Yafei Shen

Waste-to-energy: Dehalogenation of plastic-containing wastes

The dehalogenation measurements could be carried out with the decomposition of plastic wastes simultaneously or successively. This paper reviewed the progresses in dehalogenation followed by thermochemical conversion of plastic-containing wastes for clean energy production. The pre-treatment method of MCT or HTT can eliminate the halogen in plastic wastes. The additives such as alkali-based metal oxides (e.g., CaO, NaOH), iron powders and minerals (e.g., quartz) can work as reaction mediums and accelerators with the objective of enhancing the mechanochemical reaction. The dehalogenation of waste plastics could be achieved by co-grinding with sustainable additives such as bio-wastes (e.g., rice husk), recyclable minerals (e.g., red mud) via MCT for solid fuels production. Interestingly, the solid fuel properties (e.g., particle size) could be significantly improved by HTT in addition with lignocellulosic biomass. Furthermore, the halogenated compounds in downstream thermal process could be eliminated by using catalysts and adsorbents. Most dehalogenation of plastic wastes primarily focuses on the transformation of organic halogen into inorganic halogen in terms of halogen hydrides or salts. The integrated process of MCT or HTT with the catalytic thermal decomposition is a promising way for clean energy production. The low-cost additives (e.g., red mud) used in the pre-treatment by MCT or HTT lead to a considerable synergistic effects including catalytic effect contributing to the follow-up thermal decomposition.

Catalytic oxidation of nitric oxide (NO) with carbonaceous materials

The catalytic oxidation of NO to NO2 at ambient temperatures has been a promising route for controlling NO emissions, since NO2 is subsequently removed as nitric acid in the presence of water. Because of their large surface area, high porosity, and relative chemical inertness, carbon-based materials are very attractive in de-nitrification (De-NOx) as catalysts or catalyst supports. This paper reviewed the catalytic oxidation of NO to NO2 over commonly-used carbon materials including activated carbons (ACs), activated carbon fibers (ACFs) and carbon xerogels (CXs). The NO conversion is often influenced by the surface characteristics of carbon materials (e.g., pore structure, surface areas, functional groups, and morphology), O2 concentration, and reaction temperature. With the addition of metal actives, the catalytic performance could be significantly improved. Catalytic reaction and adsorption are two key points. Further, the strong dependence of NO conversion on the O2 concentration concludes that O2 is first adsorbed on the carbon surface, and then it reacts with NO to form adsorbed NO2, which desorbs to the gas phase. Considering the economic efficiency, carbon precursors from biomasses could be fabricated into the desired carbonaceous materials by means of functionalization. In addition, the integrated strategy of desulfurization (De-SOx) and De-NOx could be developed by carbon materials with the proper modification methods.

Toxicological effects of chlorpyrifos on growth, enzyme activity and chlorophyll a synthesis of freshwater microalgae

This paper aims to acquire the experimental data on the eco-toxicological effects of agricultural pollutants on the aquatic plants and the data can support the assessment of toxicity on the phytoplankton. The pesticide of Chlorpyrifos used as a good model to investigate its eco-toxicological effect on the different microalgae in freshwater. In order to address the pollutants derived from forestry and agricultural applications, freshwater microalgae were considered as a good sample to investigate the impact of pesticides such as Chlorpyrifos on aquatic life species. Two microalgae of Chlorella pyrenoidosa and Merismopedia sp. were employed to evaluate toxicity of Chlorpyrifos in short time and long time by means of measuring the growth inhibition rate, the redox system and the content of chlorophyll a, respectively. In this study, the results showed that EC50 values ranging from 7.63 to 19.64mg/L, indicating the Chlorpyrifos had a relatively limited to the growth of algae during the period of the acute toxicity experiment. Moreover, when two kinds of algae were exposed to a medium level of Chlorpyrifos, SOD and CAT activities were importantly advanced. Therefore, the growth rate and SOD and CAT activities can be highly recommended for the eco-toxicological assessment. In addition, chlorophyll a also could be used as a targeted parameter for assessing the eco-toxicity of Chlorpyrifos on both Chlorella pyrenoidosa and Merismopedia sp.

