Physical and Chemical Characterization of Bio-Pitch as a Potential Binder for Anode

Picard

2021

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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.

Section: ■ Introductionmentioning

confidence: 99%

“…BP showed significantly lower coking value (CV) and primary quinoline insoluble (QI) than the CTP . The low CV implies removal of more volatiles from the binder phase during the anode baking.…”

Section: Introductionmentioning

confidence: 99%

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

Picard

2021

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“…Biopitch, driven from bio-oil, is one of these potential alternatives. Previous investigations showed that biopitch is characterized by sulfur-free and low PAHs and ash content, − all being positive characteristics for anode formulation. However, it was reported that the biopitch exhibits lower coking value and quinoline-insoluble (QI) content than does CTP .…”

Section: Introductionmentioning

confidence: 99%

Biochar as an Additive to Modify Biopitch Binder for Carbon Anodes

Lauzon-Gauthier

et al. 2021

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Looking for alternative materials to coal-tar pitch (CTP), as a binder in anode manufacturing, in aluminum production is of great interest. Such a material should be able to mitigate the cost and health issues without decreasing the carbon anode quality. Biopitch (BP) could be considered as a potential candidate. Previous studies show that biomass-based pitch has generally a low coking value compared to that of CTP, which might negatively affect its properties as a binder in carbon anodes. To increase its coking value, biopitch was modified by using additives. A solid bio-based material, namely, biochar, was considered as an additive. The prepared biopitch samples, containing different quantities of biochars, were analyzed for their softening point (SP), QI content, coking value (CV), molecular weight distribution, viscosity, surface tension, chemical groups, and surface composition, as well as their wettability with coke particles. The differences in texture and topography of different pitches, as well as the interface between pitch and aggregate particles in sessile drop after wettability test, were studied. The results revealed that increasing the quantities of biochars in biopitch increases their coking value, QI content, density, viscosity, and softening point. Furthermore, biochar addition only shows a minor influence on surface tension and molecular weight distribution of biopitch. An optimum amount (9.0 wt %) of biochar addition in biopitch could therefore be beneficial in anode formulation while using biopitch as a binder, compared to those of the reference anodes. The properties of the laboratory anodes (green/baked density, air/CO2 reactivity, compressive strength and electrical resistivity, carbon structure of the carbonized pitch) were investigated. Addition of biochar into biopitch could reduce the overall consumption of biopitch in the carbon anode formulation.

“…The penetration of the pitch into the coke pores is related to the rheological properties of the pitch. It has been reported that the CTP and bio-pitches behave as Newtonian fluids within the temperature range of 160–190 °C . It implies that the pitch viscosity does not vary with the shear rate at a constant temperature and pressure during the mixing stage.…”

Section: Resultsmentioning

confidence: 99%

“…It has been reported that the CTP and bio-pitches behave as Newtonian fluids within the temperature range of 160−190 °C. 17 It implies that the pitch viscosity does not vary with the shear rate at a constant temperature and pressure during the mixing stage. The surface tension of the pitch affects its wettability on the coke surface.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Properties of Bio-pitch and Its Wettability on Coke

et al. 2020

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Bio-pitch, driven from biomass, is a potential green alternative of coal-tar-pitch in the production of carbon anodes for the aluminum electrolysis process. Information on the wetting capacity of bio-pitch on the surface of the coke particle is of great interest in assessing its possible use as a renewable and environment-friendly binder. In this study, the wettability of various bio-pitches and one reference coal-tar-pitch on the same type of coke was investigated at a temperature of 178 °C using a sessile-drop setup. Bio-oil, the parental material of the bio-pitch, was produced by commercial pyrolysis from woody biomass. Postpyrolysis treatment was run to synthesize 10 different pitch samples from bio-oil, i.e., bio-pitches. Various techniques were used to analyze the physical and chemical characteristics of the bio-pitch samples and their interactions with coke. It was shown that the wettability of bio-pitch is highly influenced by its viscosity, surface tension, surface chemical functional groups, amount of quinoline insoluble, and molecular weight distribution.