Introduction to making Biodiesel
Biodiesel Processing Guide
1. The base amount of lye catalyst needed
2. Titrating waste vegetable oil (WVO)
4. The Process of a test Batch
5. Processing Larger Batches of Biodiesel
6. 3/27 Methanol Test / 10% Biodiesel Test - Testing for a Complete Reaction
7. Washing Biodiesel
Methanol Recovery Systems
Two-Stage Process (Acid/Base)
Biodiesel can be burned in any diesel engine or home oil heater and even experimentally in gasoline engines when heavily diluted with gasoline. Biodiesel burns cleaner than traditional petro-diesel. There is basically no sulfur content.
Biodiesel is also renewable. Since biodiesel originates from a modern day plant instead of hundreds of thousands of years worth of dead organic material, we are also using the fuel in a recycling process. The plant harvests energy from the sun and CO2 from the air using photosynthesis, which is further processed into fuel by us, then burned in an engine or heater for its energy, and CO2 is released back into the atmosphere for another plant to breathe in and begin the process all over again. When petrol fuels are used, CO2 is being added to the Earth system and requires extra plants to maintain current CO2 levels in the atmosphere.
Biodiesel is more lubricating than diesel fuel. It will lubricate your injection pump and injectors, thus increasing the life span of your diesel engine. Biodiesel is also a good cleaning agent, so it will clean out your injectors and even your fuel tank, which is why most users will notice that they need to change their fuel filters after running one full tank when introducing biodiesel into their vehicle. It may take a few filter changes before the tank is entirely clean. Your engine will perform better and eliminate the need for fuel additives commonly used in petro-diesel to enhance performance. Most users will also notice a lot less black smoking coming from their exhaust when using biodiesel and most likely, no smoke at all when B100 (100% Biodiesel) is used. The best part of all is that the exhaust smells like the oil which was used, which is a lot more of a delightful smell than the dirtier petrol diesel.
Biodiesel has about 5-10% less energy density than petroleum diesel. This will result in a slight loss in power or fuel economy. However, most users do not notice a difference at all, since this is a minimal change. Gasoline fuels mixed with 10% ethanol have exactly the same effect since ethanol has half the energy density of gasoline and most users have not noticed a difference in that either since it has been introduced as a standard into our fuel economy.
Biodiesel also has more of a gelling issue than petro-diesel. It will begin to cloud at about 40°F and gel in lower temperatures. Users of 100% biodiesel can mix into petro-diesel during the winter months to avoid any issues with cold starts and operation in the winter. There is one type of anti-gel formula on the market which actually works with specifically B100 called Technol B100 Cold-flow Improver. It will reduce the gel point by about 30°F. So for biodiesel which gels at 36°F, the new gel point will be 6°F with the proper amount of Technol dissolved into the B100.
B100 (100% Biodiesel) will also corrode rubber lines, seals and gaskets. Most newer vehicles already have the necessary parts for handling biodiesel, but it is best to check with the manufacturer before filling up your tank. users of B20 and less mixtures will not experience any issues with rubber fuel lines. those using B100 can experience line failure within 6 months of use, assuming the lines are new when it is started. If you should need to find a substitute for rubber fuel lines or gaskets, or if your existing fuel system requires a change, you should use Fluoroelastomer hose, which is 100% compatible with Biodiesel. The most common brand name for this type of hose is known as Viton®, and there are many generic versions of it such as our own fluoroelastomer hose which is much more cost effective and works just the same.
Introduction to making Biodiesel
Biodiesel is most commonly made from fats derived from vegetable oils. Its viscosity is similar to diesel and can run in any diesel vehicle without any modification of the engine, with the exception of old fuel lines and gaskets found in older diesels from the 1980's which may be corroded by biodiesel.
Most makers of biodiesel obtain their vegetable oil sources from restaurants. Restaurants will give away their used frying oil since it must be properly recycled and not thrown away. Aside from many other recycling methods, biodiesel is one of the best ways to recycle this used cooking oil since it helps aid an expensive fuel market and its by-products can be used for many other things.
How Biodiesel is Produced
Biodiesel is produced by using an alcohol and a caustic catalyst such as sodium hydroxide or potassium hydroxide. Methanol is the most commonly used alcohol since it is cheap and easy to obtain. It is possible to use ethanol, but it is a more difficult process and it cannot be purchased economically for producing biodiesel due to high taxes imposed on it.
The Very Basics of Making Biodiesel
In the process, methanol and the catalyst are mixed together into a solution. The methyl catalyst is then slowly mixed into the vegetable oil for a certain period of time. Once a complete reaction is made, the methyl esters will replace the free fatty acids in the vegetable oil and drop out as a glycerin by-product. After a few hours of settling, you’re left with biodiesel on the top and glycerin on the bottom.
Differences Between NAOH and KOH
Both NAOH (Sodium Hydroxide) and KOH (Potassium Hydroxide) can be used for making biodiesel. Both catalysts are highly hygroscopic, which means they absorb moisture from the air rapidly. This will interfere with the biodiesel process and produce soaps if too much moisture is present.
NAOH is cheaper, more pure and less is required in the reaction. However, KOH makes a better reaction, a better by-product and is easier to use. Please refer to the table below for a specific comparison on the advantages and disadvantages.
||KOH (Potassium Hydroxide)
||NAOH (Sodium Hydroxide)
||Requires more catalyst 1.4025 more than NaOH
||Less catalyst required
||Dusty when scooping, requires more caution
||Sticks to the body easier since moisture absorption is more rapid
||More forgiving when moisture is present in biodiesel reaction
||absorbs moisture from the air faster than KOH
|Dissolved in Methanol
||More forgiving when wrong catalyst amount is used
||doesn’t work well for high titration levels
||more liquid, Can be used to make liquid soap or fertilizer
||more viscous or even solid, Can be used to make solid soap
Simple Steps to Making Biodiesel
1. The base amount of lye catalyst needed
For clean, un-used vegetable oil, there is a base amount of catalyst which will need to be dissolved into the methanol to make a complete reaction. For NaOH, the commonly accepted amount is 5 grams of NaOH per 1 liter of vegetable oil to be converted. Since KOH is less dense, it requires 1.4025 times as much, which is 7 grams of KOH per 1 liter of vegetable oil to be converted.
Purity must also be taken into account. Usually with NaOH, purity can be neglected, since it is often nearly 100%. However, it is important to factor in purity with KOH since it is usually about 90%. To factor in purity in your calculations, divide the base catalyst amount by the % purity. We usually carry NAOH with a purity of 99.1% or so, which makes the calculation 5g/0.99 = 5.05g of NaOH per liter of oil. For KOH, it’s usually about 90%, which calculates as 7g/0.90 = 7.77g of KOH per liter of oil. Check the current certificate of analysis for the catalyst you are using to calculate the most accurate amounts possible. Usually, going with the 99% or 90% is sufficient since the differences in hundredths or even tenths of a decimal can be lost in the weighing process, especially when doing larger batches.
When converting WVO (waste vegetable oil) to biodiesel, more catalyst is needed than for clean oil. The recipe will require the base catalyst plus an additional amount which must be determined by a titration each time a different batch of biodiesel is made.
