As the use of fossil fuel has increased since industrialization, various environmental problems such as exhaustion of fossil energy and emission of greenhouse gases have continued to occur. Therefore, it is necessary to develop technologies that can r...
As the use of fossil fuel has increased since industrialization, various environmental problems such as exhaustion of fossil energy and emission of greenhouse gases have continued to occur. Therefore, it is necessary to develop technologies that can reduce carbon dioxide, one of the most abundant greenhouse gases, and convert it to resources. CO2 methanation technology can convert CO2 to CH4 which is useful in industry, energy and transportation. CO2 methanation technology converts a large quantity of CO2 to CH4 by using catalysts. Currently, various catalysts are developing for higher CO2 conversion performance at low temperature. In this study, Ni was supported on various support materials to optimize the contents of reactive metal on CO2 methanation reactivity for development of high performing catalyst at low temperature.
In this study, Al2O3, CeO2, TiO2, and Y2O3 were selected as support materials based on precedent studies. Then, Ni was supported on the materials to figure out the methanation reaction in different temperature conditions. As a result, Ni/CeO2 (N) catalyst showed the best performance among the catalysts at low temperature. To figure out the effects of calcination temperature, catalysts were manufactured at the temperature of 300-700 °C and it was found that 10 wt.% Ni/CeO2 (N, 500 ˚C) catalyst has very high performance on CO2 methanation at low temperature of 180 ˚C and CH4 selectivity was also high. Accordingly, It was ascertained that using CeO2 precursor has an optimum calcination temperature in its production.
Then, catalytic activity in different temperatures and Ni amounts was conducted to figure out the effects of reaction site increase caused by increase of Ni content on catalytic activity in optimized calcination temperature mentioned. For 10 wt.% Ni catalyst, catalytic activity was observed as 70% (CH4 yield) at 180 °C. As Ni content increases, more sites for H2 adsorption and dissociation can be provided. Therefore, consumption of H2 was evaluated by performing H2-TPR. For 10 wt.% Ni/CeO2 (N, 500 °C) catalyst, there was high consumption of H2 near 200 °C. The H2 consumption is caused by reduction of O2 at low temperature, which means dissociation of H2 is occurred actively leading to higher activity on CO2 conversion at low temperature.
Ni/CeO2 (N, 500 °C) catalyst was selected based on precedent studies and coated it on honeycomb supporter for commercialization. A small amount of catalyst was coated on the surface of a structure evenly. This study adjusted cpsi, coating liquid, coating rate and amount of catalyst coated on honeycomb to maximize utilization of catalyst.
This study looked into a difference in activity performance according to aperture ratio of honeycomb at temperature of under 300 oC for 10 wt.% Ni/CeO2 (N, 500 °C) coated on honeycomb. Honeycomb type catalyst coated on 300 cpsi aperture ratio showed better conversion rate than honeycomb type catalyst penetrated in 100 cpsi aperture ratio. Selecting proper coating liquid is important for maintenance of activity of catalyst coated on support and durability when coating catalyst on honeycomb. Honeycomb catalyst using D.W. showed better performance than honeycomb catalyst using other coating liquids at high temperature. It was found that D.W. coating liquid is limited in coating amount for powder catalyst. conversion rate at high temperature is slightly lower than D.W but it is desirable to use isopropanol which is easy to be coated. This study examined coating amount, coating liquid rate, temperature and space velocity as various coating and operation conditions. As space velocity decrease, CO2 methanation has increased. Coating liquid rate did not show a significant influence. When temperature rose up to 340 oC, CO2 methanation increased. Optimum coating amount was determined by changes in other conditions. This study found simulation of CO2 methanation reaction and optimum operation conditions for factors influencing catalytic activity by using RSM statistics program. Consequently, It was found that optimum condition to elicit over 80% CO2 conversion by using 10 wt.% Ni/CeO2 (N, 500 °C) Honeycomb catalyst is temperature of 298 °C, space velocity of 743 hr-1 and catalyst loading of 134 g/L.
For application of catalysts to plant scale, this study evaluated CO2 methanation efficiency according to temperature, pressure and composition of reactants(O2, CH4).
Efficiency of honeycomb catalyst was evaluated in different temperature and pressure conditions and found honeycomb is difficult for pressure to increase and there was a difference in efficiency ranging from 60% to 98% as H2 rate rise to 1:3-6. This study evaluated activity influence of O2, CH4 gases that can be included in gases when applying technology to biogas plant. There was no significant influence at 1% which is normal concentration of O2 in biogas plant and from 3% or higher, efficiency decreased by over 10%. This seems to be caused by a reduction in H2 that should react to CO2 with increased reaction between O2 and H2 as temperature rise. When conducting an experiment assuming that maximum concentration of CH4 in biogas is 13%, it was found that an influence on catalyst is not significant. It seems that applying CO2 methanation at the end of bio process is possible. This study evaluated application according to operation conditions of honeycomb catalyst by examining maintenance of CO2 methanation efficiency through long term monitoring. This study conducted 160 hr experiment and found that 65% CO2 methanation is kept under condition of CO2:N2:H2=1:1:4, S.V. 1,190 hr-1 and 280 oC.
Findings of this study could be used as basic data for application of 10 wt.% Ni/CeO2 (N, 500 °C) Honeycomb catalyst.