CN102603905B - Preparation method of oxidized starch containing aldehyde group on C6 position of glucose unit - Google Patents

Abstract

The invention discloses a preparation method of aldehyde group-containing oxidized starch in starch molecules. Nitric acid and dilute hydrochloric acid are mixed to form a strong oxidant of nitric acid chloride, so that 40%-85% of the primary hydroxyl group on the C6 position of the glucose unit in the starch molecule is oxidized. , the number of moles of aldehyde groups in the generated oxidized starch is 0.15-0.25, and the number of moles of carboxyl groups is 0.25-0.60. acid chlorides, and cycle through the starch oxidation process. The invention has the advantages of being able to control the content of aldehyde groups and carboxyl groups in the oxidized starch, broadening the application range of the oxidized starch, overcoming the problems of poor oxidation selectivity, large consumption of oxidant and high production cost in the existing oxidized starch preparation process, and has broad application prospects.

Description

A kind of preparation method of oxidized starch containing aldehyde group on the C6 position of glucose unit

technical field

The invention relates to a preparation method of oxidized starch, in particular to a preparation method of oxidized starch containing aldehyde groups in the 6-position of starch molecules, which belongs to the field of fine chemical industry.

Background technique

Starch is a kind of biodegradable natural macromolecular compound with wide sources, low price and semi-crystalline granular polymer. The glucose units that make up starch have hydroxyl groups at the C2, C3 and C6 positions, and their oxidation can change the properties of starch a lot. Starch has the advantages of environmental protection and low price, and has been widely used in the fields of papermaking, textiles, adhesives and building interior wall coatings. In order to expand the application range of starch and improve its performance, a series of oxidized starches with different structures and properties have been developed at home and abroad. Oxidized starch generally refers to carboxyl starch, and starch with more aldehyde groups is also oxidized starch. Aldehyde-containing oxidized starch contains many reactive aldehyde functional groups, so it has many superior characteristics. For example, it has good alkali solubility, easy cross-linking and branching, strong cohesive force, easy gelatinization and not easy to mold.

The oxidants that can be used to prepare oxidized starch include sodium hypochlorite, hydrogen peroxide, potassium permanganate, periodic acid, chlorine dioxide, persulfate, dichromate, ozone, nitric acid, catalytic oxidants, and biological enzymatic hydrolysis. Different oxidants make the degree of oxidation and oxidation site of starch different, and the structure and performance of the obtained oxidized starch are also different.

Ordinary industrial oxidized starch is generally produced by using sodium hypochlorite as an oxidizing agent. The hydroxyl groups in starch molecules are mainly oxidized to carboxyl groups, and only a small amount of hydroxyl groups are oxidized to carbonyl groups. In order to prevent the degradation of a large number of molecular chains in starch, the oxidation depth of industrial oxidized starch is not high, generally controlled within 6%.

Dialdehyde starch is a special kind of oxidized starch. Periodic acid is used as the oxidant to oxidize the hydroxyl groups at the C2 and C3 positions of the glucose unit in the starch molecule into two aldehyde groups, which exist in the form of intramolecular and intermolecular hemiacetals. , this potential aldehyde group can undergo many reactions of aldehydes and hemiacetals, and has been widely used in the field of medicine. Due to the high price of periodic acid and the high production cost of dialdehyde starch, its application range is limited.

U.S. Patent No. 5,565,556 (1996-10-15) discloses a method for preparing high-degree-of-oxidation starch at the C6/C2-C3 position of low-temperature oxidation starch with nitric acid in a sulfuric acid medium. The preparation process includes dispersing the starch in aqueous sulfuric acid; Oxidize starch with nitric acid in the presence of catalyst and catalytic amount of nitrite ions; precipitate oxidized starch from sulfuric acid solution with methanol; neutralize precipitated oxidized starch with alkali; reduce residual ketone groups in oxidized starch with sodium borohydride, etc. , The resulting product can be used as a cleaning agent component. U.S. Patent No. 3,665,000 (1975-05-23) discloses a tricarboxyl starch derivative. Dinitrogen tetroxide can be used to oxidize dialdehyde starch into tricarboxyl starch in an organic solvent.

In order to broaden the application scope of oxidized starch and increase its added value, Chinese patent CN101177459 (2008-05-14) discloses a kind of oxidized starch with high carbonyl content and its preparation method. Oxidation with hydrogen peroxide, static layering, centrifugal separation of the emulsion, and drying to obtain oxidized starch with a carbonyl content of 15.5%-55.4%, and a molecular weight of more than 25,000. The hydrogen peroxide oxidizing agent used in this method is not selective. Usually, the C6 hydroxyl of the glucose unit in the starch molecule is oxidized to a carboxyl group, and the C2 and C3 hydroxyl are oxidized to an aldehyde group. The oxidation process is accompanied by the degradation of a large number of starch molecules. This method has poor selectivity in the oxidation process, unstable product quality, large consumption of oxidant and high cost of raw materials.

