Alternative extractive distillation system for CO2-ethane azeotrope separation in enhanced oil recovery processes

CO2 is a common constituent of natural gas. Standards for its maximum concentration differ from about 2% for pipeline to 50 ppm for liquefaction. All natural gas constituents absorb CO2 to some degree when in the liquid phase, requiring multi-step natural gas treatment processes. The existence of a minimum boiling temperature azeotrope between ethane and carbon dioxide particularly complicates CO2 separation. Extractive distillation with higher molecular weight hydrocarbons as the solvent represents the most competitive means for the separating CO2 from ethane. The conventional separation method involves two distillation columns in series and rather high amount of energy. This investigation proposes an efficient method for CO2-ethane separation that produces all products at high purity with less capital and operating costs in comparison with the conventional system. The new operating flowsheet includes three columns: a CO2 recovery column, a solvent recovery column, and a concentrator column. The proposed system requires 10% less total annual cost (TAC) and 16% less energy compared to the conventional system at the same purification. Additionally, unlike the conventional system, the proposed design separates CO2 in the form of a liquid product, which avoids the high amount of energy required for the liquefaction. Thus, this technology provides a useful alternative toward the less expensive CO2-ethane separation process. (C) 2016 Elsevier Ltd. All rights reserved.