Coal tar is one of the products of crude gas generated by coal pyrolysis in coking industry, and its output accounts for about 3% to 4% of the furnace coal. Its composition is extremely complex, and in most cases it is specially separated and purified by coal tar industry. At room temperature and atmospheric pressure, the product is black viscous liquid, and each fraction can be further processed to separate a variety of products, such as mothballs, asphalt, plastics, pesticides and so on.