HACCP numa indústria corticeira: implementação, identificação de pontos críticos e proposta de acções correctivas

Mestrado em Engenharia Química

Projeto de uma unidade de produção de biodiesel num reator ultrassónico pela via supercrítica

A concretização deste estágio na INCBIO teve como principal objetivo o projeto e dimensionamento de uma unidade de produção de biodiesel por transesterificação nãocatalítica num reator ultrassónico com condições supercríticas de pressão e temperatura. Com vista à concretização do trabalho, iniciou-se a realização do estudo do estado da arte relativo à produção de biodiesel, com particular enfoque na produção de biodiesel por via catalítica e por via supercrítica e na produção de biodiesel com uso de tecnologia ultrassónica. Conclui-se que nenhum estudo contempla a combinação simultânea da produção de biodiesel por via supercrítica através da tecnologia ultrassónica. Este estudo do estado da arte permitiu ainda definir as condições de temperatura, pressão e rácio mássico (250 °C, 95 bar e 1:1 respetivamente) a considerar no projeto da unidade de produção de biodiesel deste trabalho. Com base no estudo do estado da arte efetuado e com base nas características da matéria procedeu-se à definição do processo de produção de biodiesel. Para a definição do processo começou-se por elaborar o diagrama de blocos do processo (BFD) e o diagrama de fluxo do processo (PFD). Com base nos diagramas e na composição da matéria-prima, procedeu-se à quantificação dos reagentes (metanol) com base na estequiometria das reações envolvidas e ao cálculo do balanço de massa. O balanço de massa foi calculado com base na estequiometria das reações envolvidas e foi também calculado através do software de simulação ASPEN PLUS. Após o cálculo do balanço de massa elaborou-se o diagrama de tubulação e instrumentação (P&ID), que contém todos os equipamentos, válvulas, instrumentação e tubagens existentes na unidade. Após a definição do processo e cálculo do balanço de massa procedeu-se ao dimensionamento mecânico e cálculo hidráulico dos tanques, tubagem, bombas, permutador de calor, reator ultrassónico, válvulas de controlo e instrumentação de acordo com as normas ASME. Nesta fase do trabalho foram consultados diversos fornecedores possíveis para a compra de todo o material necessário. O dimensionamento mecânico e cálculo hidráulico efetuados permitiram, entre outras informações relevantes, obter as dimensões necessárias à construção do layout e à elaboração do desenho 3D. Com os resultados obtidos e desenhos elaborados, é possível avançar com a construção da unidade, pelo que pode-se inferir que o objetivo de projetar uma unidade de produção de biodiesel num reator ultrassónico com condições supercríticas foi alcançado. Por fim, efetuou-se uma análise económica detalhada que possibilita a comparação de uma unidade de produção de biodiesel por via catalítica (unidade de produção da INCBIO) com a unidade de produção de biodiesel num reator ultrassónico com condições supercríticas (unidade projetada neste trabalho). Por questões de confidencialidade, não foram revelados maior parte dos resultados da análise económica efetuada. No entanto, conclui-se que os custos de construção da unidade de produção de biodiesel num reator ultrassónico com condições supercríticas são mais baixos cerca de 35 a 40%, quando comparados com os custos de construção da unidade de produção de biodiesel por via catalítica, evidenciando assim que a combinação em simultâneo das condições supercríticas com a tecnologia ultrassónica possibilita a diminuição dos custos de produção.

Definition of MV Load Diagrams via Weighted Evidence Accumulation Clustering using Subsampling

A definition of medium voltage (MV) load diagrams was made, based on the data base knowledge discovery process. Clustering techniques were used as support for the agents of the electric power retail markets to obtain specific knowledge of their customers’ consumption habits. Each customer class resulting from the clustering operation is represented by its load diagram. The Two-step clustering algorithm and the WEACS approach based on evidence accumulation (EAC) were applied to an electricity consumption data from a utility client’s database in order to form the customer’s classes and to find a set of representative consumption patterns. The WEACS approach is a clustering ensemble combination approach that uses subsampling and that weights differently the partitions in the co-association matrix. As a complementary step to the WEACS approach, all the final data partitions produced by the different variations of the method are combined and the Ward Link algorithm is used to obtain the final data partition. Experiment results showed that WEACS approach led to better accuracy than many other clustering approaches. In this paper the WEACS approach separates better the customer’s population than Two-step clustering algorithm.

