Preparation method of ultra-low viscosity low-nitrogen content nitrocellulose

Abstract

The application discloses a preparation method of super-low-viscosity low-nitrogen-content nitrocellulose, and belongs to the technical field of cellulose. The application provides a preparation method of super-low-viscosity low-nitrogen-content nitrocellulose to solve the problems of low yield and poor form of super-low-viscosity low-nitrogen-content wood pulp nitrocellulose, and the method comprises the following steps: taking wood pulp as raw material, and the indexes of the wood pulp are as follows: whiteness is greater than or equal to 91.5%, viscosity is 50-100 MPa.S, alpha-cellulose content is greater than or equal to 90 wt%, ash content is less than or equal to 0.15 wt%, iron content is less than or equal to 10 mg / kg, moisture content is less than or equal to 8 wt%, and density is 0.48-0.65 g / cm 3 Then, esterification is carried out to obtain acid wood pulp nitrocellulose, the cooking and washing conditions are controlled, and finally, super-low-viscosity low-nitrogen-content nitrocellulose is obtained through washing and dehydration. The material selection, cooking and washing and other processes are optimized, so that the viscosity of the nitrocellulose is as low as 0.61 s, the nitrogen content is as low as 171.2 ml / g, the dissolution quality is good, and the yield is as high as 90%.

Description

Technical Field

[0001] This invention belongs to the field of cellulose technology, specifically relating to a method for preparing ultra-low viscosity, low nitrogen content nitrocellulose. Background Technology

[0002] Nitrocellulose, scientifically known as cellulose nitrate, is a product of the reaction between cellulose and nitric acid, with the molecular formula C6H7O2(ONO2). a (OH) 3-an Where a is the degree of esterification and n is the degree of polymerization; it is a white or slightly yellow amorphous solid, made from cellulose (refined cotton, wood pulp, bamboo pulp, etc.) as raw material through esterification reaction under the action of concentrated sulfuric acid and concentrated nitric acid. Its viscosity and stability are subsequently controlled by high-temperature washing. Depending on the product brand, it appears as fluffy, flake, or powder. It is insoluble in water but readily soluble in organic solvents such as alcohols, ethers, and esters.

[0003] Nitrocellulose is a dual-use product, primarily used in civilian applications such as coatings, inks, and films. In recent years, the civilian market demand for nitrocellulose has been approximately 170,000-180,000 tons, with coatings (mainly used in the production of nitrocellulose lacquer) accounting for about 45%, inks (mainly used in the production of packaging and printing inks) accounting for about 45%, and other applications (celluloid products, films, adhesives, nail polish, etc.) accounting for about 10% of total consumption. With the continuous changes in the global economic environment and safety and environmental protection situation, demand in the coatings sector is shrinking; in the ink industry, demand has maintained stable single-digit growth in recent years, mainly driven by demand for alcohol-soluble nitrocellulose products with low nitrogen content, low viscosity, high quality, and good flowability.

[0004] 201110223454.1 discloses a method for producing wood pulp nitrocellulose, which includes the following steps: (1) the mixed acid used in the nitration of wood pulp nitrocellulose is a mixture of nitric acid, sulfuric acid and water, wherein the mixed acid contains 20-55% nitric acid and 10-18% water by mass fraction, and the remainder is sulfuric acid; (2) acidic wood pulp nitrocellulose is obtained after centrifugation to remove the acid; (3) acidic wood pulp nitrocellulose is boiled and washed, and water is added to adjust the initial acidity to 0.5-1.0 g / L, and the boiling and washing temperature is 101-150℃; (4) dehydration; (5) water removal. This method uses wood as raw material, and the color, whiteness, and light transmittance of the product are all better than those of nitrocellulose produced from refined cotton. However, its viscosity ranges from 1.7 to 60 s, and its nitrogen content ranges from 184.0 to 195.2 ml / g, both of which are relatively high. At the same time, because ultra-low viscosity and low nitrogen content wood pulp nitrocellulose is easily hydrolyzed and has poor morphology, it is easily lost during filtration and washing, resulting in a low product yield. Summary of the Invention

[0005] This invention addresses the problems of low yield and poor morphology in the preparation of ultra-low viscosity, low nitrogen content wood pulp nitrocellulose in existing technologies. It improves the processes of material selection, nitration, and washing in the preparation of ultra-low viscosity, low nitrogen content nitrocellulose, thereby ensuring that the product meets all indicators, has good solubility, and significantly improves the yield.

