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The Consequences of Surface Confinement on Free Radical Chemistry

Description: 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-C<sub>aryl</sub>, 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 <i>ipso-</i> 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.
Date: August 22, 1999
Creator: Birtt, P.F. & Buchanan, A.C., III
Partner: UNT Libraries Government Documents Department

Impact of organic-mineral matter interactions on thermal reaction pathways for coal model compounds

Description: Coal is a complex, heterogeneous solid that includes interdispersed mineral matter. However, knowledge of organic-mineral matter interactions is embryonic, and the impact of these interactions on coal pyrolysis and liquefaction is incomplete. Clay minerals, for example, are known to be effective catalysts for organic reactions. Furthermore, clays such as montmorillonite have been proposed to be key catalysts in the thermal alteration of lignin into vitrinite during the coalification process. Recent studies by Hatcher and coworkers on the evolution of coalified woods using microscopy and NMR have led them to propose selective, acid-catalyzed, solid state reaction chemistry to account for retained structural integrity in the wood. However, the chemical feasibility of such reactions in relevant solids is difficult to demonstrate. The authors have begun a model compound study to gain a better molecular level understanding of the effects in the solid state of organic-mineral matter interactions relevant to both coal formation and processing. To satisfy the need for model compounds that remain nonvolatile solids at temperatures ranging to 450 C, model compounds are employed that are chemically bound to the surface of a fumed silica (Si-O-C{sub aryl}linkage). The organic structures currently under investigation are phenethyl phenyl ether (C{sub 6}H{sub 5}CH{sub 2}CH{sub 2}OC{sub 6}H{sub 5}) derivatives, which serve as models for {beta}-alkyl aryl ether units that are present in lignin and lignitic coals. The solid-state chemistry of these materials at 200--450 C in the presence of interdispersed acid catalysts such as small particle size silica-aluminas and montmorillonite clay will be reported. Initial focus will be on defining the potential impact of these interactions on coal pyrolysis and liquefaction.
Date: July 1, 1995
Creator: Buchanan, A.C. III; Britt, P.F. & Struss, J.A.
Partner: UNT Libraries Government Documents Department

Pyrolysis of simple coal model compounds containing aromatic carboxylic acids: Does decarboxylation lead to cross-linking?

Description: The thermolysis of two aromatic carboxylic acids 1,2-(3,3`-dicarboxyphenyl)ethane (2) have been investigated at 400{degree} C as models of carboxylic acids in low rank coals. The major decomposition pathway observed is decarboxylation, which mainly occurs by an ionic pathway. This decarboxylation route does not lead to any significant amount of coupling or high molecular weight products that would be indicative of cross-linking products in coal. The pyrolysis of 1 and 2 will be investigated under a variety of conditions that better mimic the enviromment found in coal to further delineate the role that decarboxylation plays in coal cross-linking chemistry.
Date: February 1, 1996
Creator: Eskay, T.P.; Britt, P.F. & Buchanan, A.C. III
Partner: UNT Libraries Government Documents Department

Thermal reaction studies of organic model compound-mineral matter interactions in solids

Description: The solid-state chemistry of silica-immobilized phenethyl phenyl ethers is being investigated in the presence of interdispersed aluininosilicates at temperatures relevant to coal processing to gain a better understanding of the impact of mineral matter on pyrolysis and liquefaction mechanisms. Results demonstrate the dramatic effect that aluminosilicates can have in altering the normal thermal reaction pathways for these models of ether linkages in lignin and low rank coals. An investigation of the chemistry of these model compounds at low temperatures (ca. 150-200{degrees}C) in the presence of aluminosilicates, including montmorillonite, is currently being investigated to delineate the chemical transformations that can occur during lignin maturation.
Date: July 1, 1995
Creator: Buchanan, A.C. III; Britt, P.F. & Thomas, K.B.
Partner: UNT Libraries Government Documents Department

