The Synthesis of Succinic Acid and its Extraction From Fermentation Broth Using a Two-Phase Partitioning Bioreactor
Hepburn, Adam James
Succinic Acid , In-Situ Product Removal
Succinic Acid (SA) is an intermediate in the production of fine and commodity chemicals. No commercial SA bioproduction process exists due to process limitations including end product inhibition and high product separation costs, which account for 70% of total production costs. Two-Phase Partitioning Bioreactors (TPPBs) can increase volumetric productivity through in-situ product removal, although SA uptake by polymers requires a pH below the pKA2 of SA (4.2). Sparging CO2 gas into the bioreactor was proposed to temporarily lower the pH of the medium, allowing for SA uptake. At 1atm CO2 sparging lowered the pH of Reverse Osmosis (RO) water to 3.8 but only to 4.75 in medium, requiring the use of H2SO4 and KOH for pH adjustment in subsequent experiments. Polymers were screened for SA uptake and the effect of pH on uptake from 2.2 to 6.2 was also studied. Only Hytrel® 8206 showed non-zero uptake with a partition coefficient for SA of 1.3. Cell cultures of Actinobacillus succinogenes was exposed to pH 4.2 for times from 5 minutes to 4 hours to determine whether cells could grow after low pH exposure. A. succinogenes resumed growth after up to 4 hours of low pH exposure, giving a sufficient time span for SA uptake in the bioreactor. A single-phase run was operated as a benchmark for comparison to the TPPB system which removed SA from the fermentation broth by pH cycling; lowering the pH to 3.8 for uptake, then increasing it to 6.7 to continue bioproduction. Uptake from fermentation broth took 60 minutes, within the time causing no effect on cell growth from low pH exposure. The two-phase run yielded 1.39g/L•h, unchanged compared to the single-phase run which gave 39g/L of SA after 28 hours. Though pH cycling reduced the concentration of SA through polymer uptake, the salts added for pH adjustment hindered further cell growth. The TPPB system demonstrated that SA can be efficiently removed from solution without complex separation methods. Future work will use pressurized vessels to increase the solubility of CO2 and lower the pH of fermentation broth for SA uptake without the need for strong acids.