Showing papers in "Chemical Engineering Research & Design in 2014"

Catalytic carbon dioxide hydrogenation to methanol: A review of recent studies

Abstract: Methanol demand is continuously increasing in the chemical and energy industries. It is commercially produced from synthesis gas (CO + CO 2 + H 2 ) using CuO/ZnO/Al 2 O 3 catalysts. Today, much effort is being put on the development of technologies for its production from carbon dioxide (CO 2 ). In this way, the Greenhouse effect may be mitigated. Over the years, several useful works on CO 2 hydrogenation to methanol have been reported in the literature. In this article, we present a comprehensive overview of all the recent studies published during the past decade. Various aspects on this reaction system (such as thermodynamic considerations, innovations in catalysts, influences of reaction variables, overall catalyst performance, reaction mechanism and kinetics, and recent technological advances) are described in detail. The major challenges confronting methanol production from CO 2 are considered. By now, such a discussion is still missing, and we intend to close this gap in this paper.

Static mixers: Mechanisms, applications, and characterization methods – A review

Abstract: Static mixers and multifunctional heat exchangers/reactors (MHE/R) are qualified as efficient receptacles for processes including physical or chemical transformations accompanied by heat transfer due to their high productivity and reduced energy expenditures. The present work reviews recent conceptual and technological innovations in passive static mixers and continuous in-line reactors. Current industrial applications are discussed from a process intensification perspective, focusing on mixing and mass transfer performance. Typical experimental techniques employed to characterize and quantify the mixing process are explored. The work is complemented by a review of mixing fundamentals, knowledge of which allows the development of theoretical models crucial for the analysis of experimental data, like the chemical probe mixing assessment method. Considering the development of continuous flow equipment in numerous processes, advances in this field will certainly be of increasing interest to the scientific and industrial communities.

A review of mathematical modeling of fixed-bed columns for carbon dioxide adsorption

Abstract: a b s t r a c t Carbon dioxide emissions must be stabilized to mitigate the unfettered release of greenhouse gases into the atmosphere. The removal of carbon dioxide from flue gases, an important first step in addressing the problem of CO2 emissions, can be achieved through adsorption separation technologies. In most adsorption processes, the adsorbent is in contact with fluid in a fixed bed. Fixed-bed column mathematical models are required to predict the performance of the adsorptive separation of carbon dioxide for optimizing design and operating conditions. A comprehensive mathematical model consists of coupled partial differential equations distributed over time and space that describe material, energy, and the momentum balances together with transport rates and equilibrium equations. Due to the complexities associated with the solution of a coupled stiff partial differential equation system, the use of accurate and efficient simplified models is desirable to decrease the required computational time. The simplified model is primarily established based on the description of mass transfer within adsorption systems. This paper presents a review of efforts over the last three decades toward mathematical modeling of the fixed-bed adsorption of carbon dioxide. The nature of various gas–solid equilibrium relationships as well as different descriptions of the mass transfer mechanisms within the adsorbent particle are reviewed. In addition to mass transfer, other aspects of adsorption in a fixed bed, such as heat and momentum transfer, are also studied. Both single- and multi-component CO2 adsorption systems are discussed in the review. © 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Correlating the chemical engineering plant cost index with macro-economic indicators

Abstract: The chemical engineering plant cost index (CEPCI) is widely used for updating the capital costs of process engineering projects. Typically, forecasting it requires twenty or so parameters. As an alternative, we suggest a correlation for predicting the index as a function of readily available and forecast macro-economic indicators: CEPCI ( n ) = 0.135 × CEPCI ( k 0 ) × exp A × ∑ k = k o n i k + B × P oil + C , with k 0 the first year of the period under consideration, i k the interest rate on US bank prime loans in year k , and P oil the US domestic oil price in year n. Best fit was obtained when choosing distinct sets of values of the constants A , B and C for each of the three periods 1958 to 1980; 1981 to 1999; and 2000 to 2011. These changes could have resulted from the impact of the oil shocks in the 1970s and very high interest rates in the 1980s, which perhaps heralded changes to the index formula in 1982 and 2002. The error was within 3% in any year from 1958 to 2011, and within 1% from 2004 to 2011 after readjusting the weighting of the price of oil. The correlation was applied to forecast the CEPCI under different scenarios modelled by the Energy Information Administration or predicted from oil futures contracts.

