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This article was downloaded by: [Bucharest Polytechnic University]On: 21 April 2013, At: 02:14Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

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Chemical Recycling of Polystyrene.

Sulfonation with Different SulfonationAgentsWiesaw W. Sukowski

a, Krzysztof Nowak

a, Anna Sukowska

b

, Agnieszka Woliska

a

, Wioletta M. Bajdur

c

, Danuta Pentak

a

&Barbara Mikua

d

aDepartment of Environmental Chemistry and Technology, Institute

of Chemistry, University of Silesia, Szkolna, Katowice, Polandb

Department of Physical Pharmacy, Medical University of Silesia,

Jagielloska, Sosnowiec, Polandc

Department of Ergonomics and Workplace Safety, Technical

University of Czstochowa, Armii Krajowej, Czstochowa, Polandd

Department of Analytical Chemistry, Institute of Chemistry,

University of Silesia, Szkolna, Katowice, PolandVersion of record first published: 28 May 2010.

To cite this article: Wiesaw W. Sukowski , Krzysztof Nowak , Anna Sukowska , Agnieszka

Woliska , Wioletta M. Bajdur , Danuta Pentak & Barbara Mikua (2010): Chemical Recycling of

Polystyrene. Sulfonation with Different Sulfonation Agents, Molecular Crystals and Liquid Crystals,

523:1, 218/[790]-227/[799]

To link to this article: http://dx.doi.org/10.1080/15421401003720140

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Chemical Recycling of Polystyrene. Sulfonationwith Different Sulfonation Agents

WIESAW W. SUKOWSKI,1 KRZYSZTOF NOWAK,1

ANNA SUKOWSKA,2 AGNIESZKA WOLINSKA,1

WIOLETTA M. BAJDUR,3 DANUTA PENTAK,1 ANDBARBARA MIKUA4

1Department of Environmental Chemistry and Technology, Institute of

Chemistry, University of Silesia, Szkolna, Katowice, Poland2Department of Physical Pharmacy, Medical University of Silesia,Jagiellonska, Sosnowiec, Poland3Department of Ergonomics and Workplace Safety, Technical Universityof Czestochowa, Armii Krajowej, Czestochowa, Poland4Department of Analytical Chemistry, Institute of Chemistry, Universityof Silesia, Szkolna, Katowice, Poland

In this study waste polystyrene foam and virgin polystyrene as a reference materialswere converted by chemical reactions under heterogeneous conditions into usefulproducts. Polymeric flocculants were obtained from polystyrene during the sulfona-tion with sulfuric acid as the sulfonating agent and Ag2SO4 as the catalyst. Theinfluence of temperature and time of reaction on the properties of the products werestudied. The products were successfully used as flocculants in the treatment of thewaste water. Solid silica sulfuric acid was also used to convert polystyrene. In com-parison with the conventional sulfonation methods this sulfonating agent simplifiesthe reaction and makes easier separation of products from acid and solvent. Theobtained products were cross-linked and exhibited cation-exchange properties.The batch method was used to study purification of solutions of Zn2 and Cu2

by the yielded resins. The performed study proved the usefulness of wastepolystyrene derivatives for water treatment process.

Keywords Chemical recycling; flocculent; heterogeneous sulfonation;

ion-exchange; polystyrene waste

Introduction

Unique properties arise from incorporating sulfonic groups into polymers via sulfo-nation. The features like increased strength, hydrophilicity and proton conductivityhave led to an exploration of a variety of applications for sulfonated polymers, such

Address correspondence to Wiesaw W. Su

kowski, Department of Environmental Chem-istry and Technology, Institute of Chemistry, University of Silesia, Szkolna 9, Katowice

40-006, Poland. E-mail: [email protected]

Mol. Cryst. Liq. Cryst., Vol. 523: pp. 218=[790]227=[799], 2010

Copyright# Taylor & Francis Group, LLC

ISSN: 1542-1406 print=1563-5287 online

DOI: 10.1080/15421401003720140

218=[790]

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as membranes for fuel cells, plasticizers for macro-defect-free concretes, flocculantsand ion-exchange resins [1].

