A starch liquefaction method

Abstract

The invention discloses a method for liquefying starch, wherein the starch is alcoholyzed in a hydrothermal environment, and a low eutectic agent and a liquefying agent need to be added during the alcoholysis process. The low eutectic agent is obtained by melting choline chloride, a polyol and an acid under heating, the polyol is polyethylene glycol or glycerol, the acid is oxalic acid, citric acid or p-toluenesulfonic acid, the liquefying agent is polyethylene glycol or glycerol, and the sum of the mass of the alcoholysis aid and the liquefying agent is 2 to 6 times the mass of the starch. In terms of mass fractions, the low eutectic solvent is 0.6 to 1 part, the liquefying agent is 2.2 to 5 parts, and the starch is 1 part. The present invention greatly improves the liquefaction efficiency, and the liquefaction time is significantly shortened without corroding the equipment, and the starch liquefaction rate is as high as 98%.

Description

Technical Field

[0001] The present invention relates to the field of starch liquefaction, and in particular to a starch liquefaction method. Background Art

[0002] Starch is one of the most abundant natural polymers in the world. Its molecules contain a large number of hydroxyl groups, which can be degraded and liquefied to obtain bio-based polyols.

[0003] Currently, starch liquefaction is primarily achieved through acid catalysis, such as concentrated sulfuric acid. However, concentrated sulfuric acid is extremely corrosive to equipment, prompting the use of other acids for catalytic liquefaction. For example, CN201910431327.7 uses polyether polyols and an active epoxy diluent, catalyzed by the small organic acid hydroxyethylidene diphosphonic acid (hydroxyethylidene diphosphonic acid) with functional groups, to liquefy starch at temperatures above 110°C for 2-4 hours. CN201910304048.4 uses a mixture of a tetrafunctional polyether polyol and glycerol as a liquefying agent and hydroxyethylidene sulfonic acid as a catalyst, reacting at 120-180°C for 3-6 hours to liquefy starch and produce polyether polyols. CN107129570B uses a mixed solution of polyethylene glycol 200 and glycerol with starch as raw materials, reacting them without catalyst for 3-9 hours at a liquefaction temperature of 130-170°C. The polyether polyols have a hydroxyl value of 274.89-426.36 mgKOH / g and a starch liquefaction rate of 90.4%. Unreacted raw materials are recycled as raw materials for the next reaction. Solid acids can also catalyze starch liquefaction, but the liquefaction process presents challenges with catalyst separation and reuse. Furthermore, these technologies suffer from high reaction temperatures, long reaction times, and insufficient liquefaction efficiency. Summary of the Invention

[0004] To address the above-mentioned problems, the present invention provides a new starch liquefaction method. This liquefaction method constructs a liquefaction system with four functions: accelerating the penetration of the liquefying agent, disintegrating the starch structure, strengthening it, and accelerating its liquefaction and degradation. This greatly improves the liquefaction efficiency. On the basis of not corroding the equipment, the liquefaction conditions are reduced, the liquefaction time is significantly shortened, and the starch liquefaction rate is as high as 98%.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for liquefying starch involves alcoholyzing the starch in a hydrothermal environment. A deep eutectic solvent and a liquefying agent are added during the alcoholysis process. The deep eutectic solvent is obtained by heating and melting choline chloride, a polyol, and an acid. The polyol is polyethylene glycol or glycerol, and the acid is oxalic acid, citric acid, or p-toluenesulfonic acid. The liquefying agent is polyethylene glycol or glycerol. The combined weight of the alcoholysis aid and the liquefying agent is 2 to 6 times the weight of the starch. In parts by mass, the deep eutectic solvent comprises 0.6 to 1 part, the liquefying agent comprises 2.2 to 5 parts, and the starch comprises 1 part.

