A reaction engineering approach to homogeneously catalyzed glycerol hydrochlorination

The production of biodiesel through transesterification has created a surplus of glycerol on the international market. In few years, glycerol has become an inexpensive and abundant raw material, subject to numerous plausible valorisation strategies. Glycerol hydrochlorination stands out as an economically attractive alternative to the production of biobased epichlorohydrin, an important raw material for the manufacturing of epoxy resins and plasticizers. Glycerol hydrochlorination using gaseous hydrogen chloride (HCl) was studied from a reaction engineering viewpoint. Firstly, a more general and rigorous kinetic model was derived based on a consistent reaction mechanism proposed in the literature. The model was validated with experimental data reported in the literature as well as with new data of our own. Semi-batch experiments were conducted in which the influence of the stirring speed, HCl partial pressure, catalyst concentration and temperature were thoroughly analysed and discussed. Acetic acid was used as a homogeneous catalyst for the experiments. For the first time, it was demonstrated that the liquid-phase volume undergoes a significant increase due to the accumulation of HCl in the liquid phase. Novel and relevant features concerning hydrochlorination kinetics, HCl solubility and mass transfer were investigated. An extended reaction mechanism was proposed and a new kinetic model was derived. The model was tested with the experimental data by means of regression analysis, in which kinetic and mass transfer parameters were successfully estimated. A dimensionless number, called Catalyst Modulus, was proposed as a tool for corroborating the kinetic model. Reactive flash distillation experiments were conducted to check the commonly accepted hypothesis that removal of water should enhance the glycerol hydrochlorination kinetics. The performance of the reactive flash distillation experiments were compared to the semi-batch data previously obtained. An unforeseen effect was observed once the water was let to be stripped out from the liquid phase, exposing a strong correlation between the HCl liquid uptake and the presence of water in the system. Water has revealed to play an important role also in the HCl dissociation: as water was removed, the dissociation of HCl was diminished, which had a retarding effect on the reaction kinetics. In order to obtain a further insight on the influence of water on the hydrochlorination reaction, extra semi-batch experiments were conducted in which initial amounts of water and the desired product were added. This study revealed the possibility to use the desired product as an ideal “solvent” for the glycerol hydrochlorination process. A co-current bubble column was used to investigate the glycerol hydrochlorination process under continuous operation. The influence of liquid flow rate, gas flow rate, temperature and catalyst concentration on the glycerol conversion and product distribution was studied. The fluid dynamics of the system showed a remarkable behaviour, which was carefully investigated and described. Highspeed camera images and residence time distribution experiments were conducted to collect relevant information about the flow conditions inside the tube. A model based on the axial dispersion concept was proposed and confronted with the experimental data. The kinetic and solubility parameters estimated from the semi-batch experiments were successfully used in the description of mass transfer and fluid dynamics of the bubble column reactor. In light of the results brought by the present work, the glycerol hydrochlorination reaction mechanism has been finally clarified. It has been demonstrated that the reactive distillation technology may cause drawbacks to the glycerol hydrochlorination reaction rate under certain conditions. Furthermore, continuous reactor technology showed a high selectivity towards monochlorohydrins, whilst semibatch technology was demonstrated to be more efficient towards the production of dichlorohydrins. Based on the novel and revealing discoveries brought by the present work, many insightful suggestions are made towards the improvement of the production of αγ-dichlorohydrin on an industrial scale.

Flow injection analysis (FIA) determination of lead by hydride generation in banded coral skeletons /

A flow injection hydride generation direct current plasma atomic emission spectrometric (FI-HG-DCP-AES) method was developed for the determination of lead at ng.ml-l level. Potassium ferricyanide (K3Fe(CN)6) was used along with sodium tetrahydroborate(III) (NaBH4) to produce plumbane (PbH4) in an acid medium. The design of a gas-liquid separator (hydride generator) was tested and the parameters of the flow injection system were optimized to achieve a good detection limit and sample throughput. The technique developed gave a detection limit of 0.7 ng.ml-l(3ob). The precision at 20 ng.ml"* level was 1.6 % RSD with 1 1 measurements (n=l 1). Volume of sample loop was 500 |J.l. A sample throughput of 120 h"^ was achieved. The transition elements, Fe(II), FeOH), Cd(n), Co(II), Mn(n), Ni(II) and Zn(n) do not interfere in this method but 1 mg,l'l Cu(II) will suppress 50 % of the signal from a sample containing 20 ng.ml'l Pb. This method was successfully applied to determine lead in a calcium carbonate (CaC03) matrix of banded coral skeletons from Si-Chang Island in Thailand.

