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Hydrothermal Liquefaction in the Green Energy Transition

Giulio Italo Rodio, ETA Florence Renewable Energies, Italy

HTL is a fast-developing technology that can provide multiple advantages for the circular economy. A recent event explored both the status of the technology and the perspectives of different end users.

The European Green New Deal is pushing for the pursuit of novel technologies that are able to reverse the fossil fuel-based paradigm funded on a linear economy by shifting towards a circular economy sustained by renewable energy sources. In this context, Hydrothermal Liquefaction (HTL), a thermochemical conversion approach for the production of advanced biofuels, is an emerging and promising technology in the currently Research & Development (R&D) phase; in recent years, it has been attracting the interest of the industry which has high stakes in decarbonizing its operations. The interest in HTL is surging due to its feedstock flexibility which can unlock the use of biogenic urban residuals such as sewage sludge.

The main obstacle concerning the reutilization of sewage sludge is caused by its high-water content and complex mixture of multiple compounds. The valorization of wet sewage sludge into valuable and useful products has the potential of augmenting energy production and to tackle disposal and waste management issues. However, the wet characteristics of this feedstock are not particularly well suited for several available thermochemical conversion processes (e.g., fast pyrolysis, gasification, and incineration) requiring a dry intake. In contrast, HTL does not only tolerate but also appreciate high water content feedstock, which clearly convey the additional value of this technology.

The advantages of HTL for the circular bioeconomy Embedded into HTL there are other advantages that can potentially offset stable industrial symbiosis scenarios where the waste produced in an industry is used as a source into another, strengthening the entire value chain. In fact, wastewater treatment plants (WWTP) and the urban biogenic waste management sector can find in HTL a solution to retain value from their disposals. In order to access this market, one of the main challenges for HTL technology is proving that it can compete with already mature and established technologies such as Anaerobic Digestion (AD). A crucial competitive advantage of HTL over AD lies in the size and location of the plant. Thanks to the reduced dimensions of the plant, HTL features the possibility of being installed in urban and semi-urban settings in proximity, for instance, to a WWTP. A further benefit that arises from the HTL process is the possibility to recover nutrients from the feedstock, such as phosphorous and nitrogen, that could be potentially reused in a wide spectrum of applications ranging from fertilizers to cosmetics and electronics. The combination of the abovementioned elements of HTL matches with the circular bioeconomy principles by simultaneously delivering an energy carrier as biocrude, goods as phosphorus and services as acting as a disposal facility for the waste management sector. The coupling of industrial symbiosis concepts and bioeconomy paradigms are in line with the long-term vision of the European Union of becoming the first climateneutral continent by 2050.


In order to have an overview of the state of the art of HTL and to understand the standpoints of the stakeholders involved in the technology value chain, a virtual workshop was organized on the 28th of January 2021 by the consortium of NextGenRoadFuels, a Horizon 2020 project developing sustainable drop-in transport fuels from HTL of low value urban feedstocks. In this event, existing pilot projects and initiatives both at EU and international level were displayed. The perspectives of developers and technology users and developers was in regard to the technology scale up exploration, together with the policy outlook and the market uptake. The first analysis on go-to-market possibilities showed that the timeframe for the introduction of the technology into the market is shortening as more interest and leverage from the stakeholders of the full value chain is increasing. However, demo-scale projects are required to prove the competitiveness of HTL in comparison with other established technologies The European Union is at the forefront of demonstrating the feasibility and the capacities of HTL with several R&D H2020 projects running demo and lab-scale plants and cutting-edge innovative improvements.

Figure 2 - The HTL plant at the Pacific NorthWest National Laboratory (US) has recently converted biocrude to renewable diesel operating for more than 2,000 hours continuously. Photo: PNNL

The NextGenRoadFuels project has recently achieved the production of 100kg of high-quality bio crude from urban waste, mostly sewage sludge, finding the optimum balance with inorganics and water content. During the pre-treatment process, protein extraction was accomplished, even if costly, and constant yields of phosphorous recovery were achieved. Other two relevant European projects, HyFlexFuel & Waste2Road, are demonstrating the compatibility of HTL-based fuels production with a diverse biomass feedstock portfolio. The 4refinery project, on the other hand, is testing the integration of the bio crude generated by HTL into the existing refinery process. Last March, LowCarbFuels, a new project gathering leading European and Danish organizations, was launched in Denmark to produce and commercialize sustainable aviation and marine fuels using HTL as the basic technology. The promising technology is being developed all across the world. An Australian company based in Sydney, Licella Holdings, has developed the Cat-HTRTM platform and claims to be ready to build the world’s first commercialscale HTL plant. In India, the Reliance Industries Limited, is demonstrating the robustness at scale of HTL plants to reduce the risks and proceed to commercialization. In the USA, the Pacific Northwest National Laboratory (PNNL) recently announced a major milestone: a large-scale demonstration plant converting biocrude to renewable diesel fuel has operated for more than 2000 hours continuously without losing effectiveness. In the latter, the HTL’s biocrude is moved into the hydrotreating operation that introduces hydrogen into a catalytic process that removes sulfur and nitrogen contaminants found in biocrude, producing a combustible end-product of longchain alkanes, the desirable fuel used in internal combustion engines (ICE). Steeper Energy is a leading company in the field of advanced biofuels operating in Norway and Canada. The firm has found in Silva Green Fuel licensed Hydrofaction® the preferred way to achieve commercial viability through the use of forestry residues and is poised to enter the urban biogenic waste management market segment leveraging the forestry know-how and efforts.


This series of R&D projects is thus showing important and concreate results. Multiple end users are involved in the front end of the value chain of HTL. A panel discussion at the virtual workshop highlighted the ways end users are perceiving the attributes of the technology. In particular, Niras, GoodFuels, Concawe and Parkland Refining

were called to share their end user standpoint as representatives of their respective industry. The wastewater management industry is evaluating the very high potential of HTL that, thanks to its process design, can be fed with multiple wet streams and it can be installed in close proximity with the WWTP reducing the logistics expenditures. The marine industry sees HTL as a breakthrough to meet sustainability, scalability, and affordability goals in transportation fuel and confirmed its readiness to test the product once consistent quality is ensured and enough quantities are delivered. The refineries viewpoint underlined the requirement of an oftenunderestimated aspect: handling and storage. In fact, these two aspects need to be addressed to be effective on a large scale, as acquainting with the specifics of new feedstocks is constant volumes of biocrudes of larger magnitude. Even if the projects are demonstrating concrete results and market uptake is becoming within reach highlighting the gained momentum of the technology, the HTL value chain as whole has still to make efforts into refining the technology to provide it with constant and continuous sustainable outcomes. This will allow HTL technology to make an important contribution to the achievement of a circular bioeconomy model as called for by the Green Deal objectives. Slides and recordings of the event can be found at nextgenroadfuels.eu

a lengthy procedure. Moreover, also consistency in volumes is to be reached for a complete evaluation. Even though HTL can be integrated in the refinery sector through different routes, such as centralized and decentralized paths and regional settings, cross sectorial cooperation is crucial in order to include the entire value chain.


HTL is proving to be a highly promising and rapidly developing technology. However, there are still technological hurdles to overcome, for which it is important that R&D&I efforts are maintained. In particular, the focus must be placed on demonstrating the technology at a scale compatible with industrial use obtaining This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 818413