•Zeolites and mesoporous catalysts were subject to catalytic pyrolysis of Br-HIPS.•The highest oil yield of 67.9 wt.% was obtained in the presence of all-silica MCM-41.•HZSM-5 and all-silica MCM-41 produced more valuable single ring aromatics.•High debromination efficiency of 70.47% was achieved by Hβ zeolite.•Provided an efficient approach for further upgrading of pyrolysis oilsThe catalytic pyrolysis of flame retarded high impact polystyrene (Br-HIPS) was performed in the presence of five different solid acid catalysts in order to remove the bromine from the derived pyrolysis oil. The catalysts were three zeolite materials (HY, Hβ and HZSM-5) and two mesoporous solids (all-silica MCM-41 and active Al2O3). The results showed that in the presence of HY and Hβ zeolites, a reduction of approximate 50 wt.% in oil yield and a corresponding increase in wax and gas yields were obtained compared to thermal degradation. The addition of HZSM-5 showed less impact on product distribution and produced more oil compared with the other zeolites. The mesoporous catalyst of all-silica MCM-41 obtained the highest oil yield of 67.9 wt.% and reduced the wax yield to 8.73 wt.%. In terms of the composition of the pyrolysis oil, HZSM-5 and all-silica MCM-41 were favorable to produce more valuable single ring aromatics, such as toluene, ethylbenzene and cumene. Moreover, the catalysts exhibited pronounced debromination performance, especially the Hβ catalyst, achieving the debromination efficiency of 70.47%. The results confirmed the catalytic pyrolysis of Br-HIPS and debromination performance was well related to the textural properties of catalysts.

The pyrolysis-catalytic upgrading process of brominated high impact polystyrene (Br-HIPS) was performed using Fe and Ni modified ZSM-5 and MCM-41 catalysts in a two-stage fixed bed reactor. The characterization of catalysts, the product yield and debromination performance in relation to different catalysts were investigated. The results showed that the addition of HZSM-5 and MCM-41 reduced the yield of oil from 69.0 wt % to 64.4 wt % and 62.3 wt %, respectively. The modified catalysts of Fe/ZSM-5 and Ni/ZSM-5 exhibited prominent cracking performance, resulting in the decrease of the oil to 63.2 wt % and 61.2 wt %, respectively, corresponding with an increase of gas products from 7.7 wt % to 16.1 wt % and 20.3 wt %, respectively. However, the mesoporous catalysts of Fe/MCM-41 and Ni/MCM-41 tended to preserve the yield of oil to 65.9 wt % and 65.3 wt %, respectively. In terms of the composition of the oils, a higher yield of single ring aromatics was obtained with Fe modified catalysts, while the addition of ZSM-5 and Ni/ZSM-5 catalysts promoted increased formation of 2 ring aromatics at the expense of single ring aromatics. In addition, the modified catalysts were found to be highly effective at removing bromine from the oils. The Fe modified catalysts exhibited a better debromination performance than Ni modified catalysts, which was in favor of capturing more inorganic bromine and removing bromine from the oils.

•The mechanism of H2O2 decomposition and OH generation on Fe3O4 (1 1 1) was studied.•Hg0 oxidation processes on hydroxyl pre-adsorbed surface were compared.•The major reaction pathway of Hg oxidation product on Fe3O4 (1 1 1) was discussed.Elemental mercury oxidation mechanism by gaseous advanced oxidation method was studied using density functional theory on Fe3O4 (1 1 1) surface containing H2O2 molecule. Fetet1- and Feoct2-terminated Fe3O4 (1 1 1) surfaces have been simultaneously considered both in H2O2 decomposition and hydroxyl pre-adsorbed Fe3O4 (1 1 1) interfaces. It is found that the Feoct2-terminated surface was more favored for H2O2 decomposition, and H2O2 was easier to decompose and generate two hydroxyls than Fetet1-terminated surface. Through the discussion of Fetet1- and Feoct2-terminal mechanisms, the Mulliken charge population, and the partial density of states, we found that OH had different reaction activity generated on different Fe-terminal. Hg strongly interacted with the free state OH mainly due to the highly reactive and strong electrophilic ability of OH radical. The oxidation of Hg formed stable oxidized mercury species on Fe-terminated surface and most of the lost electron transferred from Hg to unbonded hydroxyl during Hg oxidation. The result showed that the combination of Hg and hydroxyl was exothermic reaction, which was favorable to spontaneous processes of Hg oxidation. The OH–Hg–OH and Hg–OH intermediates had a lower desorption energy when they detached from the surface and was the major reaction pathway.The optimized configurations of Hg on Fetet1-terminal and Feoct2-terminal OH/Fe3O4 (1 1 1) surface.Download high-res image (86KB)Download full-size image

