Activated MgAl-layered double hydroxide as solid base catalysts for the conversion of fatty acid methyl esters to monoethanolamides

Increasing concern about the environment demands that the chemical industry develop alternative greener routes to traditional processes. Two of the ways to achieve this aim are the replacement of homogeneous catalysts by heterogeneous analogs and the use of renewable raw materials. Fatty acid esters, in the form of biodiesel, have been suggested as raw materials for the sustainable production of high value chemicals. Here, we report a green route to the synthesis of fatty acid monoethanolamides using fatty acid methyl esters as the raw materials and activated layered double hydroxide (LDH) as a solid catalyst. Two kinds of MgAl-LDH precursors with different crystal morphologies were synthesized by the SNAS (separate nucleation and aging steps) method and the urea decomposition method. Activated LDH samples obtained from the LDH precursor synthesized by the SNAS method showed a higher catalytic activity in the amidation of methyl stearate than those prepared from the LDH precursor synthesized by the urea decomposition method, with about 87.0% methyl stearate conversion at 393K for 4h. The higher activity may be attributed to the smaller crystallite size and the larger surface area of the activated LDH obtained from the LDH precursor synthesized by the SNAS method. Moreover, activated LDH with an Mg/Al ratio of 4.0 exhibited a higher conversion of methyl stearate compared to those with Mg/Al ratios of 2.0 or 3.0 prepared by the same method.