Hydrothermal Decarboxylation and Hydrogenation of Fatty Acids over Pt/C

We report herein on the conversion of saturated and unsaturated fatty acids to alkanes over Pt/C in high-temperature water. The reactions were done with no added H 2 . The saturated fatty acids (stearic, palmitic, and lauric acid) gave the corresponding decarboxylation products ( n -alkanes) with greater than 90 % selectivity, and the formation rates were independent of the fatty acid carbon number. The unsaturated fatty acids (oleic and linoleic acid) exhibited low selectivities to the decarboxylation product. Rather, the main pathway was hydrogenation to from stearic acid, the corresponding saturated fatty acid. This compound then underwent decarboxylation to form heptadecane. On the basis of these results, it appears that this reaction system promotes in situ H 2 formation. This hydrothermal decarboxylation route represents a new path for using renewable resources to make molecules with value as liquid transportation fuels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83752/1/481_ftp.pd

A potassium tert-butoxide and hydrosilane system for ultra-deep desulfurization of fuels

Hydrodesulfurization (HDS) is the process by which sulfur-containing impurities are removed from petroleum streams, typically using a heterogeneous, sulfided transition metal catalyst under high H_2 pressures and temperatures. Although generally effective, a major obstacle that remains is the desulfurization of highly refractory sulfur-containing heterocycles, such as 4,6-dimethyldibenzothiophene (4,6-Me_2DBT), which are naturally occurring in fossil fuels. Homogeneous HDS strategies using well-defined molecular catalysts have been designed to target these recalcitrant S-heterocycles; however, the formation of stable transition metal sulfide complexes following C–S bond activation has largely prevented catalytic turnover. Here we show that a robust potassium (K) alkoxide (O)/hydrosilane (Si)-based (‘KOSi’) system efficiently desulfurizes refractory sulfur heterocycles. Subjecting sulfur-rich diesel (that is, [S] ∼ 10,000 ppm) to KOSi conditions results in a fuel with [S] ∼ 2 ppm, surpassing ambitious future governmental regulatory goals set for fuel sulfur content in all countries. Fossil fuels contain naturally occurring organosulfur impurities, with quantities varying depending on the type of feedstock. These sulfur-containing organic small molecules poison catalytic converters and generate polluting sulfur dioxides when combusted. Hydrodesulfurization (HDS) is the industrial process by which sulfur impurities are removed from petroleum fractions prior to their use as fuels. Currently, HDS is performed by treating petroleum with H_2 at high pressures and temperatures (that is, 150–2,250 psi and 400 °C) over heterogeneous catalysts such as cobalt-doped molybdenum sulfide supported on alumina (that is, CoMoS_x∕γ-Al_2O_3; Fig. 1a). However, certain organosulfur species, in particular dibenzothiophenes alkylated at positions 4 and 6, are not efficiently removed. Homogeneous strategies employing sophisticated, well-defined transition metal complexes—including those based on platinum, nickel, tungsten, molybdenum, palladium, ruthenium, rhodium, iron, cobalt, and others—have been extensively investigated. While these studies have provided valuable mechanistic insights, several fundamental issues, such as the formation of stable organometallic S–M species upon C–S bond activation by the metal centre (Fig. 1b), generally restrict industrial implementation of such methods. Rare examples of desulfurization of dibenzothiophenes alkylated at the 4 and 6 positions by homogeneous transition metal catalysis utilized either Ni compounds in combination with superstoichiometric alkyl Grignard reagents or Ni or Co phosphoranimide complexes in the presence of superstoichiometric KH. These issues pose a formidable challenge for the development of new HDS methods. Moreover, increasingly strict governmental regulations require limiting the sulfur content in diesel fuel and gasoline (in the US: typically <15 and <30 ppm, respectively) as well as other fuels, rendering the development of new powerful HDS methods a primary global concern. In 2013, Grubbs and co-workers reported the KO^tBu mediated cleavage of aryl C–O bonds in lignin models in the absence of transition metals using hydrosilanes. Careful inductively coupled plasma mass spectrometry (ICP-MS) analyses of the reagents and reaction mixtures ruled out catalysis with transition metals. We thus became interested in extending this method to sulfur heterocycles of relevance in oil and gas refining applications. Herein, we report that the robust KOtBu/silane-based (that is, KOSi) system is a powerful and effective homogeneous HDS method, which desulfurizes HDS-resistant dibenzothiophenes in good yield and reduces the sulfur content in diesel fuel to remarkably low levels (Fig. 1c)

Towards the conversion of carbohydrate biomass feedstocks to biofuels via hydroxylmethylfurfural

This review appraises the chemical conversion processes recently reported for the production of hydroxylmethylfurfural (HMF), a key biorefining intermediate, from carbohydrate biomass feedstocks. Catalytic sites or groups required for the efficient and selective conversion of hexose substrates to HMF are examined. The principle of concerted catalysis was used to rationalise the dehydration of fructose and glucose to HMF in non-aqueous media. A survey of reported reaction routes to diesel-range biofuel intermediates from HMF or furfural is presented and self-condensation reaction routes for linking two or more HMF and furfural units together toward obtaining kerosene and diesel-range biofuel intermediates are highlighted. The reaction routes include: benzoin condensation, condensation of furfuryl alcohols, hetero Diels–Alder reaction and ketonisation reaction. These reaction routes are yet to be exploited despite their potential for obtaining kerosene and diesel-range biofuel intermediates exclusively from furfural or hydroxylmethylfurfural

A potassium tert-butoxide and hydrosilane system for ultra-deep desulfurization of fuels

