and higher capital and energy costs due to the involvement of multiple processes. Moreover, it contributes to a larger carbon footprint. Thermal cracking The thermal process is an established route to produce light olefins such as ethylene and propylene. The feed is typically composed of naphtha, ethane, or propane. The feed is diluted with steam to reduce the coke formation and heated in a furnace to a high temperature. The reaction follows free radical mechanism. The C-C bond breaks and forms highly reactive free radicals, which propagate the reaction. Quenching stops the reaction, and the products are separated to arrest the reaction and separated in subsequent process units. Steam consumption in thermal cracking varies by feedstock: approximately 0.2 kg of steam per kg of ethane and around 0.8 kg per kg of naphtha. Operating temperatures typically “ Olefin production through thermal cracking faces efficiency challenges due to the high energy requirements range between 750°C and 950°C. However, olefin production through thermal cracking faces efficiency challenges due to the high energy requirements and substantial CO₂ emissions associated with these elevated temperatures. Catalytic cracking FCC is a well-established and reliable refining technology, with hundreds of units operating worldwide. The zeolite-based catalysts used in FCC have seen significant advancements, enabling tailored applications such as naphtha mode, diesel mode, and petrochemical production. The typical petrochemicals produced are propylene, ethylene, butylenes, and BTX. Unlike thermal cracking, catalytic cracking offers greater control over product distribution by adjusting operating conditions, catalyst formulations, and feedstock types. Legacy FCCUs, originally designed to and substantial CO₂ emissions associated with these elevated temperatures ”
maximise naphtha or diesel production, face inherent limitations when it comes to propylene yield. These units typically lack the high- severity operating conditions and advanced configurations found in modern FCCUs. To partially overcome this constraint, ZSM-5-based catalyst additives are employed. These additives promote selective cracking of naphtha-range hydrocarbons into light olefins, particularly propylene, thereby enhancing olefin output while reducing naphtha yield. To address the increasing demand for light olefins, FCCU design has been evolved to enhance propylene production. Modern FCC units primarily process hydrotreated vacuum gas oil and operate under high-severity conditions, such as a reaction temperature of >540°C and a catalyst-to-oil ratio of >7 wt/wt. In some configurations, cracked naphtha, which contains a high concentration of olefins, is recycled to the bottom of the riser. These olefins are highly reactive and readily crack into lighter products such as ethylene and propylene, contributing to improved light olefin yields. Modern FCCUs often feature a dedicated secondary riser designed specifically for handling recycled streams. A portion of cracked naphtha and optionally C 4 olefins is routed to this riser, which operates at a higher severity than the primary riser. This design significantly boosts the overall petrochemical output, particularly for light olefins. Nevertheless, the core objective of the FCC remains the conversion of vacuum gas oil (VGO) or heavy residues into high-value products such as liquefied petroleum gas (LPG), high-octane gasoline. Although FCC units contribute notably to global propylene production, the yield per barrel of crude oil remains relatively low. While propylene output can be moderately enhanced using catalyst additives, the growing demand for light olefins has prompted refiners to explore new technologies that offer higher yields and lower production costs. Development of crude cracking technology The two primary routes for petrochemical production are the catalytic and thermal methods. While the thermal route can produce ethylene and propylene, it comes with high
Refining India
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