Ultrasonic Processors for Biodiesel Production
When you make biodiesel, slow reaction kinetics and poor mass transfer are lowering your biodiesel plant capacity and your biodiesel yield and quality. Hielscher ultrasonic reactors improve the transesterification kinetics significantly. Therefore lower excess methanol and less catalyst are required for biodiesel processing.
Biodiesel is commonly produced in batch reactors using heat and mechanical mixing as energy input. Ultrasonic cavitational mixing is an effective alternative means to achieve a better mixing in commercial biodiesel processing. Ultrasonic cavitation provides the necessary activation energy for the industrial biodiesel transesterification.
Manufacturing biodiesel from vegetable oils (e.g. soy, canola, jatropha, sunflower seed or algae) or animal fats, involves the base-catalyzed transesterification of fatty acids with methanol or ethanol to give the corresponding methyl esters or ethyl esters. Glycerin is an inevitable byproduct of this reaction.
Vegetable oils as animal fats are triglycerides composed of three chains of fatty acids bound by a glycerin molecule. Triglycerides are esters. Esters are acids, like fatty acids, combined with an alcohol. Glycerine (= glycerol) is a heavy alcohol. In the conversion process triglyceride esters are turned into alkyl esters (= biodiesel) using a catalyst (lye) and an alcohol reagent, e.g. methanol, which yields methyl esters biodiesel. The methanol replaces the glycerin.
The glycerine – the heavier phase – will sink to the bottom. Biodiesel – the lighter phase – floats on top and can be separated, e.g. by decanters or centrifuges. This conversion process is called transesterification.
The conventional esterification reaction in batch processing tends to be slow, and phase separation of the glycerin is time-consuming, often taking 5 hours or more.
Today, biodiesel is primarily produced in batch reactors. Ultrasonic biodiesel processing allows for the continuous inline processing. Ultrasonication can achieve a biodiesel yield in excess of 99%. Ultrasonic reactors reduce the processing time from the conventional 1 to 4 hour batch processing to less than 30 seconds. More important, ultrasonication reduces the separation time from 5 to 10 hours (using conventional agitation) to less than 60 minutes. The ultrasonication does also help to decrease to amount of catalyst required by up to 50% due to the increased chemical activity in the presence of cavitation (see also sonochemistry). When using ultrasonication the amount of excess methanol required is reduced, too. Another benefit is the resulting increase in the purity of the glycerin.
Ultrasonic processing of biodiesel involves the following steps:
- the vegetable oil or animal fat is being mixed with the methanol (which makes methyl esters) or ethanol (for ethyl esters) and sodium or potassium methoxide or hydroxide
- the mix is heated, e.g. to temperatures between 45 and 65degC
- the heated mix is being sonicated inline for 5 to 15 seconds
- glycerin drops out or is separated using centrifuges
- the converted biodiesel is washed with water
Most commonly, the sonication is performed at an elevated pressure (1 to 3bar, gauge pressure) using a feed pump and an adjustable back-pressure valve next to the flow cell.
Industrial biodiesel processing does not need much ultrasonic energy. The table above shows typical power requirements for various flow rates. The actual energy requirement can be determined using a 1kW ultrasonic processor in bench-top scale. All results from such bench-top trials can be scaled up easily. If required, FM and ATEX-certified ultrasonic devices are available, such as the UIP1000-Exd.
Hielscher supplies industrial ultrasonic biodiesel processing equipment, worldwide. With ultrasonic processors of up to 16kW power per single device, there is no limit in biodiesel plant size or processing capacity.
Ultrasonication is an effective means to increase the reaction speed and conversion rate in the commercial biodiesel processing. Ultrasonic processing costs result mainly from the investment
for ultrasonic equipment, utility costs and maintenance. The outstanding energy efficiency (click chart to the right) of Hielscher ultrasonic devices helps to reduce the utility costs and by this to make this process even greener. The resulting costs for the ultrasonication vary between 0.1ct and 1.0ct per liter (0.4ct to 1.9ct/gallon) when used in commercial scale. For more information about ultrasonic processing costs, please click here.
Frost & Sullivan Technology Innovation of the Year
Hielscher Ultrasonics received the prestigious Frost & Sullivan Technology Innovation of the Year Award in recognition of the company’s development of novel ultrasonics technology for bio-diesel production. Click here to read more.
Ultrasonication can be used for the conversion of oil into biodiesel at any scale. The picture to the right (Click for larger view!) shows a small scale setup for the processing of 60-70L (16 to 19 gallons). This is the typical setup for initial studies and process demonstration.