A fixed-bed reactor modeling study on the methanation of CO2

Abstract: The methanation of carbon dioxide has gained renewed interest during the last years as a possible technology to synthesize a feasible chemical energy carrier. This modeling study aims at a basic understanding of the aspects relevant for designing an externally cooled fixed-bed reactor for the methanation of a pure, stoichiometric feed gas. It is shown that the reaction rates and the exothermicity (ΔH° = −165 kJ/mol) prevent a fixed-bed reactor of technical dimensions to be operated at high conversions without runaway of the reactor. The model predictions of differently detailed pseudo-homogeneous reactor models and a heterogeneous reactor model where the intraparticle transport of mass is described according to a dusty-gas approach are compared to assess the needed level of detail in terms of modeling the heat transfer, fluid flow characteristics and transport resistances on the pellet scale. Under specific conditions, intraparticle mass transfer and external heat transfer need to be considered for describing the temperature and concentration profiles adequately. The study is completed by modeling a fixed-bed membrane reactor as an example of a structured reactor that offers improved temperature control by separated and controlled feeding of hydrogen and carbon dioxide.

ePC-SAFT revised

Abstract: So far, the electrolyte PC-SAFT equation of state developed in Cameretti et al. (2005) has been applied to model solution densities, vapor–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and solid–liquid equilibria (SLE) of solutions containing electrolytes. For that purpose, two ion-specific parameters were used to characterize any ion: the diameter of the solvated ion and the dispersion-energy parameter between ion and solvent. Dispersion was only considered between ions and solvents. Considering the small number of adjustable parameters, this approach yielded acceptable results especially for low and moderate electrolyte concentrations. However, for high salt concentrations, a distinct deviation between modeled and experimental data was observed. In this work a new modeling approach is suggested that accounts explicitly also for dispersion interactions between anions and cations. This yields a much more precise description of electrolyte solutions at higher concentrations compared to original ePC-SAFT. With this new approach it is also possible to directly model weak electrolyte solutions without using an additional approach that accounts for ion-pair formation. The new approach for applying ePC-SAFT is now able to model phase equilibria (VLE, LLE, SLE) of ternary electrolyte solutions containing water, organic solvents, salts, and amino acids even at high salt concentrations in good agreement with experimental data.

Solubility of CO2 in deep eutectic solvents: Experiments and modelling using the Peng-Robinson equation of state

Abstract: Carbon dioxide capture and sequestration is drawing increasing attention as a potential method for controlling greenhouse gas emissions Low cost ionic liquid analogues, namely, deep eutectic solvents (DESs), have attracted more attention for use in a diversity of applications DESs exhibit many favourable properties, such as availability, non-toxicity, biodegradability, recyclability, non-flammability, and low price In this work, phosphonium- and ammonium-based DESs with different hydrogen bond donors (HBD) have been synthesised Then, the CO 2 solubility in the synthesised DESs at a fixed pressure and temperature was determined, experimentally Furthermore, a mathematical model based on the Peng–Robinson (PR) equation of state (EoS) was developed to correlate the CO 2 solubility in these types of DESs The model was validated with the obtained experimental data and tested with other specific DESs reported in the literature over a wide range of temperature and pressure values In general, there was a good agreement between the experimental data and the calculated data using PR EoS The obtained model can be utilised to study the effectiveness of using DES in CO 2 capturing processes or any other separation processes

Modeling and kinetics study of conventional and assisted batch solvent extraction

Abstract: Batch solvent extraction techniques have been widely explored. On understanding its potential significance, this article aims to review kinetics and modeling of various extraction techniques which involve assisted means including microwave-assisted extraction (MAE), ultrasonicassisted extraction (UAE), pulse electric field (PEF) and high voltage electrical discharge (HVED). This review includes a detailed discussion of the instrumental setup, extraction mechanisms and their distinct advantages and disadvantages. Additionally, the impact of the operating parameters on the extraction kinetics of the mentioned techniques are highlighted. The review also covers the mathematical modeling based on Fick’s law, chemical rate law and empirical models. The established kinetic models of various extractions are also summarized to facilitate better understanding.

