Pulping of fibrous plant materials and recovery of resultant by-products

Filtrates from the bleaching and delignification of the pulp are recycled for reuse in pulping, separation, and recovery of lignin and other by-products which results in significant energy savings and mitigation if not the elimination of pollution typically associated with bleaching. This invention also relates to products derived from the process and apparatus for carrying out the process. Lignins of various molecular weights and by-products of the pulping process are also recovered (13). The lignins are precipitated (20) in high yields and at a high rate from a black liquor (40) produced by pulping wood (100) at high temperature and pressures. As a by-product of this process a purified furfural product is recovered (71). This furfural may be recycled for use in the recovery of the low molecular weight lignin of this process.