Galo A.C. Le Roux

Thermally activated peroxydisulfate in the presence of additives: a clean method for the degradation of pollutants.

The kinetics and mechanism of the thermal activation of peroxydisulfate, in the temperature range from 60 to 80 degrees C, was investigated in the presence and absence of sodium formate as an additive to turn the oxidizing capacity of the reaction mixture into a reductive one. Trichloroacetic acid, TCA, whose degradation by a reductive mechanism is well reported in the literature, was used as a probe. The chemistry of thermally activated peroxydisulfate is described by a reaction scheme involving free radical generation. The proposed mechanism is evaluated by a computer simulation of the concentration profiles obtained under different experimental conditions. In the presence of formate, SO(4)(-) radicals yield CO(2)(-), which are the main species available for degrading TCA. Under the latter conditions, TCA is more efficiently depleted than in the absence of formate, but otherwise identical conditions of temperature and [S(2)O(8)(2-)]. We therefore conclude that activated peroxydisulfate in the presence of formate as an additive is a convenient method for the mineralization of substrates that are refractory to oxidation, such as perchlorinated hydrocarbons and TCA. This method has the advantage that leaves no toxic residues.

Improving steady-state identification

Abstract The use of online data together with steady-state models, as in Real Time Optimization applications, requires the identification of steady-state regimes in a process and the detection of the presence of gross erros. In this paper a method is proposed which makes use of polynomial interpolation on time windows. The method is simple because the parameters in which it is based are easy to tune as they are rather intuitive. In order to assess the performance of the method, a comparison based on Monte-Carlo simulations was performed, comparing the proposed method to three methods extracted from literature, for different noise to signal ratios and autocorrelations. The comparison was extended to real data corresponding to 197 variables of the atmospheric distillation unit of an important Brazilian refinery. A hierarchical approach was applied in order to manage the dimension of the problem.

Biopolymers from Composted Biowaste as Stabilizers for the Synthesis of Spherical and Homogeneously Sized Silver Nanoparticles for Textile Applications on Natural Fibers

The use of bio-based substances (BBS) obtained from composted biowaste as stabilizers for the production of silver nanoparticles (AgNPs) in substitution to citrate is investigated herein, evaluating the functionalization of natural fibers for textile antibacterial applications. The results obtained evidenced that BBS can substitute citrate as reducing/stabilizing agent in the synthesis, inducing a geometrical control (in shape and size) of the AgNPs. Two different substrates were selected (wool and cotton) and two dip-coating deposition techniques investigated. The release of AgNPs from the supports in water was evaluated under two different experimental conditions: 1) soaking (static conditions) for 7 and 15 days, simulating the contact with sweat, and 2) centrifugation (dynamic conditions), simulating a washing machine treatment. A wide physicochemical characterization was carried out to evaluate the effects of BBS on the morphology and stability of AgNPs suspensions as well as the functionalization effectiveness.

Computer-Aided Lipid Design: phase equilibrium modeling for product design

Abstract The aim of this work is to use phase equilibrium modeling as an auxiliary tool for product design, especially for lipids whose desired final properties are directly related to solid fat content (SFC) and melting behaviour through Solid-liquid equilibrium (SLE) modeling. This has been implemented for triacylglycerols mixtures, the main components of vegetable oils, a renewable raw-material for a wide variety of products. Excess Gibbs energy models were used to model the solid phases. Optimization of Gibbs free energy using Generalized Reduced Gradient was performed aiming to compute the number of molecules in each phase at the whole range of melting. As a result, the computed phase diagram was compared with experimental data from literature as well as a DSC curve. The model was also used to simulate a four-component DSC curve as a predictive tool.

Beyond biofuels: economic opportunities, recent advances and challenges in property modeling for vegetable oils

Abstract Despite the greater attention given to biofuels application in the literature, there are many economic and environmental drivers to use vegetables oils (VOs) as a renewable feedstock for other applications. These drivers are discussed in the present work and the technological challenges imposed by this shift towards new VOs uses are also discussed. They are mainly associated to the reaction routes issues, the performance regarding end-user properties, experimental procedures and property prediction models. The need for more holistic approaches (life cycle analysis) is briefly discussed and the potential benefits arising from new computer-aided tools are highlighted as well.