2. Titrating waste vegetable oil (WVO)
Waste vegetable oil (WVO) containers Free fatty acids (FFA) which cause vegetable oil to be viscous and even gel at room temperature. The more FFA an oil has, the more lye catalyst you will need to replace the FFA with methyl esters.
Since FFA content increases with continued use in a fryer at a restaurant, you must perform a titration to find out the FFA content. To do this, you will need the following:
- 99+% Isopropyl Alcohol
- 1% Phenolphthalein Solution in alcohol
- Accurate Syringes
- Beakers (50 ml is ideal) or small containers to mix the solution in
- 1 liter (or larger) bottle
- distilled water
- Lye Catalyst (sodium hydroxide or potassium hydroxide)
- Pocket Scale accurate to at least 0.1 grams, preferably 0.01 grams.
all of the above is sold at the Duda Diesel store in a single titration kit.
Create the 0.1% by weight Lye Catalyst Solution
First, you will need to make a 0.1% by weight catalyst solution in distilled water. To do this, measure out exactly 1 gram of sodium hydroxide or potassium hydroxide, depending on which catalyst you will be using in your process. Dissolve the 1 gram of catalyst into 1 liter of distilled water. For most accuracy, weigh your water rather than measuring it. 1 liter of water weighs 1 kg. it should actually be 1g of catalyst in 999ml/999g of water, but most are unable to be exact on such a measurement for such a small correction in error since scales that weigh up to a kg usually do not weigh accurate to the tenth of a gram.
Should your measuring devices have an accuracy concern, proportionally increase the amount of your solution. For example, add 3 grams of catalyst into 3 liters of distilled water. Making larger measurements will leave less room for error, but may not be worth it if you don't plan to use that much solution.
Once you have a 0.1% lye catalyst solution prepared, you will be able to perform your titration. Catalyst solutions are only good for about a month before they begin to weaken. Make a fresh solution every month.
Perform a blank titration
It is important to make sure that your isopropyl alcohol (IPA) is fresh. Since IPA does not have a ph rating, you cannot simply test it with a ph meter. However, you can perform a blank titration. To do so, measure out 10 ml of IPA and place it into your beaker. Add a couple drops of phenolphthalein. Next, use a 3ml or 5 ml syringe to measure out your lye catalyst solution. Put a drop or two at a time into the isopropyl alcohol. It should turn magenta within a few drops, usually on the first one. If it takes more than a few drops to turn magenta, your IPA is bad and you should replace it. You still can use it however, but you must make sure to perform the blank titration up until it begins to turn a light magenta before starting the titration process. If your IPA is good, you will not need to perform this step again unless the IPA has been stored for a long period of time or you suspect contamination.
Performing the Titration
Use a 10 ml syringe to measure out 10 ml of IPA. It is preferred to use at least 99% industrial grade or better IPA, since the water content in dilute solutions will affect results. Put the 10 ml of IPA into a small beaker, 50 ml beakers work the best. Add a couple of drops of the 1% phenolphthalein in alcohol solution.
Measure out exactly 1 ml of your WVO sample using a 1 ml syringe which is accurate to at least a 10th of a ml, preferably accurate to a 100th of a ml. Dispense the 1 ml of WVO into the beaker with the IPA. Swirl it around a little by moving the beaker to ensure it dissolves completely into the IPA. It could be a white cloudy mixture or almost clear.
There are two methods for measuring the titration process. Using a pocket scale accurate to at least a tenth of a gram is the best way. Place the beaker onto the scale and tare the weight. After the titration, you can place the beaker back onto the scale to see how many grams of catalyst solution you have added. 1 gram of water = 1 ml of water.The other method is to use syringes. usually, a 3ml syringe works fine for NaOH and a 5 ml for KOH, depending on titration levels.
If you have a magnetic stirrer, this is a great time to use it. Use the stirrer to gently stir the mixture in the beaker, or if one is not available, gently stir the mixture with a stirring rod or by swirling it with movement of the beaker. next, slowly dispense the catalyst solution into the beaker while mixing it. It will usually turn a cloudy white color and then begin to show signs of pink. when you start seeing the pink, add the catalyst solution drop by drop until it remains that pink/magenta color for 30 seconds. Once you have achieved this result, you are ready to measure your results and calculate the titration amounts.
Calculating lye catalyst needed from titration results.
Count how many grams (or ml for syringes) of catalyst solution it took to complete your titration. Each gram/ml of solution required represents 1 gram of lye catalyst needed in addition to the base catalyst to process your WVO. base catalyst + ml needed to titrate = total grams needed to process the oil.
As an example:
Let’s say it takes 2.3 ml of lye catalyst solution to complete your titration. If you are using sodium hydroxide, the base catalyst needed is 5 grams. So that’s 5g + 2.3 g = 7.3g of sodium hydroxide per liter of oil. Divide the base catalyst by 0.99 and then add the 2.3g to get 7.35g for purity corrections. As you can see, it doesn't really matter much with NaOH but it's a good practice. Be sure to only factor purity into the base catalyst. If you're using the same catalyst in your catalyst solution, purity corrections have already been made within the mixture itself.
For potassium hydroxide, the base catalyst is 7 g. So that’s 7g + 2.3g = 9.3g per liter of oil. Don’t forget that potassium hydroxide is not normally anywhere near 100% pure, so you will need to factor in the purity by dividing the base catalyst by the purity. Assuming 91% purity, it would be: 7g/0.91 + 2.3g = 9.99g of KOH needed per liter of oil.
Methanol, like the catalysts, also absorbs moisture from the air. Be sure that when working with methanol, to work quickly and seal the containers in between uses as soon as possible. The less moisture you have in your process, the less soaps you'll end up with in the finished product.
The amount of methanol required for the process is about 20% of the volume of the oil to be processed. Some brewers use 21% or even 22% to be sure there is enough. To be clear of how much methanol to use, if you were to process 100 liters of vegetable oil, the process would require 20 liters of methanol for 20%.
Once the methanol has been measured out, the catalyst now needs to be mixed into a solution with the methanol. For clean oil, use the base catalyst amount and for used vegetable oil, use the base catalyst + titration amount.
The reaction between methanol and the catalyst is exothermic. It will release a large amount of heat during the reaction. In the case of plastic tanks used in processors, the amount of heat released is usually not enough to make the methanol boil off, but it is good practice to add half first, let some heat bleed off and then add the rest if a lot of catalyst is needed.
NaOH releases more heat in the dissolving into methanol. KOH tends to be a lot cooler when dissolving into the methanol and can usually be mixed immediately and be ready to go in minutes.
For small amounts of mixtures of methanol and catalyst, it can be mixed together quite easily by putting the methanol and catalyst into a sealed container and then shaking and swirling it around. Once all of the catalyst is dissolved, it’s ready. For larger applications, it’s best to attach a propeller to a stainless steel shaft which can connect to a power drill. The drill can be run for only about a minute and there should be enough agitation to fully dissolve the catalyst into the methanol. Since methanol is flammable and drills can spark, this shaft should be attached through the cover to the tank as a permanent attachment. We have ours installed with ball bearings inside of the cover for an easy spin.
