Advancements in CO2 hydrogenation – Investigating a CNG pilot plant in Poland

Abstract

CO₂ hydrogenation technology has regained interest in recent years due to changes in global climate and energy policies. There is also a need to develop efficient methods for disposing of carbon dioxide and storing excess renewable electricity. A well-known Sabatier reaction is used for the CO₂ hydrogenation process. However, large-scale implementation of CO₂ hydrogenation has not been pursued due to the widespread availability and low cost of natural gas. In addition, most research to date has used technically clean CO₂. This gap leads the researchers to investigate the process using real CO₂ taken directly from an industrial plant at this technological readiness level of 6. In addition, the CO₂ for the hydrogenation process was separated from the flue gas using amine absorption. Synthetic methane (SNG) was produced by the reaction of CO₂ captured from flue gas (using amine absorption) with H₂ obtained from water electrolysis using surplus renewable energy. The CO₂ hydrogenation process takes place in a two-stage catalytic reactor.

The process also involves using part of the energy from the exothermic reaction process of CO₂ hydrogenation. The energy feeds the desorption process in the CO₂ amine capture plant. The authors of the article have patented the method of integration. The study tested the impact of process parameters on the conversion rates of CO₂ to methane (temperature, system pressure, CO₂ source, and cooling temperature between reactor stages). The study also investigated the process’s repeatability and addressed the issue of heat loss during the hydrogenation stages. A long-term (200 h) hydrogenation test was conducted to determine the CO₂ conversion for the novel microchannel reactor design and catalyst performance over time. The system achieved a CO₂ conversion rate of 99.4 % at a gas flow rate of 8.8 kg/h and a temperature of 299.8˚C for the first hydrogenation stage and 335.2˚C for the second hydrogenation stage, with a system pressure of 9.3 bar_a. This highlights the importance of optimizing temperature and pressure to improve CO₂ conversion rates and designing processes that minimize heat loss during hydrogenation. A comparison of the operation of a pilot plant for synthetic CO₂ and CO₂ generated from an amine carbon capture plant was also performed. The higher-produced CNG comprised approximately 94.6 % CH₄, 4.8 % H₂, and 0.9 % CO₂. The gas composition allows for its injection into the gas grid.