Model analysis and catalysts study of CO2 methanation in fluidized bed reactor

With the increasing greenhouse gas carbon dioxide (CO2) emission due to the consumption of fossil fuels, various methods have been investigated for the capture and recycle of CO2. In these processes, catalytic conversion of CO2 into chemicals and fuels is an alternative to alleviate climate change and ocean acidification. This thesis contains mainly three parts: Firstly, considering the catalytic reduction of CO2 by H2 can lead to the formation of various products: carbon, carbon monoxide, carboxylic acids, aldehydes, alcohols and hydrocarbons, a comprehensive thermodynamics analysis of CO2 hydrogenation is conducted using the Gibbs free energy minimization method. The results show that CO2 reduction to CO needs a high temperature and H2/CO2 ratio to achieve a high CO2 conversion. However, synthesis of methanol from CO2 needs a relatively high pressure and low temperature to minimize the reverse water-gas shift reaction. Direct CO2 hydrogenation to formic acid or formaldehyde is thermodynamically limited. On the contrary, production of CH4 from CO2 hydrogenation is the thermodynamically easiest reaction with nearly 100 % CH4 yield at moderate conditions. In addition, complex reactions with more than one product are also calculated in this project. The thermodynamic calculations are partially validated with some experimental results, suggesting that the Gibbs free energy minimization method is effective for thermodynamically understanding the reaction network involved in the CO2 hydrogenation process, which is helpful for the development of high-performance catalysts. Second, through above thermodynamics analysis, it is known that the reduction of carbon dioxide to methane by hydrogen (CO2 + 4H2 → CH4 + 2H2O, termed CO2 methanation) from renewable energy is a promising process for CO2 recycling. However, both the development of better catalysts and better reactors for the subsequent implementation are critical for the practical application of CO2 methanation. Towards large-scale implementation, (i) fluidized beds, which have excellent heat transfer, are promising for the highly exothermic reaction; and (ii) catalysts suitable for long-term use in fluidized beds are needed. This project focused on the former, specifically on the understanding of the operating parameters affecting CO2 methanation in the highly efficient fluidized bed reactor. A fluidized bed reactor model was developed based on an earlier one reported for CO methanation. The reaction kinetics of the Ni-Mg-W catalyst, which has been reported to exhibit superior catalytic performance, was experimentally measured. The fluidized bed model results indicated that the Ni-Mg-W was indeed superior to two other catalysts reported earlier in terms of faster depletion of reactants and higher concentrations of product CH4 throughout the reactor. Moreover, regarding the effect of operating parameters, the overall productivity of CH4 increases with decreased inlet reactant flow rate, increased temperature, increased H2/CO2 ratio, decreased catalyst particle diameter and decreased catalyst particle sphericity. The results presented in this part are expected to be valuable for both the further development of catalysts and of the reactors needed for practical CO2 methanation processes. Last part focuses on the catalyst study for carbon dioxide (CO2) methanation. In this project, a novel Ni-Co bimetal catalyst supported on TiO2-coated SiO2 spheres (NiCo/TiO2@SiO2) was rationally designed and evaluated for CO2 methanation in fluidized bed reactor. The results demonstrated that NiCo/TiO2@SiO2 exhibited high CO2 conversion with CH4 selectivity of greater than 95%. Moreover, the superior performance was sustained for more than 100 hours in the fluidized bed reactor, affirming the long-term stability of the catalyst. Comprehensive characterizations were conducted to understand the relationship between structure and performance. This study is expected to be valuable for the potential implementation of the CO2 methanation process in fluidized beds. In all, this thesis would be a useful guidance for the process development of CO2 utilization through hydrogenation process.Doctor of Philosoph

Nickel–cobalt catalyst supported on TiO2-coated SiO2 spheres for CO2 methanation in a fluidized bed

Carbon dioxide (CO2) methanation, which is the reduction of carbon dioxide to methane by hydrogen generated from renewable energy, is a promising process for carbon recycling. Towards large-scale implementation, (i) fluidized beds, which have excellent heat transfer, are promising to perform the highly exothermic reaction; and (ii) catalysts suitable for long-term use in fluidized beds are needed. In this study, a novel Nisingle bondCo bimetal catalyst supported on TiO2-coated SiO2 spheres (NiCo/TiO2@SiO2) was rationally designed and evaluated for CO2 methanation in fluidized bed reactor. The results demonstrate that NiCo/TiO2@SiO2 exhibited high CO2 conversion with CH4 selectivity of greater than 95%. Moreover, the superior performance was sustained for more than 100 h in the fluidized bed reactor, affirming the long-term stability of the catalyst. Comprehensive characterizations were conducted to understand the relationship between structure and performance. This study is expected to be valuable for the potential implementation of the CO2 methanation process in fluidized beds.National Research Foundation (NRF)This project is funded by the National Research Foundation (NRF), Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and the 2nd Intra-CREATE Seed Collaboration Grant (NRF2017-ITS002-013)

