Method for preparing nitrated chitosan with different substitution degrees

Abstract

The invention discloses a method for preparing nitrated chitosan with different substitution degrees, and belongs to the technical field of energetic materials. In order to prepare nitrated chitosan with different nitration degrees under mild conditions, the invention provides a method for preparing nitrated chitosan with different substitution degrees, which comprises the following steps: controlling the formula proportion of nitric acid and sulfuric acid, mixing the nitric acid and sulfuric acid with chitosan, and carrying out nitration reaction at 20-60 DEG C to obtain nitrated chitosan with the substitution degrees of 1.5-2.1 and 2.1-2.8. The nitrated chitosan with different substitution degrees is obtained by researching the influence of a mixed acid formula on the substitution degrees and strictly controlling the ratio of the nitrated acid to the sulfur acid, so that the accurate control on the product quality is realized; the nitrated chitosan with different substitution degrees can be prepared under mild conditions, and the energy consumption is low.

Description

Technical Field

[0001] The invention belongs to the technical field of energetic materials, and in particular relates to a method for preparing nitrated chitosans with different substitution degrees. Background Art

[0002] Chitosan is a natural polymer obtained by deacetylation of chitin from shrimps and crabs. Chitosan and its derivatives have excellent biocompatibility, safety, degradability and adsorption capacity, and are widely used in many fields such as medicine, food, cosmetics and water treatment. Nitrochitosan, as an important derivative of chitosan, has application potential in propellants and electrochemical devices. However, the preparation methods of nitrated chitosan reported so far have harsh conditions (reaction at -2°C), some methods require the use of difficult-to-recycle solvents such as ionic liquids, and the nitrogen content of the prepared nitrated chitosan is difficult to adjust, which limits the industrial production of nitrated chitosan.

[0003] CN109627358A discloses a preparation method and application of nitrated chitosan, and the preparation method comprises: adding chitosan to acetic anhydride according to the formula amount, adding fuming nitric acid during stirring, and then adding concentrated sulfuric acid, reacting at 0°C to 5°C for 4h to 7h, and the reactant is post-treated to obtain nitrated chitosan, and its nitration substitution degree is 1.8 to 2.1. Although this method improves the nitration substitution degree of nitrated chitosan. However, there are the following problems: 1. This method cannot obtain nitrated chitosan with a higher degree of substitution; 2. This method requires the use of acetic anhydride, which is costly, and is used together with nitric and sulfuric acid mixed acid, which is difficult to recycle; 3. After adding acetic anhydride, it is difficult to control the mixed acid ratio, which affects the accuracy and production efficiency, resulting in difficult control of product quality; 4. This method needs to react at low temperature, which is not conducive to control and has high energy consumption; 5. Acetic anhydride is flammable and explosive, toxic and has a pungent odor, and the production process is very dangerous.

[0004] Therefore, it is necessary to develop a new process for producing nitrated chitosan and study how to obtain nitrated chitosan with different nitration degrees. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a general method for preparing nitrated chitosan with different nitration degrees under mild conditions.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing nitrated chitosan with different degrees of substitution, which comprises the following steps: mixing nitric acid, sulfuric acid and water to obtain a nitric-sulfur mixed acid; mixing the nitric-sulfur mixed acid and chitosan, and performing a nitration reaction at 20-60° C. After the nitration reaction is completed, filtering, washing and drying to obtain the nitrated chitosan;

[0007] When preparing nitrated chitosan with a degree of substitution of 1.5 to 2.1, the nitric-sulfuric acid mixture is controlled to consist of 12 to 40 wt% HNO3, 50 to 80 wt% H2SO4 and 10 to 20 wt% water;

[0008] When preparing nitrated chitosan with a substitution degree of 2.1 < substitution degree ≤ 2.8, the nitric-sulfuric acid mixture is controlled to consist of 25-60wt% HNO3, 40-60wt% H2SO4 and 5-9.5wt% water.

[0009] The present invention studies the influence of mixed acid formula on substitution degree and strictly controls the ratio of nitric acid and sulfuric acid mixed acid to obtain nitrated chitosan with different substitution degrees; at the same time, the ratio of nitrating agent affects the uniformity of the product. Under comprehensive consideration, in the present invention, when a nitric acid and sulfuric acid mixed acid composed of 12-40wt% HNO3, 50-80wt% H2SO4 and 10-20wt% water is used to prepare nitrated chitosan with a substitution degree of 1.5-2.1; when a nitric acid and sulfuric acid mixed acid composed of 25-60wt% HNO3, 40-60wt% H2SO4 and 5-9.5wt% water is used, a nitrated chitosan with a substitution degree of 2.1 < substitution degree ≤ 2.8 is prepared.

