Amino acid ionic liquid cellulose solvent as well as preparation and application thereof

Abstract

The invention belongs to the technical field of cellulose solvents, and discloses an amino acid ionic liquid cellulose solvent as well as preparation and application thereof. The general formula of the chemical structure of the cellulose solvent is formula I, R1 to R4 are respectively linear chain or branched chain alkyl and aryl, and Xm <-> is a group formed by hydrogen loss of carboxyl in amino acid. The invention also discloses a preparation method of the amino acid ionic liquid cellulose solvent. The preparation method is simple and efficient, natural amino acid is used, the cost is low, and the problem that metal equipment is seriously corroded by halogen-containing ionic liquid is solved. The amino acid ionic liquid provided by the invention realizes efficient dissolution of cellulose, and the dissolving liquid can be applied to preparation of a high-performance regenerated cellulose film material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cellulose solvent, and relates to a cellulose solvent amino acid ionic liquid as well as preparation and application thereof. BACKGROUND

[0002] Cellulose is one of the most abundant natural macromolecular polymers on earth, and has excellent properties such as renewability, environmental friendliness, biocompatibility and biodegradability, and exists in large quantities in wood, cotton, hemp and other plants. Cellulose can be used to prepare various forms of materials such as films, fibers, aerogels and the like, and is widely used in various fields such as packaging, textiles and medical devices. However, although cellulose has great application potential, its internal rich intramolecular and intermolecular hydrogen bonds and highly crystallized aggregate structure result in that cellulose cannot be melt-processed or dissolved in common solvents for solution processing. Therefore, the development of cellulose solvent has become the key to efficient utilization of cellulose resources.

[0003] Currently commonly used cellulose solvents include NaOH / CS2, LiCl / DMAc, NMMO, ZnCl2 aqueous solution and alkali urea aqueous solution. These solvents have certain effects on cellulose dissolution, but still have many problems. For example, NaOH / CS2 as a cellulose derivatization solvent produces toxic gases CS2 and HS2, acid and alkali pollutants during use, has high disposal cost and high operation cost; LiCl / DMAc is harsh in requirements for cellulose during use, and cellulose needs to be pretreated or activated, and the system is extremely sensitive to water content in the solution; NMMO is unstable at high temperature, has a narrow dissolution window and the like; ZnCl2 aqueous solution is strict in requirements for concentration and temperature of the solution during use, is highly corrosive and has high requirements for equipment; alkali urea aqueous solution needs to dissolve cellulose at low temperature during use, has high energy consumption and can only dissolve cellulose with low polymerization degree, which is not conducive to industrialization. The above harsh dissolution conditions limit the practical application of cellulose.

[0004] As a kind of efficient green solvent, ionic liquid has the advantages of non-volatility, non-flammability, recyclability, structure adjustable, etc., and has broad application prospect. At present, the ionic liquid used for efficient dissolution of cellulose is mainly imidazole-based, and most of the imidazole-based ionic liquids contain halogen anions (such as chloride, bromide, etc.), which can corrode the equipment, shorten the service life of the equipment, and limit its popularization in industrial application. Secondly, the synthesis process of the solvent system is complex, involving multiple steps of reaction and purification, and the production cost is high. In addition, the viscosity of the system is large, which is not conducive to the subsequent processing and utilization of cellulose. Therefore, it is urgent to develop a cellulose solvent with small equipment corrosion, simple preparation process, reasonable cost and low viscosity. Amino acid ionic liquid has the advantages of rich functional groups, low toxicity, biodegradability and easy preparation. At present, only a few amino acid ionic liquids show the ability to dissolve cellulose, but they are limited to low cellulose solubility. SUMMARY

[0005] In view of the problems of the current cellulose solvent system, such as complex preparation process, high cost, strong equipment corrosion and limited cellulose solubility, the present application provides an amino acid ionic liquid and its preparation and application. The amino acid ionic liquid of the present application is composed of quaternary ammonium cation and carboxyl anion formed by amino acid, which is obtained by neutralization of quaternary ammonium base and amino acid. The amino acid ionic liquid of the present application can be efficiently synthesized at room temperature and normal pressure, not only the preparation process is simple, but also the cost of natural amino acid used is low, and the problem of serious corrosion of halogen-containing ionic liquid (such as imidazole) to metal equipment is avoided. In addition, the ionic liquid can realize efficient dissolution of cellulose and preparation of high-performance cellulose film.

