The production process of high viscosity pulp for cellulose ether was studied. The main factors affecting cooking and bleaching in the process of high-viscosity pulp production were discussed. According to the customer’s requirements, through single factor test and orthogonal test method, combined with the company’s actual equipment capacity, the production process parameters of high viscosity refined cotton pulp raw material for cellulose ether are determined. Using this production process, the whiteness of the high-viscosity refined cotton pulp produced for cellulose ether is ≥85%, and the viscosity is ≥1800 mL/g.
Key words: high viscosity pulp for cellulose ether; production process; cooking; bleaching
Cellulose is the most abundant and renewable natural polymer compound in nature. It has a wide range of sources, low price, and environmental friendliness. A series of cellulose derivatives can be obtained through chemical modification. Cellulose ether is a polymer compound in which the hydrogen in the hydroxyl group on the cellulose glucose unit is replaced by a hydrocarbon group. After etherification, cellulose is soluble in water, dilute alkali solution and organic solvent, and has thermoplasticity. China is the world’s largest producer and consumer of cellulose ether, with an average annual growth rate of more than 20%. There are many kinds of cellulose ethers with excellent performance, and they are widely used in construction, cement, petroleum, food, textile, detergent, paint, medicine, papermaking and electronic components and other industries.
With the rapid development of the field of derivatives such as cellulose ether, the demand for raw materials for its production is also increasing. The main raw materials for cellulose ether production are cotton pulp, wood pulp, bamboo pulp, etc. Among them, cotton is the natural product with the highest cellulose content in nature, and my country is a large cotton producing country, so cotton pulp is an ideal raw material for the production of cellulose ether. Exclusively introduced foreign special equipment and technology for special cellulose production, adopts low-temperature low-alkali cooking, green continuous bleaching production technology, fully automatic control of production process, process control accuracy has reached the advanced level of the same industry at home and abroad. At the request of customers at home and abroad, the company has carried out research and development experiments on high-viscosity cotton pulp for cellulose ether, and the samples have been well received by customers.
1. Experiment
1.1 Raw materials
High viscosity pulp for cellulose ether needs to meet the requirements of high whiteness, high viscosity and low dustiness. In view of the characteristics of high-viscosity cotton pulp for cellulose ether, first of all, strict control was carried out on the selection of raw materials, and cotton linters with high maturity, high viscosity, no three-filament, and low cotton seed hull content were selected as raw materials. According to the above cotton linters According to the requirements of various indicators, it is determined to use cotton linters in Xinjiang as the raw material for the production of high-viscosity pulp for cellulose ether. The quality indicators of Xinjiang cashmere are: viscosity ≥ 2000 mL/g, maturity ≥ 70%, sulfuric acid insoluble matter ≤ 6.0%, ash content ≤ 1.7%.
1.2 Instruments and medicines
Experimental equipment: PL-100 electric cooking pot (Chengyang Taisite Experimental Equipment Co., Ltd.), instrument constant temperature water bath (Longkou Electric Furnace Factory), PHSJ 3F precision pH meter (Shanghai Yidian Scientific Instrument Co., Ltd.), Capillary viscometer, WSB～2 whiteness meter (Jinan Sanquan Zhongshishi
Laboratory Instrument Co., Ltd.).
Experimental drugs: NaOH, HCl, NaClO, H2O2, NaSiO3.
1.3 Process route
Cotton linters→alkali cooking→washing→pulping→bleaching (including acid treatment)→pulp making→finished product→index testing
1.4 Experimental content
The cooking process is based on the actual production process, using wet material preparation and alkaline cooking methods. Simply clean and remove the quantitative cotton linters, add the calculated lye according to the liquid ratio and the amount of alkali used, fully mix the cotton linters and lye, put them into a cooking tank, and cook according to different cooking temperatures and holding times Cook it. The pulp after cooking is washed, beaten and bleached for later use.
Bleaching process: parameters such as pulp concentration and pH value are directly selected according to the actual capacity of the equipment and bleaching routines, and relevant parameters such as the amount of bleaching agent are discussed through experiments.