Sample preparation and heavy metal determination by atomic spectrometry /

Microwave digestions of mercury in Standards Reference Material (SRM) coal samples with nitric acid and hydrogen peroxide in quartz vessels were compared with Teflon® vessel digestion by using flow injection cold vapor atomic absorption spectrometry. Teflon® vessels gave poor reproducibiUty and tended to deliver high values, while the digestion results from quartz vessel show good agreement with certificate values and better standard deviations. Trace level elements (Ag, Ba, Cd, Cr, Co, Cu, Fe, Mg, Mn, Mo, Pb, Sn, Ti, V and Zn) in used oil and residual oil samples were determined by inductively coupled plasma-optical emission spectrometry. Different microwave digestion programs were developed for each sample and most of the results are in good agreement with certified values. The disagreement with values for Ag was due to the precipitation of Ag in sample; while Sn, V and Zn values had good recoveries from the spike test, which suggests that these certified values might need to be reconsidered. Gold, silver, copper, cadmium, cobalt, nickel and zinc were determined by continuous hydride generation inductively coupled plasma-optical emission spectrometry. The performance of two sample introduction systems: MSIS™ and gas-liquid separator were compared. Under the respective optimum conditions, MSIS^"^ showed better sensitivity and lower detection limits for Ag, Cd, Cu, Co and similar values for Au, Ni and Zn to those for the gas-liquid separator.

Investigations in flow injection analysis (FIA): conventional FIA determination of chloride in water; sequential injection (SI)-FIA determination of mercury in water

Flow injection analysis (FIA) was applied to the determination of both chloride ion and mercury in water. Conventional FIA was employed for the chloride study. Investigations of the Fe3 +/Hg(SCN)2/CI-,450 nm spectrophotometric system for chloride determination led to the discovery of an absorbance in the 250-260 nm region when Hg(SCN)2 and CI- are combined in solution, in the absence of iron(III). Employing an in-house FIA system, absorbance observed at 254 nm exhibited a linear relation from essentially 0 - 2000 Jlg ml- 1 injected chloride. This linear range spanning three orders of magnitude is superior to the Fe3+/Hg(SCN)2/CI- system currently employed by laboratories worldwide. The detection limit obtainable with the proposed method was determin~d to be 0.16 Jlg ml- 1 and the relative standard deviation was determined to be 3.5 % over the concentration range of 0-200 Jig ml- 1. Other halogen ions were found to interfere with chloride determination at 254 nm whereas cations did not interfere. This system was successfully applied to the determination of chloride ion in laboratory water. Sequential injection (SI)-FIA was employed for mercury determination in water with the PSA Galahad mercury amalgamation, and Merlin mercury fluorescence detection systems. Initial mercury in air determinations involved injections of mercury saturated air directly into the Galahad whereas mercury in water determinations involved solution delivery via peristaltic pump to a gas/liquid separator, after reduction by stannous chloride. A series of changes were made to the internal hardware and valving systems of the Galahad mercury preconcentrator. Sequential injection solution delivery replaced the continuous peristaltic pump system and computer control was implemented to control and integrate all aspects of solution delivery, sample preconcentration and signal processing. Detection limits currently obtainable with this system are 0.1 ng ml-1 HgO.

Impact of considering the effects of latent heat on caldera-hosted hydrothermal systems

To investigate the thennal effects of latent heat in hydrothennal settings, an extension was made to the existing finite-element numerical modelling software, Aquarius. The latent heat algorithm was validated using a series of column models, which analysed the effects of penneability (flow rate), thennal gradient, and position along the two-phase curve (pressure). Increasing the flow rate and pressure increases displacement of the liquid-steam boundary from an initial position detennined without accounting for latent heat while increasing the thennal gradient decreases that displacement. Application to a regional scale model of a caldera-hosted hydrothennal system based on a representative suite of calderas (e.g., Yellowstone, Creede, Valles Grande) led to oscillations in the model solution. Oscillations can be reduced or eliminated by mesh refinement, which requires greater computation effort. Results indicate that latent heat should be accounted for to accurately model phase change conditions in hydrothennal settings.

