Thermal cracking of methyl esters in castor oil and production of heptaldehyde and methyl undecenoate

Abstract

The main aim of this study was to investigate experimentally the thermal cracking of methyl esters in castor oil with a view to the production of heptaldehyde and methyl undecenoate as precursors for flavors and perfumes for the cosmetics and pharmaceutical industries. Experiments were carried out in a pilot plant with a screw reactor, under isothermal and continuous conditions at temperatures ranging from 475 to 525°C and residence times of 44–104s, with bio-oil production ranging from 48 to 228g/h. Mass balances were obtained by means of mass and chemical species measurements, using gravimetric and GC-FID/GC–MS analysis, respectively. Global bio-oil yields of 50–80wt.% were achieved, of which 2–12wt.% was methyl undecenoate and 14–18wt.% was heptaldehyde. The variations are attributed to the operational conditions in terms of temperature and residence time. The best conditions were a higher temperature and shorter residence time, which provided a mass fraction of 12–18wt.% for both products. In addition, a proposal for the simplified mechanism involved in the thermal cracking of methyl esters in castor oil, showing one pathway for the desired products and two pathways for the undesired products, is presented and discussed. All results were verified by experimental data on the mass fractions of the components in the bio-oil obtained from CG–MS analysis, as a function of the temperature and residence time.