Spectroscopic and Computational Analyses of Liquid-Liquid Interfacial Reaction Mechanism of Boric Acid Esterification with 2,2,4-Trimethyl-1,3-pentanediol in Boron Extraction Processes

Masahiro Kunimoto, Dieter Bothe, Risa Tamura, Takahiro Oyanagi, Yasuhiro Fukunaka, Hiromi Nakai, Takayuki Homma

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    Abstract

    Purification of silica solution to chemically remove impurities is a novel approach for preparing solar-grade Si. Complete elimination of boron is necessary, as it significantly affects the semiconductor properties of Si if included. To build an efficient reactor for boron extraction, the mechanism of extraction reaction based on molecular behavior should be well understood. Here, we investigated the liquid-liquid extraction of boron (boric-acid) using 2,2,4-trimethyl-1,3-pentanediol as an extractant, which takes place at the liquid-liquid interface experimentally and theoretically. Raman spectroscopy for the microflow reactor provided the concentration of boric acid after extraction, whereas density functional theory calculation showed the reaction energy profiles of the underlying chemical reactions. Calculation results suggested that H2O molecules from the aqueous phase promote extraction by enabling the formation of [BOH-HOH-HOC], a sufficiently stable, nonsteric structure, which stabilizes the transition state and facilitates boric acid esterification. Otherwise, this reaction cannot take place in standard conditions. Raman spectroscopy applied to the extraction process in a microflow reactor supported this conclusion experimentally. These results suggest that the extraction reaction at the liquid-liquid interface is mass transfer-limited. This can help the design of effective reactors to eliminate boron impurity from silica solution.

    Original languageEnglish
    Pages (from-to)10423-10429
    Number of pages7
    JournalJournal of Physical Chemistry C
    Volume122
    Issue number19
    DOIs
    Publication statusPublished - 2018 May 17

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    ASJC Scopus subject areas

    • Electronic, Optical and Magnetic Materials
    • Energy(all)
    • Physical and Theoretical Chemistry
    • Surfaces, Coatings and Films

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