•MAP of wood sawdust for preparing phenolic chemicals with a yield of 78.7% at 500 °C.•MV-TGA with KAS method is applied to reveal pyrolytic behavior and activation energy.•Effective pyrolytic range and average activation energy are 250–400 °C and 42.78 kJ/mol.•Low temperature pyrolysis is attributed to the formation of instantaneous “hot spots”.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 42.78 kJ/mol, which were 50–100 °C and 50–100 kJ/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”.Phenolic compounds reached up to 78.7% (area) at 500 °C along with low activation energy were attributed to the generated instantaneous “hot spots” in microwave-assisted pyrolysis.Download high-res image (138KB)Download full-size image

Herein, we report a one-pot approach to produce HMF from aquatic microalgae (Chlorococcum sp.) with a yield up to 48.0% under mild reaction conditions (200 °C, 2 h) over the commercial cheap H-ZSM-5 catalyst. Conversion of microalgae to HMF involved three steps: (1) degradation of microalgae to carbohydrates; (2) hydrolysis of polysaccharides to glucose and mannose; (3) their isomerization to fructose on Lewis acid sites and its further dehydration to HMF over Brønsted acid sites. Proteins and lipids in microalgal cells play an important role in stabilizing HMF in water. Ball-milling pretreatment or addition of another organic solvent enhanced the productivity of HMF from microalgae. Besides, this cheap H-ZSM-5 catalyst also demonstrated excellent stability, and a slight loss of its activity can be easily recovered by simple calcination treatment.

N-Doped activated carbons with high CO2 adsorption capacity have been prepared from sugar-rich microalgae (Chlorococcum sp.) feedstock via simple hydrothermal carbonization coupled with KOH activation or NH3 modification. The KOH activated carbons exhibit higher CO2 capture performance compared with the ones treated by NH3. The nitrogen-enriched hydro-char derived from microalgae was activated with KOH at 700 °C to improve the textural characteristics (surface area, pores size, and total pore volume), and the resulting carbon showed a highly ordered structure with a surface area of 1745 m2 g−1, and narrow pore size distribution with the maxima peak located in the micropore range (<1.0 nm). The activated carbon exhibited CO2 uptakes of 4.03 and 6.68 mmol g−1 at 25 °C and 0 °C, respectively. Further XPS analysis revealed the effective pyridonic-nitrogen species (up to 58.32%) on the carbon surface favored a higher CO2 capture capacity. The N-doped activated carbons displayed rapid adsorption kinetics with ultrahigh selectivity for CO2 over N2 (up to 11 at 25 °C), and no obvious decrease in the CO2 uptake capacity was observed even after seven cycles, which may be due to the dominant physisorption between CO2 and the surface of carbon.

The conversion of isotope-labeled glucose (D-1-13C-glucose) into alkanediols was carried out in a batch reactor over a Ni–MgO–ZnO catalyst to reveal the C–C cleavage mechanisms. The unique role of the MgO–ZnO support was highlighted by 13C NMR and GC-MS analysis qualitatively and the MgO–ZnO favored isomerization of glucose to fructose. 13C NMR, GC-MS and HPLC analysis demonstrated that the C1 position of ethylene glycol, the C1 and C3 positions of 1,2-propanediol and the C1 position of glycerin were labeled with 13C, which is attributed to a C–C cleavage at D-1-13C-glucose's corresponding positions through retro-aldol condensation. A hydrogenolysis followed by hydrogenation pathway was proposed for glucose converted into alkanediols at 493 K with 6.0 MPa of H2 pressure over Ni based catalysts.

The catalytic valorization of microalgae, a sustainable feedstock to alleviate dependence on fossil fuel and offset greenhouse gases emissions, is of great significance for production of biofuels and value-added chemicals from aquatic plants. Here, an interesting catalytic process is reported to convert microalgae (Chlorococcum sp.) into 1,2-propanediol (1,2-PDO) and ethylene glycol (EG) in water over nickel-based catalysts. The influences of reaction temperature, initial H2 pressure and reaction time on the product distribution were systematically investigated by using a batch reactor. Under optimal reaction conditions (at 250 °C for 3 h with 6.0 MPa of H2 pressure), microalgae were directly and efficiently converted over a Ni–MgO–ZnO catalyst and the total yield of polyols was up to 41.5%. The excellent catalytic activity was attributed to the smaller size and better dispersion of Ni particles on the MgO–ZnO supporter based on the characterization results as well as its tolerance to nitrogen-containing compounds. Besides, the reaction pathway was proposed based on the formation of reaction intermediates and the results of model compound conversion.

•Microwave reduces 200 °C compared with conventional heating to obtain same results.•Syngas with 60 vol.% H2 and H2 + CO > 90% are obtained under Ca(OH)2 catalyst at 550 °C.•AAEM catalytic effects on gasification is related to forming of intermediate C(O).A novel microwave assisted gasification technique was developed whereby pyrolytic biochar obtained from rice straw was used as the feedstock. The conversion efficiencies and gas composition obtained at 800 °C by conventional heating method were similar to that obtained at 550 °C by microwave-assisted gasification. At 550 °C using microwave heating, the CO + H2 yields were over 90 vol.% and H2 content was 60 vol.%. The effects of alkali and alkaline earth metals (AAEM) on microwave-assisted gasification activity of biochar were also investigated. The results indicated that 5% K2CO3 and 5% KOH increased the carbon conversion efficiency from 74.39% to 79.95% and 85.04%, respectively, but CO2 content increased remarkably. Ca(OH)2 was a suitable gasification catalyst and excellent CO2 absorber. 10% Ca(OH)2 reduced CO2 percentage from 21.92 vol.% to 10.83 vol.% and shortened reaction time from 90 to 60 min. Based on the AAEM catalytic mechanisms and microwave heating function, the intermediate C(O) and dipole rotation of materials molecules played a crucial role in the microwave-assisted gasification of biochar. This study proves that microwave heating coupled with the addition of AAEM result in low-temperature microwave-assisted gasification of biochar.

•Peanut shell active carbons containing ultramicropores were made by KOH activation.•We studied effects of impregnation ratio (IR) and activation time on ultramicropores.•Increasing IR varied ultramicropore volume (V<0.7 nm) and ultramicropore fraction.•Prolonging the activation time varied ultramicropore fraction, not varying V<0.7 nm.•The highest V<0.7 nm was obtained by activation for 1–2 h using an IR of 2.We studied effects of impregnation ratio and activation time on ultramicropores of KOH-activated peanut shell active carbons (ACs). The ultramicropores were characterized in terms of ultramicropore volume (V<0.7 nm), ultramicropore fraction (V<0.7 nm/Vt), and pore size distribution. The ultramicropores of the ACs were mostly in the range of 0.45–0.70 nm. Increasing the impregnation ratio from 1 to 3 first increased the V<0.7 nm and V<0.7 nm/Vt, and then decreased them. Prolonging the activation time from 1 h to 2 h resulted in a minimum V<0.7 nm/Vt, but hardly affected the V<0.7 nm. The AC with the highest V<0.7 nm (0.11 ml/g) was obtained by activation for 1–2 h at an impregnation ratio of 2. The V<0.7 nm bore a linear relationship with the CO2 uptakes at 0.1 and 0.2 bar (0 °C). This research was significant for preparation of ACs with developed ultramicropores.