[0006] The amino acid ionic liquid of the present application is used for the dissolution of cellulose, used as a cellulose solvent, to prepare cellulose film.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0008] An amino acid ionic liquid cellulose solvent, the chemical structure general formula is formula I:

[0009]

[0010] Wherein, R1, R2, R3, R4 are linear or branched alkyl, aryl, X m- is the group formed by losing hydrogen from the carboxyl group of amino acid, m is 1 or 2, n is 1 or 2, m=n.

[0011] The alkyl group is preferably methyl, ethyl, propyl, butyl;

[0012] The aryl group is preferably benzyl.

[0013] The cation in the structure of the amino acid ionic liquid cellulose solvent is preferably one of tetramethyl quaternary amine (R1, R2, R3, R4 are methyl), tetraethyl quaternary amine (R1, R2, R3, R4 are ethyl), tetrapropyl quaternary amine (R1, R2, R3, R4 are propyl), tetrabutyl quaternary amine (R1, R2, R3, R4 are butyl), benzyl trimethyl quaternary amine (three of R1, R2, R3, R4 are methyl, and one is benzyl), benzyl triethyl quaternary amine (three of R1, R2, R3, R4 are ethyl, and one is benzyl).

[0014] The anion X in the structure of the amino acid ionic liquid m- is selected from one of the following structures:

[0015]

[0016] The amino acid ionic liquid is preferably one or more of tetraethylammonium leucine, tetraethylammonium valine, tetraethylammonium threonine, tetraethylammonium lysine.

[0017] The preparation method of the amino acid ionic liquid cellulose solvent comprises the following steps: reacting quaternary ammonium base with amino acid in water, purifying to obtain the amino acid ionic liquid cellulose solvent.

[0018] The structure of the quaternary ammonium base is

[0019] The amino acid is an amino acid: HX or H2X;

[0020] The molar ratio of the amino acid to the quaternary ammonium base is 1:2.5-2:1, preferably 1:1-2:1, wherein R1, R2, R3, R4 and X are as defined in the structure formula I of the amino acid ionic liquid cellulose solvent.

[0021] The mass ratio of the amino acid to water is 1:10-1:25.

[0022] The reaction conditions are a temperature of 25-40°C and a time of 6-12h.

[0023] The purification refers to removing water after the reaction, alcohol precipitation and filtering insoluble substances, removing ethanol, drying to obtain the amino acid ionic liquid.

[0024] The water removal refers to removing water by vacuum rotary evaporation at 65-75°C after the reaction, and vacuum drying at 55-65°C for 20-26h.

[0025] The ethanol removal refers to removing ethanol by vacuum rotary evaporation. The drying refers to vacuum drying at 55-65°C for 20-26h.

[0026] The amino acid ionic liquid cellulose solvent is used for dissolving cellulose, thereby preparing a cellulose film.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1) The ion liquid preparation process of the present application is simple, only the quaternary ammonium base and amino acid need to be neutralized by acid and base. And the solvent system has a significantly lower viscosity than most ion liquids, and has excellent solubility for different cellulose raw materials, low solution viscosity, which is beneficial to subsequent processing and application.

[0029] 2) The amino acid ion liquid has low corrosion to the equipment, which is beneficial to its popularization in industrial application.

[0030] 3) The amino acid raw material selected by the present application is widely present in beans, meat, dairy products and other foods, has the advantages of low toxicity, wide source and low cost, and is beneficial to large-scale production.

[0031] 4) The ion liquid can realize efficient cellulose dissolution, and the regenerated cellulose film prepared has excellent mechanical properties.

[0032] 5) After the ion liquid of the present application dissolves cellulose, the cellulose solution can be regenerated by adding an anti-solvent, and the used solvent can be recycled, which meets the green environmental protection concept. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is the nuclear magnetic resonance hydrogen spectrum of the ion liquid [TEA][Leu] in Example 1.

