Biodiesel by base catalysed transesterification: Where does the base catalyst end up?
In the production of biodiesel by the base catalysed transesterification process, the catalyst (eg NaOH or KOH) remains in the final reaction mixture (mostly in the glycerol layer). I understand the catalyst can not be economically recovered for reuse but clearly can not be disposed of in the waste water either. How is the residual NaOH dealt with?
Also I understand much research has been done on the production of biodiesel by the lipase catalysed method which uses the enzyme lipase to catalyse the reaction instead of using a strong base. Has this process been commercialized as yet and if so who is doing it?
Great questions. My experience with biodiesel is in on-farm based processes which are small scale and tend to be close-loop.
Base Catalysis: My understanding is that the base catalyst (NaOH or KOH) does not survive the reaction, but rather the base salts (Na or K) do and are mainly in the glycerin. The glycerin has often been cited as a marketable byproduct (e.g. soap production, cosmetics, etc.) but I have not seen these markets develop with the folks I work with. Rather, we remove (and recovery) methanol from the glycerin (glycerol) and use the purified glycerin either as a fuel in a waste oil boiler (to heat the biodiesel process and other heat loads) or as a compost amendment / field spread. So the residual salts need to be accounted for in these disposal / use methods either as ash (when combusted) or as a soil addition via compost or direct spread.
Lipase: I am not very familiar with this process. From a relatively quick literature review, it appears to still be non-commercial. A good recent (2013) summary is available here: http://web.ornl.gov/sci/ees/cbes/forums/CBES_ORNL_Burton.pdf
Thanks so much for your helpful reply. As suggested I have found the ‘Oak Ridge National Laboratory’ site to be most useful with some excellent information on the enzymatic approach to biodiesel production. This has lead me to Piedmont Biofuels and Novozymes, both organisations look like they will be able to provide up to date industry information on the commercial use of enzymes for biodiesel production.