W9 Issue 22 Instruction Manual

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Ion Exchange Apparatus

Instruction Manual W9

ISSUE 22

August 2011





Table of Contents

iii

Laboratory Teaching Exercises................................................................................. 16

Index to Exercises ................................................................................................. 16

Water Softening Theory......................................................................................... 16

Regeneration Theory............................................................................................. 16

Demineralisation Theory........................................................................................ 17

Resin Volume and Density .................................................................................... 18

Exchange Capacity................................................................................................ 18

Data Sheet I........................................................................................................... 18

Data Sheet II.......................................................................................................... 20

Data Sheet III......................................................................................................... 23

Data Sheet IV ........................................................................................................ 23

Exercise A................................................................................................................. 25

Exercise B................................................................................................................. 27

Exercise C................................................................................................................. 29

Exercise D................................................................................................................. 32

Contact Details for Further Information..................................................................... 33





1

Disclaimer

This document and all the information contained within it is proprietary to ArmfieldLimited. This document must not be used for any purpose other than that for which itis supplied and its contents must not be reproduced, modified, adapted, published,translated or disclosed to any third party, in whole or in part, without the prior written

permission of Armfield Limited.

Should you have any queries or comments, please contact the Armfield CustomerSupport helpdesk (Monday to Thursday: 0830 – 1730 and Friday: 0830 - 1300 UKtime). Contact details are as follows:

United Kingdom International (0) 1425 478781

(calls charged at local rate)+44 (0) 1425 478781

(international rates apply) Email: [email protected]

Fax: +44 (0) 1425 470916

Copyright and Trademarks

Copyright © 2011 Armfield Limited. All rights reserved.

Any technical documentation made available by Armfield Limited is the copyrightwork of Armfield Limited and wholly owned by Armfield Limited.

Brands and product names mentioned in this manual may be trademarks orregistered trademarks of their respective companies and are hereby acknowledged.



2

General Overview

Ion exchange is a natural process in which ions held on the surface of a soliddisplace other ions, of similar and equivalent electrical charge, from a solution incontact with the solid. The displaced ions become attached (ie. held by electrostaticattraction) to the surface, while those originally on the surface go into solution. This

process of exchange continues until the relative concentration of the two types ofions, on the surface and in solution, reach equilibrium. The process is reversible, thedirection of the exchange depending upon these relative concentrations.

The simplest example of practical ion exchange is in the softening of water, whenCa2+ ions in the water (causing hardness) are exchanged for Na+ ions on theexchange material. When equilibrium is reached, i.e. when the exchange capacity ofthe material is exhausted, it can be regenerated by applying a concentrated solutionof a sodium salt, usually sodium chloride, to restore Na+ ions on the surface.

By the use of suitable ion exchange materials in two or more stages it is possible toremove all dissolved salts from solution - the process of demineralisation.

The ion exchange apparatus described in this manual enables both softening anddemineralisation to be studied.

Besides these uses in the treatment of water supplies, ion exchange processes arealso widely employed in industry.

History

The phenomenon of ion exchange was discovered in the middle of the nineteenthcentury, when H.S.M. Thompson observed that ammonium sulphate fertilizer appliedto soil emerged as a solution of calcium sulphate. In 1850-54 the process was closely

studied by J.T. Way, Consulting Chemist to the Royal Agricultural Society in England.He found that many forms of ion exchange occurred in various soils, and that thematerials involved were complex hydrated aluminosilicates, known as zeolites. Waywas able to prepare artificial aluminosilicates with ion exchange properties.

The first practical use of ion exchange in water treatment was by the German R.Gans in 1905, when he used a synthetic material to soften water, regenerating it withsodium chloride.

Since then, the range of synthetic materials has been greatly extended, with theintroduction of sulphonated coals by Liebknicht in 1934, phenol-formaldehyde resinsby Adams and Holmes in 1935 and polymerization resins based on styrene, by

d’Alelio in 1944. The properties sought in the newer synthetic materials includephysical and chemical stability as well as greatly increased exchange capacities.They can be made as either cation- or anion-exchangers and by using both types inseries demineralization is possible. The first commercial ion-exchangedemineralization plant was installed in 1937 at a brewery in Guildford, England.



3

Equipment Diagrams

Figure 1: W9 Ion Exchange Apparatus



4

Important Safety Information

Introduction

All practical work areas and laboratories should be covered by local safetyregulations which must be followed at all times.

It is the responsibility of the owner to ensure that all users are made aware ofrelevant local regulations, and that the apparatus is operated in accordance withthose regulations. If requested then Armfield can supply a typical set of standardlaboratory safety rules, but these are guidelines only and should be modified asrequired. Supervision of users should be provided whenever appropriate.

Your W9 Ion Exchange Apparatus has been designed to be safe in use wheninstalled, operated and maintained in accordance with the instructions in this manual. As with any piece of sophisticated equipment, dangers exist if the equipment ismisused, mishandled or badly maintained.

