42 Pol. J. Chem. Tech., Vol. 15, No. 3, 2013 Polish Journal of Chemical Technology, 15, 3, 42 — 47, 10.2478/pjct-2013-0042 Esterification of fatty acids with C 8 -C 9 alcohols over selected sulfonic heterogeneous catalysts Janusz Nowicki * , Jan Mosio-Mosiewski Institute of Heavy Organic Synthesis „Blachownia”, Energetykow 9, 47-225 Kedzierzyn-Kozle, Poland * Corresponding author: e-mail: nowicki.j@icso.com.pl A study on the synthesis of esters of fatty acids of natural origin (oleic acid from rapeseed oil) and branched synthetic isostearic acid with commercially available alcohols C 8 -C 9 i.e. 2-ethylhexanol (2-EH) and 3,5,5-trimethylhexanol (TMH) in the presence of selected heterogeneous catalysts containing active sulfonic groups has been made. The catalysts were obtained using ready available amorphous silicas with different textural characteristics. The influence of catalyst porosity on the catalytic properties in the esterification of fatty acids has been investigated. The effect of the synthesis temperature has also been studied. The results were compared with the results of esterification with the use of acidic ion exchange resins. It was shown that catalysts obtained on the basis of amorphous silicas are good and reusable catalysts for the esterification of fatty acids with higher alcohols. Keywords: esterification of fatty acids, C 8 -C 9 alcohols, sulfonic acid catalysts. INTRODUCTION Esters of C 12 –C 20 fatty acids are among major gro- ups of products derived from fatty acids coming from vegetable oils or animal fats as well as acids produced through the chemical synthesis. In this group the most important products for industrial applications are methyl and ethyl esters of fatty acids derived from vegetable oils of different species. The basic method of their synthesis is transesterification of oils with methanol or ethanol in the presence of alkaline catalysts. Direct esterification of an acid by an alcohol in this case is unprofitable from the economic point of view. A direct esterification method is the most commonly used in the case of esters of higher alcohols (> C 4 ). These esters can also be obtained by transesterification of fatty acids methyl esters (FAME) with suitable and easily accessible higher alcohols 1 . This approach is often applied to the present on the market in large quantities various types of methyl esters deri- ved from vegetable oils. This method, however, cannot be applied to esters of petrochemical origin due to the unavailability on the market of relevant methyl esters. Thus, esters of fatty acids of petrochemical origin are obtained only by direct esterification of fatty acids with corresponding alcohols. Esters of C 8 –C 18 aliphatic alcohols and fatty acid are widely used in cosmetics, pharmaceuticals and also as components of oil bases and lubricants 2–4 . Due to the specific requirements for the esters used in cosmetic or pharmaceutical products they are usually produced using enzymatic catalysis 5, 6 . The basic method of preparation of such esters, however, is the direct esterification of alcohol with acid in the presence of homogeneous acid catalysts, such as H 2 SO 4 , RSO 3 H or H 3 PO 4 7–11 . Esterification is a reversible reaction so in order for it to progress toward the desired product an excess of one of the reactants, usually alcohol, is necessary. In addition, the reaction is favored by removal of water made in the course of the reaction. In the case of higher alcohols the use of additional solvents such as toluene or xylene is not necessary because these alcohols typically form heteroazeotropic mixtures with water and that fa- cilitates water removal. Reactivity between alcohols and fatty acids is dependent on their structure. The rate of esterification varies in the following order 1 : CH 3 OH > primary alcohols > secondary alcohols > tertiary alcohols and: HCO 2 H > CH 3 CO 2 H > RCH 2 CO 2 H > R 2 CHCO 2 H > R 3 CCO 2 H The acid strength has smaller effect on the rate of esterification. These dependencies are important in the synthesis of fatty acid esters of petrochemical origin, especially those with a secondary carboxyl group (eg. Guerbet acids). Homogeneous esterification catalysts are very effecti- ve, but require their careful removal from the reaction mixture. In addition, they can adversely affect the color of the product. This is especially noticeable in the case of polyunsaturated fatty acids. More often for the esterification reaction heterogeneous catalysts are used. A number of zeolites such as H-Y, H-Beta and H-ZSM-5 were studied in reactions of esterification of fatty acids with polyols, among them glycerol was the most common 2, 12, 13 . The study has shown that for an efficient removal of the produced water a very important factor is the hy- drophobicity showed by this type of catalysts. Therefore, MCM-type mesoporous materials were proven to be poor catalysts for the esterification. Only the modification of their surface by sulfonic groups leads to a stable and active catalyst, suitable for the esterification process. Esterification of fatty acids by glycerol was the subject of many studies, whose results were published in litera- ture 14–19 . In the temperature of 120 o C, after 6 h lauric acid conversion reaches 97% and 95% for oleic acid. Conversion of > 96% were obtained also for sieve SBA- 15 modified with sulfonic groups 20 . Worse results were obtained for MCF mesoporous silica foams containing sulfonic groups. In the esterification of acetic acid with butanol conversion has reached only 65% 21 . For the synthesis of a catalysts containing sulfonic groups, in addition to synthetically produced materials with mesoporous structure, also widely used is the com- Unauthenticated Download Date | 3/4/16 7:21 AM