Research Outputs
Tetrabutyl ammonium salts of keggin-type vanadium-substituted phosphomolybdates and phosphotungstates for selective aerobic catalytic oxidation of benzyl alcohol
A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed higher activity. The maximum benzyl alcohol conversions obtained were 93% and 97% using (TBA)5PMo10V2O40 and (TBA)5PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%.
Brown pellet production using wheat straw from southern cities in Chile
In this study, the torrefaction process was optimized to improve the energy yield (Yenergy) in wheat straw pellet production. Wheat is the main agricultural product of Chile and cultivated in approximately 262 000 ha of land. Additionally, solid biofuel alternatives are necessary in the southern cities of Chile to reduce the pollution produced by low-quality firewood used as fuel. That being the case, it appears that wheat straw is a feasible raw material for solid biofuel production. In the current study, the torrefaction of wheat straw was optimized in a thermogravimetric analyzer using the response surface methodology (RSM). The polynomial model generated from the RSM study showed that heating rate and temperature were significant variables on the response variable, Yenergy; time was insignificant. It was shown that a decrease in temperature of up to 130 °C resulted in an enhancement of the Yenergy value, and at the aforementioned temperature, a low heating rate improved Yenergy. Following the conditions predicted by the model, torrefaction assays were conducted in a bench scale reactor under light torrefaction conditions: a torrefaction temperature of 145 °C, heating rate of 3 °C/min, and final torrefaction time of 50 min. The torrefied biomass was employed in a pellet production process that was performed in a pilot plant facility. The pellet produced from the torrefied biomass under light torrefaction conditions was named “brown pellet” because of its color. Most of the pellet properties satisfy the Standards for Industrial pellets (ISO 17225-6). This showed that light torrefaction temperature can be a potential pretreatment to achieve a commercial production process. Finally, an interesting result was obtained—the bulk density of brown pellets (568 ± 8 kg/m3) was considerably higher compared to that of wheat straw pellets (469 ± 8 kg/m3). This was probably caused by an increment in grinding characteristics. Further studies that focus on identifying the effects of light torrefaction conditions on the mechanical properties of wheat straw pellets should be conducted.
Catalytic Selective Oxidation of β-O-4 Bond in Phenethoxybenzene as a Lignin Model Using (TBA)5[PMo10V2O40] Nanocatalyst: Optimization of Operational Conditions
The catalytic oxidation of phenethoxybenzene as a lignin model compound with a β-O-4 bond was conducted using the Keggin-type polyoxometalate nanocatalyst (TBA)5[PMo10V2O40]. The optimization of the process’s operational conditions was carried out using response surface methodology. The statistically significant variables in the process were determined using a fractional factorial design. Based on this selection, a central circumscribed composite experimental design was used to maximize the phenethoxybenzene conversion, varying temperature, reaction time, and catalyst load. The optimal conditions that maximized the phenethoxybenzene conversion were 137 ◦C, 3.5 h, and 200 mg of catalyst. In addition, under the optimized conditions, the Kraft lignin catalytic depolymerization was carried out to validate the effectiveness of the process. The depolymerization degree was assessed by gel permeation chromatography from which a significant decrease in the molar mass distribution Mw from 7.34 kDa to 1.97 kDa and a reduction in the polydispersity index PDI from 6 to 3 were observed. Furthermore, the successful cleavage of the β-O-4 bond in the Kraft lignin was verified by gas chromatography–mass spectrometry analysis of the reaction products. These results offer a sustainable alternative to efficiently converting lignin into valuable products
Carbonization of microalgae for bio-coal production as a solid biofuel similar to bituminous coal
The carbonization of Nannochloropsis gaditana microalgae biomass was found to produce bio-coal that is similar to bituminous coal used in thermal power plants. Currently, microalgae that capture CO2 while they are in the growth stage are considered a source for the production of biofuels. The carbonization of biomass for producing bio-coal has received attention for its ability to improve the biomass quality for producing solid biofuels. The research was focused on optimizing a fixed carbon index (FCindex), which allows finding operational conditions of carbonization to favor the fixed carbon content without significantly affecting the bio-coal yield. The optimization carried out by response surface methodology in a thermogravimetric analyzer allowed the prediction of optimal carbonization conditions to achieve an FCindex of 191% at 403 °C, 71 °C/min, and 60 min of residence time. The bio-coal produced under optimized conditions was characterized by 59% of fixed carbon and 41% of volatiles on a dry and ash-free basis, which is similar to bituminous coal. The promising results of dry carbonization producing bio-coal similar to bituminous coal could promote this technology, avoiding the necessity of hydrothermal carbonization. Because a high ash content was detected in the final product, further studies using the optimized conditions and a washing step should be conducted.