Son Ki Ihm

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: A review

Catalytic wet air oxidation (CWAO) is one of the most economical and environmental-friendly advanced oxidation process. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. Various heterogeneous catalysts including noble metals and metal oxides have been extensively studied to enhance the efficiency of CWAO. The present review is concerned about the literatures published in this regard. Phenolics, carboxylic acids, and nitrogen-containing compounds were taken as model pollutants in most cases, and noble metals such as Ru, Rh, Pd, Ir, and Pt as well as oxides of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and Ce were applied as heterogeneous catalysts. Reports on their characterization and catalytic performances for the CWAO of aqueous pollutants are reviewed. Discussions are also made on the reaction mechanisms and kinetics proposed for heterogeneous CWAO and also on the typical catalyst deactivations in heterogeneous CWAO, i.e. carbonaceous deposits and metal leaching.

THE EFFECTS OF THE LOCAL CONCENTRATION AND DISTRIBUTION OF SULFONIC-ACID GROUPS ON 1-BUTENE ISOMERIZATION CATALYZED BY MACROPOROUS ION-EXCHANGE RESIN CATALYSTS

The catalytic activities of sulfonated macroporous poly(styrene-divinylbenzene) beads in 1-butene isomerization were investigated through a model concerning the effects of the distribution and concentration of the sulfonic acid groups. The reaction rate constant increased nonlinearly with the sulfonic acid group concentration and the order of nonlinear power dependence was about 2.4. The values of effectiveness factors of the microparticles in the macroporous resin catalysts with 40 and 50% DVB ranged from 0.1 to 0.3. The diffusivities were 10−13 and 10−14cm2/sec for 40 and 50% DVB, respectively. The result showed that the major reaction arena was the pore space between the microparticles.

Emulsion polymerization of tetrafluoroethylene: Effects of reaction conditions on the polymerization rate and polymer molecular weight

The emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles. Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 × 10−3 and 32.48 × 10−3 mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions.

The influence of the Ti3+ species on the microstructure of ethylene/1-hexene copolymers

Copolymerization of ethylene and 1-hexene was carried out with catalysts having isolated Ti 3+ and multinuclear Ti 3+ species. Carbon-13 nuclear magnetic resonance spectroscopy ( 13 C NMR), crystallization analysis fractionation (CRYSTAF), and gel permeation chromatography (GPC) studies showed that the microstructure of ethylene and 1-hexene copolymers strongly depends upon the structure of the Ti 3+ species. Isolated Ti 3+ species increase the relative reactivity of ethylene in copolymerizations and produce copolymers with high molecular weight and broad short chain branching distribution (SCBD), with a large ethylene-rich fraction. Multinuclear Ti 3+ species increase the relative reactivity of 1-hexene and produce copolymers with low molecular weight and broad SCBD, with a large rubbery ethylene/1-hexene fraction. Comparative studies of the copolymer microstructure from isolated Ti 3+ and multinuclear Ti 3+ in combination with different cocatalysts, Al(CH 3 ) 3 , Al(C 2 H 5 ) 3 , and methylaluminoxane (MAO) were also carried out. Isolated Ti 3+ species in combination with MAO cause remarkable changes in the 1-hexene incorporation rate and SCBD in comparison with Al(CH 3 ) 3 and Al(C 2 H 5 ) 3 , while multinuclear Ti 3+ species in combination with MAO do not affect as much the 1-hexene incorporation rate. This difference may be related to the mechanism of active site formation between the different Ti 3+ structures and MAO.

Columnar grain growth of yttria-stabilized-zirconia in inductively coupled plasma spraying

Yttria-stabilized-zirconia (YSZ) was deposited 7 mm thick by inductively coupled plasma spraying (ICP) and a theory of nucleation and solidification of YSZ was introduced. The concentration was homogeneous within a particle, but different from particle to particle. The solute rejection by diffusion occurred in a layer during solidification, but the interface condition of (dTq/dz)z=0 > m(dC/dz)z=0 led columnar grains to facilitate. The microstructure of the bottom part showed small equiaxed grains. In the middle part, large columnar grains, about 100 µm thick and 300 µm long, were developed through the layers with strong adhesion. Heat of droplets, latent heat of solidification, small pore array in the splat boundaries, and low thermal conductivity retard the heat transfer, and thus thick and long columnar grains could be facilitated. The long columnar grain growth through the layers was supposed to be possible when the previously solidified surface of the deposit acts as seed.

HOLLOW GELULAR BEADS OF STYRENE-DIVINYLBENZENE COPOLYMER PREPARED BY SUSPENSION POLYMERIZATION

Hollow gelular beads of styrene-divinylbenzene copolymer have been prepared only by controlling the polymerization temperature and the amount of initiator. A mechanism for the formation of hollow beads is described.

