CN115785295B - Method for preparing high-substitution-degree cationic starch by mechanochemistry - Google Patents

Abstract

The invention discloses a method for preparing high-substitution cationic starch by mechanochemistry, belonging to the technical field of flocculant preparation and starch modification. The invention uses a very small amount of mixed alkali and ball milling mechanical force to jointly act on the raw starch, and under the premise of fully damaging a crystallization area, etherification reaction is carried out in mechanical reaction equipment, 2, 3-epoxypropyl trimethyl ammonium chloride is fully grafted, a small amount of butyl glycidyl ether is grafted, a cationic starch crude product with high substitution degree is prepared, and then ethanol aqueous solution and petroleum ether are used for washing to prepare a pure product. Compared with all the prior art, the invention has the outstanding advantages of simple process, high substitution degree of the prepared cation modified starch, high reaction efficiency, environmental friendliness, large-scale production potential and the like. The prepared cation modified starch with high substitution degree has very good effect when applied to wastewater treatment, in particular to anion dispersion wastewater flocculation.

Description

Method for preparing high-substitution-degree cationic starch by mechanochemistry

Technical Field

The invention belongs to the technical field of flocculant preparation and the technical field of starch modification, relates to a method for preparing cationic starch with high substitution degree by mechanochemistry, and relates to a method for preparing cationic modified starch under the dry condition by using a small amount of mixed alkali for catalysis.

Background

In nature, starch is almost ubiquitous, and plant seeds, tubers and roots can be used for extracting starch, so that the starch is used as an energy storage substance in plants, is huge in quantity and easy to obtain, is low in production cost, belongs to natural substances and is environment-friendly, and further, the starch is quite wide in application range, and can be used in the chemical fields of food processing, medicine, spinning, papermaking and the like. Although it is widely available, there are four main sources at present: corn, wheat, potato and tapioca, the most common of which is corn starch, are also the most prominent sources of current commercialization. The starch is simply identified as a cyclic tri-hydroxyl compound from chemical composition analysis, and the presence of polyhydroxy makes the starch easily react with nucleophile, and simultaneously makes hydrogen bond acting force generated between each unit sugar ring, so that the starch property is changeable. Starch is almost insoluble in water, but because starch can form hydrogen bonds with water, starch gelatinizes when heated. The starch composition is a polysaccharide, glucose is taken as a basic unit, and the main connection modes are two types: alpha-1, 4 glycosidic linkages or alpha-1, 6 glycosidic linkages. Because the linking mode is not unique, starch is divided into amylose and amylopectin, and the composition ratio of the amylose to the amylopectin directly influences the physicochemical property of the starch. The starch microscopic particles have non-unique morphology, and the starch contains a crystallization area and an amorphous area due to different arrangement modes of the amylose and the amylopectin, the crystallization area mainly presents a continuous double-spiral structure, and the existence of the crystallization area can be judged by whether the crystallization area has a polarized cross under a microscope. The opening modes of the crystallization area are various, and the important introduction is that the mechanical force acts to destroy the crystallization area for reaction, the physicochemical properties of starch are mainly determined by the crystal structure, the specific surface area of particles, the chain length of starch molecules and the like, the mechanical force comprises shearing force, extrusion force, bending force and the like, and when the solid substance is acted by mechanical energy, the solid form and the crystal structure generate corresponding physical induction and chemical change. In particular, when the starch is acted by mechanical force, the molecular chain of the starch is continuously reduced, the chain length of the molecule is continuously reduced, which means that the exposed reaction sites are continuously increased, and the chemical reaction activity of the starch is correspondingly and continuously enhanced; meanwhile, the starch can cause distortion and defect of the crystal lattice under the action of mechanical force, and the break and recombination of chemical bonds are caused, so that the crystallization area can be continuously destroyed, the reaction area is reduced until the crystal area disappears, and the way for blocking the reaction is opened due to the destruction of hydrogen bonds in the crystal area, so that the reactivity is increased; the mechanical force also increases the specific surface area of the starch, which means that the reaction proceeds in a larger number of places because the starch is a loose porous structure, thereby promoting the progress of the reaction. At present, three main methods for preparing the cationic starch are wet method, semi-dry method and dry method, and few reports are about the preparation of the hydrophobized cationic starch by using the dry method in an industrial formation system, so that a novel method for producing the hydrophobized cationic starch is needed.

