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Numerical examples show that clock wise hysteresis loop can exist in the hydrogenation of ethylene over pt catalyst when one molecule of ethylene is chemisorbed on one atom of platinium, but rate multiplicity cannot be found when one molecule of ethylene is chemisorbed associatively on two atoms of platinium. Also numerical analysis shows that rate multiplicity can exist in the case of associative adsorption of ethylene on the two site of platinium by considering hydrogen spillover to support.
Ethylene hydrogenation experiments were carried out respectively over 0.01wt.% pt/?? -Al₂O₃and 0.05wt.% pt/α-Al₂O₃ catalysts and rate multiplicity including ignition and extinction points was found. Over 0.01 wt.% pt/?? -Al₂O₃catalyst, the width of rate-concentration hysteresis loop increased with hydrogen concentration, but above some hydrogen concentration the extinction point abruptly increased and existed at very high ethulene concentratoin. Over 0.05wt.% pt/α-Al₂O₃, extinction points were found on the decreasing path of ethylene concentration but ignition points could not be found on any path. The difference between feed temperature and catalyst layer temperature is small at a narrow width and much large at a very wide width. This result suggests that the multiplicity in ethylene hydrogenation may be caused by the coupling effect of kinetic and heat transfer limitation.
This paper examines the effect of ratio of the inner radius to the outer one ξ₁ on the conversion of isothermal single reaction in a radial flow fixed-bed reactor. The velocity of reactant gas is only related to ξ₁at the given feed condition and catalyst volume, so that the conversion of radial flow fixed bed is affected by the values of ξ₁. The results of exact and numerical analysis show that lower values of ξ₁ give higer conversion for the positive reaction order and lower conversion for the negative ones, but the values of ξ₁ have no effect on the conversion for the zeroth order reaction or in the plug flow reactor.
In this study we observed the possible existence of multiple steady states for CO oxidation over Pt/Boehmite catalysts, which is one of instabilities, and also analyzed numerically these phenomena with some proper reactor models. The form of our reactor was a non-adiabatic fixed bed with recycle. The reactor models include both one phase model with plug flow and two phase model with heat transfer resistance between gas phase and solid one. Especially, it was attempted to explain the multiplicity features with a very wide region, whose features could not have been clearly explained by means of any other model, by the modified two phase model which includes a term related with memory effect of catalyst temperature. The experiments showed that the effect of recycle ratio on multiplicity region could not be revealed definitely for our experimental conditions. This may arise from the facts that the multiplicity for the CO oxidation over Pt/Boehmite cataysts resulted mainly from strong heat transfer limitation rather than from mixing effect related with recycle flow since the CO oxidation was a reaction with both very high generation and rapid reaction rate.
Sustained oscillation, including a constant amplitude of less than 10℃ in temperature and a short period between several seconds and several minutes, was experimentally found in the CO oxidation over fixed bed of platinium/γ-alumina catalysts. From this study, it was believed that the oscillation could occur within the kinetic region in exclusion of heat transfer limitation. On the other hand, under some more strong heat transfer limitation,the temperature-oscillation had a long period of several ten minutes and two types of concentration-oscillation, which periods were short and long, could simultaneously exist at one period. Finally, under a strong heat transfer limitation, the oscillation disappeared but rate-multiplicity phenomenon only appeared.
공기중 휘발성유기화합물의 처리를 위해 전자빔 가속기를 이용하여 Trichloroethylene(TCE)의 분해특성에 대해 연구하였다. TCE를 포함한 공기는 서로 다른 반응분위기, 초기농도의 변화, 수증기 존재유무와 같은 변수하에서 분해실험이 행해졌다. 산소를 반응분위기가스로 사용하였을 경우 최대분해율이 나타났는데, TCE 초기농도 2000 ppm에 대해 20kGy에서 99%의 분해율을 보였다. TCE 농도는 산소와 공기 조건하에서 지수함수적으로 감소했으며, TCE 분해효율에 대한 수증기 효과가 행해졌다. 수증기 (5600ppm) 존재하에서 TCE분해율은 수증기가 존재하지 않을 경우보다 약 10% 높게 나타났다. 1차 생성물로 Dichloroacetic acid, Dichloroacethyl chloride, Dichloroacethyl ester acetic acid 등이 생성되었고 분해와 산화반응을 통해 CO, CO2로 전환되었다. 또한 Perchloroethylene, Hexachloroethane, Chlorofona Carbon tetrachloride와 같은 과염소탄소 화합물이 생성되었다. Decomposition of trichloroethylene (TCE) in electron beam irradiation was examined in order to get information on treatment of VOC/air. Air containing vaporized TCE has been studied in a flow reactor with different reaction environments, various initial TCE concentration and in presence and absence of water vapor. Maximum decomposition was observed in oxygen reaction environment and degree of decomposition was about 99 % at 20 kGy for 2000 ppm initial TCE. The concentration of TCE exponentially decreased with dose in oxygen and air. The effect of water vapor on TCE decomposition efficiency was examined. The decomposition of TCE in presence of water vapor (5600 ppm) was by ca. 10% higher than in absence of water vapor. Dichloroacetic acid, dichloroacethyl chloride and dichloroethyl ester acetic acid which were identified as primary products, were decomposed and oxidized to give CO and CO2. Perchloroethylene, hexachloroethane, chloroform and carbon tetrachloride were also observed as highly chlorinated products.
Electron beam curing of acrylated epoxy resin diluted with mono-functional monomer EGDA has been investigated under circumstances contacted with air and without air. The formulated resin in contact with N2 or covered with film could be cured up to 95% even with low dose of 5kGy and the surface of cured resin became very hard, but cured resin in existence of oxygen and without any additive had a low degree of curing and the surface became sticky due to insufficient curing. Additives such as curing agent P-115 or initiator BPO could increase the degree of curing to more or less one, but these additives could not remove completely surface stickiness. While, at high dose(more than 100kGy), addition of BPO were possible to make the irradiated surface of the resin be non-sticky even in existence of air. Degree of curing of the resin which contained pigment was very high at dose of around 20kGy. Elongation and stress at break on the cured resin with ferric oxide pigment were be higher than with non-ferric oxide pigment. Adhesion and anti-firing of the resin coated on cement block could be excellent.
<P>The high melt viscosity of polypropylene was studied by grafting bifunctional monomers, 1,6-hexanediol diacrylate (HDDA) and tripropylene glycol diacrylate (TPGDA), onto homopolypropylene (HPP) and random ter-polypropylene (RTPP) under electron-beam irradiation. Creation of the high-melt-viscosity polypropylene was possible at low radiation dosage and low monomer content, under a prohibition of both radiation degradation and homopolymerization. TPGDA monomer was more effective in increasing the melt viscosity of HPP compared with RTPP, whereas HDDA monomer was more effective for enhancing the melt viscosity of RTPP. Such different effects of monomers on melt viscosity may arise from different monomer structures, namely, TPGDA has additional three methyl groups, but HDDA has no methyl groups. Electron-beam radiation technology, on an increase of the melt viscosity, was much more effective in HPP than RTPP, when compared with virgin polymers. Modified RTPP and HPP with high melt viscosity were capable of foaming with numerous fine cells, of which the modified HPP with 1.5 mmol TPGDA and 0.5 kGy could create more spherical foam cells and its bending strength was 1.5 times more than that of the foamed RTPP. POLYM. ENG. SCI., 46:431–437, 2006. © 2006 Society of Plastics Engineers.</P>