Abstract
The performance of boron oxide (B2O3)-promoted Cu/Al2O3 catalyst in the selective hydrogenolysis of glycerol and crude glycerol (a by-product or waste stream from the biodiesel industry) to produce 1,2-propanediol (1,2-PDO) was investigated. The catalysts were characterized using N2-adsorption-desorption isotherm, Inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), ammonia temperature programmed desorption (NH3-TPD), thermogravimetric analysis (TGA), temperature programmed reduction (TPR), and transmission electron microscopy (TEM). Incorporation of B2O3 to Cu/Al2O3 was found to enhance the catalytic activity. At the optimum condition (250 °C, 6 MPa H2 pressure, 0.1 h−1 WHSV (weight hourly space velocity), and 5Cu-B/Al2O3 catalyst), 10 wt% aqueous solution of glycerol was converted into 1,2-PDO at 98 ± 2% glycerol conversion and 98 ± 2% selectivity. The effects of temperature, pressure, boron addition amount, and liquid hourly space velocity were studied. Different grades of glycerol (pharmaceutical, technical, or crude glycerol) were used in the process to investigate the stability and resistance to deactivation of the selected 5Cu-B/Al2O3 catalyst.
Highlights
Owing to its environmental and sustainability benefits, biodiesel, produced mainly by transesterification of vegetable oils or animal fats, has been regarded as a promising substitute to the fossil-based transportation fuels
Figure 3), the addition of B2 O3 enhanced the acidity of the Cu/Al2 O3 catalysts, as reported in the literature [38]
Temperature-programmed reduction (TPR) profiles of the catalysts were determined using a Micromeritics Autochem 2920 equipped with a thermal conductivity detector (TCD)
Summary
Owing to its environmental and sustainability benefits, biodiesel, produced mainly by transesterification of vegetable oils or animal fats, has been regarded as a promising substitute to the fossil-based transportation fuels. The conversion of glycerol to 1,2-PDO involves the selective cleavage of a C–O bond at one of the primary carbon atoms without breaking the C–C bonds of glycerol to eliminate a water molecule, forming acetol as an intermediate compound or side-product, and subsequently absorb a molecule of hydrogen through hydrogenation, requiring a catalyst with dehydration sites which are usually acid sites and hydrogenation sites which usually need a transition metal. The catalytic activity of Cu-based catalyst on different supports such as SiO2 [31], ZnO [32,33], Al2 O3 [34,35], Cr2 O3 [14], zeolite [36], MgO [2], etc., have been investigated Most of these studies were carried out in a batch reactor, while a continuous-flow process would be more desirable due to the ease of the process scale-up and the potential for commercialization of the process.
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