Getting Competitive Advantage from the Needle Coke Market

Question - Can high-grade needle coke (such as P66 or Seadrift) be used for synthetic graphite in EV battery anode materials? If the quality exceeds specifications and needs to be downgraded, is it easy to modify the needle coke manufacturing process? Or, is it easy to source lower-grade decant oil??

Response:

According to some forecasts, the needle coke market was evaluated 3,5 bilion US dollars in 2022 and is expected to reach 5,1 bilion US dollars in 2029 under an Compound Annual Growth Rate (CAGR) of 5,6 % in the period. This data shows the attractiveness of the needle coke market for refiners with adequate refining hardware as well as acess to adequate crude oil.

The needle coke production route from crude oil

The production of Ultra-Premium needle cokes based on heavy petroleum residuals is limited to FCCDO residuals as a precursor. Fluidised Catalytic Cracking (FCC) is a carbon rejection conversion technology using heavier residuals to produce lower molecular weight distillates. While FCC process conditions are not usually altered to enhance residual (FCCDO) quality it may be utilised as a bunker fuel viscosity cutter stock or as a needle coke precursor.

Fluid Catalytic Cracking (FCC) is one of the main processes which give higher operational flexibility and profitability to refiners. The catalytic cracking process was widely studied over last decades and became the principal and most employed process dedicated to converting heavy oil fractions in higher economic value streams.

The installation of catalytic cracking units allows the refiners to process heavier crude oils and consequently cheaper, raising the refining margin, mainly in higher crude oil prices scenario or in geopolitics crises that can become difficult the access to light oils.? The typical Catalytic Cracking Unit feed stream is gas oils from vacuum distillation process. However, some variations are found in some refineries, like sending heavy coke naphtha, coke gas oils and deasphalted oils from deasphalting units to processing in the FCC unit.

The catalyst normally employed in fluid catalytic cracking units is a solid constituted by small particles of alumina (Al2O3) and silica (SiO2) (zeolite). By the catalyst characteristics and the operational conditions in the catalytic cracking process (temperature higher than 500 °C), the process is inefficient to cracking aromatic compounds, therefore, how much more paraffinic is the feed stream, higher is the unit conversion. Figure 1 presents a process scheme for a typical Fluid Catalytic Cracking Unit (FCCU).?

In a conventional scheme, the catalyst regeneration process consists in the carbon partial burning deposited over the catalyst, according to chemical reaction below:

C + ? O2 → CO

The carbon monoxide is burned in a boiler capable of generating higher pressure steam that supplies others process units in the refinery.

Figure 1 – Schematic Process Flow for a Typical Fluid Catalytic Cracking Process Unit (FCCU)

The principal operational variables in a fluid catalytic cracking unit are reaction temperature, normally considered the temperature in the top of the reactor (called riser), feed stream temperature, feed stream quality (mainly carbon residue), feed stream flow rate and catalyst quality. Feedstock quality is especially relevant, but this variable is a function of the crude oil processed by the refinery, so is difficultly can be changed, but for example, aromatic feedstock’s with high metals content are refractory to cracking and conducting to a quick catalyst deactivation.?

An important variation of the fluid catalytic cracking technology is the residue fluid catalytic cracking unit (RFCC). In this case, the feedstock to the process is basically residue from atmospheric distillation column, due to the high carbon residue and contaminants (metals, sulphur, nitrogen, etc.) are necessary some adaptations in the unit like catalyst with higher resistance to metals and nitrogen and catalyst coolers furthermore, it’s necessary apply materials with most noble metallurgy due the higher temperatures reached in the catalyst regeneration step (due the higher coke quantity deposited on the catalyst), that raises significantly the capital investment to the unit installation. Nitrogen is a strong contaminant to the FCC catalyst because they neutralize the acid sites of the catalyst which are responsible for the cracking reactions.??

When the residue has high contaminants content, is common the feed stream treatment in hydrotreating units to reduce the metals and heteroatoms concentration to protect the FCC catalyst.

Typically, the average yield in fluid catalytic cracking units is 55% in volume in cracked naphtha and 30 % in LPG.? Figure 2 presents a scheme for the main fractionator of the FCC unit with the principal product streams.?

Figure 2 – Main Fractionator Scheme for a Typical Fluid Catalytic Cracking Unit

The decanted oil stream contains the heavier products and have high aromatic content, is common that this product are contaminated with catalyst fines and normally this stream is directed to use like fuel oil diluent, but in some refineries, this stream can be used to produce black carbon.

Light Cycle Oil (LCO) has a distillation range close to diesel and normally this stream is directed to treatment in severe hydrotreating units (due to the high aromaticity), after this treatment the LCO is sent to the refinery diesel pool.

Heavy cracked naphtha is normally directed to refinery gasoline pool, however, in scenarios where the objective is to raise the production of middle distillates, this stream can be sent to hydrotreating units for further diesel production.

Refiners focused to produce high quality needle coke tend to operate their FCC units optimized to maximize the Decanted Oil (DO) due the high aromaticity. This is the less common operation mode in FCC units, where the main objective is to maximize the yield of decanted oil and achieve the quality requirements of aromatic residue. The aromatic residue is normally applied to produce black carbon, these derivative presents great demand in some markets.

