concentration of 40 g/L. Before to carry out the culture, the medium was autoclaved
at 121 °C for 15 min. Then the inoculum was added.
Cultivation was performed in such a way that an average residence time of
15 days was generated. Then to carry out a concentration of the biomass obtained,
the mixture from the culture step was passed by a centrifugation process
(Luangpipat and Chisti 2016). At this point, a cell disruption stage is carried out, in
which autoclaving was used at 125 °C with 1.5 MPa for 5 min. To carry out the
removal of the lipids from the previous step, a mixture of chloroform–methanol
(1:1 v/v) was added in a ratio of 1:1 (Lee et al. 2010).
For the production of biodiesel, a mixture of ethanol and sodium hydroxide was
realized (Bambase et al. 2007). The resulting mixture is added to the lipids previously obtained. Heating was carried out to 60 °C and passed to the transesterification reactor. This reactor is designed based on kinetics reported by Mussatto
et al. (2014). In order to recover the ethanol which not reacts, a distillation step was
carried out. The bottom product is mixed with hot water in a 1:3 v/v ratio. The
mixture was decanted allowing the separation of the unreacted oil and a mixture of
biodiesel and glycerol. This mixture was brought to a separation train in which a
purity of 95% biodiesel was achieved. The obtained glycerol was mixed with the
catalyst, which was sulfuric acid, which allows the precipitation of the salt generated obtaining a glycerol with a purity of 80%.
7.2 Energy and Exergy Analysis
The energy and exergetic analyses are performed from the data obtained in the
simulated Aspen Plus. For the energy analysis, a quantification of the energy
required by each equipment involved in each processing step was performed.
Similarly for the exergetic analysis, the exergy consumed in each stage is quantified
and additionally the calculation of the exergy of the currents involved in each stage
of processing was carried out in order to determine the energy efficiency of the
process as mentioned above. To carry out the energy and exergetic analyses of
biodiesel production from microalga oil, three stages of processing are considered:
culture and harvesting of microalgae, oil extraction, and biodiesel production (see
Fig. 1). From this, the following results can be obtained for the analyzed case.
7.3 Economic Analysis
Using the mass and energy balances obtained by simulating the process of
obtaining biodiesel, an economic analysis was carried out. For this purpose, Aspen
Process Economic Analyzer software was used. In this analysis, the method of
depreciation of straight line is considered. This allows to determine the economic
9 Biofuels from Microalgae: Energy and Exergy Analysis for the …
191
at 121 °C for 15 min. Then the inoculum was added.
Cultivation was performed in such a way that an average residence time of
15 days was generated. Then to carry out a concentration of the biomass obtained,
the mixture from the culture step was passed by a centrifugation process
(Luangpipat and Chisti 2016). At this point, a cell disruption stage is carried out, in
which autoclaving was used at 125 °C with 1.5 MPa for 5 min. To carry out the
removal of the lipids from the previous step, a mixture of chloroform–methanol
(1:1 v/v) was added in a ratio of 1:1 (Lee et al. 2010).
For the production of biodiesel, a mixture of ethanol and sodium hydroxide was
realized (Bambase et al. 2007). The resulting mixture is added to the lipids previously obtained. Heating was carried out to 60 °C and passed to the transesterification reactor. This reactor is designed based on kinetics reported by Mussatto
et al. (2014). In order to recover the ethanol which not reacts, a distillation step was
carried out. The bottom product is mixed with hot water in a 1:3 v/v ratio. The
mixture was decanted allowing the separation of the unreacted oil and a mixture of
biodiesel and glycerol. This mixture was brought to a separation train in which a
purity of 95% biodiesel was achieved. The obtained glycerol was mixed with the
catalyst, which was sulfuric acid, which allows the precipitation of the salt generated obtaining a glycerol with a purity of 80%.
7.2 Energy and Exergy Analysis
The energy and exergetic analyses are performed from the data obtained in the
simulated Aspen Plus. For the energy analysis, a quantification of the energy
required by each equipment involved in each processing step was performed.
Similarly for the exergetic analysis, the exergy consumed in each stage is quantified
and additionally the calculation of the exergy of the currents involved in each stage
of processing was carried out in order to determine the energy efficiency of the
process as mentioned above. To carry out the energy and exergetic analyses of
biodiesel production from microalga oil, three stages of processing are considered:
culture and harvesting of microalgae, oil extraction, and biodiesel production (see
Fig. 1). From this, the following results can be obtained for the analyzed case.
7.3 Economic Analysis
Using the mass and energy balances obtained by simulating the process of
obtaining biodiesel, an economic analysis was carried out. For this purpose, Aspen
Process Economic Analyzer software was used. In this analysis, the method of
depreciation of straight line is considered. This allows to determine the economic
9 Biofuels from Microalgae: Energy and Exergy Analysis for the …
191