António Ferreira

University of Porto | UP · LEPABE-Faculty of Engineering

Optical fiber sensors were implemented to measure in-situ temperature variations in an oscillatory flow crystallizer operating in continuous. The sensors were fabricated by cleaved in the middle 8 mm-length fiber Bragg gratings, forming tips with a Bragg grating of 4 mm inscribed at the fiber ends. The geometry of the sensors fabricated, with a dia...

In this study, different configurations based on linear fiber lasers were proposed and experimentally demonstrated to measure the concentration of liquid solutions. Samples of paracetamol liquid solutions with different concentrations, in the range from 52.61 to 201.33 g/kg, were used as a case-study. The optical gain was provided by a commercial b...

In this study, different configurations based on linear fiber lasers were proposed and experimentally demonstrated to measure the concentration of paracetamol liquid solutions in a range of 52.61 to 201.33 g/kg. The optical gain was provided by a commercial bidirectional Erbium-Doped Fiber Amplifier (EDFA) and the linear cavity was obtained using t...

The refractometric analysis of ethanol-water mixtures is hampered because this type of binary solution does not present a linear behaviour. In this work it is proposed a multimode Graded-Index Fiber (GIF) tip sensor for the measurement of ethanol in binary liquid solutions of ethanol-water. The probe is fabricated by fusion-splicing a 500 µm GIF to...

The refractometric analysis of ethanol-water mixtures is hampered because this type of binary solution does not present a linear behavior. In this work it is proposed a multimode Graded-Index Fiber (GIF) tip sensor for the measurement of ethanol in binary liquid solutions of ethanol-water. The prove is fabricated by the fusion-splicing of a 500 μm...

A paracetamol concentration-sensing scheme based on a linear cavity fiber laser configuration is demonstrated experimentally. The laser cavity has a fiber sensor at one end, that allows refractive index measurements. The refractometer consists of a cleaved fiber tip combined with an FBG functioning as a reflecting mirror. The combination of a fiber...

Process Analytical Technology (PAT) has been increasingly used in the pharmaceutical industry to monitor essential parameters in real-time during pharmaceutical processes. The concentration of Active Pharmaceutical Ingredients (APIs), such as paracetamol, is one of these parameters, and controlling its variations allows for optimization of the prod...

In bioprocesses, the microorganisms’ growth is ruled by physical, chemical, and biological conditions being the electrolyte concentration one of the most important parameters to control. In this study, the effect of three electrolytes (HCl, NaOH, NaCl) in aqueous solutions on the volumetric (kLa) and liquid-side (kL) mass transfer coefficients and...

Several technologies and synthesis routes have been implemented to produce calcium phosphates (CaPs) with distinct characteristics for biomedical applications. However, produce CaPs in a controlled way still represents a challenge. Oscillatory flow reactors (OFRs) are a technology ready to deliver in terms of mixing intensification in multiphase sy...

Protein crystallisation has been shown as a viable alternative to conventional protein purification methods. However, the stochastic and spontaneous nature of the primary nucleation process makes protein crystallization difficult to control. An approach often used in the crystallization of small organic and inorganic molecules to improve the reprod...

Although very promising, the use of microalgae for CO2 capture still faces some limitations. Due to the low solubility of this gas in the liquid medium, poor CO2 utilisation efficiencies by microalgae are very common, resulting in low CO2 fixation rates and CO2 losses to the atmosphere. Considering this limitation, several researchers have focused...

In bioprocess, the microorganism’s growth is ruled by physical, chemical, and biological conditions, being the pH one of the most important parameters to control. Hence, this paper aims to analyse the pH influence on volumetric liquid-side mass transfer coefficient (k_L a), gas holdup (ε_G) and Sauter mean diameter (d_32) over a range of oscillator...

An active pharmaceutical ingredient is currently produced in a traditional batch antisolvent crystallization process. Although well-established, this process lacks flexibility to control the crystal size distribution (CSD). Therefore, a new process was developed to enable the control of the CSD according to different specifications. This new proces...

A refractometric sensor was applied to measure in real-time the concentration of Active Pharmaceutical Ingredients (APIs) in crystallization experiments. Paracetamol was used as a model system due to the extensive literature available for this API. The refractometric sensor was fabricated by a simple and inexpensive method that consisted in splicin...