The current intense research and the general interest in heterogeneous sulfona-tion is the result of the opportunities such systems present for basic research andof the undisputable importance such systems have for industry and in developingtechnologies. Therefore we applied Neihoff method of sulfonation to convert poly-styrene (VPS - virgin polystyrene, EPS - expanded polystyrene) into a polymericwater soluble flocculant [2]. These sulfonated derivatives usually find applicationin the industrial water treatment due to the several times lower consumption ofthe coagulants used, short flocculation time and improved sedimentation propertiesof suspensions [35].

Unfortunately the Neihof method of sulfonation poses problems due to thedesulfonation processes. Moreover this method as many sulfonation methodsrequires a large excess of sulfonation agent because the water by-product slowsthe reaction down by diluting the acid. In this case a large amount of used acid

is obtained which in batch reactions is usually neutralized and disposed of whilein continuous processes it has to be recycled by complex techniques. Also, theseparation of the products from the sulfonation agent is a difficult and energyconsuming process that habitually implies a basic aqueous work-up. Moreover,many sulfonation agents are corrosive and dangerous to transport and handle.Consequently, any reduction in the amount of the sulfonation agent required and=or any simplification in the handling procedures would be highly convenient in termsof risk reduction, economic advantages and environment protection.

In order to decrease the environmental hazard of the reaction and to increase itseconomy we decided to study the usefulness of the silica sulfuric acid in thepolystyrene sulfonation reaction. Up till now this solid sulfonating agent was mainlyused in the sulfonation reaction of small aromatic compounds [6]. However using sil-ica sulfuric acid for sulfonation of polystyrene we yielded insoluble in water productwith the cation-exchange properties. Generally cation-exchange resins are used forsoftening of water, water purification and even demineralization as well asseparation and purifying metals.

Experimental

Samples of expanded polystyrene wastes (EPS) Mr,vEPS 230 000 and virgin polystyrenefrom Chemical Company Dwory in Oswiecim Poland (VPS) Mr,vVPS 200 000 were

used. Sulfuric acid, calcium carbonate, and sodium carbonate produced by ChemicalCompany POCh in Gliwice Poland were also used in the synthesis.

Polystyrene sulfonation was carried out according to the Neihof method [2]. Thedried sample of each polystyrene was pulverized in a mill and fractions of the size of0.401.04 mm were separated. They were sulfonated by mixing with concentratedsulfuric acid (5 times its weight) and silver sulfate (1% of its weight) as a catalyst.In a glass flask equipped with mechanical agitator, vertical condenser andthermometer, a certain amount of Ag2SO4 was dissolved in H2SO4 (9597%), poly-styrene (EPS, VPS) was added at 80C and the reaction mixture was stirred in thetemperature range 8090C. To find the dependence of the properties of the obtainedderivatives on the sulfonation conditions the temperature and time of reaction werechanged. The duration of the sulfonation ranged from 0.25 to 12 h. After a fewminutes, the reaction mixture became highly viscous and seemingly homogeneous.

Chemical Recycling of Polystyrene 219=[791]

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The product of the completed reaction, separated by filtration, was dissolved indeionised water. The products were precipitated in the form of sodium salt of poly(styrene sulfonic acid) in the reaction with Na2CO3 to get sodium salt of expandedpoly(styrene sulfonic acid) NaEPSS and sodium salt of virgin poly(styrene sulfonicacid) NaVPSS [7]. The same experiments were repeated in the temperature rangefrom 100 to 110C.

