Are biomass-based hydrocarbons a utopia? We think not!

It is well known that there are challenges in transforming biomass into hydrocarbons that are useful to mankind. The main differences between biomass and the hydrocarbons we use, to make our everyday chemicals or to propel our cars, is the size of the molecules, and the high content of oxygen and sulphur. This can be changed using the right catalysts.

The size of the molecules can be reduced, e.g. using catalyst-assisted pyrolysis or catalysed depolymerization, but when it comes to the oxygen and sulphur removal, things start to get truly intriguing. The removal of heteroatoms, i.e. oxygen, sulfur and nitrogen, from both fossil and biomass-based feedstocks. The processes are known as hydrodesulfurization (HDS) and hydrodeoxygenation (HDO), and uses hydrogen in the process. These processes for traditional fuels in the petroleum industry are well established and are fully commercial.

The catalysts developed for these reactions, however, are not suitable for biological feedstocks for several reasons. First of all, the high levels of oxygen may negatively affect the long-term performance of the catalyst, both based on the water produced, but also due to the heat of reaction. Secondly, the pore sizes of the catalysts are not made to encompass larger molecules, such as lignin derivatives. This final point will slow down the reaction significantly and increase the risk of bed plugging.

To address this Hulteberg Chemistry & Engineering AB has developed a suite of catalysts that, when working together, combines the effect of high availability for larger biobased molecules with a resistance to the environment. The catalysts work by stacking different varieties in series, where each catalyst has a tuned pore system for allowing the biobased molecules to enter and react. This allows for also the largest biobased molecules to access the inside of the catalyst surface for a ten-to a hundred-fold higher reaction rate compared to ordinary hydrotreating catalysts. The catalyst is also combined with suitable reactor design for extended operation to maximise the catalyst lifetime.