Hydrothermal Biomass Conversion as the Enabler of Sustainable Biorefinery

The objectives of this dissertation are to determine the role of biomass conversion processes in sustainable biorefinery and to develop a hydrothermal conversion process as the enabler of sustainable process. The societal and environmental aspects directs the biomass conversion towards 2nd generation. The criteria of sustainable biorefinery include fossil-independent production without compromising the food and animal feed, and flexibility to adapt the changes in market demand and feedstock availability. These criteria can be achieved with multi-product-multi-feed, flexible conversion processes efficient for the high-moisture biomass. Biomass conversion processes are the heart of supply chain networks, influencing the economic and environmental performance and the structure of the whole chain. The conversion processes are to be selected and improved in accordance with the target products and biomass feedstocks. Hydrothermal processes are suitable for biomass conversion regarding the high moisture and flexibility. It was concluded through a preliminary evaluation that partial wet oxidation can be an intermediate operation of an advanced hydrothermal process, rather than chemical production. Consequently, the experiments included supercritical water gasification of black liquor and partial wet oxidation of saw dust. The dissertation included also feasibility analysis of integrating supercritical water gasification of Kraft black liquor to a pulp mill. Compiling the results, the dissertation proposes a new hydrothermal process for the production of lignin, syngas and bio-oil from the lignocellulosic wastes of various sectors. The proposed conversion process enhances the economic and environmental performance of the involved biomass sectors by valorizing wastes and by-products. This enables sectoral integration network as the supply chain structure. The sectoral integration network involves pre-treatment of wastes in biomass sites, regional conversion processes and centralized upgrading plants. The advantages of this network includes additional revenue via utilizing wastes of various sectors, distributed financial benefits involving rural areas as well, and reduced financial risks through multiple value creation and adapting the changes in market demand and feedstock availability.