Pyrolysis and combustion of Aroclor 1254 contaminated dielectric fluids

Chemosphere, Vol.15, Nos.9-12, Printed in Great Britain

pp 1265-1271,

1986

0045-6535/86 $3.00 + .OO Pergamon Journals Ltd.

PYROLYSIS AND COMBUSTIONOF AROCLOR1254 CONTAMINATEDDIELECTRIC FLUIDS Gilbert Addis Electric Power Research Institute

DIOXlN 85-5th In t e r n a ti o n a l Symposium on Chlorinated Dioxins and Related Compounds

ABSTRACT Pyrolysis and combustion products were determined f or several levels o f PCB contamination in mineral o i l and other d i e l e c t r i c f l u i d s . Yields of PCDFs were roughly proportional to the quantity o f PCB in the feed. ~ACKGROIIND

The e l e c t r i c u t i l i t y industry as a major purchaser of PCBs in the past has been l e f t with a legacy of PCR problems of two d i f f e r e n t dimensions. Although the r e a l i t y of PCB as a problem is s t i l l heing dehated and evaluated, the industry is r e t r o f i l l i n g or replacing i t s PCB equipment at a steady pace. A short time ago, there were about 4N,O00 ( I ) PCB transformers in u t i l i t y hands with perhaps an equal or larger number owned by n o n u t i l i t y e n t i t i e s . Several well publicized PCR f i r e s (2,3) in the United States have accelerated the e f f o r t toward removal of the askarel (geneTic-term for PCB or PCB/tri-/tetrachlorobenzene) equipment. Two options are open for e l i m i n a t i o n of PCBs in transformers. The f i r s t is r e t r o f i l l i n g and the second is replacement of the transformer. Each method has i t s adherents and it s detractors. R e t r o f i l l i n g , in the absence of f u r t h e r improvement of the technology, takes more than a year before a transformer can be r e c l a s s i f i e d as uncontaminated (in the United States, below 50 ppm PCR). During most of this time, PCB concentration in the transformer f l u i d is s t i l l above 500 ppm because even i f one uses the best a v a i l a b l e technology, between 2 and 5% of the old l i q u i d remains behind a f t e r draining a transformer as thoroughly as possible. I t is estimated that t h i s residual takes approximately 3 months to come to e q u i l i b r i u m with the replacement f l u i d . The d i l u t i o n process must therefore be repeated several times before an appropriately low PCB level is reached. We understand that there is considerable research presently underway to speed up the removal of t h i s trapped mat er ial; however, the work has not yet come to f r u i t i o n . 14here physically possible, complete replacement of the transformer appears to be the easy way out. However, disposal of the transformer requires draining of the PCB followed by flushing with a solvent. The l i q u i d s must then be destroyed in a licensed i n c i n e r a t o r while the transformer carcass must go to a c e r t i f i e d l a n d f i l l . C e r t i f i e d l a n d f i l l s in the USA are rapidly disappearing and i t is also considered possible that these may become the next generation of problem cleanup s i t e s . A second area of concern is the roughly 2,000,ONO ( I ) mineral o i l transformers, which over the years have i n a d v e r t e n t l y become contaminated wit--h PCBs at the 50 ppm level or higher. About 10% of these are contaminated above 500 ppm and must be treated as PCB transformers. This pair of problems has fostered a need to learn more about the pyrolysis and combustion of PCB, both in i t s concentrated state, and at various levels of contamination in r e t r o f i l l f l u i d s , such as s i l i c o n e and mineral o i l . PCB is also of i n t e r e s t as a contaminant in t e t r a c h l o r o e t h y l e n e , because i t is a p o t e n tia l r e t r o f i l l f l u i d , although i t is more l i k e l y to be used as a replacement f l u i d . WORK PLAN

A project has been sponsored and p a r t i a l l y funded by the E l e c t r i c Power Research I n s t i t u t e (EPRI) for the New York State Department of Health to study pyrolysis and combustion 1265

