Catalysis of Organic..

Kiss, Rothenberg and Dimian 407C 10 H 23O+ HO n-BuOH160 ºC120 minC 10 H 23OOn-Bu + H2 O(1)The following experimental results are presented on the use of solid catalysts inesterification of dodecanoic acid with 2-ethylhexanol and methanol. In the nextfigures, conversion is defined as: X [%] = 100 · (1 – [Acid] final / [Acid] initial ), and theamount of catalyst used is normalized: W cat [%] = M cat / (M acid + M alcohol ).In our experiments we screened zeolites, ion-exchange resins, heteropolycompounds and mixed metal oxides. Several alcohols were used to show the range ofapplicability. The selectivity was assessed by testing the formation of side productsin a suspension of catalyst in alcohol (e.g. SZ in 2-ethylhexanol) under reflux for 24hours. Under the reaction conditions, no by-products were detected by GC analysis.Three types of zeolites were investigated: H-ZSM-5, Y and Beta. Zeolitesshowed only an insignificant increase in acid conversion compared to the noncatalysedreaction. This agrees with previous findings suggesting that the reaction islimited by the diffusion of the bulky reactant into the zeolite pores (9). The Si/Alratio can be used to control the acid strength and hydrophobicity of zeolites. Whileacid strength increases at lower Si/Al ratio, hydrophobicity increases at higher Si/Alratios. Thus, a balance is necessary for optimal performance (9). In our experiments,we observed only minor activity differences even for large variations of Si/Al ratio.We tested then two ion-exchange organic resins: Amberlyst-15 and Nafion-NR50 (10). In spite of the high activity (Figure 2, left), Amberlyst-15 is not stable attemperatures higher than 150 °C, making it unsuitable for industrial RD applications.As for Nafion, its activity was lower than our prepared sulfated metal oxides.The tungstophosphoric acid shows high activity, close to H 2 SO 4 used as abenchmark. Regrettably, this acid is soluble in water and hence not usable as a solidcatalyst. However, the corresponding cesium salt (Cs2.5) is also super acidic and itsmesoporous structure has no limitations on the diffusion of the reactants. Cs2.5exhibits low activity per weight, hence it is not suitable for industrial applications.100H 2 SO 4 1%wt100Conversion / [%]80604020H 3 PW 12 O 40AmbSZ00 30 60 90 120Time / [min]NafionCs2.5Non-catalyzedAlcohol:Acid = 2:1T=130°C, 2 %wt cat.Conversion / [%]806040205%31.50.5%w00 30 60 90 120Time / [min]Non-catalyzedSZ catalystFigure 2. Esterification of dodecanoic acid with 2-ethylhexanol (left); non-catalyzedand catalyzed (0.5-5 wt% SZ catalyst) reaction profiles (right).