Lubricant Production Routes and Competitiveness in the Downstream Market

Introduction and Context

According to the recent forecasts, the global market of lubricants is growing by annual rates around 4,0 % and can reach a total value of USD 166 billion in 2025. Figure 1 presents the growing trend for the lubricants market. The high added value of lubricants in comparison with the transportation fuels accompanied by the trend of reduction in transportation fuels demand indicates an attractive alternative to refiners with adequate refining hardware to improve his revenues and the competitiveness in the downstream market. 

Figure 1 – Growing Trend in the Demand by Lubricants (McKinsey & Company, 2018)

Like others crude oil derivatives, the economic and technology development have been required the production of lubricating oils with higher quality and performance, moreover with lower contaminants content.

The main quality requirements for lubricating oils are viscosity, flash point, viscosity index (viscosity change with temperature), fluidity point, chemical stability, and volatility.  

According to the American Petroleum Institute (API), the lubricating base oils can be classified as described in Table 1. 

The lube oils from groups II, III, and IV have higher quality than base oils from the group I, the content of contaminants like sulfur and unsaturated compounds are significantly reduced, moreover, the viscosity index is superior for Groups II, III, and IV.

Lubricant Production Routes

           The first step in the lubricant production process is the vacuum distillation of atmospheric residue obtained like the bottom product in the atmospheric distillation processes.  For vacuum distillation units dedicated to producing lubricating fractions the fractionating need a better control than in the units dedicated to producing gas oils to fuels conversion, the objective is to avoid the thermal degradation and to control the distillation curve of the side streams, a typical arrangement for vacuum distillation unit to produce lubricating fractions is presented in Figure 2. A secondary vacuum distillation column is necessary when is desired to separate the heavy neutral oil stream from vacuum residue. 

Figure 2 – Typical Arrangement for Vacuum Distillation Process to Lubricating Oil Production

In lubricating production units based on the solvent route the following steps are basically physical separation processes with the objective to remove from the process streams the components which can prejudice the desired properties of base oils, mainly the viscosity index, and chemical stability. 

Figure 3 shows a block diagram corresponding to the process steps to produce base lubricating oils through the solvent extraction route.  

Figure 3 – Processing Scheme for Base Lubricating Oil Production through Solvent Route 

As aforementioned in the vacuum distillation step, the fractionating quality obtained between the cuts is critical for these streams to reach the quality requirements like flash point and viscosity. After the vacuum distillation step the side cuts are pumped to the aromatic extraction unit and the vacuum residue is sent to the propane deasphalting unit.  The Propane deasphalting process seeks to remove from vacuum residue the heavier fractions which can be applied as lubricating oil.  The Propane deasphalting units dedicated to producing lubricating oils apply pure propane like solvent because this solvent has higher selectivity to remove resins and asphaltenes from deasphalted oil.  

           In the aromatic extraction step, the process streams are put in contact with solvents selective to remove aromatics compounds, mainly polyaromatics. The main objective in remove these compounds is the fact that they have low viscosity index and low chemical stability, this is strongly undesired in lubricating oils.  As the nitrogen and sulfur compounds are normally present in the polyaromatic structures, in this step the major part of sulfur and nitrogen content of the process stream is removed. The solvents normally applied in the aromatics extraction process are phenol, furfural, and N-methyl pyrrolidone.

           The subsequent step is to remove the linear paraffin with high molecular weight through solvent extraction.  This step is important because these compounds prejudice the lubricating oils flow at low temperatures, a typical solvent employed in the solvent dewaxing units is the Methyl-Isobutyl-Ketone (MIK), but some process plants apply toluene and/or methyl ethylketone for this purpose. 

After paraffin removing, the lubricating oil is sent to the finishing process, in this step are removed heteroatom’s compounds (oxygen, sulfur, and nitrogen), these compounds can give color and chemical instability for the lube oil, furthermore are removed some remaining polyaromatic molecules. Some process plants with low investment and processing capacity apply a clay treatment in this step, however, modern plants and with higher processing capacity use mild hydrotreating units, this is especially important when the petroleum processed to have higher contaminants content, in this case, the Clay bed saturates very quickly.   

