Effects of additives on the formation of organochlorine compounds during the combustion of a chlorine-containing polymer

WASTE MANAGEMENT, Vol. 13, pp. 77-82, 1993 Printed in the U.S.A. All rights reserved.

0956-053X/93 $6.00 + .00 Copyright © 1993 Pergamon Press Ltd.

ORIGINAL CONTRIBUTION

EFFECTS OF ADDITIVES ON THE FORMATION OF O R G A N O C H L O R I N E C O M P O U N D S DURING THE C O M B U S T I O N OF A CHLORINE-CONTAINING POLYMER ]ila Banaee and Richard A. Larson* University (fflllinois, Institute for Environmental Studies, 1101 W Peabody Drive, Urbana, IL 61801, U.S.A.

ABSTRACT. A plastic film (largely polyvinylidene chloride) was thermally decomposed by heating in air in the presence

and absence of alkaline radical scavengers (K2CO3, KOH, CaO, and Ca(OH)2) at 500°C. Addition of KOH in a 1:2 stoichiometric ratio (based on chlorine) diminished the total output of chlorinated compounds by 51%.

tively. Saran ®plastic food wrap, for example, consists of about 80% polyvinylidene chloride, with the remainder being PVC and phthalate plasticizers. Consumption of vinyl resins, one of the most common classes of synthetic monomers, exceeds 1 billion kg/ year in the United States, a volume of use close to that of polystyrene and about 60% of that of polyethylene. There have been efforts to diminish the production of chlorinated chemical emissions in combustion processes. Dougherty and Callazo-Lopez (3) used solid calcium oxide (CaO) in a fluidized bed placed above the combustion zone as a scavenger for chlorine-containing radicals. These workers experimentally demonstrated a significant decrease in the levels of organochlorine emissions in a laboratory reactor, although a trend toward somewhat larger molecules was apparent. Nielsen et al. (4) and Gullett et al. (5) have identified a proposed control technology called "lime injection" that depends on removing HCI and/ or chlorine gas from incinerator emissions by scrubbers and spray driers.

INTRODUCTION

Plastic wastes, mainly from packaging, constitute a large and important fraction of the United States domestic refuse. The weight percentage doubled (to about 8%) from 1980 to 1988, and is forecast to further increase. The presence of chlorinated organic matter in the wastes, such as polyvinyl chloride (PVC) plastic, pesticides, flame retardants, etc. results in formation of corrosive or toxic substances like organochlorine compounds, HCI, and other halogenated acids in the incineration exit gases and particles (1). Of special concern is the formation of chlorinated polycyclic compounds such as polychlorinated biphenyls (PCBs), dibenzodioxins (PCDDs), and dibenzofurans (PCDFs). These compounds could be produced either homogeneously, by gas-phase reactions, or heterogeneously in surface-catalyzed processes. Polymers and co-polymers of PVC and polyvinylidene chloride (known in the industry as "vinyl resins"), the source of most of the HC1 in municipal incinerator emissions (2), are very widely used as food covering films, sheeting, floor covering, cable coating, rainwear, shower curtains, etc. The two possible monomers, vinyl chloride (CH2=CHCI) and 1,1-dichloroethylene ("vinylidene chloride," C H 2 = C C I 2 ) are high in chlorine content, 57% and 71% C1 respec-

M E T H O D S AND MATERIALS Combustion experiments were performed using a temperature-programmed Lindberg furnace. In each combustion experiment, 0.5 g of Saran ®plastic wrap was used. The sample was placed in a porcelain boat for combustion. Compressed air was passed through the furnace tube at a flow rate of 2 L/min. The additives (from Fisher Scientific Co., Chicago, IL) were potassium carbonate, calcium oxide, calcium hydroxide, and potassium hydroxide. Each additive was spread uniformly over the plastic. They were added in

RECEIVED l 0 APRIL 1992; ACCEPTED 24 AUGUST 1992.

*To w h o m correspondence m a y be addressed.

Acknowledgement--The a u t h o r s would like to t h a n k the Illinois Office o f Solid Waste Research for financial support (Grant # 0 3 0 0 1 ). 77

J. BANAEE AND R. A. LARSON

78

a 1: 1 stoichiometric (equimolar) ratio (based on chlorine), except for potassium hydroxide which was added in 1: 1 and 1:2 ratios. The combustion products were swept into a trap cooled externally by isopropyl alcohol and dry ice in a Dewar flask. The trap contained 20 mL of CH2C12. After the completion of the combustion, the solvent was thawed, removed, dried (MgSO4), filtered, and concentrated to 0.2 mL in a Kuderna-Danish concentration tube under a flow of argon. Subsequently, 20 #L of an external standard (1-bromonaphthalene) was added. The concentrated solution was analyzed by gas chromatography-mass spectrometry (GC/MS) using a Finnigan (San Jose, CA) Model 800 Ion Trap with a Hewlett-Packard (Downers Grove, IL) Model 5890A gas chromatograph. The GC column conditions were: 30°C for 10 min, 300C to 280°C at 5°C/ min, and hold at 280°C for 10 min. Identification of compounds was accomplished by computerized library searches and comparison with literature mass spectra. The area of every detectable ion current peak was integrated and compared to the area of the standard, and normalized to the mass of the solid to provide a semi-quantitative indication of the amount of material collected in the trap. RESULTS

