Resumo em Inglês:

Abstract Accurate representation of the physical properties of a solvent is essential for design and simulation of processes. Density and viscosity, for instance, have an important role in modelling and designing absorption and desorption towers. In the present work, a model to accurately calculate the density of aqueous amine solutions used in CO2 capture was developed as a function of temperature and composition. The model is based on excess Gibbs energy functions, and in this work the functional form of the non-random two-liquid (NRTL) model was used. The model is able to accurately represent the density of the tested systems with deviations below 0.2% for most cases. The pure component density was calculated using the modified Rackett equation with the parameter ZRA as a function of the temperature and pressure of the system. The calculated deviation (AARD) for pure component density was below 0.09%.

Resumo em Inglês:

Abstract Bio-catalysis has attracted the special attention of industrial flavour producers in the production of valuable ester compounds. In this study, the synthesis of pentyl nonanoate ester (a short chain ester with fruity aroma) was carried out with a commercial immobilized lipase from Rhizomucor meihei Lipozyme (RMIM) as biocatalyst in the esterification reaction between nonanoic acid and pentanol. Various reaction parameters such as enzyme concentration, substrate concentration, reaction temperature and reaction time in solvent-free system were screened to enhance the ester formation with the best yield. A maximum yield for pentyl nonanoate (86.08 %) in a solvent-free system was obtained within 150 min, at a reaction temperature of 45 OC, molar ratio of 1:9 M, amount of enzyme of 0.2 g, water addition of 0.2 % v/v and shaking speed of 150 rpm. This work suggests that pentyl nonanoate ester can be produced in a very high yield and in a short period by lipase-catalysed reactions of nonanoic acid and pentanol, using immobilized lipase from RMIM (lipase from Rhizomucor miehei immobilized on anionic exchange support).

Resumo em Inglês:

Abstract In the present study, an innovative cultivation strategy of Rhodotorula mucilaginosa CCT 7688 to accumulate both lipids and high added value carotenoids was proposed, with the potential to contribute to the economic feasibility of microbial oils in comparison with vegetable oils. The stepwise fed-batch cultivation with crude glycerol feeding at 24 h, 96 h, and 144 h, with the addition of magnesium to the initial culture medium, resulted in a lipid content of 51.0 ± 0.3 % CDW, biomass concentration of 21.00 ± 0.48 g L-1, total lipid production of 10.72 ± 0.18 g L-1, lipid productivity of 0.037 ± 0.001 g L-1 h-1, volumetric carotenoid production of 2843.2 ± 282.0 μg L-1, and carotenoid productivity of 9.87 ± 0.98 μg L-1 h-1. These values represent a 6-fold increase in lipid content, a 19-fold increase in lipid production, and a 2-fold increase in carotenoid production compared to batch cultivation.

Resumo em Inglês:

Abstract This study assessed the effect of hydraulic retention time (HRT) on biohydrogen production by dark fermentation using an anaerobic fluidized bed reactor fed with cheese whey synthetic wastewater. The reactor of 1.2 L was operated with an approximate carbohydrate concentration of 2800 mg L-1, and HRTs of 6, 4, 2, 1 and 0.5 h. Acetic and butyric acids were the main metabolites produced in the reactor. The hydrogen production increased from 0.039 to 1.43 L-H2 h-1 L-1-reactor as the HRT decreased from 6 to 0.5 h. The best hydrogen yield (HY) (2.73 mol-H2 mol-carbohydrate-1) and carbohydrate consumption (81.02%) were achieved at a HRT of 6 h (12.34 kg-COD m-3 d-1) followed by the HY of 2.43 mol-H2 mol-carbohydrate-1 at a HRT of 0.5h (163.02 kg-COD m-3.d-1). An increase in the influent pH in the operational phase 05 (HRT of 0.5 h) favored hydrogen production despite the reduced carbohydrate conversion compared to phase 01 (HRT of 6 h). In both conditions, the reactor presented the highest amount of acetic acid, indicating that the acetate route favored the hydrogen yield production. The HRT reduction led to an increase in microbial diversity, as evidenced by the Shannon-Wiener coefficient of 2.586, which corresponds to the operational phase with a HRT of 2 h.

