MIXTURES OF SALTS FOR DISSOLVING CELLULOSE

Abstract

Mixtures of salts to dissolve cellulose. The present invention refers to a composition based in a eutectic mixture of imidazolium salts and natural biopolymers, in particular cellulose, its manufacturing process and method of use to obtain foils or films.

The composition is based in a eutectic mixture of imidazolium salts with 0.1 to 50 wt % of biomass.

Claims

1. A composition comprising a mixture of two or more imidazolium ionic liquids and between 0.1 and 50% wt of biomass, wherein the mixed ionic liquids configure a eutectic system and their anions are selected from chloride and acetate.

2. The composition according to claim 1, wherein the imidazolium ionic liquids are 1-(C2-C6)alkyl-3-(C2-C6)alkyl-imidazolium.

3. The composition according to claim 1, wherein the ionic liquids are selected from 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, and 1-butyl-3-methylimidazolium chloride.

4. The composition according to claim 1, wherein two of those ionic liquids are in a relation between 1:10 to 10:1.

5. The composition according to claim 1, wherein two of those ionic liquids are in a relation between 1:5 to 5:1.

6. The composition according to claim 1, wherein two of those ionic liquids are in a relation between 1:3 to 3:1.

7. The composition according to claim 1, comprising 1-ethyl-3-methylimidazolium chloride and at least one more ionic liquid selected from 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium chloride in a relation between 1:5 to 5:1.

8. The composition according to claim 1, comprising 1-ethyl-3-methylimidazolium chloride and at least one more ionic liquid selected from 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium chloride in a relation between 1:3 to 3:1.

9. The composition according to claim 1, selected from: i) 1-ethyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate in a 3:7 molar ratio, ii) 1-ethyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride in a 1:1 molar ratio, iii)) 1-ethyl-3-methylimidazolium chloride in a molar ratio from 1:5 to 5:1 with mixture of 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium chloride in any molar ratio.

10. The composition according to claim 1, wherein the biomass is cellulose.

11. The composition according to claim 1, further comprising a viscosity-reducing agent, preferably dimethyl sulfoxide, in an amount from 0.1 to 70% wt.

12. A method of obtaining the composition as described in claim 1, comprising: a) mixing biomass in an amount of from 0.1 to 50 wt % with a mixture of two or more imidazolium ionic liquids, wherein the mixed ionic liquids configure a eutectic system and their anions are selected from chloride and acetate, and b) heating the mixture obtained in step (a) at a temperature below 105 C.

13. The method according to claim 12, wherein the temperature in the step (b) is between 50 C. and 105 C.

14. The method according to claim 12, wherein the temperature in the step (b) is between 70 C. and 100 C.

15. The method according to claim 12, comprising: a) mixing the biomass with 1-ethyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate in a 3:7 molar ratio, and b) heating the mixture obtained in step (a) at a temperature below 80 C.

16. The method according to claim 12, wherein a viscosity-reducing agent is further added to step (a) in an amount from 0.1 to 70 wt %.

17. The method according to claim 12, wherein the biomass is cellulose.

18. Use of the composition according to claim 1, to prepare cellulose fibers beads, sheets, and other elements.

19. Use of the composition according to claim 1, as non-derivatizing solvent for the chemical modification of cellulose in solution.

Description

DESCRIPTION OF THE FIGURES

[0050] FIG. 1. Temperature-composition phase diagram for the system [C.sub.4mim]Cl+[C.sub.2mim]Cl.

[0051] Legend -- melting point of the excess component [C.sub.4mim]Cl in the mixture; -- melting point of the excess component [C.sub.2mim]Cl in the mixture; -.box-tangle-solidup.- eutectic mixture thermal transition; -X- glass transition observed below the eutectic point transition.

[0052] Next, for a greater understanding of the characteristics and advantages of the present invention, reference is made to a number of explanatory examples which complete the previous description, without the invention being limited in any way to them.

