PTQ Q4 2023 Issue

Olefin purification: Why selecting the right adsorbent matters Removing difficult-to-detect contaminants helps minimise adsorbent reactivity while avoiding side reactions and excessive heat release

Florence Pennetreau and Todd Burkes Evonik Catalysts Steffen Görlich PCK Refinery

T he global economic climate is volatile, and maintaining profitability is a constant challenge for operators in the downstream hydrocarbon processing industries. Staying competitive in a continually changing economic envi - ronment is no small task. The use of new process technologies may allow those in the hydrocarbon processing industries the operational flexibility and reliability to adapt to the changing economic environment while maintaining profitability. Naturally, profitability challenges place even greater importance on optimising operational efficiencies to maxim - ise productivity while keeping operating costs to a minimum. But crucially, this must be done without compromising safety and reliability levels, which are of the utmost importance. For refiners, the selection of the proper adsorbent, or com - bination of adsorbents, is critical to ensure the removal of all contaminants. Failing to remove difficult-to-detect contam - inants can result in system failures, unplanned downtime, and lost production, which can impact profitability. Choosing the correct adsorbent is about more than production efficien - cies and effectiveness. Reliability and safety (including heat release and reactivity) should also be key considerations. To increase their resilience within the market, refiners can invest in solutions to reduce these risks. Hybrid adsorbents offer a viable solution for businesses to remove contaminants reliably and safely and simultaneously maximise process efficiencies, therefore protecting profitability. Reliability and performance predictability of the adsorption unit are prereq - uisites, and adsorbent lifespan is another important element. A primary factor of success is minimising adsorbent reactivity to reduce or avoid side reactions, ensuring safe and effective contaminant removal while guaranteeing process safety. Olefin purification Due to their high reactivity, the purification of olefins at an industrial scale has always been challenging in terms of efficiency, reliability, and operational safety. While typ - ical adsorbent materials (promoted activated alumina and molecular sieves) can be used for olefin purification, a third class of adsorbent (hybrid) has been developed for their treatment. The selection of the proper class of adsorbent, or combination of adsorbents, must be dictated by the type of contaminants to be removed and the need for a high level of process safety:

• Promoted alumina: Promoted activated alumina adsor - bents have the capacity for acid gases (H₂S, COS, and CO₂) in olefinic streams. These adsorbents are not a major safety concern as alumina-based adsorbents cause very low heat release when put in contact with olefins. • Molecular sieves: Large pore diameter molecular sieves have the capacity for water and polar organic compounds (light alcohols, aldehydes, ketones, nitriles, mercaptans, and sulphides) removal from olefins. However, their use for ole - fins treatment can cause safety issues because they gener - ate large amounts of heat (heat of adsorption) when put in contact with olefinic streams. If not properly controlled, the generated heat can lead to temperature excursion, causing olefin polymerisation and uncontrollable runaway reactions. When this type of product is used for unsaturated feed puri - fication, particular care must therefore be taken. A pre-load step of dosing the reactive stream in inert media is highly recommended. Conversely, small pore diameter molecular sieves (3A-type) do not require a pre-load step but have capacity for water only. • Hybrid (co-formed) adsorbent: Hybrid adsorbents contain both alumina and large molecular sieves. They, thus, have adsorption capacity for water, polar compounds, and acid gases removal from olefin streams. In addition, thanks to the presence of alumina, the overall heat of adsorption is lower than for large pore diameter molecular sieves alone. Three main companies offer hybrid adsorbents. Even if based on the same principle, the different hybrid products are not equivalent in efficiency and, more importantly, from a safety point of view. To benefit from the full potential of a hybrid adsorbent, it must guarantee the efficient removal of con - taminants and the safest possible process. R&D investments led to Dynocel 680, a hybrid adsorbent whose formulation has been specially tuned to provide effi - cient removal of contaminants and process safety. In pilot tests, safety performance was confirmed via the measure - ment of two different parameters: reactivity towards unsatu - rated streams and heat release when put in contact with unsaturated streams.  Reactivity towards olefin streams: Reactivity tests were performed by charging the adsorbent and olefin in a sealed autoclave. The temperature was raised to 300°C, and pres - sure was monitored. In this type of test, reactivity can be

PTQ Q4 2023