Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1996-11-12
1998-11-03
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C 5142
Patent
active
058311220
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and extractant composition for extracting and recovering acids from aqueous solutions.
More particularly, the present invention relates to an improved extractant composition and process for the recovery of a water-soluble carboxylic or mineral acid having a pKa higher than 2, from an aqueous solution containing said acid or salt thereof.
Acid-containing aqueous streams are obtained in many industrial processes such as chemical and biosynthesis of acids, leaching, surface treatment, etc. Of particular interest to the present invention are fermentation liquors comprising carboxylic acids of relatively low concentrations or fermentation liquors comprising salts of carboxylic acids. Two important examples are the fermentation liquor comprising about 15% citric acid and the one comprising a lactate salt. (Lactic acid fermentation is usually maintained at pH of about 5 or higher by addition of a base. The fermentation liquors thus contain mainly the lactate salt). The recovery of the acids from such liquors accounts for a major part of total production cost.
Traditional separation methods are based on consuming reagents, and thus also entail the production of by-products requiring disposal. These are avoided on using liquid-liquid extraction, which has additional important advantages, such as low energy consumption and avoidance of high temperatures that may lead to unwanted reactions of the product. In liquid-liquid extraction, the aqueous solution (feed) is contacted with an extractant, preferably in a multi-stage, counter-current operation. Some components transfer from the aqueous phase to the extractant. The loaded extractant (extract) is separated and treated in a separate operation to recover the extracted components and to regenerate the extractant. Many basic organic compounds were found suitable for extraction of acids, including alkanols, aldehydes, ketones, ethers, esters, amines, trialkyl phosphates and phosphine oxides.
Long straight chain amines are in many cases most desired extractants due to high efficiency, high selectivity and low miscibility in the aqueous phase. Amines are usually used in a diluent to avoid high viscosity, particularly in the acid-loaded extract. The diluent, or a third component, may also provide for modification of extractant properties. Thus, Baniel, et al. (U.S. Pat. Nos. 4,291,007 and 4,334,095) have found that adding an organic acid to the extractant provides for easier back-extraction of the extracted acids, while having just a limited suppressing effect on forward extraction.
It is well known that polar and protic compounds provide for enhancement of acid extraction by amines (Wojtech, et. al., U.S. Pat. No. 4,720,577). These compounds may act as acid extractants by themselves, but are much weaker extractants than the amines. Extractants comprising amines and enhancers show, in most cases, synergistic effects, i.e., acid extraction by such extractants is much higher than the added contribution of the components.
In the description hereinafter, and to avoid confusion, the term "primary extractant" will be used for relatively strong, long chain amines used for extractions, and the term "enhancer" for polar extractant components, the extraction power of which is smaller than that of the primary extractant. Relatively weak amines are considered enhancers when present in extractants comprising relatively strong amines as the primary extractant.
Desired extractants should provide for high efficiency in extraction (relatively low extractant volumes and small number of extraction stages), high selectivity, low water miscibility, low toxicity (particularly for food grade products) and for efficient stripping of the extracted acid from the extract. The latter can be removed from the extract through interaction with an aqueous solution of a base. In most cases, however, the acid is the required product rather than the salt, and acid recovery from the extract is performed by back-extraction with water, or by distillation.
As is known,
REFERENCES:
patent: 4275234 (1981-06-01), Baniel et al.
Killos Paul J.
Yissum Research Development Company of the Hebrew University of
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