Question
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What optimal hydrocracking catalysts and operating strategies are needed to co-hydroprocess waste oils with VGO?
Jun-2023
Answers
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Andrew Layton, KBC (A Yokogawa Company), Andrew.layton@kbc.global
There are several steps involved in co-processing waste oils. The levels of sulphur aromatics and N2 are exceptionally low, but fatty acids – unsats/oxygenates and pour point – are high. When the feed boils in the kero/diesel range at 5-10% in total reactor feed, the considerations for processing are less severe than when processing 100% waste oils. However, considerations apart from catalysts include:
υ Feed quality/storage
• Flowability at temperature. Waste oils have a flowability problem at ambient temperatures
• Contaminant removal/metals content. Feed contamination removal from solids to metals occurs at several distinct levels dependent on the upstream pretreatment of the purchased feedstock.
ϖ Concentration of the waste oil in total feed
• Impacts materials; reactor heat rise control; corrosion control; metals build-up
• Typically, around 5-10% maximum on an existing unit.
ω Number of reactors; beds available; heat rise control. This may not be a major issue at low concentrations, especially in VGO service.
ξ Product quality target
• O₂; olefins removal; cloud reduction
ψ COx control (as discussed in the following).The question targets co-processing with VGO rather than diesel. Thus, cloud and flowability control may not be a main concern when sending it to an FCC or VGO hydrocracker. Although very waxy, VGO from waste oil is unlikely to be used for lubes production without new testing. The key catalyst issues are discussed as follows:
• Some residual metals, notably phosphorus, will be present and must be considered when setting up any special metal trap catalyst at the top of the reactor system
• The feed contains oxygenates that will generate COx. At higher temperatures, CO formation will increase, which may impact catalyst activity. Nickel Molybdenum (Ni/Mo) catalyst is less sensitive and should be the preferred catalyst. The presence of a recycle gas amine contactor can help control COx, but it is essential to check its impact on the amine system
• Heat rise will increase in the earlier beds, so monitoring the impact on temperature control is important
• When VGO service is moving towards an FCC, further treatment consideration may be unnecessary. However, if the feed is going to a diesel product, there might be a need to add a dewaxing zeolite catalyst in a lower bed. For 100% waste oil in diesel/kero service, a second reactor for dewaxing is typically necessary.Jun-2023
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