Search

Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via the electrostatic layer-by-layer (LbL) method. The charged mass transport phenomena of these thin films have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+) as the redox probes. By adding a film resistance and a film capacitance to the conventional Randles equivalent circuit, we can calculate the diffusion coefficient values that help understand the microscopic nature of the thin films. When the negatively charged probe [Fe(CN)(6)](3-/4-) was used, lower diffusion coefficients were obtained for multilayers deposited from higher ionic strength solutions. This relationship was less obvious when the positively charged probe [Ru(NH(3))(6)](3+/2+) was used, in which the electrostatic attraction between PMo(12) clusters and the probe ions complicates the mass-transfer process. It is believed that the addition of salt to dipping solutions increases the tortuosity of the films so the mass transport takes longer paths, inducing lower diffusion coefficients. Higher PMo(12) loading causes lower diffusion coefficients due to the polyoxometalate clusters blocking the paths for charged probe ions.

An ethylene plant employs multiple cracking furnaces in parallel to convert various hydrocarbon feedstocks to smaller hydrocarbon molecules, mostly ethylene and propylene. The continuous operational performance of cracking furnaces gradually decays because of coke formation in the reaction coils, which requires each furnace to be periodically shut down for decoking. Given multiple feeds and different cracking furnaces as well as various product prices and manufacturing costs, the operational scheduling for the entire furnace system should be optimized to achieve the best economic performance. In this paper, a new MINLP (mixed-integer nonlinear programming) model has been developed to obtain cyclic scheduling strategies for cracking furnace systems. Compared to previous studies, the new model has more capabilities to address operation profitability of multiple feeds cracked in multiple furnaces. Meanwhile, it inherently avoids unpractical conditions such as simultaneous shutdown of multiple furnaces. Case studies demonstrate the efficacy of the developed methodology.

This study investigates the products, kinetics, and reactor design of atrazine photolysis under 254-nm ultraviolet-C (UVC) irradiation. With an initial atrazine concentration of 60 microg/L (60 ppbm), only two products remain in detectable levels. Up to 77% of decomposed atrazine becomes hydroxyatrazine, the major product. Both atrazine and hydroxyatrazine photodecompose following the first-order rate equation, but the hydroxyatrazine photodecomposition rate is significantly slower than that of atrazine. For atrazine photodecomposition, the rate constant is proportional to the square of UVC output, but inversely proportional to the reactor volume. For a photochemical reactor design, a series of equations are proposed to calculate the needed UVC output power, water treatment capacity, and atrazine outlet concentration.

Photocatalytic oxidation (PCO) of nitric oxide (NO) over TiO 2 catalyst was studied at source levels (5–60 ppm). The PCO process involves a series of oxidation steps by the OH radical: NO→HNO 2 →NO 2 →HNO 3 . The product NO 2 can be collected in an adsorbent bed and either recycled back to the combustion chamber or recovered as nitric acid. The ratio of NO 2 − to NO 3 − from spent catalyst liquor drops with irradiation time until a steady state is reached. The reactions are limited by thermodynamic equilibrium after ∼12 s space time. The steady-state experimental data from space time and inlet concentration effects can be described with the Langmuir–Hinshelwood (L–H) kinetic model with R 2 =0.9208.

The oxygen uptake process in a respirometer was analyzed by a mathematical model consisting of oxygen transfer accompanied with oxygen consumption reaction. The criterion to avoid an oxygen-transfer limitation was derived on the basis of the ratio of the maximum biochemical reaction rate to the maximum possible oxygen-transfer rate. The maximum biochemical reaction is described by the first-order rate equation, whereas the maximum possible oxygen-transfer rate is calculated by multiplying the oxygen-transfer coefficient with the solubility of oxygen in water. An oxygen-transfer coefficient in a respirometric reactor was estimated as 1.8 h -1 , by using the model analysis of an oxygen uptake data from the same reactor. A simplified criterion for respirometer without oxygen-transfer limitation is then obtained as XS? 16.51/ K 1 , where X and S represent concentration of biomass and substrate, respectively, and K 1 is the first-order rate constant, (L/mg VSS)/h.

not Available.

not Available.