57
Microalgae fabricate a variety of volatile organic compounds that can be used as
an important alternative resource of bulk and fine chemicals (Santos et al. 2016b).
Due to their low odor thresholds, aldehydes are important VOCs generated by
microalgae because they contribute desirable aromas. Saturated aldehydes have a
green-like grass odor, while unsaturated aldehydes have a rancid odor (Hosoglu
2018; Santos et al. 2016a).
Concerning the petrochemical industry, hydrocarbons and short-chain alcohols
are interesting to generate bioenergy (Severo et al. 2018a). Alternatively, renewable
biofuels could be produced from these so-called “greener” routes. Some studies
have shown that short-chain alcohols or higher alcohols could in the future be
inserted to gasoline as oxygenated or, in other cases, substituted for it because it has
high energy density and low solubility in water and butanol has comparable energy
to gasoline (Peralta-Yahya et al. 2012).
Ketones, such as 1-penten-3-one, 2,3-butanedione, and 2,3-pentenedione, are
used as flavors and floral fragrances. The esters are used in the flavor and fragrance
industry; methyl octanoate, for example, is applied in the food and perfumery industries as a flavoring and scent additive, respectively (Durme et al. 2013; Hosoglu
2018).
Already terpenes are a class of compounds applied as aromas and pharmaceuticals; however, they also could be used as biofuels due to the branches and rings in
their hydrocarbon chain (Peralta-Yahya et al. 2012). Table 2.3 shows the main VOCs
from microalgae found in scientific studies with potential industrial application.
Despite the possibility of broad industrial application of VOCs, there is a bottleneck concerning the isolation and fractionation of specific molecules (Severo et al.
2018b): firstly, because it is generally not possible to obtain high yields in the photobioreactor and secondly, due to the biosynthesis of volatile substances by microalgae being very low. So, although not an easy task, it is imperative to select a
suitable system for this purpose. Currently, some techniques can be exploited for the
separation and recovery of VOCs in the photobioreactor exhaust gases, which may
assist microalgae-based processes when it is desired to obtain a compound or a
group thereof separately (Wylock et al. 2015). In this sense, Table 2.4 summarizes
the main available technologies for the recovery of volatile organic compounds.
Continuous and nondestructive recovery can be through technologies based on
condensation, adsorption, membranes, distillation, and supercritical fluid extraction
(SFE). Many studies reported in the scientific literature aim to minimize losses and
recover useful volatile compounds and, therefore, have a final product of high quality (Akacha and Gargouri 2015).
Among the various technologies, the most accepted is distillation for the recovery of volatiles, for its simplicity. When it is desired to obtain a final product with
peculiar characteristics, it is recommended to use the adsorption technology, which
has the potential to be used as a highly selective recovery method. Already
membrane- based technology may be a promising alternative to be used in conjunction with other conventional processes. It offers ideal conditions for optimizing the
recovery system and increases the selectivity of specific target compounds.
2 Biological Conversion of Carbon Dioxide into Volatile Organic Compounds
Microalgae fabricate a variety of volatile organic compounds that can be used as
an important alternative resource of bulk and fine chemicals (Santos et al. 2016b).
Due to their low odor thresholds, aldehydes are important VOCs generated by
microalgae because they contribute desirable aromas. Saturated aldehydes have a
green-like grass odor, while unsaturated aldehydes have a rancid odor (Hosoglu
2018; Santos et al. 2016a).
Concerning the petrochemical industry, hydrocarbons and short-chain alcohols
are interesting to generate bioenergy (Severo et al. 2018a). Alternatively, renewable
biofuels could be produced from these so-called “greener” routes. Some studies
have shown that short-chain alcohols or higher alcohols could in the future be
inserted to gasoline as oxygenated or, in other cases, substituted for it because it has
high energy density and low solubility in water and butanol has comparable energy
to gasoline (Peralta-Yahya et al. 2012).
Ketones, such as 1-penten-3-one, 2,3-butanedione, and 2,3-pentenedione, are
used as flavors and floral fragrances. The esters are used in the flavor and fragrance
industry; methyl octanoate, for example, is applied in the food and perfumery industries as a flavoring and scent additive, respectively (Durme et al. 2013; Hosoglu
2018).
Already terpenes are a class of compounds applied as aromas and pharmaceuticals; however, they also could be used as biofuels due to the branches and rings in
their hydrocarbon chain (Peralta-Yahya et al. 2012). Table 2.3 shows the main VOCs
from microalgae found in scientific studies with potential industrial application.
Despite the possibility of broad industrial application of VOCs, there is a bottleneck concerning the isolation and fractionation of specific molecules (Severo et al.
2018b): firstly, because it is generally not possible to obtain high yields in the photobioreactor and secondly, due to the biosynthesis of volatile substances by microalgae being very low. So, although not an easy task, it is imperative to select a
suitable system for this purpose. Currently, some techniques can be exploited for the
separation and recovery of VOCs in the photobioreactor exhaust gases, which may
assist microalgae-based processes when it is desired to obtain a compound or a
group thereof separately (Wylock et al. 2015). In this sense, Table 2.4 summarizes
the main available technologies for the recovery of volatile organic compounds.
Continuous and nondestructive recovery can be through technologies based on
condensation, adsorption, membranes, distillation, and supercritical fluid extraction
(SFE). Many studies reported in the scientific literature aim to minimize losses and
recover useful volatile compounds and, therefore, have a final product of high quality (Akacha and Gargouri 2015).
Among the various technologies, the most accepted is distillation for the recovery of volatiles, for its simplicity. When it is desired to obtain a final product with
peculiar characteristics, it is recommended to use the adsorption technology, which
has the potential to be used as a highly selective recovery method. Already
membrane- based technology may be a promising alternative to be used in conjunction with other conventional processes. It offers ideal conditions for optimizing the
recovery system and increases the selectivity of specific target compounds.
2 Biological Conversion of Carbon Dioxide into Volatile Organic Compounds