The lush flowery green water- hyacinth is a common view across the length and breadth of India growing in lakes, dams and irrigation channels without any intervention. This weed – which contains up to 50% hemicelluloses –can now be used as an economic and abundant source of biofuel, thanks to researchers at IIT Kharagpur. Hemicelluloses are natural polymers present along with cellulose in almost all plant cell walls. The key to producing commercially viable, low carbon footprint biofuels is to supplement cellulosic ethanol with hemicellulosic alcohols.While cellulose is used for cellulosic fuel production, hemicelluloses are often ignored as biofuel sources, primarily because surface reactions are capable of releasing only one-quarter of the soluble sugars from the hemicellulose matrix for bioethanol production.
Chemical engineers at IIT Kharagpur have uncovered the pore-scale phenomena that result in fourfold increase in the yields of fermentable sugars and bioethanol from hemicelluloses. Apart from water-hyacinth, hemicellulose based bioethanol can also be produced from commonly available grasses, red and green algae, etc., which have 2.5 to 3 times more hemicellulose than cellulose. 1 kg of such dry hemicellulosic biomass can produce 0.62 kg of soluble sugarafter required hydrolysis at 40⁰C, which in turn will – depending on the yeast strain used for fermentation – produce 0.18-0.29 kg of bioethanol with a significant calorific value. The research explains that the secret to rapidly producing soluble sugars required for bioethanol production from hemicelluloses lies in their smallest scale – the pores. This was unknown till now, hence hindering biofuel productivity.The average cellulose to hemicellulose ratio in plant cell walls is slightly below 2:1, suggesting that supplementing cellulosic fuels with hemicellulosic ones would enhance biofuel productivity and cost-effectiveness by more than 50%. Simultaneous production of cellulosic and hemicellulosic fuels from the same biomass source would considerably improve the combined Net Energy Value (energy content of ethanol minus energy input) from what it presently is for cellulosic ethanol (about 21.5 MJ/lit).
‘It turns out that three quarters of the soluble sugars we obtain for generation of bioethanol are produced from the pore-scale reactions. So increasing the polymer’s porosity and degree of swelling will enhance the deconstruction of hemicelluloses from plant cell walls, thus increasing bioethanol,’ said Professor Saikat Chakraborty, faculty at the Dept. of Chemical Engineering, and lead researcher of the Bioenergy Research Group at IIT Kharagpur.
‘Hemicelluloses are the second most abundant natural polymer on earth – after cellulose – and a new technology engendered from this pore-scale phenomena could rapidly produce biofuels from locally available plant sources’ added Professor Chakraborty.
This novel research work, though being fundamental in nature, would go a long way in transforming the biofuel industry. It has been recently been published in the much coveted Nature’s Scientific Reports (http://www.nature.com/articles/srep38173).
‘Our experiments show that the enzymes that break down these polymers diffuse and adsorb into the pores. Capillary action and Coulombic forces of attraction in the mesoporous matrix together produce two to fourfold swelling of the hemicelluloses. This accelerates enzyme adsorption on the pore walls, and rapidly transforms the hemicelluloses to produce fermentable sugars for bioethanol production,’ said Sajal Kanti Dutta, PhD student associated with the research.
‘Though, some of these soluble sugars as well the hemicellulose itself inhibit the hydrolysis process, the interesting thing is that we have found a solution so as to minimize these inhibitions, thus sustaining the bioethanol production,’ he added.
Scientists at IIT Kharagpur’s Chemical Engineering Department and PK Sinha Center for Bioenergy are working to transform these fundamental insights into new biofuel technologies that would help fight climate change – possibly, the biggest threat to life on our planet today. The coupled challenges of greenhouse gas emissions, fossil fuel depletion and a sharp rise in global energy consumption expected by 2030 can be only addressed through alternate, renewable fuel technologies such as this.