Preferred structures in large-scale circulation and the effect of doubling greenhouse gas concentration in HadCM3

Preferred structures in the surface pressure variability are investigated in and compared between two 100-year simulations of the Hadley Centre climate model HadCM3. In the first (control) simulation, the model is forced with pre-industrial carbon dioxide concentration (1×CO2) and in the second simulation the model is forced with doubled CO2 concentration (2×CO2). Daily winter (December-January-February) surface pressures over the Northern Hemisphere are analysed. The identification of preferred patterns is addressed using multivariate mixture models. For the control simulation, two significant flow regimes are obtained at 5% and 2.5% significance levels within the state space spanned by the leading two principal components. They show a high pressure centre over the North Pacific/Aleutian Islands associated with a low pressure centre over the North Atlantic, and its reverse. For the 2×CO2 simulation, no such behaviour is obtained. At higher-dimensional state space, flow patterns are obtained from both simulations. They are found to be significant at the 1% level for the control simulation and at the 2.5% level for the 2×CO2 simulation. Hence under CO2 doubling, regime behaviour in the large-scale wave dynamics weakens. Doubling greenhouse gas concentration affects both the frequency of occurrence of regimes and also the pattern structures. The less frequent regime becomes amplified and the more frequent regime weakens. The largest change is observed over the Pacific where a significant deepening of the Aleutian low is obtained under CO2 doubling.

Self-assembly of two-component gels: stoichiometric control and component selection

Two-component systems capable of self-assembling into soft gel-phase materials are of considerable interest due to their tunability and versatility. This paper investigates two-component gels based on a combination of a L-lysine-based dendron and a rigid diamine spacer (1,4-diaminobenzene or 1,4-diaminocyclohexane). The networked gelator was investigated using thermal measurements, circular dichroism, NMR spectroscopy and small angle neutron scattering (SANS) giving insight into the macroscopic properties, nanostructure and molecular-scale organisation. Surprisingly, all of these techniques confirmed that irrespective of the molar ratio of the components employed, the "solid-like" gel network always consisted of a 1:1 mixture of dendron/diamine. Additionally, the gel network was able to tolerate a significant excess of diamine in the "liquid-like" phase before being disrupted. In the light of this observation, we investigated the ability of the gel network structure to evolve from mixtures of different aromatic diamines present in excess. We found that these two-component gels assembled in a component-selective manner, with the dendron preferentially recognising 1,4-diaminobenzene (>70%). when similar competitor diamines (1,2- and 1,3-diaminobenzene) are present. Furthermore, NMR relaxation measurements demonstrated that the gel based oil 1,4-diaminobenzene was better able to form a selective ternary complex with pyrene than the gel based oil 1,4-diaminocyclohexane, indicative of controlled and selective pi-pi interactions within a three-component assembly. As such, the results ill this paper demonstrate how component selection processes in two-component gel systems call control hierarchical self-assembly.

Chapter 17: X-Ray rheology of liquid crystal polymers

X-ray Rheology is an experimental technique which uses time-ressolved x-ray scattering as probe of the molecular level structural reorganisation which accompanies flow. It provides quantitative information on the direction alignment and on the level of global orientation. This information is very helpful in interpreting the classic rheological data on liquid crystal polymers. In this research we use data obtained from a cellulose derivate which exhibits a thermotropic liquid crystal phase. We show how increased shear rates lead to a rapid rise in the global orientation and we related this to therories of flow in liquid crystal polymers from the literature. We show that the relaxation time is independent of the prior shear rate.

