JOURNAL OF CHEMICAL ENGINEERING OF JAPAN Vol. 50(2017) No. 7

Outstanding Paper Awards Subcommittee of Journal of Chemical Engineering of Japan has assessed the 140 papers published in volume 49 in 2016, and the editorial board finally selected the five papers for JCEJ Outstanding Paper Awards of 2016; these are the papers on “Kinetic Analysis of Decomposition of Ammonia over Nickel and Ruthenium Catalysts,” “Numerical Simulation of Molten Slag Deposition in Radiant Syngas Cooler with a CFD-Based Model,” “Measurement and Calculation of the Liquid–Liquid Phase Boundaries and Phase Equilibria for the Hexane+Polyethylene System at High Temperatures,” “Shear-Induced Microbubble Generation at High Pressures,” and “Water Solubility of Complexes between a Peptide Mixture and Poorly Water-Soluble Ionic and Nonionic Drugs.”

A study on thermodynamics of the various steps involved in the polysilicon manufacture in the Siemens process is presented in this paper. The synthesis of SiHCl₃ (TCS), silicon deposition from SiHCl₃ and hydrogenation of by-production SiCl₄ (STC) for recycle are the main processes studied in this paper. Based on the thermodynamic data for related pure substances, the relation of (n_Cl/n_H)_Eq (i.e. the mole ratio of Si to Cl at equilibrium) and the feeding mole ratio of Cl to H (n_Cl/n_H) was plotted in the Si-Cl-H system. Then, the effects of temperature, pressure and feed fraction on TCS selectivity in the synthesis of SiHCl₃ process, polysilicon yield in the silicon deposition process and SiCl₄ conversion ratio in the SiCl₄ hydrogenation process have been studied. Useful conclusions for improving these processes have been drawn. Finally, the optimum conditions have been obtained and compared with limited published data in the literature. The results show that comparison with the limited reported values in the literature indicates that the operating conditions are close to those predicted by the thermodynamics for all three reactions. However, the reported conversion or yield is lower. It is hoped that this paper makes a contribution as future polysilicon plants move to higher capacity and seek a reduction in the cost of production.

By using isothermal dissolution method, phase equilibrium of the quaternary system Li⁺, Rb⁺, Mg²⁺//Borate–H₂O at 298.2 K was investigated. The solubility, density and refractive index of equilibrated solution were measured experimentally. Based on the experimental data, the stable phase diagram, the density vs J(Rb₂B₄O₇) diagram, water content vs J(Rb₂B₄O₇) and refractive index vs J(Rb₂B₄O₇) diagram were constructed. Results indicate that the quaternary system at 298.2 K is of a simple type, its phase diagram consists of one invariant point, three univariant curve and three crystalline phase areas. The size of crystallization areas of salt is in the order MgB₄O₇·9H₂O>RbB₅O₈·4H₂O>Li₂B₄O₇·3H₂O, which demonstrates MgB₄O₇·9H₂O can be more easily separated from the solution in this quaternary system at 298.2 K. The comparisons between the stable phase diagrams at 298 K and 348 K show that with the decrease of temperature, the precipitation of rubidium borate becomes easier, while that of lithium borate becomes more difficult. With the increase of J(Rb₂B₄O₇), the water contents decrease obviously, the refractive index and the density increase obviously on the univariant curve cosaturated with RbB₅O₈·4H₂O and MgB₄O₇·9H₂O.

In the present study analyzes the fractal characteristic of multi-source information of gas–solid two-phase flow. The differential pressure fluctuation signals in a riser were collected by a data acquisition module with a measured region of 15–55 cm above the air distributor. Daubechies second order wavelet and Hilbert–Huang transform were used to decompose the original signals. The R/S analysis was applied on the decomposed signals. Besides, the gas–solid flow process of this region was recorded by a CCD high speed camera. The box–counting dimensions of the images were calculated as image’s fractal dimensions. By combining the box–counting dimension algorithm theory and actual flow process, the fractal characteristic of two-source information sets were connected. The results show that the decomposed differential pressure signals based on different decomposition methods have similar fractal characteristics. As the decomposition scales increase, the decomposed signals show single-double-single fractal characteristic in turn, which correspond to micro-scale, meso-scale and macro-scale effects of the gas–solid two-phase flow system, respectively. The energy distribution of meso-scale signals is higher than 90%, which indicates that the fluctuation of the differential pressure mainly reflects the interactions between the gas and solid phases in the meso-scale. The image’s box–counting dimension mainly reflects the proportion and distribution of the bubbles in the image. As the superficial gas velocity increases, the mean value of the box–counting dimension also increases, while its corresponding fluctuation range becomes narrower. Besides, the image’s box–counting dimension corresponds to the decomposed differential pressure signals in micro-scale. Both of these can be used to represent the degree of movement and energy consumption of the discrete particles. It is conducive to deepen the understanding of the complicated flow behavior in gas–solid two-phase systems, provided that the fractal characteristic of multi-source information can be correlated.

