Alcohol-salt system for efficiently dissolving carbohydrates

Abstract

The invention discloses an alcohol-salt system capable of efficiently dissolving carbohydrates. Alcohol with high-concentration salt is dissolved to form a molten salt alcohol adduct solvent system, and the solubility of carbohydrate in an alcohol solvent is improved by utilizing the complexing action between salt cations and hydroxyl of a pyranose ring. According to the invention, the problem of solubility of carbohydrates in alcohol solvents is solved, and a basis is provided for efficient conversion of carbohydrates in alcohol solvents.

Description

Technical Field

[0001] This invention relates to the field of chemical solvent technology, and more specifically to an alcohol-salt system for improving the solubility of carbohydrates in alcohol solvents. Background Technology

[0002] The conversion of carbohydrates, especially glucose and xylose (the structural units of cellulose and hemicellulose, respectively), into chemicals is an important area for the high-value utilization of biomass. Therefore, in addition to researching more efficient catalysts, the development of more environmentally friendly and sustainable solvents has also attracted considerable research interest. Water is a recognized green solvent and the most commonly used reaction solvent for carbohydrates. However, reacting carbohydrates in aqueous solvents causes numerous side reactions and high post-processing costs. Organic solvents have been widely used in biomass conversion, but the poor solubility of carbohydrates in organic solvents results in large quantities of organic solvents, making large-scale application difficult.

[0003] Among traditional organic solvents, alcohols have the advantages of low boiling point and ease of handling, making them more suitable for sugar conversion. For example, glucose conversion (such as isomerization) and dehydration have yielded good results in methanol, ethanol, butanol, and other alcohol solvents (ACS Catal. 2019, 9(3): 2101-2109; ChemCatChem 2019, 11(16): 4182-4188.). Upare et al. determined the solvation energy and hydroxyl bond dissociation energy of glucose in 1-butanol, GVL, DMF, and water. Among these solvents, 1-butanol was the most efficient solvent for glucose isomerization due to its higher solvation energy and lower bond dissociation energy (ACS Catal. 2019, 10(2): 1388-1396). In addition, according to density functional theory (DFT) calculations on glucose on aluminum-based catalysts, in methanol, Al 3+ Carbohydrates tend to coordinate with methanol and β-D-glucopyranose, making them more readily isomerized to fructose (ACS Resustainable Chem. Eng. 2019, 7(17): 14962-14972). However, carbohydrates have very low solubility in alcohol solvents, limiting their application in biomass conversion. For example, glucose, xylose, and lactose often have a solubility of less than 1% in methanol.

[0004] Molten salt alcoholates (MSH) are highly concentrated aqueous solutions of inorganic salts. Because the molar ratio of water to salt is less than or equal to the coordination number of the cation, water molecules are tightly bound to the inner coordination spheres of the salt cation, while the anions are exposed (uncoordinated). This allows for strong hydrogen bonding between the cation and the hydroxyl groups of the pyranose ring, resulting in good coordination dissolution capabilities. Therefore, MSH is often used as an excellent solvent for swelling or dissolving cellulose. Based on this, we constructed an alcohol-salt solvent system that forms a molten salt alcoholate (MSA) solvent system similar to MSH under high salt concentration conditions. By utilizing the complexation between the salt cation and the hydroxyl groups of the pyranose ring, we can improve the solubility of carbohydrates in alcohol solvents, achieving efficient dissolution of carbohydrates in alcohol solvents. Summary of the Invention

[0005] To address the poor solubility of carbohydrates in alcohol solvents, this invention provides an efficient alcohol-salt system for dissolving carbohydrates. This system involves forming a molten salt ethanolate solvent system by dissolving a high concentration of salt in an alcohol. The complexation between the salt cation and the hydroxyl group of the pyranose ring improves the solubility of carbohydrates in alcohol solvents. The specific process includes:

[0006] (1) Construction of alcohol-salt system: Different types of salts were dissolved in alcohol solvent, and alcohol-salt systems with high concentrations of salt dissolved were screened.

