Gas Reaction Process Research Articles

Continuous Production of Formic Acid from Biomass in a Three-Phase Liquid–Liquid–Gas Reaction Process

In this contribution, we present for the first time a continuous production of formic acid under industrially relevant conditions using real biomass as a feedstock. A scale up to 2 L of reaction volume including product separation and catalyst recycling in an automated continuous miniplant has been realized and demonstrated for 670 h time-on-stream using sucrose as a feedstock with space-time yields of 1.1 gFA L–1 h–1, a turnover number (TON) of 840, and an average turnover frequency (TOF) of 1.3 h–1. Very remarkably, by performing a sensitivity analysis, a maximum space-time yield of 1.7 gFA L–1 h–1 was achieved. Moreover, we could demonstrate that oxygen pressures of only 0.5 bar are sufficient for complete catalyst reoxidation in our miniplant. This shows great potential for simply using air as the oxidant in a large-scale application. Very importantly, an experiment with molasses as the substrate showed the use of a technically relevant biomass for a long-term economic application of the continuous OxFA process. By using optimized conditions from the sensitivity analysis, a total amount of 1.2 g h–1 of formic acid could be continuously produced by our miniplant.

ZnO@ZIF-8: Gas sensitive core-shell hetero-structures show reduced cross-sensitivity to humidity

A ‘lawn-like’ distribution of interconnected zinc oxide nanorods, coated with a metal-organic compound based on zeolitic imidazolate frameworks – ZIF-8 was prepared on microstructured thin-film interdigitated Pt-electrodes forming ZnO@ZIF-8 core-shell heterostructures and investigated as gas sensor material in relation to the identical, but uncovered pure ZnO-layer. This composite combines the gas sensing properties of the metal oxide ZnO with the specific properties of the metal-organic framework material which result in a distinct change of the conditions of gas sensing at the ZnO/ZIF-8-interface. Herein, for the first time it is reported that as prepared ZnO@ZIF-8 composite material is an attractive choice to reduce the cross-sensitivity to water vapour (humidity) in the gas sensing response towards propene and ethene. The observed change of sensitivity in relation to uncovered ZnO is discussed to be due to (i) the specific interaction of the ZIF-8 at the interface with the ZnO taking influence on the gas reaction processes, (ii) the diffusivity of ZIF-8 for the different gas components, and (iii) the sorption behaviour of the used gases at the ZnO interface and inside the ZIF-8 material.

Influence of stress on the photocatalytic properties of sprayed ZnO thin films

Zinc oxide (ZnO) thin films grown on glass substrates are prepared by means of the Ion Layer Gas Reaction process. The XRD pattern revealed that the ZnO lattice parameters decrease continuously, with the increasing of the film thickness, indicating a continuous variation in the compressive strain. The influence of the thickness on the optical, morphological and structural properties of deposited ZnO thin films was investigated. The UV–Vis absorption spectra of deposited thin films were shown to exhibit a blue-shift, resulting in an increase in the optical band gap from 3.13 eV to 3.24 eV. Structural parameters such as crystallite size, lattice parameters, Zn–O bond length, and residual stress have been determined, and the compressive strain (tensile stress) is found to increase with the increasing of spray time and in turn deposited thin film thickness. The PL spectra of deposited ZnO films, show stronger PL intensity with increasing deposited thin film thickness, which confirm the influence of deposited film thickness on the recombination process of charge carriers and thus on its optical properties. These results, were confirmed by the photo-electrochemical experiments. In addition, a wettability alteration and shift from hydrophobic to hydrophilic surface is observed under UV light exposure, which shows that structural defects and surface morphology of deposited thin films were also demonstrated to have a direct impact on deposited films’ optical properties. Furthermore, to further confirm these experimental optical results, theoretical first principle calculations were conducted. In addition, a wettability alteration and shift from hydrophobic to hydrophilic surface is observed under UV light exposure.

When Catalysts Breathe

In this issue of Joule, Yi Cui and colleagues developed a breath-mimicking structure for electrocatalysis applications where gas no longer has to be dissolved into the electrolyte. Specifically, a highly efficient three-phase contact between gas, electrolyte, and catalyst is formed, facilitating both O2 evolution (OER) and reduction (ORR) reaction processes. A low overpotential of 190 mV at 10 mA/cm2 is reported in the OER process while in the ORR process significantly higher current densities are observed.

