Mingde Yang

Direct liquefaction of Dunaliella tertiolecta for bio-oil in sub/supercritical ethanol–water

This paper presents bio-oil preparation by direct liquefaction of Dunaliella tertiolecta (D. tertiolecta) with sub/supercritical ethanol-water as the medium in a batch autoclave with high temperature and high pressure. The results indicated that ethanol and water showed synergistic effects on direct liquefaction of D. tertiolecta. The maximum bio-oil yield was 64.68%, with an optimal D. tertiolecta conversion of 98.24% in sub/supercritical ethanol-water. The detailed chemical compositional analysis of the bio-oil was performed using an EA, FT-IR, and GC-MS. The empirical formulas of the bio-oil obtained using the ethanol-water co-solvent (40%, v/v) and sole water as the reaction medium were CH(1.52)O(0.14)N(0.06) and CH(1.43)O(0.23)N(0.09), with calorific values of 34.96 and 29.80 MJ kg(-1), respectively. XPS and SEM results showed that ethanol-water is a very effective reaction medium in the liquefaction. A plausible reaction mechanism of the main chemical component in D. tertiolecta is proposed based on our results and the literatures.

Thermochemical conversion of low-lipid microalgae for the production of liquid fuels: challenges and opportunities

The development of renewable biomass energy sources has attracted attention because of the potential for a sustainable fuel with a low carbon intensity. Microalgae are considered as a third generation biofuel, and have a notable advantage over other biomass in that they do not compete with food or cropland resources. The conversion of algal biomass into liquid fuels provides a long-term sustainable option for fuels production, which can be achieved in an environmentally compatible manner. Among the microalgal conversion methods, thermochemical conversion, which can make full use of all components in the algae, is viewed as one of the best conversion methods, especially for low-lipid microalgae. This article reviews recent developments in the field of algal biomass conversion into liquid fuels, with particular attention focused on the thermochemical conversion of low-lipid microalgae. We start with a brief introduction of microalgae and its biochemical components. After an overview of the main strategies involved in algal biomass conversion, we focus on the thermochemical conversion of algae, including pyrolysis and hydrothermal liquefaction and compare the two methods in detail. In addition, the catalytic upgrading of algae-derived crude bio-oil was also examined. An assessment is made of the challenges and opportunities of a commercial-scale microalgae-to-fuels process in light of mitigating technical, environmental, and logistical issues.

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.

Catalytic hydrodeoxygenation of palmitic acid over a bifunctional Co-doped MoO2/CNTs catalyst: an insight into the promoting effect of cobalt

Novel Co-doped MoO2/CNTs catalysts were prepared by a wet-impregnation method and employed in catalytic hydrodeoxygenation (HDO) of palmitic acid. The obtained catalysts were systematically characterized using various techniques, namely, XRD, BET surface area, XPS, FT-IR spectroscopy of adsorbed pyridine, Raman, H2-TPD, and H2-TPR. Characterization studies revealed the doping of Co ions into the lattice of MoO2, the interaction between metal species modified the electrical properties of the catalytic active sites, and the formation of new active sites and defects. The catalytic results showed that Co ions could significantly improve catalytic performance, and the best selectivity to hexadecane reached 89.3% at an extremely low temperature of 180 °C. The increased presence of Mo2C particles, Lewis acidic sites and oxygen vacancies were all responsible for the noticeable catalytic performance of the Co doped catalyst. The mechanistic insights from this work confirmed the bifunctional role of Co-doped MoO2/CNTs catalysts for HDO of palmitic acid, which was catalyzed either solely by Mo2C or synergistically by Mo2C and MoO2. Insights into the nature of the active site would provide a useful knowledge for rational design of effective Mo-based HDO catalysts and assist future studies on more efficient catalytic conversion systems.

On the second-order moment turbulence model for simulating a bubble column

Abstract Two versions of the second-order moment two-phase turbulence model are proposed in this study for simulating bubble–liquid two-phase turbulent velocity fluctuations and their interactions in bubble–liquid flows under the dispersed bubble regime. One of them is a full transport equation model; the other is an algebraic stresses model. The proposed model is used to simulate liquid and gas mean velocities, gas volume fraction, liquid and gas Reynolds stresses and turbulent kinetic energy in a 2-D bubble column. Furthermore, the bubble and liquid velocities, Reynolds stresses and gas volume fraction are measured using the PIV. The simulation results are in good agreement with the PIV results and experimental data in the literature. The studies reveal the liquid recirculation and bubble up-rising flow patterns, and anisotropic liquid and bubble normal Reynolds stresses. Bubble fluctuation is observed to be stronger than liquid fluctuation. Moreover, both the liquid velocity gradient and bubble–liquid interaction are important for the generation of liquid turbulence.

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.

Thermal characterization and kinetic analysis of nesquehonite, hydromagnesite, and brucite, using TG–DTG and DSC techniques

Nesquehonite, hydromagnesite, and brucite are important precursors for the preparation of high-purity magnesia (MgO) using magnesium resources from salt lake as raw materials. In this paper, TG–DTG and DSC were used to investigate the thermal decomposition behaviors of the three precursors. Decomposition kinetic parameters at each stage were evaluated based on the TG data using the iso-conversional method. Decomposition mechanisms were determined using the master-plots method. The decomposition temperature range, heat absorption, and kinetic parameters of the three phases were then compared. The most probable mechanism of each stage from the perspective of crystal structure was found to be consistent with the calculation results from the master-plots method. Results led to the conclusion that nesquehonite is the most appropriate precursor for the preparation of high-purity MgO. Further studies on precursor selection and calcining condition selection for the preparation of MgO using bischofite will benefit from this research.

Upgrading of palmitic acid to iso-alkanes over bi-functional Mo/ZSM-22 catalysts

Bi-functional Mo/ZSM-22 catalysts were designed to upgrade palmitic acid and further to isomerize n-alkanes. Besides the effects on acidity, H+ cations might be beneficial for the distribution of MoOx particles, the higher surface Mo/Si ratio and the greater surface Mo4+ content of bi-functional Mo/ZSM-22 catalysts. In the upgrading of palmitic acid, strong acid sites of catalysts were proven to favor hydrodecarbonylation (HDC), isomerization and cracking. Mo6+ (or MoO3) preferred to support the HDC reaction, whereas Mo4+ (or MoO2) suitably improved the hydrodeoxygenation (HDO) reaction without carbon atom loss. That is, the Mo4+/Mo6+ ratio of Mo/ZSM-22 catalysts significantly influenced HDO/HDC selectivity. More importantly the improvement in HDO rather than HDC with the complete conversion of palmitic acid, could significantly decrease the negative effects of strong acid sites (such as HDC and cracking) to facilitate isomerization of n-alkanes to afford more branched alkanes with a higher iso-alkanes/n-alkanes ratio.

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.