Purification of Lactic Acid with Ultrafiltration Membranes

In recent years, there has been a drive to commercialize degradable polymers such as poly(lactic acid) to help tackle the current plastic crisis. For the technology to be successful, it is imperative to find cost-effective methods of extracting lactic acid from different waste streams such as agricultural waste, food waste, or reaction byproducts. One promising technology is pressure-driven membrane filtration where molecules are separated by their size. In this work, we aimed to study how different commercially available membranes can extract lactic acid from different streams. To accomplish this goal, we evaluated the performance of different commercial nanofiltration membranes at filtering the lactic acid solutions. First, we identified the best method to determine lactic acid concentration in different solutions. We evaluated two methods: UV-Vis Spectroscopy based on and high-performance liquid chromatography (HPLC). We determined that the HPLC method, while more accurate, took a significantly larger amount of time. Having identified the method, we proceeded to test membranes made up of different polymers and of different pore sizes. We evaluated the resistance of the membranes to lactic acid and tested their performance in both pure water and in lactic acid solutions. We found that poly(ether sulfone) membranes exhibited significant degradation under short contact (<30min) in lactic acid containing solution. Further studies will evaluate the purity of the samples and ways to simplify the separation process.