Electrical SafetyThe equipment described in this Instruction Manual operates from a mains voltageelectrical supply. It must be connected to a supply of the same frequency and voltageas marked on the equipment or the mains lead. If in doubt, consult a qualifiedelectrician or contact Armfield.

The equipment must not be operated with any of the panels removed.

To give increased operator protection, the unit incorporates a Residual CurrentDevice (RCD), alternatively called an Earth Leakage Circuit Breaker, as an integralpart of this equipment. If through misuse or accident the equipment becomes

electrically dangerous, the RCD will switch off the electrical supply and reduce theseverity of any electric shock received by an operator to a level which, under normalcircumstances, will not cause injury to that person.

At least once each month, check that the RCD is operating correctly by pressing theTEST button. The circuit breaker MUST trip when the button is pressed. Failure totrip means that the operator is not protected and the equipment must be checked andrepaired by a competent electrician before it is used.

Wet Environment

The storage tanks on the equipment require filling and draining in use. During use itis possible that there will be some spillage and splashing.

All users should be made aware that they may be splashed while operatingthe equipment, and should wear appropriate clothing and non-slip footwear.

‘Wet Floor’ warnings should be displayed where appropriate.

Electrical devices in the vicinity of the equipment must be suitable for use inwet environments or be properly protected from wetting.



Important Safety Information

5

High Pressure

This apparatus is designed to operate with internal pressures greater than that of thesurrounding atmosphere.

The feed pump can produce more flow that is required by the process so it is

important to adjust the bypass on the feed pump to allow liquid to return to thefeed tank and avoid excessive pressure in the pipework. The setting of theclip on the bypass tubing is described in the Commissioning section.

Ensure that the selector valves are set correctly to configure the flow throughthe apparatus before switching on the feed pump. This will avoid excessivepressure in the system.

Heavy Equipment

This apparatus is heavy.

The apparatus should be placed in a location that is sufficiently strong tosupport its weight, as described in the Installation section of the manual.

Chemical Safety

Details of the chemicals intended for use with this equipment are given in theOperational Procedures section. Chemicals purchased by the user are normallysupplied with a COSHH data sheet which provides information on safe handling,health and safety and other issues. It is important that these guidelines are adheredto.

It is the user’s responsibility to handle chemicals safely.

Prepare chemicals and operate the equipment in well ventilated areas.

Only use chemicals specified in the equipment manuals and in theconcentrations recommended.

Follow local regulations regarding chemical storage and disposal.

Water Borne Hazards

The equipment described in this instruction manual involves the use of water, whichunder certain conditions can create a health hazard due to infection by harmfulmicro-organisms.

For example, the microscopic bacterium called Legionella pneumophila will feed onany scale, rust, algae or sludge in water and will breed rapidly if the temperature ofwater is between 20 and 45°C. Any water containing this bacterium which is sprayedor splashed creating air-borne droplets can produce a form of pneumonia calledLegionnaires Disease which is potentially fatal.

Legionella is not the only harmful micro-organism which can infect water, but itserves as a useful example of the need for cleanliness.

Under the COSHH regulations, the following precautions must be observed:

Any water contained within the product must not be allowed to stagnate, ie.

the water must be changed regularly.



Armfield Instruction Manual

6

Any rust, sludge, scale or algae on which micro-organisms can feed must beremoved regularly, i.e. the equipment must be cleaned regularly.

Where practicable the water should be maintained at a temperature below20°C. If this is not practicable then the water should be disinfected if it is safeand appropriate to do so. Note that other hazards may exist in the handling ofbiocides used to disinfect the water.

A scheme should be prepared for preventing or controlling the riskincorporating all of the actions listed above.

Further details on preventing infection are contained in the publication “The Controlof Legionellosis including Legionnaires Disease” - Health and Safety Series bookletHS (G) 70.



7

Description

Where necessary, refer to the drawings in the Equipment Diagrams section.

Overview

All numerical references relate to Figure 1. Also refer to the schematic diagramshowing the valve positions in Data Sheet III.

The apparatus, which is designed for experiments on both water softening anddemineralisation, is supplied split into two major components; a backboard (1)incorporating the main process components and a sump tank arrangement (14) forstoring and pumping the associated liquids.

Ion exchange takes place inside two vertical transparent columns (5 & 6), ofapproximately 16mm internal diameter, mounted on the backboard via manifolds atthe top (7) and bottom (2). In use the left hand column (5) contains Cation exchangeresin (golden coloured granules) and the right hand column (6) contains Anion

exchange resin (white coloured granules).

The manifolds at the top (7) and bottom (2) of the columns are fitted with leveroperated isolating valves which allow the flow to be directed through one or bothcolumns, in either direction, to suit the process requirements. Screwed connectorsfitted with ‘O’ ring seals (3) allow the columns to be removed for cleaning or changingthe type of exchange resin.

