Formation of PCDDs and PCDFs during the combustion of polyvinylidene chloride

Preparation and characterization of poly(ethylene terephthalate) films coated by chitosan and vermiculite nanoclay

Chitosan (CS) layers are coated on a poly(ethylene terephthalate) (PET) film in order to decrease the oxygen permeability through the polymeric films for food packaging applications. Oxygen transmission rate (OTR) of the 130 μm PET films can be decreased from 11 to only 0.31 cm³/m².day with a coated layer of 2 μm of CS. Additional decrease is obtained with the addition of vermiculite (VMT) to CS matrix in high proportion (40 to 50 w/w%). The OTR of the coated PET films decreased to very low values, below the detection limit of commercial instrumentation (≤0.008 cm³/m² day). This high-barrier behavior is believed to be due to the brick wall nanostructure, which produces an extremely tortuous path for oxygen molecules.

Dioxins from medical waste incineration: Normal operation and transient conditions

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are key pollutants in waste incineration. At present, incinerator managers and official supervisors focus only on emissions evolving during steady-state operation. Yet, these emissions may considerably be raised during periods of poor combustion, plant shutdown, and especially when starting-up from cold. Until now there were no data on transient emissions from medical (or hospital) waste incineration (MWI). However, MWI is reputed to engender higher emissions than those from municipal solid waste incineration (MSWI). The emission levels in this study recorded for shutdown and start-up, however, were significantly higher: 483 ± 184 ng Nm(-3) (1.47 ± 0.17 ng I-TEQ Nm(-3)) for shutdown and 735 ng Nm(-3) (7.73 ng I-TEQ Nm(-3)) for start-up conditions, respectively. Thus, the average (I-TEQ) concentration during shutdown is 2.6 (3.8) times higher than the average concentration during normal operation, and the average (I-TEQ) concentration during start-up is 4.0 (almost 20) times higher. So monitoring should cover the entire incineration cycle, including start-up, operation and shutdown, rather than optimised operation only. This suggestion is important for medical waste incinerators, as these facilities frequently start up and shut down, because of their small size, or of lacking waste supply. Forthcoming operation should shift towards much longer operating cycles, i.e., a single weekly start-up and shutdown.

Role of temperature and hydrochloric acid on the formation of chlorinated hydrocarbons and polycyclic aromatic hydrocarbons during combustion of paraffin powder, polymers, and newspaper

Formation of chlorinated hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were determined using a laboratory-scale incinerator when combusting materials at different temperatures, different concentrations of hydrochloric acid (HCl), and when combusting various types of polymers/newspaper. Polychlorobenzenes (PCBz), polychlorophenols (PCPhs), polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and their toxic equivalency (TEQ) and PAHs were highlighted and reported. Our results imply maximum formation of chlorinated hydrocarbons at 400 degrees C in the following order; PCBz>or=PCPhs>>PCDFs>PCDDs>TEQ on a parts-per-billion level. Similarly, a maximum concentration of chlorinated hydrocarbons was noticed with an HCl concentration at 1000 ppm with the presence of paraffin powder in the following order; PAHs>PCBz>or=PCPhs>>PCDFs>PCDDs>TEQ an a parts-per-billion level. PAHs were not measured at different temperatures. Elevated PAHs were noticed with different HCl concentrations and paraffin powder combustion (range: 27-32 microg/g). While, different polymers and newspaper combusted, nylon and acrylonitrile butadiene styrene (ABS) produced the maximum hydrogen cyanide (HCN) concentration, concentrations of PCDD/FS, dioxin-like polychlorinated biphenyls (DL-PCBs), and TEQ were in a decreasing order: polyvinylchloride (PVC)<newspaper<polyethyleneterephthalate (PET)< polyethylene (PE)< polypropylene (PP)< ABS = blank. Precursors of PCBs were in a decreasing order: PP<nylon<PE<newspaper<ABS<PVC<blank<PET. Precursors of PCDD/Fs were in a decreasing order: newspaper <PP=nylon<PE<ABS<PVC= blank<PET. BTX formation was in a decreasing order; PE<nylon<newspaper<ABS<PP. PAHs formation were elevated with parts-per-million levels in the decreasing order of PP<nylon<PE<newspaper<blank<ABS< PET<PVC.

