(3dx) Oxidative Depolymerization of Lignin in Perfluorodecalin

Past Research: As a junior student in my undergraduate program, I began my first research study on modeling and comparison of water desalination by the humidification-dehumidification and adsorption methods. My passion and interest in discovering new things, along with my hardworking, resulted in publishing a conference paper from my bachelor’s final project. My master project was focused on the heat transfer of SiO₂/water nanofluid in jacket side of agitated vessels through experimental and numerical techniques. My research findings was published as two conference papers and one peer-reviewed article. I subsequently expanded my academic knowledge through collaboration with other scholars in conducting both experimental and numerical studies on heat exchangers and renewable energies. To this end, a series of studies were conducted on the hydrodynamic performance of a new wave energy converter called Searaser and evaluated its efficiency for use in the Caspian Sea.

Current Research: I receieved a PhD addimision from the Department of Mechanical Engineering at Iowa State University. My Ph.D. project included an innovative method of lignocellulosic biomass deconstruction with an emphasis on lignin. I started to work on lignin depolymerization by oxygen to produce valuable phenolic monomers. Lignin oxidation is a promising method for lignin valorization. It can produce a range of functionalized chemicals of significant economic value such as aromatic acids, aromatic aldehydes, and aliphatic carboxylic acids. I designed a small batch reactor system to perform lignin oxidation tests. This system enabled us to demonstrate the non-catalytic depolymerization of native lignin to oxygenated phenolic monomers. Oxidation tests were performed in perfluorodecalin. Perfluorodecalin is a perfluorocarbon (PFC), characterized by their chemical stability and exceptionally high solubility for O₂. High yiled of valuable phenolic monomers was achieved from lignin oxidation using perfluorodecalin. Moreover, the role of molecular oxygen was elucidated as both an oxidant to achieve oxidative depolymerization and a radical scavenger to mitigate the condensation of phenolic monomers. The lignin oxidation process was scaled up from 5 ml to 250 ml without losing yield. For scaling up the process, a stirred reactor was used. Since the reaction time is a key factor in oxidation tests, the reactor was modified.Our new batch system is a unique system with fast heating and cooling capability. My research findings on this topic have been presented in several well-known conferences, and a paper is currently under review in the Journal of Energy and Environmental Science .

As the second phase of this project, I am currently working on oxidative depolymerization of lignin in a biphasic system. In this study, technical and native lignin sources are depolymerized in the presence of oxygen inside a biphasic system composed of solvents with high lignin solubility and perfluorodecalin of high oxygen solubility. We hypothesis that organic species formed by oxidative cleavage of lignin in perfluorodecalin can be extracted and stabilized into the organic phase with much lower oxygen concentration to improve the phenolic monomer yield. I am also working on lignin depolymerization and esterification using carboxylic acids to produce phenyl ester. The net carbon emissions from biodiesel could be decreased if methanol is replaced by a biobased reactant in the production of methyl esters. We hypothesize that lignin can be used in the production of phenyl esters. To this end, a series of tests on native and technical lignin have been performed. We would like to test both one-pot and two-stage esterification of lignin.

Future Research:

Lignin-first biorefinery: To retain the intrinsic value of virgin lignin, biorefineries will have to employ either mild depolymerization processes, such as ammonia-based fractionation and low-temperature organosolv techniques employ processes that continuously stabilize phenolic products as they are released from biomass. This second approach, sometimes referred to as the lignin-first strategy for deconstructing lignocellulose, is receiving increasing attention with reductive catalytic fractionation (RCF) and formaldehyde-assisted fractionation, as prominent examples. I intend to use my knowledge in lignin chemistry and depolymerization to introduce new methods of delignification to biorefineries to produce a more reactive, less condensed lignin.

Lignin depolymerization to chemicals, fuels, and material: There are two different categories of products from lignin. The first category, which currently is the main application of lignin other than heat and power production, utilizes the polymeric structure of lignin to produce carbon nanofibers, polymer composites, adsorbents, and glues. Recently, the utilization of lignin to produce bio-based chemicals and fuels has received increasing attention. In this method, lignin is first depolymerized and then upgraded to a wide array of valuable products. There is still a long way to go to convert lignin to high-quality material and produce high yield of chemicals and fuels economically. Therefore, I intend to work on this area to improve the economic viability of biorefineries.