Flow characteristics with gel reaction of 10 mass% PVA and 3 mass% borax solutions in a Non–element mixer were experimentally investigated. The mixer consisted of a transparent main flow pipe and transparent branch flow pipes that were connected vertically to the main flow pipe. The PVA solution was supplied to the main flow pipe at a constant inlet pressure 20 kPa. The Reynolds number of the main flow (Re) was varied from 0.5 to 10.0. The borax solution was dyed blue to visualize the flow patterns and was injected periodically from one of the branch flow pipes at a mean speed of 40 mm/s. A pressure sensor was used to measure the pressure variation at 100 mm upstream from the first branch flow pipe. When Re was low, the borax periodically formed a capsule-like slug similar to those that occur in multiphase flows. As Re was increased, the borax capsule was stretched by the shear stress of the main flow and adhered to the upside wall of the mixer. At Re=10.0, the pipe was prone to becoming blocked by excess gel product, which resulted in the pressure increasing to the inlet pressure of the system.

Cyclone separators are used in many processes to remove powders for collection in a wide range of diameters. When the cyclone separator is used as a classification device that requires high effectiveness, the 50% cut-off size (D_p50) is restricted to less than several microns owing to the strong centrifugal force. We developed a cyclone-type classifier to effectively classify coarse particles collected by the normal cyclone, as discussed in our previous study. The classifier comprises inner and outer collection boxes with a sloping channel region between the upper sections. The sloping channel could derive the additional air, called blow-up flow, from the tangent nozzle established in the outer box. The blow-up flow becomes confluent with the main swirling flow of the cyclone. In the channel, the fine particles affected by the drag of the blow-up flow were collected in the inner box. Additionally, the coarse particles affected by the centrifugal force induced by the swirling flow were collected in the outer box. The previous study, regarding a classifier with a channel length of 6 mm, demonstrated that D_p50 and the effectiveness of the classification κ, which is the ratio of the 25% cut-off size to the 75% cut-off size (D_p25/D_p75), increase linearly with the increase in blow-up flow rate (Δq). In this study, we increased the channel length from 6 to 23 mm. This resulted in the following beneficial characteristics for separating acrylic particles having a size distribution of 15–35 µm. Unlike the previous study, D_p50 depended on the main flow rate at the entrance regardless of Δq since the increase in Δq increases the centrifugal force, which acts simultaneously on the D_p50 particles, and the drag force. Meanwhile, κ increased significantly with the increase in Δq. The classifier classified the particles with high effectiveness (κ ranging from 0.75 to 0.92).

A circulated flow mixing method with a tubular crystallizer was designed to separate the nucleation and crystal growth phases of pharmaceutical polymorphs for anti-solvent crystallization. The proposed method provides a fluctuating anti-solvent concentration due to the circulation of the active pharmaceutical ingredient (API) solution, whereas the anti-solvent concentration continually decreases in the simple addition method. The two methods were compared in the anti-solvent crystallization of indomethacin (IMC), a non-steroidal anti-inflammatory drug, in a water-acetone system at 50°C. Furthermore, appropriate operating conditions that control the formation of two IMC polymorphs (i.e., a stable form γ and an unstable form α) were investigated. The water addition rate was a key parameter controlling polymorph formation in both methods. Additionally, the proposed method provided a broader operation window to obtain the stable polymorph form γ by controlling the water addition rate, which yielded a 20-fold higher productivity than the simple addition method.

