Utilization of Petroleum Coke Soot as Energy Storage Material

1. Introduction

Petroleum coke is often used as fuel for power generation in power plants and cement production mainly in China and India [ 1 ]. Recently, other countries are also constructing facilities using petroleum coke as a fuel to save energy cost, and its usage is gradually increasing [ 2 ]. For example, Egypt, which is the largest cement producer in the Middle East and North Africa region, has initiated the process of changing the fuel used in the various plants from gas to petroleum coke. Japan has increased the petroleum coke imports for the gasifier project, and a few plants in South Korea are also initiating the move to change the fuel from liquefied natural gas (LNG) to petroleum coke. [ 3 ] Furthermore, several other cases regarding the use of petroleum coke to reduce energy costs have been reported [ 4 5 ].

Another characteristic of petroleum coke that is drawing attention for use as a power generation fuel includes its calorific value, which is similar to those of Bunker C and LNG, which are the most commonly used fuels, and its energy price (cost per producing one ton of steam) is cheaper [ 6 ]. Moreover, because petroleum coke is the by-product in the process of refining and commercializing crude oils [ 7 11 ], refineries can provide long-term stable supplies of petroleum coke through the construction and extension of related facilities. The price stabilization based on this also contributes to the increasing use of petroleum coke [ 12 13 ].

Consequently, petroleum coke has become a fuel that cannot be ignored owing to the various reasons mentioned above. With an increase in the use of petroleum coke, the amount of soot and other by-products produced from the combustion of petroleum coke are also increasing, and methods to process them efficiently are being studied extensively.

To examine various research and development endeavors using the characteristics of petroleum coke soot, the Nanjing University in China reported a case where volume stability was achieved by adjusting the curing time of cement using the soot obtained from the circulating fluidized bed combustion of petroleum coke and coal. They published the result of the study and concluded that soot could be used as a good admixture, which allowed less water content [ 14 ]. Another study reported the application of the petroleum coke-mixed fuel to the development of the gasification technology through the slagging of petroleum coke soot using a mixture of anthracite and petroleum coke. With the development of the gasification technology, the use of various types of solid carbon fuels such as lignite and petroleum cokes has increased, and the results of a comparative study on the structural characteristics of soot generated using lignite, bituminous coal, and petroleum coke as fuels have been reported [ 15 ]. Additionally, a technology for the production of an anhydrous plaster substitute using the boiler combustion material of petroleum coke has been patented. As described above, many attempts are being made to develop technologies to recycle soot and by-products generated after using petroleum coke as fuel.

Therefore, our research team attempted to recycle petroleum coke soot as an anode active material for lithium ion batteries (LIBs), which has not been previously investigated. The materials of LIBs consist of anode materials, cathode materials, electrolytes, and separation membranes. The graphite-based carbon materials are typically used for anode materials [ 16 18 ]. As petroleum coke soot is known to be mainly composed of carbons, its value can be further increased by recycling the soot (which is a pollutant) as an energy storage material via reprocessing it as artificial graphite using the graphitization process. Hence, the soot generated after combustion in plants using petroleum coke as fuel was collected, annealed, and examined using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) analyses. These analyses were conducted on the samples collected before and after annealing. Furthermore, elemental analysis (EA) and thermogravimetric analysis (TGA) were performed to determine the residual impurities. Finally, the applicability of the petroleum coke soot was shown by testing the electrochemical performance of the LIB fabricated using the annealed soot as an anode material.