The Consequences of Surface Confinement on Free Radical Chemistry

Mass transport limitations impact the thermochemical processing of fossil and renewable energy resources, which involves the breakdown of cross-linked, macromolecular networks. To Investigate the molecular level details of the consequences of molecular confinement on high temperature (275-500°C) free-radical reaction pathways, we have been examining the pyrolysis of model compounds attached to the surface of non-porous silica nanoparticles through a thermally robust Si-O-Caryl, tetha. Pyrolysis of silica-immobilized diphenylalkanes and related ethers have been studied in detail and compared with the corresponding behavior in fluid phases. The diffusional constraints can lead to reduced rates of radical termination on the surface, and enhancement of neophyl-like rearrangements, cyclization-dehydrogenation pathways, and ipso- aromatic substitutions. Furthermore, studies of two-component surfaces have revealed the importance of a radical relay mechanism involving rapid serial hydrogen transfer steps resulting from the molecular pre-organization on the low fractal dimension silica surface. Key findings are reviewed in this paper, and the implications of these results for fuel processing are described

Flash vacuum pyrolysis of lignin model compounds

Despite the extensive research into the pyrolysis of lignin, the underlying chemical reactions that lead to product formation are poorly understood. Detailed mechanistic studies on the pyrolysis of biomass and lignin under conditions relevant to current process conditions could provide insight into utilizing this renewable resource for the production of chemicals and fuel. Currently, flash or fast pyrolysis is the most promising process to maximize the yields of liquid products (up to 80 wt %) from biomass by rapidly heating the substrate to moderate temperatures, typically 500{degrees}C, for short residence times, typically less than two seconds. To provide mechanistic insight into the primary reaction pathways under process relevant conditions, we are investigating the flash vacuum pyrolysis (FVP) of lignin model compounds that contain a {beta}-ether. linkage and {alpha}- or {gamma}-alcohol, which are key structural elements in lignin. The dominant products from the FVP of PhCH{sub 2}CH{sub 2}OPh (PPE), PhC(OH)HCH{sub 2}OPh, and PhCH{sub 2}CH(CH{sub 2}OH)OPh at 500{degrees}C can be attributed to homolysis of the weakest bond in the molecule (C-O bond) or 1,2-elimination. Surprisingly, the hydroxy-substituent dramatically increases the decomposition of PPE. It is proposed that internal hydrogen bonding is accelerating the reaction

Investigation of the role of aromatic carboxylic acids in cross-linking processes in low-rank coals

In the pyrolysis and liquefaction of low-rank coals, low-temperature cross-linking reactions have been correlated with the loss of carboxyl groups and the evolution of CO{sub 2} and H{sub 2}O. It is not clearly understood how decarboxylation leads to cross-linking beyond the suggestion that decarboxylation could be a radical process that involves radical recombination or radical addition reactions. We have recently conducted a study of the pyrolysis of 1,2-(3,3{prime}-dicarboxyphenyl)ethane (1) and 1,2-(4,4{prime}-dicarboxyphenyl)ethane (2) and found that decarboxylation occurs readily between 350-425 {degrees}C with no evidence of coupling products or products representative of cross-links. We proposed that decarboxylation occurred primarily by an acid-promoted cationic pathway, and the source of acid was a second carboxylic acid. The decarboxylation of 1 and 2 was investigated in diphenyl ether and naphthalene as inert diluents. In each solvent, the rate of decarboxylation dropped by roughly a factor of 2 upon dilution from the neat liquid to ca. 0.4 mole fraction of acid, but further dilution had no effect on the rate. This could be a consequence of hydrogen bonding or an intramolecular protonation. Molecular mechanics calculations indicated that 1 and 2 can adopt an appropriate conformation for internal proton transfer from a carboxy group on one ring to the second aryl ring without a significant energy penalty. In addition, the dicarboxylic acid could internally hydrogen bond, which may further complicate the reaction mechanism. Therefore, we have conducted a study of the pyrolysis of a monocarboxybibenzyl, 1-(3-carboxyphenyl)-2-(4-biphenyl)ethane (3), to determine if decarboxylation occurs by an ionic pathway in the absence of intramolecular pathways

Thermolysis of a polymer model of aromatic carboxylic acids in low-rank coal

To compliment our current investigation into the role that decarboxylation of aromatic carboxylic acids plays in the low-temperature cross-linking of low-rank coals, we are investigating the thermolysis of a polymeric coal model compound to determine if the polymeric network structure of coal can alter the decarboxylation pathways. In this investigation, a bibenzylic polymer, poly-(m-xylylene-co-5-carboxy-m-xylylene), 1, was synthesized containing 2.3 carboxylic acids per 100 carbons, which is similar to that found in Zapp lignite. The pyrolysis of 1 was compared to poly-m-xylylene, 2, and the methyl ester of 1, 3, to determine if the carboxy group enhances cross-linking reactions. The major product from the pyrolysis of 1 at 375{degrees} C or 400{degrees} C for 1 h was a THF insoluble residue (60-75 wt%), while pyrolysis of 2 or the methyl ester of 1 produced only a THF soluble product. The mechanistic pathways leading to cross-linking will be discussed

Contrasting retrogressive rearrangement pathways during thermolysis of silica-immobilized benzyl phenyl ether

