Microwave-Assisted Pyrolysis-A New Way for the Sustainable Recycling and Upgrading of Plastic and Biomass: A Review.

The efficient utilization of organic solid waste resources can help reducing the consumption of conventional fossil fuels, mitigating environmental pollution, and achieving green sustainable development. Due to its dual nature of being both a resource and a source of pollution, it is crucial to implement suitable recycling technologies throughout the recycling and upgrading processes for plastics and biomass, which are organic solid wastes with complex mixture of components. The conventional pyrolysis and hydropyrolysis were summarized for recycling plastics and biomass into high-value fuels, chemicals, and materials. To enhance reaction efficiency and improve product selectivity, microwave-assisted pyrolysis was introduced to the upgrading of plastics and biomass through efficient energy supply especially with the aid of catalysts and microwave absorbers. This review provides a detail summary of microwave-assisted pyrolysis for plastics and biomass from the technical, applied, and mechanistic perspectives. Based on the recent technological advances, the future directions for the development of microwave-assisted pyrolysis technologies are predicted.

Insights into oil recovery, soil rehabilitation and low temperature behaviors of microwave-assisted petroleum-contaminated soil remediation.

As an environmental contaminant, petroleum-contaminated soil will pollute water, stunt agricultural growth, and cause serious harms to human health if it wasn't safely disposed and remediated. Here, low-temperature microwave-assisted treatment of petroleum-contaminated soil was developed for simultaneous soil rehabilitation, oil recovery and revegetation. The results indicated the concentration of petroleum contaminant was decreased to regulatory standard after 20 min treatment at 250-300 °C. 91.6% of the oil was recovered, and it mainly consisted of C11-C30 hydrocarbons. Using the soil remediated at 250 °C for plant growth test, no adverse effect or fertility loss was observed and an optimal clover germination rate was reached. The results of microwave thermogravimetric analysis, dielectric property and EDX mapping revealed that the efficient remediation was attributed to the presence of hot spots, and the efficient heat /mass transfer during microwave heating. A three-stage petroleum removal mechanism was proposed, where the hydrocarbons were gradually removed via steam stripping, thermal desorption, and pyrolysis/carbonization as the temperature increased.

Paper-Derived Flexible 3D Interconnected Carbon Microfiber Networks with Controllable Pore Sizes for Supercapacitors.

Heteroatom-doped three-dimensional (3D) carbon fiber networks have attracted immense interest because of their extensive applications in energy-storage devices. However, their practical production and usage remain a great challenge because of the costly and complex synthetic procedures. In this work, flexible B, N, and O heteroatom-doped 3D interconnected carbon microfiber networks (BNOCs) with controllable pore sizes and elemental contents were successfully synthesized via a facile one-step "chemical vapor etching and doping" method using cellulose-made paper, the most abundant and cost-effective biomass, as an original network-frame precursor. Under a rational design, the BNOCs exhibited interconnected microfiber-network structure as expressways for electron transport, spacious accessible surface area for charge accumulation, abundant mesopores and macropores for rapid inner-pore ion diffusion, and lots of functional groups for additional pseudocapacitance. Being applied as binder-free electrodes for supercapacitors, BNOC-based supercapacitors not only revealed a high specific capacitance of 357 F g-1, a high capacitance retention of 150 F g-1 at 200 A g-1, a high energy density of 12.4 W h kg-1, and a maximum power density of 300.6 kW kg-1 with an aqueous electrolyte in two-electrode configuration but also exhibited a high specific capacitance of up to 242.4 F g-1 in an all-solid-state supercapacitor.

Microwave-assisted in-situ elimination of primary tars over biochar: Low temperature behaviours and mechanistic insights.

An efficient method for microwave-assisted low temperature catalytic elimination of primary tars using cheap biochar as catalyst has been developed along with H2 rich syngas production. Tar removal efficiency reached 94.03% after 8 min reaction at 600 °C, while the concentration of H2 and syngas was up to 50.5 vol% and 94.5 vol% respectively, which were significantly comparable to conventional technologies at 700-900 °C. The FT-IR, ICP and EDX results indicated that the biochar surface contained O-containing functional groups and 12.6 wt% uniformly dispersed alkali and alkaline earth metals (AAEMs) in the carbon skeleton. The low temperature behaviours were attributed to the hot spots, which were induced by the increased dielectric properties of biochar and decentralized AAEMs under microwave heating. Possible reaction mechanism for the elimination of primary tars over biochar catalysts were discussed based on this experimental study.

Formic Acid-Induced Controlled-Release Hydrolysis of Microalgae (Scenedesmus) to Lactic Acid over Sn-Beta Catalyst.

Formic acid-induced controlled-release hydrolysis of sugar-rich microalgae (Scenedesmus) over the Sn-Beta catalyst was found to be a highly efficient process for producing lactic acid as a platform chemical. One-pot reaction with a very high lactic acid yield of 83.0 % was realized in a batch reactor using water as the solvent. Under the attack of formic acid, the cell wall of Scenedesmus was disintegrated, and hydrolysis of the starch inside the cell was strengthened in a controlled-release mode, resulting in a stable and relatively low glucose concentration. Subsequently, the Sn-Beta catalyst was employed for the efficient conversion of glucose into lactic acid with stable catalytic performance through isomerization, retro-aldol and de-/rehydration reactions. Thus, the hydrolysis of polysaccharides and the catalytic conversion of the monosaccharide into lactic acid was realized by the combination of an organic Brønsted acid and a heterogeneous Lewis acid catalyst.

