How to improve Cellulose Ether Production?

Kima Chemical Co.,Ltd would like to introduce the improvement of cellulose ether production process and equipment in the last ten years, and analyzes the different characteristics of kneader and coulter reactor in cellulose ether production process. With the rapid development of the cellulose ether industry, the production capacity of a single set of equipment is transitioning from hundreds of tons to several thousand tons. It is an inevitable trend for new equipment to replace old equipment.

Key words: cellulose ether; production equipment; kneader; coulter reactor

Looking back on the past ten years of China’s cellulose ether industry, it is a glorious decade for the development of the cellulose ether industry. The production capacity of cellulose ether has reached more than 250,000 tons. In 2007, the output of CMC was 122,000 tons, and the output of non-ionic cellulose ether was 62,000 tons. 10,000 tons of cellulose ether (in 1999, China’s total cellulose ether output was only 25,660 tons), accounting for more than a quarter of the world’s output; a number of thousand-ton-level enterprises have successfully entered the ranks of 10,000-ton-level enterprises; product varieties have increased significantly , The product quality has been steadily improved; behind all this is the further maturity of the process technology and the further improvement of the production equipment level. Compared with the foreign advanced level, the gap has been significantly narrowed.

This article introduces the latest development of domestic cellulose ether production process and equipment improvement in recent years, and introduces the work done by Zhejiang Chemical Industry Research Institute in researching and developing cellulose ether production equipment based on the theory and thinking of green chemical industry. Research work on cellulose ether alkalization etherification reactor.

1. Production technology and equipment of domestic cellulose ether CMC in the 1990s

Since Shanghai Celluloid Factory developed the water-medium process in 1958, the single-equipment low-power solvent process and other production processes have been used to produce CMC. Domestically, kneaders are mainly used for etherification reactions. In the 1990s, the annual production capacity of a single production plant CMC of most manufacturers was 200-500 tons, and the mainstream models of etherification reaction were 1.5m³ and 3m³ kneaders. However, when the kneader is used as the reaction equipment, because of the slow speed of the kneading arm, the long etherification reaction time, the high proportion of side reactions, the low utilization rate of the etherification agent, and the poor uniformity of the etherification reaction substituent distribution, the main reaction conditions For example, the controllability of bath ratio, alkali concentration and kneading arm speed is poor, so it is difficult to realize the approximate homogeneity of etherification reaction, and it is even more difficult to conduct mass transfer and permeation research of deep etherification reaction. Therefore, the kneader has certain limitations as the reaction equipment of CMC, and it is the bottleneck of the development of the cellulose ether industry. The inadequacies of the mainstream models of etherification reaction in the 1990s can be summarized in three words: small (small output of a single device), low (low utilization rate of etherification agent), poor (etherification reaction replaces The uniformity of the base distribution is poor). In view of the defects in the structure of the kneader, it is necessary to develop a reaction equipment that can speed up the etherification reaction of the material, and the distribution of the substituents in the etherification reaction is more uniform, so that the utilization rate of the etherification agent is higher. In the late 1990s, many domestic cellulose ether enterprises hoped that Zhejiang Research Institute of Chemical Industry would research and develop production equipment urgently needed by the cellulose ether industry. Zhejiang Research Institute of Chemical Industry began to get involved in the research of powder mixing process and equipment in the 1970s, formed a strong R & D team, and achieved gratifying results. Many technologies and equipment have been awarded by the Ministry of Chemical Industry and Zhejiang Science and Technology Progress Award. In the 1980s, we cooperated with the Tianjin Fire Research Institute of the Ministry of Public Security to develop special equipment for the production of dry powder, which won the third prize of the Ministry of Public Security’s Science and Technology Progress Award; in the 1990s, we researched and developed solid-liquid mixing technology and equipment. Aware of the future development prospects of the cellulose ether industry, the researchers of the Zhejiang Provincial Research Institute of Chemical Industry began to research and develop special production equipment for cellulose ether.

2. The development process of special reactor for cellulose ether

2.1 Features of coulter mixer

The working principle of the coulter mixer is that under the action of the plowshare-shaped agitator, the powder in the machine is turbulent along the cylinder wall in the circumferential and radial directions on the one hand, and the powder is thrown along the two sides of the plowshare on the other hand. The trajectories of the movement are criss-crossed and collide with each other, thus generating a turbulent vortex and forming a full range of three-dimensional space movement. Due to the relatively poor fluidity of the fibrous reaction raw materials, other models cannot drive the circumferential, radial and axial movements of the cellulose in the cylinder. Through the research on the CMC production process and equipment of the cellulose ether industry at home and abroad, making full use of its 30 years of research results, the coulter mixer developed in the 1980s was initially selected as the basic model for the development of cellulose ether reaction equipment .

2.2 Development process of coulter reactor

Through the test of a small experimental machine, it has indeed obtained a better effect than the kneader. However, when they are directly used in the cellulose ether industry, there are still the following problems: 1) In the etherification reaction, the fluidity of the fibrous reaction raw material is relatively poor, so the structure of its coulter and flying knife is not sufficient. Drive the cellulose to move in the circumferential, radial and axial directions of the barrel, so the mixing of the reactants is not sufficient, resulting in low utilization of the reactants and relatively few products. 2) Due to the poor rigidity of the main shaft supported by ribs, it is easy to cause eccentricity after operation and the problem of shaft seal leakage; therefore, the outside air easily invades the cylinder through the shaft seal and affects the vacuum operation in the cylinder, resulting in powder in the cylinder. Escape. 3) Their discharge valves are flapper valves or disc valves. The former is easy to inhale outside air due to poor sealing performance, while the latter is easy to retain materials and cause loss of reactants. Therefore, these problems must be solved one by one.