Many coal model compound studies have focused on the mechanisms of bond cleavage reactions, and the means to alter reaction conditions to promote such reactions. However, there has become increasing interest in elucidating mechanisms associated with retrogressive or retrograde reactions in coal processing, which involve the formation of refractory bonds. Retrograde reactions inhibit efficient thermochemical processing of coals into liquid fuels, which has been particularly well-documented for low rank coals where abundant oxygen-containing functional groups are thought to play a key role in the chemistry. Much less is known about retrogressive reactions for ether-containing model compounds. Radical recombination through ring coupling of phenoxy radicals in benzyl phenyl ether (BPE) is known to lead to more refractory diphenylmethane linkages to a limited extent. Since this chemistry may be attributed at least in part to cage recombination, it could be promoted in a diffusionally constrained environment such as in the coal macromolecule. Using silica-immobilization to simulate restricted diffusion in coal, the authors have found that retrogressive reactions can be promoted for certain hydrocarbon model compounds. The authors have now begun an examination of the thermolysis behavior of silica-immobilized benzyl phenyl ether at 275--325 C. The initial results indicate that two retrogressive reaction pathways, radical recombination and molecular rearrangement through Si-O-C linkage to the surface of PhOCH{center_dot}Ph, are promoted by restricted diffusion. Remarkably, the retrograde products typically account for 50 mol% of the thermolysis products

Pyrolysis of coal model compounds containing aromatic carboxylic acids: The role of carboxylic acids in cross-linking reactions in low-rank coal

The pyrolysis of 1-(3-carboxyphenyl)-2(4-biphenyl)ethane (1) diluted in 10-fold excess of naphthalene has been studied at 400 {degrees}C to investigate whether decarboxylation of aromatic carboxylic acids can lead to cross-linked products. The dominant mechanism for decarboxylation was found to be an acid-promoted ionic pathway that does not lead to cross-linking. However, a small amount of cross-linked products (i.e. naphthalene grafted onto decarboxylated 1) were formed. The yields of the cross-linked products were found to be decreased in the presence of a hydrogen donor solvent, tetralin, suggesting that these products were formed by a free-radical pathway. The mechanism for the formation of cross-linked products was proposed to occur from the formation and decomposition of anhydrides of 1 during pyrolysis

Flash Vacuum Pyrolysis of Lignin Model Compounds: Reaction Pathways of Aromatic Methoxy Groups

Currently, there is interest in utilizing lignin, a major constituent of biomass, as a renewable source of chemicals and fuels. High yields of liquid products can be obtained from the flash or fast pyrolysis of biomass, but the reaction pathways that lead to product formation are not understood. To provide insight into the primary reaction pathways under process relevant conditions, we are investigating the flash vacuum pyrolysis (FVP) of lignin model compounds at 500 C. This presentation will focus on the FVP of {beta}-ether linkages containing aromatic methoxy groups and the reaction pathways of methoxy-substituted phenoxy radicals

Inventing and implementing future-ready archival education

The Archival / Preservation Education SIG panel engages with community-responsive master's-level archival education. Seven ten-minute individual presentations and audience discussion traverse the decision points in managing curricular change; presenters bring perspectives from multiple states. "Audio Preservation as Metacognitive Archival Education" by Sarah Buchanan discusses how audiovisual archiving experiences support the continual development of students' metacognitive skills during their graduate program. Based on community collaboration, the activity progressions provide students with digital experiences, faculty with curricular guidance, and online audiences with more representative primary sources. "LIS Students Contributing to Building a Sustainable Digital Community Archive" by Krystyna Matusiak describes a community-based two-year project aimed at preserving and promoting the Park County Local History Archive in rural Colorado, now available at https://pclha.cvlcollections.org/. The presentation illustrates students' many contributions: organizing materials and assessing their copyright status, digitizing photographs, converting oral histories, creating metadata records, building exhibits, and showcasing community resilience. "Changing Horses Midstream: Revising Curriculum and Student Engagement to Ensure a Resilient Future" by Edward Benoit, III and Amanda Lima discusses the revision process for transitioning two programs to LSU Online, compares assessments from the traditional and LSU Online programs, and reflects on completing the first year. Additionally, the presenters will highlight the use of student-run Slack channels and virtual coffee hours as online student community building tools for the new LSU Online students, and discuss the school's future in the platform. "Producing Practical Professionals with Curriculum for Equity, Diversity, and Inclusion" by Aisha Johnson acknowledges that cultural heritage programs should address the need for cultural preservation and reflection, for archivists of Black, Indigenous, and Persons of Color (BIPOC) heritage. The presentation will review a reestablished Archives and Records Management concentration, with core archival and complementary knowledge curriculum, as a case study for exploring new approaches to pedagogy on the purpose, value, and importance of archives in society. "Learning from Experience: Lessons from a Virtual Service-Learning Experiment" by Colin Post discusses a service-learning project documenting an artist's performance as well as their artwork archives. While such projects place even greater pressure on the instructor as a project manager, they enhance connections between theory and practice in online courses. "Lessons Learned from the Digital Preservation Outreach and Education Network" by Anthony Cocciolo and Erin Barsan discusses the types of needs they have uncovered, the communities served, and the lessons learned over the course of a year running DPOE-N. The Network's response to the COVID-19 pandemic comprises microfunding for professional development and emergency hardware support for cultural heritage professionals. "National Forum Grant Project: Exploring New Frontiers in 21st Century Archival Education" by Alex Poole and Jane Zhang discusses the environmental scan, National Forum event, and final outputs of their year-long project. The presentation addresses motivation and need, historical and current context, research components, and intended results and impact. The moderator will facilitate Q&A within and across the presentations