Journal of Scientific & Industrial Research Vol.59, January 2000, pp 44-48

Comparative Study of Polyacrylamide and Homopolymer of Acrylonitrile As Antiscaling Agent on Jalgaon Ground Water

S Mishra*, I D Patil andY P Patil University Department of Chemical Technology, North Maharashtra University, Jalgaon 425 00 I, India

Received: 05 July 1999; accepeted: 08 October 1999

Hardness of water results in scale formation and affects efficiency and life span of heat exchangers and evaporators by salt

deposition. Low molecular weight water soluble polymers are used to prevent scale formation. In the present study, polyacrylamide and polyacrylonitrile are used as scale inhibitors. Ground water is retluxed from I to 24 h with and without polymers. When only water is boiled the effect of sal t precipitation is found to increase with increase in time of reflux. But when the polymers are added individually, the precipitation of salt decreases with increase in amount of polymer (200 ppm to 800 ppm) as well as with increase in re fl ux time for all of the pol ymer concentrations. It is also observed that polyacrylamide is more effective than polyacrylonitri le as an antiscaling agent. Polyacrylonitrile shows better results up to 12 h of retluxing and thereafter polyacrylamide appears better. Antiscaling activ ity of an

inhibitor compound involves either diminution of the crys tal growth rate and prevention of the homogeneous and I or hetero­geneous germination mechanism.

Introduction Numerous chemicals from simple alum, iron salts, and

chlorine to complex ion exchange resins, polyacrylamide, polyaluminium chloride, cotTosion inhibitors, biocides, etc., are used in specific combinations for treatment 1

•

The process described by Roques2 relates to scale inhib­iting compositions. Here the scale inhibitor containing fluorocarbon compounds along with conventional boiler compounds such as organophosphates are emphas ized together with methods for preventing the deposition of scale from aqueous solutions . In one embodiment of pro­cess the compositions for inhibiting the formation of scale on the surface are prepared with at least one fluorocar­bon derivative that affixes itse lf to the surface.

Durham3 has found composition involving the phos­phate esters derived from an oxyalkylated urea that are effective in inhibiting scale deposition . These phosphate esters of oxyalky lated urea are particularly suitable for oil-well application. A method for inhibiting the precipi­tation of scale fanning salts of calcium, magnes ium, barium and stroncium from aqueous sys tem is provided

"' To whom correspondence should be made

by Smith4. The method involves addition of a telomeric

compound to the aqueous system. Miles' has provided a method of inhibiting sca le for­

mation by salts of calcium, magnesium, barium and stroncium from aqueous solutions. The method com­prises an adequate addition of a product comprising a telomer to the aqueous soluti on an amount within the range from 0.2 to 500 ppm based on the water to be treated .

In accordance with the process of Goodmanr', a pro­cess for inhibiting formation of magnesium scale or sludge in evaporative desalination units is provided. The process compri ses adding to the water being processed an effective amount of mixture of polyanionic and polycationic polymers. In the present work , polyacry­lonitril e and polyacrylamide are used as anti sca ling agents and their comparative study is done on Jal gaon ground water.

Experimental Procedure

H omopolymerisation of Acrylonitrile

900 ml of freshly boiled water and 0 .029 g of cone. sulphuric acid is placed in a four-necked two liter resin

MISHRA et al.: POLYACRYLAMIDE & HOMOPOLYMER OF ACRYLONITRILE 45

kettle fitted with a nitrogen inlet tube, addition funnel , stirrer, thermometer, and condenser. The mixture is stirred and a rapid stream of nitrogen is passed into the solution for 20 min, while the reactor is surrounded by a constant temperature bath maintained at 35°C.

53 g of acrylonitrile is added while maintaining a rapid nitrogen stream for additionallO min . The nitrogen flow is reduced and the gas inlet tube is raised to just above the surface of the stirred solution.

A solution of 1.17 g of ammonium persulphate in 50 ml water is slowly added to reactor, followed by slow

· addition of a solution of0.17 g of sodium metabisulphite in 50 ml of water. While in 3 min the solution becomes cloudy. Some heat is evolved during first 30 min . Gradu­ally a thick slurry deve lops. After 4 h the stirring is stopped, polymer is filtered off and washed with I 000 ml of water followed by 175 ml of methanol. The poly­mer is dried overnight at 70°C, preferably under reduced pressure. Yield obtained is approx. 92 per cent.