           The paraffin removed from lubricating oils are treated to removing the oil excess in the unit called wax deoiling unit, in this step, the process stream is submitted to reduced temperatures to remove the low branched paraffin which has a low melting point.  Like the lubricating oils, the subsequent step is a finishing process to remove heteroatoms (N,S,O) and to saturate polyaromatic compounds, in the paraffin case generally, is applied a hydrotreating process with sufficient severity to saturate the aromatic compounds that can allow to reaching the food grade in the final product.       As cited earlier, the solvent route is capable of producing group I lubricating oil, however, lube oils employed in severe work conditions (large temperature variation) need be had higher saturated compounds content and higher viscosity index, in this case, is necessary apply the hydro-refining route.    

           In the lubricating oil production by hydro-refining, the physical processes are substituted by catalytic processes, basically hydrotreating processes. Figure 4 shows a block diagram of the processing sequence to produce base lube oils through the hydrorefining route.  

Figure 4 - Processing Scheme for Base Lubricating Oil Production through Hydro-refining Route 

In this case the fractionating in the vacuum distillation step have more flexibility than in the solvent route, once that the streams will be cracked in the hydrocracking unit, so another distillation step is necessary.

After the vacuum distillation and propane deasphalting steps, the process streams are sent to a hydrotreating unit, this step seeks to saturate polyaromatic compounds and remove contaminants like sulfur and mainly nitrogen which is a strong deactivation agent for the hydrocracking catalyst.

           In the hydrocracking step, the feed stream is cracked under controlled conditions and chemical reactions like dehydrocyclization and aromatics saturation occur which gives to the process stream the adequate characteristics to the application as lubricants. The following step, hydroisomerization, seeks to promote isomerization of linear paraffin (which can reduce de viscosity index) producing branched paraffin.

After the hydroisomerization, the process stream is pumped to hydrofinishing units to saturate the remaining polyaromatic compounds and to remove heteroatoms, in the hydrofininshing step the water content in the lube oil is controlled to avoid turbidity in the final product.

Solvent Deasphalting Technologies - Introduction

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 the 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 a solvent containing the heavier compounds and with high contaminants content, mainly sulfur, nitrogen and metals called asphaltic residue (Raffinate phase).

           Figure 5 shows a basic process flow diagram for a typical process deasphalting unit. 

Figure 5 – 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 solubilization of the saturated compound, 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 has 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 a higher quantity of residual carbon in the deasphalted oil, consequently the content of the contaminants raises too. As normally the deasphalting unit aims 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.

The main operational variables of the deasphalting process are feedstock quality, solvent composition, the relation solvent/feedstream, extraction temperature, and temperature gradient in the extraction tower. Despite being 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 the 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/feed stream 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 contaminant content. In this case, the deasphalted oil is directed to the 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 to send the asphaltic residue to a Delayed Coking Unit. As the aromatics content in the asphaltic residue is high, the coke produced presents very good quality.

The principal step in the solvent deasphalting process is the liquid-liquid extraction which depends on the strength of the solvent properties, in this sense, some licensors developed deasphalting processes based on the solvent in supercritical conditions. Above the critical point, the solvent properties are more favorable to the extraction process, mainly solvency power and the vaporization and compression facility, which reduce the power consumption in the process leading to lower operating costs.

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.

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 conditions. 

Hydrotreating Technologies – An Overview

The hydrotreating process 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 commons 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 can be 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 represents a hydrocarbon.

           The hydrotreating reactions are exothermic, and the reactor temperature is controlled through the injection of cold hydrogen between the catalyst beds.

           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 reactional severity like hydrodesulfurization, while the catalyst Ni/Mo is normally applied in reactions that need higher severity, like hydrodenitrogenation and aromatics saturation. Due to the higher activity, the required catalyst volume is lower when Ni/Mo is applied.

           The hydrotreating is applied in the finishing of the final products like gasoline, diesel, or kerosene or like an intermediate step in the refining scheme in refineries to prepare feed charges to other processes like Residues Fluid Catalytic Cracking (RFCC) or Hydrocracking (HCC) where the main objective is to protect the catalyst applied in these processes. In the hydrocracking process, the reactions are conducted under most severe conditions with temperatures that vary to 300 to 480 oC and pressures between 35 to 260 bar.  Due to process severity, hydrocracking units can process a large variety of feed streams, which can vary from gas oils to residues that can be converted into light and medium derivates, with high value added. For this reason, the hydroprocessing route offers higher flexibility than the solvent route related to the processed crude oil.

           The basic process flow is similar to the various hydrotreating processes (hydrodesulfurization, hydrodenitrogenation, etc.), however, the process severity, determined by variables like hydrogen partial pressure, temperature, and catalyst varies and the removal of the contaminants is affected.

