Hydrogenation

Pines, Herman; Stalick, Wayne M.

doi:10.1016/b978-0-12-557150-0.50016-2

Cited by 10 publications

(13 citation statements)

References 38 publications

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“…All of the aforementioned processes were developed for application of alkali metal conversion above 250 °C but mainly at temperatures in excess of 340 °C. This was in stark contrast to most of the fundamental studies in base catalysis of alkali metals, which were conducted at much milder conditions. − …”

Section: Introductionmentioning

confidence: 90%

Sodium Conversion of Oilsands Bitumen-Derived Asphaltenes

Styles

Klerk

2016

Energy Fuels

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Alkali metals are strong electron donors and can form electron donor−acceptor ion pairs with multinuclear aromatics. Single electron donation converts the aromatic into a radial ion, and two electron donations convert the aromatic into a dianion. The anionic aromatic species are more susceptible to reductive addition reactions, such as hydrogen transfer from more hydrogen-rich molecules, such as employed in Birch reduction. The conversion of heavy oils in the presence of alkali metals is claimed to be capable of bulk desulfurization with little hydrogen consumption. In this work, the conversion of oilsands bitumen asphaltenes with sodium was investigated over the temperature range of 60−250 °C under an inert atmosphere to limit the contribution of thermal conversion. Control experiments conducted with asphaltenes without sodium revealed that the asphaltenes were reactive on their own, and the nature of products was affected by the phase behavior of the asphaltenes that gradually changed from a solid to liquid between 124 and 142 °C. When fluidity was limited, intermolecular hydrogen transfer was restricted; intramolecular hydrogen disproportionation and "in cage" intermolecular reactions resulted in the formation of more condensed and potentially more aromatic products. Sodium markedly affected the natural hydrogen transfer and disproportionation. Conversion of the asphaltenes with sodium did not result in an increased maltene yield, but the maltenes had a higher hydrogen/carbon ratio, less sulfur, and less nitrogen. Model compound reactions were employed to study the influence of the reaction atmosphere (N 2 or H 2 ) and hydrogen donor properties of the organic matrix. In the presence of H 2 , the formation and reaction of NaH appeared to influence selectivity and the reaction network. In the absence of H 2 , desulfurization of thiophenic compounds by sodium proceeded by hydrogenolysis and hydrogenation pathways, with the hydrogenolysis pathway being favored by the lack of hydrogen donor molecules. It was also found that hydrogenolysis of the carbon−carbon bond in the thiophenic ring of dibenzothiophene is reversible.

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Section: Introductionmentioning

confidence: 90%

Sodium Conversion of Oilsands Bitumen-Derived Asphaltenes

Styles

Klerk

2016

Energy Fuels

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“…Alkali metals supported on oxides have been used as base catalysts ,, for many classes of reactions because they are good electron donors (Lewis bases). The ionization energies calculated here show that the solvated electrons produced when an alkali is dissolved in a molten salt are likely to catalyze the same reactions as supported alkali metals.…”

Section: Resultsmentioning

confidence: 99%

“…A variety of systems that catalyze many types of reactions are classified as base catalysts. − These catalysts share two characteristics: they are Lewis bases and they catalyze reactions that proceed through a negative ion intermediate. A few examples of such catalysts are irreducible oxides pretreated at high temperature, supported alkali metals, zeolites doped with alkali metals, − alkali hydroxides, amines tethered to solid surfaces, hydrotalcite, supported metal clusters with alkali metal promoters, − and others. − Examples of the type of reactions affected by the base catalysts are alkene and alkyne isomerization, alkylation reactions, Tishchenko reactions, Michael addition, Knovenagel condensations, epoxide reactions with CO 2 to make organic carbonates, and others. − It is believed that most (or perhaps all) base catalysts act by donating an electron to the substrate to create a negative ion intermediate which then reacts to generate products. The electron donated to the substrate is returned to the catalyst when the products are desorbed.…”

Section: Introductionmentioning

confidence: 99%

Chemistry of Solvated Electrons in Molten Alkali Chloride Salts

Kristoffersen

Metiu

2018

J. Phys. Chem. C

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We use ab initio molecular dynamics to study the electronic structure and the chemistry of the solvated electrons created when alkali atoms are dissolved in alkali chloride molten salt. We find that solvated electrons pair up to form a two-electron species. This species is a very strong reductant which reduces Ag+ to Ag– or Ag(s), dissociates H2 to form 2H–, dissociates CH4 to form CH3 – and H–, and converts N2 to N2 2–. We also study how these properties depend on the composition of the alkali chloride salt.

