Ti Tamás Korányi

Catalytic depolymerization of lignin in supercritical ethanol.

One-step valorization of soda lignin in supercritical ethanol using a CuMgAlOx catalyst results in high monomer yield (23 wt%) without char formation. Aromatics are the main products. The catalyst combines excellent deoxygenation with low ring-hydrogenation activity. Almost half of the monomer fraction is free from oxygen. Elemental analysis of the THF-soluble lignin residue after 8 h reaction showed a 68% reduction in O/C and 24% increase in H/C atomic ratios as compared to the starting Protobind P1000 lignin. Prolonged reaction times enhanced lignin depolymerization and reduced the amount of repolymerized products. Phenolic hydroxyl groups were found to be the main actors in repolymerization and char formation. 2D HSQC NMR analysis evidenced that ethanol reacts by alkylation and esterification with lignin fragments. Alkylation was found to play an important role in suppressing repolymerization. Ethanol acts as a capping agent, stabilizing the highly reactive phenolic intermediates by O-alkylating the hydroxyl groups and by C-alkylating the aromatic rings. The use of ethanol is significantly more effective in producing monomers and avoiding char than the use of methanol. A possible reaction network of the reactions between the ethanol and lignin fragments is discussed.

Phosphorus promotion of Ni (Co)-containing Mo-free catalysts in thiophene hydrodesulfurization

Several unsupported nickel (cobalt)–phosphorus (sulfur) model compounds were prepared, identified and characterized by X-ray diffraction (XRD), electron microscope (EM)/energy dispersive X-ray analysis (EDAX), temperature programmed sulfidation (TPS), BET, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). They were characterized again following pretreatments (in He, H2 or H2/H2S) at different pressures, then by thiophene hydrodesulfurization (HDS) catalytic activity test at atmospheric pressure. The presence of sulfur (presulfidation by H 2S) was not required to convert the model compounds into active catalysts, a beneficial influence of H 2S on the activity was only to facilitate the reduction process into the most active Ni2P or less active Co2P phases. Ni(P)/SiO2 catalysts were also prepared, characterized and tested in thiophene HDS. For sulfided P-free Ni/SiO 2 catalysts the HDS activity correlated with the Ni3S2 surface area determined by dynamic oxygen chemisorption (DOC). The addition of phosphorus causes a strong increase in HDS activity of silica supported catalysts, which are much higher than could be expected by their nickel sulfide surface area, therefore, the formation of Ni2P (identified by XRD) again explains their high activity. The HDS activity of phosphorus promoted nickel (or cobalt) containing molybdenum-free catalysts is related to the amount and dispersion of Ni 2 Po r Co 2P present in the material.

Ethanol as capping agent and formaldehyde scavenger for efficient depolymerization of lignin to aromatics

Obtaining renewable fuels and chemicals from lignin presents an important challenge to the use of lignocellulosic biomass to meet sustainability and energy goals. We report on a thermocatalytic process for the depolymerization of lignin in supercritical ethanol over a CuMgAlOx catalyst. Ethanol as solvent results in much higher monomer yields than methanol. In contrast to methanol, ethanol acts as a scavenger of formaldehyde derived from lignin decomposition. Studies with phenol and alkylated phenols evidence the critical role of the phenolic –OH groups and formaldehyde in undesired repolymerization reactions. O-alkylation and C-alkylation capping reactions with ethanol hinder repolymerization of the phenolic monomers formed during lignin disassembly. After reaction in ethanol at 380 °C for 8 h, this process delivers high yields of mainly alkylated mono-aromatics (60–86 wt%, depending on the lignin used) with a significant degree of deoxygenation. The oxygen-free aromatics can be used to replace reformate or can serve as base aromatic chemicals; the oxygenated aromatics can be used as low-sooting diesel fuel additives and as building blocks for polymers.

Reductive fractionation of woody biomass into lignin monomers and cellulose by tandem metal triflate and Pd/C catalysis

A catalytic process for the upgrading of woody biomass into mono-aromatics, hemi-cellulose sugars and a solid cellulose-rich carbohydrate residue is presented. Lignin fragments are extracted from the lignocellulosic matrix by cleavage of ester and ether linkages between lignin and carbohydrates by the catalytic action of homogeneous Lewis acid metal triflates in methanol. The released lignin fragments are converted into lignin monomers by the combined catalytic action of Pd/C and metal triflates in hydrogen. The mechanism of ether bond cleavage is investigated by lignin dimer models (benzyl phenyl ether, guaiacylglycerol-β-guaiacyl ether, 2-phenylethyl phenyl ether and 2-phenoxy-1-phenylethanol). Metal triflates are involved in cleaving not only ester and ether linkages between lignin and the carbohydrates but also β-O-4 ether linkages within the aromatic lignin structure. Metal triflates are more active for β-O-4 ether bond cleavage than Pd/C. On the other hand, Pd/C is required for cleaving α-O-4, 4-O-5 and β–β linkages. Insight into the synergy between Pd/C and metal triflates allowed optimizing the reductive fractionation process. Under optimized conditions, 55 wt% mono-aromatics – mainly alkylmethoxyphenols – can be obtained from the lignin fraction (23.8 wt%) of birch wood in a reaction system comprising birch wood, methanol and small amounts of Pd/C and Al(III)-triflate as catalysts. The promise of scale-up of this process is demonstrated.

