Search

Formic acid is one of the key components in green chemistry being involved in energy storage, production of chemical intermediates and fuel components. Therefore the knowledge of its stability is of crucial importance and a systematic study of its decomposition is needed. The kinetics of formic acid decomposition to hydrogen and carbon dioxide was investigated in a laboratory-scale fixed bed reactor at 150–225 °C and atmospheric pressure. Palladium nanoparticles deposited on porous active carbon Sibunit were used as the heterogeneous catalyst. The catalyst was characterized by nitrogen physisorption and high-resolution transmission electron microscopy. The average palladium nanoparticle size was 5–6 nm. The impacts of mass transfer resistance and formic acid dimerization were negligible under the reaction conditions. Prolonged experiments revealed that the catalyst had a good stability. Hydrogen and carbon dioxide were the absolutely dominant reaction products, whereas the amounts of carbon monoxide and water were negligible. The experimental data were described with three kinetic models: first order kinetics, two-step adsorption-reaction model and multistep adsorption-decomposition model of formic acid. The multistep model gave the best description of the data.

This work describes an effective method for the preparation of open-cell ceramic foams for their further use as catalyst supports. The polyurethane sponge replica technique was applied using a ceramic suspension based on a mixture of α-alumina, magnesia and titania and polyvinyl alcohol solution as a liquid component. The polyurethane sponge was etched with NaOH and covered with colloidal silica to obtain better adhesion of the slurry to the walls of the polymeric material onto it. The surface area of the ceramic carrier was increased by adding a layer of γ-alumina. Deposition of an active catalytic phase (Pt) was done by impregnation. Properties of the carriers and the final catalyst were investigated by a number of physico-chemical methods such as TEM, SEM, XRD and computer tomography. Hydrogenation of ethyl benzoylformate was performed to elucidate the catalytic properties of foam catalysts illustrating their applicability.

Direct epoxidation of light olefin mixtures with hydrogen peroxide and titanium silicalite (TS-1) catalyst is interesting from a pure scientific viewpoint and it might have a considerable economic and environmental advantages. Direct epoxidation of olefin mixtures implies a significant process intensification as the separation steps of alkenes prior to the epoxidation process is avoided. Binary and ternary mixtures of ethene, oxide and 1-butene were selectively epoxidized with hydrogen peroxide in the presence of TS-1 as the heterogeneous catalyst. Methanol was used as the solvent. Transient and stationary kinetic experiments were conducted in a laboratory-scale trickle bed reactor, which was operated under atmospheric pressure and isothermal conditions at 15–55 °C. The experiments were designed to investigate the kinetics of the epoxidation of light olefins at different temperatures, alkene-to-hydrogen peroxide molar ratios as well as gas and liquid residence times in the trickle bed reactor. The recorded transient responses of the reaction products confirmed that the components in the alkene mixtures are epoxidized simultaneously. The epoxide selectivity was 90 % or higher in most experiments; ring-opening products formed from the epoxides and methanol were observed as by-products. The concentration maxima of epoxides during the transient experiments were explained by accumulation of the epoxide products inside the catalyst, which resulted in partial blocking of active sites. After-treatment of the catalyst with methanol and nitrogen completely restored the initial activity. Kinetic modeling was applied, based on presumed elementary steps on the TS-1 surface to describe the behavior of the system at steady state conditions. The trickle bed reactor was described with a dynamic multiphase model, taking into account the kinetic and mass transfer effects. The numerical values of the activation energies, kinetic constants and mass transfer parameters were estimated by nonlinear regression analysis. The model gave a satisfactory description of the experimental data.

Oxidation of sugars from hemicelluloses represents an important lignocellulosic biomass valorization process and has been considered as an option to decrease high dependency of chemical industry on fossil feedstock. Gold nanoparticles as an arabinose oxidation catalyst under alkaline conditions result in high selectivity towards aldonic acids. In this work, kinetics of selective oxidation of l -arabinose to arabinonic acid over Au/Al2O3 was studied using data from experiments in a semibatch shaker reactor under pH-controlled conditions at atmospheric pressure. A novel model considering molecular adsorption of oxygen, production of H2O2 and different skeletal isomers of arabinose as reactants is reported. An experiment with d -arabinose was carried out in a conventional semibatch reactor and the model adequately predicted the results.