Dioxin formation from waste incineration

There has been great concern about dioxins-polychlorinated dibenzo dioxins (PCDDs), polychlorinated dibenzo furans (PCDFs), and polychlorinated biphenyls (PCBs)-causing contamination in the environment because the adverse effects of these chemicals on human health have been known for many years. Possible dioxin-contamination has received much attention recently not only by environmental scientists but also by the public, because dioxins are known to be formed during the combustion of industrial and domestic wastes and to escape into the environment via exhaust gases from incinerators. Consequently, there is a pressing need to investigate the formation mechanisms or reaction pathways of these chlorinated chemicals to be able to devise ways to reduce their environmental contamination. A well-controlled small-scale incinerator was used for the experiments in the core references of this review. These articles report the investigation of dioxin formation from the combustion of various waste-simulated samples, including different kinds of paper, various kinds of wood, fallen leaves, food samples, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene chloride, polyethylene tetraphthalate (PET), and various kinds of plastic products. These samples were also incinerated with inorganic chlorides (NaCl, KCl, CuCI2, MgCl2, MnCl2, FeCl2, CoCl2, fly ash, and seawater) or organic chlorides (PVC, chlordane, and pentachlorophenol) to investigate the role of chlorine content and/or the presence of different metals in dioxin formation. Some samples, such as newspapers, were burned after they were impregnated with NaCl or PVC, as well as being cocombusted with chlorides. The roles of incineration conditions, including chamber temperatures, O2 concentrations, and CO concentrations, in dioxin formation were also investigated. Dioxins (PCDDs, PCDFs, and coplanar-PCBs) formed in the exhaust gases from a controlled small-scale incinerator, where experimental waste samples were burned, were analyzed by gas chromatography/mass spectrometry. Formation of total PCDFs was much higher than that of PCDDs in all samples. The total PCDFs comprised 70%-90% of the total dioxin formed. The amount of total PCDFs formed ranged from 0.78 ng/g (newspaper) to 8,490ng/g (PVC burned in high CO concentration). The amount of total PCDDs formed ranged from 0.02ng/g (newspaper) to 430ng/g (PVC). Coplanar PCBs were found at the lowest level of the dioxins formed. Their formation levels ranged from 0ng/g (newspaper) to 77.6ng/g (PVC). It is obvious that the samples with either inorganic or organic chlorides produced much more dioxins than the sample without chlorides when incinerated under similar conditions. It is not clear how inorganic and organic chloride contribute differently to dioxin formation. Among the metals examined, copper seems to have higher activity toward dioxin formation than other metals. It acted not only as a catalyst but also as a transmitter of heterogeneous chlorine. The toxicity equivalence quantity (TEQ) values generally correlated with the amount of chlorine content in the samples and the amount of dioxin formed in exhaust gases from an incinerator. When the same sample was incinerated at different temperatures, however, the sample burned at low temperature yielded a higher TEQ value than did the sample burned at high temperature. The samples that did not contain chlorine or were not combusted with chlorides exhibited low TEQ values. In contrast, samples with high chlorine content, such as PVC (51.3%), gave high TEQ values. Combustion temperatures may play an important role in dioxin formation in exhaust gases from the incineration of waste materials. However, no significant relationship between dioxin formation and chamber temperatures was reported in the core articles. However, It is obvious that dioxin formation occurred at temperatures above 450'C and was reduced significantly at temperatures above 850 degrees C. The reaction occurring in an incinerator is extremely complex, and there are many factors in addition to combustion temperature influencing dioxin formation. Even though it is possible to hypothesize reasonable formation mechanisms of dioxins produced in exhaust gases according to the results obtained from experiments in classical chemistry, the reactions involved in an incinerator are extremely complex and heterogeneous. More detailed investigation of the many individual factors influencing dioxin formation is needed to find ways to reduce their formation in individual and municipal incinerators.

Simultaneous determination of gaseous and particulate chlorinated polycyclic aromatic hydrocarbons in emissions from the scorching of polyvinylidene chloride film

An analytical method for the determination of gaseous and particulate chlorinated polycyclic aromatic hydrocarbons (ClPAHs) was investigated. By means of this method, concentrations and isomer profiles of the 27 target ClPAHs could be analyzed. To evaluate the usefulness of the method for analyzing ClPAH emissions, laboratory-scale scorching tests were performed on polyvinylidene chloride (PVDC) plastic wrap over a flame of the gas burner. Only seven of the target ClPAHs were detected, and all compounds detected had 2, 3, or 4 rings. The detected ClPAHs were present in both the particulate phase and the gaseous phase, but they were present at higher concentrations in the gaseous phase than in the particulate phase. Relationships between the number of chlorine substituents on the naphthalene/phenanthrene rings and the overall concentration and the percentage in the particulate phase were also investigated.

