Influence of Flocculating Agents on the Performance of Ion Exchange Resins, Boiler Feed Water

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1 Journal of Scientific & Industrial Research Vol. 60, May 200 I, pp Influence of Flocculating Agents on the Performance of Ion Exchange Resins, Boiler Feed Water A P Gupta' J S Thakur 2, R K Patel' and Himanshu Agrawal'' 1 Department of Applied Chemistry & Polymer Technology, Delhi Co llege of Engineering, Bawana Road, Delhi II 0042 ~ R &D Centre, at ional Thermal Power Station, A-8A, Scctor-24, NO IDA 20 I 30 I Received: 04 Jul y 2000; accepted: 25 Janu ary The effect of flocculating agents. i.e. ferric alum, non ferric alum, and polyaluminium chloride (PAC) on ion exchange capac ities of ion exc hange resins (I DION), arc investigated. The comparison of data reveals th at the use of PAC in the pretreatment of raw water causes lesser decrement in the total ion exchange capacities and sa lt splitting capacities of resins and ca n be used as a coagul ating agent in pretreatment of water. Introduction The most demanding of all app lications of ion exchange technology is the condensate polishing of feed water in high-pressure boilers. The ion exchange res ins are employed in two condensate-polish ing techniques. The first method utilizes powdered resins, regenerated mixtures of anion and cation exchange res ins in thin layers ( em) on conventional spiral wound fiber septum filters. The second method uses conventional deep mixed bed, which performs both filtration and deionization. The removal of high concentration of salts, ionic moieties and particulates require highl y efficient filtration. Recently, Patel eta/.,_ 4 ha ve worked on several of ion exchange resi ns. Many researchers ha ve worked on preparation '-~, characterization, and utili zation of new ion exchange resins for academic interest, as well as practical interests. For conven ti onal mixed beds the bas ic operating cycles H+JOR provide a product of high quality. The leakage ranges are such as up to 20 ppb for Si0, 2 Cu 2 + and Fe 3 +, and 1-5 ppb for other ions. The boiler feed water is the prime sector of ion exchange resins utilizati on. The res ins play a vi tal role in the production of ultra-pure water. Their functioning depends on the total exchange capacity and salt splitting capacity. The influence of flocculating agents on these 'Author for correspondence capacities has been investigated with fl occulating agents such as ferric alum, non-ferric alum and polyaluminium chloride (PAC). The doses va ri ed from 25 to I 00 ppm and the soaking period va ries from I to 90 d. The study revealed PAC to be a better flocculating agent. Experimental Materials - The followin g requ ired materials we re obtained from mentioned sources; strong cation exchange resin lndion-225 [Ion Exchange (I) Ltd,. Bombay], strong base anion exchange res in lndion-nip [Ion Exchange (I) Ltd. Bombay], Polyaluminium Chloride (E Merck), ferric alum (CDH, Indi a) and non-ferric alum (CD H, India). The other reagents used during other reagents used during in vestigat ion were of analytical grade. (i) Soakin~-: of Resins - I 00 ml of strong acid cation exchange resi n and of strong base anion exchan ge res in s were soaked in two bed volumes (200 ml of demineralized water) in 500 ml beakers separately. The fl occulants such as ferric alum, non-ferric alum, and PA C closes were va ried from 25, 50, 75 and I 00 ppm. Al l resi n samples were subjected to maximum soaking peri od of 90 d with intermittent shak ing. (ii) Determination of Total Exchange Capacity and Salt Split. tin~-: Capacity - The cation exchange and anion exchange resin sample. were eva luated

