Rice husks: a future in biofuel production?

We live in a world undergoing innumerable changes, such as climate change, many of which are due to humanity’s activities, such as climate change. As President Barack Obama noted at the 2015 United Nations Climate Change Conference in Paris: “We are the first generation to feel the effect of climate change and the last generation who can do something about it.” Obama’s words reflect the urgency in acting to stem the effects of climate change, which is influenced by a myriad of factors.

The production of biofuels from rice feedstocks is a hot topic

One of the major contributors to climate change is the emission of CO₂ by the transportation sector. This sector alone accounts for 14% of the global CO₂ emissions each year. One promising approach to decrease CO₂ emissions by the transportation sector is to use alternative fuels tosuch as biofuels instead of traditional fossil fuels such as biofuels.

The biofuel alternative

Biofuels are energy sources derived from biological or natural resources such as plants, food waste or even algae, whose use can have a number of benefits. The wholesale use of biofuels would lead to a decrease in the net emission of CO₂ as facilitated by_. It would facilitate a “‘carbon neutral cycle”cycle’ where the CO₂ released by burning fuels would ideally be equivalent to the CO₂ captured by plants during growth.

Biofuels are also a renewable energy source since the biomass raw material source used in the production of biofuels can be repeatedly grown or harvested at the same location. Different biomass materials can be cultivated in different countries, depending on their climate and natural flora. This can increase energy security and allow countries to become more independent with regards to energy production and management.

Biomass material options

First generation biofuels are made from edible crops, vegetable oils and animal fats, while second generation biofuels can be produced from lignocellulosic biomass or wood. Third generation biofuels originate from marine feedstock such as algae, while fourth generation biofuels have emerged from advanced biochemistry.

As part of our research, we explored six different second and third generation material options that could be used to produce biofuels in industrial devices, such as fluidised bed reactors. We compared the feedstocks in terms of sustainability, feasibility and ethical responsibility. Our study indicates that willow, rice straw and rice husk are the best options for biofuel production. Willow has favourable material properties as it contains a low amount of ash and alkali metals. On the other hand, the rice feedstocks represent an ethically responsible option, as these are waste from rice production. Thus, extra land or other resources, such as fertiliser and water, are not necessary for production.

Rice husks could be the answer

Currently, the production of biofuels from rice feedstocks is a hot topic that is of interest to numerous bio-energy researchers. For example, in a paper published in Bioresource Technology by Bijoy Biswas and colleagues in India, several agricultural materials, including rice straw and husks, were assessed to determine the optimal temperature for pyrolysis and to find their maximum bio-oil yield. Pyrolysis is a process by which organic materials are heated in the absence of oxygen. Their research shows that rice husk (38.1 wt%) has a higher yield than rice straw (28.4 wt%).  Here, wt% is the percentage yield of bio-oil from a given mass of rice husks or rice straw. The pyrolysis process also leads to the production of solid residues and gas products, which can in turn be used to produce other fuels.

Biofuels are not the only product that can be made from biomass

On the other hand, in a paper published in Energy Procedia, M.S. Hossain and their colleagues (2017) presented an alternative pyrolysis approach to address both renewable energy and waste management issues. Motivated by the planet’s increasing energy demands and the depletion of fossil fuels, the researchers fed mixtures of solid tyre waste and rice husks into fixed bed reactors for co-pryolysispyrolysis at a temperature of 450°C. The research gave a maximum liquid yield of 52 wt% for a mixture of 50% tyre and 50% rice husk, showing a better yield than pure rice husks. More importantly, the study provides a possible future approach for the processing and management of biomass waste and car tyre waste.

However, biofuels are not the only product that can be made from biomass such as rice husks, as shown by Yafei Shen in a paper published in the journal Renewable and Sustainable Energy Reviews. Shen investigates the possibility of creating functional nanomaterials from silica-rich rice husks. The harvesting of silica, which is a key material for making electronics, from rice husks can help in minimising environmental issues such as the energy waste, greenhouse gas emissions and air pollution associated with the traditional open field burning of rice husks. In addition, biochar, which is a product of the pyrolysis of rice husk, can be used in the removal of pollutants from soil and for silicon battery materials.  

A biofuel future for rice husks?

Biofuels can certainly contribute to the reduction of greenhouse gas (GHG) emissions. Deriving biofuels from agricultural wastes such as rice husks fits within the current trend of a circular economy, provided that this is implemented in an ethically correctethic manner. We believe that producing biofuels, when done correctly, can contribute to a more sustainable and ethical society. 

Also read ‘Are the shipping industry and biofuels the perfect match?’ by three other students from this project

 

• About this project

Luna, Ivar and Steven are part of a Student Project Group (SPG) following a minor in Responsible Innovation, which is facilitated through a collaboration of the universities of Leiden, Delft and Rotterdam. Each university contributeshas a specific focus onin the field of Responsible Innovation. The students follow courses and complete projects on responsible innovation, responsible management and ethics over two study blocks. 

• About the mentor:

Barry W. Fitzgerald is a research scientist based in the Process & Energy Department of 3mE, TU Delft. His main research interests include biomass processing, polymer physics, fluid dynamics, granular materials and science education. He is also actively involved in scientific communication outreach and has published the popular science book Secrets of Superhero Science. In addition, Barry is the editor-in-chief of the TU Delft open access journal Superhero Science and Technology. Contact him here.

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