Efficient Retrofitting Approach for Improving Heat Recovery in Heat Exchanger Networks with Heat Transfer Intensification

In this paper, an efficient design method is presented to implement heat transfer intensification technologies for increasing energy saving in industrial scale heat exchanger networks (HENs). First of all, the detailed models of shell-and-tube heat exchangers are utilized to estimate exchanger performances under normal and intensified conditions, and an optimization method based on simulated annealing is proposed to find appropriate retrofitting options in the existing HENs. Then, a novel retrofit approach based on the exchanger models and optimization method is introduced to retrofit HENs with several possible retrofit strategies, including exchanger relocations, heat transfer intensification, additional area, and stream repiping. Moreover, a new efficient software package (int-HEAT) is developed for the addressed retrofit problems. The interface of int-HEAT is designed to focus on a clear presentation of HEN retrofit procedure, which allows users to easily control all the retrofit stages. An industrial problem of preheat train for crude oil distillation is solved with the use of the new developed software through all the main steps of the proposed retrofit procedure, namely reducing energy consumption, identifying retrofitted exchangers, selecting retrofit strategies, and implementing heat transfer intensification techniques. The case study demonstrates the validity and efficiency of the developed software tool and the proposed approach

Methanol O–H Bond Dissociation on H‑Precovered Gold Originating from a Structure with a Wide Range of Surface Stability

Gold has been shown to exhibit promising catalytic activity, and understanding the fundamental interactions of reactants and hydrogen atoms on a gold surface is key to gaining insight into hydrogenation reaction mechanisms. In this paper, we report that the adsorption of methanol onto a H-precovered Au(111) surface induces an adsorbate structure, or set of structures, on the surface involving both methanol and hydrogen adatoms with a wide range of stability on the surface. Coadsorption of H/MeOD or D/MeOH indicates H/D exchange between the two surface species, providing evidence that the H-precovered gold surface can dissociate the methanol O–H bond at low temperature (<120 K). These isotopic experiments also demonstrate that hydrogen/deuterium atoms released from a methanol molecule desorb at higher temperatures than hydrogen/deuterium atoms originating from the surface, providing insight into the adsorbate structure(s) present. Additionally, the presence of MeOH on the surface is shown to inhibit the ability of adsorbed MeOD to undergo hydrogen exchange, providing additional clues regarding the exchange reaction mechanism. These phenomena are also shown to exist for ethanol on H-precovered Au(111), suggesting that this behavior may be common to alcohols or species with an O–H functional group in general. These observations give insight into the behavior of the O–H group on a gold surface, which can aid in determining reaction mechanisms and directing future catalytic research

Low-Temperature Hydrogenation of Acetaldehyde to Ethanol on H-Precovered Au(111)

Gold-based classical high surface area catalysts have been widely investigated for hydrogenation reactions, but fundamental studies on model catalysts are lacking. We present experimental measurements of the reaction of hydrogen adatoms and adsorbed acetaldehyde on the Au(111) surface employing temperature-programmed desorption. Here, we show that chemisorbed hydrogen adatoms bind weakly with desorption peaks at ∼110 K, indicating an activation energy for recombinative desorption of ∼28 kJ/mol. We further demonstrate that acetaldehyde (CH₃CHO) can be hydrogenated to ethanol (CH₃CH₂OH) on the H-atom-precovered Au(111) surface at cryogenic temperatures. Isotopic experiments employing D atoms indicate a lower hydrogenation reactivity

Catalyst-Substrate Helical Character Matching Determines the Enantioselectivity in the Ishihara-Type Iodoarenes Catalyzed Asymmetric Kita-Dearomative Spirolactonization

