Faculty Profiles - MACHIDA, Hiroshi

Papers - MACHIDA, Hiroshi

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Numerical analysis of gas-liquid countercurrent flow in a pressure-swing CO2 desorber operated at reduced pressure Reviewed

Saito, Y; Tashiro, G; Chairunnisa; Miyazaki, T; Uehara, Y; Machida, H; Norinaga, K

CHEMICAL ENGINEERING SCIENCE Vol. 325 2026.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Engineering Science

Understanding fluid behavior in packed columns is essential for improving the efficiency of CO<inf>2</inf> capture processes. This study presents three-dimensional numerical simulations of gas–liquid countercurrent flow in a random packed bed of a desorber operated under reduced pressure in a pressure-swing mode. The applicability of existing correlations for liquid holdup, originally developed for absorbers, was evaluated under desorber conditions. A realistic random packing structure was numerically reconstructed, and variations in liquid viscosity and surface tension along the bed height were incorporated to represent CO<inf>2</inf> release during desorption. The results showed that liquid holdup increased with the progress of CO<inf>2</inf> desorption, while both liquid flux and the number of liquid nozzles had a strong influence on the gas–liquid interfacial area and liquid distribution. Numerical predictions of liquid holdup showed reasonable consistency with existing correlations, providing a comparative basis for discussing liquid distribution under desorber conditions. Overall, this study provides a quantitative framework for analyzing liquid flow behavior with property variations in random packed beds, contributing to the improved design and operation of CO<inf>2</inf> capture units.

DOI： 10.1016/j.ces.2026.123395

Numerical investigation of polycyclic aromatic hydrocarbons (PAHs) and soot formation from various coals in a two-stage entrained flow gasifier with detailed chemistry Reviewed

Li, TL; Fukumoto, K; Zhang, LJ; Lin, YX; Choi, C; Machida, H; Norinaga, K

JOURNAL OF ANALYTICAL AND APPLIED PYROLYSIS Vol. 188 2025.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Analytical and Applied Pyrolysis

The substitution of air with O2/CO2 atmosphere is a promising solution for CO2 recirculation during coal gasification. However, a comprehensive understanding on the formation mechanism of PAHs and soot under different conditions is necessary to reduce their emissions. This work presents simulation results of a two-stage entrained flow coal gasifier in a 250 MW industrial-scale plant using detailed chemistry. The influences of reductor temperature (1000–1200 ℃) and coal types (bituminous coal, sub-bituminous coal, and lignite) on PAHs and soot formations from the coal volatiles in the reductor were simulated through a detailed chemical kinetic model under air and O2/CO2 atmospheres. Results show that 2- and 3-ring aromatics are main PAHs products. Rising temperature has inhibitory effects on PAHs formation, especially for lignite. The O2/CO2 condition reduces the PAHs yield compared with the air condition. Rate of production analysis reveals that conversion of major PAHs occurs mainly between PAHs and their radicals. Vinyl-naphthyl radical and indenyl radical play an important role in the acenaphthylene conversion. In addition, soot production increases with a higher temperature under both air and O2/CO2 conditions. The O2/CO2 condition effectively suppressed soot production through a weaker HACA surface growth route than the air condition. lignite produces the least soot, and sub-bituminous coal produces the most. This study deeply reveals the formation mechanisms of PAHs and soot in a two-stage entrained flow gasifier through detailed chemical kinetic modeling, giving an insight into the complex PAHs and soot formations to assess the design and the operating condition of gasifier with O2/CO2 injection.

