Is it viable to use nHexane to extract 0.6-0.7% by weight vegetable oils from a palm oil mill effluent? How often can the solvent be recycled before it's extraction capacity is reduced? i.e., Hexane: Hexane-oil miscella ratio?
Oils properly dissolve in the n-hexane phase but you will have a continued loss of hexane with the water phase similar to the solubility of n-hexane in water.
You need to consider the value of the lost n-hexane compared to the value of the oil you extract. You should also consider if the n-hexane in the water phase causes a wastewater problem.
Thank you for comments. n-Hexane solubility is reported to be quite low in water (9.5 mg/L). If that is not a concern, do you have any idea what the oil absorption capacity would be on a w/w basis of n-Hexane? The idea is to recycle n-Hexane after high efficiency liquid/liquid separation, until saturated.
Lau: The MWCO of most membranes is not suitable for vegetable oil MW. Once you step out of micro and ultra filtration, pretreatment for nano and RO becomes too critical to operate with simplicity at rural mill locations. If you have experience otherwise, I would love to hear about it. I have successfully tried Forward Osmosis with low pressure flow, but the costs were prohibitive.
Juzer Jangbarwala: You are right that most of the membranes are not suitable in separating vegetable oil due to its small MW. But, considering the MW of vegetable oils which fall in the range of 800-900 g/mol (depending on the number of carbon in tryglycerides) and water MW (18 g/mol), it is still possible to use nanofiltration membrane having average pore size between 400-600 Dalton in performing the separation. Since the oil concentration in the wastewater is around 0.6-0.7%, it will not create significant osmotic pressure for NF membrane and low operating pressure might do the job.
By the way, can you share with me the purpose of treating this wastewater? Is it to comply with discharge regulation or you have other purpose?
Nanofiltration membranes cannot work with the tiny sub micron cellulosic fibers from the mesocarp, loaded with surfactants. NFs usually have an advantage due to surface charges, and to separate di valent ions from a solution. Their application based on MWCO is risky.
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