Kejing Wu

Pyrolysis characteristics and kinetics of aquatic biomass using thermogravimetric analyzer

The differences in pyrolysis process of three species of aquatic biomass (microalgae, macroalgae and duckweed) were investigated by thermogravimetric analysis (TGA). Three stages were observed during the pyrolysis process and the main decomposition stage could be divided further into three zones. The pyrolysis characteristics of various biomasses were different at each zone, which could be attributed to the differences in their components. A stepwise procedure based on iso-conversional and master-plots methods was used for the kinetic and mechanism analysis of the main decomposition stage. The calculation results based on the kinetic model was in good agreement with the experimental data of weight loss, and each biomass had an increasing activation energy of 118.35-156.13 kJ/mol, 171.85-186.46 kJ/mol and 258.51-268.71 kJ/mol in zone 1, 2 and 3, respectively. This study compares the pyrolysis behavior of various aquatic biomasses and provides basis for further applications of the biomass thermochemical conversion.

Heterogeneous Catalytic Conversion of Biobased Chemicals into Liquid Fuels in the Aqueous Phase

Different biobased chemicals are produced during the conversion of biomass into fuels through various feasible technologies (e.g., hydrolysis, hydrothermal liquefaction, and pyrolysis). The challenge of transforming these biobased chemicals with high hydrophilicity is ascribed to the high water content of the feedstock and the inevitable formation of water. Therefore, aqueous-phase processing is an interesting technology for the heterogeneous catalytic conversion of biobased chemicals. Different reactions, such as dehydration, isomerization, aldol condensation, ketonization, and hydrogenation, are applied for the conversion of sugars, furfural/hydroxymethylfurfural, acids, phenolics, and so on over heterogeneous catalysts. The activity, stability, and reusability of the heterogeneous catalysts in water are summarized, and deactivation processes and several strategies are introduced to improve the stability of heterogeneous catalysts in the aqueous phase.

Study on pyrolytic kinetics and behavior: The co-pyrolysis of microalgae and polypropylene

In the current work, the co-pyrolysis kinetics of Dunaliella tertiolecta and PP were investigated via TGA, while TG-FTIR and TG-MS were used for the analysis of gas-phase components and volatiles transition. The TGA results show that PP with certain small particle size accelerates the pyrolysis process of the microalgae, while the existence of D. tertiolecta delayed that of PP. This significant interaction achieves maximum when mass ratio of PP and D. tertiolecta is 6:4. The activation energy estimated from FWO kinetic model also supports this interaction. The TG-FTIR and TG-MS results show that a significant decrease of CO2 occurs at PP and D. tertiolecta mass ratio of 6:4, indicating that small molecules (such as radicals) released by PP might react with CO2 produced by D. tertiolecta or carbonyl groups in the microalgae.

Recent progress on upgrading of bio-oil to hydrocarbons over metal/zeolite bifunctional catalysts

Upgrading of bio-oil is of high necessity and popularity in converting biomass to high-quality hydrocarbons (transportation fuels and petrochemicals) to reduce the overall CO2 emissions of fossil based materials. There are hundreds of different oxygenated compounds identified in bio-oil, resulting in a high oxygen content (30% to 50%). This review focuses on recent progress in the upgrading of bio-oil over metal/zeolite bifunctional catalysts, with model compounds and real bio-oil included. Firstly, typical model compounds and corresponding reaction routes are summarized, based upon the composition of the bio-oil and a basic knowledge of chemical reactions. Secondly, careful analyses are conducted on the deoxygenation mechanisms over different metal active centers and acid-catalyzed reactions, such as isomerization and cracking, over zeolitic acid sites, respectively. Moreover, detailed analyses have focused on the effect of metal loadings on zeolites, the effects of zeolitic porosity and acidity on the metal, and their overall effects on reaction activity, selectivity and stability. Thirdly, the fundamental understanding of the interaction between the metal centers and zeolite acid sites in bifunctional catalysts and their influences on complex reaction networks, including deoxygenation and acid-catalyzed reactions, is analyzed. The metal/acid balance may be the key in improving the catalytic activity and product selectivity in the upgrading of bio-oil, which needs further careful design. Finally, the potential challenges and opportunities for the upgrading of bio-oil over metal/zeolite bifunctional catalysts are outlined.

Catalytic hydrothermal liquefaction of Euglena sp. microalgae over zeolite catalysts for the production of bio-oil

In this paper, Euglena sp. microalgae with low lipid and high ash contents were successfully converted into bio-oil with/without catalysts through hydrothermal liquefaction (HTL) at 280 °C and a reaction time of 30 min. The introduction of acidic microporous zeolite catalysts (HZSM-22, HZSM-5, H beta, MCM-22, and SAPO-11) with high hydrothermal stability further improved the bio-oil quality in situ. Various methods, including elemental analysis, high heat value (HHV), and gas chromatography (GC)-mass spectrometry (MS), were used to analyze the physicochemical properties of the obtained bio-oil. Results indicated that catalyst addition could enhance C and H contents, reduce O and N contents, and also improve HHV (the maximum value of 37.08 MJ kg−1 was obtained for the H beta catalyst). GC-MS revealed that the bio-oil obtained by direct HTL contained relatively high amounts of N-containing compounds (30.87%) and acid compounds (16.44%). Meanwhile, the catalysts introduced in situ not only lowered the contents of nitrogen and acids to some extent, but also simultaneously increased the hydrocarbon content. This result was most pronounced over the H beta catalyst, which reduced the nitrogen content to 16.68% and decreased the acid content to 9.50%. The hydrocarbon content increased to 43.43%. Ultimately, a reasonable reaction network for Euglena sp. HTL was proposed and provides a basis for the processs further industrialization.