DOI： 10.1016/j.jaap.2025.107027

Coal Gasification in a Two-Stage Entrained Flow Gasifier under O<sub>2</sub>/CO<sub>2</sub> Conditions Reviewed

Li, TL; Choi, C; Fukumoto, K; Machida, H; Norinaga, K

ENERGY & FUELS Vol. 39 ( 20 ) page： 9345 - 9358 2025.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Energy and Fuels

Coal gasification in industrial gasifiers faces challenges related to tar and soot formation, which affect performance and emissions. This study proposes a new numerical approach for simulating coal gasification in a two-stage entrained flow gasifier under different O<inf>2</inf>/CO<inf>2</inf> ratios-blown conditions. The modeling framework incorporates a static simulation for the combustor and couples a multistep coal devolatilization model with an expanded gas-phase reaction model in the reductor. Model validation against experimental data showed prediction accuracies ranging from 4 to 20% for the devolatilization model and from 3 to 25% for the gas-phase reaction model across various species. The validated framework was employed to investigate the effect of varying O<inf>2</inf>/CO<inf>2</inf> ratios in gasifying agents on the gasification performance. Results showed that increasing the O<inf>2</inf>/CO<inf>2</inf> ratio from 30% to 50% increased H<inf>2</inf> production from 3.69% to 13.03% and CO from 34.40% to 55.04% while reducing CO<inf>2</inf> from 48.27% to 19.96%. Higher O<inf>2</inf>/CO<inf>2</inf> ratios inhibited soot formation but increased the tar yield, although the final tar concentration remained well below 1 mg/Nm<sup>3</sup>. This study highlights the potential of using oxy-fuel gasification with CO<inf>2</inf> recirculation for optimizing syngas quality and advancing CO<inf>2</inf> capture, offering valuable insights for industrial gasifier design and operation within oxy-fuel IGCC systems.

DOI： 10.1021/acs.energyfuels.5c00098

Mechanism investigation of direct electrochemical reduction of CO<sub>2</sub>-loaded 2-(ethylamino)ethanol solution into CO

Dai, RC; Zhang, LJ; Tran, KVB; Sirisomboonchai, S; Machida, H; Norinaga, K

SEPARATION AND PURIFICATION TECHNOLOGY Vol. 355 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Separation and Purification Technology

Carbon capture and utilization (CCU) has attracted considerable interest recently as CO2 emission and global warming have greatly affected various aspects of the environment, economy, and society. However, energy consumption during CCU must be substantially reduced. In this study, we propose an alternative approach using electrochemical reduction to directly convert CO2-loaded amine solutions into CO. The effects of the electrodes, temperature, potential, and CO2 loading on the Faradaic efficiency (FE) of CO were comprehensively investigated. The Ag NPs/CP electrode showed good catalytic performance on the electrochemical reduction of CO2-loaded amine solution to CO. By comparing the chemical composition in the solution before and after the electrochemical reaction, we determined that the main source of CO might be free CO2, which is mainly converted from bicarbonate rather than carbamate. In addition, electrochemical impedance spectroscopy was used to investigate the resistance during the reaction. The electric double-layer was found over the electrode surface when different amine solutions were used as the electrolyte. The spatial structure of ammonium cations and carbamate plays a key role in the FE of CO in this process.

DOI： 10.1016/j.seppur.2024.129575

Design of an efficient CO<sub>2</sub> methanation process and techno-economic analysis with CO<sub>2</sub> capture from the flue gas of automotive shredder residue Reviewed

Wasnik, CG; Nakamura, M; Machida, H; Ito, J; Shiratori, K; Norinaga, K

CHEMICAL ENGINEERING JOURNAL Vol. 507 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Engineering Journal

Recycling and utilizing automotive shredder residue (ASR) is necessary for realizing a sustainable automotive industry. This study conducted a feasibility analysis using a process simulator for Case I, where fuel gas is produced through the gasification of ASR followed by combined heat and power generation using a gas engine, CO2 capture from exhaust gas through chemical absorption, and production of synthetic methane (CH4) using the captured CO2 and renewable hydrogen produced via water electrolysis powered by renewable energy sources. This process produces not only CH4 but also surplus electricity, which can be used to produce H2 or power adjacent equipment. Case II, where fuel gas obtained from ASR gasification was directly methanated, was considered for comparison. This study compared the economic potential of both processes for kiln-type ASR gasification that can process 1,200 kg-ASR/h to produce 3,350 Nm3/h of fuel gas. Case I produced 4,800 tons/year of CH4 with an energy efficiency of 46.5 %, whereas Case II produced 2,720 tons/year. The levelized production cost of methane in 2050 can be estimated at $1,241/ton and $1,568/ton for Cases I and II, respectively, which are lower than the expected cost of natural gas in market environments by 2050. This study highlights the potential of ASR-derived CO2 methanation as a carbon–neutral technology that can effectively achieve carbon conversion while producing high-value synthetic methane.