Polymerisation of Methacrylamide in Toluene

Solution of 1.5 g methacrylamide in 61 ml of toluene is taken in a 500 ml fl ask fitted with a nitrogen inl et tube, mechanical stirrer, reflux condenser, and in addi­

tion burette kept at 120 °C (± 1.5 °C). 9.0 ml solution of 4.0 per cent benzoyl peroxide in toluene is added to this mixture with constant stirring. Meanwhile the ni­trogen was bubbled continuously. At approx. 15 min in­terval, 9 .0 ml of 4.0 per cent benzoyl peroxide solution in toluene is added until 100.00 ml of the solution has been added (eleven parts in 3 h) .

After the addition of initiator the reaction is completed, heating and stirring is continued for half-an- hour. The polymer is filtered off and purified by retluxing three ­times with 30 .00 ml of methylene chloride. The pol y­mer is dried at 1 00°C to constant weight and cooling it under reduced pressure in the presence of calcium chlo­ride and paraffin. The yield obtained is approx. 75 .00 per cent in the form of fine white powder.

Infra Red Spectra of PAN and PAM

TheIR spectra of PAN and PAM are recorded on PYE UNICHEM, UK model SP3-l 00 especially used for poly­mer identificati on by pyro lysis technique (courtesy: KBX Ltd, Jalgaon).

In IR spectra of PAN, there is streching peak at 2800 - 2790 cm·1 fo r -CH streching. The -CN strech ing at 2220 cnY 1 is observed. It is lower due to the polymeric nature of the material. The -CH

2 and -CH bending are also ob-

served at 1445 and 1340 cm· 1, respectively.

TheIR spectrum of PAM shows the -NH2

strechging at 3400 - 3150 em·', -CH streching at 2930- 2850 cm·1

,

and- CO streching at 1420 cm·1• The -CH bending at

1310 em·' is also observed.

Molecular Weight Determination.

The molecular weights of PAN and PAM are deter­mined by viscosity method using Ostwald Viscometer.

The PAN is dissolved in Dimethyl Fonnamide (DMF) and very dilute solutions with polymer concetrations 0.0625 , 0 .125, 0.25, 0.5 , and 1.0 per cent (w/v) are pre­

pared. The k and a values of PAN for DMF are 1.7 X

I o-' and 0.78, respectively. The molecular weight of PAN is observed to be 9,200.

The PAM is dissolved in distilled water and very di­lute solutions with polymer cone. 0.1, 0.2, 0.3 , 0.4, and

0.5 per cent (w/v) are prepared. The k and a values of

PAM for water are 6.31 X I o-3 and 0 .80, respectively. The molecular weight of PAM is observed to be 3,280.

Determination. of Hardn ess

The hardness of water is determined by s imple complexometric titration method using EDTA, as de­scribed by DiehF and Diehl et afX . EDTA forms com­plex with the metalic salt in water. To find out the hard­ness caused by calcium and magnesium, pH was main­tained at 10 by using ammonium buffer solution (am­monium chloride-ammonium hydroxide solution) hav­ing pH 10. By using Eriochrome Black-T indicator the titrant value of water sample corresponded to the tota l hardness present. Value of temporary hardness was de­termined by the same method, on ly difference be ing that the water sample used was boiled for half-an-hour. Dif­ference between total hardness value and temporary hard­ness value gave value of permenant hardness of water sample .

Determination. of Salt Precipitation

Different water samples are refluxed for different durations and filtered off. The salt deposited on glass vessel (round bottom f lask) are dissolved in dilute hy­drochloric acid (di l. HCI). Dilute sodium hydroxide (di l. NaOH) solution is added in solution of dissolved salts to neutral ize the added acid . The precipitated salts are f iltered off and washed with distilled water till the so­dium chloride formed is removed . The precipitate is dried at I 00° C up to constant weight.

