Sergio Carrà

Bio: Sergio Carrà is an academic researcher from Polytechnic University of Milan. The author has contributed to research in topics: Deposition (phase transition) & Catalysis. The author has an hindex of 27, co-authored 139 publications receiving 2461 citations.

Robust design of binary countercurrent adsorption separation processes

Abstract: The separation of a binary mixture, using a third component having intermediate adsorptivity as desorbent, in a four section countercurrent adsorption separation unit is considered. A procedure for the optimal and robust design of the unit is developed in the frame of Equilibrium Theory, using a model where the adsorption equilibria are described through the constant selectivity stoichiometric model, while mass-transfer resistances and axial mixing are neglected. By requiring that the unit achieves complete separation, it is possible to identify a set of implicity constraints on the operating parameters, that is, the flow rate ratios in the four sections of the unit. From these constraints explicit bounds on the operating parameters are obtained, thus yielding a region in the operating parameters space, which can be drawn a priori in terms of the adsorption equilibrium constants and the feed composition. This result provides a very convenient tool to determine both optimal and robust operating conditions. The latter issue is addressed by first analyzing the various possible sources of disturbances, as well as their effect on the separation performance. Next, the criteria for the robust design of the unit are discussed. Finally, these theoretical findings are compared with a set of experimentalmore » results obtained in a six port simulated moving bed adsorption separation unit operated in the vapor phase.« less

Optimal design of multicomponent countercurrent adsorption separation processes involving nonlinear equilibria

Abstract: A simple model, based on equilibrium theory, for simulating countercurrent adsorption separation processed involving multiple components and nonlinear equilibrium has been developed. The reliability of this model has been tested by comparison with a detailed model in the context of the separation process for the aromatic fraction C 8 by adsorption on zeolites. Based on this model, a simple and accurate procedure has been developed for designing optimal separation units, where adsorbent and desorbent requirements are minimized while enrichments of both extract and the raffinate are maximized. The emphasis has been placed on the role of the desorbent and the effect of the physical state of the fluid, i.e. vapor or liquid phase operation.

Separation of xylenes on Y zeolites. 2. Breakthrough curves and their interpretation

Abstract: The adsorption separation process of xylene isomers on molecular sieves has been investigated by performing a set of breakthrough curves, for both adsorption and desorption processes. Different columns with one, two, and four adsorbable components have been considered. The mentioned experimental data have been simulated by means of a mathematical model in which the material balances of all the components present in the system are stated. The solution of the model equations has been pursued by means of the orthogonal collocation method, while the parameters involved in the model have been evaluated either through available correlations or independent experiments.

The peculiar kinetics of the reaction between acetylene and the cyclopentadienyl radical.

Abstract: The cyclopentadienyl radical (cC5H5) is a fascinating molecule characterized by several peculiar properties, such as its high internal symmetry and resonance enhanced stability. This makes cC5H5 one of the most abundant radicals present in high temperature gaseous environments, such as flames. Therefore it is generally considered an interesting candidate as the starting point of reaction pathways leading to the formation of polycyclic aromatic hydrocarbons (PAH) and soot in combustion processes. However, known reaction pathways are not able to explain some recent experimental findings concerning the rapid conversion of cC5H5 into C7H7 and C9H8 in the presence of acetylene. In this work, we used ab initio calculations and quantum Rice−Ramsperger−Kassel (QRRK) theory to investigate the cC5H5 + C2H2 reaction kinetics. We found that cC5H5 can add acetylene to form, through a fast and not previously known reaction, the heptatrienyl radical (cC7H7), which, in many ways, can be considered the superior homologue ...

Separation of xylenes on Y zeolites. 1. Determination of the adsorption equilibrium parameters, selectivities, and mass transfer coefficients through finite bath experiments

Abstract: The adsorption of xylene isomers on completely potassium exchanged Y zeolite has been investigated. The adsorption equilibrium data for single components and mixtures have been described with the Langmuir and Fowler isotherms. The kinetics of adsorption of the different components on zeolite pellets and powder have also been studied. The obtained experimental data have been interpreted by means of a kinetic model in which the role of inter-and intraphase diffusion processes are emphasized.

Application of layered double hydroxides for removal of oxyanions: A review

Abstract: Layered double hydroxides (LDHs) are lamellar mixed hydroxides containing positively charged main layers and undergoing anion exchange chemistry. In recent years, many studies have been devoted to investigating the ability of LDHs to remove harmful oxyanions such as arsenate, chromate, phosphate, etc. from contaminated waters by both surface adsorption and anion exchange of the oxyanions for interlayer anions in the LDH structure. This review article provides an overview of the LDH synthesis methods, the LDH characterization techniques, and the recent advancement that has been achieved in oxyanion removal using LDHs, highlighting areas of consensus and currently unresolved issues. Experimental studies relating to the sorption behaviors of LDHs with various oxyanions, and the kinetic models adopted to explain the adsorption rate of oxyanions from aqueous solution onto LDHs, have been comprehensively reviewed. This review discusses several key factors such as pH, competitive anions, temperature, etc., that influence the oxyanion adsorption on LDHs. The reusability of LDHs is discussed and some mechanistic studies of oxyanion adsorption on LDHs are highlighted. The sorption capacities of LDHs for various oxyanions are also compared with those of other adsorbents. In addition, this review critically identifies the shortcomings in current research on LDHs, such as the common weaknesses in the adopted methodology, discrepancies among reported results and ambiguous conclusions. Possible improvement of LDHs and potential areas for future application of LDHs are also proposed.

