Control of NO x emissions from diesel engine by selective catalytic reduction (SCR) with urea

Topics in Catalysis - Among the catalysts screened, Cu-ion exchanged ZSM5 zeolite exhibited the highest NO removal activity, particularly at low reaction temperatures below 200 °C,...     

SEQUENTIAL LOOP CLOSING IDENTIFICATION OF MULTIVARIABLE PROCESSES USING THE BIASED RELAY FEEDBACK METHOD

Each controller in multiloop control systems for multivariable processes can be tuned sequentially with the ultimate information for the paired input and output while former loops have been closed, and hence, single-input single-output autotuning methods can be applied. In this sequential autotuning for multiloop control systems, several iterations are usually required for better control performances. Especially when pairings are undesirable, the autotuning sequences should be repeated with correct pairings, which result in long field experiments. Here, to avoid this drawback, a simple method to identify process models while loops are being sequentially tuned is proposed. The identified models can be used to correct pairings of multiloop control systems and to improve tuning performances without several field iterations. In addition, they can be used to obtain model-based control systems such as decoupling control systems.     

Catalytic Combustion of Methane over Rare Earth Stannate Pyrochlore

Well-defined Ln₂Sn₂O₇ powders (Ln = La, Sm and Gd) with a phase-pure pyrochlore structure were synthesized by hydrothermal reaction. The catalytic activities of Ln₂Sn₂O₇ powders for methane combustion were measured. Methane oxidation started at 500 °C and increased with oxidation temperature. Catalytic methane combustion is strongly influenced by the presence of oxygen vacancies that form by breaking Sn–O lattice bonds as the temperature increases. Addition of manganese to the rare earth pyrochlores improved methane oxidation activity. Manganese-doped samarium stannate pyrochlore (Sm₂Sn_1.8Mn_0.2O₇) shows highest the catalytic activity. Light-off and complete oxidation temperatures were measured at about 400 and 650 °C, respectively.     

INVESTIGATION OF THE USE OF LASER-DOPPLER VELOCIMETRY IN TWO-PHASE BUBBLY FLOWS

Understanding the dynamic phenomena of viability loss of shear sensitive cells and bubble breakage and coalescence within airlift reactors requires knowledge of local, liquid-phase hydrodynamics. The laser-Doppler velocimeter (LDV) is a non-invasive instrument which may be used to obtain this information. Experimental procedures and software were developed to detect and measure Doppler bursts in two-phase flow in a split-cylinder airlift reactor. Off-line analysis of the data indicated a detection rate approximately one order of magnitude greater than that observed using an available commercial frequency tracker. Approximately 400 to 500 observations are needed for the ensemble mean to characterize the local mean velocity to within ±5% for a superficial gas velocity of 10.4 cm/s, the highest superficial gas velocity used in these studies. The limitations, prospects, and signal-processing options for LDV in this application are also discussed     

THE “UCKRON-1” TEST PROBLEM FOR REACTION ENGINEERING MODELING

Testing kinetic models against a “true” and detailed kinetic expression was the aim of the Workshop on Kinetic Model Development at the Denver AIChE Meeting in August, 1983. For this purpose an artificial reaction mechanism was created, based on the known thermodynamics of the methanol synthesis as a framework. The kinetic rate laws, that were derived from this mechanism, were made thermodynamically consistent by achieving agreement between equilibrium constants calculated at various temperatures from the given, real original thermodynamic relationship and those calculated from the detailed reversible kinetic expressions.

Using the artificial kinetics as the "true" one, CSTR experiments were simulated. The results of a statistically designed set of experiments were published after 5% random error was added to the data. Participation was invited for all interested to correlate the data, develop kinetic models and to calculate the performance of the specified reactor.

The results of 19 submitted entries are summarized with the conclusion that the models had more differences than were expected, but their predictive values were not as different as was anticipated, if the extreme high production rates due to thermal runaways are not considered. This in turn points out the necessity to check models experimentally, in pilot plant, not only for predicted optimum, but also for calculated runaway conditions. Models which did not capture the true character of this reaction failed to predict the onset of runaway reactions.     

Electrochemical pitting behaviour of type 321 stainless steel in sulfide-containing chloride solutions

The pitting behaviour of type 321 stainless steel in sulfide-containing chloride aqueous environments was studied using cyclic potentiodynamic polarization. A well-established correlation between H₂S and Na₂S₂O₃ in the study of corrosion was applied, that is, H₂S was simulated by Na₂S₂O₃. The major factors affecting the pitting corrosion of type 321 stainless steel are the Cl^- concentration, solution pH and temperature. The results clearly indicate that both E_pit and E _pp decrease with increasing Cl^- concentration and temperature, while I _pass is more sensitive to temperature variation. E _pit decreased with decreasing pH in the range 2 < pH < 7.5. The surface morphology and chemistry of the corroded type 321 stainless steel resulting from anodic polarization in 0.01 M S₂O ₃ ^2- -containing Cl^- solution were analysed by XRD, SEM and EPMA. A higher concentration of sulfur was found in the pits, and the dark surface film was mainly composed of FeS and -Fe₂O₃. The results describe the pitting behaviour of type 321 stainless steel in sulfide-containing Cl^- aqueous environments.     

Sol-Gel Alumina Coating for Improved Cyclic Oxidation Resistance of Silicon Nitride

A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride.     

Blends of chlorinated isotactic polypropylene with poly(ethylene-co-vinyl acetate) II. Phase studies of the miscible blends

By measuring T_g, T_m and T_c (cloud point) phase diagrams for the four miscible blends of chlorinated isotactic polypropylenes (chlorine content 39.2 (CPP-40) and 49.8 wt.-% (CP-50)) with Poly(ethylene-co-vinyl acetate)s (vinyl acetate contents 40 (EVA-40) and 45 wt.-% (EVA-45)) were investigated. The blend of CPP-50 with EVA-40 was the most compatible of the four blend pairs.     

Complex Phase Equilibria in Refractories Design and Use

The current applications of phase diagrams and thermodynamic calculations to studies of refractories are reviewed highlighting links to microstructural analyses. Improved understanding of microstructural evolution and chemical corrosion mechanisms has resulted from such work. The limitation of the calculations/diagrams to thermodynamic equilibria has led to imaginative attempts to incorporate some dynamic aspect in them so they are more relevant to practical conditions. These include varying temperature to model a temperature gradient, P _O2 to model atmosphere permeation into a brick, slag/refractory ratio to model slag penetration and altering the slag composition after reaction with the fine matrix phases. The potential future development of such techniques is discussed.     

负载奈米银之二氧化钛光触媒及其光催化活性之研究

利用自制之奈米银粒子,或用化学还原法将银微粒直接沉淀在市售二氧化钛粉末上,并比较二者对亚甲基蓝光催化效果,由于银微粒可降低电子与电洞对再结合之效果,而使二氧化钛粒子光催化活性提高,其中并以直接沉淀法为佳.此外亦藉由高温氢气对二氧化钛粉末进行还原,形成部分的Ti3+,藉此亦达到提升光催化之效果.最后将奈米银负载于经还原过后之二氧化钛粒子,于紫外光与可见光下对酚作光催化分解,发现其亦得到一定程度的分解效果.