[0034] Figure 2 It is the appearance of part of the amino acid ion liquid in Example 1, wherein (a) is [TEA][Val], (b) is [TEA][Leu], (c) is [TEA][Lys], and (d) is [TEA][Thr].

[0035] Figure 3 It is the picture of cellulose before and after dissolution in [TEA][Val] in Example 3, wherein (a) and (b) are respectively the pictures of microcrystalline cellulose (DP=180) before and after dissolution; (c) and (d) are respectively the pictures of wood pulp cellulose (DP=900) before and after dissolution.

[0036] Figure 4 It is the shear viscosity curve of the cellulose solution obtained by dissolving wood pulp cellulose in the amino acid ion liquid in Example 3.

[0037] Figure 5(a) the light transmittance curve of the regenerated cellulose film obtained after dissolving cellulose, (b) the stress-strain curve of the regenerated cellulose film, (c) the photo of the regenerated cellulose film prepared in the [TEA][Val] system. DETAILED DESCRIPTION

[0038] The present application is further described in detail by the following specific examples. The examples are not intended to limit the scope of the present application. In the examples, [TEA][Thr]: tetraethylammonium threonine; [TEA][Leu]: tetraethylammonium leucine; [TEA][Val]: tetraethylammonium valine; [TEA][Lys]: tetraethylammonium lysine; [TEA][Glu]: tetraethylammonium glutamic acid; [TEA][Asp]: tetraethylammonium aspartic acid.

[0039] Example 1

[0040] Synthesis of amino acid ionic liquid:

[0041] (1) Synthesis of ionic liquid [TEA][Leu]:

[0042]

[0043] 1.2 mol L-leucine (L-Leu) was added to an aqueous solution containing 1.0 mol tetraethylammonium hydroxide (TEAH), and the mixture was stirred at 25°C for 12 h. After the reaction was completed, water was removed by vacuum rotary evaporation at 70°C, and then the mixture was placed in a vacuum drying oven at 60°C for 24 h. The obtained solution was precipitated with anhydrous ethanol and the insoluble matter was filtered. The obtained solution was removed by vacuum rotary evaporation at 60°C, and then the mixture was placed in a vacuum drying oven at 60°C for 24 h. Thus, purified tetraethylammonium leucine ionic liquid was obtained.

[0044] (2) Synthesis of ionic liquid [TEA][Val]:

[0045]

[0046] 1.2 mol L-valine (L-Val) was added to an aqueous solution containing 1.0 mol tetraethylammonium hydroxide (TEAH), and the mixture was stirred at 25°C for 12 h. After the reaction was completed, water was removed by vacuum rotary evaporation at 70°C, and then the mixture was placed in a vacuum drying oven at 60°C for 24 h. The obtained solution was precipitated with anhydrous ethanol and the insoluble matter was filtered. The obtained solution was removed by vacuum rotary evaporation at 60°C, and then the mixture was placed in a vacuum drying oven at 60°C for 24 h. Thus, purified tetraethylammonium valine ionic liquid was obtained.

[0047] (3) Synthesis of ionic liquid [TEA][Thr]:

[0048]

[0049] 1.2 mol L-threonine (L-Thr) was added to 1.0 mol of aqueous tetraethylammonium hydroxide (TEAH) solution, and the mixture was stirred at 25 °C for 12 h. After the reaction was completed, water was removed by vacuum rotary evaporation at 70 °C, and then the mixture was placed in a vacuum drying oven at 60 °C for 24 h. The resulting solution was precipitated with anhydrous ethanol and the insoluble matter was filtered. The ethanol was removed from the resulting solution by vacuum rotary evaporation at 60 °C, and then the mixture was placed in a vacuum drying oven at 60 °C for 24 h. Thus, purified tetraethylammonium threonine ionic liquid was obtained.