Hydrodesulfurization (HDS) is the process by which sulfur-containing impurities are removed from petroleum streams, typically using a heterogeneous, sulfided transition metal catalyst under high H_2 pressures and temperatures. Although generally effective, a major obstacle that remains is the desulfurization of highly refractory sulfur-containing heterocycles, such as 4,6-dimethyldibenzothiophene (4,6-Me_2DBT), which are naturally occurring in fossil fuels. Homogeneous HDS strategies using well-defined molecular catalysts have been designed to target these recalcitrant S-heterocycles; however, the formation of stable transition metal sulfide complexes following C–S bond activation has largely prevented catalytic turnover. Here we show that a robust potassium (K) alkoxide (O)/hydrosilane (Si)-based (‘KOSi’) system efficiently desulfurizes refractory sulfur heterocycles. Subjecting sulfur-rich diesel (that is, [S] ∼ 10,000 ppm) to KOSi conditions results in a fuel with [S] ∼ 2 ppm, surpassing ambitious future governmental regulatory goals set for fuel sulfur content in all countries. Fossil fuels contain naturally occurring organosulfur impurities, with quantities varying depending on the type of feedstock. These sulfur-containing organic small molecules poison catalytic converters and generate polluting sulfur dioxides when combusted. Hydrodesulfurization (HDS) is the industrial process by which sulfur impurities are removed from petroleum fractions prior to their use as fuels. Currently, HDS is performed by treating petroleum with H_2 at high pressures and temperatures (that is, 150–2,250 psi and 400 °C) over heterogeneous catalysts such as cobalt-doped molybdenum sulfide supported on alumina (that is, CoMoS_x∕γ-Al_2O_3; Fig. 1a). However, certain organosulfur species, in particular dibenzothiophenes alkylated at positions 4 and 6, are not efficiently removed. Homogeneous strategies employing sophisticated, well-defined transition metal complexes—including those based on platinum, nickel, tungsten, molybdenum, palladium, ruthenium, rhodium, iron, cobalt, and others—have been extensively investigated. While these studies have provided valuable mechanistic insights, several fundamental issues, such as the formation of stable organometallic S–M species upon C–S bond activation by the metal centre (Fig. 1b), generally restrict industrial implementation of such methods. Rare examples of desulfurization of dibenzothiophenes alkylated at the 4 and 6 positions by homogeneous transition metal catalysis utilized either Ni compounds in combination with superstoichiometric alkyl Grignard reagents or Ni or Co phosphoranimide complexes in the presence of superstoichiometric KH. These issues pose a formidable challenge for the development of new HDS methods. Moreover, increasingly strict governmental regulations require limiting the sulfur content in diesel fuel and gasoline (in the US: typically <15 and <30 ppm, respectively) as well as other fuels, rendering the development of new powerful HDS methods a primary global concern. In 2013, Grubbs and co-workers reported the KO^tBu mediated cleavage of aryl C–O bonds in lignin models in the absence of transition metals using hydrosilanes. Careful inductively coupled plasma mass spectrometry (ICP-MS) analyses of the reagents and reaction mixtures ruled out catalysis with transition metals. We thus became interested in extending this method to sulfur heterocycles of relevance in oil and gas refining applications. Herein, we report that the robust KOtBu/silane-based (that is, KOSi) system is a powerful and effective homogeneous HDS method, which desulfurizes HDS-resistant dibenzothiophenes in good yield and reduces the sulfur content in diesel fuel to remarkably low levels (Fig. 1c)

Conversion of biomass platform molecules into fuel additives and liquid hydrocarbon fuels

[EN] In this work some relevant processes for the preparation of liquid hydrocarbon fuels and fuel additives from cellulose, hemicellulose and triglycerides derived platform molecules are discussed. Thus, it is shown that a series of platform molecules such as levulinic acid, furans, fatty acids and polyols can be converted into a variety of fuel additives through catalytic transformations that include reduction, esterification, etherification, and acetalization reactions. Moreover, we will show that liquid hydrocarbon fuels can be obtained by combining oxygen removal processes (e.g. dehydration, hydrogenolysis, hydrogenation, decarbonylation/descarboxylation etc.) with the adjustment of the molecular weight via C C coupling reactions (e.g. aldol condensation, hydroxyalkylation, oligomerization, ketonization) of the reactive platform molecules.This work has been supported by the Spanish Government-MINECO through Consolider Ingenio 2010-Multicat and CTQ.-2011-27550, ITQ thanks the "Program Severo Ochoa" for financial support.Climent Olmedo, MJ.; Corma Canós, A.; Iborra Chornet, S. (2014). Conversion of biomass platform molecules into fuel additives and liquid hydrocarbon fuels. Green Chemistry. 16(2):516-547. https://doi.org/10.1039/c3gc41492bS51654716

Reaction Mechanisms for Renewable Hydrogen from Liquid Phase Reforming of Sugar Compunds

Hydrogen is anticipated to become a major source of energy in the future. Hydrogen is a clean burning fuel and has been described as a long-term replacement for natural gas. It has been demonstrated here that hydrogen can be produced from biomass in the temperature range of 185-220°C using a single batch reactor pressurised at 25-30 bar. The current work is based on sugars which are considered here as the biomass resource. Glucose, fructose and sucrose solutions were used for the liquid phase reforming using supported platinum catalyst. The sugar molecules might go through reversible dehydrogenation steps to give adsorbed species on metal sites. This adsorption might be either on C-C or C-O bond cleavage. Platinum is one of the best catalysts for the reforming of hydrocarbons due to its high selectivity for C-C bond cleavage. The C-C bond cleavage is the limiting factor for the reforming and leads to a high rate of formation of hydrogen. On the other hand C-O bond cleavage results information of alcohols, acids and other organic groups