A fluidized-bed model for NiMgW-catalyzed CO2 methanation

The reduction of carbon dioxide to methane by hydrogen (“CO2 methanation”) using renewable energy is a promising process for recycling CO2. Better catalysts and better reactors are both required for the practical application of CO2 methanation. This study examines how the operating parameters affect CO2 methanation in a highly efficient fluidized-bed reactor. We first measured the kinetics of the CO2 methanation reaction using an NiMgW catalyst, which has been reported to exhibit superior catalytic performance. We then developed a fluidized-bed reactor model based on an earlier model for CO2 methanation. The fluidized bed model indicated that the NiMgW was indeed superior to two other previously studied catalysts in terms of faster conversion of reactants and higher concentrations of product CH4 throughout the reactor. The overall rate of production of CH4 increased with temperature and H2/CO2 ratio and decreased as the inlet reactant flow rate, catalyst particle diameter, and catalyst particle sphericity increased.National Research Foundation (NRF)We acknowledge funding from the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and the 2nd Intra-CREATE Seed Collaboration Grant (NRF2017-ITS002-013)

Effect of nickel nanoparticle size in Ni/alpha-Al2O3 on CO methanation reaction for the production of synthetic natural gas

A series of alpha-Al2O3-supported Ni catalysts with different Ni particle sizes (5-10, 10-20, and 20-35 nm) were prepared and applied in the CO methanation reaction for the production of synthetic natural gas (SNG). The catalytic tests showed that the Ni nanoparticles influenced the catalytic performance in the CO methanation, and the catalyst with a Ni nanoparticle size of 10-20 nm showed the highest CO conversion, CH4 yield, and turnover frequency, and the lowest carbon deposition, demonstrating the possibility of improving the Ni/alpha-Al2O3 catalysts in the CO methanation for SNG production by controlling their Ni particle size

Study on the production law and optimization parameters of CO2 huff ‘n’ puff for continental shale oil

Abstract In this study, nuclear magnetic resonance and computed tomography scanning were used to analyze the production law and displacement mechanism of Jimusaer continental shale oil during CO2 huff ‘n’ puff, and the optimal parameters were determined. The results indicated that CO2 huff ‘n’ puff mainly produces crude oil in pore throats with 0.1–1 μm radii, while crude oil in pore throats with radii below 0.1 μm cannot be produced. Multiple CO2 huff ‘n’ puff cycles can connect fluids in fractures with fluids in large–medium pore throats, eliminate fracture effects on the oil recovery factor, and achieve coefficient development of both fractured and unfractured shales. In the CO2 huff ‘n’ puff process, core pressure change could be divided into three stages of injection–holding–depletion, and the oil displacement mode was the piston type. The study of huff ‘n’ puff parameters revealed that huff ‘n’ puff cycles and injection pressure have a great influence on the CO2 huff ‘n’ puff efficiency, while the injection timing and soaking time imposed relatively small effects. For continental shale in the Jimusaer Sag, the optimal CO2 huff ‘n’ puff parameters are five cycles, 4‐MPa injection timing, 25‐MPa injection pressure, and 12‐h soaking time

Nickel catalysts supported on calcium titanate for enhanced CO methanation

Nickel catalysts supported on the perovskite oxide CaTiO3 (CTO) were prepared by an impregnation method for CO methanation to produce synthetic natural gas (SNG). X-Ray diffraction, nitrogen adsorption, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, H-2-temperature programmed reduction and desorption, and X-Ray photoelectron spectroscopy were employed for the characterization of samples. The results revealed that the Ni/CTO catalysts showed a better performance than Ni/Al2O3 for CO methanation at various reaction conditions. The life time test at 600 degrees C and 3.0 MPa indicates that Ni/CTO is also more active, thermally stable and resistant to carbon deposition. This is because of the relatively weak Ni-CTO support interaction, highly stable CTO support, the absence of acidic sites on the surface of CTO and the proper Ni particle size of about 20-30 nm. The work is important for the development of effective methanation catalysts for SNG production

Template preparation of high-surface-area barium hexaaluminate as nickel catalyst support for improved CO methanation

We report the simple preparation of the barium hexaaluminate (BaO center dot 6Al(2)O(3), BHA) with high surface area (BHA-HSA) (>100 m(2) g(-1)) through a coprecipitation method using carbon black as the hard template. Ni catalysts supported on BHA-HSA (Ni/BHA-HSA) with different NiO loadings (10, 20, and 40 wt%) were investigated in CO methanation for the production of synthetic natural gas (SNG). The CO methanation reaction was carried out at 0.1 and 3.0 MPa with a weight hourly space velocity of 30 000 mL g(-1) h(-1). It was found that Ni/BHA-HSA catalysts showed increased activity at low temperature (240-400 degrees C) compared with more conventional Ni/BHA catalysts with the same NiO loadings. A highest CH4 yield of 95.7% can be obtained over Ni/BHA-HSA (40 wt% of NiO loading) at 400 degrees C and 3.0 MPa, and a lifetime test shows that, at 500 degrees C and 3.0 MPa, it is more stable than Ni/BHA. The serious aggregation of Ni nanoparticles is the major reason for the deactivation of the latter. The work demonstrates that BHA-HSA can be effectively prepared using carbon black as the hard template and is more suitable as a Ni catalyst support for CO methanation