[0050] (4) Synthesis of ionic liquid [TEA][Lys]:

[0051]

[0052] 1.2 mol L-threonine (L-Thr) was added to 1.0 mol of aqueous tetraethylammonium hydroxide (TEAH) solution, and the mixture was stirred at 25 °C for 12 h. After the reaction was completed, water was removed by vacuum rotary evaporation at 70 °C, and then the mixture was placed in a vacuum drying oven at 60 °C for 24 h. The resulting solution was precipitated with anhydrous ethanol and the insoluble matter was filtered. The ethanol was removed from the resulting solution by vacuum rotary evaporation at 60 °C, and then the mixture was placed in a vacuum drying oven at 60 °C for 24 h. Thus, purified tetraethylammonium threonine ionic liquid was obtained.

[0053] (5) Synthesis of ionic liquid [TEA][Glu]:

[0054]

[0055] 1.2 mol L-threonine (L-Thr) was added to 1.0 mol of aqueous tetraethylammonium hydroxide (TEAH) solution, and the mixture was stirred at 25 °C for 12 h. After the reaction was completed, water was removed by vacuum rotary evaporation at 70 °C, and then the mixture was placed in a vacuum drying oven at 60 °C for 24 h. The resulting solution was precipitated with anhydrous ethanol and the insoluble matter was filtered. The ethanol was removed from the resulting solution by vacuum rotary evaporation at 60 °C, and then the mixture was placed in a vacuum drying oven at 60 °C for 24 h. Thus, purified tetraethylammonium threonine ionic liquid was obtained.

[0056] (6) Synthesis of ionic liquid [TEA][Asp]:

[0057]

[0058] 1 mol L-Aspartic acid (L-Asp) was added into 2.2 mol tetraethylammonium hydroxide (TEAH) aqueous solution, the mixture was stirred at 25 °C for 12 h, after the reaction was completed, water was removed by vacuum rotary evaporation at 70 °C, then the mixture was placed in a vacuum drying oven at 60 °C for 24 h, precipitated with anhydrous ethanol and filtered the insoluble, the obtained solution was removed ethanol by vacuum rotary evaporation at 60 °C, then the mixture was placed in a vacuum drying oven at 60 °C for 24 h, to obtain the purified tetraethylammonium aspartate ionic liquid.

[0059] Other amino acid ionic liquids can be synthesized according to the above steps by replacing different quaternary ammonium bases and amino acids according to the molar ratio (amino acid: organic base = 1.2:1).

[0060] Figure 1 The nuclear magnetic resonance spectrum of [TEA][Leu] indicates that the synthesis of the ionic liquid of the structure is successful. Figure 2 The appearance of some amino acid ionic liquids in Example 1 is shown in the figure, wherein (a) [TEA][Val], (b) [TEA][Leu], (c) [TEA][Lys], (d) [TEA][Thr].

[0061] Example 2

[0062] Measurement of viscosity values of amino acid ionic liquids:

[0063] 100 g of some amino acid ionic liquids in Example 1 was taken, the temperature of the solvent was controlled by water bath heating, a rotary viscometer (Shanghai Lichen) was used to measure the viscosity values of the solvent system at different temperatures, the rotor was immersed in the solvent system, the liquid was above the notch mark on the rotor rod, the appropriate rotor and rotation speed were selected to make the torque percentage reading between 10-90%, the viscosity value at each temperature was measured three times and the average value was taken, and the test results are shown in Table 1.

[0064] Table 1 Viscosity values of amino acid ionic liquids

[0065]

[0066]

[0067] From Table 1, it can be seen that the viscosity values of amino acid ionic liquids gradually decrease with the increase of temperature, the viscosity values of [TEA][Leu], [TEA][Lys], [TEA][Val] and [TEA][Thr] at 70 °C or above are all lower than 100 mPa·s, and the lower viscosity of the solvent system is conducive to promoting the dissolution of cellulose and the processing of the dissolved solution.

[0068] Example 3

[0069] Dissolution of amino acid ionic liquids on cellulose:

[0070] (1) Microcrystalline cellulose dissolution: 10 g of [TEA][Val] was taken, 0.42 g of microcrystalline cellulose (DP = 180) was added, and the mixture was stirred at 100°C and 150 rpm for 0.5 h to obtain a transparent cellulose solution. A small amount of the sample before and after dissolution was observed under a polarizing microscope, as shown in Figs. Figure 3 (a) and (b), respectively, the field of view was free of microcrystalline cellulose, indicating that the solvent system completely dissolved the microcrystalline cellulose. Figure 3 Figs. (a) and (b) are pictures of microcrystalline cellulose (DP = 180) before and after dissolution, respectively.

