The authors have recently presented a degradative solvent extraction method to dewater, upgrade, and convert biomass wastes into three solid fractions which we call Soluble, Deposit, and Residue. The carbon based yield of Soluble, which is the smallest molecular weight fraction, reached as high as 70% for some biomass wastes. Solubles were free from water and mineral matters, and their physical and chemical properties were almost independent of raw materials. Soluble is expected to be utilized for preparing functional carbon materials such as carbon fiber, and hence, it is requested to maximize the Soluble yield with minimum energy requirement from a practical viewpoint. Since the largest energy consumption of this extraction method comes from the separation of Soluble from solvent, it is essential to minimize the solvent to Soluble ratio before separating Soluble from the solvent. On the other hand, a large solvent to biomass ratio is required to disperse the biomass in the solvent during the solvent treatment at around 350 degrees C. To compromise the conflicting demands and to minimize the solvent to Soluble ratio, a new operating scheme, which uses the Soluble-solvent mixture repeatedly before separating Soluble from the solvent by replacing around 10% of the mixture by fresh solvent on every solvent treatment, was proposed. The validity of this operating scheme was examined by treating Thai rice straw (RS) with a general-purpose petroleum based solvent called A150 through 10 repeated uses of the Soluble-A150 mixture. It was found that the new operation scheme was effective from the viewpoints of quality and the yield of the Soluble produced.