The hydrotreatment process units are optimized aiming an equilibrium between cited operational variables because chemical reactions are exothermic and the decontrolled raising in the temperature can affect negatively the reactional equilibrium besides it’s possible the sintering of the catalysts, to minimize this risk normally the hydrotreating reactors have points between the catalyst beds where are injected hydrogen in lower temperature (quench lines) to permit better control of the reactor temperature.

 Figure 6 shows a typical arrangement for a hydrotreating process unit with a single separating vessel. 

Figure 6 – Basic Process Flow Diagram for Low Severity Hydrotreating Process Units 

The configuration with a single separating vessel is normally applied in lower severity units, like hydrodesulfurization units. This arrangement is possible in this case because under reduced pressures the difference between water and hydrocarbons properties is large and the separation process needs reducing contact areas, so a single vessel can realize the separation process. 

           In hydrotreating units dedicated to producing lubricant, one of the focus of the hydrotreating process is to reduce the concentration of long chain paraffin, to achieve this goal is applied specific catalyst beds containing dewaxing catalysts (ZSM-5). One of the most known hydrodewaxing technology in the market is the MSDW? process, commercialized by ExxonMobil Company. A basic process flow diagram for MSDW? process is shown in Figure 7.

Figure 7 – Basic Process Flow Diagram for MSDW? Dewaxing Technology by ExxonMobil Company (ExxonMobil Website).

HDF = Hydrofininshing

Solvent Route x Hydrorefining Route

As aforementioned, comparing the lubricant production routes can be observed that the hydro-refining route gives more flexibility in the relation of the petroleum to be processed. As the solvent route applies basically physical processes, is necessary to select crude oils with a higher content of paraffin and low contaminants content (mainly nitrogen) to the processing, which can be a critical disadvantage in a geopolitical instability scenario.  The main disadvantage of the solvent route, when compared with the hydrorefining route, is that the solvent route can produce only Group I lubricating oil, this can limit his application to restricted consumer markets, which can reflect in the economic viability. Figure 8 presents a forecast for the market share evolution to different kinds of base oils in the market.

Figure 8 – Base Oil Demand Distribution (STATISTA, 2020)

According to the data from Figure 8, is expected a significant reduction in the demand by Group I base oils, leading to a great competitive loss to refiners relying on base oil production exclusively through solvent routes.

 Another solvent route disadvantage is the solvents applying which can cause environmental damage and needs specials security requirements during the processing, production of low value-added streams like aromatic extract is another disadvantage.   

As advantages of the solvent route over the hydro-refining route can be cited lower capital investment and the fact that the solvent route produces paraffin that can be directed to the consumer market like products with higher added value. 

Conclusion

           As aforementioned, despite the high capital investment of the hydroprocessing units, the higher added value of the Groups II and III lubricants and the growing market can justify the investment mainly considering the trend of reduction in transportation fuels demand at a global level in the middle term that has been leading the refiners to look ways to ensure market share and revenues in the downstream industry through the maximization of high added value derivatives with the growing market as petrochemicals and lubricating oils. Due to the accelerated technological development, especially in the automotive market, the Group I lubricating oil tend to lose market in the next years this fact tends to lead the refiners to look for capital investment aiming to sustain their competitiveness in the lubricating market. Another side effect for lubricating producers based on solvent routes like Brazil due to the competitiveness loss is raising the imports to supply the internal market, leading to an external dependence of critical production input as well as negative effects on the balance of payments.  

References:

GARY, J. H.; HANDWERK, G. E. Petroleum Refining – Technology and Economics.4th ed. Marcel Dekker., 2001.

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

Mckinsey & Company. Lubes growth opportunities remain despite switch to electric vehicles, 2018.

ZHU, F.; HOEHN, R.; THAKKAR, V.; YUH, E. Hydroprocessing for Clean Energy – Design, Operation, and Optimization. 1st ed. Wiley Press, 2017.

Dr. Marcio Wagner da Silva is Process Engineer at Henrique Lage Refinery (PETROBRAS) based in S?o José dos Campos, Brazil. Bachelor in Chemical Engineering from the University of Maringa (UEM), Brazil, and PhD. in Chemical Engineering from the 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 has an MBA in Project Management from the Federal University of Rio de Janeiro (UFRJ) and is certified in Business from Getulio Vargas Foundation (FGV).