The use of hydrate formation for the continuous recovery of ethylene and hydrogen from fluid catalytic cracking dry gas

A large amount of fluid catalytic cracking (FCC) dry gas, which contains high concentrations of ethylene and hydrogen, is used as low heat value fuel or simply flared every year, resulting in not only a waste of resources but also greenhouse gas emission. This study provides a continuous hydrate separation technology to solve this problem. The FCC dry gas flow was continuously separated into two gas flows: a C2H4-rich, low H2 stream and a residual gas stream with low C2H4 and high H2 contents. This paper experimentally investigated the effects of temperature and the concentration of tetra butyl ammonium bromide (TBAB) on the hydrate forming pressure of FCC dry gas, the time evolution of the gas compositions and the gas flow rates during long-term operation of the hydrate-based separation, and the effects of different influential factors on the separation. The concentration of C2H4 was increased from 47.17% to 71.56%, and the maximum recovery rate of C2H4 reached 90.47%. The maximum separation factor of ethylene was 8.13. The concentration of H2 was increased from 31.08% to 63.60%, and the maximum recovery rate of H2 was 91.45%. The maximum separation factor of hydrogen was 8.87.