Another method would be to use a pump, drawing the methanol from the bottom of the tank to the top of the container, with a screen blocking the catalyst from flowing through the bottom until dissolved. Some processors use the mixing pump for the biodiesel reaction to perform the methanol mixing task by the switching of a few ball valves. it works, but it will get some biodiesel/oil and maybe glycerin into your methanol mixing tank.
4. The Process of a test Batch
For first-time users, it is best to do a few test batches first to be sure that measurements are being made correctly and to see how the process works. If a new brewer jumps right to the processor, lack of experience can lead to a processor full of badly reacted biodiesel and a lot of headaches.
On a small-scale, accuracy in weights and volumes of the vegetable oil and catalyst is key, so if a user can master using the right amounts for a small batch, larger batches can easily be made since there is more room for error in a large batch. Most test batches process 1 liter of vegetable oil, which requires a standard 200 ml of methanol with 5g of naoh or 7g KOH base catalyst (purity not factored in) + titration amount for used oil. First-time users should start with fresh oil so the reaction alone can be familiarized with, and then move onto waste vegetable oil to practice processing successfully with a titration involved. If you change your type of process at any time, such as changing from naoh to KOH or even changing to a different oil from a different restaurant, it is best to perform a test batch before a larger batch.
1 Liter Test Batches
For a small batch of biodiesel (test batch) usually a cheap blender is an easy way to perform the mixing process. Heat the 1 liter of oil up to about 140°F (60°C) using an old pot on a stove. Don’t let it get any hotter or you will end up boiling your methanol when you add it.
Prepare your methanol/catalyst mix by mixing the methanol and required catalyst in a compatible container. Be careful not to use just any plastic like a water bottle as the mixture is corrosive and is likely to eat the bottle away. Stick to tough plastics such as HDPE (High density polyethylene). Keep the container closed while mixing, it can be shook vigorously and the cap partially unscrewed in between shakes to release the pressure from the gases created in the reaction. CAUTION: Do not breathe in these gases. They are toxic! Once the catalyst has been fully dissolved into the methanol, you are ready for the reaction.
A magnetic stirrer would be ideal for the mixing process, however, most people starting out will probably want to use an old blender. It's best if the blender is made of glass and not plastic. Plastic ones are usually cheap and may crack under the chemical mixes and heat.
Pour the oil carefully into the blender, cover with the cover and then start the mixing on a low speed while holding down on the cover. Once all the initial turbulence has settled down in the mixing, remove the cover and then slowly pour the methanol/catalyst mixture into the oil. Cover the blender again and turn on to a higher speed.
Agitation in a blender is plenty enough for making biodiesel. You should only need to run it for about 15-20 minutes. Once the mixing is completed, stop the blender and pour the mixture into another container, preferably clear HDPE for watching the glycerin by-product drop out. Don’t leave it in the blender. The regular rubber gaskets will deteriorate over time when exposed to biodiesel. You can expect the blender to only last for a few test batches and to never be used again for anything else.
Whichever mixing method you use, after about an hour, most of the glycerin will drop out of your product and settle to the bottom. it will be a darker color and appear much more viscous than the clearer biodiesel on the top. You should wait at least 12 hours before washing it, preferably 24 hours. The longer you wait, the more glycerin will drop out and the easier the wash will be. Some users will wait 2-3 weeks to let all impurities drop out, and then the water wash will be perfect and clean.
Washing a test batch
Washing is the most difficult part of the biodiesel process. It is extremely important to wash out all of the impurities left over in biodiesel that do not drop out with the glycerin. This includes soaps, salts and other such non-filter friendly contaminants.
Water washing is the simplest method for washing biodiesel but can be the most difficult to perform successfully especially with heavily contaminated batches. There are some dry washing methods available which are much more convenient and effective than water washing. The best dry wash method is the use of ion-exchange resin such as Dudalite in a dry wash tower. Another available dry wash media is Magnesol. for washing a test batch, it is best to stick to the simple water wash method and then move onto the dry wash media on larger batches.
To water wash your test batch, drain off the glycerin from the bottom. Most likely, you don’t have a drain on the small container you put the biodiesel into. Even if there is a drain, it will not be convenient like in a larger batch. You will be likely to end up draining out half of the biodiesel before you can get all of the glycerin out of the bottom. What I do is pour the top part (the biodiesel) into another container and then pour the bottom part (mostly glycerin but still some biodiesel) into one of our tri-pour beakers. Once resettled in the beaker, almost all of the biodiesel can be poured into the container, leaving all of the glycerin set aside in the beaker.
Next, once you have just biodiesel and NO glycerine, add 1/3 as much water as biodiesel in a slow manner so as not to agitate the biodiesel too much. the water will sink to the bottom quite readily if it’s not agitated. Now, turn the bottom upside down and let the water settle down to the top, which is now the bottom upside down. And continue to do this over and over until the water becomes very murky. Be careful not to agitate the biodiesel too much, or you will have to wait a long time for it to separate, possibly up to a week or longer.
After the water is dirty, it has captured a lot of the excess methanol, soaps and other contaminates in the biodiesel. Let it settle for a good amount of time so that you have all biodiesel on the top. if you are gentle enough, it should only need about 15-30 minutes to completely settle out. Proceed to drain out the biodiesel into another container as you did before when removing the glycerin, and then add 1/3 water again and wash again. Each time you wash, the water should start to become less and less murky. As the biodiesel gets cleaner, you will also notice that you can be a little more vigorous in the washing. Be careful not to agitate it too much so you don’t have to wait too long for it to settle. The goal is to get to a point where the water no longer gets cloudy at all and remains clear. This happens when the biodiesel has been washed completely. usually this is achieved after 3-4 washes. The wash water should be at a neutral ph of 7 when the biodiesel is completely washed.
Drying a test batch
Although properly washed, biodiesel will not appear fully clear until it has been dried of all of the water. this can be achieved in a few different ways. The easiest but longest way is to set the container out into the sun so the water can slowly evaporate out. It can take up to 3 weeks for this process to be complete. To speed up drying for small test batches, you can pour the biodiesel into a pot and gently heat it up to 212 degrees. Above its boiling temperature, water cannot exist in liquid form. So once your biodiesel has passed 212°F and the bubbling has stopped, there is no need for additional heat as all of the water will have boiled off. Some people like to heat to something like 250°F to be sure, but this is a bad practice and a waste of energy since it is impossible for water to exist beyond 212°F at sea level.
When the final biodiesel product has been fully dried, it will be a nice clear or almost translucent color. This is your finished product, ready to be filtered and filled to your fuel tank for use.
5. Processing Larger Batches of Biodiesel
Once you have mastered 1 liter test batches of biodiesel, it will be time to start thinking more about the processor than the process. Building a processor is quite simple, and you don’t need all of the fancy looks of expensive processors to get the job done.
Building your own processor
It is most common for biodiesel makers to use conical bottom shaped tanks for the purpose of easy draining and separation of by-products from the biodiesel. The most common set-up is to attach a valve to the bottom drain which leads to some plumbing going to a circulation pump and also to another drain which can be used to actually drain off the bottom. I find it best to attach that drain to a hose so that by-products and biodiesel can be drained to any container. Some people even attach a 2nd pump for pumping the finished biodiesel out of the tank.
