1,721,096 research outputs found
Influence of the vapor-liquid equilibria (VLE) on the kinetics in gas-liquid and gas-liquid-solid systems
No full textGas-liquid and gas-liquid-solid reactors are frequently characterized by the presence of components, reagents or products, that are partitioned between liquid and vapor phase. In this case we have a difficulty in describing the kinetic behaviour of such type of reactors when it occurs that: (i) the amount of partitioned component in the two phases is never negligible in both phases; (ii) the vapor-liquid equilibrium could have a non-ideal behaviour. We need therefore, to introduce in the kinetic model the mass balance equations for describing the partition of the components affecting their concentration in liquid phase also considering, when necessary, the non-ideal behaviour of the involved phases. Vapor-liquid equilibria (VLE) in reactive systems are poorly treated in the literature, especially for reactions occurring at high pressures. In the present work we will examine the different possibilities occurring in practice and the methods to solve them. Some practical examples are reported for better explaining both the theoretical and practical approach. © 2003 Elsevier Science B.V. All rights reserved
Advances in catalysts for liquid biofuel: Production processes
No full textIn this chapter, the state-of-the-art catalysts used to produce the most common liquid biofuels are reviewed. In particular, the catalysts used to produce biofuels from either oils and fats or cellulose lignin feedstocks will be discussed. Attention will be paid to discussing the recent advances in the current catalytic technologies, showing for each the related drawbacks and possible perspectives
Copolimerizzazione stirene-etilene catalizzata da composti metallorganici del gruppo IV attivati da metilallumossano
No full textSkeletal isomerization of 1-butene to isobuten over acid catalysts obtained by grafting silicon alkoxide on γ-alumina
No full textA study was made of the preparation and properties of some acid catalysts obtained by grafting silicon alkoxides on γ-alumina. All the prepared catalysts were tested in the skeletal isomerization of 1-butene to isobutene. Isobutene is an intermediate in the production of MTBE, today the most important oxygenated compound used as an additive in lead-free gasoline. The discussion covers introduction; experimental (catalyst preparation and characterization); results (determination of the catalyst surface properties by potentiometric titrations and TGA analyses; TPD determination of acid surface properties; XPS determination of surface properties of silicated alumina catalysts; and catalytic activities and selectivities in skeletal isomerization of 1-butene to isobutene). The type of acidity, Lewis or Brönsted, and its strength affects selectivity, and by examining published data, the best catalysts seemed to be those with acid sites of medium strength because the selectivity toward isobutene is enhanced and catalyst deactivation prevented. Silicate aluminas have these requisites. Therefore, the acidities of the catalysts A1S1, A1S2, A1S3, A1S4, and A1SM were tested and, for comparison, those of silica, silica-alumina, and alumina support. The highest conversion and selectivity to isobutene was over A1S4. The conversion was 83.3% and the products distribution was isobutane 0.69, n-butane 0.18, 2-trans-butene 23.7, isobutene 36.7, 2-cis-butene 17.5, and 2-cis/2-trans butene 0.74. The catalysts A1S4 and A1SM also showed a remarkable stability
Design of a continuous device for ethoxylation reaction: The choice between micro and milli scale
No full textA laminar flow model was developed to investigate the reaction kinetics of 1-dodecanol ethoxylation promoted by KOH, elaborating the data collected in microreactors. A generic laminar flow model was coded, and a sensitivity analysis was conducted highlighting the good flexibility of the model to simulate a wide range of conditions. Ethylene oxide diffusivity and liquid mixture viscosity were determined by applying existing correlations, carefully considering the change in viscosity with ethylene oxide conversion, temperature, and feed ethylene oxide/1-octanol ratio. The model was tested on literature data obtaining in every case good results. The obtained kinetic data were demonstrated to be in line with the ones obtained in separate investigations conducted in a fed-batch reactor, demonstrating that there was a real need in adopting the laminar flow reactor approach, as it allowed to retrieve of more precise information about the intrinsic kinetics of the ethoxylation reaction, when working with microreactors, compared with the ones obtainable with a plug-flow ideal fluid-dynamic model. The developed model was used to simulate the behavior of a milli-reactor (this device allows to reach sufficient productivity for industrial application) and it was forecasted the possibility to use continuous ethoxylation milli-reactors using fluid-dynamic conditions characterized by a high Reynolds number (>10000)
Comprehensive reverse flow reactor model for fluid–solid systems
No full textA comprehensive model for a Reverse Flow Reactor was developed and implemented in the present article. The model consists of the combination of mass and energy balance equations written for a fluid–solid packed reactor, where the feed and outlet positions are alternated periodically using dedicated boundary conditions. Several non-idealities were considered, dealing with both the particle and the fluid phases. Different chemical systems were simulated numerically to investigate the behavior of the reverse flow reactor and to determine the optimal operation policy. Intraparticle diffusion resistance allowed to predict concentration gradients in each case, while intraparticle heat transfer was demonstrated to be non-influent. The impact of the main kinetic and heat/mass transfer parameters was checked via a parametric investigation, demonstrating the high flexibility of the model, even predicting harsh operation conditions. The model was tested in the description of data taken from the literature, demonstrating a good descriptive power
The euro-area government spending multiplier at the effective lower bound
No full textWe build a factor-augmented interacted panel vector-autoregressive model of the Euro Area (EA) and estimate it with Bayesian methods to compute government spending multipliers. The multipliers are contingent on the overall monetary policy stance, captured by a shadow monetary policy rate. Whether the fiscal shock occurs when the economy is at the effective lower bound (ELB) or in normal times matters for the size of the multiplier. Median estimates vary conditional on the specification, but the difference between multipliers at the ELB and in normal times is systematically positive with very high probability. Over the medium run (5 years), median cumulated multipliers range between 0.3 and 1.4 in normal times, and between 1.6 and 2.9 at the ELB. We show that the results are not driven by the state of the business cycle and that the multiplier is inversely correlated with the level of the shadow monetary policy rate. The econometric approach deals with several technical problems highlighted in the empirical macroeconomic literature, including the issues of fiscal foresight and limited information
Polyethoxylation and polypropoxylation reactions: Kinetics, mass transfer and industrial reactor design
No full textEthoxylation and propoxylation reactions are performed in the industry to produce mainly non-ionic surfactants and ethylene oxide (EO)–propylene oxide (PO) copolymers. Both the reactions occur in gas–liquid reactors by feeding gaseous EO, PO or both into the reactor containing a solution of an alkaline catalyst (KOH or NaOH).
Non-ionic surfactants are produced by using liquid starters like fatty alcohols, fatty acids or alkyl-phenols, while when the scope is to prepare EO–PO copolymers the starter can be a mono- or multi-functional alcoholof low molecular weight. Both reactions are strongly exothermic, and EO and PO, in some conditions, can give place to runaway and also to explosive side reactions. Therefore, the choice of a suitable reactor is a key factor for operating in safe conditions. A correct reactor design requires: (i) the knowledge of the kinetic laws governing the rates of the occurring reactions; (ii) the role of mass and heat transfer in affecting the reaction rate; (iii) the solubility of EO and PO in the reacting mixturewith the non-ideality of the reacting solutions considered; (iv) the density of the reacting mixture. All these aspects have been studied by our research group for different starters of industrial interest, and the data collected by using semibatch well stirred laboratory reactors have been employed for the simulation of industrial reactors, in particular Gas–Liquid Spray Tower Loop Reactors
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