[0071] (2) Maximum solubility test: 5 g of the ionic liquid obtained in Example 1 was taken, 0.05 g of microcrystalline cellulose was added, and the mixture was stirred at 100°C to dissolve. After 1 h, a small amount of the dissolved solution was taken with a glass rod and placed on a glass slide under an optical microscope to observe the dissolution. After dissolution was determined, microcrystalline cellulose was continuously added and the above microscope observation step was repeated. When no undissolved cellulose raw material was observed in the microscope image, the addition of cellulose was stopped, and the amount of cellulose added was accumulated. The mass percentage solubility of the ionic liquid for cellulose was obtained by dividing the amount of cellulose added by the amount of solvent (5 g).

[0072] The maximum solubility of the amino acid ionic liquid for cellulose is shown in Table 2.

[0073] Table 2 Maximum solubility of amino acid ionic liquid for microcrystalline cellulose

[0074] Solvent Solubility (wt%) [TEA][Leu] 18.0 [TEA][Val] 16.9 [TEA][Thr] 16.7 [TEA][Lys] 15.3 [TEA][Glu] 7.4 [TEA][Asp] 3.6

[0075] As can be seen from Table 2, the amino acid ionic liquid of the present application has good solubility for cellulose, such as [TEA][Thr], [TEA][Leu], [TEA][Val], and [TEA][Lys], which have a maximum solubility for microcrystalline cellulose of more than 15 wt% at 100°C.

[0076] (3) Wood pulp cellulose dissolution: 10 g of the amino acid ionic liquid [TEA][Val] was taken, 0.42 g of broadleaf wood pulp cellulose was added, and the mixture was stirred at 100°C and 200 rpm for 2 h to obtain a transparent cellulose solution. After dissolution was completed, a small amount of the solution before and after dissolution was observed under a polarizing microscope, as shown in Figs. Figure 3 (c) and (d), respectively, the wood pulp cellulose was completely dissolved in the solvent system, indicating that the solvent system completely dissolved the wood pulp cellulose. The dissolution of wood pulp cellulose in other solvent systems was carried out using the same procedure. The shear viscosities of the wood pulp solutions obtained from the various systems were measured at 25°C using a rotational rheometer, a suitable rotor was selected, the shear viscosity was measured three times and the average value was taken. The test results are shown in Table 3. Figure 4As shown, the viscosity of the dissolution solution decreases with the increase of the shear rate, showing the shear thinning non-Newtonian fluid characteristics.

[0077] Figure 3 Figures of wood pulp cellulose (DP=900) before and after dissolution in (c), (d), respectively.

[0078] Figure 4 Shear viscosity curves of the cellulose dissolution solution obtained by dissolving wood pulp cellulose in the amino acid ionic liquid in Example 3.

[0079] The above results show that the solvent system obtained by the present application can not only dissolve microcrystalline cellulose with low degree of polymerization, but also dissolve wood pulp cellulose with high degree of polymerization. In addition, the obtained wood pulp dissolution solution has good rheological properties and good processability.

[0080] Example 4

[0081] The preparation of regenerated cellulose film is as follows:

[0082] Take 10 g of the solvent system [TEA][Thr], [TEA][Leu], [TEA][Val], [TEA][Lys], and heat to 100℃. Add 0.40 g of wood pulp cellulose under stirring at 280 rmp, and continue stirring for 2 h to obtain a clear and transparent cellulose solution. After dissolution, pour the cellulose solution into a glass culture dish and stand for defoaming at 100℃, then immerse in a coagulation bath for a period of time, take out, continue to rinse with water, and dry with a flat plate dryer to obtain a regenerated cellulose film. The tensile stress-strain curve of the regenerated cellulose film is tested by a universal material testing machine, and the light transmittance curve is tested by a UV spectrophotometer. The light transmittance test shows that the light transmittance of the regenerated film is more than 90% in the visible light range Figure 5 (a). The tensile test Figure 5 (b) shows that the strength of the regenerated film is in the range of 100-140 MPa, and the regenerated film prepared in the [TEA][Leu] solvent system has the best mechanical strength, with a tensile stress of 138 MPa. The photos of the regenerated cellulose films prepared in some solvents are shown in Figure 5 (c), and the cellulose film prepared in this system has good transparency and excellent mechanical properties, which can be used as a substitute for plastic-based packaging materials, and used in the packaging field of food, daily chemical products, etc.