DOI： 10.1016/j.cej.2025.160737

Observation and kinetic modeling of carbon dioxide deposition under reduced pressures at cryogenic temperatures Reviewed

Xiao, SW; Hirayama, M; Machida, H; Norinaga, K

CHEMICAL ENGINEERING SCIENCE Vol. 305 2025.2

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Engineering Science

Liquefied natural gas (LNG) is typically vaporized through heat exchange with seawater or other sources and used as city gas or power generation fuel, but its cold energy remains underutilized. This study proposes a new CO2 capture process leveraging LNG's cryogenic temperatures to create a vacuum environment, recovering CO2 from amine-based solutions as dry ice. CO2 deposition under cryogenic and vacuum conditions was observed, and a deposition rate model was developed. In the experiment, liquid nitrogen circulated through the tube side of a glass vertical single-tube shell-and-tube heat exchanger (230 mm long), while CO2 was supplied to the shell side. CO2 was deposited on the outer surface of a 5-mm diameter tube, with its growth rate measured by a laser displacement sensor. At 293 K and pressures of 140–1000 Pa, experimental results matched a rate model based on energy balance and mass transfer.

DOI： 10.1016/j.ces.2024.121177

Nickel/Zirconia-Catalyzed CO<sub>2</sub> Methanation in Differential and Integral Fixed-Bed Reactors: Experimental and Computational Fluid Dynamics Studies Reviewed

Shimada, T; Nakamura, M; Fukumoto, K; Ibrahim, M; Wasnik, CG; Machida, H; Norinaga, K

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH Vol. 64 ( 3 ) page： 1473 - 1487 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Industrial and Engineering Chemistry Research

Isothermal conditions and a chemical-kinetics-limited rate should be maintained when measuring the reaction rates of gases on solid catalysts. However, in highly exothermic reactions─such as the Sabatier reaction─temperature variations within the catalyst bed make it challenging to achieve isothermality. In this study, temperature changes in a Ni/ZrO2 catalyst bed were minimized using α-Al2O3 diluent and high gas hourly space velocities (GHSVs) to achieve low feed gas conversion (differential conditions: 0.9 MPa; 523-873 K; GHSV = 7600-30,000 L/h/g cat). The temperature profile within the catalyst bed was obtained by coupling a previously reported kinetic model with three-dimensional computational fluid dynamics (CFD) simulations. Experiments were also conducted under integral conditions at low GHSVs, resulting in high conversion rates and heat release. CFD simulations accurately reproduced the experimental feed gas conversion and temperature, suggesting that the CFD-simulation-guided kinetic parameters appropriately predicted the methanation characteristics at practically relevant high conversion rates.

DOI： 10.1021/acs.iecr.4c03789

CFD simulation of crude oil fouling from laboratory- to industrial-scale heat exchangers using a weak coupling approach Reviewed

Fukumoto, K; Zhang, W; Choi, C; Tang, F; Machida, H; Norinaga, K

APPLIED THERMAL ENGINEERING Vol. 258 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Thermal Engineering

