Selective Hydrogenation of 1-Heptyne in a Mini Trickle Bed Reactor

Abstract

The selective hydrogenation of 1-heptyne over a 2 wt % Pd/Al2O3 catalyst was studied in a trickle bed reactor operating in both batch recycle and continuous modes. The reaction was studied in a range of different solvents, including isopropanol, hexane, mixtures of these two solvents, and also isopropanol with small quantities of water and base (NaOH) added. It was found that the rate of reaction was fastest in hexane, owing to the higher hydrogen solubility in this solvent. However, the selectivity toward 1-heptene was higher in isopropanol, with over 95% selectivity being maintained for 120 min of the total 240 min reaction time. The addition of water or base led to an increase in reaction rate, possibly through modification of the adsorption equilibria at the catalyst surface or direct involvement in the reaction. The hydrodynamics of trickle flow upon the reaction were investigated, showing that increasing liquid flow rate led to enhancement of reaction rate, although a plateau was eventually reached at the higher flows. The higher flows led to improved catalyst wetting, liquid hold up, and mass transfer rates, thus explaining the enhanced reaction rate. The concentration profiles were fitted according to a Langmuir–Hinshelwood kinetic expression. Operation in continuous flow was demonstrated, although a long residence time was required for high conversion, leading to lower 1-heptene selectivity compared with batch recycle operation.

Liquid phase hydrogenation of phenylacetylene over Pd and PdZn catalysts in toluene: effects of alloying and CO2 pressurization

“…Compared to ZnO-supported Pd catalyst prepared by impregnation and reduced at ambient temperature, alloyed PdZn/ZnO one reduced at 500 ºC is less active but more selective to the hydrogenation of phenylacetylene to styrene in toluene. For the latter, the selectivity to styrene does not depend on the amount of Pd loaded (1,10,30 wt.-%) so much but it decreases with increasing Pd loading for the former. The chemical state of active Pd species on the surface of PdZn crystallites is unlikely to change with the Pd loading due to its nature that Pd and Zn species are regularly exposed irrespective of the Pd loading (the size of PdZn crystallites).…”

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

“…The continuous flow partial hydrogenation of 1-heptyne ( 2 ) to 1-heptene ( 2a ), an additive for lubricants and a surfactant [ 125 ], was also reported using packed 2% Pd@Al 2 O 3 catalyst, showing 49% selectivity at 81% conversion under room temperature and 1 bar H 2 (STY for 2a : 0.12 kg L −1 h −1 ), with no detectable signs of deactivation over 6 h reaction time [ 126 ].…”

The liquid-phase hydrogenation of 1-heptyne over Pd–Au/TiO 2 catalysts prepared by the combination of incipient wetness impregnation and deposition–precipitation

“…The reactions involving alkyne and alkene hydrogenation have become of both industrial and academic importance. A number of products from these reactions are used in the food (flavors), pharmaceutical (sedatives, anesthetics, vitamins), cosmetics (fragrances), plastics (resins and polymers), and lubricants industries [1]. Such reactions are often carried out in three-phase catalytic systems using batch and semibatch reactors.…”

“…Such reactions are often carried out in three-phase catalytic systems using batch and semibatch reactors. Different alkynic compounds have been employed as model reactants for evaluation of the liquid-phase selective hydrogenation catalysts under mild reaction conditions such as 1-hexyne [2][3], 3-hexyne [4], 1-heptyne [1,[5][6][7], 4octyne [8], phenylacetylene [9,10], and 1-phenyl-1-pentyne [11]. Palladium is the most common hydrogenation catalyst used in industry and studied in fundamental research because of its ability to selectively hydrogenate multiple unsaturated hydrocarbons.…”