petrochemical obtained as a co-product in ethylene plants and has more than 80% of
its demand associated with the production of elastomers. Benzene is almost entirely
used as a raw material in the production of other petrochemical products and is rarely
used as a solvent because of its potential toxicity. One of the leaders of the basic
petrochemicals, toluene, is fourth in the ranking in importance after ethylene,
propylene, and benzene [53].
Recently, the appearance of new shale/natural gas (light feedstocks) resources has
been changing the availability of the key chemical building blocks, increasing the
tendency to use light feedstock (shale/natural gas) sources to the detriment of the
heavier (crude oil) ones. Light feedstocks are mostly used to make ethylene, while
heavy feedstocks produce propylene, butadiene, and benzene [54]. It is also expected
that the production of methane will increase due to the exploitation of the new
nonconventional natural gas (including shale gas) reserves. Indeed, the use of natural
gas has been growing as an energy option and chemical raw material due to the
exceptional combination of properties, price, and the guarantee of available reserves.
Natural gas is a mixture of light hydrocarbons, especially methane that can reach
concentrations above 80%, and various impurities in smaller quantities, usually N 2
and CO 2 [20]. Several factors can affect the composition of natural gas once the
composition is determined by the field in which the gas is produced, the production
process, conditioning, processing, and transportation [48]. To meet the specifications
of commercial natural gas, the so-called pipeline quality methane, it is necessary to
remove ethane, hydrocarbons of higher molecular weight, carbon dioxide, helium,
and nitrogen. Typically the amount of N 2 may not surpass 2–4%, while the amount
of CO 2 cannot exceed 2% [55]. Among the several separations required to achieve
“pipeline quality methane,” CH 4 /CO 2 is the most expensive one, once CO 2 content
in natural gas is usually higher than 25% [50]. CO 2 is an inert gas that decreases the
combustion power of natural gas, and also in the presence of moisture, CO 2 forms
carbonic acid that causes the pipeline and equipment damage. The main technologies
employed to remove CO 2 from natural gas are cryogenic distillation, solvent extraction by alkylamines, and adsorbent-based processes. Despite the high operating
costs, cryogenic distillation and solvent extraction by alkylamines are appropriate
technologies when H 2 S and other impurities need to be removed at the same time;
when the required final product is liquefied natural gas (LNG); and when it is
necessary to treat large quantities of gas. For intermediate quantities of gas,
adsorptive-based technologies become economically more attractive [40]. The
high operating and capital costs of the current commercially practiced separation
processes have been the driving force to seek more sustainable options to reach the
products with the purity desired. The high-energy demand has been the driving force
to develop new technologies and materials which must be cheaper, yet environmentally friendly. In this field, the separation based on adsorption appears as a reliable
substitute, to the currently available distillation processes in use. Pressure swing
adsorption (PSA) [10, 23, 56] and simulated moving bed (SMB) [9, 42, 47, 57, 58]
arose as potential adsorptive processes for the target separations.
The concept of adsorption-based separation in the gas phase is relatively simple.
To understand the basic idea, we first can consider a binary mixture, composed by
Perspectives of Scaling Up the Use of Zeolites for Selective Separations from. . .
149
its demand associated with the production of elastomers. Benzene is almost entirely
used as a raw material in the production of other petrochemical products and is rarely
used as a solvent because of its potential toxicity. One of the leaders of the basic
petrochemicals, toluene, is fourth in the ranking in importance after ethylene,
propylene, and benzene [53].
Recently, the appearance of new shale/natural gas (light feedstocks) resources has
been changing the availability of the key chemical building blocks, increasing the
tendency to use light feedstock (shale/natural gas) sources to the detriment of the
heavier (crude oil) ones. Light feedstocks are mostly used to make ethylene, while
heavy feedstocks produce propylene, butadiene, and benzene [54]. It is also expected
that the production of methane will increase due to the exploitation of the new
nonconventional natural gas (including shale gas) reserves. Indeed, the use of natural
gas has been growing as an energy option and chemical raw material due to the
exceptional combination of properties, price, and the guarantee of available reserves.
Natural gas is a mixture of light hydrocarbons, especially methane that can reach
concentrations above 80%, and various impurities in smaller quantities, usually N 2
and CO 2 [20]. Several factors can affect the composition of natural gas once the
composition is determined by the field in which the gas is produced, the production
process, conditioning, processing, and transportation [48]. To meet the specifications
of commercial natural gas, the so-called pipeline quality methane, it is necessary to
remove ethane, hydrocarbons of higher molecular weight, carbon dioxide, helium,
and nitrogen. Typically the amount of N 2 may not surpass 2–4%, while the amount
of CO 2 cannot exceed 2% [55]. Among the several separations required to achieve
“pipeline quality methane,” CH 4 /CO 2 is the most expensive one, once CO 2 content
in natural gas is usually higher than 25% [50]. CO 2 is an inert gas that decreases the
combustion power of natural gas, and also in the presence of moisture, CO 2 forms
carbonic acid that causes the pipeline and equipment damage. The main technologies
employed to remove CO 2 from natural gas are cryogenic distillation, solvent extraction by alkylamines, and adsorbent-based processes. Despite the high operating
costs, cryogenic distillation and solvent extraction by alkylamines are appropriate
technologies when H 2 S and other impurities need to be removed at the same time;
when the required final product is liquefied natural gas (LNG); and when it is
necessary to treat large quantities of gas. For intermediate quantities of gas,
adsorptive-based technologies become economically more attractive [40]. The
high operating and capital costs of the current commercially practiced separation
processes have been the driving force to seek more sustainable options to reach the
products with the purity desired. The high-energy demand has been the driving force
to develop new technologies and materials which must be cheaper, yet environmentally friendly. In this field, the separation based on adsorption appears as a reliable
substitute, to the currently available distillation processes in use. Pressure swing
adsorption (PSA) [10, 23, 56] and simulated moving bed (SMB) [9, 42, 47, 57, 58]
arose as potential adsorptive processes for the target separations.
The concept of adsorption-based separation in the gas phase is relatively simple.
To understand the basic idea, we first can consider a binary mixture, composed by
Perspectives of Scaling Up the Use of Zeolites for Selective Separations from. . .
149