Recovering Maximum Added Value from Crude Oil – The Residue Upgrading Technologies Based on Hydrogen Addition

Introduction and Context

The hard scenario faced by the whole oil and gas industry requires alternatives routes to ensure maximum added value to crude oil. The downstream sector faces with a transitive period where the focus change from transportation fuels to petrochemicals put under pressure the refining margins and competitiveness, mainly to refiners relying on refining hardware with low complexity and poor capacity of bottom barrel conversion and capable to produce lower yields of added value derivatives. In the current scenario, the players of the downstream sector can consider capital investments aiming to achieve higher operational flexibility and achieve the capacity to processing heavier crude slates, improving his refining margins once these crudes present low cost when compared with lighter crude oils or, in some cases, there is a great availability of heavy crudes.

In this scenario, process units capable to add value to bottom barrel streams, able to improve the quality of crude oil residue streams (Vacuum residue, Gas oils, etc.) or convert them to higher added value products gain strategic importance, mainly in countries that have large heavy crude oil reserves like Venezuela, Canada, and Mexico. These process units are fundamental to comply with the environmental and quality regulations, as well as to ensure the profitability and competitiveness of refiners through raising the refining margin. The necessity to add value to bottom barrel streams raised, even more, after January of 2020 when started the IMO 2020 which requires a deep reduction in the sulfur content of the marine fuel oil (Bunker) from 3,5 % (m.m) to 0,5 % (m.m).

Available technologies to processing bottom barrel streams involve processes that aim to raise the H/C relation in the molecule, either through reducing the carbon quantity (processes based on carbon rejection) or through hydrogen addition. Technologies that involve hydrogen addition encompass hydrotreating and hydrocracking processes while technologies based on carbon rejection refer to thermal cracking processes like Visbreaking, Delayed Coking, and Fluid Coking, catalytic cracking processes like Fluid Catalytic Cracking (FCC) and physical separation processes like Solvent Deasphalting units. Despite the alternative of carbon rejection technologies and their relatively low capital cost, these technologies limit the operational flexibility of the refining hardware mainly related to the processed crude oil, requiring that the refiner choose crude oils with low sulfur contents which normally presents higher costs. Although the hydrogen addition technologies like deep hydrotreating and hydrocracking presents higher capital requirement, these technologies can offer a highlighted competitive advantage among the refiners, especially considering the scenario of the downstream industry post IMO 2020. 

Hydrogen Addition Technologies – An Overview

Normally, the hydroprocessing is applied to distillates streams like naphtha, kerosene, and diesel, however, the growing of heavier (and high contaminants content) crude oil reserves have been lead to a higher relevance of the hydroprocessing of bottom barrel streams to the downstream industry.

The hydrotreating process (less severe hydroprocessing) involves a series of chemical reactions between hydrogen and organic compounds containing the contaminants (N, S, O, etc.). According to the target contaminant of the hydrotreating, the process can be called hydrodesulfurization (removing S), hydrodenitrogenation (removing N), hydrodeoxygenation (removing O) or hydrodearomatization when the main objective is to saturate of aromatic compounds, among others.

The most common hydrotreating forms are hydrodesulfurization (where the objective is to remove compounds like benzothiophene, dibenzothiophene, etc.) and the hydrodenitrogenation (removing porphyrins, quinolines, etc.) These compounds, besides provoke emissions of SOx and NOx when are burned, produce in the derivates acidity, color, and chemical instability.

The main chemical reactions associated with the hydrotreating process are represented below:

R-CH=CH2 + H2 → R-CH2-CH3 (Olefins Saturation)

R-SH + H2 → R-H + H2S (Hydrodesulfurization)

R-NH2 + H2 → R-H + NH3 (Hydrodenitrogenation)

R-OH + H2 → R-H + H2O (Hydrodeoxigenation)

Where R is a hydrocarbon.

The hydroprocessing of residual streams presents additional challenges when compared with the treating of lighter streams, mainly due to the higher contaminants content and residual carbon (RCR) related with the high concentration of resins and asphaltenes in the bottom barrel streams. Figure 1 shows a schematic diagram of the residue upgrading technologies applied according to the metals and asphaltenes content in the feed stream. 

