Decarbonisation Technology November 2025 Issue

Reactor designs: fixed- bed vs slurry There are several benefits to using fixed-bed tubular reactors ( Dry, The Fischer- Tropsch Process: 1950- 2000, 2002 ) ( Dry, Practical and theoretical aspects of the catalytic Fischer- Tropsch process, 1996 ), which is why JM and bp have favoured this design. Fixed-bed tubular reactors are widely used. These reactors hold the catalyst in static beds, minimising catalyst loss and contamination. Their modular design allows for capacity expansion by adding more tubes, making

Figure 2 Nikiski demonstration plant

Courtesy of bp PLC

and catalyst longevity. A single catalyst charge operated for more than 7,000 hours, creating a high-quality dataset to underpin JM’s long catalyst life predictions, under operational conditions and without the need for regeneration. The integrated facility tested three core FT technologies: a novel compact reformer for syngas production, a fixed-bed FT reactor, and mild hydrocracking of FT waxes to yield synthetic crude. Originally, this reactor design aimed to monetise stranded natural gas in remote areas. However, it was only economically viable at large scales, above 30,000 barrels per day (~3,850 metric tonnes per day), and in regions with low gas prices and high oil prices. Recent interest in FT technology has shifted toward smaller-scale applications that convert municipal solid waste and cellulosic biomass into renewable fuels. To make this economically viable, JM and bp focused on reducing costs and improving process efficiency. In 2009, JM developed a novel catalyst carrier designed to fit inside tubular reactors, enabling the use of smaller catalyst particles. Simultaneously, bp created a second-generation (Gen2) FT catalyst with enhanced performance ( Peacock, et al., 2020 ). When combined, these innovations delivered a step change in FT synthesis efficiency and scalability (see Figure 3 ). The resulting FT CANS technology has received global recognition, including the IChemE Global

scale-up relatively simple. However, they require careful balancing of tube diameter and catalyst pellet size to manage heat and pressure drop effectively. Typical designs use thousands of 25 mm (1 inch) tubes filled with 1-2 mm catalyst pellets, which can limit mass/heat transfer, productivity, and selectivity. Slurry reactors , on the other hand, offer superior heat removal and use fine catalyst powders (tens of microns in diameter) to reduce diffusion limitations. However, they are more prone to catalyst attrition, which can lead to catalyst losses and compromised product purity and are generally more complex to scale up. Demonstrating industrial FT: The Nikiski Plant milestone Since 1996, JM and bp have collaborated to scale up FT synthesis for industrial use. The first major milestone was the construction of bp’s Nikiski demonstration plant in Alaska in 2002 (see Figure 2 ), which used a first-generation (Gen1) FT catalyst within a conventional tubular fixed- bed reactor ( Font Freide, et al., 2003 ). Designed to process natural gas, the plant produced approximately 300 barrels per day of synthetic crude. By the time it was decommissioned in 2009, it had surpassed all performance targets, including catalyst productivity, hydrocarbon selectivity, CO conversion, methane suppression,