Undesired Reactions

Undesired Reactions

Hydrocracking is an undesired side reaction in catalytic reforming because it consumes hydrogen and decreases the reformate yield by producing gaseous hydrocarbons. Hydrocracking reactions are exothermic, but they can still be kinetically favored at high temperatures, and favored, obviously, by high hydrogen pressures. Below lists the heat of reactions for catalytic reforming reactions. Typically, reformers operate at pressures from 50 to 350 psig (345–2415 kPa), a hydrogen/feed ratio of 3–8 mol H2/mol feed, and liquid hourly space velocities of 1–3 h^-1[1]. These conditions are chosen to promote the desired conversion reactions and inhibit hydrocracking while limiting coke deposition on the catalyst surfaces.

Undesired Reactions in Catalytic Reforming

Hydrocracking

n-C₁₀+H₂ → n-C₆+n-C₄

to inhibit this reaction, use

1. high T
2. high SV
3. Low H₂P

Catalytic reformers are normally run at low H₂ pressure to inhibit hydrocracking!

Heats of Reactions:

paraffin to naphthene → 44 kJ/mol H₂ - endothermic

naphthenes to aromatics → 71 kJ/mol H₂ - endothermic

hydrocracking → -56 kJ/mol H₂ - exothermic