Abstract
A packed-bed plug-flow reactor, denoted as the lab-scale liquid-solid (LS)² reactor, has been developed for the assessment of heterogeneous catalyst deactivation in liquid-phase reactions. The possibility to measure intrinsic kinetics was first verified with the model transesterification of ethyl acetate with methanol, catalyzed by the stable commercial resin Lewatit K2629, for which a turnover frequency (TOF) of 6.2 ± 0.4 × 10−3 s−1 was obtained. The absence of temperature and concentration gradients was verified with correlations and experimental tests. The potential for assessing the deactivation of a catalyst was demonstrated by a second intrinsic kinetics evaluation where a methylaminopropyl (MAP)-functionalized mesoporous silica catalyst was used for the aldol reaction of acetone with 4-nitrobenzaldehyde in different solvents. The cooperative MAP catalyst deactivated as a function of time on stream when using hexane as solvent. Yet, the monofunctional MAP catalyst exhibited stable activity for at least 4 h on stream, which resulted in a TOF of 1.2 ± 0.1 × 10−3 s−1. It did, however, deactivate with dry acetone or DMSO as solvent due to the formation of site-blocking species. This deactivation was mitigated by co-feeding 2 wt % of water to DMSO, resulting in stable catalyst activity.
Highlights
The activity of heterogeneous catalysts in liquid-phase reactions is often evaluated using a batch type reactor [1,2,3,4,5]
Catalyst deactivation phenomena are assessed with a model model aldol aldol reaction reaction between between acetone acetone and and 4-nitrobenzaldehyde, 4-nitrobenzaldehyde, catalyzed catalyzed by by an an aminated aminated mesoporous mesoporous silica
A lab-scale continuous-flow reactor was built for assessing heterogeneous catalyst stability in liquid-phase reactions, and is referred to as the (LS)2 reactor, i.e., the lab-scale liquid-solid reactor
Summary
The activity of heterogeneous catalysts in liquid-phase reactions is often evaluated using a batch type reactor [1,2,3,4,5]. The activity of the catalyst, and its stability is an important factor in the assessment for a potential application [6]. All too often, catalyst stability is concluded from repeated high yields that are either at full reactant conversion or at the thermodynamic equilibrium [8,9,10,11,12,13,14,15,16,17,18,19]. As a result, such experimental information does not provide any indication of the catalyst stability. Deactivation is a kinetic phenomenon for which initial rates, far from thermodynamically controlled conversion levels, should be measured in consecutive batch experiments [20,21,22]
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