Decarbonisation Technology August 2026 Issue

Light/middle distillates

Atmospheric residue

Lube oil + waxes

Vacuum distillates

Dewaxed oil

Base lubricant

Vacuum distillation

Hydroisomerisation (HIDW)

Hydrotreating unit

Hydrocracking unit

Hydronishing

Vacuum residue

Deasphalted oil

Propane deasphalting

Asphalt

Figure 5 Processing scheme for base lubricating oil production through hydrorefining route

and, as a result, a lower performance compared with Group II-IV oils. Figure 5 shows that the market share of Group I and II lubricating oils is declining, mainly due to the technology requirements of the newest automotive engines, which need higher-specification lubricants. Many lube oil-producing refiners have invested, or are investing, capital to produce higher-quality lubricating oils via the hydrorefining route. Hydrorefining route In the hydrorefining route for lube oil production, physical processes are substituted by catalytic processes, basically hydroprocessing, as shown in Figure 5. The hydrorefining route also offers more flexibility during fractionation in the vacuum distillation step, as hydrocracking can be used to crack heavier streams and, together with another distillation step, increase the yield of lighter streams. hydrotreating unit. This saturates the polyaromatic compounds and removes contaminants such as sulphur and mainly nitrogen, a strong deactivation agent for the hydrocracking catalyst. In the hydrocracking step, the feed stream is cracked under controlled conditions, which promote dehydrocyclisation and aromatics saturation, required to meet the higher lube oil specifications. The next step, hydroisomerisation, seeks to promote isomerisation of linear paraffin (which reduces the viscosity index), producing branched paraffin. The process stream is then pumped to hydrofinishing units to saturate any remaining polyaromatic compounds and remove heteroatoms. The water content in the lube oil is controlled to avoid turbidity in the final product. Comparing the production routes, it should be noted that the hydrorefining route offers greater After vacuum distillation and propane deasphalting, the streams are sent to a

flexibility in selecting crude oils. The solvent route applies basic physical processes, which makes it necessary to select crude oils with a higher paraffin content and lower contaminants (mainly nitrogen). A second disadvantage of the solvent route is that the solvents themselves can cause environmental damage, requiring special health and safety requirements during handling and processing. A third disadvantage is the production of lower-value-added streams, such as aromatic extracts. The only advantage of the solvent route is that it requires a lower capital investment and produces paraffins that can be used as food- grade lubricants. Used lubricating oil re-refining process As previously mentioned, a significant part of the lube oil market is supplied with recycled lubricating oil. Recycling or re-refining of used lubricating oil plays a double role: • Recovers a useful product (lube oil) from hazardous waste oils. • Reduces demand for crude oil for the production of base lubricating oils. The first industrial process developed to recover used lubricating oil is called the acid-clay, or Meiken, process. Due to its simplicity, the acid-clay process needs relatively low capital investment; however, operational cost is very high due to the high quantities of sulphuric acid and clay required. The main disadvantage of the acid-clay process is the acid-sludge production, a hazardous residue that is difficult to treat. Furthermore, it is akin to the solvent process, so it can only produce Group I base oils, the demand for which, as already mentioned, is declining. Another process technology widely employed to re-refine used lubricating oil is the wiped film evaporator. In this process, the used lubricating oil passes through a deasphalting step under vacuum.