Figure 1 – Residue Upgrading Technologies According to the Contaminants Content (Encyclopedia of Hydrocarbons, 2006)

Higher metals and asphaltenes content lead to a quick deactivation of the catalysts through high coke deposition rate, catalytic matrix degradation by metals like nickel and vanadium or even by the plugging of catalyst pores produced by the adsorption of metals and high molecular weight molecules in the catalyst surface. By this reason, according to the content of asphaltenes and metals in the feed stream are adopted more versatile technologies aiming to ensure an adequate operational campaign and an effective treatment.

To demonstrate the mechanism of catalyst plugging, Figure 2 presents a scheme of reactants and products flows involved in a heterogeneous catalytic reaction as carried out in the hydroprocessing treatments.  

Figure 2 – Reactants and Products Flows in a Generic Porous Catalyst (GONZALEZ, 2003)

In order to carry out the hydroprocessing reactions, it’s necessary the mass transfer of reactants to the catalyst pores, adsorption on the active sites to posterior chemical reactions and desorption. In the case of bottom barrel streams processing, the high molecular weight and high contaminants content require a higher catalyst porosity aiming to allow the access of these reactants to the active sites allowing the reactions of hydrodemetallization, hydrodesulfurization, hydrodenitrogenation, etc. Furthermore, part of the feed stream can be in the liquid phase, creating additional difficulties to the mass transfer due to the lower diffusivity. To minimize the plugging effect, in fixed bed reactors, the first beds are filled with higher porosity solids without catalytic activity and act as filters to the solids present in the feed stream protecting the most active catalyst from the deactivation (guard beds).

The process conditions are severer in the residue hydrotreating. The feed stream characteristics lead to a strong tendency of coke deposition on the catalyst requiring higher hydrogen partial pressures (until 160 bar to fixed bed reactors) and higher temperatures (400 – 420 oC).

Bottom barrel streams hydroprocessing can be applied aiming to prepare the feed stream for another deep conversion processes like FCC and RFCC, it’s also common apply high severity hydrotreating process units to reduce the contaminants content to the processing in hydrocracking units, with the objective to protect the hydrocracking catalyst. The gas oil hydrotreating is very common in the preparation of feed stream to fluid catalytic cracking units (FCC) aiming to control the content f sulfur, metals and nitrogen as well as promote the opening of aromatics rings that are refractory of the catalytic cracking reactions.  Figure 3 presents a basic process flow diagram for a typical high severity hydrotreating unit.

The hydrotreating process is normally conducted in fixed bed reactors and the most applied catalysts are Cobalt (Co), Nickel (Ni), Molybdenum (Mo) and Tungsten (W), commonly in association with then and supported in alumina (Al2O3).  The association Co/Mo is applied in reactions that need lower reaction severity like hydrodesulfurization, while the catalyst Ni/Mo is normally applied in reactions that need higher severity, like hydrodenitrogenation and aromatics saturation. To the hydrotreating of bottom barrel streams (vacuum gas oil, delayed coking gas oil, etc.), due to the higher severity needed, is applied Nickel-Molybdenum (Ni-Mo) catalysts. 

Figure 3 – Basic Process Flow Diagram for High Severity Hydrotreating Process Units

Among the bottom barrel streams hydrotreating technologies we can quote the process Aroshift? developed by Haldor Topsoe Company, the Unionfining? process developed by UOP Company, the Hyvahl? technology by Axens Company and the RHU? process by Shell Company.

The residue hydroprocessing also can be realized through hydrocracking process units according to the feed stream characteristics and the chosen refining configuration. Table 1 presents the main differences between the hydrotreating and hydrocracking processes.  

As presented in Figure 1, streams with higher contaminants content, especially metals, requires treatment by hydrocracking. As aforementioned, in some refining schemes, hydrotreating units can be applied to prepare the feed stream to hydrocracking units aiming to control the concentration of metals and nitrogen and protect the hydrocracking catalysts that normally have high cost. Figure 4 presents a typical hydrocracking process unit with two reaction stage. 

Figure 4 – Typical Arrangement for Two Stage Hydrocracking Units

The process unit presented in Figure 4 relies on intermediate separation of gases between the reaction stages. This configuration is adopted when the contaminants content (especially nitrogen) is high, in this case, the catalyst deactivation is minimized through the reduction of NH3 and H2S concentration in the reactors. Among the main hydrocracking process technologies available commercially we can quote the process H-Oil? developed by Axens Company, the EST? process by ENI Company, the Uniflex? Processes by UOP, and the LC-Fining? technology by Chevron Company. Figure 5 presents a typical process flow diagram for a LC-Fining? process unit, developed by Chevron Lummus Company while the H-Oil? process by Axens Company is presented in Figure 6.

