Development of a thermodynamic model for carbon crystallites and their impurities

碳微晶由石墨烯层的堆叠形成。 它们的尺寸由平均微晶长度（Lc）表征，其通常在纳米范围内。 它们构成了用于铝生产的Hall-Heroult工艺中的大部分碳阳极（在煅烧焦炭中）和石墨阴极。 它们也存在于锂电池的石墨阳极中。 在Hall-Heroult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2-4重量%），来自石油焦 在处理碳阳极之前进行的焦炭煅烧期间，形成碳微晶，并且硫和其他杂质（H、Na、Ca等）被氧化。与他们建立了联系 最终，硫在该过程中被消耗，并被氧化和排放到大气中。 但与此同时，焦炭中的硫和几种杂质正或负地参与空气和CO2对碳氧化的催化作用。该项目的短期目标是获得碳微晶及其主要杂质（S，H，Na，.）的吉布斯能函数形式的热力学模型。在铝工业使用的碳材料中发现。 该模型将取决于杂质的质量分数、温度、总压力和平均微晶长度（Lc）。 这包括硫在石墨烯层（S，H）的末端C原子中的附着以及与Na，Li和K形成的所谓的石墨插层化合物。 该模型将与微晶的结构相关，并且旨在用于在焦炭煅烧、阳极焙烧和电解（阳极+阴极）期间作为操作条件的函数的碳材料中的杂质的行为。 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申请人已经获得的碳材料中无机杂质（基于C-S-O-Na-K-Ca-Fe-Ni-Al-F的盐、氧化物）的其他热力学模型相结合，以获得Hall-Heroult工艺中阳极过量碳消耗（25-40%）的工艺建模能力，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.