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• Primary cracking: paraffin and olefins are formed initially.
• Secondary cracking: light products are formed that are rich in olefins.
Thermal steam cracking (TSC) process needs high energy; around 3.050 kcal/kg
of energy is consumed for per kg of produced olefin [7]. In steam cracking, a liquid
hydrocarbon (such as naphtha or gas oil) or a gaseous feedstock such as ethane,
propane, or butane is mixed with steam and then introduced into a heated furnace at
790–850 °C in the absence of oxygen [8]. The products composition depends on the
properties of hydrocarbon feedstock, hydrocarbon to steam ratio, cracking temperature, and furnace residence time. In the modern cracking furnaces, the residence
time is precisely controlled to improve the yield of desired products [9]. Steam
cracking leads to the formation of small paraffin molecules through C–C bond
breaking and alkenes through C–H bond breaking by radical mechanism. Alkene at
high temperature undergoes side reactions and thus coke is also formed after cyclodehydrogenation. Propylene to ethylene ratio can be altered by changing feedstock
and cracking severity [10]. Light hydrocarbon feedstocks (such as ethane, LPG, or
light naphtha) predominantly produce ethylene, propylene, and butadiene. On the
other hand, heavier feedstocks (such as heavy naphtha or gas oil) produce lighter
olefins such as ethylene, propylene, butadiene as well as aromatic-rich hydrocarbon
fractions suitable for gasoline blend or as fuel oil [9]. The higher cracking severity
favors the production of ethylene and benzene, whereas lower severity favors relatively higher amounts of propylene, C 4 -hydrocarbons, and liquid products. The
decision of steam cracker configuration depends on the feedstock availability such
as liquid feedstock is used predominately in the Europe and Asia but less so in the
Middle East and North America [11]. Most of the recent gas crackers have been
constructed and under construction are located in the North America and the Middle
East because of the availability of shale gas and natural gas. A number of technology licensors such as KBR, ABB Lummus, Technip, Linde AG, Stone & Webster
offer steam cracking technology [12].
2.1.2 Catalytic Routes
The second-largest source of propylene is the refinery fluid catalytic cracking (FCC)
unit. FCC is a major secondary refinery process and traditionally it has been operated either in gasoline or distillate mode. As the refining sector is facing various new
challenges such as surplus refining capacity, competitive refinery margins, and
lower demand of transportation fuels, refiners are paying more attention for the
integration of petrochemicals production with refineries. As a result, refiners are
focusing on improvement of the propylene yield in the traditional FCC and setting
up Resid FCC (RFCC) units. RFCC process is a modified version of traditional
FCC process and was conceptualized in the early 1980s [13]. Technip and Stone &
Webster Process Technology formed an Alliance with Total, IFP, and Axens to
develop a Resid FCC process which is known as R2R™ (Reactor-2-Regenerator).
Since then, this Alliance has been the leader in the refining industry for RFCC
C. Samanta and R. K. Das
• Primary cracking: paraffin and olefins are formed initially.
• Secondary cracking: light products are formed that are rich in olefins.
Thermal steam cracking (TSC) process needs high energy; around 3.050 kcal/kg
of energy is consumed for per kg of produced olefin [7]. In steam cracking, a liquid
hydrocarbon (such as naphtha or gas oil) or a gaseous feedstock such as ethane,
propane, or butane is mixed with steam and then introduced into a heated furnace at
790–850 °C in the absence of oxygen [8]. The products composition depends on the
properties of hydrocarbon feedstock, hydrocarbon to steam ratio, cracking temperature, and furnace residence time. In the modern cracking furnaces, the residence
time is precisely controlled to improve the yield of desired products [9]. Steam
cracking leads to the formation of small paraffin molecules through C–C bond
breaking and alkenes through C–H bond breaking by radical mechanism. Alkene at
high temperature undergoes side reactions and thus coke is also formed after cyclodehydrogenation. Propylene to ethylene ratio can be altered by changing feedstock
and cracking severity [10]. Light hydrocarbon feedstocks (such as ethane, LPG, or
light naphtha) predominantly produce ethylene, propylene, and butadiene. On the
other hand, heavier feedstocks (such as heavy naphtha or gas oil) produce lighter
olefins such as ethylene, propylene, butadiene as well as aromatic-rich hydrocarbon
fractions suitable for gasoline blend or as fuel oil [9]. The higher cracking severity
favors the production of ethylene and benzene, whereas lower severity favors relatively higher amounts of propylene, C 4 -hydrocarbons, and liquid products. The
decision of steam cracker configuration depends on the feedstock availability such
as liquid feedstock is used predominately in the Europe and Asia but less so in the
Middle East and North America [11]. Most of the recent gas crackers have been
constructed and under construction are located in the North America and the Middle
East because of the availability of shale gas and natural gas. A number of technology licensors such as KBR, ABB Lummus, Technip, Linde AG, Stone & Webster
offer steam cracking technology [12].
2.1.2 Catalytic Routes
The second-largest source of propylene is the refinery fluid catalytic cracking (FCC)
unit. FCC is a major secondary refinery process and traditionally it has been operated either in gasoline or distillate mode. As the refining sector is facing various new
challenges such as surplus refining capacity, competitive refinery margins, and
lower demand of transportation fuels, refiners are paying more attention for the
integration of petrochemicals production with refineries. As a result, refiners are
focusing on improvement of the propylene yield in the traditional FCC and setting
up Resid FCC (RFCC) units. RFCC process is a modified version of traditional
FCC process and was conceptualized in the early 1980s [13]. Technip and Stone &
Webster Process Technology formed an Alliance with Total, IFP, and Axens to
develop a Resid FCC process which is known as R2R™ (Reactor-2-Regenerator).
Since then, this Alliance has been the leader in the refining industry for RFCC
C. Samanta and R. K. Das