46 J SCI IND RES VOL.59 JANUARY 2000

1.4

12

Cl c: 1 c: 0

:;::; 0.8 .~ a. ·u 0.6 ~ a. - 0.4 iii rJ)

02

0

1 6 12 18 24

Reflux Time in h

Figure 1- Salt precipitation in water

Table- I Stati stical analysis of water samp le for a year

Parameters

pH Total hardness Permanent hardness Dissolved solids Iron Fluroide Chlorides Nitrates Nitrites

Observed value

7.2-8.0 300 - 446 ppm. 136 - 246 ppm. 576 - 735 ppm. 0.2- 0.8 ppm.

0.31 - 0.5 ppm. 59.0 - 108.0 ppm. 2.56- 2.89 ppm.

Nil

The water sample collected in the month of January, May, July, and November are analysed. The range of stati stical data are given in Table I.

Results and Discussion

Effect of Different Concentrations of Polyacrylonitrile (PAN) and Polyacrylamide (PAM) on Scaling for 24 h

Figure I shows the results of precipitation of salt di s­solved in water with increase in time, where precipita­tion of salt increases with increase in reflux time from I to 24 h. The minimum salt precipitation (0.1242 g) is recorded for 1 h, while the maximum (1.3560 g) is re-

corded for 24 h for 1000 ml of water.

I I '

0.09 LJPAN .PAM

0.08

Cl 0.(17 s::: s::: 0.06 0 ~ 0.00 co :!:: .9- 0.04 (.) Q) ....

0.00 c. --m 0.02 rJ)

0.01

0

200 400 600 800

Reflux Time in h

Figure 2- Isochronous comparison of salt precipitation using PAN and PAM polymers.

Individually, the PAN and PAM are added with 200, 400, 600, and 800 ppm concentration in water and re­fluxed for 24 h.

It is observed from the results, (Figure 2), that the salt precipitation decreases with increase in amount of poly­mer. The PAN with 200 ppm in same quantity of water shows maximum (0.09 g) salt precipitation which is 27 per cent less than the blank. Same ppm of PAM shows 0.078 g of salt precipitation (37 per cent less than the blank) for the same duration and quantity of water.

The PAN shows more effectiveness with a constant rate with increase in amount from 200 to 800 ppm. While the PAM shows a little impact from 200 to 600 ppm and further there is a sudden decrease in salt precipitatibn from 600 to 800 ppm of PAM in water. The salt precipi­tation obtained by adding 800 ppm PAN in water is 0.053 g (57 per cent less than blank water.) However same concentration of PAM reduces salt precipitation up to 61 per cent i.e. (0.048 g of salt precipitation) with re­spect to the blank water, sample. Thus the higher con­centration of PAM behaves better than PAN.

Optimization of Concentration of PAM and PAN for Th eir Antiscaling Effect from 1 - 24 h

To optimize the time from 1 to 24 h with different concentration of PAN and PAM, respectively, 200 ppm concentration of polymer in water is taken to reflux with respect to blank water sample (Figure I and 3).

MISHRA et al.: POLYACRYLAMIDE & HOMOPOLYMER OF ACRYLONITRILE 47

Sl no.

2

3

0.12

0.1 Ol c:: c:: 0.08 0

~ :!::: 0.06 a. "(j Cl) ,_ a. 0.04 -iii Ul

0.02

0

1 6 12 18 24

Reflux Time in h

Figure 3 - Comparison of salt precipitation usi ng 200 ppm of PAN and PAM polymers

Table 2- Hardness of Jalgaon ground water

Type of hardness

Total hardness

Permanent hardness

Temporary hardness

Hardness in ppm

320

136

184

Up to 6 h the PAN shows less precipitation in com­parison with PAM, but above 8 h reflux time the PAM appears as a better antiscaling agent for 200 ppm con­centration.

On increasing the concentration of these polymers in water from 200 to 400 ppm, there is a decrease in salt precipitation in both the cases but the PAN shows better results as antiscaling agent for 22 h. Also for 24 h, PAM gives bette r performance (Figure 4).

F igure 5 and 6 show the results of anti-sca ling effect of 600 and 800 ppm concentrations of PAN and PAM in water. PAN and PAM show drastic reduction, i.e ., up to 12 h in scale formation and prec ipitation for both the polymers, also there is no change in scale precipitation for 24 h (Figure 5). At thi s particular concentration, PAN exhibits less prec ipitation of salts for all the durations. On further increas ing the concentration of polymers. there is reduction in sa lt precipitati on.