The liquids to be passed through the exchange columns are stored in the sump tankarrangement (14) to the left of the apparatus and supplied via a pump (12) andflowmeter (9). The liquids are selected by lifting and traversing the sliding tubearrangement (13) at the front of the sump tank. The pump is operated using the

electrical switch (4) at the right hand side of the process backboard and is connectedvia an in-line electrical connector (16). The flexible tube from the pump outlet to theselector assembly returns excess liquid to the feed tank for reuse. An adjustablepinch valve (19) on the bypass tube is adjusted to give the correct flow conditions.This valve must not be fully closed to avoid excess pressure in the system.

A flow control valve (10) at the base of the flowmeter allows the flow of water,regenerating solution etc. to be adjusted as required. A distribution manifold (8)above the flowmeter allows the pumped liquid to be supplied to the top of the Anioncolumn, to the top of the Cation column or to the base of both columns as required bythe process, simply by opening the appropriate lever operated valve.

After passing through the columns the treated water, exhausted regenerating solutionor wash water is fed to an effluent storage tank at the rear of the sump tankarrangement via flexible tube (11) from the top of the columns or flexible tube (17)from the bottom of the columns. This tank incorporates a lever operated valve (15) tofacilitate draining. Lever operated valves (V4, V10 or V16) allow samples of water tobe collected for analysis if required.

The equipment includes a battery operated digital conductivity meter (19) that isconnected to an inline sensor (18) in the return line (17) to the effluent tank. Thisallows the quality of the water emerging from the ion exchange column(s) to bemonitored.




8

The various processes involved in the experiments are as follows:

a. Water to be softened, which will pass downwards through the Cationexchanger only.

b. Water to be demineralised, which will pass downwards through the Cation

exchanger and then upwards through the Anion exchanger.

c. Regeneration solutions (followed by distilled or demineralised water forflushing), which are stored in separate tanks, and will pass downwardsthrough either the Cation or the Anion exchange column.

d. Water (preferably distilled or demineralised) which will pass upwards througheither column to flush out any sediment and to release any air trapped in theresin.



9

Installation

Adv isory

Before operating the equipment, it must be unpacked, assembled and installed asdescribed in the steps that follow. Safe use of the equipment depends on following

the correct installation procedure.

Installation may be completed using a basic tool kit.

Electrical Supply

Electrical supply for version W9-A

The equipment requires connection to a single phase, fused electrical supply. Thestandard electrical supply for this equipment is 220-240V, 50Hz. Check that thevoltage and frequency of the electrical supply agree with the label attached to thesupply cable on the equipment. Connection should be made to the supply cable as

follows:

GREEN/YELLOW - EARTH

BROWN - LIVE (HOT)

BLUE - NEUTRAL

Maximum Current - 1 AMP

Electrical supply for version W9-B

The equipment requires connection to a single phase, fused electrical supply. The

standard electrical supply for this equipment is 120V, 60Hz. Check that the voltageand frequency of the electrical supply agree with the label attached to the supplycable on the equipment. Connection should be made to the supply cable as follows:


BROWN - LIVE (HOT)

BLUE - NEUTRAL


Note: Version W9-B consists of a W9-G with a loose transformer to step-up the 120Vsupply to 220V to suit the equipment. The transformer should be sited adjacent to the120V mains outlet socket in the laboratory, in a dry location. The mains lead from theW9-G is simply plugged into the 220V outlet socket on the front of the transformer.

Where a 220V electrical supply is available in the laboratory, the mains lead from theW9-G can be connected directly to the 220V electrical socket in the laboratory (step-up transformer not used).




10

Electrical supply for version W9-G

The equipment requires connection to a single phase, fused electrical supply. Thestandard electrical supply for this equipment is 220V, 60Hz. Check that the voltageand frequency of the electrical supply agree with the label attached to the supplycable on the equipment. Connection should be made to the supply cable as follows:


BROWN - LIVE (HOT)

BLUE - NEUTRAL


Installing the Equipment

All numerical references relate to Figure 1.

Position the equipment in the desired location on a firm level bench, with regard tothe service connections listed in Electrical Supply above. Locate the sump tankarrangement to the left hand side of the process backboard.

The diaphragm pump (12) is removed to avoid damage during transit and should beattached to the mounting plate on top of the sump tank assembly (14) using thefixings provided. The easiest method may be to insert the screws from underneath,with the nuts positioned on the outside of the tank assembly.

Connect the sliding tube arrangement (13) at the front of the tank to the pump (12)using the flexible tubing supplied. The tube which projects furthest into the tankshould be connected to the side connection on the pump inlet (see Connection 1).

The tube with the shortest projection should be connected to one side of the T-connector on the pump outlet (see Connection 2).

Connection 1

Connection 2



Installation

11

Connect the inlet of the control valve (10) at the bottom of the flowmeter (9) to theoutlet of the pump using the flexible tubing supplied.

Connect the two flexible effluent return tubes (11) from the top manifold and (17)from the inline conductivity electrode to the tappings on the side of the tank

assembly.