Co-liquefaction of microalgae and polypropylene in sub-/super-critical water

In the current study, Dunaliella tertiolecta (D. tertiolecta) and polypropylene (PP) were chosen to investigate the co-liquefaction process of microalgae and plastic. The results show that a maximum synergistic effect was found when the mass ratio of D. tertiolecta to PP was 8 : 2. The addition of PP mainly impacts the composition of the bio-oil products, particularly reducing the acid content. When D. tertiolecta was liquefied individually, the relative content of acid in bio-oil could reach 18.73%, while for D. tertiolecta and PP co-liquefaction in a ratio of 8 : 2, the acid content of bio-oil was lower than the detection limit of GC-MS (lower than 100 ppm). The reaction mechanism for the co-liquefaction process of PP and the main components of microalgae has also been studied. The addition of PP has a significant effect on the transformation pathways of carbohydrates in microalgae, and this also promotes the Maillard reaction between carbohydrates and proteins or their hydrolysates.

Upgrading of palmitic acid over MOF catalysts in supercritical fluid of n-hexane

The addition of phosphotungstic acid (PTA) to the synthesis mixture of PdCu@FeIII–MOF-5 yields the direct encapsulation of PTA inside the MOF structure (i.e. PTA@PdCu@FeIII–MOF-5) through a facile solvothermal approach. The deoxygenation reaction of palmitic acid has been investigated over PdCu@FeIII–MOF-5 and PTA@PdCu@FeIII–MOF-5 under a hydrogen atmosphere in the supercritical fluid (SCF) of n-hexane. The results showed that palmitic acid can be converted completely at 240 °C on PTA@PdCu@FeIII–MOF-5 with a high selectivity of hexadecane. Owning to the improvement of acidity of the MOF catalyst by the encapsulation of PTA inside the hollow octahedral nanostructures of PdCu@FeIII–MOF-5, the selectivity for hexadecane over the PTA@PdCu@FeIII–MOF-5 catalyst is higher than that over PdCu@FeIII–MOF-5. The excellent performance in the catalytic hydrodeoxygenation (HDO) of palmitic acid is associated with the synergistic effect between yolk–shell PTA@PdCu@FeIII–MOF-5 nanostructures and SCF medium.

ZrMn Oxides for Aqueous-Phase Ketonization of Acetic Acid: Effect of Crystal and Porosity

Aqueous-phase ketonization of bio-based acetic acid is important to improve the conversion efficiency of biomass resources. In this study, ZrMn mixed oxides (ZrMnOx ) with high aqueous-phase ketonization activity are synthetized through a carbonization/oxidation method (COM) and solvothermal method (STM). The results show that ZrMnOx prepared by COM possesses tetragonal ZrO2 , and hausmannite Mn3 O4 is observed only at a high oxidation temperature of 750 °C. Low-temperature and long oxidation results in decreased crystallinity and crystallite size, which is related to highly dispersed Mnn+ species. The catalysts with improved acid sites possess high ketonization activity. Surface areas and pore size of ZrMnOx synthetized by STM are controlled by the solvents for thermal treatment. Compared with water as solvent, ethanol increases the surface area and pore size, resulting in high ketonization activity.

Role of Co-solvents in Biomass Conversion Reactions Using Sub/Supercritical Water

Water above its critical point (T c = 647 K, P c = 22.1 MPa), which is regarded as supercritical water (SCW), is being given increasing attention as a medium for organic chemistry. This interest in SCW is mainly driven by the search for more “green” or environmentally benign chemical processes. The use of SCW instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution prevention. SCW has been applied in synthetic fuels production, biomass processing, waste treatment, materials synthesis, and geochemistry. However, higher critical parameters of water indicate that the operation process is performed at harsh conditions, thereby increasing cost. Other drawbacks of the use of water as the medium for biomass liquefaction reaction include lower biofuel yield and higher oxygen content. Organic solvents, such as methanol, ethanol, and 2-propanol, have been utilized as co-solvents of SCW to enhance the biofuel yield with lower oxygen content and higher heating value. This paper mainly expounds the basic characteristics of the co-solvent in sub/supercritical water and analyzes the function of the co-solvent in reactions to provide readers with a more comprehensive knowledge of the co-solvent. Based on literature and related studies conducted by our group, systematic analysis about selection and application of co-solvent was conducted.