During the laboratory experiment of hydrocracking process, the experiment was set up at 16:43pm and the reaction temperature was 154C and pressure of hydrogen gas was 40bar. Then after 17:55pm temperature was increased to 166C and the liquid flow rate was 40mL/min. After temperature increased, the hydrogen sulphide gas was suddenly started to emit in the form of fume, while unconverted liquid which was on the bottom of heat exchanger or a chiller was completed black. My question is what would make the H2S to start emitted when temperature in the trickle bed reactor is increasing? And when temperature is constant H2S is not emitted?