Evaluation of thermal drying for the recycling of flexible plastics.

The drying of flexible plastic waste is a current industrial problem in the plastic recycling sector. The thermal drying of plastic flakes is considered the most expensive and the most energy-consuming step in the recycling chain, which represents an environmental issue. This process is already present on the industrial scale but not well described in the literature. A better understanding of this process for this material will lead to the design of environmentally efficient dryers with an improved performance. The objective of this research was to investigate the behavior of flexible plastic in a convective drying process at a laboratory scale. The focus was to study the factors affecting this process such as velocity, moisture, size and thickness of the plastic flakes in both fixed and fluidized bed systems and to develop a mathematical model for predicting the drying rate considering heat and mass transfer of convective drying. Three models were investigated: the first one was based on a kinetic correlation of the drying, and the second and third models were based on heat and mass transfer mechanisms, respectively. It was found that heat transfer was the predominant mechanism of this process, and the prediction of the drying was possible. The mass transfer model, on the other hand, did not give good results. Amongst five semi-empirical drying kinetic equations, three equations (Wang and Singh, logarithmic and 3rd-degree polynomial) provided the best prediction for both fixed and fluidized bed systems.

Debromination of Waste Circuit Boards by Reaction in Solid and Liquid Phases: Phenomenological Behavior and Kinetics.

The debromination of waste circuit boards (WCBs) used in computer motherboards and components has been studied with two different pieces of equipment. Firstly, the reaction of small particles (around one millimeter in diameter) and larger pieces obtained from WCBs was carried out with several solutions of K2CO3 in small non-stirred batch reactors at 200-225 °C. The kinetics of this heterogeneous reaction has been studied considering both the mass transfer and chemical reaction steps, concluding that the chemical step is much slower than diffusion. Additionally, similar WCBs were debrominated using a planetary ball mill and solid reactants, namely calcined CaO, marble sludge, and calcined marble sludge. A kinetic model has been applied to this reaction, finding that an exponential model is able to explain the results quite satisfactorily. The activity of the marble sludge is about 13% of that of pure CaO and is increased to 29% when slightly calcinating its calcite at only 800 °C for 2 h.

Debromination and Reusable Glass Fiber Recovery from Large Waste Circuit Board Pieces in Subcritical Water Treatment.

The great economic, social, and environmental interest that favors an effective management of the recycling of waste printed circuit boards (WCBs) encourages research on the improvement of processes capable of mitigating their harmful effects. In this work, the debromination of large WCBs was first performed through a hydrothermal process employing potassium carbonate as an additive. A total of 32 runs were carried out at 225 °C, various CO3 2-/Br- anionic ratios of 1:1, 2:1, 4:1, and 6:1, treatment times from 30 to 360 min, proportion of submerged WCBs in the liquid of 100, 50, and 25% that corresponded with the use of three WCB sizes of 20 mm × 16.5 mm, 20 mm × 33 mm, and 80 mm × 33 mm, respectively, and solid/liquid ratios of 1:2 and 1:1 g/mL without other metallic catalysts. A debromination efficiency of 50 wt % was reached at only 225 °C (limited by mechanical reasons) and 360 min, using a CO3 2-/Br- anionic ratio of 4:1 and a solid/liquid ratio of 1:2 for a large WCB with only 25% of its volume submerged in the liquid. This means conservation of water and energy compared to previous studies. A muffle furnace was used later to thermally treat a total of 101 debrominated samples, at constant temperature or following a temperature scaling program. An estimated decrease in resistance to rupture of glass fibers of only around 50% was accomplished by following a temperature scaling program up to 475 °C, obtaining clean glass fibers of large size. The simple techniques proposed to obtain reusable glass fibers from WCBs as large as the size of the reactor allows (as it might be in their original size) could significantly improve interest in the industry.

Mechanochemical debromination of waste printed circuit boards with marble sludge in a planetary ball milling process.