[0007] (2) Solubility of carbohydrates in alcohol-salt system: Based on the alcohol-salt system obtained in (1), different types of sugars such as monosaccharides, disaccharides and polysaccharides were added and dissolved at different temperatures to investigate the solubility of carbohydrates in alcohol-salt system.

[0008] The technical solution adopted in this invention is as follows:

[0009] An alcohol-salt system for dissolving carbohydrates, wherein the alcohol-salt system is prepared by dissolving different types of salts in different alcohol solvents, wherein the alcohol solvents are primary alcohols, secondary alcohols or diols, and the salts are halide salts.

[0010] The alcohols include, but are not limited to, methanol, ethanol, propanol, butanol, isopropanol, isobutanol, ethylene glycol, glycerol, etc.

[0011] The halides include, but are not limited to, lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, potassium bromide, magnesium chloride, magnesium bromide, calcium chloride, calcium bromide, or zinc chloride.

[0012] The alcohol-salt system is obtained by dissolving lithium bromide, calcium chloride, or zinc chloride in methanol, ethanol, or ethylene glycol, including but not limited to methanol-lithium bromide, ethanol-lithium bromide, ethylene glycol-lithium bromide, methanol-calcium chloride, methanol-zinc chloride, and ethylene glycol-zinc chloride systems.

[0013] The concentration range of the salt in the alcohol-salt system is 5-50 g / 100 mL.

[0014] An alcohol-salt system is prepared by dissolving a salt in an alcohol solvent. The dissolution temperature of the salt in the alcohol solvent is 30-60℃.

[0015] The alcohol-salt system is intended for use as a solvent for carbohydrates.

[0016] The carbohydrates are monosaccharides, disaccharides, and polysaccharides, and may specifically include: glucose, mannose, xylose, arabinose, ribose, galactose, cellobiose, lactose, and cellulose.

[0017] The temperature at which carbohydrates dissolve in a salt-alcohol solvent is 20-100°C, preferably 30-60°C.

[0018] In this invention, the preferred alcohol-salt systems selected include: methanol-calcium chloride (MSA-1), methanol-lithium bromide (MSA-2), ethylene glycol-lithium bromide (MSA-3), and methanol-zinc chloride (MSA-4). In these systems, the salts are soluble in alcohol solvents at relatively high concentrations.

[0019] In the preferred alcohol-salt systems, the solubility of different carbohydrates is significantly greater than that of a single alcohol solvent. For example, the solubility of glucose in 20 g / 100 mL CaCl2-methanol, 40 g / 100 mL LiBr-methanol, 50 g / 100 mL LiBr-ethylene glycol, and 80 g / 100 mL ZnCl2-methanol systems are 59, 24, 12, and 28 g / 100 mL, respectively, while the solubility of glucose in methanol alone is less than 1 g / 100 mL. Other monosaccharides, such as xylose, arabinose, fructose, mannose, and ribose, and disaccharides, such as cellobiose and lactose, all exhibit higher solubility in the preferred alcohol-salt systems than in a single alcohol solvent.

[0020] An alcohol-salt system for dissolving glucose, wherein the alcohol is methanol and the salt is one of calcium chloride, lithium bromide or zinc chloride; the concentration of the salt is in the range of 20-50 g / 100 mL.

[0021] More preferably, the alcohol-salt system for dissolving glucose is a calcium chloride-methanol system, and the concentration of calcium chloride is in the range of 10-20 g / 100 mL. More preferably, the concentration of calcium chloride is 20 g / 100 mL.

[0022] The calcium chloride-methanol system is used as a solvent for carbohydrates, including glucose, xylose, galactose, cellobiose, arabinose, lactose, mannose, fructose, ribose, and lythose, with a dissolution temperature of 30-60℃.

[0023] A methanol-calcium chloride system for dissolving carbohydrates, wherein the concentration of calcium chloride ranges from 10 to 20 g / 100 mL;

[0024] A methanol-lithium bromide system for dissolving carbohydrates, wherein the concentration of lithium bromide is in the range of 25–50 g / 100 mL, and more preferably 40 g / 100 mL.