Knowledge extraction from medium voltage load diagrams to support the definition of electrical tariffs

With the electricity market liberalization, distribution and retail companies are looking for better market strategies based on adequate information upon the consumption patterns of its electricity customers. In this environment all consumers are free to choose their electricity supplier. A fair insight on the customer´s behaviour will permit the definition of specific contract aspects based on the different consumption patterns. In this paper Data Mining (DM) techniques are applied to electricity consumption data from a utility client’s database. To form the different customer´s classes, and find a set of representative consumption patterns, we have used the Two-Step algorithm which is a hierarchical clustering algorithm. Each consumer class will be represented by its load profile resulting from the clustering operation. Next, to characterize each consumer class a classification model will be constructed with the C5.0 classification algorithm.

Simulated annealing metaheuristic to solve the optimal power flow

The optimal power flow problem has been widely studied in order to improve power systems operation and planning. For real power systems, the problem is formulated as a non-linear and as a large combinatorial problem. The first approaches used to solve this problem were based on mathematical methods which required huge computational efforts. Lately, artificial intelligence techniques, such as metaheuristics based on biological processes, were adopted. Metaheuristics require lower computational resources, which is a clear advantage for addressing the problem in large power systems. This paper proposes a methodology to solve optimal power flow on economic dispatch context using a Simulated Annealing algorithm inspired on the cooling temperature process seen in metallurgy. The main contribution of the proposed method is the specific neighborhood generation according to the optimal power flow problem characteristics. The proposed methodology has been tested with IEEE 6 bus and 30 bus networks. The obtained results are compared with other wellknown methodologies presented in the literature, showing the effectiveness of the proposed method.

Ant colony search algorithm for the optimal power flow problem

To maintain a power system within operation limits, a level ahead planning it is necessary to apply competitive techniques to solve the optimal power flow (OPF). OPF is a non-linear and a large combinatorial problem. The Ant Colony Search (ACS) optimization algorithm is inspired by the organized natural movement of real ants and has been successfully applied to different large combinatorial optimization problems. This paper presents an implementation of Ant Colony optimization to solve the OPF in an economic dispatch context. The proposed methodology has been developed to be used for maintenance and repairing planning with 48 to 24 hours antecipation. The main advantage of this method is its low execution time that allows the use of OPF when a large set of scenarios has to be analyzed. The paper includes a case study using the IEEE 30 bus network. The results are compared with other well-known methodologies presented in the literature.

Flow amperometric determination of carbofuran and fenobucarb

A simple, rapid, and precise amperometric method for quantification of N-methylcarbamate pesticides in water samples and phytopharmaceuticals is presented. Carbofuran and fenobucarb are the target analytes. The method is developed in flow conditions providing the anodic oxidation of phenolic-based compounds formed after alkaline hydrolysis. Optimization of instrumental and chemical variables is presented. Under the optimal conditions, the amperometric signal is linear for carbofuran and fenobucarb concentrations over the range of 1.0*10-7 to 1.0*10-5 molL-1, with a detection limit of about 2 ngmL-1. The amperometric method is successfully applied to the analysis of spiked environmental waters and commercial formulations. The proposed method allows 90 samples to be analysed per hour, using 500 mL of sample, and producing wastewaters of low toxicity. The proposed method permits determinations at the mgL 1 level and offers advantages of simplicity, accuracy, precision, and applicability to coloured and turbid samples, and automation feasibility.

Sulfadiazine-potentiometric sensors for flow and batch determinations of sulfadiazine in drugs and biological fluids

New PVC membrane electrodes for the determination of sulfadiazine (SDZ) are presented. The electrodes are fabricated with conventional and tubular configurations with a graphite-based electrical contact, and no internal reference solution. The selective membranes consist of bis(triphenylphosphoranilidene)ammonium·SDZ (electrode A), tetraoctylammonium bromide (electrode B), or iron(II)-phthalocyanine (FePC) (electrode C) electroactive materials dispersed in a PVC matrix of o-nitrophenyl octyl ether (o-NPOE) plasticizer. The sensors A, B, and C displayed linear responses over the concentration ranges 1.0*10-2 – 1.0*10–5, 1.0*10–2 – 7.5*10–6, and 3.2*10–2 – 7.0* 10–6 mol l–1 (detection limits of 1.09, 2.04 and 0.87 mg ml–1) with anionic slopes of –57.3 ± 0.1, –46.7 ± 0.5, and –65.1 ± 0.2 mV decade–1, respectively. No effect from pH was observed within 4.0 – 5.5, 4.8 – 10, and 4.5 – 8, respectively, and good selectivity was found. The sensors were applied to the analysis of pharmaceuticals and biological fluids in steady state and in flow conditions.

