2.7.1
BIOX Co-Solvent Method
BIOX is a technology development company which is a joint venture between the University of Toronto Innovations Foundation and Madison Ventures
Ltd. The BIOX co-solvent method was developed by Boocock et al. in 1996.150
In this process, TGs are converted to esters through the selection of inert co-
solvents that generate a one-phase oil-rich system.102,150,151Co-solvent is used
the alcohol in the triglyceride phase. Tetrahydrofuran (THF) as a co-solvent
was used to make the methanol soluble.151After completion of the reaction,
the biodiesel–glycerol phase separation was cleaned and both the excess alcohol and the THF co-solvent were recovered in a single step. However, due to the possible hazard and toxicity of the co-solvents, they must be completely removed from the glycerol phase as well as the biodiesel phase and the final
products should be water-free.150The main advantage of the BIOX co-solvent
process is that it uses inert, reclaimable co-solvents in a single-pass reaction that takes only seconds at ambient temperature and pressure, and no catalyst
residues appear in either the biodiesel phase or the glycerol phase.102 This
process can handle not only grain-based feedstocks but also waste cooking oils and animal fats. It was however found that the recovery of excess alcohol is difficult when using this process because the boiling point of the THF co-
solvent is very close to that of methanol.102,152
2.7.2
Non-Catalytic Supercritical Alcohol Transesterification
Supercritical methanol transesterification is a method through which the vegetable oils or animal fats can be converted into biodiesel in a highly reduced reaction time without the use of any type of catalyst. The feedstock is reacted with supercritical methanol at extremely high pressure and temperature. Due to the absence of catalyst, no washing and neutralization is required. Another advantage of this process is that the water content does not affect the reaction. However, there are also problems associated with this method such as the requirement of high pressure and temperature resulting in the high cost of the apparatus. The reported time, temperature and pressure vary from 222 s to 6
min, 222 to 400 uC, and 80 to 650 bars respectively for 95 to 100% yield of
biodiesel.150,153–156
2.7.3
Catalytic Supercritical Methanol Transesterification
Catalytic supercritical methanol transesterification is performed in an autoclave in the presence of 1–5% NaOH, CaO, and MgO as a catalyst at
520 K. The yield of conversion rises to 60–90% for the first minute.157
Transesterification of rapeseed oil with supercritical/subcritical methanol in the presence of a relatively low amount of NaOH (1%) was successfully carried
out, without the occurrence of soap formation.158
2.7.4
Ultrasound- and Radio-Frequency-Assisted
Transesterification
Ultrasound is defined as sound of frequency within the range 20 kHz to beyond 100 MHz and it has proven to be a useful tool in enhancing reaction rates in many reaction systems. During transesterification, ultrasonication provides the mechanical energy for mixing and the activation energy needed to
start the transesterification reaction and it increases the chemical reaction speed, the efficient molar ratio of methanol to oil, the yield of transesterifica- tion of vegetable oils and animal fats into biodiesel with less energy
consumption than for conventional mechanical stirring methods.159–161
Transesterification is also carried out using high-frequency microwave irradiation. Microwave irradiation increases the rate of chemical reactions, reducing the time from hours to minutes and minutes to seconds. Microwave radiations mainly consist of infrared and radio waves. Generally the wavelength of microwaves lies between 1 mm and 1 m and frequency from
300 MHz to 300 GHz.162 Used cooking oil was transesterified using 20%
methanol and 1% NaOH at 65uC.163
The reaction was completed in 60 min and the separation phase was completed in 8 h using a conventional method. The process was repeated with same amounts of alcohol and catalyst using microwave irradiation. The reaction was completed within 2 min and the separation phase was completed in 30 min. The conversion efficiency was 100%, as compared to 96% for the conventional method. There are also
various reports of the use of this technique for biodiesel production.124,164–169
2.7.5
In situ Biodiesel Techniques
The in situ biodiesel production is a novel technique to convert oil to biodiesel
which was developed by Harrington and D’Arcy Evans in 1985.170 In this
technique, the oilseeds are directly treated at ambient temperature and pressure with a methanol solution in which the catalyst has been previously dissolved. It implies that the oil in the oilseeds is not isolated prior to transesterification to
fatty acid esters.170–172To reduce the alcohol requirement for high efficiency
during in situ transesterification, the oilseeds need to be dried before the
reaction takes place.173Milled oilseeds are then mixed with alcohol in which
the catalyst had been dissolved and the mixture is heated under reflux for 1–5 h. Two layers are formed around the time of completion of the reaction. The lower layer is the alcohol phase and can be recovered. The upper layer, including the crude biodiesel, is washed with water to remove the contaminants until the washing solution is neutral. After the washing step, the upper layer is dried over anhydrous sodium sulfate, then filtered, and the residual product is
biodiesel.174 However, this process cannot handle waste cooking oils and
animal fats.