Effect of chemical pretreatment on pyrolysis of non-metallic fraction recycled from waste printed circuit boards

The non-metallic fraction from waste printed circuit boards (NMF-WPCB) generally consists of plastics with high content of Br, glass fibers and metals (e.g. Cu), which are normally difficult to dispose. This work aims to study the chemical pretreatments by using alkalis, acids and alkali-earth-metal salts on pyrolysis of NMF-WPCB. Char (60-79%) and volatile matter (21-40%) can be produced via the pyrolysis process. In particular, the ash content can reach up to 42-56%, which was attributed to the high content of glass fibers and other minerals. Copper (Cu, 2.5%), calcium (Ca, 28.7%), and aluminum (Al, 6.9%) were the main metal constituents. Meanwhile, silicon (Si, 28.3%) and bromine (Br, 26.4%) were the predominant non-metallic constituents. The heavy metals such as Cu were significantly reduced by 92.4% with the acid (i.e. HCl) pretreatment. It has been proved that the organic Br in the plastics (e.g. BFR) can be transformed into HBr via the pyrolysis process at relatively high temperature. It was noteworthy that the alkali pretreatment was more benefit for the Br fixation in the solid char. Particularly, the Br fixation efficiency can reach up to 53.6% by the sodium hydroxide (NaOH) pretreatment with the pyrolysis process. The formed HBr can react with NaOH to generate NaBr.

Micro-mesoporous carbons from original and pelletized rice husk via one-step catalytic pyrolysis

This paper studied the KOH-catalyzed pyrolysis of rice husk (RH) and its pellet (RHP) at a high temperature (750u202f°C) for activated bio-carbons production. The mass ratio of KOH and biomass greatly impacted the pyrolysis kinetic and biochar property. The KOH catalysis (mass ratio: 1) reduced significantly the activation energy to 41u202fkJ/mol. During carbonization with KOH, the in-situ generated K2CO3 tailored the morphology and size of the self-template (SiO2 nanoparticles), giving rise to the chars with the open foam-like porous architectures enrich in micro- and meso-pores. Thus, the KOH activation via one-step pyrolysis could produce the micro-mesoporous carbons (e.g., RH-char 1 and RHP-char 1) with high specific surface areas and high content of oxygen-functionalities. Furthermore, the hierarchical porous carbons have high potential applications in adsorption process and electrochemical energy storage (e.g., supercapacitor) because of their unique physicochemical properties.

Activated bio-chars derived from rice husk via one- and two-step KOH-catalyzed pyrolysis for phenol adsorption

The activated bio-chars (AB) were successfully synthesized from rice husk by one- and two-step KOH-catalyzed pyrolysis. The two-step pyrolysis can produce the high yields of AB compared to the one-step pyrolysis. Moreover, the yield of AB decreased with the increase of the mass ratio of KOH and char, which had a significant effect on the development of the surface area and porosity of carbon. In particular, the AB derived from the two-step pyrolysis at 750°C (mass ratio of KOH and char was 3) had the highest specific surface area (SBET=2138m2/g) with many micro-porous structures, which was favored for the phenol adsorption. The maximum adsorption capacity of AB2-3-750 reached 201mg/g because of its excellent surface porosity property. The phenol can be efficiently removed from water by only several minutes. The Langmuir model defined well the adsorption isotherm with a high correlation coefficient value, indicating a monolayer adsorption behavior. And the adsorption process defined well with the pseudo-second-order model. The phenol molecules passed into the internal surface via the liquid-film controlled diffusion, so the behavior of phenol adsorption onto the AB was predominantly controlled via the chemisorption. Furthermore, the functional groups on the outer surfaces of AB can attract the phenol molecules onto the internal surfaces via π-π dispersion interaction and donor-acceptor effect.