Yugo Osaka

Development of low-temperature desulfurization performance of a MnO2/AC composite for a combined SO2 trap for diesel exhaust

Growing concern about the removal of sulfur dioxide (SO2) from combustion exhaust has resulted in the development of desulfurization materials for a SO2 trap. In this study, a manganese dioxide/activated carbon (MnO2/AC) composite was proposed as a low temperature desulfurization material for a combined SO2 trap. The MnO2/AC composite was synthesized using a redox deposition method and characterized using scanning electron microscopy (SEM), nitrogen adsorption, X-ray fluorescence spectrometry (XRF) and Fourier transform infrared (FTIR) spectroscopy. The SO2 adsorption capacity of the composites was measured using thermogravimetry and the SO2 adsorption characteristics were also investigated. In the low temperature region (50–200 °C), the MnO2/AC composite exhibits good SO2 trap performance and the MnO2 conversion of the composite is significantly improved. It was found that the SO2 adsorption on the MnO2/AC composite is a chemisorption process. The experimental data for SO2 adsorption on the MnO2/AC composite could fit the Freundlich model well. Changes in the thermodynamic parameters were determined. The calculated values of ΔG0 and ΔH0 indicate that the SO2 adsorption on the MnO2/AC composite is spontaneous and thermodynamically favorable.

Study on SO2-Absorption Behavior of Composite Materials for DeSOx Filter From Diesel Exhaust

NOx emitted from diesel engines is one of the major air pollutants in most countries. To reduce NOx emission, NOx storage/reduction (NSR) catalysts have been developed for diesel systems. The catalyst for NSR is strongly poisoned with sulfur. This paper reports the synthesis of Na-doped CaCO3 as a new material for SO2 adsorption. Measurements of the desulfurization breakthrough characteristics using monolith washcoated Na-doped CaCO3 were investigated at 450°C. The Na-doped CaCO3 absorbed ∼77.6–90.6 mg-SO2/g-material of SO2 at 450°C (where CaCO3 is 8 mg-SO2/g-material). Investigation of the source of the improved sulfur absorption capacity of the Na-doped CaCO3 relative to the parent material via x-ray diffraction (XRD) and scanning electron microscopy–energy-dispersive x-ray spectroscopy (SEM-EDX) analyses revealed that the new material forms a composite partially composed of Na2Ca(CO3)2. The enhanced SO2 absorption capacity derived from the formation of composite materials is demonstrated herein. SO2 contained in the exhaust gas is absorbed at a lower temperature than with previously reported systems. In order to elucidate the SO2 absorption mechanism of the composite materials, further studies and synthesis of materials with greater absorption capacity are required.

Development of a compact MnO2 filter for removal of SO2 from diesel vehicle emissions

Increasing concern about sulfur dioxide (SO2) from diesel vehicle exhausts causing detrimental effects on NOx removal catalysts has resulted in the development of dry desulfurization filters for complete removal of SO2. In this study, a compact MnO2 filter was developed for diesel emission control. The SO2-capture behavior of the compact MnO2 filter was investigated by using a volumetric device in a low temperature range (200–400 °C) and low SO2 pressure conditions. The maximal capacity of the MnO2 filter was 304.1 mgSO2 per gMnO2 at 400 °C. Based on the experimental results, the required volume of the MnO2 filter was estimated as only 0.6 L for a diesel car with 30 000 km distance traveled per year. The thickness of the MnO2 filter had significant influence on its SO2-capture performance. The sulfate reaction mechanism was also discussed by using a grain model under four reaction temperature conditions for improving the efficiency of the design of the desulfurization filter. The sulfate process can be divided into two control stages (the chemical reaction control stage and the solid diffusion control stage) and the prediction models fit the experimental data well for both control stages, indicating that the two-stage grain model is suitable for the sulfate reaction between the MnO2 filter and SO2. The calculated apparent activation energy of 18.8 kJ mol−1 indicates that the MnO2 filter exhibits high activity for SO2 adsorption in a pure SO2 atmosphere.

Study on performance of chemical heat storage system for direct steam generation

A heat storage system that is used to generate steam directly by exploiting the dissolution phenomenon between CaBr2 and water was studied. The performance of the system in terms of the coefficient of performance (COP) or volumetric heat capacity (VHC) yielded maximal values for the amount of water supplied. The COP was 0.072 to 0.115 for steam pressures of 20–50 kPa at x = 7.5. VHC values recorded were 177.2 to 250.1 kJ/l for steam pressures of 20–50 kPa at x = 7.5. This calculation was validated by comparing the calculated value with the experimental result. The pressure settled at the equilibrium state for a very short duration at the heat release step, proving that the dissolution phenomenon involved a high mass transfer rate and was able to transform the heat of dissolution into enthalpy of steam. The amount of steam generated in the experiment conformed very well to the calculations, thus validating the calculation method.