International audience; Epoxidation of oleic acid by peracetic acid (PAA) was studied in a recycled reactor system under conventional heating and microwave irradiation. This reaction system consists of several steps. Thus, a kinetic modelling strategy to diminish the number of parameters to be estimated was developed by investigating each reaction step: PAA synthesis and decomposition, epoxidation and ring-opening. The energy balance for microwave heating was correlated with the concentration of the microwave-absorbent species and the total input power of the microwaves. The epoxidation reaction was conducted in the vigorously stirred tank reactor under isothermal conditions within a temperature range of 50–70 °C. The organic phase content was 32–45% v/v. The interfacial mass transfer was supposed to be faster than the intrinsic reaction kinetics suppressing the use of mass transfer correlations. Nonlinear regression was used to estimate the kinetic parameters. Two models were developed for microwave and conventional heating respectively. The perhydrolysis showed to be the slowest reaction, followed by the epoxidation and the ring-opening. The use of microwave irradiation resulted in considerable process intensification for the epoxidation process. By employing microwave heating, the perhydrolysis step in the aqueous phase was enhanced, and the reaction time was reduced by 50% in best cases, which implies that the reactor size can be diminished by microwave technology.

A mathematical model for the synthesis of sodium borohydride (NaBH4) from finely dispersed solid sodium hydride (NaH) and dissolved trimethyl borate (B(OH)3) in inert mineral oil was developed. The model is based on a plausible reaction mechanism of dissolved and adsorbed trimethyl borate on the surface of sodium hydride, where the reaction is presumed to take place. The surface reaction between sodium hydride and trimethyl borate leads to the formation of main (NaBH4) and side products (methoxy borohydrides), which was verified by chemical analysis of sodium borohydride and methanol in the water extract of the oil phase. Extensive kinetic experiments in a laboratory-scale isothermal and isobaric slurry reactor enabled a detailed kinetic analysis of the data, including the derivation of a mathematical model for the formation of sodium borohydride in a semibatch slurry reactor. The kinetic model was verified with experimental information and can be used as an element for process design.

Oxychlorination of ethene was conducted in a microreactor (150–375 °C) over a thin layer of CeO2 prepared in the current work with the specific surface area of 80 m2/g and compared with the same reaction in millireactors (250–500 °C). The kinetic analysis revealed influence of the ethene concentration on the apparent activation energy which was different in micro- and millireactors. The previously developed reaction network was completed by including two parallel reactions for formation of ethylchloride and vinylchloride and two consecutive reactions accounting for formation of dichloroethane and vinylchloride via ethyl chloride. The reaction orders with respect to HCl and O2 in the microreactor were comparable with the literature data for millireactors. Kinetic modeling was successfully carried for all reactants by using a steady state model of a packed bed reactor.

A new bis-layered supported ionic liquid catalyst (SILCA) loaded with palladium was designed and successfully applied for the Heck reaction of iodobenzene and methyl acrylate. The silica modified c ...

In this study, protein isolate was prepared from Baltic herring (Clupea harengus membras) using alkaline pH-shift process. The aim of this research was to characterize the protein isolate and to study its potential in food models. A special focus was placed on characterization of odour profile and volatile compounds contributing to the odour profile of the protein isolate using gas chromatography - olfactometry. 2,3-Pentanedione, hexanal, 4(Z)-heptenal, 2,4(E,E)-nonadienal, and three compounds tentatively identified as 1,5(E)-octadien-3-ol, 1,5(Z)-octadien-3-ol, and 1,5(Z)-octadien-3-one were the most important odour-contributing compounds in the protein isolate (Nasal Impact Factor 83-100%, intensity 2.6-3.3 on a scale 0-4). 2-Methylpropanal, 2- and 3-methylbutanal, and three unknown compounds were less intense in the protein isolate than in the raw material, which might have contributed to the lower intensity of fishiness observed for the protein isolate (2.2 vs 3.3 on a scale 0-4). Surimi-type gels prepared from the Baltic herring protein isolate had texture properties (hardness and cohesiveness) similar to those of commercial products. Due to the abundancy of dark muscle tissue in Baltic herring, the protein isolate had a significantly lower whiteness (W = 63) compared to the commercial surimi products (W = 80-83). Increasing the solubilisation or precipitation pH did not improve the whiteness, but resulted in significantly softer, less cohesive, and less chewy gels. The findings of this study indicate that alkaline-based pH-shift processing is a potential way to increase the food application of Baltic herring.

