A process for the preparation of isomannide from biobased mannitol

Abstract

The application discloses a method for preparing isomannitol from bio-based mannitol, which comprises the following steps: mixing bio-based mannitol with a ketone compound, an organic solvent and a catalyst, and reacting to obtain isomannitol; the yield of the isomannitol can reach more than 73%, the reaction condition is mild, the operation is simple, the catalyst can be recycled and reused, and the method provides a method for efficiently preparing isomannitol with controllable dehydration reaction sites.

Description

Technical Field

[0001] This application relates to a method for preparing isomannitol from bio-based mannitol, which belongs to the field of chemical engineering. Background Technology

[0002] The catalytic conversion of bio-based platform molecules into renewable chemicals and biofuels is a crucial measure to alleviate fossil resource scarcity and CO2 greenhouse gas emissions. Mannitol is an important bio-based building block, obtainable directly from widely available sugars such as fructose, glucose, inulin, starch, hemicellulose, and cellulose, and its industrial production has already been achieved. However, the polyhydroxyl functional groups in the mannitol molecule's structure pose a major challenge to its high-value conversion, a common problem encountered in the conversion of polyhydroxyl biomass such as cellulose. Therefore, catalytic dehydration, as the lowest energy-consuming dehydroxylation technology, is a key strategy for realizing the value-added transformation of mannitol into high-value oxygenated chemicals.

[0003] Isomannitol, a secondary dehydration product of mannitol, is a functional diol. Based on its inherent rigid structure, chiral center, and non-toxic properties, it is used as a bio-based building block in surfactants, pharmaceuticals, and polymers. Furthermore, due to the highly symmetrical structure of mannitol, isomannitol-based polymers exhibit superior optical, thermal, and dielectric properties compared to isosorbide-based polymers.

[0004] The dehydration of mannitol to isomannitol is a typical acid-catalyzed reaction, specifically a two-step dehydration cyclization via an acid-catalyzed intermediate, proceeding through a 1,4-dehydrated mannitol intermediate. However, the polyhydroxyl structure of the mannitol molecule provides multiple dehydration reaction sites, leading to 1,4-, 2,5-, and 1,5-dehydration, resulting in various primary dehydration products. Furthermore, the hydroxyl groups of mannitol readily generate unsaturated reactive species under acidic conditions, further polymerizing to form scavenging compounds. For example, literature reports that sulfuric acid-catalyzed dehydration of mannitol yielded a total yield of 43% for 1,4-dehydrated mannitol and isomannitol, while the yield of 2,5-dehydrated sorbitol was 48% (Energy Fuels, 2015, 29, 6529-6535). For example, Yamaguchi et al. dehydrated mannitol in a high-temperature aqueous medium, yielding isomannitol and 2,5-dehydrated sorbitol at 31% and 41%, respectively (RSC Adv., 2014, 4, 45575-45578). More recently, Chen Hanming et al. used 30% PW / SiO2 as a catalyst in a vacuum system to catalyze the dehydration of mannitol, obtaining a total yield of 36% for 1,4-dehydrated mannitol and isomannitol, and a yield of 56% for 2,5-dehydrated sorbitol (Chemical Reaction Engineering and Technology, 2024, 40, 2013, 289-298). This indicates that, unlike sorbitol where the 1,4-position is the main dehydration site, the dehydration reaction of mannitol mainly occurs at the 2,5-position, and 2,5-dehydrated sorbitol cannot be further dehydrated to generate isomannitol, which severely limits the selectivity of isomannitol.

[0005] In summary, the preparation of isomannitol faces several pressing problems: (1) the reaction conditions for synthesizing isomannitol are quite demanding, requiring high-vacuum or high-temperature operations with high energy consumption and demanding equipment requirements; (2) the uncontrollable dehydration site and polymer formation lead to low isomannitol yields. Existing technologies are unable to overcome the bottleneck of low isomannitol yields, and it is urgent to construct efficient mannitol dehydration routes and catalytic systems to achieve directional conversion of mannitol and highly selective generation of isomannitol, which has significant scientific value and application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing isomannitol from bio-based mannitol. This method uses ketone compounds as ketalizing agents, and in the presence of an organic solvent, achieves selective dehydration of mannitol to generate isomannitol via solid acid catalysis.

[0007] Under solid acid catalysis, the terminal ortho-dihydroxyl group of mannitol readily undergoes ketalization with ketone compounds to form mannitol ketal intermediates. Ketalization modification of mannitol solves the problem of its poor solubility in organic solvents, thus facilitating collisions and contact between reactant molecules and the catalyst, and promoting the dehydration reaction.

[0008] According to one aspect of this application, a method for preparing isomannitol from bio-based mannitol is provided, characterized in that...

[0009] Includes the following steps:

[0010] Bio-based mannitol was mixed with ketone compounds, organic solvents, and catalysts, and reacted to obtain isomannitol.

[0011] The ketone compound is a ketone compound with 3 to 6 carbon atoms, selected from at least one of acetone, 2-butanone, 2-pentanone, 3-pentanone, methyl isopropyl ketone or methyl isobutyl ketone;

[0012] The organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, γ-valerolactone, dibutyl ether, cyclohexane, toluene, xylene, methylcyclohexane, and methylcyclopentane.

