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How To Make Bio-diesel from WASTE Vegetable Oil

Bio-diesel is a diesel fuel that is made by reacting new or used vegetable oil (cooking oil) with other common chemicals. Bio-diesel may be used in any diesel automotive engine in its pure form or blended with petroleum-based diesel. No modifications are required, and the result is a less-expensive, renewable, clean-burning fuel. Below is how to make bio-diesel from Used oil.

You can also make bio-diesel from new cooking oil, but making it from Used oil is a little more involved, so let's start with the basics.

Some information is from

General (links to this page )

About Bio-diesel.

Introduction to making Bio-diesel.


Bio-diesel Processing Guides

1. The base amount of lye catalyst needed

2. Titrating waste vegetable oil (WVO)

3. Methanol

4. Heating or Filtering

This is the best information we could source.

About bio-diesel

The Benefits

Bio-diesel can be burned in any diesel engine or home oil heater and even experimentally in gasoline engines when heavily diluted with gasoline. Bio-diesel burns cleaner than traditional petro-diesel. There is basically no sulphur content.

Bio-diesel is also renewable. Since bio-diesel 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.

Bio-diesel is more lubricating than diesel fuel. It will lubricate your injection pump and injectors, thus increasing the life span of your diesel engine. Bio-diesel 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 bio-diesel 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 bio-diesel and most likely, no smoke at all when B100 (100% Bio-diesel) 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.

The Disadvantages

Bio-diesel 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.

Bio-diesel 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% bio-diesel 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 bio-diesel 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% Bio-diesel) will also corrode rubber lines, seals and gaskets. Most newer vehicles already have the necessary parts for handling bio-diesel, 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 Bio-diesel. 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 Bio-diesel

Bio-diesel 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 bio-diesel.

Most makers of bio-diesel 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, bio-diesel 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 Bio-diesel is Produced

Bio-diesel 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 bio-diesel due to high taxes imposed on it.

The Very Basics of Making Bio-diesel

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 bio-diesel 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 bio-diesel. Both catalysts are highly hygroscopic, which means they absorb moisture from the air rapidly. This will interfere with the bio-diesel 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.

Catalyst Name KOH (Potassium Hydroxide) NAOH (Sodium Hydroxide)
Purity 90+% 99+%
Amount Needed Requires more catalyst 1.4025 more than NaOH Less catalyst required
Safety Dusty when scooping, requires more caution Sticks to the body easier since moisture absorption is more rapid
Common Forms Flakes Micropearls
Moisture More forgiving when moisture is present in bio-diesel reaction absorbs moisture from the air faster than KOH
Dissolved in Methanol Fast Dissolving Slow dissolving
Bio-diesel Quality More forgiving when wrong catalyst amount is used doesn't work well for high titration levels
Bio-diesel By-product 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 Bio-diesel

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 litre 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 litre 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 litre of oil. For KOH, it’s usually about 90%, which calculates as 7g/0.90 = 7.77g of KOH per litre 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 bio-diesel, 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 bio-diesel 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 some 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 litre (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.

The process:

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 litre of distilled water. For most accuracy, weigh your water rather than measuring it. 1 litre 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 litres 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 colour 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 colour 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 litre 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 litre 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 litre of oil.

3. Methanol

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 litres of vegetable oil, the process would require 20 litres 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 bio-diesel reaction to perform the methanol mixing task by the switching of a few ball valves. It works, but it will get some bio-diesel/oil and maybe glycerin into your methanol mixing tank.

-------- // --------

Making Bio-diesel - Heating or Filtering the Vegetable Oil

You can brew homemade bio-diesel from waste vegetable oil in heavy duty plastic 20lt buckets. This keep batches small to allow for easy handling and transporting of the finished product.

The first step is to heat the oil to approximately 38°C. We accomplish this by putting the oil in a steel pot and warming it on a camp stove. That does allow us to do this in the basement, keeping all processes concentrated in one area. Be sure not to overheat the oil. If it gets too hot, it will cause secondary ingredients to adversely react. In warmer weather, we skip the stove heating and set buckets of oil in the sun. In just a few hours, they're ready to process. While the oil is heating, we move on to the next steps.

Our preferred method is to simply Filter the oil through a 2 micron, Water blocking Marine Filter, it is a lot quicker method to clean the oil of contaminants !

Wondering where to get used vegetable oil ?

We scout around to local Cafés, Restaurants, Service Stations, & even Council disposal depots, the best oil is either light or dark brown oil, if there is any sign of a milky colour in the oil, this is a sign of water &/or Lard contamination, DON'T use this type of oil unless you are going to let it settle in the sun for weeks or you will have to heat it for extended time.


Using Bio-diesel:

Normally you can use pure bio-diesel or a mixture of bio-diesel and petroleum diesel as a fuel in any unmodified diesel engine. There are two situations in which you definitely should mix bio-diesel with petroleum-based diesel.

If you are going to be running the engine at a temperature lower than 13° C (55° F), you should mix bio-diesel with petroleum diesel. A 50:50 mixture will work for cold weather. Pure bio-diesel will thicken and cloud at 55° F, which could clog your fuel line and stop your engine. Pure petroleum diesel, in contrast, has a cloud point of -24° C (-10° F). The colder your conditions, the higher percentage of petroleum diesel you will want to use. Above 13° C you can use pure bio-diesel without any problem. Both types of diesel return to normal as soon as the temperature warms above their cloud point.

You will want to use a mixture of 20% bio-diesel with 80% petroleum diesel (called B20) if your engine has natural rubber seals or hoses. Pure bio-diesel can degrade natural rubber, though B20 tends not to cause problems. If you have an older engine (which is where natural rubber parts are found), you could replace the rubber with polymer parts and run pure bio-diesel.\

Bio-diesel Stability & Shelf Life: 

You probably don't stop to think about it, but all fuels have a shelf life that depends on their chemical composition and storage conditions. The chemical stability of bio-diesel depends on the oil from which it was derived.

Bio-diesel from oils that naturally contain the antioxidant tocopherol or vitamin E (e.g., rapeseed oil) remain usable longer than bio-diesel from other types of vegetable oils. According to belief, stability is noticeably diminished after 10 days and the fuel may be unusable after 2 months. Temperature also affects fuel stability in that excessive temperatures may denature the fuel.


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