Resumo em Inglês:

Abstract This paper investigates the effect of operating conditions such as coil pitch, fiber diameter, distance between fiber and absorber internal wall and absorber diameter for a vacuum membrane installation coupled with solar energy and using helically coiled fiber to maximize the permeate flow rate. The model is based on a system of equations composed of two-dimensional Navier-Stokes equations. Matlab and FemLab were used to solve this system of equations. The results showed that the best values of fiber geometric configuration are 3.22 cm for the coil pitch, 6 mm for the fiber diameter, 4.3 mm for the distance between the fiber and the absorber internal wall and 14 cm for the absorber diameter. For this configuration, the permeate flow rate is 18.6 10-5 kg/s. In conclusion, these results are important in the membrane module design for practical membrane distillation applications.

Resumo em Inglês:

Abstract Maximum water holding capacity of a mixture of sugarcane bagasse and wheat bran was determined in static conditions and in a drum rotated at 1 rpm. The variables filling degree, water flow rate, volume of added water and number of sprinklers were tested to control the moisture content of the solid and the number of rotations to achieve homogeneous moisture content. None of the selected variables was significant, giving the apparatus high flexibility to control moisture content. For the heat transfer experiments, the tested variables were introduction of air through an inner tube amidst the particles, water sprinkling over the bed and drum rotation. The selected variables represented limited mechanisms of heat removal, although efficient when coupled with the drum rotation. The results are of value to control the temperature and the moisture content in solid-state cultivation bioreactors.

Resumo em Inglês:

Abstract The heat transfer process in a stirred tank of diameter T=0.5m equipped with dual-layer improved Intermig impellers and helical coils was investigated by experiment and numerical simulation methods. The temperature field, the temperature boundary layer lateral to the coil and the heat transfer coefficient were measured at different rotational speeds. The standard k-ε turbulence model and multiple reference frames combined with a sliding mesh method were adopted in the numerical simulation. The results show that the temperature errors between numerical simulation and experimental measurement were within 2K. The temperature in the stirred tank gradually rose from top to bottom and inside to outside, and the maximum temperature difference was within 2K. The average thickness of the temperature boundary layer outside the helical coil is 3.66 mm. According to the experiments and numerical simulations, the heat transfer coefficient correlations, including Nu and Re, Nu and ε of the helical coil outer side, were obtained, and the trends of heat transfer coefficients are consistent and regular. The correlation of the heat transfer coefficient lateral to the coil was acquired from the experimentally measured data. The research results can serve as a guide for the design and engineering application of mass and heat transfer processes in stirred tanks with improved Intermig impellers.

Resumo em Inglês:

Abstract This work aimed to study nickel-based oxygen carriers (OC) for Chemical Looping Combustion (CLC) using H2 and CH4 as fuel. The reactivity and reaction kinetics of the OC were investigated, applying the shrinking core, nucleation and diffusion models in three dimensions, as well as whether the OC is thermodynamically favorable for the reaction. The results showed that the OC achieved high conversion for both fuels, proving to be quite reactive, while the fuel gas concentration and the temperature have a strong effect on the solids conversion. For the H2 combustion, the reaction rate can be described well by the shrinking core model, whereas for CH4 the nucleation model may better represent the experimental data. With respect to reactions that occur in the reduction reactor with the NiO/Ni redox system, it was observed that, for the investigated temperatures used in CLC, high values of the equilibrium constant were obtained, showing that practically complete conversion of the fuels is possible.

Resumo em Inglês:

Abstract In this work, the grapheme oxide (GO) and GO/ZnO nanocomposite were successfully obtained from the oxidation of graphite and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). In the GO/ZnO nanocomposite, the GO sheets were coated with aggregated ZnO nanoneedles with ca. 20 nm of diameter. The obtained materials were used as heterogeneous catalysts for acetylation of Soybean Fatty Acids Methyl Esters (FAME), promoting the epoxy ring-opening using acetic anhydride. The epoxy ring was almost completely opened in the presence of GO or GO/ZnO nanocomposites, with conversion rates up to 99% and selectivity of ca. 90%, and partially opened using only ZnO. The GO/Zn and GO catalysts were reused three times with conversion rates of ca. 85 and 74%, respectively.

