HYDROTREATING:
Hydrotreating serves these main purposes:
1. Removing Impurities:
o Eliminates sulfur, nitrogen, and oxygen to meet product specifications or prepare
feeds for further processes like naphtha reforming and FCC.
2. Metal Removal:
o Removes metals by hydrogenating and breaking down organo-metallic
compounds, which deposit on catalyst pores.
3. Saturating Unstable Compounds:
o Stabilizes compounds by saturating olefins.
Role of Hydrotreating:
1. Ensuring Product Quality:
o Removes sulfur in kerosene, gas oil, and lube oil.
o Saturates olefins for stability.
o Removes nitrogen.
o Reduces aromatics in kerosene to improve cetane number.
2. Preparing Feed for Further Processing:
o Cleans naphtha by removing sulfur and metals.
o Removes sulfur, metals, and other impurities from vacuum gas oil (VGO) for
FCC.
o Prepares hydrocracking feed by reducing sulfur, nitrogen, and aromatics.
HYDROTREATING PROCESS:
In hydrotreating:
1. Process Overview:
o Liquid feed is mixed with hydrogen and heated in a furnace to reach reaction
temperature.
o The mixture is sent to a fixed-bed catalytic reactor.
o The reactor's output is cooled, and hydrogen-rich gas is separated using a high-
pressure separator.
o Hydrogen sulfide is removed from recycled hydrogen using an amine scrubber.
o Some recycled gas is purged to prevent the buildup of light hydrocarbons.
o The liquid product is sent to a fractionator for separation.
2. Hydrogen Requirements:
o Chemical Use: Hydrogen is used to remove impurities like sulfur, nitrogen,
oxygen, olefins, and metals, and sometimes to convert aromatics and naphthenes
into paraffins.
o Dissolved Hydrogen: Some hydrogen is lost when it dissolves in treated
hydrocarbons.
o Purged Gas Loss: Hydrogen is lost when purging light hydrocarbons (C1–C4)
and hydrogen sulfide if not removed by the scrubber.
Fluidized cataylitic reactor:
Introduction to FCC:
The Fluidized Catalytic Cracking (FCC) unit is the core of a refinery. It converts heavy, low-
value petroleum streams like vacuum gas oil (VGO) into high-value products, primarily gasoline
and C3/C4 olefins.
FCC Feed:
Vacuum Gas Oil (VGO)
Vacuum Residue (VR)
Unconverted Oil (UCO)
Deasphalted Oil (DAO)
Fluidization:
At low fluid velocity, catalyst particles in a packed bed stay stationary.
As velocity increases, pressure increases until it balances the gravitational force on the
particles, causing them to move. This is the minimum fluidization velocity.
Once fluidization starts, the bed becomes stable, expands, and its porosity increases, but
the pressure drop stays constant.
Catalytic reforming:
1. Process Description
Catalytic reforming upgrades low-octane naphtha into higher-octane motor fuels by
promoting chemical reactions.
The process rearranges hydrocarbon (HC) molecules instead of cracking them, producing
high-octane aromatics. It increases octane numbers rather than fuel yield.
Feedstock and Product Composition:
Feedstock (Heavy Naphtha):
o Paraffins: 45–55%
o Olefins: 0–2%
o Naphthenes: 30–40%
o Aromatics: 5–10%
Product (High-Octane Gasoline):
o Paraffins: 30–50%
o Olefins: 0%
o Naphthenes: 5–10%
o Aromatics: 45–60%
2. Catalyst Selection
Reforming catalysts contain platinum on a silica-alumina base.
Adding rhenium improves stability, allowing lower-pressure operation.
Platinum: Catalyzes hydrogenation and dehydrogenation reactions.
Chlorinated alumina: Provides acidity for isomerization, hydrocracking, and cyclization
reactions.
Feed sulfur and nitrogen must be below 1 ppm to protect the catalyst.
3. Types of Reforming
1. Continuous Reforming:
o Catalyst is continuously regenerated for high activity.
o Higher capital cost.
2. Semi-Regeneration:
o Regeneration needed every 3–24 months.
o Lower capital cost.
3. Cyclic Reforming:
o A compromise using a swing reactor for periodic regeneration.
4. Reforming Reactions
PONA Reactions:
o Paraffins (P): Isomerize or convert to naphthenes (N), then to aromatics (A).
o Olefins (O): Saturate to form paraffins, which react like above.
o Naphthenes (N): Dehydrogenate into aromatics.
o Aromatics (A): Remain unchanged.
Undesirable Reactions:
o Breaking side chains from aromatics and naphthenes forms lighter paraffins (e.g.,
butane).
o Cracking paraffins and naphthenes produces lighter paraffins.
Key Reactions:
1. Dehydrogenation of Naphthenes:
o Converts naphthenes (e.g., cyclohexane) to aromatics, producing hydrogen.
2. Isomerization of Paraffins and Naphthenes:
o Rearranges molecules to create higher-octane isomers at high temperatures.
3. Dehydrocyclization of Paraffins:
o Converts paraffins into naphthenes, then aromatics.
o Easier with heavier paraffins.
4. Hydrocracking:
o Breaks paraffins into lighter hydrocarbons, increasing aromatics but lowering
yield.
5. Process Flow Terms
Space Velocity:
o Measures the feed flow rate relative to the amount of catalyst.
o High space velocity means shorter reaction time.
WHSV (Weight Hour Space Velocity):
o Weight of feed per hour per weight of catalyst.
LHSV (Liquid Hour Space Velocity):
o Volume of feed per hour per volume of catalyst.
