(334u) Lignin Depolymerization and Esterification By Carboxylic Acids to Produce Biodiesel

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.

Abstract

Global energy consumption has significantly increased in the last 40 years and approximately 80% of this demand is supported by fossil fuels. Environmental and human health concerns regarding fossil fuels consumption has encouraged researchers to find sustainable alternatives for the current petrochemical industry. Within this context, biodiesel production has received increasing attention in recent years. Biodiesel is a form of diesel fuel which is composed of esters formed by chemically reacting alcohols and long chain carboxylic acids. Lignin as the only component of biomass containing aromatic structure is a great precursor for producing chemicals and fuels. Interestingly, phenols can be esterified by carboxylic acids to produce esters. We hypothesize that lignin can be used as a potential precursor for biodiesel production. Phenolic products obtained from lignin depolymerization could be esterified with a carboxylic acid to produce phenyl esters. In order to test our hypothesis, technical and native lignin sources were applied as phenolic source and carboxylic acids like acetic acid and hexanoic acid were used as acetylating agents. Both in-situ and ex-situ esterification of lignin were studied. In the in-situ esterification process, lignin was depolymerized and esterified in one pot, while in the ex-situ esterification process, lignin was first depolymerized, and then the obtained lignin-oil was esterified. Lignin-oil was further characterized by GC-FID, FTIR and 2D HSQC NMR spectroscopy.