Resumo em Inglês:

Abstract Isopropyl alcohol (IPA) catalytic oxidation remains one of the most popular techniques to remove volatile organic compounds from indoor places. In our study, catalytic oxidation of IPA was investigated on catalysts based on platinum deposited on mullite (Al6Si2O13), known for its excellent thermal stability. Pt/Al6Si2O13 catalysts were prepared by impregnation with and without methyl cellulose (MC) and were tested in order to study the influence of MC on the platinum particle dispersion over the support. The catalytic reactivity was compared with Pt/α-alumina and Pt/SiO2. Moreover, the resulting materials were characterized by BET, XRD, TEM and H2-chemisorption. This study showed that platinum exhibits better dispersion on alumina sites than silica sites. This can be due to a strong interaction between platinum and alumina, leading to a higher dispersion of platinum species. Furthermore, the addition of MC enhanced the Pt dispersion over the mullite, leading to an improvement in the catalytic performance.

Resumo em Inglês:

Abstract In recent years, the replacement of homogeneous catalysts by heterogeneous catalysts has been investigated as a sustainable alternative technology to obtain different products. In this context, this study investigated the activity of the heterogeneous catalyst DAPTS-MCM-41, obtained from the reaction between the MCM-41 molecular sieve and an organic base 3-ethylenediamine (trimethoxy) propyl silane (DAPTS) in the interesterification reaction of palm oil and palm kernel oil blends. The catalyst was characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD) and textural analysis (ASAP). The interesterified blends were evaluated by fatty acid profiles (FAME) and solid fat content (SFC). The significant changes observed in the solid fat contents of the blends before and after interesterification led to changes in physical properties due the random distribution of acyl groups on glycerol positions. No undesirable reactions such as degradation and trans isomer formation occurred since the fatty acid composition of the blends remained constant.

Resumo em Inglês:

Abstract Biodiesel production using acid oils is an important alternative for biofuel cost reduction. However, it is a huge challenge for homogeneous transesterification, the main industrial route commonly used. This paper presents macauba oil with high acidity, 43.90 w/w%, as a potential raw material for biodiesel production. The acidity was reduced to 0.8 w/w% after re-esterification (80 min) with glycerol at high temperature (235 °C), without catalysts. Zinc (powder and coating) and NbOPO4 were also tested as catalysts in comparison with the reaction without a catalyst. Reactions catalyzed by metallic Zn produced a large amount of Zn carboxylate, an undesirable soap, due to the high Zn leaching. In contrast with the literature, Zinc did not show good catalytic activity, as confirmed by the kinetic parameters. NbOPO4 was not a good catalyst, too. Reaction without catalysts was performed using nitrogen as a carrier gas and it was compared with reaction under vacuum to remove co-produced water. Nitrogen showed the best result for re-esterification, avoiding degradation reactions. Triglycerides (TG) were the prevalent products in reactions using nitrogen. After re-esterification, the oil was easily converted into biodiesel with high ester content (98.4%) of methyl ester by alkaline transesterification.

Resumo em Inglês:

Abstract This work reports the integration of Real Time Optimization and Model Predictive Control in the multi-layer control structure of an existing Crude Distillation Unit (CDU) of an oil refinery. The MPC considers output control zones and targets for the inputs or outputs. Both the infinite horizon and the finite output horizon controllers were tested. The plant results show that the infinite horizon controller tends to perform similarly or better then the finite horizon MPC when the CDU system needs to operate at quite different conditions. Although the dynamic layer based on the infinite horizon controller is nominally stable for any set of tuning parameters, in practice, it is observed that the interaction between the layers of the control structure associated to model uncertainty may result in oscillations in some variables that fail to converge to the optimum operation point. This problem can be solved with the retuning of the intermediary layer (target calculation layer), which indicates that the frequent tuning of the MPC is recommended and should be performed in conjunction with tuning of the intermediary layer.

Resumo em Inglês:

Abstract Ensuring that industrial effluents meet quality standards to be released into water bodies is still one of the major environmental concerns. Liquid phase adsoption in fixed bed collumns is one of the most known treatments. Measurements are needed to monitor the process. However, as they are often corrupted by noise from the measuring equipment, performing an accurate analysis becomes an important challenge. The present work demonstrates the effectiveness of particle filter Sampling Importance Resampling as a fast and robust tool for monitoring a problem of sulfate ion removal. Experimental measurements were used to validate the methodology and the particle filter (PF) performance was evaluated by means of error metrics, computational time and compared to the Unscented Kalman Filter. The results show that the PF provides sequentially very accurate estimates for the sulfate adsorption breakthrough curve.