Crude oil fouling is described as an accumulation of unwanted materials such as asphaltene and metallic salt on a heat transfer surface in a pre-heat train of the crude distillation unit in oil refineries, causing an economic loss of 1–1.2 billion U.S. dollars per year in 2019. Computational fluid dynamics is one of the useful simulation tools for numerical research on this topic. However, crude oil fouling is a long-term phenomenon; therefore, the time scale is longer than general computational fluid dynamics problems. The fouling layer in oil refineries grows over several months to several years despite the small pipe diameter of several or several tens of millimetres. For this reason, it is not easy to satisfy the Courant–Friedrichs–Lewy condition. To overcome this problem, we developed a new algorithm based on a weak coupling approach, validated this scheme, and exhibited the application of this technology. In the new algorithm, momentum and pressure fields and enthalpy and mass fraction fields are solved separately. The algorithm was implemented as FoulingFOAM, a crude oil fouling simulator based on OpenFOAM v2006. Then, the solver was first validated with the lab-scale measurements, showing good agreement with the experimental data. Next, industrial-scale data in the two refineries were simulated for validation. It was possible to predict the peak fouling resistance against time. Finally, for both lab- and industrial-scale simulations, the predictions of our numerical tool showed that fouling resistance increased with higher wall temperature, lower crude oil velocity, and higher concentration of fouling species, which were identical to previous measurements. Hence, we concluded that the weak coupling approach is promising for investigating crude oil fouling problems.

DOI： 10.1016/j.applthermaleng.2024.124614

Design and Optimization of Large-Scale Green Liquid Hydrogen Production Integrated with Heat Recovery and Absorption Precooling Reviewed

Li, Q; Machida, H; Norinaga, K

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH Vol. 63 ( 44 ) page： 19063 - 19075 2024.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Industrial and Engineering Chemistry Research

Liquid hydrogen (LH2) presents a viable solution for energy storage and transportation, particularly when produced by using renewable electricity. In this study, the energy efficiency of large-scale PEM water electrolysis for hydrogen production was investigated to be 59.74%, with the levelized electricity cost of hydrogen of 57.48 kWh/kg. To recover the waste heat from the PEM electrolyzer, two heat integration approaches have been proposed: the organic Rankine cycle (ORC) and the absorption refrigeration cycle (ARC). The ORC converted waste heat into electricity, while the ARC generated cold energy to precool the refrigerant, alongside electricity generation, both of which reduced energy consumption in the hydrogen liquefaction process. Subsequently, the process parameters were optimized through Matlab with the Mesh Adaptive Direct Search algorithm aimed at minimizing the specific energy consumption (SEC) of hydrogen liquefaction integrated with ORC or ARC, resulting in SECs of 6.76 and 6.61 kWh/kg LH2, with 21.33% and 22.87% reductions compared with the liquefaction process without heat recovery, respectively. The corresponding exergy efficiencies were 56.96% and 57.16% for the liquid hydrogen production process, with 86.69% and 87.73% for the hydrogen liquefaction process, respectively.

DOI： 10.1021/acs.iecr.4c02383

Modeling and uncertainty quantification of CO<sub>2</sub> absorption process using phase separation solvent Reviewed

Yuyama, S; Machida, H; Yajima, T; Kawajiri, Y

CHEMICAL ENGINEERING SCIENCE Vol. 298 2024.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Engineering Science

Absorption using an amine solvent is one of the primary means for capturing CO2 from many combustion sources such as fossil fuel power plants. CO2 capture systems by absorption need a large amount of thermal energy to strip CO2 from the amine solvent. In recent years, absorption using a phase separation solvent, which forms two phases when CO2 is absorbed, has been demonstrated as a promising technique to reduce the energy consumption. In this study, we examine several process models for the CO2 absorption process using a phase separation solvent, and quantify the uncertainty of the model parameters. We estimated model parameters, including equilibrium and mass transfer parameters, from two sources of experimental data: solubility tests, as well as lab-scale absorber tests. Model parameters were estimated by Bayesian inference using the Markov chain Monte Carlo method. The proposed approach successfully quantified the uncertainties of the model parameters.