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“…8−10 Currently, trans -anethole is obtained by estragole isomerization (Scheme 1), promoted by an excess of NaOH or KOH. 11,12 However, there are a number of disadvantages for this process, including the requirement of high temperatures (>200 °C), low conversion in anethole (∼60%), a lack of stereoselectivity (trans/cis ratio 82:18), and the significant amounts of basic wastes that are generated.…”

Section: Introductionmentioning

confidence: 99%

“…Extraction of trans -anethole from natural sources cannot supply the growing market (food, drugs, and cosmetics), − generating the need for a synthetic alternative. For industrial purposes, only trans -anethole is of use, as the cis isomer has a higher toxicity and unpleasant organoleptic properties. − Currently, trans -anethole is obtained by estragole isomerization (Scheme ), promoted by an excess of NaOH or KOH. , However, there are a number of disadvantages for this process, including the requirement of high temperatures (>200 °C), low conversion in anethole (∼60%), a lack of stereoselectivity (trans/cis ratio 82:18), and the significant amounts of basic wastes that are generated.…”

Section: Introductionmentioning

confidence: 99%

Ru-Catalyzed Estragole Isomerization under Homogeneous and Ionic Liquid Biphasic Conditions

et al. 2017

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The isomerization of estragole to trans-anethole is an important reaction and is industrially performed using an excess of NaOH or KOH in ethanol at high temperatures with very low selectivity. Simple Ru-based transition-metal complexes, under homogeneous, ionic liquid (IL)-supported (biphasic) and “solventless” conditions, can be used for this reaction. The selectivity of this reaction is more sensitive to the solvent/support used than the ligands associated with the metal catalyst. Thus, under the optimized reaction conditions, 100% conversion can be achieved in the estragole isomerization, using as little as 4 × 10–3 mol % (40 ppm) of [RuHCl(CO)(PPh3)3] in toluene, reflecting a total turnover number (TON) of 25 000 and turnover frequencies (TOFs) of up to 500 min–1 at 80 °C. Using a dimeric Ru precursor, [RuCl(μ-Cl)(η3:η3-C10H16)]2, in ethanol associated with P(OEt)3, a TON of 10 000 and a TOF of 125 min–1 are obtained with 100% conversion and 99% selectivity. These two Ru catalytic systems can be transposed to biphasic IL systems by using ionic-tagged P-ligands such as 1-(3-(diphenylphosphanyl)propyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide immobilized in 1-(3-hydroxypropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl) imide with up to 99% selectivity and almost complete estragole conversion. However, the reaction is much slower than that performed under solventless or homogeneous conditions. The use of ionic-tagged ligands significantly reduces the Ru leaching to the organic phase, compared to that in reactions performed under homogeneous conditions, where the catalytic system loses catalytic performance after the second recycling. Detailed kinetic investigations of the reaction catalyzed by [RuHCl(CO)(PPh3)3] indicate that a simplified kinetic model (a monomolecular reversible first-order reaction) is adequate for fitting the homogeneous reaction at 80 °C and under biphasic conditions. However, the kinetics of the reaction are better described if all of the elementary steps are taken into consideration, especially at 40 °C.

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Hydrogenation

Cited by 10 publications

References 38 publications

Sodium Conversion of Oilsands Bitumen-Derived Asphaltenes

Sodium Conversion of Oilsands Bitumen-Derived Asphaltenes

Chemistry of Solvated Electrons in Molten Alkali Chloride Salts

Ru-Catalyzed Estragole Isomerization under Homogeneous and Ionic Liquid Biphasic Conditions

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