Hydrocarbon Processing - August 2021 - 50

Process Optimization
produces a favorable yield, relatively high space velocity and
a standard lifetime.
One of the challenges in the field of heterogeneous
catalysis is the conversion of methane to valuable
petrochemical materials, providing opportunities
to improve the local petrochemical industries in
Egypt. OCM technology developments are having
a significant impact on chemical industries.
The process is based on a two-stage adiabatic reactor approach.
It operates adiabatically with fewer stages at several
hundred °C lower inlet temperatures, and at higher pressures,
compared with the original processes.
Reactor heat recovery is a significant feature, where the exothermic
heat from OCM is used to thermally crack the byproduct
and fresh ethane balance to ethylene production.
To enhance the overall carbon efficiency of the process,
a catalytic methanation step is included in the process. This
reaction converts all generated CO and a portion of the CO2
back to methane by using the hydrogen generated in both the
OCM and ethane cracking-reaction sections of the post-OCM
section of the reactor.
The reactor outlet stream is directed to the olefins cracking
separation, recovery and fractionation steps.
Reaction mechanisms are summarized as follows:
(1) 2CH4
(2) C2
(3) CH4
(4) C2
+ 0.5O2
H6 + 0.5O2
+ 2O2
H4 + 3O2
→ C2
→ C2
→ CO2
H6
H4
→ 2CO2
+ H2
+ H2
+ 2H2
O
+2H2
O
Reaction stoichiometry is used as information to engineer
catalyst and tailor process conditions to favor reaction equilibOxygen
Steam
generation
Methane
OCM reaction
removal
CO2
Ethane
EDH reaction
Deethanizer
C3
FIG. 1. A process flow diagram of the OCM process structures.
50 AUGUST 2021 | HydrocarbonProcessing.com
+
C2
-splitter
Compression
CO2
Demethanizer
Feed specifications. The specification of the feed stream
entering the OCM reactor has a direct impact on the ethylene
selectivity and yield and on the reaction-thermal stable operation
of the OCM reactor.
Lights
Ethylene
O
O
Thermodynamic considerations and economics. Difficulties
in methane conversion exist due to its high molecular
stability relative to any product to which it might be converted.
Also, there are limitations to attain high ethylene yield in a
methane OCM process where ethylene and ethane are more
susceptible to oxidation than methane.
From the process performance side, it has been verified
that OCM reactor performance of 50% ethylene selectivity
and 18% ethylene yield-generating C2
(ethylene and ethane)
from methane in an OCM reactor and then converting ethane
into ethylene via an EDH reactor-is economically attractive.
The feasibility of OCM depends on catalyst performance:
a methane conversion in the range of 38% and C2
of 85% (equivalent to 32% yield) can render this process economically
competitive. In general, economics are highly sensitive
to the price of feedstocks.
PROCESS OPERATING PARAMETERS
selectivity
rium, such as improving selectivity and shifting reaction toward
better ethylene and ethane yields. Adding oxygen to methane,
the thermodynamic barrier can be overcome
and methane practical conversion limits can
be achieved-i.e., the conversion of methane
can be feasible at lower temperatures than the
original process constraint limitations.
However, the methane/oxygen ratio should
be below 2 for safe operations of the OCM reaction
system. Note that ethylene deep oxidation
to CO2
is intensified during longer contact
periods and endothermic gas phase EDH
reaction is intensified in higher temperatures.
http://www.HydrocarbonProcessing.com
Hydrocarbon Processing - August 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - August 2021
