Biofuel from algae is another feasible 2nd generation biomass processing industry. The advantages of this type of product include: the possibility of obtaining significant volumes of biofuel in relatively small areas, even unsuitable for agricultural production; when growing algae, there is no acute need for fresh water; microalgae can contain a record high oil level – up to 60-80%; these plants are classified as fast-growing, and some species in favourable conditions can double their weight within a few hours; during their growth, microalgae assimilate carbon dioxide from the atmospheric air.
The term algae means a large number of bio organisms with more than 100,000 genetically diverse strains . Some of them belong to macroalgae, which are multicellular plants. Another part refers to microalgae, which unlike the first group, have a unicellular structure . Most microalgae exist through photosynthesis, absorbing carbon dioxide and water and converting them under the influence of sunlight into organic matter and oxygen. Comparing potential of oil yields demonstrates the amazing properties of microalgae. For example, the extraction rates of palm oil, which is also used for the production of biodiesel, are 635 oil yield gallons/acre, and in the case of the simplest microalgae it is about twice as high .
Microalgae contain several important chemicals that determine their beneficial properties – lipids, proteins, carbohydrates, and other residues (ash). Proteins are the main components of most microalgae, and their concentration ranges between 30%-7%, for carbohydrates, the range of possible concentration is from 4% to 58% of dry weight . From the point of view of extracting liquid oil from microalgae, the most important substance in microalgae is lipids, the content of which can vary within wide limits – from 5% to 58% (Chlorella vulgaris) of dry weight . The concentration of lipids in microalgae depends on their species, growing conditions, and nutrients.
The accumulated knowledge about the vital activity of microalgae has made it possible to construct a process flow diagram . In general terms, this diagram includes:
– Algae species selection (Algae species, Nutrients, Pathogens, predators);
– Siting (Land, CO2, Facilities, Primary Energy, Water);
– Cultivation (Closed systems, Open systems, Hybrid systems, Wastewater Photoautotrophic & Heterotrophic; Co-generation, Biological Assist);
– Harvesting / De-watering, Flocculation & settling, Airlift flocculation, Filtering, Centrifuge, Biological Assist Harvesting (shrimp, fish excrement, etc.);
– Extraction & Separation (Lipids, Carbohydrates, Proteins, Other metabolites);
– Conversion to Biofuels;
– Conversion to Co-products.
The centrepiece of this diagram is the cultivation of microalgae. There are three principal ways: phototrophic cultivation, with light and CO2; heterotrophic cultivation, when there is no light, but a special organic substrate is additionally supplied; mixotrophic cultivation – where the growth of microalgae can take place under both of the above conditions . The process of growing microalgae is carried out either in open (Open Raceway Pond (ORP) or closed systems (PBR). Open systems are natural or artificial reservoirs where microalgae are grown. Closed systems can be placed both outdoors and indoors under artificial light. Open systems have the following advantages – simple cleaning and maintenance, low energy consumption; however, at the same time, this system is characterized by low productivity, requires large areas of land, but a limited number of algae strains. Closed tubular systems require a large illumination area, but there is good biomass productivity. Limiting factors include active fouling, the need to control gradients of pH dissolved oxygen and CO2 along the tubes, and others .
A schematic diagram of the production of biodiesel from microalgae may look like this (Figure 1).
Figure 1. Possible scheme of biofuel production from microalgae
1. Water 2. Sunlight for algae growth 3. Facility emitting carbon dioxide 4. Nutrients 5. Gas, water and nutrient conditioning unit or incubation tank 6. Bioreactor network(microalgae ponds) 7. Second conditioning unit 7a. Oxygen 8. Algae harvesting reactors 9. Screw process unit 10. Recycled water 11. Algae biomass 12. Algae hexane solvent mixer 13. Transesterification unit 13a. Sodium hydroxide 13b. Methanol 14. Fuel conditioning 15. Biodiesel fuel combined with a glycerol 15a. Glycerol 15b. Algae biodiesel
The production of biodiesel from microalgae is costly, which is one of the main obstacles to industrial deployment of this technology. The largest part of expenditure falls on material resources (material cost), including nutrients, carbon source (carbon source), energy costs (energy), catalysts (catalyst) .
