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58Comparative study of the radiolysis and photolysis of the ethanol solutions of polychlorinebiphenyls
Section 7. High energy chemistry
Jamalov Punhan Jamaleddin, Qafqaz University, Baku, Azerbaijan, dissertant
Abdullayev Elshad Tofiq, Institue of Radiation Problems, ANAN, senior reseacher
Kurbanov Muslum Ahmad, Institue of Radiation Problems, ANAN, the Head of Laboratory
Mammadov Sahib Giyas, Institue of Radiation Problems, ANAN, senior reseacher E-mail: mammadov_sahib@yahoo.com
Inkenderova Zenfira Iskender, Institue of Radiation Problems, ANAN, leading researcher
Comparative study of the radiolysis and photolysis of the ethanol solutions of polychlorinebiphenyls
Abstract: Model solutions of polychlorinebiphenyls, containing 12 congeners in ethanol were irradiated by gamma rays at 14-140 kGy absorption doses, as well as by UV-rays for 2-30 minutes using middle pressure mercury lamp (PRK-4, \ = 253 ^ 546 nm.), and the kinetics of the radiolytic PCBs degradation processes was investigated. The PCBs identification was conducted using a Gas Chromatography (Agilent Technologies 7820A).
Keywords: Polychlorinebiphenyls (PCBs), radiolysis, gamma radiation, photolysis, UV-rays, degradation.
Introduction
Polychlorinebiphenyls (PCBs) containing oils are being used at existing power facilities (transformer, capacitor, electric switches) though its production has been banned during 1987-1990. This case causes a “cross” pollution of “PCB clean” transformers. PCBs were included to the list of the Stockholm Convention on Persistent Organic Compounds, where it was stated that oils containing more than 50 ppm PCBs must be discontinued and utilized by the members states by 2028.
Several methods exist in the utilization of oils containing PCBs. These methods are divided into 2 major groups: full fractioning of PCBs (pyrolysis or high temperature incineration processes) and dechlorination (low temperature processes). Among
second group processes the application of radiation technology has a special importance. By this method the processes are made at room temperature, one-phased, without additional reagents and in the result, biphenyls and chloride acid are generated. Some research works have been conducted in this sphere [1-4]. One of the limitations of the application of the radiation chemical method is relatively week studies of radiation and photo stability of PCBs.
Results and discussion
The comparative radiolysis and photolysis process ofthe ethanol solutions ofPCBs have been presented in this work. For this purpose, model solutions of PCBs containing 12 congeners in hexane were irradiated by gamma-rays at 14-140 kGy absorption doses, as
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Section 7. High energy chemistry
well as by UV-rays for 2-30 minutes using middle pressure mercury lamp (PRK-4, \ = 253 + 546 nm., f = 1,5T0 15 quant/(sm 3^sec), and the kinetics of the PCBs degradation processes was investigated.
A standard (CEN PCB Congener Mix 1, 10 ug/ml in heptane, Supelco), containing 12 PCBs congeners (PCB 18 (2, 2’, 5 - trichlorbiphenyl), PXB 28+31 (2, 4, 4’- trichlorbiphenyl + 2, 4’, 5 - trichlorbiphenyl), PXB 52 (2, 2’, 5, 5’ - tetrachlorobiphenyl), PCB 44 (2,2’,3,5- tetrachlorobiphenyl), PCB 101 (2, 2’, 4, 5, 5’ - pentachlorobiphenyl), PCB 118 + 149 (2, 3’, 4, 4’, 5 - pentachlorobiphenyl+2, 2’, 3, 4’, 5’, 6 - he-xachlorobiphenyl), PCB 153 (2, 2’, 4, 4’, 5, 5’ - he-xachlorobiphenyl), PCB 138 (2, 2’, 3, 4, 4’, 5’ - he-xachlorobiphenyl), PCB 180 (2, 2’, 3, 4, 4’, 5, 5’ - he-ptachlorbiphenyl),PCB194(2, 2’, 3, 3’, 4, 4’, 5, 5’ - octa-chlorobiphenyl)) was used in order to prepare model
solutions. Primary concentration of PCBs in the model solution was as follows:
• PXB 18 - 3.0 • 10-7 mol/l;
• PCB 28+31 - 5.9 • 10-7 mol/l,
• PCB 52 - 2.6 • 10-7 mol/l,
• PCB 44 - 2.6 • 10-7 mol/l,
• PCB 101 - 2.3 • 10-7 mol/l,
• PCB 118 + 149 - 4.4 • 10-7 mol/l,
• PCB 153 - 2.1 • 10-7 mol/l,
• PCB 138 - 2.1 • 10-7 mol/l,
• PCB 180 - 1.9 • 10-7 mol/l,
• PCB 194 - 1.8 • 10-7 mol/l.
