[NicoletaRascol]

I tried different ways to dissolve a grease but without a solution. i don't know the grease composition and I'm afraid I can't find it. The issue it's that I need to dissolve the grease and then i need to filtrate it through a 3 microns membrane.
I tried tricloretylene, solvents based on alkanes (C9-C12) and every time i got a thin layer on top of the membrane. I even tried to dissolve that thin layer with DMSO (i read somewhere about it) but it's not working. Any ideas, please?

[Enthalpy]

"Grease" can be a triglyceride (a fat) or a suspension of a soap in a mineral oil (used as a lubricant) - and possibly more meanings. You'd choose different solvents depending on that.

[NicoletaRascol]

Thank you for the observation, my question is about a lubricant grease, used for bearing. I want to dissolve it in order to check the contaminants found in the sample.

[Arkcon]

Good.  Now we know what "grease" actually is (possibly.)  Something like a higher alkane, or perhaps, white lithium grease, as Enthalpy: said, a higher lithium soap.

Now, what are you analyzing for?  Depending on the analyate and method, you may not have to remove all the grease.

Example: checking for engine wear in lubricating oil is often done with "arcs and sparks" -- essentially just ionizing the grease and contaminants and analyzing the spectra of excited metal ions.  Or you can completely destroy the grease and soluble metals with powerful acids for ICP.  Or you're doing something else or looking for something else.

[Enthalpy]

A lubricating grease's oil would dissolve in alkanes. The lithium soap I'm not sure, but its amount would be big.

Then, greases can carry additives, like graphite powder or molybdenum disulphide powder - which make the new grease grey or black - and possibly minor ones like corrosion inhibitors, viscosity index promoters and all these known from lubricating oils.

Old grease contains also wear chips (tiny metal fragments) and some degradation products, typically from air oxidation.

[marquis]

Check the EPA method for oil and grease in waste water.  It should be a good starting point.

Good luck.

[lohjxMARCUS]

Try using Hexanes for the dissolution of oil and greases. Based off APHA methods