Nitrocellulose environment-friendly bleaching process based on reclaimed water reuse

Abstract

The invention discloses an environment-friendly nitrocellulose bleaching process based on reclaimed water reuse, and belongs to the technical field of fine chemical engineering. The invention provides an environment-friendly efficient bleaching process for nitrocellulose, which adopts hydrogen peroxide with the concentration of 4-8g / L to realize efficient bleaching of nitrocellulose under the conditions that the pH value is 7-10 and the bleaching temperature is 45-65 DEG C, the bleached nitrocellulose is heated to 85-100 DEG C or above, and hydrogen peroxide remained on the surface of the bleached nitrocellulose can be removed in a short time. The whiteness of the nitrocellulose can meet the index requirement. According to the method, the washing frequency is reduced, the water consumption is reduced, the defects of environmental pollution, occupational health hazards, pipeline equipment corrosion and the like caused by an existing sodium hypochlorite bleaching process are overcome, the quality of recycled reclaimed water is improved, the utilization rate of the reclaimed water is increased, and the water consumption of a product is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fine chemical industry, and particularly relates to an environmentally friendly bleaching process for nitrocellulose based on reclaimed water. BACKGROUND

[0002] Cellophane uses nitrocellulose, and paint uses nitrocellulose (high-viscosity product) due to customer demand, and needs to be bleached during production to improve product whiteness. The industry usually uses sodium hypochlorite as a bleaching agent. The bleached nitrocellulose needs to be washed with hot and cold water to remove the sodium hypochlorite attached to the surface of the fiber, and to improve the product stability. To reduce water consumption in the production process, the washing water needs to be reused. This makes a small amount of sodium hypochlorite enter the reclaimed water recycling system. During transportation and storage, sodium hypochlorite will decompose when it meets heat and acid. The chlorine gas released by the decomposition seriously affects the physical and mental health of the operators, causes corrosion of the storage or transportation equipment, and affects the quality of the reclaimed water, which is not conducive to reducing water consumption. Therefore, a new bleaching process for nitrocellulose needs to be developed.

[0003] CN116752368A discloses a method for bleaching sulfate pulp, comprising the following steps: 1) acid, chelating agent and viscosity protective agent pretreatment: washing, screening and concentrating the sulfate pulp after cooking treatment, and then adding sulfuric acid, chelating agent and viscosity protective agent for pretreatment; 2) ozone bleaching: concentrating the pretreated sulfate pulp, and then transferring it to an ozone reactor, and then introducing ozone for ozone bleaching; 3) hydrogen peroxide bleaching: washing and concentrating the ozone-bleached sulfate pulp, and then adding hydrogen peroxide, sodium hydroxide, sodium silicate and stabilizer, and then introducing steam to heat, and then transferring it to a hydrogen peroxide bleaching tower for hydrogen peroxide bleaching.

[0004] CN1176673A discloses a method for bleaching wood pulp and other cellulose and lignocellulose fiber materials (pulp) with hydrogen peroxide, comprising: adjusting the concentration of the pulp to 8-18%; adding alkali to make the pH of the pulp greater than 8.5; adding hydrogen peroxide in an amount of at least 0.5% based on the dry weight of the pulp; heating the temperature of the pulp to greater than 100℃, while maintaining sufficient pressure to prevent the pulp from boiling; passing the pulp through a reaction tower at a rate such that the reaction time in the reaction tower is less than 45 minutes; cooling the temperature of the pulp to less than 100℃; depositing the pulp in the reaction tower under normal pressure and allowing the reaction to proceed for 1-5 hours until most of the remaining hydrogen peroxide is consumed.

[0005] However, the above method is not suitable for nitrocellulose. SUMMARY

[0006] The existing nitrocellulose bleaching process using sodium hypochlorite as a bleaching agent has the problems of occupational health hazards, easy corrosion of storage or conveying equipment, and the like, and the present application develops an environment-friendly high-efficiency bleaching process using hydrogen peroxide as a bleaching agent, effectively solves the problems of environmental pollution, occupational health hazards, and corrosion of pipeline equipment caused by the existing sodium hypochlorite bleaching process, improves the quality of recycled water, improves the utilization rate of water, and reduces the water consumption of products.

[0007] The present application provides an environment-friendly bleaching process for nitrocellulose based on water reuse, which comprises the following steps: 1. The environment-friendly bleaching process for nitrocellulose based on water reuse, characterized by comprising the following steps: A. Nitrocellulose preparation: adjust the pulp mass concentration of the boiled and washed qualified nitrocellulose to 3-10% by adding water; B. Hydrogen peroxide solution addition: add hydrogen peroxide aqueous solution to the system, adjust the H2O2 concentration to 4-8 g / L, and add alkali solution to control the pH value to 7-10; C. Temperature rising bleaching: raise the temperature to 45-65 DEG C to perform bleaching; D. Removal of excess hydrogen peroxide: after bleaching, raise the temperature to 85-100 DEG C to remove the excess hydrogen peroxide.

