Rigorous synthesis and simulation of complex distillation networks

Recent insights for better understanding the thermodynamic foundations of separation processes have renewed the interest in exploring energy‐efficient distillation networks. Complex column networks have substantial potential for energy savings over conventional configurations. This article introduces a computational algorithm for synthesizing such complex energy‐efficient networks. A robust feasibility criterion drives the selection of design specification and operating conditions. It will be shown that columns composed of sections whose liquid stage composition profiles have no gaps are realizable. To prove the rigor of design computations, numerous separation networks were synthesized and validated with the Aspen flowsheet simulator. By using our computational results as input, AspenPlus simulations converged in a few iterations. Our method builds on temperature collocation, a thermodynamically motivated search method for determining feasible operating conditions and design details for achieving the desired product targets. Our findings suggest that significant energy savings can be realized with rigorous complex networks synthesis for industrial separation problems. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Energy shaping plus damping injection control for a class of chemical reactors

Traditionally, stabilization of chemical reacting systems has been achieved with linear P or PD compensation schemes. Practical and numerical results have showed that classical linear compensation can yield acceptable performance. On the other hand, recent years have witnessed the emergence of systematic feedback control strategies based on energy and port-interconnected systems. These approaches exploit the physical structure of the chemical reactor to construct compensation schemes with physical appealing. The aim of this work is to show that traditional PD compensation for CSTRs can be interpreted in terms of mechanical system analogies. In the line of energy shaping plus damping injection for robotic systems, it is shown that proportional feedback is a type of potential energy shaping to accommodate a unique equilibrium point. On the other hand, derivative control acts as a damping injector for the energy balance within the chemical reactor. The stability proof uses a novel approach to convert the temperature dynamics into a second-order systems where the mechanical analogies become more evident. In this way, the stability analysis can be performed with singular perturbation methods with a Lyapunov function for the energy balance derived from a “potential plus kinetics” energy construction.     

Synthesis of N,N-diethyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}amine via in situ diazotisation and coupling in supercritical carbon dioxide

The synthesis of azo dyes via a conventional aqueous-based diazotisation and coupling reaction requires the use of relatively high concentrations of mineral acids, which leads to high electrolyte concentrations in wastewater. Reported in this paper is an environmentally benign one-pot method for the synthesis of a nonionic azo dye, N,N -diethyl- N -{4-[( E )-(4-nitrophenyl)diazenyl]phenyl}amine, in supercritical carbon dioxide without using a mineral acid. The product yield increased significantly with temperature, with 91% theoretical yield afforded at 80 °C. The pressure of the system had little influence on product yield.     

Iron Oxide Nanoparticles Employed as Seeds for the Induction of Microcrystalline Diamond Synthesis

Iron nanoparticles were employed to induce the synthesis of diamond on molybdenum, silicon, and quartz substrates. Diamond films were grown using conventional conditions for diamond synthesis by hot filament chemical vapor deposition, except that dispersed iron oxide nanoparticles replaced the seeding. X-ray diffraction, visible, and ultraviolet Raman Spectroscopy, energy-filtered transmission electron microscopy , electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to study the carbon bonding nature of the films and to analyze the carbon clustering around the seed nanoparticles leading to diamond synthesis. The results indicate that iron oxide nanoparticles lose the O atoms, becoming thus active C traps that induce the formation of a dense region of trigonally and tetrahedrally bonded carbon around them with the ensuing precipitation of diamond-type bonds that develop into microcrystalline diamond films under chemical vapor deposition conditions. This approach to diamond induction can be combined with dip pen nanolithography for the selective deposition of diamond and diamond patterning while avoiding surface damage associated to diamond-seeding methods.     

Silicon Encapsulated Carbon Nanotubes

A dual stage process of depositing bamboo-like carbon nanotubes (BCNTs) by hot filament chemical vapor deposition (HFCVD) and coating Si using Radio frequency sputtering (RFS) technique. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron field emission studies (EFE). SEM results suggest a dense network of homogeneous silicon-coated BCNTs. From the comprehensive analysis of the results provided by these techniques emerges the picture of Si encapsulated BCNTs.     

The Bark Beetle Dendroctonus rhizophagus (Curculionidae: Scolytinae) Has Digestive Capacity to Degrade Complex Substrates: Functional Characterization and Heterologous Expression of an α-Amylase

Dendroctonus-bark beetles are natural agents contributing to vital processes in coniferous forests, such as regeneration, succession, and material recycling, as they colonize and kill damaged, stressed, or old pine trees. These beetles spend most of their life cycle under stem and roots bark where they breed, develop, and feed on phloem. This tissue is rich in essential nutrients and complex molecules such as starch, cellulose, hemicellulose, and lignin, which apparently are not available for these beetles. We evaluated the digestive capacity of Dendroctonus rhizophagus to hydrolyze starch. Our aim was to identify α-amylases and characterize them both molecularly and biochemically. The findings showed that D. rhizophagus has an α-amylase gene (AmyDr) with a single isoform, and ORF of 1452 bp encoding a 483-amino acid protein (53.15 kDa) with a predicted signal peptide of 16 amino acids. AmyDr has a mutation in the chlorine-binding site, present in other phytophagous insects and in a marine bacterium. Docking analysis showed that AmyDr presents a higher binding affinity to amylopectin compared to amylose, and an affinity binding equally stable to calcium, chlorine, and nitrate ions. AmyDr native protein showed amylolytic activity in the head-pronotum and gut, and its recombinant protein, a polypeptide of ~53 kDa, showed conformational stability, and its activity is maintained both in the presence and absence of chlorine and nitrate ions. The AmyDr gene showed a differential expression significantly higher in the gut than the head-pronotum, indicating that starch hydrolysis occurs mainly in the midgut. An overview of the AmyDr gene expression suggests that the amylolytic activity is regulated through the developmental stages of this bark beetle and associated with starch availability in the host tree.