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LIGHT OLEFINS PRODUCTION
Publication date:3Q 2015
Light olefins production
The production of light olefins—ethylene, propylene, and butenes—is garnering attention around the world as demand for petrochemical products is on the rise in many regions. Up until a few years ago, light olefins were primarily produced from steam crackers, where propylene and butylene were recovered as byproducts from the ethylene-producing units. However, natural gas availability has turned ethane into a primary feedstock for steam crackers in many regions, essentially eliminating propylene and butylene production from the units. Propylene remains a primary feedstock for petrochemical plants, while butylene has been in high demand for alkylation units for high-octane gasoline. This means that other technological approaches must be turned to in order to meet rising demand, in particular FCCUs and on-purpose olefin production. Besides steam cracking, there are currently five processes available for improved olefins production.
First there is fluid catalytic cracking (FCC) which can produce propylene and butylene from gasoil and resid streams along with other fuel products. Process adjustments and commercial catalysts and additives allow for increased propylene/butylene yields. Current offerings allow refiners to increase light olefin yield while decreasing either naphtha or LCO yield, depending on the technology and operational changes applied. Olefins produced in FCCUs must be recovered via separation from their paraffinic counterparts. This requires the use of distillation columns to separate propylene and propane in order to recover the valuable product. Other methods such as membrane separation, cryogenic separation and pressure swing absorption (PSA) are used to recover light olefins from other hydrocarbon streams.
Additionally, there are four methods that produce light olefins as a primary product. Cracking of heavy olefins converts long chain olefin streams into lighter propylene and butylene. Propane dehydrogenation (PDH) and butane dehydrogenation (BDH) involve the removal of a hydrogen atom from a paraffin molecule to form and olefin. Next is metathesis, which combines ethylene and n-butenes together to undergo disproportionation to produce propylene. Finally, methanol-to-olefins (MTO) or methanol-to-propylene take a methanol feedstock and pass it over a zeolitic catalyst to form olefins.
All technological approaches are dependent on the available feedstocks and corresponding process differential between feedstock and product. For example regions where propane is readily available due to large natural gas reserves could consider PDH units for on-purpose production, while regions with coal reserves can consider MTO or importing propane. Furthermore, the boost in demand for butadiene in coming years may wan producers to consider ramping up production of that product, mainly through oxidative butane dehydrogenation (OXO-BDH), which can yield both butylene and butadiene depending on the setup. Ultimately, the units in question must be efficient enough and flexible enough to effectively produce light olefins amidst and evolving marketplace.
Additionally, the light olefins section features the latest trends and technology offerings, including:
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Keywords: propylene, on-purpose propylene, light olefins, ethylene, butylenes, butadiene, steam cracking, shale gas, heavy olefins cracking, LPG, propane, liquefied petroleum gas, ethane, naphtha, PDH, propane dehydrogenation, BDH, butane dehydrogenation, metathesis, methanol-to-olefins, MTO, coal-to-olefins, CTO, methanol-to-propylene, MTP, fluid catalytic cracking, FCC, ZSM-5, dual riser, HS-FCC, downflow reactor, direct dehydrogenation, oxidative dehydrogenation, offgas recovery, pressure swing absorption, PSA, co-product, butenes