Hydrothermal carbonization coupled with fast pyrolysis of almond shells: Valorization and production of valuable chemicals.

In this study, it was found that hydrothermal carbonization (HTC) can be an effective method for almond shell (AS) valorization. The severity of HTC treatment had a significant effect on hydrochar yields, with higher severity promoting carbonization but reducing yields. Furthermore, the work found that HTC treatment effectively demineralized biomass samples by removing inorganic material that could catalyze carbonization. As residence time or temperature increased, the amount of carbon increased, while the amount of oxygen decreased. An acceleration in thermal degradation was detected for hydrochars after pretreating for 4 h. The hydrochars showed they had a higher volatile content than untreated biomass, making them potentially useful for producing quality bio-oil through fast pyrolysis. Finally, HTC treatment led to the production of valuable chemicals such as guaiacol and syringol. For syringol production, HTC residence time had more effect than HTC temperature. However, high HTC temperatures benefited levoglucosan production. Overall, the results demonstrated the potential for HTC treatment to be an effective method for valorizing agricultural waste, offering the possibility of producing valuable chemicals.

Mexican biomasses valorization through pyrolysis process: Environmental and costs analysis.

Biomasses valorization by pyrolysis is a good option for reducing environmental problems. In this study, the environmental performance of three Mexican biomass valorizations (castor husk, coffee pulp and Pinus sawdust) by the pyrolysis was compared. The environmental impacts of all equipment involved in pyrolysis were evaluated. In addition, the financial viability of pyrolysis technology of coffee pulp was studied. The biomass with the lowest impact for all the selected categories was the Pinus sawdust, followed by castor husk and coffee pulp. The GWP category had values greater than 700 kg CO2eq for all the biomass studied. GWP category is caused by the emissions, mainly due to the high amounts of CH4 and CO2 released for all the studied biomasses. Furthermore, the equipment with the greatest impact are the separator, the pyrolyzer and the cyclone. Finally, it was observed that even the least favorable biomass with the environment is viable from a financial point of view.

Kinetic analysis of manure pyrolysis and combustion processes.

Due to the depletion of fossil fuel reserves and the environmental issues derived from their use, biomass seems to be an excellent source of renewable energy. In this work, the kinetics of the pyrolysis and combustion of three different biomass waste samples (two dairy manure samples before (Pre) and after (Dig R) anaerobic digestion and one swine manure sample (SW)) was studied by means of thermogravimetric analysis. In this work, three iso-conversional methods (Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) were compared with the Coats-Redfern method. The Ea values of devolatilization stages were in the range of 152-170kJ/mol, 148-178kJ/mol and 156-209kJ/mol for samples Pre, Dig R and SW, respectively. Concerning combustion process, char oxidation stages showed lower Ea values than that obtained for the combustion devolatilization stage, being in the range of 140-175kJ/mol, 178-199kJ/mol and 122-144kJ/mol for samples Pre, Dig R and SW, respectively. These results were practically the same for samples Pre and Dig R, which means that the kinetics of the thermochemical processes were not affected by anaerobic digestion. Finally, the distributed activation energy model (DAEM) and the pseudo-multi component stage model (PMSM) were applied to predict the weight loss curves of pyrolysis and combustion. DAEM was the best model that fitted the experimental data.

Life cycle assessment of swine and dairy manure: pyrolysis and combustion processes.

The valorization of three different manure samples via pyrolysis and combustion processes was evaluated. Dairy manure (sample Pre) was biologically pretreated by anaerobic digestion (sample Dig R) whereas swine manure (sample SW) was pretreated by a biodrying process. Thermal behavior of manure samples were studied by means of thermogravimetric analysis coupled with mass spectrometry (TGA-MS). These processes could be divided into four general stages: dehydration, devolatilization, char transformation (oxidation for combustion) and inorganic matter decomposition. The main differences observed among the samples were attributed to their different composition and pretreatment. The economic feasibility, energetic and environmental impacts of pyrolysis and combustion technologies for dairy samples were carried out by means of life cycle assessment (LCA) methodology. Four different scenarios were analyzed. The economic feasibility of the pyrolysis process was demonstrated, being sample Dig R the best environmental option. However, the combustion of sample Pre was the best energetic option.

