BCool wrote:
do you have to wash the bio after seperating the glycerin by product? What do you do with all that dirty water after washing?
Yes, you typically need to wash the fuel somehow once the glycerine is removed, because there may be contaminants such as ions from the catalyst, free glycerides, soaps (making soap is a side reaction, particularly if the oil has any water in it...and it will once you add the methanol because water is a side reaction of creating the esters...it's complex), and so forth. If you have an old diesel engine like a mid-80's Mercedes, just run it and you'll probably be fine for a very long time. If you have a picky fuel system, you'll want to clean these contaminants out somehow. There are several methods for doing so without water, but they are also nontrivial.
Disposal of the wash water is one difficulty...you also have to dispose of the glycerine properly. With methanol in is, it can be considered hazardous waste. The waste water disposal depends largely on which catalyst is used. Sodium hydroxide is not terribly good for most living things. Potassium hydroxide is a fertilizer.
Another factor that hasn't been discussed yet is time: how valuable is yours? Let's say that you can brew 40 gallons of oil at a time (assuming you have a 60 gallon water heater reactor that is already completely set up and ready to go...otherwise, add 2 days). If you have a good collection system, you'll spend half an hour or so getting the oil. It takes me about 3 hours to dewater the oil, then I wait another couple of hours while it comes back down to reaction temperature (130+F). Meanwhile, I titrate; 15 minutes or so. Then I transfer the oil into the reactor, and measure the quantity of oil so I know how much reactants to put in: 15 minutes. Then I mix the methoxide: 15 minutes. Then I start the reactor and pull in the methoxide: 10 minutes. Then I let the reactor run...that time will vary greatly according to how much water is in the oil, how good your mixing is, etc.: 1-3 hours, including time to pull samples for quality testing. Then you wait from 1-24 hours while the glycerine settles out, and drain that off...but that gets tricky at the interface: 30 minutes or so. Then you start washing. People who water wash often have 3 washes, each about an hour long or so, but this time can vary greatly, too.
Some of this is admittedly "start it and walk away" time, but a lot of it isn't if you're smart. For one thing, imagine having 50 gallons of methanol-contaminated oil spewing out of the system and into your garage/shop/kitchen/whereveryouhaveit. So you may want to stick around to make sure that everything goes well. All in all, I figure I spend about 6 hours per batch of dedicated on-site time to get really good fuel that I know is better than what comes out of a pump. That figure would stay the same no matter how large your batch is, as long as you scale the reactor, mixer, wash system, etc. So it pays to go big. If you only make 40 gallons at a time, say that's $120 worth of fuel. Is your time worth $20/hour? And that doesn't include the costs of energy, reactants, etc. So for this to be worthwhile, I think that most brewers need to have something other than cheap fuel in mind. The environment is certainly a good cause!
I don't want to discourage anyone from trying this: I just want to be realistic. There are lots of used reactors being sold by people who thought it was "like baking a cake" but found out the hard way that it isn't. I'd like to keep people from damaging a perfectly good vehicle or hurting themselves, and help them make informed choices. Supporting a commercial brewer is arguably an even better way of helping the environment in this capitalist society.
By the way, the days of being able to get free waste oil from restaurants are likely to be over soon. Rendering companies, who formerly charged restaurants for the privilege of having their oil removed, finally have gotten a clue that they're being undercut by home brewers of biodiesel and people running SVO. In many parts of the country, the rendering companies now either do this for free or pay a bit for the oil. In some parts of the country, the rendering companies have links to organized crime, and they are particularly sensitive to having private parties horn in on their territory.
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