Contents of the invention

The purpose of the present invention is to provide a method for preparing aldehyde group-containing oxidized starch on the C6 position of glucose unit in starch molecules, which can control the content of aldehyde groups and carboxyl groups in oxidized starch, prevent a large number of starch molecules from breaking and degrading, and overcome the existing preparation method of oxidized starch The problems of poor process oxidation selectivity, large consumption of oxidant and high production cost.

The principle and innovative ideas of the present invention are to utilize the relatively active nature of the primary hydroxyl group on the C6 position of the glucose unit in the starch molecule, which is easily oxidized to an aldehyde group, and then oxidized to a carboxyl group; while the secondary hydroxyl groups on the C2 and C3 positions are relatively stable and strong oxidizing agents. It can be oxidized to aldehyde or carboxyl. Selecting an appropriate oxidant can only oxidize the primary hydroxyl group at the C6 position in the starch molecule, while the secondary hydroxyl groups at the C2 and C3 positions in the starch molecule are not oxidized, and at the same time control the oxidizing ability of the oxidant, so that the oxidation process can be carried out step by step , to generate a mixture of aldehyde and carboxyl to prevent further oxidation of the product.

The reaction of nitric acid and dilute hydrochloric acid can generate a certain concentration of strong oxidizing agent nitric acid chloride. Studies have found that nitric acid chloride can oxidize the primary hydroxyl group on the C6 position of the glucose unit in the starch molecule to a carboxyl group. The oxidation ability can be controlled by adjusting the concentration of nitric acid and hydrochloric acid. Under controlled oxidation conditions, nitroxyl chloride oxidizes the primary hydroxyl group on the C6 position of the glucose unit in the starch molecule to form a mixture of aldehyde and carboxyl groups. Air is introduced into the reactor during the oxidation process, and oxygen oxidizes and regenerates nitrosyl chloride generated by reducing nitroxyl chloride to nitroxyl chloride, which can be recycled for starch oxidation process. The chemical reaction formula is as follows:

HCl+HNO ₃ →NO ₂ Cl+H ₂ O

2NO ₂ Cl+starch→2NOCl+O-starch+H ₂ O

2NOCl+O ₂ →2NO ₂ Cl

In order to prove that the starch oxidation reaction in the present invention is only carried out on the C6 position of the glucose unit in the starch molecule, the prepared oxidized starch is then reacted with periodic acid, and the oxidized starch reacts almost quantitatively with the periodate, proving that the glucose unit C2 in the starch molecule , The secondary hydroxyl group at the C3 position is not oxidized.

The technical scheme that the present invention takes is:

1. Mix nitric acid and dilute hydrochloric acid to generate a strong oxidizing agent of nitroxyl chloride, so that 40%-85% of the primary hydroxyl group on the C6 position of the glucose unit in the starch molecule is oxidized, and the molar number of aldehyde groups in the generated oxidized starch is 0.15-0.25, The molar number of carboxyl groups is 0.25-0.60. Air is introduced into the reactor during the oxidation process. Oxygen then oxidizes and regenerates the nitrosyl chloride generated by the reduction of nitroxyl chloride into nitroxyl chloride. The starch oxidation process is carried out in a cycle. The preparation steps are as follows:

(1) In a four-neck flask equipped with an agitator and a thermometer, respectively add 30% by weight starch milk and 30% by weight hydrochloric acid solution, and carry out starch acidolysis reaction for 0.5 hours;

(2) Slowly introduce air through a gas distributor under stirring, add sodium nitrite to initiate an oxidation reaction, control the reaction temperature at 30-60° C. and add nitric acid with a weight percentage of 65% dropwise, and carry out the oxidation reaction for 1-6 hours.

(3) After nitric acid oxidation is completed, add sodium sulfite to remove residual nitrogen oxides in the oxidation solution, and neutralize the hydrochloric acid in the reaction solution with sodium hydroxide solution;

(4) Centrifuge the generated oxidized starch emulsion, wash the salt entrained in the filter cake, and dry it at 50° C. to obtain white fluffy oxidized starch.

2. The raw material oxidized starch used is one of corn starch, wheat starch, bean starch or sweet potato starch.

3. Select and control the concentration of hydrochloric acid in the oxidation reaction solution to be 0.25-1.2mol/L.

4. Controlling the molar ratio of nitric acid and starch in the oxidation reaction is 0.6-1.0:1.

During the preparation of oxidized starch, it is necessary to regularly sample and measure its carboxyl and aldehyde content in order to optimize and improve the reaction conditions. The carboxyl content in oxidized starch can be determined by hot paste titration, and the carbonyl content in oxidized starch can be determined by hydroxylamine method.

Advantage and beneficial effect of the inventive method are embodied in:

(1) The content of aldehyde groups and carboxyl groups in the oxidized starch can be selectively controlled to overcome the problems of poor oxidation selectivity, large consumption of oxidant and high production cost in the existing oxidized starch preparation process.

