A process for upgrading a bio-oil stream is disclosed. The process comprises reacting a bio-oil stream with hydrogen in the presence of a catalyst and a stable oil in a reactor to produce an upgraded bio-oil stream. A recycle oil stream is taken from the upgraded bio-oil stream. The recycle oil stream is recycled to the reactor to provide the stable oil. The content of the reactor can be measured using various techniques and characterized based on the concentration of one or more functional groups for example oxygenates. Further, a fuel oil stream can be taken from the upgraded bio-oil stream.

A process for upgrading a bio-oil stream is disclosed. The process comprises reacting a bio-oil stream with hydrogen in the presence of a catalyst and a stable oil in a reactor to produce an upgraded bio-oil stream. A recycle oil stream is taken from the upgraded bio-oil stream. The recycle oil stream is recycled to the reactor to provide the stable oil. The content of the reactor can be measured using various techniques and characterized based on the concentration of one or more functional groups for example oxygenates. Further, a fuel oil stream can be taken from the upgraded bio-oil stream.