Thermochemical liquefaction of high-diversity grassland perennials

The hydrothermal liquefaction of low-input high-diversity mixtures of native grassland perennials (LIHD), LIHD pretreated with dilute acid, and lignin extracted from LIHD was studied. The liquid yields were optimized using the following treatment variables: heating rate (5–140 °C/min), cooling rate (5–66 °C/min), reaction temperature (300–450 °C, corresponding to a pressure range of 10–35 MPa), residence time (1–30 min), particle sizes, and catalysts (1% and 0.1% sulfuric acid, 1% NaOH, solid superacid SO42−/ZrO2–Al2O3, and solid alkali CaO–ZrO2). The liquefaction yields were found to be dependent on the final liquefaction temperature, the liquefaction time, and the heating rate. The highest liquid yield, 82.1%, was achieved within a short residence time of 1 min at 374 °C. The major compounds of the liquid products from the various LIHD fractions were identified by GC–MS. LIHD could be a good candidate for the liquefaction process with a fast heating rate.