Catalyst design has traditionally focused on rigid structural elements to prevent conformational flexibility. Ishihara’s elegant design of conformationally flexible C2-symmetric iodoarenes, a new class of privileged organocatalysts, for the catalytic asymmetric dearomatization (CADA) of naphthols is a notable exception. Despite the widespread use of the Ishihara catalysts for CADAs, the reaction mechanism remains the subject of debate, and the mode of asymmetric induction has not been well established. Here, we report an in-depth computational investigation of three possible mechanisms in the literature. Our results, however, reveal that this reaction is best rationalized by a fourth mechanism called “proton-transfer-coupled-dearomatization (PTCD)”, which is predicted to be strongly favored over other competing pathways. The PTCD mechanism is consistent with a control experiment and further validated by applying it to rationalize the enantioselectivities. Oxidation of the flexible I(I) catalyst to catalytic active I(III) species induces a defined C2-symmetric helical chiral environment with a delicate balance between flexibility and rigidity. A match/mismatch effect between the active catalyst and the substrate’s helical shape in the dearomatization transition states was observed. The helical shape match allows the active catalyst to adapt its conformation to maximize attractive noncovalent interactions, including I(III)···O halogen bond, N–H···O hydrogen bond, and π···π stacking, to stabilize the favored transition state. A stereochemical model capable of rationalizing the effect of catalyst structural variation on the enantioselectivities is developed. The present study enriches our understanding of how flexible catalysts achieve high stereoinduction and may serve as an inspiration for the future exploration of conformational flexibility for new catalyst designs

Structure Revealing H/D Exchange with Co-Adsorbed Hydrogen and Water on Gold

A fundamental understanding of the interactions between coadsorbed water and hydrogen on metallic surfaces is critical to many chemical processes including catalysis and electrochemistry. Here, we report on the strong and intricate interactions between coadsorbed H/D and water on the close-packed (111) surface of gold. Deuterium isotopic labeling shows H/D exchange in H–D₂O and D–H₂O systems, indicating water dissociation and suggesting a nonrandom scrambling process by revealing the origin of hydrogen evolution (from surface H atoms or from water molecules) during annealing. In this reaction, the protonation of the H-bonding ice network (i.e., the formation of (H₂O)_<i>n</i>H⁺) is energetically favorable and is responsible for water dissociation. Density functional theory (DFT) modeling suggests that the thermodynamics and structure of the protonated clusters are predominant factors for yielding the traceable H₂ desorption features from the surface interaction with H atoms, providing insights into reaction mechanisms

Optimal Synthesis of Water Networks for Addressing High-Concentration Wastewater in Coal-Based Chemical Plants

This paper outlines the development of an optimization-based method for synthesizing a water network, which incorporates various treatment technologies to address the high-concentration wastewater in coal-based chemical plants. One important feature of the proposed approach is that it associates a multistep wastewater treatment design within a source–regeneration–sink superstructure. This design can enforce certain design and structural specifications to tighten the model formulation and enhance solution convergence. A mixed integer nonlinear programming problem is formulated based on the proposed superstructure, which involves unit-specific shortcut models instead of the fixed impurities removal model to describe it accurately. The proposed method for water network synthesis is demonstrated using two case studies, which determine the effect of streams composition and wastewater treatment technologies on the total network cost, freshwater consumption, and water network design. The results highlight the ability of the proposed model for the developed water network synthesis by computing quickly and realizing the goals of cost savings and discharge reduction

Highly Selective, Facile NO₂ Reduction to NO at Cryogenic Temperatures on Hydrogen Precovered Gold

We have discovered that NO₂ is reduced to NO at 77 K by hydrogen precovered gold in vacuum. Here, we investigate the partial reduction of NO₂ to NO on an atomic-hydrogen populated model gold catalyst for a more fundamental understanding of the surface chemistry of hydrogenation. Gold-based catalysts have been found to be active for many hydrogenation reactions, but few related fundamental studies have been conducted. Our experimental results reveal a high catalytic activity for gold: indeed, NO₂ is reduced to NO with 100% conversion and 100% selectivity at temperatures lower than 120 K. Density functional theory calculations and reflection–absorption infrared spectroscopy measurements indicate that HNO₂ and N₂O₃ are intermediates which are highly dependent on surface hydrogen concentrations; subsequent hydrogenation of HNO₂ and dissociation of N₂O₃ upon annealing induces the production of NO and H₂O

