We experimentally investigated the effects of turbine blade shapes and aspect ratio of the stirred vessel on the exchange rate of a three–stage vertical stirring vessel equipped with three turbine blades. The exchange rate of the three–stage vertical stirring vessel was measured by changing the impeller diameter, disk diameter of impeller, blade width of impeller, blade length of impeller, blade number of impeller and aspect ratio of the stirred vessel. No effect of blade length on the exchange rate was observed. We found that the dependence of the modified dimensionless exchange rate Q/(nD_i³A_r) on the agitated Reynolds number changed when the blade number was changed. Other design and operation factors differed in the absolute value of the modified dimensionless exchange rate, but their agitated Reynolds number dependence was the same.

Three types of coke deposits (A, B, C) recovered from commercial ethylene plant was analyzed and oxidized to reveal the chemical properties and oxidized kinetic parameters. Carbon content in these coke deposits were more than 90%, and A and B contained about 3 wt% of ash, the main component of ash was Fe₃O₄. Iron compounds on coke deposits surface was removed by acid treatment of A and B for 24 h, then iron content inside the deposits slowly eluted. Hence, Fe₃O₄ was both on surface and inside the coke deposits. Coke is often removed by combustion. Hence, oxidative reaction of these coke deposits was conducted at various heating rates, and activation energy was determined. Activation energy of oxidative reaction of A was almost same as C. H/C ratio, interlayer spacing and stacking height of A is almost same as C, indicating that structure of A and C is similar. Main component of B had not been graphitized compared to A and C, and activation energy of oxidative reaction of main component of B was lower than those of A and C. The oxidative reaction rate equations of the coke deposits were formulated using nucleation and growth model, and the evaluated equations well predicted experimental data.

By electrolyzing sulfuric acid, two types of oxidative species, peroxymonosulfuric acid and peroxodisulfuric acid, are generated without the addition of hydrogen peroxide. We are developing a technology called “electrolytic sulfuric acid method” to decompose only the resin component of waste carbon fiber reinforced plastics (CFRP) into CO₂ and water using the highly oxidative liquid obtained by electrolyzing sulfuric acid, thereby recycling the carbon fibers. To establish this process, it is necessary to understand the stability of the oxidative species in electrolytic sulfuric acid. However, although detailed studies have been conducted on the generation of oxidative species and their stability immediately after generation through the electrolysis of sulfuric acid, there has been little investigation into their long-term stability suitable for industrial processes. Therefore, in this paper, we conducted experimental investigations on the stability of oxidative species at room temperature and predicted stability using Arrhenius plots at high temperatures. As a result of the investigation, the stability (half-life) of oxidative species generated by the electrolysis of sulfuric acid at 23°C was 224.3 d for peroxymonosulfuric acid and 213.1 d for peroxodisulfuric acid. Thus, it was found that these liquid solutions containing oxidative species can be stored for long periods at room temperature, making them adaptable to industrial processes. The highly oxidative liquid obtained by the electrolysis of sulfuric acid is widely used in the industrial field. Research on the stability of this oxidative power is believed to contribute to the development of these industrial sectors.

We are developing a novel DAC system (Cryo-DAC system) that directly captures atmospheric CO₂ using the cryogenic heat (−162°C) of liquefied natural gas (LNG), and we aim to obtain design and development guidelines for a Cryo-DAC system combining an amine absorption method and a cryo-sublimation pump. In particular, it has been pointed out that when a non-phase-change gas such as N₂ mixes into the sublimation tank from the regeneration tower, it accumulates downstream of the sublimation tank and strongly inhibits dry ice production. Therefore, it is essential to elucidate the changes in the gas distribution in the sublimation tank and how the gas accumulation reduces the dry ice production rate. An unsteady lumped parameter system numerical model consisting of a regeneration tower, a connecting passage, and a sublimation tank divided into three parts was developed and numerically analyzed to investigate the influence of the non-phase-change gas on the temporal change of various quantities in the process and on the formation characteristics of dry ice. We set various analytical conditions for this process, such as the CO₂ regeneration rate, the regeneration rate of the non-phase-change gas N₂, the cooling wall area, the amine absorption liquid temperature, the refrigerant temperature, the modification factor in the Lewis relationship and heat transfer coefficient of the dry ice surface. The previous report showed various process quantities’ temporal variations when referencing the analytical conditions’ parameters. Compared with this, we clarified the effects of various analytical parameters on unsteady variations of the pressure, temperature, CO₂ regeneration rate in the regeneration tower, and CO₂ solidification rate in the sublimation tank, and also on the dry ice production efficiency and production quantity.