Abstract: Merox caustic washing extraction and caustic liquor air oxidation recycling process are widely used in the Merox mercaptan removal system for liquefied petroleum gas（LPG) at present. By analyzing the waste residue，waste water，waste gas emission and energy saving and emission reduction of the NO.3 FCC unit in SINOPEC Beijing Yanshan Company，a series of technological innovations was adopted to optimize the production. The measures for technical transformation of two-stage high-efficiency extraction, the tail gas desulfurization，control of the discharge of alkali residue of the catalytic cracking unit were adopted and realized the treatment of alkali residue in plant，reduced use of washing water for LPG，and processed the tail gas in regenerator. Through the above measures，the alkali residue，waste water and VOC emissions of the device were effectively reduced.

Key words: catalytic cracking, LPG, alkali residue, tail gas, energy saving and emission reduction