Bleaching is divided into three stages: (1) Conventional pre-chlorination stage bleaching, adjust the pulp concentration to 3%, add acid to control the pH value of the pulp to 2.2-2.3, add a certain amount of sodium hypochlorite to bleach at room temperature for 40 minutes. (2) Hydrogen peroxide section bleaching, adjust pulp concentration to be 8%, add sodium hydroxide to alkalinize slurry, add hydrogen peroxide and carry out bleaching at a certain temperature (the hydrogen peroxide bleaching section adds a certain amount of stabilizer sodium silicate ). The specific bleaching temperature, hydrogen peroxide dosage and bleaching time were explored through experiments. (3) Acid treatment section: adjust the pulp concentration to 6%, add acid and metal ion removal aids for acid treatment, the process of this section is carried out according to the company’s conventional special cotton pulp production process, and the specific process does not need to be further experimentally discussed.
During the experiment process, each stage of bleaching adjusts the pulp concentration and pH, adds a certain proportion of bleaching reagent, mixes the pulp and bleaching reagent evenly in a polyethylene plastic sealed bag, and puts it in a constant temperature water bath for constant temperature bleaching for a specified time. The bleaching process Take out the medium slurry every 10 minutes, mix and knead it evenly to ensure the uniformity of bleaching. After each stage of bleaching, it is washed with water, and then proceeds to the next stage of bleaching.
1.5 Slurry analysis and detection
GB/T8940.2-2002 and GB/T7974-2002 were used for the preparation and whiteness measurement of slurry whiteness samples respectively; GB/T1548-2004 was used for slurry viscosity measurement.
2. Results and discussion
2.1 Target analysis
According to the needs of customers, the main technical indicators of high viscosity pulp for cellulose ether are: whiteness ≥ 85%, viscosity ≥ 1800 mL/g, α-cellulose ≥ 90%, ash content ≤ 0.1%, iron ≤ 12 mg /kg etc. According to the company’s many years of experience in the production of special cotton pulp, by controlling the appropriate cooking conditions, washing and acid treatment conditions in the bleaching process, α-cellulose, ash, iron content and other indicators, it is easy to meet the requirements in actual production. Therefore, the whiteness and viscosity are taken as the focus of this experimental development.
2.2 Cooking process
The cooking process is to destroy the primary wall of the fiber with sodium hydroxide under a certain cooking temperature and pressure, so that the water-soluble and alkali-soluble non-cellulose impurities, fat and wax in the cotton linters are dissolved, and the content of α-cellulose is increased. . Due to the cleavage of cellulose macromolecular chains during the cooking process, the degree of polymerization is reduced and the viscosity is reduced. If the degree of cooking is too light, the pulp will not be cooked thoroughly, the subsequent bleaching will be poor, and the product quality will be unstable; if the degree of cooking is too heavy, the cellulose molecular chains will depolymerize violently and the viscosity will be too low. Comprehensively considering the bleachability and viscosity index requirements of the slurry, it is determined that the viscosity of the slurry after cooking is ≥1900 mL/g, and the whiteness is ≥55%.
According to the main factors that affect the cooking effect: the amount of alkali used, the cooking temperature, and the holding time, the orthogonal test method is used to conduct experiments to select the appropriate cooking process conditions.
According to the extremely poor data of the orthogonal test results, the influence of the three factors on the cooking effect is as follows: cooking temperature > alkali amount > holding time. The cooking temperature and the amount of alkali have a great influence on the viscosity and whiteness of cotton pulp. With the increase of the cooking temperature and the amount of alkali, the whiteness tends to increase, but the viscosity tends to decrease. For the production of high-viscosity pulp, moderate cooking conditions should be adopted as much as possible while ensuring whiteness. Therefore, in combination with the experimental data, the cooking temperature is 115°C, and the amount of alkali used is 9%. The effect of holding time among the three factors is relatively weaker than that of the other two factors. Since this cooking adopts a low-alkali and low-temperature cooking method, in order to increase the uniformity of cooking and ensure the stability of cooking viscosity, the holding time is selected as 70 minutes. Therefore, the combination A2B2C3 was determined to be the best cooking process for high-viscosity pulp. Under the production process conditions, the whiteness of the final pulp was 55.3%, and the viscosity was 1945 mL/g.
2.3 Bleaching process
2.3.1 Pre-chlorination process
In the pre-chlorination section, a very small amount of sodium hypochlorite is added to the cotton pulp to convert the lignin in the cotton pulp into chlorinated lignin and be dissolved. After bleaching in the pre-chlorination stage, the viscosity of the slurry must be controlled to be ≥1850 mL/g, and the whiteness ≥63%.