Water Vapor Adsorption–Desorption Behavior of a Small Piece of Desiccant Rotor in Temperature Swing

This study aims to clarify the adsorption / desorption behavior of water vapor onto / from a desiccant rotor in temperature swing. A magnetic suspension balance followed time variations of the weight of a small piece of desiccant rotor at various desorption temperature, adsorption / desorption time and their duration time ratio. Adsorption-desorption swing in steady state settled down at certain amplitude of the amount adsorbed keeping the balance of the adsorption and desorption rates averaged over each period. At low regeneration temperature around 40–50°C, adsorption and desorption rates were affected considerably by the change of driving force of adsorption q*-q rather than the temperature dependence of the mass transfer coefficient. At constant adsorption and desorption air conditions, the adsorption /desorption rates could be summarized by the amount of adsorption and temperature, independently of the length of cycle time. Also, region of the amount of adsorption at which adsorption–desorption swing occurred was predicted considering the adsorption / desorption rates – amount adsorbed relationship and the adsorption / desorption duration ratio.Copyright

The effect of 3D carbon nanoadditives on lithium hydroxide monohydrate based composite materials for highly efficient low temperature thermochemical heat storage

Lithium hydroxide monohydrate based thermochemical heat storage materials were modified with in situ formed 3D-nickel-carbon nanotubes (Ni-CNTs). The nanoscale (5–15 nm) LiOH·H2O particles were well dispersed in the composite formed with Ni-CNTs. These composite materials exhibited improved heat storage capacity, thermal conductivity, and hydration rate owing to hydrogen bonding between H2O and hydrophilic groups on the surface of Ni-CNTs, as concluded from combined results of in situ DRIFT spectroscopy and heat storage performance test. The introduction of 3D-carbon nanomaterials leads to a considerable decrease in the activation energy for the thermochemical reaction process. This phenomenon is probably due to Ni-CNTs providing an efficient hydrophilic reaction interface and exhibiting a surface effect on the hydration reaction. Among the thermochemical materials, Ni-CNTs–LiOH·H2O-1 showed the lowest activation energy (23.3 kJ mol−1), the highest thermal conductivity (3.78 W m−1 K−1) and the highest heat storage density (3935 kJ kg−1), which is 5.9 times higher than that of pure lithium hydroxide after the same hydration time. The heat storage density and the thermal conductivity of Ni-CNTs–LiOH·H2O are much higher than 1D MWCNTs and 2D graphene oxide modified LiOH·H2O. The selection of 3D carbon nanoadditives that formed part of the chemical heat storage materials is a very efficient way to enhance comprehensive performance of heat storage activity components.

The heat and mass transfer performance of facile synthesized silica gel/carbon-fiber based consolidated composite adsorbents developed by freeze-drying method

ABSTRACT A series of experimental investigations had been performed to analyze the heat and mass transfer performance for two novel types of silica-based consolidated composite adsorbents developed by the freeze-drying method. The first type of adsorbent is silica gel consolidated with carboxymethyl cellulose (CMC) (SC), while the other is silica gel consolidated with CMC and carbon fiber powder (SCC). Results indicate that the thermal conductivity of consolidated composite adsorbents increases with the mass proportion of carbon fiber powder, while it decreases with the increasing moisture content in the preparation process of the adsorbents. When the mass ratio of silica gel, CMC, and carbon fiber powder is 4:1:4, the highest thermal conductivity of consolidated composite adsorbent obtained from experiments reaches 1.66 W m−1 K−1, which is 13.4 times greater than that of pure silica gel. Furthermore, the results of macroporous properties analysis of typical samples including SC20 and SCC20 (where the 20 means that the undried samples have a water content of 20% by mass during the preparation process) show that heat transfer additives effectively improve the macroporous porosity and permeability of the consolidated composite adsorbents. The study on adsorption dynamic performance indicates that the freeze-drying method helps to improve the adsorption performance including adsorption rate and equilibrium water uptake. The experimental results also show that the mass transfer coefficient K of the two typical samples are approximately stable at 5 × 10−3 s−1 when the adsorption temperature is ranged between 30 and 40°C, which are almost twice the corresponding values of the samples developed by heating–drying method. Therefore, the proposed approach which is the consolidation with heat transfer additives combined with freeze-drying method is effective for simultaneously enhancing the heat and mass transfer performance of the silica gel adsorbents.