A novel process of bioethanol production from lignocellulosics was developed by acetic acid fermentation followed by hydrogenolysis of acetic acid to ethanol. This process includes a two-step hot-compressed water treatment of lignocellulosics to C6 and C5 sugars, decomposed products and lignin-derived compounds. In the subsequent fermentation, most of these products are to be anaerobically fermented into acetic acid in form of sodium acetate by free and/or immobilized co-culturing system (Clostridium thermocellum and C. thermoaceticum) by batch or fed-batch fermenter with pH controlled by NaOH or Ca(OH)2 to be 6.5-7.0. The obtained acetate aqueous solution was then converted and concentrated into acetic acid up to 200 g/L by bipolar membrane electrodialysis. The acetic acid was then converted to bioethanol without emitting CO2 via hydrogenolysis with Lewis acid-supported catalyst (Ru–Sn/TiO2). To evaluate a potential of this process, it was compared with the conventional alcoholic fermentation process, and found that, although conventional process can produce only 200-300 L bioethanol from one dried ton of Japanese cedar, this process can produce double in amount. In addition, energy recovery is higher than the conventional process, with CO2 emission unit (kg/GJ) being lower. Consequently, this process can be promising to reduce CO2 so as to mitigate environmental loading.
High sulfur petroleum coke (HSPC, 7.6 wt-S%) was employed to prepare activated carbons (ACs) using KOH to develop pore structure with remaining sulfur content for supplying post oxidation treatments to effectively generate sulfo groups which could be a stronger adsorption sites of cationic heavy metal ions in aqueous solutions than carboxy groups. KOH activation was conducted at 550-800 °C by two methods of physical mixing (KOH and HSPC solid-solid mechanical mixture) and impregnation (KOH solution and HSPC liquid-solid mixture and then dried in oven). Prepared samples were characterized with nitrogen adsorption-desorption isotherms and elemental analysis. Physical mixing was effective for HSPC of large particle size, whereas impregnation was effective for small particle. Based on the experimental results, mild activation conditions such as KOH/HSPC ratio of 1 and temperature of 550 °C were preferable; specific surface areas and remaining sulfur contents of the resultant ACs by physical mixing and impregnation methods could be achieved 651 m2/g, 2.9 wt-S% and 812 m2/g, 5.2 wt-S%, respectively. Post oxidation of the ACs and the consecutive Ni(II) adsorption experiments implied that sulfo groups that could work even in acidic region might be generated on ACs from HSPC comparing with ACs from low sulfur petroleum coke.
Silica membranes for use in a membrane reactor were developed by the counter diffusion chemical vapor deposition (CVD) method. Tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS), n-butyltrimethoxysilane (BTMOS) and 3-aminopropyltrimethoxysilane (APrTMOS) were used as the silica precursors and the high temperature separation performances were evaluated. The membranes prepared using TMOS and MTMOS at high temperature deposition showed H2/N2 selectivity of over 100. The membranes prepared using BTMOS and APrTMOS at 270 °C showed H2/N2 selectivity of about 100 and N2/SF6 selectivity about 100. Therefore, thermal stability of the organic group of the silica precursor must be important for the membrane performances. Decomposition of the organic group and deposition time were investigated. The membrane prepared by extending the deposition time of APrTMOS to 240 min showed high hydrogen permeance of 7.2 × 10−7 mol m−2 s−1 Pa−1 and H2/C3H8 selectivity of 21000. In addition, high temperature gas permeation tests at 500 °C were conducted using the membrane prepared using MTMOS. The mixed gas separation factor of about 100 for H2/C3H8 separation test was the same as the single gas permeance ratio of 98 calculated from the result of the single gas permeance. From the above results, in order to prepare a silica membrane having high separation performance in a binary system, it is necessary to develop a silica membrane that exhibits high separation performance in one-component permeation tests using a silica precursor having thermal stability of organic substituents.
Herein, we report a protocol for rapid preparation of uniformly sized Ru, Rh, Pd, Ir, and Pt nanoparticles stabilized by poly(N-vinyl-2-pyrrolidone) via microwave-assisted chemical reduction with ethanol. Although the boiling point of ethanol, which has high reduction ability, is much lower than the temperature required for metal cation reduction, this solvent could be used as a reductant because the preparation was carried out in a sealed vessel. All metal nanoparticles showed similar sizes and amounts of poly(N-vinyl-2-pyrrolidone). The crystallite size of the Pd and Pt nanoparticles could be controlled by changing the ethanol concentration. The catalytic performance of the prepared metal nanoparticles was evaluated for the hydrogenation of benzonitrile under ambient conditions (25 °C, 1 bar H2). Rh nanoparticles showed the highest benzonitrile conversion and highest selectivity for secondary imine product. Interestingly, the particle-size dependence of the catalytic activity of the Rh nanoparticles showed volcano-type behavior; that is, the second smallest Rh nanoparticles (3.3 nm) showed the highest activity, which was attributed to high metal surface area and high turnover frequency. Notably, this is the first report of nitrile hydrogenation to afford a secondary imine under ambient conditions.
Lignin depolymerization to form useful aromatic compounds has attracted considerable research attention. Depolymerization of lignin, a complex three-dimensional polymer consisting of aromatic monomers, requires cleavage of C–O–C ether bonds and C–C bonds between the monomers. Previously, we reported the bond cleavage characteristics of several lignin model compounds during treatment with supported metal catalysts in supercritical water in the absence of hydrogen gas. Here, we used our model compound data to predict the yields of aromatic monomers from treatment of lignin (derived from hardwood and softwood biomass) with supported metal catalysts (Pd/C, Rh/C, Pt/C, and Ru/C) in supercritical water. The calculated yields decreased in the order Pd/C>Rh/C>Pt/C>Ru/C, and the calculated yields from hardwood biomass were higher than those from softwood biomass. We also compared the calculated yields with the experimental yields for depolymerization of organosolv-lignin powder. The experimental yields decreased in the same order as the predicted yields but were lower than the predicted yields, possibly because repolymerization during decomposition of the lignin model compounds may have been much less than during lignin decomposition.
Nitrogen oxide (NOx) is the main pollutant produced from power plants and boiler. The development of catalysts that can work to reduce NOx under ambient conditions at a low reaction temperature has been required. In this work, we examined the NH3-selective catalytic reduction (SCR) activity of metal oxide-supported gold catalysts in order to develop NH3-SCR catalysts working at low temperatures (<200 °C). Au/CuO showed NH3-SCR activity at 100 °C (NO conversion = 20 %, N2 selectivity = ca. 100 %), though the production of N2O as a by-product caused by NH3 oxidation was observed at a higher reaction temperature. We found that deposition of 0.1 wt% of gold on CuO is sufficient for NH3-SCR to proceed and that NH3 oxidation proceeds with increase in the loading amount of gold (<0.5 %) at a high reaction temperature. Although we measured the NH3-SCR activities of Pt/CuO and Pd/CuO, Au/CuO showed better activity than those of other precious metal catalysts. We also tested binary metal oxide-supported gold catalysts and found that 1 wt%Au/10 wt%CuO/Al2O3 showed the largest N2 yield (45 %) owing to the introduction of other metal oxide species to CuO. The results indicated that a gold catalyst has the potential to catalyze NH3-SCR at low temperatures.