(2ag) Decarbonizing Chemical Manufacturing: CO2 Capture & Utilization from Point Sources and Electrochemical Synthesis of Chemicals Using Renewable Energy

Background and Motivation

The biggest challenge of the 21^st century is mitigating climate change. To reverse the effects of global warming and prevent further damage, it is required to achieve net zero carbon emissions by 2050. Industrial production of commodity chemicals contributes to greenhouse gas emissions by a larger extent. Most greenhouse gas emissions come from the production of cement, steel, plastics, and fertilizers. Production of ethylene, ammonia, urea, hydrogen which act as the feedstock for several commodities can be decarbonized by electrification – electrochemical synthesis using renewable energy. Green premium (cost of going green) is an important parameter to be considered when switching to a carbon free technology. If the green premium is more than 20 % then the process will be economically unfeasible. Carbon capture will be the best option in such cases to make the process free of greenhouse gas emissions. It is required to develop carbon neutral and carbon zero technologies which use renewable energy to produce fuels and commodity chemicals. Energy and Environment will be the research theme of my lab focusing on both fundamental and applied research towards decarbonizing chemical manufacturing.

Carbon Capture and Utilization from Point Sources

Carbon emissions from cement plants which are produced as a result of the decomposition of calcium carbonate to calcium oxide is inevitable. Green premium for processes such as steel production which uses green hydrogen instead of carbon to reduce the iron ore to iron is extremely high. It is economically preferable to capture the carbon from such processes making the process carbon neutral. The conventional method of carbon capture involves pressure swing method and absorption using monoethanol amine. Such processes are energy intensive and expensive. Bipolar membrane electrodialysis (BPMED) assisted carbon capture gives the opportunity to capture the CO₂ selectively from dilute point sources such as flue gas from fossil fuel power plants, and fossil fuel-based commodity chemical productions such as plastics, steel, cement etc. The concentration of CO₂ in the flue gas can vary between 10 % to 40 %. The separation of CO₂ from the flue gas mixture involves 1) Cooling of the flue gas to room temperature using heat exchangers 2) Contact of flue gas with 1 M KOH using high surface area sintered sparger for enhanced mass transfer. The CO₂ in the flue gas is absorbed as Potassium Carbonate solution. 3) The absorbed potassium carbonate is sent to an Electrodialysis stack where the carbonate ions from the basic solution migrates via anion exchange membrane to the acidic solution where it is released as pure CO₂. The captured CO₂ can be electrochemically reduced into value added chemicals such as CO, Methanol and Ethylene. One of the major challenges in the carbon capture is the variability of the flue gas depending on the fossil fuel used. Flue gas from coal-based fuels would have significant amounts of NOx and SOx which would affect the capture efficiency and membrane stability. The research objectives for the carbon capture and utilization from point sources are as follows:

• CO₂ capture by using realistic flue gas composition from fossil fuel based chemical manufacturing companies and studying the effects of NOx and SOx on the CO₂ capture efficiency.
• Fundamental analysis on the effect of different Anion Exchange membranes and Bipolar membranes for enhanced CO₂ capture and long-term operation.
• Fundamental electrocatalytic studies for identifying selective and stable catalysts for the electrochemical conversion of CO₂ to CO/CH₃OH/C₂H₄.
• Electrolyte and Reactor engineering for efficient conversion of CO₂ into CO/CH₃OH/C₂H₄ and industrialization of this technology.
• Integration of the CO₂ capture unit with the CO₂ utilization unit for continuous capture of CO₂ and continuous synthesis of CO/CH₃OH/C₂H₄ based on the requirement.