The 1st pump should be plumbed in so that it can take biodiesel and anything mixed in with it such as biodiesel and pump it up to the top of the tank. This is the best mixing method of the processor. This pump should be powerful and ideally should be able to circulate 1/3 of the tank within a minute’s time. the slower the pump, the less agitation you have and the longer the processor will need to run.
Circulate the batch from the bottom and back to the top in a continuous loop. It is often a common practice to install temperature gauges or thermostats into this part of the plumbing as well as a water heating element for temperature control. We install plate heat exchangers into this part of the line so we can use the hot water coming from our solar water heater. We are all about being green and efficient, and if you want to truly be green, i highly suggest adopting solar water heaters into your process. Not only will it save you a lot of energy on biodiesel making and drying, but it will also take away from your energy bill when it comes to using hot water elsewhere in your home.
A 2nd smaller tank is often plumbed in line with the 1st tank for mixing the methanol-catalyst solution and then slowly adding it to the process as vegetable oil is pumped from the bigger tank’s bottom and back to the top. the best way to do this is to run the bottom of the methanol-catalyst solution tank through a small pump and down to a tee just before the circulation pump. Use a one way check valve right at the connection point to ensure that vegetable oil doesn’t find its way up into your methanol-catalyst solution tank from the pressure created by a lot of fluid in the larger tank and gravity overpowering the circulation pump’s ability to suck in both the vegetable oil and methanol-catalyst solution at the same time. the purpose of the methanol-catalyst solution pump is to help push the methanol-catalyst solution through that check valve to completely empty the methanol-catalyst solution tank. it should also be as close to the check valve as possible and preferably with a little bit of head pressure to help push it. A ball valve should also be installed on the drain of the methanol-catalyst solution tank so that the methanol can mix evenly with the catalyst prior to dispensing it.
Mixing the methanol-catalyst solution can be tricky. Since you’re dealing with larger amounts of methanol, you cannot simply shake it up like in a test batch and sometimes there’s too much catalyst required to just let it sit overnight and dissolve. The best solution to this, is to find a propeller like what you find on a boat motor, run it to a shaft which comes up and through the cover in the tank and is sealed off with some washers so that it’s free to rotate, and then use a power drill to attach to the shaft and spin the propeller at rapid speeds. Amazingly, it will only take less than a minute for KOH to dissolve into methanol with this set-up, if even that long. You should also attach a fine screen on the top of the drain of the tank to prevent the catalyst from falling into the plumbing. This usually isn’t much of a problem though if you have a ball valve, but is still recommended. be sure the propeller does not touch the screen.
Sizing your processor
the methanol-catalyst solution mixing tank needs to be at least 20% the size of the batches you are planning to do, and the mixing tank needs to be at least 120% the size of the batches you are doing to account for the vegetable oil and methanol added. Most standard processors have a 60 gallon mixing tank with a 15 gallon tank for mixing methanol-catalyst solution Other sizes could be an 85 gallon tank with maybe a 15 gallon methanol-catalyst solution tank or a 110 gallon tank with a 30 gallon methanol-catalyst solution tank. for the 60 gallon the largest possible batch would be 45 gallons of vegetable oil and for the 85 gallon it’s 65 gallons and 110 gallon would be 85 gallons. since the tanks’ max capacity is based on the top most height of the tank however, it’s usually best to process about 5 or 10 gallons less than these max capacities in order to avoid spillage from overflow during pumping or when there is a bad measurement.
Materials for your processor
HDPE and other resistant to biodiesel/caustic/methanol materials should be used when building a processor. Stainless steel is the absolute best metal to use and regular steel, galvanized steel and especially copper and aluminum should be avoided since they will corrode quickly and affect the quality of the process. PVC pipe can be used, but it’s best to stick to threaded piping since glued pieces can spring leaks after awhile and cause more headache than it’s worth.
Regular rubber hoses cannot be used. Biodiesel quickly degrades the quality of rubber and rubber hoses would need to be replaced often. Clear vinyl hose tends to be the hose of choice since it holds up against biodiesel for quite some time and you can see the fluid inside of it. This is especially great for the drain hoses. Fluoroelastomer hose will last the longest when exposed to biodiesel and processing biodiesel, however, it is not so good when up against the pure methanol-catalyst solution since methanol degrades grade a Fluoroelastomer hose. it is a very good idea to use vinyl hose when connecting from the methanol-catalyst solution tank to the plumbing of the larger mixing tank so you know when it has been fully emptied.
It is extremely important to make sure there is no water in your vegetable oil before processing. Depending on how often you need to process biodiesel, you may need a few settling tanks for removal of water. Settling is the easiest way to remove water. If vegetable oil is left in a cone tank for 2-3 weeks and left untouched, all of the water can be drained out the bottom readily. This process can be sped up by installing a heating element at the bottom of the tank and gently heating the veggie oil up to and maintaining it at about 100°F to 110°F for 4-6 hours. The heat decreases the density of the vegetable oil greatly while the water’s density remains about the same, settling the water down faster than normal. After the initial 4-6 hours of maintaining heat, the vegetable oil should be completely separated after 12 hours, preferably 24 hours. use the crackle test to ensure no water is present once you have removed the water from the bottom.
Processing with your own Processor
No matter how powerful your pump is, you will not achieve as much agitation as in a blender or magnetic stirrer. You could use a blender like set-up instead of a pumping system, but blades are likely to degrade when left in the biodiesel for a long period of time and it’s not so easy to set such a system up. There is also a better chance of spillage when this method is used, and you won’t be able to access the top of the processor very easily when you need to.
The time it takes to successfully process a large batch of biodiesel will depend on the power of your pump. Generally, it takes about 1.5 to 2 hours of circulation to fully complete the reaction. Some users need to run it for as long as 4 hours and others can get away with shorter times. Heating of the biodiesel is also very important. The temperature should be maintained at about 150°F for the entire mixing process. if lower temperatures are used, it will require longer mixing times.
Once the process has been completed, you can stop the pump and turn off the heat. let the biodiesel settle overnight just like you would with a test batch. Settling is mostly done in 12 hours, but you should wait 24 hours to be sure. the longer you wait, the better.
6. 3/27 Methanol Test / 10% Biodiesel Test - Testing for a Complete Reaction
How to Know When the Biodiesel Reaction is Complete
Biodiesel dissolves quite readily into biodiesel while vegetable oils or fats do not. The 3/27 Methanol test, or 10% biodiesel/methanol test can be used to determine whether a reaction in your process is complete and you are able to turn off the process to settle out the glycerine.
Performing the 10% Biodiesel/Methanol Test
1. Take a small sample from your processing batch into a beaker and let it settle for a few minutes.
2. Draw exactly 27 ml of methanol using a syringe and place it into a clear, thin glass jar with a good lid which is able to hold at least 30ml of fluid but not too much more than 100ml.
3. Once the glycerin in the biodiesel sample has appeared to mostly settle out, draw exactly 3 ml from the top and add it to the 27ml of methanol in the jar to make a 30 ml solution.
