Hydroxyethyl Cellulose (HEC) is a common water-soluble polymer widely used in daily chemicals, construction, coatings, medicine, food and other industries. It is a non-ionic cellulose ether made by chemically modifying natural cellulose. The manufacturing process of hydroxyethyl cellulose involves complex chemical reactions, including cellulose extraction, alkalization treatment, etherification reaction, etc. The following is a detailed introduction to its manufacturing process.
1. Selection of raw materials and extraction of cellulose
The basic raw material of hydroxyethyl cellulose is natural cellulose, which mainly comes from wood, cotton or other plant fibers. The cellulose content in plant cell walls is high, and pure cellulose can be extracted from these natural materials by mechanical or chemical means. The extraction process includes crushing, removal of impurities (such as lignin, hemicellulose), bleaching and other steps.
Cellulose extraction: Natural cellulose is usually mechanically or chemically treated to remove non-cellulose substances to obtain high-purity cellulose. Cotton fiber, wood pulp, etc. can all be common sources of raw materials. During the treatment process, alkali (such as sodium hydroxide) is used to help dissolve non-cellulose components, and the remaining is mainly cellulose.
2. Alkalization treatment
The purified cellulose must first be alkalized. This step is to make the hydroxyl groups on the cellulose molecular chain more active so that they can react more easily with the etherifying agent. The main steps of the alkalization treatment are as follows:
Reaction of cellulose with alkali: cellulose is mixed with a strong alkali (usually sodium hydroxide) to produce alkali cellulose (Alkali Cellulose). This process is usually carried out in an aqueous medium. Alkali cellulose is the reaction product of cellulose and sodium hydroxide. This substance has a looser structure and higher reactivity, which is conducive to the subsequent etherification reaction.
The alkalization process mainly occurs at appropriate temperature and humidity, usually in the range of 20℃~30℃ for several hours to ensure that the hydroxyl groups in the cellulose molecules are fully activated.
3. Etherification reaction
Etherification is a key step in the production of hydroxyethyl cellulose. Hydroxyethyl cellulose is produced by reacting alkali cellulose with ethylene oxide to introduce hydroxyethyl groups. The specific steps are as follows:
Reaction with ethylene oxide: Alkali cellulose reacts with a certain amount of ethylene oxide under certain temperature and pressure conditions. The ring structure in ethylene oxide opens to form an ether bond, reacts with the hydroxyl groups in the cellulose molecules, and introduces hydroxyethyl groups (–CH2CH2OH). This process can adjust the degree of etherification by controlling the reaction conditions (such as temperature, pressure, and time).
The reaction is usually carried out in an alkaline environment to ensure the efficiency of etherification. The reaction temperature is generally 50℃~100℃, and the reaction time is several hours. By adjusting the amount of ethylene oxide, the degree of substitution of the final product can be controlled, that is, how many hydroxyl groups in the cellulose molecules are replaced by hydroxyethyl groups.
4. Neutralization and washing
After the etherification reaction is completed, the alkaline substances in the reaction system need to be neutralized. Commonly used neutralizers are acidic substances, such as acetic acid or hydrochloric acid. The neutralization process will neutralize the excess alkali into salts, which will not affect the performance of the product.
Neutralization reaction: Take the product out of the reactor and add an appropriate amount of acid for neutralization until the pH value in the system reaches neutral. This process not only removes residual alkali, but also reduces the impact of reaction by-products on the performance of hydroxyethyl cellulose.
Washing and dehydration: The neutralized product needs to be washed several times, usually with water or ethanol and other solvents to wash away residual impurities and by-products. The washed product is dehydrated by centrifugation, filter pressing and other methods to reduce the moisture content.
5. Drying and crushing
After washing and dehydration, the hydroxyethyl cellulose still contains a certain amount of moisture and needs to be further dried. The drying process can be carried out by air drying or vacuum drying to ensure that the product has good stability during storage and use.
Drying: Dry the product at a certain temperature (usually below 60°C) to remove residual moisture. The drying temperature should not be too high, otherwise it may cause product degradation and affect its performance.
Crushing and screening: The dried hydroxyethyl cellulose usually exists in blocks or lumps, and must be crushed to obtain fine powder. The crushed product also needs to be screened to obtain a particle size distribution that meets the requirements to ensure its solubility and dispersibility in practical applications.
6. Testing and packaging of final products
After manufacturing, hydroxyethyl cellulose needs to be tested for quality to ensure that its performance indicators meet the standard requirements. Testing items usually include:
Viscosity measurement: The viscosity of hydroxyethyl cellulose after dissolving in water is an important quality indicator, which affects its use in coatings, construction, daily chemicals and other fields.
Moisture content: Test the moisture content of the product to ensure its storage stability.
Degree of substitution (DS) and molar substitution (MS): Determine the degree of substitution and molar substitution in the product through chemical analysis to ensure the effect of the etherification reaction.
After passing the test, hydroxyethyl cellulose will be packaged into powder or granular products, usually in moisture-proof plastic bags or paper bags to prevent it from getting damp or contaminated.
The manufacturing process of hydroxyethyl cellulose mainly includes the steps of cellulose extraction, alkalization treatment, etherification reaction, neutralization and washing, drying and crushing. The whole process depends on the alkalization and etherification in the chemical reaction, and the cellulose is given good water solubility and thickening properties by introducing hydroxyethyl groups. Hydroxyethyl cellulose is widely used in many industries, such as thickener for coatings, water-retaining agent for building materials, stabilizer in daily chemical products, etc. Each link in the production process needs to be strictly controlled to ensure the high quality and stable performance of the product.
Post time: Oct-25-2024