245
1.4.2 Effect of Pressure
Thermodynamically, it has been shown that a decrease in pressure favours the conversion rate; however, selectivity towards benzene is observed with a slight decrease
in MDA reaction as per previous reports [17]. According to previous experimental
report, at lower pressure range below 1 bar, the benzene formation rate rapidly
decreases with time on stream, whereas at higher pressure (above 1 bar), the rate of
benzene formation is observed to increase with time on stream achieving higher
stability [61]. Generally, moderate pressure range (1–3 bar) applied to MDA reaction results in higher stability and activity to the Mo/Zeolite catalyst [61]. In recent
studies of Hensen et al. (2019), the advantageous effect of high pressure (up to
15 bar) has been claimed for Mo/ZSM-5 catalyst in MDA reaction [12]. Fast coke
hydrogenation at higher pressure results in lower coke selectivity and retains active
catalyst surface for further reaction. Thus modification in pressure range can
improve benzene yield with lower coke deposition and can take the MDA process at
the commercial level.
1.4.3 Effect of Space Velocity
Generally, increase in space velocity leads to decrease in conversion rate as per
reaction engineering. Different experimental reports have been claimed on space
velocity effect for the reaction and it has been observed that decrease in the space
velocity increases the methane conversion to aromatic hydrocarbons at 873–998 K
[27, 62] with increased duration of the induction period. In the product distribution,
an increase in the space velocity results in higher ethylene selectivity whereas lower
selectivity towards benzene [63]. Lower space velocity favours the catalyst deactivation due to high residence time as also experimentally observed in earlier reports.
Thus a rigorous optimization controlling temperature, pressure and space velocity
can upgrade the MDA process.
1.5 Reactor Configuration
Reactor design is another major aspect in the MDA process which significantly
controls methane conversion and product yield. Fixed-bed reactor is the most widely
used setup for MDA reaction. For the industrial and academic community, MDA
process is being a challenge for commercialization due to its thermodynamic and
kinetic limitations. However, MDA process is upgraded via increase in temperature
or decrease in pressure, but these parameters cannot take the process at the industrial level. Reactor configuration considering different factors such as multiple pas
conversion instead of single pas conversion, catalyst regeneration via in situ coke
removal, in situ H 2 removal from the reaction mixture, etc. can actually improve the
technology for commercial purposes. Circulating fluidized-bed reactor setup and
Thermocatalytic Conversion of Natural Gas to Petrochemical Feedstocks…
1.4.2 Effect of Pressure
Thermodynamically, it has been shown that a decrease in pressure favours the conversion rate; however, selectivity towards benzene is observed with a slight decrease
in MDA reaction as per previous reports [17]. According to previous experimental
report, at lower pressure range below 1 bar, the benzene formation rate rapidly
decreases with time on stream, whereas at higher pressure (above 1 bar), the rate of
benzene formation is observed to increase with time on stream achieving higher
stability [61]. Generally, moderate pressure range (1–3 bar) applied to MDA reaction results in higher stability and activity to the Mo/Zeolite catalyst [61]. In recent
studies of Hensen et al. (2019), the advantageous effect of high pressure (up to
15 bar) has been claimed for Mo/ZSM-5 catalyst in MDA reaction [12]. Fast coke
hydrogenation at higher pressure results in lower coke selectivity and retains active
catalyst surface for further reaction. Thus modification in pressure range can
improve benzene yield with lower coke deposition and can take the MDA process at
the commercial level.
1.4.3 Effect of Space Velocity
Generally, increase in space velocity leads to decrease in conversion rate as per
reaction engineering. Different experimental reports have been claimed on space
velocity effect for the reaction and it has been observed that decrease in the space
velocity increases the methane conversion to aromatic hydrocarbons at 873–998 K
[27, 62] with increased duration of the induction period. In the product distribution,
an increase in the space velocity results in higher ethylene selectivity whereas lower
selectivity towards benzene [63]. Lower space velocity favours the catalyst deactivation due to high residence time as also experimentally observed in earlier reports.
Thus a rigorous optimization controlling temperature, pressure and space velocity
can upgrade the MDA process.
1.5 Reactor Configuration
Reactor design is another major aspect in the MDA process which significantly
controls methane conversion and product yield. Fixed-bed reactor is the most widely
used setup for MDA reaction. For the industrial and academic community, MDA
process is being a challenge for commercialization due to its thermodynamic and
kinetic limitations. However, MDA process is upgraded via increase in temperature
or decrease in pressure, but these parameters cannot take the process at the industrial level. Reactor configuration considering different factors such as multiple pas
conversion instead of single pas conversion, catalyst regeneration via in situ coke
removal, in situ H 2 removal from the reaction mixture, etc. can actually improve the
technology for commercial purposes. Circulating fluidized-bed reactor setup and
Thermocatalytic Conversion of Natural Gas to Petrochemical Feedstocks…