A process for the plasma-assisted treatment of coal in which coal is directly converted to heavy hydrocarbons. The first step in the process is direct conversion of coal to aliphatic hydrocarbons under plasma conditions in the presence of light hydrocarbons, such as natural gas. In the second process step, the aliphatic hydrocarbons are upgraded to a liquid fuel. The energy for the process can be provided by radio frequency energy, such as microwave energy, that is powered by a renewable energy source. The process has flexibility to adjust aromatic content in the fuel to match fuel specification requirements.