Lingzhao Kong

Hydrogen Production from Biomass Wastes by Hydrothermal Gasification

Abstract Biomass is a useful feed material for energy and chemical resources. Hydrothermal gasification of biomass wastes has been identified as a possible system for producing hydrogen. Supercritical and subcritical water has attracted much attention as an environmentally benign reaction medium and reactant. The main objective of this study is to assess and introduce the hydrothermal gasification of biomass wastes containing various quantities of the model compounds and real biomass. The decomposition of biomass, as a basis of hydrothermal treatment of organic wastes, is introduced. To eliminate chars and tars formation and obtain higher yields of hydrogen, catalyzed hydrothermal gasification of biomass wastes is summarized.

One-pot catalytic conversion of microalgae (Chlorococcum sp.) into 5-hydroxymethylfurfural over the commercial H-ZSM-5 zeolite

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 Bronsted 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.

Efficient one-pot production of 1,2-propanediol and ethylene glycol from microalgae (Chlorococcum sp.) in water

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.

Preparation of N-doped activated carbons with high CO2 capture performance from microalgae (Chlorococcum sp.)

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.

Re-utilization Disposal of Sawdust and Maize Straw by Hydrothermal Reaction

Abstract Sawdust and maize straw were treated by hydrothermal reactions using oxygen or no oxygen from 250°C to 374°C. The reaction product was separated into aqueous phase, gases, and residue (oil and char). Increased temperatures benefited the conversion of aqueous intermediates and residue to gas. The yields of aqueous products were increased simultaneously under hydrolysis conditions. The increased yield of gaseous phase was ascribed to oxidation decomposition of aqueous and residue. The intra- and intermolecular structures through the hydrogen bonds were partly changed. A plentiful amount of acetic acid was produced in an oxidative environment, but the yield of maleic acid was kept relatively stable.

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.

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.

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.

Catalytic conversion of glucose into alkanediols over nickel-based catalysts: a mechanism study

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-glucoses 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.

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.