DOI： 10.1016/j.ces.2024.120348

LNG Oxy-Fuel Power and Green Methanol Poly Generation Systems Associated with CO<sub>2</sub> Condensation Capture: Techno-Economic Environmental Assessment Reviewed

Li, Q; Machida, H; Feng, ZM; Norinaga, K

ENERGY & FUELS Vol. 38 ( 14 ) page： 13089 - 13103 2024.7

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Energy and Fuels

To achieve energy-environment synergy and sustainability, this study proposes a poly generation system that integrates the energy release process of liquefied natural gas (LNG) oxy-fuel power generation with the energy storage process of green methanol synthesis from renewable energy. In this system, oxygen, the byproduct of water hydrolysis to hydrogen, can support LNG oxy-fuel power generation; while the cold energy released during LNG regasification can serve as a cold source for carbon capture, the captured CO2 can be utilized as the carbon source for methanol synthesis, thus realizing cleaner methanol production and an efficient power generation process with near-zero carbon emission. Following the process design, the parameters were optimized with minimum levelized production cost of methanol and electricity as the objective function through Matlab using the “MADS” algorithm, resulting in 683.79 $/tonne and 68.05 $/MW h, respectively, with overall exergy efficiency of 50.28%. Notably, as green methanol synthesis requires additional CO2, a reduction of 2272.59 kg/h can be achieved. The study concludes that the novel poly generation process is superior in exergy efficiency and CO2 capture and utilization but inferior in high production costs.

DOI： 10.1021/acs.energyfuels.4c01250

Environmental-friendly extraction of di(2-ethylhexyl) phthalate from poly (vinyl chloride) using liquefied dimethyl ether Reviewed

Wang, T; Kanda, H; Kusumi, K; Mei, L; Zhang, LJ; Machida, H; Norinaga, K; Yamamoto, T; Sekikawa, H; Yasui, K; Zhu, L

WASTE MANAGEMENT Vol. 183 page： 21 - 31 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Waste Management

Poly(vinyl chloride) (PVC) is one of the most widely used plastics. However, a major challenge in recycling PVC is that there is no economical method to separate and remove its toxic phthalate plasticizers. This research made a breakthrough by extracting PVC with liquefied dimethyl ether (DME) and successfully separating the plasticizer components. Nearly all (97.1 %) of the di(2-ethylhexyl) phthalate plasticizer was extracted within 30 min by passing liquefied DME (285 g) through PVC at 25 °C. The compatibility of PVC with organic solvents, including liquefied DME, was derived theoretically from their Hansen solubility parameters (HSP), and actual dissolution experiments were conducted to determine the optimal PVC solvents. A liquefied DME mixture was used to dissolve PVC, and the extract was diluted with ethanol to precipitate the dissolved PVC. We demonstrated that liquefied DME is a promising method for producing high quality recycled products and that the process retains the fundamental properties of plasticizers and PVC without inducing degradation or depolymerization. Because of its low boiling point, DME can be easily separated from the solute after extraction, allowing for efficient reuse of the solvent, extracted plasticizer, and PVC. DME does not require heat and produces little harmful wastewater, which significantly reduces the energy consumption of the plasticizer additive separation process.

DOI： 10.1016/j.wasman.2024.04.050

Energy optimization of a non-aqueous solvent CO<sub>2</sub> absorption system with pressure swing regeneration Reviewed

Chairunnisaa; Zhou, YX; Wu, YT; You, C; Thu, K; Miyazaki, T; Uehara, Y; Machida, H; Norinaga, K

INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL Vol. 135 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Greenhouse Gas Control

This study focuses on optimizing the energy requirement in the post-combustion CO2 capture system using pressure swing regeneration through a model-based design (MBD). The simulation results highlight the significant impact of CO2 recovery, inlet gas and liquid flow rate, and CO2 concentration in the flue gas on the overall energy demand of the system. Moreover, an investigation into the de-sublimation chamber was undertaken, revealing a relationship between dry ice formation and the heat transfer between the LNG stream and CO2 in the heat exchanger. The parametric analysis study reveals that the sensible heat of the lean solvent is significantly influenced by the CO2 concentration in the liquid, consequently affecting the overall system energy. According to the results, the utilization of cold energy from LNG could save 80 % of the total energy requirement. The optimization results found the best working condition, which consumes energy of 0.190 GJ/ton CO2, 31 % lower than the basic scenario.