Temperature Studies The first set of combustion experiments was undertaken to examine the effects of temperature on the yield and the types of chlorinated compounds. Halfa gram of Saran® plastic wrap was used for each combustion experiment, which was carried out at 400, 500, 600 and 700°C. The length of each combustion experiment was one hour. The types of compounds formed are listed in Table 1. The most important chlorinated compounds produced were benzenes (1-6 C1 atoms), styrenes (1-5 and possibly 8 CI atoms), naphthalenes (1-5 C1 atoms), and biphenyls (1-6 CI atoms). The results are largely consistent with the data obtained in similar experiments by Yasuhara and Morita (6). The highest yield and variety of chlorinated organic compounds were produced at temperatures between 400 to 600"C; production oforganochlorine compounds decreased as the temperature increased further (Fig. 1). Of the temperatures tested, the optimum at which the chlorinated compounds (with the exception of benzenes) were most efficiently formed was 500°C.

Quencher Studies The second set of experiments was a study of the effects of the addition of alkaline substances that are expected to be scavengers of hydrochloric acid, chlorine atoms, or molecular chlorine: potassium carbonate, sodium hydroxide, and lime (CaO). They were added to the Saran ®wrap in a stoichiometrically equivalent

TABLE I List of Identified Compounds from Combustion of Saran® Wrap

Retention Time 5.58 7.27 11.37 13.56 17.07 19.15 22.17 23.35 28.16 28.40 29.35 30.15 32.05 32.19 33.23 33.54 34.00 34.14 34.23 35.07 36.26 36.45 37.18 37.56 38.00 38.17 39.15 39.37 40.41 41.05 42.01 42.39 42.46 43.13 44.13 45.11 45.22 45.37 46.11

Compound Identification tetrachloroethylene monochlorobenzene alkane (chlorinated?) trichloropropene dichlorobenzene chlorocyclohexene trichlorobenzene trichlorobenzene isomer tetrachlorobenzene trichlorostyrene tetrachlorobenzene isomer phthalic anhydride bromonaphthalene & tetrachlorostyrene tetrachlorostyrene isomer & bromonaphthalene pentachlorobenzene dichloronaphthalene tetrachlorostyrene isomer dichloronaphthalene isomer tetrachlorostyrene isomer pentachlorostyrene petachlorostyrene isomer tetrachloropropylbenzene hexachlorostyrene hexachlorobenzene trichloronaphthalene trichloronaphthalene isomer dichlorobiphenyl trichloronaphthalene isomer trichlorobiphenyl trichlorobiphenyl isomer tetrachloronaphthalene trichlorobiphenyl isomer tetrachloronaphthalene isomer phthalate tetrachlorobiphenyl trichlorobiphenyl isomer contaminant (unidentified) pentachlorobiphenyl pentachloronaphthalene

quantity to the organic chlorine in the polymer. When K2CO3 was used, the total yield of chlorinated organic compounds remained about the same; however, a shift towards larger molecular weight compounds was observed, with the exception of chlorinated naphthalenes (Fig. 2). Similar trends were observed in studies done by Larson and Ellis (7) using FeC13-treated paper and K2CO 3. With the additives CaO, KOH, and Ca(OH)2, this shift did not occur systematically (Fig. 3). In the case of CaO, a shift towards larger molecular weight compounds was observed for chlorinated styrenes, naphthalenes, and biphenyls. However, with KOH, a shift occurred only for chlorinated styrenes; and there was no shift in the case of Ca(OH)2. The data for these quenchers indicate that the total amount of chlorinated organic compound production diminished, especially with K O H (Fig. 4). Addition of KOH in 1: 1 and 1:2 stoichiometric ratios diminished the total

FORMATION OF ORGANOCHLORINE COMPOUNDS

79

125x

10-

8-

Z

~. 45)

~

5x

ei

i

t

i

i

i

f

r

t

600

500

400

700

Combustion Temperature C

]F ~

benzenes

~

styrenes

~

naphthalenes ~

biphenyls

FIGURE 1. Relative yields of the most important chlorinated compounds at different combustion temperatures.