•NO and H2O2 adsorption on perfect and oxygen defect α-Fe2O3 (0 0 1) surface were studied by DFT calculations.•H2O2 shows high chemical reactivity for its adsorption on oxygen defect α-Fe2O3 (0 0 1) surface.•Oxygen vacancy plays an important role of the catalytic oxidation of NO by H2O2 over the α-Fe2O3 catalyst surfaces.•Mechanism of NO oxidation over α-Fe2O3 (0 0 1) surface by H2O2 was explained.Catalytic oxidation with H2O2 is a promising method for NOx emission control in coal-fired power plants. Hematite-based catalysts are attracting increased attention because of their surface redox reactivity. To elucidate the NO oxidation mechanism on α-Fe2O3 surfaces, density functional theory (DFT) calculations were conducted by investigating the adsorption characteristics of nitric oxide (NO) and hydrogen peroxide (H2O2) on perfect and oxygen defect α-Fe2O3 (0 0 1) surfaces. Results show that NO was molecularly adsorbed on two kinds of surfaces. H2O2 adsorption on perfect surface was also in a molecular form; however, H2O2 dissociation occurred on oxygen defect α-Fe2O3 (0 0 1) surface. The adsorption intensities of the two gas molecules in perfect α-Fe2O3 (0 0 1) surface followed the order NO > H2O2, and the opposite was true for the oxygen defect α-Fe2O3 (0 0 1). Oxygen vacancy remarkably enhanced the adsorption intensities of NO and H2O2 and promoted H2O2 decomposition on catalyst surface. As an oxidative product of NO, HNO2 was synthesized when NO and H2O2 co-adsorbed on the oxygen defect α-Fe2O3 (0 0 1) surface. Analyses of Mulliken population, electron density difference, and partial density of states showed that H2O2 decomposition followed the Haber–Weiss mechanism. The trends of equilibrium constants suggested that NO adsorption on α-Fe2O3 (0 0 1) surface was more favorable at low than at high temperatures, whereas H2O2 adsorption was favorable between 375 and 450 K. These calculations results well agreed with the experimental ones and further elucidates the reaction mechanisms.

•Electron transfer occurred from Hg0 to the produced OH species.•Hg0 possible oxidation intermediates during the processes were compared.•The major reaction pathway of Hg oxidation products on the surface was discussed.Density functional theory calculations have been carried out for H2O2 and Hg0 co-interaction on Fe3O4 (111) surface. On the Fetet1-terminated Fe3O4 (111) surface, the most favored configurations are H2O2 decomposition and produce two OH groups, which have strong interaction with Hg atom to form an OHHgOH intermediate. The adsorbed OHHgOH is stable and hardly detaches from the catalyst surface due to the highly endothermic process. A large amount of electron transfer has been found from Hg to the produced OH groups and has little irreversible effect on the Fe3O4 (111) surface. On the Feoct2-terminated Fe3O4 (111) surface, the Feoct2 site is more active than Fetet1 site. H2O2 decomposition and Hg0 oxidation processes are more likely to occur due to that the Feoct2 site both contains Fe2+ and Fe3+ cations. The calculations reveal that Hg0 oxidation by the OH radical produced from H2O2 is energetically favored. Additionally, Hg0 and H2O2 co-interaction mechanism on the Fe3O4 (111) interface has been investigated on the basis of partial local density of state calculation.Download high-res image (163KB)Download full-size image