Beyond Mono-, Di-, and Trisulfides: Synthesizing Vanadium Tetrasulfide (VS4) Films for Energy Conversion

Vanadium tetrasulfide (VS4, called patronite as a mineral) is a one-dimensional compound with promising properties for energy conversion applications. However, it has been scarcely investigated because of its complex synthesis. In this work, we report a detailed investigation about the formation mechanism of VS4 (V4+(S22–)2) as well as its structural, transport, and photoelectrochemical properties. To this aim, VS4 films were grown by a solid–gas reaction process between vanadium films and sulfur at temperatures between 350 and 450 °C during different reaction times. Film characterization (X-ray diffraction, energy-dispersive analysis of X-ray, micro-Raman spectroscopy, and scanning electron microscopy) reveals the formation of monoclinic VS4 nanorods (I2/C) as single crystalline phase in very short reaction times (t < 5 h). Optical characterization was carried out by reflectance and transmittance measurements to obtain the optical absorption coefficient (α = 104 cm–1 at photon energies higher than 1.6 eV...

Kinetic Models for Coal Hydrogasification and Analyses of Hydrogasification Characteristics in Entrained-Flow Gasifiers

Coal hydrogasification (CHG) is a promising technology for clean and efficient coal utilization. However, the kinetic mechanism of CHG has not been fully understood, and multidimensional numerical simulations of CHG in entrained-flow gasifiers are still rarely reported. To evaluate and optimize hydrogasification parameters in an entrained-flow-bed gasifier, it is necessary to develop a reasonable CHG kinetic model and carry out the corresponding numerical simulations. In this work, a CHG kinetic model, including five homogeneous reactions and three heterogeneous reactions, is established. Thereinto, for the heterogeneous reactions, a novel combined random pore and shrinking-core model with pressure correction (CRPSC–PC) is put forward to predict the char–gas reaction process. When the CHG model is set up, it is then loaded to the commercial computational fluid dynamics (CFD) package, Fluent, via the user-defined function (UDF), and the simulation results are validated against literature-available experime...

Continuous Catalytic Hydrogenation of Carbon Dioxides on Immobilized Ru Functionalistic Catalysts

Functionalized catalyst preparation is a new and attractive method for hydrogenation of carbon dioxides. Three kind of carriers were functionalized firstly and then Ru was immobilized on the carriers. Continuous catalytic hydrogenation process was used to evaluate the activity of the catalyst on fixed-bed. It was found that the main production are formic acid and CO at 10MPa, and both the selectivity and recovery of CO are more than 90%, the hydrogen reaction mechanism could be explained with the reversed water gas reaction process. This may offer a new way for the reuse of CO2.

X-ray absorption measurements on an ultrasonic spray aerosol

Spray deposition of thin films and coatings is a widely used manufacturing process owing to its low cost, versatility and simple implementation. The objective of the presented experiments was to investigate whether X-ray absorption measurements on solutes carried by aerosols are possible, and what count rates can be achieved depending on solution flow through and the resulting mass density in the interrogation volume. The investigated prototypical spray aerosol was InCl(3) dissolved in water or ethanol dispersed via an ultrasonic nebulizer. InCl(3) spray is essential for the ion layer gas reaction process used for the deposition of In(2)S(3) buffer layers for highly efficient chalcopyrite solar cells. The discussed experiments demonstrate that measurements are possible, but that the achievement of good signal-to-noise ratios requires extended sampling times and concentrated solutions.

The reaction mechanism of the spray Ion Layer Gas Reaction process to deposit In 2S 3 thin films

The spray Ion Layer Gas Reaction (ILGAR) is a well-established, patented and commercial process used primarily to deposit In 2S 3 as buffer layers in thin film solar cells. In this paper we investigate the growth mechanism of the spray In 2S 3 ILGAR process by characterising the intermediate growth stages of films, following the growth mechanism with a quartz crystal microbalance and tracking the gaseous side-and-intermediate products during film growth, using a mass spectrometer. A basic growth mechanism model is then proposed based on an aerosol assisted chemical vapour deposition of an In(O x,Cl y,(OH) z) film, as the first stage process, followed by the conversion of the intermediate film using H 2S gas to In 2S 3.

An investigation of the dip-Ion Layer Gas Reaction process to produce ZnO films with increased deposition rates

Intrinsic ZnO thin film layers have previously been deposited using the dip-ILGAR ‘Ion Layer Gas Reaction’ method. This deposition method and material has been effectively employed to deposit the buffer layers in chalcopyrite solar cells [M. Bär, H.-J. Muffler, Ch.-H. Fischer, S. Zweigart, F. Karg, M.C. Lux-Steiner Prog. Photovolt: Res. Appl. 10 (2002) 173]. The original parameters for the ZnO dip ILGAR deposition process were optimised for film quality. These parameters, however, were not suitable for an up-scaled technology transfer to tape deposition as the dip speed and growth rate meant impractically long deposition times. The results presented here are from an investigation, using the laboratory scale ILGAR apparatus with 2.5 × 5 cm 2 substrates, into parameters e.g. solvent, salt and apparatus parameters, which could allow an increased deposition rate and dip speed yet retains film quality. Simple dip mechanics and the Landau–Levich equation, which describes film thickness as a function of dip withdrawal speed, gravitational acceleration and the properties of the solution, are considered. The recently optimised deposition parameters given here will allow a dip speed of more than 7 m/min and deposition rate of 7.5 nm/cycle.