1266

products of PCBs, both as a concentrated f l u i d and as a contaminant in mineral o i l and several replacement f l u i d s . In this project we define pyrolysis as the high-temperature decomposition of a f l u i d in an oxygen-depleted atmosphere. Combustionis defined as oxidation in the presence of an open flame and an excess of a i r . The work plan includes the investigation of Aroclor 1254, "neat," as well as at a 50, 500, and 5000 ppm impurity level in mineral o i l , silicone and tetrachloroethylene. Since a mixture of t r i - and tetrachlorobenzene is frequently found as diluent in askarels, these two compounds, both separately and as a blend, also are being investigated. EQUIPMENT & PROCESS

Pyrolysis Pyrolysis t r i a l s as described by Eadon (4) were conducted using a simple thermostatically controlled apparatus, capable of accommoTating a 6-cm diameter metal block within its 9-cm-long heated region. In order to minimize hazards and disposal problems, yet permit sufficient product formation to f a c i l i t a t e detection of PCDDs and PCDFs, pyrolyses were performed on 100 ul samples. In an attempt to d i f f e r e n t i a t e this work from other e a r l i e r and ongoing investigations, as well as to simulate more accurately certain catastrophic incidents, pyrolyses were conducted at atmospheric pressure. The necessity of containing the starting materials and nongaseous pyrolysis products in an open system led to the use of an 8 mm ID x 0.5 m glass tube, sealed at one end, and mounted v e r t i c a l l y . The material to be pyrolyzed was deposited at the sealed end, then inserted into a t i g h t - f i t t i n g hole in the preheated metal block in the heating apparatus. Typically, the liquid refluxed up .~,~; the inner walls of the tube; the length of ~ii~ ~ the tube and its comparatively large unheated volume kept the r e f l u x l e v e l well below the open end in a l l e x p e r i m e n t s . To assure containment, the topmost 5 cm of the tube was c h i l l e d in dry ice and the end of the tube was connected to a charcoal t r a p . No v i s i b l e m a t e r i a l was trapped in the c h i l l e d r e g i o n , and e x c e l l e n t mass balances were g e n e r a l l y observed• Combustion The design of the combustion apparatus was C.~r~.¢ also c o n s t r a i n e d by the necessity of assuring ~.~.e~-) t h a t a l l discharged gases pass through a r t r a p p i n g system capable of e f f i c i e n t removal of PCBs and any p o t e n t i a l l y t o x i c products. The combustion chamber c o n s i s t s of a I m ~ f I ..... ,, quartz tube w i t h a 22-mm ID. One end of the ~ ~ ~ ~! I~7 chamber accommodates a m o d i f i e d b l a s t burner ~. ~ ~ I ~ and inlet4'tube2" through which the end of a ~A ~.~! 1/16" x (1.6 x 635 mm) syringe needle is ~--" introduced via a i r t i g h t connections • The ~ i n l e t tube and needle are mounted to a l l o w ,~.,j sample i n t r o d u c t i o n i n t o the flame of the b l a s t b u r n e r . Sample a d d i t i o n is accomp l i s h e d using a lO-ml s y r i n g e mounted in a worm syringe drive. The combustion chamber Figure I : Pyrolysis Equipment is mounted in a furnace capable of maintaining temperatures of IO0-100Q°C in three independently controlled zones. The effluent of the combustion chamber is passed through a water f i l l e d impinger, then through an XAD-2 packed adsorbent tube which in turn is attached through an o r i f i c e to a vacuum l i n e . XAD-2 has been shown here and elsewhere to be an e f f i c i e n t trapping agent for polychlorinated dibenzofurans (PCDFs) and dibenzo-p-dioxins (PCDDs).