[0010] To ensure product uniformity, in the method for nitrating chitosan with different substitution degrees adopted by the present invention, the mass ratio of nitric-sulfuric acid mixed acid and chitosan is controlled to be 20-100 mL:1 g.

[0011] In the method for nitrating chitosan with different substitution degrees adopted by the present invention, the nitration reaction can be carried out at room temperature, and the nitration reaction time is 30 to 90 minutes.

[0012] When preparing the nitric-sulfuric mixed acid according to the present invention, nitric acid and sulfuric acid of different concentrations can be used, as long as the mixed acid meets the requirements.

[0013] During drying, the present invention directly dries in an oven, and to ensure safety, the oven door is kept open.

[0014] Beneficial effects of the present invention:

[0015] The present invention adopts nitric acid and sulfuric acid mixed acid as the nitrating agent without using a solvent, the nitric acid and sulfuric acid recovery technology is mature, and the preparation cost is low; by strictly controlling the ratio of the nitric acid and sulfuric acid mixed acid, nitrated chitosan with different substitution degrees is obtained, and accurate control of product quality is achieved; the present invention can prepare nitrated chitosan with different substitution degrees under mild conditions, and energy consumption is low. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0017] Example 1

[0018] After mixing sulfuric acid, nitric acid and water in proportion (H2SO4 70wt%, HNO3 20wt%, water 10wt%), adjust the temperature to the set temperature (30°C), take 300ml of nitric-sulfuric acid mixed acid and add 5g of chitosan, stir at a constant temperature of 30°C for 60min, filter and wash, and use the filtrate to recover nitric acid and sulfuric acid. Dry the filter cake to obtain nitrated chitosan. The degree of substitution of the sample is tested to be 2.03.

[0019] Example 2

[0020] After mixing sulfuric acid, nitric acid and water in proportion (H2SO4 70wt%, HNO3 15wt%, water 15wt%), adjust the temperature to the set temperature (50°C), take 500ml of nitric-sulfuric acid mixed acid and add 8g of chitosan, stir at a constant temperature of 50°C for 40min, filter and wash, and use the filtrate to recover nitric acid and sulfuric acid. Dry the filter cake to obtain nitrated chitosan. The degree of substitution of the sample is tested to be 1.51.

[0021] Example 3

[0022] After mixing sulfuric acid, nitric acid and water in proportion (H2SO4 55wt%, HNO3 36wt%, water 9wt%), adjust the temperature to the set temperature (50°C), take 300ml of nitric-sulfuric acid mixed acid and add 5g of chitosan, stir at a constant temperature of 50°C for 45min, filter and wash, and use the filtrate to recover nitric acid and sulfuric acid. Dry the filter cake to obtain nitrated chitosan. The degree of substitution of the sample is tested to be 2.38.

[0023] Example 4

[0024] After mixing sulfuric acid, nitric acid and water in proportion (H2SO4 48wt%, HNO3 45wt%, water 7wt%), adjust the temperature to the set temperature (55°C), take 500ml of nitric-sulfuric acid mixed acid and add 6g of chitosan, stir at a constant temperature of 55°C for 45min, filter and wash, and use the filtrate to recover nitric acid and sulfuric acid. Dry the filter cake to obtain nitrated chitosan. The degree of substitution of the sample is tested to be 2.65.

Claims

1. A method for preparing nitrated chitosans with different degrees of substitution, characterized in that: The following steps are involved: Mix nitric acid, sulfuric acid and water to obtain nitric acid and sulfuric acid mixed acid; mix the nitric acid and sulfuric acid mixed acid with chitosan, and carry out nitration reaction at 20-60° C. After the nitration reaction is completed, filter, wash and dry to obtain nitrated chitosan; When preparing nitrated chitosan with a degree of substitution of 1.5 to 2.1, the nitric-sulfuric acid mixture is controlled to consist of 12 to 40 wt% HNO3, 50 to 80 wt% H2SO4 and 10 to 20 wt% water; When preparing nitrated chitosan with a substitution degree of 2.1 < ≤ 2.8, the nitric-sulfuric acid mixture is controlled to consist of 25-60wt% HNO3, 40-60wt% H2SO4 and 5-9.5wt% water.

2. The method for preparing nitrated chitosan with different degrees of substitution according to claim 1, characterized in that: The mass ratio of the nitric-sulfuric acid mixture to chitosan is 20-100 mL:1 g.

3. The method for preparing nitrated chitosan with different degrees of substitution according to claim 1 or 2, characterized in that: The nitration reaction time is 30 to 90 minutes.