S. Vishnu Sharma
IIT Madras research team has developed a simple microwave process to produce good quality bio-oil from agricultural waste products like straw and bagasse and discarded plastics.
GAIL India Limited funded this project of IIT Madras research team. The environmental impact of extracting fossil fuels combined with the volatility in oil prices and the political unrest across the world have led to the urgency in search of renewable fuels.
IIT Madras research team 2020
Extracting bio-fuel oils generated from renewable biological sources are considered a practical and pragmatic replacement for petroleum and petrochemicals.
Amidst this situation the work done by IIT Madras research team is likely to have lot of significance. IIT Madras research team was led by Dr. R. Vinu, Associate Professor, Department of Chemical Engineering, IIT Madras.
The other members of IIT Madras research team comprised Dr. Dadi Suriapparao and Ms. Banupriya Boruah.
The results of the work done by IIT Madras research team have been published recently in the reputed peer-reviewed journal Bioresource Technology and Fuel Processing Technology.
Speaking about the work by IIT Madras research team Dr Vinu said biomass is the only renewable source of carbon on earth with immense potential for the production of energy, chemicals and materials with zero carbon footprint on the environment.
Agricultural waste products such as rice straw, sugarcane bagasse and wood chips, among others, can potentially serve as bio-oil producing biomass, he said.
One of the common methods to produce bio-oil from biomass is ‘pyrolysis’ or heat-induced breakdown of the biomass components into fuel components.
However, bio-oil produced by the pyrolysis of biomass contains large amounts of oxygenated groups or ‘oxygenates,’ far greater than in fossil fuels.
These ‘oxygenates’ result in lower heating value of bio-oils, compared to fossil fuels and in addition, increase their acidity and corrosiveness.
The leader of IIT Madras research team further said in order to make bio-oils competitive with fossil fuels, their oxygenate content must be reduced and hydrogen content increased.
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Mixing biomass with hydrogen-rich materials during pyrolysis can conceivably make biomass derived bio-oil comparable to fossil-derived fuels in calorific value and chemical/physical properties, said Dr. Vinu.
Plastics that are rich in hydrogen, can serve as the hydrogen supplier to biomass in its conversion to low-oxygenate bio-oils.
The use of plastics as a supporting material in the pyrolysis of biomass would ultimately serve two purposes, it would produce bio-oils with better properties and also help in repurposing used plastic.
The co-pyrolysis of biomass and plastics, in addition to increasing the calorific value of the fuel, also reduces char formation, thereby increasing efficiency of the process and yield of fuel.
The bio-oils produced by co-pyrolysing the biomasses with the plastics had higher energy yields than those of bio-oils produced by pyrolysis of pure biomass, without the plastics.
IIT Madras research team took this a step further and used microwave to co-pyrolyse biomass and plastics. Microwave heats materials quickly and uniformly and is a selective and energy-saving technology.
They used a microwave oven to co-pyrolyse a variety of biomass including rice straw, sugarcane bagasse, groundnut shell, wood sawdust and wood from the tree called ‘Seemai Karuvelam’ in Tamil (‘Angaraji Babul’ in Hindi, scientific name Prosopis juliflora) with two synthetic plastics, polypropylene and polystyrene.
In the case of rice straw and bagasse, the team also used a zeolite catalyst to upgrade the quality of the bio-oil to light fuel oil (LFO) and heavy fuel oil (HFO).
The use of catalyst resulted in better yields of the bio-oil, in addition to conferring better properties to it – the properties of bio-oil made from biomass-polypropylene mixtures were similar to that of light fuel oil and had high calorific value (43 MJ/kg), low viscosity (1 cP), optimum density (0.850 g/cc) and flash point (70 °C).
This was because the oils had very little oxygenates, much like fossil-derived fuel oils. The findings of the team provide the much-needed incentive for development of such a technology that could take us closer to self-sufficiency in the energy sector.
‘We believe that microwave-assisted pyrolysis process is a sustainable and energy efficient approach for resource recovery from a wide variety of wastes such as biomass agri residues, plastic wastes including disposed single-use plastics and non-reusable face masks, and a mixture of these,’ said Dr. Vinu who led the IIT Madras research team.