(2) The new process of preparing oxidized starch by oxidizing starch with nitroxyl chloride is simple. Air is used as an auxiliary oxidant, and the nitrosyl chloride produced by reduction can be recycled, which reduces the consumption of nitric acid and the generation of nitrogen oxide tail gas.

(3) The obtained oxidized starch has a high content of aldehyde groups and carboxyl groups, which broadens the scope of application and has broad application prospects.

Detailed ways

Example 1-4

Add 5mL, 10mL, 15mL, and 20mL of concentrated hydrochloric acid to four parts of 30% starch milk (270g) respectively, so that the concentration of hydrochloric acid is 0.25, 0.50, 0.75, and 1.0mol/L respectively, and slowly introduce air at 45°C , 28.5 mL of 65% nitric acid was added dropwise within 3 hours, and the oxidized starch was prepared by reacting for 4 hours. The content of carboxyl and aldehyde groups in oxidized starch and the viscosity of the solution were determined by sampling as shown in Table 1.

Table 1 Effect of hydrochloric acid concentration on carboxyl and aldehyde content in oxidized starch

Example 5-9

Add 15mL of concentrated hydrochloric acid to five parts of 30% starch milk (270g) respectively to make the concentration of hydrochloric acid 0.75mol/L, slowly pass air at 45°C, add 65% nitric acid 22mL, 25mL, 28.5mL, 32mL and 35.7mL, so that the molar ratio of nitric acid to starch was 0.6, 0.7, 0.8, 0.9 and 1.0 respectively, reacted for 4h to prepare oxidized starch, and sampled to determine the content of carboxyl and aldehyde groups in oxidized starch as shown in Table 2.

Table 2 Effect of nitric acid dosage on carboxyl and aldehyde content in oxidized starch

Examples 10-15

Add 15 mL of concentrated hydrochloric acid to six parts of 30% starch milk (270 g) to make the concentration of hydrochloric acid 0.75 mol/L, and slowly introduce air at 45 ° C, within 1, 2, 3, 4, and 5 hours respectively 28.5mL of 65% nitric acid was added dropwise, so that the molar ratio of nitric acid to starch was 0.8, and the oxidized starch was prepared by reacting for 4h, and the content of carboxyl and aldehyde groups in the oxidized starch was sampled and determined as shown in Table 3.

Table 3 Effect of reaction time on carboxyl and aldehyde content in oxidized starch

Examples 16-21

Add 15 mL of concentrated hydrochloric acid to six parts of 30% starch milk (270 g) to make the concentration of hydrochloric acid 0.75 mol/L, and slowly add 15 mL of concentrated hydrochloric acid at 30°C, 35°C, 40°C, 45°C, 50°C and 60°C, respectively. Air was introduced, and 28.5 mL of 65% nitric acid was added dropwise within 3 hours, so that the molar ratio of nitric acid to starch was 0.8, and the oxidized starch was prepared by reacting for 4 hours. The content of carboxyl and aldehyde groups in the oxidized starch was sampled and determined as shown in Table 4.

Table 4 Effect of reaction temperature on carboxyl and aldehyde content in oxidized starch

Claims (2)

1. in a starch molecule, contain the preparation method of aldehyde radical Sumstar 190, it is characterized in that nitric acid and dilute hydrochloric acid to mix generation nitryl chloride strong oxidizer, make it that primary hydroxyl 40%-85% on glucose unit C6 position in starch molecule is oxidized, in the Sumstar 190 generating, aldehyde radical mole number is 0.15-0.25, carboxyl mole number is 0.25-0.60, in oxidising process, in reactor, pass into air, the nitrosyl chloride oxidation regeneration that oxygen generates nitryl chloride reduction is again nitryl chloride, loop starch oxidation process, preparation process is as follows:

(1) in the four-hole bottle of agitator and thermometer is housed, add respectively the starch milk of weight percent 30% and the hydrochloric acid soln of weight percent 30%, carry out starch acidolysis reaction 0.5 hour;

(2) under agitation by gas distributor, slowly pass into air, add Sodium Nitrite initiated oxidation reaction, control the nitric acid that drips weight percent 65% at 30-60 ℃ of temperature of reaction, selecting and controlling concentration of hydrochloric acid in oxidation liquid is 0.25-1.2mol/L, controlling oxidizing reaction Raw nitric acid and starch molar ratio is 0.6-1.0:1, and oxidizing reaction is carried out 1-6h;

(3) nitric acid oxidation adds S-WAT to remove remaining nitrogen oxide in oxidation solution after completing, with the hydrochloric acid in sodium hydroxide solution neutralization reaction liquid;

(4) the Sumstar 190 emulsion that centrifugation generates, the salinity that washing leaching cake is carried secretly is dried it at 50 ℃, obtains white puffy Sumstar 190.

2. preparation method according to claim 1, is characterized in that raw material Sumstar 190 is one of W-Gum, wheat starch, legume starch or sweet potato starch.