Disclosure of Invention

Aiming at the problems of higher cost, complexity, serious environmental pollution and the like in the prior art, the invention provides the preparation method of the quaternary ammonium type cation modified starch, which has the advantages of simple production process, environmental protection and high application efficiency.

In order to achieve the above purpose, the specific technical implementation scheme is as follows:

a method for preparing high substitution degree cationic starch by mechanochemistry, comprising the following steps:

and (1) firstly, carrying out alkalization pretreatment on starch, uniformly mixing mixed alkali, water and starch in a molar ratio of (0.005-0.03) to (3.07-6.32) 1 in a zirconia ball milling tank, wherein the ball-milling speed is 300r/min-650r/min, the ball milling time is 0.5-2.5h, and repeatedly preparing ball milling materials for multiple times, wherein the ball-milling ratio of the ball to the small balls is 1 (3-25).

And (2) uniformly mixing the ball-milling material prepared in the step (1) with 2, 3-epoxypropyl trimethyl ammonium chloride according to the molar ratio of starch in the ball-milling material to 2, 3-epoxypropyl trimethyl ammonium chloride of 2.5:1-0.5:1, adding the mixture into mechanical reaction equipment, stirring the mixture for reaction, and reacting at 40-90 ℃ for 0.5-3h.

And (3) fully reacting the ball-milling material in the step (2) with 2, 3-epoxypropyl trimethyl ammonium chloride, adding butyl glycidyl ether, mixing according to the mol ratio of the starch to the butyl glycidyl ether of 9.3:1-1.6:1, and reacting at 70-95 ℃ for 0.5-3 hours to obtain a modified starch crude product.

And (4) washing the modified starch crude product obtained in the step (3) with an ethanol water solution with the mass fraction of 60% -80% for a plurality of times, then detecting whether chloride ions remain or not by using a silver nitrate solution, if so, continuing washing, and if not, washing with absolute ethanol for a plurality of times to remove water, then washing with petroleum ether to remove unreacted hydrophobizing reagent, and then drying to obtain the high-substitution-degree cationic starch.

The mixed alkali is a mixture of sodium hydroxide and calcium oxide, calcium hydroxide or calcium carbonate.

The mechanical reaction apparatus used may be an internal mixer, kneader or twin-screw extruder.

The invention has the beneficial effects that:

flocculation experiments prove that the flocculant produced by the process has obvious effect in water purification treatment; compared with the prior art, the invention has the following advantages by the simultaneous action of mechanical force and chemistry:

(1) The process is simple. The existing technology is characterized in that the modification treatment of the cationic starch is generally mainly carried out by a wet method, which causes serious three wastes, especially serious wastewater, causes environmental pollution, and is difficult to post-treat.

(2) The prepared cation modified starch has high substitution degree. The substitution degree of the cationic starch prepared by a common dry method is 0.3-0.4; the substitution degree of the cationic starch prepared by a general wet method is 0.15-0.5; the substitution degree of the cationic starch produced by the process is 0.5-0.75.

(3) The reaction efficiency is high. The reaction efficiency of preparing the cationic starch by a general dry method is below 60%, the reaction conversion rate of the wet method is lower than 40%, and the reaction rate of the quaternary ammonium type cationic starch produced by the process is between 75% and 85%, so that the utilization rate of an etherifying agent is improved, and the production cost is reduced.

