PTQ Q4 2022 Issue

from China. This demand decline has exerted downwards pressure on needle coke pricing to under $1000 per tonne. However, in 2018-2020, there has been a resurgence in the demand for needle coke and associated pricing, which, although sluggish, has rebounded with sustained growth. The demand for needle coke is witnessed by the substan- tial ramp-up of Chinese EAF capacity. The demand has further been impacted by market diversification based on the exponential growth of the EV automotive sector (needle coke is utilised for the produc- tion of synthetic graphite anodes in lithium ion batteries). Competition as an EV battery graphite source is provided by natural graphite, which, while commanding a lower price, is also associated with lower comparative quality (higher natural impurities). The sustained requirement for graphite for the EV market is demonstrated by the fact that the Tesla Model S contains up to 85 kg of graphite. While the growth of the EV market has been exponential, it has been off a small base. Growth of the EV market is expected to command a 30% automotive market share by 2030. To demonstrate the expected impact of this sector (on needle coke demand), a 6% EV growth would relate to a 250 kilo-tonne per annum (ktpa) demand increase. The comparative demand from the graphite electrode market has historically remained stable at approximately one mil- lion tpa. Competition for the battery market between natural and synthetic (needle coke-based) graphite will depend on a variety of factors. Compared to synthetic graphite, natural graphite is: • More abundant with a simplified mining process flow • The inherent ash content is comparatively high, requiring substantial floatation and purification • The effect of purification to remove impurities may leave voids affecting both microstructural order and density • Natural graphite purity is linked to price, which has his- torically been comparatively lower • Purified natural graphite exhibits a larger BET surface area, which may be associated with the removal of impuri- ties. While this may be beneficial, especially in light of bat - tery applications, both the impurities themselves and their removal introduce crystalline imperfections, limiting elec- tronic performance characteristics. One of the determining choice factors between natural or synthetic (coal tar or petroleum-based) graphite is the cost of purification steps required to enhance purity and thus operational performance. The majority of these contami- nants (for example, nitrogen, sulphur, ash, and semi-car- bonaceous MIQ) find their origin at the source of the value chain. Most contaminants act as physical occlusions, lead- ing to crystalline imperfections and microstructural defects during the phase transition between liquid and solid hydro- carbons (during delayed coking). After this, further thermal treatment or purification pro - cesses only amplify these imperfections and translate to restricted electronic properties and an elevated CTE. Finding a graphite precursor that naturally excludes these contaminants would produce a higher purity needle coke and improved performance with lower process costs.

Ultra

Super

Intermediate

Premium

Premium

Premium

CTE value, x 10 -⁶/ºC Sulphur content, wt% Nitrogen content, wt% V/Ni content, ppm Ash content, wt% Real denisty, g/cm³ Hydrogen content, wt%

0.25

0.35

0.6

Trace Trace Trace

0.2-0.4

0.4-0.6

<0.2

<0.3

<10

<10

<0.1 2.15

<0.2

<0.3

2.13-2.15

2.13-2.14 0.03-0.05

Trace

0.03-0.05

Table 1 Calcined needle coke specifications (Reproduced in part from Lee, C W et al 2013 and Clark, J 2011)

electrodes. Petroleum-based needle cokes have historically dominated the market; however, all recent expansion initia- tives in China are based on coal-tar needle cokes (which have historically been plagued by inconstant quality and problematic electrode graphitisation). A diagram showing highly ordered needle coke microstructure with parallel aligned porosity is shown in Figure 1 . Being a speciality and derived from a by-product, needle coke exhibits a concentrated supply structure. There are around 10 major producers globally, while most refineries do not have delayed cokers (especially those suitable for needle coke production) or calciners. Following delayed coking (450-480°C), the green needle coke is calcined (1350°C) to reduce volatiles and promote microstructural densification. The science associated with the needle coke value chain is complex and beyond the scope of this discussion, which merely serves to introduce the topic. Needle coke: a resurgent market Over the last decade, the appetite for needle coke has diminished, given the abundance of scrap steel emanating

Pore

Pore

Figure 1 Diagram of the microstructure of highly ordered needle coke 13

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PTQ Q4 2022

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