An effective management of waste printed circuit board (WCB) recycling presents significant advantages of an economic, social, and environmental nature. This is particularly the case when a suitable valorisation is made of the non-metallic parts of the WCBs, well known for their "hidden" toxicological risks. Such benefits motivate research on techniques that could contribute to mitigating their adverse socio-environmental impacts. In this work, waste printed circuit boards (WCBs) containing tetrabromobisphenol A (TBBPA) as a brominated flame retardant (BFR) underwent debromination using a mechanochemical treatment (MCT) and marble sludge, another recoverable waste, as well as pure CaO as additives. All runs in this work were performed at an intermediate rotation speed of 450 rpm, using additive/WCB mass ratios (Rm) of 4:1 and 8:1, ball to powder ratios (BPR) of 20:1 and 50:1, treatment times from 2.5 h to 10 h, two WCB sizes (powder and 0.84 mm) and marble sludge, from original to precalcined conditioning. Stainless steel jars and balls were used to verify the effect of each parameter on the system and to seek an optimum process. Complete debromination of 0.84 mm WCBs was achieved at 450 rpm, using a Rm of 8:1, a BPR of 50:1, a residence time of 10 h (more than 95% in only 5 h), and a precalcined marble sludge as additive. The results revealed that when using a Rm of 4:1 instead of 8:1, more waste could be effectively treated, per batch with a lesser need for additives, at the expense of a slightly lower level of debromination efficiency. In the same way, an appropriate apparent ball diameter (with respect to the volume of the used jar) should be carefully studied in relation to WCB size in order to achieve a beneficial total amount of energy transfer during milling.

A Win-Win Combination to Inhibit Persistent Organic Pollutant Formation via the Co-Incineration of Polyvinyl Chloride E-Waste and Sewage Sludge.

Persistent organic pollutant inhibition in the combustion process of polyvinyl chloride (PVC) by prior addition of an inhibitor is currently being studied, reducing the emission of pollutants, and thus reducing the large amount of waste PVC destined for landfill. In this work, the use of sewage sludge (SS) as an alternative to chemical inhibitors to improve the quality emissions of the incineration of polyvinyl chloride waste (PVC e-waste) was studied and optimized. Different combustion runs were carried out at 850 °C in a laboratory tubular reactor, varying both the molar ratio Ri (0.25, 0.50, 0.75) between inhibitors (N + S) and chlorine (Cl) and the oxygen ratio λ (0.15, 0.50) between actual oxygen and stoichiometric oxygen. The emissions of several semivolatile compounds families such as polycyclic aromatic hydrocarbons (PAHs), polychlorobenzenes (ClBzs), and polychlorophenols (ClPhs), with special interest in the emissions of the most toxic compounds, i.e., polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs), were analyzed. A notable decrease in PCDD/F and dl-PCB formation was achieved in most of the experiments, especially for those runs performed under an oxygen-rich atmosphere (λ = 0.50), where the addition of sludge was beneficial with inhibition ratios Ri ≥ 0.25. An inhibition ratio of 0.75 showed the best results with almost a 100% reduction in PCDD/F formation and a 95% reduction in dl-PCB formation.

Dechlorination of polyvinyl chloride electric wires by hydrothermal treatment using K2CO3 in subcritical water.

Polyvinyl chloride (PVC) waste generation has significantly increased in recent years and their disposal is considered a major environmental concern. Removal techniques of chlorine from PVC waste are being studied to minimize a negative environmental impact. In this work, the use of K2CO3 as an alkaline additive to improve the dechlorination efficiency (DE) in the hydrothermal degradation of PVC wires was studied. Different experiments were carried out varying both temperature (175, 200, 225, 235 and 250 °C) and K2CO3 concentration (0.025, 0.050 and 0.125 M), using a solid/liquid ratio of 1:5 in order to determine the evolution of the dechlorination efficiency with time. About 4.66, 21.1, 24.4, 45.7 and 92.6 wt% of chlorine in PVC wire was removed during hydrothermal dechlorination (HTD) with an additive/chlorine ratio of 1:25 (K2CO3 solution of 0.050 M) at 175, 200, 225, 235 and 250 °C, respectively. Optimal additive/chlorine ratio decreased to 1:50 (K2CO3 solution of 0.025 M) at 250 °C, obtaining a dechlorination degree of 99.1% after 4 h without the need of metallic catalysts. Concerning the solid phase behavior during dechlorination, a linear correlation between the DE reached and the weight loss of PVC was found.