(4) Is environment-friendly. The consumption of the mixed alkali in the reaction process is almost negligible, the three wastes can not be generated in dry production, and the etherification reaction of the starch and the etherifying agent 2, 3-epoxypropyl trimethyl ammonium chloride is required to be carried out under alkaline conditions, so that the process is complicated, the wastewater treatment capacity is large, and the environmental pollution is easy to cause.

(5) Has large-scale production potential. The process is simple, the process is controlled by a machine, the artificial interference is little, the crude product of the cation modified starch can be obtained within 3 hours, the reaction efficiency and the substitution degree are high, the method has the potential of replacing the preparation mode of the cation modified starch in the current market, and the method is easy for industrialized large-scale preparation.

(6) The cation modified starch produced by the method can be used as a flocculant, and the flocculant can be applied to wastewater purification.

Drawings

FIG. 1 is a flow chart of a cationic starch prepared;

FIG. 2 is an infrared spectrum of starch and starch derivatives of example 1;

FIG. 3 is an XRD diffraction pattern of starch and starch derivatives of example 1;

FIG. 4 is a graph showing the temperature response of the cationic starch prepared in example 1;

FIG. 5 is a graph of the pH response of the cationic starch prepared in example 1;

FIG. 6 is a graph showing the comparison of the flocculation optimum dosage of cationic starch (a), polyaluminum chloride (b) and cationic polyacrylamide (c) prepared in example 1;

FIG. 7 is a graph showing flocculation pH response comparison of cationic starch (a) prepared in example 1 with polyaluminum chloride (b) and cationic polyacrylamide (c);

FIG. 8 is a graph showing the relationship between the degree of substitution and the reaction efficiency of cationic starch and alkali mixture in the preparation of example 2;

Detailed Description

The following describes the embodiments of the present invention further with reference to the drawings and technical schemes.

Example 1

(1) Firstly, carrying out alkalization pretreatment on starch, adding sodium hydroxide and calcium oxide into the starch according to the mass ratio of 1:1, uniformly mixing the mixed alkali, water and starch in a mol ratio of 0.01:4:1 in a zirconia ball milling tank, wherein the ball milling speed is 450r/min for ball milling for 1h, and preparing ball milling materials for three times;

(2) Ball milling materials and 2, 3-epoxypropyl trimethyl ammonium chloride are uniformly mixed according to the mol ratio of starch to the mixture of 1:1, and then the mixture is added into an internal mixer for stirring reaction, and the reaction is carried out at 70 ℃ for 1h;

(3) Fully reacting the ball-milling material with 2, 3-epoxypropyl trimethyl ammonium chloride, adding butyl glycidyl ether, and reacting for 0.5h at the temperature of 85 ℃ according to the molar ratio of starch to butyl glycidyl ether of 4.72:1 to obtain a modified starch crude product;

(4) Washing and purifying the obtained modified starch crude product with an ethanol water solution (60% -80%) for three times until the existence of chloride ions cannot be detected by the silver nitrate solution, removing unreacted etherifying agent, washing water contained in the product with absolute ethyl alcohol, washing and purifying with petroleum ether for two times, removing unreacted hydrophobizing agent, and drying to obtain the cationic modified starch product.

(5) The obtained cation modified starch product is subjected to conventional flocculation performance tests of optimal dosage, temperature, pH value and the like, and is subjected to flocculation comparison with common flocculating agents such as cation polyacrylamide, polyaluminium chloride and the like in the market.