[0008] Among the above-mentioned environment-friendly bleaching process for nitrocellulose based on water reuse, in step A, the water used is recycled water.

[0009] Among the above-mentioned environment-friendly bleaching process for nitrocellulose based on water reuse, in step B, the H2O2 mass concentration of the hydrogen peroxide aqueous solution is 25-30%.

[0010] Among the above-mentioned environment-friendly bleaching process for nitrocellulose based on water reuse, in step B, the alkali solution is sodium carbonate aqueous solution, and the concentration is 20-100 g / L.

[0011] Among the above-mentioned environment-friendly bleaching process for nitrocellulose based on water reuse, in step C, the bleaching time is 60-120 min.

[0012] Among the above-mentioned environment-friendly bleaching process for nitrocellulose based on water reuse, in step C, the temperature is 85-100 DEG C for 60-120 min.

[0013] The present application has the following advantages: (1) The present application uses hydrogen peroxide as a bleaching agent, which is more environmentally friendly than the traditional sodium hypochlorite bleaching agent which can produce chlorine gas and affect the health of operators.

[0014] (2) The present application uses hydrogen peroxide as a bleaching agent, and by virtue of the unstable characteristics of hydrogen peroxide in a high-temperature environment, the excess hydrogen peroxide in the bleaching process can be removed by increasing the temperature, thereby reducing the process of rinsing after bleaching to remove excess sodium hypochlorite, reducing the amount of water used in production and the amount of wastewater generated, and improving the overall environmental benefits.

[0015] (3) The present application uses hydrogen peroxide as a bleaching agent, compared with the traditional sodium hypochlorite bleaching agent, the chlorine ion entering the pipe network or equipment can easily cause equipment corrosion, and the hydrogen peroxide bleaching agent has no corrosion to the equipment, and is more environmentally friendly.

[0016] (4) The present application performs hydrogen peroxide bleaching in an alkaline environment, improves the bleaching performance of hydrogen peroxide, and makes the bleaching effect better. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The present application is a process flow chart for hydrogen peroxide bleaching of nitrocellulose. DETAILED DESCRIPTION

[0018] Specifically, an environmentally friendly bleaching process for nitrocellulose based on water reuse includes the following steps: A. Nitrocellulose material preparation: Pump the cooked and washed qualified nitrocellulose into the bleaching equipment, add water to adjust the slurry mass concentration to 3-10%; B. Hydrogen peroxide solution addition: According to the volume of water in the bleaching equipment, add a certain amount of hydrogen peroxide solution to make the H2O2 concentration in the system 4-8 g / L (hydrogen peroxide is 100%), and add a certain amount of sodium carbonate aqueous solution with a concentration of 20-100 g / L, and control the pH value of the system to 7-10; C. Temperature rising and rinsing: After preparation, increase the temperature to 45-65℃, and bleach for 60-120min; D. Remove excess hydrogen peroxide: After bleaching, increase the temperature to 85-100℃, and keep the temperature for 60-120min to remove excess hydrogen peroxide. At this time, the whiteness of the nitrocellulose product can meet the index requirements and enter the next process.

[0019] In the present application, after removing excess hydrogen peroxide, the material is pumped to the next process by pipeline through the pump, the conveying medium is water, and the material needs to be concentrated after the next process to meet the subsequent production requirements. The concentrated filter water is collected through the collection pipeline and then returned to the middle water recovery tank, and then recycled for the bleaching process. In the traditional process, when sodium hypochlorite is used as a bleaching agent, chloride ions will enter the middle water system, causing corrosion to the equipment and pipelines, and multiple rinsing is required to remove excess sodium hypochlorite. In the present application, hydrogen peroxide is used as a bleaching agent, and excess hydrogen peroxide can be removed by increasing the temperature, and the rinsing process is reduced, which is more conducive to the recycling of the water.

[0020] In the present application, the cooked and washed nitrocellulose is pumped to the bleaching equipment to adjust the slurry concentration to 3-10%, so that the bleaching of nitrocellulose is carried out in a large amount of water, and effective safety control measures are realized. The present application strictly controls the slurry concentration, which is more conducive to the bleaching performance of hydrogen peroxide, and avoids excessive concentration, excessive load of the stirring device, and inability to stir, or low concentration, low production efficiency, and high cost.