Asphaltene precipitation and deposition in oil reservoirs –technical aspects, experimental and hybrid neural network predictive tools

Abstract: Precipitation of asphaltene is considered as an undesired process during oil production via natural depletion and gas injection as it blocks the pore space and reduces the oil flow rate. In addition, it lessens the efficiency of the gas injection into oil reservoirs. This paper presents static and dynamic experiments conducted to investigate the effects of temperature, pressure, pressure drop, dilution ratio, and mixture compositions on asphaltene precipitation and deposition. Important technical aspects of asphaltene precipitation such as equation of state, analysis tools, and predictive methods are also discussed. Different methodologies to analyze asphaltene precipitation are reviewed, as well. Artificial neural networks (ANNs) joined with imperialist competitive algorithm (ICA) and particle swarm optimization (PSO) are employed to approximate asphaltene precipitation and deposition with and without CO2 injection. The connectionist model is built based on experimental data covering wide ranges of process and thermodynamic conditions. A good match was obtained between the real data and the model predictions. Temperature and pressure drop have the highest influence on asphaltene deposition during dynamic tests. ICA-ANN attains more reliable outputs compared with PSO-ANN, the conventional ANN, and scaling models. In addition, high pressure microscopy (HPM) technique leads to more accurate results compared with quantitative methods when studying asphaltene precipitation.

Enzymatic transesterification for production of biodiesel using yeast lipases: An overview

Abstract: Biodiesel has provided an eco-friendly solution to fuel crisis, as it is renewable, biodegradable and a non-toxic fuel that can be easily produced through enzymatic transesterification of vegetable oils and animal fats. Enzymatic production of biodiesel has many advantages over the conventional methods as high yields can be obtained at low reaction temperatures with easy recovery of glycerol. Microbial lipases are powerful biocatalysts for industrial applications including biodiesel production at lower costs due to its potential in hydrolyzing waste industrial materials. Among them, lipases from yeasts, Candida antarctica, Candida rugosa, Cryptococcus sp., Trichosporon asahii and Yarrowia lipolytica are known to catalyze such reactions. Moreover, stepwise addition of methanol in a three step, two step and single step reactions have been developed using yeast lipases to minimize the inhibitory effects of methanol. The latest trend in biodiesel production is the use of whole-cell as biocatalysts, since the process requires no downstream processing of the enzyme. Synthesis of value added products from the byproduct glycerol further reduces the production cost of biodiesel. This review aims at compiling the information on various yeast lipase catalyzed transesterification reactions for greener production of biodiesel.

A kinetic study of microwave and fluidized-bed drying of a Chinese lignite

Abstract: a b s t r a c t The drying kinetics of Chinese lignite in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave were investigated. The changes in the mass as a function of drying time were measured under various drying conditions. The variations of moisture ratio with time were used to test ten different thin-layer empirical drying models given in the literature. In studying the consistency of all the models, some statistical tests, such as � 2 , residual sum of squares (RSS) and F-value were also used as well as coefficient of determination R2. In nitrogen fluidized-bed and superheated steam fluidized-bed, the Midilli–Kucuk model best described the lignite drying process. Drying data in microwave were best described by the Page model, indicative of a difference in kinetics between the two drying methods. This difference was attributed to different heat transfer mechanisms under conventional and microwave drying conditions. The effects of drying parameters in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying on the constants and coefficients of the selected models were studied by multiple regression analysis. The apparent diffusion coefficient of moisture in samples was obtained from the kinetics data and the apparent activation energies under nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying were found to be rather similar.