Description of the drawings in combination: under the optimal condition, the substitution degree prepared by the method can reach about 0.8, the conversion rate is about 80 percent, and fig. 1 is a flow chart of the prepared cationic starch, in brief, the starch is impacted by mechanical force, a crystallization area is opened under the catalysis of mixed alkali, the operation is completed in a ball mill, and then an internal mixer, a kneader and a double-screw extruder are used for fully etherifying under the control of temperature and stirring rate. FIG. 2 is an infrared spectrum of cationic starch (A), cationic starch (B), starch (C) and GTA (D), from which analysis the C-N stretching vibration absorption peak on the quaternary ammonium group of GTA is found to be 1489cm ^-1 This peak was present on the original starch, demonstrating successful grafting of the GTA on the starch; 1133cm ^-1 An asymmetric stretching vibration peak of C-O-C appears at the position; 1070cm ^-1 The stretching vibration peak of C-O appears at the position, but the original starch and the cationic starch have no peak above, which proves that the butyl glycidyl ether is successfully grafted on the cationic starch. FIG. 3 is an XRD diffraction pattern of starch and starch derivatives, for raw corn starch at 15 °, 17 °, 18 °, 2 by comparing diffraction pattern standard cards of starch and cationic starchThe 3 DEG shows a relatively sharp diffraction peak, but the peak type of the cationic starch is obviously changed, which indicates that the crystallization area of the corn starch is destroyed, because the water molecules in the starch molecules are destroyed under the combined action of mechanical force and chemical catalysis, so that the crystallization area is continuously reduced until the crystallization area disappears. FIG. 4 is a graph showing the temperature response of a cationic starch prepared by grafting two groups, namely hydrophilic GTA and hydrophobic butyl glycidyl ether, to form two forms in water, wherein the molecules have good linear compatibility with water at low temperature, and the sedimentation is mainly carried out by adsorption and rolling scanning, so that larger flocculating body sedimentation is formed: when the temperature increases, its hydrophobicity increases, and when the LCST is reached, the linear molecules shrink and curl, and then the compatibility with water decreases abruptly, thereby settling rapidly. FIG. 5 is a graph showing the pH response of cationic starch prepared, and the flocculant has good effect at pH 3-12, and has large volume of floccules under weak acid, neutral and alkaline conditions, and the sedimentation rate is fast, so that flocculation can be completed within 5 minutes. Fig. 6 is a graph showing the comparison of the optimal dosage of the prepared cationic starch, polyaluminium chloride and cationic polyacrylamide for flocculation, and the graph shows that the turbidity after flocculation is not much different, but the optimal dosage of the product is obviously smaller than that of other two products. FIG. 7 is a graph showing comparison of pH response of prepared cationic starch, polyaluminium chloride and cationic polyacrylamide, and the product has good flocculation effect in the pH range of 3-12, and the flocculation effect of the product is obviously superior to that of cationic polyacrylamide, and the pH range of the polyaluminium chloride is narrower although the flocculation effect of the polyaluminium chloride is better, so that the product is superior in comprehensive consideration.

Example 2

The ratio of the amount of sodium hydroxide to the amount of the substance (calcium oxide, calcium hydroxide, calcium carbonate) was ensured to be unchanged, the ratio of the amount of the substance occupied by calcium oxide was changed from (1.fwdarw.0.5.fwdarw.0), the internal mixer used for the reaction was changed to a kneader, a twin-screw extruder, and the other was the same as in example 1, and the description was made with reference to FIG. 8, because the alkali mixing was conducted to provide an alkaline environment and Ca ²⁺ Catalytic, proper alkalinity and moderate concentration of Ca ²⁺ Can play a role in catalysis, and too little or too much can influence the taking of the catalystSubstitution degree and reaction efficiency, along with the change of the ratio of calcium oxide in mixed alkali, the substitution degree is changed from 0.6 to 0.78 to 0.45, the reaction efficiency is 45-78%, and under the same condition, calcium hydroxide > calcium oxide > calcium carbonate is catalyzed.

