Microchannel reactors—compact reactors featuring channels with diameters in the millimeter range—are potentially the best candidates for this job. They enable more efficient and precise temperature control, and the small diameter channels dissipate heat more quickly than conventional reactors with larger channel diameters in the 20-30 mm (i.e. inch) range so more active catalysts can be used. As a result, microchannel reactors can exhibit conversion efficiencies in the range of 70% per pass.

Microchannel reactors are designed for economical production on a small scale. A single microchannel reactor block might produce up to 50 barrels (bbls) of liquid fuel/day. Conventional FT plants, in contrast, are designed to work at minimum capacities of 2,000 bbls/day, and function well and economically at capacities of 30,000 bbls/day or higher. They exhibit conversion efficiencies in the range of 50% or less per pass.

To work efficiently, microchannel reactors require an FT catalyst with a high level of activity in order to boost the conversion rates to an economic level. The new FT catalyst is designed to meet those requirements.

Commercial fixed bed FT reactors operate with a GHSV (Gas Hourly Space Velocity) of between 800 and 2,000 hr^-1. GHSV is a measure of the feed flow rate relative to the volume of catalyst. These commercial fixed bed systems run to around 50% CO conversion per pass—mostly liquids and waxes but also some gases. They achieve this conversion at 230 - 240°C. By contrast, our catalyst in an FT microchannel reactor system can operate at GHSVs of over 24,000 hr^-1 (well over an order of magnitude higher) and achieve a conversion per pass of over 70% at a temperature less than 220°C.

Since our catalyst in these microchannel systems are highly stable, the upshot is that these systems are over 20 times more productive per kg of catalyst than conventional systems. It is this higher productivity that will enable FT technology to be commercialized for small scale distributed biomass.

—Derek Atkinson, Business Development Director, Oxford Catalysts

The level of catalyst activity is related to the surface area of the catalyst. This, in turn, is related to crystal size, so producing catalysts with the optimal crystal size for a given application is a key goal for catalyst developers. One challenge is in achieving the right balance between catalyst activity and stability. If the crystal size is too large, the catalyst activity—and hence, conversion rates—will be reduced. If too small, the catalyst becomes unstable.

Oxford Catalysts’ organic matrix combustion (OMX) technology makes it possible to produce catalysts with higher metal loadings, which still maintaining small crystal sizes. The OMX method combines the metal salt and an organic component to make a complex that effectively stabilizes the metal. On calcination, combustion occurs that fixes the crystallites at this very small size. Since the calcination is quick, the metal crystallites do not have time to grow, and hence remain in the ideal size for catalytic reactions. The OMX crystallite size is independent of metal loading and support morphology, thereby producing more active FT catalysts with less metal.

The OMX method produces a crystallite size distribution 50% narrower than conventional Incipient Wetness Impregnation (IWI), leading to more active and stable FT catalysts. Click to enlarge.

Compared to conventional catalyst production methods, such as Incipient Wetness Impregnation (IWI), OMX produces a narrower particle size distribution of crystallites in the 8-15 nanometer diameter range which exhibit terraced surfaces. These are both features that enhance catalyst activity. OMX also produces fewer very small crystallites that could sinter at an early stage of operation. This results in greater catalyst stability. OMX catalysts also require less precious metal.

Following several thousands of hours of testing, Oxford Catalysts has signed a memorandum of understanding (MOU) with a leading developer of small scale FT microchannel reactors to deploy the new catalyst in small-scale FT applications, including the conversion of bio-waste or flare gas into liquid fuels.

We have spent 12 months working on developing this particular catalyst, using our state-of-the-art equipment and our patented OMX method, and are very pleased with the results. The next stage will involve working closely with a catalyst producer to supply tonnage quantities for use in demonstration units.

— Derek Atkinson