Influence of alkali carbonates on benzyl phenyl ether cleavage pathways in superheated water

Roberts, Virginia; Fendt, S.; Lemonidou, Angeliki A.; Li, Xuebing; Lercher, Johannes A.

doi:10.1016/j.apcatb.2009.12.010

Cited by 80 publications

(97 citation statements)

References 8 publications

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“…[25] Beyond 320 8C yields dropped markedly and higher molecular compounds were formed due to polymerization reactions of the monomers. In the case of benzyl phenyl ether, oligomerization was likewise initiated by a carbanion formed from the main hydrolysis product phenolate.…”

Section: Mechanism Of Monomer Oligomerizationmentioning

confidence: 98%

“…It belongs to the group of the aryl-alkyl ether bonds, which can be cleaved in subcritical water without adding a catalyst. [25] In contrast, aryl-aryl ether bonds are very stable, [26] and likewise carbon-carbon bonds between aromatic lignin units need more severe conditions to be broken. Our preliminary results using model compounds showed that C À C bonds (aryl-aryl bonds and methylene bridging bonds) can only be cleaved below 400 8C when applying an appropriate base catalyst.…”

mentioning

confidence: 96%

“…The aryl-alkyl ether bond, however, is readily cleaved above 270 8C. [25] Thus, it is concluded that among the bonds connecting the aromatic units predominantly aryl-alkyl ether bonds, specifically the b-O-4 ether bond will be cleaved under the conditions applied.…”

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confidence: 98%

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Towards Quantitative Catalytic Lignin Depolymerization

Roberts

Stein

Reiner

et al. 2011

Chemistry A European J

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The products of base-catalyzed liquid-phase hydrolysis of lignin depend markedly on the operating conditions. By varying temperature, pressure, catalyst concentration, and residence time, the yield of monomers and oligomers from depolymerized lignin can be adjusted. It is shown that monomers of phenolic derivatives are the only primary products of base-catalyzed hydrolysis and that oligomers form as secondary products. Oligomerization and polymerization of these highly reactive products, however, limit the amount of obtainable product oil containing low-molecular-weight phenolic products. Therefore, inhibition of concurrent oligomerization and polymerization reactions during hydrothermal lignin depolymerization is important to enhance product yields. Applying boric acid as a capping agent to suppress addition and condensation reactions of initially formed products is presented as a successful approach in this direction. Combination of base-catalyzed lignin hydrolysis with addition of boric acid protecting agent shifts the product distribution to lower molecular weight compounds and increases product yields beyond 85%.

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Section: Mechanism Of Monomer Oligomerizationmentioning

confidence: 98%

mentioning

confidence: 96%

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Towards Quantitative Catalytic Lignin Depolymerization

Roberts

Stein

Reiner

et al. 2011

Chemistry A European J

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500

372

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“…Hydrothermal conversion of the a-O-4 dimer in superheated water also followed ionic and radical pathways, yielding a broad product distribution with phenols and many secondary recombination products. [11] Recently, it was reported that the combination of [Ni(cod) 2 ] (COD = cyclooctadiene), 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride (SIPr·HCl), and sodium tert-butoxide (NaOtBu) could selectively hydrogenolyze the CÀO bonds in aryl ethers to substituted phenols and arenes in m-xylene as solvent in the presence of hydrogen. [12] The proposed mechanism includes that the nickel component cleaving the CÀO bond could be nickel hydride, a neutral nickel(0) complex, or an anionic nickel species.…”

Section: Wwwchemcatchemorgmentioning

confidence: 99%

Selective Hydrodeoxygenation of Lignin‐Derived Phenolic Monomers and Dimers to Cycloalkanes on Pd/C and HZSM‐5 Catalysts