The PCBs identification was conducted using a Gas Chromatography (Agilent Technologies 7820A) [5]. The primary (a), after radiolysis (30 kGy) (b) and photolysis (5 min.) (c) chromatogrammies of PCB solutions in hexane are presented in Fig. 1.
a)
b)
c)
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Fig. 1. The chromatogrammies of the PCB solutions in ethanol: a) — primary, b) — after radiolysis (30 kGy), c) — after photolysis (5 min.) (1 — PCB 18; 2 — PCB 28+31; 3 — PCB 52; 4 — PCB 44; 5 — PCB 101; 6 — PCB 118 + 149; 7 — PCB 153; 8 — PCB 138; 9 — PCB 180; 10 — PCB 194)
Comparative study of the radiolysis and photolysis of the ethanol solutions of polychlorinebiphenyls
As seen from the Fig. 1, in the result of PCB dechlorination process the quantity ofPCBs (the area of corresponding peaks) strongly decreases during both radiolysis (b) and photolysis (c) process. The number of the peaks at the chromatogrammies of the photolysed and radiolysed samples is more than the number of the peaks at the chromatogrammies from the original solution analysis. It seems, that the
PCBs, contaning a low chlorine atoms are formed during the dechlorination process of PCBs having more chlorine atoms.
The dose (D) dependency of concentration (C) of PCB 18, 52, 101, 153 and 180 at the radiolysis in ethanol solution is illustrated in Fig. 2 and the
dependency for concentration (C) of irradiation time (t) at photolysis is illustrated in Fig. 3.
Fig. 2. The kinetics of PCBs degradation at the radiolysis of ethanol solutions (1 — PCB 18, 2 — PCB 52, 3 — PCB 101,4 — PCB 153, 5 — PCB 180)
Fig. 3. The kinetics of PCBs degradation (1 — PCB 18, 2 — PCB 52, 3 — PCB
As seen from the Fig. 2 and 3, PCB 153 and 180 in ethanol solution at both radiolysis and photolysis are quickly dechlorinated at low irradiation doses (up to 30 kGy — radiolysis and 10 minutes — photolysis accordingly), but the dechlorination rate slows down at the further doses. The degradation
at the photolisys of ethanol solutions 101,4 — PCB 153, 5 — PCB 180)
kinetics of PCB 28+31, 44, 118+149, 138 and 194 are analogous to PCB 153 and 180. The quantity of PCB 18, 52 and 101 increases (up to ~14 kGy and ~5 minutes) at both radiolysis and photolysis at low irradiation doses, but their quantity decreases at further irradiation doses. 51
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Section 7. High energy chemistry
The reason of the difference in PCBs degrada- PCB 101 molecule, PCB 18 from PCB 44 and
tion kinetics at the radiolysis and photolysis is that PCB 52, PCB 180 from PCB 194, and PCB 153
new PCB congener is formed in the result dechlo- from PCB 180.
rination. Thus, PCB 101 may be formed when one The degradation degrees of PCB at the radiolysis
chlorine atom comes off the PCB 153 molecule, (30 kGy) and photolysis (15 min) are presented on
PCB 52 when one chlorine atom comes off the the Table 1. 52
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Comparative study of the radiolysis and photolysis of the ethanol solutions of polychlorinebiphenyls Table 1. - The degradation degrees of the hexane solutions of PCBs during radiolysis and photolysis
PCB 18 28+31 52 44 101 118+149 153 138 180 194
Initial concentration, 10-7 mol/l 3.0 5.9 2.6 2.6 2.3 4.4 2.1 2.1 1.9 1.8
Degradation degrees, % (mol) Radiolysis (30 kQr) 55.8 72.5 30.0 68.7 42.1 76.4 79.3 83.1 87.0 94.3
Photolysis (15 min.) 56.6 100 18.7 95.7 76.7 100 93.9 100 98.6 96.9
As seen from table 1, the degradation degree of sing et state happens in PCB mo ecules with t he UV-
PXB 18, 52, and 101 is less than other components.
Also, it’s seen from the degradation degree numbers of the hexane solutions of PCBs during radiolysis and photolysis that the photolysis process is more effective than radiolysis. 1.
At the radiolysis y-rays are absorbed by ethanol molecules as the electronic density of ethanol in solution is more than PCBs and the dissolved oxygen. And the PCBs transformation happens at the reactions of radicals derived from ethanol radiolysis. 2. The ethanol molecules don’t absorb UV-rays during photolysis as its absorbing spectrum is not within 253-546 nm. wave length (Amax= 180 nm). In this range of A. = 253 ^ 546 nm. a selective excitation of
References:
irradiation of 200-300 nm. wave length [8]. Excitation is transferred to a triple state with the inter-combination conversion and the PCBs are dechlorinated. Conclusion
Kinetics of radiolytic and UV-photochemical degradation of12 PCBs congeners in ethanol was studied. Degradation degrees of PCBs were about 56-94 % at 30 kGy and 57-97 % at 15 min. of UV-radiation.
The specification of the degradation kinetics of the given PCBs congeners was identified. For the some congeners the analogy of the degradation kinetics at the radiolysis and UV-photolysis was observed.
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