The kinetics of formation and decomposition of peroxyformic acid was studied. From experimental evidences taken from literature, we noticed the decomposition reaction depends on the source of the hydrogen peroxide used as a reactant, so we focused on the idea that stabilizing agents present in the hydrogen peroxide solutions affect the reaction rate, inhibiting the peracid decomposition. The nature of the stabilizing agents and the concentration used might in fact change from a supplier to another. A kinetic model was proposed, in which the decomposition model takes into account this effect and, as a first approximation, the stabilizing agent concentration is quantified indirectly through the initial concentration of hydrogen peroxide loaded in the reactive system. The present model aims to lay the foundations for a new approach to the study of the decomposition of peracids in reactive systems.

Main obstacle for adopting continuous processes as a standard technology for Mizoroki-Heck reaction usually lies in its specific reaction mechanism. Here we present an important step forward answering the challenges unraveled through a comprehensive study that provides deeper understanding on the Mizoroki-Heck reaction, in particular the case when iodobenzene and butyl acrylate react in a continuous packed bed reactor in the presence of a Pd Supported Ionic Liquid Catalyst (SILCA). On-line UV–VIS spectrometry supported by ICP-OES, TEM and XPS measurements were carried out and the catalyst leaching was minimized. Finally, simple continuous flow process was proposed resulting in a high catalytic activity (up to 1470 molArI molPd−1h−1) and reaching productivity in the range of 12,000 to 16,000 molArI molPd−1 thus competing with the performance of commercial catalysts. Volume 433, Part 1.

The immobilized enzyme lipase acts as an efficient, selective and durable catalyst in the direct transformation of unsaturated carboxylic acids to epoxides, which are used as chemical intermediates and bio-lubricants. Experimental data obtained from the epoxidation of a model molecule, oleic acid in a laboratory-scale isothermal batch reactor were critically evaluated and mathematically modelled in the most precise way. Several rival surface reaction mechanisms were proposed and rate equations based on these mechanisms were derived. The rate equations were implemented in a multiphase model for the laboratory-scale batch reactor and the kinetic and adsorption parameters included in the rate equations were estimated with non-linear regression analysis. Based on the parameter estimation statistics and chemical knowledge, the most plausible kinetic models for the chemo-enzymatic epoxidation of oleic acid on the immobilized lipase catalyst were selected. The best kinetic models gave a good reproduction of the experimental data. The models can be used to predict the performance of enzymatic epoxidation of unsaturated fatty acids.

Oxychlorination of ethene was performed over CuCl2/γ-Al2O3 catalyst in a microreactor (460 µm in diameter) and for comparison in a millireactor (1 cm in diameter). A copper-modified catalyst was prepared by a conventional evaporation–impregnation method without any promotors (e.g., K, Na, La) using copper (II) chloride as a precursor. The catalyst was characterized by nitrogen physisorption , Fourier transform infrared spectroscopy using pyridine , temperature-programmed desorption of CO 2, scanning electron microscopy, energy-dispersive X-ray microanalysis, and transmission electron microscopy. Different reactor types led to notable differences in catalytic performance at the same partial pressures in terms of both activity and selectivity. A higher reaction rate was achieved in the microreactor, which was 4.5 times faster. The activity decline and different selectivity to the desired product are explained by a change in the oxychlorination mechanism due to a different ratio of reagents in the mixture during the reaction.

Five different support materials were modified with 5 wt.% Cu, using an evaporation impregnation method. The synthesized CuCl 2 /γ-Al 2 O 3 , CuCl 2 /TiO 2 (Hombikat), CuCl 2 /TiO 2 (Alfa Aesar), CuCl 2 /SiO 2 and CuCl 2 /H-Beta-25 materials were characterized by nitrogen physisorption, X-ray powder diffraction, scanning electron microscopy, energy dispersive Xray microanalysis, transmission electron microscopy, Fourier transform infrared spectroscopy and CO 2 -temperature programmed desorption. The physical-chemical characterization was correlated with catalytic activity, stability and selectivity in the ethylene oxychlorination. It was found that γ-Al 2 O 3 and TiO 2 support materials demonstrate very good activity and 1,2dichloroethane selectivity compare to other catalysts. Zeolite H-Beta-25 and SiO 2 support materials proved to be unusable for this reaction.

