Renewable CO2 absorbent for carbon capture and biogas upgrading by membrane contactor

This study employs novel renewable absorbents derived from biogas slurry (BS) for biogas upgrading via membrane contactors. CO2 absorption capacity of biogas slurry can be enhanced by adding alkali solutions, vacuum regeneration or vacuum membrane distillation (VMD). These methods are used to produce four types of renewable CO2 solvents, including vacuum regenerated BS, recovered aqueous ammonia (RAA) from BS by VMD, calcium oxide treated BS and potassium hydroxide treated BS. These renewable absorbents for CO2 capture from biogas by membrane contactors are investigated. CO2 removal efficiency reduces but absorption rates increase with the rise in CO2 volume fraction in the feed gas stream. Absorption temperature has a limited effect on CO2 absorption rates of the renewable absorbents. RAA shows the best CO2 absorption performance among the four types of renewable absorbents in the membrane contactor. RAA flowing on the tube side leads to a 50% higher CO2 removal efficiency compared with RAA on the shell side. At low gas flow rates, partial absorbents and hollow fibers may not be utilized. Thus, selection of membrane module parameters, including the length of module, the number of hollow fibers, biogas flow rates and absorption performance, should be carefully considered when using membrane contactors for biogas upgrading.