Action to mitigate climate change requires a move away from fossil fuels in transport, energy and chemicals. However, cost-competitive liquefaction and bio-oil upgrading processes and the efficient use of bio-oil and process sidestreams in a wide range of end products can help to reduce the need for fossil feedstock in chemical industry.
Refining processes, honed over decades, have evolved to be energy- and feedstock-efficient, effectively utilising the various fractions of crude oil in high-volume products such as transportation fuels, as well as in numerous lower-volume but higher value-added chemical applications. For example, organic chemicals and polymers are made almost entirely from fossil crude oil, and a complete phase-out of crude oil will require the development of alternative products or production methods for these products as well.
It is also important to note that, despite the electrification of light road transport, the demand for sustainable fuels in Europe will remain high, especially in aviation and maritime transport, even beyond 2050 due to regulations (ReFuelEU Aviation, FuelEU Maritime).
Fast pyrolysis is a so-called thermochemical liquefaction technology that can be used to convert biogenic solid waste and residues from the forest industry, for example, into liquid bio-oil. The composition of bio-oil produced through pyrolysis is very different from that of fossil crude oil, which places special demands on the downstream processes of bio-oil. While crude oil is largely composed of carbon and hydrogen, or hydrocarbons, the composition of bio-oil is much more complex.
Bio-oil is rich in water and various oxygen-containing compounds, and oxygen removal in particular is critical if the aim is to produce bio-based hydrocarbons as fuels or feedstocks for the chemical industry. Nevertheless, bio-oil is a highly potential feedstock for replacing crude oil. Liquefaction technologies open up opportunities to exploit solid bio-based wastes and residues, which as such are challenging to exploit in the chemical industry.
Various catalytic upgrading technologies have been developed to remove oxygen from bio-oils. The most promising of these are hydrotreatment technologies where bio-oil is treated at high temperature and pressure using hydrogen gas and a solid catalyst. Hydrogen reacts with oxygen-containing molecules in the bio-oil to form hydrocarbons and water, which can be removed from the product.
However, hydrotreatment technologies for bio-oils have not yet been commercialised due to challenges such as the durability of catalysts. VTT has developed a new type of hydrogenation technology for bio-oils, where fresh catalyst can be continuously added to the process and used catalyst removed, hopefully solving the challenges of commercialisation.
The challenge of sustainability and economic viability
Fast pyrolysis processes have been developed for years and, in the first wave of commercialisation, bio-oils have been used as a substitute for fuel oil in heat production. Quality standards have also been developed for this application, which have contributed to the commercialisation of the technology and the construction of plants. However, fuel oil is a very low value-added product, which poses challenges to the economic viability of plants. In addition, the biochar and gaseous products generated as a by-product of fast pyrolysis are currently largely used for energy purposes.
It would therefore be important to make bio-oil into higher value-added products, such as transport fuels and feedstocks for organic chemicals and polymers, and to make more efficient use of the sidestreams to improve the profitability of plants. That is why research into the downstream processing technologies for bio-oils, such as hydrogenation, is important. In addition, the recovery of sidestreams for use in purposes other than energy has the potential to improve the sustainability of the process. In particular, biochar from pyrolysis is a promising material for carbon storage if it can be used in long-term applications.
High value-added products through pyrolysis
Around the fast pyrolysis of biomass, key research topics include the development of higher value-added products and production routes from bio-oil and sidestreams. The development of processing routes is also important for carbon neutrality objectives. For example, the Chemical Industry Federation of Finland has set a target of a carbon-neutral chemical industry in Finland by 2045 (Nature-positive and carbon neutral chemistry).
We also see that fast pyrolysis and other solid biomass liquefaction and downstream processing technologies can play an important role in meeting future carbon neutrality and sustainability targets. Maximising the use of sidestreams from liquefaction processes also opens up opportunities for new sustainable products such as biochar. Developments in biomass liquefaction technologies are creating opportunities to exploit hard-to-recover waste and residues in a wider range of industries. The development work will be continued in the Bio4all-project coordinated by VTT and funded by Business Finland.
More efficient use of process sidestreams, such as biochar, from liquefaction and upgrading processes can increase the profitability and sustainability of liquefaction-based value chains. (Picture VTT)