Hydrothermal Carbonization of Microalgae (Chlorococcum sp.) for Porous Carbons With High Cr(VI) Adsorption Performance.

Porous carbon adsorbents were prepared from microalgae (Chlorococcum sp.) via directly hydrothermal carbonization coupled with KOH or NH3 activation for Cr(VI) adsorption. KOH-activated porous carbons exhibit high Cr(VI) adsorption capacities than those obtained via NH3 modification (370.37 > 95.70 mg/g). The superior Cr(VI) adsorption capacity is due to high surface areas (1784 m2/g) and pore volumes of porous carbon with mesoporous and macroporous structures. The Cr(VI) adsorption result was well fitted to the Langmuir model, showing that the removal of Cr(VI) was attributed to the monolayer adsorption of activity site on carbon surface.

Exploring stress tolerance mechanism of evolved freshwater strain Chlorella sp. S30 under 30 g/L salt.

Enhancement of stress tolerance to high concentration of salt and CO2 is beneficial for CO2 capture by microalgae. Adaptive evolution was performed for improving the tolerance of a freshwater strain, Chlorella sp. AE10, to 30 g/L salt. A resulting strain denoted as Chlorella sp. S30 was obtained after 46 cycles (138 days). The stress tolerance mechanism was analyzed by comparative transcriptomic analysis. Although the evolved strain could tolerate 30 g/L salt, high salinity caused loss to photosynthesis, oxidative phosphorylation, fatty acid biosynthesis and tyrosine metabolism. The related genes of antioxidant enzymes, CO2 fixation, amino acid biosynthesis, central carbon metabolism and ABC transporter proteins were up-regulated. Besides the up-regulation of several genes in Calvin-Benson cycle, they were also identified in C4 photosynthetic pathway and crassulacean acid metabolism pathway. They were essential for the survival and CO2 fixation of Chlorella sp. S30 under 30 g/L salt and 10% CO2.

Mechanism of Microwave-Assisted Pyrolysis of Glucose to Furfural Revealed by Isotopic Tracer and Quantum Chemical Calculations.

Glucose labeled with 13 C or 18 O was used to investigate the mechanism of its conversion into furfural by microwaveassisted pyrolysis. The isotopic content and location in furfural were determined from GC-MS and 13 C NMR spectroscopic measurements and data analysis. The results suggest that the carbon skeleton in furfural is mainly derived from C1 to C5 of glucose, whereas the C of the aldehyde group and the O of the furan ring in furfural primarily originate from C1 and O5 of glucose, respectively. For the first time, the source of O in the furan ring of furfural was elucidated directly by experiment, providing results that are consistent with predictions from recent quantum chemical calculations. Moreover, further theoretical calculations indicate substantially lower energy barriers than previous predictions by considering the potential catalytic effect of formic acid, which is one of the pyrolysis products. The catalytic role of formic acid is further confirmed by experimental evidence.

Low temperature microwave-assisted pyrolysis of wood sawdust for phenolic rich compounds: Kinetics and dielectric properties analysis.

Microwave-assisted pyrolysis of wood sawdust for phenolic rich compounds was carried out between 400 and 550°C in a batch reactor. An efficient preparation of liquid products was observed at 500°C with a yield of 58.50%, which was similar to conventional fast pyrolysis. The highest concentration of phenolic compounds in liquid product reached up to 78.7% (area) in which the alkoxy phenols contributed 81.8% at 500°C. Microwave thermogravimetric analysis using KAS method was used firstly to investigate the low-temperature pyrolytic behaviors and activation energy. The results indicated that effective pyrolytic range was 250-400°C and average activation energy was 42.78kJ/mol, which were 50-100°C and 50-100kJ/mol lower than conventional pyrolysis, respectively. Analysis on dielectric properties of pyrolytic products confirmed that accelerated pyrolysis and low temperature were attributed to the formation of instantaneous "hot spots".

Formation of THMs and HANs during bromination of Microcystis aeruginosa.

Bromine-contained disinfectants and biocides are widely used in swimming pools, recreational waters and cooling towers. The objective of this study was to evaluate the formation of thrihalomethanes (THMs) and haloacetonitriles (HANs) and their cytotoxicity in algae solutions during free bromine disinfection. Disinfection by-products formation potential experiments were conducted using model solutions containing 7 mg/L (as total organic carbon) Microcystis aeruginosa cells. Effects of free bromine dosage, pH and ammonia were investigated. The results showed that brominated disinfection by-products were the major products when free bromine was applied. The total THMs formed during bromination was much as that formed during chlorination, whereas HANs were elevated by using bromination instead of chlorination. Dibromoacetonitrice (C2H2NBr2) and bromoform (CHBr3) were the only detected species during free bromine disinfection. The production of C2H2NBr2 and CHBr3 increased with disinfectant dosage but decreased with dosing ammonia. CHBr3 increased with the pH changing from 5 to 9. However, C2H2NBr2 achieved the highest production at neutral pH, which was due to a joint effect of variation in hydrolysis rate and free bromine reactivity. The hydrolysis of C2H2NBr2 was base-catalytic and nearly unaffected by disinfectant. Finally, estimation of cytotoxicity of the disinfected algae solutions showed that HANs formation was responsible for the majority of toxicity. Considering its highest toxicity among the measured disinfection by-products, the elevated C2H2NBr2 should be considered when using bromine-related algaecide.