[0007] In parts by mass, the polyol comprises 0.9-1.4 parts, the acid comprises 0.6-1.1 parts, and the choline chloride comprises 1 part. The combined mass of the polyol and acid is 2-2.5 times that of the choline chloride. The combined mass of the polyol and acid is twice that of the choline chloride. Unlike the prior art, the deep eutectic solvent in the reaction system of the present invention is formed by melting three specific components (choline chloride, polyol, and acid, such as oxalic acid). The inventors considered how to fully and effectively utilize the functions of these three components in this reaction system during the implementation of the present invention. Choline chloride acts as a hydrogen bond acceptor, while the polyol and acid, in appropriate proportions, can function as both a hydrogen bond donor (HBD) and a hydrogen bond acceptor, with the polyol acting as a donor. When different carboxylic acids are combined as HBDs with choline chloride, the resulting deep eutectic solvents exhibit differences in thermophysical properties, particularly viscosity. Therefore, the heating method has a certain impact on the preparation of the deep eutectic solvent from the acid and choline chloride. Based on this, the inventors of the present invention chose to use choline chloride, polyols, and acids as the components of the deep eutectic solvent at the same time. By controlling the composition and proportion of each component, the roles of hydrogen bond donors and hydrogen bond acceptors were controlled, and the adverse effects of carboxylic acids on the viscosity of the deep eutectic solvent were eliminated or reduced, so that the deep eutectic solvent can play a sufficiently effective role. During liquefaction, it has a significant destructive ability on the H bonds and crystalline structure between starch molecules, accelerates the penetration of the liquefaction agent in the starch granules, disintegrates the starch granule structure, and strengthens the degradation effect of the liquefaction agent. In addition, it can also provide protons to catalyze the alcoholysis and liquefaction of starch. Therefore, in the liquefaction process of the present invention, the entire liquefaction system simultaneously has the quadruple effect of accelerating the penetration of the liquefaction agent, promoting the disintegration of the starch structure, strengthening and accelerating the liquefaction degradation, significantly improving the liquefaction efficiency and reducing the liquefaction conditions. The liquefaction reaction system established by the present invention constructs a balanced relationship between hydrogen acceptor-hydrogen acceptor-hydrogen donor, achieving a high liquefaction rate at a high catalytic efficiency.

[0008] The mass ratio of polyol to acid determines the hydrogen bonding roles of the polyol and acid in the deep eutectic solvent, thereby providing the necessary conditions for accelerating the entire reaction system and reducing the reaction conditions.

[0009] The alcoholysis reaction time is 30-40 minutes. When the alcoholysis time is 35 minutes and the temperature is 110℃, the starch liquefaction rate reaches 98%.

[0010] The alcoholysis reaction temperature is 110-130°C. The present invention also incorporates a liquefier polyol as a component of the deep eutectic solvent. This not only prepares the deep eutectic solvent, but also acts as a liquefier in the starch alcoholysis reaction, where it dissociates H protons and acts as a catalyst when paired with choline chloride. Furthermore, it can act as a liquefier in the starch alcoholysis reaction and, as a component of the starch liquefaction product (i.e., the polyol), serve as an active ingredient in subsequent applications of the liquefied product.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0012] The present invention greatly improves the liquefaction efficiency, significantly shortens the liquefaction time without corroding the equipment, and achieves a starch liquefaction rate of up to 98%. Implementation Method

[0013] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention. Example

[0014] Choline chloride, p-toluenesulfonic acid, and PEG200 were mixed in a mass ratio of 1:1:1 (10 g of each) and melted at 80°C to obtain a deep eutectic solvent. The deep eutectic solvent, PEG200, and corn starch were added to a hydrothermal kettle in a mass ratio of 0.8:2.2:1 (16 g, 44 g, and 20 g, respectively). The mixture was reacted at 110°C for 35 minutes to obtain a starch-based biopolyol with a hydroxyl value of 312 mgKOH / g and a liquefaction rate of 94%. Example

[0015] Choline chloride was mixed with p-toluenesulfonic acid and PEG200 in a mass ratio of 1:0.8:1.2 (masses of 10 g, 8 g and 12 g, respectively), and melted at 80°C to obtain a deep eutectic solvent; the deep eutectic solvent, PEG200 and corn starch were added to a hydrothermal kettle in a mass ratio of 0.6:2.4:1 (masses of 12 g, 48 g and 20 g, respectively) and reacted at 130°C for 35 minutes to obtain a starch-based biopolyol with a hydroxyl value of 294 mgKOH / g and a liquefaction rate of 95%. Example

[0016] Choline chloride, oxalic acid, and PEG400 were mixed in a mass ratio of 1:1.1:0.9 (masses of 10 g, 11 g, and 9 g, respectively), and then melted at 80°C to obtain a deep eutectic solvent. The deep eutectic solvent, PEG400, and corn starch were added to a hydrothermal kettle in a mass ratio of 1:4:1 (masses of 20 g, 80 g, and 20 g, respectively), and reacted at 110°C for 35 minutes to obtain a starch-based biopolyol with a hydroxyl value of 385 mgKOH / g and a liquefaction rate of 98%. Example

[0017] Choline chloride was mixed with citric acid and PEG300 in a mass ratio of 1:0.7:1.4 (masses of 10 g, 7 g and 14 g, respectively) and melted at 80°C to obtain a deep eutectic solvent. The deep eutectic solvent, PEG300 and corn starch were added to a hydrothermal kettle in a mass ratio of 1:5:1 (masses of 20 g, 100 g and 20 g, respectively) and reacted at 110°C for 35 minutes to obtain a starch-based biopolyol with a hydroxyl value of 403 mgKOH / g and a liquefaction rate of 97%.

