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Topic: Converting Byproduct from Biodisessel Process into Fertiliser  (Read 29586 times)

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Offline Murphy

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Hello everyone,
This is my first post.. I'm a newbie!!

I'm not much of a chemist and I need a bit of help with a project I am working on.

I am making diesel fuel from waste vegetable oil and need some directions on how to use one of my by-products of the process.

First, let me explain a bit..  The process is called "Base catalyst transesterfication"..  This process results in some byproducts that must be disposed of properly.   I am small time and don't produce much but I want to make sure I do it right.

Anyhow,  the last part of my process requires that I "wash" the biodiesel by spraying the fuel with a very fine mist of water.  The mist settles on top of the fuel and eventually ends up at the bottom of the tank. As the micro droplets of water travel down through the biofuel, it picks up the remaining contaminants in the fuel.

Here is my problem.
For every 50 gallons of fuel I make, I end up with about 50 gallons of this wash water.  The wash water is at a PH of about 9.6 or so and as the processes progresses and wash water is drained off the bottom, its PH falls to around 7 or 7.5.  I am using KOH (Potassium Hydroxide @ 90% purity) for my catalyst so this is the main ingredient in the wash water.  There are some other things in there as well like soap (an undesired effect of the reaction), hard well water (not softened), and a few other minor things. The wash water appears a milky white color when first drained. By the end of the misting process, the wash water is clear as the incoming water and pretty much PH neutral.

I am on a large farm and I want to spread this was water out on the grass and maybe even some crops. (we grow a little bit of everything)  How do I go about making this a poor-mans fertilizer? 

Is there something simple that I can do to make this stuff plant friendly?  I did a small control test on some grass / weeds by just hand pouring about 20 gallons into an area 10 x 10 feet..  After about 2 weeks, the grass is starting to turn brown..  Not exactly a quick death but none the less its dying..

Thanks,
Murphy
« Last Edit: June 21, 2006, 12:52:25 PM by geodome »

Offline Dude

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #1 on: June 19, 2006, 04:11:49 PM »
You have in your wash water (at a minimum):
1.  Glycerol   reaction product
2.  base (diluted KOH)  catalyst
3.  waste oil sludge and salts (from the free fatty acids)
4.  methanol or ethanol, whatever you use

I would want to isolate what portion is responsible for browning the grass.  One approach would be to see if it is simply a pH issue.  Use the same amount of base and dilute with water (or scale it down in proportion to use less water).  Pour it on the same size area of the grass and see if the grass dies just from the base (no biodiesel).  If so, you might be able to get away with neutralizing the base with a weak acid (ie phosphoric acid).

I would do the same thing with the alcohol that you use to see if it is responsible.  You can probably assume that all of the unreacted alcohol goes into the water phase.

If it isn't a simple pH issue, you are probably out of luck and will have to send it to wastewater or use it as a weedkiller.  Another site you might want to ask. 

http://forums.biodieselnow.com/topic.asp?TOPIC_ID=10431

Offline Murphy

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #2 on: June 19, 2006, 09:57:38 PM »

Dude,
Thanks for your response.. I was begining to think no one was going to even try to answer it..

Anyhow,
Glycerol, (we call it glycerin) is drained off at the reaction tank.  While there may be some present in the wash water it would be a very small amount.  The whole idea is to get the glycerol seperated from the bio that is to be washed before it gets transfered to the wash tank.  Reaction tank designs are based on this fact..

Base (diluted KOH) catalyst is the big one.. There is left over catalyst.. This is why I decided to go with KOH instead of NaOH.. (NaOH is toxic to plants no matter what you do to it)

Waste oil sludge and salts from the free fatty acids end up in the glycerol by-product which is drained off before transfer to the wash tank.  While they may be present in the wash water, they would also be in extremely small quantities.

Methanol or ethanol could be there also.. I use Methanol instead of ethanol..  Most of the left over methanol that is not used up in the reaction is also drained off in the glycerol layer.. So much of it that many biodiesel makers set up revovery stills to get it back from the glycerine.  However, there is some left in the biodiesel and I could get this out if required.

Lets assume for the sake of this discussion that I am just dealing with diluted KOH left-over catalyst..
You are suggestin phosphoric acid?  What about nitric acid?   
Is there more involved in making potassium phosphate than just neutralizing with phos acid?  Or is it really that simple for a poor-mans fertilizer?