Preparation of silica sulfuric acid: a 500 mL suction flask equipped with aconstant-pressure dropping funnel and a gas inlet tube for conducting the HCl gasover the adsorbing solution (i.e., water) was used. It was filled with silica gel driedat 160C (27 mm particle size, from POCh). Chlorosulfonic acid from Sigma-Aldrich was added dropwise over a period of 30 min at room temperature. Thesubstrates was mixed with constant quantities of silica gel: 4,5 g to 1 mL chlorosul-fonic acid [8]. Thus the HCl gas was immediately released from the reaction vessel.After completing the addition of the chlorosulfonic acid the mixture was shaken forat least 3 h. Probably chlorosulfonic acid reacts with silanol SiOH and silano-

diol Si(OH)2 groups from silica gel surface and gives silica sulfuric acid.Samples consisting of 5 g of virgin polystyrene (other VPS from Chemical Com-

pany Dwory in Oswiecim Poland, Mr,vVPS 170 000) were dissolved in 100 mL of1,2-dichloroethane each. This substrate was then mixed with an appropriateamount of silica sulfuric acid in thermostated reaction vessel. Since 1.5 to 4 molesof ClSO3H was used per 1 monomeric unit of PS to synthesize silica sulfuric acid,the polystyrene to sulfonating agent molar ratio was 1:1.5 1:4. The experimentswere performed in a wide range of time (2 to 14 h) and temperature (3060C).Sulfonation was also conducted using expanded polystyrene (EPS) waste underexperimentally defined optimal conditions 1PS:2ClSO3H, 7 h at 60

C. Thesuspended small particles of sulfonated derivatives of polystyrene (VPSS and EPSS)were separated from much bigger particles of silica sulfuric acid by filtration andfrom solvent by decantation and evaporation. Polystyrene derivative was thenflushed using water and dried to get rid of the possible presence of H2SO4, theby-product of sulfones formation.

The IR spectra for the selected products were obtained on the Perkin-ElmerSpectrum One FT-IR spectrometer. Samples were prepared in the form of KBr discs.

The content of sulfur and carbon in products of polystyrene sulfonation wasdetermined by using a Perkin-Elmer CHNS=O elemental analyser. These data werethen used for calculations of the number of sulfonic groups per monomer unit(n.sulf). The calculated molecular weight (Mcal) count from the formula:

Mcal n:sulf 102 MPS Mr;vPS

=MPS

where:

n.sulf number of sulfonic groups per monomer unit,MPS molecular weight of the monomer unit of polystyrene,Mr,vPS molecular weight of polystyrene,102 the difference between molecular weights of the monomer unit of NaEPSS orNaVPSS and polystyrene.

The studies of the flocculation were carried out on TURB 550 IR turbidimeter.The initial value of turbidity of the investigated water was measured and then theoptimal dose of polymeric flocculant was determined. The experiments were

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performed for the obtained compounds (NaVPSS, NaEPSS) and for commercialNaPSS with the use of waste water discharge model and actual sewage from theZawiercie steelwork, the Galwanex Poreba galvanising plant, and Kleofasmine water. The waste water discharge model was prepared by acidic hydrolysis of1.8

102 M FeCl

3solution containing 103 M HCl at room temperature for a dur-

ation of 3 weeks.Fractional precipitation procedure: the sodium salts of poly(styrene sulfonic

acids) (NaEPSS, NaVPSS) were dissolved in aqueous 0.5 M NaOH solution andfractionated into several fractions by stepwise precipitation with an appropriate vol-ume of 2-propanol as precipitant. The obtained fractions were used to study theirflocculation properties.

In sewages from the steelwork and the galvanising plant the concentration ofthe following metals: Fe, Mn, Zn, Pb, Cu, Cr, Ni, Cd, was determined with theuse of ICP-AES spectroscopy (Optima 3000 DV, Perkin-Elmer) before and afterflocculation.

The ion-exchange capacity IEC (with unit of mmol=g of dry polymer) of sulfo-nated polystyrene (VPSS, EPSS) was determined by measuring the concentration ofH that was exchanged with sodium cation in 24 h at constant temperature of 25Cwhen acid-form resin (about 0.2 g of dry resin) samples were equilibrated with100 mL 0.2 mol=L NaCl solution.

