What are the main types of gas-liquid reactors and their selection criteria?

Types include: Stirred tank (good mixing, flexible, batch/continuous), Bubble column (simple, good heat transfer, limited mass transfer), Packed column (continuous, good mass transfer, low liquid holdup), Spray tower (simple, low pressure drop, limited contact time), and Trickle bed (catalyst pellets with liquid trickling down, gas-liquid-solid contact). Selection based on: reaction kinetics (fast reactions need high mass transfer), heat transfer needs, phase ratio requirements, pressure, and whether catalyst is needed. Gas-liquid mass transfer is often rate-limiting.