Isobutane alkylation catalyzed by a composite ionic liquid is a new technology for the production of clean gasoline blending components. In this process, efficient effluent cooling plays a crucial role in energy conservation. A new cooling application by effluent (mainly isobutane) evaporation was proposed for this target, in which the effluent was released into a low-pressure environment to enhance and control the evaporation of isobutane. The transient temperature of isobutane droplets was measured by suspending them on the tip of a thermocouple while a high-speed camera recorded the evaporation process. The effects of final pressures, different initial droplet diameters, initial droplet temperatures, and gas concentrations of isobutane on evaporation behavior and droplet temperature were investigated. The results demonstrated that isobutane droplets underwent intense evaporation and stable evaporation phases. The evaporation rate constant (k 0 ) exhibited a linear increase with decreasing final pressure and increasing initial droplet diameter. With the decrease in k 0 , the droplet evaporated in three states: expansion and breaking, only expanding but not disintegrating, and surface evaporation. The evaporation rate constant (k 1 ) during the stable evaporation phase was influenced by the initial droplet diameter and the concentration gradient between the droplet and the environment due to the concentration difference around the droplet. The lower the final pressure, the lower the droplet temperature in the stable evaporation stage, and the droplet diameter and initial temperature did not appear to affect the droplet equilibrium temperature. Adjusting the final pressure allows for precise control of the temperature of the droplets during the stabilization phase of evaporation.