Transesterification Catalysts from Iron Doped Hydrotalcite-like Precursors: Solid Bases for Biodiesel Production
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Transesterification Catalysts from Iron Doped Hydrotalcite-like Precursors: Solid Bases for Biodiesel Production Gerald S. Macala Æ Andrew W. Robertson Æ Charles L. Johnson Æ Zachary B. Day Æ Robert S. Lewis Æ Mark G. White Æ Alexei V. Iretskii Æ Peter C. Ford
Received: 16 January 2008 / Accepted: 18 March 2008 / Published online: 10 April 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Described are new solid base catalysts for transesterification of seed oil triglycerides to fatty acid methyl esters, a key step in biodiesel production. These were prepared by substituting Fe3+ ions substitute for a fraction of the Al3+ ions in the Mg/Al layered double hydroxide lattices of hydrotalcites (HTC) and calcining to give porous metal oxides (PMOs). These iron-doped PMOs are much stronger bases than those derived from undoped or Ga3+ doped HTCs and are effective catalysts for the methanol transesterification of triacetin (glycerol triacetate) and of soybean oil. Keywords Catalysis Biodiesel Transesterification Solid base Hydrotalcite Iron Triglycerides 1 Introduction The base catalyzed transesterification of triglycerides such as seed oils with methanol or ethanol (Eq. 1) produces a non-toxic, biodegradable, renewable, and clean burning fuel that can directly replace petroleum diesel in most
applications. Commercial technology for biodiesel production generally employs homogeneous bases such as NaOH in methanol solution as catalysts [1]. Such catalysis requires an aqueous wash to remove the dissolved catalyst and glycerol from the product phase and suffers from separation problems due to emulsion formation and from waste treatment issues. Thus, it is desirable to utilize solid bases to avoid these pitfalls that may be adaptable for use in flow reactors. In this context, there have been several recent reports of base catalysis by solids such as CaO, KF or Eu2O3 supported on alumina or silica [2–4]. Here, we report new solid base catalysts prepared from ferric ion doped hydrotalcite (HTC) precursors. Calcination of such HTCs gives porous metal oxides (PMOs) that are effective for the transesterification of triacetin (Eq. 1, R = CH3) and of soybean oil (Eq. 1, R = C16 and C18 hydrocarbon chains [5]). CH2OC(O)R CHOC(O)R CH2OC(O)R
G. S. Macala A. W. Robertson Z. B. Day R. S. Lewis A. V. Iretskii (&) P. C. Ford (&) Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA e-mail: [email protected] P. C. Ford e-mail: [email protected] A. W. Robertson C. L. Johnson A. V. Iretskii Department of Chemistry, Lake Superior State University, Sault Ste Marie, MI 49783, USA M. G. White School of Chemical Engineering, Mississippi State University, Starkville, MS 39762, USA
CH2OH + 3 CH3OH
catalyst
CHOH CH 2OH
+ 3 CH3OC(O)R (1)
Hydrotalcites are Mg2+/Al3+ layered double hydroxides with the general formula Mg1-xAlx(OH)2(CO3)x/2 nH2O, calcination of which gives amorphous PMOs upon evolution of H2O and CO2. Earlier reports have shown that Ga3+ doped calc
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