Why HDS is 5 times more heat-generating than HDS

The main reason for the large difference in heat generation between hydrosaturation and hydrodesulfurization is the difference in their reaction paths and reaction products.

In a hydrosaturation reaction, an unsaturated compound (such as an olefin or aromatic hydrocarbon) reacts with hydrogen in an addition reaction under the action of a catalyst to produce a saturated compound (such as an alkane). This reaction process is an exothermic reaction because during the reaction, the formation of chemical bonds releases energy, which causes the enthalpy of the system to decrease, and a decrease in enthalpy means that heat is released from the system.

And in a hydrodesulfurization reaction, a sulfur compound (such as a mercaptan or thiophenol) is hydrogenated with hydrogen in the presence of a catalyst to produce hydrogen sulfide and a saturated compound. This process is also exothermic, but the hydrogen sulfide generated needs to be separated and processed, and this process requires energy, so the heat generation of the whole reaction is much smaller than that of HDS.

In short, the reactants and products of HDS and HDS are different, resulting in different heat generation.