Optimization of the catalytic production of methyl stearate by applying response surface Box-Behnken design: an intensified green option for high-cetane biofuel manufacture.

To enhance the efficiency of processes by decreasing the reaction severity and energy consumption, and reducing the equipment size, facilities' space and operation cost, process intensification is an increasingly used option in the chemical industry. Within this framework and in agreement with some of the green chemistry principles (design for energy efficiency and use of renewable feedstocks), this work deals with the implementation of high-shear mixing (HSM) to intensify the homogeneous esterification of stearic acid (SA) with methanol to methyl stearate, a high-cetane number alkyl ester suitable to be added into biofuel streams. The response surface Box-Behnken design (BBD) is applied to quantify the main effects and two-way interactions of four key input reaction factors: methanol : SA ratio (7-16 mol mol-1), catalyst mass (0.25-4.0 wt%), temperature (40-60 °C), time (1-12 min), and to approximate the optimal conditions on the intensified SA esterification. The statistical BBD results indicates that the four linear effects, two of the four possible quadratic effects (catalyst mass and temperature) and only one (catalyst mass-time) of the six existing two-way interactions are statistically relevant at the 95% confidence level. Catalyst mass is the most influencing factor in the reaction, followed by methanol : SA ratio, temperature, and time. The proposed second-order regression model predicts that the intensified esterification requires only 12 min to practically convert all SA (99% ± 6.8%) running the reaction at 12.4 methanol : SA ratio, 4 wt% catalyst mass, 60 °C and 500 rpm, a value experimentally validated (93.2% ± 0.7%). Under these conditions and with the assistance of HSM, the typical reaction length of conventional heterogeneous and homogeneous-phase esterification processes decreases from 5 to 117 and 35 to 90 times, respectively.

Discerning the Metal Doping Effect on Surface Redox and Acidic Properties in a MoVTeNbO x for Propa(e)ne Oxidation.

Adding a small quantity of K or Bi to a MoVTeNbO x via impregnation with inorganic solutions modifies its surface acid and redox properties and its catalytic performance in propa(e)ne partial oxidation to acrylic acid (AA) without detriment to its pristine crystalline structure. Bi-doping encourages propane oxydehydrogenation to propene, thus enlarging the net production rate of AA up to 35% more. The easier propane activation/higher AA production over the Bi-doped catalyst is ascribed to its higher content of surface V leading to a larger amount of total V5+ species, the isolation site effect of NbO x species on V, and its higher Lewis acidity. K-doping does not affect propane oxydehydrogenation to propene but mainly acts over propene once formed, also increasing AA to a similar extent as Bi-doping. Although K-doping lowers propene conversion, it is converted more selectively to acrylic acid owing to its reduced Brønsted acidity and the presence of more Mo6+ species, thereby favoring propene transformation via the π-allylic species route producing acrylic acid over that forming acetic acid and CO x via acetone oxidation and that yielding directly CO x .