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Hydroprocessing Of Low-temperature Coal Tar To Produce Jet Fuel

- Feb 08, 2019 -

In recent years, the decline of world oil resources and the rising trend of global oil prices have drawn more and more attention. Exploration of an alternative energy is urgently needed to ensure national defence safety and national interests. In this context, some alternative new energy sources such as bio-oil, shale oil and coal-derived liquid have been developed. However, there are still some problems with bio-oil, such as low heat value and fast aging, which restricts the development and application of industrialization.1 Coal tar is a by-product of coal processing and its output accounts for about 2.5–10% of coal. China has a large number of coal resources, which produce a large amount of coal tar each year. In 2015 alone, domestic coal tar production exceeded 10 million tons. However, coal tar is a complex mixture, which contains a large number of important industrial products. Since coal tar contains a lot of polycyclic aromatic hydrocarbons and hetero atoms, the extensive combustion will exert tremendous pressure on the environment, in addition, this has not achieved the rational utilization of coal tar. As an alternative to petroleum, coal tar is considered an ideal raw material for the preparation of clean fuels. On the one hand, it can solve the environmental problems, on the other hand, it can also improve the added value of coal resources by catalytic hydrogenation.

At present, the technology for hydrotreating LTCT to produce clean liquid fuels has achieved an enormous breakthrough, which also provides some technical support for the preparation of higher value-added oil products. With the rapid development of the aviation industry, the demand for jet fuel is increasing. For example, the consumption of jet fuel reached an astonishing 20 million tons in 2013, and the annual growth rate remained at about 13% in China. At present, jet fuel is mostly derived from petroleum refining, but it accounts for only about 6.3% of the crude oil. In the future, with the development of supersonic aircraft, higher requirements for jet fuel properties are required. However, petroleum-based jet fuel does not possess these properties, such as high density and better endothermic performance. Therefore, it is of great strategic significance to prepare coal-based jet fuel.

Compared with petroleum, coal tar has a significant difference. Specific as follows: polycyclic aromatic hydrocarbons and the content of heavy component is relatively large; there are more metals and nitrogenous compounds than petroleum, which causes the deactivation of the catalyst. Therefore, it is a huge challenge for coal tar to produce clean fuel. Hydroprocessing is considered as one of the most effective means of treating heavy oils, such as hydrofining, hydroisomerization, hydrocracking and catalytic cracking, etc., to meet the requirements of clean fuel by removing heteroatoms and saturated unsaturated hydrocarbons.22 Generally, the operation temperature of hydrocracking and catalytic cracking process is generally higher than 300 °C, which causes a higher coking rate and a large amount of C1–C4 light hydrocarbon. However, the composition of jet fuel is mostly C8–C15, and the content of aromatics is relatively low. In general, the heat value decreased in order alkane > cycloalkane > aromatic. In addition, olefins and aromatics were translated into alkanes (isoalkanes) and cycloalkanes via hydropressing, which improved the low-temperature fluidity and the heat value and so on of the oil products. For instance, the condensation point of the hexadecane and the naphthalene was 18.2 °C and 80.5 °C, while the condensation point of the 3-methylpentadecane and the c-decalin was −23 °C and −43 °C, respectively. Therefore, hydroisomerization is suitable process for preparation of jet fuel in this paper.