Conclusions of the work: A simple, green, and affordable process for biomass conversion was presented in this work as a new biorefinery approach for HTT. Overall, it suggests application of all process streams for high-value products in contrast to the traditional current biorefinery, focused on the bioethanol or monomeric sugars only, by operating in a new range of HTT conditions. In the current research, we studied the effect of HTT conditions on the yields and characteristics of extracted lignins. High purity lignins of high yields (up to ca. 90% per original biomass lignin) were successfully extracted from hydrothermal treated solids under ambient conditions. By varying HTT conditions, we were able to control lignin yields and properties. More specifically, the chemical structure and molecular mass of the lignin could be tailored by the selection of the process variables. For example, the average molecular mass (Mw) of the isolated lignins was in the range of 2.5–5 kDa, while the amount of β-O-4 linkages was 4–28 per 100 Ar. Significant reduction in manufacturing costs (by 58%) of lignin particles by aerosol-flow method was achieved when the biorefinery lignin was used in an LMNP integrated production process. Our biorefinery approach brings an alternative to lignin valorization while the extracted solids (cellulose-rich fraction) can be considered for integration in potential materials for emerging applications or as a feedstock for traditional bioethanol production.