PTQ Q3 2023 Issue

routes. Two new entrants in PDH, Dow’s FCDh and KBR’s K-PRO are challenging the status quo, UOP’s Oleflex and Lummus’ Catofin technologies. Both Dow and KBR have developed fluidised catalyst reactors and regenerators and claim propane consumption on par with UOP and Lummus. KBR’s process is interesting because their proprietary cata - lyst uses nonprecious metals and no chromium. Dow announced in 2019 that it would retrofit the FCDh technology in a Louisiana mixed-feed cracker. KBR announced in early 2020 a 600 kt/y unit in Asia and another licence in Pakistan in 2021. Linde’s EDHOX (oxi - dative dehydrogenation) converts ethane and oxygen to ethylene and acetic acid, with a claimed combined yield of more than 93% and lower Capex compared to an ethane steam cracker. There is also the ability to recover purified CO₂ for a 60% reduced CO₂ footprint. Methanol-to-olefins Methanol-to-olefins (MTO) is a technology where methanol is catalytically dehydrated and partially converted to ethyl - ene over alumina and zeolite catalysts. To be competitive vs mega-scale ethane crackers with feedstock cost advan - tages, methanol has to be produced in huge quantities of approximately 5 × 10 6 t/y, leading to an olefins output of approximately 2 × 106 t/y of ethylene and propylene. MTO, even based on methane, is not a sustainable option based on the carbon footprint. Figure 1 shows total CO₂ emissions, in tons CO₂ per ton of high-value chemicals (HVC), such as ethylene, propylene, and aromatics. A distinction is made between the CO₂ emis - sion resulting from the process’s energy requirement (fuel combustion) and the chemical CO₂ produced in the reaction. It is clear from the figure that steam cracking (SC) is still the best-performing technology, even from a CO₂ point of view. If the process were to be electrified, the emissions would fall 80-90%. There is nearly no chemical CO₂ produced, and the process’s energy efficiency has been optimised so that the process CO₂ is also very low in comparison to the other techniques. Oxidative coupling of methane (OCM) also looks very promising, as it has the lowest process CO₂. However, because of the relatively low ethylene selectivi - ties, the chemical CO₂ for this technology is still quite high. From a sustainability point of view, coal-based techniques are difficult to justify, both energetically and chemically.⁴ Ongoing MTO research includes modifications for improv - ing light olefin yields, reducing catalyst consumption costs, increasing single-train unit capacities, and expanding the sources of raw material feedstocks. Carbon capture and storage can be applied to MTO (also coal-to-olefins, or CTO) to reduce CO₂ emissions by about 73%. There is currently a lot of research activity to further improve CO₂ recovery from process streams by using amine systems enhanced with more selective amines or other process configurations. These will likely further reduce the CO₂ footprint for CTO and other pathways to light olefins. Oxidative coupling of methane Several companies have been developing these bespoke light olefins processes via OCM. Examples include Siluria

Energy CO Chemical CO

2.71

3.77

0.01

3.14

1.16 0.01

0.65 0.25

0.88 0.01

0.80 0.01

0.70 0.01

1.58

Figure 1 Total CO₂ emissions [tCO₂/tHVC] for different technologies⁴

polyolefins in a single step could be a fundamental and eco - nomically viable solution to deal with a waste stream that has proven notoriously difficult to recycle. At present, under ideal lab-scale conditions, maximally 75% of C2-C4 olefins can be produced via thermal or catalytic pyrolysis if pure polyolefin feeds are used. For industrial reactors, yields are typically lower than 60%. Zeolite and zeo-type catalysts with micropores in the range between 4 and 5.6 Å (8 or 10 MR) are favoured due to their high activity and favourable selectivity for light ole - fins. In line with the tuning of zeolite catalysts for high olefin selectivity, modifications such as bimodal microporous- mesoporous matrices and promoters with, for example, phosphorus are beneficial for improving the selectivity in polyolefins’ catalytic cracking and to reach targets of 90%. Propane dehydrogenation PDH is a growing catalytic technology utilised for pro - pane- to-propylene conversion. On-purpose propane tech - nologies are today responsible for approximately 20% of propylene production. PDH has been an invaluable technol - ogy for providing additional propylene supply at economical prices, and as with many other petrochemical processes, carbon intensity remains an issue. The scaling of renewable propane feedstock will be key to addressing the lifecycle footprint of PDH as well as the use of renewable utilities and off-gas CO₂ capture and utilisation. If these improve - ments are not introduced, PDH technologies could be dis - rupted by newer, up-and-coming unconventional olefins technologies. Several industrial and academic research groups are col - laborating to further develop, scale up, and demonstrate a toolbox of novel, efficient, and flexible PDH technologies. Specifically, two electrically heated catalytic reactor con - cepts (EHCR) are under investigation. One system is based on ohmic heating rods inserted in optimally designed 3D catalytic structures, and the second one is an intensified catalytic membrane reactor (CMR) with electrically conduc - tive catalyst supports.³ Dehydrogenation of ethane over Cr or Pt catalysts is limited by equilibrium and allows only very poor yields of ethylene. This route is not competitive with conventional

PTQ Q3 2023