Example 3

Except that the alkali, water and starch are mixed uniformly in a molar ratio of (0.005-0.01-0.03) (3.07-5.45-6.32) 1 in a zirconia ball milling tank, an internal mixer used in the reaction is changed into a kneader and a double-screw extruder, the influence of the alkali amount and the water amount on the alkalization pretreatment starch can be seen by changing the mixing proportion in the same way as in the embodiment 1, the too low catalytic effect is small, the surface of the starch is gelled due to the too high alkali amount, the reaction is not easy to proceed, the too low water amount is not easy to penetrate the etherifying agent into the starch, the too high water amount is also not easy to catalyze the reaction, so that the alkali amount and the water amount are moderate, the substitution degree of the cationic starch prepared under the condition is between 0.53-0.76, the reaction efficiency is between 53-76%, the substitution degree can be influenced by different mechanical equipment, and the internal mixer is more than the kneader and the double-screw extruder.

Example 4

Except that the ratio of the large spheres to the small spheres in the zirconia spheres is (1:3) → (1:5) → (1:15) → (1:25), the internal mixer used in the reaction is changed into a kneader or a twin-screw extruder, and the other is the same as that in example 1, the ratio of the large spheres to the small spheres influences the crushing degree, the reactivity is influenced, the substitution degree of cationic starch is changed from 0.48 to 0.68 along with the adjustment of the ratio of the large spheres, the reaction efficiency is between 48% and 68%, and the substitution degree is influenced by the same mechanical equipment as that of the internal mixer > the kneader > the twin-screw extruder.

Example 5

Except that the ball milling rotation speed is (300 r/min to 450r/min to 650 r/min), the internal mixer used in the reaction is replaced by a kneader or a double-screw extruder, the ball milling rotation speed can directly influence the applied mechanical force, the damage degree of a starch crystallization area is related to the ball milling rotation speed, the materials cannot be effectively ground, the ball milling rotation speed is too high, the crushed crystallization area is recycled and reaggregated, the reaction is not easy to carry out, so that the proper rotation speed is important, the substitution degree of the prepared cationic starch is 0.56-0.83, the reaction efficiency is 56-83%, and the substitution degree can be influenced by mechanical equipment as well under the conditions that the internal mixer is more than the kneader and the double-screw extruder.

Example 6

Except that the ball milling time is (0.5 h-1 h-2.5 h), the internal mixer used in the reaction is replaced by a kneader or a twin-screw extruder, and the ball milling time is the same as that in example 1, the ball milling time directly affects the application of mechanical force, and the main characteristic is that the too long time can cause the crushed crystallization area to be repolymerized, under the condition, the substitution degree of the prepared cationic starch is between 0.38 and 0.76, the reaction efficiency is between 38 and 76%, the substitution degree is affected by the same mechanical equipment, and the internal mixer > kneader > twin-screw extruder.

Example 7

Except that the starch and 2, 3-epoxypropyl trimethyl ammonium chloride are uniformly mixed according to the molar ratio of (2.5:1) to (1:1) to (0.5:1), the internal mixer used in the reaction is changed into a kneader or a double-screw extruder, the other materials which are added with GTA are all the same as those in the embodiment 1, the smaller the amount is, the more thorough the reaction is, but the lower the substitution degree is, the higher the reaction efficiency is, under the condition, the substitution degree of the prepared cationic starch is between 0.37 and 0.95, the reaction efficiency is between 40 and 93 percent, and the substitution degree and the reaction efficiency of the cationic starch prepared by the kneader or the double-screw extruder are all different from those of the internal mixer.

Example 8

The same as in example 1 except that the mechanical equipment used in the reaction is an internal mixer, a kneader or a twin-screw extruder, the reaction is carried out at the temperature of (40 to 70 to 90) DEG C, the reaction time is (0.5 to 1.5 to 3 hours), other conditions of the reaction are changed to affect the reaction environment, the temperature affects the activity of the reaction, side reactions occur, the reaction time affects the progress of the reaction, the reaction progress affects the side reactions, so that the substitution degree of the prepared cations is changed from 0.37 to 0.78, the reaction efficiency is between 37 and 78%, and the mechanical equipment also affects the substitution degree.