[0021] In the present application, hydrogen peroxide is used as a bleaching agent, and the H2O2 concentration in the system is strictly controlled to be 4-8 g / L, and sodium carbonate solution is added to control the pH value of the system to be 7-10. The hydrogen peroxide bleaching is carried out in an alkaline environment, which improves the bleaching performance of hydrogen peroxide, so that the bleaching effect can be ensured at a lower temperature, the decomposition of hydrogen peroxide caused by high temperature is avoided, and more importantly, the safety hazard caused by high temperature is avoided. If the concentration of hydrogen peroxide is too high, it will damage the nitrocellulose due to its strong oxidizing property and instability, and there will be problems of equipment corrosion and production safety; if the concentration is too low, the bleaching effect will be poor. At the same time, in an alkaline environment, the bleaching ability and efficiency of hydrogen peroxide can be effectively improved, but high alkalinity can easily cause saponification of nitrocellulose and damage its structure. Therefore, the H2O2 concentration in the system is strictly controlled to be 4-8 g / L, and the pH value of the system is controlled to be 7-10.

[0022] In the present application, the bleaching process strictly controls the temperature to be 45-65℃, and the bleaching time is 60-120 min, so that the hydrogen peroxide will not decompose at high temperature, and the whiteness of the product can meet the process requirements at a lower temperature.

[0023] The present application will be further described in detail by examples, but the scope of protection of the present application is not limited in the range of the examples.

[0024] In the examples, the hydrogen peroxide solution used is commercially available hydrogen peroxide solution with a concentration of 30%; the alkali solution used is sodium carbonate aqueous solution with a concentration of 50 g / L.

[0025] Example 1 Take a certain mass of washed nitrocellulose, placed in the reuse of water, adjust the slurry mass concentration of 3%, add a certain mass of hydrogen peroxide solution, adjust the system hydrogen peroxide (calculated as H2O2 100%) concentration of 4g / L, while adding a certain mass of alkali solution, adjust the pH value to 10, heated to 45℃, and keep 120min bleaching, after bleaching, increase the temperature to 85℃ for 120min, remove the incomplete reaction of hydrogen peroxide, the product whiteness (whiteness reached 88%) can meet the process requirements.

[0026] Example 2 Take a certain mass of washed nitrocellulose, placed in the reuse of water, adjust the slurry mass concentration of 6%, add a certain mass of hydrogen peroxide solution, adjust the system hydrogen peroxide (calculated as H2O2 100%) concentration of 6g / L, while adding a certain mass of alkali solution, adjust the pH value to 8, heated to 55℃, and keep 90min bleaching, after bleaching, increase the temperature to 90℃ for 90min, remove the incomplete reaction of hydrogen peroxide, the product whiteness (whiteness reached 88%) can meet the process requirements.

[0027] Example 3 Take a certain mass of washed nitrocellulose, placed in the reuse of water, adjust the slurry mass concentration of 10%, add a certain mass of hydrogen peroxide solution, adjust the system hydrogen peroxide (calculated as H2O2 100%) concentration of 8g / L, while adding a certain mass of alkali solution, adjust the pH value to 7, heated to 65℃, and keep 60min bleaching, after bleaching, increase the temperature to 100℃ for 60min, remove the incomplete reaction of hydrogen peroxide, the product whiteness (whiteness reached 88%) can meet the process requirements.

Claims

1. An environmentally friendly bleaching process for nitrocellulose based on reclaimed water, characterized in that: The method comprises the following steps: A. Preparation of nitrocellulose: the washed and cooked nitrocellulose is adjusted to a pulp mass concentration of 3-10% by adding water; B. Addition of hydrogen peroxide solution: hydrogen peroxide aqueous solution is added to the system, the H2O2 concentration is adjusted to 4-8 g / L, and an alkali solution is added to control the pH value to 7-10; C. Temperature increase and bleaching: the temperature is increased to 45-65 ℃ for bleaching; D. Removal of excess hydrogen peroxide: after the bleaching is completed, the temperature is increased to 85-100 ℃ to remove the excess hydrogen peroxide.

2. The environmentally friendly bleaching process of nitrocellulose based on reclaimed water reuse according to claim 1, characterized by: In step A, the water used is recycled and circulated water.

3. The environmentally friendly bleaching process for nitrocellulose based on reclaimed water reuse according to claim 1, characterized in that: In step B, the H2O2 mass concentration of the hydrogen peroxide aqueous solution is 25-30%.

4. The environmentally friendly bleaching process for nitrocellulose based on reclaimed water reuse according to claim 1, characterized in that: In step B, the alkali solution is a sodium carbonate aqueous solution, and the concentration is 20-100 g / L.

5. The environmentally friendly bleaching process for nitrocellulose based on reclaimed water reuse according to claim 1, characterized in that: In step C, the bleaching time is 60-120 min.

6. The environmentally friendly bleaching process of cellulose nitrate based on reclaimed water according to any one of claims 1 to 5, characterized in that: In step C, the temperature is kept at 85-100 ℃ for 60-120 min.

Images