Extraction of hemicelluloses with subcritical water is an efficient and environmentally benign way of fractionating biomass, including lignocelluloses. The composition and extraction behavior of hemicelluloses from wood depends significantly on the species, which affects the obtained product and the requirements of the extraction process. The current work focuses on the extraction of hemicelluloses from three chemically and structurally different, interesting and economically important tree species namely stone pine ( Pinus pinea ), holm oak ( Quercus ilex ), and Norway spruce ( Picea abies ), for which the literature on holm oak and stone pine hemicelluloses is almost non-existent. The work was performed with identical experimental methods, to obtain completely comparable results. The effect of temperature, raw material and solid-liquid ratio on the extraction kinetics, pH and molar mass, was studied. The results revealed significant differences in the extraction behavior and composition of the different species.

A microreactor was used to oxidize ethanol to valuable products under atmospheric pressure. Nano-sized gold on alumina was used as heterogeneous catalyst in the microreactor. A uniform and stable catalyst coating in the microchannels was achieved by suspension method. The catalyst was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, nitrogen-physisorption and X-ray diffraction. The reaction system was studied by changing the operation conditions, i.e. the residence time and temperature (100–250 °C). The product stream was analyzed by on-line gas chromatography. The identified products were acetaldehyde, ethyl acetate, diethyl ether and ethylene. The aim of the study was to find out the operation conditions that favored the generation of the desired product. A detailed modelling work was included. A kinetic model was developed for the reaction system. Dynamic mass balance-based generic modelling was applied to estimate the rate parameters. gPROMs ModelBuilder, a highly advanced process modelling tool was used. The obtained selectivity for acetaldehyde formation was around 90% already at low temperatures. The mathematical model described the ethanol conversion and acetaldehyde selectivity very well. The experimental equipment, the catalyst, and the modelling approach are applicable for other gas-phase oxidation studies.

The increasing use of structured reactors and catalysts, particularly solid open foams requires a new touch to the interaction of intrinsic chemical kinetics and mass transfer. In spite that the internal mass transfer resistance in the catalyst pores is efficiently suppressed because of thin washcoat layers on structured catalysts, the low flow velocities applied in many liquid-phase processes impair the mass transfer efficiency at the outer surface of the catalyst layer inside the channels of monoliths and open foams. The coupling of external mass transfer resistance and intrinsic kinetics was considered for various power-law and adsorption kinetics in tubular reactors filled with structural catalysts. The relevant mass balance equations were derived and solved numerically and the behaviors of single-channel systems were illustrated in the parameter spaces of Damkohler numbers. The single-channel model was successfully extended to a system of parallel channels with a distribution of channel sizes. The effect of the channel size distribution on the Reynolds and Sherwood numbers was illustrated by numerical simulations. The proposed approach is a potential tool for the design of structured catalysts.

Holm oak (Quercus ilex) sapwood was submitted to a hydrothermal treatment and liquid fractions rich in hemicelluloses were obtained. The chemical composition as well as the molar mass were analysed during the experiments. The effect of temperature (130–170 °C) and reaction time (5–220 min) on the conversion and molar mass of the obtained hemicelluloses was investigated. The results were compared to previously published data obtained using Norway spruce. The results show that the extraction rate depends strongly on the wood species used. The maximum yield (approximately 60%) was obtained at 170 °C after 20 min. The molar mass of the hemicelluloses decreased during the extraction due to hydrolysis and the pH of the solution decreased as deacetylation occurred simultaneously. Temperature influenced significantly the hydrolysis rate of the macromolecules. Compared to Norway spruce (softwood), the average molar mass in Holm oak (hardwood) was lower under the same reaction conditions., Ministerio de Economía, Industria y Competitividad (Project CTQ2015-64892-R), Junta de Castillay León (Proyecto VA254B11-2), Ministerio de Economía, Industria y Competitividad (Project CTQ2013-44143-R), Ministerio de Economía, Industria y Competitividad (Project CTQ2011-23293), Ministerio de Economía, Industria y Competitividad (Project CTQ2011-27347)