I

,

.L_

1267

Syringe needle and makeup gas

/

/Collection ,(

32 mm OD 25 mm ID

<

< Burner

IL

J

Heated zone 94.5 cm - 385 ml 115.5 cm

> EPRI6234

Figure 2:

Combustion Tube

Syringe needle 16 Ga

Septum

/

Ill

~ T o combustion tube

drive

N2 or makeup gas EPR~6234

Figure 3:

Feed Syringe

ANALYSIS Because of the hazardous nature of the compounds to be prepared and to check out equipment expeditiously using rapid analytical techniques, the t r i a l s were approached stepwise. I n i t i a l runs in each case were made with unchlorinated biphenyl to determine the s u i t a b i l i t y of the equipment and to find a f i r s t approximation of proper operating conditions. These runs were followed by t r i a l s using individual PCB congeners known to form specific PCDF mixtures. I t was anticipated that the r e l a t i v e l y simple products formed could be analyzed by capillary GC/EC or GC/FID after chromatographic cleanup. This technique was successful, except in the pyrolysis of contaminated mineral o i l . The mineral o i l i t s e l f produced a complex mixture, and i t was necessary, after appropriate up-front cleanup, to resort to the use of GC/MS from the start. Having thus optimized as far as possible operating conditions and analytical procedures, runs were f i n a l l y made using Aroclor 1254 as the test f l u i d .

1268

Figure 4:

Co~oustion Product Trap

RESULTS

Pyrolysis of Aroclor 1254 in Mineral Oil, Silicone, and C2Cl4 Under the conditions chosen for this project, conversion of PCBs to PCDFs in the t r i a l runs reached an approximate maximum around 550°C. Most of the subsequent runs with Aroclor 1254 were then made at this temperature setting. Where other temperatures were used, they have been noted in the text or tables. All runs were of 15 minutes duration. To minimize run-to-run experimental variations found in the preliminary work, and to produce larger samples for analysis, a series of six runs was made at each set of conditions. The six runs of each set were always made during a single day and combined randomly (prior to cleanup) into two composites for analysis. Results are tabulated in Tables I and 2. Note

TABLE h

Sample

PCDF Formed (ng~/Graa of "Mlxtume" py~lyzed:

Description

42682

100%Aroclor 1254

42583

100%Aroclor 1254

50854 50855

23782 TCDF

Total TCDF

1,300

123782 Base Peak PeCDF PeCDF

Total PeCDF

Base Peak HxCDF

Total HxCDF

Total HeCDF

8,200

16,000

8,000

8,000

965

5,500

10,000

5,100

5,100

5,000 ppmI in mineral oil

15.0

45.0

17.0

62.0

165

87.0

162

24.0

5,000 ppm in mineral oil

11.8

33.0

17.2

55.0

171

60.0

205

14.0

1.8

6.7

17.2

6.3

16.8

< 10

1.9

5.8

18.2

6.8

18.1

2.2

0.4

1.1

3.1

1.5

3.5

50856

500 ppm in mineral oil

1.6

60857

500 ppm in mineral oil

1.1

50858

50 ppm in mineral oil

3.1

50859

60 ppm in mineral oil

o.g

].7

45298

5,000 ppm8,4 in silicone

g.g

107.0

4.5

-

44295

5,000 ppm6 in tetrachloroethylene

1.2

2.g

4.6

42571

Native mix6 in mineral oil Added Found

(I)

Arcwclor 1254 in Insulating Fluids

g.3 9.1

17.2 (23478) 17.6

60

3.4

1.3

70.0

2.2

6.9

0.16

28.0

5.5

12.5

0.9

32.4 (234678) 23.0

OCDF

47

<2 0.23

56 (OCDD)

(2)

Each mineral oil sample represents a composite of three separate pyrolyses which were combined prior to analysis to minimize run-to-run variation. All pyrolyses at 560"C for 15 minutes. Includes coeluters on 0B-5 column.

(4) (5) (6)

Chlorinated fluorenes(?) at 10x higher level. 600°C. Mineral oil spiked with PCDFs to test method.

(3) 65o-c.