2 GUPTA el a/.: FLOCCULATING AGENTS for total exchange capacity and salt splitting capacity after every 7, I 5, 30, 45, 60, and 90 d of soaking periods. ASTM procedures 10 were followed to determine these capacities. The total exchange capacity and salt splitting capacity of cation and anion exchange resins were determined five-times in each case to establish the precision and accuracy of testing methods. The analytical results obtained were within acceptable limits. The results are shown in Tables 1-4. il y in comparison with other flocculants i.e. ferri c and non-ferric alums. After hydrolysis, chl oride constitutes from hydrogen chl oride and subsequentl y hydroxyl groups get attached. Hydroxyl groups give ri se to polynuclear complexes by means of coordinate bonds wi th aluminium atoms. Hence polyaluminium chloride after hydrolysis may be represented in following manner: Results and Discussion The flocculation involves aggregation of loose masses within the emulsion whose properties are influenced by the effect of impurities and added substances due to interfacial tension. The emulsifying agent reduces the interfacial tension. The most commonly used emulsifying agents are soap, long chain polymeric compounds, sulphonic acids and sulphates. We already know that very fine suspended particles are not removed easily by sedimentation only. The sedimentation with coagulation is a process of removing of fine suspended and colloidal impurities. This composite process is carried out by the addition of requisite amount of coagulants to water before sedimentation. The coagulant when added to water forms an insoluble gelatinous precipitate, which during its formation adsorbs and entangles very fine suspended impurities. After entanglement it becomes bigger floc which settles down easily coagulants like alum or ferrous sulphate provide AP+ or Fe 3 + ion which neutralizes the negative charge on colloidal clay particles after which clay particles come nearer to one another and combine to form bigger particles which settle down under gravity. Thus the gelatinous precipitate formed due to added coagulant has the property of removing fine suspended and colloidal particles quickly and completely. The coagulants also possess an additional advantage of removing colour, odour and taste from water being treated. Alums are the most commonly used flocculating agents, but recently polyaluminium chloride (PAC) is being tried to employ as flocculating agent instead of alumns. Polyaluminium chloride (PAC) is the polymeric compound of hydrates of aluminium variously chlorinated. It is indicated by the general formula [AI (OH) CL ] where n, m and x have different vain m.m m x. ues. Polyaluminium chloride undergoes hydrolysis eas- (Polyaluminium chloride after hydrolysis) The parameters involved in characterizing the exchangers for condensate treatment include the follo w mg: (i) Selectivity of the ion exchange resins for ions involved as well as the ease of elution with regenerants. (ii) The capacity of the ion exchange resins. (iii) Physical and chemical stability of the resins in the environment of operations. (iv) Capability for filtration of particulates. (v) Resistance to organic fouling. (vi) Ease and completeness of separation. The water retention capacity of ion exchange resin is proportional to its pore volume. The higher value of water retention indicates lower effective cross-linking. The increase in water retention capacity of used resin as compared to unused resins shows decross-linking. The decrease may indicate either loss of functionally or fouling of ion exchange resins. The water retention capacities of resins used in this investigation were per cent for cation exchange resins and per cent for an ion exchange resins respectively. The density of resins was found as g/ml for cation exchange resins and g/ml for anion exchange resi ns. The total exchange capacity and salt splitting capacity of cation and anion exchange resins as determined experimentally are given in Tables 1-4 with the use of alums SO/" anions contribute to the formation of bi o logical slime which serves as a source of food for th e bacterial colonies subsequently SO/ ion get reduced.

