Boron Extraction with 2-Ethyl-1,3-hexanediol Using a Microchannel Device for High-Purity Source of Solar-Grade Silicon

Abstract

A novel approach toward the purification of silica and removal of boron impurities via solvent extraction with 2-ethyl-1,3-hexanediol using a microchannel device is presented. The microchannel, fabricated on Si substrates using lithographic techniques, had 100 μm width, 100 μm depth, and 10 mm length. Amorphous silica spiked with a trace amount of boric acid and refined diatomaceous earth used as silica feedstock were purified. Residual boron content was determined by inductively coupled argon plasma atomic emission spectrometry. Following extraction using a microchannel device, the residual boron content was less than 1.0 ppm for the former silica feedstock and than 2.5 ppm for the latter one, and the contact reaction period was 0.03 seconds for both type of silica feedstock. These are lower and significantly shorter due to much shorter diffusion distance and much larger specific interfacial area as compared to those observed when using a conventional separatory funnel, for both types of silica feedstock. Hence, it is suggested that microchannel devices can be utilized as an attractive approach toward the production of high-purity silica as a source for solar-grade silicon.

High purity silicon materials prepared through wet-chemical and electrochemical approaches

“…6. In this figure, flow rate was 100 mL min À1 and the reaction duration was estimated to be 30 msec, and under this condition, it turned out that high efficiency for B extraction could be obtained as is listed in Table 1 [13]; the initial contents of some 5 ppm of B has been decreased to be 0.5 ppm, and the elimination ratio is 90%. This performance is almost equal to that obtained by using separatory funnel for 120 min (2 stages for 60 min treatment), showing the high potential of this process for effective purification of silica.…”

“…4 and 5 show overall process for the purification of silica and schematic image of the reactor we applied for the initial investigation [12,13], which is Y-shaped flow reactor made of micromachined Si wafer and glass-sealing with 10 mm-long and 100 mm-wide single channel. Toluene solution containing 0.5 mol L À1 of EHD and aqueous solution with dissolved silica were introduced to the inlets (1) and (2), respectively, and by adjusting their flow rates, stable liquid-liquid interface was formed as is shown in Fig.…”

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

“…The microchannel pattern was fabricated on a Si wafer with dimensions of 20 mm × 20 mm and 280 μm thickness by etching to a depth of 50 μm by the deep reactive ion etching technique using photolithography. , Figure shows the schematic view of the design of the channel: the width of two inlets is 50 μm (the total width of the center part of the channel is 100 μm), the height (depth) is 50 μm, the channel length for the center part is 10 mm, and the lengths of the inlet and outlet are ∼4.0 mm. The channel was sealed with Pyrex glass by anode bonding, that is, the top part of the channel is glass, whereas the bottom and the walls are Si.…”

“…We have been developing a new chemical wet process to prepare SOG-Si using diatomaceous earth as the Si source, in which we remove impurities chemically from the silica-dissolving solution to produce highly purified silica. − Diatomaceous earth is advantageous for two reasons: − (i) it is evenly distributed in the earth and is abundant and (ii) it is easily applicable to chemical wet processes because of its high solubility owing to its porous structure. Our previous studies − demonstrated efficient processes for impurity removal from silica solution prepared from diatomaceous earth, as well as a direct electrochemical process for the reduction of silica to Si. Several impurities included in the raw material, such as Na, Mg, K, Al, and so forth, were shown to be removed effectively by specific leaching processes, which are however not effective for the removal of B impurity.…”

Elimination of Boron from Soluble Silica Via Solvent Extraction with 2,2,4-Trimethyl-1,3-Pentanediol Using a Multistage Flow-Type Reactor

“…Microchannel device is, however, a promising tool for efficient reaction due to short diffusion distance and large specific interfacial area (4). We have proposed the application of microchannel device for the solvent extraction of boron with 2-ethyl-1,3-hexanediol (EHD) (5). While the short diffusion distance as well as the large specific interfacial area of microchannel enabled fast and efficient elimination of boron to SOG-purity, however, improvement of throughput was required for the practical application.…”