Marcel Schlaf

The hydrodeoxygenation of bioderived furans into alkanes

The conversion of biomass into fuels and chemical feedstocks is one part of a drive to reduce the worlds dependence on crude oil. For transportation fuels in particular, wholesale replacement of a fuel is logistically problematic, not least because of the infrastructure that is already in place. Here, we describe the catalytic defunctionalization of a series of biomass-derived molecules to provide linear alkanes suitable for use as transportation fuels. These biomass-derived molecules contain a variety of functional groups, including olefins, furan rings and carbonyl groups. We describe the removal of these in either a stepwise process or a one-pot process using common reagents and catalysts under mild reaction conditions to provide n-alkanes in good yields and with high selectivities. Our general synthetic approach is applicable to a range of precursors with different carbon content (chain length). This allows the selective generation of linear alkanes with carbon chain lengths between eight and sixteen carbons.

Selective deoxygenation of sugar polyols to α,ω-diols and other oxygen content reduced materials—a new challenge to homogeneous ionic hydrogenation and hydrogenolysis catalysis

An oxygen atom on every carbon--this is the problem! While nature provides linear C(3) to C(6) building blocks in the form of sugar alcohols in large and renewable abundance, they are overfunctionalized for the purpose of most chemical applications. Selective deoxygenation by anthropogenic catalyst systems may be one answer to this challenge.

Metal-Catalyzed Selective Deoxygenation of Diols to Alcohols

The internal OH group of 1,2-propanediol is selectively removed in the deoxygenation catalyzed by [{Cp*Ru(CO)2 }2 (μ-H)]+ OTf- (1, Cp*=C3 Me5 , OTf=trifluoromethanesulfonate; see scheme). This reaction provides a model for deoxygenation of polyols derived from carbohydrates, for use in alternative, biomass-based feedstock applications. An ionic mechanism is proposed that involves the dihydrogen complex [Cp*Ru(CO)2 (η2 -H2 )]+ .

Homogeneous catalytic hydrogenation of long-chain esters by an osmium pincer complex and its potential application in the direct conversion of triglycerides into fatty alcohols

The osmium hydride complexes OsH2(CO)[NH(CH2PiPr2)2] (1) and OsHCl(CO)[NH(CH2PiPr2)2] (2) were evaluated in the catalytic hydrogenation of hexyl octanoate and cis-3-hexenyl hexanoate to alcohols as model substrates for triglycerides. Both complexes achieve full conversion of the saturated ester at 220 °C and 800 psi pressure of hydrogen gas. In the presence of unsaturated substrates, the complexes hydrogenate CC bonds, but are subsequently ineffective in the reduction of the ester moiety. However complex 1 is capable of hydrogenating fully saturated triglycerides (i.e., hardened fats as obtained by separate initial hydrogenation of seed oils using either 1 or 2 or a standard heterogeneous hydrogenation catalyst) giving cetyl and stearyl alcohols as the main products.

Cyclopentadienyl and pentamethylcyclopentadienyl ruthenium complexes as catalysts for the total deoxygenation of 1,2-hexanediol and glycerol

The ruthenium aqua complexes [cp*Ru(OH2)(N–N)](OTf) (cp* = η5-pentamethylcyclopentadienyl, N–N = 2,2′-bipyridine, phen = 1,10-phenanthroline, OTf− = trifluoromethanesulfonate) and the acetonitrile complex [cpRu(CH3CN)(bipy)](OTf) (cp = η5-cyclopentadienyl) are water-, acid-, and thermally stable (>200 °C) catalysts for the hydrogenation of aldehydes and ketones in sulfolane solution. In the presence of HOTf as a co-catalyst, they effect the deoxygenation of 1,2-hexanediol to 1-hexanol and hexane. Glycerol is deoxygenated to 1-propanol in up to 18% yield and under more forcing conditions completely deoxygenated to propene. The structure of the acetonitrile pro-catalyst [cpRu(CH3CN)(bipy)](OTf) has been determined by X-ray crystallography (space groupP (a = 9.3778(10) A; b = 10.7852(10) A; c = 11.1818(13) A; α = 101.718(5)°; β = 114.717(4)°; γ = 102.712(5)°; R = 3.95%).