Resumo em Inglês:

Abstract This work describes a phenomenological model of the two-massecuite system for sucrose crystallization, developed using EMSO software. In most Brazilian sugarcane industries, sucrose crystallization is performed using this system. This process is considered to be a fundamental step in obtaining sugar of the desired quality and accounts for a substantial fraction of the production costs. The simulation results - crystal percentage in massecuite, brix and purity of molasses, magma purity, sugar pol, crystal size distribution - were validated by comparing them with real process data of an industrial plant. The interest of the phenomenological model to study the possible impacts of impurities and process instability was illustrated by varying the simulation inputs related with the syrup purity, syrup brix and steam conditions.

Resumo em Inglês:

Abstract Model Predictive Control, MPC and NMPC, and real-time optimization, RTO and D-RTO, are known to help plant operability through the mitigation of impacts caused by external disturbances. However, the usage of these tools in industry requires overcoming some challenges, for instance: accurate models of the process, particularly in regard to nonlinearities; suitable computational time for obtaining the solution of large-scale problems and model mismatch between the RTO or D-RTO and NMPC. In this paper, we present a methodology to obtain analytical model predictions based on a Hammerstein structure to represent the process nonlinearities, reducing the computational effort in real-time applications. Unlike most common approaches that transform NMPC internal models, described by differential-algebraic equations (DAE), into an approximate system of nonlinear algebraic (NLA) equations using, for instance, orthogonal collocation, in the proposed approach, the obtained NLA is an exact description of the original DAEs system. The proposed algorithm was applied to a non-isothermal CSTR (continuous stirred tank reactor) integrated with an optimization layer. The results show that the proposed structure presented a significant reduction in computational time without performance loss, when compared with the NMPC using a rigorous model. Moreover, the proposed strategy demonstrated good performance in tracking the targets sent by the optimization layer, without model mismatches between layers.

Resumo em Inglês:

Abstract Identification of stagnant regions of viscoplastic fluid flows in production lines and equipment is of paramount importance owing to potential material degradation and process contamination. The present work introduces an assessment strategy to identify, classify and quantify unyielded regions with the objective of optimizing the flow conditions with the purpose of minimizing stagnant regions. Flow of Carbopol® 980 in a T-bifurcation channel is adopted to illustrate the procedure. The rheological behavior of Carbopol® 980 was simulated using the Herschel-Bulkley viscoplastic model regularized by Papanastasiou’s exponential approach. The analysis shows that three distinct types of stagnant unyielded regions take place in the bifurcation channel depending upon the Reynolds condition. Furthermore, the rheological characteristics of the fluid indicate the existence of an ideal Reynolds condition which allows the smallest flow stagnant area at the bifurcation zone.

Resumo em Inglês:

Abstract This paper presents a 3D full-loop simulation of a circulating fluidized bed gasifier. The model is validated with experimental results from the literature. The validated model is thereupon used to compare Bubbling Fluidized Bed (BFB) and Circulating Fluidized Bed (CFB) gasifiers to highlight the effect of a change in fluidization regime from bubbling to fast fluidization on hydrodynamics, temperature and gas composition. Feed temperature as well as Air/Coal (A/C) and Steam/Coal (S/C) ratios are kept constant, whereas the velocity of the feed (Air-Steam) is increased so as to get into the fast fluidization regime. It was concluded that the flue gas from the CFB is richer in desired gases, i.e., CO and H2 than that from BFB. H2 remains approximately the same, CO2 and CH4 decreased to a negligible amount and CO approximately doubles when the regime is changed. In addition, tar content in the gas also decreases.

Resumo em Inglês:

Abstract Several methods for computing the Gauss-Christoffel quadrature used for the adaptive characterization of continuous mixtures were compared as to their efficiency and robustness. Two mixtures with molar fraction distribution given by truncated gamma distributions were used. We analyzed the Product-Difference, the Golub-Welsch, the Long Quotient-Modified Difference and the Chebyshev algorithms using regular and generalized moments, when applicable. The robustness and computational efficiency of changes in the distribution variable and in the orthogonal polynomial family used to calculate the generalized moments were analyzed. The methods using generalized moments proved to be more robust than those that use regular moments. Although they are computationally more expensive, this cost increase is just around 20% for the Chebyshev algorithm. The resulting adaptive characterization was employed to solve the adiabatic vapor-liquid flash of these mixtures. The results showed that eight pseudocomponents were able to well represent the properties of the equilibrium streams, showing the high accuracy of this method.