Tremor Types in Parkinson Disease: A Descriptive Study Using a New Classification.

BACKGROUND: The current classification of tremor types in Parkinson disease (PD) is potentially confusing, particularly for mixed tremor, and there is no label for pure resting tremor. With a view to better defining the clinical phenomenological classification of these tremors, our group relabeled the different types as follows: pure resting tremor (type I); mixed resting and action tremor with similar frequencies (type II) divided, according to action tremor presentation, into II-R when there is a time lag and II-C otherwise; pure action tremor (type III); and mixed resting and action tremor with differing frequencies (type IV). We performed a descriptive study to determine prevalence and clinical correlates for this new tremor classification. PATIENT/METHODS: A total of 315 consecutively recruited patients with PD and tremor were clinically evaluated. X 2 tests were used to assess tremor type associations with categorical variables, namely, sex, family history of PD, motor fluctuations, and anticholinergic and beta-blocker use. With tremor type as the independent variable, ANOVA was performed to study the relationship between dependent quantitative variables, namely, age, age at PD diagnosis, disease duration, and UPDRS scores for rigidity. RESULTS: The studied patients had tremor types as follows: type I, 30%; type II, 50% (II-R, 25% and II-C, 25%); type III, 19%; and type IV, 1%. No significant association was found between the studied clinical variables and tremor types. CONCLUSIONS: Mixed tremor was the most common tremor type in our series of patients with PD according to our proposed classification, which we hope will enhance understanding of the broad clinical phenomenology of PD.

Study of the presence of PCDDs/PCDFs on zero-valent iron nanoparticles.

Studies show that nanoscale zero-valent iron (nZVI) particles enhance the formation of chlorinated compounds such as polychlorinated dioxins and furans (PCDD/Fs) during thermal processes. However, it is unclear whether nZVI acts as a catalyst for the formation of these compounds or contains impurities, such as PCDD/Fs, within its structure. We analyzed the presence of PCDD/Fs in nZVI particles synthesized through various production methods to elucidate this uncertainty. None of the 2,3,7,8-substituted congeners were found in the commercially-produced nZVI, but they were present in the laboratory-synthesized nZVI produced through the borohydride method, particularly in particles synthesized from iron (III) chloride rather than from iron sulfate. Total PCDD/F WHO-TEQ concentrations of up to 35 pg/g were observed in nZVI particles, with hepta- and octa-chlorinated congeners being the most abundant. The reagents used in the borohydride method were also analyzed, and our findings suggest that FeCl3 effectively contains PCDD/Fs at concentrations that could explain the concentrations observed in the nZVI product. Both FeCl3 and nZVI showed a similar PCDD/F patterns with slight differences. These results suggest that PCDD/Fs might transfer from FeCl3 to nZVI during the production method, and thus, care should be taken when employing certain nZVI for environmental remediation.

Pollutant formation in the pyrolysis and combustion of Automotive Shredder Residue.

The present work has been carried out to verify the feasibility of thermal valorization of an automobile shredder residue (ASR). With this aim, the thermal decomposition of this waste has been studied in a laboratory scale reactor, analyzing the pollutants emitted under different operating conditions. The emission factors of carbon oxides, light hydrocarbons, PAHs, PCPhs, PCBzs, PBPhs, PCDD/Fs, dioxin-like PCBs and PBDD/Fs were determined at two temperatures, 600 and 850°C, and under different oxygen ratios ranging from 0 (pure pyrolysis) to 1.5 (over-stoichiometric oxidation). After analyzing all these compounds, we conclude that thermal valorization of ASR is a clean way to treat this waste.

Viability study of automobile shredder residue as fuel.