Fabrication and characterization of Matrimid/MIL-53 mixed matrix membrane for CO2/CH4 separation

Abstract: In this study, gas separation properties of Matrimid/MIL-53 mixed matrix membranes with different MOF weight percentages (0–20 wt.%) were investigated. TEM, XRD and DLS analysis were implemented to investigate MIL-53, structure and particles size distribution. SEM, FTIR, DSC and TGA analyses were conducted to characterize the fabricated membranes. The SEM images of these membranes showed good adhesion between polymer and particles, although for 20% MIL-53 loading, particles agglomeration was observed in some areas. Moreover, surface images of the membranes showed adequate dispersion of the particles in the polymer matrix, especially at lower MOF loadings. The permeability of pure CO 2 and CH 4 gases for all membranes were measured and the ideal CO 2 /CH 4 selectivity was calculated. CH 4 permeability of membranes increased slightly as the percentage of loading increased. At 20 wt.% MOF loading, void formation led to a significant increase in CH 4 permeability (300% over pure Matrimid). CO 2 permeability showed the same trend; there was a 94% increase in permeability compared to pure Matrimid for 15 wt.% MMMs. CO 2 /CH 4 selectivity also increased as MOF loading increased. The highest selectivity was shown for 15 wt.% MOF loading. This membrane had 84% growth in selectivity over pure Matrimid. Although at 20 wt.% MIL-53 loading, membrane separation performance was destroyed.

Mixing performance of a planar micromixer with circular obstructions in a curved microchannel

Abstract: A numerical investigation of the mixing and fluid flow in a new design of passive micromixer employing several cylindrical obstructions within a curved microchannel is presented in this work. Mixing in the channels is analyzed using Navier–Stokes equations and the diffusion equation between two working fluids (water and ethanol) for Reynolds numbers from 0.1 to 60. The proposed micromixer shows far better mixing performance than a T-micromixer with circular obstructions and a simple curved micromixer. The effects of cross-sectional shape, height, and placement of the obstructions on mixing performance and the pressure drop of the proposed micromixer are evaluated.

Kinetics of ultrasound assisted extraction of anthocyanins from Aronia melanocarpa (black chokeberry) wastes

Abstract: Black chokeberry fruits are very rich in antioxidant phenolics. After juice extraction, the wastes of pressed berries (juice production by-products) still contain important amount of phenolic species and namely anthocyanins. Ultrasound assisted extraction (UAE) from such wastes was studied. The influence of extraction time (0–240 min), temperature (20–70 °C), solvent composition (0–50% ethanol in water) and ultrasound power (0–100 W) on anthocyanins and polyphenols yields and on antioxidant capacity of the extracts was studied. High temperature and ethanol content in the solvent improved greatly the extraction yields. Ultrasounds improved mainly the extraction kinetics. Ultrasound effect was higher in the beginning of extraction process and at low temperatures. Suitability of UAE for preparation of antioxidant-rich plant extracts at reduced time and energy was confirmed obtaining high extraction efficiencies and high antioxidant capacities of Aronia extracts. To optimize extraction conditions a kinetic mathematical model, based on Peleg's equation and considering also the rate of anthocyanins thermal degradation, was proposed. The influences of extraction time, temperature, solvent composition and ultrasound power on polyphenols and anthocyanins yields and on antioxidant capacity were considered. The optimal conditions for anthocyanins extraction predicted by this model were experimentally validated.

Stability and extraction study of phenolic wastewater treatment by supported liquid membrane using tributyl phosphate and sesame oil as liquid membrane

Abstract: Phenols pose a risk to the environment and to human health. Phenol and its derivatives are toxic pollutants, frequently found in surface and tap waters, and in aqueous effluents from various manufacturing processes. In this paper, an experimental study regarding transport of phenol through a supported liquid membrane (SLM) using tributyl phosphate (TBP) and sesame oil as liquid membrane (LM) was performed. Factors affecting permeation of phenol such as initial phenol concentration, carrier concentration, feed phase pH and stripping phase concentration were analyzed using Taguchi method. Optimal experimental condition of phenol transport was obtained using analysis of variance (ANOVA) after 7 h extraction (feed concentration: 200 mg/L; carrier concentration (%TBP): 40%; feed pH: 2; strip phase concentration: 1.1 M). Mass transfer coefficient for this system was evaluated, and compared with similar works, and it was shown that it has the highest mass transfer rate. In addition to transport study, stability of the membrane was investigated by examination of stripping phase concentration, carrier concentration and salt concentration effects.

