in various fields including catalysis16-17, electrochemistry18-19, separation20-21, chemical synthesis, polymer chemistry and nanotechnology. 22-23 Swatloski et al. (2000) reported the use of an ionic liquid as a solvent for cellulose both for the regeneration of cellulose and for the chemical modification of polysaccharide.24 1-butyl-3-methylimidazolium chloride (BMIMCl), was found to be capable of dissolving up to 25% cellulose (by weight).24 This provided a new platform for the ‘‘green’’ comprehensive utilization of cellulose resources. Although the fact that most of carbohydrates are soluble only in protic solvents, such as water, and insoluble in most organic aprotic solvents as they contain a high number of hydroxyl groups which hinder their dissolution, ionic liquids have been reported as new potential media to dissolve carbohydrates.25-27 The solubility data of carbohydrates in ionic liquids is an important issue in order to develop chemical or bio-process involving these compounds. Nevertheless, the literature mainly concerns the application of ILs in the modification of cellulose trapped in the lignocellulosic biomass.28 Studies on the dissolution and on the extraction of carbohydrates other than cellulose in ILs are limited.29-30 The data reported in the literature concerning the solubility of biomass-derived compounds such as carbohydrates in ionic liquids is far from being enough to have a good knowledge on phase equilibria. In most cases, these data are not available in a sufficiently large range of temperature which turns the modeling process into a very difficult task.31 Some ILs have been demonstrated to be excellent solvents for carbohydrates, Sheldon et al. were the first to connect ILs and carbohydrates by exploring their potential as media for carbohydrates transformations.32 Park et al. and Kimizuka et al. reported the solubility of glucose in imidazolium based ILs.30,33,34 These ILs containing an ether pendant substituent are currently named “sugar-philic” ILs due to their capacity to establish hydrogen bonds with the hydroxyl groups of the carbohydrate. MacFarlane et al.35,36 and Sheldon et al. 37 described the dicyanamide as an attractive anion to dissolve carbohydrates due to its hydrogen bond acceptor properties. V. M. Egorov et al. found that BMIMCl is capable of dissolving until 56% fructose at 110°C. Many antisolvents have been used to separate carbohydrates from ionic liquids. The performance of dichloromethane for the extraction of carbohydrates from ionic liquids was studied by Rosatella et al. while Liu et al. studied the solubility of glucose in a binary mixture containing an IL and ethanol.38 Ethanol precipitation is a separation technology with many advantages, such as safe solvent, easy operation, and high removal for high polarity components, such as saccharides, proteins, and inorganic salts. The correlation of carbohydrates solubility data in ionic liquids could be achieved using local composition thermodynamic models. Carneiro et al. measured the solubility of monosaccharides in ILs and these solubility data were correlated using the NRTL and UNIQUAC thermodynamic models.31
This work is focused on the dissolution of carbohydrates in ionic liquids and the extraction using the antisolvent method. This work is mainly divided into three parts, the first part aims to study the influence solubility of carbohydrates in ionic liquids in a temperature range from 280 K to 390 K. Solubility data have been successfully correlated with local composition thermodynamic models such as NRTL and UNIQUAC and compared with solubility data in the literature. The second part of the article is devoted to the solubility of carbohydrates in binary mixtures {ethanol + ionic liquids} in order to evaluate the possible use of the anti solvent method for the extraction of carbohydrates from ionic liquids. The influence of different parameters such as temperature, ionic liquid/ethanol ratio, water content but also the structure of the IL on the performance of the extraction is evaluated. Then, in the third part the anti solvent method is tested for the extraction of carbohydrates from 1-butyl-3-methylimidazolium chloride.