We studied the deposition of non-aggregated nickel nanoparticles formed by hydrogen reduction of nickel chloride onto silica microparticles in a tubular furnace reactor for catalysts. To produce the non-aggregated nickel nanoparticles, rapid cooling with a Laval nozzle was applied to nickel particles. The diameter of the particles could be controlled by the concentration of NiCl₂ vapor and the flow rate of carrier gas N₂ for NiCl₂ vapor. Furthermore, we developed a technique for preventing the sintering of nickel nanoparticles by depositing nickel particles onto silica particles with surfaces softened by high temperatures.

The solubility of aluminum sulfate in sulfuric aqueous solution was determined and analyzed thermodynamically. Aluminum sulfate dissolved in sulfuric acid aqueous solution not spontaneously, because the dissolution enthalpy is a positive value. The solubility of aluminum sulfate had a temperature dependency and hardly dissolved with higher concentration of sulfuric acid. On the other hand, aluminum sulfate solubility did not depend on the existence of oxalic acid, which was dissolved to saturation concentration as an additive. Moreover, the solubility curves of aluminum sulfate and oxalic acid were different in the range between 1.5 M and 6 M sulfuric acid aqueous solution at 25°C. Therefore, using the difference of solubility characteristics, aluminum sulfate could be recovered selectively from waste acid containing oxalic acid. An aluminum sulfate crystal generated from the model waste acid, which was 3.5 M sulfuric acid aqueous solution containing 20 g⋅L⁻¹ oxalic acid, was determined as one of aluminum sulfate hydrate by powder-XRD and its purity was 94%.

The recovery and separation of platinum group metals (PGMs) are of considerable significance for metal sustainability. To establish an efficient extraction process for PGMs, the novel extractant N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]phenylalanine (D2EHAF), containing a phenylalanine moiety as the metal-affinity group, was synthesized. The extraction of PGMs from aqueous HCl and HNO₃ solutions with D2EHAF, or our previously developed N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG), in n-dodecane was investigated. Both D2EHAF and D2EHAG exhibited high extraction affinities for Os⁴⁺, Pt⁴⁺, and Pd²⁺ in aqueous HCl. In a HNO₃ solution, D2EHAF extracted Pd²⁺ more efficiently than D2EHAG, and the extraction of Pd²⁺ from a 1 mol dm⁻³ HNO₃ solution with D2EHAF proceeded quantitatively. The extracted metal ions were stripped from the organic solution using a highly acidic solution, or thiourea.

Fire hazards caused by the self-ignition of coal are perennial disasters, which constitute a severe threat to the global environment. In this study, an innovative Zn foam material, mainly comprising water, foaming agents, zinc acetate, diethanolamine, and hydroxyethyl cellulose, was developed for controlling the spontaneous combustion of coal. These Zn foams exhibited a foaming multiple greater than 30 and a half-life greater than 7 h, indicative of excellent performance. The inhibition mechanism for the spontaneous combustion of coal after the addition of Zn foam was investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. Results indicated that after treatment, ultrafine zinc oxides are uniformly deposited on the coal specimen surface, and functional groups, such as C–O and –OH, in the coal significantly decrease, which effectively inhibit the oxidation of coal.

Oxygen tends to be deficient in a narrow space or in a microgravity environment where natural convection is suppressed. When a combustible solid is burned in such an environment, smoldering combustion without flame occurs. Since smoldering combustion is often observed in the initial stage of a fire, insights into smoldering combustion help understand fire growth behaviors at an early stage of a fire. This paper presents a numerical model of the smoldering combustion of a thin solid in a narrow channel. The smoldering spread rate and the fingering pattern formed by a instability mechanism are particularly studied. It is found that heat loss has a significant influence on the smoldering behavior. With an increase in heat loss, instability tends to be enhanced, leading to more frequent fingertip splits and local extinction.

