Removal of Carbon Dioxide from a Multicomponent Gas Mixture by Absorption Using a Y‑Type Microreactor

The direct commercialization of natural gas and biomethane of biogas as fuels is limited by their high carbon dioxide content (>30 mol %), so capturing of carbon dioxide is required. Despite the consolidated application of packaging columns for this purpose, there is a search for alternative gas–liquid contactors with high efficiency. Microreactors are devices that offer a high surface area–volume ratio, which can decrease heat and mass resistances and increase the reaction rate and energy efficiency. Several studies have already shown the success of using microreactors to capture carbon dioxide, but systematic studies have not been carried out using gas mixtures similar to natural gas and biogas. Therefore, the present study investigated the physical and chemical absorption (with monoethanolamine; MEA) of carbon dioxide from multicomponent gas mixtures (carbon dioxide–methane–nitrogen) using a Y-type microreactor. The dimensions of the microreactor were 0.4 × 0.4 × 260 mm3 (104 m2·m–3), and the experiments were carried out under different operational conditions, including changes in the feed composition, gas-phase velocity (0.729–4.687 m·s–1), liquid-phase velocity (1.042–3.125 m·s–1), and type of liquid phase (water and MEA solution). As expected, the increase in liquid-phase velocity increased the carbon dioxide absorption. The presence of methane did not affect either the removal efficiency or the overall mass transfer coefficient in the absorption experiments with water. Compared to other gas–liquid contactors, the Y-type microreactor obtained high values of the overall mass transfer coefficient (K L a = 24.68 s–1 for the gas-phase velocity of 2.083 m·s–1 and liquid superficial velocity of 3.125 m·s–1). Despite the increase in physical absorption performance, the addition of MEA was required to reduce the carbon dioxide content to attractive levels (∼3 mol %). The ionic reaction between MEA and carbon dioxide was intensified in the microreactor so that even diluted MEA solutions were able to remove 100% of the carbon dioxide with residence times of up to 50 ms.