International audience; Fossil depletion and global warming have pushed industrial and academic communities to rethink the present way of consumption by diminishing waste and by using renewable raw materials. For this reason, several research programs are focused on the valorization of biomass and carbon dioxide. To promote the use of these feedstocks in industrial scale, kinetic and thermodynamic data are needed for a better energy integration and cost optimization. Industrial production of methanol, urea and inorganic carbonate from carbon dioxide should be used as examples. A kinetic model including mass transfer phenomena for the carbonation of epoxidized cottonseed oil was proposed. We observed that the absorption rate of CO2 increases in the following order: cottonseed oil (CSO)> epoxidized cottonseed oil (ECSO)> carbonated cottonseed oil (CCSO), which was confirmed by our model. For liquid temperature exceeding 120 °C, the Henry’s coefficients increase in the following order: HeCCSO > HeCSO ⩾ HeECSO. Kinetic experiments were conducted at different temperatures (110–140 °C), catalyst tetra-n-butylammonium bromide (TBABr) concentrations (0.06–0.30 mol/L), epoxidized group concentrations (1.67–3.80 mol/L) and CO2 pressure (21.1–49.7 bar). The kinetic parameters identified by nonlinear regression fit the experimental data well.

The reactivity of soluble solid particles with liquids was described with extended film theory: the solid material dissolves in the liquid phase and diffuses through the liquid film surrounding the particle. In both the liquid film and bulk liquid, chemical reactions take place. The solid particle shrinks due to the dissolution and consequent reactions and the film becomes thinner and thinner due to the decreasing particle size. A general mathematical model was developed for the solid particle, the liquid film and the liquid bulk phase. The dynamic models were based on mass balances for the solid, film and bulk liquid. The models consisting of coupled parabolic partial differential equations and ordinary differential equations were solved numerically by applying the method of lines. The gPROMS ModelBuilder was used in the computations of generic cases. The models predict the shift of the reaction domain being predominantly located in the liquid film towards the liquid bulk during the progress of the solid-liquid process. The roles of the liquid film and the liquid bulk phases were illustrated with contribution analysis.

Packed bed reactors are often used for catalyst screening studies due to their simple construction and ease of operation. The use of gold nanoparticles for partial oxidation reactions of alcohols has arisen interest of the scientific community. A model was generated to explain the experimentally observed reactor behavior (conversion of alcohol, yields of products) in the alcohol oxidation over gold nanoparticles. The model for this gas-phase heterogeneously catalyzed multi-reaction system consisted of the dynamic mass and energy balances and Langmuir–Hinshelwood–Hougen–Watson, Mars van Krevelen or Power law expressions for the reaction kinetics. Fluid flow was described with convection and dispersion terms. A semi-empirical pressure drop correlation was used. This resulted in a rapidly running model by reducing the problem size significantly. Powerful gPROMS Modelbuilder software was used as the model development, simulation and parameter estimation platform. The primary task was to punctually define and solve the complete set of equations (Partial Differential Equations (PDEs) together with algebraic equations). The modeling effort focused on the selection of the complete set of equations to adjust the degrees of freedom 0 and on the simultaneous solution of the whole set. Numerical method of lines was applied to convert the partial differential equations to ordinary ones. All reactions were assumed to take place on evenly distributed active sites of the porous catalyst particles. The dynamic mass balances consisting of internal diffusion and surface reaction within the porous particles were solved simultaneously with the mass and energy balances of the whole reactor. The axial and radial concentration and temperature profiles inside the reactor and the concentration profiles within the particles were then obtained results. Starting from experiments performed at T = 125–250 °C, p = 1 atm and superficial gas velocity of 0.03 m/s, a parameter estimation analysis was conducted. After the parameter estimation, the calculated alcohol conversion and yields of the main products (acetaldehyde and acetic acid) followed relatively closely the experimentally observed ones. The estimated parameters were the rate constants and the activation energies and the adsorption parameters (with LHHW kinetics, Mars van Krevelen kinetics) and reaction orders of oxygen (Power law kinetics). Simulation studies were done to show how feed temperature and catalyst loading influenced the results and how the Peclet number reflected on obtained results.

Open foam structures are very beneficial as heterogeneous catalysts for three-phase processes, because they have high efficiency and low pressure drop. A mathematical model for open foam catalyst structures was developed. It was based on the concept of axial dispersion as flow pattern, on liquid-solid mass transfer effects and intrinsic kinetics on the active sites of the catalyst. Rate equations were presented for the hydrogenation of individual sugars and binary sugar mixtures on Ru/C catalysts and they were implemented in the mass transfer and flow models of the open foam catalyst. The flow pattern in the foam structure was confirmed with step change experiments with an inert tracer. The multiphase model was applied on the hydrogenation of arabinose and galactose in a laboratory-scale open foam catalyst bed. The model was able to reproduce the main features of the experimental observations, both for individual sugars and binary sugar mixtures.

