Algae are largely single-celled organisms lacking roots, stems and leaves. Most algae, like plants, use photosynthesis to produce energy. Their simple structure makes them highly energy efficient as well. They can vary in size from a few microns to large macroscopic multi-cellular organisms which can be up to 60 metres in length and can grow as fast as 50 centimetres a day. Microalgae generally refer to all those species of algae with sizes between 10 and 100 microns. Most of the estimated 500,000+ species of algae are expected to be unicellular and fall within this range.
But why do we care about these tiny organisms? For starters, their absence would take your breath away, quite literally! It is a common misconception that most of the oxygen we breathe comes from forests. On the contrary, forests consume almost as much oxygen as they produce. It is estimated that about three-fourths of the oxygen we breathe comes from algae alone.
Perhaps more relevant to the state of the environment today is the fact that when nutrients are available in plenty, algae populations can grow very rapidly, doubling in number every few hours. They can then be harvested quickly to produce usable biofuel. Traditional crops would require 300 times the land to produce an equivalent amount of biofuel as microalgae. Part of the reason why algae have survived on this planet for so long is that they adapt very quickly. This suggests that we might be able to grow algae in conditions where traditional crops fail to grow.
The idea of fuel sustainability is considered to be the Holy Grail for global ecological health. But we are still quite far away from a state of sustainable growth, since we have thus far failed to find and utilise a source of energy that is renewable and can act as a substitute to fossil fuels. Some argue that usage of biofuels derived from algae will take us closer to that goal, since algae take in carbon dioxide from the atmosphere during the process of photosynthesis and effectively close the carbon cycle. On the other hand, fossil fuels would bring additional carbon into the atmosphere. At the very least, we can say that algae based fuels are greener than fossil fuels.
Other sources of energy like solar and wind have high capital costs, and since the demand for energy is only ever going to increase, it is unlikely that solar and wind will completely cater to them. We definitely need to find some other sources of energy. Some argue that microalgae might just be the perfect solution.
In the conventional method of producing algal fuels, algae are fed carbohydrates and their secretions are collected. The high fat content in these secretions results in a high calorific value. It has been estimated that a total area the size of France would be enough to power the whole world’s energy demands. Algae can grow on land which is otherwise unsuitable for agriculture or even in water bodies; therefore it might be precisely what mankind needs to avoid the energy crisis without compromising much on our other dependencies on land.
But Dr. R Vinu from the Department of Chemical Engineering, IIT Madras, believes that there is a lot more about algae we haven’t explored yet. He says, “Currently, uses of algae are mostly focused on generation of energy worldwide. Use of algae as an ingredient in the manufacture of fine chemicals is a futuristic thought.” Recently, it has been observed that when algae are burnt in the absence of air (a process known as pyrolysis), the resultant chemical composition, which differs from species to species, sometimes contains compounds which are of high value. These compounds can be used in pharmaceuticals, cosmetics and various other industries. Dr. Vinu and his team have been analysing the process of pyrolysis with several species of algae to try and understand the structure of the species and more importantly, find out if any valuable chemicals can be obtained using the same process in a large scale.
In chemical engineering, there are two kinds of products manufactured. Bulk chemicals, including most petroleum products, are those which are manufactured in large quantities and usually have a continuous supply. Fine chemicals, such as ingredients for synthetic drugs and cosmetics, are much more valuable and are usually manufactured and marketed in relatively small quantities. Recent observations suggest that pyrolysis of algae can be used as a process to manufacture several fine chemicals.
It has been known for a few years that direct algal pyrolysis of some algae species gives us an end product which is rich in a class of organic compounds known as aromatics, which are characterised by pleasant smells. These compounds are used extensively in the manufacture of various plastics, detergents and drugs including aspirin. But only recently, Dr. Vinu and his team have discovered that some species yield another class of organic compounds, called cycloalkanes. These compounds have a plethora of uses in fields like refrigeration, pharmaceuticals and the manufacture of other important chemicals. But there are several challenges that have to be addressed before the manufacture of these compounds can be commercialised.