The isothermal crystallization of paracetamol from aqueous solutions in a planar oscillatory flow crystallizer was used as a model system to study the effect of the oscillation conditions on the...

Isothermal seeded desupersaturation experiments were performed in a planar oscillatory flow crystallizer (planar-OFC) to investigate the effect of the oscillation conditions on the crystal growth kinetics for the isothermal crystallization...

Ozone-water mass transfer was investigated in continuous mode using a macroscale oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC). The effects of oscillation amplitude (x0) and frequency (f) on the mass transfer coefficient (kLa) were assessed through a Doehlert experimental design. Different gas and liquid flow rates...

The increase in carbon dioxide (CO2) emissions to the atmosphere is provoking an environmental crisis, as CO2 is considered the main responsible for the greenhouse effect and, consequently, global warming. The constant search for effective systems to capture CO2 has revealed the potential of microalgal cultures to perform this task. Microalgae are...

A configuration of a refractometer sensor is described with the aim of optically detecting the crystallization process of paracetamol. The developed sensing head is based on a conventional cleaved multi-mode fiber. The fiber tip sensor structure was submitted to contact with the liquid of interest (paracetamol fully dissolved in 40% v/v of ethanol/...

Microalgae are fast-growing microorganisms proposed as a viable alternative for CO2 capture from the atmosphere [1]. To improve the CO2 utilisation efficiency by microalgae, optimisation of CO2 mass transfer is an important factor to consider, as it promotes an increase in the residence time of CO2 in the culture medium [2]. This study focused on t...

Paracetamol is a popular antipyretic and analgesic active pharmaceutical ingredient that is used worldwide in the production of several millions of tablets and other dosage forms every year. Paracetamol has three fully characterized polymorphs (forms I, II and III), and also two high pressure polymorphs with unknown crystal structure (forms IV and...

Over the year's gas-liquid mass transfer studies have been conducted on bubble columns, airlift and stirred tanks. Recently, a novel reactor, oscillatory flow reactor provided with smooth periodic (OFR-SPC) has been used on gas-liquid mass transfer studies. The results have been shown a significant enhancement in the mass transfer process in presen...

The planar oscillatory flow crystallizer (planar‐OFC) was designed with a rectangular cross‐section to improve the flow and suspension of solids of conventional OFCs. Residence time distribution experiments with liquid and solid tracers were performed to assess the effect of the net flow rate, Q, the frequency, f, and the amplitude of oscillation,...

In this research paper the residence time distribution (RTD) was monitored for a range of fluid oscillation, frequency, amplitude and flow rate in two oscillatory flow reactors (OFR) provided with 2D smooth periodic constrictions (2D-SPC) with different designs. It was studied the axial liquid dispersion using axial dispersion model and the mixing...

The influence of mixing intensity on protein crystallization has been investigated for the first time in a meso oscillatory flow reactor (meso-OFR). For this, lysozyme crystallization was studied in batch at different oscillation amplitudes and frequencies. Turbidity was monitored over time to measure induction time and follow the crystallization p...

A simple approach was employed to determine the critical mixing intensity for secondary nucleation of paracetamol, Reoc, in an oscillatory flow crystallizer, i.e., the mixing intensity at which the transition from crystal growth to secondary nucleation control of crystal size occurs. Reoc was determined for different initial supersaturations as a b...

Bubble column and airlift reactors are normally the first choice in many applications, especially ones involving biomaterials. Their popularity is essentially related to the simple design, nonmechanical agitation, and satisfactory heat and mass transfer properties. However, problems related to poor mixing, scale-up, product quality, and process rep...

Multiphase contactors are intensively used in chemical, biochemical, pharmaceutical, petrochemical, and others industries. The complexity and diversity of industrial processes implies that different types of gas-liquid contactors have been developed and constructed, such as bubble columns, airlifts, oscillatory flow reactors, pipes and tubes, mecha...

In the present work, it is studied for the first time the use of an oscillatory flow reactor provided with smooth period constrictions (OFR-SPC) in gas-liquid mass transfer process when a solid phase is present. The superficial gas velocities ( ), solids loading (calcium alginate beads: 0-15% (v/v)) and the oscillatory conditions (frequency and amp...