Experimental measurements of the reaction kinetics of complex consecutive and parallel-consecutive reactions is a challenge, because the reaction rates of the sequence are often very different, the primary reactions being much more rapid while the secondary and tertiary reactions might be much slower requiring very long kinetic experiments. An approach to surmount this dilemma is proposed for homogeneously catalyzed liquid-phase reactions by adding the catalyst gradually into the reaction mixture: in this way the primary reactions are slowed down but the secondary and tertiary reactions are accelerated. A mathematical model for this approach was developed and complex reaction systems were simulated numerically in the Damkohler space. The applicability of the approach was illustrated with experimental data obtained for the formation of mono- and diesters from carboxylic acids and dialcohols in the presence of homogeneous strong acid catalysts. Acetic acid and ethylene glycol were used as reagents in the experimental work and aqueous hydrogen chloride was the homogeneous catalyst. Rate equations for this reaction systems were derived based on molecular mechanisms and the kinetic parameters in the rate equations were estimated with regression analysis. Simulation of the esterification model illustrated the benefits of the proposed experimental semibatch approach for complex reaction systems.

A Re2O7-B2O3/Al2O3 catalyst was demonstrated to reveal significant activity in cyclohexene dimerization into 1-cyclohexenylcyclohexane with a total yield of 95 % and a selectivity close to 100 % in the batch mode at 75−80°C and atmospheric pressure.

Transformations of glucose to 1,2-propylene glycol were studied over a mechanical mixture of ZnO and Ru/C catalysts in the presence of hydrogen. Different reaction conditions were evaluated by changing the reaction temperature and hydrogen pressure. In addition to the cascade mode of operation, also separate steps in the overall reaction network, such as hydrogenation of pyruvaldehyde and hydroxyacetone to 1,2-propylene glycol were investigated. Fructose as a starting material was also studied resulting in a propylene glycol yield of 37.5%. The optimal temperature for glucose transformation to propylene glycol was found to be 165 °C. The influence of temperature on the catalytic behavior was more prominent than the effect of hydrogen pressure. Thermodynamic analysis of glucose transformation to 1,2-propylene glycol was performed and a plausible kinetic model reflecting a complex reaction network was developed being able to describe the data in a reliable way.

Dehydration and etherification of bio-ethanol was studied in a microreactor using γ-alumina, H-Beta-38 and Sn-Beta-38 as catalysts. An extensive series of kinetic experiments was carried out in the microreactor device operating at ambient pressure and temperatures 225–325 °C. The H-Beta-38 catalyst coated microplates exhibited the highest production rate of ethene. While the fresh H-Beta-38 catalyst allowed complete conversion of ethanol and 98% selectivity towards ethene, the catalyst deactivated significantly with time-on-stream. Diethyl ether was the dominating co-product, whereas trace amounts of acetaldehyde were detected in the experiments. Based on the kinetic studies, thermodynamic analysis and catalyst characterization results obtained with SEM-EDX, TEM, nitrogen physisorption, FTIR-Pyridine and white light confocal microscopy, a surface reaction mechanism was proposed. The fundamental hypothesis of the reaction mechanism was the co-existence of two kinds of active sites on the catalyst surface, namely the Bronsted sites promoting dehydration and the Lewis sites responsible for etherification. The Bronsted sites deactivate, whereas the Lewis sites are more stable, which leads to a shift of the product distribution during long-term experiments, from ethene to diethyl ether. The rate equations were implemented in the microreactor model. The kinetic and adsorption parameters included in the model were estimated by non-linear regression analysis. The experimental data were satisfactorily described by the proposed mechanism. The work demonstrated that microreactors are strong tools in the determination of catalytic kinetics and catalyst durability.

The density, viscosity and hydrogen solubility of selected sugars (l-arabinose, d-galactose, d-maltose and l-rhamnose) were determined at different temperatures (generally 60, 90 and 130 °C). The r ...