Effective release of lignin fragments from Lignocellulose by Lewis Acid Metal triflates in the lignin-first approach

Adding value to lignin, the most complex and recalcitrant fraction in lignocellulosic biomass, is highly relevant to costefficient operation of biorefineries. We report the use of homogeneous metal triflates to rapidly release lignin from biomass. Combined with metal-catalyzed hydrogenolysis, the process separates woody biomass into few lignin-derived alkylmethoxyphenols and cellulose under mild conditions. Model compound studies show the unique catalytic properties of metal triflates in cleaving lignin-carbohydrate interlinkages. The lignin fragments can then be disassembled by hydrogenolysis. The tandem process is flexible and allows obtaining good aromatic monomer yields from different woods (36-48 wt %, lignin base). The cellulose-rich residue is an ideal feedstock for established biorefining processes. The highly productive strategy is characterized by short reaction times, low metal triflate catalyst requirement, and leaving cellulose largely untouched.

Comparison of (non)-sulfided NiNaY zeolite catalysts prepared by ion-exchange and impregnation by xenon adsorption and xenon-129 NMR

Ni2+ exchanged and NiCl2 impregnated non-sulfided and sulfided NaY zeolites were characterized by xenon adsorption isotherms,129 Xe NMR and thiophene hydrodesulfurization. The nickel species are located mainly inside the micropores of the zeolites in all samples. Ion-exchange results in a more homogeneous distribution of these species than impregnation. This explains their lower hydrodesulfurization activity compared to the ion-exchanged samples.

Catalytic Depolymerization of Lignin and Woody Biomass in Supercritical Ethanol : Influence of Reaction Temperature and Feedstock

The one-step ethanolysis approach to upgrade lignin to monomeric aromatics using a CuMgAl mixed oxide catalyst is studied in detail. The influence of reaction temperature (200–420 °C) on the product distribution is investigated. At low temperature (200–250 °C), recondensation is dominant, while char-forming reactions become significant at high reaction temperature (>380 °C). At preferred intermediate temperatures (300–340 °C), char-forming reactions are effectively suppressed by alkylation and Guerbet and esterification reactions. This shifts the reaction toward depolymerization, explaining high monomeric aromatics yield. Carbon-14 dating analysis of the lignin residue revealed that a substantial amount of the carbon in the lignin residue originates from reactions of lignin with ethanol. Recycling tests show that the activity of the regenerated catalyst was strongly decreased due to a loss of basic sites due to hydrolysis of the MgO function and a loss of surface area due to spinel oxide formation of the Cu and Al components. The utility of this one-step approach for upgrading woody biomass was also demonstrated. An important observation is that conversion of the native lignin contained in the lignocellulosic matrix is much easier than the conversion of technical lignin.

Characterization of aluminium siting in MOR and BEA zeolites by 27Al, 29Si NMR and FTIR spectroscopy

Commercial and dealuminated mordenites (MOR) as well as home made and cobalt modified beta (BEA) zeolites have been characterized by 29 Si and 27 Al solid state Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. The quantitative contributions of Si(nAl) and Si(OH) x sites to the NMR signal intensities were calculated from the various Si/Al ratios and relative 29 Si and 27 Al NMR signal intensities assuming twin, lone and no Al containing periodical building units of the zeolite framework. More lone compared to twin and silicate units were suggested for BEA than for MOR zeolites. Some octahedral Al transformed back to tetrahedral coordination due to ion-exchange of HBEA to Co/BEA zeolites. We conclude that we are able to distinguish the Si(OH) x groups which are original defect sites or produced in a dealumination or calcination process.

Synergy in lignin upgrading by a combination of Cu-based mixed oxide and Ni-phosphide catalysts in supercritical ethanol

The depolymerization of lignin to bioaromatics usually requires a hydrodeoxygenation (HDO) step to lower the oxygen content. A mixed Cu–Mg–Al oxide (CuMgAlOx) is an effective catalyst for the depolymerization of lignin in supercritical ethanol. We explored the use of Ni-based cocatalysts, i.e. Ni/SiO2, Ni2P/SiO2, and Ni/ASA (ASA = amorphous silica alumina), with the aim of combining lignin depolymerization and HDO in a single reaction step. While the silica-supported catalysts were themselves hardly active in lignin upgrading, Ni/ASA displayed comparable lignin monomer yield as CuMgAlOx. A drawback of using an acidic support is extensive dehydration of the ethanol solvent. Instead, combining CuMgAlOx with Ni/SiO2 and especially Ni2P/SiO2 proved to be effective in increasing the lignin monomer yield, while at the same time reducing the oxygen content of the products. With Ni2P/SiO2, the lignin monomer yield was 53 wt %, leading to nearly complete deoxygenation of the aromatic products.

Hydrodesulfurization activity of zeolite-supported nickel and cobalt sulfide catalysts

Abstract Various zeolite (NaY or CaY) supported metal sulfide (Ni or Co) catalysts were prepared (impregnation or ion exchange) and characterized by means of thiophene HDS, 129 Xe NMR and TPS. Especially the acidic zeolites showed a very high initial activity. The observed activity differences are discussed in terms of sulfidation, dispersion, position of the metalsulfide relative to the zeolite pore system and acidity, the latter two being the most important. It is concluded that small Ni and Co sulfide clusters are very efficient thiophene desulfurization catalysts.