Example 9

The same procedure as in example 1 was followed except that the molar ratio of starch to butyl glycidyl ether was changed to a kneader or twin screw extruder (9.3:1. Fwdarw.4.5:1. Fwdarw.1.6:1), butyl glycidyl ether provided a hydrophobe group, reduced the hydrophilicity of the highly substituted cationic starch, and flocculated very rapidly after combination with the dispersing agent, and the change in reaction conditions was such that the degree of substitution was varied between 0.1 and 0.18, the reaction efficiency was between 20% and 32%, and the same mechanical equipment affected the degree of substitution, with an internal mixer > kneader > twin screw extruder.

Example 10

The same as in example 1 except that the mechanical equipment used in the reaction is an internal mixer, a kneader or a twin-screw extruder, the reaction is carried out at the temperature of (70- > 85- > 95) DEG C for the duration of (0.5- > 1.5 h- > 3 h), the conditions of the reaction are changed to affect the reaction environment, the temperature affects the activity of the reaction, the occurrence of side reaction, the reaction time affects the progress of the reaction, the reaction progress affects the occurrence of the side reaction, so that the change of the conditions can change the substitution degree of the prepared hydrophobed group between 0.13 and 0.24, the reaction efficiency is between 23 and 37 percent, and the mechanical equipment also affects the substitution degree.

In summary, the invention discloses a method for preparing high-substitution cationic starch by mechanochemistry, which provides a preparation method for quaternary ammonium type cationic modified starch with simple production process, environment friendliness and high application efficiency, and flocculation experiments prove that the flocculant produced by the process has very obvious effect in water purification treatment and can be applied to wastewater treatment with high efficiency. The process has the advantages of outstanding advantages, simple process, high substitution degree of the prepared cation modified starch, high reaction efficiency and environmental friendliness, accords with the concepts of green chemistry and sustainable development, and has large-scale production potential.

Claims (2)

1. A method for preparing high substitution degree cationic starch by mechanochemistry, which is characterized by comprising the following steps:

firstly, carrying out alkalization pretreatment on starch, uniformly mixing mixed alkali, water and starch in a molar ratio of (0.005-0.03) (3.07-6.32) 1 in a zirconia ball milling tank, wherein the ball-to-ball ratio in zirconia balls is 1 (3-25), the ball milling rotating speed is 300r/min-650r/min, the ball milling time is 0.5-2.5h, and repeatedly preparing ball milling materials for multiple times;

step (2), uniformly mixing the ball-milling material prepared in the step (1) with 2, 3-epoxypropyl trimethyl ammonium chloride according to the molar ratio of starch in the ball-milling material to 2, 3-epoxypropyl trimethyl ammonium chloride of 2.5:1-0.5:1, adding the mixture into mechanical reaction equipment, stirring the mixture for reaction, and reacting at 40-90 ℃ for 0.5-3h;

step (3), fully reacting the ball-milling material in the step (2) with 2, 3-epoxypropyl trimethyl ammonium chloride, adding butyl glycidyl ether, mixing according to the mol ratio of the starch to the butyl glycidyl ether of 9.3:1-1.6:1, and reacting at 70-95 ℃ for 0.5-3 hours to obtain a modified starch crude product;

washing the modified starch crude product obtained in the step (3) with an ethanol water solution with the mass fraction of 60% -80% for a plurality of times, then detecting whether chloride ions remain or not with a silver nitrate solution, if so, continuing washing, and if not, washing with absolute ethanol for a plurality of times to remove water, then washing with petroleum ether to remove unreacted hydrophobizing reagent, and then drying to obtain the high-substitution-degree cationic starch;

the mixed alkali is a mixture of sodium hydroxide and calcium oxide, calcium hydroxide or calcium carbonate.

2. A method for the mechanochemical preparation of cationic starches having a high degree of substitution according to claim 1, wherein the mechanical reaction equipment used is an internal mixer, kneader or twin-screw extruder.