(540d) Replacement of Toxic Organic Solvents with Natural Non-Toxic Diluents for the Recovery of Pyruvic Acid

Lately, 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. It is a modified version of traditional solvent extraction (SE) process. Different from SE, the organic phase in RE involves a chemical extraction using an extraction agent that has the ability to form complex structures with the target molecule, carboxylic acids. The technique is preferred due to its high efficiency, low energy demand and simplicity of the approach. It is also favored for its availability to be used for heat-sensitive chemicals since the process is generally carried out at room temperature. However, high toxicity levels of the organic solvents used during the process is the most critical disadvantage of the method. Various alternatives have been used to replace these solvents; however, low efficiency and high cost still prevent the commercially use of the process.

Pyruvic acid (PA) is an important biochemical, mostly utilized in the production of amino acids and pharmaceuticals. Following to its biological production; an efficient, low-cost and environmentally-friendly recovery process is required. Several methods have been tested for the purpose; however, none of them could be widely accepted yet. As previously stated, RE is shown to be a promising candidate for the aim due to its several advantages. In addition, the use of non-toxic diluents to replace the traditional organic solvents will make the process environmentally-friendly and will significantly reduce the hazard level.

In this study, 12 different vegetable oil types (sunflower, soybean, corn, almond, canola, hazelnut, olive, sesame, linseed, safflower, castor and black cumin (black seed) oils) were tested with various extractants for the purpose. Low-cost of these non-toxic solvents will add a significant advantage to the commercialization of the operation. 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. Results were compared with the ones obtained with 1-octanol, which is accepted as the state of art solvent for the technique. For all types of extractants, highest extraction efficiencies were obtained with almond oil. Among the extractants, tertiary amines (TAs) provided the highest recovery rates, and the quaternary ammonium salts and organophosphorus extractants followed TAs. Extraction efficiencies with vegetable oils+trioctylamine were about 94.5-96% when [PA]/[TA]=1.0-1.7 while it was 95-97% with 1-octanol. Consistent with the literature, distribution ratio increased with extractant concentration while decreased with the initial aqueous pH, PA concentration and temperature. Back extraction of the target molecule was performed using various back extraction agents. Firstly, several types of sodium salts were tested for the purpose and highest recovery was reached as 88% with sodium nitrate. Alternatively, water soluble amines were used and over 95% recovery was achieved. Results of the related experiments also exhibited that the organic phase can be successfully utilized for the consecutive forward reactive extraction operations.

The results obtained in this study showed that toxic organic solvents widely preferred in industrial extractive separations of bio-molecules (e.g. carboxylic acids) can be replaced with non-toxic and natural vegetable oils. Efficient back extractions resulted in an aqueous solution of PA and allowed the organic phase to be re-used in the following RE, which significantly reduce the costs. Therefore, an efficient, low-cost and environmentally-friendly recovery of PA was achieved in the present study.