Decarbonisation Technology August 2026 Issue

to control the distillation curve of the side streams and avoid thermal degradation. In lube oil production units using the solvent route, the initial steps are physical separation processes to remove components that can

Atmospheric residue

Ranate oil

Vacuum distillates

Dewaxed oil

Base lubricant

Vacuum distillation

Aromatic extraction

Finishing

Solvent dewaxing

Waxes

Vacuum residue

Deasphalted oil

Wax to consumers

Deoiled wax

Propane deasphalting

Wax deoiling

Wax nishing

Asphalt

Figure 3 Processing scheme for base lubricating oil production through solvent route

prejudice the desired properties of base oils (viscosity index and chemical stability). Figure 3 summarises the solvent extraction route for the production of lube base oils. Again, the quality of the fractionation into the different cuts is critical to meeting the flash point and viscosity specifications for each stream. After vacuum distillation, the side cuts are pumped to the aromatic extraction unit, while the vacuum residue is sent to the propane deasphalting unit. The propane deasphalting process removes heavier fractions from the vacuum residue, which can be applied as lubricating oil. Propane is used because it has greater selectivity for removing resins and asphaltenes. In the aromatic extraction step, solvents such as phenol, furfural, and N-methyl pyrrolidone are used, as they are more selective for the removal of aromatic compounds, mainly polyaromatics. Aromatics and polyaromatics are undesirable as they reduce the viscosity index and chemical stability. This step also removes a significant share of the nitrogen and sulphur compounds normally present in the polyaromatic structures. The next step is to remove high molecular weight linear paraffins in solvent dewaxing units using methyl-isobutyl-ketone (MIK), or alternatively with toluene and/or methyl-ethyl- ketone (MEK). This step improves the low- temperature flow properties of lube oils. After paraffin removal, the lube oil is sent to the finishing process to remove any remaining heteroatoms (oxygen, sulphur, and nitrogen), which can give colour and chemical instability to the lube oil. This step also removes any remaining polyaromatic molecules. Some process plants with low investment and processing capacity apply clay treatment in this step. However, modern plants with higher processing capacity use mild hydrotreating units, especially important when the petroleum processed has a

higher contaminants content, which would quickly saturate a clay bed. The paraffins removed from lube oils are treated to remove excess oil in a wax deoiling unit. The process stream is then submitted to reduced temperatures to separate low-melting- point branched paraffins. As with lubricating oils, the next step is a finishing process to remove heteroatoms (N, S, O) and to saturate polyaromatic compounds. For food-grade lube oils, the final step is a hydrotreating process with sufficient severity to saturate the aromatic compounds. Changes in the lubricants market While the solvent route is sufficient for the production of Group I lubricant oils, lube oils used in more severe conditions (such as larger temperature variations) require a higher content of saturated compounds and a higher viscosity index. The hydro-refining route is used to achieve this. The solvent route for lube oil production requires more paraffinic crude oils, which are higher cost and reduce refiners’ operational flexibility. This restriction in crude oil supply can be especially challenging during a geopolitical crisis. Group I lubricating oils have lower specifications

125%

16% 7% 8% 0%

100%

22% 8% 10%

12% 10%

75%

25%

31%

50%

54%

25%

44%

39%

2015

2020

2030

Paranic Group I

Paranic Group II

Paranic Group III

Naphthenic Synthetic Other

Figure 4 Base oils market development (Statista, 2023)