Question
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Regarding visual inspection of Vacuum Distillation Bottom Product of Used Oil Re-refining, the sample appears to be more viscous after heating, and less viscous on cooling! Is there an explanation for that?
Sep-2024
Answers
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Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br
If it is real, this is a very uncommon situation. According to my knowledge about used lubricating oil re-refining, the bottom of the vacuum distillation column is composed of an asphaltic residue which represents close to 13 % of the total used lube oil feed to the plant.
This residue contains high quantity of polymers and metals and can be used for asphalt blending, production of paving asphalt, bitumen protective covering or as fuel in the cement factories, and the expected behaviour of this hydrocarbon is a lower viscosity as the temperature increases.
The inverse behaviour of viscosity of a liquid with temperature increase is not common and is not expected for hydrocarbons. Among the liquids with this uncommon viscosity behaviour (higher viscosity with higher temperature) we can quote the sulfur between 150 oC to 200 oC and some polymers once the polymerization reactions occur by condensation and addition mechanisms. The condensation mechanism generally, involves the formation of water or other small molecule, unlike the process of addition polymerisation that simply combines the monomers such as ethylene to produce polyethylene, heating the liquid mixture, accelerates the mechanism of polymerisation which results in rapidly increasing the viscosity until the liquid components interact to produce solid long-chain polymers.
My suggestion is to carry out an adequate characterisation and viscosity analysis in the laboratory to identify the viscosity behaviour with the temperature variation of the sample.
Sep-2024
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