Selective catalytic reduction of NOₓ in marine engine exhaust gas over supported transition metal oxide catalysts

The selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the presence of methanol (methanol-SCR) was investigated over commercial oxide (γ-Al2O3 and TiO2) supported transition-metal oxide catalysts in lab scale. Of all the prepared catalysts, CuO/γ-Al2O3 catalyst exhibited the highest reduction efficiency in the methanol-SCR process. The practical test results in a marine engine further showed that the 2 wt% CuO/γ-Al2O3 catalyst can remove 93.9% of NOx without catalyst deactivation in several hours. Evidenced by relevant characterization results, the fast-redox properties of copper and rich acidic sites of γ-Al2O3 support were responsible for the excellent catalytic activity of the CuO/γ-Al2O3 catalyst. Revealed by In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), formate-like species derived from methanol dehydrogenation act as the reaction intermediates for NOx reduction. Moreover, this work provides a novel process to reduce NOx and make use of adverse hydrocarbons in the flue gas simultaneously, opening a new research direction in NOx reduction technologies.Singapore Maritime Institute (SMI)This work is supported by Singapore Maritime Institute Maritime Sustainability (MSA) R&D Programme (grant number M4061829)

Ind. Eng. Chem. Res.

We report the preparation and characterization of Ni nanoparticles supported on barium hexaaluminate (BHA) as CO methanation catalysts for the production of synthetic natural gas (SNG). BHA with a high thermal stability was synthesized by a coprecipitation method using aluminum nitrate, barium nitrate, and ammonium carbonate as the precursors. The Ni catalysts supported on the BHA support (Ni/BHA) were prepared by an impregnation method. X-ray diffraction, nitrogen adsorption, transmission electron microscopy, thermogravimetric analysis, H-2 temperature-programmed reduction, O-2 temperature-programmed oxidation, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy are used to characterize the samples. The CO methanation reaction was carried out at pressures of 0.1 and 3.0 MPa, weight hourly space velocities (WHSVs) of 30000, 120 000, and 240 000 mL.g(-1).h(-1), with a H-2/CO feed ratio of 3, and in the temperature range 300-600 degrees C. The results show that although the BHA support has a relatively low surface area, Ni/BHA catalysts displayed much higher activity than Al2O3-supported Ni catalysts (Ni/Al2O3) with a similar level of NiO loading even after high temperature hydrothermal treatment. Nearly 100% CO conversion and 90% CH4 yield were achieved over Ni/BHA (NiO, 10 wt %) at 400 degrees C, 3.0 MPa, and a WHSV of 30 000 mL.g(-1).h(-1). Long time testing indicates that, compared to Ni/Al2O3 catalyst, Ni/BHA is more stable and is highly resistant to carbon deposition. The superior catalytic performance of the Ni/BHA catalyst is probably related to the relatively larger Ni particle size (20-40 nm), the high thermal stability of BHA support with nonacidic nature, and moderate Ni-BHA interaction. The work demonstrates BHA would be a promising alternative support for the efficient Ni catalysts to SNG production.We report the preparation and characterization of Ni nanoparticles supported on barium hexaaluminate (BHA) as CO methanation catalysts for the production of synthetic natural gas (SNG). BHA with a high thermal stability was synthesized by a coprecipitation method using aluminum nitrate, barium nitrate, and ammonium carbonate as the precursors. The Ni catalysts supported on the BHA support (Ni/BHA) were prepared by an impregnation method. X-ray diffraction, nitrogen adsorption, transmission electron microscopy, thermogravimetric analysis, H-2 temperature-programmed reduction, O-2 temperature-programmed oxidation, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy are used to characterize the samples. The CO methanation reaction was carried out at pressures of 0.1 and 3.0 MPa, weight hourly space velocities (WHSVs) of 30000, 120 000, and 240 000 mL.g(-1).h(-1), with a H-2/CO feed ratio of 3, and in the temperature range 300-600 degrees C. The results show that although the BHA support has a relatively low surface area, Ni/BHA catalysts displayed much higher activity than Al2O3-supported Ni catalysts (Ni/Al2O3) with a similar level of NiO loading even after high temperature hydrothermal treatment. Nearly 100% CO conversion and 90% CH4 yield were achieved over Ni/BHA (NiO, 10 wt %) at 400 degrees C, 3.0 MPa, and a WHSV of 30 000 mL.g(-1).h(-1). Long time testing indicates that, compared to Ni/Al2O3 catalyst, Ni/BHA is more stable and is highly resistant to carbon deposition. The superior catalytic performance of the Ni/BHA catalyst is probably related to the relatively larger Ni particle size (20-40 nm), the high thermal stability of BHA support with nonacidic nature, and moderate Ni-BHA interaction. The work demonstrates BHA would be a promising alternative support for the efficient Ni catalysts to SNG production