Guido Grause

TG–MS investigation of brominated products from the degradation of brominated flame retardants in high-impact polystyrene

The thermal degradation of flame retardant containing high-impact polystyrene (HIPS-Br), one of the most commonly employed plastics in electric and electronic appliances, was examined by thermogravimetry coupled with mass spectroscopy (TG-MS) in order to understand the threat that is posed by the release of hazardous brominated compounds. The HIPS samples contained decabromodiphenylether (DPE) and decabromodibenzyl (DDB) as the flame retardants as well as Sb2O3 as the synergist. The largest number of brominated compounds was obtained in the presence of DPE and Sb2O3 and DDB without Sb2O3. From the degradation of DPE, brominated benzenes, phenols, diphenylethers, and dibenzofurans were identified, and from the degradation of DDB, brominated benzenes, dibenzyls, and phenanthrenes were formed. The interaction between the flame retardant and the polymer matrix resulted in α-bromoethylbenzene. The formation of brominated dibenzodioxins was not observed, probably, due to the low phenol concentration in the polymer melt. No other report has, to our knowledge, ever reported on the formation of brominated phenanthrenes from flame retardants. Because they share similar steric features, it may well be that brominated phenanthrenes are similar in their carcinogen and mutagen potential to dibenzofurans and dibenzodioxins. A plausible mechanism for the formation of the observed compounds is presented, and the role of the synergist is considered.

Enhancement of bio-oil production via pyrolysis of wood biomass by pretreatment with H2SO4

In this work, a Japanese cedar wood sample was treated during the first step at ambient temperature and atmospheric pressure using several concentrations of sulfuric acid (H2SO4) in a stirred flask. During this pretreatment C-O bonds of cellulose, hemicellulose, and lignin were cleaved. The second step involved the pyrolysis of the pretreated wood sample at 550 °C in a quartz glass tube reactor. A maximum oil yield of 46.8 wt% with the minimum char yield of 10.1 wt% was obtained by the treatment with 3 M H2SO4, whereas untreated wood samples resulted in a 30.1 wt% yield of oil. The main components in the oils were levoglucosan and tar. These results suggest that moderate acid pretreatment produced shorter chain units of cellulose, hemicellulose, and lignin, thereby facilitating the conversion into oil by pyrolysis. The results of thermogravimetry-mass spectroscopy supported the presence of shorter chain units in the pretreated wood samples.

Simultaneous recovery of benzene-rich oil and metals by steam pyrolysis of metal-poly(ethylene terephthalate) composite waste.

The possibility of simultaneous recovery of benzene and metals from the hydrolysis of poly(ethylene terephthalate) (PET)-based materials such as X-ray films, magnetic tape, and prepaid cards under a steam atmosphere at a temperature of 450 °C was evaluated. The hydrolysis resulted in metal-containing carbonaceous residue and volatile terephthalic acid (TPA). The effects of metals and additives on the recovery process were also investigated. All metals were quantitatively recovered, and silver, maghemite (γ-Fe2O3), and anatase (TiO2) were recovered without any changes in their crystal structures or compositions. In a second step, TPA was decarboxylized in the presence of calcium oxide (CaO) at 700 °C, producing benzene with an average yield of 34% and purity of 76%. Maghemite (γ-Fe2O3) incorporated in magnetic tape and prepaid cards could decarboxylate TPA. Aluminum present in the prepaid cards produced hydrogen by the reaction with steam. However, the presence of metals had no adverse influence on the recovery of benzene-rich oil in the presence of CaO. Therefore, this method can be applied to PET-based materials containing inorganic substances, which cannot be recycled effectively otherwise.

Removal of hydrogen chloride from gaseous streams using magnesium–aluminum oxide

Magnesium-aluminum oxide (Mg-Al oxide) obtained by thermal decomposition of Mg-Al layered double hydroxide (Mg-Al LDH) effectively removed HCl from gaseous streams. HCl removal was greater in the presence of added water vapor at all temperatures examined and increased with decreasing temperature in both the presence and absence of added water vapor. Wet and dry removal of gaseous HCl were attributed to the production of MgCl2 . 6H2O and MgCl2 . 4H2O, respectively. For the wet scrubbing process, the reconstruction reaction of Mg-Al LDH from Mg-Al oxide was the primary mechanism for increased HCl removal.

Efficient dehalogenation of automobile shredder residue in NaOH/ethylene glycol using a ball mill.

We investigated the effectiveness of sodium hydroxide/ethylene glycol (NaOH/EG) for dehalogenation of automobile shredder residue (ASR) using a ball mill. Efficient dehalogenation was achieved at atmospheric pressure by combining the use of EG (196 degrees C b.p.) as a replacement solvent for NaOH with ball milling, which improved contact between ASR and OH(-) in solution. Moderate NaOH concentrations and increased ball mill rotation speeds produced high dechlorination that was not significantly affected by the weight ratio of ASR to EG. NaOH/EG dechlorination increased with temperature with an apparent activation energy of 50 kJ mol(-1) confirming that the reaction proceeded under chemical reaction control. The modified shrinking-core model was appropriate to explain the dechlorination process. Low chloro levels in our NaOH/EG-treated ASR suggested that this material could be used for feedstock recycling and the wet process may be applicable for dehalogenation of other important waste streams.

Pyrolysis versus hydrolysis behavior during steam decomposition of polyesters using 18O-labeled steam

Steam decomposition, a method employed for the depolymerization of polyesters, does not require solvents, catalysts, or high pressure. During steam decomposition, the fission of the ester group occurs by hydrolysis, whereas the ester group is cleaved without the action of water during pyrolysis, affording reduced monomer yields. Hence, elucidating the contribution of hydrolysis and pyrolysis to depolymerization in a steam atmosphere, as well as the effect of polyester structure on selectivity, will improve the accuracy of kinetic analyses and maximize monomer yields. In this study, the selectivities for pyrolysis and hydrolysis during the steam decomposition of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene 2,6-naphthalate (PEN) were quantified using 18O-labeled steam at different steam concentrations and decomposition temperatures. The decomposition temperature strongly affected the hydrolysis selectivity for PET and PBT, whereas that for PEN was hardly affected. The selectivity for polyester hydrolysis increased with increasing steam concentration for both PET and PEN, with the exception of PBT. These results revealed that the selectivities for both pyrolysis and hydrolysis were significantly affected by the structure of the polyester. In addition, the thermogravimetric kinetic analysis of steam decomposition was consistent with the results of the 18O-labeling experiments.