4. Shake up the solution vigorously for a few seconds and then place it onto a level surface for observance. Within ten seconds, the solution should clear and you should be able to see right through it. Most likely if it is perfectly clear, the reaction is complete.
5. Inspect the solution for non-miscible parts of oil floating in the solution. If you can see any dots or traces of oil, typically floating on top of the solution or possibly lingering at the bottom, the reaction is not complete. Usually solutions with spots in them will also be cloudy, so when it is completely clear, it is often a safe bet that the process is complete. Some complete batches may not be of the highest quality and will be a little hazey but still have no floating oil.
If your solution is clear and without any oil spots, your reaction is complete and you may shut off your processor and begin the settling process. If there are oil spots found, leaving your processor on for further mixing and test again. continue processing and testing until you reach a clear, unspotted solution. After performing this method a few times on a few batches, you will get a good idea of exactly how long each batch should take.
7. Washing Biodiesel
Clean fuel is essential for keeping an engine away from maintenance later on. Washing biodiesel, whether by dry wash resin or with water will remove soaps and other contaminates. This is essential to ensure your fuel filters will not get clogged and also to be sure your engine will not get beat up. If using water washing, it is best to remove the methanol first prior to doing the wash. If using dry wash resin, whether you remove the methanol first or not will depend on your soap content. Do a soap titration on your fuel prior to the dry wash and determine if utilizing a methanol wash is necessary or not.
Washing is easiest when all possible glycerin has been removed. Glycerin drops out fastest when excessive methanol has been removed from the biodiesel. This can be taken out by one of two ways, distillation (methanol recovery) or by simply evaporating it into the atmosphere. Distillation is covered later under methanol recovery. If you do not wish to recover the methanol for re-use, you can simply bubble the biodiesel with a fish tank compressor, while blowing a fan above the tank to help force the air with methanol fumes out of it. The methanol should be completely gone after about 24 hours. Note that this cannot be done in a closed area and the methanol fumes should be vented outside. Once the methanol is removed, excess glycerin should rapidly drop out in about 24-48 hours.
If you use a full drain tank, meaning, there is no bulk head, you will be able to fully drain your glycerin and you can potentially use your mixing tank as a wash tank when washing with water. Even though this may work, it is recommended to have a separate tank from water washing. If you mess up, you’re stuck with waiting until your batch is fixed before you can do another, and you will need to wait for the tank to dry after using it before you can use it on a new batch. If you are dry washing, you can pull the biodiesel right from the tank, through your towers and into your clean storage tank.
Assuming you transfer the biodiesel to a wash tank, drain off the glycerin into a storage container and set it aside, then transfer the biodiesel to your wash tank. there are several ways to perform a wash, and depending on which one you use will determine how you set this tank up. do not try to just pump from bottom to top like you did with the mixing, that’s too much agitation and it will make a mess.
The Bubble wash method
The theory behind bubble washing is that when a bubble emerges from water at the bottom of the wash tank, the outer lining of the bubble will carry trace amounts of water up and through the biodiesel to the top of the tank, pop and then descend down slowly through the biodiesel again, pulling down with it contaminates found in the biodiesel.
To perform a bubble wash, fill the bottom of your wash tank gently with 1/3 as much water as you have biodiesel. Once settled, place an air stone attached to any air compressor used in fish tanks at the bottom and run it for about 6 hours. The many small bubbles make from the air stone will rise up and allow water to slowly and gently circulate through the biodiesel, drawing out the contaminates. after 6 hours, stop the compressor and let it settle for 12-24 hours, drain the wash water out and then add another 1/3 water and perform again until the wash water comes out clear.
Bubble washing uses the least amount of water of the water washing methods. However, if the batches are too small, it can agitate the biodiesel too much and cause an emulsion. The final clear water can be used for the first wash of your next batch and if the 2nd to last wash water was not very cloudy, it can also be re-used.
Mist washing is done by installing misting nozzles at the top of the wash tank and slowly introducing water through them and into the biodiesel. The fine spray of water slowly travels down through the biodiesel, taking contaminates with it. After the tank fills up from the water, usually with about 1/3 worth of water, you can drain off the water and then continue spraying. the process will need to be completed until the water comes out clear, which means there are no contaminates left.
Mist washing uses more water than bubble washing because it is not circulated continuously through the biodiesel, however, it is a little more convenient since there is less waiting involved since the biodiesel doesn’t need so much time to settle out except for in the final draining of the water.
What to do with your wash water
Wash water should not be dumped down the drain, especially if you have a septic tank installed. The methanol, soaps and other contaminates pulled out of the biodiesel can be hazardous to marine life and will kill the bacteria needed in a septic system. Check with local laws and codes about disposal of your wash water. Some larger operations tend to have a holding tank outside which can dry in the sun and once the water has all evaporated, the solids can be scooped out and disposed of into a landfill, according to local laws. if you do this, make sure your tank/wash water holding area is much wider than it is tall. you will need as much surface area contact with the sun as possible for fast evaporation. Water takes a lot of energy to heat, and even more to evaporate. If you live in a rainy area, this is probably not the best way to handle this.
We used to rid of our wash water through evaporation by using coolant from our bus engine while driving and circulating it through a radiator in a metal tank. Since most people are doing this process at home, this isn’t really an option, however, it brings out other ideas as described below.
Another option to consider would be to again utilize a solar water heater.The best way to do this is to get a metal drum or some sort of temperature resistant container, drop an old radiator into it with the wash water, and circulate the hot water from your water tank or even fluids directly from the solar heater through the radiator. It will heat up the water throughout the day and evaporate it out much more quickly than just plain sunlight.
other users may find it convenient to boil the water out of a drum by burning a fire under the drum or using heat from a boiler or wood stove with a medium fluid similar to the set-up for the solar water heater. Most methods will work if it involves adding heat to the water for a good amount of time, but i only really want to promote the greener way of doing it. Other methods that expend energy may save time but are essentially wasteful. If you don’t have the patience for getting out the water to save money on the wash water disposal, i would recommend dry washing instead.
Water washing is often complicated and requires a lot of time and care for each batch of biodiesel. A few dry-washing methods have been developed to help speed up the process and make it a lot easier. Dry-washing also prevents chances of an emulsion when a bad batch has been made and can even produce a higher quality product if the dry-wash is done properly. Best of all, dry-washing does not leave you with messy wash water that has to be disposed of properly and it saves you the cost of water as well. For some locations, dry-washing is more cost effective. Dry-wash resins are commonly used in the Biodiesel Industry and is preferred for the speed and quality of fuel made.
DudaLite, PuroLite® and Amberlite®
The use of DudaLite (Ion-exchange resin) is the most cost effective and easiest way to purify biodiesel. The set-up has a higher initial cost than other methods because of the tower, but once set up and in operation, the cost to operate is usually about only 2-3 cents per gallon(depending on quantities purchased at a time). The purification system is very simple and can be left on overnight so little attendance is required. Loading of the towers is quite simple and the resin can be thrown away into the regular garbage system when exhausted.
Ion-Exchange resin is what all of the big Biodiesel producers use for their product because it is simply the best way to dry wash Biodiesel.