Formation of nascent soot and other condensed-phase materials in flames

Abstract: Over the last two decades, our understanding of soot formation has evolved from an empirical, phenomenological description to an age of quantitative modeling for at least small fuel compounds. In this paper, we review the current state of knowledge of the fundamental sooting processes, including the chemistry of soot precursors, particle nucleation and mass/size growth. The discussion shows that though much progress has been made, critical gaps remain in many areas of our knowledge. We propose the roles of certain aromatic radicals resulting from localized π electron structures in particle nucleation and subsequent mass growth. The existence of these free radicals provides a rational explanation for the strong binding forces needed for forming initial clusters of polycyclic aromatic hydrocarbons. They may also explain a range of currently unexplained sooting phenomena, including the large amount of aliphatics observed in nascent soot formed in laminar premixed flames and the mass growth of soot in the absence of gas-phase H atoms. While the above suggestions are inspired, to an extent, by recent theoretical findings from the materials research community, this paper also demonstrates that the knowledge garnered through our longstanding interest in soot formation may well be carried over to flame synthesis of functional nanomaterials for clean and renewable energy applications. In particular, work on flame-synthesized thin films of nanocrystalline titania illustrates how our combustion knowledge might be useful for developing advanced yet inexpensive thin-film solar cells and chemical sensors for detecting gaseous air pollutants.

Modeling nitrogen chemistry in combustion

Abstract: Understanding of the chemical processes that govern formation and destruction of nitrogen oxides (NOx) in combustion processes continues to be a challenge. Even though this area has been the subject of extensive research over the last four decades, there are still unresolved issues that may limit the accuracy of engineering calculations and thereby the potential of primary measures for NOx control. In this review our current understanding of the mechanisms that are responsible for combustion-generated nitrogen-containing air pollutants is discussed. The thermochemistry of the relevant nitrogen compounds is updated, using the Active Thermochemical Tables (ATcT) approach. Rate parameters for the key gas-phase reactions of the nitrogen species are surveyed, based on available information from experiments and high-level theory. The mechanisms for thermal and prompt-NO, for fuel-NO, and NO formation via NNH or N2O are discussed, along with the chemistry of NO removal processes such as reburning and Selective Non-Catalytic Reduction of NO. Each subset of the mechanism is evaluated against experimental data and the accuracy of modeling predictions is discussed.

Modelling reactive distillation

Abstract: The design and operation issues for reactive distillation systems are considerably more complex than those involved for either conventional reactors or conventional distillation columns. The introduction of an in situ separation function within the reaction zone leads to complex interactions between vapor–liquid equilibrium, vapor–liquid mass transfer, intra-catalyst diffusion (for heterogeneously catalysed processes) and chemical kinetics. Such interactions have been shown to lead to the phenomenon of multiple steady-states and complex dynamics, which have been verified in experimental laboratory and pilot plant units. We trace the development of models that have been used for design of reactive distillation columns and suggest future research directions.

Emulsion polymerization mechanisms and kinetics

Abstract: Emulsion polymerization involves the propagation reaction of free radicals with monomer molecules in a very large number of discrete polymer particles (10 16 –10 18 dm −3 ) dispersed in the continuous aqueous phase. The nucleation and growth of latex particles control the colloidal and physical properties of latex products. This review article focused on the polymerization mechanisms and kinetics involved in such a heterogeneous polymerization system over the preceding 10-year period. First, an overview of the general features of emulsion polymerization was given, followed by the discussion of several techniques useful for studying the related polymerization mechanisms and kinetics. Emulsion polymerizations using different stabilizers were studied extensively in the last few years and representative publications were reviewed. The performance properties of some specialty polymerizable, degradable or polymeric surfactants and surface-active initiators were also evaluated in emulsion polymerization. At present, the particle nucleation process is still not well understood and deserves more research efforts. This article continued to discuss the origin of non-uniform latex particles from both the thermodynamic and kinetic points of view. This was followed by the discussion of various reaction parameters that had significant effects on the development of particle morphology. Recent studies on the polymerization in non-uniform polymer particles were then reviewed. Finally, the polymerization mechanisms, kinetics and colloidal stability involved in the versatile semibatch emulsion polymerization were reviewed extensively.