Development of a thermodynamic model for carbon crystallites and their impurities

碳微晶是由层叠的石墨烯层形成的。它们的大小由平均微晶长度(LC)来表征，这通常在纳米范围内。它们构成了用于铝生产的Hall-Heroult工艺中使用的碳阳极(在焙烧焦炭中)和石墨阴极的大部分。它们也存在于锂电池的石墨阳极中。在霍尔-赫鲁特工艺中，每年使用数百万吨碳阳极。硫是这些阳极中的主要杂质(通常为2-4wt.%)，来自石油焦炭。在焦炭焙烧过程中，在加工碳阳极之前，碳微晶正在形成，硫和其他杂质(H、Na、Ca等)正在形成。都与他们建立了联系。最终，硫在这个过程中被消耗，并被氧化并排入大气。但与此同时，焦炭中的硫和几种杂质正或负地参与了碳被空气和二氧化碳氧化的催化作用。这个项目的短期目标是获得一个吉布斯能量函数形式的碳微晶及其主要杂质(S，氢，钠，…)的热力学模型。在铝工业使用的碳材料中发现。该模型依赖于杂质的质量分数、温度、总压力和平均微晶长度(LC)。这包括硫在石墨烯层(S，H)末端C原子中的吸附以及与Na、Li和K形成的所谓的石墨层间化合物。该模型将与微晶结构有关，旨在用于研究焦炭焙烧、阳极焙烧和电解(阳极+阴极)过程中碳材料中杂质的行为。该模型也可用于锂电池的应用。本项目的长期目标是将上述模型与碳材料(基于C-S-O-Na-K-Ca-Fe-Ni-Al-F的盐和氧化物)申请者已经获得的其他热力学模型相耦合，以获得对Hall-Heroult工艺中阳极的超额碳消耗(25%-40%)的过程建模能力，从而减少能源和环境影响。

Carbon crystallites are formed of stacks of graphene layers. Their size is characterized by the average crystallite length (Lc), which is typically in the nanometric range. They compose the majority of carbon anodes (in the calcined coke) and graphite cathodes used in the Hall-Heroult process for aluminum production. They are also present in graphite anodes in lithium batteries. In the Hall-Heroult process, millions of tons of carbon anodes are used every year. Sulfur is a major impurity in these anodes (typically 2-4 wt.%), coming from petroleum cokes. During coke calcining, done before processing the carbon anodes, the carbon crystallites are being formed, and sulfur and other impurities (H, Na, Ca, etc.) are bonding to them. Ultimately, sulfur is being consumed in the process and is oxidized and rejected to the atmosphere. But in the meantime, sulfur and several impurities in the coke are taking part positively or negatively in the catalysis of carbon oxidation by air and by CO2. The short-term objective of this project is to obtain a thermodynamic model, in the form of a Gibbs energy function, for carbon crystallites and their major impurities (S, H, Na, ...) found in carbon materials used by the aluminum industry. The model will be dependent on the mass fractions of the impurities, the temperature, the total pressure, and the average crystallite length (Lc). This includes the attachment of sulfur in the terminal C atoms of the graphene layers (S, H) and the so-called graphite intercalation compounds formed with Na, Li and K. The model will be related to the structure of the crystallites, and is intended to be used for the behavior of impurities in carbon materials as a function of operating conditions during coke calcining, anode baking and electrolysis (anode + cathode). The model can also be used in Li batteries applications. The long-term objective of this project is to couple the above model with other thermodynamic models already obtained by the applicant for inorganic impurities in carbon materials (salts, oxides based on C-S-O-Na-K-Ca-Fe-Ni-Al-F) to gain process modeling capabilities of the excess carbon consumption (25-40%) of anodes in the Hall-Heroult process, thus reducing the energy and the environmental impacts.