In-situ biogas upgrading with H2 addition in an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge.

Biological in-situ biogas upgrading is a promising approach for sustainable energy-powered technologies. This method increases the CH4 content in biogas via hydrogenotrophic methanogenesis with an external H2 supply. In this study, an anaerobic membrane bioreactor (AnMBR) was employed for in-situ biogas upgrading. The AnMBR was operated in semi-batch mode using waste activated sludge as the substrate. Pulsed H2 addition into the reactor and biogas recirculation effectively increased the CH4 content in the biogas. The addition of 4 equivalents of H2 relative to CO2 did not lead to appreciable biogas upgrading, although the acetate concentration increased significantly. When 11 equivalents of H2 were introduced, the biogas was successfully upgraded, and the CH4 content increased to 92%. The CH4 yield and CH4 production rate were 0.31 L/g-VSinput and 0.086 L/L/d, respectively. In this phase of the process, H2 addition increased the acetate concentration and the pH because of CO2 depletion. Compared with a continuously-stirred tank reactor, the AnMBR system attained higher CH4 content, even without the addition of H2. The longer solid retention time (100 d) in the AnMBR led to greater degradation of volatile solids. Severe membrane fouling was not observed, and the transmembrane pressure remained stable under 10 kPa for 117 d of continuous filtration without cleaning of the membrane. The AnMBR could be a promising reactor configuration to achieve in-situ biogas upgrading during sludge digestion.

Effect of phosphate compound on the reduction of the pressure drop of laboratory-scale fabric filter.

Fabric filters are generally used to eliminate the particulate matter of flue gas that is generated from waste incinerators. The pressure drop of fabric filter (ΔP) is accompanied by the build-up of a dust layer on the fabric filter, and ΔP increase leads to an increase in the energy consumption of induced draft fan in an incineration facility. In this study, phosphoric acid (H3PO4) and monobasic calcium phosphate (Ca(H2PO4)2) are tested as chemicals to reduce ΔP in fabric filter using a laboratory-scale equipment. The phosphorus concentration of collected dust was correlated to the increment of ΔP per unit weight of dust deposited on the filter fabric. The effect on ΔP reduction was apparent at the phosphorus concentrations of 2.2-5.3 wt% in the collected dust. As a result, the gas permeability was enhanced by 2-6 times as compared to that was observed at phosphorus concentrations less than 0.6 wt%. Based on the result of XRD analysis of the dust sampled from the filer bag, it was concluded that H3PO4 reacted with the Ca compounds even though Ca-P compound could not be identified exactly. When H3PO4 was sprayed, dust particles grew in size and the surface roughness of dust layer increased too. Such changes in the physicochemical properties of dust seemed to enhance the gas permeability of the dust layer, which caused a reduction in the value of ΔP.

Effects of phosphoric acid sprayed into an incinerator furnace on the flue gas pressure drop at fabric filters.

Fabric filters are widely used to remove dust from flue gas generated by waste incineration. However, a pressure drop occurs at the filters, caused by growth of a dust layer on the filter fabric despite regular cleaning by pulsed-jet air. The pressure drop at the fabric filters leads to energy consumption at induced draft fan to keep the incinerator on negative pressure, so that its proper control is important to operate incineration facility efficiently. The pressure drop at fabric filters decreased whenever phosphoric acid wastewater (PAW) was sprayed into an incinerator for treating industrial waste. Operational data obtained from the incineration facility were analyzed to determine the short- and long-term effects of PAW spraying on the pressure drop. For the short-term effect, it was confirmed that the pressure drop at the fabric filters always decreased to 0.3-1.2kPa within about 5h after spraying PAW. This effect was expected to be obtained by about one third of present PAW spraying amount. However, from the long-term perspective, the pressure drop showed an increase in the periods of PAW spraying compared with periods for which PAW spraying was not performed. The pressure drop increase was particularly noticeable after the initial PAW spraying, regardless of the age and type of fabric filters used. These results suggest that present PAW spraying causes a temporary pressure drop reduction, leading to short-term energy consumption savings; however, it also causes an increase of the pressure drop over the long-term, degrading the overall operating conditions. Thus, appropriate PAW spraying conditions are needed to make effective use of PAW to reduce the pressure drop at fabric filters from a short- and long-term point of view.

Decomposition of organochlorine compounds in flue gas from municipal solid waste incinerators using natural and activated acid clays.

