Ways to Create New CHNO‐Oxidizers for Stoichiometric Gas‐Generating Compositions with Low Combustion Temperature

The investigation is aimed to study the possibility of creation of new CHNO‐oxidizers for smokeless gas‐generating compositions for airbag inflators. For ensuring low amount of CO and nitrogen oxides in combustion products it is necessary to create stoichiometric compositions with a relatively low combustion temperature. Ways to create new oxidizers acceptable to this requirement are examined, mainly by introducing low‐enthalpy oxygen‐containing groups into the oxidizer molecule. Standard enthalpy of formation (Δ_fH°) has been calculated for substances with unknown Δ_fH°, thermal stability has been qualitatively estimated, and combustion temperatures of stoichiometric compositions have been calculated.     

Ways to Create Fuels for Stoichiometric Gas‐Generating CHNO‐Compositions with Low Ammonium Nitrate Fraction

The investigation is aimed to study the possibility of the creation of new CHNO‐fuels for smokeless stoichiometric gas‐generating compositions for airbag inflators. New fuels must have a rather high content of oxygen (to decrease the ammonium nitrate content) as well as a moderate enthalpy of formation in order to prevent an increase of the combustion temperature and of the amount of toxic gases (CO and nitrogen oxides) in the combustion products. Ways to create such new fuels are examined, mainly by introducing low‐enthalpy oxygen containing groups together with oxidizing groups (such as NO₂, ONO₂, NNO₂) into molecules. For several hypothetic substances, the enthalpy of formation has been calculated, thermal stability has been qualitatively estimated, combustion temperatures of stoichiometric compositions have been calculated, and possible ways of their synthesis have been considered.     

Properties of Gas‐Generating Mixtures Related to Different Fuel and Oxidizer Compositions

This work focuses on solid energetic materials designed to produce high‐pressure gas for pressurizing or inflating devices. In small gas generators sodium azide is often used. Unfortunately, this chemical exhibits drawbacks concerning toxicity and yield of gas. Other classical gas‐generating agents are double base propellants. However, they deliver toxic and reactive gases and their combustion temperatures are high. In previous work a series of alternative gas‐generating compositions have been proposed, fuelled with double base propellants, azodicarbonamide, nitroguanidine or guanidine nitrate and oxidized with potassium nitrate or potassium perchlorate. They were theoretically and experimentally evaluated on a series of combustion properties, such as ignition delay, burning rate, vivacity, specific energy, etc. The purpose of this paper is to experimentally examine the gas production of the previously proposed compositions. The yield of gas is determined through static pressure measurements after a closed vessel test, while the composition of the combustion gases is investigated through gas analysis. The addition of an oxidizer causes a significant drop in the yield of gas, but avoids the formation of hazardous gases, such as H₂ and CO, in most of the studied cases. The only exception is the mixture of a double base propellant with potassium nitrate: potassium nitrate does not fully react with the double base propellant and therefore the formation of CO and H₂ is not prevented.     

Effect of Porosity on the Burn Rate of a Gas‐Generating Composition

In the course of the development of an oxidizer‐based extruded composite propellant for use as gas generant, a simple model to describe and evaluate the actual porosity using simple methods was developed. It is briefly described and used to assess the influence of porosity on the burn rate of propellants produced. For the formulation studied the presence of microporosities does not seem to significantly influence the burn rate. On the other hand, volume fraction of porosities in extruded composition grains can exert a large influence and can increase considerably under thermal treatment with a resulting augmentation in burn rate.     

Microwave‐Assisted Heterogeneous Gas‐Phase Catalysis

This article reviews microwave‐assisted heterogeneous gas‐phase catalysis. To date, this special means of non‐classical energy input by microwave radiation is still a fringe area of catalysis research, and alternative reaction engineering in chemistry and chemical engineering. However, microwave‐assisted heterogeneous gas‐phase catalysis is expected to gain significant popularity in academia and industry in the near future. Experimental set‐ups that have been described in literature are critically reviewed, and concepts for the design of improved experimental set‐ups are provided in this article. Historical developments, current tendencies, and a short introduction to the theory of dielectric heating are discussed.     

