From Pulp to Aromatic Products-Reaction Pathways of Lignin Depolymerization.

This study investigated the depolymerization of lignin into aromatic monomer compounds under hydrothermal conditions. A reaction scheme highlighting secondary alkylation reactions as well as the molecular weight shift was developed based on the experimental data. Lignin is produced in large quantities in paper production and dissolved in what is known as black liquor (BL). To avoid lignin recovery as an additional process step, BL is used directly as feedstock in the hydrothermal liquefaction (HTL) in this work. We performed various batch experiments in micro autoclaves with BL and model substances at different reaction temperatures (TR = 250-400 °C) and a holdingtime of tR = 20 min, as well as continuous experiments (TR = 325-375 °C, tR = 20 min). We were able to show that different derivatives of catechols are the main products among the monomers in our process. With the help of the model substance experiments, we were able to work out three main reactions: demethoxylation, demethylation, and alkylation. This behavior could be observed in the case of BL from hardwood as well as from softwood. 31P nuclear magnetic resonance (NMR) spectroscopy analysis has shown that these reactions take place on aromatic monomers as well as on larger aromatic oligomer structures. At higher temperatures, a large fraction of the carbon ends up in the solid product, while the yields of the monomers decrease sharply. 13C NMR spectroscopy of the solid material shows that the monomers are probably incorporated into the solid phase by repolymerization. We were also able to see this effect using size exclusion chromatography analysis based on the relative molecular weight. From all of the analytical results of the products, a reaction scheme was developed that describes the reaction pathways of the lignin during HTL. Based on this, a reaction kinetic model can be developed in the next step.

Efficient noble metal promoted bimetallic cobalt catalysts in the selective synthesis of acetaldehyde dimethyl acetal.

Herein we report the one-pot cobalt catalysed synthesis of the dimethylacetal of acetaldehyde from synthesis gas and methanol. The product can be used as a fuel additive either as it is or after transacetalisation with long-chain alcohols. The product is obtained at moderate temperatures in good selectivities and high CO-conversions. A variation of the promotor metal (Au, Pt, Pd, and Ru) and of the support (γ-Al2O3 and CeO2) in the catalyst was conducted, which showed a great impact of both the support and promotor on the activity and structure of the catalyst. Furthermore, a specific variation of temperatures and pressure for the most active catalyst and a model catalyst was conducted giving an interesting insight into ongoing processes.

Aldehydes and ketones in pyrolysis oil: analytical determination and their role in the aging process.

Aldehydes and ketones are known to play a role in the aging process of pyrolysis oil and generally, aldehydes are known for their high reactivity. In order to discern in pyrolysis oil the total aldehyde concentration from that of the ketones, a procedure for the quantification of aldehydes by 1H-NMR was developed. Its capability is demonstrated with a hardwood pyrolysis oil at different stages of the aging process. It was treated by the Accelerated Aging Test at 80 °C for durations of up to 48 h. The aldehyde concentration was complemented by the total concentration of carbonyls, quantified by carbonyl titration. The measurements show, that the examined hardwood pyrolysis oil contained 0.31-0.40 mmol g-1 aldehydes and 4.36-4.45 mmol g-1 ketones. During the first 24 h, the aldehyde concentration declined by 23-39% and the ketone concentration by 9%. The rate of decline of aldehyde concentration slows down within 24 h but is still measureable. In contrast, the total carbonyl content does not change significantly after an initial decline within the first 4 h. Changes for vinylic, acetalic, phenolic and hydroxyl protons and for protons in the α-position to hydroxy, ether, acetalic and ester groups were detected, by 1H-NMR. In the context of characterizing pyrolysis oil and monitoring the aging process, 1H-NMR is a reliable tool to assess the total concentration of aldehydes. It confirms the reactivity of aldehydes and ketones and indicates their contribution to the instability of pyrolysis oil.

Direct DME synthesis on CZZ/H-FER from variable CO2/CO syngas feeds.