DOI： 10.1016/j.ijggc.2024.104154

High-Throughput CO<sub>2</sub> Solubility Measurement in Miscible and Liquid-Liquid Phase Separation Types of Amine Solvent Using Headspace Gas Chromatography

Tran, KVB; Yanase, K; Rao, TU; Hirayama, M; Norinaga, K; Machida, H

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH Vol. 63 ( 13 ) page： 5823 - 5832 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Industrial and Engineering Chemistry Research

CO2 solubility is one of the key factors in evaluating not only the efficiency of the absorbent but also the energy consumption of the CO2 capture process from flue gas. In this study, a system namely headspace gas chromatography (HS-GC), which is a combination of gas chromatography (GC-3200, GL Sciences) and a headspace autosampler (Turbomatrix HS16, PerkinElmer), was developed to measure the CO2 solubility of amine solutions. The equilibrium time and calibration curve of this system were checked and compared with those of the literature data. The developed system showed high reproducibility with reference CO2 solubility data of benchmark amine solutions. Distinct from conventional measurement methods of CO2 solubility, high-throughput CO2 solubility measurement by HS-GC shows its advantages such as a small amount sample requirement, rapid achievement of equilibration time, automation of sample exchange, and high reproducibility, which is superior in the amine solvent screening phase. Moreover, this system can evaluate new types of CO2 capture solvents, including the phase separation solvent. By acquiring continuous data, the inflection point in the solubility curve indicated by phase separation was observed. The absorption heat estimated from those CO2 solubility curves measured by this system also agrees well with the experimental data.

DOI： 10.1021/acs.iecr.3c03314

Design and Optimization for Sustainable Synthesis of Tetrahydrofurfuryl Alcohol by Furfural Hydrogenation: Kinetic and Techno-economic Investigations

Li Q., Rao T.U., Uehara Y., Machida H., Huo Z., Norinaga K.

ACS Sustainable Resource Management Vol. 1 ( 2 ) page： 316 - 327 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Sustainable Resource Management

To address energy challenges, we propose synthesizing tetrahydrofurfuryl alcohol from biomass-derived furfural and hydrogen produced through electrolysis. Building upon prior research [Energy Convers. Manage.2022 2022, 265, 115736], the kinetic parameters of the developed catalysts for two-step reactions including furfural hydrogenation to furfuryl alcohol and tetrahydrofurfuryl alcohol were investigated, in which the activation energies were E<inf>a1</inf>= 29.35 and E<inf>a2</inf>= 38.97 kJ/mol, respectively. Subsequently, we designed the complete production process, including hydrogen generation, furfural hydrogenation, and tetrahydrofurfuryl alcohol purification. To enhance economic efficiency by minimizing energy consumption, the organic Rankine cycle-coupled heat pump was integrated into the process. Following the process design, the parameters were optimized with minimum levelized production cost of tetrahydrofurfuryl alcohol as the objective function by Matlab using the “MADS” algorithm, which resulted in 1855.85 $/tonne with 76.62 % overall energy efficiency. Finally, sensitivity analyses were performed to determine the cost factors affecting the economic indicators. This work provides a sustainable and profitable process route for producing high-quality chemicals from biomass, particularly in the context of potential future fossil energy crises.

