A Laboratory Study of Current Efficiency in Cryolitic Melts

Solli, P. A.; Haarberg, Torstein; Eggen, Tor Gunnar; Skybakmoen, Egil; Sterten, Å.

doi:10.1007/978-3-319-48156-2_28

“…Metal impurities present in calcined coke are undesirable for anodes for several reasons, including contamination of the produced Al, increase of anode oxidation, − and decrease of the current efficiency. , First, impurities that contaminate the Al and catalyze anode oxidation are discussed (Ni and V). The biocokes had very low concentrations of these impurities (∼10 ppm vs typical coke specifications of 250 and 350 ppm, respectively Table ).…”

Section: Resultsmentioning

confidence: 99%

Renewable Biomass-Derived Coke with Texture Suitable for Aluminum Smelting Anodes

Elkasabi

¹

,

Darmstadt

²

,

Boateng

³

2018

ACS Sustainable Chem. Eng.

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Industrial producers of calcined petroleum coke encounter issues pertaining to product quality and environmental ramifications. While previous attempts to produce biorenewable versions of calcined coke address CO2 footprint, sulfur, and metals poisoning, none have demonstrated a sufficient degree of anisotropy, which is critical for performance in aluminum smelting anodes. Using fast pyrolysis of biomass, we produced bio-oils of sufficient quality whereby coke can be formed through distilling off the volatiles. Tail-gas reactive pyrolysis (TGRP) produced bio-oils with low oxygen content, low viscosity, and high polyaromatic content, all of which are critical for alignment of coke precursors. Distillations at controlled rates and temperatures ensured the alignment of polyaromatic domains leading to coke anisotropy. Bio-oils with oxygen content below 16 wt % successfully produced coke with mixtures of isotropic and anisotropic domains. In coprocessing experiments, mixtures of pyrolysis bio-oil and green petroleum coke coked under similar conditions to produce highly anisotropic textures, although degrees of discontinuity exist within merged particles. When baked with coal tar pitch as an additive, calcined biocokes exhibited resistivity values of 100–200 μΩ·m, which correlated well with the calcination time at 1200 °C.

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“…Although eq. [3] appears to describe the experimental results very well, it is possible that the fit is partly incidental. The effect of superheat is probably indirect: 1) Low superheat gives lower temperature (at constant electrolyte composition), which is beneficial due to reduced metal solubility.…”

Section: Resultsmentioning

confidence: 89%

“…[2] and the value of the constant term in eq. [3] was determined to be 0.65 for the good agreement between calculated and actual values. From this relationship, the current efficiency could be estimated by the composition and the temperature of the electrolysis cell.…”

Section: Resultsmentioning

confidence: 95%

Effects of Composition and Temperature on Current Efficiency for Aluminium Electrolysis from Cryolite-Based Molten Alumina Electrolytes

Morishige

¹

,

Haarberg

²

,

Gudbrandsen

³

et al. 2017

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The current efficiency (CE) for aluminium electrolysis in modern cells can be as high as 96 %. The main reason for loss in current efficiency is the so-called back reaction between dissolved metal and the anode product of CO2. Decreasing temperature of the cell may give higher current efficiency. However, low superheat may cause solidification of melt. A laboratory cell to determine the current efficiency was recently modified to obtain more reliable results. Electrolysis was performed at constant current density and the current efficiency was determined from the weight of deposited aluminium. Effects of electrolyte composition by addition of LiF and temperature were studied. The loss in current efficiency is strongly related to the content of dissolved metal in the electrolyte. The effect of LiF addition on the current efficiency was discussed in this study. * Liquidus temperature was calculated by eq. [2].

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“…It was also reported by Dewing that the current efficiency varies as a function of superheat, AlF3 and LiF contents of the electrolyte 20 . The relationship between the CE loss value and cell conditions was expressed by the following equation; [3] Figure 4 shows the relationship between the calculated CE loss and the actual CE values. The superheat was calculated by eq.…”

Section: Resultsmentioning

confidence: 99%

Effect of Composition and Temperature on Current Efficiency for Aluminium Electrolysis from Cryolite-Based Molten Alumina Electrolytes

Morishige,

Haarberg,

Gudbrandsen

et al. 2017

Meet. Abstr.

0

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The current efficiency (CE) for aluminium electrolysis in modern cells can be as high as 96 %. The main reason for loss in current efficiency is the so-called back reaction between dissolved metal and the anode product of CO2. Decreasing temperature of the cell may give higher current efficiency. However, low superheat may cause solidification of melt. A laboratory cell to determine the current efficiency was recently modified to obtain more reliable results. Electrolysis was performed at constant current density and the current efficiency was determined from the weight of deposited aluminium. Effects of electrolyte composition by addition of LiF and temperature were studied. The loss in current efficiency is strongly related to the content of dissolved metal in the electrolyte. The effect of LiF addition on the current efficiency was discussed in this study. * Liquidus temperature was calculated by eq. [2].

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A Laboratory Study of Current Efficiency in Cryolitic Melts

Cited by 7 publications

References 7 publications

Renewable Biomass-Derived Coke with Texture Suitable for Aluminum Smelting Anodes

Renewable Biomass-Derived Coke with Texture Suitable for Aluminum Smelting Anodes

Effects of Composition and Temperature on Current Efficiency for Aluminium Electrolysis from Cryolite-Based Molten Alumina Electrolytes

Effect of Composition and Temperature on Current Efficiency for Aluminium Electrolysis from Cryolite-Based Molten Alumina Electrolytes

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