A combination of ultrasonication and silica gel seed was studied as a silica scale prevention method in geothermal water. The effects of ultrasonic frequency, initial monosilicic acid concentration, pH, concentration, particle diameter and pore size of the silica gel on the removal ratio of silicic acid were examined. For comparison, stirring without and with silica gel, and ultrasonication with the addition of hydrogen peroxide or t-butanol were performed. Ultrasonication enhances the removal of silicic acid by silica gel seed. Ultrasonication at 500 kHz was more effective for the removal of silicic acid than ultrasonication at 28 kHz and stirring. The removal ratio of silicic acid increased with an increase in silica gel concentration. The small seed particle diameter of 60 µm and large seed pore size of 7 nm performed well in the removal of silicic acid. When the initial concentration of monosilicic acid was 1.1 g/L and the silica gel concentration was 1.5 g/L, the removal ratio of silicic acid was highest at pH 6 because the reaction between polymer and polymer is dominant. However, in the case of an initial monosilicic acid concentration of 0.5 g/L, the removal ratio was highest at pH 9 because reaction between polymer and monomer is dominant. The polymerization rate of monosilicic acid was increased by the addition of hydrogen peroxide due to a higher formation rate of hydroxide radicals. In contrast, the addition of t-butanol lowered the polymerization rate of monosilicic acid because the hydroxide radicals were scavenged. The frequency switching from 500 kHz to 28 kHz at 90 min for each ultrasonication enhanced the removal ratio of silicic acid.

In the present study, mixed-phase Cu–Al catalysts have been synthesized by an autocombustion method using glycine as fuel. By adjusting the ratio of glycine, the self-reductive Cu–Al mixed oxides were prepared and demonstrated higher activity than a commercial Cu-based catalyst in the catalytic performance test, where the WHSV was 12/h and the steam/methanol ratio was 1.1. The relationships between the physicochemical properties of the prepared Cu–Al catalysts and the catalytic performance have thoroughly been investigated by various characterization methods, such as BET, in-situ XRD and TEM.

Effects of high H₂ and H₂O (steam) partial pressure (H₂ from 0 to 1.2 MPa, H₂O from 2 to 1.2 MPa) on gasification rates of coal char and Ca-loaded coal char were investigated by using a thermogravimetric apparatus with the temperature range 923 K to 1,173 K. The gasification rate increased rapidly as the H₂ partial pressure was reduced in the reaction gases. The presence of H₂ gas strongly inhibited the char steam gasification rate. However, the gasification rate of Ca-loaded coal char was much higher than that of coal char, and the inhibition by H₂ of the gasification rate was smaller for Ca-loaded coal char than for coal char. The Langmuir–Hinshelwood model was used to analyze the effects of the H₂O and H₂ partial pressures on char and Ca-loaded coal char gasification rates. The temperature-dependent activation energies k_a, k_b, and k_c in the Langmuir–Hinshelwood model were obtained from experimental data and were used to simulate gasification rates for char and Ca-loaded coal char over a wide range of temperatures and P_H2/P_H2O ratios. The effects of H₂ partial pressure were greater (smaller) for Ca-loaded coal char than for char at 1,173 K (1,023 K).

The present study investigates the use of modified red mud as a solid base catalyst for biodiesel production. Red mud, a waste from the Bayer process, was treated using soda-lime calcination at various temperatures. The modified red mud was characterized using TG-DTA, XRD, SEM, BET and the Hammett indicator method. The catalytic activity was investigated for the transesterification of canola oil with methanol to biodiesel with a yield of more than 99% under the following conditions: 12 : 1 methanol/oil molar ratio, 4 wt% catalyst concentration, 60°C reaction temperature, and 2 h reaction time. Furthermore, the catalyst can be reused for up to three cycles without any significant loss of activity.

Plant layout is one of the most important factors for reducing plant construction costs. In the research field of plant layouts, the main purpose is to minimize the total length and cost of pipelines between equipment by satisfying various constraints, such as safety regulations and passages for operators. However, previous research overlooks the consideration of operating conditions. Additionally, sufficient safety distances between equipment have to be guaranteed to mitigate danger or domino accidents, and maintenance spaces should be considered for on-site repairs or maintenance. Moreover, various multi-floor plants have been constructed. Therefore, an appropriate algorithm for handling these issues urgently needs to be developed. Equations for the mixed integer non-linear programming problem considering various issues are proposed in this study. In these equations, the objective function is the total summation of pipeline and additional energy costs generated by pressure drop and heat transfer. Additionally, predefined safety and maintenance spaces are transformed into inequality constraints. Because it is not always possible to use the derivatives of equations, such as in this study, an original particle swarm optimization technique is employed. Two case studies are illustrated to verify the efficacy of the proposed algorithm.