The basic properties of ion exchange resins include the following aspects, which are briefly described as follows:
1、 Appearance of resin
The new resin has various colors such as yellow, brown, white, brown, black, gray, etc. due to different factors such as structure, functional groups, ion morphology, and manufacturing process, to meet the needs of different occasions in specific use. The appearance of resins commonly used for water treatment is generally as follows: gel type styrene resin is generally transparent yellowish particles; Macroporous resins, on the other hand, are opaque (or slightly transparent) particles; Macroporous styrene based cation resins generally have light yellow or light grayish brown particles, while macroporous styrene based anion resins have white particles; Acrylic resins are white or milky white particles. The same resin will undergo color changes in different ion forms, such as the color of 001x7 resin changing from deep to light, from failure to re ecology, and then from light to deep. This change can be reversed,
When a resin is contaminated, its color will also undergo fundamental changes, and the degree of color change is generally proportional to the degree of resin contamination, and it is difficult to reverse. Therefore, during the use of resin, it is necessary to always pay attention to the changes in its color to determine the degree of resin contamination. When 201x7 resin is contaminated with iron or organic matter, the color becomes darker or even dark brown. When 001x7 resin is damaged by oxidants, its resin cross-linking and exchange groups will be oxidized, the color of the resin will also become lighter, the resin volume will increase, and thus the resin is fragile and the volume exchange capacity will decrease.
2、 Particle size
The particle size and uniformity of the resin have a significant impact on its operation. The larger the particle size, the smaller the specific surface area, and the slower the exchange speed; The particle size is too small, although the exchange speed is fast, the resistance during operation is also large; Therefore, the national standard specifies a relatively reasonable particle size range (refer to the national standard) based on the resin model corresponding to different exchanger bed types (different bed types have different operating flow rates).
3、 Swelling and transformation volume change rate of resin
Resins in a dry state (excluding inert resins) will rapidly expand when exposed to water. Therefore, when the resin is dehydrated, it should not be in direct contact with water, but should be soaked in saturated salt water to slow down the expansion rate and prevent the resin from cracking.
The coefficient of expansion varies with the degree of crosslinking of the resin, and the magnitude of the volume change rate is inversely proportional to the degree of crosslinking. The size of the exchange capacity is directly proportional to the swelling rate.
The higher the valence of exchangeable ions, the smaller the swelling rate. The stronger the hydration ability of isovalent ions, the greater the swelling rate.
Of course, the law of resin transformation expansion rate is more complex in practical applications, as it often involves the exchange of multiple ions. However, mastering these rules has important reference value for designing expansion spaces reserved for different exchanger bed types (especially for double chamber fixed beds, double chamber floating beds, etc.).
4、 Moisture
The equilibrium water content in the particles of a certain ion type resin is an inherent characteristic of the resin. The water content of the same resin varies with different ion forms. Therefore, national standards also specify the water content of various resins in specific ionic states. During the use of resin, its water content will also change as various factors damage it. Therefore, the change in resin moisture content is also one of the criteria for determining the degree of resin damage.
5、 Density
The density of resin is a frequently used data in its use. Due to the fact that resins generally operate in a wet state, the most commonly used are wet true density and wet apparent density.
Wet true density refers to the mass of wet resin per unit true volume. True volume refers to the volume occupied by resin particles themselves, excluding the volume of voids between particles.
The wet true density of the same batch of resins with different particle sizes is the same. The wet true density determines the settling speed of the resin and directly affects the characteristics of the backwash expansion rate. Therefore, in mixed bed, double bed, and triple bed resins with strict requirements for backwash layering, there are also strict range requirements for their wet true density.
Wet apparent density refers to the mass of wet resin per unit apparent volume. Apparent volume, also known as stacking volume or apparent volume, includes the inherent volume of resin particles themselves and the volume of voids between particles. The wet apparent density of the same batch of resin varies with different particle sizes. The conversion between weight and volume during resin filling is done using wet apparent density.
Based on the wet true density and wet true density, the porosity in the resin layer can be estimated as follows:
P=1-d visual/d true
In the formula: P refers to the porosity of the resin;
D refers to the apparent density of the resin;
D refers to the true density of the resin;
6、 Exchange capacity
There are various ways to express the exchange capacity of resins, with the most commonly used being weight full exchange capacity, volume full exchange capacity, and working exchange capacity. Full crosslinking is the inherent capacity of the reaction resin and is a constant value. On the other hand, work handover is a variable that reflects the capacity of resin in actual work. It is determined by numerous on-site factors and is related to factors such as process design, equipment production, operating methods, quality of regenerants, human factors, and the quality of media. It will be introduced later.
7、 Heat resistance
The temperature tolerance range of various resins varies, and exceeding this value has a certain impact on their lifespan.
At room temperature (10-30 ℃), the basic properties of the resin will not change, but at very high temperatures, the resin will undergo some changes. The general rule of heat resistance stability of resins is that cation resins have better temperature resistance than anion resins; Resin produced by addition polymerization has better temperature resistance than resin produced by condensation polymerization; Salt based resins have better temperature resistance than free acid or free alkali based resins (excluding weak acid and weak alkali resins); Type I strong alkali resin has better temperature resistance than type II strong alkali resin; Weak alkali resins have better temperature resistance than strong alkali resins; Styrene based resins have better temperature resistance than acrylic based resins.
General requirements for the most commonly used resins in water treatment (not at such high temperatures in actual use):
The cation resin has good temperature resistance, and strong acid cation resin can withstand a temperature of 120 ℃; The weak acid cation resin can be controlled at 80 ℃; The temperature of styrene based strong alkali resin shall not exceed 60 ℃, and the temperature of weak alkali resin shall not exceed 80 ℃; The temperature of acrylic based strong alkaline resin should not exceed 35 ℃.
Understanding the temperature resistance characteristics of these commonly used resins has certain reference value for resin selection in the early stages of design.
8、 Frost resistance of resin
According to practical experience, the frost resistance of macroporous resin is better than that of gel resin, and the frost resistance of gel anion resin is better than that of cation resin; Resin has better frost resistance in water than in air. The preservation methods of resins in different states will be introduced later.