Dra. Azócar-Ulloa, Laura

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.

Copper contamination in watercourses is a recent issue in countries where mining operations are prevalent. In this study, the application of copper precipitation through microbe-induced carbonate precipitation (MICP) was analyzed using urea hydrolysis by bacteria to evaluate precipitated copper carbonates. This article demonstrates the application of a copper precipitation assay involving Sporosarcina pasteurii (in 0.5 mM Cu2þ and 333 mM urea) and analyzes the resultant low removal (10%). The analysis indicates that the low removal was a consequence of Cu2þ complexation with the ammonia resulting from the hydrolysis of urea. However, the results indicate that there should be a positive correlation between the initial urea concentration and the bacterial tolerance to copper. This identifies a challenge in the industrial application of the process, wherein a minimum consumption of urea represents an economic advantage. Therefore, it is necessary to design a sequential process that decouples bacterial growth and copper precipitation, thereby decreasing the urea requirement.

A Biomass Quality Index (BQI) developed using a previously reported tool was shown to be a promising method to rank biomass suitable for solid biofuel production. The BQI was developed by selecting 12 chemical parameters to be analyzed among ten available biomasses produced in the north, central and south of Chile. Furthermore, a Parameter Quality Index (PQI) was calculated to estimate the contribution of each parameter in the BQI. The sum of all PQIs for each biomass allowed the BQI to be determined, and biomasses with lower BQIs were more highly ranked. The results showed that the first 3 ranks were dominated by biomasses collected in central Chile, hazelnut shell, cherry pits and corn cobs (BQI ≤ 16.1). Furthermore, a promising candidate that was ranked fourth place was wheat straw (BQI = 17.7), which may be able to be used the highly polluted southern zone. Meanwhile, grass and the microalgae N. gaditana were ranked last (BQI ≥ 69.5). The low BQI obtained for the studied biomasses were related to their low PQIs regarding moisture content, low trace element content, low ash percentage and high carbon content and HHV. By contrast, high BQI values were related to high PQIs for moisture, Cl, Na and K content. K had a high contribution and Cu had a low contribution in the index. Due to the difficulty of milling the top ranked biomass, further studies should include a grindability analysis orother physical parameters to complete the BQI methodology.

The production of fatty acid methyl esters (FAME) from waste frying oil (WFO) was studied using fly ash as received as a heterogeneous catalyst. The fly ash used in this research had a high content of both CaO and SO3, two compounds that have been previously proposed as catalysts in FAME production. The study was carried out on the basis of a response surface methodology (RSM). The model generated by RSM predicted as optimal conditions to obtain a 100% FAME yield at a methanol-to-oil molar ratio of 3.1:1, 11.2 (wt.% based on oil weight) fly ash and a temperature of 59 C with agitation at 245 rpm and 6 h of reaction time. Additional experiments comparing anhydrous with aqueous medium showed that fly ash presented a high catalytic capacity to transform free fatty acids (FFA) into FAME through consecutive hydrolysis and esterification processes (hydroesterification) compared with that associated with the transesterification mechanism. According to the results, the fly ash used in this study would act as a multipurpose or “versatile” catalyst due to its chemical composition with constituents that act as acidic and basic catalysts, therefore, catalyzing the transesterification and hydroesterification reactions simultaneously and increasing the conversion yields of FAME.

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.