Hydrocarbon Processing - May 2022 - 40

Biofuels, Alternative Fuels and Green Petrochemicals
CO2
tion of CO2
as a chemicals building block. In principle, the utilizaas
a chemicals building block applies CO2
catalytic
hydrogenation. The simplest C1
(CH3
When capitalizing on CO2
liquid product is methanol
.
OH), which can be easily obtained from recycled CO2
as a C1-building block in industry,
its low energy level is certainly a major barrier. However, highenergy
co-reactants [e.g., hydrogen (H2
), unsaturated compounds
or strained cyclic molecules] must be used.5
Consequently, the overall energy balance and the primary
source of energy employed to generate the starting materials
are carefully evaluated to assess the net effect of envisaged
CO2
utilization.
Three main routes are the basis of recycled CO2
, are commonly applied in CO2
) and methanol synthesis].6,7
* Electrochemical activation of CO2
synthesis:
* Heterogeneous catalysts, based on the metal complexes
of CO2
conversion
processes in petrochemical industries [e.g., the
production of dimethyl carbonate, synthesis gas
(CO, H2
can result in the
production of a number of valuable petrochemical
products, such as methanol, ethylene (C2
(C2
H4), ethanol
H5OH), and other hydrocarbons and oxygenates.
Photocatalysts application is also used to enhance a chemiH5OH,
methane (CH4
), and
cal reaction, producing valuable products, such as carbon
monoxide (CO), methanol, C2
higher hydrocarbons.8
The application of nanocarbons (carbon nanotube, graphene
oxide, etc.) possessing high thermal conductivity, high
theoretical specific surface area, unique carrier mobility and
an sp2
N4) is applied successfully for improved
-hybridized carbon configuration, have shown promotion
to CO2 photocatalysis applications. Graphitic carbon
nitride (g- C3
photocatalytic activity.
MAIN APPLICATIONS OF RECYCLED CO2
IN PETROCHEMICAL PLANTS
As has been discussed previously, CO2
of methanol production is the low H2/CO (S = 1) ratio in the
product gas, which is not suitable for methanol synthesis.1,2,4
Hydrogenation of CO2
to methanol. A potential use of CO2
exists as an alternative feed in place of CO methanol production.
CO2
hydrogenation to produce methanol is accompanied
by a simultaneous reverse water-gas-shift reaction. In this process,
the methanol formation is an exothermic reaction and the
molecular weight of the carbon-containing molecule decreases.
Hence, the thermodynamics foresee a decreased temperature
and an increased pressure for selectivity.
The accompanying reverse water-gas shift reaction is undesirable
as it consumes H2
methanol. In the meantime, the large amount of water produced
by both reactions has a certain inhibitory effect on the
catalyst, leading to its eventual deactivation-therefore, catalyst
selectivity has critical importance. Recent processes for
CO2
, resulting in a decreased yield of
hydrogenation reaction apply ternary CueZneAl oxide
catalyst with additional modifiers and carbides.
Bi-reforming of methane for methanol production. This
process is utilized for methanol synthesis through syngas production-H2
:CO
(S ≈ 2) can be achieved by a selective process,
termed " bi-reforming, " a combined steam reforming and
dry reforming process of methane giving exclusively syngas,
the needed feed for subsequent methanol synthesis. The bireforming
of methane is also a practical procedure for natural
gas that contains CO2
.
Bi-reforming compared to methane dry reforming (MDR)
exclusively provides the 2H2/CO ratio; the fact that similar catalysts
active for steam reforming or dry reforming (Ni/MgO at
800°C-1,000°C) can be used is also an advantage.
Urea, formaldehyde and melamine. Urea synthesis is a major
process utilizing CO2
(Eq. 2):
recycling is under increasing
scrutiny as one of the most important approaches to
mitigate CO2
emissions to the environment, as well as to find a
low-cost carbon source. The main applications of recycled CO2
in the petrochemical industries are discussed here.
CO2
chemicals by combining CH4
reforming of methane. The production of value-added
and CO2
been attractive. The process is called " dry " reforming, indicating
the reaction between an equimolar amount of CO2
giving a 1:1 ratio of CO and H2 (S = 1). In this endothermic
reaction, CH4 adsorbs on a noble metal [such as platinum (Pt)],
whereas CO2
on Ni/MgO or Ni/MgAl2O4 catalyst at temperatures from
800°C-1,000°C (1,472°F-1,832°F), calculated in Eq. 1:
Dry reforming CO2
+ CH4 } 2CO +
2H2 ΔH298K = 59.1 kcal mol−1
(1)
The advantages of dry reforming are that it utilizes very costeffective
raw materials, and that one molecule of CO2
for each CH4
molecule, making the process even more attractive.
However, the process suffers from coking, and the context
40 MAY 2022 | HydrocarbonProcessing.com
is used
molecules has always
and CH4
adsorbs on a support. The reaction is conducted
Carbonate syntheses.
* Monomeric carbonates: Carbonates are becoming
an industrial viable alternative to toxic phosgene
(COCL 2). An example is the carbonation of ethylene
oxide, as opposed to phosgenation of ethylene glycol for
ethylene carbonate synthesis. These carbonates
are used in producing polycarbonates.
* Dimethyl carbonate: Dimethyl carbonate (DMC)
is a linear carbonate and is produced by the
2 NH3 + CO2 r (H2
(H2
of CO2
N - COO) (NH4
N - COO) (NH4
)
r NH2 CONH2
+ H2
O
(2)
The CO2 conversion/fixation potential is the incorporation
as a C1 source, such as UF-resins and MF-resins, which
are used in many applications (wood additives, electrical insulators,
etc.).
Acrylates synthesis. Sodium acrylate is a basic intermediate
for polyacrylate production (Eq. 3):
H2
C = CH2
+ CO2
nickel lactones.
r H2C = CH - COOH
(3)
For acrylate synthesis, the catalytic pathway includes
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