Three zeolite materials (HY, Hβ, and HZSM-5) and two mesoporous solids (all-silica MCM-41 and active Al2O3) with different textural properties were investigated for their catalytic effects on the pyrolysis of brominated acrylonitrile–butadiene–styrene (Br-ABS). The results indicated that, in the absence of a catalyst, the maximum liquid yield was obtained from the pyrolysis of Br-ABS, including oil and wax. The addition of HY and Hβ zeolites significantly decreased the oil yield from 63.6 to 45 and 44.3 wt %, respectively, with a corresponding increase in the yields of wax and gas. HZSM-5 zeolite slightly changed the product distribution and increased the gas yield at the expense of wax. Noteworthy, the mesoporous catalyst of all-silica MCM-41 retained the oil production while significantly reduced the wax yield to 7.9 wt %. In terms of the composition of the oils, the catalysts could promote the formation of valuable single-ring aromatics in oils. Moreover, the catalysts exhibited pronounced debromination efficiency, especially the zeolites, which could achieve the removal of bromine in oils by over 50% compared to thermal pyrolysis. The results indicated that the product distributions of Br-ABS had interrelationship with the textural properties of catalysts.

•Provided an efficient approach for recycling the WEEE plastics•Improved the recycle efficiency of HIPS plastics by mixing with polyolefins•Interpreted the decomposition characteristics of the co-pyrolysis of Br–Sb–HIPS and PP•Proposed a useful method for debromination in the pyrolysis oilsPyrolysis of high impact polystyrene (HIPS), containing decabromodiphenyl oxide as brominated flame retardant (BFR) with Sb2O3 as a synergist (Br–Sb–HIPS), often leads to high concentrations of toxic brominated organic compounds in the pyrolysis oils which would detrimentally impact the reuse of these pyrolysis oils. In this work, the pyrolysis of Br–Sb–HIPS in the presence of polypropylene (PP) at different blending mass ratios using a fixed bed reactor at 410 °C was performed to investigate what the effect of PP has on the pyrolysis of Br–Sb–HIPS. The thermal decomposition characterization of Br–Sb–HIPS and PP was investigated using thermogravimetry analysis (TGA). The pyrolysis oils were analyzed using Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC–MS). TGA revealed that there was a synergistic interaction between Br–Sb–HIPS and PP during co-pyrolysis process. More wax/oil and less gas were produced and the yields of toluene, ethylbenzene, styrene and many other compounds in the pyrolysis oil reversely increased in the presence of PP. Moreover, PP was found to be effective to reduce bromine in the pyrolysis oil. When 30 wt.% PP was blended into Br–Sb–HIPS, it could reduce the amount of bromine in pyrolysis oil to 38% of the original value.This graph shows the effect of PP on debromination (red solid, experimental; blue dash, expected; black solid, debromination rate). It was found that the content of bromine in the pyrolysis oil decreased as PP increases and the most important point was that the trend was below the expected trend without considering the effect of PP.

The unconsumed pulverized coal and coke in flue dusts from two blast furances (BFs) were investigated in this paper. The percentage of unconsumed pulverized coal and coke were determined by means of chemical and petrographical microanalyses, which were time-consuming, requiring special expertise, and cannot be practiced routinely. Therefore, a simplified quantification method was proposed. The percentage of these materials in the BF flue dust samples was established on the basis of a suitable calibration using char and coke standards by Raman spectroscopy. The ratios of ID/IG, IV/IG, and I2D/IG were used to estimate constitutents of the BF flue dust. The amount of unconsumed pulverized coal in 1BF and 2BF was 9.7 and 11.6%, respectively, by means of petrographical microanalysis, and that in 1BF and 2BF established by Raman spectroscopy was in the ranges of 8–10 and 10.5–12%, respectively. The results showed that Raman spectroscopy was a relatively rapid and effective monitoring technique for the purpose of differentitation between coke and uncomsumed pulverized coal in BF flue dust.

