Helping create alternate route to renewable fuels from lignocellulose

Rapidly depleting fossil fuels is arguably one of the most important energy-related challenges the world faces today.

As fossil fuels deplete at a fast pace, there is high demand for alternative renewable sources of energy. One that is available in plenty is lignocellulosic biomass, or plant dry matter, which can be used to produce biofuels, mainly bio-ethanol.

The conversion of biomass into transportation fuels has become increasingly important due to the shortage of petroleum and concerns about global warming. However, it is difficult to deconstruct lignocellulose without producing by-products inhibitory to further downstream fermentation process, because of its highly complex structure.

Glucose can be converted into ethanol by a simple fermentation process. However, obtaining monomeric glucose from lignocellulose is not so easy, due to its highly complex structure and the presence of crystalline form of cellulose. Therefore, an effective pre-treatment method is required in order to deconstruct biomass before it can be used as fuel.

Fig. 1 Structure of the lignocellulosic biomass
(modified from Jianq, et. al. and Sanderson, et.al.)

And this is where Vasudha Kotia, a researcher with the IITB-Monash Research Academy, is hoping to make a difference.

The Academy, a Joint Venture between IIT Bombay and Monash University, operates a graduate research program in Mumbai. Research is conducted by scholars in both countries, while studying for a dually-badged PhD from both organisations. Vasudha is working on an exciting project titled, 'Solvent Assisted Cellulose Depolymerization', under the supervision of Prof Santosh B Noronha, Prof Douglas MacFarlane, and Prof Antonio Patti.

There are a number of methods to hydrolyse lignocellulose—including steam, acid, alkaline hydrolysis, microwave, ultrasound, etc. However, these methods have certain disadvantages including high energy consumption and harmful effects to the environment.

"Acid treatment is the most frequently followed method," explains Vasudha. "Dilute acid treatment of lignocellulose is carried out at high temperature (200-240 0C), and as by-products HMF, furfural and phenolics are formed which inhibit further fermentation. This method is neither environmental-friendly nor economical since the substrate has to undergo acid recycling before it can be fermented."

There is a way out, however. Says Vasudha, "This problem can be overcome if cellulose is hydrolysed by the enzymatic method. The conversion of cellulose into fermentable sugars is brought about by the synergistic action of three enzymes—namely exoglucanase, endoglucanase and beta-glucosidase. However, the crystalline form of cellulose and the close association and intricacy of the carbohydrates–lignin complex is the main obstacle in the enzymatic hydrolysis of lignocellulose. It is therefore necessary to pre-treat the biomass to reduce this recalcitrance for effective enzymatic hydrolysis. Recently ionic liquids (ILs) are being increasingly explored as solvents for lignocellulosic biomass. An ionic liquid is a molten salt, melts below 100oC, composed of organic cations and anions, often exist as liquids at room temperature. ILs have various useful properties such as low volatility, thermal stability, effective dissolution and negligible degradation of biomass."

Fig. 2 Impact of pretreatment on lignocellulosic biomass.
(modified from Mosier, et al.)

Explaining her work so far, Vasudha says, "We have investigated various ionic liquids as pre-treatment solvent for biomass deconstruction. This has significantly enhanced the glucose yields from lignocellulosic biomass. The sugars obtained as a result of IL pretreatment were successfully converted into ethanol upon fermentation process. Since the method is working with significant yields of sugars and ethanol, we are now looking at scaling up the process. We can expect pilot scale production biofuel from lignocellulosic waste material which would be a breakthrough in the petrochemical industry."

Prof Murali Sastry, CEO, the IITB-Monash Research Academy is excited about the expected outcomes of Vasudha's project. "The Academy was conceived as a unique model for how two leading, globally focused academic organisations can come together in the spirit of collaboration to deliver solutions and outcomes to grand challenge research questions facing industry and society," he says.

What better than helping find a solution to the global energy crisis?

Research scholar: Vasudha Kotia, IITB-Monash Research Academy

Project title: Solvent Assisted Cellulose Depolymerization

Supervisors: Prof Santosh B Noronha, Prof Douglas MacFarlane, and Prof Antonio Patti

Contact details: vasudha.kotia@monash.edu

This story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.