(2fj) Thermochemical Processing of Biomass, Plastics and Waste Feedstocks

As chemical engineers, we know that the future of humankind depends on sustainable practices. This includes developing energy sources that are not based on fossil fuels, as well as dealing with the enormous amounts of wastes being generated worldwide. Waste-to-value concept has gained much interest in the recent decades, which combines the issues of impending fuel crisis as well as improper waste management. Thermochemical conversion processes have been leading the waste-to-value cause for the last few decades due to their ability to convert a variety of waste feedstocks in to fuels and chemicals. Hydrothermal liquefaction (HTL) is one such thermochemical process, which uses water at near-critical conditions, to convert a variety of (waste) feedstocks to fuels and chemicals. The concept is that, at critical conditions, water undergoes a variety of change in its properties, which makes water behave like a non-polar solvent. This helps water break down organic components in the feedstock to produce bio-crude (which is an oxygenated analogue to petroleum crude), hydrochar (which is similar to low-quality coal), aqueous phase (rich in water-soluble organics and nutrients), and gaseous phase (mainly CO₂). Although HTL shows huge potential, there are various issues that needs to be addressed.

Research Interests:

My research interests focus on the pursuit of alternative fuels and chemicals, particularly focusing on conversion of waste feedstocks, through fundamental studies including experiments and various analytical techniques. This pursuit started during my undergraduate days, where I investigated the feasibility of blending diesel with upgraded tyre pyrolysis oils. Using a novel technique, ‘oxidative desulphurization’, we achieved a sulphur content of <0.1 wt.% in the tyre pyrolysis oil, and blended it with commercial diesel. The blends were then used to run a 4-stroke diesel engine, and their characteristics and CO₂ emissions were analysed.

Currently, I am pursuing my doctoral program under the supervision of Prof. R. Vinu, at the Indian Institute of Technology Madras, India. I was awarded the Prime Minister’s Research Fellowship to pursue my doctoral research, which also focused on converting waste feedstocks to valuable chemicals and fuels, through HTL. For the past 5 years, I’ve been working on HTL of a variety of real-world feedstock, such as agricultural wastes (rice straw), macroalgae, plastics, black liquor from paper and pulp mills, and other industrial wastes. Some of the major breakthroughs achieved from my recent HTL studies include:

1. Process intensification of the HTL process by aqueous phase recirculation and use of seawater and wastewaters
2. Production of diesel-grade fuels from real industrial wastes and wastewater from a tube manufacturing unit
3. Production of a single targeted chemical (phenol) from waste plastics, with concentrations as high as 80 wt.% in the crude oil, using low-cost homogeneous catalysts

Currently I’m experimenting with various other waste plastics to produce targeted chemicals via HTL in collaboration with Terrawaste Ltd. During the current academic year, I am planning to conduct experiments with residual lignin from ethanol biorefinery based in Finland, to produce heavy residue, that can be utilized for road construction. I am also hoping to explore the possibilities of producing phenol-based bio-resins using waste plastics and low-cost catalysts, in a one-pot synthesis mode.

In the near-future, I would like to explore the possibilities of catalytic studies of the conversion processes, to produce bio-based polymers through thermochemical processes, as well as to study the feasibility of scaling, commercialising and integrating these waste-to-value processes in the existing markets and infrastructures.

Teaching interests and experience:

During my graduate studies, I have assisted in teaching various subjects, including ‘Biomass Conversion Processes and Analyses’, ‘Transport Phenomena in Catalysis’, as well as take chemical engineering lab sessions for graduate and undergraduate students at IIT Madras. I’ve also taken online classes on Chemical Reaction Engineering, Mass Transfer and Mechanical Operations to undergraduate students preparing for competitive exams, under the National Programme on Technology Enhanced Learning, by the Ministry of Education, Govt. of India.