Burning vegetable oil as fuel [closed]








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I heard just recently that vegetable oil (i.e palm oil) does burn.


I am also aware that burning used motor/engine oil, does emit hazardous gases such as nitro or sulfur oxide, hence prohibited by government.


How about burning used cooking oil?


I am not saying convert them first to methyl ester, but straight put them directly on a burner/fire. What gases do they emit and is it harmful too?




The short answer: with technical adjustments, it is possible (cf. e.g., [Wikipedia's article](https://en.wikipedia.org/wiki/Vegetable_oil_fuel)).


Note, the levels of sulfur in modern gas/petrol are low; for one, to limit the generation of sulfur oxides during the combustion (e.g., $\ce{SO2}$) contributing to [*acid rain*](https://en.wikipedia.org/wiki/Acid_rain). However, desulfurization equally is economically interesting to access sulfur which is used *as such* for [vulcanization](https://en.wikipedia.org/wiki/Vulcanization), or the controlled combustion to yield $\ce{SO3}$ and eventually sulfuric acid. One of the commonly known processes of desulfurization is the [Claus process](https://en.wikipedia.org/wiki/Claus_process).


The potential problem with burning used cooking oil is its chemical composition. Like gas/petrol for a car, vegetable oil is *a blend of chemicals*. Gas/petrol mainly consists of hydrocarbons (compounds only consisting of carbon and hydrogen) and some additives (like methyl *tert*-butyl ether ([MTBE](https://en.wikipedia.org/wiki/Methyl_tert-butyl_ether) or/and methyl *tert*-butyl ether ([ETBE](https://en.wikipedia.org/wiki/Ethyl_tert-butyl_ether))):


[![enter image description here](https://i.stack.imgur.com/PXzcP.png)](https://i.stack.imgur.com/PXzcP.png)


(image credit to [Wikipedia](https://en.wikipedia.org/wiki/Gasoline))


Vegetable oils, on the other hand, are *esters* of glycerol. Because each of the three hydroxyl groups may be esterified differently, the chemical composition of the oil however may vary much more (*plus* effects by season of harvest/how it is processed lining up for their use e.g., in the kitchen):


[![enter image description here](https://i.stack.imgur.com/RwDSM.png)](https://i.stack.imgur.com/RwDSM.png)


(image credit to [Wikipedia](https://en.wikipedia.org/wiki/Triglyceride))


In comparison to molecules in gas/petrol for a car, the molecules in vegetable oils tend to consist of a larger number of atoms per molecule. This and aforementioned greater variability of chemical composition of vegetable oil *requires an adjustment* of the air intake during the combustion to yield an exhaustive combustion while reducing the generation of nitrogen oxides and [soot](https://en.wikipedia.org/wiki/Soot). (Some of the later passes the exhaust pipe, some may deposit next and on the burner/oil atomizer nozzle.) It has been possible for long time (e.g., [youtube video](https://www.youtube.com/watch?v=P2_0EhPWO50) about an old omnivore combustion engine) and vegetable oils seem to attract again interest (cf. e.g., [Wikipedia's article](https://en.wikipedia.org/wiki/Vegetable_oil_fuel)) to contribute as a form of energy. Technology aside, it equally is a topic of discussion to balance production of e.g., canola/oilseed for food *vs.* combustion.


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