Life Cycle Assessment of lignin extraction in a softwood kraft pulp mill

Lignin extracted from kraft pulp mills represent an emerging opportunity for novel biomaterials from a renewable resource. The lignin extraction process has the potential to create a new lignin co-product for increased mill revenue. The objective of this work was to examine the environmental life cycle impact of integrating a commercial scale lignin extraction process to an existing kraft pulp mill producing southern bleached softwood kraft (SBSK) pulp. This life cycle assessment study includes a cradle-to-gate analysis of the production of SBSK pulp, with and without lignin extraction, using a detailed mass and energy balance modeled in WinGEMS. Both system expansion and mass allocation were used to account for placement of environmental burdens to both products. Key differences in TRACI environmental impacts were observed, with global warming potential for the SBSK pulp product with lignin extraction reported as 602 kg CO(2)eq per ADmt SBSK pulp as compared to 722 kg CO(2)eq per ADmt SBSK pulp for the base case without lignin extraction. When system expansion was utilized, the global warming potential for the SBSK pulp product was reported as 234 kg CO(2)eq. This reduction was primarily due to the displacement of petroleum derived phenolic resins by the lignin co-product. Sodium chlorate and natural gas were identified as process streams contributing significantly to environmental burdens at the mill. Overall, this study demonstrated that the kraft pulp mill system has reduced environmental impact with the addition of a lignin co-product.