Abstract: The present invention discloses a process of pretreating a waste black liquor which results from the pulping of various vegetative fibers and wherein the pulping liquor contains as its active pulping ingredient sodium and sulfur with the pretreatment taking place prior to the subjecting of the waste black liquor to a hydropyrolysis reaction. The method and the materials used in the pretreatment are derived from the reaction products resulting from the hydropyrolysis reaction. The pretreatment serves to enable one to regenerate the inorganic chemical values a pulping liquor in an easy and economical manner and the pretreatment, also, serves to appropriately adjust the physical and chemical characteristics of the char produced in the hydropyrolysis reaction. This is accomplished primarily by utilizing the products resulting from the hydropyrolysis reaction.