The batch and continuous crystallization of paracetamol from aqueous solutions is studied in a novel oscillatory flow mesoreactor equipped with smooth periodic constrictions. The aim of this study is to evaluate the influence of the operating and thermodynamic variables on the size of the crystals for enhanced direct crystallization of micronized p...

This work reports the biological evaluation of nanosized hydroxyapatite (HAp) previously synthesized by continuous-flow precipitation in a scaled-up meso oscillatory flow reactor (meso-OFR). Physicochemical characterization of the synthesized HApsuggests high surface reactivity namely because of its high specific surface area and low crystallinity....

In the present work, it is reported for the first time the study of the applicability of a novel meso oscillatory flow reactor (meso-OFR) for protein crystallization as a process step. Crystallization assays carried out in the designed device enabled to derive a two-dimensional lysozyme phase diagram (lysozyme concentration against sodium chloride...

The study of local hydrodynamic properties of three-phase bioreactors in biotechnology processes is of great importance, mainly because of the complex interaction between bioreactor and microorganisms. However, classical techniques used for measuring local hydrodynamic properties such as single needle probes are mainly limited to two-phase flows. I...

In the present work the superficial gas velocities (u(G)) and the oscillatory conditions (frequency and amplitude) effects on the gas-liquid mass transfer process in a novel oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) are experimentally evaluated. The liquid-side mass transfer coefficient, k(L), and the specific i...

An extensive characterization of photobioreactors (PBRs) must be made in order to optimize their operational conditions, operate design improvements and perform scale-up. In this work, a hydrodynamic characterization of liquid and gas phases was performed, as well as the determination of the mass transfer coefficient of three different PBRs (bubble...

A meso oscillatory flow reactor (meso-OFR) was successfully applied for the precipitation of hydroxyapatite (HAp) nanoparticles. Mixing efficiency of the mesoreactor operated batchwise in a vertical tube was evaluated at constant power density, by monitoring variation of hue values upon mixing both spatially and temporally. The best operating condi...

Experiments were performed in a laboratory scale bubble column (10 L), to investigate the pH influence on oxygen mass transfer coefficient, in order to achieve a better control of biological processes. The liquid-side mass transfer coefficient, kL, and the specific interfacial area, a, were studied individually. The specific interfacial area was ob...

Precipitation processes are widely used in industry for the production of particulate solids. Efficient mixing of the reagents is of major importance for the chemical and physical nature of the synthesized particles. Recently, microreactors have been studied to overcome homogeneity problems found when using stirred tank batch reactors. The present...

Continuous-flow precipitation of hydroxyapatite (HAp) was investigated in a meso oscillatory flow reactor (meso-OFR) and in a scaled-up meso-OFR, obtained by associating in series eight vertical meso-ORFs. Experiments were carried out under near-physiological conditions of temperature and pH, using fixed frequency (f = 0.83 Hz) and amplitude (x0 =...

In biotechnology, oxygen mass transfer is a key parameter involved in the design and operation of bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (kLa). Due to the fact that oxygen has a very low solubility in an aqueous media (8-10 ppm at 20°C), actively growing cells can consume all the dissolved oxygen very fa...

This paper describes the continuous-flow precipitation of hydroxyapatite Ca-5(PO4)(3)OH (HAp) in two ultrasonic microreactors using diluted aqueous solutions of calcium and phosphate at 37 degrees C. Precipitation of HAp was first carried out in a tubular microreactor immersed in an ultrasonic bath, where single-phase (laminar) flow and segmented g...

The effects of variable concentrations of different molecular weight fractions of dextran on the interfacial free energies and the kinetic coefficients of the overall linear growth rates of the sucrose crystal were evaluated at 40 and 50 °C. Dextrans-reducing effects on the interfacial free energy increased the overall linear growth rates of sucros...

Precipitation of hydroxyapatite Ca5(PO4)3OH (HAp) was carried out by mixing a saturated calcium hydroxide aqueous solution with an orthophosphoric acid aqueous solution at 37 °C. In order to promote optimal conditions for the production of HAp with high yields, mixing of the reaction medium was assured by a novel metal stirrer. Different experiment...

