The initial phase of the project has included plant modifications, as well as knowledge-building across the consortium in terms of feedstock and product handling, characterization and processing. Thus, a preliminary HTL production campaign has produced biocrude and aqueous product for the partnership as well as data for the initial model building. In this phase, significant efforts have been dedicated to by-product valorization in terms of protein extraction from the feedstock (waste water sludge), before slurrying for HTL. Residual proteins are present in the sludge, and as they potentially represent a high value market, efforts have been directed towards their extraction by thermal and enzymatic hydrolysis. This also has the benefit of reducing nitrogen content of the feedstock for HTL, as this will end up in the biocrude and put additional strain on the upgrading process, as nitrogen is an unwanted element in fuels due to formation of NOx. Although proven technically possible to solubilize more than 65 % of amino acids as precursors to proteins, it was also found that the carbon loss from the feedstock was so high that overall process economy would be unsustainable.
In parallel to this, batch experimentation has been carried out to establish elements of nitrogen chemistry in HTL and aqueous phase characteristics. For the latter, it has been focused on two aspects: to establish and quantify the effect, if any, of recycling of a concentrated soluble organic phase, and to establish a methodology to extract inorganic compounds such as phosphorous and nitrogen from this stream. Both are feasible and integrated into the process models that form the basis of the technoeconomic scenario assessments of the project. Implementation pathways for water phase purification are being studied, including by micro-/nano-filtration, and membrane distillation. The latter shows both technically and economically promising results.
Upgrading activities have focused on establishing a baseline before moving to continuous campaigns. Furthermore, work on a novel nitrogen-based catalyst has been carried out, in order to move away from sulphur-based catalysts as are common in refineries. These, however, need sulphur in the feed in order to remain activated, which is a challenge for biocrudes that typically contain virtually no sulphur. In parallel with this, activities on the more fundamental aspects of electrocatalysis have been going on, in order to establish this next-generation technology as viable in the upgrading scheme of HTL biocrudes. At the end of the project, several hundred hours on-stream hydroprocessing have been demonstrated. Distillation of both biocrudes and upgraded samples has also been performed. Different combinations of these products have been used for engine testing in an optical engine within a lab environment.
Following the preliminary production campaigns and upgrade of the CBS1 pilot plant, approximately 8 tons of urban waste, mostly sewage sludge but also organic fraction of municipal solid waste, has been processed in order to obtain experience with continuous processing of these feedstocks, and identifying specific challenges associated with this. A very detailed database of process and chemical data has been produced, on which to base mass, energy and elemental balances, as well as to supply the detailed process models. On-going at this time is interpretation of these data as well as relating them to batch-type experimental data under similar conditions in order to fully understand how to conclude.
Biocrude from the production campaigns has been distributed to upgrading partners in order to look into details of catalytic upgrading in parallel with lower TRL electrocatalysis work. Different types of reactors have been developed and used, addressing stability of biocrudes and the use of multiple stages of hydrotreatment, gradually increasing temperature and catalyst activity in order to produce a hydrocarbon product with as little remaining heteroatoms as possible. Nitrogen remains a challenge, as does the separation of inorganics from the biocrude to sufficiently low levels in order not to deactivate the catalysts, or otherwise protect them using a guard bed.
On the non-technical side, implementation analysis and country scenarios have been carried out, linking availability of feedstock to location of refineries etc. In these, the Netherlands and Sweden have been singled out as likely first locations of an HTL plant.
