(345b) Replacing Toxic Solvents with Environmentally-Friendly Diluents for the Recovery of Pyruvic Acid from Aqueous Solutions

Recently, reactive extraction (RE) has been shown to be one of the most promising techniques for the recovery of bio-molecules, e.g. carboxylic acids, from biological production media. The method is a modified version of traditional liquid-liquid (solvent) extraction (LLE) process. Different from LLE, the organic phase in RE contains chemical extraction via an extractant that has the ability to form complex structures with the target product. The technique is favored due to its high efficiency, low energy demand and also simplicity of the approach. Reactive extraction is also preferred for its availability to be used during the recovery of heat-sensitive chemicals since the process is operated at room- or low temperatures. However, high toxicity of the solvents (e.g., 1-octanol, hexane, etc.) utilized in the process is an important disadvantage of the technique. Several chemicals have been tested to replace these traditional solvents; however, low efficiency and high expense still prevent the commercialization of the process with these novel diluents.

Pyruvic acid (PA) is a critical fine bio-chemical, generally used in pharmaceutical productions. Likewise for many biochemicals; following to its bio-based synthesis, an effective, selective, low-cost and environmentally-friendly recovery of the target molecule, PA is required. Several techniques have been tested for the purpose; however, none of them could be commercialized yet. As mentioned above, RE is shown to be a promising candidate for the purpose. It is efficient, simple and inexpensive. The use of non-toxic diluents instead of traditional organic solvents will make the process environmentally-friendly or at least considerably reduce the level of hazard. 

In the present study, several (12) types of vegetable oils (sunflower, soybean, corn, almond, canola, hazelnut, olive, sesame, linseed, safflower, castor and black cumin (black seed) oils) were evaluated to be used in the process with different types of extractants. Their low cost will also add another benefit to the commercialization of the process. Equilibrium studies were performed to determine the most effective non-toxic diluent and extractant type; and investigate the effects of the process parameters on the recovery. For all types of extractants, highest extraction efficiencies were obtained with almond and sesame oils. Among the extractants tested, tertiary amines (TAs) gave the highest recovery rates. The quaternary ammonium salts and organophosphorus extractants followed them. The efficiency values with these effective non-toxic diluents+trioctylamine were about 94.5-96% when [PA]/[TA]=1.0-1.7 while it was 95-97% with 1-octanol, which is accepted to be the state of art solvent for the process. Consistent with the reports in the literature for different reactive extraction systems, distribution ratio increased with extractant concentration while decreased with the initial aqueous pH, PA concentration and temperature. Back extraction of the target molecule was achieved via various back extraction strategies. Firstly, several types of sodium salts were tested for the purpose and more than 90% recovery was obtained. As an alternative strategy, water soluble amines were used as back extraction agents and 100% recovery was achieved. The studies on the re-use of organic phase in the following reactive extraction operations are on-going. Next, the recovery process should be tested using a biological PA production media.

The results show that organic solvents widely used in extractive separations of carboxylic acids can be replaced with vegetable oils. Effective back extractions result in an aqueous solution of PA and allow for the re-use of the organic phase for the following RE, which significantly reduce the costs. Hence, an efficient, low-cost and environmentally-friendly recovery of PA is achieved with the process proposed in this study.