Characteristics of mesoporous carbons supported Mo catalysts in thiophene hydrodesulfurization

Abstract The potential of two different mesoporous carbon materials, CMK-1 and CMK-3 supported sulfided Mo catalysts for hydrodesulfurization of thiophene at specific conditions was explored to investigate the effect of different pore sizes, surface oxygen functional groups, metal dispersion, and presulfidation temperature. The Mo catalysts (1∼14.8 wt % of Mo) supported on mesoporous carbons were prepared with (NH 4 ) 6 Mo 7 O 24 ·4H 2 O. For comparison, commercial activated carbon (Darco G-60) and alumina (γ-Al 2 O 3 ) were used as a support for the Mo supported catalysts. Characterization of the supports and the catalysts was carried out by XRD, BET, EDS, FT-IR, acid-base titration, TEM and CO chemisorption. Sulfidation of carbon supported catalysts was favored at 573 K, whereas 673 K promoted the sulfidation of alumina supported catalysts. 10 wt % Mo supported catalysts showed the highest thiophene hydrodesulfurization activity in all supports. CMK-3 supported Mo catalysts were superior to all other catalysts because of the larger pore size and higher acidic functional groups.

Different modes of pore blockage by coke deposit over Mo/(Al-)MCM-41 and Mo/(Al-)MCM-48 catalysts for hydrodesulfurization

Abstract M41S materials contain mesopores large enough to expand the scope of application as molecular sieve catalysts, since they can be endowed with acidity by incorporating trivalent cation such as Al 3+ . While MCM-41 based catalysts are reported to show good catalytic activities for many types of reactions, they are vulnerable to coke deposit due to pore blockage. MCM-48 with two independent three-dimensional channel systems could be expected to be much more resistant to pore blockage. MCM-41 and MCM-48 were chosen to prepare the supported molybdenum catalysts, which were used for the hydrodesulfurization of thiophene. The coke deposit resulted in different deactivation obviously due to the difference in channel connectivity between MCM-41 and MCM-48. Mo/MCM-48 with biporous channels showed a better stability than Mo/MCM-41 with unidimensional channels, which can be explained by different modes of pore blockage.

Epoxidation of olefins over thermally stable polyimide-supported Mo(VI) complexes

Publisher Summary Unlike polybenzimidazole-based thermo-oxidatively stable supports, polyimides can be prepared under relatively mild conditions from starting materials of only low or modest cost. Polyimide particulates were prepared in a bead form without functional. This chapter discusses the synthesis of functional polyimide beads and their use as epoxidation catalyst supports. The presence of the functional group in the polyimides allows further chemical exploitation, particularly as a catalyst support capable of operating under rather severe oxidative conditions. In the study described in this chapter, polyimide-supported Mo(VI) complexes were prepared and employed as heterogeneous catalysts in the epoxidation of cyclohexene, using t-butylhydroperoxide (TBHP), as the oxidant. The polyimide bead bearing a triazole residue was used to immobilize a stable and active Mo(VI) epoxidation catalyst. The polyimide was refluxed with molybdenyl acetylacetonate in ethanol for three days. Upon completion, a polyimide-Mo complex catalyst was filtered and extracted with ethanol in a Soxhlet apparatus for three days. The supported complex was dried thoroughly under vacuum. The molybdenum content was measured by inductively coupled plasma (ICP) to be 1.08mmolg −1 for PI-DAT.Mo and 1.10mmolg −1 for CPI-DAT.Mo. As the soluble species MoO 2 (acac) 2 is a potent catalyst in the epoxidation of olefinic compound, the chapter shows the conversion curves for the epoxidation of cyclohexene by TBHP catalyzed by homogeneous MoO 2 (acac) 2 and heterogeneous CPI-DAT.Mo. The initial activity of homogeneous MoO 2 (acac) 2 was higher than that of CPI-DAT.Mo. However, the activity of CPI-DAT.Mo should be comparable with that of the homogeneous analogue after 30min.

Design of metal loaded zeolites as dual functional adsorbent/catalyst system for VOC control

Abstract Metal loaded zeolite HY was proposed as dual functional adsorbent/catalyst media for the control of low concentration VOC streams, which has both high adsorption capacity and catalytic activity. To design a good dual functional system, both adsorption and catalytic activity test were carried out. Hydrophobic HY zeolite showed a high adsorption capacity comparable to activated carbon and better desorption features for the cyclic operation. Metal addition endowed HY zeolite adsorbent with catalytic activity for VOC oxidation, which should be applicable to the dual functional adsorption/catalytic oxidation system. The temperature programmed surface reaction (TPSR) of toluene and methylethylketone suggested the silver as the best candidate among the tested transition metals. Temperature programmed reductions (TPR) and O 2 - temperature programmed desorption (O 2 -TPD) on Ag/HY catalysts were carried out to explain the nature of active centre of Ag catalyst for the toluene oxidation. Silver oxide species or partially oxidized metallic silver on to the surface of metallic silver phase was proposed as an active redox site during the oxidation reaction.