Hong-shik Lee

Synthesis of biodiesel from rapeseed oil using supercritical methanol with metal oxide catalysts.

This study examined the synthesis of biodiesel using supercritical or subcritical methanol with metal oxide catalysts. The transesterification of rapeseed oil was carried out with the metal oxide catalysts (SrO, CaO, ZnO, TiO(2) and ZrO(2)) to determine the most effective heterogeneous catalyst having the highest catalytic activity with minimum weight loss caused by dissolution. SrO and CaO dissolved in the biodiesel during the reaction because they were transformed to strontium methoxide and calcium methoxide, respectively. ZnO was the optimum catalyst for the transesterification of rapeseed oil owing to its high activity and minimum weight loss in supercritical methanol. The optimal reaction conditions included a molar ratio of methanol to oil of 40 in the presence of 1.0wt.% ZnO and a reaction time of 10min. The supercritical process with ZnO as a catalyst appears economically viable.

Synergetic effect of copper-plating wastewater as a catalyst for the destruction of acrylonitrile wastewater in supercritical water oxidation.

A new supercritical water oxidation process for the simultaneous treatment of mixed wastewater containing wastewater from acrylonitrile manufacturing processes and copper-plating processes was investigated using a continuous tubular reactor system. Experiments were carried out at temperatures ranging from 400 to 600 degrees C and a pressure of 25 MPa. The residence time was fixed at 2s by changing the flow rates of feeds, depending on reaction temperature. The initial total organic carbon (TOC) concentration of the wastewaters and the O(2) concentration at the reactor inlet were kept constant at 0.49 and 0.74 mol/L. It was confirmed that the copper-plating wastewater accelerated the TOC conversion of acrylonitrile wastewater from 17.6% to 67.3% at a temperature of 450 degrees C. Moreover, copper and copper oxide nanoparticles were generated in the process of supercritical water oxidation (SCWO) of mixed wastewater. 99.8% of copper in mixed wastewater was recovered as solid copper and copper oxides at a temperature of 600 degrees C, with their average sizes ranging from 150 to 160 nm. Our study showed that SCWO provides a synergetic effect for simultaneous treatment of acrylonitrile and copper-plating wastewater. During the reaction, the oxidation rate of acrylonitrile wastewater was enhanced due to the in situ formation of nano-catalysts of copper and/or copper oxides, while the exothermic decomposition of acrylonitrile wastewater supplied enough heat for the recovery of solid copper and copper oxides from copper-plating wastewater. The synergetic effect of wastewater treatment by the newly proposed SCWO process leads to full TOC conversion, color removal, detoxification, and odor elimination, as well as full recovery of copper.

Hydro- and solvothermolysis of kraft lignin for maximizing production of monomeric aromatic chemicals

The hydro-/solvothermolysis of kraft lignin using water and ethanol as a solvent were investigated in this study. The effect of the water-to-ethanol ratio on the yields of monomeric aromatic chemicals (MACs) and the kinetic behavior of MACs was studied in a series of batch experiments. The yields of MACs other than catechol increased as the ratio of ethanol increased, and the content of the total MACs in bio-crude oil (BCO) reached 35% when the ratio of ethanol was 100% at a reaction temperature of 300 °C. The formation of phenol, guaiacol, and alkylguaiacols was enhanced in ethanol, while the formation of catechol was dominant in water. The formation of more substituted MACs such as vanillin, acetoguaiacone, and homovanillic acid was not affected by the solvent. The role of reaction parameters on the yields of MACs was elucidated, and the main reaction pathways in water and in ethanol were proposed.

Physical and rheological properties of thermoplasticized crosslinked-polyethylene foam in supercritical methanol

The physical and rheological properties of thermoplasticized irradiation-crosslinked polyethylene foam using supercritical methanol treatment were investigated by GPC, FTIR, DSC, WAXS, DMTA and UDS. The polyethylene foam was selectively decrosslinked into thermoplasticized polyethylene in an appropriate supercritical methanol condition without any undesirable side reactions such as oxidation and disproportionation. The thermoplasticization was promoted with increasing reaction temperature to reach completion above 380 °C. The supercritical reaction condition affected the crystallization behavior, and mechanical and rheological properties of the decrosslinked polyethylene foam, but not its crystallographic structure or crystallinity.

Low-temperature, Selective Catalytic Deoxygenation of Vegetable Oil in Supercritical Fluid Media

The effects of supercritical fluids on the production of renewable diesel-range hydrocarbons from natural triglycerides were investigated. Various supercritical fluids, which included CO2 (scCO2 ), propane (scC3 H8 ) and n-hexane (scC6 H14 ), were introduced with H2 and soybean oil into a fixed-bed reactor that contained pre-activated CoMo/γ-Al2 O3 . Among these supercritical fluids, scC3 H8 and scC6 H14 efficiently allowed the reduction of the reaction temperature by as much as 50 °C as a result of facilitated heat and mass transfer and afforded similar yields to reactions in the absence of supercritical fluids. The compositional analyses of the gas and liquid products indicated that the addition of scC3 H8 during the hydrotreatment of soybean oil promoted specific deoxygenation pathways, decarbonylation and decarboxylation, which consumed less H2 than the hydrodeoxygenation pathway. As a result, the quantity of H2 required to obtain a high yield of diesel-range hydrocarbons could be reduced to 57 % if scC3 H8 was used. As decarboxylation and decarbonylation are mildly endothermic reactions, the reduced heat transfer resistance in scC3 H8 may drive the deoxygenation reaction to thermodynamically favourable pathways.

Vegetable oil aided hydrothermal synthesis of cerium oxide nanocrystals

Hydrothermal synthesis of cerium oxide nanocrystals was performed with in-situ surface modification using soybean oil and palm oil as capping agents. The synthesized nanocrystals were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). TEM results showed single crystalline nature with stable dispersion. FT-IR spectra and TGA plots further confirmed the adsorption of fatty acid molecules onto cerium oxide surface. Our findings have the advantages of reduced materials costs compared to using single component surfactants and the production of valuable by-product glycerol.

SYNTHESIS OF HYDROUS RUTHENIUM OXIDE NANOPARTICLES IN SUB- AND SUPERCRITICAL WATER AND THEIR CAPACITIVE PROPERTIES

Hydrous ruthenium oxide (RuO2 · nH2O) nanoparticles with various particle sizes and water contents were synthesized in sub- and supercritical water in a very short reaction time of 15 min. The particle size, surface area, morphology, crystalline structure, and electrochemical properties were analyzed and compared with those of commercial RuO2 particles. Ultrafine spherical RuO2 · 0.6H2O nanoparticles with an average size of 4.2 nm were produced in subcritical water (250°C, 300 bar), while larger and more highly crystalline rod-shaped RuO2 · (0.3–0.5)H2O particles were produced in supercritical water (400°C, 300 bar). The use of NaOH under the supercritical water conditions resulted in a decrease in particle size. The hydrous RuO2 nanoparticles synthesized in subcritical water exhibited a much higher specific capacitance (255 F g−1) at a scan rate of 10 mV s−1 than those synthesized in supercritical water (77 F g−1) and commercial RuO2 (8 F g−1).