Process performance in lignin separation from softwood black liquor by membrane filtration

Abstract: Black liquor is a side-stream in the production of kraft pulp. The extraction of lignin and hemicelluloses from black liquor would reduce the load on the recovery boiler and give valuable by-products. Lignin was separated from black liquor by membrane filtration, using one ceramic and three polymeric nanofiltration membranes, with molecular weight cut-offs in the range of 200 Da to 1 kDa. Ultrafiltration was tested as a form of pretreatment prior to nanofiltration to separate hemicelluloses from lignin. The use of ultrafiltration prior to nanofiltration increased the flux drastically in the nanofiltration step with three of the membranes. The ceramic membrane exhibited a higher flux and lower lignin retention than the polymeric membranes. The two membranes with a molecular weight cut-off of 1 kDa were found to have the best performance in parametric studies, and were therefore used in concentration studies. The results were used for a preliminary economic evaluation of the process. These calculations showed that the most cost-effective alternative for the extraction of lignin was with the polymeric 1 kDa membrane without pretreatment, and that the production cost for a lignin solution with a concentration of 230 g L−1 would be 46 € per ton of lignin.

Hexavalent chromium adsorption on superparamagnetic multi-wall carbon nanotubes and activated carbon composites

Abstract: Hexavalent chromium (Cr(VI)) adsorption from aqueous solutions on magnetically modified multi-wall carbon nanotubes (M-MWCNT) and activated carbon (M-AC) was investigated. M-MWCNT and M-AC were prepared by co-precipitation method with Fe 2+ :Fe 3+ salts as precursors. The magnetic adsorbents were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The effects of amount of adsorbents, contact time, initial pH, temperature and the initial concentration of Cr(VI) solution were determined. The adsorption equilibrium, kinetics, thermodynamics and desorption of Cr(VI) were investigated. Equilibrium data fitted well with the Langmuir isotherm for both of the adsorbents. The theoretical adsorption capacities are 14.28 mg/g of M-MWCNT and 2.84 mg/g of M-AC. Cr(VI) adsorption kinetics was modeled with pseudo-second order model, intra-particle diffusion model and Bangham model. Thermodynamic parameters were calculated and Δ G °, Δ H ° and Δ S ° indicate that the adsorption of Cr(VI) onto M-MWCNT and M-AC was exothermic and spontaneous in nature. Results revealed that M-MWCNT is an easily separated effective adsorbent for Cr(VI) adsorption from aqueous solution.

Heterogenization of the biodiesel synthesis catalysis: CaO and novel calcium compounds as transesterification catalysts

Abstract: Although CaO is one of the most studied basic heterogeneous catalysts for the synthesis of biodiesel, there are important issues that have been addressed by only a few research groups and that deserve further investigation. This is the case of the difficulties introduced by the poisoning of CaO upon exposure to ambient air and the role played by CaO-glycerol complexes on the catalytic performance. The purpose of this work is to provide new information on these issues in order to contribute to a better understanding of the underlying phenomena. Four commercial CaO samples have been considered to investigate their activation and stability under reaction conditions. In addition, calcium glyceroxide, and, for the first time, calcium glycerolate, have been synthesized and compared with the materials obtained from the commercial samples. The solids have been characterized with special emphasis on the assessment of their basic properties. The catalytic tests revealed big differences between the performance of the commercial solids that were substantially reduced after calcination and, specially, Ca-glyceroxide formation during reaction. Ca-glycerolate was the most resistant catalyst to ambient air although it was characterized by a low initial activity. Ca-glyceroxide could be reutilized for at least 5 reaction cycles without activity loss.

Roles of drag reducing polymers in single- and multi-phase flows

Abstract: It has become a well-known fact that finding sustainable solutions to the unavoidable high pressure losses accompanying pipeline flows to increase the pumping capacity without necessarily adding more pump stations is inevitable. Polymers, as one of the drag reducing agents which have been found to offer such an economic relieve, is the most widely investigated and most often employed in industries because they can produce drag reduction up to 80% when they are added in minute concentrations. In addition, polymer additives modify the flow configurations of multiphase flows to such an extent that stratification of individual phases is enhanced thereby making the separation of the phases at the fluid destination much easier. The achievements so far made and the challenges facing the use of polymers as drag reducers in turbulent single and multiphase flows are comprehensively reviewed. This review discusses the experimental studies of the effects of polymer additives in turbulent flows, the analytical studies, and the proposed models as well as the suggested mechanisms that explain the drag reduction. Likewise, specific areas of interest in the review include phenomena of drag reduction by polymers, factors influencing the effectiveness of the drag reducing polymers, methods of injecting the polymers into the base fluids, degradation of the polymers and industrial applications of polymers as drag reducing agents. The current and future research interests are also addressed. Although finding reveals that there are quite a lot of research in this area, most of the experimental and theoretical works are devoted to single phase flows while the remaining ones are mostly directed towards gas–liquid flows except in very recent time when investigation into the use of polymers in liquid–liquid flows is being focused. Despite this voluminous works on drag reducing polymers, there are no universally accepted models and hence the mechanisms of drag reductions by polymers.