Resumo em Inglês:

Abstract Oxygen enriched porous carbons have been synthesized by a nanocasting technique using mesoporous zeolite as template and epoxy resin as precursor. Characterization results show the effect of the nanocasting technique on the development of heterogeneous surface, high basicity, and high surface area of 686.37 m2g-1, beneficial for CO2 adsorption. Pure component adsorption isotherms were correlated with Langmuir, Sips, and dual-site Langmuir (DSL) models and found that Sips and DSL isotherm models fitted well, indicating thre heterogeneous nature of the adsorbent surface. Dynamic breakthrough data for the binary system CO2-N2 were obtained using a fixed-bed column at different adsorption temperatures (30-100 °C) and CO2 feed concentrations (5-12.5% by volume). The developed adsorbent shows high adsorption capacity with complete regenerability over four adsorption/desorption cycles. Prediction of binary components (CO2-N2) was made by using extended Sips, extended DSL and IAST (ideal adsorbed solution theory) by utilizing pure component adsorption isotherm data. Experimental and predicted equilibrium data were compared with breakthrough curve data and it was found that the extended forms (Sips and DSL) indicated under-predicted CO2 adsorption equilibria because of differences in adsorptive strengths of CO2 and N2 molecules. Also, adsorption equilibria were closely predicted using IAST theory. Asymmetric x-y diagrams from Raoult’s law indicated positive deviation, implying that as the CO2 gas phase molar fraction increases, total adsorbed amounts increase. Negative values of molar Gibbs free energy change suggested feasibility of the adsorption process. Formation of a more ordered configuration of CO2 molecules on the adsorbent surface was seen as a higher heat of adsorption was exhibited for CO2 as compared to N2.

Resumo em Inglês:

Abstract In this study, a novel strategy for controlling the mass transfer rate in a gas-liquid system was reported and used for the industrially important system of CO2 absorption. The strategy used Fe3O4 nanoparticles in the liquid phase and also exerting an external electric field. To demonstrate this approach, a unique experimental set up was applied to form a falling liquid film, which was water, to be in contact with the gas phase, which was pure carbon dioxide. Nanofluid with concentrations less than 0.03% by volume and field intensities of 133, 200, 266 kV/m were used in this study. Experimental results showed that the external electric field was able to remarkably enhance the gas absorption rate in dilute nanofluids, while it deteriorated mass transfer in concentrated nanofluids. In order to explain the results, the viscosity of the nanofluid was also experimentally measured in the presence of the electric field.

Resumo em Inglês:

Abstract Oxidative desulfurization (ODS) is an attractive complementary or alternative process for the hydrodesulfurization (HDS) process due to advantages such as mild operating conditions. In the ODS process, the sulfur-containing compounds are oxidized first to polar sulfoxide and sulfone products and then these polar compounds are separated using solvent extraction or an adsorption process. In the present study, the separation of oxidized sulfur-containing compounds of diesel as a real fuel has been investigated using extraction in a single drop column. The oxidation system was hydrogen peroxide/formic acid. The selected solvent for the extraction of oxidized sulfur-containing compounds was dimethylformamide (DMF). In single drop tests, the effect of various parameters including the drop size (1.70-4.60 mm) and column height (228-550 mm) on the different parameters such as drop velocity and sulfur concentration in the dispersed and continuous phases has been investigated. The outcome of this study provides valuable insights for designing the extraction column for separation of oxidized sulfur-containing compounds from middle distillate fuels in an ODS process.

Resumo em Inglês:

Abstract Multicomponent separation of synthetic petrochemical naphtha (hexane, cyclohexane, toluene and xylene) was carried out in a falling film distillation sequence with heat supply using a vapor chamber (thermosyphon). Tests were carried out by varying feed flow rate and temperatures of the feed and the vapor chamber in two ways of heat supply: isothermal and with a vapor chamber temperature profile. Regarding the distillation behavior of the multicomponent separation with the proposed falling film column, it was verified that the lower values of the studied variables and the profile temperature mode promoted the best results for hexane recuperation. With an indirect sequence of three columns, hexane mass fraction in the top column increases to the value of 0.82. Higher thermodynamic efficiency was found for two columns of the sequence in comparison with the conventional ones. This behavior is related to smaller energy consumption, showing a total energy reduction of 12% compared to the same separation performed in a conventional unit. Energy and exergetic efficiency values were higher than 95% and 85% in the three columns used. These analyses demonstrated that the falling film separation proposal is an energy efficient arrangement and could be considered for multicomponent separation.