It is well known that anion resins are susceptible to fouling by the humic and fulvic acids sometimes found in surface waters.
These organic species, because of the relatively large molecular weights, become trapped within the resin matrix (to a greater or lesser degree depending upon the resin) and specific procedures have to be employed to cause recovery of the original ion exchange properties of the resin.
The symptoms of organic fouling include long rinse requirements, poor capacity and, in the case of strong base resins, higher silica leakage.
Treatment
The most common forms of treatment involve the use of brine solution; the procedure is as follows :-
The resin should be treated at the end of the normal exhaustion cycle.
Three bed volumes of 10% w/v brine solution containing 2% w/v caustic soda should be prepared.
One bed volume should be introduced into the ion exchange unit at a flow rate not exceeding 2 BV’s per hour followed by a second bed volume -this second bed volume should be retained in the unit for as long as possible, but at least 4 hours. Some agitation, if possible, should be employed periodically throughout the retention period.
At the end of the retention period the last bed volume of brine should be passed through the resin at a rate of 1 BV per hour and the resin thoroughly rinsed with clean water until free from brine.
The resin should be subject to at least two complete regeneration cycles before being put back on line.
N.B. Brine at minimum 35°C should be employed or preferably as high as 60°C so as to produce a better organic elution effect.
Iron/Organic Complexes
This subject is covered to some extent in the section on iron fouling.
Occasionally the presence of iron is detected on the anion resin. This can arise from an iron/organic complex being present in the raw feed water.
In these cases, it is advisable to consider treatment of the anion resin with 6% hydrochloric acid immediately after the brine treatment. The procedure that should be followed is similar to that given for brining.
It is extremely important that all traces of hydrochloric acid are removed from the unit before introduction of the caustic soda regenerant.
It is important to ensure that the materials of construction are suitably resistant to hydrochloric acid.
Ion exchange takes away undesirable ions from the raw waters by simply shifting it to a solid substance, known as an ion exchanger, that takes these at the same time providing back again an comparable quantity of suitable varieties located in the ion exchanger skeleton.
The ion exchanger possesses a minimal ability to store ions upon it’s skeletal system, known as it’s exchange capacity; due to this, the actual ion exchanger ultimately will become exhausted of it’s desired ions and over loaded with undesirable ions. It’s after that washed using a powerful regenerating treatment that contains the desired varieties of ions, and all of these after that exchange the accrued undesired ions, returning the exchange material back to a functional condition. This particular procedure can be described as a cyclic chemical process, and the whole pattern typically consists of backwashing, regeneration, rinsing, as well as service.
The first ion exchangers were actually inorganic sodium aluminosilicates, a number of which were being produced synthetically while others produced by processing organic greensand, that is known as a mineral referred to as zeolite, in to much more stable, greater capacity forms. Despite the fact that these types of zeolites have merely minimal usage for water treatment, the title has persisted, and also artificial organic ion exchangers are usually called zeolites.
The ion exchangers found in water conditioning are skeleton like systems possessing many ion exchange sites. The insoluble plastic-type material skeletal system is an significantly sizeable ion that’s electrically charged to support ions of reverse charge. As a result, the ion exchanger is associated with the polyelectrolytes used by coagulation and also flocculation, but intentionally designed really at high level in molecular weight as to become fundamentally insoluble. Exchangers having negatively charged sites are cation exchangers simply because they consume positively charged ions. Anion exchangers have got positively charged sites and, as a result, occupy negative ions. The plastic material structure is permeable, therefore the whole ion exchange particle participates in the operation.
In the industry implementing ion exchange to water treatment, you will find a number of essential concepts:
1. The majority of ion exchange systems are pretty straight forward vessels comprising a bed of ion exchange resin controlled downflow on a cyclic basis: a unit is controlled to a established loss level, in which it’s regarded as exhausted, the unit is next regenerated, first through upflow cleaning (backwash) after which by chemical elution, downflow, the resin bed is next washed downflow. Since equally water and regenerant flow in the very same path, water departing the system is connected with the resin obtaining the greatest amount of contaminating ions, so quality and also performance each are affected.
