LIVESTOCK-DERIVED BIOGAS UPGRADING TO BIOFUEL USING HIGH-PERFORMANCE THIN-FILM COMPOSITE MEMBRANES

The major goal of this project is the fabrication of thin-film composite membranes containing Ni2(m-dobdc) metal-organic frameworks (MOFs) as nanoparticle fillers. We will investigate the potential utility of these materials for unprecedented performance in upgrading livestock-derived biogas. The following goals, tasks, and objectives will be completed to achieve this goal:Goal 1: Fabricate MOF-embedded thin-film composite (TFC) membranes (Months 1-4)Two of the most commercially used TFC membrane fabrication strategies will be used to make our MOF-incorporated TFC membranes: phase inversion (solvent evaporation, Task 1.1), and interfacial polymerization (Task 1.2). Our proposed strategies will be based on methods and TFC structures widely adopted on the commercial level, allowing us to innovate toward scalable membrane production processes.Task 1.1: Fabricate TFC polyimide membranes using a solvent evaporation approach. Our thicker (~40 µm), freestanding, lab-scale MOF membranes have been fabricated using simple solvent evaporation approaches. Here, we disperse our MOF nanoparticles in a polymer solution that is dissolved in a low boiling point solvent, which is slowly evaporated at ambient conditions to leave behind a solid MMM film.12,13,28 We will adopt a similar strategy to make our TFC membranes.Objective 1.1: By the end of Month 3, each TFC membrane type will be fabricated to yield ≥ 100-cm2 membrane areas that appear uniform and crack-free, using protocols that require < 24-hour casting times. Nanoscale material properties will be characterized as part of Milestone 2.1.Task 1.2: Fabricate TFC polyamide membranes using an interfacial polymerization approach. Interfacial polymerization (IP) methods offer operational strengths in TFC fabrication such as excellent large-scale processibility, fast fabrication times, and relative ease in creating ultrathin (< 200 nm) active layers.We will apply these methods for TFC fabrication and create polyamide-based selective layers, which exhibit promising CO­2 gas permeance and selectivity for biogas upgrading applications.Objective 1.2: By the end of Month 4, each TFC membrane type will be fabricated to yield ≥ 100-cm2 membrane areas that appear uniform and crack-free, using protocols that require < 24-hour casting times. Nanoscale material properties will be characterized as part of Milestone 2.1.Goal 2: Demonstrate defect-free membrane properties and excellent biogas separation performance (Months 1-6, $75K)Task 2.1: Characterize the thin film materials. We will image each of the ten TFC membranes fabricated in Objective 1, to determine MOF dispersibility, the presence of potential defects and cracks in the membranes, and active layer thicknesses. Defects and cracks that compromise separation selectivity can arise during thin-film fabrication due to the presence of impurities, poor filler dispersibility, poor filler-polymer compatibility, or suboptimal casting conditions. Field-emission scanning electron microscopy (FESEM) will be performed to image both the top surface and cross section of each fabricated membrane. Multiple images on different randomly sampled membrane areas will be taken to assess variability across the films.Objective 2.1: By the end of Month 5, characterizations will show membrane morphologies without MOF agglomerations (> 500 nm agglomerations), without defects, and with thin (submicron) active layers, for all types of MOF thin film membranes from Objective 1.Task 2.2: Evaluate the biogas separation performance of the membranes via single-gas permeation. Single-gas permeation tests will be conducted on each type of fabricated TFC membrane for three gases (N2, CH4, and CO2). N2 permeation will first be measured as a detection tool to identify any defects or pinholes in the membranes, due to the cheap cost and inert nature of N2. N2 permeance rates that are unreasonably high (e.g., close to those achieved by the support or gutter layers alone) will indicate defects in our MOF membranes that allow gases to freely pass. CH4 and CO2 membrane permeance rates will then be measured as essential indicators of biogas upgrading performance, as dairy manure-derived biogas consists mainly of these two gases (55-68% CH4 and 32-45% CO2).Objective 2.2: By the end of Month 6, at least two types of MOF TFC membranes will achieve a CO2 gas permeance of at least 50 gas permeation units (GPU) and CO2/CH4 selectivity of at least 25. These MOF composite membranes will also achieve higher separation values compared to the neat membranes fabricated without the MOFs.Goal 3: Achieve high plasticization- and aging-resistance in thin-film composite membranes (Months 6-8)Task 3.1. Demonstrate plasticization resistance at high pressures. We will measure the plasticization pressure of the neat thin-film membranes and the corresponding MOF-loaded films that show the best separation performance.Objective 3.1: By end of Month 7, high-pressure permeation measurements will show the plasticization pressures of the neat and MOF-loaded thin-film membranes. An increase of plasticization pressure by at least 50% will be observed due to the interactions between Ni2(m-dobdc) nanoparticles and the polymer matrix.Task 3.2. Demonstrate resistance to aging by maintaining similar performance for 1 month.We will measure the aging of our best thin-film membrane by monitoring the CO2 permeability at 10 bar over a period of 1 month.Objective 3.2: By end of Month 8, aging studies will be completed on the most promising MOF-loaded thin-film membrane. The MOF TFC membrane will maintain ≥ 90% of its initial CO2 permeance after 1 month, demonstrating aging resistance.