Eliminating greenhouse gas (GHG) emissions in pulping: sustainable solutions for lignin extraction

Abstract

Mitigating greenhouse gas (GHG) emissions is one of the most important challenges in various industries, including the pulp and paper industry. This thesis explores potential pathways for the separation of lignin and the recovery of pulping chemicals such as sodium hydroxide (NaOH), sodium sulfide (Na2S), and calcium carbonate (CaCO3) without generating GHG emissions. The research includes a comprehensive literature review of existing processes and interviews with experts in the Finnish bioproduct field. Stora Enso is a partner in the Polestar 0 project, which aims to produce a completely climate-neutral car by 2030. This study focuses on producing lignin-based battery anode material, Lignode, by Stora Enso. Traditional kraft processes used for lignin separation involve combustion-based recovery methods that significantly contribute to carbon dioxide (CO2) and other GHG emissions. The primary aim of this research is to conduct a comparative analysis of alternative methods to identify the most effective solutions for greenhouse gas-free lignin separation and chemical recovery. Qualitative methods were employed to analyze various lignin separation and chemical recovery technologies. This process involves examining existing literature, conducting expert interviews, and analyzing case studies. The research identified several potential technologies that could significantly reduce or eliminate GHG emissions from pulp mills. The study showed that replacing traditional lime kilns with electrical lime kilns could reduce CO2 emissions, as electrical kilns do not require boilers, which use the combustion of biomasses or fossil fuels to generate heat. Furthermore, the research highlighted the potential of alternative lignin separation processes, such as the organosolv method, which can offer a more sustainable solution compared to the traditional kraft process.