Screening of active solid catalysts for esterification of tall oil fatty acids with methanol Jaroslav Kocík a, * , Ajaikumar Samikannu b , Hasna Bourajoini b , Tung Ngoc Pham b , Jyri-Pekka Mikkola b, c , Martin H  ajek a , Libor  Capek a a Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentsk a 573, Pardubice 532 10, Czech Republic b Department of Chemistry, Technical Chemistry, Chemical-Biological Centre, Umeå University, Linnaeus v€ ag 10, 901 87, Umeå, Sweden c Faculty of Science and Engineering, Industrial Chemistry & Reaction Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Biskopsgatan 8, 20 500, Åbo-Turku, Finland article info Article history: Received 8 February 2016 Received in revised form 21 September 2016 Accepted 21 September 2016 Available online xxx Keywords: Esterification Biodiesel TOFA Mixed oxides SBA-15 Al-SBA-15 abstract The paper is focused on the description of the activity/selectivity of mesoporous silica based materials loaded with various types of active species in the esterification of tall oil free fatty acids. The metals such as aluminium, molybdenum, gallium and zinc, including their combinations were impregnated on the mesoporous silica, which was tested in esterification reaction. All these catalysts preserved its tall oil free fatty conversion in the first and the second catalytic cycles. However, while only insignificant amount of gallium or molybdenum was lost from the solid catalyst into the liquid phases, zinc leached from every studied solid catalyst. In contrast to impregnated gallium on mesoporous silica, which exhibited higher acidity and higher tall oil free fatty acids conversion in the first catalytic cycle, but its value was not preserved in the second catalytic test. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Biodiesel (mixture of methyl esters of higher fatty acids) is usually prepared by transesterification of triglycerides, which are contained in vegetable or waste cooking oils and animal fats (Nair et al., 2012), with low molecular alcohol, the most often meth- anol (Math et al., 2010). The reaction is usually catalysed by alkoxide or homogeneous base (KOH, NaOH). The disadvantage is used of oil with low content of free fatty acids (FFAs) and moisture (Kwiecien et al., 2009, 2010), which is not cheap. This disadvantage can be tackled when using solid catalyst such as a solid acid sup- ported catalyst (Bala et al., 2015), or bifunctional heterogeneous catalysts (Farooq et al., 2013). The price of vegetable oil accounts for 75%e85% of the biodiesel price (Narkhede et al., 2014), therefore new cheaper raw material resources are still being discovered. Biodiesel can also be produced via esterification of free fatty acids, which can be contained in low quality feedstock (Bala et al., in press). This reaction is usually catalysed by sulfuric acid but this approach suffers from disadvantages such as corrosion, problems with separation and a lack of catalyst reusability. Tall oil free fatty acids (TOFA) are an attractive raw material in biodiesel production. TOFA consists of approximately 97% free fatty acids. It is a side-product from the Kraft pulping process of (coniferous) wood. In principal, biodiesel can be prepared from TOFA without catalysts at high pressures and temperatures, if the alcohol (mostly methanol) is present in supercritical state (White et al., 2011). However, more attractive is the esterification of TOFA with methanol in the presence of a stable solid a catalyst containing a high amount of strong Broensted acid sites. Nevertheless, the catalyst stability and activity in the subsequent catalytic cycles represents the most important problem and has not been fully solved for any of the studied solid catalysts. The aim of this paper was to describe various types of supported solid catalysts with a potential for esterification of TOFA. We selected for our study mesoporous silica SBA-15 (Santa Barbara Amorphous type material) loaded with zeolite ZSM-5 (Zeolite Socony Mobil-5), niobium (Nb) and cerium dioxide (CeO 2 ). Next, we selected the aluminium SBA-15 loaded with zinc oxide (ZnO), gallium oxide (Ga 2 O 3 ) and they combination, molybdenum trioxide (MoO 3 ) together with ZnO and Ga 2 O 3 together with zirconium * Corresponding author. E-mail address: jaroslav.kocik@student.upce.cz (J. Kocík). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro http://dx.doi.org/10.1016/j.jclepro.2016.09.174 0959-6526/© 2016 Elsevier Ltd. All rights reserved. Journal of Cleaner Production xxx (2016) 1e5 Please cite this article in press as: Kocík, J., et al., Screening of active solid catalysts for esterification of tall oil fatty acids with methanol, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.09.174