Recently the oxyfuel combustion of coal chars having a significant impact on reducing greenhouse emissions is gradually paid extensive attention by many researchers, but only a limited number of studies have focused on its reaction mechanism. Therefore, it is important to investigate the combustion mechanism of coal chars in oxyfuel atmosphere, while random pore model (RPM) is usually recommended as a model for the comprehensive simulation of coal chars reaction. In this context, the values of structure parameter ψ in RPM were calculated based on pore structural character at various carbon conversions, and show interesting evolution phenomena keeping constant at the preceding reaction stage before increasing remarkably at the end of stage. Consequently, a new model, two-stage random pore model (TRPM), was applied to the coal chars combustion in oxyfuel atmosphere. Compared to other models such as RPM, the Struis model (Model I), the Liu model (Model II), and fractal random pore model (FRPM), it shows that two-stage random pore model was more accurate to describe coal chars combustion under oxyfuel conditions, especially at higher carbon conversions. In addition, the oxyfuel combustion process of coal chars at 1323 K and 1373 K were analyzed.

LaMnAl11O19 catalysts were prepared by co-precipitation method and characterized by XRD, BET, and XPS. The conversion of NH3 under the conditions of catalytic and homogeneous combustion was studied by the combustion of simulated biomass gasification gas and NH3 oxidation, respectively. Moreover, the NH3 adsorption and oxidation on the surfaces of the catalyst samples were examined by in-situ DRIFT experiments. It was found that calcination of the precursors at 1200°C led to the formation of a final monophasic material with an MP structure and a high surface area, whereas the Mn ions were either divalent or trivalent. Under homogeneous combustion condition, NH3 in a simulated biomass gasification gas started reacting at 500°C; then, NO was formed. Under catalytic combustion condition, the curves of NH3 oxidation both with and without addition of simulated gasification gas showed no obvious differences. NH3 started reacting at 310°C, and NO exhibited a higher concentration in the temperature range of approximately 350–800°C. However, NO2 was generated at a higher temperature within a narrow temperature range. The concentration of N2O during the reaction was less than 10 × 10−6. More than 40% of the NH3 was converted to NO during the experiment. The results of in-situ DRIFT indicated that the reaction of ammonia conversion followed the imide (-NH) mechanism, that is, the ammonia adsorbed on the catalyst surface was first decomposed to -NH, then the -NH reacted with atomic oxygen (O) to further form nitroxyl (HNO) and N2 or nitrous oxide (N2O), or −NH reacted with molecular O2 to produce nitric oxide (NO) directly.

•MgCl2⋅6H2O released HCl between 150 and 500 °C.•Cd and Pb can be nearly completely removed for all conditions.•MgCl2⋅6H2O can promote removal of Cu by formation of CuCl2.•The removal of Zn and Cr was low due to formation of stable compounds.•Removal of Zn was accelerated and Cu was hindered in N2.This work aims to study the mechanism of heavy metals vaporization by MgCl2⋅6H2O. Firstly, the decomposition mechanism of MgCl2⋅6H2O was investigated by thermodynamic equilibrium calculations, XRD and TG. Upon heating, MgCl2⋅6H2O went through the processes of dehydration and hydrolysis simultaneously accompanied by the release of HCl between 150 and 500 °C. At temperature higher than 500 °C, Mg(OH)Cl gradually release part of HCl. MgCl2⋅6H2O followed the similar processes of decomposition at both oxidative and reductive atmospheres. In oxidative atmosphere, vaporization of Zn and Cu was significantly accelerated by MgCl2⋅6H2O. However, in inert atmosphere, vaporization of Cu was not promoted since copper chloride was only stable in oxidative atmosphere. Under slow heating condition, vaporization of heavy metals were close to that under fast heating condition. This may be partially attributed to that most heavy metals already reacted with HCl forming metal chlorides below 500 °C, which can be vaporized at higher temperature. Moreover, the Mg(OH)Cl contributed to release HCl up to 800 °C. At such high temperature, the metal chlorides continue to be formed and then vaporized. After treatment, the leaching concentration of heavy metals from treated fly ashes were much lower than that from raw fly ash and met the regulatory limit of leachate. Since a large amount of MgSiO3 were formed during thermal treatment, the fly ash treated with MgCl2⋅6H2O can be used as raw materials for glass–ceramics production.