含叠氮化钠气体发生剂热动力学试验研究

通过ＤＳＣ热分析方法对叠氮化钠气体发生剂的热分解动力学特性进行研究，揭示了叠氮化钠以及其他添加剂对化学反应的影响程度。     

High‐Pressure High‐Temperature Transparent Fixed‐Bed Reactor for Operando Gas‐Liquid Reaction Follow‐up

A 3‐MPa, 350 °C fixed‐bed reactor was designed to follow‐up gas‐liquid‐solid reactions on a millimetric size heterogeneous catalyst with Raman spectroscopy. The transparent reactor is a quartz cylinder enclosed in a Joule effect heated stainless‐steel tube. A methodology to determine how to focus the microscope for liquid and solid phase characterization is presented. The setup was validated by performing diesel hydrodesulfurization on a CoMo/alumina extrudate catalyst with a conversion very close to expected values along with the acquisition of Raman spectra of the solid catalyst showing an evolution of the catalyst phase during sulfidation.     

Synthesis Gas Production Configurations for Gas‐to‐Liquid Applications

Different syngas configurations in a gas‐to‐liquid plant are studied including autothermal reformer (ATR), combined reformer, and series arrangement of gas‐heated reformer and ATR. The Fischer‐Tropsch (FT) reactor is based on a cobalt catalyst and the degrees of freedom are steam‐to‐carbon ratio, purge ratio of light ends, amount of tail gas recycled to synthesis gas (syngas) and FT synthesis units, and reactor volume. The production rate of liquid hydrocarbons is maximized for each syngas configuration. Installing a steam methane reformer in front of an ATR will reduce the total oxygen consumption per barrel of product by 40 % compared to the process with only an ATR. The production rate of liquid hydrocarbons is increased by 25.3 % since the flow rate of the purge stream for the ATR is the highest one compared to other configurations and contains mainly CO₂.     

Heat Transfer from Immersed Vertical Cylinders in Gas‐Liquid and Gas‐Liquid‐Solid Fluidized Beds

The heat transfer coefficient, h, was measured using a cylindrical heater vertically immersed in liquid‐solid and gas‐liquid‐solid fluidized beds. The gas used was air and the liquids used were water and 0.7 and 1.5 wt‐% carboxymethylcellulose (CMC) aqueous solutions. The fluidized particles were sieved glass beads with 0.25, 0.5, 1.1, 2.6, and 5.2 mm average diameters. We tried to obtain unified dimensionless correlations for the cylinder surface‐to‐liquid heat transfer coefficients in the liquid‐solid and gas‐liquid‐solid fluidized beds. In the first approach, the heat transfer coefficients were successfully correlated in a unified formula in terms of a modified j_H‐factor and the modified liquid Reynolds number considering the effect of spatial expansion for the fluidized bed within an error of 36.1 %. In the second approach, the heat transfer coefficients were also correlated in a unified formula in terms of the dimensionless quantities, Nu/Pr^1/3, and the specific power group including energy dissipation rate per unit mass of liquid, E^1/3D^4/3/ν_l, within a smaller error of 24.7 %. It is also confirmed that a good analogy exists between the surface‐to‐liquid heat transfer and mass transfer on the immersed cylinder in the liquid‐solid and gas‐liquid‐solid fluidization systems.     

Energy‐Efficient Gas‐Phase Electrolysis of Hydrogen Chloride

Hydrogen chloride is a by‐product in important processes like the polyurethane production. The currently most efficient electrochemical process for recycling it to chlorine is based on a liquid‐phase reactor, utilizing aqueous hydrochloric acid as a feedstock. Recent investigations showed that employing a gas‐phase reactor and according novel strategies for product purification leads to significant exergetic savings. This article aims to discuss the efficient electrolysis of gaseous HCl on the reactor level but also on the overall process level in comparison to the current state of the art.     

Gas‐Liquid Direct‐Contact Evaporation: A Review

Gas‐liquid direct‐contact evaporators are characterized by the bubbling of a superheated gas through the solution to be concentrated. In other words, they are nonisothermal bubble columns. Despite their simplicity of construction, these units exhibit rather complex hydrodynamics and, similar to what occurs to isothermal bubble columns, the design of such units still poses a problem. The present paper reviews the literature regarding this kind of equipment, addressing both experimental studies and modeling efforts. The covered issues include classic and potential applications, bubbling regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit. Additionally, pertinent literature on isothermal bubble columns is also discussed. Recommendations are made for future research.     