Optimization of the neutralization of Red Mud by pyrolysis bio-oil using a design of experiments approach

A factorial design and response surface approach has been employed to optimize the neutralization, partial reduction, magnetization and carbonization of highly alkaline Red Mud bauxite residues as derived from the Bayer process using highly acidic pyrolysis bio-oil as the limiting reagent. The impact of the factors temperature, reaction time and – most importantly – the minimum bio-oil/Red Mud ratio required was explored. The significant response parameters evaluated were the minimization of the sodium content and the quantity of the aqueous phase, the maximization of the carbon content and magnetization of the solid neutralized Red Mud phase as well as the stabilization of the pH of both phases close to 7. The optimum process parameters determined provide a starting point for a possible scale-up and suggest a potential pathway for the environmental remediation of Red Mud lagoons using a renewable biomass derived resource.

Red Mud waste from the Bayer process as a catalyst for the desulfurization of hydrocarbon fuels

The management of Red Mud generated as a waste by-product of bauxite processing in the aluminum industry is key to the long-term sustainability of alumina production. At the same time, the desulfurization of fuel oil to low-level sulfur is an ongoing challenge to the petroleum industry. In an attempt to address both these issue in an integrated fashion, Red Mud waste was studied as a catalyst in a desulfurization process using a simulated Diesel containing dibenzothiophene (DBT) as a model heterocyclic organic sulfur compound. The new process combines an oxidative-adsorptive desulfurization in which a combination of H2O2//H3CCOOH and Red Mud was able to catalytically oxidize the sulfur compound to the corresponding sulfoxide (DBTO) and sulfone (DBTO2) which are then reversibly adsorbed onto the Red Mud. Regenerative tests of Red Mud were performed, maintaining a high activity in recycles suggesting that the Red Mud could be reused after a simple thermal treatment releasing DBTO and DBTO2. The approach synergistically addresses both problems: removal of sulfur compounds while at the same time offering a potential useful application of Red Mud. Red Mud was characterized by Mossbauer Spectroscopy, Infrared Spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy with dispersive energy (SEM-EDS), BET Surface area (BET), and release of volatile compounds from Red Mud by Gas chromatography-Mass Spectrometry (GC-MS) using a solvent-free solid injector (SFSI). The kinetics of the desulfurization reactions were monitored by GC-MS.

Optimized Synthesis of Vinyl Ether Sugars and Vinyl Glycosides through Transfer Vinylation Catalyzed by (4,7‐Ph2‐phen)Pd(OOCCF3)2

Sugar vinyl ethers and vinyl glycosides are conveniently synthesized by catalytic transfer vinylation with butyl vinyl ether, which serves as both the solvent and source of vinyl. The air‐stable catalyst (4,7‐diphenyl‐1,10‐phenanthroline)Pd(OOCCF3)2 is prepared in situ from commercially available components.

Homogeneous Catalysts for the Hydrodeoxygenation of Biomass-Derived Carbohydrate Feedstocks

The use of homogeneous rather than heterogeneous catalysts for the hydrodeoxygenation of sugars, sugar alcohols, and their condensates such as furfural, 5-hydroxymethylfurfural, levulinic acid, and isosorbide may offer reaction pathways that have distinct advantages, notably with respect to catalyst deactivation by coking and fouling as observed on many heterogeneous systems with these highly reactive and polar substrates. Homogeneous systems, however, also face unique challenges in ligand, catalyst, and process design. The catalyst systems employed will have to be stable to the required aqueous acidic high-temperature (T > 150 °C) reaction conditions while exhibiting activities that make them kinetically competent over acid-catalyzed decomposition and oligo- and polymerization reactions leading to humin formation. For each of the hydrodeoxygenation reaction cascades for the C3 (glycerol), C4 (erythritol), C5 (xylose and derivatives or levulinic acid), and C6 (glucose and derivatives) value chains, comparatively few homogeneous catalyst systems have been evaluated to date. Key issues remain the thermal and redox stability of the complexes employed against decomposition and reduction to bulk metal acting as a heterogeneous catalysts and the recovery and recycling of the catalyst from the often very complex reaction and product mixtures.

Bioenergy II: Group 8 Metal Complexes as Homogeneous Ionic Hydrogenation and Hydrogenolysis Catalysts for the Deoxygenation of Biomass to Petrochemicals - Opportunities, Challenges, Strategies and the Story so Far

Biomass is characterized by a high oxygen content (typically ? 40 % w/w). Its conversion into feedstocks that can directly be used in existing petrochemical feed streams will therefore require an efficient and selective deoxygenation chemistry. Ruthenium or iron-based water/acid-tolerant and high-temperature stable metal complexes that are active ionic hydrogenation and hydrogenolysis catalysts maybe ideally suited for this purpose.