Optimal Design of Synthesis Gas Production Process with Recycled Carbon Dioxide Utilization

Many countries are trying to reduce their primary energy demand and greenhouse gas (such as carbon dioxide (CO2)) emissions. There has been much research on CO2 utilization to reduce CO2 emission and increase economic efficiency in industries. In this paper, an integrated optimization strategy of an industrial synthesis gas production plant with additional CO2 recycling processes using carbon dioxide as a reactant is presented. The CO2 recycling process allows three different kinds of alternative synthesis gas reaction processes in parallel: steam reforming, dry methane reforming, and reverse water−gas shift reaction. The strategy is based on the integrated superstructure optimization that assists the formulation of the optimal process design problem such that mixed integer programming can be derived. The mathematical programming problem which has flexibility in selecting different synthesis gas reaction processes is used to find the optimal configuration of the process. The industrial synthesis gas plan...

RELEASE OF CHLORINE AND ITS RETENTION IN ASH DURING CO-COMBUSTION OF BIOMASS AND COAL IN A PULVERIZED FUEL COMBUSTOR

Chlorine is a harmful element in fuels such as biomass, waste, and some coals, and it emits in gas or is retained as impurities in various components of ash during the process of combustion and gasification. In this paper, the chlorine behavior is predicted by the global equilibrium analysis (GEA) for co-combustion of coal with straw in a pulverized fuel combustor and the results are analyzed based on experimental data. The emission of HCl and the content of chlorine in ash have been estimated for various blend ratios of biomass and coal. For co-combustion of hard coal with straw, most of chlorine releases as HCl. For co-combustion of brown coal with straw, more gas alkali chloride will be formed. The minor elements play various roles on the chlorine release and its retention. The interaction of HCl and emission species (CO, SOx, NO) during the gas reaction process implies that chlorine in fuels affect the emission of pollutants to some extent. Finally, the reaction mechanism of the chlorine release and its retention during co-combustion is proposed. It is seen that various compositions of fuel blends have influence on the detailed mechanism of chlorine behavior.

Effect of surface oxyfluorination on the bonding between acrylic coated optical fiber and cementitious and polyester resin matrices

We examine the effect of fiber surface oxyfluorination on the interfacial bonding between acrylic coated optical fiber and a cementitious matrix and polyester resin respectively. The optical fiber is surface oxyfluorinated through a gas reaction process at room temperature in which elemental oxygen and fluorine are introduced into the acrylic molecular chain to replace the hydrogen atoms partially. After surface fluo- rination, the wettability of the optical fiber improves. Through an optical fiber embedment pull-out test, it is found that the surface oxyfluorination treatment improves on average the adhesional shear bond strength between the optical fiber and the cementitious matrix by 22% and the interfacial bonding between the optical fiber and the polyester resin matrix by 66%. The debonding of the unmodified optical fiber and the polyester matrix exhibits catastrophic failure characteristics, whereas that of the oxyfluorinated optical fiber with the polyester matrix is more gradual and there is still a substantial bond at the interface after the interfacial adhesive bond is broken. The mechanisms for the increase in interfacial bonding between the oxyfluorinated acrylic coated optical fiber and the cementitious and polyester resin matrices are proposed.

Reflection electron microscopy: studies of surface structures and surface dynamic processes

Reflection electron microscope (REM) studies of surface structures and surface dynamic processes are reviewed. The techniques, image contrast and capabilities to characterize surface structures are described. REM has been successfully used to study surface dynamic processes such as sublimation, surface structural phase transitions, adsorption processes, epitaxial growth processes, gas reaction processes and surface electromigration. These results are briefly summarized. Finally, some future problems are discussed.

High Temperature Gas Reaction Specimen Chamber for an Electron Microscope

High temperature gas reaction specimen chamber for an electron microscope has been constructed. The specimen under electron microscopic observation can be heated at about 1000°C in a gas layer at a pressure of about 300 Torr. The specimen is placed on a film covering the minute hole in the platinum ribbon and heated by an electric current sent through the ribbon. The gas is supplied around the specimen through a pipe and overflows into the vacuum of microscope column through the two platinum apertures on either side of the ribbon. The overflows gas from the specimen chamber is pumped out seperately from the evacuation system of main column. The minute hole in the ribbon and platinum apertures on either side of the ribbon are set to enable the passage of electron beams. The specimen stage can be taken out from the vacuum of electron microscope column through an air lock system without breaking down the vacuum. Some observations of gas reaction processes at elevated temperature by using the present device are presented.