Mechanistic Investigation into the Decarboxylation of Aromatic Carboxylic Acids

Description: It has been proposed that carboxylic acids and carboxylates are major contributors to cross-linking reactions in low-rank coals and inhibit its thermochemical processing. Therefore, the thermolysis of aromatic carboxylic acids was investigated to determine the mechanisms of decarboxylation at temperatures relevant to coal processing, and to determine if decarboxylation leads to cross-linking (i.e., formation of more refractory products). From the thcrmolysis of simple and polymeric coal model compounds containing aromatic carboxylic acids at 250-425 �C, decarboxylation was found to occur primarily by an acid promoted ionic pathway. Carboxylate salts were found to enhance the decarboxylation rate, which is consistent with the proposed cationic mechanism. Thermolysis of the acid in an aromatic solvent, such as naphthalene, produced a small amount of arylated products (~5 mol%)), which constitute a low-temperature cross-link. These arylated products were formed by the rapid decomposition of aromatic anhydrides, which are in equilibrium with the acid. These anhydrides decompose by a free radical induced decomposition pathway to form atyl radicals that can add to aromatic rings to form cross-links or abstract hydrogen. Large amounts of CO were formed in the thennolysis of the anhydrides which is consistent with the induced decomposition pathway. CO was also formed in the thermolysis of the carboxylic acids in aromatic solvents which is consistent with the formation and decomposition of the anhydride. The formation of anhydride linkages and cross-links was found to be very sensitive to the reactions conditions. Hydrogen donor solvents, such as tetralin, and water were found to decrease the formation of arylated products. Silar reaction pathways were also found in the thermolysis of a polymeric model that contained aromatic carboxylic acids. In this case, anhydride formation and decomposition produced an insoluble polymer, while the O-methylated polymer and the non-carboxylated polymer produced a soluble thermolysis product.
Date: August 22, 1999
Creator: Britt, P.F.; Buchanan, A.C., III; Eskay, T.P. & Mungall, W.S.
Partner: UNT Libraries Government Documents Department

Flash vacuum pyrolysis of lignin model compounds

Description: 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.
Date: March 1, 1997
Creator: Cooney, M.J.; Britt, P.F. & Buchanan, A.C. III
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: March 1997
Creator: Mungall, W. S.; Britt, P. F. & Buchanan, A. C., III
Partner: UNT Libraries Government Documents Department

Retrograde reactions in coal processing: The behavior of ether and sulfide model compounds

Description: Retrograde reactions that produce more refractory molecular structures are undesirable in coal liquefaction. The authors previously found that restricted mass transport, induced by immobilization on a silica support, promotes retrograde reactions for 1,2-diphenylethane (C{sub 6}H{sub 5}CH{sub 2}CH{sub 2}C{sub 6}H{sub 5}) by both skeletal rearrangement and ring growth (cyclization-dehydrogenation) pathways involving free-radical intermediates. They are now examining the influence of heteroatoms on the retrograde pathways for the corresponding surface-immobilized ether (C{sub 6}H{sub 5}OCH{sub 2}C{sub 6}H{sub 5}) and sulfide (C{sub 6}H{sub 5}SCH{sub 2}C{sub 6}H{sub 5}) model compounds at 275--350 C. Cyclization-dehydrogenation pathways are not detected for either model compound. However, retrograde skeletal rearrangements involving 1,2-phenyl shifts in C{sub 6}H{sub 5}XCH{center_dot}C{sub 6}H{sub 5} (X = O,S) are found to be significant under restricted diffusion, and for X = O, radical coupling at ring carbons to form benzylphenols is also observed as a major pathway. For surface-immobilized benzyl phenyl ether, the two retrograde processes account for ca. 50% of the thermolysis products, and also generate reactive hydroxyl and keto functionalities that can be involved in additional retrograde reactions.
Date: April 1, 1997
Creator: Buchanan, A. C., III; Britt, P. F. & Skeen, J. T.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: March 1, 1997
Creator: Eskay, T.P.; Britt, P.F. & Buchanan, A.C. III
Partner: UNT Libraries Government Documents Department

Machine tool evaluation (development of environmentally conscious machining fluids and systems). CRADA final report

Description: The overall purpose of this CRADA is to select or develop as required a group of cutting fluids, for use with metals and/or ceramic materials, which are more environmentally benign and which will reduce or eliminate the environmental problems associated with management and disposal of these cutting fluids. This CRADA was initially funded by DOE/DP, and was expanded to include DOE/ER funding with an added focus on environmental issues related to synthetic cutting fluids. The specific objective of this DOE-ER funded project (one of ten technical tasks within the CRADA) is to determine and demonstrate chemical methods of degrading and/or improving the disposability of synthetic cutting fluids. Photochemical advanced oxidation processes were developed and demonstrated to successfully remove all carbon from new and used cutting fluids, and from surrogate solutions containing up to 15,000 ppm of total organic carbon in the initial solutions. Chemical and energy costs for the process were evaluated. Commercial providers of advanced oxidation process technologies were consulted concerning scale-up, and associated costs in industrial systems were estimated to be well represented by the laboratory bench-scale measured values. Engineering aspects and alternative oxidation methodologies were explored through consultation with an internationally recognized chemical engineer, and it was concluded that no clear alternatives were available for treating aqueous fluids with extremely high initial carbon content (i.e., 15,000 popm total organic carbon).
Date: August 1, 1998
Creator: Buchanan, A.C. III; Sigman, M.E. & Yang, C.L.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: June 1, 1997
Creator: Eskay, T.P.; Britt, P.F. & Buchanan, A.C. III
Partner: UNT Libraries Government Documents Department