Over the past decades, Taylor flow has got an increasing interest due to its potential to intensify reaction processes with fast kinetics which are usually controlled by mass transfer processes. Besides high mass transfer rates, the segmented flow regime offers a sharp residence time distribution of the liquid phase and a low pressure drop. Taylor flow appears in micro and minichannels whereas the terms have not always been used with a clear distinction. Minichannels are channels with characteristic diameters between 400 μm and about 1 mm, which will be in the centre of this work. These channel dimensions appear in monolithic reactors also known as reactors with honeycomb catalyst packings, in concepts using bundles of capillary tubes, as well as in microchannel plate reactors. This article presents a comprehensive overview of hydrodynamics and mass transfer in the minichannels of an open flow structure, i.e. in channels without internals, operated in the Taylor flow regime. The review summarises available correlations to predict Taylor flow characteristics, as well as mass transfer coefficients between all involved phases (gas–liquid, liquid–solid, gas–solid). Within this scope, the impact of operational and design parameters is critically discussed and limits of application for the individual correlations are defined. Special attention is given to the interaction of these mass transfer steps in heterogeneously catalysed chemical reactions.

The homogeneously catalysed glycerol hydrochlorination was thoroughly investigated in a continuous isothermal co-current bubble column reactor over a wide range of reaction parameters, such as temp ...

Epichlorohydrin is an important chemical intermediate, which can be obtained by valorisation of glycerol, an inexpensive raw material obtained as a stoichiometric co-product from biodiesel production. A continuous milliscale tubular reactor was developed to conduct the synthesis of epichlorohydrin and to measure the very rapid reaction kinetics. 1,3-dichloro-2-propanol (αγ-DCP) was dehydrochlorinated with sodium hydroxide at 30–70 °C. The residence times in the millireactor system were less than 25 s. The kinetic data were interpreted with a plug flow model and a rate equation based on a plausible reaction mechanism. The model – the rate equation and the plug flow concept – gave a perfect description of the experimental data.

International audience; Process safety is an important topic in the curriculum vitae of a chemical engineer. It can be a difficult course for the students and professors, because it is a frontier course between chemical engineering and safety. How to introduce this course? We think that this course should be introduced during the chemical reaction engineering, and more particularly during the mass and energy balances lectures. Thus, the students can more easily understand the concept of isoperibolic mode, secondary reactions, heat-flow rate due to chemical reactions, Semenov curves, etc. In this manuscript, we propose a pedagogical method to introduce this concept by using numerical simulation. In the first section, the roots of energy balance for the different reactors is derived. In the second section, mass and energy balances coupling is derived for the different chemical reactors. In the third section, the different thermal modes, i.e., isothermal, isoperibolic and adiabatic are described. Then, a tutorial by using a batch reactor with several exothermic reactions is treated and corrected. At this moment of the course, the instructor can introduce the last section about safety criteria by using the zero-order approximation. The rigorous mass and energy balances coupling should be introduced to the students before the current approximation made by the safety community, i.e., zero order, in process safety.

An advanced kinetic and diffusion model was developed and verified for the oxidation of starch by hydrogen peroxide in the presence of a homogeneous iron tetrasulphonatophtalocyanine (FePcS) catalyst. The model takes into account several experimentally confirmed observations, such as the oxidative formation of carbonyl and carboxyl groups in starch, as well as the decomposition of starch, catalyst and H 2 O 2 . The model is based on molecular mechanisms for the oxidation and decomposition reactions as well as on the dual structure of starch particles comprising an outer reaction layer and an internal porous layer, in which diffusion resistance retards the reaction rate. Adsorption of the catalyst on the starch surface is included in the model. The mathematical model explained very well the experimentally observed complex behavior of starch oxidation kinetics and hydrogen peroxide decomposition.

Epoxidized vegetable oils are used as chemical intermediates and biolubricants. Epoxidation of oleic acid as model compound for vegetable oils was performed in a batch-loop reactor. The system comprised a loop where the mixture was pumped through a cavity in which microwaves were irradiated. The reaction was executed by peroxyacetic acid formed in situ from acetic acid and hydrogen peroxide. An extensive kinetic study of oleic acid epoxidation in the batch-loop reactor was conducted by varying the reaction temperature (40–60 °C), the stirring and pumping speeds as well as the molar ratios of the components. Both conventional heating and microwave irradiation were used in the experiments. Epoxidation of the double bonds in oleic acid proceeded as the main reaction, while acid-catalyzed ring opening of the epoxide appeared as the side reaction. The results obtained showed that temperature, acetic acid amount and hydrogen peroxide amount accelerated both rate of epoxidation and ring opening processes. A clear enhancement of the epoxidation kinetics was accomplished with microwave heating in comparison to conventional heating, which was attributed to selective heating by the microwaves that enabled a higher interfacial mass transfer. Microwave application to epoxidation of vegetable oils is a promising process that successfully meets all the green chemistry requirements: energy saving and eco-friendly process and products.