[0025] An ethylene glycol-lithium bromide system for dissolving carbohydrates, wherein the concentration of lithium bromide ranges from 25 to 60 g / 100 mL, and more preferably the concentration of lithium bromide is 50 g / 100 mL;

[0026] A methanol-zinc chloride system for dissolving carbohydrates, wherein the concentration of zinc chloride ranges from 40 to 100 g / 100 mL, and more preferably the concentration of zinc chloride is 80 g / 100 mL.

[0027] The above description is only for illustrating the alcohol-salt system and the dissolution of carbohydrates in the alcohol-salt system, and should not be construed as limiting the scope of the present invention.

[0028] Beneficial effects:

[0029] This invention provides an efficient alcohol-salt system for dissolving carbohydrates. Specifically, it involves dissolving a high concentration of salt in an alcohol solvent to form a molten salt ethanolate solvent system. The complexation between the salt cation and the hydroxyl group of the pyranose ring improves the solubility of carbohydrates in alcohol solvents. This invention solves the problem of poor carbohydrate solubility in alcoholic organic solvents, providing a solution for using alcohols as solvents for large-scale carbohydrate conversion and utilization. Detailed Implementation

[0030] The invention can be better understood from the following embodiments. However, the descriptions of the examples are for illustrative purposes only and should not, and will not, limit the invention as described in detail in the claims.

[0031] Methods for calculating carbohydrate solubility:

[0032] The solubility of sugars in alcohol-salt solvents is determined in the following two ways:

[0033] (1) After the sugars have dissolved in the alcohol-salt system, solid-liquid separation is performed by centrifugation. The resulting precipitate is dried in a vacuum drying oven and weighed to determine the undissolved carbohydrates. The solubility of carbohydrates in different alcohol-salt systems is calculated by the mass difference between the added carbohydrates and the undissolved carbohydrates.

[0034] (2) The concentration of sugars dissolved in the alcohol-salt system was determined by high performance liquid chromatography (HPLC). Column type: Bio-Rad Aminex HPX-87H (300*7.8mm); Detector: differential detector and ultraviolet detector; Mobile phase: 5mM dilute sulfuric acid aqueous solution; Flow rate: 0.6mL / min; Column temperature: 35℃; Detector temperature: 35℃; Injection volume: 10μL.

[0035] Example 1: Solubility of different salts in alcohol solvents

[0036] Excess amounts of LiBr, LiCl, NaCl, NaBr, MgCl2, CaCl2, and ZnCl2 were weighed and dissolved in methanol, ethanol, propanol, butanol, and ethylene glycol, respectively. The solutions were fully dissolved at 30°C. After dissolution, solid-liquid separation was performed by centrifugation. The resulting precipitates were dried in a vacuum drying oven and weighed to determine the undissolved salts. The solubility of different salts in different alcohol solvents was calculated by the mass difference between the added salt and the undissolved salt. The results are shown in Table 1.

[0037] Table 1

[0038]

[0039] As shown in Table 1, the solubility of different halide salts varies in different alcohols. Lithium salts exhibit high solubility in all alcohol solvents, with lithium bromide showing the best solubility. Sodium salts show poor solubility in all alcohol solvents. Among the alkaline earth metal salts magnesium chloride and calcium chloride, calcium chloride shows better solubility in various alcohol solvents. Zinc chloride shows good solubility in methanol and ethanol, but poor solubility in propanol, butanol, and ethylene glycol.

[0040] Example 2: Effect of increasing temperature on the solubility of salts in alcohol solvents

[0041] Excess amounts of LiBr, LiCl, NaCl, NaBr, MgCl2, CaCl2, and ZnCl2 were weighed and dissolved in methanol, ethanol, propanol, butanol, and ethylene glycol, respectively. The solutions were fully dissolved at 60°C. After dissolution, solid-liquid separation was performed by centrifugation. The resulting precipitates were dried in a vacuum drying oven and weighed to determine the undissolved salts. The solubility of different salts in different alcohol solvents was calculated by the mass difference between the added salt and the undissolved salt. The results are shown in Table 2.

