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We are using a nickel catalyst in our hydrogenation process to help convert vegetable oil to vegetable wax. The issue is ensuring all additives are successfully removed once hydrogenation is complete.

There are numerous catalysts that can be used to assist this process.

The question is: what catalyst is effective for hydrogenation but also extremely efficient to filter back out of the finished wax? Or, is there a cleaner way to hydrogenate oil such that almost no residue remains?

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Nickel is usually a good catalyst for this sort of hydrogenation as it's cheap and effective. As to residues, I'm assuming that alludes to residual catalyst; there are a few ways to mitigate against this. Initially, ensure you have minimal fines in the catalyst. The easiest way is to ask your supplier to ensure this. If it's not that sort of process and you just use off the shelf material, then settle your catalyst in water, give it a mix and remove supernatant after a few seconds. Fines will suspend for longer and can be removed in this way. Large particle size material will sink faster. By using the larger particles, you make it easier to remove the catalyst by filtration later. The definitive check is residue on ignition of the final samples. The downside to nickel in batch (as opposed to continuous or flow) is that it's very dense and needs the right agitator type and speed to get it suspended effectively. However, this is not normally an issue unless you have inappropriately sized the agitator and type e.g. anchor, to the vessel size and geometry. It may not be worth using precious metal (PM) catalysts for this sort of transformation, but they are easier to suspend when supported on carbon. The advantage of PM catalysts is lower loading. In all references to catalysts above, they are of the heterogeneous type.

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  • $\begingroup$ Excellent suggestion - thank you. Perhaps it would be easier/faster if we also used a solvent like hexane which we could boil off. We're just trying to minimize any possibility of contamination in the finished wax. I would upvote your response but not enough reputation yet. Thanks for the ideas! $\endgroup$ – Gr3go Aug 4 '17 at 23:58
  • $\begingroup$ Another advantage of Nickel is that it is magnetic. On a lab scale Ni residues can be removed by standing the suspension over a fridge magnet for a few minutes before decanting. $\endgroup$ – Waylander Aug 5 '17 at 8:45
  • $\begingroup$ Excellent point Waylander. When I did screening, I would use a cross magnetic stirrer. At the end if the reaction, most of the nickel was stuck to the stirrer and caught most on decanting/filtering also. @Gr3go for minimal contamination, I would use a packed bed reactor i.e. A column packed with catalyst, like a hplc column. However, this technology is not always available. I would get nickel test strips to get a good idea of any nickel content. Also, use heptane instead of hexane. Less toxic, category 3 solvent and faster static discharge i.e. Much less build up of charge $\endgroup$ – Beerhunter Aug 5 '17 at 9:34
  • $\begingroup$ Great ideas. I had hoped nickel's magnetic properties would help us and this is a good confirmation. Also, heptane and nickel strips are perfect suggestions to minimize and verify purity. I assume heptane has a low boiling point as well, but will confirm in a bit. Thanks guys! $\endgroup$ – Gr3go Aug 5 '17 at 17:13
  • $\begingroup$ Heptane actually has a higher boiling point than you'd anticipate but is easy to remove under vacuum. In fact, I've removed it to appropriate levels in a custom synthesis - confirmed by GC - simply by bubbling nitrogen through a solution in a fume cupboard, back in the day. $\endgroup$ – Beerhunter Aug 5 '17 at 20:28

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