(187a) Layer Melt Crystallization of Long-Chain Aldehydes From Hydroformylation Processes

The hydroformylation of long-chain olefins, an industrially highly relevant reaction, produces a mixture of isomeric long-chain aldehydes. The purified substances are used as intermediates for further bulk and fine chemicals, such as diluent or for the flavour and fragrance industry. Conventional methods like stand-alone distillation tend to be costly or even infeasible, due to a decreasing difference in boiling points with increasing chain lengths. Layer melt crystallization in contrast is a technically proven and selective method for separating isomeric compounds and has generally the advantages of an easy scale up, facile solid-liquid separation and process handling. Despite these advantages, the promising method of separating isomeric long‑chain aldehydes with melt crystallization has not been investigated yet.

In this work the applicability of layer melt crystallization for various isomeric long‑chain aldehyde systems with different chain lengths was evaluated. Necessary parameters like related phase-equilibria were measured and modeled. Layer melt crystallization experiments were conducted, in which achievable growth rates and the corresponding purities were studied. The growth rates were modeled using the physical properties of the aldehyde systems as a function of process conditions like concentration, temperature and cooling rate. Additionally, the efficiency of sweating as a post-purification step was investigated. The sweating behavior can mathematically be described in high accordance to the experimental values as a function of temperature, crystal purity and layer thickness.

Summing up we show that melt crystallization should, due to its high efficiency, be considered as the method of choice for the separation of isomeric long-chain aldehydes. Furthermore our results reveal useful methods for the extrapolation of melt crystallization including the sweating step to systems with different chain-lengths, notably without conduction of further experiments.