[0006] This invention provides a method for preparing ultra-low viscosity, low-nitrogen nitrocellulose, which includes the following steps:

[0007] A. Raw Material Selection: Wood pulp meal is selected, and its quality indicators are controlled as follows: whiteness ≥ 91.5%, viscosity 50~100MPa·S, α-cellulose content ≥ 90wt%, ash content ≤ 0.15wt%, iron content ≤ 10mg / kg, moisture ≤ 8wt%, and density 0.48~0.65g / cm³. 3 ;

[0008] B. Esterification: The wood pulp and mixed acid are mixed and esterified. The amount of mixed acid used is 0.01-0.05 mg / kg of wood pulp. 3 The esterification temperature is 35–55℃;

[0009] C. Acid removal: After esterification, the product is washed with cold water and centrifuged to obtain acidic wood pulp nitrocellulose.

[0010] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 8-15%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0-2 g / L, raise the temperature to 100-160℃ at a heating rate of 1.0-3.0℃ / min, boil and wash for 1-7 hours, and then cool down to room temperature at a cooling rate of 2.0-5.0℃ / min.

[0011] E. Washing and dehydration: After boiling and washing, the cotton is washed and dehydrated with hot water to obtain ultra-low viscosity and low nitrogen content nitrocellulose.

[0012] In the preparation method of the above-mentioned ultra-low viscosity and low nitrogen content nitrocellulose, in step A, the wood pulp is sliced ​​to a length of 6 mm, a width of 1.5 to 3.0 mm, and a thickness of 1.0 to 1.5 mm.

[0013] In the preparation method of the ultra-low viscosity, low nitrogen content nitrocellulose mentioned above, in step B, the mixed acid contains 25-50% nitric acid, 8-20% water by mass fraction, and the remainder is sulfuric acid.

[0014] In the preparation method of the above-mentioned ultra-low viscosity low nitrogen content nitrocellulose, the esterification time in step B is 50-90 min.

[0015] In the preparation method of the above-mentioned ultra-low viscosity and low nitrogen content nitrocellulose, in step D, the acidity of the system is adjusted to 0.2-1.0 g / L.

[0016] In the preparation method of the ultra-low viscosity, low nitrogen content nitrocellulose mentioned above, in step D, intermittent stirring is carried out during the boiling and washing process.

[0017] In the preparation method of the ultra-low viscosity, low nitrogen content nitrocellulose mentioned above, in step E, the hot water washing is performed 2 to 3 times.

[0018] In the preparation method of the ultra-low viscosity and low nitrogen content nitrocellulose mentioned above, in step E, the viscosity of the obtained nitrocellulose is 0.61 to 1.6 s and the nitrogen content is 171.2 to 183.0 ml / g.

[0019] The beneficial effects of this invention are:

[0020] This invention uses wood as raw material and studies the selection, boiling and washing processes. The final product meets all the required indicators. The viscosity of the nitrocellulose is as low as 0.61 to 1.6s, the nitrogen content is as low as 171.2 to 183.0 ml / g, the solubility is good, the morphology and yield are moderate, and the yield can reach 80 to 90%. Attached Figure Description

[0021] Figure 1 The wood pulp nitrocellulose obtained in Example 1. Detailed Implementation

[0022] Specifically, a method for preparing ultra-low viscosity, low-nitrogen nitrocellulose includes the following steps:

[0023] A. Raw Material Selection: Wood pulp meal is selected, and its quality indicators are controlled as follows: whiteness ≥ 91.5%, viscosity 50~100MPa·S, α-cellulose content ≥ 90wt%, ash content ≤ 0.15wt%, iron content ≤ 10mg / kg, moisture ≤ 8wt%, and density 0.48~0.65g / cm³. 3 ;

[0024] B. Esterification: The wood pulp and mixed acid are mixed and esterified. The amount of mixed acid used is 0.01-0.05 mg / kg of wood pulp. 3 The esterification temperature is 35–55℃;

[0025] C. Acid removal: After esterification, the product is washed with cold water and centrifuged to obtain acidic wood pulp nitrocellulose.

[0026] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 8-15%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0-2 g / L, raise the temperature to 100-160℃ at a heating rate of 1.0-3.0℃ / min, boil and wash for 1-7 hours, and then cool down to room temperature at a cooling rate of 2.0-5.0℃ / min.

[0027] E. Washing and dehydration: After boiling and washing, the cotton is washed and dehydrated with hot water to obtain ultra-low viscosity and low nitrogen content nitrocellulose.

