Refining of Hydroxyethyl Cellulose

Hydroxyethyl cellulose (HEC for short) is a white or light yellow, odorless, non-toxic, non-ionic fiber or powder, which is etherified from alkaline cellulose and ethylene oxide (or chlorohydrin). HEC is soluble in hot and cold water and has no gelling properties. It has a wide range of substitution degrees, solubility and viscosity, good thermal stability (below 140°C), and does not precipitate under acidic conditions. HEC solution can form a transparent film. It has non-ionic characteristics that are incompatible with positive and negative ions, and has good compatibility. Therefore, it can be used as coating agent, adhesive, cement and gypsum additive, thickener, suspending agent and medicine, excipient, anti-fogging agent, oil well fracturing fluid, drilling treatment agent, fiber and paper sizing Agents, cosmetics, toothpaste, etc.

After the etherification of HEC is completed, it needs to be refined. The refining process includes neutralization, cross-linking, washing, filtering and drying. The neutralizing agent is usually an organic acid, such as one or more of acetic acid, propionic acid and formic acid.

When neutralized with organic acids such as acetic acid, propionic acid or formic acid, the following disadvantages occur:

1. The neutralized material has swelling phenomenon, the appearance is viscous, and the material has a certain viscosity, which will block the filter cloth;

2. The water content of the material is high, reaching about 65-80%. When the filter cake is formed by a centrifuge or a filter press, the material will be pressed too densely and tightly due to the swelling degree of the material. When the washing liquid continuously enters the filter cake for washing, the pressure of the washing liquid reaches the highest pressure that the filter press can withstand. Therefore, the washing liquid flow rate is small, and the device operation flexibility is small;

3. Due to the large molecular weight of the organic acid, the solubility of the formed sodium salt in the washing solvent is low, and the ash content of the product after washing cannot be reduced below 5%. Therefore, the material entering the dryer has a high moisture content and may need to be washed and dried again.

4. After drying, the material is relatively hard and rough due to two times of washing and drying. During the pulverization process, the crushing load is heavy, the temperature at the top of the pulverizer reaches 80°C and 120°C, and the crushing capacity decreases.

To sum up, the current use of organic acids as neutralizers leads to complicated follow-up processes, high production costs, and low quality of refined hydroxyethyl cellulose products.

Another commonly used neutralizing agent is an inorganic acid with a concentration of 15-90%, which can effectively remove alkaline substances in crude hydroxyethyl cellulose pulp. The concentration of inorganic acid is preferably 35-50%, and 40-50% is the best. The inorganic acid is at least one or more of sulfuric acid, phosphoric acid, nitric acid or hydrochloric acid. When the material is neutralized with mineral acids, the following advantages are obtained:

1. The appearance of the neutralized material is sandy. After etherification, it is suspended in the solvent and can be washed continuously by a drum type continuous filter press washing device. The material is evenly distributed on the filter screen, washed with aqueous organic solvent under a certain pressure, and washed and separated at the same time. Moreover, the washing pressure of each section is not high during washing, which is beneficial to the flexibility of the filter press.

2. Inorganic acid is cheaper than organic acid, easier to buy in the market, stable source, and guaranteed quality.

3. After the inorganic acid neutralizing material is washed, dried and pulverized, the appearance of the product has high whiteness and dispersibility, and the product has good stability. In addition, the continuous production line greatly improves production efficiency, reduces the labor intensity of workers, improves the intrinsic safety of the production line, and reduces the consumption of energy and raw materials.