DOI： 10.1021/acssusresmgt.3c00084

Design and optimization of the flexible poly- generation process for methanol and formic acid from CO<sub>2 </sub>hydrogenation under uncertain product prices

Li, Q; Machida, H; Ren, XS; Feng, ZM; Norinaga, K

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY Vol. 54 page： 635 - 651 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Hydrogen Energy

During the design of the carbon capture and hydrogen storage process, a static CO2 hydrogenation poly-generation process for methanol and formic acid synthesis was developed, thereby reducing recycling flow and feedstock losses in the single methanol synthesis process and increasing product diversity. Additionally, a novel flexible poly-generation process was proposed as the product prices fluctuated with the market environment throughout the plant's life cycle. For the static poly-generation process, a mixed integer nonlinear programming model was established, followed by the Mesh Adaptive Direct Search algorithm to determine the optimal parameter design. For flexible processes, with the unscented transform tool, a two-stage optimization strategy is proposed for obtaining optimal design and operating parameters that are computationally tractable. With an input CO2 flow rate of 200 kmol/h, the results show (1) the static process with an optimal Return On Investment of 13.05%, a fixed investment cost of $ 34.14 × 106, and an annual net profit of 4.46 × 106 $/year; and (2) the flexible process, in which the flexibility indices of the methanol and formic acid production units are 1.088 and 1.194, respectively, resulting the fixed investment cost increase to $ 39.19 × 106, an increase of 14.79%. Accordingly, the annual net profit increased by 8.97% to 4.86 × 106 $/year, while the Return On Investment decreased by 4.67%–12.44%. For investment decision-makers, the flexible poly-generation process can achieve higher profits and reduce potential market risks when they have adequate financing.

DOI： 10.1016/j.ijhydene.2023.01.205

CO<inf>2</inf> methanation over low-loaded Ni-M, Ru-M (M = Co, Mn) catalysts supported on CeO<inf>2</inf> and SiC Open Access

Wasnik C.G., Nakamura M., Shimada T., Machida H., Norinaga K.

Carbon Resources Conversion 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon Resources Conversion

The concentration of the major greenhouse gas CO2 is rapidly increasing in the atmosphere, leading to global warming and a range of environmental issues. An efficient circulation and utilization of CO2 is critical in the current environmental context. Methanation, an exothermic process, emerges as a critical strategy for effective CO2 utilization. On this front, there is a significant demand for rational design of catalysts that maintain high activity and methane selectivity over a wide temperature range (250–550 °C). The catalyst that can promise a consistent reaction even at 500 °C under an atmospheric pressure is thus obliged. The present study investigated bimetallic catalysts with SiC, which is known for its exceptional thermal conductivity, and CeO2, which is characterized by its CO₂ affinity, as base materials. We incorporated Ni-M and Ru-M (M = Co and Mn) as the active metals, each loaded at 2 %. Impressively, with merely 20 mg, the Ni-Co/SiC catalyst achieved a CO2 conversion rate of 77 % and CH₄ selectivity of 88 % at 500 °C, in a fixed-bed tubular reactor system with conditions of H2/CO2 = 4, a total flow rate of 70 ml min−1, and a steady GHSV of 12,000 h−1. Moreover, 2Ni-2Co/CeO2 catalyst demonstrated exceptional performance with a 76 % conversion of CO2 and a 83 % selectivity for CH4, all under identical conditions. The catalyst's durability was confirmed by a subsequent 40-hour stability test, which showed only a 3–5 % degradation. The developed catalysts were comprehensively characterized by BET/BJH, CO pulse chemisorption, H2-TPR, HAADF-STEM-EDS, SEM-EDS and XRD etc. to unveil their physicochemical and surface traits. It was found that Co and Mn, when integrated, effectively restrained the agglomeration of Ni and Ru particles, ensuring optimal metal dispersion on the support. In conclusion, our synthesized bimetallic catalysts shown a sustained catalytic capability, even in the high-temperature environment.