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Experimental techniques

Materials

D-(+)-Glucose anhydrous was purchased from Merck. D-(-)-Fructose, Sucrose and α-Lactose monohydrate were purchased from Sigma Aldrich. Ethyl alcohol absolute with a mass fraction purity of 0.999 was from Carlo Erba. Acetonitrile with a mass fraction purity of 0.999 was from Sigma-Aldrich.
The ionic liquids used in this work, 1-butyl-3-methylimidazolium chloride (BMIMCl), 1-ethanol-3- methylimidazolium chloride (EtOHMIMCl), 1-butyl-1-methylpyrrolidinium chloride (BMPyrCl), and 1,3-dimethyl-imidazolium methyl phosphonate (DMIMMPh), with purity 98%, were from Solvionic, and 1-ethyl-3-methylimidazolium thiocyanate (EMIMSCN) with purity 95% was from Sigma Aldrich. The physical properties of the selected ionic liquids are shown in table II.1. These ionic liquids were dried under vacuum for 3 hours at 363 K before use.

Apparatus and procedures

Solid-liquid equilibrium phase diagrams of the studied systems were obtained at atmospheric pressure and at temperature ranges starting from 283 to 373 K. The solubility experiments of carbohydrates in pure ILs and in a binary mixture of IL with ethanol have been performed in jacketed glass cells using a dynamic method described in the literature. 39 The experimental set up consists of a cell with an internal volume of about 50 cm3. The temperature of the cell was maintained constant using a thermostatic bath (polystat 5D +37, Fisher scientific.) with a precision of0.1 K. The internal temperature of the cell was also measured with a calibrated platinum probes Pt100 with an accuracy of ± 0.1 K. The mixtures, with compositions inside the immiscible region of the system, are weighed using a METTLER analytical balance with a precision of ± 0.0001 g.
For the solubility of carbohydrates in pure ILs, desired amounts of pure IL and sugar were loaded into a prepared cell. The cell was sealed and connected to the temperature controller. The mixture was rigorously stirred for 6 hours and was then heated very slowly (about 1K.h-1) until complete dissolution of the sugar in the ionic liquid. The solubility measurements were confirmed by the visual observation of the solution under microscope.
For the experiments of solubility of carbohydrates in a binary mixture (IL + EtOH), a desired amount of ethanol was loaded into a prepared cell, and then, a desired amount of IL with a given mass ratio of ethanol to IL was added quickly into the above ethanol solution. The cell was sealed and connected to the temperature controller until a transparent solution was formed. When the temperature of the system attained a desired value, an excessive amount of sugar was added to the mixture. At different time intervals, samples were withdrawn, filtrated with 0.45 μm film, and analyzed by a high performance liquid chromatography (HPLC) to determine the carbohydrate concentration.
An HPLC (SHIMADZU, USA) with a SHODEX Asahipak NH2-50 4E column (Shodex, Japan) and a differential refractive index detector (SHIMADZU, USA) was employed for analyzing concentrations of carbohydrates in the mixtures. The column oven temperature was 308 K, the mobile phase was a mixture of acetonitrile and water with a ratio (75:25), and the flow rate was 1 ml/min. The correlation coefficient of the sugars standard curve by the HPLC reached a value of 0.999. The expanded relative uncertainty of carbohydrate solubility in IL and antisolvent mixtures was estimated at 1.0%. The equilibration temperature was measured with an uncertainty of 0.2 K.

Results and discussion

Only a limited number of ionic liquids available have been studied until now in the various applications including the solubility studies. In this work, three ionic liquids, 1-ethanol-3-methylimidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, and 1,3-dimethyl-imidazolium methyl phosphonate, were investigated in order to increase the number of the potentially interesting solvents for carbohydrates. Two other classical ILs, BMIMCl and EMIMSCN used in the biomass conversion process were also studied to evaluate their behavior in the presence of carbohydrates.

Table of contents :

