Liquid Transportation Fuels From Nova Scotia Coals
Authors: Starzomski J.J. 
Published: March 2010

This paper provides an introduction to the various processes for the liquefaction of coal, including pyrolysis, solvent extraction catalytic hydrogenation and indirect conversion. It then goes on to describe the Scotia Coal Synfuels Project, the Initial phases of which are currently underway.

Introduction

The utilization of coal in Canada and the United States will increase significantly over the next several decades in an effort to reduce our dependence on foreign oil sources. This strategy combined with a delicate supply/demand balance for petroleum products has prompted considerable interest in the production of liquid fuels from coal. During the past fifty years, technological advances in coal conversion have been made in several countries around the world. The objective of this paper is to discuss briefly the methods of converting coal into liquid fuels and outline the activities of the Scotia Coal Synfuels Project, a consortium of five major Canadian companies formed to determine the feasibility of producing liquid transportation fuels from the indigenous coal resources of Cape Breton.

Coal has a much lower atomic ratio of hydrogen to carbon than natural petroleum. Therefore, in order to liquefy coal it is essential to increase the hydrogen-to-carbon ratio to higher levels typical of liquid fuels. However, increasing the hydrogen content of coal to + 10% does not mean that the liquids that are produced will be similar or have the same uses as petroleum-derived liquids of the same hydrogen content. The basic reason for this is that petroleum-derived liquids are mostly straight-chain molecules which are termed aliphatic, whereas those derived from coal are mostly ring-type molecules which are called aromatic.

The ring-type structure of coal liquids is directly related to the fundamental structure of coal itself. Although the structure of coal is complex, there is a rather general agreement that the skeletal structure of bituminous coal is mostly aromatic. Recent work indicates that ring clusters range from one to perhaps seven rings, the average cluster being comprised of about three rings(l). It is known that about 70% of all carbon atoms are in aromatic rings, but only about 23% of the hydrogen atoms are bound to aromatic carbon atoms(2). The aromatic and hydroaromatic carbons form the skeletal structures aliphatic carbon is found in side-chains and bridges connecting the clusters.

Process Schemes to Produce Coal Liquids

Known processes for converting coal into liquid fuels can be classified into four broad categories: pyrolysis, solvent extraction, catalytic hydrogenation and indirect liquefaction. These approaches to liquefaction differ primarily in the degree of processing severity.

Pyrolysis

Pyrolysis, also known as destructive distillation or carbonization, is the least severe approach.

(Figure in full paper)

general process scheme. Pyrolysis involves the heating of coal in the absence of air or oxygen to yield liquids, gases and char. In this method, the hydrogen-to-carbon ratio is increased because carbon is removed from the system as a solid residue.