Solutions of heavy metals (Zn, Cu as nitrate; reagent grade; POCh) were pre-pared in distilled water without adjusting the pH. In order to estimate the adsorptioncapacity, stock solutions of 1000 mg=L of each metal were diluted to obtain standardsolutions containing 25400 mg=L of metal ions. Under these experimental con-ditions it was confirmed that no chemical precipitation had occurred. The solutions(in convertion to 100 mL per 0.14 g of dry resin) were shaken (180 rpm) in 150 mLflasks with appropriate amounts of resins in an incubator at 25C for a period of24 h. Thermo E.C. Solaar M AAS spectrometer was used to determine initial andfinal metals concentrations in solutions. In each case the final concentration of eachmetal ions was determined after 24 h.

The percent of metal adsorption (Metal Adsorption) and distribution ratio (Kd)were calculated using the following equations:

MetalAdsorption ci cf 100=ci%

where ci and cfare the concentrations of the metal ion in initial and final solutions,respectively,

Kd amount of metal in adsorbent

amount of metal in solution

V

m

mL

g

!

where V is the volume of the solution [mL] and m is the weight of the adsorbent.Kd is defined as the ratio of metal ion concentration in the resin to that in aque-

ous solution.

Results and Discussion

In the process of chemical modification the sulfonated derivatives of polystyrenewastes (NaVPSS, NaEPSS) were obtained using sulfuric acid and silica sulfuric acid(VPSS, EPSS) as sulfonating agent.


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The molecular weights Mr,v of the products of polystyrene sulfonation obtainedby the Neihof method were compared with the molecular weights Mcal calculatedfrom the value of n.sulf.

It seems that some desulfonation and=or degradation of the polymer occurswhen the reaction time is longer than 1.5 h. Derivatives with a higher value ofMr,v and n.sulf were obtained during the sulfonation of VPS and EPS at a highertemperature range (100110C) than at a lower one (8090C) for the same reactiontime (Table 1).

For NaEPSS the maximum value ofMr,v

was obtained for the reaction conduc-ted for 5 h. The value ofn.sulf for this product is lower than the one obtained for aperiod of 1.5 h of sulfonation. Probably some intramolecular and=or intermolecularsulfone-type cross-linking and=or oxidative degradation takes place in the case ofsulfonation conducted at a longer reaction time than 1.5 h. In these conditions theincrease of n.sulf was observed but the Mr,v did not change significantly. ForNaVPSS it can be seen that longer reaction time results in a decrease of the n.sulf.For the NaEPSS and NaVPSS obtained at 100110C the values of n.sulf increasewith the increase of the reaction time up to 1.5 or 2 h, respectively, yieldingmaximum values. The n.sulf decreases with the increase of the reaction time up to12 h. The products obtained during sulfonation conducted at 100110C were used

to investigate the flocculation properties of the synthesized NaEPSS. The floccu-lation of colloidal suspensions induced by polyelectrolytes of anionic type dependson the adsorption affinity of polymer chains to the particle surface.

The turbidity values decreased with the increase in the polyelectrolyte dosageand reached the minimum value. The excess of flocculant concentration causedthe increase in the turbidity value of the studied water. The obtained results dependon the type of polyelectrolyte used in the experiment (Table 2).

Good purification of the supernatant was observed in each case when differentsynthesized NaPSS were used. It was found that the higher polyelectrolyte molecularweight the smaller the dosage of the appropriate polyelectrolyte required to obtainthe maximum decrease in the turbidity. It was also noticed that the turbidity valuesof sewages from the Zawiercie steelworks and the Galwanex Poreba galvaniz-ing plant decreased after flocculation (Table 3).

