Carbon Dioxide Absorption By Monoethanolamine In Microporous Tube-in-Tube Microchannel Reactor

Microchemical technology is a new direction to the development of chemical engineering science and has become a very hot topic in the field of chemical industry and academy. As an important componet of microchemical technology, the microreactors have the advantages in intensification of heat and mass transfer dramatically, comparing with traditional gas-liquid contactors, which contribute to the potential opportunities in many applications in chemical or energy industry. However, the maximum throughputs of most reported microreactors are much smaller than those of conventional reactors, which is hard to meet the demand of industrial applications. Aiming to obtain a high throughput, a high-throughput microporous tube-in-tube microchannel reactor (MTMCR) was firstly designed and fabricated as a novel liquid-liquid reactor and gas-liquid contactor in our laboratory. The objective of this paper is to systematically investigate the absorption process of carbon dioxide (CO2) by utilizing monoethanolamine (MEA) solution as absorbent in MTMCR. The main contents and findings are summarized as follows.1. The effects of the operation parameters such as gas and liquid flow rate, liquid temperature, absorbent concentration, the mean size of micropore, the annular channel width and the length of MTMCR were explored. The experimental results obtained as CO2 removal efficiency was used to evaluate the CO2 absorption performance of MEA solution in MTMCR. The results indicated that the absorbent concentration was a key factor for consideration since the CO2 removal efficiency increased with an increase of the concentration, and could reach 99% with the MEA solution of 30 wt.%. The effects of other operating parameters were explored with low absorbent concentration and have also shown their significance in increasing CO2 removal efficiency. With a decrease of the superficial gas velocity or an increase of the superficial liquid velocity, the CO2 removal efficiency increased. Increasing the absorbent temperature could yield better absorption performance. Reducing the most important structure parameters of MTMCR, such as the micropore size and the annular channel width, would lead to higher mass transfer rate and be beneficial to CO2 removal. Therefore, even with the low absorbent concentration, the high removal efficiency (higher than 90%) could be realized when other parameters were rationally designed.2. Based on H2O-CO2/N2 and MEA-CO2/N2 absorption system, the characteristics of the pressure drop of two-phase flows through MTMCR during the absorption process were firstly presented in detail. The results indicated that the pressure drop increased with the superficial gas and liquid velocities increased, and the microporous section occupied very important part in the pressure drop of the microchannel system. The pressure drop dramatically decreased with the increased micropore size and increased as the annual width decreased at the fixed UG and UL. It is obvious that the micropore size and the annual width need to be designed in an optimum range to avoid excessive pressure drop for meeting the requirements of CO2 removal in industry.The results obtained implied a great potential of MTMCR applied to the separation of the greenhouse gas CO2 from the exhausted gases.