Ion-exchange resins can be used for dry-washing biodiesel by use of an ion-exchange tower. The process is performed by slowly pumping biodiesel to the top of the tower and down through the resin, or from bottom to top. Bottom to top is preferred to ensure proper flow as gravity can pull the initial biodiesel down through the tower too quickly. The resin will slowly purify the biodiesel as it passes through the resin bed. When the biodiesel comes out the exit point of the tower, it will be clean of all contaminates and ready for use.
Ion-exchange resins such as DudaLite are like tiny little beads which have tiny little pores that the biodiesel flows through as it channels through an exchange tower. As the biodiesel flows through the resin, soaps, glycerin, water and salts are absorbed, leaving just Biodiesel on exit from the tower. The use of Ion-exchange resins will guarantee that you have ASTM quality fuel with every batch.
Ion-exchange towers are often made of metal since the resins expand as they are used. Plastic or PVC towers run the risk of being blown open from the expansion since the biodiesel is pumped under pressure. Some resins will expand up to 130% of their initial volume before they are fully used up. Towers should be built to accommodate for this expansion. Metal also helps resist this expansion. Screens should be installed on the bottom and top of the tower to prevent the resin from falling out as the biodiesel exits. Never fill a tower more than 45% full its maximum volume with dry resin to avoid explosion of the tower during expansion of the resin.
The towers should be built to be taller than they are wide. The aspect ratio should be at least a 1:3 ratio. That is, the height should be 3 times as much as the width. The height should also be at least 24 inches to ensure enough contact with the resin. The wider the tower is, the more flow rate it will be able to handle. The taller the tower is, the more purification can be performed on the biodiesel passing through it. These heights and widths are based on the part of the tower which will be filled with resin. Don’t forget to at least double the height to accommodate for expansion.
Larger diameter towers allow for faster flow rates. Most small biodiesel makers won't need a large tower since they can use a diaphragm pump and leave it on overnight in a smaller tower. Large diameter towers are intended for more industrial applications where batches are being washed continuously.
The ideal pump to use for pumping the biodiesel through the tower is a diaphragm pump with a pressure regulator. This allows the user to control the flow by use of a ball valve or flow regulator. The diaphragm pump will pump until a max pressure is obtained, and then stop pumping until the pressure begins to relieve, allowing a perfectly smooth flow of biodiesel at regulated pressure through the tower at the desired rate. Diaphragm pumps can run non-stop, even dry without damage and are easier to control. Flow control is very important since the biodiesel needs to flow at the right speed to be fully purified. Our diaphragm pumps will build up to 40 psi and then shut off, slowly releasing the biodiesel through the piping and into the tower at the flow rate needed. Place a ball valve at the exit point of the tower and a perfectly even flow can be achieved.
For more information on how to use ion-exchange dry wash resins, please see our dry wash resin information page.
Magnesol is a simple and cheap way to dry-wash biodiesel. The D-60 product has been produced by The Dallas Company and tested specifically for dry-washing Biodiesel, guaranteed to yield a high quality product. Magnesol is basically a Magnesium Silicate compound, similar to common talc powder. The powder is extremely fine and will get everywhere if you drop it on the ground. Take care when using it as it can get into your lungs and irritate them if breathed in.
Magnesol is simple to use. Simply add the appropriate amount to your biodiesel after draining off the glycerin and then circulate/mix the biodiesel for about 15 to 20 minutes. The magnesol will dissolve into the Biodiesel and then attach itself to the soap particles suspended in the biodiesel.
Once you are finished mixing the Biodiesel with the magnesol, you will need to settle it out the bottom, much like you do with glycerin. drain the magnesol through the bottom once most has settled. From here, simply run your biodiesel through a 1 micron filter to remove the rest of the fine particles of magnesol. It’s best to use polyester bag filters for this since they are cheap and have large surface area. It is also best to pass through 2 or 3 filter bags to ensure all of the magnesol is removed. This can be done by passing it through the same bag 2-3 times or stuffing 2-3 bags inside of each other and doing it all in one pass. Filtering can be done with gravity filtering or also with a pump. If you use a pump you can push the biodiesel through the bag filters with our adapter heads and pass through 2 or 3 bags at a time. You can also use our filter bag housing for constant and fast re circulation. When we filter out our magnesol, we circulate the biodiesel through an adapter head with 3 bag filters attached, back into the mixing tank and then when finished, pump through the filter bag housing as a final filtering device before dispensing into our tanks. since magnesol particles are very fine, it is important to filter as much as possible to be sure all have been removed.
Some users will find that a lot of magnesol is required to fully clean their biodiesel. Part of the reason is that methanol still exists in the biodiesel and it should be removed before performing the wash. Excess methanol can be removed by distillation (heating to boil and then condensing into another container). This excess methanol can be used for the next biodiesel batch so it is often cost-effective to have a methanol recovery system.
In order to determine how much magnesol should be used, a soap titration must be performed. The soap titration requires a 0.01N Hydrochloric acid solution, isopropyl alcohol and a sample of the biodiesel. Since lab grade 0.01N Hydrochloric acid is expensive, most users will mix our 32% Industrial grade hydrochloric acid with distilled water to make it themselves. See the soap titration instructions for more information.
My personal preference on Magnesol is that while it is more convenient than water washing, it is easily trumped by the Ion-Exchange resin. The amount of time put into Magnesol versus the Ion-Exchange resin in a tower does not pay off for the money saved on not having to buy or build a tower.
Soap Titrations are important for understanding how much soap is in unwashed Biodiesel. It is important to know soap content for many reasons. One is to have an idea if you are using too much catalyst, or if your process needs fine-tuning. Another is so you know how much magnesol to use when using the magnesol dry-wash method. Ion-exchange resins are also optimally used when you are aware of general soap content. If soap content is high, methanol washes of the resin will be economical as opposed to where soap content is low and it is not economical to methanol wash the resins. Soap titrations are also needed to tell when ion-exchange resins are exhausted and there is a need to discard the resin from the tower and refill. Please see our soap Titration page for information on performing the soap titration.
Methanol Recovery Systems
The theoretical amount of methanol needed to produce Biodiesel is about 12-15% of the oil being processed. However, since the chemical reaction is reversible, the amount needed to make a complete and full reaction is 20+%. This leaves left-over methanol in the finished product and especially in the glycerol. Methanol should be removed from Biodiesel before use as a fuel. Glycerol requires further treatment (methanol removal) before it can be further processed into a more pure glycerin for other recycling purposes.
Methanol recovery may not be worth it for everyone. The average amount of methanol which can be recovered from the biodiesel after a 24 hour settling period is about 1.5%-2% the volume of the biodiesel. Even with the use of solar technology for free heating, I personally have found the time and effort needed to distill 3 to 6 liters of methanol from my 95 gallon batches of biodiesel a waste of time. I prefer to evaporate my methanol into the air through agitation from a fishtank compressor. The remaining excess methanol will be in the glycerol, which can also be recovered by distillation or evaporated into the air. Whether it is worth the time and energy put into it or not is up to the user, and based on how expensive the methanol cost is and time needed to do the distillation.
