Digestion of cellulosic biomass solids may be complicated by lignin release therefrom, which can produce a highly viscous phenolics liquid phase comprising lignin polymer. Systems for processing a phenolics liquid phase comprising lignin polymer may comprise: a hydrothermal digestion unit; a viscosity measurement device within the hydrothermal digestion unit or in flow communication with the hydrothermal digestion unit; a temperature control device within the hydrothermal digestion unit or in flow communication with the hydrothermal digestion unit; and a processing device communicatively coupled to the viscosity measurement device and the temperature control device, the processing device being configured to actuate the temperature control device if the viscosity of a fluid phase comprising lignin exceeds a threshold value in the biomass conversion system.

An aspect of a chemical synthesis device according to the invention includes a substrate in which a channel for chemically synthesizing a plurality of fluids with each other is formed, and a wiring portion that is provided in the substrate, in which an electric resistance value of the wiring portion changes due to the wiring portion coming into contact with the fluids.