Pyrolysis Mechanisms of Aromatic Carboxylic Acids

Description: Although decarboxylation of carboxylic acids is widely used in organic synthesis, there is limited mechanistic information on the uncatalyzed reaction pathways of aromatic carboxylic acids at 300-400 {degrees} C. The pyrolysis mechanisms of 1,2-(3,3-dicarboxyphenyl)ethane, 1,2-(4,4-dicarboxylphenyl)ethane, 1-(3-carboxyphenyl)-2-(4- biphenyl)ethane, and substituted benzoic acids have been investigated at 325-425 {degrees} C neat and diluted in an inert solvent. Decarboxylation is the dominant pyrolysis path. Arrhenius parameters, substituent effects, and deuterium isotope effects are consistent with decarboxylation by an electrophilic aromatic substitution reaction. Pyrolysis of benzoic acid in naphthalene, as a solvent, produces significant amounts of 1- and 2-phenylnaphthalenes. The mechanistic pathways for decarboxylation and arylation with be presented.
Date: December 31, 1997
Creator: Britt, P.F.; Eskay, T.P. & Buchanan, A.C. III
Partner: UNT Libraries Government Documents Department

Pyrolysis mechanisms of lignin model compounds

Description: The flash vacuum pyrolysis of lignin model compounds was studied under conditions optimized for the production of liquid products to provide mechanistic insight into the reaction pathways that lead to product formation. The major reaction products can be explained by cleavage of the C-O either linkage by a free radial or concerted 1,2-elimination.
Date: June 1, 1997
Creator: Britt, P.F.; Buchanan, A.C. III & Cooney, M.J.
Partner: UNT Libraries Government Documents Department

New approach to immobilization of coal-model compounds on silica using a calcium carboxylate linkage

Description: In an earlier report, the authors described efforts to study the hydrothermolysis of surface-immobilized coal model compounds by attaching 1-(4{prime}-hydroxyphenyl)-2-phenylethane to the surface of fumed silica via a Si-OAr linkage using procedures developed by Buchanan, Poutsma and coworkers and heating the resultant material (SiO-DPE) under D{sub 2} pressure. Despite the successes noted here, they sought to find a method for constructing links between silica and organic materials which might better survive hydroliquefaction conditions. Attachment of long-chain aliphatic carboxylic acids to silica through Mg{sup ++} or Ca{sup ++} ions is a patented method for silica flotation which they thought might be adapted to their purposes. This preprint is a preliminary report on the preparation, thermolysis and hydrothermolysis of materials believed to have the general structure, SiO{sup {minus}}Ca{sup ++}{sup {minus}}O{sub 2}CAr.
Date: December 31, 1995
Creator: Ramakrishnan, S.; Guthrie, R.D.; Britt, P.F.; Buchanan, A.C. III & Davis, B.H.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: March 1, 1997
Creator: Buchanan, A.C. III; Britt, P.F. & Skeen, J.T.
Partner: UNT Libraries Government Documents Department

Fission-Product Separation Based on Room-Temperature Ionic Liquids

Description: The objectives of this project are (a) to synthesize new ionic liquids tailored for the extractive separation of Cs + and Sr 2+; (b) to select optimum macrocyclic extractants through studies of complexation of fission products with macrocyclic extractants and transport in new extraction systems based on ionic liquids; (c) to develop efficient processes to recycle ionic liquids and crown ethers; and (d) to investigate chemical stabilities of ionic liquids under strong acid, strong base, and high-level-radiation conditions.
Date: June 16, 2003
Creator: Luo, Huimin; Rogers, Robin D.; Dai, Sheng, Dai; Bonnesen, Peter V.; Buchanan, A. C. III & Hussey, Charles L.
Partner: UNT Libraries Government Documents Department

Fission-Product Separation Based on Room-Temperature Ionic Liquids (OR08SP24-16)

Description: The objectives of this project are (a) to synthesize new ionic liquids tailored for the extractive separation of Cs + and Sr 2+; (b) to select optimum macrocyclic extractants through studies of complexation of fission products with macrocyclic extractants and transport in new extraction systems based on ionic liquids; (c) to develop efficient processes to recycle ionic liquids and crown ethers; and (d) to investigate chemical stabilities of ionic liquids under strong acid, strong base, and high-level-radiation conditions.
Date: June 15, 2002
Creator: Luo, Huimin; Bonnesen, Peter V.; Rogers, Robin D.; Dai, Sheng; Buchanan, A. C. III & Hussey, Charles L.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: March 21, 1999
Creator: Britt, P. F.; Buchanan, A. C., III & Martineau, D. R.
Partner: UNT Libraries Government Documents Department