Process intensification for heavy oil upgrading using supercritical water

Abstract: Demand for light hydrocarbons has been steadily increasing in the market with a corresponding decrease in heavy hydrocarbon demand. Therefore, there is a need to develop environmentally friendly and efficient technologies for conversion of heavy molecular weight hydrocarbons. Supercritical fluids (SCF) are attracting increased attention as solvents for green chemistry and among those supercritical water (SCH2O) is promising for the upgrading of heavy hydrocarbons. Because of a sharp decrease in its dielectric constant, water loses its polarity when brought to the supercritical conditions and its properties starts to resemble the properties of hydrocarbons and becomes an excellent solvent for organic compounds. Moreover, increased ionic product of water leads to an increasing [H3O+] concentration and thus promotes the reactions requiring the addition of an acid. Solvation power enables the extraction of lighter compounds while increased [H3O+] concentration makes the reactive extractions of heavy hydrocarbons possible. As a result of its favorable properties, a wide variety of process intensification studies have been carried out using near critical or SCH2O such as combined distillation-cracking-fractionation and in some cases even without the utilization of catalysts and/or hydrogen. In this review, recent advances on reactions of hydrocarbons occurring in a SCH2O environment will be highlighted. Fundamental aspects of these reactions including their thermodynamics and kinetics will be discussed. Experimental and theoretical developments on phase equilibria of relevant water–hydrocarbons systems will be presented.

Prediction of effective area and liquid hold-up in structured packings by CFD

Abstract: Interfacial effective area and liquid hold-up in structured packing geometries are investigated using the volume of fluid method. Three-dimensional numerical simulations of gas–liquid flow on inclined plane plate and in a structured packing are performed. The VOF method is used to capture the gas–liquid interface motion. After a first validation case on the wetting phenomena prediction on an inclined plane plate, the effective interfacial area, the liquid hold-up and the degree of wetting of packing are studied as function of liquid flow rate and wall surface characteristic (adherence contact angle). Results show that the liquid flow-rate and the contact angle play a significant role. It is found that the interfacial effective area and the degree of wetting of packing increase as the liquid flow rate increases and as the contact angle decreases. Moreover, under the influence of the contact angle, different liquid film shapes are observed. The simulations results are compared to experimental data available in literature. This work shows that the CFD is a powerful tool to investigate performance characteristics of structured packings. Moreover, this work shows how CFD can be used as an effective tool to provide information on fluid flow behavior and determination of interfacial area, liquid hold-up and minimum flow-rate to ensure complete wetting. These parameters could be further used in process simulation at larger scale for the development and the design of efficient packings.

Optimization of a plate-fin heat exchanger design through an improved multi-objective teaching-learning based optimization (MO-ITLBO) algorithm

Abstract: Teaching-learning-based optimization (TLBO) is a recently developed heuristic algorithm based on the natural phenomenon of teaching-learning process. In the present work, multi-objective improved teaching-learning-based optimization (MO-ITLBO) algorithm is introduced and applied for the multi-objective optimization of plate-fin heat exchangers. The basic TLBO algorithm is improved to enhance its exploration and exploitation capacities by introducing the concept of number of teachers, adaptive teaching factor, tutorial training and self-motivated learning. The MO-ITLBO algorithm uses a grid-based approach to adaptively assess the non-dominated solutions maintained in an external archive. Minimizing total annual cost and the total weight of heat exchanger as well as minimization of total pressure drop and maximization of heat exchanger effectiveness for specific heat duty requirement are considered as objective functions. Two application examples are presented to demonstrate the effectiveness and accuracy of the proposed algorithm.

