PCBs, polychlorinated biphenyls (polychlorinated biphenyls), are the generic names given to the class of organochlorine compounds resulting from the reaction of the biphenyl group with anhydrous chlorine in the presence of a catalyst. They are toxic, persistent, bioaccumulative and pose the risk of causing harm to human health and the environment. Large quantities of PCBs were produced in several countries between 1927 and 1977. In the United States the prohibition occurred in 1977. Due to high toxicity, production and marketing of PCBs have been banned worldwide since 1980. It was carried out at the Chemistry Institute of Sao Carlos—University of Sao Paulo, and developed a procedure for decontamination of mineral insulating oil containing PCBs values above 50 mg/kg. In the procedure, the contaminated oil was passed by percolation in a column containing polyurethane foam derived from vegetable oil, produced by the Laboratory of Analytical Chemistry and Polymer Technology (GQATP), thus obtaining a 55% reduction in the levels of PCBs.
The term “mineral oils” refers to oils derived directly from natural petroleum, thus distinguishing it from other oils of vegetable or animal origin. Insulating mineral oils are obtained by appropriate refining and extraction processes from certain fractions of natural petroleum distillation. In principle they consist exclusively of hydrocarbons and may also contain impurities or traces of special additives [
The procedure for insulating mineral oils was performed according to ABNT NBR 13882 [
The extraction of PCBs present in insulating mineral oil was performed using a ratio of 1:20 (v/v) oil and n-hexane. This dilution of the oil in n-hexane facilitated the interaction of the PCBs with the polyurethane foam, increasing the extraction efficiency. Clean-up is an analytical procedure that removes interfering compounds in the determination of specific analytes such as PCBs. A 2.0 mL volume of oil was eluted by gravity in FlorisilÒ SPE adsorbent cartridge purchased from Agilent Technologies. The eluted fraction was diluted in n-hexane, then injected in triplicate in CG-DCE, through an automated system, thus reducing the possibility of injected volume errors in the quantification of PCBs.
Gas chromatography analyzes were performed on a Shimadzu GC-2010 Chromatograph equipped with electron capture detector (DCE). An RTX5MS capillary column, 30 m long, 0.25 mm internal diameter, 0.25μm film thickness, 5% Diphenyl, 95% Dimethylpolysiloxane was used. The conditions of the chromatographic analysis method were: Temp.; Column: 170˚C (1 min.) 5˚C/min. to 200˚C (0.0 min.) 10˚C/min. to 300˚C (5 min). Temp.; DCE Detector: 300˚C; Injector: 280˚C; Vol. Injection: 1.5 mL; Pressure: 64.6 Kpa; Total Flow: 13.3 mL/min, Column Flow: 0.94 mL/min, Purge Flow: 3.0 mL/min, Split: 1:10, Carrier Gas: N2.
Solutions of the standards of Arocloros 1242, 1254 and 1260 were obtained from Supelco USA. Initially they were prepared separately and then using a mixture of the three standards, as shown in
The analytical curve (
The method used in the determination of PCBs in insulating mineral oil was by comparing the total area called the “arochloric region” obtained in the sample, with the total area obtained by the analytical curve. This method has been recommended mainly for the analysis of mineral insulating oil used in transformers [
In order to verify the adsorption efficiency of PCBs in polyurethane foam
derived from vegetable oil, a sample of PCB-free insulation mineral oil was used for saturated column percolation immediately after the elution of a contaminated oil. This oil, free of PCBs, should not show traces of PCBs after passage through the column. As the limits of detection considered were three times the height of the noise, the values obtained for the oil used, about 2.0 mg・kg−1, are within the limit of detection of the method.
Sorption of a compound of a solution into a solid occurs as a result of one of two characteristics in a given system, or the combination of both. The first driving force may be a consequence of the lack of affinity of the compound for the solvent, lipophilicity, while the second is due to the higher affinity of the solute for the solid. In most situations there is a combination of the two forces [
In order to verify the behavior of the saturation curves determining the non adsorbed quantity after the elutions, three types of foams were used: 1) Functionalized foam containing ammonium polysulfide, 2) Functionalized foam containing thiodiglycol, 3) Non-functionalized foam.
50 mL of insulating oil (65 mg・kg−1 PCBs) were eluted at 40˚C through 2.0 g of ammonium polysulphide-containing functionalized foam, as shown in
again by separating a new aliquot, and so on, until 10 aliquots were obtained.
In
50 mL of mineral insulating oil (65 mg・kg−1 of PCBs) was eluted at 40˚C through 2.0 g of thiodiglycol containing functionalized foam, as shown in
The results of
50 mL of insulating oil (65 mg・kg−1 of PCBs) were eluted at 40˚C through 0.1 g (
The previous results (
The results shown in
elutions suggest that when using the functionalized foam with thiodiglycol and ammonium polysulfide, there is a marked increase in PCB adsorption by the foam only at the beginning of the process. After this adsorption is decreased,
indicating that there may be some competition from the solute (PCBs) to reach the active centers of the surface (triglyceride of the ricinoleic acid present in the foam) it is well evident that the nonfunctionalized foam adsorbed a larger amount of PCBs, result shows a smaller amount of it after the elutions.
The results of
The results presented in
In
The results of
solvent in the desorption of PCBs adsorbed on non-functionalized polyurethane foam at 40˚C, that temperature was used because of better adsorption. The PCB values were obtained after five cycles of solvent extraction until removal of the PCBs, every five cycles of approximately 2 hours in a total of 8 hours the solvent was replaced until the PCBs value did not vary further, within the chromatographic error.
The extraction results of PCBs adsorbed onto the foam using the n-hexane solvent, shown in
The adsorption of polychlorinated biphenyls (PCBs) in mineral insulating oil was studied in a thermostatic glass column containing foam disc and pulverized rigid polyurethane foam derived from vegetable oil.
Analyzing the results of these experiments it was verified that the objective of the research was reached, since the reduction of the initial content of 65 mg・kg−1 of PCBs contained in the oil to 29 mg・kg−1 presented a reduction of 55% above the specified minimum value of 50 mg・kg−1. Therefore, this research reached the proposed objective for the reuse of the insulating mineral oils subjected to this adsorption and desorption process aiming at decontamination, minimization of costs and environmental impacts.
Our sincere thanks to CAPES, CNPq and FAPEMIG for financial support.
The authors declare no conflicts of interest regarding the publication of this paper.
Camargo, M.A.F., dos Santos, A.M., Chierice, G.O., Neto, S.C. and Landgraf, M.D. (2018) Polyurethane Foams Derived from Vegetable Oil Used in the Adsorption of Polychlorinated Biphenyls Present in Insulating Mineral Oil. Open Access Library Journal, 5: e4945. https://doi.org/10.4236/oalib.1104945