PTQ Q4 2022 Issue

A Ludo Boot, R&D Advisor, Albemarle Corporation, ludo. boot@albemarle.com: The answer to this question is very much dependent on the actual case at hand. The most applicable solution, whether pyrolysis or gasification, depends on many factors, one being capital investment. If a petrochemical company has certain assets in place, that may lead to using either pyroly- sis or gasification technologies. In terms of environmental impact analysis, LCA, GHG or GWP, there are studies showing a small advantage to one, some to another. Contaminants in waste-derived oils considered for a project can also differ, favouring either of the two technologies. These combined factors determine whether a pyrolysis or gasification technology application makes more sense for a certain case. Moreover, there may be enough space in the market for pyrolysis-based tech- nologies and gasification to co-exist in the future. A Scott Sayles, Manager of Renewable Fuels and Alternate Feeds, Becht, ssayles@becht.com: Pyrolysis is a promising technology to convert cellulous or plastic waste into an oil that allows processing into either fuels or petrochemical. Pyrolysis designs are varied depend- ing on the process basis. Some are nearing commercial operations, and others are in the pilot stage. The conversion of plastics into feedstock ready for the aromatic extractor tower to produce BTX is an example of pilot stage-level development showing some promise. The liquefaction of plastic using pyrolysis produces an oil that is the decompo- sition product of the plastic being introduced. To produce aromatics directly seems to require selective plastic pyrolysis. Gasification is a direct route, converting the plastic into a syngas which can be converted into BTX by Fischer-Tropsch, followed by cyclisation. The gasification of plastic is relatively new, but the conversion to desirable products is well proven commercial technology. Many fac- tors enter the final plans for plastic conversion into mar - ketable products. The technological risk is a key factor, as are the requirements to recover and collect the plastic from the community. The social-economic factors are difficult. Socially plastic recycling is favourable. However, capital investment and operational factors require a governmental position to ensure a future that will encourage investment. A Mitrajit Mukherjee, President, Exelus, mmukherjee@ exelusinc.com: Catalytic processing of plastics-rich waste streams in a hydrocracker is a preferred alternative. Compared to pyrol- ysis or catalytic cracking, it delivers a highly saturated liq- uid product that can be used directly without subsequent processing as a transportation fuel or fuel oil. There are five main types of recyclable plastics. Effective recycling of mixed plastics waste is a major challenge for the plastics recycling sector. The advantage of using the hydrocracking approach is the ability to handle all types of plastic waste (including PVC and PS), which allows a wider variety of materials to be recycled. To enable the use of plastics as a raw material, a suitable catalyst and optimum operating conditions are critical. One company,

hydrocracker conversion rate, the cracking bed tempera- ture of the unit can be increased, the nitrogen slip from the pretreat reactor can be reduced, or both can be done. Furthermore, reducing the nitrogen slip from the pretreat reactor will lead to fewer chances of forming incremental heavy polynuclear aromatics (HPNAs), which are known to foul process equipment and shorten catalyst life during con- version. While a variety of methods can be used to achieve high conversion, where each method offers a different yield/ economic impact, the rate of HPNA formation increases with higher conversion and heavier feedstocks. By recycling unconverted oils (UCO), HPNA formation and the per pass conversion are reduced for constant over- all conversion. Following are some of the ways industry can manage HPNA issues: • Limit feed FBP <600ºC, especially for HCGO (crack feed) • Monitor the UCO colour as it changes from white to yellow to orange to red as HPNA concentrations rise and increase bleed as much as possible • Use bulk metal pretreat catalysts to saturate/remove HPNA precursors • Saturate HPNAs by using superior hydrogenation func- tion catalysts in the second-stage cracking reactor • Employ hot, high-pressure separator design to avoid HPNA deposits on the reactor effluent air cooler (REAC), the main location where HPNAs cause problems • Adjust the unit design, such as installing liquid recycle filters, designing the separator with trays, and exporting unconverted oil with high HPNA content from the bottom while recycling material from the upper tray. A Ole Frej Alkilde, lead scientist, Haldor Topsoe A/S, ofc@topsoe.com: When the severity of a hydrocracking unit is increased by increasing the reactor temperatures and/or process- ing heavier feedstocks, the fouling tendency of the UCO increases, and ultimately the UCO can become unstable, and a solid phase will precipitate out. The reason for this is an increased content of HPNA. The conventional way to control the HPNAs is to limit overall conversion by draw- ing a UCO bleed stream from the unit, typically 2-5% of the feed rate to the unit. Other strategies are to reduce the reactor temperatures by using a more active hydrocracking catalyst, control the endpoint of the VGO feed to the hydrocracking unit, or revamp the unit by installing a hot separator, which removes the heavy product from the reactor effluent air cooler and thereby reduces the fouling. It is also possible to selectively remove HPNA by various industrially proven technologies like carbon bed absorption or advanced separation like Topsoe’s proprietary HPNA-Trim. This can reduce the UCO bleed rate from the unit by 60-80% and thereby increase overall conversion without reducing unit cycle length. Q Pyrolysis-based technology can convert plastics-rich refuse-derived fuel into extractor-ready BTX product, but the substantial energy input and processing challenges compel the petrochemical industry to consider waste gas- ification alternatives. How do you see this evolving?

17

PTQ Q4 2022

www.digitalrefining.com

Powered by