Electrification of Chemical Manufacturing

Ammonia, Ethylene, Propylene, Methanol, BTX (Benzene, Toluene, Xylene), and urea are the chemicals that involve larger carbon footprint for manufacturing. Electrification of the manufacturing of these chemicals using renewable energy gives the opportunity to produce the chemicals in a green manner with net zero carbon emissions. Ammonia is an important commodity chemical to manufacture fertilizers, pharmaceuticals, ammunition etc. Nearly 1 % of the total carbon emissions across the globe annually is attributed to ammonia synthesis. Ammonia is produced industrially by an energy intensive Haber-Bosch process which has a massive carbon footprint. Electrochemical synthesis by reduction of Nitrogen to Ammonia is an attractive to produce ammonia in a green manner. The process is very challenging and so far, there has not been a breakthrough for the direct electrochemical reduction of nitrogen to ammonia in aqueous media at ambient conditions. There has been a significant progress in the Lithium mediated ammonia synthesis, but the process suffers from sacrificial oxidation of organic solvents and Lithium recovery. One of the research goals would be synthesis of ammonia via lithium mediated nitrogen reduction for longer durations. Recent progress has been made for the electrochemical reduction of nitrates to ammonia on oxide derived Cobalt (https://doi.org/10.1039/D1EE01879E). The study was performed with pure concentrated nitrates, the challenge would be extending the study to dilute sources (agricultural run-off water) and concentrated sources with significant impurities (ammunition waste). Mechanistic understanding of nitrate reduction to ammonia on Cobalt and the effect of pH on the reactions would help us extending the study to dilute and impure sources.

Agricultural wastes such as bagasse, rice husk and corn husk are a major problem in developing countries. The farmers burn off the stubble waste to get rid of the waste and produce biochar which is an excellent fertilizer. Stubble waste burning causes huge pollution in developing countries and an alternate solution is required. Biochar is generally produced by pyrolysis which is quite energy intensive. Biochar can be produced at moderate temperatures (< than 200 °C) by sulfonation. The resultant biochar will be in acidic medium which can be neutralized by adding ammonium hydroxide or potassium hydroxide and used as a fertilizer. Syngas can be produced by the electrolysis of biochar. The biochar is oxidized to CO on anode and water is reduced to hydrogen on the cathode at potentials (~ 1 V) much lower than water splitting potential. The resulting syngas produced is green and free of O₂ which can be used to synthesize wide variety of fuels including methanol, methane, and other feedstocks for petrochemicals such as ethylene and propylene. The challenge would be to develop stable and selective catalysts that can continuously produce syngas selectively for a longer duration. The research objectives for this section are as follows:

• Fundamental studies on the electrode and electrolyte engineering for lithium mediated nitrogen reduction to ammonia for long term operation focusing on electrode and electrolyte stability.
• Mechanism of electrochemical nitrate/nitrite reduction to ammonia on Cobalt with pH dependance for nitrate waste recovery from ammunition waste and agricultural run-off water.
• Electrochemical reduction of nitrogen to ammonia in aqueous media at moderate pressures.
• Catalyst screening for the electrochemical synthesis of syngas by oxidation of biochar focusing on stability.
• Effect of the source of biochar from various agricultural wastes such as rice husk, corn husk, bagasse towards electrochemical syngas synthesis.

Teaching Statement

“A poor teacher complains, an average teacher explains, a good teacher teaches, a great teacher inspires.” – Hosur Narasimhaiah

I want to inspire students apart from teaching. I believe that there is no such thing as a “tough course”. Every subject is easy, provided they are explained in a lucid manner. I want to provide the joy of learning which I attain every time, when I understand the so-called tough concept. The interest towards the subject can be cultivated in students by relating the subject matter to day-to-day examples using analogies and by explaining the relevance of the subject matter to practical applications and real-world problems.

There will be several myths and misunderstandings especially in the field of Science and Engineering. My role as a teacher is to make sure that students don’t have misunderstandings in the concepts. In this fast-changing world, it is much required to be updated regularly, with the current research findings and equip the students to provide solutions to the existing and upcoming scientific challenges. A single teaching methodology cannot be applied for all the situations. For example, swimming cannot be taught in a class and math cannot be taught using case studies. I believe that the methodology should be chosen based on the subject as well as the students. Each student is unique, and it is my sole duty to accommodate the needs of each student.

Overall, my sole ideology on teaching is that students must learn how to learn. At the end of the course, they should know the purpose of the course and should be able to apply the skills obtained during the course to real world problems. I consider myself as a student and teaching is the best way to master a subject. Every time when students ask me doubts, I always learn from their questions and find new ways to explain it better. The joy of seeing happy faces, when students finally understand an intricate concept is priceless and I always crave for that every time I teach.