Volatile emitted microalgae during pyrolysis
Héctor Alfredo López-Aguilar, Antonino Pérez-Hernández
Summary
The purpose of the present analysis was to characterize a sample of microalgae grown using wastewater in the SFIR photobioreactor of the startup Alis Algae Innovation Solutions. Thermo-gravimetry coupled to gas chromatography-mass spectrometry (TG-GC/MS) technique was used and the gaseous products emitted during pyrolysis were determined. Volatile species were identified that have the potential to be used as precursors toluene and benzaldehydes are generated. Without the proper management, these compounds can be very harmful to the environment and human health.
Method
An analysis was carried out to see the thermochemical behavior of a sample of A. maxima microalgae cultivated with wastewater in a SFIR photobioreactor (Img. 1), installed at the Tecnológico de Monterrey campus Chihuahua of the startup Alis Algae Innovations Solutions, in the NOVA incubation program. After harvesting, the sample was subjected to a drying pretreatment at 150ºC (302ºF) and stored in a desiccator for subsequent characterization.
A thermo-gravimetic analysis (TGA) was perfomed by inducing a pyrolytic process in a helium atmosphere (99.999%) in a STA2500 Regulus equipment at a temperature above the threshold temperature. Simultaneously, qualitative and semi-quantitative analysis of the volatile compounds was performed with an Agilent 7890B Gas Chromatograph and 5977B mass spectrometer (GC/MS) coupled to the TGA by means of a JAS transfer line (Img. 2) belonging to the Centro de Investigación en Materiales Avanzados (CIMAV). Helium injections were performed during the heat treatment at a constant temperature of 150ºC (302ºF) in the column.
Results and discussions
The results obtained from the TGA analysis are presented in the Data Table 1. A 4.7% moisture content was determined even after drying at 150% associated to the water strongly iterated to the cellulosic structure of the microalgae. The highest degradation of the material to volatile compounds was observed between 300ºC (572ºF) AND 400ºC (752ºF), this temperature range was identified as the region where the saccharides (cellulose) of the sample are volatilized. From 550ºC onwards, decarbonation occurs, and the presence of carbonates and sulfate in the sample of up to 20% can be deduced.
A generation of 6.96 g of volatile compounds per 10 g of sample was determined. The mixture is mainly composed of the species presented in Data Table 2.
In addition to the volatile compounds with industrial value detected during pyrolytic degradation, aromatic compounds such as toluene and benzaldehyde were identified, which when burned emit substances that are harmful to the ecosystem. Because of this, it is not recommended as a fuel for limited direct use due to the potential risk of generating toxic gases.
Conclusion
Most of the material (>96%) degraded to volatile compounds under TGA conditions. Likewise, the volatile compounds with the highest abundance in this study present potential applications in the generation and as intermediates for the synthesis of industrially valuable chemicals. The study was limited to a qualitative and semi-analytical analysis of the species.
Quantitative analyses of the substances produced are pertinent to evaluate their feasibility as valuable products for industrial use. The integral use of microalgae as part of a circular economy is imperative to achieve the use and implementation of photobioreactors as greenhouse gas capture systems in urban and peri-urban areas.
