(472d) Novel Purification Process for Bio-Derived Citric Acid Using Solvent Extraction and CO2 Antisolvent Purification

Citric acid (CA) is a chemical commodity directly used in food and confectionery, as well as in the pharmaceutical and chemical industry. CA is used as raw material for calcium supplements to prevent osteoporosis, for the manufacture of biobased plasticizers, and to produce citrate salts used as food preservatives, buffer and chelating agents. Generally, CA is produced from a fungal broth fermentation with Aspergillus niger using sucrose as the main substrate. As the microorganism is able to withstand acidic condition, CA is obtained in the acidic form at the end of the fermentation process. Traditional downstream processing involves removal of biomass and suspended solids by filtration, followed by CA precipitation with calcium hydroxide. Impure calcium citrate is acidified with sulfuric acid to release CA in aqueous solution, and precipitating gypsum.

In a typical purification process, CA solution is subjected to ion exchange to remove metal and remaining sucrose, adsorption with activated carbon, followed by evaporation and crystallization. Sucrose traces removal is of major concern as it heavily affects CA crystallization, and prevents from obtaining high CA purity (i. e. higher market value). This process is energy and mass intensive, and generates considerable amounts of liquid and solid waste.

Taking the aforementioned into account, this work describes a novel CA purification process using direct solvent extraction from the clarified fermentation broth and compressed gas (CO₂) as an antisolvent treatment to remove impurities. After the CA is extracted with a medium polarity solvent mixture, precipitation of impurities was carried out by compressing the liquid under CO2 pressure between 10 and 45 Bar, and different contact times (from 2 to 30 h). Under these conditions the impurities, mostly containing sucrose, precipitate out from the solution, allowing high purity CA recovery after solvent evaporation.