Optimization of a lignin valorization process superstructure using a MILP approach

Lignocellulosic biomass, including both herbaceous and woody feedstock, is currently widely used in many biorefineries. The lignin fraction (20-35 %DRY) is typically thermochemically converted into the cogeneration section of the biorefinery to produce heat and electricity. However, lignin holds a greater potential in several industrial sectors to produce biobased materials and several chemical building blocks. In particular, novel technologies allow obtaining low molecular weight compounds, such as aromatic or hydrocarbons. In this work, a mathematical methodology was developed to evaluate the best option in terms of lignin valorization. A process superstructure was built to compare alternative process pathways from lignocellulosic biomass. The following conversion options were considered: Jet-fuels (JF), phenol-formaldehyde resins (PFR), polyurethane foams (PUF), and syngas for green electricity generation. By AIMMS optimization software, a Mixed Integer Linear Programming (MILP) was applied to obtain a simplified mathematical analysis and, consequently, the maximum lignin cost maximization for each lignin valorization process. In particular, process conversion, required utilities, product values were assessed for each process technology. Preliminary results show that the production of phenol-formaldehyde resins is the process closer to the market uptake. On the other side, polyurethane and jet-fuels appear still far from the market and their production would be feasible at a polyurethane foams and jet-fuel selling price at 300 % of the current selling price