Aldol-condensation of furfural by activated dolomite catalyst

Aldol-condensation of furfural with acetone catalysed by activated dolomite was investigated at temperatures from 306 to 413 K. The process of activation by calcination and hydration produced catalytically active calcium and magnesium hydroxides with improved surface area and surface basicity. The aldolcondensation mechanism began with a deprotonation of acetone forming a carbanion intermediate by hydroxyl ions, which then reacted with the carbonyl group of furfural to form a water soluble C-8 monomer (4-(furan-2-yl)-4-hydroxybutan-2-one). This C-8 monomer readily dehydrated to form selectively alpha,beta-unsaturated ketone (4-(2-furyl)-3-buten-2-one), which in turn, reacted with furfural forming a C-13 dimer (1,4-pentadien-3-one,1,5-di-2-furanyl). Compared with conventional sodium hydroxide catalyst, activated dolomite was less selective towards lumped C-8 monomers and C-13 dimers owing to carbon losses and deactivation, particularly at high temperatures. Activated dolomite was more selective to C-13 dimer owing to higher adsorption enthalpy of C-8 monomer compared with acetone competitor. Activated dolomite is therefore a promising catalyst to produce C-13 dimers which can be transformed upon hydrogenation and deep hydrodeoxygenation in high-quality diesel fuels. The first-order kinetic model with respect to furfural and acetone fitted well with actual experimental results with an average normalised standard deviation of 6.2%. (C) 2013 Elsevier B.V. All rights reserved.