Biopitch as a Binder for Carbon Anodes: Impact on Carbon Anode Properties

Abstract

Aluminum industry depends on coal-tar-pitch as a binder to produce carbon anodes used for aluminum electrolysis. This binder is nonrenewable and mainly composed of polycyclic aromatic hydrocarbons which are harmful for the human health and the environment. The biomass-driven pitch is considered to be a green and abundant binder. In this study, we synthesized biopitch from bio-oil by heat treatment of the bio-oil at 160 and 180 °C. The biopitch was then baked at 1100 °C to produce its carbonized form. In comparison to the carbonized coal-tar-pitch, the baked biopitch showed amorphous microstructure, higher air reactivity and higher specific electrical resistivity. Biopitch is known to have high wettability and adhesion with the coke particles which could reduce the negative effect of inferior characteristics of its baked form on the resulting anodes. Biopitch was used to replace 100 % of the conventional coal-tar-pitch binder in the anode recipe. Green anodes were produced by mixing the coke aggregates with the biopitch at 178 °C. The baked anode properties were measured and compared to those of classical reference anodes (made of coal-tar-pitch and calcined coke). Although, the air and CO 2 reactivity of the biopitch anodes is slightly higher than that of the reference ones, the biopitch anodes showed similar density, coefficient of thermal expansion, specific electrical resistivity, mechanical strength, and lower air permeability in comparison to those of the reference anodes.

Biochar as an Additive to Modify Biopitch Binder for Carbon Anodes

“…The specific electrical resistivity of the anode slightly increases by increasing the biochar content in biopitch (Anode-BP-9.0 > Anode-BP-0). It is important to notice that the carbonized BP shows significantly higher specific electrical resistivity in comparison to the carbonized CTP . This lets us believe that the anode made of BP may exhibit much higher electrical resistivity.…”

“…It is important to notice that the carbonized BP shows significantly higher specific electrical resistivity in comparison to the carbonized CTP. 24 This lets us believe that the anode made of BP may exhibit much higher electrical resistivity. Figure 5b also displays the higher compressive strength of BP anodes compared to that of CTP anode.…”

“…The test duration against air and CO 2 was 3 and 6 h, respectively. The detailed test conditions were presented in previous work by our group . It must be mentioned that in the industry the air/CO 2 reactivity for the baked anode is measured by ASTM-D6559-00a or ASTM-D6558-00a using big anode samples.…”

“…The detailed test conditions were presented in previous work by our group. 24 It must be mentioned that in the industry the air/CO 2 reactivity for the baked anode is measured by ASTM-D6559-00a 25 or ASTM-D6558-00a 26 using big anode samples. In this study, the 2 mg crushed powder anode samples were used to have a single even layer of carbon to study its intrinsic reactivity (chemically controlled reactivity in the absence of diffusion effects).…”

Use of Plasticized Biochar Intermediate for Producing Biocarbons with Improved Mechanical Properties

“…One approach is to use fast pyrolysis to convert the solid biomass into a bio-oil which can be further fractionated and used as a green binder and/or as carbonization feedstock. − This processing route has been shown to significantly improve material properties, but it requires multiple unit operations to thermochemically fractionate biomass components, reformulate to obtain desired mixtures, and finally carbonize to obtain the final product. The compressive strength reported for anodes produced from calcined petroleum cokes with bio-oil/pitch binders range from 22 to 36 MPa at binder content of 15–25 wt %. , An alternative, pressurized thermochemical processing, avoids the bio-oil intermediate. One approach applies a compressive load (2–5 MPa) during heating (similar to ablative pyrolysis), resulting in a plasticized biochar that, with additional thermal processing, produces a carbonized material with higher density, improved graphitic order and reduced thermal expansion coefficient .…”