In this work, cellulose acetate was synthesized under homogeneous conditions. Cellulose was first dispersed in acetone, acetonitrile, 1,5-diazabicyclo(4.3.0)non-5-ene (DBN) or dimethyl sulphoxide (DMSO) and the resulting suspension was dissolved in an ionic liquid, 1,5-diazabicyclo(4.3.0)non-5-enium acetate [HDBN][OAc] at 70°C for 0.5h. It was possible to dissolve more than 12wt% cellulose with a degree of polymerization in the range of 1000-1100. The dissolved cellulose was derivatized with acetic anhydride (Ac2O) to yield acetylated cellulose. As expected, the use of the co-solvents improved the acetylation process significantly. In fact, cellulose acetates with different properties could be obtained in half an hour, thus facilitating rapid processing. When DBN was used as the dispersing agent (the precursor of the ionic liquid), the problems associated with recycling of the ionic liquid were significantly reduced. In fact, additional [HDBN][OAc] was obtained from the interaction of the DBN and the by-product, acetic acid (from Ac2O). However, the cellulose acetate obtained in this manner had the lowest DS. Consequently, the native cellulose and acetylated celluloses were characterized by means of (1)H- and (13)C-NMR, FT-IR, GPC/SEC and by titration. The cellulose acetates produced were soluble in organic solvents such as acetone, chloroform, dichloromethane and DMSO which is essential for their further processing. It was demonstrated that the ionic liquid can be recovered from the system by distillation and re-used in consecutive acetylation batches.

The public interest in usage of lignocellulosic biomass as a renewable resource has grown strongly during the last decade. Hemicelluloses are the second most abundant constituents of wood biomass, but have yet received less attention, compared to cellulose. In this work hydrolysis of xylan, as an example of hemicelluloses, was studied at moderate temperatures between 70 and 90 °C and pH values ranging from 0.5 to 3 with different liquid (HCl, H 2 SO 4 , triflouroacetic acid, oxalic acid) and solid (Smopex-101) catalysts. Experimental results showed complete cleavage of xylan with xylose yields of up to 95%.

Aqueous phase reforming (APR) can be used as an efficient method to purify and obtain added value from rather dilute side/waste streams of process waters containing e.g. alcohols or sugar alcohols. Such side streams often have none or even negative value due to purification costs, which contributes to the economy of the process. Xylitol was here used as a model compound. The desired product in the current study was hydrogen, which can be used for valorizing by-products via hydroprocessing or as a bioenergy source. In addition to hydrogen, some alkanes were also obtained, which are prime sources of bio-energy for power production. The current work focused especially on the influence of the reaction conditions (temperature, pressure and inert gas flow) on the xylitol conversion and hydrogen selectivity, which has not been reported previously. The influence of reaction conditions on the aqueous phase reforming of xylitol on Pt/Al2O3 catalyst was studied in a trickle-bed reactor. Selectivity to hydrogen was dependent on gas flow through the reactor, especially the absence of any gas resulted in a low selectivity. A higher reaction temperature and a higher inert gas flow gave a better xylitol conversion, while an increase of the overall pressure had an opposite effect on conversion. The activation energy for xylitol conversion was determined for the first time being 79.3 kJ/mol. The results demonstrate that aqueous phase reforming is a viable method for energy efficient value added processing of sugar alcohol containing dilute side streams in modern bio-refinery applications.

Kinetic modelling of furfural oxidation with hydrogen peroxide over a fibrous polymer-supported sulphonic acid catalyst was performed. The proposed kinetic model describes the concentration profiles of the reactants, intermediates and products as a function of reaction time at different temperature. Parameter estimation has been performed followed by their statistical analysis showing that the kinetic parameters were statistically well identified.

The kinetics of maltose hydrogenation using Ru-containing nanoparticles (NPs) formed in the pores of hypercrosslinked polystyrene (HPS) was studied in this work at 110–140 °C and 2–7 MPa. The concept of two sites and non-competitive adsorption of hydrogen and maltose was used due to large differences in the sizes of molecules. The proposed model was able to describe experimental data with sufficient accuracy.

The isomerisation of β-pinene oxide was studied over supported ionic liquid catalysts (SILCAs) consisting of Lewis acids in immobilized ionic liquid. SILCAs were demonstrated as efficient catalysts ...