Car Fluff samples collected from a shredding plant in Italy were classified based on particle size, and three different size fractions were obtained in this way. A comparison between these size fractions and the original light fluff was made from two different points of view: (i) the properties of each size fraction as a fuel were evaluated and (ii) the pollutants evolved when each size fraction was subjected to combustion were studied. The aim was to establish which size fraction would be the most suitable for the purposes of energy recovery. The light fluff analyzed contained up to 50 wt.% fines (particle size<20 mm). However, its low calorific value and high emissions of polychlorinated dioxins and furans (PCDD/Fs), generated during combustion, make the fines fraction inappropriate for energy recovery, and therefore, landfilling would be the best option. The 50-100 mm fraction exhibited a high calorific value and low PCDD/F emissions were generated when the sample was combusted, making it the most suitable fraction for use as refuse-derived fuel (RDF). Results obtained suggest that removing fines from the original ASR sample would lead to a material product that is more suitable for use as RDF.

Chlorinated and nonchlorinated compounds from the pyrolysis and combustion of polychloroprene.

Thermal decomposition of polychloroprene was studied under inert and oxidative atmospheres at temperatures of 500 and 850 degrees C in a horizontal quartz tubular laboratory reactor in order to determine the products generated. More than two hundred compounds, mainly aromatic hydrocarbons, were identified and quantified, with special focus on chlorinated aromatic compounds, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), chlorobenzenes (CBzs) and chlorophenols (CPhs). The results showed that pyrolysis of polychloroprene at high temperatures leaded to the formation of many aromatic hydrocarbons in high yields. In addition, the yields of total PCDD/Fs in the combustion experiment at 850 degrees C were more than three hundred times higher than those from pyrolysis at the same temperature. Results were also compared with those obtained in a previous work for polyvinyl chloride under similar operating conditions.

Formation of polychlorinated compounds in the combustion of PVC with iron nanoparticles.

The influence of iron nanoparticles in the fuel-rich combustion of PVC has been studied in this work. Dynamic runs for PVC and the mixture PVC and iron nanoparticles were firstly carried out by TGA-MS in order to study the influence of iron on the compounds evolved in the thermal degradation of PVC. To complete the study both PVC and a mixture of PVC and iron nanoparticles were burnt in a laboratory reactor under two different operating conditions: at 850 degrees C and in two stages, the first one at 375 degrees C and the resulting char cooled and subsequently burnt at 850 degrees C. Carbon oxides, light hydrocarbons, PAHs, chlorophenols, chlorobenzenes and PCDD/Fs were analyzed. It was observed that the mixture of PVC with iron nanoparticles at 375 degrees C greatly enhances the formation of light hydrocarbons and polychlorinated compounds, probably indicating that the presence of iron during the thermal decomposition of PVC causes the formation of iron chloride which may have a high catalytic effect.

Semivolatile and volatile compounds in combustion of polyethylene.

The evolution of semivolatile and volatile compounds in the combustion of polyethylene (PE) was studied at different operating conditions in a horizontal quartz reactor. Four combustion runs at 500 and 850 degrees C with two different sample mass/air flow ratios and two pyrolytic runs at the same temperatures were carried out. Thermal behavior of different compounds was analyzed and the data obtained were compared with those of literature. It was observed that alpha,omega-olefins, alpha-olefins and n-paraffins were formed from the pyrolytic decomposition at low temperatures. On the other hand, oxygenated compounds such as aldehydes were also formed in the presence of oxygen. High yields were obtained of carbon oxides and light hydrocarbons, too. At high temperatures, the formation of polycyclic aromatic hydrocarbons (PAHs) took place. These compounds are harmful and their presence in the combustion processes is related with the evolution of pyrolytic puffs inside the combustion chamber with a poor mixture of semivolatile compounds evolved with oxygen. Altogether, the yields of more than 200 compounds were determined. The collection of the semivolatile compounds was carried out with XAD-2 adsorbent and were analyzed by GC-MS, whereas volatile compounds and gases were collected in a Tedlar bag and analyzed by GC with thermal conductivity and flame ionization detectors.