[0042] Table 2

[0043]

[0044] As shown in Table 2, increasing the dissolution temperature from 30℃ to 60℃ did not significantly change the solubility of lithium salts in different alcohol solvents, except for a significant increase in solubility in ethylene glycol; sodium salts remained poorly soluble in alcohol solvents; the solubility of calcium chloride in different alcohols did not change significantly; and the solubility of zinc chloride increased significantly in all alcohols. We selected four systems—methanol-calcium chloride (MSA-1), methanol-lithium bromide (MSA-2), ethylene glycol-lithium bromide (MSA-3), and methanol-zinc chloride (MSA-4)—to study the solubility of carbohydrates.

[0045] Example 3: Solubility of carbohydrates in alcohol-salt systems

[0046] Based on the maximum solubility of salts in alcohols in Example 1, LiBr, CaCl2, and ZnCl2 were weighed and dissolved in methanol and ethylene glycol, respectively, to prepare 20 g / 100 mL CaCl2-methanol (MSA-1), 40 g / 100 mL LiBr-methanol (MSA-2), 30 g / 100 mL LiBr-ethylene glycol (MSA-3), and 80 g / 100 mL ZnCl2-methanol (MSA-4). Glucose, xylose, lactose, cellobiose, and cellulose were dissolved completely at 60℃. After dissolution, solid-liquid separation was performed by centrifugation. The resulting precipitates were dried in a vacuum drying oven and weighed to determine the undissolved carbohydrates. The solubility of carbohydrates in different alcohol-salt mixtures was calculated by the mass difference between the added carbohydrates and the undissolved carbohydrates, as well as the sugar concentration detected by the liquid phase. The results are shown in Table 3.

[0047] Table 3

[0048]

[0049] As shown in Table 3, in the CaCl2-methanol system, the solubility of glucose, xylose, and lactose reached approximately 50 g / 100 mL, while cellobiose also showed some solubility (8 g / 100 mL), and cellulose was completely insoluble (<0.5 g / 100 mL). In the LiBr-methanol system, glucose had a good solubility of 24 g / 100 mL, but xylose and lactose had poor solubility, while cellobiose and cellulose both had poor solubility. In the LiBr-ethylene glycol system, the solubility of glucose, xylose, and lactose reached 12-18 g / 100 mL, while the solubility of cellobiose remained poor, but the solubility of cellulose improved somewhat. In the ZnCl2-methanol system, the solubility of glucose and cellobiose was greater than 20 g / 100 mL, while the solubility of xylose, lactose, and cellulose was poor.

[0050] Example 4: Solubility of glucose in the calcium chloride-alcohol system

[0051] Since the CaCl2-methanol system exhibits good solubility for glucose, xylose, and lactose, we combined calcium chloride with different alcohol solvents to obtain a calcium chloride-alcohol system and investigated its solubility for glucose. Based on the maximum solubility of calcium chloride in different alcohol solvents in Example 1, CaCl2 was weighed and dissolved in methanol, ethanol, propanol, butanol, and pentanol to prepare 10 and 20 g / 100 mL CaCl2-methanol, 10 and 25 g / 100 mL CaCl2-ethanol, 15 g / 100 mL CaCl2-propanol, 24 g / 100 mL CaCl2-butanol, and 11 g / 100 mL CaCl2-pentanol, respectively. A fixed amount of glucose was weighed and fully dissolved. If it was not completely dissolved, the temperature was slowly increased until it was completely dissolved. Based on the mass of glucose added and the glucose concentration detected by the liquid phase, the solubility of glucose in different CaCl2-alcohol systems was calculated. The results are shown in Table 4.

[0052] Table 4

[0053]

[0054]

[0055] a. This is carried out under pressure.

[0056] As shown in Table 4, in the CaCl2-methanol system, the glucose solubility can reach more than 20g / 100mL, and the glucose solubility increases with the increase of CaCl2 concentration; in the CaCl2-ethanol / propanol / n-butanol / n-pentanol system, the glucose solubility does not show an increase with the increase of CaCl2 concentration or temperature.

[0057] Example 5: Solubility of glucose-calcium chloride-alcohol system at different temperatures

[0058] Weigh CaCl2 and dissolve it in methanol to prepare a 10-20 g / 100 mL CaCl2-methanol solution. Weigh a measured amount of glucose and dissolve it completely. If it is not completely dissolved, slowly increase the temperature until it is completely dissolved. After complete dissolution, continue adding glucose to dissolve it. Calculate the solubility of glucose at different temperatures based on the mass of glucose added and the glucose concentration detected by the liquid chromatography. The results are shown in Table 5.