[0013] The catalyst is selected from at least one of H-ZSM5, H-beta, and HY molecular sieves.

[0014] The catalyst is acid-modified by using at least one of phosphoric acid, nitric acid, acetic acid, citric acid, tartaric acid or oxalic acid at a concentration of 0.01 to 10 mol / L.

[0015] The molar ratio of the ketone compound to bio-based mannitol is 1:1 to 30:1;

[0016] Optionally, the molar ratio of the ketone compound to bio-based mannitol is 1:1 to 20:1.

[0017] The molar ratio of the organic solvent to bio-based mannitol is 2:1 to 50:1;

[0018] Optionally, the molar ratio of the organic solvent to bio-based mannitol is 5:1 to 40:1.

[0019] The mass ratio of the catalyst to bio-based mannitol is 0.01:1 to 1:1;

[0020] Optionally, the mass ratio of the catalyst to bio-based mannitol is 0.05:1 to 0.5:1.

[0021] The reaction temperature is 120–200°C;

[0022] Optionally, the reaction temperature is 130–180°C.

[0023] The reaction time is 0.5 to 12 hours;

[0024] Optionally, the reaction time is 1 to 10 hours.

[0025] The beneficial effects that this application can produce include:

[0026] This invention uses ketone compounds as ketalizing agents. In the presence of an organic solvent and catalyzed by an environmentally friendly solid acid, mannitol undergoes a tandem reaction of ketalization and intramolecular etherification to generate isomannitol with high selectivity and a yield of over 73%. The reaction conditions are mild, the operation is simple, and the catalyst can be recovered and reused. This invention provides a method for the efficient preparation of isomannitol with controllable dehydration reaction sites. Detailed Implementation

[0027] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0028] All reagents and raw materials used in this invention are commercially available. The hydrogen-form zeolite molecular sieves are all commercially available. The acid-modified hydrogen-form zeolite molecular sieves are prepared by impregnation in phosphoric acid, nitric acid, acetic acid, citric acid, tartaric acid or oxalic acid solution using the excess impregnation method.

[0029] Example 1

[0030] Mannitol, acetone, methylcyclopentane, and a 2 mol / L acetic acid-modified H-beta catalyst were added to a reaction vessel. The reaction vessel was sealed and heated to 160°C, then magnetically stirred for 3 hours. The molar ratio of acetone to mannitol was 2:1, the molar ratio of methylcyclopentane to mannitol was 10:1, and the mass ratio of catalyst to mannitol was 0.2:1. After the reaction was complete, the reaction vessel was rapidly cooled to room temperature. Quantitative analysis of the raw material mannitol, the dehydrated products 1,4-dehydrated mannitol, 2,5-dehydrated sorbitol, and the target product isomannitol was performed using high-performance liquid chromatography (HPLC) with external standard and gas chromatography with internal standard, respectively. The results, expressed as molar percentage (mol%), showed a mannitol conversion of 100%, a 2,5-dehydrated sorbitol yield of 2%, and a target product isomannitol yield of 75%. 1,4-dehydrated mannitol was not detected.

[0031] Example 2

[0032] Mannitol, ketone compounds, cyclohexane, and a 5 mol / L nitric acid-modified H-beta catalyst were added to a reaction vessel. The reaction vessel was sealed and heated to 150°C, then magnetically stirred for 5 hours. The molar ratio of ketone compounds to mannitol was 10:1, the molar ratio of cyclohexane to mannitol was 30:1, and the mass ratio of catalyst to mannitol was 0.3:1. After the reaction was complete, the reaction vessel was rapidly cooled to room temperature. High-performance liquid chromatography (HPLC) with external standard and gas chromatography with internal standard were used to quantitatively analyze the raw material mannitol, the dehydrated products 1,4-dehydrated mannitol and 2,5-dehydrated sorbitol, and the target product isomannitol, respectively, expressed as molar percentage (mol%).

[0033] The reaction results are shown in Table 1.

[0034] Table 1: Results of H-beta-catalyzed preparation of isomannitol from mannitol in the presence of different ketone compounds modified with nitric acid.

[0035]

[0036] Example 3

[0037] Mannitol, acetone, xylene, and 0.1 mol / L tartaric acid-modified HY catalyst were added to the reactor. The reactor was sealed and heated to 180°C, then magnetically stirred for 4 hours. The molar ratio of xylene to mannitol was 5:1, and the mass ratio of catalyst to mannitol was 0.05:1. After the reaction was complete, the reactor was rapidly cooled to room temperature. High-performance liquid chromatography (HPLC) with external standard and gas chromatography with internal standard were used to quantitatively analyze the raw material mannitol, the dehydrated products 1,4-dehydrated mannitol and 2,5-dehydrated sorbitol, and the target product isomannitol, respectively, expressed as molar percentage (mol%).

[0038] The reaction results are shown in Table 2.

[0039] Table 2: Results of the preparation of isomannitol from mannitol by HY catalysis with tartaric acid modification under different amounts of acetone.