Synthesis and characterization of graphene: influence of synthesis variables.

The optimization of graphene growth on copper foils using an atmospheric pressure chemical vapor deposition setup is reported. CH4 and H2 were used as precursor gases and Raman spectroscopy as the main graphene characterization technique. Different growth parameters, including temperature and reaction time, the molar ratio of CH4/H2 in the feed and total flow of gases during the reaction step, were studied in detail. It was shown that graphene growth was not homogeneous in the entire sample, multilayer graphene was present in most of the sample, however as the synthesis parameters were optimized, graphene gained better quality, obtaining bilayer graphene over most of the sheet in the final optimized sample. Homemade software was used to analyze the quality of the synthesised graphene, obtaining a more quality graphene according to the synthesis parameters optimized. An optimal bilayer graphene sample was prepared at the lowest growth time (10 min) and the highest synthesis temperature (1050 °C), using a CH4/H2 flow ratio and a total flow rate ratio of precursors of 7% and 60 Nml (CH4 + H4) per min respectively.

Thermogravimetric-mass spectrometric analysis on combustion of lignocellulosic biomass.

Combustion characteristics of biomass main components and three lignocellulosic biomass (fir wood, eucalyptus wood and pine bark) were investigated by thermogravimetric analysis coupled with mass spectrometry. The combustion of biomass was divided into two main steps, devolatilization and char oxidation stage. Heating rate effect was also studied. Generally, the higher the heating rate, the higher the decomposition temperature. Furthermore, the weight loss rate decreased due to particle temperature gradients. Combustion kinetics were studied. Models based on reaction order (Oi), nucleation (Ni) and diffusion (Di) achieved the best fitting to the experimental data. Cellulose oxidation presented the highest activation energies. CO, CO2 and H2O were the main components evolved from combustion. Additionally, light hydrocarbons (CH4 and C2H5) were also present. Finally, nitrogen compounds were in a higher proportion than sulfur compounds being released as primary amines and NOx.

Pyrolysis, combustion and gasification characteristics of Nannochloropsis gaditana microalgae.

Pyrolysis, combustion and gasification characteristics of Nannochloropsis gaditana microalgae (NG microalgae) were investigated by thermogravimetric analysis (TGA). NG microalgae pyrolysis and combustion could be divided into three main stages: dehydration, proteins and polysaccharides degradation and char decomposition. The effects of the initial sample mass, particle size and gas flow on the pyrolysis and combustion processes were studied. In addition, gasification operation conditions such as temperature, initial sample mass, particle size, sweep gas flow and steam concentration, were experimentally evaluated. The evolved gases were analyzed online using mass spectroscopy (MS). In pyrolysis and combustion processes, most of the gas products were generated at the second degradation step. N-compounds evolution was associated with the degradation of proteins. Furthermore, SO(2) release from combustion could be related to sulphated polysaccharides decomposition. The main products detected during gasification were CO(2), CO, H(2), indicating that oxidation reactions, water gas and water gas shift reactions, were predominant.

Thermogravimetric-mass spectrometric analysis of lignocellulosic and marine biomass pyrolysis.

The pyrolysis characteristics of three lignocellulosic biomasses (fir wood, eucalyptus and pine bark) and a marine biomass (Nannochloropsis gaditana microalgae) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA-MS). Thermal degradation of lignocellulosic biomass was divided into four zones, corresponding to the decomposition of their main components (cellulose, hemicellulose and lignin) and a first step associated to water removal. Differences in volatile matter and cellulose content of lignocellulosic species resulted in different degradation rates. Microalgae pyrolysis occurred in three stages due to the main components of them (proteins), which are greatly different from lignocellulosic biomass. Heating rate effect was also studied. The main gaseous products formed were CO(2), light hydrocarbons and H(2)O. H(2) was detected at high temperatures, being associated to secondary reactions (char self-gasification). Pyrolysis kinetics were studied using a multiple-step model. The proposed model successfully predicted the pyrolytic behaviour of these samples resulting to be statistically meaningful.