a m o u n t o f chlorinated c o m p o u n d s by 35% and 51% respectively (Fig. 5). DISCUSSION Yasuhara and Morita (6) reported that pyrolysis o f polyvinylidene chloride polymers gave rise to a large n u m b e r o f chlorinated organic compounds, such as

chlorinated benzenes, naphthalenes, styrenes, biphenyls, and some alkanes. In other studies, combustion products from both PVC and polyvinylidene chloride-containing plastic materials under various conditions were examined by Ahling and co-workers (8). The results indicated that benzene derivatives containing two to six chlorine atoms were formed during combustion. Hawley-Fedder et al. (9) re-

30~. 25Z 20m 15 ~

¢ ~

5/ SARAN '

[ - - ] benzenes biphenyls

' ' SARAN/K2CO3 Combustion Temperature 500 C

~--~ styrenes ~ total

1

naphthalenes

FIGURE 2. Relative yields of chlorinated benzenes, styrenes, naphthalenes, hiphenyls, and their total from combustion of Saran®and Saran®/K2CO3at 500"C.

80

J. B A N A E E A N D R. A. L A R S O N

25-

20-

;•150)

~J

~ 10~J

5-

0-

-

-

q

SARAN

3

SARAN/CaO

q-

F

$ARAN/KOH

F

SARAN/Ca(OH)2

Combustion Temperature 500 C FIGURE 3. Relative yields of chlorinated benzenes, styrenes, naphthalenes, and biphenyls from combustion of Saran ®,and co-combustion of Saran ®and the additives (CaO, KOH, and Ca(OH)2) at 500"C.

ing combustion could be formed by mechanisms involving either HC1, C12, or atomic C1 (5,10,11). (The role of HC1 is probably limited, as shown by the findings ofGullett et al. (5) that C12 gas, when introduced into a furnace together with phenol, gave amounts of chlorinated organic compounds that were around

ported that at 800°C, the major products of PVC combustion were principally a few aliphatic organochlorine compounds. The results of the present study are in general agreement with the earlier observations. In principle, organochlorine species produced dur14

12~10Z

8J

2 ,p-i

~

4" 2I

SARAN

I

'SARAN'CaO

'SARAN/I(OH'

L

SARAN/Ca(OH)2

Combustion Temperature 500 C

I

I benzenes

~

styrenes

I

naphthalenes~

biphenyls

I

FIGURE 4. Relative yields of the total organochlorine compounds (chlorinated benzenes, styrenes, naphthalenes, and biphenyls) from 1 combustion of Saran @ , and the co-combustion with the addrives (Sara n ® /CaO, Saran ® /KOH, and Saran ® /Ca(OH)z) at 500°C.

FORMATION OF ORGANOCHLORINE COMPOUNDS

81

100 9080-

70-' ~

-~

--

k5

6050-

~ N

,

40-

.

30 .

.

20-.

.

.

.

.

.

.

.

)

.

1°-I 0

.

.

@ SARAN

I

I

r I

I

I

SARAN/KOH (I :I) SARAN/KOH (I :2) Combustion Temperature 500 C

FIGURE 5. Comparison between the relative yieldsof the total important chlorinated organiccompounds from co-combustionof Saran® /KOH in a l:l and 1:2 ratios (based on chlorine) at 500"C. three orders o f magnitude greater than when HC1 was used.) Given these possibilities, the quenching effects o f the alkaline additives used in our study might be explained either by the neutralization o f HC1 or by reactions with •CI, produced during combustion• Two possible mechanisms have been proposed for thermal production of chlorinated c o m p o u n d s (12) as follows: U n d e r oxygen-surplus conditions, C12, produced from the reaction o f HC1 with oxygen, would be available to react further with organic compounds: HCI + .O. ~ C 1 .

+ -OH

HC1 + •O H ~ H 2 0 + "C1 2 •C1 --" C12 U n d e r oxygen-deficient conditions, transient hydrocarbon radicals may strip chlorine atoms from HC1, leading to direct chlorination:

In aqueous solution, carbonate anion is able to react with hydroxyl radical, •OH, and to deactivate this very reactive species• The carbonate radical, the product o f this reaction, is very much less reactive (13). H O . + CO3 2 ~ H O - + "CO3 Although there appear to be no reports on the kinetics o f a similar reaction between C1. and CO3 2-, in combustion experiments with paper pretreated with ferric chloride (7), it was reported that the yield o f o r ganochlorine c o m p o u n d s decreased significantly when carbonate was added. However, a shift toward higher molecular weight products was noted. The observed inhibition may have also been due to reaction o f C l . and O H - , since this reaction has been observed by K1/ining and Wolff (14) to be very fast. • C1 + CO3 2- ---" C1- + •CO3

•C I + • C H 3 + HC1 ~

HO

~CI

+ HO.

CH3CI + H.

:CH2 + HCI ~ CH2C1 + H .