1269

TABLE 2: PCOFFormed (rig) per Gram of "Aroclor 1254 Pyrolyzed in Insulating Fluid

Sample Description

23782 TCDF

42582 42583 50854 50855 50856 50857 50858 50859 45298 44295

1,300 8,200 965 5,500 3,000 9,000 3,400 2,360 6,600 3,440 3,200 3,600 2,200 6,200 3,800 8,000 18,000 1,980 21,400 900 240 580 960

]00%Aroclor 1254 ]00%Aroclor 1254 5,000ppmI in mineral oil 5,000ppm in mineral oil 500 ppm in mineral oil 500 ppm in mineral oil 50 ppm in mineral oil 50 ppm in mineral oil 5,000ppm3 in silicone 5,000ppm4 in tetrachloroethylene

T o t a l 123782 BasePeak Total BasePeak Total TCDF PeCDF PeCDF PeCDF HxCDF HxCDF 12,400 11,000 13,400 11,600 22,000 34,000

16,000 10,000 33,000 34,200 34,400 36,400 62,000 68,000 14,000 5,600

8,000 5,I00 17,400 12,000 12,600 13,600 30,000 26,000 440 i,I00

Total HeCDF

OCDF

8,000 60 5,100 32,400 4,800 41,000 2,800 33,600 36,200 4,400 70,000 1,380 2,500

64

46

30 180

(I)

Eachmineral oil samplerepresents a couposite of three separatepyrolyses. Thesewere combinedprior to analysis to minimize run-to-run variation. All pyrolysesat 550°C for 15 minutes. (2) Includescoeluters on DB-5column. (3) 65ooc. (4) 600oc.

t h a t Tables I and 2 report the same data but expressed in d i f f e r e n t form. Table i shows ng PCDF formed per gram of t o t a l mixture p y r o l y z e d , while Table 2 shows ng PCDF per gram of Aroclor 1254. I t may be seen t h a t conversions of PCBs t o PCDFs are s u b s t a n t i a l l y i d e n t i c a l f o r a l l congeners and c h l o r i n a t i o n groups measured f o r 5000 and 500 ppm, and are less than an order of magnitude d i f f e r e n t f o r 100% PCB. Conversion appears t o increase s l i g h t l y at 50 ppm, but t h i s may be the r e s u l t of measuring e r r o r due to a n a l y t i c a l d i f f i c u l t i e s at t h i s l e v e l . Pyrolyses in s i l i c o n e and t e t r a c h l o r o e t h y l e n e show conversion e f f i c i e n c i e s q u a l i t a t i v e l y s i m i l a r to mineral o i l f o r t e t r a - and penta-CDF, but are apparently dropping o f f f o r higher c h l o r i n a t i o n l e v e l s . Added work must be done t o confirm these l e v e l s . Analysis of the p y r o l y s i s products of PCBs in both s i l i c o n e and t e t r a c h l o r o e t h y l e n e y i e l d e d q u a l i t a t i v e i n d i c a t i o n s of several products r e l a t e d to PCDF/PCDD. In s i l i c o n e , compounds t e n t a t i v e l y i d e n t i f i e d as c h l o r i nated fluorenes were found in the MS scans. Also, in p y r o l y z i n g I , Z , 3 , 4 , 5 pentachlorobiphenyl in CH3 H2 s i l i c o n e , a series of compounds CI CI (which may be methylated c h l o r i n a t e d C= fluorene) was found. Chlorine atoms plus methyl-groups t o t a l four in C Cly CI CI each case (Figure 5).

Tetrachloroethyleneadduci of PCB

P y r o l y s i s of 2-chlorobiphenyl in s i l i c o n e has fluorene as a major product. This has been compared with an authentic standard. Other compounds l i s t e d above as products in the s i l i c o n e and discussed in the t e t r a c h l o r o e t h y l e n e work below w i l l be compared with authentic standards before t h e i r presence is considered confirmed.