[0083] Figure 5 The light transmittance curve of the regenerated cellulose film obtained after dissolving cellulose in the amino acid ionic liquid in Example 4, (b) the stress-strain curve of the regenerated cellulose film, (c) the photo of the regenerated cellulose film prepared in the [TEA][Val] system.

[0084] Comparative Example 1

[0085] A synthesis of an amino acid ionic liquid comprising the steps of:

[0086] Synthesis of ionic liquid [DBN][Pro]: 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) was mixed with L-proline (L-Pro) under nitrogen atmosphere. The molar ratio of DBN superbase to amino acid carboxyl group was 1:1. The reaction was stirred at 90 °C for 2 h until the mixture was uniformly transparent, then repeatedly washed with ethanol / ethyl acetate. [DBN][Pro] was obtained after vacuum drying at 60 °C for 24 h.

[0087] Comparative Example 2

[0088] A synthesis of an amino acid ionic liquid comprising the steps of:

[0089] Synthesis of ionic liquid [DBU][Asp]: 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was mixed with L-aspartic acid (L-Asp) under nitrogen atmosphere. The molar ratio of DBU superbase to amino acid carboxyl group was 1:1. The reaction was stirred at 90 °C for 2 h until the mixture was uniformly transparent, then repeatedly washed with ethanol / ethyl acetate. [DBU][Asp] was obtained after vacuum drying at 60 °C for 24 h.

[0090] Comparative Example 3

[0091] A synthesis of an amino acid ionic liquid comprising the steps of:

[0092] Synthesis of ionic liquid [Ch][Val]: 1 mol of aqueous choline hydroxide ([Ch][OH]) was added dropwise to 1.2 mol of slightly excess aqueous L-valine (L-Val) solution, stirred in an ice bath for 48 h, then water was removed by 50 °C vacuum rotary evaporation. Acetonitrile / methanol was added for repeated washing, and excess amino acid was filtered. The filtrate was removed by 50 °C vacuum rotary evaporation, then [Ch][Val] was obtained after vacuum drying at 70 °C for 24 h.

[0093] Comparative Example 4

[0094] A synthesis of an amino acid ionic liquid comprising the steps of:

[0095] Synthesis of ionic liquid [EMIM] [Thr]: 1 mol of 1-ethyl-3-methylimidazolium hydroxide ([EMIM] [OH]) aqueous solution was added dropwise to 1.2 mol of L-threonine (L-Thr) aqueous solution, and the mixture was stirred at room temperature for 24 h, and then water was removed by vacuum rotary evaporation at 60 °C. The excess amino acid was precipitated with anhydrous ethanol and filtered, and then the filtrate was removed of ethanol by vacuum rotary evaporation at 50 °C. [EMIM] [Thr] was obtained after vacuum drying at 60 °C for 24 h.

[0096] Comparative Example 5

[0097] A synthesis of an amino acid ionic liquid comprising the steps of:

[0098] Synthesis of ionic liquid [N 221ME [Trp]: 1 mol of N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium hydroxide ([N 221ME [OH]) aqueous solution was added dropwise to 1.2 mol of L-tryptophan (L-Trp) aqueous solution, and the mixture was stirred in an ice bath for 24 h, and then water was removed by vacuum rotary evaporation at 60 °C. Acetonitrile / methanol was added for repeated washing, and the excess amino acid was filtered. The filtrate was removed of solvent by vacuum rotary evaporation at 60 °C, and then [N 221ME [Trp] was obtained after vacuum drying at 70 °C for 24 h.

