I'm stuck at a point where previously I used to get a clear separation of the Biodiesel and glycerol from used cooking oil (checked FFA + esterified) using CaO nanoparticles as the catalyst, but since a few batches, I don't see the glycerol layer at all for UCO as well as fresh vegetable oils. I have tried all possibilities I could think of and have also tried using fresh oils (Sunflower oil) from the market as well, tested the FFA content which is less than 0.5%, and tried the below parameters for the same
1) catalyst used is CaO (LR grade) (tried using 1-3%) tried activating it as well
2) temperature (60 and 80 degrees)
3) Time (1.5, 2 and 4 hours)
4) Tried doing the reaction in a beaker as well as a round bottom flask with a condenser
5) oil to methanol ratio (1:6, 1:8, 1:10 and so on)
also tried using KOH for fresh oil, but still no glycerol layer. I really don't understand what could be going so wrong that there is no glycerol at all. PLEASE HELP!!!
Dear friend Prachi Bhat. I am very curious if your problem has already been solved and what was the reason if it has. If it hasn’t, let me make some assumptions and give your some advises.
There may be two root causes for the absence of glycerol layer separation – either no enough full conversion of oil, or formation of stable emulsion of the reaction products.
It is difficult to judge the completeness of the transesterification reaction only by observing the separation of glycerol. Even in case of proper separation it is not guaranteed the completely full conversion. As result, your final product may contain too much unreacted acylglycerides (either mono-, di- or tri-) to meet the biodiesel normative. If reaction does not full enough, only di- and monoacylglycerides may be formed, but not free glycerol. Obviously, there is nothing to separate in this case. You desperately need to use certain methods of quantitative analysis, allowing to determine the FAME yield or acylglycerides conversion (preferably both). The commonly used methods are FID-GC and 1H NMR, LC also may be an option.
The possible second reason, implying the formation of stable emulsion of products, is less straightforward. Usually, such a problem is typical for the processes of homogeneous alkaline-catalyzed transesterification by longer-chain alcohols (ethanol, butanols etc.), which are necessarily accompanied by saponification. Not going for details, formed soaps strongly contribute to the phase stability and prevent separation. As for the CaO catalyst, it is not as «heterogeneous» as it might seem. CaO-catalyzed processes also are usually complicated by calcium soaps formation. By your words, you intended to use CaO nanoparticles in your work. But you also mentioned, that catalyst used is lab-grade CaO. Just keep in mind, that CaO nanoparticles utilization should provide the very high interfacial contact area of reagent with catalyst. This may facilitate not only main reaction, but also calcium soaps formation, leading to catalyst and products losses.
I don’t really think, that namely soaps caused the difficulties you were faced. However, determination of the calcium soaps content may be very useful for your research. There is a simple method to do this. Just titrate 5-10 g of your product, dissolved in i-propyl alcohol, with 0.1 HCl in presence of bromophenol blue. Also, your may do the same using phenolphthalein to check the presence of the strong base (catalyst) in your products (soaps are not titrated with phenolphthalein). IMAO, your problem is more likely caused by inactivation of CaO due to unproper handling or storage. Сheck the thermal activation procedure and the storage conditions. At least 600 °C is needed to decompose Ca(OH)2 and 900 °C to decompose CaCO3. As much as possible, exclude contact of the sample with air. Keep it in a sealed container, placed in a dry desiccator.
Let me also support my answer-post with some recent data obtained in our lab. We carried out transesterification of UCO (sunflower, 1,5 % FFA) by isobutyl alcohol in presence of CaO at following conditions: 10 : 1 mol/mol, 110 °C, 6 h, 5 % of catalyst on the oil basis. CaO initially was analytic grade, but it was stored for a long time at not ideal conditions. Without calcination, esters yield was only ~10 % (calculated from GC analysis). After calcination (600 °C) yield increased up to ~60 % (also the same yield was achieved with ethanol). Use of calcium glyceroxide (synthesized from the same CaO) resulted in 76 % yield. In latter case conversion of oil was almost complete. Not too impressive yield was caused by the formation of huge amount of soaps – vast majority of catalyst was spent. In the case of CaO, the amount of soap formed was an order of magnitude smaller. It is interested also to mention some unsuccess experience. At the very begining, we try to use another CaO sample (earlier calcinated and kept in desiccator for few years in open cup) and dіdn’t observe any sing of reaction (0.00 % yield). Also, no success was gained in the experiment using CaO (600 °C, analytic grade), subjected to ultrasonic treatment in alcohol media berofe transesterification. Such treatment resulted in formation of stable milk-like CaO/alcohol suspension, but i-butyl esters yield was < 1 %.
Even if my assumptions and advises is enough obvious to the researchers, experienced in the field, I hope it would be at least partially useful for you. If any additional questions arise, please do not hesitated to ask. Good luck.
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