MerOx

MerOx Sweetening Process.
Muhammad Fahad Khan
Engineer Operations

SWEETNING
 Conversion/Removal of Mercaptans (RSH), H2S
and elementary Sulfur present in Hydrocarbon
stream.

Types Of Sweetening
 Removal Process : Removal of Hazardous
Sulfur and sulfur containing compounds is called
Desulfurization.
 Conversion Process: Conversion of Mercaptans
through Oxygen is called Oxidation and the
Process is called Conversion.

Mercaptan’s Disadvantages
 Impart foul smell.
 Reduce Octane Number by reducing its
susceptibility to MMT.
 Elementary Sulfur and Presence of Mercaptans
Cause Corrosion.
 Pollute Environment.
 Dangerous to Human Health.

MerOx
 Stands for Mercaptans Oxidation.
 Mercaptans are Alkyl sulfide Halides (RSH)
 MerOx is Oxidation of Mercaptans to Alkyl
disulfides.

Types Of MerOx
 Fix Bed Process.
 Fix Bed Continuous Catalytic Process.
 Liquid/Liquid Counter Current Flow Process.

Liquid / Liquid Sweetening
 Hydro Carbon (containing Mercaptans), Air and
Caustic Containing dispersed MerOx catalyst are
simultaneously contacted in a mixer.
 Counter current flow of Caustic containing
Dispersed MerOx Catalyst (coming down) and
hydrocarbon (moving upward) in Reactor.

Fixed Bed Sweetening
 H2S free feed from Pre-Wash comes in contact
with Air in the presence of Catalyst in Reactor.
 Reactor contain Fix Bed of activated Charcoal
along with catalyst placed on Johnson Retaining
Screen.

Process
 MerOx Process completed in Three main Vessels.
 Vessel I (Pre- Wash).
 Vessel II (Reactor).
 Vessel III (Settler).

PRE-WASH (Vessel I)
 Contains Caustic Solution of Strength 3 to 5 mole
percent.
 50 to 60 percent level of Caustic Solution in Pre-
Wash.
 Product obtained from Pre-Wash, called Caustic
Washed Product.

Why to use Caustic (NaOH)???
 It has ability to dissolve low molecular weight
Mercaptans.
 It can dissolve H2S gas.
 It convert Mercaptans to Sodium Mercaptide
which is the intermediate Product.

Reactions at Pre-Wash
 RSH + NaOH NaSR + H2O
 H2S + NaOH Na2S + H2O
Na2S + H2S NaHS (Sodium Hydrosulfide)

60 % Level
3% Caustic Strength
LSRN Inlet
Caustic Washed LSRN
LSRN Distributer
Caustic/Water Inlet
Drain Point
Caustic Solution
(10 % Strength)
Pre-Wash Of LSRN

REACTOR (Vessel II)
It contain:
 Catalyst.
 Activated Charcoal.
 Bed Retaining Screen (Johnson Screen).
 Air.

Catalyst
 Metal (Iron) Chelate used as catalyst.
 Iron Chelate, catalyst to Rate of Reaction and
inhibitor to gum and peroxides formation.
 Per oxides formed due to reaction between Metals
and oxygen.
 Increase in catalyst concentration speed up the
Process.

Activated Charcoal
 It is used for bed formation.
 Iron Chelate diffuse on surface of Activated
charcoal to increase its surface area.
 Maximum exposure of Catalyst possible.
 Contact time increased.

Air (Oxygen)
 Air as a source of Oxygen.
 Air introduce at the inlet of Reactor along with
Caustic Washed Product.
 Air flow maintained according to Pre-Treatment
Graph.

Vent
Drain
Point
Caustic Washed
LSRN
Bed of MerOx
Catalyst and
Activated
Charcoal
Caustic
Circulation
Doctor Sweet
Product to
Settler
Reactor Of LSRN
Air

Reactions at Reactor
 NaSH + O2 Na2S2O3(Sodium thiosulfate)
 2NaSR + ½ O2 + H2O 2NaOH + RSSR

Caustic Regeneration
 In Reactor:
NaSR + ¼ O2 + ½ H2O NaOH + RSSR
Favorite Conditions for Regeneration of NaOH;
 High Temperature
 Increasing Amount of Air (according to Pre-Treatment Graph )
 Increasing contact time.
 Increasing catalyst concentration.

Overall Reactions
 RSH + NaOH + O2 RSSR + H2O + NaOH
 H2S + NaOH +O2 Na2S2O3 + H2O

SETTLER (Vessel III)
 Settling under gravity.
 Caustic level from 30 to 40 Percent.
 Caustic Strength from 10 to 12 mole Percent.
 Strength maintain for long because of
Regeneration of Caustic in Reactor.

Drain
Point
Doctor Sweet Product
along with Caustic from
Reactor
Caustic Level (40%)
Caustic Strength
(10%)
Caustic Circulation
Doctor Sweet Product to
Storage Tank
Settler Of LSRN

LSRN from Reformer / Storage
Doctor Sweet
ProductSettler
Caustic Circulation
Reactor
Excess Air
MerOx Catalyst
Strainer
Air
Pre-Wash
Drain Point
Dil. Caustic (3% Strength)
LSRN
Settling Tank
10% Caustic Strength
Process Flow Diagram of MerOx

Doctor Test
Take sample of sweet product in the tube.
Add approximately same amount of doctor solution
(Sodium plum bite).
Add small amount of Sulfur powder.
Shake the tube well.
If there is brownish color then the doctor test is
positive .
If the color of sulfur crystal remains unchanged then
the Test is Negative.

Steps in Case of Off Spec. Product
 Circulation of caustic from Settler to Reactor
should be carried out for at least half an hour.
 Darin exhaust Caustic from Pre-Wash and Settler
as and when required.
 If required Renew Caustic completely in both
Settler and Reactor.
 Hot Water Wash should be carried out.
 Re-Impregnation.

MerOx

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