High-temperature particle control (HTPC) using a ceramic filter is a dust collection method without inefficient cooling and reheating of flue gas treatment; thus, its use is expected to improve the energy recovery efficiency of municipal solid waste incinerators (MSWIs). However there are concerns regarding de novo synthesis and a decrease in the adsorptive removal efficiency of dioxins (DXNs) at approximately 300 degrees C. In this study, the effect of natural and activated acid clays on the decomposition of monochlorobenzene (MCB), one of the organochlorine compounds in MSW flue gas, was investigated. From the results of MCB removal tests at 30-300 degrees C, the clays were classified as adsorption, decomposition, and low removal types. More than half of the clays (four kinds of natural acid clays and two kinds of activated acid clays) were of the decomposition type. In addition, the presence of Cl atoms detached from MCB was confirmed by washing the clay used in the MCB removal test at 300 degrees C. Activated acid clay was expected to have high dechlorination performance because of its proton-rich-composition, but only two clays were classed as decomposition type. Conversely, all the natural acid clays used in this work were of the decomposition type, which contained relatively higher di- and trivalent metal oxides such as Al2O3, Fe2O3, MgO, and CaO. These metal oxides might contribute to the catalytic dechlorination of MCB at 300 degrees C. Therefore, natural and activated acid clays can be used as alternatives for activated carbon at 300 degrees C to remove organochloride compounds such as DXNs. Their utilization is expected to mitigate the latent risks related to the adoption of HTPC, and also to contribute to the improvement of energy recovery efficiency of MSWI. Implications: The effect of natural and activated acid clays on MCB decomposition was investigated to evaluate their suitability as materials for the removal of organochlorine compounds, such as DXNs, from MSWI flue gas at approximately 300 degrees C. More than half of the clays used in this study showed the decomposition characteristics of MCB. The presence of Cl atoms in the clay used in the MCB removal test at 300 degrees C proved the occurrence of MCB decomposition. The results of this study suggest a novel flue gas treatment method to establish high-energy efficient MSWI systems.

Synthesis and redox properties of trinuclear ruthenium-acetylide complexes with tri(ethynylphenyl)amine bridge.

Novel trinuclear ruthenium complexes have been prepared by using tri(4-ethynylphenyl)amine as a bridging ligand. Cyclic voltammetry of the trinuclear ruthenium complexes revealed stepwise quasi-reversible redox behavior of three ruthenium-acetylide species and the central triphenylamine unit, whereas the mononuclear analog showed two sequential quasi-reversible redox waves. The spectroelectrochemical UV-VIS spectral studies suggested that the 1e- oxidized triruthenium species was stable and showed a characteristic absorption at lambda(max) = 505 nm. Chemical oxidation of the triruthenium complex with ferrocenium hexafluorophosphate led to the isolation of the 1e- oxidized complex, the near-IR spectrum of which revealed an intervalence charge transfer band due to the electronic coupling among three ruthenium species. The 1e(-) oxidized triruthenium complexes can be classified as class II mixed-valence compounds.

Convergent synthesis of platinum-acetylide dendrimers.

An efficient convergent route to the main chain type of organometallic dendrimers, in which platinum moieties are linked by 1,3,5-triethynylbenzene, has been developed. The synthesis of platinum-acetylide dendrons involved the use of two types of trialkylsilyl groups for protection of the terminal acetylene. The platinum-acetylide dendrimers were prepared up to the third generation by reacting dendrons with a triplatinum core and a tetraplatinum core. Spectroscopic characterization and trace experiments by gel permeation chromatography indicated that the dendrimer molecules have no structural defects. Although a pi-conjugated system was used as the bridging ligand, electronic and fluorescence spectra suggested that the interaction among the platinum-acetylide moieties in the dendrimers was small.

Stereoselective ligand-exchange reaction of planar-chiral cyclopentadienyl-ruthenium complexes: thermodynamic control of configuration at a stereogenic metal center.

The reaction of planar-chiral cyclopentadienyl-ruthenium complexes with Bu4NI resulted in the formation of iodo complexes with high diastereoselectivity (up to >99%de). The stereochemistry of the ruthenium center in the starting material did not influence the diastereoselectivity of the products. Epimerization of a diastereomerically pure sample gave a mixture of two diastereomers in the same ratio as with the ligand-exchange reaction, suggesting that the selectivity is determined by the difference in thermodynamic stability between the diastereomeric pair of iodo complexes. The ratio of the products depends on the nature of the substituent on the cyclopentadienyl ring and P ligands on the ruthenium atom. A combination of small substituents on the cyclopentadienyl group and small P ligands with strong electron-donating ability favored the formation of 2-I. The bulkiness of the substituents on the cyclopentadienyl group or of the P ligands, and low electron-donating ability of the P ligands increased the ratio of 2-II complexes to 2-I isomer.

