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HYDROTREATING, AND LIGHT OLEFINS PRODUCTION
Publication date:3Q 2015
Hydrotreating, and Light olefins production
Hydrotreating is a process that has become synonymous with removing impurities from petroleum feedstocks. By mixing hydrogen and feedstocks under controlled conditions in the presence of a catalyst, contaminants in the form of sulfur-, nitrogen-, and oxygen-containing compounds, as well as metals, can be removed. When the catalyst is designed to remove a specific class of compounds, that fact is reflected in the name of the process, e.g., hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and hydrodearomatization (HDA)/hydrogenation (HYD). Hydrotreating is suitable for removing contaminants from product streams or feedstreams. For the feedstocks intended for other refinery processes—catalytic cracking, hydrocracking, catalytic reforming—hydrotreating serves two purposes: (1) it improves the quality of the products of those processes (especially quality specifications mandated by law, e.g., benzene reduction in motor gasoline), and (2) it protects the sensitive (and costly) catalysts from contamination. Hydrotreating is not without drawbacks: the capital investment is significant; operating costs (catalysts and hydrogen) can be high; and product quality may be adversely affected by the potential saturation of aromatics and olefins.
As oil becomes more difficult to access and process, the supply of energy may struggle to keep pace with demand. Along with demand growth, tighter environmental regulations for on-road fuels and an increased focus on reducing CO2 emissions from industrial sources will force refiners to alter operations, and these alterations could be a challenge as capital and operating budgets continue to decline. Hydrotreaters will help refiners cope with this changing market, as these units offer the ability to upgrade unconventional (resid and renewable) feeds to produce more diesel while helping meet stricter environmental regulations. The following discussion relates to the market factors and technology trends that are shaping demand for hydrotreating capacity.
New, more stringent standards with regard to sulfur content within transportation fuels has been a major driver for hydrotreating technology over the past year. As more countries continue to adopt Euro V standards, which calls for 10 ppm sulfur within diesel, refiners seek to improve the production of ultra-low sulfur diesel (ULSD). Companies and licensers continue to research on and release highly active HDS catalysts that allow for high HDS conversion while limiting the weighted average bed temperature (WABT) of their reactors. Furthermore, the ongoing shale boom and natural gas supply in the US have led to cheaper hydrogen production for refineries, which has opened the door for increased diesel production by increasing the volume swell of a particular unit. New offerings allow for saturation of aromatics in feeds like LCO in order to decrease diesel density and therefore increase the potential gains of incoming crude. Improvement to diesel quality has also been addressed through hydrodewaxing (HDW), which can improve the cloud point and pour point for better cold flow properties. Numerous companies have released technologies which aim to efficiently and effectively dewax a diesel stream through the use of selective catalysts.
Another challenge for refiners comes from the Tier III gasoline standard, in the US which calls for 10 ppm sulfur in gasoline, which is a third of the previous standard. This change greatly impacts the production of FCC gasoline, as it accounts for the around a third of the gasoline blending pool, and is the main contributor of sulfur in the final gasoline product. Different refiners and licensers offer technologies and recommendations when deciding between FCC pretreatment and FCC posttreatment. Both options can reduce sulfur levels to meet the new standards, but at a cost. Pretreatment requires reactors to operate at higher severities, which can decrease catalyst cycles by as much as 40%. Companies are releasing and carrying out research into highly active FCC pretreat catalysts that can produce low sulfur FCC feeds while maintaining desired cycle lengths. Meanwhile, posttreatment of FCC naphtha can lead to olefin saturation and significant octane loss as a result. New offerings and current research aim to find ways to increase HDS activity while decreasing olefin saturation by making the HDS process more selective.
Additionally, the hydrotreating section features the latest trends and technology offerings, including:
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: hydrogen, hydrotreating, middle distillates, diesel, ULSD, heavy oil, tight oil, fixed-bed, single-stage, two-stage, two-stage with recycle, jet fuel, kerosene, gasoil, gas oil, coker gas oil, coker naphtha, DAO, VGO, HVGO, LCO, resid hydrotreating, renewable hydrotreating, renewable jet fuel, renewable diesel, biodiesel, dewaxing, cold flow properties, cloud point, pour point, cetane, Tier III, gasoline, FCC pretreatment, FCC posttreatment, hydrocracker pretreatment, HDS, hydrodesulfurization, hydrodemetallization, HDM, hydrodenitrogenation, HDN, hydrodearomatization, HDA, hydrogenation, HYD, 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