PTQ Q2 2023 Issue

Gases to burn

Gases

Water

Used lubricating oil

Flash vessels

Grating

Pre-heater

Dehydration

Light neutral oil

Spindle oil

Diesel

Sulphuric acid

Wiped lm evaporators deasphalting process

CaO + activated clay

Clay to recovery

Decanter

Sulphonation reactor

Lubricating base oil

Fired heater

Filter

Acid sludge

Clarication

Neutral sludge

Figure 6 Process flow diagram for the wiped film re-refining process

demanded for clay and sulphuric acid, the operational cost is very high. The main acid-clay process disadvantage is that acid-sludge production is a hazardous residue with very dif- ficult treatment. Another significant disadvantage of the acid-clay process is that the technology can produce only Group I base oils. This fact limits the consumer market and strongly impacts profit - ability when compared with other available technologies. Another process technology widely employed in used lubricating oil re-refining is the wiped film evaporator pro - cess. In this process, used lubricating oil passes through a deasphalting step under vacuum, as shown in Figure 6 . After the feed stream dehydration step, the lighter fractions are separated in flash vessels. The heavy fraction is heated and sent to wiped film evaporators where the deasphalt - ing process under vacuum at temperatures close to 350°C occurs. The heavier fraction of the oil containing the majority of the contaminants and lubricant degraded products is then removed, such as neutral sludge, which can be directed to the asphalt industry.

The deasphalting process is insufficient for removing all the degraded compounds of the used lubricating oil. Hence, the used oil passes through a step involving a reaction with sulphuric acid (sulphonation), where the remaining contami- nants are removed and separated from the base lube oil as acid sludge in a decanter. Acid sludge production is strongly reduced in comparison to the acid-clay process, and the environmental impact is relatively reduced. This is the main advantage of the wiped film evaporator process when compared with the acid-clay process. Nevertheless, the base oil produced by this route follows only the quality specifications of the Group I lubricat - ing oils, according to API classification. Some re-refiners apply a propane deasphalting process to replace the wiped film evaporators. However, the necessity of constant solvent replacement and additional security require- ments can raise the operational costs in this case, although the capital investment is similar to both technologies. Base lubricating oil production with higher quality can be reached through the application of hydrotreating processes. Figure 7 presents a basic process flow for used lubricating oil re-refining through the hydrorefining route. After the dehydration step, the used oil passes through a distillation column where the lubricating oil is separated from the lighter fractions. The bottom product of the distil- lation column is mixed with hydrogen and heated before the reactor. The process is conducted under mild conditions with temperatures varying from 250 to 300°C and pressures close to 30 bar; the normally applied catalyst is Co-Mo/Al 2 O 3 . The main advantages of the hydrorefining route in com - parison to other available technologies are the higher qual- ity of the base lubricating oil produced and the reduction in the environmental footprint. However, the necessary capital investment is relatively high and is only attractive for process plants with a large capacity. Some researchers have dedicated efforts to the develop- ment of new re-refining technologies for treating used lubri - cating oils. Some of these technologies look promising, like ultrafiltration in membranes, but the technology is still in the initial stage of development. In Brazil, close to 40% of lubricating oil consumption is recovered and sent to processing by re-refiners, accord - ing to the ANP. Despite this substantial data, Brazilian

Diesel

Gases to burn

Used lubricating oil

Light neutral oil Spindle oil

Distillation

Grating

Dehydration

To vacuum system

Hydrotreating reactor

Gases to burn

Make-up hydrogen

Fired heater

Separation drum

Recycle gas compressor

Hydrogen recycle

Purge gas

Lubricating base oil

Gas scrubber

Figure 7 Basic arrangement to hydrotreating process for re-refining of used lubricating oil

PTQ Q2 2023