Figure 5 – Process Flow Diagram for LC-Fining? Technology by CLG Company (MUKHERJEE & GILLIS, 2018)

Catalysts applied in hydrocracking processes can be amorphous (alumina and silica-alumina) and crystalline (zeolites) and have bifunctional characteristics, once the cracking reactions (in the acid sites) and hydrogenation (in the metals sites) occurs simultaneously. 

Figure 6 – Process Flow Diagram for H-Oil? Process by Axens Company (FRECON et. al, 2019)

The active metals used to this process are normally Ni, Co, Mo and W in combination with noble metals like Pt and Pd. The hydrocracking process is normally conducted under severe reaction conditions with temperatures that vary to 300 to 480 oC and pressures between 35 to 260 bar.

It’s necessary a synergic effect between the catalyst and the hydrogen because the cracking reactions are exothermic and the hydrogenation reactions are endothermic, so the reaction is conducted under high partial hydrogen pressures and the temperature is controlled in the minimum necessary to convert the feed stream. Despite these characteristic, the hydrocracking global process is exothermic and the reaction temperature control is normally made through cold hydrogen injection between the catalytic beds as well as occurred in the hydrotreating processes.

Due to the severe operational conditions, the operational costs tends to be higher to the bottom barrel hydroprocessing units when compared with units dedicated to treat distillate streams (Diesel, Kerosene, and Nafta). The most intense hydrogenation process led to most robust catalytic bed cooling systems (quench), higher hydrogen replacing rates and complexes phase separation systems (multiple stages).

An improvement in relation of ebullated bed technologies is the slurry phase reactors, which can achieve conversions higher than 95 %. In this case, the main available technologies are the HDH? process (Hydrocracking-Distillation-Hydrotreatment), developed by PDVSA-Intevep, VEBA-Combicracking Process (VCC)? commercialized by KBR Company, the EST? process (Eni Slurry Technology) developed by Italian state oil company ENI, and the Uniflex? technology developed by UOP Company. Figure 7 presents a basic process flow diagram for the VCC? technology by KBR Company.

Figure 7 – Basic Process Arrangement for VCC? Slurry Hydrocracking by KBR Company (KBR Company, 2019)

In the slurry phase hydrocracking units, the catalysts in injected with the feedstock and activated in situ while the reactions are carried out in slurry phase reactors, minimizing the reactivation issue, and ensuring higher conversions and operating lifecycle. Figure 8 presents a basic process flow diagram for the Uniflex? slurry hydrocracking technology by UOP Company.

Figure 8 – Process Flow Diagram for Uniflex? Slurry Phase Hydrocracking Technology by UOP Company (UOP Company, 2019).

Aiming to meet the new bunker quality requirements, noblest streams, normally directed to produce middle distillates can be applied to produce low sulfur fuel oil, this can lead to a shortage of intermediate streams to produce these derivatives, raising his prices. The market of high sulfur content fuel oil should strongly be reduced, due to the higher prices gap when compared with diesel, his production tends to be economically unattractive.

The Residue Desulfurization Strategy – Valuation of Heavy and Sour Crudes

           One of the technologies that have been widely considered in the downstream industry in the IMO 2020 scenario the desulphurization of atmospheric residue, aiming to allow not only the compliance with the new regulation but the quality improvement of the other derivatives and reliability of the downstream process units like FCC or hydrocracking. As presented in Figure 9, the atmospheric residue corresponds to the bottom stream of the atmospheric crude oil distillation column.  

Figure 9 – Typical Process Arrangement of Atmospheric Crude Oil Distillation Unit. 

Once heteroatoms like sulfur, nitrogen, and metals tend to concentrate in the heavier fractions of the crude oil, the atmospheric residue drags a major part of the contaminants present in the crude oil. Considering the current quality and environmental requirements over the derivatives, posterior treatments are required aiming to reduce the contaminants content (mainly sulfur and nitrogen) in the derivatives. 

           Before to 2020, the production of marine fuel oil (BUNKER) involved basically the dilution of vacuum residue (bottom barrel stream from vacuum distillation column) or deasphalted oil (to refiners that rely on solvent deasphalting unit in the refining scheme) with lighter streams like LCO (Light Cycle Oil) and gas oils, as presented in Figure 10. 

