(770f) Synthesis of Mesoporous Nanocrystalline Sulfated Zirconia and Its Application for Esterification of FFA in Used Oils

Biodiesel has become one of the premier forms of alternative energy source. However, biodiesel growth is hindered by the cost of production which makes it uncompetitive compared to petro-diesel. Biodiesel is produced by the reaction of lipid feedstocks with an alcohol such as methanol in the presence of a catalyst (NaOH, KOH or their methoxides) to yield methyl esters (biodiesel) and byproduct glycerin used to make soaps and cosmetics. However, the conventional transesterification process is complicated if the oil contains large amounts of FFA (> 2% w/w) due to soap formation with the commercially used alkaline catalysts, enormously reducing the yield of biodiesel. Also, this reaction does not tolerate the presence of water or fatty acids and the use of acids such as H₂SO₄, H₃PO₄, and HCl pose environmental and corrosion problems. On the other hand, using feeds stocks having higher FFA levels such as used cooking oil, waste fats etc, is of vital importance in order to reduce the cost of biodiesel production and make biofuel production more economical. Hence, there is a need for solid superacid catalysts. An ideal solid acid catalyst or base should possess certain inherent characteristics such as interconnected large pore architecture, moderate-to-high concentration of strong acid and base sites and a surface that is hydrophobic. Heterogeneous acid catalyst especially sulfated zirconia is a promising catalyst owing to its strong acidic properties and high catalytic activity for various hydrocarbon reactions. We have prepared mesoporous nanocrystalline sulfated zirconia with high surface area and acidity by using two different sulfonating agents, namely, sulfuric acid and chlorosulfonic acid.  Nanocrystalline mesoporous zirconium hydroxide powder with very high surface area was synthesized using ethylene diamine and zirconyl chloride octahydrate. Ethylene diamine used as precipitating agent also acted as a colloidal protecting agent. The zirconium hydroxide prepared at different digestion times of 0, 1, 3, 6, 12, 24 and 48 hrs was sulfonated by wet impregnation method. These preparation conditions such as digestion time, sulfonating agent and the calcination temperature significantly affected the structural stability, crystal size, crystal phase and the number and types of available active acidic sites on the surface of the final sulfated zirconia. Preliminary results showed that for the calcined sulfated zirconia, surface area varied between 80 m²/g and 260 m²/g while total number of acid sites ranged from 0.345 mmol/gm to 1.104 mmol/gm, depending upon the process parameters used. X ray diffraction showed that the number of acidic sites on the surface has strong influence of the crystal size and crystal phase of the sulfated zirconia. The material was characterized by nitrogen adsorption–desorption (BET), ammonia temperature programmed desorption (NH₃-TPD), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential scanning calorimetry (TGA-DSC), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR). The sulfated zirconia prepared at optimized conditions was tested for the esterification of free fatty acids in the used cooking oils. The synthesis procedure, catalyst characterization, and results and analysis of fatty acid methyl esters (FAME) production from the esterification studies will be presented.

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