Continuous electrochemical reduction of carbon dioxide into formate using a tin cathode: Comparison with lead cathode

Abstract: Electrochemical reduction has been pointed out as a promising method for CO 2 valorisation into useful chemicals. This paper studies the influence of key variables on the performance of an experimental system for continuous electro-reduction of CO 2 to formate, when a tin plate is used as working electrode. Particular emphasis is placed on comparing the performance of Sn and Pb as cathodes. As was previously found with Pb, the influence of current density (“ j ”) using Sn was particularly noteworthy, and when j was raised up to a limit value of 8.5 mA cm −2 , important increases of the rate of formate production were observed at the expense of lowering the Faradaic efficiency. However, unlike what was found with Pb, the performance using Sn improved when the electrolyte flow rate/electrode area ratio was increased within the range studied (0.57–2.3 mL min −1 cm −2 ). In this way, the use of Sn as cathode allowed achieving rates of formate production that were 25% higher than the maximum rates obtained with Pb, together with Faradaic efficiencies close to 70%, which were 15 points higher than those with Pb. These results reinforce the interest in Sn as electrode material in the electro-reduction of CO 2 to formate.

Adsorption of Cd(II), Hg(II) and Zn(II) from aqueous solution using mesoporous activated carbon produced from Bambusa vulgaris striata

Abstract: Mesoporous activated carbon (surface area of 608 m2/g) has achieved high efficiency in removal of cadmium, mercury and zinc ions from water solution The proposed low-cost adsorbent was physically activated with water steam from the bamboo species Bambusa vulgaris striata The batch studies suggested an activated carbon dose of 06 g/L, solution pH of 9 and an equilibrium time of 16 h in static conditions The pseudo-second order equations represented the adsorption kinetics with high correlation Fitting of the experimental results to the Langmuir, Freundlich, Redlich–Peterson and Toth isotherm models showed an almost homogeneous surface coverage and presence of physical adsorption The highest adsorption capacities, calculated from the Langmuir model, are 23945, 24805 and 25439 mg/g of cadmium, mercury and zinc, respectively

Diffusional mass transfer model for the adsorption of food dyes on chitosan films

Abstract: The adsorption kinetics of erythrosine B and indigo carmine on chitosan films was studied by a diffusional mass transfer model The experimental curves were obtained in batch system under different conditions of stirring rate (80–200 rpm) and initial dye concentration (20–100 mg L −1 ) For the model development, external mass transfer and intraparticle diffusion steps were considered and the specific simplifications were based on the system characteristics The proposed diffusional mass transfer model agreed very well with the experimental curves, indicating that the surface diffusion was the rate limiting step The external mass transfer coefficient ( k f ) was dependent of the operating conditions and ranged from 132 × 10 −4 to 217 × 10 −4 m s −1 The values of surface diffusion coefficient ( D s ) increased with the initial dye concentration and were in the range from 041 × 10 −14 to 2290 × 10 −14 m 2 s −1 The Biot number ranged from 170 to 4785, confirming that the intraparticle diffusion due to surface diffusion was the rate limiting step in the adsorption of erythrosine B and indigo carmine on chitosan films

Synthesis of biodiesel from Scenedesmus sp. by microwave and ultrasound assisted in situ transesterification using tungstated zirconia as a solid acid catalyst

Abstract: Copyright: 2014. Elsevier. Due to copyright restrictions, only the abstract is available. For access to the full text item, please consult the publisher's website. The definitive version of the work is published in Chemical Engineering Research and Design, August 2014, Vol. 92, Issue 8, pp. 1503-1511

Advanced oxidation removal of NO and SO2 from flue gas by using ultraviolet/H2O2/NaOH process