2011

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Lignin is an abundant renewable resource with a high energy density, but it is considered to be difficult to process because of the high reactivity of its building blocks, that is, the substituted phenol units, which tend to react even at small concentrations and reaction temperatures.[1] It has been shown recently that this reactivity can be overcome by combining metallic (Pd) and acidic functions (H 3 PO 4 , CH 3 COOH, ÀSO 3 H, and ÀOH) in the appropriate concentrations in an aqueous phase or ionic liquids. [2] This has led to the successful hydrodeoxygenation of phenol derivatives and the synthesis of a pure cycloalkane product. Because of the different polarity of the substituted phenols and the alkanes, a second hydrocarbon phase is formed during the process, which can be easily separated. Noble and base metals have been found to be active for hydrogenation in the aqueous phase. Replacing liquid mineral acids by a solid acid (Nafion/SiO 2 ) allowed for an increase in efficiency. [3] In addition to the hydrodeoxygenation of phenolic monomers, the selective cleavage of the aromatic carbon-oxygen (CÀO) bonds in aryl ethers is also challenging because of the strength and stability of these linkages.[4] This cleavage is very important for facilitating the depolymerization of oxygenrich lignin by breaking down the CÀOÀC linkages, and for the hydrodeoxygenation of lignin-derived phenolic dimer fragments to the deoxygenated biofuels. Here, we report on the use of a weaker solid acid, that is, a zeolite (HZSM-5), as a selective catalyst component for the quantitative hydrodeoxygenation of diversely substituted lignin-derived mono-and binuclear phenols to cycloalkanes in combination with a noble metal (Pd) in aqueous solutions at a mild temperature (473 K).We have shown previously that phenol is converted to cyclohexane in water through the sequential hydrogenation of phenol to cyclohexanone and cyclohexanol on metal sites (Pd or Ni), dehydration of cyclohexanol on acid sites (H 3 PO 4 , CH 3 COOH, or Nafion/SiO 2 ), and finally the hydrogenation of cyclohexene to cyclohexane on metal sites. [1][2][3] To maximize the hydrodeoxygenation rate and selectivity under milder conditions (low reaction temperatures and pressures) in addition to the catalyst stability, various solid acids (acid-site densities and specific surface areas are listed in Table S1 in the Supporting Information) are explored in the presence of palladium Pd/C as hydrogenation catalyst. The characterization of the catalyst was achieved by determining the Brunauer-Emmett-Teller (BET) surface area and by using XRD, SEM, and TEM and is compiled in the Supporting Information. As a suitable solid acid should have a high acid-site density in combination with a sufficient stability in an aqueous phase above 473 K, the results (see Table S3 in the Supporting Information) for the conversion of 4-n-propylphenol show that solid Lewis acids, such as alumina, silica, and amorphous silica alumina, are not effective for oxygen removal (through dehydration of cycloalc...

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“…Aryl-alkyl (b-O-4) ether bonds in lignin are easier to cleave than C-C bonds in basecatalyzed lignin depolymerisation [54], although mineral bases typically require harsh reaction temperatures of around 340°C [55][56][57], which can generate significant gaseous products via side reactions and consequent lower monomeric hydrocarbon yields [58]. In base-catalyzed depolymerization, the choice of lignin influences the yield of bio-oil, but not the resulting composition [59]; however, the use of mineral bases may necessitate neutralisation of the subsequent bio-oil, in addition to reactor corrosion.…”

Section: Base-catalyzed Depolymerizationmentioning

confidence: 99%

Heterogeneously catalyzed lignin depolymerization

Pineda

Lee

2016

Appl Petrochem Res

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Biomass offers a unique resource for the sustainable production of bio-derived chemical and fuels as drop-in replacements for the current fossil fuel products. Lignin represents a major component of lignocellulosic biomass, but is particularly recalcitrant for valorization by existing chemical technologies due to its complex crosslinking polymeric network. Here, we highlight a range of catalytic approaches to lignin depolymerisation for the production of aromatic bio-oil and monomeric oxygenates.

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Influence of alkali carbonates on benzyl phenyl ether cleavage pathways in superheated water

Cited by 80 publications

References 8 publications

Towards Quantitative Catalytic Lignin Depolymerization

Towards Quantitative Catalytic Lignin Depolymerization

Selective Hydrodeoxygenation of Lignin‐Derived Phenolic Monomers and Dimers to Cycloalkanes on Pd/C and HZSM‐5 Catalysts

Heterogeneously catalyzed lignin depolymerization

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