Ruthenium-catalyzed cyclocarbonylation of allenyl alcohols and amines: selective synthesis of lactones and lactams.

Allenyl alcohols such as 4-hydroxybuta-1,2-dienes and 5-hydroxypenta-1,2-dienes having a variety of substituents undergo cyclocarbonylation in the presence of a ruthenium catalyst under mild conditions selectively to give five- and six-membered lactones in a high yield with 100% atom economy. 5-Aminopenta-1,2-dines are also cyclocarbonylated to give gamma-lactams. A possible carbonylation mechanism involving a ruthenium cluster intermediate is proposed on the basis of experimental results.

A divergent approach to the precise synthesis of giant organometallic dendrimers using platinum-acetylides as building blocks.

Giant platinum-acetylides dendrimers were precisely synthesized by a divergent method; the sixth generation dendrimer, the diameter of which is larger than 10 nm, has 189 Pt atoms per molecule, and its molecular weight is as high as 139750.

Metallodendrimers composed of organometallic building blocks.

The incorporation of metallic species into dendritic molecules has been attracting much attention, because the addition of properties characteristic of metallic complexes, such as magnetic, electronic, and photo-optical properties, as well as reactivity, may lead to the realization of new functionalized dendrimers. Organometallic dendrimers offer several advantages in the design of a dendritic molecule with the desired functions due to the diversity of the structure and properties of the organometallic complexes. In the past, the focus was on organometallic dendrimers with metallic species only at specific positions of the molecules, such as the core and the periphery. In this chapter, we summarize recent developments in the synthesis of organometallic dendrimers, in which organometallic species act as building block in every generation. Such dendrimers are generated by successive reactions characteristic of organometallic complexes, and some of them show interesting properties.

Ruthenium-catalyzed carbonylation of allene: direct synthesis of methacrylates and methacrylamides.

Carbonylation reactions of allene in alcohols and amines in the presence of a ruthenium carbonyl catalyst under mild conditions gave methacrylates and methacrylamides, respectively, in good yields with an atom economy of 100%.

New artificial host compounds containing galactose end groups for binding chiral organic amine guests: chiral discrimination and their complex structures.

New linear host (1) and cyclic hosts (2 and 3), which have galactopyranose skeletons as chiral origins and oxyethylenes skeletons as binding sites, were designed based on the structural features extracted from the fructo-oligosaccharide derivatives, having a large chiral discrimination ability, and were then synthesized. These hosts showed chiral discrimination toward chiral organic ammonium salts. For example, the chiral discrimination ability (the ratio of association constants: K(R)/K(S)) of host 1, which has the highest value among them, was K(R)/K(S) = 3 for Trp-O-(i)Pr(+) and K(R)/K(S) = 0.7 for 1-(1-naphthyl)ethylammonium (NEA(+)) at 298 K in CHCl(3). It was clarified that host 1 changed the conformation from a linear structure to the pseudo-ring structure by complexation with cations such as alkali metallic ions and chiral organic ammonium ions. The (1)H NMR induced shifts of host 1 by adding the NEA(+) guests showed that the host-guest complex structures are clearly different, depending upon the chirality of the guest; in the complex with (R)-NEA(+), the naphthyl group of the guest is located above the oxyethylene skeleton of the host and in the complex with (S)-NEA(+), and the naphthyl group is located between the edges of the pseudo-ring of the host. The clearly different structure of the complex of host 1 with NEA(+) may be caused by the dynamic molecular recognition, thus the induced-fitting mechanism.

Helical Chiral Polyisocyanides Possessing Porphyrin Pendants: Determination of Helicity by Exciton-Coupled Circular Dichroism.

Exciton-coupled circular dichroism of the porphyrin Soret band of triblock copolymers prepared from chiral isocyanide monomers and an achiral tetraphenylporphyrin derivative (TPP) provides a novel method for determining the helical sense of poly(aryl isocyanide)s (see the schematic representation of the structure).

Convergent Route to Organometallic Dendrimers Composed of Platinum-Acetylide Units.

The third-generation dendrimer with 45 platinum atoms (shown schematically) was synthesized efficiently by a convergent methodology in which two different trialkylsilyl groups (symbolized by the nodal points) are used to protect the bridging triethynylbenzene derivatives. PT=[Pt(PEt3 )2 ].