Current state-of-the-art methods for production of liquid fuels from biomass involve fermentation or other intermediate steps which have low energy efficiency and possibly create waste. A new technology investigated in a joint industry project at DTU Chemical Engineering offers direct production of bio-gasoline or bio-diesel, and methane. The main side-product is char which is also useful – either as a fertilizer if returned to the field or as a source of more gas.
The process in question is catalytic hydro-pyrolysis. Biomass pyrolysis is a well-established process, where the biomass is heated rapidly in an anaerobic atmosphere resulting in a mixture of char, bio-oil, and methane. However, the bio-oil will contain considerable amounts of both water and a range of oxygen-containing organic compounds. The water content reduces the energy potential of the oil, while the oxygen-containing organic compounds make the oil less stable and thus hamper the potential for storage. Also, the oil is highly acidic, which is a risk factor for corrosion in fuel systems. Therefore, bio-fuel produced through pyrolysis may need post-treatment by hydrogenation. Reheating the oil for hydrogenation, however, may cause operational problems due to the reactive nature of the oil. The idea behind catalytic hydro-pyrolysis is to produce the desired end-products in one step.
“Producing the end-products directly reduces energy consumption and costs. And most importantly, the direct approach causes less operational issues. We have shown the feasibility of the method,” states Professor Anker D. Jensen from CHEC at DTU Chemical Engineering.
The core of the system is a catalyst-loaded fluid bed reactor. The biomass is fed into the reactor and fluidized by hydrogen. Hereby, the oxygen-containing organic components react with hydrogen at the catalyst surface, and they are thus pacified before they polymerize and cause the catalyst to deactivate.
“We have demonstrated that the conditions for maintaining the efficiency of the involved catalysts are actually much better in the direct process” says Anker D. Jensen.
The process produces a mixture of oxygen-free bio-hydrocarbons in the gasoline and diesel boiling point range along with a very clean water phase. Therefore, the produced biofuel has a high energy content and may be stored just like fuels produced from fossil feedstock.
“The technology is generally applicable, and is highly relevant for a country like Denmark. The produced methane can be used directly in our natural gas distribution system, and we have a large production of sustainable energy, mainly power from wind turbines. In windy periods we actually have excess wind power. This could be used to produce hydrogen.” notes Anker D. Jensen. “Furthermore, DTU Mechanical Engineering, which was partner in the project, has shown that the process has a very high energy efficiency, making the process look even better.”
Entitled ‘Hydrogen assisted catalytic pyrolysis’—or H2CAP for short—the 4.5-year project was initiated in 2014 on a grant from The Strategic Research Council. At that time, ideas of commercialization were still in their infancy. This may soon change, as several large energy corporations such as Shell and Phillips 66 are looking at various catalytic hydro-pyrolysis designs with an eye to commercialization.
“We strive to make our results available to as wide an audience as possible, not least since the method is a potential solution to a large societal challenge”, says Anker D. Jensen. “Besides biomass, the process also has potential using waste plastics as feedstock converting it into fuels or monomers that could be recycled. This is something we would like to investigate in future projects.”
He is pleased to note that no less than ten articles are in the pipeline for scientific publication from the H2CAP project, while several others have already been published, including a large review article in the prestigious journal Progress in Energy & Combustion Science.
Besides the group at DTU Chemical Engineering, the H2CAP project involves DTU Mechanical Engineering, Stanford University (USA), Karlsruhe Institute of Technology (Germany), and the catalyst producer Haldor Topsøe.
Source: DTU Chemical Engineering, press release, 2019-05-07.