The effects of temperature on rinse performance.
Changes in water temperature can affect the operating capacity and effluent quality levels of ion exchange systems to some degree.
Changing the temperature changes the degree of ionization. This has a much greater effect on systems that are only slightly ionized than systems that are nearly fully ionized. Therefore, temperature changes have a greater effect on the weakly basic and weakly acidic ion exchange resins, than for the strongly basic or strongly acidic ion exchange resins.
Increasing temperatures tends to increase the diffusion rate of ions, which make ion exchange reactions occur more rapidly. It is reasonable to expect that increasing temperatures will result in sharper exhaustion zones, more rapid exchange rates, and therefore higher capacity and better quality. However, higher temperatures can cause increased solubilities for ions, such as silica that are left at the bottom of the bed from a previous cycle, increasing silica leakage. It can also reduce the relative affinities of ions, making it easier for monovalent ions like sodium, to displace higher amounts of divalent ions like calcium in water softening applications.
STRONG ACID CATION EXCHANGE RESINS
Increasing operating temperatures will increase the diffusion rates, which shortens the length of bed necessary to achieve the desired quality. This means a greater portion of the bed is used during the service cycle, which leads to a higher operating capacity. Increasing or decreasing the temperature a few degrees has little and sometimes no noticeable effect on operating capacity.
STRONG BASE ANION EXCHANGE RESINS
Operating temperatures have more of an effect on strongly basic resins when they are run to a silica endpoint then for strongly basic resins run to a conductivity endpoint, because of the effect on silica. Higher temperatures increases the rate of silica ionization, which allows it to be removed more rapidly, and therefore results in higher utilization of the bed. On the other hand, higher operating temperatures increase silica solubility and cause greater leakages during the operating cycle. When strongly basic resins are run in a salt cycle exchange or in an acid absorption mode where silica endpoints are not involved, the temperature effect on capacity is minimal.
WEAK ACID CATION EXCHANGE RESINS
Weakly acidic resins are very slightly ionized. Consequently, the exchange zone is very long and very sensitive to flow rate. Increasing the water temperature increases the degree of disassociation which shortens the exchange zone. This increases the operating capacity and also the effluent quality at the same time. Changes of 10ºF can make significant changes in the operating capacity of these resins when they are operated in the hydrogen cycle.
WEAK BASE ANION EXCHANGE RESINS
Weakly basic resins are largely not disassociated and operate primarily as acid absorbers. Increased operating temperature can result in higher leakages and reduced capacity, but kinetics are enhanced so the net result may be a slight increase in capacity. Effluent quality is not significantly affected in weakly basic resins.