Zhiwen Qi

Residue curve maps for reactive distillation systems with liquid-phase splitting

Abstract A model has been developed to study the effects of chemical kinetics on the residue curve maps (RCM) for reactive distillation systems with liquid phase splitting. In the model, chemical reaction can occur in both or only one of the two liquid phases. The heating policy V / V 0 = H / H 0 is applied so that the kinetic effect can be described by a single parameter, the Damkohler number Da . The effects of reaction kinetics on pseudohomogeneous and heterogeneous mixtures have been compared. The properties of their RCMs are the same outside, but are fully different inside the liquid–liquid (L–L) region if they have different chemical equilibrium curves. Inside the L–L region, the chemical equilibrium curve coincides to a unique reactive liquid–liquid tie line in case that the pseudohomogeneous chemical equilibrium curve intersects with the L–L envelope. When the reaction occurs in only one of the two liquid phases, the residue curves inside the L–L region are strongly affected by the L–L envelope, especially at high Da . In the present paper, first an illustrative arbitrary reaction system, and then the reaction of cyclohexene with water to cyclohexanol are analysed with respect to their RCMs.

Synthesis of cylohexanol by three-phase reactive distillation: influence of kinetics on phase equilibria

A reactive distillation process is being suggested for the production of the commercially interesting intermediate cyclohexanol from cyclohexene and water, which avoids some of the drawbacks of the conventional liquid-phase cyclohexane oxidation process, especially with respect to operational safety. This reactive distillation process has its own intricate challenges due to the fact that reaction, distillative separation and liquid-phase splitting occur simultaneously. The interaction of these three phenomena is studied using residue curve maps for both, model simulations and experimental data. Based on the fixed point analysis of the residue curves, a novel process is proposed for the reactive separation of cyclohexene/cyclohexane mixtures which is difficult to be carried out by conventional distillation due to very close boiling temperatures.

Selective oxidation of cyclohexanol to cyclohexanone in the ionic liquid 1-octyl-3-methylimidazolium chloride

Ionic liquid (IL) 1-octyl-3-methylimidazolium chloride was found to effectively intensify cyclohexanol oxidation and resulted in 100% conversion of cyclohexanol with 100% selectivity to cyclohexanone using hydrogen peroxide as an oxidant and WO(3) as a catalyst. The effect of the IL as a solvent is discussed with the support of COSMO-RS theory.

Efficient Aerobic Oxidation of 5-Hydroxymethylfurfural in Aqueous Media with Au-Pd Supported on Zinc Hydroxycarbonate

Bimetallic catalysts with Au–Pd supported on zinc hydroxycarbonate (ZOC) were synthesized by a simple deposition–precipitation method and analyzed by transmission electron microscopy to have a narrow‐size distribution of predominantly 1–2 nm. The prepared Au–Pd/ZOC catalysts exhibited excellent activity towards 5‐hydoxymethylfurfural (HMF) oxidation in water in the presence of the base NaHCO3 at benign conditions of 80 °C and 3 bar O2, resulting in quantitative yield of 2,5‐furandicarboxylic acid (FDCA). The addition of base not only enhanced the yield of FDCA but also stabilized the support ZOC by preventing ZOC from the reaction with formed carboxylic acid intermediates/products, thus allowing Au–Pd/ZOC to be recycled for at least six times without significant loss of activity. The basicity of ZOC could play an important role in obtaining the improved yield of FDCA as compared to other supports.

Reactive separation of isobutene from C4 crack fractions by catalytic distillation processes

Reactive distillation is a hybrid process where chemical reaction and distillative separation are performed in a single equipment. Even though reactive distillation could increase the selectivity of the desired product by the selective reaction this is not always true as shown in this work. A study on the MTBE reaction system using two coupled reactive distillation columns to separate a C4 crack mixture is carried out, where methanol acts as reactive entrainer and MTBE is the intermediate product. In the first column, isobutene and methanol react to form MTBE hence separating the inert C4 component, while in the second column MTBE splits back to methanol and isobutene. Methanol is recycled back to the MTBE formation column and isobutene is obtained as a product. This coupled process with direct recycle of methanol is possible only if no side reactions occur. When the side reactions are taken into account, byproducts such as diisobutene, dimethyl ether and water will be produced so that higher purity methanol can not be obtained at the bottom of the splitting column. The outlet of the splitting column must be firstly separated rather than being recycled directly to the formation column. Moreover, an attempt has been made to show how the selectivity of the desired product isobutene can be critically influenced by the operating parameters such as the reflux ratio. If the reflux ratio increases, a high quantity of diisobutene and dimethyl ether will be obtained which seriously affects the selectivity of isobutene. The influence of operating parameters is investigated by using a continuation method, which shows that bifurcation behavior can appear in both MTBE formation and decomposition process.