To recover methanol, distillation must be used. Distillation is when the methanol is boiled out of the other fluids it is mixed in with. Since methanol boils at a much lower temperature than biodiesel, water and the glycerin, this is not too hard to do. However, it is important to have a fully closed metal vessel with gradual heating and pressure gauges to be sure the methanol does not cause rupture of the tank and that the tank is sure to survive the pressure and heat. Most plastic tanks can only handle about 140°F and not much pressure. methanol needs to be about 150°F at normal atmospheric pressure before it will boil.
Also, when methanol is dissolved into biodiesel or glycerin, it will require good amount of agitation or higher temperatures to get all of it out. Instead of expending lots of energy trying to use only heat, , it is best to utilize a vacuum pump or diaphragm pump. When the methanol is put under vacuum, it will boil at lower temperatures. The vacuum suction from a diaphragm pump also helps force the fumes through the condenser, so there is less waiting. I personally use our 40 psi diaphragm pumps, which will pull up to a 15mm HG vacuum, plenty enough to boil out all of the methanol with low enough temperatures. On a final note, remember to never allow your fluid temperature to go above the boiling point of water so that water in your biodiesel/glycerin will not end up in the methanol. Keep in mind that the boiling point of water will also drop when under a vacuum.
If a diaphragm pump is used for creating the vacuum in the vessel, the outlet of the diaphragm pump can push the methanol into a closed container. A check valve can be installed on the top of that container to blow out air when pressure is gained from the diaphragm pump pushing air and methanol into it. The check valve will keep the container closed from ambient air but prevent dangerous pressure build-up.
Once the methanol has begun boiling off, it will need to be captured and directed through a tube into a condenser. a condenser is simply a heat exchanger where a cooler fluid is used to cool the methanol vapors, causing it to condense back into a liquid and drop into a new container, free of the other fluids it was once in. Condensers are easy to build. You can use a simple copper tubing going through a bucket of water as a simple and cost-effective method. However, if you want to use something a bit more effective, it would be ideal to use one of our plate heat exchangers, pumping cold water from a container through one side of the heat exchanger and allowing the methanol to travel through the other side, condensing into a sealed container. You can also hook up the exchanger directly to a water line if you choose not to use a pump but this will waste a lot of water. The methanol does not take too much heat loss to reduce it back to a liquid, and so having the coldest water is not so important unless the flow is very slow. I usually use a drum of water for my batches, circulating through a plate heat exchanger. When finished, the warm water remains in the drum so heat can slowly bleed off back into the ambient air.
You can find metal fabricators who can build closed vessels for methanol recovery out of drums, welding off most areas for a complete seal. Usually, a drum with a tight lever seal and gasket is good enough to prevent methanol leakage as well. Ports will need to be drilled and welded together to allow for the methanol to escape, draining of the treated fluid after demethylization, and other ports for filling and possibly circulation with a pump. We have found that using old water heater tanks is ideal when there is a stainless steel lining, since it is already fully closed and the stainless steel is ideal for resisting biodiesel and the glycerol.
One methanol has been recovered, it can be reused in your next batch. The less water that gets into the methanol, the better. It is best to add recovered methanol directly to a fresh drum of methanol so any water in it will evenly distribute to the larger volume of pure methanol, this keeping a much more pure methanol and less chance of soaps in the next batch.
After recovering methanol, it is good to test the purity of it before using it. To test the purity is simple. Take a 100 ml sample of the methanol, weigh it in grams. Take the number of grams you weighed, divide by 100ml and you get the density in g/ml. Check the density you find against a methanol density chart to see what percentage you have. This is also a great method to test old methanol that has been stored for a long time. When the purity is in question, a density check can tell you if it's still good and free of water.
Please take caution when recovering methanol vapors. Methanol is poisonous and can cause blindness or death when inhaled in large concentrations. be sure everything is sealed off, and use in a very well-ventilated area.
The use of biodiesel is simple. make sure you filter it, preferably down to 1 micron and then just add it to your tank and go! If your vehicle is new to biodiesel, your fuel filter will require 1-2 changes about a tank or 2 after first use. This is because it is a very good cleaning agent and will soak up all of the junk in your tank from years of filling it with petro-diesel.
We recommend using 1 micron filters because there can be losses in efficiency during the filtration process and your onboard fuel filters will have to do the work if your own filtering does not. Onboard filters are much more expensive than our filter bags and will reduce your fuel economy if they are clogged. We usually pump right from our storage tank, through a filter bag housing with a 1 micron filter bag and then right to the vehicle’s tank using a gas nozzle.
Once you have filled your tank with your own Biodiesel, you will never want to use petro-diesel again. It’s cleaner, cheaper and smells really nice. You can also feel good about it by knowing that you are saving the planet.
Two-Stage Process (Acid/Base)
WVO with high FFA content is difficult to convert to biodiesel using the single stage base process. Many users will find that as titration levels get higher and higher, there will be more and more glycerin byproduct and less fuel yied. If the FFA content is too high, the conversion will not be successful, even with the best and most careful process. For this reason, the acid/base two-stage process was developed in order to convert higher titrating oils. This process is usually intended for titration levels of 12 or more (using KOH) but is also very successful for lower titration numbers and even nearly clean oil. .
Here at Duda Diesel, we've found the two-stage process to be the best way to go for experienced users. It makes a higher quality biodiesel, and will generate the greatest yield. There also appears to be less soap generation, which is likely due to the fact that less base catalyst is required. Once a user is familiar with the two-stage process, the process can also save a lot of time on the mixing part of the process. The two stage process is sometimes referred to as the Fool Proof method to making biodiesel. While it makes the process easier, one who does not make proper measurements or overestimates the amount of acid required wastes chemicals and will end up with a lot of unnecessary salts and water as a byproduct of the process. However, overshooting with too much acid will not ruin a batch, unlike in the one stage process where too much base catalyst will make soap.
The two stage process starts with concentrated sulfuric acid. The sulfuric acid acts as a catalyst and allows for the FFA to undergo esterfication prior to the transesterfication process with the base method. By converting all of the FFA using the sulfuric acid, theoretically any oil, no matter how high the titration, can be converted to biodiesel using the second stage base process after acid esterfication.
Biodiesel processed using the two-stage process tends to be a better product and provide a better yield of biodiesel. With low FFA levels, the extra yield is not really much, but the process itself is a lot cleaner and easier to convert. Less mixing time is needed, but more settling time will be required. Users in a rush to make biodiesel as fast as possible with low titration levels may not want to bother with the two stage process. Those with extra time and a desire to get the batch right every time with less soap problems should utilize the two-stage process.
First Stage (Acid Stage)
The first stage is performed by using sulfuric acid and methanol. The sulfuric acid should be mixed with the methanol prior to injection into the oil to be processed to avoid burning of the oil from the highly concentrated acid. Please be cautious when mixing: wear gloves, an apron/lab coat and goggles as the two chemicals can spit and splatter if mixed together too quickly. If too much sulfuric acid were to be mixed in at once, much like with a base catalyst, it could cause an exothermic reaction so great that the methanol could reach its flash point. Users should be very cautious when pouring the sulfuric acid into methanol and be sure not to let it over heat. It would take more sulfuric acid than is necessary in the process to cause a fire, but you can never be too careful with such dangerous combinations of chemicals.I personally like to use a bulkhead fitting in the top of the cone tank lid with a funnel so that the sulfuric acid can't jump straight back up through the funnel at my face.