Formation of dioxins from combustion of polyvinylidene chloride in a well-controlled incinerator

Polyvinylidene chloride (PVDC; polymer of 1,1-dichloroethylene) was combusted with paper in a well-controlled, small-scale incinerator at an average grate temperature of 700 degrees C, and then dioxins (PCDDs, PCDFs, and coplanar-PCBs) formed in the exhaust gases were analyzed by gas chromatography/mass spectrometry. PVDC lowered the combustion temperature due to its less flammable character. The amount of total dioxins (PCDDs+PCDFs+coplanar-PCBs) formed in the exhaust gas was 58.0 ng/g of a combustion sample and its toxicity equivalency quantity (TEQ) value was 0.64 ng-TEQ/g. The amount of PCDDs formed in the sample ranged from 2.33 ng/g (Cl(8)-isomer) to 0.048 ng/g (Cl(1)-isomer). The lower the number of chloride, the less production of PCDDs. On the other hand, there was no relation between the number of chloride and PCDF formation. The amount of PCDFs formed in the sample ranged from 8.02 ng/g (Cl(2)-isomer) to 4.46 ng/g (Cl(8)-isomer). A polyvinylchloride (PVC) sample produced 207 ng/g of total dioxins and a PVDC sample produced 57.4 ng/g of total dioxins when they were combusted under the same conditions. An approximately equal composition of dioxin isomers was formed from PVDC and PVC samples. Paper was found to contribute to PCDF formation when it was combusted with plastics.

Emission characteristics of PCDD/Fs, PCBs, chlorobenzenes, chlorophenols, and PAHs from polyvinylchloride combustion at various temperatures

The effect of temperature on polyvinylchloride (PVC) combustion using a downstream tubular furnace was investigated for the formation of polycylcic aromatic hydrocarbons (PAHs) and chlorinated compounds. As the temperature increased, higher levels of PAHs were generated. Chlorinated compounds reached a peak at 600 degrees C, with low emissions recorded at 300 and 900 degrees C. There was a close correlation (R2 = 0.97) among polychlorinated biphenyls (PCBs), hexachlorobenzene, pentachlorobenzene, and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). PAHs at all temperatures were analyzed in the gas phase. PCDD/Fs and PCBs were emitted as a solid phase at 300 and 600 degrees C and as a gas phase at 900 degrees C. For some PAHs, chlorobenzenes, and PCDD/Fs, a mathematical equation between the gas and solid phase and the reciprocal temperature in semilog proportion was derived. The proposed equation, which is log (amount in gas phase/amount in solid phase) = -A/T + B, where T is the temperature of the furnace and A and B are constants, for these species relating their gas/solid distributions showed a good relationship.

Formation of PCDDs and PCDFs during the combustion of polyvinylidene chloride and other polymers in the presence of HCl

PVDC and three non-chlorinated polymers (PP, PET, and PA) were incinerated at 700-850 degrees C in a laboratory-scale quartz tubular furnace in the presence of HCl (ca. 500 ppm congruent with 0.8 mg/l), and the gas-phase formation of PCDD/Fs, their putative precursors and their homologue profiles were investigated. The addition of HCl had little or no apparent effect on the level of PCDD/Fs formation during PVDC combustion, and their homologue profiles were quite different from those of the three non-chlorinated polymers. With PVDC, O8CDD and particularly O8CDF were by far most prevalent, apparently as a result of the selective formation of the precursors. With each of the three non-chlorinated polymers, combustion at 800 degrees C or higher in the presence of HCl resulted in PCDD/Fs formation at levels equaling or exceeding those observed with PVDC. In trials made with one of them (PP) under the same conditions but using a large polymer sample (100 mg vs 20 mg in all other trials), the level of PCDD/Fs formation was far higher than with the smaller polymer samples, and thus demonstrated the importance of appropriate combustion conditions for polymer incineration.

Chlorinated aromatics from combustion: influence of chlorine, combustion conditions, and catalytic activity

Research on the formation of chlorinated aromatics in combustion processes has mainly taken place in the laboratory. Previous attempts to correlate observation data from commercial plants have been inconclusive. This study reports on the outcome of an industrial experiment in a full-scale afterburner. The influence of chlorine input, combustion temperature, and catalytic activity was investigated in a factorial design with two blocks. Polychlorinated benzenes, dibenzo-p-dioxins, and dibenzofurans were formed both at combustion temperatures and below 400 degrees C. The results show that all three experimental factors have statistically significant impact on the formation and release of these toxic byproducts. The quantitative dependence between chlorine input and the occurrence of chlorinated aromatics is of particular interest due to previous controversy. The purpose with this study was to ensure that the installation of a boiler for energy recovery would not cause elevated emissions of chlorinated aromatics. The experiment demonstrated that this risk is probably low, since the presence of catalytic material or an increase in chlorine input is required for this to happen. A general conclusion was that industrial experimentation employing the principles of statistical design could improve the validity in recommendations regarding commercial plant operation.