Materials:

[0053] The ionic liquids 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, and 1-butyl-3-methylimidazolium chloride were purchased from commercial vendors with a quoted purity>95% for 1-ethyl-3-methylimidazolium acetate, and >98% for 1-ethyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride. All salts were dried under vacuum for 72 h at 90 C., achieving a final water content<0.9% determined by Karl Fischer titration using a Metrohm 831 KF coulometer.

[0054] Microcrystalline cellulose (Cellulose no. 435236) was purchased from a commercial vendor, and used as received.

Example 1. Characterisation of the Eutectic Behaviour of an Exemplary Ionic Liquid Mixture System of the Invention

[0055] Several mixtures of the ionic liquid 1-ethyl-3-methylimidazolium chloride ([C.sub.2mim]Cl), with a melting point of 88 C., and the ionic liquid 1-butyl-3-methylimidazolium chloride ([C.sub.4mim]Cl), with a melting point of 65 C., were prepared by dissolving each ionic liquid separately in methanol, combining both methanol solutions in the desired proportion, and evaporating completely the methanol. Mixtures were prepared so that their compositions ranged from pure [C.sub.2mim]Cl to pure [C.sub.4mim]Cl, evenly distributed over the entire composition range at intervals of 5 mol %. A sample of each mixture was subjected to analysis by differential scanning calorimetry (DSC). By plotting the signals of the corresponding thermograms in a temperature-composition phase diagram, the existence of a eutectic behaviour could be corroborated. By extrapolation of the trend of the signals of the excess components in such diagram (FIG. 1), a melting temperature of 46 C. and a composition of 0.51 in mole fraction of [C.sub.2mim]Cl and 0.49 in molar fraction of [C.sub.4mim]Cl were identified for the eutectic point of this particular eutectic mixture.

Example 2. Preparation of an Exemplary Ionic Liquid Mixture of the Invention

[0056] The ionic liquid 1-ethyl-3-methylimidazolium chloride ([C.sub.2mim]Cl) has a melting temperature of 88 C., and therefore it is a solid at room temperature (for instance 22 C.). The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C.sub.2mim][OAc]) is a liquid at room temperature and also at much lower temperatures, with no melting temperature above 73 C. These two ionic liquids were mixed in a vial in a 3:7 molar ratio (previously determined as the eutectic composition for this system), and the mixture was heated and stirred for 10 minutes at 100 C. A homogeneous liquid was obtained, which remained stable in that condition when cooled down to room temperature. No melting temperature could be detected by DSC for the obtained mixture above 73 C.

Example 3. Cellulose Dissolution in the Mixture of 1-Ethyl-3-Methylimidazolium Chloride and 1-Ethyl-3-Methylimidazolium Acetate at 75 C.

[0057] 5 g of a 3:7 molar ratio mixture of [C.sub.2mim]Cl and [C.sub.2mim][OAc] was placed in a jacketed glass vessel equipped with an overhead mechanical stirrer. The mixture was heated to 75 C., and 0.5 g of microcrystalline cellulose was added. The content of the thermostated vessel was stirred until complete dissolution of the cellulose (visually clear solution). 0.25 g was subsequently added, and then the content was newly stirred until complete dissolution of the cellulose. This action was repeated several times. After addition of a total amount of 1.50 g of cellulose (corresponding to 30 g of cellulose per 100 g of ionic liquid mixture), a clear solution was still obtained. No further additions of cellulose were made, because at this point the solution had turned excessively viscous.

Example 4. Cellulose Dissolution in the Mixture of 1-Ethyl-3-Methylimidazolium Chloride and 1-Ethyl-3-Methylimidazolium Acetate at 100 C.

[0058] 5 g of a 3:7 molar ratio mixture of [C.sub.2mim]Cl and [C.sub.2mim][OAc] was placed in a jacketed glass vessel equipped with an overhead mechanical stirrer. The mixture was heated to 100 C., and 0.5 g of microcrystalline cellulose was added. The content of the thermostated vessel was stirred until complete dissolution of the cellulose (visually clear solution). 0.25 g was subsequently added, and then the content was newly stirred until complete dissolution of the cellulose. This action was repeated several times. After addition of a total amount of 2.00 g of cellulose (corresponding to 40 g of cellulose per 100 g of ionic liquid mixture), a clear solution was still obtained.

