Using cellulose as raw material, CMC-Na was prepared by a two-step method. The first is the alkalization process of cellulose. The cellulose reacts with sodium hydroxide to generate alkali cellulose, and then the alkali cellulose reacts with chloroacetic acid to generate CMC-Na, which is called etherification.
The reaction system must be alkaline. This process belongs to the Williamson ether synthesis method. The reaction mechanism is nucleophilic substitution. The reaction system is alkaline, and it is accompanied by some side reactions in the presence of water, such as sodium glycolate, glycolic acid and other by-products. Due to the existence of side reactions, the consumption of alkali and etherification agent will be increased, thereby reducing the etherification efficiency; Simultaneously, sodium glycolate, glycolic acid and more salt impurities can be generated in the side reaction, causing the purity and performance reduction of the product. In order to suppress side reactions, it is necessary not only to use alkali reasonably, but also to control the amount of water system, the concentration of alkali and the stirring method for the purpose of sufficient alkalization. At the same time, the requirements of the product on viscosity and degree of substitution should be considered, and the stirring speed and temperature should be considered comprehensively. Control and other factors, increase the rate of etherification, and inhibit the occurrence of side reactions.
According to different etherification media, the industrial production of CMC-Na can be divided into two categories: water-based method and solvent-based method. The method using water as the reaction medium is called the water medium method, which is used to produce alkaline medium and low-grade CMC-Na. The method of using organic solvent as the reaction medium is called the solvent method, which is suitable for the production of medium and high-grade CMC-Na. These two reactions are carried out in a kneader, which belongs to the kneading process and is currently the main method for producing CMC-Na.
Water medium method：
The water-borne method is an earlier industrial production process, which is to react alkali cellulose and etherification agent under the conditions of free alkali and water. During alkalization and etherification, there is no organic medium in the system. The equipment requirements of the water media method are relatively simple, with less investment and low cost. The disadvantage is the lack of a large amount of liquid medium, the heat generated by the reaction increases the temperature, accelerates the speed of side reactions, leads to low etherification efficiency, and poor product quality. The method is used to prepare medium and low-grade CMC-Na products, such as detergents, textile sizing agents and the like.
Solvent method：
The solvent method is also called the organic solvent method, and its main feature is that the alkalization and etherification reactions are carried out under the condition of an organic solvent as the reaction medium (diluent). According to the amount of reactive diluent, it is divided into kneading method and slurry method. The solvent method is the same as the reaction process of the water method, and also consists of two stages of alkalization and etherification, but the reaction medium of these two stages is different. The solvent method saves the process of soaking alkali, pressing, crushing, aging and so on inherent in the water method, and the alkalization and etherification are all carried out in the kneader. The disadvantage is that the temperature controllability is relatively poor, and the space requirement and cost are high. Of course, for the production of different equipment layouts, it is necessary to strictly control the system temperature, feeding time, etc., so that products with excellent quality and performance can be prepared.
Post time: Apr-25-2024