DOI： 10.1016/j.crcon.2024.100241

CFD simulation of CO2 methanation through the Sabatier reaction in a shell-and-tube reactor incorporating phase change on the shell side

Fukumoto, K; Zhang, W; Mizoguchi, R; Lin, YX; Choi, C; Machida, H; Norinaga, K

FUEL Vol. 349 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Fuel

This paper reports a computational fluid dynamics simulation of carbon dioxide (CO2) methanation via the Sabatier process in a shell-and-tube reactor, incorporating a water phase change simulation on the shell side using the volume of fluid (VOF) method. The essential heat removal factors and their mechanisms, such as the catalyst size, bed porosity, thermal conductivity, coolant flow rate, and coolant boiling, were primarily investigated. The computational code was a newly developed in-house version of ChtMultiRegionFOAM based on OpenFOAM v2006. This code can simulate catalyst-gas heat transfer, which is called the two-temperature model. The code was extended to new methanation and phase-change models based on the VOF method. The computational code was first validated using existing experimental data. After sufficient accuracy was confirmed, several parametric studies were conducted. Catalyst heat conductivity was the most influential factor among the catalyst-related parameters. The flow rate of the oil coolant significantly affected the cooling performance. Finally, the use of boiling water significantly reduced the coolant flow rate. Moreover, the cooling performance remained unchanged until the total heat release rate from the gas exceeded the total latent heat of the water.

DOI： 10.1016/j.fuel.2023.128126

Polycyclic aromatic hydrocarbons (PAHs) and soot formations under different gasifying agents: Detailed chemical kinetic analysis of a two-stage entrained flow coal gasifier

Li, TL; Choi, C; Fukomoto, K; Machida, H; Norinaga, K

FUEL Vol. 343 2023.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Fuel

The injection of CO2 with coal into coal gasifier is a promising approach to achieve CO2 recirculation. Predicting the formation and evolution of polycyclic aromatic hydrocarbons (PAHs) and soot during coal gasification is particularly important as their presence poses challenges to the gasifier operation and environment. However, the effect of CO2 injection on their formation must be elucidated in more detail to optimize the gasifier design. This work investigates PAHs and soot formations in gas-phase reactions under different gasifying agents (Air, O2/CO2, O2/H2O) in a two-stage entrained flow coal gasifier using a detailed chemical kinetic model (DCKM). Under the O2/CO2– and O2/H2O-blown conditions, aromatics reforming was progressed whereas the yields of tar and soot were effectively suppressed. The benzene was observed as the most abundant PAHs species, followed by naphthalene and acenaphthalene. Regarding the relative oxygen concentration, the conversion behavior of aromatics was significantly influenced in the O2/CO2-blown condition, while the somewhat effect was found in the O2/H2O-blown condition. Tar yield peaked at 50% relative oxygen concentration in the O2/CO2-blown condition. The present finding may have practical significance in the O2/CO2-blown gasifier to facilitate CO2 recirculation for the oxy-fuel IGCC system.

DOI： 10.1016/j.fuel.2023.127876

CFD simulation of CVD reactors in the CH3SiCl3(MTS)/H2 system using a two-step MTS decomposition and one-step SiC growth models Open Access

Ogawa, T; Fukumoto, K; Machida, H; Norinaga, K

HELIYON Vol. 9 ( 4 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Heliyon

In this study, we report on a computational fluid dynamics (CFD) simulation of the chemical vapor deposition reactor of silicon carbide (SiC) in the methyltrichlorosilane (MTS, CH3SiCl3)/H2 system. The formation of SiC thin film is controlled by various process parameters, such as temperature and pressure. In this study, we propose a reaction mechanism of MTS decomposition to SiC growth on a substrate surface for CVD reactors in the CH3SiCl3(MTS)/H2 system. The reaction mechanism has two gas-phase pyrolysis reactions and one SiC film formation reaction. However, we individually build and validate MTS decomposition and SiC growth models to reduce uncertainty. An in-house version of reactingFoam, a reactive flow solver within OpenFOAM v2006, was used as the simulation tool. Our model accurately reproduced MTS decomposition for T = 1100–1350 K and [H2]/[MTS] = 2.65–14 at p = 101,325 Pa. Then, the MTS decomposition model was coupled with the SiC growth model, and the coupled model was applied to the SiC deposition data. The model could reproduce multiple datasets through validation studies.

DOI： 10.1016/j.heliyon.2023.e15061

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