Example 5. Cellulose Dissolution in the Mixture of 1-Ethyl-3-Methylimidazolium Chloride and 1-Butyl-3-Methylimidazolium Chloride

[0059] 5 g of a mixture of the ionic liquid [C.sub.2mim]Cl and [C.sub.4mim]Cl at a molar ratio 49:51 (eutectic composition) was prepared and placed in a jacketed glass vessel equipped with a mechanical stirrer, and was heated to 50 C., which is below the melting point of both [C.sub.2mim]Cl and [C.sub.4mim]Cl. Microcrystalline cellulose (0.5 g) was added. The solution (with a concentration of 10 g of cellulose per 100 g of ionic liquid mixture) was stirred mechanically until the complete dissolution of the cellulose, obtaining an optically clear and viscous solution.

Example 6. Influence of Dimethylsulfoxide (DMSO) Addition on the Process of Cellulose Dissolution in Ionic Liquid Mixtures

[0060] 4.25 g of a 3:7 molar ratio mixture of [C.sub.2mim]Cl and [C.sub.2mim][OAc] and 0.75 g DMSO was placed in a jacketed glass vessel equipped with an overhead mechanical stirrer. The mixture was heated to 75 C., and 0.5 g of microcrystalline cellulose was added. The content of the thermostated vessel was stirred until complete dissolution of the cellulose (visually clear solution). 0.25 g of microcrystalline cellulose was subsequently added, and then the content was stirred again until complete dissolution of the cellulose. Further additions of microcrystalline cellulose and subsequent dissolution were carried out. After addition of a total amount of 1.75 g of cellulose (corresponding to 35 g of cellulose per 100 g of ionic liquid mixture), a clear solution was still obtained. No further additions of cellulose were made, because at this point the solution turned into gel.

Example 7

[0061] A mixture of imidazolium salts: 1-ethyl-3-methylimidazolium chloride [C.sub.2mim]Cl in a molar ratio of from 1:5 to 5:1 with a mixture of 1-ethyl-3-methylimidazolium acetate [C.sub.2mim][OAc] and 1-butyl-3-methylimidazolium chloride [C.sub.4mim]Cl in any molar ratio, prepared in an analogous manner as in Example 1, was placed in a jacketed glass vessel equipped with an overhead mechanical stirrer. The mixture was heated to 75 C., and microcrystalline cellulose in an amount greater than 30 g of cellulose to 100 g of the used mixture of imidazolium salts was added. During the addition of cellulose, the content of the reactor was thermostated and stirred until the complete dissolution of the cellulose, obtaining an optically clear and viscous solution.

Example 8. Inability of the Eutectic Mixture of 1-Ethyl-3-Methylimidazolium Nitrate and 1-Ethyl-3-Methylimidazolium Hexafluorophosphate to Dissolve Cellulose

[0062] As an example of ionic liquid eutectic mixture not able to dissolve cellulose, the eutectic mixture of 1-ethyl-3-methylimidazolium nitrate ([C.sub.2mim][NO.sub.3]) and 1-ethyl-3-methylimidazolium hexafluorophosphate ([C.sub.2mim][PF.sub.6] was used. The ionic liquids were mixed in a 60:40 molar ratio to form a eutectic mixture (with a melting point of 19 C.). 5 g of the prepared mixture was placed in a jacketed glass vessel equipped with a mechanical stirrer, and was heated to 75 C. Microcrystalline cellulose (0.5 g) was added, and the content of the vessel mechanically stirred. After 48 h at those conditions, cellulose remained suspended in the ionic liquid mixture, forming a cloudy paste, with no signs of dissolution.

Example of Use

[0063] The composite prepared according to Example 5, is reprocessed in a known manner, to obtain film or foil. It yields the product with properties comparable to the products obtained using currently known methods.