Discussion on membrane separation technology
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It seems that membrane separation technology has become more advanced in recent years; I wonder if it’s possible to separate glycerin from water The process involves using membrane separation (or reverse osmosis) to convert a 1–2% glycerin aqueous solution into a 10% glycerin aqueous solution. I asked a few years ago; it seems that the sizes of glycerol molecules and water molecules are too similar to make such membrane filtration possible. I wonder if it’s now achievable
It’s coming. We have tried using reverse osmosis or nanofiltration to concentrate dilute aqueous solutions of glycerol, but it didn’t work. The main issue is that the rejection rate of glycerol by the reverse osmosis membrane is too low. Other concentration techniques besides biochemical destruction include multi-effect evaporation, multi-stage flash evaporation, and pressure steam distillation. If a membrane separation process must be used, there is only one such process, namely membrane distillation, that can be employed ； If energy savings are taken into account, only multi-effect membrane distillation is available ； And only here do we carry out industrial applications of the multi-effect membrane distillation process. Multi-effect membrane distillation requires steam (steam at 100-160 degrees is suitable) and a small amount of electricity. The water production ratio in the membrane distillation process is generally around 6, which is equivalent to the energy-saving effect of an eight-effect evaporator. What is the daily processing capacity for this aqueous solution of glycerin, and what are the organic and inorganic impurities present in it?
The concentration of glycerin in water required for effective evaporation is 10%; 1–2% is too dilute. At present, there is no good way to utilize this amount of glycerin, so it can only be discarded. . . There are basically no impurities; it is a pure glycerin aqueous solution.
In the oil industry, we actually also have a process for producing glycerin: 10% glycerin in water is evaporated multiple times to reach 80% concentration, and then concentrated through distillation to over 99%. During this process, the vacuum draws out some of the glycerin; what needs to be done now is to deal with this portion. Membrane filtration is the best method for this purpose, but if that’s not available, it’s more energy-efficient to simply dispose of it. . . The processing volume shouldn’t be large; it seems to be only 50 tons of glycerin water per day.
I’m not sure if separation can be achieved using the hydrophilic and lipophilic properties of the membrane. But glycerol is also a glycerin, and it is hydrophilic as well.
If that is the case, some work should be done to avoid foam entrainment. The glycerin content in the evaporated condensate will also decrease significantly.