New biomimetic sensors for the determination of tetracycline in biological samples: batch and flow mode operations

New potentiometric membrane sensors with cylindrical configuration for tetracycline (TC) are described based on the use of a newly designed molecularly imprinted polymer (MIP) material consisting of 2-vinylpyridine as a functional monomer in a plasticized PVC membrane. The sensor exhibited significantly enhanced response towards TC over the concentration range 1.59 10 5–1.0 10 3 mol L 1 at pH 3–5 with a lower detection limit of 1.29 10 5 mol L 1. The response was near-Nernstian, with average slopes of 63.9 mV decade 1. The effect of lipophilic salts and various foreign common ions were tested and were found to be negligible. The possibility of applying the proposed sensor to TC determination in spiked biological fluid samples was demonstrated.

Direct electroanalytical determination of fluvastatin in a pharmaceutical dosage form: batch and flow analysis

The reduction of luvastatin (FLV) at a hanging mercury-drop electrode (HMDE) was studied by square-wave adsorptive-stripping voltammetry (SWAdSV). FLV can be accumulated and reduced at the electrode, with a maximum peak current intensity at a potential of approximately 1.26V vs. AgCl=Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity between peak current intensity and FLV concentration between 1.0 10 8 and 2.7 10 6 mol L 1. Limits of detection (LOD) and quantification (LOQ) were found to be 9.9 10 9 mol L 1 and 3.3 10 8 mol L 1, respectively. Furthermore, FLV oxidation at a glassy carbon electrode surface was used for its hydrodynamic monitoring by amperometric detection in a flow-injection system. The amperometric signal was linear with FLV concentration over the range 1.0 10 6 to 1.0 10 5 mol L 1, with an LOD of 2.4 10 7 mol L 1 and an LOQ of 8.0 10 7 mol L 1. A sample rate of 50 injections per hour was achieved. Both methods were validated and showed to be precise and accurate, being satisfactorily applied to the determination of FLV in a commercial pharmaceutical.

Flow injection electrochemical determination of apomorphine

Few analytical methods are currently available for determination of apomorphine, the active substance of a new oral formulation used in the treatment of erectile dysfunction. In this way a flow injection electrochemical method (FIA-EC) was developed for its quantification and applied to pharmaceutical dosage forms. Based in previous findings regarding the stability of apomorphine in borate buffer and after optimization of several analytical parameters a single channel flow injection manifold was set up that enables the determination of this drug over the concentration range of 3 to 16 µmol L-1 with a detection limit of 0.5 µmol L-1 at a sampling rateof 90 h-1. The simplicity and rapidity of the FIA-EC method used, its reproducibility and sensitivity make it suitable for quality control of pharmaceutical preparations of apomorphine intended for clinical use and research.

Citrate selective electrodes for the flow injection analysis of soft drinks, beers and pharmaceutical products

Aiming the establishment of simple and accurate readings of citric acid (CA) in complex samples, citrate (CIT) selective electrodes with tubular configuration and polymeric membranes plus a quaternary ammonium ion exchanger were constructed. Several selective membranes were prepared for this purpose, having distinct mediator solvents (with quite different polarities) and, in some cases, p-tert-octylphenol (TOP) as additive. The latter was used regarding a possible increase in selectivity. The general working characteristics of all prepared electrodes were evaluated in a low dispersion flow injection analysis (FIA) manifold by injecting 500µl of citrate standard solutions into an ionic strength (IS) adjuster carrier (10−2 mol l−1) flowing at 3ml min−1. Good potentiometric response, with an average slope and a repeatability of 61.9mV per decade and ±0.8%, respectively, resulted from selective membranes comprising additive and bis(2-ethylhexyl)sebacate (bEHS) as mediator solvent. The same membranes conducted as well to the best selectivity characteristics, assessed by the separated solutions method and for several chemical species, such as chloride, nitrate, ascorbate, glucose, fructose and sucrose. Pharmaceutical preparations, soft drinks and beers were analyzed under conditions that enabled simultaneous pH and ionic strength adjustment (pH = 3.2; ionic strength = 10−2 mol l−1), and the attained results agreed well with the used reference method (relative error < 4%). The above experimental conditions promoted a significant increase in sensitivity of the potentiometric response, with a supra-Nernstian slope of 80.2mV per decade, and allowed the analysis of about 90 samples per hour, with a relative standard deviation <1.0%.

