Weijuan Yang

Impacts of Particle Size and Pressure on Reactivity of Boron Oxidation

Thermogravimetric measurements were conducted on the oxidation of boron particles to elucidate the influence of particle size and pressure on the reaction process and mechanism. The experimental results showed that the initial temperature increased slightly as the particle size of boron powder increased and increased greatly as the total ambient pressure decreased. The boron oxide covering on the surface of the boron particles had a significant effect on the reactivity of the boron powder. For the particles in the studied size range, the reaction efficiency showed an incremental trend as the particle size increased. High pressure could decrease the reaction efficiency greatly because the evaporation rate of boron oxide would slow down as the ambient pressure increased. Furthermore, it was found that the effect of O2 partial pressure on the reaction efficiency was not only related to the total ambient pressure but also to the O2 mole fraction. Both a higher O2 mole fraction and smaller ambient pressure wer...

Biodiesel production from wet microalgae by using graphene oxide as solid acid catalyst.

In order to produce biodiesel from lipids in wet microalgae with graphene oxide (GO) as solid acid catalyst, the effects on lipids conversion efficiencies of catalyst dosage, transesterification temperature, reaction time, methanol dosage and chloroform dosage were investigated. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that GO contained 0.997mmol SO3H groups per gram and high amounts of OH groups. Scanning electron microscopy showed that wet microalgae cells were adsorbed on hydrophilic GO surfaces covered with many OH groups. Lipids extracted by chloroform from microalgal cells were transformed into fatty acids methyl esters (FAMEs) through transesterification catalyzed by the acid centers (SO3H groups) in GO catalysts. The lipids conversion efficiency into FAMEs was 95.1% in microwave-assisted transesterification reactions of 5wt.% GO catalyst at 90°C for 40min.

The Impact of Preheating on Stability Limits of Premixed Hydrogen-Air Combustion in a Microcombustor

For the purpose of investigating the effects of preheating on microcombustion, an experiment of premixed flame in a microcombustor with inner diameter of 2 mm is conducted. The reactants are preheated, with the preheating temperatures of 23, 250, and 500°C, respectively. According to the experimental results, proper preheating temperature enhances the flame stability to some extent. For example, at 0.08 L/min, the stability limits change from 0.336–5.185 to 0.347–5.704, while the preheating temperature increases from 23°C to 250°C. Computational fluid dynamic simulation reveals that preheating intensifies the reaction, and increases the reaction temperature accordingly. Therefore, the micro flame has higher stability after preheating. But in the cases with extremely high preheating temperature of 500°C, blowout becomes more serious. According to the simulation results, the thermal expansion of preheated reactants increases the flow velocity in the micro-scale combustor. Subsequently, the imbalance between flow velocity and burning velocity causes blowout.

Conversion of lipids from wet microalgae into biodiesel using sulfonated graphene oxide catalysts

Four solid acid catalysts including graphene oxide (GO), sulfonated graphene oxide (SGO), sulfonated graphene (SG), and sulfonated active carbon (SAC) were used to convert lipids in wet microalgae into biodiesel. The physiochemical properties of the catalysts were characterized with scanning electron microscope, X-ray diffraction, and thermogravimetric analysis. SGO provided the highest conversion efficiency (84.6% of sulfuric acid) of lipids to fatty acid methyl esters (FAME). Whereas SAC converted few lipids into FAME. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that much higher hydrophilic hydroxyl content in SGO catalyst resulted in a considerable higher conversion efficiency of lipids to FAME than that (48.6%) catalyzed by SG, although SO3H groups (0.44mmol/g) in SGO were less than those (1.69mmol/g) in SG. Given its higher SO3H group content than GO (0.38mmol/g), SGO had higher conversion efficiency than GO (73.1%), when they had similar hydrophilic hydroxyl contents.

Microstructure and antioxidative capacity of the microalgae mutant Chlorella PY-ZU1 during tilmicosin removal from wastewater under 15% CO2

The response mechanisms of microalgal mutant Chlorella PY-ZU1 cells were investigated in their removal of antibiotic tilmicosin from wastewater under 15% CO2. Low concentrations (0.01-2mgL-1) of tilmicosin in wastewater stimulated the growth of microalgal cells, whereas high concentrations (5-50mgL-1) of tilmicosin significantly inhibited cell growth. When initial tilmicosin concentration increased from 0 to 50mgL-1, fractal dimension of microalgal cells monotonically increased from 1.36 to 1.62 and cell size monotonically decreased from 4.86 to 3.75μm. In parallel, malondialdehyde content, which represented the degree of cellular oxidative damage, monotonically increased from 1.92×10-7 to 7.07×10-7 nmol cell-1. Superoxide dismutase activity that represented cellular antioxidant capacity first increased from 2.59×10-4 to the peak of 6.60×10-4U cell-1, then gradually decreased to 2.39×10-4U cell-1. The maximum tilmicosin removal efficiency of 99.8% by Chlorella PY-ZU1 was obtained at the initial tilmicosin concentration of 50mgL-1.