[0059] Table 5

[0060]

[0061] As shown in Table 5, in the methanol system, the solubility of glucose increases with increasing temperature but remains below 5 g / 100 mL; even with an increase in the boiling point of methanol, the solubility does not increase significantly. In the CaCl2-methanol (10 g / 100 mL) system, the solubility of glucose increases significantly with increasing temperature, reaching a maximum of 31 g / 100 mL; further increasing the CaCl2 concentration (20 g / 100 mL) further enhances the increase in glucose solubility with increasing temperature, reaching a maximum of 59 g / 100 mL. This is the highest known reported solubility of glucose in methanol. Further increases in temperature will cause methanol to vaporize, affecting the solubility of glucose.

[0062] Example 6: Solubility of different sugars in the calcium chloride-methanol system

[0063] To investigate the suitability of the CaCl2-methanol system, CaCl2 was weighed and dissolved in methanol to prepare a 20 g / 100 mL CaCl2-methanol solution. Quantities of glucose, xylose, galactose, cellobiose, arabinose, lactose, mannose, fructose, ribose, and lythose were weighed and fully dissolved at 30°C. After dissolution, solid-liquid separation was performed by centrifugation. The resulting precipitate was dried in a vacuum drying oven and weighed to determine the undissolved sugars. The solubility of different sugars in calcium chloride-methanol was calculated by the mass difference between the added sugars and the undissolved sugars, as well as the sugar concentration detected by the liquid phase. The results are shown in Table 6.

[0064] Table 6

[0065]

[0066] As shown in Table 6, almost all monomers, disaccharides, and polysaccharides, except for cellobiose, exhibit high solubility in the CaCl2-methanol system, demonstrating the adaptability of the CaCl2-methanol system to carbohydrate solubility. Conversion at such high carbohydrate concentrations can significantly reduce solvent usage, demonstrating good economic efficiency.

Claims

1. An alcohol-salt system for dissolving carbohydrates, characterized in that, The alcohol-salt system is prepared by dissolving different types of salts in different alcohol solvents, wherein the alcohol solvent is a primary alcohol, secondary alcohol, or diol, and the salt is a halide salt.

2. The alcohol-salt system for dissolving carbohydrates according to claim 1, characterized in that, The alcohol is at least one of methanol, ethanol, propanol, butanol, isopropanol, isobutanol, ethylene glycol, and glycerol.

3. The alcohol-salt system for dissolving carbohydrates according to claim 1, characterized in that, The halide salt is lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, potassium bromide, magnesium chloride, magnesium bromide, calcium chloride, calcium bromide, or zinc chloride.

4. The alcohol-salt system for dissolving carbohydrates according to claim 1, characterized in that, The alcohol-salt system is obtained by dissolving lithium bromide, calcium chloride, or zinc chloride in methanol, ethanol, or ethylene glycol.

5. The alcohol-salt system for dissolving carbohydrates according to claim 1, characterized in that, The concentration range of the salt in the alcohol-salt system is 5-50 g / 100 mL.

6. A method for preparing an alcohol-salt system for dissolving carbohydrates according to any one of claims 1 to 5, characterized in that, An alcohol-salt system is prepared by dissolving a salt in an alcohol solvent. The dissolution temperature of the salt in the alcohol solvent is 30-60℃.

7. The use of the alcohol-salt system for dissolving carbohydrates according to any one of claims 1 to 5 as a solvent for carbohydrates.

8. The application according to claim 7, characterized in that, The carbohydrates are monosaccharides, disaccharides, and polysaccharides.

9. The application according to claim 8, characterized in that, The carbohydrates are glucose, mannose, xylose, arabinose, ribose, galactose, cellobiose, lactose, and cellulose.

10. The application according to claim 8, characterized in that, The temperature at which carbohydrates dissolve in a salt-alcohol solvent is 20-100°C, preferably 30-60°C.

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