The main difficulty to comply with the aromatic residue specification is regarding to ash content in the decanted oil. This parameter is strictly related to the cyclones efficiency in the catalyst regeneration section, to achieve this objective some refiners apply additives to promote de ash decantation in the final tanks or specific filtration systems that requires more capital spending.

Another key quality parameter to meet aromatic residue specification is the BMCI (Bureau of Mines Correlation Index) that is related to the aromaticity of the decanted oil, to achieve the current specifications of black carbon it’s necessary to achieve a minimum BMCI higher than 120. The BMCI is calculated based on viscosity of the decanted oil at the temperature of 210 °F. The metals content in the decanted oil needs to be also controlled, especially, sodium, aluminium, and silicon.

The operating severity in maximum aromatic residue mode tends to be high with high TRX, high catalyst/Oil ratio, and high catalyst activity. As side effect is observed the raise of octane number in cracked naphtha due to the incorporation of aromatics compounds in this intermediate.

In maximum aromatic residue operation mode the main restrictions are the temperature of the bottom section in the main fractionators that can lead to coke formation, metallurgic limitations in the hot sections as well as the capacity of blowers and cold area compressors.

The use of FCCDO as a needle precursor in a Delayed Coker Unit (DCU) is determined by a multitude of factors:

·??????? The relatively high temperature (approximately 700°C) of the FCC reaction promotes aromaticity (although not to the same degree as HT-CTP). Thus long chain alkyl functions may persist on the aromatic ring structure leading to steric hindrance during polycondensation and a reduction of microstructural order during delayed coking

·??????? As a carbon rejection conversion process, FCC is dehydrogenative. While this favours aromatisation, it may additionally lead to the production of olefins or conjugated dienes which are known to promote crosslinking during delayed coking leading to microstructural defects and a higher coke CTE. However, olefin formation is usually associated with lighter distillates and its effect on heavier residual molecules may not be so profound

·??????? The reference to Vanadium (V) and Nickel (Ni) impurities in Table 1 would (based on an initial assessment) seem out of place. However, it holds considerable value as both Ni and V are bound as organo-metallics (and not inorganically as with other metallic contaminants). Thus Ni and V pyphorins cannot be extracted using traditional filtration methods. The only unintended (and undesirable) refinery reaction to reduce the Ni / V content is through hydrocracking (when Ni and V deposit on the Nickel-Molybdenum fixed bed catalyst reducing activity)

·??????? The formation of coke on the fluidised bed FCC catalyst causes significant deactivation and is an undesirable reaction. However, it does serve to initiate polycondensation of thermally reactive species (asphaltenes and unstable hydrocarbons) forming coke on the catalyst. It thus leaves a thermally stable residual (FCCDO) which is highly desirable during the coking reaction resulting in greater microstructural order

·??????? The prevalence of sulphur heterocycles may form three dimensional structures providing steric hinderance (also known as ONS Obstruction) disrupting the formation of an ordered microstructure

·??????? The thermal stability of sulphur heterocycles result in their incorporation in the coke matrix, even surviving calcination (1350°C). However, within the electrode graphitisation cycle (between 1500°C and 1800°C), sulphur dissociates (CS2) causing irreversible volumetric expansion potentially causing electrode cracks due to the puffing reaction. The market dominance of petroleum-based needle cokes has meant that the study of sulphur puffing inhibitors (e.g. borates, iron oxides and sodium carbonates) has received greater attention

·??????? A potential concern with FCCDO is the incorporation of the catalyst (alumina-silicates) in the DCU feed. As with other metal complexes they can disrupt the crystalline structure by forming obstruction to microstructural order and resulting in an increased CTE

Petroleum based needle cokes are typically associated with lighter, sweeter crude oil. Refineries are increasingly having to process cheaper, heavier and higher sulphur crudes. This substantially increases the concentration of thermally stable sulphur heterocycles presenting both in the FCCDO and ultimately in the coke (eventually contributing to increased electrode puffing). However, perhaps more of an immediate impact is the competition for low sulphur crude oil derivatives from the bunker fuel market. From 1 January 2020, the International Maritime Organization (IMO) requires ships to reduce their SOx emissions. Thus in accordance, the sulphur content of marine fuels has been reduced from a 3.5% max to 0.5% max. This will result in substantial refinery reforms away from Heavy Fuel Oil (HFO) towards lower sulphur lighter fuels (e.g. Marine Gas Oil [MGO] or Very Low Sulphur Fuel Oil [VLSFO]) at least over the medium term. This will lead to increased competition for the downstream refinery products associated with lighter sweeter crude oils, increasing the value of these residuals.

Future quality assurance measures will very much relate to the nature of the crude oil and development of the FCC process to further ensure consistent precursor characteristics.

Dr. Marcio Wagner da Silva is Process Engineer and Stockpiling Manager on Crude Oil Refining Industry based in S?o José dos Campos, Brazil. Bachelor’s in chemical engineering from University of Maringa (UEM), Brazil and PhD. in Chemical Engineering from University of Campinas (UNICAMP), Brazil. Has extensive experience in research, design and construction to oil and gas industry including developing and coordinating projects to operational improvements and debottlenecking to bottom barrel units, moreover Dr. Marcio Wagner have MBA in Project Management from Federal University of Rio de Janeiro (UFRJ), in Digital Transformation at PUC/RS, and is certified in Business from Getulio Vargas Foundation (FGV).