Hydrogenation of pyrolysis gasoline in pilot trickle-bed reactor with periodic modulated feed rate
Advancing the chemical engineering fundamentals
Chemical Reaction Engineering: Advanced Concepts (T2-2b)
Keywords: Hydrogenation, pyrolysis gasoline, trickle-bed reactor, periodic operation
Hydrogenation of pyrolysis gasoline is widely applied in industry to prevent gum-formation and catalyst deactivation caused by dienes oligomerization. Advantages of trickle bed reactor, which is usually adopted for this hydrogenation, like continuous operation, simple construction, etc. are accompanied by drawbacks like bad external heat exchange, liquid maldistribution and mass transfer limitation, namely concerning transfer of hydrogen to catalyst. Promising solution of these disadvantages consists in periodic liquid feed rate modulation to create forced pulsing flow pattern in catalyst bed. Typical benefits are periodically renewal of wetted catalyst surface, more intensive interaction between gas and liquid phases in catalyst bed, higher mean reaction temperature and intensification of heat transport during liquid rich part of feeding period, which result in higher reactor throughput, increased productivity and also operation safety. The goal of this work was to compare hydrogenation rate of pyrolysis gasoline with hydrogenation rates of its typical individual components, i.e., styrene and dicyclopentadiene. Both steady-state continuous and periodic modulated liquid feed rate were carried out in pilot scale trickle–bed reactor. Pilot plant experiments were organized in RD centre of Chemopetrol Litvínov. Pilot scale trickle-bed reactor of 100 mm I.D. and 2000 mm height was equipped by automatic controlling and data acquisition system. Due to thick insulation the reactor behavior was close to adiabatic one. Catalyst bed layer depth 1000 mm of pelleted 0.1 % palladium on alumina catalyst (Degussa Noblyst 1505, mean diameter 3 mm) was applied for selective olefinic bond hydrogenation. Adiabatic reaction temperature rise for pyrolysis gasoline, styrene and/or dicyclopentadiene both individual and as a mixture was controlled by solvent dilution to 10 %wt. dienes solution in toluene. Temperature and pressure longitudinal axial profiles in catalyst bed were scanned with distance of 100 mm by thermocouples and pressure transreducers. An excess of hydrogen to stoichiometric demand at level 100 % was maintained in all experiments. During pilot plant tests a parametric sensitivity of the reactor both to inlet temperature and pressure, so as to parameters of periodic liquid feed modulation mode like period length, split as well as ratio of peek to base liquid feed rate was found. Also mass transfer of reactants, catalyst deactivation and hysteresis of hydrodynamics exhibit oneselves in adiabatic catalytic trickle-bed. Hydrogenation reactions in question exhibit important adiabatic temperature rise, which results in nonisothermal axial temperature profile. In case of periodic liquid feed modulation a higher mean temperature in the bed was found in comparison with steady state mode of operation with constant feed rate. It was stated, that mean reaction rate over whole catalyst bed (which represents reactor productivity) is higher at convenient modulation by 30 % in comparison to the value typical for steady state continuous one.
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Presented Monday 17, 15:00 to 15:20, in session Chemical Reaction Engineering: Advanced Concepts (T2-2b).