[0040]

[0041] [1]: Molar ratio of acetone to mannitol.

[0042] Example 4

[0043] Mannitol, 2-butanone, toluene, and 1 mol / L oxalic acid-modified H-ZSM5 catalyst were added to a reaction vessel. The reaction vessel was sealed, heated to the specified temperature, and magnetically stirred for 3 hours. The molar ratio of 2-butanone to mannitol was 20:1, the molar ratio of toluene to mannitol was 30:1, and the mass ratio of catalyst to mannitol was 0.2:1. After the reaction was completed, the reaction vessel was rapidly cooled to room temperature. High-performance liquid chromatography (HPLC) with external standard method and gas chromatography with internal standard method were used to quantitatively analyze the raw material mannitol, the dehydrated products 1,4-dehydrated mannitol, 2,5-dehydrated sorbitol, and the target product isomannitol, respectively, expressed as molar percentage (mol%).

[0044] The reaction results are shown in Table 3.

[0045] Table 3: Results of the preparation of isomannitol from mannitol catalyzed by oxalic acid-modified H-ZSM5 at different temperatures.

[0046]

[0047] Example 5

[0048] Mannitol, methyl isobutyl ketone, dibutyl ether, and H-beta catalyst were added to a reaction vessel. The reaction vessel was sealed and heated to 160°C, with magnetic stirring for a certain period of time. The molar ratio of methyl isobutyl ketone to mannitol was 10:1, the mass ratio of dibutyl ether to mannitol was 5:1, and the mass ratio of catalyst to mannitol was 0.25:1. After the reaction was completed, the reaction vessel was rapidly cooled to room temperature. High-performance liquid chromatography (HPLC) with external standard and gas chromatography with internal standard were used to quantitatively analyze the raw material mannitol, the dehydrated products 1,4-dehydrated mannitol and 2,5-dehydrated sorbitol, and the target product isomannitol, respectively, expressed as molar percentage (mol%).

[0049] The reaction results are shown in Table 4.

[0050] Table 4: Results of H-beta-catalyzed preparation of isomannitol from mannitol at different reaction times.

[0051]

[0052] Example 6

[0053] Mannitol, acetone, γ-valerol, and a 0.2 mol / L citric acid-modified H-beta catalyst were added to a reaction vessel. The reaction vessel was sealed and heated to 150 °C, with magnetic stirring for 4 hours. The molar ratio of acetone to mannitol was 20:1, and the molar ratio of γ-valerol to mannitol was 10:1. After the reaction was completed, the reaction vessel was rapidly cooled to room temperature. High-performance liquid chromatography (HPLC) with external standard and gas chromatography with internal standard were used to quantitatively analyze the raw material mannitol, the dehydrated products 1,4-dehydrated mannitol and 2,5-dehydrated sorbitol, and the target product isomannitol, respectively, expressed as molar percentage (mol%).

[0054] The reaction results are shown in Table 5.

[0055] Table 5: Results of mannitol dehydration reaction under different amounts of citric acid-modified H-beta catalyst.

[0056]

[0057] [1]: The mass ratio of citric acid-modified H-beta catalyst to mannitol.

[0058] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing isomannitol from bio-based mannitol, characterized in that, Includes the following steps: Bio-based mannitol is mixed with ketone compounds, organic solvents, and catalysts, and reacted to obtain isomannitol.

2. The method according to claim 1, characterized in that, The ketone compound is a ketone compound with 3 to 6 carbon atoms, selected from at least one of acetone, 2-butanone, 2-pentanone, 3-pentanone, methyl isopropyl ketone or methyl isobutyl ketone; The organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, γ-valerolactone, dibutyl ether, cyclohexane, toluene, xylene, methylcyclohexane, and methylcyclopentane. The catalyst is selected from at least one of H-ZSM5, H-beta, and HY molecular sieves.

3. The method according to claim 2, characterized in that, The catalyst is acid-modified by using at least one of phosphoric acid, nitric acid, acetic acid, citric acid, tartaric acid or oxalic acid at a concentration of 0.01 to 10 mol / L.

4. The method according to claim 1, characterized in that, The molar ratio of the ketone compound to bio-based mannitol is 1:1 to 30:1; Preferably, the molar ratio of the ketone compound to bio-based mannitol is 1:1 to 20:

1.

5. The method according to claim 1, characterized in that, The molar ratio of the organic solvent to bio-based mannitol is 2:1 to 50:1; Preferably, the molar ratio of the organic solvent to bio-based mannitol is 5:1 to 40:

1.

6. The method according to claim 1, characterized in that, The mass ratio of the catalyst to bio-based mannitol is 0.01:1 to 1:1; Preferably, the mass ratio of the catalyst to bio-based mannitol is 0.05:1 to 0.5:

1.

7. The method according to claim 1, characterized in that, The reaction temperature is 120–200°C; Preferably, the reaction temperature is 130–180°C.

8. The method according to claim 1, characterized in that, The reaction time is 0.5 to 12 hours; Preferably, the reaction time is 1 to 10 hours.

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