Advantages of Solvent Deasphalting Route as Residue Upgrading Strategy

Introduction and Context

In the last decades, restrictive environmental regulations allies with the technological development of processes and equipment which require petroleum derivates more environmentally friendly and with better performance reduced drastically the consumer market for residue streams. Nowadays, the capacity to add value to the bottom barrel streams represents great competitive advantage among refiners, especially considering the stricter regulations as IMO 2020 that imposes significant reduction in sulfur content of marine fuel oils (BUNKER), requiring even more capacity to treat bottom barrel streams, especially to refiners processing heavier crude oils.

In this scenario, process units called bottom barrel processing, 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. These processing units are fundamental to comply the environmental and quality regulations, as well as to ensure profitability and competitivity of refiners through raising refining margins.

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 refers 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.

Taking into account the trend of reduction in transportation fuels demand, some refiners can adopt the non energetic production as an alternative to ensure added value to processed crude oil and the lubricant production through solvent route can be an alternative to refiners relying on solvent deasphalting units in the refining hardware, despite the contraction profile of market to Group I and II base oils. Another advantage of solvent deasphalting technologies is the relative low capital investment when compared with other residue upgrading technologies, especially the hydrogen addition technologies like hydrocracking. Figure 1 presents a comparison between residue upgrading alternatives related to the capital investment (CAPEX) and effectiveness in the bottom barrel processing.

Figure 1 – Capital Spending x Residue Conversion to Residue Upgrading Technologies (Shell Catalysts and Technologies, 2019)

As presented in Figure 1, the solvent deasphalting technologies present lower capital cost, but present limitations especially related to the characteristics of the processed crude oil, despite this limitation this alternative can be attractive to some refiners, mainly for those with access to low sulfur crude oils.

Solvent Deasphalting Technologies – Effectiveness to Sweet Crudes

The typical feedstock for deasphalting units is the residue from vacuum distillation that contains the heavier fractions of the crude oil. The residue stability depends on of equilibrium among resins and asphaltenes, once which they resins solubilize the asphaltenes, keeping a dispersed phase.

The deasphalting process is based on liquid-liquid extraction operation where is applied light paraffin (propane, butane, pentane, etc.) to promotes resins solubilization inducing the asphaltenes precipitation, that correspond to the heavier fraction of the vacuum residue and concentrate the major part of the contaminants and heteroatoms (nitrogen, sulfur, metals, etc.). The process produces a heavy stream with low contaminants content called deasphalted oil (Extract phase) and a stream poor in solvent containing?the heavier compounds and with high contaminants content, mainly sulfur, nitrogen and metals called asphaltic residue (Raffinate phase).

???????????Figure 2 shows a basic process flow diagram for a typical process deasphalting unit.?

Figure 2 – Typical Arrangement for a Solvent Deasphalting Process Unit

???????????The vacuum residue is fed to the extracting tower where occurs the contact with the solvent leading to the saturated compounds solubilization, in the sequence, the mixture solvent/vacuum residue is sent to separation vessels where occurs the separation of asphaltic residue from deasphalted oil, as well as the solvent recovery.

The choice of solvent employed have fundamental importance to the deasphalting process, solvents that have higher molar mass (higher carbon chain) presents higher solvency power and raise the yield of deasphalted oil, however, these solvents are less selective and the quality of the deasphalted oil is reduced once heavier resins are solubilized which leads to higher quantity of residual carbon in the deasphalted oil, consequently the contaminants content raises too. As normally the deasphalting unit aim to minimize the carbon residue, metals and heteroatoms in the deasphalted oil, propane are the usual solvent applied, mainly when the deasphalting process role in the refining scheme is to prepare feed streams for catalytic conversion processes. Figure 3 presents a relation between the Deasphalted oil (DAO) yield and the quality of the DAO in relation of contaminants content and residual carbon (CCR).

Figure 3 – Relation Between Yield and Quality of the Deasphalted Oil (Shell Global Solutions, 2020)

The main operational variables of the deasphalting process are feedstock quality, solvent composition, the relation solvent/feed stream, extraction temperature and temperature gradient in the extraction tower. Despite be a very important variable the extraction pressure is defined in the unit design step and is normally defined as the need pressure to keep the solvent in the liquid phase, in the propane case the pressure in the extraction tower is close to 40 bar.

Feedstock quality depends on crude oil characteristics processed by the refinery, as well as vacuum distillation process. Depending on the fractionating produced in the vacuum distillation unit the vacuum residue can be heavier or lighter, affecting directly the deasphalting unit yield. Using propane as solvent the relation solvent/feedstream is close to 8 and the feed temperature in the extraction tower is close to 70 oC.

In refineries focused in fuels production (mainly LPG and gasoline), the deasphalted oil stream is normally sent to the Fluid Catalytic Cracking Unit (FCCU), in this case, the contaminants content and carbon residue needs to be severely controlled to avoid premature deactivation of the catalyst which is very sensitive to metals and nitrogen. In refineries dedicated to producing middle distillates, the deasphalted oil can be directed to hydrocracking units.

