201
3 Non-catalytic Process for Biodiesel Production
The non-catalytic processes are the highly focused area in biodiesel production and
also known as the thermal processes in which the reaction is carried out at a hightemperature and high-pressure conditions. Usually, they are highly controlled reactions monitored with utmost safety and can mitigate the drawbacks associated with
a homogeneous catalyst [46]. The non-catalytic supercritical methanol process
explored by many studies achieved a yield of biodiesel as high as 97% in a very
short period. However, there are limitations in the supercritical methanol process
which limits its commercialization. The limitations of the supercritical process like
thermal degradation of esters, higher capital, and operating cost can be mitigated
using the non-catalytic subcritical esterification process [47, 48]. Together curbing
the limitation of the supercritical process, the ester yield and conversion in the noncatalytic subcritical esterification process are nearly equal to that of other processes.
Many studies were already conducted through the non-catalytic route and observed
good results. For example, at 270 °C and 200 bar using 1:0.9 rapeseed oil to methanol ratio (v/v), Minami and Sake [49] achieved a product yield of nearly 94%. A
60% conversion of C18 fatty acids non-catalytically was reported by Melo Junior
et al. [50] in a short period (60 min) under microwave irradiation. Rani et al. [51]
achieved a conversion of ~95% in 5 h using 1:4 Jatropha oil to methanol ratio (w/v),
190 °C, and 27.1 bar. Experiments conducted by Cho et al. [52] with palm fatty acid
distillate and methanol achieved a final product acid value of fewer than 0.5 mg
KOH/g in 3 h at 290 °C and 8.5 bar. The investigation by Pinnarat and Savage [11]
revealed that the non-catalytic esterification under subcritical conditions can be carried out smoothly with the advantage of tolerating a moderate amount of water
content in the feed oil. Moreover, they reported that the presence of a moderate
amount of water enhances the effectiveness of the subcritical esterification process.
3.1 Experimental Procedure
The details of the experimental setup are available elsewhere [13]. It consists of a
small batch reactor of 25 mL capacity made of stainless steel and fitted with a pressure gauge that is placed inside a jacketed vessel. Heating and mechanical agitation
were carried out using a magnetic stirrer, and the chiller was used to ensure the
constant temperature inside the reactor. There was a provision to introduce the inert
gas for maintaining the constant pressure.
The soluble impurities of Karanja oil were removed by washing thoroughly with
hot deionized water (~80 °C). Thereafter, the oil was dried and a trace amount of
water was removed by treating dried oil with silica gel. The key to the biodiesel
production through the non-catalytic route is the maintenance of volumetric filling
fraction (f). “f” is given as the volume of reactants charged to the reactor divided by
the total reactor volume [13]. The reactant amounts must be selected to meet the
required phase equilibrium criteria set by the value of “f” which controls the phases
Catalytic and Non-Catalytic Methods for Biodiesel Production
3 Non-catalytic Process for Biodiesel Production
The non-catalytic processes are the highly focused area in biodiesel production and
also known as the thermal processes in which the reaction is carried out at a hightemperature and high-pressure conditions. Usually, they are highly controlled reactions monitored with utmost safety and can mitigate the drawbacks associated with
a homogeneous catalyst [46]. The non-catalytic supercritical methanol process
explored by many studies achieved a yield of biodiesel as high as 97% in a very
short period. However, there are limitations in the supercritical methanol process
which limits its commercialization. The limitations of the supercritical process like
thermal degradation of esters, higher capital, and operating cost can be mitigated
using the non-catalytic subcritical esterification process [47, 48]. Together curbing
the limitation of the supercritical process, the ester yield and conversion in the noncatalytic subcritical esterification process are nearly equal to that of other processes.
Many studies were already conducted through the non-catalytic route and observed
good results. For example, at 270 °C and 200 bar using 1:0.9 rapeseed oil to methanol ratio (v/v), Minami and Sake [49] achieved a product yield of nearly 94%. A
60% conversion of C18 fatty acids non-catalytically was reported by Melo Junior
et al. [50] in a short period (60 min) under microwave irradiation. Rani et al. [51]
achieved a conversion of ~95% in 5 h using 1:4 Jatropha oil to methanol ratio (w/v),
190 °C, and 27.1 bar. Experiments conducted by Cho et al. [52] with palm fatty acid
distillate and methanol achieved a final product acid value of fewer than 0.5 mg
KOH/g in 3 h at 290 °C and 8.5 bar. The investigation by Pinnarat and Savage [11]
revealed that the non-catalytic esterification under subcritical conditions can be carried out smoothly with the advantage of tolerating a moderate amount of water
content in the feed oil. Moreover, they reported that the presence of a moderate
amount of water enhances the effectiveness of the subcritical esterification process.
3.1 Experimental Procedure
The details of the experimental setup are available elsewhere [13]. It consists of a
small batch reactor of 25 mL capacity made of stainless steel and fitted with a pressure gauge that is placed inside a jacketed vessel. Heating and mechanical agitation
were carried out using a magnetic stirrer, and the chiller was used to ensure the
constant temperature inside the reactor. There was a provision to introduce the inert
gas for maintaining the constant pressure.
The soluble impurities of Karanja oil were removed by washing thoroughly with
hot deionized water (~80 °C). Thereafter, the oil was dried and a trace amount of
water was removed by treating dried oil with silica gel. The key to the biodiesel
production through the non-catalytic route is the maintenance of volumetric filling
fraction (f). “f” is given as the volume of reactants charged to the reactor divided by
the total reactor volume [13]. The reactant amounts must be selected to meet the
required phase equilibrium criteria set by the value of “f” which controls the phases
Catalytic and Non-Catalytic Methods for Biodiesel Production