Reactor Modeling of Gas‐Phase Polymerization of Ethylene

A model is developed for evaluating the performance of industrial‐scale gas‐phase polyethylene production reactors. This model is able to predict the properties of the produced polymer for both linear low‐density and high‐density polyethylene grades. A pseudo‐homogeneous state was assumed in the fluidized bed reactor based on negligible heat and mass transfer resistances between the bubble and emulsion phases. The nonideal flow pattern in the fluidized bed reactor was described by the tanks‐in‐series model based on the information obtained in the literature. The kinetic model used in this work allows to predict the properties of the produced polymer. The presented model was compared with the actual data in terms of melt index and density and it was shown that there is a good agreement between the actual and calculated properties of the polymer. New correlations were developed to predict the melt index and density of polyethylene based on the operating conditions of the reactor and composition of the reactants in feed.     

Drying Kinetics in a Vertical Gas‐Solid System

A one‐dimensional steady‐state two‐fluid model has been developed to demonstrate the drying kinetics in the vertical up‐flow gas‐solid system. The model takes into account mass, momentum, and heat transfer between the continuous and dispersed phases. A set of non‐linear differential equations have been solved numerically for the velocity, moisture content, and temperature of both the continuous and dispersed phases along the dryer length. The effect of operating parameters on drying kinetics has been critically examined and the model simulations are compared with the data reported in the literature.     

Optimal Design of a Gas‐to‐Liquids Process with a Staged Fischer‐Tropsch Reactor

The optimal design of a natural gas‐to‐liquid hydrocarbons (GTL) process with a multistage cobalt‐based Fischer‐Tropsch reactor and interstage product separation is considered. The objective function is to maximize the wax (C₂₁₊) production rate at the end of the reactor path. Sectioning of the Fischer‐Tropsch reactor increases the chain growth probability inside the reactor which results in a higher production of wax. The carbon efficiency of the two‐stage reactor is distinctly higher than that of the single‐stage reactor.     

Numerical Study on Bubble Formation of a Gas‐Liquid Flow in a T‐Junction Microchannel

Bubble emergence in a gas‐liquid flow in a T‐junction microchannel of 100 μm diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number.     

Gas‐Liquid Mass Transfer Characteristics in a Rotating‐Drum Bioreactor

The oxygen volumetric mass transfer coefficient is a key parameter to characterize the performance of aerobic bioreactors. A novel rotating‐drum bioreactor (RDB) fitted with a sparger as proposed in a previous work has demonstrated its excellent gas‐liquid mass transfer performance. To provide primary information on the design and scale‐up of the novel RDB, effects of reactor configuration including the number and width of lifters and operation conditions such as rotational speed, aeration rate, and solid volume fraction on mass transfer performance were systematically investigated in a new medium‐sized RDB. Compared with the stirred bioreactor and traditional RDBs, this new RDB exhibits better mass transfer performance. Taking both operational and reactor configuration parameters into consideration, an empirical correlation to predict the volumetric mass transfer coefficient in this type of RDBs was proposed which is valuable for its design and scale‐up.     

Design and Numerical Simulation Analysis of an Integrative Gas‐Liquid‐Solid Separation Hydrocyclone

Normally, a gas‐liquid‐solid separation includes both degassing and desanding processes, which means a relatively higher facility investment and larger energy consumption. Based on an inner‐cone hydrocyclone developed before, an integrative degassing and desanding hydrocyclone was designed. Its design idea and process are described in detail. By means of a hollow inner cone (IC), the separated liquid enters into the cone through holes on it and then flows to the liquid‐phase outlet. Due to integrative separation and tangential solid outlet, the separator has a more compact size. Simulation analysis of the effect of IC diameter and IC height on separation performance was carried out. Results indicate that with a larger IC diameter the gas content in the solid outlet decreases, while as the IC height rises, the gas content in the liquid outlet increases.