I'd rather use the phosphate road than use nitric acid.. I buy KOH in 50lb bags and would hate to end up on some FBI watchlist for buying nitric acid along with it..

Thanks very much for your input..

Offline Murphy

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #3 on: June 20, 2006, 12:01:12 AM »


So my question has been moved to a forum section that no one visits?

Great...

Offline billnotgatez

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #4 on: June 20, 2006, 01:06:28 PM »
Is there any reason why you would not let the water evaporate and reuse the KOH catalyst?


Offline Murphy

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #5 on: June 20, 2006, 07:16:27 PM »
billnotgatez,
Thanks for your response.. I didnt think anyone was ever going to see my topic being that it's been moved to an almost non-active forum section...

Evaporating the water is not really an option as I generate so much of it.. A 50 gallon batch of bio will generate at least that much in wash water.. sometimes even more.  Also, there are other things in the wash water like soap.   Evaporation would require either lots of energy, or lots of space to hold the large volumes.
It just seems better to turn it into fertilizer if I can..


Offline Yggdrasil

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #6 on: June 20, 2006, 08:19:54 PM »
Maybe I don't completely understand your process, but I don't see the logic in turning the wastewater into fertilizer.  What kind of nutrients are in the wastewater that will be beneficial to the plants?

Offline Murphy

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #7 on: June 20, 2006, 09:00:20 PM »

There is left over catylist in the waste water.. The catylist is potassium hydroxide.. This also makes a small bit of soap but not a allot..

There is also methanol in the waste water but I can get rid of that pretty easy before using it for fertilizer.

Offline Mitch

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #8 on: June 20, 2006, 09:13:20 PM »
The death of the plants might be because of the alkalinity of the water. I'm not sure what could be done to remove that. http://www.wqa.org/glossary.cfm?gl=663
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Offline constant thinker

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #9 on: June 20, 2006, 09:16:07 PM »
A suggestion is nitrating the KOH with nitric acid, but the nitric acid is hard to get, and to much would make the solution acidic.
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Offline Murphy

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #10 on: June 20, 2006, 09:34:51 PM »

What about phosphoric acid?  Isnt that a very environmentaly safe stuff?  Combined with KOH rich waste water solution, would that not make a poor-mans potassium phosphate?

I can get any chemical I want.. I've been doing business with a large industrial chemical supplier for 15 years and they know who I am..

I'm not crazy about using nitric acid.. While it might make a poor-mans potassium nitrate fertilizer, the problem is that one of my major by-products is glycerine..   I'm not interested in having glycerine and nitric acid in the same building..   Nor do I think purchasing the 2 at the same time is a good idea.. I might as well call the FBI myself...   ;D

Offline mike

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #11 on: June 20, 2006, 10:08:11 PM »
If you are on such great terms with the chemical company have you thought about maybe giving them the waste to dispose of?
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Offline billnotgatez

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Re: Converting Byproduct stream from Biodisessel Process into Fertiliser
« Reply #12 on: June 21, 2006, 03:45:29 AM »
I was studying about fertilizers at http://en.wikipedia.org/wiki/Fertilizer after your posts. I am not certain that just because you have a compound with potassium in it that that element will be available as a nutrient to plants. For instance it appears that potassium sulfate is used rather than potassium nitrate as a fertilizer. Also, I seem to recollect that buffers have phosphorous compounds in them. Still I am not sure potassium phosphate would act as a nutrient.

Offline billnotgatez

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Re: Converting Byproduct from Biodisessel Process into Fertiliser
« Reply #13 on: June 22, 2006, 03:02:45 AM »
Murphy-
Is there such a thing as using too much fertilizer?

Offline Murphy

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Re: Converting Byproduct from Biodisessel Process into Fertiliser
« Reply #14 on: June 24, 2006, 01:29:28 AM »
Murphy-
Is there such a thing as using too much fertilizer?

Of course..  to much of anything is bad...

I think my problem is mostly pH as later wash batches have a lower pH value and dont seem to kill the grass no matter how much I dump on it..  The first 5 gallon batch I remove is usually up around 9.5.. Second batch falls to around 9.2, and so on until my 6th or 7th batch is barely above incoming water pH... (7.5 or so).. That means that first batch has something like 10,000 times more caustic in it than the last batch..  Is that correct?  pH is  X10 for each number higher?


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