In their experiment, they co -liquefied lignin and Illinois No. 6 bituminous coal using a series of catalysts with tetralin and phenol as solvents. They concluded that when coal and lignin react together in a solvent, they depolymerize under mild conditions to produce a filterable liquid product with yields greater than would be predicted based on a simple side -by- side, concurrent liquefaction of both components independently. One interesting finding was that the overall conversion of coal plus lignin increased as the fraction of lignin in the reaction mixture increased, while the opposite held true for increased proportion of coal in the reaction mixture. However, they noted that the overall conversion was not improved further by increasing lignin ratio beyond 0.7