Controlled Synthesis of Nanoscale Icosahedral Gold Particles at Room Temperature

The shape of nanocrystals determines surface atomic arrangement and coordination, influencing their chemical and physical properties. We present a novel and facile approach to synthesize gold icosahedra by employing glucose as reducing reagent and sodium dodecyl sulfate as directing agent in the environmentally benign medium of water at room temperature. The size of the icosahedra can be controlled in the range of 30–250 nm by altering reaction conditions. High‐resolution microscopy and diffraction studies indicate the icosahedra are composed of rotational twins that owe likely to assemblage of tetrahedral units. The gold icosahedra particles catalytic properties are probed in the borohydride reduction of p‐nitrophenols and exhibit a size‐dependence reaction property. Comparison studies with spherical particles prepared by the Turkevich method, coupled with poisoning experiments, infer that the shape has a strong influence in the abundance of active surface sites as well as their activities. The properties of nanoscale icosahedra particles has promising applications for further catalytic processes, surface enhancement spectroscopic methods, chemical or biological sensing, and the fabrication of nanoscale devices.

Bifurcation analysis of reactive distillation systems with liquid-phase splitting

Abstract The bifurcations are studied in simple reactive distillation processes, where liquid-phase splitting can happen, and the chemical reaction can occur in both or only one of the two liquid phases. Due to the different basic singular points and different chemical equilibrium curves, the bifurcations in the heterogeneous system are identical outside but fully different inside the liquid–liquid region compared to those in the pseudohomogeneous chemical equilibrium curve system. The bifurcations are also different inside the liquid–liquid region when the chemical reaction takes place in only one of the two liquid phases. There are potential singular point curves which are connected by the basic singular points in the corresponding nonreactive system. All the singular point bifurcations with respect to the normalized Damkohler number D and all the pinch point bifurcations with respect to the chemical equilibrium constant K follow these potential singular point curves. The analysis reveals that there exist critical values of the parameters D and K , at which the properties of the singular points change.

The impact of interfacial mass transfer on the feasible products of countercurrent reactive separation processes

Abstract For the conceptual design of continuous countercurrent separative reactors, there is a need to predict the composition of the feasible top and bottom products. These products can be identified as stable singular points of the rectifying and stripping sections at infinite column height. General singular point equations are derived for the top and bottom products of separative reactors at countercurrent operation. They can be applied to phase equilibrium-controlled processes as well as to mass-transfer-controlled processes. For a given reactive mixture, all singular points at the top and at the bottom of a column are located on a unique potential singular point surface. It is demonstrated that interfacial vapour–liquid mass transfer has a strong impact on the feasible reactor products. Reactive distillation and reactive pervaporation of selected ideal and real reaction systems are used as illustrative examples.

Conceptual design aspects of reactive distillation processes for ideal binary mixtures

Abstract A comparative study on the conceptual design of reactive distillation process configurations is presented, considering the reversible reaction A 1 ⇔A 2 in an ideal binary mixture as simple model system. The analysed flow schemes are a reactor-distillation column sequence with an external recycle loop, the same recycle system with a prereactor, a nonreactive distillation column on top of a reactive reboiler, a fully reactive distillation column, and a hybrid distillation column combining a reactive and a nonreactive section. For these configurations, the design aspects are discussed in terms of the most important operating parameters, kinetic parameters and design parameters.

Self-assembled single-crystalline ZnO nanostructures

We report a template-free, halide-free, efficient wet chemical method to synthesize defect-rich ZnO nanostructures with exposed {101} facets. The self-assembled ZnO nanostructures provide an active playground for catalytic reactions, such as CO2 hydrogenation, and exhibits great potential in alternative energy technologies.