Submitted to: Catalysis Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2018
Publication Date: 1/1/2019
Citation: Zhang, J., Uknalis, J., Moreau, R.A., Lew, H.N. 2019. Development of magnesium oxide-zeolite catalysts for isomerization of fatty acids. Catalysis Letters. 149:303-312. https://doi.org/10.1007/s10562-018-2601-3.
Interpretive Summary: Agriculture products are attractive because of their excellent biodegradability and low toxicity. For instance agricultural products such as fatty acids can be used as feedstocks to produce isostearic acid (IA), a unique product which is heavily used as an ingredient in lubricants, beauty care products, and cosmetics. However, the production yield of IA reported in the literature is only about 20-30%. There is a need to create new more efficient processes to produce IA at higher yields so that it will meet consumers’ demand. ARS researchers have developed a chemical process to overcome this problem by increasing the IA yield by about 4 fold (70-80%). This process involves the use of a combination of a “salt-zeolite” catalyst to convert the agricultural fatty acids to isostearic acid. Under the optimized conditions, loading of these salt-zeolites was found to decrease the amounts of unwanted byproducts while maintaining a high yield of the desired product. These salt-zeolites are insoluble in the parent feedstocks, and they should not contaminate the IA product. This finding is important as the products should be cleaner and safer, showing priority for many oleochemical applications.
Technical Abstract: Isostearic acid is a crucial component used in the formulation of bio-lubricants including cosmetics and personal care products. In this study, three zeolites were treated with magnesium nitrate (MgNO3) salt to generate highly active magnesium oxide (MgO)-zeolite catalysts for the isomerization of oleic acid to give iso-oleic acid (precursor of isostearic acid) product. The treatment step is intended to poison (or neutralize) the external acid sites of the zeolites, thus inhibiting the formation of by-products (i.e., dimer fatty acids). The acid sites, crystallinity, thermal property, morphology and elemental composition of the zeolites before and after treatments were thoroughly investigated by scanning electron microscope, fourier-transform spectroscopy, thermogravimetric analysis, and X-ray powder diffraction. Various factors of the isomerization reactions were studied, such as the amount of MgO on different kinds of zeolites, the amount of catalyst loadings, and the reaction times and temperatures. In addition, the effect of the calcination step after treatment was examined to determine if this step was necessary to obtain an active and stable catalyst. As expected, the higher the concentration of MgO on the zeolites, the less dimer was detected in the isomerization products, while the conversion of oleic acid and selectivity of iso-oleic acid remained at a relatively high level. This is promising because MgO probably forms a covalent bond to the zeolites so the potential contamination of these salts is eliminated in the isostearic acid.