Connect the two parts of the inline electrical connector (16) between the pump (12)and the rear of electrical switch (4) on the process backboard.

Install the battery in the conductivity meter following the instructions supplied with theconductivity meter.

Connect the lead from the conductivity electrode to the socket at the top of theconductivity meter.

The equipment is ready for commissioning.

Commissioning

All numerical references refer to Figure 1 in the Equipment Diagrams. Also refer tothe schematic diagram showing the valve positions in Data Sheet III.

It is suggested that clean tap water is used for initial testing of the equipment.

1. Ensure the equipment has been assembled in accordance with theinstructions in the Assembly section above.

2. Fill the four supply tanks at the front of the sump tank arrangement (14) withclean tap water (l litre approximately).

3. Ensure that the drain valve (15) on the effluent tank is closed.

4. Lift the selector tube (13) and confirm that it will traverse along to each of thefour compartments.

5. Connect the equipment to the electrical supply and confirm satisfactoryoperation of the RCD by pressing the TEST button (Refer to the notes onElectrical Safety). Reset the RCD.

6. Check all flexible connections are secure and all valves are closed.

7. Open the flow control valve at the base of the flowmeter and set the valve to

approximately mid-position.




12

8. Move the selector (13) to tank C (Test Water), open valves V3 and V6 thenswitch on the pump and allow the pump to prime. Water will flow through thebypass and return to tank C. Gradually close the Hoffman clip on the flexiblebypass tube until the flow through the flowmeter becomes steady, indicatedby a steady reading on the float. If necessary adjust the flow control valve togive a reading on the flowmeter while adjusting the bypass.

9. When the bypass is correctly adjusted, excess water will be returned to tankC when the flow control valve is closed avoiding over pressurisation of thepump and pipework. If the bypass is too far open then oscillation of the flowwill be visible in the flowmeter. If the bypass is closed too far then the systemmay become over pressurised which could result in damage to the systemand leakage of fluid.

10. Open valves V3 and V9 then check that water returns to the sump tank afterflowing upwards through the Cation column (6). Close both valves.

11. Open valves V2 and V12 and check that water returns to the sump tank after

flowing downwards through the Cation column (6). Close both valves.

12. Connect a flexible tube to sample valve V10 or place a container beneath thevalve. Open valves V2 and V10. Check that water flows from valve V10.Close both valves.

13. Open valves V3 and V9, check that water returns to the sump tank afterflowing upwards through the Anion column (5). Close both valves.

14. Open valves V1 and V15, check that water returns to the sump tank afterflowing downwards through the Anion column (5). Close both valves.

15. Open valves V2, V13 and V15, check that water returns to the sump tankafter flowing downwards through the Cation column (6) then downwardsthrough Anion column (5). Close all three valves.

16. Connect a flexible tube to sample valve V16 or place a container beneath thevalve. Open valves V2, V13 and V16. Check that water flows from valve V16.Close all three valves.

17. Open the drain valve (15) on the effluent tank and ensure that it operatescorrectly. Close the valve.

18. Connect the lead from the inline conductivity sensor to the socket marked

INPUT at the top of the conductivity meter. Switch on the conductivity meter(9) by pressing the Power button. Check that the meter indicates theconductivity and temperature of the water (a series of dashes in the displayindicates that the selected range is not correct – move the range selectorswitch until the conductivity of the water is indicated).

19. Check the equipment for any leaks.



13

Operation

Operating the Equipment

Refer to the Laboratory Teaching Exercises for details on operating the equipment.

Operation of the Conductiv ity Meter

The conductivity meter is supplied separately and is designed to sit on the bench topalongside the equipment. The conductivity meter is powered by an internal 9 volt PP3 Alkaline battery.

An inline conductivity sensor is installed at the outlet from the bottom manifold so thatit can monitor the conductivity of the water following the ion exchange process. Thelead from the inline sensor is connected to the socket marked INPUT at the top of theconductivity meter.

To operate the conductivity meter, press the POWER button and adjust the positionof the range switch until the meter indicates the Conductivity and Temperature.Dashes in the display indicate that the range switch is in the wrong position andshould be adjusted to suit. The meter gives a direct reading of conductivity, correctedfor temperature, in units of micro Siemens (μS) or milli Siemens (mS) depending onthe position of the range switch.

For further information on the conductivity meter refer to the instruction leafletsupplied with the equipment.



14

Equipment Specifications

Overall Dimensions

Height - 0.9m

Width - 1.1m

Depth - 0.45m

Electromagnetic Compatibility

This apparatus is classified as Education and Training Equipment under theElectromagnetic Compatibility (Amendment) Regulations 1994. Use of the apparatusoutside the classroom, laboratory or similar such place invalidates conformity with theprotection requirements of the Electromagnetic Compatibility Directive (89/336/EEC)and could lead to prosecution.

Equipment LocationThe equipment is fully self-contained and is designed to be bench mounted.

