Waste gas collecting device, reaction kettle and chemical production line

The utility model discloses a waste gas collecting device, a reaction kettle and a chemical production line, and belongs to the technical field of chemical equipment. The waste gas collecting device disclosed by the utility model comprises the sampling valve, the waste sample barrel and the gas collecting barrel, the gas collecting barrel adopts a closed structure, a sampler can conveniently extend into the gas collecting barrel for sampling due to the arrangement of the sealing door, and the waste gas branch pipe is connected with an external negative pressure waste gas collecting system, so that continuous negative pressure can be generated in the gas collecting barrel; volatile substances overflowing in the sampling process are prevented from diffusing into the air. Meanwhile, the waste sample barrel also adopts a closed structure and is communicated with the gas collecting barrel, so that on one hand, residual samples can be collected in a centralized manner, and on the other hand, volatile substances ove