(328c) Implementation of Process Intensification (PI) in the Removal of Carbonyl Compounds from the Water/Ethanol Solvent Mixture

Carbonyl compounds are frequently observed ingredients in biochemical, food, chemical and pharmaceutical industries. The high reactivity of such compounds is a great advantage if aldehydes/ketones are important contributors in the synthetic routes towards the final products. However, if the carbonyl compounds act as impurities, they must be removed from the reaction mixture, due to the high tendency of forming genotoxic impurities (GTIs).    

Removal of carbonyl compounds could be performed in several ways. Applications of adsorption techniques by using alumina, titanium, or activated carbon, are well-known and even commercially applicable in the petrochemical industry. Implementation of in- or ex-situ removal with pervaporation has also achieved significant advantages with the main application in fermentation processes. Furthermore, combinations of derivatization and separation processes are known, such as reactive extraction with amines or even solid-phase extraction with 2,4-dinitrophenylhidrazine (DNPH). Some new techniques are additionally getting popular, such as applications of extractant impregnated resins (EIRs).

The main aim of this work is to remove benzaldehyde from a solvent mixture consisting of 70 % water and 30 % of ethanol (volumetric ratio). Such a solvent mixture indicates formation of acetals, hemiacetals and hydrates with carbonyl compounds, and could also promote electrophilic and nucleophilic substitution reactions of aldehydes/ketones with other compounds in the reaction mixture. The main approach is focused on finding suitable derivatization agents that would convert carbonyl compounds into new impurities that are harmless. The screening procedure was therefore performed initially with primary/secondary/tertiary amines, inorganic salts, organic acids and their anhydrides. The most desired option was found to be tris(hydroxymethyl)aminomethane (TRIS), which converts carbonyl compounds into oxazolidines. A Process Systems Engineering (PSE) approach including property prediction simulations indicated that such products are more inert compared to carbonyl compounds and additionally more suitable for removal by applying other separation processes.

TRIS was used in a process development study in order to remove ppm levels of benzaldehyde. The initial process design was performed in batch mode with off-line real time process monitoring. A Process Intensification (PI) approach was implemented and the movement from batch to continuous processing was achieved by using a laminar tubular reactor. Real-time process monitoring was also moved from off-line with High Performance Liquid Chromatography (HPLC) towards in-line with UV-VIS spectroscopy in order to satisfy requirements defined within the Process Analytical Technology (PAT) guidance. Both types of processes are compared in order to evaluate advantages of implementing PI, PAT and PSE. Further work will include process control studies and automation, as well as considerations of suitable scale up/out possibilities.