Screening and VLE of Phase change Solvent

Abstract

In this work a screening apparatus of CO2 absorption has been applied to test the absorption characteristics for mixed systems. The main absorption characteristics of absorbents for CO2 removal are the absorption rate and the absorption capacity of CO2. The goal for this thesis was to find a solvent mixture system that will form two phases after 95 % of absorption. The results of both the screening and the VLE measurements are compared with the generally more used 5M (30 mass %) monoethanolamine (MEA) solution. The mixture of the tertiary amine n-tert-butyldiethanolamine (N-tBDEA) and the diamine diaminopropane (DAP) with a concentration of 3, 5 and 2 moles/litre, respectively, gave two phases. It was not observed an increase in the lower phase as expected when the CO2 partial pressure increases. It was not investigated further.The mixture of the tertiary amine Diethylethanolamine (DEEA) and DAP was run at partial pressures of 3, 5, 7, 9, 10, 13, 15, 17 and 19 kPa of CO2 at 40, 60 and 80 °C. It formed two phases after 95 % of absorption and the lower phase volume increased with increasing partial pressure. The 40 °C experiments obtained the highest loading and the cyclic capacity for the 10 kPa CO2 partial pressure at 40°C absorption and 80 °C desorption was 0,110 and for MEA it is 0,238. This is quite low. The highest absorption rate was obtained at 80 °C and 19 kPa. The lower phases from the screening were tested in a high-pressure vapour-liquid equilibrium for temperatures up to 120 °C to see how the total pressure changes, as this is an important factor for amine solvent selection. This was compared to 5 M MEA. The lower phases from the 40 °C screening experiment had a slightly higher total pressure than 5M MEA. This indicates it has a potential to lower the energy requirements in an absorption plant.