Calcium oxide could react analogously with CI-, although again there appear to be no kinetic data for the reaction:

:CH- + HC1--- :CHCI + H . 0 2- + CI" ~ " 0 - + C 1 In principle, therefore, either simple neutralization or radical reactions could be occurring in the quenching process.

A tentative mechanistic explanation (outlined below) for the observation o f higher molecular weight or-

82

J. BANAEE AND R. A. LARSON

ganic products in experiments with carbonate is that the rate of attack of small, thermally-generated chlorine-containing free radicals on carbonate ion may be greater than that for attack of the larger odd-electron species. In other words, if a radical survives to the point of having more than three conjugated double bonds, it might be more likely to survive to form a polycyclic organochlorine compound than to quenched by CO32 . XC1 ~ C1. (X -- electron, CI, transition metal, organic structure) kL

R. + . C I ~ R C I (R- = a thermally-generated free radical or radical product) k2

COs 2- + CI'--" CI- + "C03 K, p r o b a b l y > K 2 but [CO32 ] > [ R . ] K~ for small R (2-6 C atoms) > K2 for large R (8 or more C atoms) CONCLUSIONS The general focus of this study has been to establish the temperature conditions under which organochlorine compounds were most and least efficiently formed from combustion of a commercial polymerized vinyl resin, (CH2=CC12), namely Saran ®, and how the yields of these compounds were affected by changes in physical and chemical conditions of combustion. The experiments were conducted at different temperatures, ranging from 400 to 700°C. Important chlorinated compounds produced were benzenes, styrenes, naphthalenes, and biphenyls. The highest distribution of the chlorinated compounds was between 400 to 600°C; however the optimum temperature at which the compounds formed the most efficiently was at 5000C (with the exception of the

chlorinated benzenes). The second set of experiments were undertaken to investigate the effects of various additives. Among the additives used (K2CO3, KOH, and CaO), addition of K O H in a 1:2 stoichiometric ratio (based on chlorine) diminished the total amount of organochlorine compounds by 51%.

REFERENCES 1. Eiceman, G. A., Clement, R. E., Karasek, and F. W. Analysis of fly ash from municipal incinerators for trace organic compounds. Anal. Chem. 51:2343-2350 (1979). 2. California Air Resources Board. Air pollution control at resource recovery facilities (1984). 3. Dougherty, R. C. and Collazo-Lopez, H. Reduction oforganochlorine emissions from municipal and hazardous wastes incinerators. Environ. Sci. Technol. 27:602-604 (1987). 4. Nielsen, K. K., Moeller, J. T., and Rasmussen, S. Reduction of dioxins and furans by spray drier absorption from incinerator flue gas. Chemosphere 15:1247-1254 (1986). 5. Gullett, B. K., Bruce, K. R., and Beach, L. O. Formation of chlorinated organics during solid waste combustion. Waste Mgmt. Res. 8:203-214 (1990). 6. Yasuhara, A. and Morita, M. Formation of chlorinated aromatic hydrocarbons by thermal decomposition of vinylidene chloride polymer. Environ. Sci. Technol. 22:646-650 (1988). 7. Larson, R. A, and Ellis, D. D. Products of incineration of unbleached paper in the presence of inorganic additives. Solid Waste Mgmt, Newslett. 2-3 (1990). 8. Ahling, B., Bjorseth, A., and Lunde, G. Formation of chlorinated hydrocarbons during combustion of polyvinyl chloride. Chemosphere 7:799-806 (1978). 9. Hawley-Fedder, R. A., Parsons, M. L., and Karasek, F. W. Identification of organic compounds produced during combustion of a polymer mixture. J. Chromatogr. 387:207-221 (1987). 10. Eklund, G., Pedersen, J. R., and Stromberg, B. Formation of chlorinated organic compounds during combustion of propane in the presence of HC1. Chemosphere 1 6 : 1 6 1 - 1 6 6 (1987). 11. Ballschmiter, K. and Swerev, M. Reaction pathways for the formation of polychlorodibenzodioxins (PCDD) and furans (PCDF) in combustion process. I. Fresenius Z. Anal. Chem. 328:125-127 (1987). 12. Pedersen, J. R. and Kallman, B. The chlorinating species in turbulent flame combustion of methane with hydrogen chloride present. Chemosphere 22:67-76 ( 1991 ). 13. Larson, R. A. and Zepp, R. G. Reactivity of the carbonate radical with aniline derivatives. Environ. Toxicol. Chem. 7: 265274(1988). 14. Kl~ining, U. K. and Wolff, T. Laser flash photolysis of HCIO, HBrO, and BrO- in aqueous solution. Reactions of Cl and Br atoms. Ber. Bunsenges. Phys. Chem. 89:243-245 (1985).

Open for discussion until 30 April 1993.