Figure 10 – Marine Fuel Oil (BUNKER) Production Process. 

The IMO 2020 made necessary a better control of the sulfur content in the streams applied as diluents in the BUNKER production, to refiners with high bottom barrel conversion capacity the control of the sulfur content in the vacuum residue through the atmospheric residue applying hydrodesulphurization minimizes the necessity of treatment of other streams as well as can avoid the use of noblest streams like diesel and jet fuel as diluents in the BUNKER production.

The hydrodesulphurization process of atmospheric residue presents additional technologic challenges when compared with the hydrotreating process applied to final derivatives like diesel and gasoline, considering the high contaminants content, mainly metals, and the residual carbon due to the high concentration of resins and asphaltenes in the feed stream. Beyond the sulfur removal, the main goal, the atmospheric residue hydrodesulphurization unit promotes the partial removal of metals, nitrogen and residual carbon (CCR) through catalytic hydrogenation mechanism. Due to the high contaminants content in the feed, the residue hydrodesulfurization units rely on guard reactors upstream of the desulfurization reactors aiming to reduce the contaminants content, preserve the activity of the desulfurization catalysts, and improve the lifecycle of the whole unit. Figure 11 presents a typical arrangement of a residue desulfurization unit.

Figure 11 – Typical Arrangement of a Residue Hydrodesulfurization Unit (PLAIN et. al., 2006)

Among the available atmospheric residue hydrodesulphurization technologies, we can quote the RCD Unionfining? process developed by UOP Company, the process Hyvahl? by Axens Company, the technology RHU? by Shell Company, and the RDS? technology commercialized by Lummus Company.  

           Figure 12 present the basic process flow diagram for the RCD Unionfining? technology by UOP Company. 

Figure 12 – UOP RCD Unionfining? Atmospheric Residue Hydrodesulphurization Technology (UOP Company Website, 2019)

The role of the atmospheric hydrodesulphurization unit in the refinery goes beyond allowing the production of low sulfur fuel oil, in high complexity refineries the unit is applied as feedstock treatment step to conversion units as FCC/RFCC, hydrocracking, and delayed coking. The reduction of contaminants content and residual carbon promoted by the atmospheric residue hydrodesuphurization unit significantly raises the quality of derivatives produced by downstream units as well as raises the catalyst lifecycle of deep conversion processes like FCC and hydrocracking, contributing to reduce the operation costs. 

The process conditions tend to be more severe in the case of atmospheric residue hydroprocessing. The feedstock characteristics lead to a strong tendency of coke deposition over the catalyst requiring then higher hydrogen partial pressure (until 180 bar to fixed bed reactors) as well as higher temperatures (380 to 420 oC).

The hydrotreating process of atmospheric residue is normally conducted in fixed bed reactors and the most employed catalysts are Cobalt (Co), Nickel (Ni), Molybdenum (Mo), and Tungsten (W), normally in association between them and supported over alumina (Al2O3).  The combination Co/Mo is normally more active to hydrodesulphurization reactions while the Ni/Mo combination is responsible for hydrodenitrogenation and aromatics saturation reactions. A basic process flow diagram for the RDS? residue desulfurization technology, developed by Lummus Company, is shown in Figure 13.

Figure 13 – Basic Process Flow Diagram for the RDS? Technology by Lummus Company.

A typical atmospheric residue hydrodesulphurization unit can achieve 95 % of conversion in hydrodesulphurization reactions and 98 % in hydrodemetallization reactions, furthermore, it’s possible to achieve a reduction of 65 % in residual carbon according to the employed technology. Normally, atmospheric hydrodesulphurization units rely on catalytic beds focused to remove metals also called guard beds aiming to protect the catalysts in the downstream reactors and improve the operational lifecycle. As another example of Residue Hydrotreating Technology, Figure 14 presents a process flow diagram for the RHU? processing unit, licensed by Shell Company.

Figure 14 – Process Flow Scheme for the RHU? Residue Hydrotreating Technology by Shell Company (Encyclopedia of Hydrocarbons, 2006)

Due to the severe operating conditions, the operation costs of atmospheric residue desulphurization units are higher when compared with hydrotreating units dedicated to processing distillates (Diesel, Jet fuel, and Naphtha). The most intense hydrogenation process leads to a necessity of more robust quenching systems of catalytic beds, higher hydrogen make-up rates and more complex phase separation systems (multiple stages). 