Methylated- chlorinated fluorene

H2 ClxJ ~ ~ ~ Cly Polychlorinated fluorene

F i g u r e 5:

C t x ~ ~ Cly Polychlorinatedbiphenylene

Compounds R e l a t e d t o PCDF/PCDD

1270

In the combustion and pyrolysis of 1254 in tetrachloroethylene, preliminary work shows that some d i f f e r e n t t e t r a - and penta-CDFs are being formed, compared to "neat" 1254 or 1254 in mineral o i l s . Chlorinated fluorene may also be forming. In a d d i t i o n , a compound that may be a reaction product of PCB and tetrachloroethylene is possible. Combustion of Aroclor 1254 in Mineral O i l , Silicone and C2CI4 Conversion for the isomer groups studied (Table 3) was near optimum f o r a combustion wall temperature of 550°C and a 3-second residence time. W i t h feed solutions of mineral o i l containing Aroclor 1254 at 50, 500, and 5,000 ppm, t r i - , t e t r a - , and penta-CDF conversion in ng/g PCB fed f e l l within a narrow range for each of the isomer groups. Under a l l conditions, hexa- and hepta-CDF formation was not detectable. Combustion t r i a l s with PCBs in s i l i c o n e were not completed successfully. Large quanti t i e s of SiO2 formed. The f i n e l y divided SiO2 tended to plug the equipment, p a r t i c u l a r l y the feed needle and the sample c o l l e c t i o n t r a i n . In C?CI4 s o l u t i o n , combustion yields were s i m i l a r to those found with mineral o i l for the -CI 3 isomers. There were s u b s t a n t i a l l y greater yields f o r the more highly c h l o r i nated isomers, r e f l e c t i n g c h l o r i n a t i o n of lower chlorinated CDFs. Combustion in C2CI 4 under oxygen depletion provldes a substantial y i e l d of biphenylenes.

TABLE 3:

C~ustion

Solvent MineralOil Mineral Oil MineralOil c2c14 C2Cl4 C2C14

of Aroclor 1254 in Insulati~ Fluids at 5 ~ ' C - 3 Seco~s

1254 in sol. PCB's Combusted Destroyed ~g/ml % 5000

Cl3

%PCDFsFormed(1) C14 CI~ C16

82-88

0.72

0.58

0.17

500

87-92

0.4

0.33

0.084_(2)

_(2)

50

88-90

0.3

0.3

0.056 _(2)

_(2)

68

0.44

1.50

1.35

0.33

0.50

500

92

0.24

0.7

0.66

0.23

0.70

50

72

0.44

1.32

1.0

0.38

0.16

5000

_(2)

C17 _(2)

Sllicone (3)

(I) Basedon PCB in feed. (2) Nonedetected. (3) Runsunsuccessful. Equipmentpluggedwith SiO2.

OTHER WORKIN PROGRESS Pyrolysis and combustion of t r i - and tetrachlorobenzene are underway in the laboratory. These results w i l l be of value in assessing the potential f i r e products from askarels where the PCB is d i l u t e d with these solvents. Preparation of certain synthetic chemicals such as substituted fluorenes is being undertaken. These w i l l be used to confirm the structure of several of the unknowns that appeared during the GC/MS analysis.

DISCUSSION Part of the o r i g i n a l impetus in t h i s project was to determine whether formation of p a r t i a l oxidation products of PCB was l i n e a r with increasing d i l u t i o n in a solvent. This question appears to be answered. Within the constraints of variations in analytical conditions and recoveries during cleanup and analyses of extremely small quantities of m a t e r i a l , the l i n e a r i t y should be considered good; in most cases, there was no more than a factor of 10 v a r i a t i o n in a range of concentrations from 50 ppm to 1001 of the askarel tested. Improvements in the pyrolysis and combustion schemes during the course of the project provided t h i s degree of resolution. No doubt, this can be improved upon with f u r t h e r sophistication in the work. The results of these laboratory t r i a l s are found to be s i g n i f i c a n t l y d i f f e r e n t from those of other workers in the f i e l d (5-9). This fact brings with i t a word of caution in applying any of these results to real-world PCB f i r e s except for use as guiding principles because each real PCB f i r e , under completely random conditions, is d i f f e r e n t from a l l others. Even