[0028] This invention, through strict control of raw material indicators, is beneficial to the esterification and washing effects, which helps to improve the yield and ensures that the obtained product has ultra-low viscosity and low nitrogen content, while also giving the product good solubility and uniformity.

[0029] To facilitate the esterification reaction, in step A of this invention, the wood pulp is sliced ​​to a length of 6 mm, a width of 1.5–3.0 mm, and a thickness of 1.0–1.5 mm.

[0030] In step B of this invention, the mixed acid contains 25-50% nitric acid, 8-20% water by mass fraction, and the remainder is sulfuric acid.

[0031] In step B of this invention, the esterification time is 50–90 min.

[0032] In step C of this invention, cold water washing and centrifugation are conventional operations in the field, the purpose of which is to remove residual acid and facilitate subsequent operations, without affecting the yield; the specific operation is as follows: after esterification, the material is taken out of the acid and transferred into water (the amount of water is generally more than 5 times the amount of material), stirred evenly and then centrifuged to obtain acidic wood pulp nitrocellulose.

[0033] The nitration and boiling processes significantly affect the viscosity and nitrogen content of the product. Therefore, this invention optimizes the nitration and boiling processes while controlling the quality indicators of raw materials. Experiments show that nitration parameters, boiling temperature, and time significantly affect the product viscosity and nitrogen content, while the material concentration and heating / cooling rates during boiling have a significant impact on the product's solubility. This invention controls the mixed acid composition to be 25-50% nitric acid, 8-20% water, and the remainder sulfuric acid by mass fraction. The boiling temperature is 100-160℃, and the boiling time is 1-7 hours. With suitable nitration parameters, boiling temperature, and time, the viscosity of nitrocellulose is as low as 0.61-1.6s, and the nitrogen content is as low as 171.2-183.0 ml / g. This invention controls the material concentration to be 8-15%, the heating rate to be 1.0-3.0℃ / min, and the cooling rate to be 2.0-5.0℃ / min. By controlling the appropriate material concentration and heating / cooling rates, the product yield and solubility quality are guaranteed.

[0034] In step D of this invention, the acidity of the system is adjusted to 0.2–1.0 g / L.

[0035] In step D of this invention, intermittent stirring is performed during the boiling and washing process.

[0036] In step E of this invention, after boiling and washing, the material is taken out and washed with hot water 2 to 3 times (the amount of hot water used is generally 2 to 3 times the amount of material per wash) to improve the stability of the product. Then, it is centrifuged and dehydrated to obtain the finished product of ultra-low viscosity and low nitrogen content nitrocellulose.

[0037] This invention uses wood as raw material and studies the processes of material selection, nitration, and washing. In step E, the viscosity of the obtained nitrocellulose is 0.61-1.6s and the nitrogen content is 171.2-183.0ml / g.

[0038] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0039] Example 1

[0040] A. Material Selection: Wood pulp was selected, and its quality indicators were controlled as follows: whiteness 92.3%, viscosity 51 MPa·S, α-cellulose content 94 wt%, ash content 0.07 wt%, iron content 6 mg / kg, moisture 6 wt%, and density 0.58 g / cm³. 3 The wood pulp is sliced ​​to a length of 6 mm, a width of 1.5–3.0 mm, and a thickness of 1.2 mm.

[0041] B. Esterification: The mixed acid consists of 50% nitric acid, 17% moisture, and the remainder sulfuric acid by mass fraction; the wood pulp is sliced ​​and then esterified, with the mixed acid dosage being 0.02 mg / kg of wood pulp. 3 Esterification temperature 35℃, reaction time 90 min;

[0042] C. Acid removal: After esterification, the material is removed from the acid, transferred to cold water for washing, stirred evenly, and then centrifuged to obtain acidic wood pulp nitrocellulose.

[0043] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 10%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0.5 g / L, raise the temperature to 125℃ at a heating rate of 2.0℃ / min, boil and wash for 7 hours, stirring intermittently during the process, and then cool down to room temperature at a cooling rate of 3.0℃ / min.

[0044] E. Washing and dehydration: After boiling and washing, the material is taken out and washed 3 times with 3 times the amount of hot water each time, and then centrifuged to dehydrate, to obtain wood pulp nitrocellulose.

[0045] The specifications of the wood pulp nitrocellulose product obtained in this embodiment are as follows: nitrogen content 178.8 ml / g, viscosity 1.5s, light transmittance 96.1%, color 140, and yield 89%.