3 I 398 J SCI IND RES VOL 60 MAY 2001 Table 1 - Salt splitting capacity of strong acid cation exchange resin (Density = glml) Salt splitting capacity in g CaCO, / L of resin (SSC) at and after Concentration of Name of flocculants Initial 7d 15 d 30 d 45 d 60 d 90 d flocculants 25 ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC Table 2 - Salt splitting capacity of strong base anion exchange resin (Density = g/ml) Salt splitting capacity in g CaCO, / L of resin (SSC) at and after Concentration of Name of flocculants Initial 7d 15 d 30 d 45 d 60 d 90 d flocculants 25 ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC I 100 ppm Ferric alum Non-ferric alum PAC I There is no SO/" contribution in the case of PAC. The numbers of other limitations associated with alums are such as effective ph range, the presence of corrosive environment, excess of AP+ or Fe 3 +,increased suspended solids and unaccounted ionic loading in the water during treatment process. In case of alum as ph of water becomes 5.0 alum floc begins to lose its positive charge because of ph 6.5 alum floc becomes negatively charge. It explains about the poor sizing of alum floes within ph range of and also explains that no possibility to of acidic sizing with alum above ph 6.0. However, in the case of PAC the significant cationic charge remains available up to ph 7.2 therefore, it provides bigger size precipitate (floes) within ph range. It is a better agent in around of neutral ph value. PAC provides many other benefits such as low loading, lower affluent treatment costs, much reduced SO/" free environment, much less corrosive nature of treated water, much reduction in biological slime and foam formation. During the treatment of raw water with ferric and nonferric alums there are chances to carryover aluminium floes of micro-size to the downward stream of demineralization and impurities like AP+, Fe 3 +, etc., get exchanged on cation exchange resin bed resulting into de-

4 GUPTA eta/.: FLOCCULATING AGENTS 399 Table 3-Total exchange capacity of strong acid cation exchange resin (Density = g/ml) Total Exchange Capacity in g CaCO, /L of resin (TEC) at and after Concentration of Name of tlocculants Initi al 7d 15 d 30 d 45 d 60 d 90 d tlocculants 25 ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC ppm Ferric alum Non-ferric alum PAC Table 4-Total exchange capacity of strong base anion exchange resin (Density = g/ml) Total exchange capacity in gm CaCO, /L of resin (TEC) at and after Concentration of Name of llocculan ts Initial tlocculants 25 ppm Ferric alum ppm Ferric alum ppm Ferric alum ppm Ferric alum 73 7d 15 d 30 d 45 d 60 d 90 d crease in its ion exchange capacity subsequently anion exchange resin bed gets affected by silica fouling. The experimental data (Tables 1-4) of total exchange capacity and salt splitting capacities reveal that the effect of ferric, non-ferric and PAC on ion exchange resins are comparable. The decrease in salt splitting capacity and total exchange capacity is more which may be due to the fact that strong ion exchange sites (positions of exchange ions on the resin matrix) have been converted to weak sites. The decrease in salt splitting capacity and total exchange capacity varies as we increase the dose ( ppm) of flocculant as well as with increase in soaking period 7-90 d of resins. The experimental data (Tables 1-4) shows that pretreatment of raw water in clariflocculator with PAC is better option as compared to alums with respect to ion exchange resins performance. Acknowledgement The authors are thankful to Prof N L Sachdeva, Principal, Delhi College of Engineering and Dr G L Verma, Head, Department of Applied Chemistry, Delhi College of Engineering, Bawana Road, Delhi II for their encouragement and providing research facilities. The

5 400 J SCI IND RES VOL 60 MAY 2001 authors are also thankful to Mr M C Nevhani, G M, Research & Development Centre, NTPC A-8A, Sector-24, NOIDA for providing laboratory facilities; References Patel D K, Patel C G & Parmar J S, Die Angew Makromol Chem, 210 (1993) Patel D K, Patel C G & Parmar J S, Macromol Rep, 297 A31 (Suppls 3 & 4) (1994) Patel D K, Patel C G & Parmar J S, Indian J Chem, 32A (1993) Patel D K, Patel C G & Parmar J S, Indian J Chem, 31A (1992) Pancholi H B & Patel M M; Indian J Chem, 30A, (1991) Mendez Rita & Pillai V N S, Talanta, 37 (1990) Dhandhukia M M, Indusekhar V K & Govindan K P, Indian J Technol, 20 (1982) Awad M M B, Salem A M A & Swelam A A, Indian J Chem, 35A (1996) Ibrahim N A, Abo-Shosha M H, Die Allgew Makromol Chem, 210 (1993) American Standard Test Methods (ASTM), D-2187, Volume (1999) pp

Water Treatment: Coagulation

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