2. The ion exchange bed possesses a substantially greater capacity than is required, simply because uneconomical excesses of regenerating chemical can be necessary to transform the resin completely to the sought after ion form. For instance, the cation resin might possess a capacity of 2 N (about 44 kgr/ft3), but approximately 1 / 2 of it (20 to 22 kgr/ft3) is employed regarding sodium cycle conditioning. Consequently, there’s always a higher concentration of contaminating ions, calcium supplement in this instance, around the resin with a possibility of spoiling the actual treated water level of quality.
3. As a result of cyclic operation with cocurrent flow of water and regenerant, chemical
usage within regenerating ion exchange resins is commonly bad. This particular disadvantage is most obvious with strong resins. For instance, within the sodium cycle, in the event the utilised capability is 21 kgr as CaCO3 per cubic ft . (48 kg/m3) of resin, the sodium necessary is in theory only 58.5/50 X 3 = 3.5 IbNaCl/ft3. The specific salt usage is commonly six to ten Ib NaCl ft3, therefore the proficiency is approximately thirty to fifty %. Acid functionality with regard to hydrogen exchange employing a sulfonic-type resin and H2SO4 for regeneration, and caustic effectiveness with regard to regeneration of strong base anion resins tend to be even worse, around twenty to forty %. Conversely, weak cation resins (carboxylic type) as well as weak anion resins (amine type) are usually controlled at approximately 100% chemical effectiveness.
4. The majority of ion exchange resources employed in water treatment come in the size selection of twenty to fifty mesh, or approximately 0.5 mm efficient size. As a result an ion exchange bed is an effective filtration system, a attribute possessing both pros and cons. This particular filtering capability is coupled with ion exchange properties in creating commercial condensate polishing systems using ion exchange beds. However the filtering capability additionally results in fouling and erratic operating runs. Oftentimes it is due to the build up of excessive microbial populations within an exchanger bed.
Purolite C120E
Cheapest softening resin for domestic softeners, cartridges, and small industrial units. Has lowest resistance to oxidative attack, but is more open structure offers excellent kinetic performance. The E suffix indicates the resin is a Purolite food grade product.
Purolite C100E
This is the most widely used Purolite softening resin. This product is used in a wide range of softening applications from domestic through to large industrial units. The E suffix indicates the resin is a Purolite food grade product. Has been used as a food grade demin cation resin on small IWT plants.
Purolite C100
This industrial grade product was traditionally called a premium grade softening resin. Due to its higher strength it can be used in softening and demineralisation and offers excellent physical strength over a wide range of operating conditions. With its higher DVB content it offers a higher capacity and a greater resistance to oxidative attack by chlorine compared to C120E/C100E.
Purofine PFC100E
The Purofine trade name indicates that these are narrow grade versions of our Purolite C100E. The absence of large beads gives these resins enhanced physical strength, and its more uniform grading offers lower rinse water requirements and lower pressure loss in service. This resin is popular as it also offers a higher working capacity as the reduced diffusion path means more sites are regenerated and at low regeneration levels these resins offer significantly higher working capacity compared to their standard grade counterparts. This grading can also be used in all counter flow regenerated systems.
Puropack PPC100
The Puropack trade name indicates that these are narrow grade versions of our Purolite C100. Like the Purofine PFC100E the absence of large beads gives these resins enhanced physical strength, and improved as outlined for PFC100E but has a higher resistance to oxidative attack than PFC100E. It has also been used in high flow rate softeners where the load is small and the bed volume per hour rate is high. This grading can also be used in all counter flow regenerated systems but the grading is slightly different to Purofine as it has been selected to give optimum performance in counter flow regenerated packed bed systems employing either up flow or down flow service.
Purolite C100EAg
This version of Purolite C100E is a softening resin to which a small quantity of silver is present. This gives the resin some bacteriostatic properties which help to prevent the build up of bacteria and organic growth on the beads. All ion exchange resins have the potential to be breeding ground for bacteria etc. particularly where the bed is in intermittent use or where it has long periods out of service, particularly if the water or softener becomes warm.
Purolite C150
This is the most robust of all the softening resins and is normally recommended when very high temperatures and or where thermal shock is likely (*Note: Purolite C100 and PFC100 have also seen successful operation in hot softening). Its macroporous structure ensures that the effect of thermal shock resulting in premature breakdown when moving from high service temperatures to lower regeneration water temperatures is minimised. Due to its significantly higher DVB content this resin offers the greatest resistance to attack by chlorine of all the resins referred to in this summary.