Researchers have improved the design of the coulter reactor many times, and provided it to several cellulose ether enterprises for trial use, and gradually improved the design according to the feedback. By changing the structural shape of the coulters and the staggered arrangement of two adjacent coulters on both sides of the main shaft, the reactants under the action of the coulters not only turbulence in the circumferential and radial directions along the inner wall of the cylinder, but also Splash along the normal direction of both sides of the coulter, so the reactants are fully mixed, and the alkalization and etherification reactions completed in the mixing process are thorough, the utilization rate of the reactants is high, the reaction speed is fast and the energy consumption is low . Moreover, the shaft seals and bearing seats at both ends of the cylinder are fixed to the end plate of the bracket through the flange to increase the rigidity of the main shaft, so the operation is stable. At the same time, the sealing effect of the shaft seal can be ensured because the main shaft does not bend and deform, and the powder in the cylinder does not escape. By changing the structure of the discharge valve and enlarging the diameter of the exhaust tank, it can not only effectively prevent the retention of materials in the discharge valve, but also prevent the loss of material powder during exhaust, thus effectively reducing the loss of reaction products. The structure of the new reactor is reasonable. It can not only provide a stable and reliable preparation environment for cellulose ether CMC, but also effectively prevent the powder in the cylinder from escaping by improving the airtightness of the shaft seal and the discharge valve. Environmentally friendly, realizing the design idea of green chemical industry.

2.3 Development of coulter reactor

Due to the defects of small, low, and poor kneaders, the coulter reactor has entered many domestic CMC production plants, and the products include six models of 4m³, 6m³, 8m³, 10m³, 15m³, and 26m³. In 2007, the coulter reactor won the national Utility model patent authorization (patent publication number: CN200957344). After 2007, a special reactor for non-ionic cellulose ether production line (such as MC/HPMC) was developed. At present, the domestic production of CMC mainly adopts the solvent method.

According to the current feedback from cellulose ether manufacturers, the use of coulter reactors can reduce solvent usage by 20% to 30%, and with the increase in production equipment, there is a potential for further reduction in solvent usage. Since the coulter reactor can reach 15-26m³, the uniformity of substituent distribution in the etherification reaction is much better than that of the kneader.

3. Other production equipment of cellulose ether

In recent years, while developing cellulose ether alkalization and etherification reactors, other alternative models are also under development.

Air lifter (patent publication number: CN200955897). In the solvent method CMC production process, the rake vacuum dryer was mainly used in the solvent recovery and drying process in the past, but the rake vacuum dryer can only be operated intermittently, while the air lifter can realize continuous operation. The air lifter crushes the CMC material through the rapid rotation of coulters and flying knives in the cylinder to increase the heat transfer surface, and sprays steam into the cylinder to fully volatilize ethanol from the CMC material and facilitate recovery, thereby Reduce the production cost of CMC and save ethanol resources, and complete the operation of the cellulose ether drying process at the same time. The product has two models of 6.2m³and 8m³.

Granulator (patent publication number: CN200957347). In the process of producing cellulose ether by solvent method, twin-screw extrusion granulator was mainly used in the past to granulate the sodium carboxymethyl cellulose material after etherification reaction, washing and drying. The ZLH type cellulose ether granulator can not only granulate continuously like the existing twin-screw extrusion granulator, but also can continuously remove materials by feeding air into the cylinder and cooling water into the jacket. React waste heat, thereby improving the quality of granulation, and saving electricity, and can increase the product output rate by increasing the spindle speed, and can adjust the height of the material level according to the process requirements. The product has two models of 3.2m³and 4m³.

Airflow mixer (patent publication number: CN200939372). MQH type airflow mixer sends compressed air into the mixing chamber through the nozzle on the mixing head, and the material instantly rises spirally along the cylinder wall with the compressed air to form a fluidized mixing state. After several pulse blowing and pause intervals, The rapid and uniform mixing of materials in the full volume can be realized. Differences between different batches of product are brought together by blending. At present, there are five types of products: 15m³, 30m³, 50m³, 80m³, and 100m³.

Although the gap between my country’s cellulose ether production equipment and foreign advanced levels is being further narrowed, it is still necessary to further improve the process level and make further improvements to address the problems that are not compatible with the current production equipment.

4. Outlook

my country’s cellulose ether industry is actively developing the design and processing of new equipment, and combining the characteristics of the equipment to continuously improve the process. Manufacturers and equipment manufacturers have begun to jointly develop and apply new equipment. These all reflect the progress of my country’s cellulose ether industry. , this link will have an important impact on the development of the industry. In recent years, my country’s cellulose ether industry, based on the technology with Chinese characteristics, has either absorbed international advanced experience, introduced foreign devices, or made full use of domestic equipment to complete the transformation from the original “dirty, messy, poor” and labor-intensive workshop production to The transition of mechanization and automation to achieve a great leap in production capacity, quality and efficiency in the cellulose ether industry has become the common goal of my country’s cellulose ether manufacturers.