This work explores the use of carbon dioxide, water, and their mixtures as solvent for the precombustion beneficiation of raw coal without using any toxic mineral acids in the temperature range of 200–400 °C. The fluid polarity, ionic constant, and supercritical point can be adjusted by H₂O/CO₂ ratio and temperature. Adding carbon dioxide to hydrothermal fluid also increases the ionization by forming carbonic acid. Extractions with supercritical fluids have several benefits including enhanced mass transport, ease of separation and recycle, wide range of extractive capability and tunability, better inherent safety, and in the case of carbon dioxide and water–low cost. A semi-continuous extraction system was designed and built in which pressure, temperature and the relative flow rates of CO₂ and H₂O can be controlled. Coal powder is kept in a packed bed and the extraction is carried out at 143 bar pressure. Using sulfur as a model heteroatom, extractive efficiency is examined as a function of the temperature, fluid composition, fluid flow, and extraction time. The results indicate that carbon dioxide, water, and supercritical water-carbon dioxide (ScWC) all can effectively extract about 50% of total sulfur from bituminous coal in 1 h. Extraction above 350 °C decreased effectiveness, and extraction above the supercritical point of pure water caused hydrothermal carbonization. ScWC extraction may provide necessary control to prevent organic dissolution while removing sulfur.

这项工作探索了使用二氧化碳，水及其混合物作为溶剂进行原煤的预燃烧选矿，而没有使用200-400°C温度范围内的任何有毒无机酸。流体极性，离子常数和超临界点可以通过H ₂ O / CO ₂进行调节比和温度。将二氧化碳添加到热液中也会通过形成碳酸来增加电离作用。用超临界流体萃取具有许多好处，包括提高质量传递，易于分离和循环利用，广泛的萃取能力和可调性，更好的固有安全性以及二氧化碳和水的低成本。设计并构建了一个半连续萃取系统，其中压力，温度以及CO ₂和H ₂的相对流速O是可以控制的。将煤粉保存在填充床中，并在143 bar压力下进行提取。使用硫作为模型杂原子，根据温度，流体成分，流体流量和提取时间对提取效率进行了检查。结果表明，二氧化碳，水和超临界水-二氧化碳（ScWC）都可以在1小时内有效地从烟煤中提取约50％的总硫。在高于350°C的温度下萃取会降低有效性，而在纯水的超临界点以上萃取会引起水热碳化。ScWC萃取可提供必要的控制，以防止有机物溶解同时去除硫。