Loop reactor staged with structured fibrous catalytic layers for liquid-phase hydrogenations

A novel concept of a recycle loop reactor is developed with structured filamentous catalysts integrated as trays in a staged bubble column. The reactor can be operated in batch or continuous mode. Woven fabrics of activated carbon fibers (ACF) were used as support for the Pd catalyst. The loop reactor was tested in the 2-butyne-1,4-diol hydrogenation showing selectivity up to 97% towards 2-butene-1,4-diol at conversions up to 80%. The reactor behavior was described quant. assuming an ideally mixed reactor and Langmuir-Hinshelwood kinetics with weak hydrogen adsorption. Catalyst reuse was demonstrated in multiple runs over a period of 6 mo with more than 375 h on stream. [on SciFinder (R)

Solvent-Free Selective Hydrogenation of 2-Butyne-1,4-diol over Structured Palladium Catalyst

Hydrogenation of 2-butyne-1,4-diol catalyzed by Pd nanoparticles on activated carbon fibers (ACFs) was studied. The ACF support in the form of woven fabrics provides the basis for structured catalytic fixed beds. In the present study, this catalyst was integrated in the stirrer of an autoclave. Hydrogenations were carried out in pure, solvent-free butynediol at temps. from 352 to 392 K and hydrogen pressures of 1-2 MPa. The results were compared to those obtained for aq. solns. at different pH's and temps. of 293-333 K. High selectivities of >=98% toward 2-butene-1,4-diol at conversions of ?90% were attained in both systems. Turnover frequencies had comparable values at the same temp. The activation energy of 30 kJ/mol was detd. from initial reaction rates. Because this value is identical for the aq. soln. and the solvent-free system, mass-transfer limitations can be excluded for both systems. Concn.-time profiles were quant. predicted assuming the Langmuir-Hinshelwood kinetics with weak hydrogen adsorption. Estd. kinetic parameters allow a coherent interpretation of the exptl. observations. Catalyst reactivation and multiple reuses were demonstrated. [on SciFinder (R)

Palladium supported on filamentous active carbon as effective catalyst for liquid-phase hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol

Structured palladium catalysts suitable for three-phase reactions have been developed based on woven fabrics of active carbon fibers (ACF) as the catalytic supports. The Pd/ACF were tested in liq.-phase hydrogenation of 2-butyne-1,4-diol showing a selectivity towards 2-butene-1,4-diol up to 97% at conversions up to 80%. Multiple reuse of the catalyst with stable activity/selectivity in a batch reactor was also demonstrated. The reaction kinetics was studied and the main kinetic parameters were obtained. Assuming a Langmuir-Hinshelwood kinetics and a weak hydrogen adsorption a suitable kinetic model was developed consistent with the exptl. data. [on SciFinder (R)

Palladium nanoparticles stabilized in block-copolymer micelles for highly selective 2-butyne-1,4-diol partial hydrogenation

Pd nanoparticles (2 nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly(2-vinylpyridine) were studied in partial hydrogenation of 2-butyne-1,4-diol. Both unsupported micelles (0.6 kg Pd/m3) and supported ones on g-Al2O3 (0.042% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol, with up to 94% conversion. The only side product obsd. was butane-1,4-diol. The catalysis was ascribed to the surface of Pd nanoparticles modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). The TOF [turnover frequency] over unsupported and supported catalysts was 0.56 and 0.91 s-1 (at 323 K, 0.6 MPa H2 pressure, solvent 2-propanol/water = 7:3), resp. Reaction kinetics fit the Langmuir-Hinshelwood model assuming weak hydrogen adsorption. Expts. on catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles desorbed by less then 5% during the catalytic run. [on SciFinder (R)

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