The equipment requires connection to a single phase, fused electrical supply. Fourmetres of supply cable are provided with the equipment.

A source of clean water will be required for filling the sump tank and a suitable drainfor disposing of effluent from the equipment (involving dilute hydrochloric acid, dilutesodium hydroxide and dilute sodium chloride).

A mains electrical supply is required to operate this product. Refer to ElectricalSupply in the Installation section.

Environmental Conditions

This equipment has been designed for operation in the following environmentalconditions. Operation outside of these conditions may result reduced performance,damage to the equipment or hazard to the operator.

a. Indoor use;

b. Altitude up to 2000m;

c. Temperature 5°C to 40°C;

d. Maximum relative humidity 80% for temperatures up to 31°C, decreasinglinearly to 50% relative humidity at 40°C;

e. Mains supply voltage fluctuations up to ±10% of the nominal voltage;

f. Transient over-voltages typically present on the MAINS supply;

Note: The normal level of transient over-voltages is impulse withstand (over-voltage) category II of IEC 60364-4-443;

g. Pollution degree 2. Normally only nonconductive pollution occurs. Temporaryconductivity caused by condensation is to be expected. Typical of an office or

laboratory environment.



15

Routine Maintenance

Responsibility

To preserve the life and efficient operation of the equipment it is important that theequipment is properly maintained. Regular maintenance of the equipment is the

responsibility of the end user and must be performed by qualified personnel whounderstand the operation of the equipment.

General

Disconnect the equipment from the electrical supply when not in use.

Clean the storage tanks with distilled or deionised water and flush both columns ifdifferent solutions and resins are to be used.

Drain any effluent contained in the sump tank after every experiment to a suitablelaboratory drain.

The conductivity sensor is usually cleaned adequately by passing clean waterthrough the system after use. However, the sensor can be removed from the inlinehousing if manual cleaning of the electrodes becomes necessary. To remove thesensor, unscrew the large sealing plug on the side of the housing (opposite the leadfrom the sensor) then push the sensor through the opening. The sensor can betotally removed by passing the plug through the opening. The sensor body is sealedinto the housing using an ‘O’ ring. This should be lubricated with soapy water beforereinserting the sensor into the inline housing after cleaning. Push the sensor fully intothe housing then replace the large sealing plug.



16

Laboratory Teaching Exercises

Index to Exercises

Exercise A

Exercise B

Exercise C

Exercise D

Water Softening Theory

The most usual ion exchange material employed in water softening is a sulphonatedstyrene-based resin, supplied by the makers in the sodium form. This resin has astrong affinity for calcium and magnesium ions, and will also remove ferrous ionsafter the more or less complete removal of calcium and magnesium.

Softening can be carried out as a batch process by stirring a suspension of the resinin the water for a period until equilibrium, or an acceptable level of hardness, isreached.

However, it is more convenient to operate a continuous flow process by passing thewater slowly downwards through a column of resin beads. The exchange reactiontakes place rapidly enough for the upper layers of the bed to approach exhaustionbefore the lower layers being able to exchange ions. There is thus, a zone of activeexchange which moves down the column until the resin at all depths becomesexhausted. The position at an intermediate stage can be illustrated as shown below.

When the zone of active exchange reaches the bottom of the column, the emergingwater begins to show an increasing hardness. This is the breakthrough point, when itbecomes necessary to regenerate the resin with a strong sodium chloride solution.

Regeneration Theory

Theoretically, for every millequivalent (meq) of hardness as CaCO3 removed from thewater under treatment, one millequivalent of NaCl is required for regeneration, ie. 1gof hardness as CaCO3 removed requires 1.17g NaCl for regeneration (equivalent

weights: CaCO3 50.0; NaCl 58.5).




17

In practice it is not possible to achieve complete regeneration with this quantity ofNaCl, since this would require an unacceptable long contact period. Larger quantitiesof NaCl are therefore used, generally twice or more the theoretical amount. Theregeneration efficiency is thus around 50%.

A high level of regeneration gives a resin with a high exchange capacity approachingits theoretical, but it is uneconomic to operate at such a rate that this capacity is fullyused in softening. In other words, a high regeneration efficiency is associated with alow degree of column utilisation, and vice versa. The practical operation of an ion-exchange bed is therefore a compromise in which the regeneration efficiency and thecolumn utilisation are both in the region of 50%.

After regeneration, distilled or demineralised water is passed through the bed towash out any remaining regenerant.

Water to be treated by ion exchange must be free of suspended solids which wouldblock the passage-ways, reduce flow rates and interfere with the exchange process.To remove fine solids which may get into the bed, and to release any air pockets, the

column is backwashed periodically by an upward flow of water which fluidises thebed and agitates the resin beads.

The rate of flow of water through the bed in softening is usually not more than40ml/min per cm2 of surface area of bed. Regeneration rates are about one tenth ofthis.