[0046] Comparative Example 1

[0047] A. Material Selection: Wood pulp was selected, and its quality indicators were controlled as follows: whiteness 92.3%, viscosity 51 MPa·S, α-cellulose content 94 wt%, ash content 0.07 wt%, iron content 6 mg / kg, moisture 6 wt%, and density 0.58 g / cm³. 3The wood pulp is sliced ​​to a length of 6 mm, a width of 1.5–3.0 mm, and a thickness of 1.2 mm.

[0048] B. Esterification: The mixed acid consists of 50% nitric acid, 17% moisture, and the remainder sulfuric acid by mass fraction; the wood pulp is sliced ​​and then esterified, with the mixed acid dosage being 0.02 mg / kg of wood pulp. 3 Esterification temperature 35℃, reaction time 90 min;

[0049] C. Acid removal: After esterification, the material is removed from the acid, transferred to cold water for washing, stirred evenly, and then centrifuged to obtain acidic wood pulp nitrocellulose.

[0050] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 10%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0.5 g / L, raise the temperature to 131℃ at a heating rate of 1.0℃ / min, boil and wash for 8 hours, stirring intermittently during the process, and then cool down to room temperature at a cooling rate of 0.5℃ / min.

[0051] E. Washing and dehydration: After boiling and washing, the material is taken out and washed 3 times with 3 times the amount of hot water each time, and then centrifuged to dehydrate, to obtain wood pulp nitrocellulose.

[0052] The specifications of the wood pulp nitrocellulose product obtained in this comparative example are: nitrogen content 170.5 ml / g, viscosity 0.5s, light transmittance 95.8%, color number 190, and yield 72%.

[0053] Example 2

[0054] A. Material Selection: Wood pulp was selected, and its quality indicators were controlled as follows: whiteness 92.7%, viscosity 61 MPa·S, α-cellulose content 97.2 wt%, ash content 0.1 wt%, iron content 7 mg / kg, moisture 7.6 wt%, and density 0.647 g / cm³. 3 The wood pulp is sliced ​​to a length of 6mm, a width of 1.5-3.0mm, and a thickness of 1.5mm.

[0055] B. Esterification: The mixed acid consists of 35% nitric acid, 14% moisture, and the remainder sulfuric acid by mass fraction; the wood pulp is sliced ​​and then esterified, with the mixed acid dosage being 0.05 mg / kg of wood pulp. 3 Esterification temperature 55℃, reaction time 50 min;

[0056] C. Acid removal: After esterification, the material is removed from the acid, transferred to cold water for washing, stirred evenly, and then centrifuged to obtain acidic wood pulp nitrocellulose.

[0057] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 14%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0.4 g / L, raise the temperature to 145℃ at a heating rate of 2.0℃ / min, boil and wash for 5 hours, stirring intermittently during the process, and then cool down to room temperature at a cooling rate of 3.0℃ / min.

[0058] E. Washing and dehydration: After boiling and washing, the material is taken out and washed 3 times with 3 times the amount of hot water each time, and then centrifuged to dehydrate, to obtain wood pulp nitrocellulose.

[0059] The specifications of the wood pulp nitrocellulose product obtained in this embodiment are as follows: nitrogen content 178.1 ml / g, viscosity 1.2s, light transmittance 95.0%, color number 160, and yield 84%.

[0060] Comparative Example 2

[0061] A. Material Selection: Wood pulp was selected, and its quality indicators were controlled as follows: whiteness 92.7%, viscosity 61 MPa·S, α-cellulose content 97.2 wt%, ash content 0.1 wt%, iron content 7 mg / kg, moisture 7.6 wt%, and density 0.647 g / cm³. 3 The wood pulp is sliced ​​to a length of 6mm, a width of 1.5-3.0mm, and a thickness of 1.5mm.

[0062] B. Esterification: The mixed acid consists of 55% nitric acid, 14% moisture, and the remainder sulfuric acid by mass fraction; the wood pulp is sliced ​​and then esterified, with the mixed acid dosage being 0.03 mg / kg of wood pulp. 3 Esterification temperature 55℃, reaction time 40 min;

[0063] C. Acid removal: After esterification, the material is removed from the acid, transferred to cold water for washing, stirred evenly, and then centrifuged to obtain acidic wood pulp nitrocellulose.

[0064] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 5%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0.4 g / L, raise the temperature to 145℃ at a heating rate of 2.0℃ / min, boil and wash for 4 hours, stirring intermittently during the process, and then cool down to room temperature at a cooling rate of 3.0℃ / min.

