Chemical Engineering

Coal, an abundant raw material in both the U.S. and in many other parts of the world, has been considered as a suitable raw material for the production of coal oil, since the 1900s. Production of liquid fuels from coal is possible through a variety of conversion processes (e.g., Fischer−Tropsch synthesis, pyrolysis, or direct coal catalytic liquefaction) but one, in particular, hydrothermal liquefaction (HTL), often referred to as hydrous pyrolysis, is attractive due to its relatively low cost and ease of implementation. Direct coal liquefaction requires an addition of hydrogen and expensive catalysts, while a Fischer-Tropsch process is expensive and wastes a substantial amount of carbon in the form of carbon dioxide. Hydrothermal Liquefaction is a process that involves the use of subcritical liquid water in the absence of oxygen to artificially mature coal, kerogen and biomass

samples. Hydrothermal Liquefaction does not require sample drying since the reaction medium is water, saving valuable time and money. The process generates low molecular weight hydrocarbons, mainly alkanes. In this paper, the application of Hydrothermal Liquefaction simultaneously to mixtures of coal and biomass will be reviewed with the objective of generating partially carbon-neutral coal oil. With the use of coal in the U.S. dwindling for power generation, with consequent loss of jobs in several mid-western states, it is proposed to apply Hydrothermal Liquefaction to coal-waste biomass mixtures to generate partially carbon-neutral coal oil. While there is an excess of oil in the U.S. and refineries in the U.S. are operating at peak capacity, coal oil, manufactured in the U.S., can be exported to Asia, which has coal, but no oil and no natural gas. This strategy will allow U.S. to revive coal mining jobs in the U.S., balance the trade deficit with countries like China and decrease the sale of middle-east oil to Asia. Furthermore, the sale of partial carbon-neutral oil to Asia will allow Asian countries to meet their carbon emission goals as per the Paris Treaty on Global Warming. This paper will discuss the technical details of hydrothermal Liquefaction of various types of coal and compare the economics of the coal-oil produced with crude oil.