Hydrolysis behavior of tofu waste in hot compressed water

Tofu waste (TW) is a typical high water-containing biomass; and the hydrothermal process is preferred to utilize it with low energy cost. TW is also a special biomass characterized by high proportion of proteins and fatty acids, which will lead to a different hydrolysis result. In this work, TW was hydrolyzed by hot compressed water below 390 °C in a batch reactor heated by a salt bath. Four parameters including water density, reaction time, the ratio of TW to water and reaction temperature were investigated. Results showed that CO2 was the major component of the produced gas, a measurable fraction of H2 was produced above 300 °C and 65–75% or more of TW can be transformed into water-soluble fraction. It was found that the influence of the treatment temperature on TW conversion was the most significant. Based on the product distribution (gases, water-insolubles, oils, and water-solubles) along with temperature, a four-stage hydrothermal conversion mechanism was put forward in macroscopic view. In combination with the evolution of gas composition and infrared spectrum, the understanding about the conversion of TW in hot compressed water was further improved.