Where is OATS used?
Axens have formed an alliance to develop and commercialize the OATSTM (Olefin Alkylation of Thiophenic Sulfur) technology. The combination of BP's discovery with Axens leading market position (Prime-G+TM process) is a winning team in this key environmental refining process area.
Feedstock choices include light and Mid fractions from FCC (or from various cracking processes) where thiophenics concentrate and the olefins content is still high (typically 30–45 %) leading to high octane loss through conventional hydrotreatment.
OATS is a simple fixed bed process operating under mild conditions without hydrogen and using a low cost resin TA 801 catalyst. The OATS process can be designed to ensure a continuous operation between two FCC turnarounds.
The OATS process has been proved in industry and offers major advantages over competing technologies such as higher octane retention and lower RVP of the gasoline product with no need for hydrogen and low cost metallurgy equipment allowing the retrofitting of idle isomerization or etherification plants.
Two main types of reaction take place over TA 801 catalyst used in the process:
Sulfur Shift Reactions
Thiophenic sulfur and light sulfur species are essentially converted to higher boiling sulfur compounds by alkylation with olefins thus producing a sulfur-free light (120°-C) cut without the need for hydrogen. A heavier fraction is produced that is sent to a reduced-size selective HDS unit for octane retention.
Olefins Shift Reactions
Light olefins are oligomerized and isomerized to produce highly branched oligomers thus resulting in reduced gasoline production with high quality (low RVP, low olefinicity, good octane retention) and producing a distillate fraction to be sent for further hydrotreatment
Depending on the refiner’s objective, the OATS process can be designed either to optimize the light FCC fraction desulfurization or to maximize the production of distillates.
When operated under Desulfurization Mode, the OATS process severity is adjusted to meet the required sulfur target in the light cracked naphtha while minimizing oligomerization side reactions. Industrial results demonstrate the ability of the technology to convert more than 95 % of thiophene into FCC gasoline.
The OATS process is ideally installed in combination with Axens’ Prime-G+ technology leading to a low sulfur, high octane light gasoline (typically less than 20 ppm sulfur) by simple adjustment of the downstream splitter cut point. As the cut point of the OATS splitter can be raised up to 120°C, the size of the downstream selective HDS unit on the heavy cut is significantly reduced. This translates into lower capital cost, improved octane retention and lower hydrogen consumption regarding the overall desulfurization of the FCC gasoline.
When operated at higher severity, the OATS oligomerization reactions are favored and the OATS process is an efficient solution to switch gasoline fractions into distillates at low cost.
The OATS process is ideally installed downstream of Axens’ Prime-G+ selective hydrogenation technology to make the most of low sulfur, low dioefines and highly olefin concentrated feed which helps achieving longer catalyst cycles without the need for costly pre-treatment and maximizing refinery profitability in a context of increased demand for diesel.
As a result of the OATS process the gasoline production is significantly reduced while maintaining high quality (low RVP, low olefinicity and good octane retention). The distillate fraction is sent to hydrotreatment before being routed to diesel or the kerosene pool.
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