Determination of polyphenols in wines by reaction with 4-aminoantipyrine and photometric flow-injection analysis

A new flow-injection analytical procedure is proposed for the determination of the total amount of polyphenols in wines; the method is based on the formation of a colored complex between 4-aminoantipyrine and phenols, in the presence of an oxidizing reagent. The oxidizing agents hexacyanoferrate(III), peroxodisulfate, and tetroxoiodate(VII) were tested. Batch trials were first performed to select appropriate oxidizing agents, pH, and concentration ratios of reagents, on the basis of their effect on the stability of the colored complex. Conditions selected as a result of these trials were implemented in a flow-injection analytical system in which the influence of injection volume, flow rate, and reaction- coil length, was evaluated. Under the optimum conditions the total amount of polyphenols, expressed as gallic acid, could be determined within a concentration range of 36 to 544 mg L–1, and with a sensitivity of 344 L mol–1 cm–1 and an RSD <1.1%. The reproducibility of analytical readings was indicative of standard deviations <2%. Interference from sugars, tartaric acid, ascorbic acid, methanol, ammonium sulfate, and potassium chloride was negligible. The proposed system was applied to the determination of total polyphenols in red wines, and enabled analysis of approximately 55 samples h–1. Results were usually precise and accurate; the RSD was <3.9% and relative errors, by the Folin–Ciocalteu method, <5.1%.

Remediation efficiency of vapour extraction of sandy soils contaminated with cyclohexane: influence of air flow rate, water and natural organic matter content

Abstract This work reports the analysis of the efficiency and time of soil remediation using vapour extraction as well as provides comparison of results using both, prepared and real soils. The main objectives were: (i) to analyse the efficiency and time of remediation according to the water and natural organic matter content of the soil; and (ii) to assess if a previous study, performed using prepared soils, could help to preview the process viability in real conditions. For sandy soils with negligible clay content, artificially contaminated with cyclohexane before vapour extraction, it was concluded that (i) the increase of soil water content and mainly of natural organic matter content influenced negatively the remediation process, making it less efficient, more time consuming, and consequently more expensive; and (ii) a previous study using prepared soils of similar characteristics has proven helpful for previewing the process viability in real conditions.

Study of the voltammetric behaviour of metam and its application to an amperometric flow system

The electrochemical behaviour of the pesticide metam (MT) at a glassy carbon working electrode (GCE) and at a hanging mercury drop electrode (HMDE) was investigated. Different voltammetric techniques, including cyclic voltammetry (CV) and square wave voltammetry (SWV), were used. An anodic peak (independent of pH) at +1.46 V vs AgCl/Ag was observed in MTaqueous solution using the GCE. SWV calibration curves were plotted under optimized conditions (pH 2.5 and frequency 50 Hz), which showed a linear response for 17–29 mg L−1. Electrochemical reduction was also explored, using the HMDE. A well defined cathodic peak was recorded at −0.72 V vs AgCl/ Ag, dependent on pH. After optimizing the operating conditions (pH 10.1, frequency 150 Hz, potential deposition −0.20 V for 10 s), calibration curves was measured in the concentration range 2.5×10−1 to 1.0 mg L−1 using SWV. The electrochemical behaviour of this compound facilitated the development of a flow injection analysis (FIA) system with amperometric detection for the quantification of MT in commercial formulations and spiked water samples. An assessment of the optimal FIA conditions indicated that the best analytical results were obtained at a potential of +1.30 V, an injection volume of 207 μL and an overall flow rate of 2.4 ml min−1. Real samples were analysed via calibration curves over the concentration range 1.3×10−2 to 1.3 mg L−1. Recoveries from the real samples (spiked waters and commercial formulations) were between 97.4 and 105.5%. The precision of the proposed method was evaluated by assessing the relative standard deviation (RSD %) of ten consecutive determinations of one sample (1.0 mg L−1), and the value obtained was 1.5%.