[0099] Comparative Example 6

[0100] A synthesis of an amino acid ionic liquid comprising the steps of:

[0101] Synthesis of ionic liquid [DDTMA] [Leu]: 1 mol of dodecyltrimethylammonium hydroxide ([DDTMA] [OH]) aqueous solution was added dropwise to 1.2 mol of L-leucine (L-Leu) aqueous solution, and the mixture was stirred at room temperature for 24 h, and then water was removed by vacuum rotary evaporation at 60 °C. The excess amino acid was precipitated with anhydrous ethanol and filtered, and then the filtrate was removed of ethanol by vacuum rotary evaporation at 50 °C. [DDTMA] [Leu] was obtained after vacuum drying at 60 °C for 24 h.

[0102] The ionic liquids prepared in Comparative Examples 1 to 6 were tested for solubility of cellulose, and the test results are shown in Table 3.

[0103] Table 3 Maximum solubility test of microcrystalline cellulose

[0104] Solvent Solubility (wt%) [DBN][Pro] 9.6 [DBU][Asp] 2.8 [Ch][Val] 0.48 [EMIM][Thr] 4.7 [[N 221ME ][Trp]]]> 5.3 [DDTMA][Leu] 0

Claims

1. An amino acid ionic liquid cellulose solvent, characterized in that: Its general chemical structure is Formula I: Wherein, R1, R2, R3, and R4 are each a straight chain or branched chain alkyl group or an aromatic group, and X m- It is a group formed by the loss of hydrogen from the carboxyl group in an amino acid, where m is 1 or 2, n is 1 or 2, and m=n.

2. The amino acid ionic liquid cellulose solvent according to claim 1, characterized in that: The alkyl group is methyl, ethyl, propyl, n-butyl, or isobutyl; and the aromatic group is benzyl.

3. The amino acid ionic liquid cellulose solvent according to claim 1, characterized in that: In the structure of the amino acid ionic liquid, R1, R2, R3, and R4 are all methyl, ethyl, propyl, n-butyl, and isobutyl, or three of R1, R2, R3, and R4 are methyl and one is benzyl, or three of R1, R2, R3, and R4 are ethyl and one is benzyl.

4. The amino acid ionic liquid cellulose solvent according to claim 1, characterized in that: The anion X in the structure of the amino acid ionic liquid m- Select one of the following structures:

5. The amino acid ionic liquid cellulose solvent according to claim 1, characterized in that: The amino acid ionic liquid is one or more of tetraethylammonium leucine, tetraethylammonium valine, tetraethylammonium threonine and tetraethylammonium lysine.

6. The method for preparing the amino acid ionic liquid cellulose solvent according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: reacting quaternary ammonium base with amino acid in water, purifying and obtaining amino acid ionic liquid cellulose solvent; Quaternary ammonium base: Amino acids: HX or H2X; wherein R1, R2, R3, R4 and X are as defined in structural formula I of the amino acid ionic liquid cellulose solvent.

7. The method for preparing the amino acid ionic liquid cellulose solvent according to claim 6, characterized in that: The molar ratio of the amino acid to the quaternary ammonium base is 1:2.5 to 2:1; The mass ratio of amino acids to water is 1:10 to 1:25; The reaction conditions are a temperature of 25 to 40°C and a time of 6 to 12 hours; The purification refers to removing water after the reaction, precipitating with alcohol and filtering insoluble matter, removing ethanol, and drying to obtain amino acid ionic liquid.

8. The method for preparing the amino acid ionic liquid cellulose solvent according to claim 7, characterized in that: The dehydration refers to removing water by vacuum rotary evaporation at 65-75°C after the reaction is completed, and vacuum drying at 55-65°C for 20-26h; The ethanol removal refers to removing the ethanol by vacuum rotary evaporation; and the drying refers to vacuum drying at 55 to 65° C. for 20 to 26 hours.

9. Use of the amino acid ionic liquid cellulose solvent according to any one of claims 1 to 5 in cellulose dissolution.

10. The use according to claim 9, characterized in that: The amino acid ionic liquid cellulose solvent prepares a regenerated cellulose film by dissolving cellulose.

Images