1271

within a given f i r e , there w i l l be an i n f i n i t e range of competing reactions. I t can be assumed that only a small portion of the combustion process has optimum conditions, and that the combustion process varies with time, leading to the partial destruction of the various combustion by-products. Thus, all of the research being done must be considered as setting a boundary or worst-case condition that gives a general direction to the investigation of the real world. A number of new avenues for exploration have been seen here and in the work of others. Among the more significant ones are the finding of r e l a t i v e l y large quantities of other chlorinated polycyclic aromatic compounds (PCAs). A second is the need for a more rapid method of analysis. A bioassay designated the Flat-Cell Assay (10), based on a change in in v i t r o growth and morphology of a line of skin cells has been s-s'fi-own to be very sensitive and ~ t i v e l y specific for the more toxic of the PCDF and PCDDcompounds. The biological mechanism of this effect is considered to be related to the development of chloracne in humans after 2,3,7,8-TCDF exposure and is thus, a relevant end point. This method is already applicable to certain products of combustion. I t is being modified to detect and assay these products in the presence of solvents such as mineral o i l , which currently interfere with the test. Calibration against a range of chlorinated PCAs would follow.

ACKNOWLEI)&~IENTS The help of K. Aldous, R. Briggs, G. Eadon, D. Hilker, K. Kidd, A. Narang, R. Narang, P. O'Keefe, and R. Smith are gratefully acknowledged. REFERENCES

I.

RPC. Volume I l l - Report of the Study of PCBs in Equipment Owned by the Electric U t i l i t y Industry. Prepared for the Edison Electric I n s t i t u t e , Washington, D.C., February 1982.

2.

N. C. Kim and G. Eadon. The Binghamton State Office Building. PCB By-product Formation, EPRI CS/EL-4104, July 1985, p. 5-1.

3.

R. L. Wade. U t i l i z a t i o n of Quantitative Risk Assessment Techniques in the Development of Decontamination Standards (A Case Study - San Francisco, California). Ibid, p. 5-16.

4.

G. Eadon. Pyrolysis and Combustion of Mineral Oil, Tetrachloroethylene and Silicone Oil Mixtures Containing Aroclor 1254. I b i d . , p. 3-24.

5.

S. E. Swanson, M. D. Erickson, and L. Moody. Products of Thermal Degradation of Dielectric Fluids. Prepared for the U.S. Environmental Protection Agency, Washington, DC. Interim Report No. 2, May 1985.

6.

H. R. Buser, H-P. Bosshardt, and C. Rappe. Formation of Polychlorinated Dibenzofurans (PCDFs) from the Pyrolysis of PCBs. Chemosphere 7 ( I ) , 1978, pp. 109-119.

7.

H. R. Buser and C. Rappe. Formation of Polychlorinated Dibenzofurans (PCDFs) from the Pyrolysis of Individual Isomers. Chemosphere 8(3), 1979, pp. 157-174.

8.

B. Dellinger, W. Rubey, D. L. Hall, and S. L. Mazer. Laborary Investigation of the High-Temperature Formation and Destruction of PCDFs. Workshop Proceedings: PCB Byproduct Formation, EPRI CS/EL-4104, July 1985, p. 3-17.

9.

C. Rappe, S. Marklund, and L-O. Kjeller. p. 3-28.

10.

Workshop Proceedings:

Formation of PCDFs from PCBs. I b i d . ,

J. F. Gierthy and D. Crane. In Vitro Bioassy for Dioxin-Like A c t i v i t y Based on Alterations in Epithelial Cell Proliferation and Morphology. Fundamentals in Applied Toxicology, Vol. V, 1975, in press.