When the deasphalting process is installed in refining units dedicated to producing lubricants, the quality of deasphalted oil tends to be superior in view that the crude oil processed is normally lighter and with lower contaminants content. In this case, the deasphalted oil is directed to aromatic extraction unit or to hydrotreatment/hydrocracking units, in the last case, the deasphalted oil quality is more critical because of the possibility of premature catalyst deactivation.

The asphaltic residue stream is sent to the fuel oil pool after dilution with lighter compounds (gas oils) or the stream can be used to produce asphalt. Another possibility is sent the asphaltic residue to a Delayed Coking Unit. As the aromatics content in the asphaltic residue is high, the coke produced presents a very good quality.

The principal step in the solvent deasphalting process is the liquid-liquid extraction which depends on strongly of the solvent properties, in this sense, some licensors developed deasphalting processes based on the solvent in supercritical conditions.

Above of critical point, the solvent properties are more favorable to theextraction process, mainly solvency power and the vaporization and compression facility, which reduce the power consumer in the process leading to lower operating costs. According to the literature the power consumption in the supercritical separation is close to one third of the conventional processes, considering that the energy consumption is responsible of the major part of the operating costs in the crude oil refining, the revamp of conventional solvent deasphalting units to supercritical operation tends to be trend in the next years.

The processes ROSE? licensed by KBR Company, UOP-DEMEX? licensed by UOP and the process SOLVAHL? licensed by AXENS are examples of deasphalting technologies in supercritical conditions. Figure 4 presents a basic process scheme for a typical deasphalting unit under supercritical conditions.?

Figure 4 – Typical arrangement to solvent deasphalting unit under supercritical condition

In addition to the quoted processes, the FOSTER WHEELER Company in partnership with UOP developed the process UOP/FW-SDA? which also applies solvent in supercritical condition, this process is presented in Figure 5.

Figure 5 – Basic Process Flow Diagram for the UOP/FW-SDA? Solvent Deasphalting Technology

Like described earlier, the deasphalting process allows add value to residual streams as vacuum residue and, consequently, raise the refiner’s profitability furthermore the process can help in the production of higher quality and cleaner derivates.

As another residue upgrading technologies, the deasphalting process raises the refinery flexibility regarding the quality of crude oil processed, that can pass to process heavier crude oils that have normally lower cost, and this fact can improve the refining margin.

Currently, the deasphalting technology has lost ground in the more modern refining schemes to Delayed Coking units since these units can process residual streams producing streams that can be converted into products with high added value (LPG, Gasoline, and Diesel), without the need of previous feed stream treatment to removal contaminants. However, the products from delayed coking units need hydrotreatment to be commercialized which raises significantly the operational and installation costs to the refinery, and in some refining configurations the solvent deasphalting units can be applied in synergy with other residue upgrading technologies like FCC, Delayed Coking, and hydrocracking.

Synergies between Solvent Deasphalting and Other Residue Upgrading Technologies

In some refining schemes, the deasphalting and delayed coking units can be complementary technologies, as presented in Figure 6.

Figure 6 – Refining Configuration Relying on Solvent Deasphalting and Delayed Coking Units

???????????In the refining scheme presented in Figure 6, the deasphalted oil is fed to FCC unit to produce LPG, naphtha, LCO, etc. while the asphaltic residue is applied to produce fuel oil and asphalt. It’s fundamental to understand that in the current scenario, the combination of Solvent Deasphalting and FCC is possible only to refiners with access to low sulfur crude oils, once both processes are unable to reduce drastically the sulfur content in the final derivatives, in the refining scheme of Figure 6, it’s necessary a great hydroteating capacity to produce marketable crude oil derivatives. Despite this restriction, the synergy between FCC and Solvent Deasphalting units offers a relatively low capital and operating cost alternative to refiners in comparison with hydrogen addition bottom barrel upgrading alternatives as deep hydrotreating or hydrocracking units, refiners inserted in markets with high demand by transportation fuels demand can reach high yields of middle distillates (higher than 40 %) applying the refining configuration presented in Figure 6, a good result considering the relatively low capital investment when compared with Hydrocracking alternative. The participation of Delayed Coking unit processing the other part of vacuum residue to produce streams capable to be converted to high quality transportation fuels after adequate hydrotreating steps reveals another interesting possible synergy between residue upgrading technologies, in some cases the Delayed Coking and Solvent Deasphalting technologies can be faced as competitors due to the fact that both units process vacuum residue, but these units can be complimentary as presented in Figure 6. In some cases, the asphaltic residue produced by the Solvent Deasphalting unit can be fed to Delayed Coking units aiming to maximize the yield of higher added value streams, minimizing the production of fuel oils.

???????????Refiners with high capacity of capital investment can consider the synergy between Solvent Deasphalting units (SDA) and hydrocracking technologies as strategy to destroy residue streams which presents relatively low added value.

As presented above, the slurry phase hydrocracking units offers high operational flexibility and high added value to bottom barrel streams but requires a higher capital spending among the available residue upgrading alternatives, as presented in Figure 1.

???????????An intermediate alternative to refiners is the combination of residue upgrading technologies, normally a mixture of hydrogen addition and carbon rejection processes. An interesting case is the use of solvent deasphalting and hydrocracking units in the same refining configuration, Figure 7 presents an example of this refining scheme with UOP refining technologies.