[0065] E. Washing and dehydration: After boiling and washing, the material is taken out and washed 3 times with 3 times the amount of hot water each time, and then centrifuged to dehydrate, to obtain wood pulp nitrocellulose.

[0066] The specifications of the wood pulp nitrocellulose product obtained in this comparative example are: nitrogen content 184.4 ml / g, viscosity 2.0s, light transmittance 90.5%, color number 210, and yield 88%.

[0067] Comparative Example 3

[0068] A. Material Selection: Wood pulp was selected, and its quality indicators were controlled as follows: whiteness 91.0%, viscosity 121 MPa·S, α-cellulose content 94 wt%, ash content 0.10 wt%, iron content 6 mg / kg, moisture 6 wt%, and density 0.73 g / cm³. 3 The wood pulp is sliced ​​to a length of 6 mm, a width of 1.5–3.0 mm, and a thickness of 1.2 mm.

[0069] B. Esterification: The mixed acid consists of 50% nitric acid, 15% moisture, and the remainder sulfuric acid by mass fraction; the wood pulp is sliced ​​and then esterified, with the mixed acid dosage being 0.04 mg / kg of wood pulp. 3 Esterification temperature 40℃, reaction time 75 min;

[0070] C. Acid removal: After esterification, the material is removed from the acid, transferred to cold water for washing, stirred evenly, and then centrifuged to obtain acidic wood pulp nitrocellulose.

[0071] D. Boiling and washing: Mix acid wood pulp nitrocellulose and boiling water, control the mass concentration of acid wood pulp nitrocellulose to be 14%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0.8 g / L, raise the temperature to 142℃ at a rate of 0.8℃ / min, boil and wash for 7 hours, stirring intermittently during the process, and then cool down to room temperature at a rate of 0.5℃ / min.

[0072] E. Washing and dehydration: After boiling and washing, the material is taken out and washed 3 times with 3 times the amount of hot water each time, and then centrifuged to dehydrate, to obtain wood pulp nitrocellulose.

[0073] The specifications of the wood pulp nitrocellulose product obtained in this comparative example are: nitrogen content 173.5 ml / g, viscosity 2.2s, light transmittance 91.8%, color number 210, and yield 82%.

Claims

1. A method for preparing ultra-low viscosity, low-nitrogen nitrocellulose, characterized in that: Includes the following steps: A. Raw Material Selection: Wood pulp meal is selected, and its quality indicators are controlled as follows: whiteness ≥ 91.5%, viscosity 50~100MPa·S, α-cellulose content ≥ 90wt%, ash content ≤ 0.15wt%, iron content ≤ 10mg / kg, moisture ≤ 8wt%, and density 0.48~0.65g / cm³. 3 ; B. Esterification: The wood pulp and mixed acid are mixed and esterified. The amount of mixed acid used is 0.01~0.05 mg / kg of wood pulp. 3 The esterification temperature is 35~55℃; C. Acid removal: After esterification, the product is washed with cold water and centrifuged to obtain acidic wood pulp nitrocellulose. D. Boiling and washing: Mix acidic wood pulp nitrocellulose and boiling water, control the mass concentration of acidic wood pulp nitrocellulose to be 8~15%, after the water and cotton are mixed evenly, adjust the acidity of the system to 0.2~1.0g / L, raise the temperature to 100~160℃ at a heating rate of 1.0~3.0℃ / min, boil and wash for 5~7h, and then cool down to room temperature at a cooling rate of 2.0~5.0℃ / min. E. Washing and dehydration: After boiling and washing, the cotton is washed and dehydrated with hot water to obtain ultra-low viscosity and low nitrogen content nitrocellulose. In step B, the mixed acid contains 25-50% nitric acid, 8-20% water by mass fraction, and the remainder is sulfuric acid; In step B, the esterification time is 50-90 min; In step E, the viscosity of the obtained nitrocellulose is 0.61~1.6s and the nitrogen content is 171.2~183.0ml / g.

2. The method for preparing ultra-low viscosity, low-nitrogen nitrocellulose according to claim 1, characterized in that: In step A, the wood pulp is sliced ​​to a length of 6mm, a width of 1.5~3.0mm, and a thickness of 1.0~1.5mm.

3. The method for preparing ultra-low viscosity, low-nitrogen nitrocellulose according to claim 1, characterized in that: In step D, intermittent stirring is performed during the boiling and washing process.

4. The method for preparing ultra-low viscosity, low-nitrogen nitrocellulose according to claim 1, characterized in that: In step E, the hot water washing is performed 2 to 3 times.

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