Coal pitch is a residue obtained from the distillation of coal tar, which is mainly composed of aromatic compounds, with a complex chemical structure and a variety of impurities. When coal pitch is heated to a certain temperature, a pyrolysis reaction will occur, producing a series of substances.
First of all, coal pitch will decompose light hydrocarbons such as methane, ethane, propane, etc. during the heating process. These light hydrocarbons usually have a lower boiling point and a lower molecular weight, so they can volatilize at lower temperatures.
As the temperature increases, the heavy components in the coal pitch begin to decompose, producing more hydrocarbon compounds, such as benzene, toluene, xylene, etc. These compounds have a high boiling point and molecular weight and require a higher temperature to volatilize.
In addition, coal pitch also contains some oxygen-containing, nitrogen-containing and sulfur-containing compounds, such as phenols, pyridines, quinolines and mercaptans. These compounds also decompose during heating, producing the corresponding oxides, nitrides, and sulfides.
In addition to the above-mentioned hydrocarbon compounds and heteroatom-containing compounds, coal pitch heating also produces some free radicals and active species, such as hydrogen radicals, methyl radicals and oxygen radicals. These free radicals and active species are highly reactive and can chemically react with other components in coal pitch to produce more substances.
In general, coal pitch emits a variety of substances when heated to a certain temperature, including light hydrocarbons, heavy hydrocarbons, heteroatom-containing compounds, as well as free radicals and active species. These substances not only cause certain harm to the environment and human health, but also may cause corrosion and damage to industrial production and equipment. Therefore, in the process of processing and utilization of coal asphalt, corresponding measures need to be taken to reduce the generation and emission of harmful substances and protect the environment and human health.