Demineralisation Theory

The removal of all dissolved salts from water can be achieved by using a two-stageion exchange process. The water is first passed through a strong cation exchangerworking on the hydrogen ion cycle, when cations in the water are replaced by H+

ions, giving a solution of acids. This is then passed through an anion exchanger inthe hydroxyl ion form, when the acid ions are replaced by OH- ions, which with the H+ ions, produce water.

It is often sufficient to use a weakly basic anion exchanger, which will remove allanions except HCO3

- (due to dissolved carbon dioxide) and H3SiO4- (due to

dissolved silica).

For a higher quality product water, a strongly basic anion exchanger must be used asthe final stage, but it is generally more economical to precede this with a weaklybasic anion exchanger of high exchange capacity to remove the bulk of the anions,and a degassing tower to release CO2 from solution. The strongly basic resin is then

required only to remove silica and any residuals of other anions which may still bepresent. This process can reduce total dissolved solids to below 1mg/l.

Demineralisation can also be performed in a single stage by using a mixed bed ofstrong cation and anion exchangers. The water repeatedly comes in contact with thetwo resins alternately, and is ultimately of very high purity. To enable the two resinsto be regenerated with sulphuric acid and sodium hydroxide respectively, they arefirst stratified with an upward flow of water, the anion resin being of lower density andtherefore carried to the top. After regeneration, the two resins are re-mixed bycompressed air.




18

Resin Volume and Density

When dry ion-exchange resins are immersed in water the beads swell as a result ofhydration of the fixed and counter-ions (i.e. the attraction of water molecules to theions) and the repulsion between the fixed ions.

A distinction must therefore be made between the dry and wet volumes and densitiesof a resin. It is also important to wet a resin thoroughly, before placing in a testcolumn, in order to avoid damage as a result of the swelling.

The density of a resin can also be given as the true density, i.e. mass per unit volumeof the beads alone, or as the apparent density, i.e. mass per unit volume of the bed,including the voids. For typical resins the true wet density is usually between 1.1 and1.3 g/cm3, and the apparent wet density between 0.7 and 0.8 g/cm3.

The inside diameter of both exchange columns is approximately 16mm. For accurateresults it is suggested that the actual inside diameter of both columns is measuredand recorded before filling with exchange resin.

Exchange Capacity

The exchange capacity of a resin is a measure of the quantity of ions which can beexchanged per unit mass of volume of the resin. The theoretical exchange capacitymay be defined as the number of exchangeable ions which it contains per unit massor volume. In practice it is not feasible to provide a long enough contact period forcomplete equilibrium to be attained, nor is it economic to regenerate fully. Thepractical exchange capacity is therefore rather less than the theoretical.

It is expressed in various units, of which the most useful are probably millequivalents(meq) of exchanged ions per gram of dry resin, and meq/l of wet resin bed. In thesoftening of water it is also common practice to express the exchange capacity interms of mass of CaCO3 rather than millequivalents, the usual unit being kg CaCO3 /m3 of wet resin bed.

Data Sheet I

Backwash

Figure 2




19

Regenerate

Figure 3

Softening

Figure 4






21

Regenerate

Figure 7

Figure 8




22

Demineralise

Figure 9




23

Data Sheet III

Schematic Diagram of UOP7 showing valve positions

Data Sheet IV

To determine the hardness of a sample of water using Wanklyn soapsolution

Equipment required (not supplied by Armfield Ltd):

Burette, typically 100ml capacity

Stand for burette

Measuring cylinder, typically 250ml

Stoppered flask, typically 250ml capacity

Wanklyn soap solution, typically 1 litre

Procedure:

Install the burette in its stand and fill the burette with Wanklyn soap solution.




24

Measure the volume of the sample of water using the measuring cylinder. Eitheradjust the sample of water to a known volume eg. 50 or 100ml or note the actualvolume of the sample.

Transfer the sample of water from the measuring cylinder to the stoppered flask.

Titrate 1ml of soap solution into the stoppered flask. Insert the stopper and shake thecontents. Observe if a lather forms on the surface of the sample.

If no lather forms, titrate another 1ml of soap solution into the sample and shake thecontents.

Repeat the addition of soap solution until a lather forms. Note the amount of soapsolution added to the sample of water.

Calculation of Hardness:

Using Wanklyn soap solution, 1ml of soap solution = 1mg of CaCO3.

Hardness of water =

mg of caCO3 of water

Volume of water sample (ml)

For example, if 10ml of soap solution is titrated into a 100ml sample of water before alather forms, then the hardness of the water is:

= 200mg of caCO3 per litre of water



25

Exercise A

Objective

To determine the exchange capacity of a cationic resin in the softening of water.

ProcedureMake up 10 litres of water with a hardness of between 600 and 700 mg/l as CaCO3 by dissolving an appropriate amount of calcium chloride in tap water, after allowingfor the hardness already in the tap water. Determine the hardness of this solutionusing Wanklyn soap solution (described in Data Sheet IV) or other method, and placeit in the test water reservoir. (This is much harder than waters normally encountered,but is used here in order to keep the duration of the softening experiment withinreasonable limits).