Chapitre I. Synthèse bibliographique
I.1. Généralités sur les liquides ioniques
I.2. Applications des liquides ioniques
I.2.1. Utilisation des liquides ioniques dans les procédés de séparation : extraction liquide-liquide
I.2.2. Utilisation des liquides ioniques pour l’extraction de constituants issus de la biomasse
I.3. Modèles thermodynamiques pour présenter les propriétés thermodynamiques des liquides ioniques
I.3.1. Equation d’état cubique et de type SAFT
I.3.2. Modèle d’énergie de Gibbs molaire totale d’excès gE
I.4. Conclusion
Références bibliographiques
Chapter II. Study of the behavior of systems containing (Carbohydrate-ILs)
II.1. Introduction
II.2. Experimental techniques
II.2.1. Materials
II.2.2. Apparatus and procedures
II.3. Results and discussion
II.3.1. Solubility of carbohydrates in pure ionic liquids
II.3.2. Computational theory
II.3.3. Solubility of carbohydrates in a binary mixture of (IL + EtOH)
II.3.3.1. Effect of the structure of the ionic liquid
II.3.3.2. Effect of the structure of the carbohydrate
II.3.3.3. Effect of ethanol/ ionic liquid ratio
II.3.3.4. Effect of temperature
II.3.3.5. Effect of water content
II.3.3.6. The dissolution rate of sugars solubility
II.3.3.7. Applying 23Full-Factorial Design
II.3.4. Extraction process using the antisolvent method
II.5. Conclusion
Chapter III. Study of the Interaction between Carbohydrates and Ionic liquids Using AB Initio Calculations
III.1. Introduction
III.2. Methodology
III.3. Experimental techniques
III.3.1. Materials
III.3.2. Solubility and regeneration of cellulose
III.4. Results and Discussion
III.4.1. Ionic liquids structure optimization and hydrogen bond formation
III.4.1.1. Optimized structures of ionic liquids
III.4.1.2. Hydrogen bonding interaction
III.4.2. Interaction of ionic liquids with carbohydrates
III.4.3. Effect of water on IL-cellulose system
III.4.4. Experimental study on the dissolution and regeneration of cellulose
III.4.4.1. Solubility of cellulose in ionic liquids
III.4.4.2. Characterization of the regenerated cellulose
III.5. Conclusion
References
Chapter IV. Use of Ionic Liquids in the Pretreatment of Miscanthus for Biofuel Production 
IV.1. Introduction
IV.2. Experimental techniques
IV.2.1. Materials and miscanthus preparation
IV.2.2. Miscanthus dissolution
IV.2.3. Cellulose extraction and residue separation
IV.2.4. Enhancement of miscanthus delignification
IV.2.5. Determination of cellulose, lignin and hemicelluloses content
IV.2.5.1. Determination of lignin content
IV.2.5.2. Determination of cellulose content
IV.2.5.3. Determination of hemicellulose content
IV.2.6. Charecterization of the regenerated cellulose-rich extract
IV.2.6.1. XRD analysis
IV.2.6.2. NMR analysis
IV.2.6.3. FTIR analysis
IV.2.6.4. SEM analysis
IV.2.7. Enzymatic hydrolysis process
IV.2.8. Fermentation of the hydrolysates
IV.2.8.1. Yeast and culture conditions:
IV.2.8. 2. Batch fermentation
IV.3. Results and discussion
IV.3.1 Solubility of miscanthus in ionic liquids
IV.3.1.1. Effect of miscanthus particle size
IV.3.1.2. Effect of temperature and dissolution rate
IV.3.2. Extraction and regeneration of cellulose from miscanthus using ionic liquids
IV.3.2.1. Ash and extractables removal
IV.3.2.2. Effect of antisolvent type
IV.3.2.3. Effect of type of ionic liquid
IV.3.2.4. Effect of temperature
IV.3.2.5. Effect of time
IV.3.2.6. Effect of miscanthus concentration
IV.3.2.7. Applying Box-Behnken Design for the Miscanthus-DMIMMPh mixture
IV.3.2.8. Enhancement of miscanthus delignification
IV.3.2.9. Ionic liquids recycling
IV.3.2.10. Cellulose, lignin and hemicellulose recovery
IV.3.3. Charecterization of the regenerated cellulose-rich extract
IV.3.3.1. XRD analysis results
IV.3.3.2. NMR Analysis results
IV.3.3.3. FTIR analysis results
IV.3.3.4. Morphological investigation
IV.3.4. Bioethanol production
IV.3.4.1. Enzymatic hydrolysis
IV.3.4.2. Fermentation of hydrolysates
IV.3.4.3. Evaluation of fermentation results
IV.4. Conclusion
Conclusion and Perspectives

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