Solid-liquid Equilibrium Modelling and Stability Tests for Triacylglycerols Mixtures

Abstract Computer-Aided Mixture Design for product development can take advantage from equilibrium modelling. Systems composed by triacylglycerols (TAG) mixtures are widely used for many applications (foods, cosmetics, pharmaceutical and lubricants) and their end-use properties are very close related to phase behaviour (melting and crystallization). Such molecules can have different polymorphisms in solid state, leading to a lack of intersolubility and consequently formation of multiple solid phases. This work has implemented the solid-liquid equilibrium for TAG mixtures in a two step approach: stability tests and equilibrium compositions computations for two phase mixtures. The Michelsens method for stability analysis was adapted to cope with polymorphisms and was successful for phase-split detection. Melting curves for mixtures composed by 9 TAGs in different compositions and molecular structures were simulated revealing good agreement with physical background for such systems. Further implementations of other initialization independents stability tests and robust optimization techniques show, therefore, a great potential for use as auxiliary computational framework for match improved mixtures in structured lipids research.

Decomposition Techniques for the Real-time Optimization of a Propylene Production Unit

Abstract In this work an application of decomposition techniques on a propylene production unit from REPLAN refinery by Petrobras S.A. is presented. It is shown that the classic Lagrangian Relaxation (LR) technique and the alternative technique called “Pricing Interprocess Streams Using Slack Auctions” (PISUSA) do not converge for the case study presented. The issues involved in each decomposition approach are identified and discussed; then a modification of the Lagrangean Relaxation algorithm is proposed using a new constraint-updating rule. This modified algorithm is able to overcome the issues and solve the decomposed problem properly.

Ternary Blends of Vegetable Oils: Thermal Profile Predictions for Product Design

This work deals with Product Design by means of theoretical predictions of the Solid Fat Content of different formulations using 3 vegetable oils. A Soli-Liquid Equilibrium (SLE) model was implemented and integrated into an optimization algorithm based on the Generalized Reduced Gradient method. A total of 3,696 SLE problems are solved, covering 57 binary blends, 3 pure vegetable oils and 171 ternary blends problems, before and after chemical interesterification reaction and at 8 different temperatures. A combinatorial random distribution of fatty acids in the glycerol structure is used to simulate the effect of the reaction. The results were compared with 256 experimental points, giving an average absolute error of 5.4 and 4.4 in Solid Fat Content for systems before and after reaction, respectively. Computer-aided tools can be useful to deal with the large combinatorial problem faced by product design, especially when desired product performance is related to a phase behavior in multicomponent mixtures.

Design and Implementation of a Real Time Optimization Prototype for a Propylene Distillation Unit

Abstract The design of a steady state RTO system prototype to be tested in an industrial unit is presented. A software architecture (SA) approach is carried out proposing an objectoriented software framework. SA patterns are used in the architecture design. The framework aims to allow the implementation of different RTO approaches. A RTO system prototype is being developed using the framework integrating EMSO (Soares and Secchi, 2003) as the modeling and optimization engine. The framework opens opportunities for academic uses and deeper researches on the field.

Metabolic pathways analysis in PHAs production by Pseudomonas with 13C-labeling experiments

Abstract Metabolic flux analysis is a useful tool for metabolism characterization and verification of genetic modification effects; it is a support for decisions on biotechnological process improvement. Commercial production of biodegradable polymers, specifically polyhydroxyalkanoates PHAs, is restricted by production costs, which may be cut by increasing yield from substrate to product, since carbon source for PHAs production accounts up to 50% of the total production costs; additionally, in Pseudomonas sp . LMF046 the experimental yield is between 60-70% of theoretical maximum yield. This work presents metabolic pathways identification, flux quantification and analysis on this strain, employing position isotopomer balancing and measurements of labeling patterns in the polymer by GC-MS. Initial results –using [1- 13 C]glucose-allow to rule out carbohydrate catabolism by EMP pathway, whereas final ones –using a mixture of [U- 13 C]glucose and natural glucose– allow to estimate fraction of glucose metabolized by ED and PP pathways. Metabolic network includes eight intracellular metabolite and 324 isotopomer balances, and it is solved in 1.3 seconds in a Core i5 PC. Sensitivity analysis shows inclusion of carbon natural labeling improves the prediction. The estimated ratio for sugar metabolism into PP and ED pathways, 1.35:0.55, that corresponds to 77% of the theoretical yield, leads to the conclusion that the glucose metabolism in larger proportion by the Pentoses pathway is the main reason for a low yield. The problem has been solved satisfactorily, and a sensitivity analysis shows that it is necessary to reduce uncertainty on labeling measurements.