Solvent Selection for Recovery of Carboxylic Acids and Furfural from Aqueous Solution by Liquid-liquid Extraction

Publication Details
Authors: Demesa Abayneh, Laari Arto, Tirronen Esko, Turunen Ilkka
Publication year: 2013
Language: English
JUFO-Level of this publication:

Due to environmental concerns, the current trend in chemical production is to move away from fossil fuels and use bio-based raw materials. A typical biorefinery process uses acid hydrolysis to convert biomass into valuable compounds, such as sugars and carboxylic acids. Acid hydrolysis creates a side stream, an aqueous condensate, containing a mixture of formic acid, acetic acid and furfural. Liquid-liquid extraction is a promising method for the recovery of the compounds from this stream. Selection of a suitable solvent, or a solvent mixture, for this task is not trivial. There are several requirements that a solvent must fulfill. The solvent must effectively extract the compounds from water and the equilibrium for this should be favorable. At the same time, it should be possible to remove the compounds from the solvent and regenerate the used solvent at reasonably mild conditions. Extraction efficiency of solvent, rate of phase separation, easiness of product recovery and recyclability of solvents are among the factors that must be taken into account in solvent selection. The solvent should be also cheap, non-toxic and safe for environment. All these requirements make the selection of solvent challenging. In this study, different types of extractants, including amines and amides were evaluated with the aim to separate carboxylic acids and furfural from aqueous stream of a bio-based process. After extraction, samples from the aqueous and organic phases were analyzed with high performance liquid chromatography (HPLC) and the distribution coefficients (kd) were calculated accordingly. Solvent regeneration experiments were carried out under vacuum in a spinning band distillation unit. Based on the obtained results the calculated distribution coefficients for different solvents are compared and discussed. In addition to the other solvent selection criteria, solvents are also compared considering the easiness and efficiency of solvent regeneration. The obtained results show that Alamine-336 and 2-methyltetrahydrofural (2-MTHF) are the most promising solvents among the extractants studied. For Alamine-336, the rate of phase separation improved and the formation of an emulsion was avoided when operating at low mixing rates during extraction. Moreover, the use of toluene as a diluent for Alamine-336 prevents the formation of an intermediate phase. However, unlike 2-MTHF, the regeneration of Alamine-336 required relatively a higher temperature (>173 oC) under vacuum conditions. In general, the extraction of formic acid was favored more for Alamine-336 whereas the extraction of furfural was favored when 2-MTHF was used as a solvent. For acetic acid there is only a small difference in the equilibrium for both solvents. The absence of intermediate phases and the easiness to remove the product and recycle the solvent back to the extraction process are additional benefits for 2-MTHF.

Last updated on 2017-22-03 at 14:42