Metal (IV) Phosphates as Solid Catalysts for Selective Dehydration of Sorbitol to Isosorbide
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Metal (IV) Phosphates as Solid Catalysts for Selective Dehydration of Sorbitol to Isosorbide Mingyan Gu Æ Dinghua Yu Æ Hongman Zhang Æ Peng Sun Æ He Huang
Received: 2 July 2009 / Accepted: 21 August 2009 / Published online: 2 September 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Metal (IV) phosphates of tin, zirconium and titanium were used as catalysts for selective dehydration of sorbitol to isosorbide. Tin phosphate showed the highest selectivity to isosorbide with a moderate conversion. The deactivation rates of catalysts were fitted by an empirical Voorhies equation and the results showed tin phosphate had the lowest deactivation rate with the least values of m and n. Thermal analysis showed deactivation rate was in accordance with coke deposition. The acidity caused by functional groups of the catalysts was the direct factor for catalyst lifetime, which was evidenced by NH3-TPD, XRD, IR and Raman characterizations. Keywords Metal (IV) phosphates Sorbitol Isosorbide Dehydration Deactivation
1 Introduction In the past decades, sorbitol has been converted to several chemicals depending on the transformation pathways [1–3]. Among others, the catalytic dehydration as shown in Scheme 1 emerges as an important route for sorbitol conversion, which yields primarily isosorbide. It has been widely used in the manufacture of pharmaceutical
M. Gu H. Zhang College of Science, Nanjing University of Technology, 210009 Nanjing, China D. Yu P. Sun H. Huang (&) College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, 210009 Nanjing, China e-mail: [email protected]
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intermediates, food and cosmetic [4]. Recently, isosorbide has also shown a special monomer for polymers due to improving the glass transition temperature, transparency, and mechanical performance of polyester product [5]. Traditionally, isosorbide has been produced by liquid catalytic dehydration processes with mineral acids as catalysts [6–8] and these processes are often performed in the presence of a solvent, which must be improved due to environmental problems and high manufacturing cost. Recently, some solid acid catalysts [9] such as HY, H-ZSM-5 and ion exchange resin, have been used to catalyzed sorbitol dehydration to isosorbide, but with low yield. In addition, the application as novel monomer for bio-based polymer is accelerating the research on a more efficient isosorbide progress. The outstanding catalytic performance of metal (IV) phosphates for selective catalysis in the formation of mono- and bi-cyclic ethers from diols has been examined [10]. This kind of catalysts contain structural hydroxyl groups with labile protons, moderate strength acidity, the co-exist of Bro¨nsted and Lewis acid sites, and therefore are potential candidates as solid acid catalysts. They have been used in a variety of reactions like dehydration of alcohols [11], isomerization of alkenes [12] and reverse Prins reaction [10]. In the catalytic dehydration of bio-based chemicals such as glycerol, lactic acid an
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