I`m studying terpene-base microemulsion for crude oil sludge generated in refinery storage tanks and get very good results: > 90% oil fraction recovery.
Now I`m seeking proper ways for dispose the effluent generated in the process: breaking microemulsion in order to reduce the ecotoxcity or molecular modification of terpene to reduce its toxicity. I`d appreciate any suggestions in this issues.
Dear Ana Maria Travalloni Louvisse , microemulsions as you correctly said are thermodynamically stable, (mostly transparent) emulsions with droplet-sizes in the size range below let's say 100 nm (else they would scatter light and not be transparent). Common approaches for breaking emulsions will not work for these microemulsions. In my experience one makes them by accident rather than by design. Microemulsions generally only exist in specific zones in the phase diagram of your mixture and here lies the clue how to break them. Adding one of the components of your mixture in excess may bring the overall composition just outside of the microemulsion-zone causing it to form a macroemulsion which you can break using the methods common for this.
In your case I would try to dilute the microemulsion with water (it is I guess the cheapest way) until it either forms a macroemulsion or phase-separates.
But if you have the time, determine the phase diagram of your mixture as there may be other options that are more economical, perhaps adding more terpenes may not look attractive at first but it may be the fastest way.
Finally, please have a look at this open source publication for more understanding about microemulions: https://www.pnas.org/content/113/16/4260
Kind regards, Leo
Interesting question. If they truly are micro-emulsions, the stability is dependent on the ratio of anionic and nonionic surfactant, and the ionic strength (and ionic composition) of the water. However, is you break-up the micro-emulsion by changing one of these, you will get a micellar solution which will still contain considerable crude oil hydrocarbon, as micelles also solubilize hydrocarbons, but to a much lesser extent. Leo mentioned "phase-separation" - I suggest you investigate this more, but without dilution (which decreases the ionic strength). One way to do phase separation is with gas sparging, as the emulsion droplets adhere to the gas droplets and then rise to the surface. If you add the correct organic solvent to the top, the emulsions break apart and "dissolve" in the top phase. This method is called "sublation" and is one way for removing surfactants from water prior to chemical analysis. Wickbold in 1971 was one of the first to describ the method. You may also investigate membrane techniques, as there might be some nano- or micro-fitration membranes that could concentrate the emulsion prior to "breaking it up". Just some things to consider.
Hi! Dear colleagues,
Thanks, Leo Vleugels/Chad Jafvert, for the answers. In my view, all suggestions point out valuable ways to change the components proportion of the microemulsion enabling break it up by conventional methods.
I`ll certainly consider both: excess water addition and “subletion”(it seems like a flotation mechanism). Regarding excess water addition, I just worried about the great effluent volume generated(even less toxic ), as the phase diagram of this system I`m working in, shows the microemulsion domain very near the water edge (may require dilution below the CMC)..
Based on these suggestions, raising temperature may also be a path , as the surfactant and co-surfactant are non-ionic and tend to cloud out.
Kind regards
Ana
Dear Ana Maria Travalloni Louvisse ,
Well, if the phase diagram is such as you describe, dilution with water doesn't seem an option. You could still try with adding the oil-phase.... I am thinking process-wise, many processes recycle part of their product to upstream to facilitate separation. Also if your surfactants are solely nonionic adding salt will not help. I agree with you that raising the temperature would also be a method to investigate.
Kind regards, Leo
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