As quoted above, the market offers wide options of technologic solutions to residue desulfurization in the downstream industry. Despite the relatively high capital cost, the implementation of atmospheric residue hydrodesulphurization units allows refiners greater operational flexibility and high sulfur oil producers, greater value addition to crude oil.

The Deep Hydroprocessing Technologies in the Integration of Refining and Petrochemical Assets

           As aforementioned the hydrocracking units are capable to improve the quality of bottom barrel streams, the main advantage of the integration between hydrocraking and steam cracking units is the higher availability of feeds with better crackability characteristics.

           Bottom barrel streams tends to concentrate aromatics and polyaromatics compounds that present uneconomically performance in steam cracking units due the high yield of fuel oil that presents low added value, furthermore, the aromatics tends to suffer condensation reaction in the steam cracking furnaces, leading to high rates of coke deposition that reduces the operation lifecycle and raises the operating costs.

Once cracking potential is better to paraffinic molecules, and the hydrocracking technologies can improve the H/C in the molecules converting low added value bottom streams like vacuum gasoil to high quality naphtha, kerosene and diesel the synergy between hydrocracking and steam cracking units, for example, can improve the yield of petrochemical intermediates in the refining hardware, an example of highly integrated refining configuration relying on hydrocracking is presented in Figure 15.

Figure 15 – Integrated Refining Scheme Relying on Hydrocracking Technology (UOP, 2019)

Taking into account the recent trend of reduction in transportation fuels demand followed by the growth of petrochemicals market makes the presence of hydrocracking units in the refining hardware raise the availability of high quality intermediate streams capable to be converted into petrochemicals, an attractive way to maximize the value addition to processed crude oil in the refining hardware.

Conclusion

Be capable to add value to bottom barrel streams can be a great competitive advantage among the refiners, especially considering the possibility to processing heavier crude oil that present lower costs and offering the opportunity to raise the refining margins. Despite the operational costs, the hydroprocessing of bottom barrel streams can ensure higher reliability and profitability to refiners through the reduction in the global operational costs related with shorter operational campaigns due to early catalyst deactivation as aforementioned, another advantage is the capacity to processing heavy and discounted crudes that can allow a significant rising in the refining margins.

Beyond this, the relevance of residue hydroprocessing technologies raised, even more, after the start of the new regulation on Bunker (Marine Fuel Oil), the IMO 2020. Once the low sulfur crude oils are scarce, the refiners need to look for alternative routes to add value to his crude oil reserves as well as to supply the new marine fuel oil, ensuring participation in a profitable market.

The scenario faced by the players of the downstream industry requires even more competitive capacity to ensure higher value addition to the processed crude oils, mainly considering the current trend of reduction in transportation fuels demand followed by the growing market of petrochemicals that requires a higher conversion capacity in the refining hardware aiming to ensure higher yields of added value derivatives. In this scenario, high integrated refining configurations based on residue upgrading and flexible refining technologies can be economically attractive, despite the high capital investment and the hydrocracking unit can improve the offer of high quality intermediates to petrochemical industry, allowing higher yields of light olefins in the refining hardware and closer integration with petrochemical assets, which is a relevant competitive advantage in the current and short term scenario of the downstream industry.

References:

SPEIGHT, J.G. Heavy and Extra-Heavy Oil Upgrading Technologies. 1st ed. Elsevier Press, 2013.

GONZALEZ, G. S. Junior Engineer’s Training Course – Kinetics and Reactors. Oxiteno Company, 2003.

Encyclopedia of Hydrocarbons (ENI), Volume II – Refining and Petrochemicals (2006).

MUKHERJEE, U.; GILLIS, D. – Advances in Residue Hydrocracking. PTQ Magazine, 2018.

FRECON, J.; LE BARS, D.; RAULT, J. – Flexible Upgrading of Heavy Feedstocks. PTQ Magazine, 2019.

PLAIN, C.; BENAZZI, E.; GUILLAUME, D. Residue Desulphurization and Conversion. PTQ Magazine, 2006.

Dr. Marcio Wagner da Silva is Process Engineer and Project Manager focusing on Crude Oil Refining Industry based in S?o José dos Campos, Brazil. Bachelor 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) and is certified in Business from Getulio Vargas Foundation (FGV).