Make up 500ml of 10% w/v NaCl solution by dissolving 50g NaCl in distilled water.Place this solution in regenerant tank B. Fill tank D with distilled or deionised water

(clean tap water can be used if more convenient).

Backwashing

See Data Sheet I, Figure 2 (Upward flow of water through the bed).

Backwashing removes any sediment from the bed, ensures that the resin beads arefully wetted and swollen and removes any air pockets which would interfere with theion-exchange process.

Fill the left hand cation exchanger column with cation resin (golden colouredgranules) to a depth of 300mm. Select tank D, open valves V3 and V6, andbackwash for five minutes at a flow sufficient to expand the bed by not more than

50% (typically 100 ml/min). Gradually turn off the flow and measure the final depth ofthe resin. Do not drain the bed as this would allow air to enter.

Regenerate

See Data Sheet I, Figure 3 (Downward flow of salt solution through the bed).

Select tank B, open valves V2, V12 (and V10 if a sample is required). Set flowmeterto not more that 50ml/min. Before the salt solution is fully used up, add distilled waterto the regenerant tank, continue the flow through the bed until the effluent no longertastes salty.

Softening

See Data Sheet I, Figure 4 (Downward flow of hard water through the bed).

Select tank C, open valves V2 and V10. Set flowmeter to between 50 and 70ml/min.

Collect samples of 500ml at five minute intervals. Determine hardness of eachsample. Continue the softening until the hardness of the effluent rises above 100mg/las CaCO3.




26

Results and Calculations

Plot the hardness readings against the volume of water treated and note thebreakthrough point at which the increase in hardness starts. Calculate the milligramsof hardness as CaCO3 removed from the water up to the breakthrough point.Graphically, this is given by the area between the curve plotted and the horizontalline, representing the original hardness of the water.

Knowing the wet volume of the resin bed, calculate the exchange capacity of theresin as meq/ml of wet volume.



27

Exercise B

Objective

To determine the regeneration efficiency of an ion-exchange softening system.

Procedure After completion of the experiment 'SOFTENING', ie. when the hardness exchangecapacity of the resin has been used up to just beyond the breakthrough point, carryout regeneration with 500ml of 10% w/v salt solution but this time collect the whole ofthis solution after it has passed through the bed (via valve no. V10), draining the bedin doing so.

(Note that having drained the bed in this experiment it will be necessary to backwashit (Data Sheet I, Figure 2) to expel air before carrying out any further experiments.)

Determine the sodium ion concentration in the collected regenerant by measuringNa+ (after dilution) by flame photometry or other means. Knowing the volume ofsolution collected calculate the meq of NaCl which has passed through the bed.Hence by subtraction from the original quantity of NaCl applied (20g or 342 meq),determine the meq of NaCl actually used in regeneration.

Compare this with the theoretical quantity of NaCl equivalent to the amount ofhardness removed in the experiment 'SOFTENING' and hence, calculate theefficiency of regeneration as a percentage.

The efficiency so calculated is based on the NaCl actually used in regeneration.However, in operation it is not possible to apply this quantity precisely, and an excesshas to be applied. Further experiments may therefore be carried out using differentquantities of NaCl for regeneration in solution from 5 to 10% in strength, in order todetermine practical regeneration efficiencies. In these experiments the procedureshould be as in the first experiment 'SOFTENING', ie. the used regenerant solutionshould not be collected, and the distilled water should be used to flush out the last ofthe regenerant from the bed. The efficiency will then be calculated by comparing thequantity of NaCl applied with the equivalent amount of hardness removed inexperiment 'SOFTENING'.

These regeneration experiments must, of course, be alternated with softeningexperiments so that softening capacity can be correlated with regeneration efficiency.


Final resin depth (mm) =

Sodium ion concentration (meq) =

Original quantity of NaCl = 342 meq (20g).

Amount of NaCl collected =





29

Exercise C

Objective

To study the demineralisation of water and to determine the exchange capacities of ahydrogen ion cation exchanger and an anion exchanger.

Procedure

Fill the left hand cation column to a depth of 300mm with a cation exchanger resin(golden coloured granules) in the hydrogen ion form. Fill the anion column to a depthof 300mm with an anion exchange resin (white coloured granules) in the hydroxylform. Fill tank A with 500ml of a 10% hydrochloric acid solution. Fill tank B with 500mlof a 5% sodium hydroxide solution. Fill tank C with 10 litres of test water containing800 to 1000mg/l of dissolved solids. Fill tank D with distilled or demineralised water. Iftap water is used, the concentrations of the principal cations and anions, as well asthe total dissolved solids, must be determined if not already known (eg. from thewater undertaking's figures). From a knowledge of the concentrations of the main

cations and anions in the water to be used, calculate the total strength in meq/litre.This will be used in calculating the exchange capacities of the two resins. Theelectrical conductivity should also be measured.