The amount of sodium hypochlorite is the main factor affecting the bleaching effect in this section. In order to explore the appropriate amount of available chlorine, the single factor test method was used to carry out 5 parallel experiments at the same time. By adding different amounts of sodium hypochlorite in the slurry, the effective chlorine in the slurry The chlorine content was 0.01 g/L, 0.02 g/L, 0.03 g/L, 0.04 g/L, 0.05 g/L respectively. After bleaching, the viscosity and BaiDu.
From the changes of cotton pulp whiteness and viscosity with the amount of available chlorine, it can be found that with the increase of available chlorine, the whiteness of cotton pulp increases gradually, and the viscosity gradually decreases. When the amount of available chlorine is 0.01g/L and 0.02g/L, the whiteness of cotton pulp is ≤63%; when the amount of available chlorine is 0.05g/L, the viscosity of cotton pulp is ≤1850mL/g, which does not meet the pre-chlorination requirements. Segment bleaching control indicator requirements. When the amount of available chlorine is 0.03g/L and 0.04g/L, the indicators after bleaching are viscosity 1885mL/g, whiteness 63.5% and viscosity 1854mL/g, whiteness 64.8%. The dosage range is in line with the requirements of the bleaching control indicators in the pre-chlorination section, so it is preliminarily determined that the available chlorine dosage in this section is 0.03-0.04g/L.
2.3.2 Hydrogen peroxide stage bleaching process research
Hydrogen peroxide bleaching is the most important bleaching stage in the bleaching process to improve the whiteness. After this stage, a stage of acid treatment is carried out to complete the bleaching process. The acid treatment stage plus the subsequent papermaking and forming stage has no effect on the viscosity of the pulp, and can increase the whiteness by at least 2%. Therefore, according to the control index requirements of the final high-viscosity pulp, the index control requirements of the hydrogen peroxide bleaching stage are determined to be viscosity ≥ 1800 mL/g and whiteness ≥ 83%.
The main factors affecting hydrogen peroxide bleaching are the amount of hydrogen peroxide, bleaching temperature, and bleaching time. In order to achieve the whiteness and viscosity requirements of high viscous pulp, the three factors affecting the bleaching effect were analyzed by orthogonal test method to determine the appropriate hydrogen peroxide bleaching process parameters.
Through the extreme difference data of the orthogonal test, it is found that the influence of the three factors on the bleaching effect is: bleaching temperature > hydrogen peroxide dosage > bleaching time. The bleaching temperature and the amount of hydrogen peroxide are the main factors affecting the bleaching effect. With the gradual increase of the data of the two factors of the bleaching temperature and the amount of hydrogen peroxide, the whiteness of the cotton pulp increases gradually, and the viscosity gradually decreases. Considering the production cost, equipment capacity and product quality comprehensively, the hydrogen peroxide bleaching temperature is determined to be 80°C, and the hydrogen peroxide dosage is 5%. At the same time, according to the experimental results, the bleaching time of hydrogen peroxide has little influence on the bleaching effect, and the single-stage bleaching time of hydrogen peroxide is selected as 80 minutes.
According to the selected hydrogen peroxide stage bleaching process, the laboratory has carried out a large number of repeated verification experiments, and the experimental results show that the experimental parameters can meet the set target requirements.
3. Conclusion
According to the customer’s requirements, through single factor test and orthogonal test, combined with the company’s actual equipment capacity and production cost, the production process parameters of high-viscosity pulp for cellulose ether are determined as follows: (1) Cooking process: use 9% of alkali, cook The temperature is 115°C, and the holding time is 70 minutes. (2) Bleaching process: in the pre-chlorination section, the dosage of available chlorine for bleaching is 0.03-0.04 g/L; in the hydrogen peroxide section, the bleaching temperature is 80°C, the dosage of hydrogen peroxide is 5%, and the bleaching time is 80 minutes ; Acid treatment section, according to the company’s conventional process.
High viscosity pulp for cellulose ether is a special cotton pulp with wide application and high added value. On the basis of a large number of experiments, the company independently developed the production process of high-viscosity pulp for cellulose ether. At present, high-viscosity pulp for cellulose ether has become one of the Kima Chemical company’s main production varieties, and the product quality has been unanimously recognized and praised by customers at home and abroad.