Catalyst systems for the conversion of synthesis gas, which are tolerant to fluctuating CO/CO2 gas compositions, have great potential for process-technical applications, related to the expected changes in the supply of synthesis gas. Copper-based catalysts usually used in the synthesis of methanol play an important role in this context. We investigated the productivity characteristics for their application in direct dimethyl ether (DME) synthesis as a function of the CO2/CO x ratio over the complete range from 0 to 1. For this purpose, we compared an industrial Cu/ZnO/Al2O3 methanol catalyst with a self-developed Cu/ZnO/ZrO2 catalyst prepared by a continuous coprecipitation approach. For DME synthesis, catalysts were combined with two commercial dehydration catalysts, H-FER 20 and γ-Al2O3, respectively. Using a standard testing procedure, we determined the productivity characteristics in a temperature range between 483 K and 523 K in a fixed bed reactor. The combination of Cu/ZnO/ZrO2 and H-FER 20 provided the highest DME productivity with up to 1017 gDME (kgCu h)-1 at 523 K, 50 bar and 36 000 mlN (g h)-1 and achieved DME productivities higher than 689 gDME (kgCu h)-1 at all investigated CO2/CO x ratios under the mentioned conditions. With the use of Cu/ZnO/ZrO2//H-FER 20 a promising operating range between CO2/CO x 0.47 and 0.8 was found where CO as well as CO2 can be converted with high DME selectivity. First results on the long-term stability of the system Cu/ZnO/ZrO2//H-FER 20 showed an overall reduction of 27.0% over 545 h time on stream and 14.6% between 200 h and 545 h under variable feed conditions with a consistently high DME selectivity.

catena-Poly[[aqua-zinc(II)]-µ-N,N'-bis-(2-cyano-3-eth-oxy-3-oxoprop-1-en-yl)benzene-1,2-diaminido].

The slightly yellow-coloured title complex, [Zn(C18H16N4O4)(H2O)] n , crystallizes with one mol-ecule in the asymmetric unit. The structure clearly shows the mer-η(4) O,O,N,N-binding mode of the N,N'-bis-(2-cyano-ethyl-propeno-yl)-1,2-di-amido-benzene ligand stabilizing the Zn centre of a distorted octa-hedral environment. The fifth coordination site in one apical position is held by a coordinating solvent water mol-ecule whereas the complete octa-hedral coordination sphere is completed by coordination of one N atom from a CN group of a neighbouring mol-ecule, leading to the final polymeric structure consisting of zigzag staggered chains in parallel orientation along the c-axis direction. Between the coord-in-ated water solvent molecule and the N atoms of uncoord-in-ated cyano-groups of neighboured units, two H-bridge bonds are formed. One of these H-bridge bonds is of inter- whereas the other of intra-strand nature, leading to a two-dimensional network parallel to (110) stabilizing the supramolecular structure. Six Zn-O or Zn-N bonds are found with lengths ranging from 2.061 (1) to 2.185 (1) Šand bond angles about the Zn atom are clustered in the ranges 79.83 (4)-104.21 (4) and 167.05 (4)-170.28 (4)°.

Bis(dimethyl sulfoxide-κO)tetra-kis-(µ2-3,4,5-tri-meth-oxy-benzoato-κ(2) O:O')dizinc.

The colourless title complex, [Zn2(C10H11O5)4(C2H6OS)2], crystallizes with one half-mol-ecule in the asymmetric unit, the other half of the mol-ecule being generated by a crystallographic inversion center. The structure shows a µ2-O:O'-bridging mode of the four 3,4,5-tri-meth-oxy-benzoate ligands finally stabilizing the two Zn(II) atoms in the dinuclear complex in a distorted square-pyramidal environment. The fifth coord-in-ation site in the apical position of the pyramid is occupied by a coordinating dimethyl sulfoxide solvent mol-ecule equally disordered over two positions.

Solid phase synthesis of selectively deuterated arenes.

A novel access to deuterated and D(3)CO-substituted arenes has been developed using immobilized triazenes as precursors. The linker system and the deuterating cleavage methodology could be shown to be compatible with various functional groups and are therefore suitable for the synthesis of derivatives only hardly available via comparable protocols.

Study of different copper (I) catalysts for the "click chemistry" approach to carbanucleosides.

We compare herein the scope of three copper (I) catalysts on the synthesis of various 1,4-disubstitued-1,2,3-triazolo-carbanucleosides through a microwave (and thermic) assisted Huisgen 1,3-dipolar cycloaddition. The tetrakis(acetonitrile)copper hexafluorophosphate ([Cu(CH3CN)4]PF6), the imidazoline(mesythyl)copper bromide (Imes)CuBr, and the copper/copper sulfate Cu(0)/CuSO4 (II) mixture have been chosen for this study. Their influence in a catalytic amount will be analyzed according to the substituent of the alkyne, the solvent, or the heating method.