Laser and conventional flash photolysis of Na 2 S 2 O 8 aqueous solutions containing Clions were employed to investigate the reactions of chlorine atoms and Cl 2 •radical ions with toluene, benzoic acid, and chlorobenzene. A mechanism is proposed which accounts for the faster decay of Cl 2 •in aqueous solutions containing increasing concentrations of the organic substrates. Interpretation of the experimental data is supported by kinetic computer simulations. Chlorine atoms react with the three substituted aromatics studied here almost with diffusioncontrolled rate constants, k ) (1.8 ( 0.3) × 10 10 M -1 s -1 . The high reactivity observed for Cl atoms contrasts with that of the Cl 2 •radical ions, for which the rate constant for its reactions with the substituted benzenes is e 1 × 10 6 M -1 s -1 . The organic radicals produced from these reactions, as well as the nature of the reaction products are discussed. The observed results seem to support an addition mechanism yielding chlorocyclohexadienyl radicals (Cl-CHD) as the most significant reaction channel following reaction of Cl atoms and the organic compounds. In air-saturated solutions, subsequent thermal reactions of Cl-CHD radicals lead both to chlorination and oxidation of the aromatics.

SUMMARYIn this paper a non-linear adaptive feedback-linearizing control is designed for a biological wastewater treatment model. The adaptive control structure is based on the non-linear model of the process and combined with a joint observer estimator which plays the role of the software sensor for the on-line estimation of biological states and parameter variables of interest of the bioprocess. The performances of both estimation and control algorithms are illustrated by simulation results. They demonstrate e!ectiveness and signi"cant robustness against measurement noises and kinetic parameter jumps.

Optimization of the production planning is crucial for the economic success of a petroleum refinery. Nevertheless, it is a difficult task, because of the large scale of the system and the complexity of the processes involved. Part 1 of this series of two papers addresses the formulation of process models for petroleum refinery planning. First, a generic formulation of nonlinear refinery planning model is adopted from the literature. Subsequently, the formulation of nonlinear empirical models for crude distillation units (CDUs) and a fluid catalytic cracking (FCC) unit is addressed. These empirical models were successfully validated using rigorous process simulators. Finally, the results from model validation showed that the accuracy of model predictions is as good as the current empirical process models reported in the literature, while the empirical process models proposed in this work overcome the limitations of both linear and nonlinear empirical models for CDUs and FCC units previously developed by other authors. Part 2 [Ind. Eng. Chem. Res. 2011,

No abstract

This work focuses on the temperature control of a semibatch chemical reactor used for fine chemicals production. Such a reactor is equipped with a heating/cooling system composed of different thermal fluids. Without extensive modeling investigations, a feedback-feedforward control strategy is proposed for ensuring the tracking performance of the desired temperature profile. Such a strategy is derived from a family of the iterative learning control (ILC) algorithms named batch model predictive control (BMPC). Learning is achieved without requiring a detailed knowledge of the system, which may be affected by unknown but repetitive disturbances. The learning control solution is based on the minimization of a linear quadratic cost function. The synthesis of the proposed strategy is studied, and improvements of the algorithm features are proposed. First, guaranteed convergence of the algorithm is illustrated in a few experimental runs. Second, some practical considerations for the removal of high-frequency disturbance effects are outlined to improve the achieved performance. Third, a robust supervisory control procedure is employed to choose the right fluid and to reduce the superfluous fluid changeovers, mainly when different fluids are available. Finally, experimental results are presented to illustrate the practical appeal and effectiveness of the proposed scheme.

Sulfate radicals, SO 4 •-, were generated using flash photolysis of aqueous S 2 O 8 2solutions and the reactions of the inorganic radicals with the surface of suspended silica nanoparticles (NP) investigated. In the presence of colloidal silica no absorption traces due to SO 4 •radicals are observed at 100 µs after the flash of light. However, two transient species with absorption maxima around 320 and 600 nm are formed. A kinetic analysis of the experimental results indicate that SO 4 •radicals are adsorbed on the NP surface, leading to the formation of an adduct, with λ max ≈ 320 nm ( ≈ 7000 cm -1 M -1 ), and showing similar reactivity to that observed for the sulfate radical in aqueous solutions. The NP-sulfate radical adducts react with adsorbed water, and with single and geminal SiOsites with reaction rate constants of 1.5 × 10 14 × e -(58(12)kJ/mol)/RT s -1 , < 10 3 × e -(2(17)kJ/mol/RT s -1 and < 10 11 × e -(46(13)kJ/mol/RT s -1 , respectively. Two different SiO • surface defects, showing similar spectra (λ max ≈ 600 nm) but different reactivities, are formed from the reaction of NP-sulfate radicals and deprotonated geminal and single silanols.

With new EC regulations, alternative treatment and disposal techniques of the excess sludge produced by activated sludge wastewater treatment plants have to be developed. To decrease activated sludge production yield, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline and a combination) were studied to generate Ralstonia eutropha (strain model) and waste activated sludge lysates and to evaluate their biodegradability. Gentle treatment conditions by alkaline waste treatment (20 min at 60 degrees C and pH 10 by NaOH addition) allowed waste activated sludge to be solubilized by a two step process (instantaneous and post-treatment) giving a dissolved organic carbon released by the total suspended solids treated of 267 mgDOC x g(-1)TSS. The biodegradation of the soluble fraction of the lysates by fresh sludge reached 75 and 90% after 48 and 350 hrs of incubation respectively. A validation on a laboratory scale by insertion of a liquor alkaline heat treatment loop in a biological synthetic wastewater treatment process was carried out. A reduction of 37% of the excess sludge was obtained without altering the purification yield of the process.

No abstract