Fast pyrolysis and solvent liquefaction of biomass: Fast pyrolysis of biomass is a simple and robust thermochemical technology for converting biomass into bio-oil, syngas, and biochar. Solvent liquefaction has been receiving increasing attention and has the potential of becoming a robust and economical method of processing biomass . I would like to focus on both of these methods in my future research plan. Both of these methods seem promising ways to produce bio-oil from lignocellulosic biomass.

Teaching interests

During the past few years in the Department of Mechanical Engineering at Iowa State University, I have taken on the various responsibilities of a teaching assistant and an instructor in several courses. In 2019 and 2020, I was fortunate to be the instructor of the heat transfer course and laboratory. For the heat transfer course, I was responsible for teaching some parts of the course, do the grading and answer questions related to assignments. For the heat transfer lab, I was responsible for explaining the experimental procedure, helping the students to run and analyze the data, and grading the in-class assignment and lab report. During my master’s study from 2011 to 2013, I was assigned to the process control lab and heat and mass transfer courses. During that time, I obtained expertise in grading and rubric preparations for assignments, exams, etc. I received excellent reviews from students in all of my teaching assistance experiences, and I am nominated to receive the Teaching Excellence Award during my Ph.D.

I am firmly an advocate of an educational revolution, particularly for undergraduate students, to prepare them for future challenges by stressing fundamental materials and applying them to solving practical and real-life problems instead of always going through unessential theoretical details that may overshadow the main concepts. I intend to offer multidisciplinary courses useful for a broad range of students from different majors and to provide high-quality course materials reflecting many practical problems/examples and case studies. I prefer to begin my teaching by asking a few challenging questions at the beginning of each lecture, asking the student to brainstorm, then I would present appropriate theory and examples for solving the problem. Additionally, I will involve my students in class discussions, challenging them by asking questions back and forth while encouraging them to ask more questions to clarify parts that they may find vague. I will also encourage students to be involved in teamwork projects to improve their productivity, networking, and risk-taking. With respect to evaluation, the final grade would be mostly determined by performance on several assignments given during the semester, a final project, and in-class quizzes, along with a midterm and final exams. Although I have always welcomed seeing my course evaluations from both students and teachers at the end of each semester, I would rather have the mid-course evaluation in my classes to read anonymous feedback comments, discuss them with students, and accordingly modify my teaching methods. Not only does this assure my students that I care about what they want, but it also gives me a chance to improve my teaching skills during the semester.

Abstract

Lignin is one of the major components of lignocellulosic biomass, and the only component containing aromatic units. It is a by-product of the paper and pulp industry and the second-generation biofuels plants. Recently, lignin has received attention as a potential precursor for producing value-added products. In this study, the non-catalytic oxidative depolymerization of lignin was studied in perfluorodecalin and compared with some polar aprotic and polar protic solvents like acetonitrile, ethyl acetate, methanol and ethanol. Among solvents evaluated, perfluorodecalin with exceptionally high oxygen solubility, produced the highest monomer yield at 250°C in 10 min. lignin-oil obtained under oxidative condition showed smaller molecular weight and polydispersity compared to the rest of the solvents. Increasing the reaction time under oxygen atmosphere, further decreased molecular weight and polydispersity, while progression with time under inert atmosphere increased molecular weight and polydispersity, suggesting condensation reactions in the absence of oxygen. Under oxidative condition, phenoxy radicals are produced by thermally induced homolytic cleavage of lignin ether linkages. These radicals then react with oxygen to from peroxy radicals which are much less susceptible to repolymerization reactions and could oxidize more in the presence of oxygen to produce aldehydes and acids. Oxidation reaction in perfluorodecalin not only increased lignin depolymerization, but also decreased undesirable condensation reactions.