The Removal of Benzene and Toluene in Natural Gas with Cryogenic Liquid Propane: Effects and a Cyclic Purification Process

Liquefied natural gas production plants usually suffer from line blockage, which causes economic, environmental, and safety issues. The blockage, mainly caused by the solidification of heavy hydrocarbons, should be avoided or mitigated by removing the impurities as thoroughly as possible. In this work, we proposed a scheme taking cryogenic liquefied propane as absorbent to absorb heavy hydrocarbons in the liquefied natural gas production process. This paper first investigated freeze-out profiles of liquefied natural gas combined with marginal benzene and toluene by the ThermoFAST simulator, which showed that the precipitated solid tended to form under a low temperature, which posed challenges in purification. Subsequently, the feasibility of using liquefied propane as an absorbent to remove benzene and toluene was studied using Aspen Plus. A cryogenic absorption and regeneration process for liquefied natural gas purification was proposed, and factors influencing the performance were investigated. The results showed that the hydrocarbon impurities are removed more thoroughly at a high flowrate of the recycled absorbent stream. The absorption process exhibited an apparent cooling effect mainly caused by the vaporization of liquefied propane to the gas phase, and the higher operation temperature impedes the vaporization process. For a better purification effect, the system should be operated under a lower pressure or with a higher recycled absorption solution flowrate. Based on the design simulation results, utilizing liquefied propane as an absorbent to remove heavy hydrocarbons is novel and promising for LNG purification.