Additional equipment required (Not supplied by Armfield):

pH Meter

Stop Clock

Backwashing

See Data Sheet II, Figures 5 and 6 (Upward flow of water through the bed).

Each column should be separately backwashed in the manner described inexperiment 'SOFTENING'. In each case, the rate of backwashing should becontrolled to give not more than 50% expansion of the bed. Measure the final depthsof the two beds.

Regeneration (CATION)

See Data Sheet II, Figure 7 (Downward flow of acid through the cation bed).

Regenerate the cation exchanger. Select tank A, open valves V2 and V12. Follow theacid with distilled or demineralised water from tank D, to flush out any surplus acid.

Check pH of effluent and continue flushing until pH has returned to above 5.0.

Regeneration (ANION)

See Data Sheet II, Figure 8 (Downward flow of sodium hydroxide through the anionbed).

Regenerate the anion exchanger. Select tank B, open valves V1 and V15, followedby distilled or demineralised water from tank D until pH of the effluent has returned tobelow 9.0.

Demineralisation

See Data Sheet II, Figure 9 (Downward flow of test water through both columns inseries).




30

Select tank C, open valves V2, V13 and V15. Set flow rate to between 50 and70ml/min.

Note time at which flow is started and take conductivity readings at 5 minuteintervals. At 20 minute intervals draw off samples from valve V10 and measure thepH value.

Note the time when the conductivity of the demineralised water begins to rise, i.e. thebreakthrough point at which one of the resins has become exhausted. As soon aspossible after this point, take another small sample from valve no. V16 and measureits pH. If this pH is higher than the values previously recorded, it indicates that thecation exchanger has become exhausted. It is advisable to confirm this by drawingone or two further samples for pH determination.

The experiment should be stopped at this point, and the exchange capacity of thecation exchanger calculated. It is then possible to determine the exchange capacityof the anion exchanger in this experiment.

If, on the other hand, the pH of the cation exchanger effluent continues at a lowvalue, the rising conductivity of the final effluent indicates that the anion exchanger isexhausted, and its capacity can be calculated.

In the latter event, the exchange capacity of the cation exchanger can be determinedby continuing the flow of water through the first column only, collecting the waterwhich passes through it and measuring pH values until the breakthrough point, whenthe pH begins to rise.


In the demineralisation experiment, the breakthrough point is detected by readings ofpH (for the cation exchanger) or conductivity (for the anion exchanger) instead of bydirect measurement of concentrations as in the softening experiment.

In order to calculate the exchange capacities in terms of millequivalents, it isnecessary to convert pH or conductivity readings to meq/litre.

a. To convert pH values to meq/l

If pH reading is x

Hydrogen ion concentration = 10-x gram-moles/litre

= 103-x meq/litre

b. To convert conductivity values to meq/l

For water with a given content of salts, the electrical conductivity is closelyproportional to the concentration of total dissolved solids. Although thesesolids consist of several salts of varying electrolytic properties, it is sufficiently



Exercise C

31

accurate to assume that electrical conductivity is also proportional to the totalconcentration in terms of meq/litre.

The constant of proportionality was established by determination of theelectrical conductivity and the strength of meq/l of the raw water. Hence theelectrical conductivity of the demineralised water can be converted to meq/l.In any event these figures should be very low.

Final Depths: CATION =

ANION =

Exchange capacities can now be calculated.



32

Exercise D

Objective

To determine the regeneration efficiency of a cation resin and an anion resin.

ProcedureCATION RESIN

Fill tank A with 500ml of a 10% hydrochloric acid. Fill tank B with 500 ml of a 5%sodium hydroxide solution. Fill tank C with 10 litres of test water. Fill tank D withdistilled or demineralised water.

Backwash

Select tank D, open valves V3 and V6.

Regenerate

Select tank A, open valves V2 and V10. Collect the whole of the solution.

ANION RESIN

To determine the regeneration efficiency of the anion resin it will be necessary tocarry out the full demineralisation experiment 'DEMINERALISATION'.

Note: Since the exchange capacities of cation resins are generally greater thanthose of anion resins, it is expected that the anion resin will be first to be exhausted.


Final Depth (CATION) =

Final Depth (ANION) =

Sodium ion concentration (meq/ml) =

Original quantity of sodium hydroxide used =

Amount of sodium hydroxide collected =

Actual exchange capacity = Original quantity - amount used



Contact Details for Further Information

Main Office: Armf ield Limited

Bridge HouseWest StreetRingwoodHampshireEngland BH24 1DY

Tel: +44 (0)1425 478781Fax: +44 (0)1425 470916Email: [email protected]

[email protected]: http://www.armfield.co.uk

US Office: Armf ield Inc.

9 Trenton - Lakewood RoadClarksburg, NJ 08510

Tel/Fax: (609) 208 2800Email: [email protected]

Documents

W9 Issue 22 Instruction Manual