Room Temperature Ionic Liquid-Lithium Salt Mixtures: Optical Kerr Effect Dynamical Measurements

The addition of lithium salts to ionic liquids causes an increase in viscosity and a decrease in ionic mobility that hinders their possible application as an alternative solvent in lithium ion batteries. Optically heterodyne-detected optical Kerr effect spectroscopy was used to study the change in dynamics, principally orientational relaxation, caused by the addition of lithium bis(trifluoromethylsulfonyl)imide to the ionic liquid 1-buty1-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Over the time scales studied (1 ps-16 ns) for the pure ionic liquid, two temperature-independent power laws were observed: the intermediate power law (1 ps to similar to 1 ns), followed by the von Schweidler power law. The von Schweidler power law is followed by the final complete exponential relaxation, which is highly sensitive to temperature. The lithium salt concentration, however, was found to affect both power laws, and a discontinuity could be found in the trend observed for the intermediate power law when the concentration (mole fraction) of lithium salt is close to chi(LiTf(2)N) = 0.2. A mode coupling theory (MCT) schematic model was also used to fit the data for both the pure ionic liquid and the different salt concentration mixtures. It was found that dynamics in both types of liquids are described very well by MCT.

Estudo numérico de escoamento turbulento em padrão anular gás-líquido em dutos verticais

Multiphase flows in ducts can adopt several morphologies depending on the mass fluxes and the fluids properties. Annular flow is one of the most frequently encountered flow patterns in industrial applications. For gas liquid systems, it consists of a liquid film flowing adjacent to the wall and a gas core flowing in the center of the duct. This work presents a numerical study of this flow pattern in gas liquid systems in vertical ducts. For this, a solution algorithm was developed and implemented in FORTRAN 90 to numerically solve the governing transport equations. The mass and momentum conservation equations are solved simultaneously from the wall to the center of the duct, using the Finite Volumes Technique. Momentum conservation in the gas liquid interface is enforced using an equivalent effective viscosity, which also allows for the solution of both velocity fields in a single system of equations. In this way, the velocity distributions across the gas core and the liquid film are obtained iteratively, together with the global pressure gradient and the liquid film thickness. Convergence criteria are based upon satisfaction of mass balance within the liquid film and the gas core. For system closure, two different approaches are presented for the calculation of the radial turbulent viscosity distribution within the liquid film and the gas core. The first one combines a k- Ɛ one-equation model and a low Reynolds k-Ɛ model. The second one uses a low Reynolds k- Ɛ model to compute the eddy viscosity profile from the center of the duct right to the wall. Appropriate interfacial values for k e Ɛ are proposed, based on concepts and ideas previously used, with success, in stratified gas liquid flow. The proposed approaches are compared with an algebraic model found in the literature, specifically devised for annular gas liquid flow, using available experimental results. This also serves as a validation of the solution algorithm

Utilização de uma coluna de flotação para remoção de compostos orgânicos da água de produção

Innovative technologies using surfactant materials have applicability in several industrial fields, including petroleum and gas areas. This study seeks to investigate the use of a surfactant derived from coconut oil (SCO saponified coconut oil) in the recovery process of organic compounds that are present in oily effluents from petroleum industry. For this end, experiments were accomplished in a column of small dimension objectifying to verify the influence of the surfactant SCO in the efficiency of oil removal. This way, they were prepared emulsions with amount it fastens of oil (50, 100, 200 and 400 ppm), being determined the great concentrations of surfactant for each one of them. Some rehearsals were still accomplished with produced water of the industry of the petroleum to compare the result with the one of the emulsions. According to the experiments, it was verified that an increase of the surfactant concentration does not implicate in a greater oil removal. The separation process use gaseous bubbles formed when a gas stream pass a liquid column, when low surfactant concentrations are used, it occurs the coalescence of the dispersed oil droplets and their transport to the top of the column, forming a new continuous phase. Such surfactants lead to a gas-liquid interface saturation, depending on the used surfactant concentration, affecting the flotation process and influencing in the removal capacity of the oily dispersed phase. A porous plate filter, with pore size varying from 40 to 250 mm, was placed at the base of the column to allow a hydrodynamic stable operation. During the experimental procedures, the operating volume of phase liquid was held constant and the rate of air flow varied in each experiment. The resulting experimental of the study hydrodynamic demonstrated what the capturing of the oil was influenced by diameter of the bubbles and air flow. With the increase flow of 300 about to 900 cm3.min-1, occurred an increase in the removal of oil phase of 44% about to 66% and the removal kinetic of oil was defined as a reaction of 1° order

Physicochemical Characterization and Rheological Behavior Evaluation of the Liquid Crystalline Mesophases Developed with Different Silicones

This article presented physicochemical characterization and rheological behavior evaluation of the liquid crystalline mesophases developed with different silicones. There were prepared 5 ternary systems, which were carried out the determination of the relative density, the electric conductivity and polarized light microscopy analysis, being selected two systems to promote the Preliminary Stability Tests. The results showed that System 1 obtained the major liquid crystal formation and a higher stability. The temperature influences in the systems stability and phases structure. In hot oven, observed oneself the mixture of lamellar and hexagonal phase, for both systems.