Table 1. Number of sulfonic groups per monomer unit (n.sulf) and molecularweights (Mr,v, Mcal) of NaEPSS and NaVPSS obtained during sulfonation of EPSand VPS at 8090C and 100110C

NaEPSS at

8090C

NaVPSS at

8090C

NaEPSS at

100110C

NaVPSS at

100110C

Reactiontime [h] n.sulf

Mr,v=Mcal 1000 n.sulf



Mr,v=Mcal 1000

0.50 0.89 430=431 0.97 550=390 0.98 491=451 0.93 593=3821.00 0.97 470=445 0.98 590=392 1.05 510=467 1.05 613=4061.50 0.96 515=447 1.01 600=398 1.11 508=480 1.12 654=4202.00 0.96 495=447 1.00 590=396 1.09 520=476 1.15 681=4265.00 0.82 420=415 0.88 530=373 0.95 570=444 0.99 769=39412.00 0.57 368=359 0.70 480=337 0.55 570=354 0.65 750=328

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Analytical investigations were performed for the waste water discharge modeland real sewage (Table 4). It was found that the concentration of all impurities sig-nificantly decreased after flocculation. For the waste water discharge model thedecrease of Fe [mg=L] concentration was equal to 93%. For real sewage the most sig-nificant concentration drops were observed for Fe, Mn, Cu, Cr and Cd for the sew-age from the Zawiercie steelwork. For the sewage from the Galwanex Porebagalvanising plant the decrease in the metal concentration was smaller and themaximum decrease was found for Cr. It was noted that water subjected to treatmentwith polyelectrolytes satisfies the standards for disposal to water resources.

By using silica sulfuric acid as the sulfonation agent for polystyrene sulfonation,water absorbing products (non-soluble in water) were obtained. The reaction is rela-tively simple and the obtained polystyrene derivatives exhibit cation-exchangeproperties. FT-IR spectroscopy was used to study properties of the obtained

Table 3. The effect of dose of flocculant on turbidity of the sewage after flocculation

Sewage from steelwork Sewage from galvanising plant

Dosage[mg=L]

Turbidity[NTU]

Change[%]

Dosage[mg=L]

Turbidity[NTU]

Change[%]

0.000 560 0 0.000 380 00.003 120 78 0.010 374 20.008 24 95 0.051 96 750.009 11 98 0.071 68 820.010 11 98 0.074 58 850.016 11 98 0.075 53 86

0.023 11 98 0.077 53 86

Data with maximum turbidity degrease are in bold type.

Table 2. The dependence of the turbidity of the waste water discharge model afterflocculation on the appropriate dosage of the polyelectrolyte

Type of

NaEPSS

a:Turbidity [NTU]=change of the turbidity [%]

Dosage [mg=L]0.50=0.98=

490 0001.0=1.05=510 000

2.0=1.09=520 000

5.0=0.95=570 000

0.000 360=0 360=0 360=0 360=00.002 156=57 190=47 125=65 158=560.004 87=76 125=65 55=85 64=820.005 71=80 101=72 49=86 30=920.006 58=84 74=79 30=92 42=880.007 42=88 51=86 51=86 54=850.008 35=90 45=88 67=81 64=820.009 50=86 21=94 89=75 88=75

0.010 67=97 42=88 129=64 94=74

aTime of the synthesis[h)]=n.sulf=Mr,v, respectively.


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Table

4.

Themetalconcentrationinthewastewaterdischargem

odel,sewagefromthesteelw

orkZawiercieandfromthegalvanising

plant

GalwanexPorebabeforeandaftertheflocculation

Wastewaterdisc

hargemodel

Se

wagefromsteelwork

Sewagefromgalvanisi

ngplant

ca[mg

=L]

Before

b

Afterc

Changed[%]

Before

b

Afterc

Changed[%]

Before

b

Afterc

Changed[%]

Fe

10260

670

93

517

5.2

6

99

1.7

2

0.4

2

28

Mn

4.7

2

0.1

5

97

0.0

2

0.0

1

69

Zn

0.1

5

0.0

5

32

0.1

8

0.0

3

82

Pb

0.0

6

0.0

1

>84

0.0

4

0.0

2

50

Cu

5.9

0

0.1

8

97

0.6

1

0.2

3

62

Cr

1.0

5

0.0

6

95

36

4.7

87

Ni

1.9

2

0.5

2

73

2.9

5

0.6

2

79

Cd

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