Lowering oxygen con­tent in bio-oil saves money and reduces CO2 emissions

A potential future production route for renewable transportation fuels is to produce bio-oil from forest raw ma­terial through i.e. fast pyrolysis, and then upgrade it to a transportation fuel at an existing refin­ery. The oxygen content of the produced bio-oil determines the hydrogen demand to meet the required oxygen level from a refinery perspective, and for use in engines. This in turn significantly affects the cost and the associated CO₂ emissions from production of the transportation fuel, as it to a large extent is a result of the used raw material and production route for hydrogen.

A recently finished project within the f3 and Swedish Energy Agency collaborative research program Renewable transportation fuels and systems has followed up on this, taking off from an earlier project. The goal of the second project, Determination of potential improvements in bio-oil production (ImprOil),  has been to investigate emerging technologies that result in a lower oxygen con­tent of the produced bio-oil than what is currently achieved through near commercial fast pyrolysis. Value chains utilising forest residues and lignin in black liquor from kraft pulping as feedstock are simulated and analysed. The value chains combine existing know-how, infrastructure and equipment within the pulp and paper and oil refinery industry, including different technology options for bio-oil production and hydrodeoxygenation and upgrading of the produced oil to fuel components. The value chains are evaluated and compared with respect to total production cost, overall value chain fossil CO2 emissions, conversion yield and total energy effi­ciency.

Specifically, the project has studied hydropyrolysis and hydrothermal liquefaction (HTL) in more detail, showing a good potential to reach a lower total transportation fuel production cost than through fast py­rolysis, meaning that the production cost could potentially compete with the price on the European spot market. However, the data used in the analysis is still uncertain due to the lower technical maturity of both the hydropyrolysis and HTL processes. Nevertheless, the sensitivity analysis indicates that there is room for adjustments of the performance data with remaining acceptable profitability for the emerging technologies.

An additional goal within the project has been to evaluate alternative routes for production of hydrogen with a lower climate impact than the leading technology for hydrogen production today, which commonly is based on steam reforming of natural gas. Alternative hydrogen production technologies using alkaline electrolysis and biomass gasification have been investigated.

Important observations from the analysis include the strong dependence on the results on possibilities for integration of process excess energy in the pulp mill, and especially the refinery. Consumption of add-on chemicals has quite a large influence on both cost and CO2 emissions of the studied value chains, and must be investigated early in the development phase. In addition, the allocation of CO2 emissions according to the EU renewable Energy Directive (RED) results in transportation fuel CO2 footprints that are significantly different than from a systems perspective.

The project has been lead by Marie Anheden, RISE, with participants also from Chalmers University of Technology, ÅF Industry and Preem.