Influence of Surface Hydrophobicity on the Esterification of Fatty Acids over Solid Catalysts

Abstract

The relative roles of surface acidity and hydrophobicity in the methylation of fatty acids (C 8 -C 18 ) to the corresponding methyl esters were investigated over three solid acid catalysts: Fe-Zn double-metal cyanide (DMC), sulfated zirconia (SZ), and Al-MCM-41. The esterification reaction was faster and the apparent activation energy was lower over SZ and Al-MCM-41 than on DMC because of their higher acid strength, specific surface area, and pore diameter. Over SZ and Al-MCM-41, the apparent activation energy for esterification increased with the chain length of the fatty acid. A reverse trend, however, was observed over DMC. The relative adsorption of methanol and fatty acids (compared to water) was higher on DMC than on SZ and Al-MCM-41. Hence, in addition to the acidic and textural properties, surface hydrophobicity and relative surface coverage by reactants/products also play an important role in reactions of long-chain fatty acids with alcohols on solid catalysts.

Biodiesel Production from Vegetable Oils and Animal Fat over Solid Acid Double-Metal Cyanide Catalysts

“…Fe-Zn-2 and Fe-Zn-3, were prepared in a similar manner except in the absence of tri-block copolymer and in the absence of both tert-butanol and triblock copolymer, respectively. Fe-Zn- [33]. MoO x supported on phosphate modified alumina (MoO x /Al 2 O 3 ; MoO x content = 15 wt%, P content = 1.2 wt%) was obtained from Sud-Chemie India Ltd. Sulfated zirconia (1.5 mm pellets) was procured from Saint-Gobain, Norpro.…”

“…The materials were characterized as reported earlier [19,33,34]. The type and density of the acid sites were determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of adsorbed pyridine and temperature-programmed ammonia desorption (NH 3 -TPD) techniques [19,33,34].…”

“…Esterification of octanoic (C 8.0 ), decanoic (C 10.0 ), dodecanoic (C 12.0 ), palmitic (C 16.0 ) and oleic (C 18.1 ) acids with methanol was carried out in a batch reactor [33]. A known quantity of catalyst, fatty acid and methanol were taken in a Teflon-lined, stainless steel autoclave (100 mL).…”

Production of Biodiesel from Waste Cooking Oil: A Review

“…Their uses have been cited in synthesis of nanostructured materials, processing of biomass, sonofusion, sonodynamic therapy, and sonochemical degradation of pollutants [45] and hazardous chemicals [46]. A low frequency ultrasonic irradiation can be used to produce emulsions from immiscibility liquids and help generate small droplets and large interfacial areas if the ultrasonication device is placed near the liquid-liquid interface in a two phase reaction system [47,48].…”

Acidity-Reactivity Relationships in Catalytic Esterification over Ammonium Sulfate-Derived Sulfated Zirconia

“…Note that increasing the sulfate concentration not only influences surface acidity, but also the degree of surface hydration as determined by TGA-MS (low temperature mass loss and evolved water in Figure 2a, Figure S1 and Table 2). High S loadings therefore enhance the hydrophilicity of our SZ catalysts which is known to suppress fatty acid esterification with methanol due to active siteblocking and/or promotion of the reverse ester hydrolysis reaction [45][46][47]. Hence the 1.7 wt % catalyst may deliver maximum esterification performance due to the combination of a high concentration of strong acid sites with significant Brønsted character, and relatively low surface hydrophilicity.…”