Figure 7 – Synergy between Solvent Deasphalting and Hydrocracking Units (UOP Company, 2011)

???????????The synergy between solvent deasphalting and hydrocracking technologies can maximize the yield of distillates at same time that produces cleaner and high-quality bottom barrel streams, capable to meet the IMO 2020 requirements ensuring high added value to the processed crude oil. Other interesting refining technology which applies the synergy between Solvent Deasphalting and hydrocracking technologies is the LC-MAX? process developed by Chevron Lummus Global Company, as presented in Figure 8 and the processes Hyvhal? and Solvahl? processes by Axens Company.

Figure 8 – Process Arrangement for LC-MAX? Technology by Chevron Lummus Global (MUKHERJEE & GILLIS, 2018)

???????????According to the licensor data, the LC-MAX? process can achieve conversions higher than 90 % even processing heavy crude oils, reducing in a drastic manner the production of low added value streams and ensuring higher added value to the processed crude oils. According to the Figure 1, the combination of Solvent Deasphalting and hydrocracking units can offer an intermediate cost and high benefits, being an attractive residue upgrading strategy.

???????????The choice of residue upgrading technology by the refiners normally involves an economic analysis which considers the refinery production focus (middle distillates, light products, or lubricants), the market that will be served and the synergy among the processes that will be applied in the adopted refining scheme.

IMO 2020 Compliance through Solvent Deasphalting Technologies

???????????Refiners relying with solvent deasphalting technologies can apply the asphaltic residue from the processing unit to produce marine fuel oil (Bunker) in compliance with the IMO 2020, that requires a maximum sulfur content of 0,50 % (m.m). Figure 9 presents the bunker production process in a conventional crude oil refinery.

Figure 9 – Bunker Production Process Before IMO 2020

???????????As aforementioned, the solvent deasphalting unit is a residue upgrading technology based on carbon rejection and is unable to reduce the sulfur content, in true a major part of the sulfur content will concentrate in the asphaltic residue. Due to this characteristic, refiners producing marine fuel oil in compliance with the IMO 2020 through solvent deasphalting units can apply low sulfur crude oil to achieve an asphaltic residue with sulfur concentration close to the IMO specification (0,50% in mass) and apply hydrotreated diesel as dilutant.

???????????The offer of low sulfur crudes is relatively low in the crude oil market and presents high cost as well as the use of diesel as dilutant can be a disadvantage according to the local market, but some refiners with easy access to low sulfur crude oils like Brazil and North Africa refiners can produce Low Sulfur Fuel Oil (LSFO) through solvent deasphalting units in an economic and competitive way.

Figure 10 – Bunker Fuel Demand and Forecast (IEA, 2021)

???????????As presented in Figure 10, is expected a significant growth in the participation of VLSFO (Very Low Sulfur Fuel Oil) in the bunker market. This fact tends to put under pressure the refiners not able to produce VLFSO leading to these players to operate under poor refining margins supplying high sulfur bunker or, in extreme cases, leave the market or acting with intermediates producers.

Conclusion

???????????The synergy between refining technologies is a basic concept in the downstream sector and one of the first steps to define adequate refining configuration. The synergy between residue upgrading technologies is increasingly relevant to the refiners aiming to keep and improve the economic sustainability of the refiners, especially considering the downstream market after IMO 2020. Solvent Deasphalting Technologies can be especially attractive to refiners with access to low sulfur crude oil reserves and his synergy with other residue upgrading technologies like FCC and Delayed Coking can ensure a relative high conversion of bottom barrel streams and an attractive alternative to hydrocracking technologies that requires higher capital investment.

???????????For refiners with high capital investment capacity, the synergy of Solvent Deasphalting and hydrocracking units seems and interesting way to meet the new regulations and reduce, in a significant manner, the production of low added value streams like pitch.

???????????In general, the solvent deasphalting as residue upgrading is less flexible than the hydrogen addition technologies, but their lower capital requirements can become an attractive differential to some refiners, especially for those processing relatively low sulfur crudes.

References

BARIC, J. Next Level Hydrocracker Flexibility – Unlocking High Performance in Today’s Turbulent Markets. Shell Global Solutions White Paper, 2020.

CACKETT, S. – IMO 2020 and Bottom of the Barrel Opportunities (Shell Catalysts and Technologies). Presented at 2nd Residue Hydrotreat, Kuwait, 2019.

HAIZMANN, R. – Maximizing Conversion and Flexibility – UOP Uniflex? Process (UOP Company). Presented at 6th CIS & BBTC Conference, Moscow (Russia), 2011.

International Energy Agency (IEA). Oil 2021: Analysis and Forecast to 2026, 2021.

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

MYERS, R.A. Handbook of Petroleum Refining Processes. 3a ed. McGraw-Hill, 2004.

ROBINSON, P.R.; HSU, C.S. Handbook of Petroleum Technology. 1st ed. Springer, 2017.

SILVA, M. W.; CLARK, J. – Delayed Coking as a Sustainable Refinery Solution. PTQ Magazine, 2021.

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

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).