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The aldol condensation of acetaldehyde with other carbonyl molecules is a complex reaction wherein there is often formation of multiple undesirable side products. These side products include higher oligomers, which not only reduce the selectivity for the main product but also prevent the use of heterogeneous catalysts due to rapid deactivation. 3-Methylpent-3-en-2-one (MPO) is an important fine chemical used as a key intermediate in the fragrance and flavor industry and is produced by the aldol condensation of acetaldehyde (AcH) with methyl ethyl ketone (MEK). In this work, we investigate the continuous production of MPO in the presence of a cation exchange resin (Amberlyst-15) in a fixed-bed reactor. Our earlier work on batch kinetics reveals that a higher feed molar ratio of AcH:MEK results in a higher yield of MPO. Accordingly, reactions are performed in a laboratory fixed-bed reactor at different feed molar ratios, reaction temperatures, and residence times. The effect of side injection of acetaldehyde into the flow reactor was also investigated and found to favorably influence the selectivity toward MPO. A crucial observation was that maintaining a low concentration of acetaldehyde helps in reducing catalyst deactivation and hence extends its life. Based on the results obtained in the lab-scale reactor, MPO was successfully produced in the pilot-scale fixed-bed reactor by performing the reaction for an extended duration (570 h), indicating that the catalyst is sufficiently active under the conditions of interest without loss of activity. The intrinsic kinetic model developed earlier using the batch reactor data is incorporated in the fixed-bed reactor model and it was found that the predictions agree reasonably well with the experimental results. © 2021 American Chemical Society

Department of Chemical Engineering

World University root node

Industrial \& Engineering Chemistry Research

Fixed-Bed Reactor with Side Injection: A Promising Option for the Aldol Condensation of Acetaldehyde

Several industrially important liquid phase reactions which involve acetaldehyde as the main reactant are practised in the presence of acidic catalyst. However, under these conditions, acetaldehyde also undergoes oligomerization via self-aldol condensation reactions to form multiple side products thereby reducing the selectivity of the desired product. In this work, we investigate the detailed kinetics of oligomerization over a commonly used commercial cation exchange resin, Amberlyst-15 as catalyst. It is found that, crotonaldehyde and subsequent heavy aldols are formed in the reaction. Molecular weight distribution of the oligomers formed during the reaction is verified with Flory's statistical method. Kinetic studies are performed in an autoclave over a temperature range of 343−363 K. The effect of different parameters such as temperature, concentration, catalyst loading, and catalyst reusability is examined. A kinetic model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expression is proposed to explain acetaldehyde oligomerization in the presence of acidic resin. © 2020

Applied Catalysis A: General

Kinetic study for oligomerization of acetaldehyde over cation exchange resin

Synthesis of methyl pentenone (MPO) using the aldol condensation reaction of methyl ethyl ketone (MEK) and acetaldehyde (AcH) in the presence of mineral acid is a commercially practiced process. The reaction is associated with the formation of a number of side products. We propose an environment-friendly, commercially available heterogeneous cation exchange resin (e.g., Ambelryst-15) catalyst for this reaction and examine its efficacy under optimized conditions. Amberlyst-15 offers better yield as compared to its homogeneous counterpart. The selectivity of the desired product was found to be increasing with the conversion of acetaldehyde, which prompted us to explore the detailed chemistry of the process. The major side products include the oligomers of acetaldehyde of different molecular weights formed by various self- and repeated aldol condensation reactions. The reaction kinetics is studied by performing experiments in batch mode in the presence of Ambelryst-15 (average diameter of 600 μm) at 600 RPM to avoid effects of external mass transfer resistances. The effect of different parameters such as particle size, stirrer speed, temperature, composition, and catalyst loading on the reaction performance is investigated. A detailed kinetic model is proposed based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism, which explains the progress of main and side reactions satisfactorily. The proposed route that uses cation exchange resin catalyst holds a potential to make the process more compact and environment-friendly. ©