Provided is a solvent recirculation system which includes a solvent vessel discharge line configured to convey a solvent stream discharged from a solvent vessel and connect the solvent vessel and a buffer vessel, a buffer vessel discharge line configured to convey a feed stream discharged from the buffer vessel, one or more feed supply lines connected to the solvent vessel discharge line, a density meter provided at a rear end of a point where the one or more feed supply lines are connected, and a calculation part receiving information on measured values of the density meter and a mass flow meter and configured to predict a composition of the feed stream conveyed through the buffer vessel discharge line, in which the one or more feed supply lines and the buffer vessel discharge line each includes the mass flow meter.

Methods and apparatus for refining feedstocks, such as crude or synthetic oil, and like feedstocks, are disclosed herein. In some embodiments, a reactor for refining a feedstock includes: a chamber having an inner volume to hold a liquid feedstock, a feedstock inlet port, a process gas inlet port, and an outlet port; a gas diffuser housed within the chamber and coupled to the process gas inlet port; and a radical generator coupled in fluid communication with the inner volume via the gas diffuser. In some embodiments, a method for refining feedstock includes: providing liquid feedstock to an inner volume of a reactor; flowing a radicalized process gas from a radical generator into the inner volume and into contact with the feedstock via a gas diffuser to fractionate the feedstock and produce one or more fractions of product in a vaporous mixture; and collecting a desired product from the vaporous mixture.