LIGNIN MAXIMIZATION: ANALYZING THE IMPACT OF DIFFERENT FEEDSTOCKS AND FEEDSTOCK RATIOS USING ORGANOSOLV FRACTIONATION

Over-exploitation of fossil fuels coupled with increasing pressure to reduce carbon emissions are prompting a transition from conventional petrochemical feedstocks to sustainable and renewable sourced carbon. The use of lignocellulosic biomass as a feedstock for integrated biorefining is of current high interest, as separation into its component parts affords process streams of cellulose, hemicellulose and lignin, each of which can serve as a starting point for the production of biobased chemicals and fuels. Given the large number of potential sources of lignocellulosic feedstocks, the biorefinery will need to adapt to the supplies available over a normal growing season. Of particular importance is the lignin fraction, as its conversion to chemicals and materials to allow economic viability of the operation.

Previous work has demonstrated that organosolv fractionation effectively separates lignocellulosic biomass into its component parts. In this project, we investigated the use of organosolv technology for separating mixtures of lignocellulosic feedstocks to isolate pure lignin. Mixtures of switchgrass (Panicum virgatum), southern yellow pine (Pinus taeda L.), and hybrid poplar (Populus spp.) were separated using organosolv fractionation. Experiments were performed by heating the feedstock mixtures at 150oC in a 3.5 L flow-through reactor with a ternary, one-phase solvent mixture of methyl isobutylketone (MIBK), ethanol (EtOH) and water (H2O) in a wt% ratio of 16/34/50, and containing sulfuric acid as a catalyst. The impact of different process variables was examined by experimental design (‘Design of Experiments’) to minimize the number of experimental runs using a balanced approach in the response surface to maximize inference. The process variables included two different runtimes (60, 120 min), two different sulfuric acid levels (0.05, 0.15 M), and four different wt% feedstock ratios for switchgrass/pine/poplar ([10/10/80], [10/80/10], [80/10/10], [33/33/33]). After completion of the initial experimental matrix, four additional center-points were carried out using a 90 min runtime, and 0.1 M acid level to validate the results for each of the four feedstock ratios. The dependent factors were lignin yield, lignin purity, and cellulose purity. Response surface methodology (RSM) was used to evaluate the impact of the process variables and to determine optimization settings for the process.