In addition to biodiesel, modern technologies for processing microalgae make it possible to obtain Biohydrogen, Bioethanol, Biomethane.
Currently, there are several research and demonstration projects for the production of biofuels from microalgae, as well as special programs to facilitate this process [1,6], but there is no industrial production. The latest news, research results, and basic concepts can be found on the website .
Below is a short list of indicators of patent activity of inventors in the field of biofuel production from microalgae. More than 1600 patents were selected for analysis, issued by 41 patent offices around the world in 2009-2018. More than 1,250 applicants from 42 countries took part in the creating of patents.
The largest number of patents was granted by the US Patent Office – about 42%. 5% to 10% of the total patents were also granted by Australian, Chinese, European and Japanese offices. 60% of patents were created by US residents.
The most popular among inventors were technological issues related to the new aspects of Chemistry and other substances, Primary processing and the Pre-treatment of feedstock (Figure 2).
Figure 2. Distribution of technological elements identified among patents, 2009-2018, %
Source: Advanced Energy Technologies
AES – Additional equipment, substances; CD – Methods of control and diagnostics; COS – Chemistry and other substances; CS – Capture and separation; CUW – Capture, utilization of solid, liquid and gaseous wastes; FS – Feeding systems; FT – Finishing treatment; PP – Primary processing; PTF – Pre-treatment of feedstock; PTG – Processing technologies in general; SE – Secondary equipment; ST – Storage & transportation
A list of leading patent holders and their shares in the intellectual property register is presented in Table 1.
Table 1. Leading patent holders for the production of biofuels from microalgae between 2009 and 2018 and their shares in the register of intellectual property in relation to all patent holders
|Company||US||Heliae Development LLC||4.37||74.52||3.26|
|Company||US||ExxonMobil Research and Engineering Company||2.31||68.93||1.59|
|Company||US||Terravia Holdings Inc||1.75||87.5||1.53|
|Organization||AU||Commonwealth Scientific and Industrial Research Organization (CSIRO)||1.44||82.61||1.19|
Volume ratio – share of applicant documents in total number of documents
Ownership ratio – applicant's participation share in total number of documents
Market involvement ratio (bubble size) – volume ratio multiplied by ownership ratio
Source: Advanced Energy Technologies
Representatives of the US clearly dominate among patent holders, while the total share of the first five American companies in the intellectual register exceeds 15%.
 Algal Biofuels (PDF) / U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) / / www.energy.gov/eere/bioenergy/algal-biofuels
 Biofuels from algae: technology options, energy balance and GHG emissions (PDF) / Stefania Rocca, Alessandro Agostini, Jacopo Giuntoli, Luisa Marelli/ Insights from a literature review, EUR 27582, doi 10.2790/125847 / 2015/ publications.jrc.ec.europa.eu/repository/bitstream/JRC98760/algae_biofuels_report_21122015.pdf
 The Potential for Biofuels from Algae (PDF) / Philip T. Pienkos, Ph.D. / Algae Biomass Summit, San Francisco, CA, November 15, 2007 / National Renewable Energy Laboratory, National Bioenergy Center / www.nrel.gov/docs/fy08osti/42414.pdf
 Historical Overview of Algal Biofuel Technoeconomic Analyses (PDF) / National Renewable Energy Laboratory / 2008 / www.nrel.gov/docs/fy09osti/45622.pdf
 Energy from Microalgae / Eduardo Jacob-Lopes, Leila Queiroz Zepka, Maria Isabel / Queiroz Editors, © Springer International Publishing AG 2018 / www.springer.com/gp/book/9783319690926
 AgriAlgae / www.agrialgae.es
 Oilgae / www.oilgae.com