Before any reaction or a set of reactions can be conducted on a large scale, we must be able to mathematically simulate the whole process accurately. This gives us an idea as to how the whole process will react to any disturbance and also provides us with a quantitative estimate on the risks associated with the reaction, which is critical to prevent accidents. We depend on the field of chemical kinetics to provide us with an accurate mathematical description of the entire process. The set of all reactions expressed in the form of ordinary diferential equations is known as a ‘mechanistic model’.
The way chemical kinetics is taught in school is oten misleading. It gives us the impression that all chemical reactions are highly predictable in nature and it is just a matter of finding their reaction mechanism to describe the process, which is true, in a way. To find the reaction mechanism the whole process has to be studied on a laboratory scale. But in practice, some processes such as pyrolysis of algae are just too complex to get a complete mechanistic model. The number of reactions, products and intermediate species are oten so high in number that it is close to impossible to find the exact reaction mechanism. In the large scale production of energy or manufacture of fine chemicals, an incomplete predictive mathematical model of the process can give results which are completely aberrant.
The team faced a similar problem during the initial study of biomass pyrolysis. It was later understood that the problem could be simplified using predictive models which are mathematically simpler. Predictive models often include only a few reactions which have high reaction rates or which give rise to more reactive species in the process while ignoring the other reactions. You can choose a predictive model whose complexity is commensurate with the accuracy needed.
The search is on for more accurate predictive models for algal pyrolysis. But these predictive models are likely to be specific to some species since different species are different in their inherent chemical nature and result in diferent end product compositions even under similar conditions.
Most species of algae are likely to give only a small fraction of compounds which are economically valuable amongst a deluge of by-products and since value is only associated with pure chemicals, they must be separated before they are ready to be used. But separation is oten a difficult task. What makes separation difficult? According to thermodynamics, the process of mixing two pure components is often a spontaneous process, especially for compounds which are similar in structure. Since mixing is a spontaneous process, the exact opposite of it is not. Additional energy of a higher grade must be provided to separate the components of the mixture. The process of pyrolysis will oten result in compounds of similar nature which are even more difficult to separate.
It has been observed, however, that algae have high nitrogen content and when burnt in the presence of air directly, release excessive amount of nitrogen oxides. Besides this, oil obtained from pyrolysed algae will probably not be usable as transportation fuel since most conventional internal combustion engines are only suitable for fuels which have a specific behaviour. The algal based fuels can’t be modified to something which has a chemical composition similar to the conventional diesel or gasoline, but in the future we might reduce our dependence on conventional sources of fuel and build internal combustion engines which are designed for algae based fuels. Direct pyrolysis of algae may still be useful to generate energy in power plants.
The whole idea of using algae to manufacture fine chemicals is still in its infancy and has a long way to go. So far, only a handful of algae species have been studied, but it is estimated that there are more than seventy thousand other species, and perhaps many of them can be used to manufacture more useful organic compounds. Today, most of the organic chemicals are obtained from sources like crude oil which are exhaustible. But given how quickly algae can grow, in the future we might only depend on algal sources to meet most, if not all, of our demand for organic fine chemicals.
Dr. R Vinu obtained his PhD in Chemical Engineering from Indian Institute of Science, Bangalore, in 2010. He has authored over 30 research papers, one book chapter and filed a patent. He is the recipient of Young Faculty Recognition Award for excellence in teaching and research from IIT Madras in the year 2015.
Akshay Govindaraj is a student in the Department of Chemical Engineering at IIT Madras, whose interests are in certain areas of applied mathematics. While working on this project he understood much more about how applied mathematics is useful in chemical engineering. For comment or criticism, he can be reached at firstname.lastname@example.org
Cover Image Courtesy: Wikimedia Commons