Purolite C104
This weak acid cation resin has replaced Purolite C105 and is now the main weak acid cation resin used for dealkalisation. It is a direct replacement for Purolite C105 and can be mixed with C105. The product is mainly used as a standard grade product but can be supplied in special grades for specific applications. For example our DL grade (Purolite C104DL) is used where the resin works in a double layer (stratified) unit. There the resin sits on top of a DL grade of a strong acid cation resin. This is most commonly encountered in a demineralisation plant but we have supplied DL grade weak acid cation resins to work with a strong acid cation softening resin (Purolite Cl00DL) as a combined dealkalisation / softener unit. This unit is regenerated with acid first and then brine.
Purolite C104E
This is a food grade version of Purolite C104 and this type of resin is widely used within the brewing and soft drinks industry to produce water for lagers and the production of soft drinks. It has UK approval as a weak acid cation resin for potable water applications.
Purolite C107E
This weak acid cation resin is sold in large volumes for use in drinking water filters, jug filters, steam ovens and high quality vending machine cartridges and is often used in conjunction with activated carbon. This combination results in a better quality and better tasting water. The carbonic acid formed on waters with high temporary hardness gives the water a sparkling appearance. This resin is not normally used in regenerated systems. In drinking water filter applications it is used to not only to reduce temporary hardness but it will also remove trace levels of metals present and it will continue to work as a heavy metals removal resin even when the resin is exhausted to temporary hardness. Special grades / mixes of this product are available to cater for clients specific requirements.
Purolite C106
This is not commonly encountered in water treatment. Weak acid cation resins can be used in some chemical processes or applications where greater osmotic strength is required. Under these circumstances a fully macroporous weak acid cation resin is of benefit such as Purolite C106.
Purolite AC20G
Granular Activated carbon – available in 52 litre bags.
Purolite A400MBOHIND and Purolite A500MBOHIND
Anion indicator resins in OH form, used in HCl vent lines to polish out fumes with colour change indication to show exhaustion. It is normally used in transparent cartridges to witness colour change.
Purolite NRW100QR
This is a cation indicator resin used by very many power stations prior to an after cation conductivity cell. It is used normally to show in leakage on cooling water / condenser systems. By using this cation indicator resin they remove conditioning amines and hence any conductivity change is due to anions present. This therefore indicates a condenser leak.
Purolite PD206
Biodiesel polishing resin to enable producers to meet international specifications for commercial sale
Purolite IP1
Floating inert – large round beads for use in packed beds where large volume of inert is required, giving lower pressure drop than IP4.
Purolite IP4
Floating inert – small rods, used to provide a barrier to stop resin contacting top distributors, and improve top distribution / collection.
Purolite IP9
Under drain inert – replaces gravel systems. High density polymer which will help provide additional support to bottom laterals which are not always adequately supported and can fail. This product can help to retain some of the resin in the event of a bottom system failure.
Purolite MPR1000
The most interesting product launched in 2010 was Purolite MPR1000. MPR stands for Membrane Protection Resin. This product combines two anion resins, an acrylic organic scavenger resin with a colloid removal resin. It is used prior to RO plants operating on difficult waters where they struggle to give the required throughput and have to be regularly chemically cleaned. Regenerated with salt or salt with caustic this can reduce SDI levels significantly improving water quality and RO performance.
Cyclic – IEx
This is a new process introduced by purolite using our SST (Shallow Shell Technology) and is a special softening resin where the core of the bead is inert and the product is used for softening RO water either in the primary stage or secondary stage to increase RO efficiency to over 90%. This is used on higher TDS RO plants because the softening resin can be regenerated using the RO reject with no added salt required.
Chelating Resin Improvement
Many of our customers know the products S920, S930 and S940 used for metals recovery / removal. 2010 saw Purolite launch a new product Purolite S930 Plus. The performance has been dramatically improved, and now compares favourably with all our competitors products.
SST Cation Resins
Some new SST (Shallow Shell Technology) cation resins have been developed and added to our range. They are now widely sold in the Americas. These are cation resins with an inert core which means with a standard grade resin you can get enhanced performance in some applications.
PAD Adsorbents
New range of synthetic adsorbents introduced covering more than 12 products, designed for the increasing demand for these products in IWT and other applications.