•Dehydrochlorination of PVC accelerate the biomass pyrolysis at low temperature.•HCl from PVC emission was reduced by biomass.•Chlorine fixing capacity depended on basicity of oxide.•In supercritical water, chlorine atoms in PVC were recovered as HCl in water.•Degradation of PVC can be divided into three stages in supercritical water.This review summarized various chemical recycling methods for PVC, such as pyrolysis, catalytic dechlorination and hydrothermal treatment, with a view to solving the problem of energy crisis and the impact of environmental degradation of PVC. Emphasis was paid on the recent progress on the pyrolysis of PVC, including co-pyrolysis of PVC with biomass/coal and other plastics, catalytic dechlorination of raw PVC or Cl-containing oil and hydrothermal treatment using subcritical and supercritical water. Understanding the advantage and disadvantage of these treatment methods can be beneficial for treating PVC properly. The dehydrochlorination of PVC mainly happed at low temperature of 250–320 °C. The process of PVC dehydrochlorination can catalyze and accelerate the biomass pyrolysis. The intermediates from dehydrochlorination stage of PVC can increase char yield of co-pyrolysis of PVC with PP/PE/PS. For the catalytic degradation and dechlorination of PVC, metal oxides catalysts mainly acted as adsorbents for the evolved HCl or as inhibitors of HCl formation depending on their basicity, while zeolites and noble metal catalysts can produce lighter oil, depending the total number of acid sites and the number of accessible acidic sites. For hydrothermal treatment, PVC decomposed through three stages. In the first region (T < 250 °C), PVC went through dehydrochlorination to form polyene; in the second region (250 °C < T < 350 °C), polyene decomposed to low-molecular weight compounds; in the third region (350 °C < T), polyene further decomposed into a large amount of low-molecular weight compounds.

Heavy metals volatilization during thermal treatment of model solid waste was theoretically and experimentally investigated in a fluidized bed reactor. Lead, cadmium, zinc and copper, the most four conventional heavy metals were investigated. Particle temperature model and metal diffusion model were established to simulate the volatilization of CdCl2 evaporation and investigate the possible influencing factors. The diffusion coefficient, porosity and particle size had significant effects on metal volatilization. The higher diffusion coefficient and porosity resulted in the higher metal evaporation. The influence of redox conditions, HCl, water and mineral matrice were also investigated experimentally. The metal volatilization can be promoted by the injection of HCl, while oxygen played a negative role. The diffusion process of heavy metals within particles also had a significant influence on kinetics of their vaporization. The interaction between heavy metals and mineral matter can decrease metal evaporation amount by forming stable metallic species.Highlights► This paper investigated the thermal treatment of model fly ashes. ► The operating conditions on metal volatilization were studied. ► The metal volatilization was studied. ► A metal diffusion model was established.

Novel heterogeneous Fenton-like Fe3−xTixO4 catalysts prepared by co-precipitation method were used for Hg0 absorption in a self-designed bubbling reactor system. Characterization by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that Ti successfully entered the structure of Fe3−xTixO4 catalysts and was enriched on the surface of Fe3−xTixO4. Important factors affecting Fe3−xTixO4 catalysts activity toward Hg0 absorption, such as H2O2 concentration and Ti content in Fe3−xTixO4, were considered. Results showed that Fe3−xTixO4 can effectively decompose H2O2 to generate highly reactive OH radicals, and oxidize Hg0 to Hg2+ in Fenton-like solutions. The mechanism model of Hg0 absorption by heterogeneous Fenton-like reaction was preliminarily established. Theoretically calculated results using the model well agreed with the experimental results, indicating that Hg0 absorption is simultaneously controlled by solid–liquid surface oxidation and gas–liquid film oxidation. These findings can help investigations on the mechanism of Hg0 absorption by the heterogeneous Fenton-like reaction.