579
stability of the zeolites makes them suitable for application as membrane. When the
size of molecule and the pore size of material are comparable, the molecular diffusivity decreases exponentially. Thus, synthesis of zeolites is challenging as the zeolite pores are usually 0.3–1.3 nm in size and a small crystal spacing (2–3 nm) can
degrade the separation quality. Nevertheless, zeolites have been used for separation
of organic isomers, close boiling point mixture, and at high temperature and pressure reaction. Barbieri et al. [105] performed thermodynamic analysis of methanol
synthesis via CO 2 hydrogenation in zeolite membrane reactor. They proposed a
mathematical model for non-isothermal, microporous zeolites with different permeation value of methanol and water. The membrane reactors can operate at lower
pressure and higher temperature as compared to the conventional fixed bed reactor
system with 40–50% conversion and nearly 100% selectivity. The per pass methanol yield in membrane reactor (8.9%) was more than two times than in fixed bed
reactor (2.4%). The proposed modelling approach was heavily dependent on the
methanol and water permeation rates. Gallucci et al. [106] reported the application
of A-type zeolite for methanol synthesis reaction in a packed bed membrane reactor
(PBMR). The higher methanol yield at lower operating conditions in membrane
reactors compare to fixed bed reactor system suggests that operating conditions are
energy saving. They reported CO 2 conversion of 11.6% with 75% methanol selectivity at 206 °C and 20 bar pressure. The STY of 343 g methanol kgcat
−1
h
−1
with 84%
of methanol selectivity (240 °C, 7 bars, and GHSV = 18,000 L kgcat
−1
h
−1
) obtained
by using NaA membrane [107]. Zebarjad et al. [108] used 1-ethyl-3methylimidazolium tetrafluoroborate (ionic liquid) on the tube side in membrane
reactor and syngas on the shell side of the reactor. They used commercial methanol
synthesis catalyst and modified mesoporous alumina (hydrophobic) membrane.
Rahimpour and co-workers reported a reactor configuration with shell and tube
Pd membrane (H 2 permeable) reactor. The feed flow from the tube side and pure
hydrogen was on the shell side. The unique membrane configuration allows diffusion of H 2 from the shell to the tube to maintain a desired ratio of H 2 /CO 2 along the
reactor length. Methanol yield was enhanced with decrease in membrane thickness
and increasing the shell side flow rate [109]. Further, the same research group have
performed comparative study between conventional methanol synthesis reactor
and dual membrane reactors with similar shell and tube arrangement. The first reactor in dual configuration was cooled by cooling water, and second reactor was
cooled by feed syngas. The application of H 2 permeable palladium-silver (Pd-Ag)
membrane on the tube side of second reactor configuration improved methanol
yield by H 2 diffusion through the tube side of the reactor [110]. The dual membrane
reactor with two different membranes in each reactor configuration has been also
reported; one membrane was used for feeding H 2 and other for removal of water.
The objective function used to determine the optimal operating condition was a
function of outlet molar flow rate of methanol. The optimal operating conditions
were determined using genetic algorithm. The optimized dual membrane reactor
provides higher CO 2 conversion and methanol yield [111].
Increasing CO 2 concentration problem can be solved by utilizing it to convert in
valuable products in order to mitigate the global warming and its associated effects
Perspectives in Carbon Oxides Conversion to Methanol/Dimethyl Ether: Distinctive…
stability of the zeolites makes them suitable for application as membrane. When the
size of molecule and the pore size of material are comparable, the molecular diffusivity decreases exponentially. Thus, synthesis of zeolites is challenging as the zeolite pores are usually 0.3–1.3 nm in size and a small crystal spacing (2–3 nm) can
degrade the separation quality. Nevertheless, zeolites have been used for separation
of organic isomers, close boiling point mixture, and at high temperature and pressure reaction. Barbieri et al. [105] performed thermodynamic analysis of methanol
synthesis via CO 2 hydrogenation in zeolite membrane reactor. They proposed a
mathematical model for non-isothermal, microporous zeolites with different permeation value of methanol and water. The membrane reactors can operate at lower
pressure and higher temperature as compared to the conventional fixed bed reactor
system with 40–50% conversion and nearly 100% selectivity. The per pass methanol yield in membrane reactor (8.9%) was more than two times than in fixed bed
reactor (2.4%). The proposed modelling approach was heavily dependent on the
methanol and water permeation rates. Gallucci et al. [106] reported the application
of A-type zeolite for methanol synthesis reaction in a packed bed membrane reactor
(PBMR). The higher methanol yield at lower operating conditions in membrane
reactors compare to fixed bed reactor system suggests that operating conditions are
energy saving. They reported CO 2 conversion of 11.6% with 75% methanol selectivity at 206 °C and 20 bar pressure. The STY of 343 g methanol kgcat
−1
h
−1
with 84%
of methanol selectivity (240 °C, 7 bars, and GHSV = 18,000 L kgcat
−1
h
−1
) obtained
by using NaA membrane [107]. Zebarjad et al. [108] used 1-ethyl-3methylimidazolium tetrafluoroborate (ionic liquid) on the tube side in membrane
reactor and syngas on the shell side of the reactor. They used commercial methanol
synthesis catalyst and modified mesoporous alumina (hydrophobic) membrane.
Rahimpour and co-workers reported a reactor configuration with shell and tube
Pd membrane (H 2 permeable) reactor. The feed flow from the tube side and pure
hydrogen was on the shell side. The unique membrane configuration allows diffusion of H 2 from the shell to the tube to maintain a desired ratio of H 2 /CO 2 along the
reactor length. Methanol yield was enhanced with decrease in membrane thickness
and increasing the shell side flow rate [109]. Further, the same research group have
performed comparative study between conventional methanol synthesis reactor
and dual membrane reactors with similar shell and tube arrangement. The first reactor in dual configuration was cooled by cooling water, and second reactor was
cooled by feed syngas. The application of H 2 permeable palladium-silver (Pd-Ag)
membrane on the tube side of second reactor configuration improved methanol
yield by H 2 diffusion through the tube side of the reactor [110]. The dual membrane
reactor with two different membranes in each reactor configuration has been also
reported; one membrane was used for feeding H 2 and other for removal of water.
The objective function used to determine the optimal operating condition was a
function of outlet molar flow rate of methanol. The optimal operating conditions
were determined using genetic algorithm. The optimized dual membrane reactor
provides higher CO 2 conversion and methanol yield [111].
Increasing CO 2 concentration problem can be solved by utilizing it to convert in
valuable products in order to mitigate the global warming and its associated effects
Perspectives in Carbon Oxides Conversion to Methanol/Dimethyl Ether: Distinctive…