Catalytic Depolymerization Of Switchgrass-Derived Lignin From Optimized Cosolvent Enhanced Lignocellulosic Fractionation Process To Produce Aromatics And Sustainability Assessment Of Lignin Using Life Cycle Assessment
Restricted (Penn State Only)
- Author:
- Godwin, James
- Graduate Program:
- Agricultural and Biological Engineering (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 05, 2024
- Committee Members:
- Suat Irmak, Program Head/Chair
Stephen Chmely, Chair & Dissertation Advisor
Juliana Vasco-Correa, Major Field Member
Tom Richard, Major Field Member
Hilal Ezgi Toraman, Outside Unit & Field Member - Keywords:
- Transfer Hydrogenolysis
Lignin Valorization
Biomass Fractionation
Heterogeneous Catalysis
Mixed-metal Spinel
Switchgrass
Life Cycle Assessment
Response Surface Methodology
Box-Behnken Design
Optimization
Transfer Hydrogenation
Transition Metals
Lignin - Abstract:
- As we continue to witness the devastating impact of climate change, there have been renewed calls from industrial stakeholders and government policy makers on the need to accelerate the pace of development of renewable materials and a shift towards renewable forms of energy. This would reduce dependence on fossil-based products, which have been considered a major contributor to global warming. Lignin has garnered attention in recent times due to its availability as the second most abundant polymer on earth, and the potential it holds which is still yet to be fully tapped. In this work, the goal was to develop a sustainable process that can be used to extract and depolymerize lignin from switchgrass. The main objectives were to first isolate lignin from switchgrass and synthesize metal catalysts which can be used to modify the lignin structure whilst generating valuable aromatic compounds for downstream biorefining; second, to optimize the lignin isolation process to obtain a lignin with distinct structural features that make it suitable for polymer-based application using 3D printing technology; third, to access the carbon footprint of the lignin isolation process to determine its environmental performance. First, lignin was isolated from switchgrass using cosolvent enhanced lignocellulosic fractionation (CELF) and depolymerized using synthesized spinel-type mixed-metal oxide catalyst (NiCo2O4) made from earth-abundant transition metals. Catalytic transfer hydrogenolysis reaction was used to depolymerize the lignin to tune the oxidation state at the Cα. Results of catalyst activity with acetophenone as model compound showed a 75 % conversion and ~90 % selectivity for ethyl benzene. The catalyst was then used for lignin reaction, yielding a suit of aromatic compounds in the process, which were identified and semi-quantitatively analyzed using gas chromatography/mass spectrometry (GC/MS) and structural analysis was performed using two-dimension nuclear magnetic resonance (2D-NMR) spectroscopic technique. The CELF process was them optimized using Response Surface Methodology (RSM) and Box-Behnken design with targeted response variables of yield, molecular weight (Mw) and hydroxyl group (OH) content using temperature (140 – 180 °C), acid concentration (0.025 – 0.1 M), and time (10 – 30 mins) as predictors. The optimal point that maximizes yield, minimizes Mw, and maximizes OH group content, was achieved and validated at 169 °C, 0.1 M and 10 mins respectively. A life cycle assessment (LCA) was conducted using OpenLCA software, with a functional unit (F.U) of 1 kg of CELF-derived lignin from switchgrass using a cradle-to-gate approach. The system boundary was limited to contain only the switchgrass cultivation, CELF fractionation, Solvent recovery, washing, and vacuum drying. Transportation from switchgrass cultivation site to processing site was assumed to be 50 km, tetrahydrofuran (THF) and water were used as primary cosolvents, and the switchgrass had a yield of 9 Mg/ha with a 15 % moisture at harvest. The material flow was modeled using SuperPro Designer to determine the mass balance for the process, with secondary data obtained from ecoinvent 2016 and primary data from some laboratory experimentation and the farm energy analysis tool (FEAT) model. ReCipe midpoint (H) V1.13 was used as impact assessment method to quantify the associated impact categories from production of lignin. A sensitivity analysis was also performed to determine which of the parameters were most sensitive to the overall impact of the process; for this study, solvent type was the only parameter tested due to time constraints. Results showed that the overall impact was highly sensitive to solvent type resulting in a GWP reduction of ~73 % in the base case scenario when THF was substituted with methanol; and in the alternate case with 70 % and 90 % recycling of solvent. The result showed a GWP of 6 kg CO2eq. The result in the best-case scenario indicated a higher GWP than previous studies on kraft lignin. However, the biogenic carbon content of lignin was not accounted for in this study, which some previous studies had incorporated into the overall GWP to offset CO2 emissions from the process. This study presents useful data for biorefinery stakeholders exploring CELF process for high purity lignin production.