This setup consists of the following parts:
- one 500 watts or 1,000 watts ultrasonic device (20kHz) with booster, sonotrode and flow cell
- power meter for metering power and energy
- 80L processing tank (plastic, e.g. HDPE)
- heating element (1 to 2kW)
- 10L catalyst premix tank (plastic, e.g. HDPE)
- catalyst premixer (stirrer)
- pump (centrifuge, mono or gear) for approx. 10 to 20L/min at 1 to 3 barg
- back-pressure valve for adjusting pressure in the flow cell
- pressure gauge for measuring feed pressure
Potassium Hydroxide (0.2 to 0.4kg, catalyst) is being dissolved into approx. 8.5L Methanol in the catalyst pre-mix tank. This requires stirring of the catalyst premix. The processing tank is being filled with 66L vegetable oil. The oil is being heated by the heating element to 45 to 65degC.
When the catalyst is fully dissolved into the Methanol, the catalyst premix is mixed with the heated oil. The pump feeds the mixture to the flow cell. By means of the back-pressure valve, the pressure is adjusted to 1 to 3barg (15 to 45psig). Recirculation through the ultrasonic biodiesel reactor should performed for approx. 20 minutes. During this time, the oil is being converted into biodiesel. After this, the pump and the ultrasound are switched off. The glycerin (heavier phase) will separate from the biodiesel (lighter phase). The separation takes approx. 30 to 60 minutes. When the separation is finished, the glycerin can be drained.
As the converted biodiesel contains impurities, washing is required. For the washing, water is mixed into the biodiesel. Ultrasonication can benefit the mixing of the biodiesel with the water. This increases the active surface area as a result of the droplet size reduction (see: ultrasonic emulsifying). Please consider, that very intense sonication may reduce the water droplets to a size, that an almost stable emulsion is being formed that will require special means (e.g. centrifuge) to be separated.
The flow-chart below shows a typical setup for the in-line sonication of oil for the conversion into biodiesel. Click at the chart to get a larger view.
In a setup for the continuous biodiesel processing and continuous separation, the heated oil and the catalyst premix are mixed together continuously using adjustable pumps. An inline static mixer improves the homogeneity of the feed to the ultrasonic reactor. The oil/catalyst mixture passes the flow cell, where it is being exposed to ultrasonic cavitation for approx. 5 to 30 seconds. A back-pressure valve is used to control the pressure in the flow cell. The sonicated mix enters the reactor column on the top. The volume of the reactor column is designed to give approx. 1 hour retention time in the column. During that time, the transesterification reaction is completed. The reacted glycerin/biodiesel mix is pumped to the centrifuge where it is separated into the biodiesel and glycerin fractions. Post-processing involves methanol recovery, washing and drying and can be done continuously, too.
This setup eliminates biodiesel reactor batches, conventional agitators and large separator tanks.
The diagrams below show typical results of the transesterification of rapeseed oil (industrial grade) with sodium methoxide (left) and potassium hydroxide (right). For both tests, a control sample (blue line) was exposed to intense mechanical mixing. The red line represents the sonicated sample of the identical formulation with respect to volume ratio, catalyst concentration and temperature. The horizontal axis shows the time after mixing or sonication, respectively. The vertical axis shows the volume of glycerin that settled at the bottom. This is a simple means of measuring the reaction speed. In both diagrams, the sonicated sample (red) reacts much faster than the control sample (blue).
Chemical and Safety Information
Please read the information below carefully, to prevent complications and adverse health effects.
Methanol is toxic. It can cause nerve deterioration as a result of prolonged usage. It can be adsorbed by the skin, too. If splashed into eyes it may cause blindness and Methanol can be fatal when swallowed. For this reason, take the necessary precautions when handling Methanol. It is recommended to use a good respirator, an apron and rubber gloves.
Potassium hydroxide (KOH) is toxic and causes skin burn upon contact. Good ventilation is required.
Make sure the workspace is generously and thoroughly ventilated to allow fumes to escape. Vapor cartridge respirators are not effective against methanol fumes. A supplied-air system (SCBA — Self-Contained Breathing Apparatus) gives better protection against methanol vapors.
Biodiesel and Rubber Parts
Running on 100% biodiesel for longer time may cause complications to wetted rubber parts (pump, hoses, O-rings) of the engine. Replacement by steel parts or heavy duty rubber can eliminate this problem. Alternatively you can mix approx. 25% conventional (fossil) diesel into your biodiesel to prevent complications.
Biodiesel, such as rapeseed methyl ester (RME) is a renewable and biodegradable fuel. Biodiesel has several advantages when compared to straight vegetable oil (SVO). It requires no engine conversion or fuel system modification to run biodiesel on conventional diesel engines. Biodiesel is commonly added to the petrodiesel sold at pumps today to increase the lubricity of pure Ultra-Low Sulfur Diesel (ULSD), which is advantageous since Biodiesel has almost no sulfur content.
Todd Stephens, Tulsa Biofuels