Transcriptome sequencing and metabolic pathways of astaxanthin accumulated in Haematococcus pluvialis mutant under 15% CO2

Transcriptome sequencing and annotation was performed on Haematococcus pluvialis mutant red cells induced with high light under 15% CO2 to demonstrate why astaxanthin yield of the mutant was 1.7 times higher than that of a wild strain. It was found that 56% of 1947 differentially expressed genes were upregulated in mutant cells. Most significant differences were found in unigenes related to photosynthesis, carotenoid biosynthesis and fatty acid biosynthesis pathways. The pyruvate kinase increased by 3.5-fold in mutant cells. Thus, more pyruvate, which was beneficial to carotenoids and fatty acid biosynthesis, was generated. Phytoene synthase, zeta-carotene desaturase, lycopene beta-cyclase involved in β-carotene biosynthesis in mutant cells were upregulated by 10.4-, 4.4-, and 5.8-fold, respectively. Beta-carotene 3-hydroxylase catalyzing conversion of β-carotene into astaxanthin was upregulated by 18.4-fold. The fatty acid biosynthesis was promoted because of the upregulation of acetyl-CoA synthetase and acetyl-CoA carboxylase, thus increasing astaxanthin esterification and accumulation in mutant cells.

Mutation of Spirulina sp . by nuclear irradiation to improve growth rate under 15% carbon dioxide in flue gas

Spirulina sp. was mutated by γ-rays from 60Co nuclear irradiation to improve growth and CO2 fixation rate under 15vol.% CO2 (in flue gas from a power plant). Mutants with enhanced growth phenotype were obtained, with the best strain exhibiting 310% increment in biomass yield on day 4. The mutant was then domesticated with elevated CO2 concentration, and the biomass yield increased by 500% after domestication under 15vol.% CO2, with stable inheritance. Ultrastructure of Spirulina sp. shows that the fractal dimension of Spirulina cells decreased by 23% after mutation. Pore size in the cell wall of Spirulina mutant increased by 33% after 15vol.% CO2 domestication. This characteristic facilitated the direct penetration of CO2 into cells, thus improving CO2 biofixation rate.

Kinetic model of single boron particle ignition based upon both oxygen and (BO)n diffusion mechanism

A comprehensive ignition model for single boron particles in an oxygenated environment containing O2 and H2O is developed. Microcharacteristics of the boron oxide layer on the surface of boron particles at elevated temperatures are studied. Two typical distributions of species inside the surface oxide layer are detected. One is composed of three layers [B2O3, (BO)n, and B2O3], while the other is composed of two layers [(BO)n and B2O3], both according to the order from the internal to external side of the layer. In the model development, two submodels, submodel I and submodel II, are developed with regard to two different observed species distributions in the surface oxide layer. For submodel I, it is assumed that both (BO)n and O2 are the governing species diffusing into the liquid oxide layer. For submodel II, only (BO)n is the governing species. These two submodels are combined into a new bi-directional model consisting of four key kinetic processes: evaporation of the liquid oxide layer, global surface reaction between oxygen from the environment and boron, reaction between the inner boron core and oxygen, and global reaction of boron with water vapor. The ignition time predicted by the model is in good agreement with previous experimental data.

Quantum Chemical Calculations on the Reaction of Zinc and Water in Gas Phase

The reaction of zinc with water is one of two steps of the Zn/ZnO water-splitting thermochemical cycle and is of interest for the hydrogen production. The reaction of zinc with water was investigated here by ab initio quantum chemical methods, and the results provided fundamental understanding of the zinc oxide particle formation in the gas phase. The geometries and frequencies of all reactants, products, intermediates, and transition states were calculated at the B3LYP/6-311G++(3df, 2p) level. The Zn and water first form an atom–molecule adduct Zn · OH2, and then either form HZnOH by an H-migration process or directly form ZnO + H2 by an H-dissociation process. The higher-level energies, barrier heights of the two paths, and rate constants were calculated. The results showed that H-migration process was dominant in the studied temperature range.

Transcriptome-based analysis on carbon metabolism of Haematococcus pluvialis mutant under 15% CO2

To elucidate the mechanism underlying the enhanced growth rate in the Haematococcus pluvialis mutated with 60Co-γ rays and domesticated with 15% CO2, transcriptome sequencing was conducted to clarify the carbon metabolic pathways of mutant cells. The CO2 fixation rate of mutant cells increased to 2.57gL-1d-1 under 15% CO2 due to the enhanced photosynthesis, carbon fixation, glycolysis pathways. The upregulation of PetH, ATPF0A and PetJ related to photosynthetic electron transport, ATP synthase and NADPH generation promoted the photosynthesis. The upregulation of genes related to Calvin cycle and ppdK promoted carbon fixation in both C3 and C4 photosynthetic pathways. The reallocation of carbon was also enhanced under 15% CO2. The 19-, 14- and 3.5-fold upregulation of FBA, TPI and PK genes, respectively, remarkably promoted the glycolysis pathways. This accelerated the conversion of photosynthetic carbon to pyruvate, which was an essential precursor for astaxanthin and lipids biosynthesis.