[0018] Comparative Example 1:

[0019] Choline chloride was mixed with citric acid and PEG300 in a mass ratio of 1:0.6:3 (masses of 10 g, 6 g and 30 g, respectively) and melted at 80°C to obtain a deep eutectic solvent. The deep eutectic solvent, PEG300 and corn starch were added to a hydrothermal kettle in a mass ratio of 0.1:2:1 (masses of 2 g, 80 g and 20 g, respectively) and reacted at 110°C for 35 minutes. The starch liquefaction rate was 45%.

[0020] Comparative Example 2:

[0021] Choline chloride was mixed with urea and PEG400 in a mass ratio of 1:1.1:0.9 (masses of 10 g, 11 g and 9 g, respectively) and melted at 80°C to obtain a deep eutectic solvent; the deep eutectic solvent, PEG400 and corn starch were added to a hydrothermal kettle in a mass ratio of 1:4:1 (masses of 20 g, 80 g and 20 g, respectively) and reacted at 110°C for 35 minutes. The starch liquefaction rate was 38%.

[0022] Comparative Example 3:

[0023] PEG200 and corn starch were added to the hydrothermal kettle at a mass ratio of 3:1 (60 g and 20 g, respectively), and then p-toluenesulfonic acid (2.6 g) (13% of the mass of corn starch) was added. The reaction was carried out at 110°C for 35 minutes, and the starch liquefaction rate was 72%.

[0024] Comparative Example 4

[0025] Choline chloride and PEG300 were mixed in a mass ratio of 1:2.1 (masses of 10 g and 21 g, respectively) and melted at 80°C to obtain a deep eutectic solvent; the deep eutectic solvent, PEG300, and corn starch were added to a hydrothermal kettle in a mass ratio of 1:5:1 (masses of 20 g, 100 g, and 20 g, respectively) and reacted at 110°C for 35 minutes, with a liquefaction rate of 32%.

[0026] Comparative Example 5

[0027] Choline chloride and citric acid were mixed in a mass ratio of 1:2.1 and melted at 80°C to obtain a deep eutectic solvent; the deep eutectic solvent, PEG300, and corn starch were added to a hydrothermal autoclave in a mass ratio of 1:5:1 (masses of 20 g, 100 g, and 20 g, respectively), and reacted at 110°C for 35 minutes, with a liquefaction rate of 80%.

[0028] The present invention uses a weak acid as a deep eutectic solvent, achieving a higher liquefaction rate than conventional acid catalysts. This is likely because the weak acid can more easily switch between its role as a hydrogen bond donor and a hydrogen bond acceptor depending on the actual reaction, thereby providing a more effective auxiliary effect for the liquefaction reaction.

[0029] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for liquefying starch, comprising alcoholyzing the starch in a hydrothermal environment, characterized in that: A deep eutectic solvent and a liquefier need to be added during the alcoholysis process. The deep eutectic solvent is obtained by melting choline chloride, a polyol, and an acid under heating. The polyol is polyethylene glycol or glycerol, the acid is oxalic acid, citric acid, or p-toluenesulfonic acid, and the liquefier is polyethylene glycol or glycerol. The sum of the mass of the deep eutectic solvent and the liquefier is 2 to 6 times that of the starch. In terms of mass, the deep eutectic solvent is 0.6 to 1 part, the liquefier is 2.2 to 5 parts, and the starch is 1 part.

2. The liquefaction method according to claim 1, characterized in that: Calculated by mass, the polyol is 0.9-1.4 parts, the acid is 0.6-1.1 parts, and the choline chloride is 1 part. The sum of the mass of the polyol and the acid is 2-2.5 times the mass of the choline chloride.

3. The liquefaction method according to claim 2, characterized in that: The sum of the masses of the polyol and the acid is twice the mass of choline chloride.

4. The liquefaction method according to claim 1, characterized in that: The alcoholysis reaction time is 30-40 minutes.

5. The liquefaction method according to claim 1, characterized in that: The alcoholysis reaction temperature is 110-130°C.