A model to predict R134a refrigerant leakage through the radial clearance of rolling piston compressors

In this paper a non-isothermal two-phase model for oil-R134a refrigerant mixture flow is presented to predict the R134a leakage through the radial clearance of rolling piston compressors. The flow is divided in a liquid single-phase region and in a two-phase region, in which the homogeneous model is used to simulate the flow. The refrigerant leakage is determined using the mixture mass flow rate and the refrigerant mass fraction variation along the flow. The results are obtained for inlet pressures varying from 200 to 700 kPa, inlet temperatures ranging from 40 to 60 degrees C, and minimal clearances between 10 and 60 mu m. The results are firstly compared to existing isothermal model data, showing that there is a significant difference between the leakage flow rates predicted by isothermal and non-isothermal models. Finally, a useful general equation for compressor designers is proposed to calculate the refrigerant leakage for a large range of operation conditions. (C) 2012 Elsevier Ltd and IIR. All rights reserved.

Utilização de uma coluna de flotação para remoção de compostos orgânicos da água de produção

Innovative technologies using surfactant materials have applicability in several industrial fields, including petroleum and gas areas. This study seeks to investigate the use of a surfactant derived from coconut oil (SCO saponified coconut oil) in the recovery process of organic compounds that are present in oily effluents from petroleum industry. For this end, experiments were accomplished in a column of small dimension objectifying to verify the influence of the surfactant SCO in the efficiency of oil removal. This way, they were prepared emulsions with amount it fastens of oil (50, 100, 200 and 400 ppm), being determined the great concentrations of surfactant for each one of them. Some rehearsals were still accomplished with produced water of the industry of the petroleum to compare the result with the one of the emulsions. According to the experiments, it was verified that an increase of the surfactant concentration does not implicate in a greater oil removal. The separation process use gaseous bubbles formed when a gas stream pass a liquid column, when low surfactant concentrations are used, it occurs the coalescence of the dispersed oil droplets and their transport to the top of the column, forming a new continuous phase. Such surfactants lead to a gas-liquid interface saturation, depending on the used surfactant concentration, affecting the flotation process and influencing in the removal capacity of the oily dispersed phase. A porous plate filter, with pore size varying from 40 to 250 mm, was placed at the base of the column to allow a hydrodynamic stable operation. During the experimental procedures, the operating volume of phase liquid was held constant and the rate of air flow varied in each experiment. The resulting experimental of the study hydrodynamic demonstrated what the capturing of the oil was influenced by diameter of the bubbles and air flow. With the increase flow of 300 about to 900 cm3.min-1, occurred an increase in the removal of oil phase of 44% about to 66% and the removal kinetic of oil was defined as a reaction of 1° order.

Phase diagrams of a CTAB/organic solvent/buffer system applied to extraction of enzymes by reverse micelles

A partial pseudo-ternary phase diagram has been studied for the cethyltrimethylammonium bromide/isooctane:hexanol:butanol/potassium phosphate buffer system, where the two-phase diagram consisting of the reverse micelle phase (L-2) in equilibrium with the solvent is indicated. Based on these diagrams two-phase systems of reverse micelles were prepared with different compositions of the compounds and used for extraction and recovery of two enzymes, and the percentage of enzyme recovery yield monitored. The enzymes glucose-6-phosphate dehydrogenase (G6PD) and xylose redutase (XR) obtained from Candida guilliermondii yeast were used in the extraction procedures. The recovery yield data indicate that micelles having different composition give selective extraction of enzymes. The method can thus be used to optimize enzyme extraction processes. (c) 2007 Elsevier B.V. All rights reserved.