The purity of the sulfuric acid should be at least 93%. The higher the purity, the better, since the impurity in sulfuric acid is mostly water. Concentrations as high as 98% can be obtained for reasonable prices. Any higher than 98% is unstable and will break down to 98% on its own naturally, so there is no point in seeking sulfuric acid more pure than 98%.
The amount of methanol to be used in the acid stage should be 12% by volume of the oil to be processed. It is difficult to say exactly how much sulfuric acid should be used, but there are some guidelines. One way is to perform a 1 liter test batch, using 1 ml of sulfuric acid per liter of oil, and to continue adding acid until the titration level no longer drops through the process. Titrations would need to be performed every few hours in the process in order to find the ideal amount of sulfuric acid to use for the main batch. For beginning users, this is a great way to formulate the general amount of acid needed for the type of oil being process. It's a lot of work, but the research can pay off for a single users case.
One rule of thumb is that titration levels will never drop below 2 times the volume of sulfuric acid added per liter of oil. For example, if 1 ml of sulfuric acid is used, the new titration of the oil will never drop below 2 x (1ml) = 2. Because of this ruling factor, it is good to avoid overshooting the amount of sulfuric acid required to fully treat the vegetable oil, otherwise more base catalyst will be needed to neutralize the sulfuric acid, and therefore more water and salt in the end product to remove from the biodiesel later. An undershoot of the amount of acid needed will result in more processing time and more base catalyst to convert. It is important to be as exact as possible to conserve resources, processing and washing time.
For those who wish not to spend time doing test batches for each main batch, a formula through trial and error has been developed by home brewers and shared on many forums. We've tested it and found that it works quite well. The formula is (Titration - Target Titration) x 0.2 = ml of sulfuric acid to use. The target titration is recommended to be set at a minimum of 3, since the creator of the formula had never gotten his titration to go below 3 in the testing and creation of the formula. This is because we are fighting acid with acid, and while one is removed, the other still needs to be neutralized. I have, however, been able to get lower than 3 on clean oil that actually starts off with an initial titration of about 3. By using 1 or 2 as a target titration with such clean oil, it's possible to get the lower target titration levels, close to the minimum titration governed by the x2 factor. Why bother with using the two stage process for such low titrations in the first place? The quality of the fuel is better, and there is a lot less mixing time required since the conversion is quick and flawless. I personally like the two-stage process because I can just mix in the acid and methanol and leave it to convert overnight. when i resume the next morning the base process only takes half an hour as opposed to 4 hours.
Start the acid process by mixing the acid and methanol together. Heat your oil up to about 55-60°C, then slowly dispense the mixture into the circulating oil just like you would in a base process. The mixture can be mixed in a little more quickly than if you were doing the base process, but be sure not to mix too quickly as you want to evenly distribute the methanol mix into the oil. Unlike in the base process, mixing during the acid stage is actually counter productive. Sulfuric acid tends to work faster without agitation. Once everything is mixed in well, shut off the mixing and let the sulfuric acid do its job on the oil. For those with stainless steel pressurized processors, adding more pressure and heat to really cook the batch helps speed up the process. The mixture is going to look like a dark brown mess once the methanoland sulfuric have been introduced into the oil. Have no worries as this is perfectly normal.
Titrations of the batch should be taken every hour to measure the drop in FFA content. Once the titration level becomes steady and no longer decreases after each test, the acid has finished and the 2nd stage of the process should be performed. One great thing about the two-stage process is the constant sample taking step is actually unnecessary. The process can actually be left alone overnight and the 2nd stage performed the next day.
Second Stage (Base Stage)
After the acid process is completed, the sulfuric acid and some water will either float to the top of the batch or sink to the bottom. If your titration was lower than 14, the water/acid will float to the top and not be economical to remove. Proceed to the next step for the 2nd stage of the process. If the titration level was above 18, the water and sulfuric acid will drop to the bottom, and some of it needs to be drained out. For the volume of fluid drained from the bottom, additional methanol will need to be added to the 2nd stage in order to gain a complete reaction. If the titration was between 14 and 18, it is up to the user to decide whether it's worth draining some of the acid/water from the bottom as some will float and some will sink.
Next, a new titration of the batch is required to perform the 2nd stage of the process. Mix the batch up a little before pulling a sample to be sure an average titration can be found. This titration determines how much base catalyst will be required to transesterfy the Biodiesel and neutralize the remaining sulfuric acid. The titration works the same as any WVO titration, however, since the volume of the batch has changed since the first titration done prior to adding the sulfuric acid, this new volume needs to be used for analyzing how much catalyst is needed. Use the titration number found for calculating the amount of catalyst needed to process the total volume of fluid in the processor, not just the original amount of oil used as in the first titration. This total new volume to base the amount of catalyst to use on will be the original volume of oil plus the amount of methanol added, so 1.12 times the amount of original oil processed minus any amount which was drained.
Add the amount of catalyst needed based on the new titration and new volume in the batch to the remaining methanol required to complete the process. Since the normal accepted value of methanol to be used is 20% of the volume of oil and 12% was used for the acid process, use 8% of the original oil volume for the remaining of the methanol plus any volume drained off from the bottom. Users who use more methanol than 20% can simply add to that 8% in this stage.
Mix the catalyst required with the remaining methanol. Be sure to add the catalyst more slowly than in the one stage process. Since there is less methanol to absorb all of the heat generated from this exothermic reaction, the methanol temperature will be higher than usual. Depending on the amount of catalyst needed, some cooling time may be required prior to dissolving all of the catalyst into the methanol. My preference is to add about half as much catalyst as will be needed right after the sulfuric acid has been introduced to the oil, thus giving the methanol plenty of time to cool down before I add in the rest. This allows enough time for the methanol to cool off before you top it off with the remaining needed catalyst. If your titration is still rather high and it is difficult to dissolve all of the catalyst into the methanol, add a little more methanol to allow a larger amount of catalyst to be dissolved.
Once the methanol/catalyst mixture has been made, begin to process the 2nd stage. Inject the methanol mixture into the oil slowly during the mixing of the oil. Once the methanol is fully mixed into the batch, give about 15-30 minutes of mixing and then perform a 3/27 test to check for completion. In the two stage process, the base stage will complete much more rapidly than in a single stage process. Most users will find a complete reaction within 1 hour, when it is common for it to take 3 or more hours in a single stage process.
Note: Some users may notice a white textured goo which is hard to get out at the bottom of the methanol mixing tank on the initial injection into the oil. This is caused by left over sulfuric acid coming into contact with the base catalyst, thus forming a salt. To prevent this, it is good practice to run a little wash of methanol into the batch once the tank has been fully drained, and then wipe it clean with a towel, or to just use two mixing tanks, one for sulfuric acid and one for potassium hydroxide.
As with the single stage process, once the batch passes the 3/27 test, shut down the mixing and let the batch settle the glycerin to the bottom. Drain the glycerin as usual and proceed to washing.