Abstract: In this article, the effects of several process parameters (energy density per unit solution, H2O2 concentration, NaOH concentration, gas flow, solution temperature, NO concentration, O2 concentration, SO2 concentration, Fe2+ concentration and t-butanol concentration) on removal of NO from flue gas by UV (Ultraviolet)/H2O2 advanced oxidation combining with NaOH absorption (UV/H2O2/NaOH process) were investigated in a photochemical reactor. The results indicate that under all experimental conditions, SO2 can be removed completely. Increasing H2O2 concentration, NaOH concentration, energy density per unit solution, t-butanol concentration and low concentration of Fe2+ have a significant role in promoting removal of NO. NO removal efficiency sharply reduces with the increase of gas flow, NO concentration and high concentration of Fe2+. NO removal is slightly inhibited by increasing solution temperature and SO2 concentration, but is slightly enhanced by increasing O2 concentration. Oxidation of NO by OH free radicals plays an important role in the removal of NO by UV/H2O2/NaOH process. NO3− is the final reaction product of NO removal by UV/H2O2/NaOH process. The reaction mechanism of NO removal by UV/H2O2/NaOH process has also been proposed.

Role of nanoparticles on nanofluid boiling phenomenon: Nanoparticle deposition

Abstract: Suspended nanoparticles inside the nanofluids can modify the characteristics of heated surfaces and the physical properties of the base liquids, offering a great opportunity to optimize boiling heat transfer. This paper reviews the mechanisms of nanoparticle deposition and the effects induced by deposited nanoparticles on surface roughness, force balance at the triple line, surface wettability, active nucleation site density, receding and advancing contact angles, boiling heat transfer coefficient and critical heat flux. Both enhancement and deterioration effects on boiling heat transfer coefficient and critical heat flux have been discussed. Most of the existing experimental data confirms the enhancement of critical heat flux using alumina nanofluid, however there is no consistency about its boiling heat transfer coefficient.

Application of quantitative Raman spectroscopy for the monitoring of polymorphic transformation in crystallization processes using a good calibration practice procedure

Abstract: Polymorphism is the property of a substance to have more than one crystalline form. Polymorphic forms of the same chemical compound can have different physical and chemical properties that can strongly affect the manufacturing process. For this reason, determining and monitoring polymorphic transformations have become very important, especially in pharmaceutical industry. Significant work has been developed for the calibration of Raman spectroscopy to monitor the presence and amount of solid polymorphs in suspensions during crystallization, as well as the liquid concentration. Nevertheless, a clear and systematic approach to Raman calibration is missing in the literature. The present work has the aim of developing a methodical strategy for Raman calibration, taking into account the principal factors that can affect the Raman spectra of a specific compound in solution, such as solid type, solute concentration, temperature, crystal size and suspension density. Univariate and multivariate calibration techniques were investigated using pre-processing techniques to optimize the signal. The results are combined in a systematic “good calibration practice” (GCP) procedure, proposed for the first time in this work. The approach has been applied for the quantitative monitoring of the polymorphic transformation of ortho-aminobenzoic acid (OABA).

Mass transfer from nanofluid drops in a pulsed liquid-liquid extraction column

Abstract: Mass transfer in gas–liquid systems has been significantly enhanced by recent developments in nanotechnology. However, the influence of nanoparticles in liquid–liquid systems has received much less attention. In the present study, both experimental and theoretical works were performed to investigate the influence of nanoparticles on the mass transfer behaviour of drops inside a pulsed liquid–liquid extraction column (PLLEC). The chemical system of kerosene–acetic acid–water was used, and the drops were organic nanofluids containing hydrophobic SiO2 nanoparticles at concentrations of 0.01, 0.05, and 0.1 vol%. The experimental results indicate that the addition of 0.1 vol% nanoparticles to the base fluid improves the mass transfer performance by up to 60%. The increase in mass transfer with increased nanoparticle content was more apparent for lower pulsation intensities (0.3–1.3 cm/s). At high pulsation intensities, the Sauter mean diameter (d32) decreased to smaller sizes (1.1–2.2 mm), leading to decreased Brownian motion in the nanoparticles. Using an analogy for heat and mass transfer, an approach for determining the mass diffusion coefficient was suggested. A new predictive correlation was proposed to calculate the effective diffusivity and mass transfer coefficient in terms of the nanoparticle volume fraction, Reynolds number, and Schmidt number. Finally, model predictions were directly compared with the experimental results for different nanofluids. The absolute average relative error (%AARE) of the proposed correlation for the mass transfer coefficient and effective diffusivity were 5.3% and 5.4%, respectively.