The morphological forms and habits of crystals and agglomeration are important properties on crystallization processes. Online techniques for realtime measurement of these properties are mandatory for a better comprehension of crystal growth phenomenon. The present paper presents and describes a new online method to determine the complexity level o...

a b s t r a c t The knowledge about the effect of solid phase properties, at different temperatures, on gas–liquid transfer and the respective physical mechanisms has been poorly studied. In the present work, the temperature and solid properties (size and density) effects on the gas–liquid mass transfer characteristics in a bubble column were exper...

Growth rates of sucrose crystallization from pure solutions of initial relative supersaturation levels between 0.094 and 0.181 were studied in agitated crystallizer at 313.13 K. Birth and spread model was applicable for the obtained growth rate data in this range of supersaturation and used to estimate the principal growth parameters. The estimated...

In this work, we present growth rate data of sucrose crystals in the presence of impurities that can be used by both sugar technologists and crystal growth scientists. Growth rate curves measured in a pilot-scale evaporative crystallizer suggest a period of slow growth that follows the seeding of crystals into supersaturated technical solutions. Th...

The effect of crystal surface roughness on impurity adsorption was investigated in a fluidized bed crystallizer and in a batch crystallizer. The crystallisation of sucrose in pure and impure systems was the study subject. Calcium chloride was utilized as impurity in this work. The results show that the impurity adsorption is growth rate dependent a...

The roughness effect on crystal growth rate was investigated at in a fluidized bed crystallizer and in a batch crystallizer. The crystallization of sucrose in pure aqueous solutions was the study subject.The results show that the sucrose crystals exhibit time-dependent growth rate. The overall growth rate decreased continually with time until a con...

The precipitation of dicalcium phosphate dihydrate, brushite, by mixing a calcium hydroxide suspension and an orthophosphoric acid solution in equimolar quantities, has been investigated in a batch system at 25°C. The concentration of calcium hydroxide and orthophosphoric acid, before mixing, ranged from 50 to 400mmoldm−3. The precipitation process...

The precipitation of dicalcium phosphate dihydrate, brushite, by mixing a calcium hydroxide suspension and an orthophosphoric acid solution in equimolar quantities, has been investigated in a batch system at 25°C. The concentration of calcium hydroxide and orthophosphoric acid, before mixing, ranged from 50 to 400 mmol dm−3. The precipitation proce...

The objectives of this work are twofold. From academic point of view the aim is to build a dynamical macro model to fit the material balance and explain the main kinetic mechanisms that govern the transformation of the hydroxyapatite (HAP) into brushite and the growth of brushite, based on laboratory experiments and collected database. From practic...

In the present work the effect of CaCl2 on sucrose crystallization at 35°C was analysed. This study was divided in three parts: the effect of impurity concentration on global crystallization rate; the impurity adsorption into the crystal; and the effect of impurity on growth rate of the crystal faces. The influence of impurity concentration on crys...

T his paper presents and describes a methodology for morphology assessment, crystal particle classification and quantification of the complexity level of a crystal or a popu-lation of crystals. It further describes the application of such methodology to the study of the influence of MgCl 2 in the crystallization of NaCl, namely on crystal size and...

A partial analytical model of the precipitation of calcium phosphate is reported in this paper. The last two stages of the overall precipitation process are considered, namely transformation of hydroxyapatite into dicalcium phosphate dihydrate (named as brushite) and the growth of brushite. Results obtained demonstrate a good agreement between the...

The precipitation of dicalcium phosphate dihydrate, brushite, by mixing a calcium hydroxide suspension and an orthophosphoric acid solution in equimolar quantities, has been investigated in a batch system at 25°C. The concentration of calcium hydroxide and orthophosphoric acid, before mixing, ranged from 50 to 300 mmol dm−3. The phase first precipi...

The effect of the solids on the mass transfer characteristics in a bubble column was studied experimentally for the systems air/water/Polyvinyl chloride (PVC) and air/water/glass beads. Volumetric liquid side mass transfer coefficient, k L a, was determined under different solid concentrations, gas flow rates and solid sizes. The presence of solids...

Phd Thesis. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto, 2008