Encapsulation of Single Nanoparticle in Fast-Evaporating Micro-droplets Prevents Particle Agglomeration in Nanocomposites

This work describes the use of fast-evaporating micro-droplets to finely disperse nanoparticles (NPs) in a polymer matrix for the fabrication of nanocomposites. Agglomeration of particles is a key obstacle for broad applications of nanocomposites. The classical approach to ensure the dispersibility of NPs is to modify the surface chemistry of NPs with ligands. The surface properties of NPs are inevitably altered, however. To overcome the trade-off between dispersibility and surface-functionality of NPs, we develop a new approach by dispersing NPs in a volatile solvent, followed by mixing with uncured polymer precursors to form micro-droplet emulsions. Most of these micro-droplets contain no more than one NP per drop, and they evaporate rapidly to prevent the agglomeration of NPs during the polymer curing process. As a proof of concept, we demonstrate the design and fabrication of TiO₂ NP@­PDMS nanocomposites for solar fuel generation reactions with high photocatalytic efficiency and recyclability arising from the fine dispersion of TiO₂. Our simple method eliminates the need for surface functionalization of NPs. Our approach is applicable to prepare nanocomposites comprising a wide range of polymers embedded with NPs of different composition, sizes, and shapes. It has the potential for creating nanocomposites with novel functions

Fluorinated Pickering Emulsions Impede Interfacial Transport and Form Rigid Interface for the Growth of Anchorage-Dependent Cells

This study describes the design and synthesis of amphiphilic silica nanoparticles for the stabilization of aqueous drops in fluorinated oils for applications in droplet microfluidics. The success of droplet microfluidics has thus far relied on one type of surfactant for the stabilization of drops. However, surfactants are known to have two key limitations: (1) interdrop molecular transport leads to cross-contamination of droplet contents, and (2) the incompatibility with the growth of adherent mammalian cells as the liquid–liquid interface is too soft for cell adhesion. The use of nanoparticles as emulsifiers overcomes these two limitations. Particles are effective in mitigating undesirable interdrop molecular transport as they are irreversibly adsorbed to the liquid–liquid interface. They do not form micelles as surfactants do, and thus, a major pathway for interdrop transport is eliminated. In addition, particles at the droplet interface provide a rigid solid-like interface to which cells could adhere and spread, and are thus compatible with the proliferation of adherent mammalian cells such as fibroblasts and breast cancer cells. The particles described in this work can enable new applications for high-fidelity assays and for the culture of anchorage-dependent cells in droplet microfluidics, and they have the potential to become a competitive alternative to current surfactant systems for the stabilization of drops critical for the success of the technology

Conversion of Dimethyl Ether to 2,2,3-Trimethylbutane over a Cu/BEA Catalyst: Role of Cu Sites in Hydrogen Incorporation

Recently, it has been demonstrated that methanol and/or dimethyl ether can be converted into branched alkanes at low temperatures and pressures over large-pore acidic zeolites such as H-BEA. This process achieves high selectivity to branched C₄ (e.g., isobutane) and C₇ (e.g., 2,2,3-trimethylbutane) hydrocarbons. However, the direct homologation of methanol or dimethyl ether into alkanes and water is hydrogen-deficient, resulting in the formation of unsaturated alkylated aromatic residues, which reduce yield and can contribute to catalyst deactivation. In this paper we describe a Cu-modified H-BEA catalyst that is able to incorporate hydrogen from gas-phase H₂ cofed with dimethyl ether into the desired branched alkane products while maintaining the high C₄ and C₇ carbon selectivity of the parent H-BEA. This hydrogen incorporation is achieved through the combination of metallic Cu nanoparticles present on the external surface of the zeolite, which perform H₂ activation and olefin hydrogenation, and Lewis acidic ion-exchanged cationic Cu present within the H-BEA pores, which promotes hydrogen transfer. With cofed H₂, this multifunctional catalyst achieved a 2-fold increase in hydrocarbon productivity in comparison to H-BEA and shifted selectivity toward products favored by the olefin catalytic cycle over the aromatic catalytic cycle