Hardness (temporary, permanent and total) of water is illu strated in Table 2. The total hardness of the water sample is recorded as 320 ppm. Further. total hard­ness is also recorded with 100 and 200 ppm concentra­tions of PAN and PAM in water samnie ind ividually af-

Ol c:: c:: 0

:;:; 11! -·a. "(j Cl) ,_ a. -iii Ul

0.12

0.1

0.08

0.06

0 .04

0.02

0

1 6 12 18 24

Reflux Time in h

Figure 4- Compari son of salt precipitation using 400 ppm of PAN and PAM polymers

Table 3- Effect of polymer added on salts present in water.

Sl No.

2

Type of Concentrati on of polymer polymer in ppm

added

PAN

PAM

1000

2000

1000

2000

Retlux time Total harden in h in ppm

I

2

2

280

276

276

256

te r refluxing for I and 2 h for both the concentrations (Table 3).

It is observed from the resu lts that the increase in amount of polymer with reflu x time, tota l hardness de­creases. For higher concentrations, i.e., 200 ppm for 2 h reflux duration of water PAN shows lesser hardness. In another study the total hardness of water refluxed for I , 3, and 5 his estimated in a successive manner (Table 4) . There is a sharp decrease in total hardness from 180 to 20 ppm for calcium salts and 2. I 9 X I 0··1 to 2.43 X I 0·4

ppm for magnesium salts for 3 h and also no change is observed in total hardness . These results show that the PAN and PAM polymers are ac ting as anti scaling agents by the phenomenon of inhibiting the convers ion of cal­c ium bi carbonate into calc ium carbonate. Moreover, the d issolved pol ymers might be capable to envelop the di s­solved salts so that these do not come in contact wi th wa lls of vessels. Hence the germination of crystal gets hampered . The higher total hard ness. as well as the le~: scr

I

48 J SCI IND RES VOL.59 JANUARY 2000

C)

.5 c: :8 !3 ·a '(j Ql ... c. -iii rn

. 0.1

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0 1

rnPAN 118PAM

6 12 18

Reflux Time in h 24

Figure 5- Comparison of salt precipitation using 600 ppm of PAN and PAM polymers

Table 4-Total hardness in success ive manner

Sl no. Time of refluxh Salts ppm Ca2• Mgz•

0 180 0.00218800

2 I 48 0.0005836

3 3 20 0.0002432

4 5 20 0.0002432

salt precipitation with higher concentration of PAM, shows that PAM is slightly more effective than the PAN.

Conclusions The PAM is more effective at lower concentrations

than PAN for longer duration, whi le PAN is more effec­tive for shorter duration for lower concentrations. On

0.1

Q.09 [mPAN IIPAM

0.08 C)

.5 0.07 c: 0 0.06 ; !3

~~-·a 0.05 I

'(j Ql 0.04 ... c. - 0.03 iii rn

0.02

O.Ql

0 1 6 12 18 24

Reflux Time in h Figure 6 - Comparison of salt precipitation using 800 ppm

of PAN and PAM polymers

increasing the concentration of polymer the effective­ness of PAN increases up to 600 ppm for shorter dura­tion , i.e., up to 12 h, and further at 800 ppm concentra­tion the PAM is more effective after 12 h.

There is found to be reduction in total hardness by treating with polymers but PAM shows less reduction than PAN. It shows that PAM is responsible to inhibit more efficiently the precipitation of salts than PAN.

References I Editorial, Chem Eng World, 33 (No. 6) June 1998.

2 Roques H, US Pat ; 4, 148, 728; April 10, 1979.

3 Durham D K. US Pal .; 4, 155, 869; May 22, 1979.

4 Smith M J, US Pat; 4, 159, 946; July 3, 1979.

5 Mi les P, US Pal; 4, 189, 383 ; February 19, 1980.

6 Goodman R M, US Pal; 4, 166, 041; August 28 , 1979.

7 Diehl H, Anal Chem, 22 ( 1950) 503 .

8 Diehl H, Goetz C A & Hach C C, 1 Am WaterWorks

9 Assoc. 42 ( 1950).