Work

Inorganics from kraft black liquor enable rapid oxidative crosslinking and morphology control in lignin derived hard carbons

Year: 2026

Type: article

Abstract: Kraft lignin (KL) is an abundant by-product from pulp mills and a rich source of carbon, making it an attractive precursor for producing renewable carbon materials. However, its softening, fusing, and foaming behaviour during carbonization is a key challenge in processing and producing carbon materials with controlled size and morphology. Herein, we demonstrate how retaining pulping inorganics in KL can mitigate these thermal processing challenges, highlighting how otherwise undesirable inorganic impurities can play a beneficial role. KL microparticles (KL-MP) were isolated from black liquor in spherical form through membrane filtration and spray drying steps. The KL-MP have inorganics dispersed in them, whereas industrial KL (KL-REF), recovered by acid precipitation, has much lower inorganic content. Upon heat-treatment, KL-REF particles fuse, foam, and agglomerate into shapeless monoliths, while KL-MP particles remain as spherical microparticles. Using complementary thermo-analytical techniques and molecular simulations, we show how inorganics in KL significantly reduce the mobility of lignin chains during heat treatment. The inorganics catalytically crosslink and activate KL-MP during carbonization. While activation is ideal for producing activated carbon, alkali metal-ion battery applications require low surface area carbons. Subsequently, we devised a pretreatment step to catalytically crosslink lignin via inorganics, then remove the inorganics by washing before carbonization to prevent activation. Remarkably, the pretreatment stabilized lignin significantly quicker compared to similar literature methods involving morphology control of KL with low inorganics content. Also, the derived KL-MP carbon microparticles show better electrochemical performance over carbons derived from KL-REF with 23% higher de-lithiation capacity as a Li-ion battery anode.

Source: Bioresource Technology

DOI: 10.1016/j.biortech.2026.134177